Wireless Magazine - August 8, 2011 - Digikey

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Wireless Magazine - August 8, 2011 - Digikey

TZW112.US

WIRELESS SOLUTIONS

Range

Measurements

in an

Open Field

Environment

Innovations in

Connectivity:

The Digi-Key

Weather

Center Smart

Charger

Wellness

Without Wires

Online Resources







WIRELESS SOLUTIONS SUPPLIERS

Bud Industries, Inc.

®

ELECTRONIC

2

Wireless Solutions | TZ W 112.US


TZW112.US

WIRELESS SOLUTIONS

Digi-Key Features

Editorial Comment .........................................................................................5

Wireless TechZone SM Q & A ............................................................................6

Wireless Solutions Trivia ..............................................................................16

Range Measurements in an

Open Field Environment

by Tor-Inge Kvaksrud, Texas Instruments

An open field is one of the simpler environments in

which to do an RF range test. Getting accurate data

from this test setup requires a bit more than turning

on the transmitter and taking a walk. This article offers

an insight into accurately calculating the link budget in

your wireless system.

7

ZigBee: A Global Wireless Standard ............................................ 13

contributed by Atmel

ZigBee is being implemented worldwide in smart energy, home automation,

telecommunication services, remote control, and other applications at different

frequencies in different geographies. New hardware/software packages make

previously complex and expensive implementation in the different frequency bands quite

straightforward.

Moving Beyond ZigBee for Star Networks ................................... 17

by Chris Downey, Laird Technologies

ZigBee has some great features that make it a powerful protocol for machine-to-machine

communications, but that doesn’t mean it is optimized for all networks. Star networks can

benefi t from a simpler, more effective solution.

TechXchange: Leading the Way in Collaboration ......................... 21

contributed by Digi-Key Corporation

With any project, there will be obstacles to overcome, and answers to these questions are

just a click away on Digi-Key’s exciting new community forum.

Making Choices in Wireless Networks:

To Each Application Its Own ......................................................... 23

by Vince Stueve, Micrel, Inc.

In wireless industrial networks, the application and environment ultimately dictate what

type of network makes the most sense. Sub-GHz proprietary protocols are often the best

choice for low power, low data rate wireless networks due to their extended range, ease

of implementation, and small code size.

3

Wireless Solutions | TZ W 112.US


28

WIRELESS HEALTH & FITNESS:

Wellness Without Wires

Medical Systems Go Wireless .............................................. 29

by Dave Bursky, PRN Engineering Services

There are few healthcare applications that can’t benefi t from remote

wireless sensors and data logging. Choosing the right protocol is the key

to success.

Comparing Low-Power Wireless Technologies ................. 34

by Phil Smith, CSR PLC

There are literally dozens of public and proprietary wireless protocols,

each best suited to a particular range of applications. This article

analyzes the major ones according to their power and performance

profi les, indicating in which applications each makes the most sense.

Full Signal Path Solution for

Portable Ultrasound Systems ........................................... 46

by Suresh Ram, National Semiconductor

Designing a portable ultrasound device involves challenging trade-offs

in order to achieve an optimal balance between power conservation,

performance, and size.

New Design Database Gives

Digi-Key Customers a Competitive Edge ...................................... 49

contributed by Digi-Key Corporation

Digi-Key’s Reference Design Library is among the best tools for electronic design engineers.

Considerations for Sending Data over a Wireless Link ............... 50

contributed by Linx Technologies

RF designers have a great deal of freedom when creating a protocol, tailoring it to meet the

requirements and resources of a given application. This article models the communication

channel and examines what can go wrong – and how to fi x it – every step of the way.

Right-Sizing Your Wireless Design for Power and Cost .............. 60

by Nicholas Cravotta

Introducing RF to a system is not yet quite as simple as adding an antenna and reading

data off a SPI port. Designers must carefully consider how to size the power consumption

and data rate of the RF subsystem to the actual use cases of an application.

How New Antenna-Matching Technology Helps HF-RFID

Designs Perform Reliably in Difficult Environments ................... 72

by Brian Zachrel, austriamicrosystems

High-Frequency RFID (HF-RFID) applications are vulnerable to environmentally-induced

antenna detuning. A reader IC that automates the antenna tuning process as part of an

easy-to-use, software-controlled system eliminates this problem.

Passive Mixers in Downconverter Applications .......................... 75

by Tom Schiltz, Bill Beckwith, Xudong Wang, and Doug Stuetzle, Linear Technology

Most integrated-circuit mixers are based on an active or current-commutating topology

despite exhibiting a higher noise fi gure and lower gain than passive mixers at comparable

linearity. Consider using a passive mixer in your next design.

Innovations in Connectivity: The Digi-Key

Weather Center Smart Charger

by Brandon Tougas, Digi-Key Corporation

This article focuses on the Smart Charger technology

used in Digi-Key’s Weather Center. The Smart Charger

engages in alternative energies to enable power

and data collection wirelessly. 67

4

Wireless Solutions | TZ W 112.US


Editorial Comment

Mark Zack

Vice President, Semiconductor s

The adoption of wireless connectivity in

health and fi tness continues at a rapid

rate. We are moving beyond the early

products that held great promise but

were often overpriced, very specialized

and more hype than real benefi t. The

products of today and tomorrow are

providing valuable remote diagnosis of

health issues and a variety of personal

monitoring features. The market is wide

and embraced at many levels from the

elite Tour de France athletes to the fi tness

fanatic; people with severe health issues

to preventative healthcare. Fundamental design challenges remain

in developing wireless solutions to address these markets and in

this issue of Digi-Key’s TechZone SM Interactive, formerly TechZone

Magazine, we offer a number of articles to support your next Health

and Fitness project such as:

• Dave Bursky of PRN Engineering Services provides an overview

of various wireless system implementations that give patients

more mobility while giving doctors more realistic real-time

information in “Medical Systems Go Wireless” (page 29).

• Tor-Inge Kvaksrud of Texas Instruments reviews important

effects to consider when testing the practical range of

your radio system in “Range Measurements in an Open Field

Environment” (page 7).

• Headquartered in Thief River Falls, MN USA, Digi-Key

Corporation is subject to harsh environmental extremes;

temperatures of colder than -30 degrees Fahrenheit in the

winter are common and as I write this editorial, it is 90 degrees

Fahrenheit with 82 percent humidity in July. To measure, track,

and report our local weather, our Application Engineering team

designed and deployed a weather station on our rooftop. In this

issue, Brandon Tougas reports on engaging alternative energy

to power our station in “Innovations in Connectivity: The Digi-Key

Weather Center Smart Charger” (page 67).

We continue to expand our supplier base to provide you a full range

of component and module selection including Arduino (open source

prototyping platform), EnOcean (energy harvesting wireless sensor

solutions), H&D Wireless (802.11b/g SiP), and Peregrine (RF and mixedsignal

communications ICs). Digi-Key represents over 100 industryleading

manufacturers of wireless products. Visit our TechZone SM

online (www.digikey.com/wireless) for additional design support

tools; reference designs, videos, Product Training Modules and our new

Wireless Solutions Community, Digi-Key TechXchange SM .

This issue of TechZone SM Interactive features our new landscape layout.

This format fi ts today’s monitors, tablets and eReaders making it easier

for you to get the most out of the technical articles in this and future

editions. To ensure that you receive notifi cation of future editions of

TechZone SM Interactive, visit www.digikey.com/request. Enjoy this

issue and we look forward to your feedback!

Sincerely,

Mark Zack

Vice President, Semiconductors

Digi-Key Corporation

About TechZone SM Interactive

Digi-Key’s TechZone SM Interactive is a

monthly online publication featuring

technology-specifi c electronic

information and resources for Lighting,

Microcontrollers, Wireless, and Sensors,

with more technologies to come.

TechZone SM Interactive provides the

engineering community, from students

to professional design engineers, with

information about supplier innovations,

quality in-depth solutions, and a selection

of application-specifi c considerations

focused on advancing technology. The

archived and latest editions of TechZone SM

Interactive can be found on Digi-Key’s

website at www.digikey.com/magazine.

Contact Information

For questions, comments, or to submit

an article:

tzcontent@digikey.com

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Copyrights: The masthead, logo, design, articles, content

and format of TechZone are Copyright 2011, Digi-Key

Corporation. All rights are reserved. No portion of this

publication may be reproduced in part or in whole without

express permission, in writing, from Digi-Key.

Trademarks: DIGI-KEY, the Digi-Key logo, TECHZONE, and the

TechZone logo are trademarks of Digi-Key Corporation. All

other trademarks, service marks or product names are the

property of their respective holders.

All product names, descriptions, specifi cations, prices and

other information are subject to change without notice. While

the information contained in this magazine is believed to be

accurate, Digi-Key takes no responsibility for incorrect, false

or misleading information, errors or omissions. Your use of

the information in this publication is at your own risk. Some

portions of the publication may offer information regarding

a particular design or application of a product from a variety

of sources; such information is intended only as a starting

point for further investigation by you as to its suitability and

availability for your particular circumstances and should

not be relied upon in the absence of your own independent

investigation and review. Everything in this publication is

provided to you “AS IS.” Digi-Key expressly disclaims any

express or implied warranty, including any warranty of

fi tness for a particular purpose or non-infringement. Digi-Key

cannot guarantee and does not promise any specifi c results

from use of any information contained in this magazine. Any

comments may be submitted to techzone@digikey.com.

5

Wireless Solutions | TZ W 112.US


Do you have a

technical question

In the rapidly evolving

wireless market, it seems

as if there is something new

every day – technologies,

products, consumer trends,

or regulations. Time-tomarket

demands have

never been greater with the

design of many of today’s

new wireless products

requiring expertise in more

than one discipline.

Digi-Key has more than 130

technical support specialists,

product managers, and

applications engineers

who are eager to answer

your questions and assist

you with your next project.

On target to fi eld more

than 260,000 calls this

year, our technical staff

is available 24/7/365 to

answer your questions.

If you have a question,

we invite you to contact

our technical staff via

telephone, live web chat, or

by emailing your question to

techzone@digikey.com.

Wireless TechZone SM Q & A

What is the physical range limit Bluetooth devices can

successfully communicate

The range of Bluetooth devices depends on the class of device. A Class 1

device has an approximate range of 100 meters, a Class 2 device’s range

is about ten meters, and a Class 3 device has an approximate range of

fi ve meters. However, while the Bluetooth Core Specifi cation does require

minimum broadcast ranges, manufacturers may modify their product’s

maximum range to meet specifi c application designs requirements.

Is it possible to deploy ZigBee networks in sub-GHz bands

Yes. ZigBee can be confi gured to use the IEEE 802.15.4 physical

interfaces transmitting at 868 MHz or 915 MHz. However, data rates

are reduced to 20 kbps and 40 kbps, respectively. Other than the

change in transmission frequency, the ZigBee protocol stack remains

the same as in other implementations at 2.4 GHz.

What are the benefits of using wireless spread spectrum

communication

Spread spectrum uses wideband, noise-like signals that are harder to

detect and intercept or demodulate. Also, these signals are harder to jam

(interfere with) than narrowband signals. Additionally, spread spectrum

signals are so wide that they transmit at a much lower spectral power

density (watts per Hertz) than narrowband transmitters. This gives spread

spectrum and narrow band signals the ability to occupy the same band,

with little or no interference. The spread spectrum approach to wireless

communications is employed today in Wi-Fi and some cellular networks

to obtain the following benefi ts: enhanced reliability by mitigating the

impact of wireless interference on a communication channel; increased

bandwidth by exploiting additional wireless spectrum to better utilize and

share bandwidth among multiple channels; and improved security by

limiting the ability of attackers to intercept transmissions.

Is the frequency chosen for an RFID application important

Yes. Different frequencies have different performance characteristics

that make them more suitable for certain application requirements.

Low-frequency tags require the least power and are better able

to penetrate non-metallic substances. They are ideally suited for

scanning objects with high-water content, such as fruit. However,

their read range is limited to less than a foot (0.33 meter).

High-frequency tags work best on objects made of metal and can

work adequately around goods with high water content. They have

a longer maximum read range of about three feet (one meter).

UHF frequencies typically offer better range and data transfer speeds

than low- and high-frequencies. On the other hand, they use more

power and are less likely to pass through materials. Also, because

they tend to be more “directed”, UHF frequencies require a clear

path between the tag and reader. UHF tags might be best suited for

scanning goods as they pass through a dock door into or out of a

warehouse. To avoid design problems, work with a knowledgeable

consultant, integrator, or vendor that can help in the choice of the

right frequency for a specifi c application.

How are Wi-Fi and WiMAX related

Wi-Fi and WiMAX coexist and are becoming increasingly

complementary technologies for their respective applications. Wi-Fi

technology is designed and optimized for Local Area Networks

(LAN), whereas WiMAX is designed and optimized for Metropolitan

Area Networks (MAN). WiMAX is typically not considered as a

replacement for Wi-Fi. Rather, WiMAX is a complement to Wi-Fi and

extends its reach by providing a “Wi-Fi like” user experience on a

larger geographical scale.

6

Wireless Solutions | TZ W 112.US


Range Measurements in an

Open Field Environment

by Tor-Inge Kvaksrud, Texas Instruments

Article Resources

PTM and Another Geek Moment

• Texas Instruments -

Microcontrollers:

MSP430x2xx/4xx and

Wireless Overview

Calculating a link budget involves quantifying

numerous variables, but achieving it in practice is

considerably more complicated. In this article the

author examines the various factors that go into the

Friis equation and then takes to the field to check

out his results.

Range is one of the most important parameters of any radio system.

Data-rate, output power, receiver sensitivity, antennas, and the intended

operation environment all infl uence the practical range of the radio link.

An open fi eld is one of the simplest and most commonly used

environments to do RF range tests. However, there are important

effects to consider, and failing to address these often results in the test

results being misinterpreted. This article addresses non-ideal effects to

consider when doing open fi eld range measurements.

In this article, open fi eld refers to a large open area without any

interfering radio sources, e.g. a soccer fi eld. At the end of this article,

we put our theory to the test in just such a fi eld.

Path loss and propagation theory

Communication is achieved through the transmission of signal energy

from one location to another. The received signal energy must be

suffi cient to distinguish the wanted signal from the always present

noise. This relationship is described as the required signal-to-noise ratio

(SNR). The necessary SNR for a radio link is sometimes specifi ed in

receiver datasheets. More commonly, the sensitivity is specifi ed. This is

the absolute signal level (S). When sensitivity is used, one assumes that

only thermal noise is present and that the device is operated at room

temperature. This section addresses the theory used to determine the

range for radio systems in open and free space environments.

The Friis transmission equation

Given two antennas, range in radio communication is generally

described by the Friis transmission equation (see Equation 1).

Equation 1

P R

: Power available from receiving antenna

P T

: Power supplied to the transmitting antenna

G R

: Gain in receiving antenna

G T

: Gain in transmitting antenna

λ: Wavelength, where λ = c/f, c = speed of light, and f = frequency

d: Distance between two antennas

c: Speed of light in vacuum 299.972458·10 6 [m/s]

This equation describes the dependency between distance, frequency

(wavelength), antenna gain, and power.

Example 1: Using the Friis equation.

Related Products

• CC2500RTKR

• EZ430-RF2500

• CC2500EMK

Online Resources

Additional Links

• Component Reference

Guide

Wireless Solutions,

March 2011

• TechZone Library

• TechXchange

• Future Editions

7

Wireless Solutions | TZ W 112.US


In free space, the path loss is 80.2 dB over a 100 m distance when

operating at 2.445 MHz.

In more down to earth applications, higher attenuation is expected.

An open fi eld is the simplest of these environments.

Link budget

The Friis equation is often referred to as the link budget. The difference

between the received signal power, PR, and the sensitivity of the

receiver is referred to as the link margin. In a realistic link budget,

additional loss has to be added to the losses predicted by the Friis

equation. This article addresses some of these losses in an open fi eld

environment. Range is the distance at which the link is operating with

a signal level equal to the receiver sensitivity level. In digital radio

systems sensitivity is often defi ned as the input signal level where PER

(Packet Error Rate) exceeds one percent.

Ground reflection (2-ray) model

In a typical radio link, transmission waves are refl ected and

obstructed by all objects illuminated by the transmitter antenna.

Calculating range in this realistic environment is a complex task

requiring huge computing resources. Many environments include

mobile objects, adding to the complexity of the problem.

Most range measurements are performed in large open spaces

without any obstructions, moving objects, or interfering radio

sources. This is primarily done to get consistent measurements.

The Friis equation requires free space to be valid. Handheld

equipment generally operates close to the ground. This implies that

ground infl uence has to be considered to do valid range calculations.

Figure 1 illustrates the situation with an infi nite, perfectly fl at ground

plane and no objects obstructing the signal. The total energy received

can then be modeled as the vector sum of the direct transmitted wave

and one ground refl ected wave.

The two waves are added constructively or destructively depending on

their phase difference at the receiver. The magnitude and phase of the

direct transmitted wave varies with the distance traveled. The magnitude

of the refl ected wave depends on the total traveled distance and the

refl ection coeffi cient () relating to the wave before and after refl ection.

Transmit antenna G T

H1

Figure 1: Transmission with ground.

Reflection coefficient

Whenever an incident radio signal hits a junction between different

dielectric media, a portion of the energy is refl ected, while the

remaining energy is passed through the junction. The portion refl ected

depends upon the signal polarization, the incident angle, and the

different dielectrics ( r

, μ r

and ). Assuming that both substances

have equal permeability, µ r

= 1, and that one dielectric is free space,

Equation 2 and 3 are the Fresnel refl ection coeffi cients for the vertical

and horizontal polarized signals.

Equation 2

Equation 3


i

Direct transmission

Reflected transmission

Receive antenna G R

The equations require some electrical data for the soil in the test

environment. Barton and Leonov [Ref. 1, pg. 394] present a table

showing r and for some typical soil conditions. r =18 and = 0

are used for all of the calculations reported here.

ε r

d


r

Reflection law — i = — r

H2

Article Resources

PTM and Another Geek Moment

• Texas Instruments -

Microcontrollers:

MSP430x2xx/4xx and

Wireless Overview

Related Products

• CC2500RTKR

• EZ430-RF2500

• CC2500EMK

Online Resources

Additional Links

• Component Reference

Guide

Wireless Solutions,

March 2011

• TechZone Library

• TechXchange

• Future Editions

8

Wireless Solutions | TZ W 112.US


In systems where H1 and H2 are low compared to d, Equations 2 and

3 can be simplifi ed to v

= h

=−1. For example, in systems with a low

incident angle, all of the energy is refl ected. The phase change of the

refl ected wave is signifi cant to the transmission budget, as illustrated

in Figure 2.

-20

-30

-40

-50

-60

-70

-80

-90

Friis equation compared to Ground model

-100

0 20 40 60 80 100 120 140 160 180 200

H1=H2=1.15 M.r=18. freq=2.445 MHz

[m]

Figure 2: Difference in transmission loss due to polarization.

Figure 2 shows the infl uence of polarization and the ground in open

fi eld measurements. The values are calculated using the Matlab

function described later in this article. The fi gure indicates a large

difference between the Friis Transmission Equation for free space

and the expected performance when ground infl uence is included.

The fi gure also indicates that the horizontal polarization (H) is more

susceptible to multipath fading than the vertical polarized signal (V).

Over long distances, the signal level including the ground is

considerably lower than predicted by the Friis Equation. Finally,

observe that the vertically polarized signals have higher energy at long

distance, when compared to the horizontally polarized signals.

Note: In many applications, there are strong cross-polarized

components, making it diffi cult to separate the polarizations. The actual

signal level is then often between the vertical and horizontal levels

calculated above.

Friis

V

H

-20

-30

-40

-50

-60

-70

-80

Ground model horizontal polarization

Friis

H-Polarization

Sens. level(CC2500@500 kbps)

-90

0 50 100

150

H1=H2=1.5 M, r=18, freq=2.445 MHz

[m]

Figure 3: Multipath fading.

Figure 3 shows calculated values for a 2.445 MHz horizontally

polarized signal. The Friis Equation for free space and the 500 kBaud

sensitivity level are included in the fi gure for comparison. If one

wanted to measure the effective open fi eld range for the CC2500 at

this data rate, they typically would start the EB PER test and begin

to increase the distance between the two radio units. The fi gure

indicates that communication would be lost at about 35 m.

Clearly, the range potential is far greater. To identify this unused

potential, the two units have to be separated further than 39 m to

regain communication.

The location of this blind spot will vary with frequency, ground

electrical characteristics, and antenna elevation. It is important to be

aware of this during measurement to identify if you have reached a

local blind spot or the fi nal range of the equipment.

The difference between the level predicted by the Friis equation and

the receiver sensitivity is often denoted as a fade margin.

Noise

Noise is another important parameter when considering range.

Noise can be categorized by its source. Thermal noise is noise

generated by all objects due to its molecular thermal activities.

Other radio traffi c may be considered another form of noise.

Article Resources

PTM and Another Geek Moment

• Texas Instruments -

Microcontrollers:

MSP430x2xx/4xx and

Wireless Overview

Related Products

• CC2500RTKR

• EZ430-RF2500

• CC2500EMK

Online Resources

Additional Links

• Component Reference

Guide

Wireless Solutions,

March 2011

• TechZone Library

• TechXchange

• Future Editions

9

Wireless Solutions | TZ W 112.US


The noise from other electrical equipment is inherently diffi cult to

describe in mathematic/statistical models. Equation 4 describes

thermal noise.

Equation 4

Temperature, effective noise bandwidth, and impedance determine the

total thermal noise.

At room temperature (300 K, 27°C) this equation is often

approximated by -174 dBm + 10Iog 10

(B), describing the situation

with a perfect load match.

Example:

CC2500 with 500 kBaud and BW = 812.5 kHz (recommended values)

gives a room temperature noise fl oor at -174 dBm + 59.1 dBm = -114.9

dBm. The sensitivity is specifi ed to be -83 dBm, resulting in an SNR

of 31.9 dB. An SNR of 31.9 dB is more than the demodulator requires,

clearly indicating the potential range extension using an external LNA

(CC2500 has a simulated typical noise fi gure of about 16 dB).

Thermal noise is not a problem during range measurements. It should

be verifi ed that the area used is free from other noise sources on the

same frequency band. This could be done using a spectrum-analyzer

(maximum hold) to look for noise sources prior to performing the test.

This check could preferably be repeated at regular intervals during

the test. Selecting a test area with low probability of interference is

generally recommended. A photograph of the test area used in my

model validation tests can be seen at the end of this article.

Do the math

Friis equation for free space

% friis_equation(Gt,Gr,f,n,d);

% This function is based on the theory in Application report SWRA046A

% This function calculates the propagation loss.

% path_loss_indoor = Gt·Gr·(C/(4·pi·f))^2·(1/d)^n

% Gt: Gain in transmitter antenna [dB]

% Gr: Gain in receiving antenna [dB]

% f: Carrier frequency [Hz]

% d: distance in meter [m]

% n: path loss exponent (See table below)

%

% Location n std. deviation

% Free space 2.0

% Retail store 2.2 8.7

% Grocery store 1.8 5.7

% Offi ce, hard partitions 3.0 7.0

% Offi ce, soft partitions 2.6 14.1

% Metalworking factory, line of sight 1.6 5,8

% Metalworking factory, obstructed line of sight 3.3 6.8

% Constants:

% c = 299.972458e6; Speed of light in vacuum [m/s]

function out=friis_equation(Gt,Gr,f,n,d);

c = 299.972458e6; % Speed of light in vacuum [m/s]

out = (Gt + Gr + 20*log10(c/(4* pi*f)) - n*10*log 10(d)); % Loss in [dB]

Friis equation with ground reflection

% friis_equation_with_ground_presence(h1,h2,d,freq,er,pol)

% This function calculate the loss of a radio link with

ground presence

% h1: Transmitting antenna elevation above ground.

% h2: Receiving antenna elevation above ground.

% d: Distance between the two antennas (projected onto

ground plane)

% er: Relative permittivity of ground.

% pol: Polarization of signal ‘H’=horizontal, ‘V’=vertical

% freq: Signal frequency in Hz

% Transmitting and receiving antenna assumed ideal

isotropic G=0dB

% ********************************************************

**************

function retvar=friis_equation_with_ground_

presence(h1,h2,d,freq,er,pol)

Article Resources

PTM and Another Geek Moment

• Texas Instruments -

Microcontrollers:

MSP430x2xx/4xx and

Wireless Overview

Related Products

• CC2500RTKR

• EZ430-RF2500

• CC2500EMK

Online Resources

Additional Links

• Component Reference

Guide

Wireless Solutions,

March 2011

• TechZone Library

• TechXchange

• Future Editions

10

Wireless Solutions | TZ W 112.US


c=299.972458e6; % Speed of light in vaccum [m/s]

Gr=1;

% Antenna Gain receiving antenna.

Gt=1;

% Antenna Gain transmitting antenna.

Pt=1e-3; % Energy to the transmitting antenna [Watt]

lambda=c/freq;

% m

phi=atan((h1+h2)./d);

% phi incident angle

to ground.

direct_wave=sqrt(abs(h1-h2)^2+d.^2); % Distance, traveled

direct wave

refl_wave=sqrt(d.^2+(h1+h2)^2); % Distance, traveled

reflected wave

if (pol==’H’) % horizontal polarization reflection

coefficient

gamma=(sin(phi)-sqrt(er-cos(phi).^2))./

(sin(phi)+sqrt(er-cos(phi).^2));

else

if (pol==’V’)% vertical polarization reflection

coefficient

gamma=(er.*sin(phi)-sqrt(er-cos(phi).^2))./

(er.*sin(phi)+sqrt(ercos(phi).^2));

else

error([pol,’ is not an valid polarization’]);

end %if

end %if

length_diff=refl_wave-direct_wave;

cos_phase_diff=cos(length_diff.*2*pi/lambda).*sign(gamma);

Direct_energy=Pt*Gt*Gr*lambda^2./((4*pi*direct_wave).^2);

reflected_energy=Pt*Gt*Gr*lambda^2./((4*pi*refl_

wave).^2).*abs(gamma);

Total_received_energy=Direct_energy+cos_phase_

diff.*reflected_energy;

Total_received_energy_dBm=10*log10(Total_received_

energy*1e3);

retvar=Total_received_energy_dBm;

%end function

Validating the ground reflection model

0

-20

-40

-60

Measured/Simulated signal strength at different heights above ground

-80

31 cm

-100

115 cm

7 cm

-120

0 10 20 30 40 50 60 70 80 90 100

[m]

Figure 4: Signal strengths at the 7 cm, 31 cm and 115 cm elevation levels.

Figure 4 shows a comparison between the CC2500 operated in a

SmartRFO4EB and the Matlab ground refl ection model.

The measurements were performed on a football/soccer fi eld.

Dots are measurements and lines represent calculated values.

A fi xed correction level was added to the calculated values to get an

overall better match to the measured values. This correction value

represents the difference between the ideal isotropic antenna and the

effi ciency of the CC2500EM and SmartRF Studio EB. The plotted values

are the values measured.

The measured signal energy was higher for the horizontal polarized

signal. This is explained by the directivity of a horizontal-oriented,

quarter wave antenna. When the same antenna is vertically oriented,

the energy is radiated in all directions, hence reducing effective gain in

the direction of the receiver.

The open test field

A rural environment signifi cantly reduces the probability of 2.4 GHz

interference. The following photo shows the test area where the Matlab

ground model was validated.

Note that the EB was mounted on a plastic pole to minimize its

infl uence on the measurement results.

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The iron light towers showed no real infl uence on measurements.

They were suffi ciently far away to allow the direct and ground refl ected

signals to be the only signifi cant contributors to the total received power.

The body had signifi cant infl uence on the measurement.

The measurement at each distance point was performed in my

absence. This made the measurements extremely time consuming.

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Microcontrollers:

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Summary

This article addressed the ground infl uence during range measurements.

It was shown that multipath fading can generate confusion during

measurements if you are unaware of the phenomenon. Ground presence

was shown to generate more rapid signal degradation than predicted by

the Friis equation for free space. Ground reduces the effective range.

Vertical polarization was shown to be less susceptible to ground

refl ection fading and range degradation than horizontal polarization.

For handheld equipment, polarization is generally not controllable and

this observation has minor importance.

Finally, it has been emphasized that other radio traffi c infl uences range

measurements, and should be controlled or monitored throughout the

measurements. (Did you remember to turn off your mobile Bluetooth ®

during measurement) Coexistence with other equipment is generally

not implemented in test software for range measurements.

References

1. Radar Technology Encyclopedia, David K. Barton, Sergey A. Leonov 1997 Artech House Inc

Boston/London, ISBN 0-89006-893-3.

BUY NOW!

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ZigBee: A Global

Wireless Standard

ZigBee devices operate on different frequencies

in different geographies, though, to date,

multi-frequency, multi-profile solutions have been

elusive. Now by choosing the right low-power RF

transceiver, the world can be your oyster.

The ZigBee ® standard has existed for many years and has faced

similar challenges to other wireless standards. These challenges

include different development stages, early adopter incompatibilities,

and many discussions about the right direction to move forward

between the ZigBee alliance members.

However, with the introduction of the public application profiles, the

standard has reached a stage which can be now called mature – an

application layer compatibility primarily achieved by a finalized

specification and the ZigBee logo testing procedures. The test houses

ensure by their testing program that all devices not only use the same

network layer standard for sending data through the networks, but

also assure secured communication between the devices – achieved

with the ZigBee Pro feature set. In addition, testing programs

verify that end products with the ZigBee-certified product logos have

passed an intensive testing procedure, ensuring that messages sent

by the applications follow a defined protocol, as defined by the public

application profiles.

contributed by Atmel

Standard profiles

Profile compatibility will be made visible to end users by a set of

easy-to-recognize logos which show the supported application profile.

The currently existing profiles (see Figure 1) are:

• ZigBee Smart Energy

• ZigBee Home Automation

• ZigBee Health Care

• ZigBee Building Automation

• ZigBee Telecommunication Services

• ZigBee Retail Services

• ZigBee Remote Control

Figure 1: ZigBee public application profiles.

While some of these public profile specifications are still in

development, the most important ones have been finalized. There

are many certified products in the market based on these profiles.

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The profiles that currently have the most significance in the

market are Zigbee Smart Energy, ZigBee Home Automation, ZigBee

Telecommunication Services, and ZigBee Remote Control.

The ZigBee Smart Energy standard defines devices that offer many types

of energy management and control, such as electricity meters, load

control units, and in-home displays for direct user interaction with the

network. The ZigBee Home Automation standard covers devices such as

light switches, dimmers, HVAC, and blind controls.

Another new public profile for end products is the ZigBee Remote

Control profile, often referred to as ZigBee RF4CE. This profile enables

a completely new generation of RF remote controls for consumer

electronics such as TVs or set-top boxes. It enables AES-encrypted,

two-way communication links between the remote control and the

consumer electronic device which do not need a line-of-sight, such as

infrared remote controls. Due to the dedicated backchannel from a TV

to the remote control, new feature-rich remote controls will improve the

user experience.

The ZigBee standard is based on the IEEE 802.15.4-2003 standard and

implies that ZigBee applications can use the MAC and PHY features

described by this international IEEE standard. The IEEE standard’s

physical layer specification describes the modulation schemes, data

rates, device roles, data transfer concepts, and frequency bands that

can be used. The most commonly used frequency is the 2.4 GHz ISM

band. The IEEE 802.15.4 standard allows the use of a 250 Kbit/s data

rate in this global frequency band. This frequency band is also used by

technologies such as IEEE 802.11 or IEEE 802.15.1, which are better

known by the terms Wi-Fi ® and Bluetooth ® .

Going global

The IEEE 802.15.4 standard specifies a spread-spectrum technology

to enable robust resistance to interference in heavily-used frequency

bands in order to ensure the proper operation of ZigBee devices even

in the presence of Bluetooth networks. The standard also offers another

very useful option: the use of regional frequency bands.

The frequencies that can be used are commonly referred to as “sub-1

GHz,” meaning bands located in the range below 1 GHz.

There are four ratified frequency bands which provide applications with

a better signal range and propagation due to the lower frequency.

The use of these frequency bands show reduced negative effects,

inherent with multipath propagation, in indoor environments where the

2.4 GHz signals can be more easily reflected by planar surfaces and

metal structures and attenuated by moisture in the air.

Those frequency bands and their related regions are:

950 MHz – Japan

902 MHz – North America, Australia

868 MHz – Europe

780 MHz – China

The use of those bands allows developers to build products for

global as well as regional markets. This also enables products that

use identical application and network layers like ZigBee in different

frequency bands, with the advantage of flexible RF parameters such as

usable output power.

Application segments such as smart metering and home automation

also benefit from this, since it is easier to enable products that have a

better transmission range or wall penetration. It also allows wireless

networks to cover an entire building without employing expensive

power amplification circuitry. One advantage of the sub-1 GHz

signals is that they enable a direct connection between a meter in the

basement with an in-home display on the first floor of a residential

building. All that is needed to support such flexible, multi-frequency

applications is RF transmission systems that support those different

frequency bands.

Atmel ® Corporation is one of the few companies that supports the

2.4 GHz band and offers devices that can operate in three of the four

mentioned sub-1 GHz frequency bands. In the Atmel AT86RF212, there

is a low-power RF transceiver for the IEEE 802.15.4 standard that can

be used in North America, Europe, and China (see Table 1).

Together with readily available, pin-compatible devices that operate in

the 2.4 GHz band, the developer gets an ultra-flexible solution which

addresses different range requirements as well as products that can be

designed for regional markets.

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Table 1: Atmel ZigBee transceivers.

Device ISM Band (GHz/MHz) Max Bit Rate (Kbps/Mbps) Max RX Sens (dBm) TX PWR (dBm) Link Budget (dB) Vcc Range (V) Package

ATmega128RFA1 2.4 GHz 2 Mbps -100 -17 to +3.5 103.5 1.8 - 3.6 QFN64

AT86RF230 2.5 GHz 250 kbps -101 -17 to +3 104 1.8 - 3.6 QFN32

AT86RF231 2.4 GHz 2 Mbps -101 -17 to +3 104 1.8 - 3.6 QFN32

AT86RF212 780 MHz

868 MHz

915 MHz

1 Mbps -110 -11 to +10 120 1.8 - 3.6 QFN32

All of the RF devices that operate according to the IEEE standard can

be used to run identical applications such as ZigBee Smart Energy and

ZigBee Home Automation.

Atmel Corporation offers a ZigBee Pro stack-certified platform and

has enabled support for various public application profiles. These

products are available to developers with the BitCloud Profile

Suite that contains support for devices in the ZigBee Smart Energy,

ZigBee Home Automation, and ZigBee Building Automation standards

(see Figure 2). The most recent release of Atmel’s RF4CE stack

package, RF4Control, gives developers the opportunity to implement

ZigBee remote controls that support the newest ZigBee Remote

Control profile.

These software packages make the application implementation in

the different frequency bands very straightforward, since the APIs

are identical. In addition, an application developer does not need to

write different application code for products to be usable in different

regions of the world. This reduces time-to-market and increases the

addressable market segments.

The flexibility that is offered with these different public application

profiles and RF devices for these four different frequency bands

enables versatile products for most emerging wireless markets.

Atmel Corporation is one of the first companies to offer the hardware

required to run identical ZigBee stack applications in different IEEE

frequency bands.

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• ATAVRRZ201-ND

• AT86RF231-ZU-ND

• AT86RF212-ZU-ND

Application

Profiles (Zigbee

Alliance and

OEMs)

Stack Feature

Set (Zigbee

Alliance)

Medium Access

and Radio

(IEEE 802.15.4)

Zigbee Architecture

Public App

Custom OEM

ZigBee Cluster Library

APS

NWK

MAC

PHY

Figure 2: The Atmel BitCloud Profile Suite.

ZDO

Atmel Solutions

ZigBee PRO

Feature Set

IEEE 802.15.4 MAC

BitCloud

Profile

Suite

BitCloud

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Wireless Solutions Trivia

Are you a Wireless Solutions Expert Submit your answers to find

out and automatically be entered for a chance to win a Prize Pack

from Panasonic!

The Panasonic Prize Pack

includes the following:

• a black Panasonic tote

• a water bottle

• a golf hat

• a Post-It pad pack

• a password book

• black pens (2)

• a USB Double Plug

• a spiral bound book

• a power clip

Sponsored by:

CLICK HERE

to submit your answers

Official Rules: No purchase necessary to enter or claim prize. A purchase will not improve an individual’s chances of winning with such entry. Employees of Digi-Key (the

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participation in the trivia contest and providing name and e-mail address. Prizes will be randomly drawn among eligible entries on or about September 7, 2011. Ten Panasonic

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for late, lost, damaged or misdirected entries. Any attempts to deliberately damage any web site or undermine the legitimate operation of the promotion may be subject to

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1. The PAN1315/PAN1325 modules are based on what Bluetooth core IC

A: Freescale MC72000 C: Broadcom2004

B: Microchip PIC24FJ256GB110 D: Texas Instruments CC2560

2. What is the difference between the PAN1311 and PAN1321 modules

A: The PAN1311 is Bluetooth v2.0 + EDR, PAN1321 is Bluetooth v2.1 + EDR

B: The PAN1321 has an integrated antenna

C: The PAN1321 has a wider operating temperature range

D: The PAN1311 has a lower power output

3. What is the additional protocol supported by the PAN1317/PAN1327 modules besides

Bluetooth

A: ANT+ by Dynastream C: WAP

B: IEEE 802.11 D: ZigBee

4. What does ETU stand for at the end of PAN1315ETU

A: Ethernet Termination Unit C: Easy To Use

B: Elementary Time Unit D: Engineering Test Unit

5. IEEE 802.15.4 modules such as the PAN4561 operate at what frequency

A: 868 MHz C: 2.4 Ghz

B: 915 MHz D: None of the above

6. PAN1315/PAN1325 modules are made to interface with what microcontroller

A: Atmel AT32UC3A0512-ALTRA C: Maxim DS80C411-FNY+

B: Texas Instruments MSP430 D: Cypress CY8CLED03G01-56LTXI

7. In regards to Bluetooth what does HCI stand for

A: Human Computer Interface C: High Charge Interface

B: Hardware Confi guration Item D: Host Controller Interface

8. Which of the wireless applications below is not stated by Panasonic as being suitable

for the PAN1315 module

A: Sensors C: Cable replacement

B: Printers D: Ethernet router

9. Does the PAN1555 module have an integrated antenna

A: Yes B: No

10. What version of Bluetooth does the PAN1555 module run

A: v1.2 C: v3.0 + HS

B: v2.0 + EDR D: v4.0

16

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Moving Beyond ZigBee

for Star Networks

It is important to consider the actual data flow

when implementing a mesh network. Despite its

numerous advantages in M2M applications,

ZigBee may not always be the best choice.

by Chris Downey, Laird Technologies

In fact, in star networks, the amount of overhead required for a ZigBee

network may be restrictive to an optimal solution.

Figure 1 shows an example of a star network with multiple end nodes

which all communicate to a single central sever.

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Multi-hop mesh protocols, such as ZigBee ® , are getting a lot of press

for their ability to link together low data rate, machine-to-machine

(M2M) applications. ZigBee, in particular, is targeting itself as the

standard bearer for wireless, low-power mesh protocols. Many of

the features of a ZigBee solution touch on the requirements for the

expanding wireless M2M markets. Low data rate, low power, enhanced

range through the mesh, and automated on-demand routing of packet

data are key aspects of ZigBee that are creating such a buzz in the

M2M market space.

Client

Central Computer

Server

Client

Client

Requirements for star networks

It is important to consider the actual data flow through the network

when implementing a ZigBee-type mesh. While all nodes may be

capable of communicating with each other, in reality, most networks

are point to multipoint (or multipoint to point depending on your

perspective), and form a star topology. Data flows from a central server

to specific end points which collect data or provide some sort of action.

Data from the end points is also able to flow back to the central point.

This is the basic network flow for the majority of wireless sensor and

control applications including building automation, telehealth, smart

energy, and retail. For a star network, a multi-hop mesh is not a

requirement, but rather a feature to ensure connectivity from all nodes.

Figure 1: Star network.

Client

Client

Client

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Review of ZigBee for star applications

ZigBee has a dual-layer addressing scheme, with a lower-layer IEEE

address hard-coded on nodes and a dynamically assigned Network

Address used for transport. Only the Network Address is used to route

data, so an end user must translate between the IEEE address and

the Network Address to properly address packets. This is analogous

to how ARP operates in traditional Ethernet networks. This dual-layer

addressing is common for routed networks and provides a layer of

abstraction from the hardware (IEEE) layer. For star networks, it only

serves to provide another layer of complexity to a simple issue of

connectivity as seen in Figure 2.

End Device

Central Computer

Coordinator

End Device

RF which can radiate up to 100 mW per CE regulations - ten times the

output power. This limitation reduces the overall power consumption of

the module, but also limits the range of the module. ZigBee addresses

this range issue with the multi-hop mesh routing.

Adding routers to provide connectivity has drawbacks. First,

it increases the overall cost of the system, as there is a requirement

for more transceivers. Second, as each packet is routed through an

additional node, the overall latency of the system increases, because a

node only has a single transceiver and cannot transmit and receive at

the same time. The latency can be further increased if there is a need

to perform a route request prior to transporting the data packet.

The complexity of the data traffic is presented in Figure 3.

Source Node Router 1 Router 2 End Node

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End Device

Router

Router

End Device

Figure 2: Star network implemented over a multi-hop mesh.

End Device

End Device

The ZigBee mesh is based on an underlying RF protocol defined by

the IEEE 802.15.4 standard. IEEE 802.15.4 is a direct sequence spread

spectrum (DSSS) modulation system designed to operate in the 868 MHz,

900 MHz, and 2.4 GHz ISM bands. In practice, most transceivers operate

at 2.4 GHz as it provides worldwide acceptance and the higher 250 kbps

RF data rates. In many parts of the world, including Europe, 2.4 GHz DSSS

transceivers are limited to 10 mW of radiated output power. Compare

this to frequency hopping systems such as Bluetooth ® and proprietary

Figure 3: ZigBee packet delivery.

In Figure 3, if you assume each of the ten transmissions takes at least

10 ms (which would not take into account the need to retransmit any

data), then it would take over 100 ms for the user to receive their

acknowledgement back.

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ZigBee Pro, the third major revision of the ZigBee specification,

addresses this by implementing source routing. Source routing can

reduce the amount of route requests required, but adds additional

overhead to the data packets sent across the air by including each

hop’s network address in the packet. The high latency can restrict

a ZigBee network’s ability to effectively stream data from one point

to another. If the ZigBee nodes can only transmit 100 bytes of data

with every packet transmission, than at 100 bytes every 100 ms, the

actual data rate is only 8 kbps – less than the 9600 baud rate many

applications use for data transfer. It is much less than the 115,200 bps

that many more applications require. Due to these restrictions, all data

must be managed as discrete packets, sent at infrequent intervals.

Finally, if additional routers are required to provide connectivity, the

end user is responsible for providing the infrastructure to support the

intermediate routers. Additional nodes do not just bring additional

costs, they also must be located near a power source and must be

located to provide optimum coverage.

Laird Technologies Solution

Coverage issues can often be resolved by substituting the

lower-power intermediate router with higher-power transmitters at

each end of the link. Moving from 10 mW to 100 mW will provide

a 10 dBm gain in the link budget – roughly a 2.5 times increase

in range. In addition, for non-CE markets, such as North America,

higher output powers up to 1 W are available to provide additional

coverage. Once free from the constraints of ZigBee’s power and data

rate restrictions, end users can choose from a wealth of standard and

proprietary solutions for M2M applications.

One example is Laird Technologies’ LT2510 series of frequency

hopping serial-to-wireless modules. Designed for industrial M2M

applications, the LT2510 series offers best-in-class range and

throughput in a small, cost-effective form factor. The LT2510 series

features intelligent server/client architecture, ideal for point-to-point

and star networks. The intelligence of these devices abstracts the

complex underlying RF protocols, and their higher output power

eliminates the need for multiple devices to provide connectivity over

large distances. The LT2510 series allows for an unlimited number of

clients to automatically sync to a single server, the central point in a

star system. The end user then is presented with a direct serial link

from their host device to the host connected to the central server.

With ranges up to 2.5 miles, the LT2510 series provides a large

coverage area for star networks. Figure 4 shows the same user data

sent over a comparable LT2510 system.

Source Node

Figure 4: LT2510 packet delivery.

End Node

Since the LT2510 series modules are offered with higher output power,

the entire link can be managed with just the two principle nodes. There

is no need for intermediate routers or a routing protocol. The data flows

from the source to the destination, and the acknowledgment can be

received in as little as 6.5 ms (assuming there are no retries).

Acknowledgements in less than 30 ms are typical for most networks.

With optimal configurations, line rates of 115,200 bps are possible to

allow for streaming data across the wireless link.

While the LT2510 series modules provide a very easy, fully certified

implementation for a serial to wireless network, they also provide a

number of advanced features which the OEM host can use to optimize

performance. These features include a reduced idle current draw of

less than 10 mA, 50 µA sleep states with the ability to wake up and

transmit in less than 26 ms, and advanced API features to quickly

redirect transmitted data using API headers. In addition, the LT2510

series has RF modes that allow for 500 kbps RF data rate, twice the

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ate of 802.15.4 ZigBee networks. The combination of easy-to-use,

quick time-to-market, and global certifications allow the OEM to

integrate the LT2510 modules into designs for star networks quickly

and cost-effectively.

Summary

Star networks present unique challenges in managing the number of

end nodes, ensuring connectivity, and balancing data from, and to,

the source point. These challenges are enough without adding the

unnecessary overhead from a multi-hop mesh solution. Identifying the

key requirements and selecting a wireless solution which is optimized

for star networks can reduce time-to-market and provide for a more

robust solution. Table 1 highlights some of the key attributes of a

typical ZigBee 10 mW transceiver and the LT2510 100 mW transceiver.

Table 1: Comparison of the LT2510 100 mW versus the generic ZigBee 10 mW transceiver.

Feature

Output Power Radiated in

CE markets

Generic Zigbee

LT2510 Transceiver

Transceiver

10 mW 100 mW

Receiver Sensitivity -96 dBm* -98 dBm (@280 kbps RF

Rate)

Point to Point range (with

10 dBm Fade margin

Number of nodes to cover

a 1.5 mile distance

Addressing

Latency for 1.5 mile

transmission (with

requests, no retries)

.5 miles 1.5 miles (2.5 miles for

125 mW module )

2- end point + 2- Routers 2- just the end points

Complex (network and

IEEE)

100 ms (assuming 10 ms

per hop)

Simple (MAC only)

6.5 ms

Throughput 115.2 kbps

*Numbers based on average transceiver, not a specific transceiver

ZigBee has some great features which make it a powerful protocol

for M2M communications, but that does not mean it is optimized for

all networks. Star networks can benefit from a simpler, more

effective solution.

Bluetooth ® Audio and

Multimedia Modules

BTM511 Audio Modules

The BTM511 is a low-power Bluetooth ® module designed for adding

robust audio and voice capabilities. Based on the market-leading

Cambridge Silicon Radio BC05 chipset, this module provides

exceptionally low-power consumption with outstanding range. Supporting

the latest Bluetooth Version 2.1+EDR specification, the BTM511 provides

the important advantage of secure simple pairing that improves security

and enhances easy use. In addition, the BTM511

contains an onboard digital signal processor and

supports CSR’s high quality apt-X audio codec for

wire quality sound via a Bluetooth connection.

At only 14 mm x 25 mm, the compact size

of the BTM511 makes it ideal for batterypowered

or headset form factor audio and

voice devices.

BTM521 Multimedia Modules

The BTM521 is one of the most advanced low-power, multimedia

Bluetooth ® modules available in the marketplace. Designed to meet the

needs of developers requiring the ultimate Bluetooth audio performance

and flexibility, this module includes everything

required for a fully qualified and functional Bluetooth

multimedia application.

The BTM521 includes a 16-bit stereo codec and

microphone input to support both stereo and

mono applications, with the ability to drive stereo

speakers. Containing all the necessary audio

filtration and biasing components, this module only

requires the addition of speakers, microphone, and push

buttons to make a high-quality Bluetooth stereo product.

BUY NOW!

Article Resources

PTM and Another Geek Moment

• Laird Technologies -

ConnexLink Overview

Related Products

• PRM112-ND

• PRM113-ND

• DVK-PRM110-ND

• DVK-PRM111-ND

• PRM110-ND

• PRM111-ND

• DVK-PRM112-ND

• DVK-PRM113-ND

Online Resources

Additional Links

• Component Reference

Guide

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Leading the Way

in Collaboration

Whether you are a home hobbyist repairing a

television, an engineering student constructing

a robot for a final project, or an engineer for an

electronics OEM inventing the latest gadget, problems

will arise. With any project, there will be obstacles

to overcome, and answers to these questions and

concerns are not always easy to acquire. The Internet

is a fantastic resource for a myriad of opinions and

possibilities, but sifting through the inadequacies to

find credible sources is not always easy. The answers

you need are just a click away on Digi-Key’s exciting

new community forum.

21

Wireless Solutions | TZ W 112.US


engineers

Enter TechXchange SM , Digi-Key’s newest addition to an already impressive list of

features available, at no cost to you, on its award-winning website,

www.digikey.com. TechXchange was born of Digi-Key’s continuing initiative to

provide its customers with the best service possible, from design to implementation.

Help with technical problems has always been just a phone call away, as Digi-Key’s

talented staff of technical advisors are always ready and willing to help customers

with any issues that may arise. Now you can access solutions from the convenience

of your home computer through the forum on TechXchange, the next step in

improving customer access to technical assistance and allowing individuals to have a

larger role in their own problem-solving process.

TechXchange is a community forum where everyone from design engineers to

hobbyists can discuss technology, products, designs, and more. Users can participate

in discussions, ask questions of the community, and learn about new products and the

22

hobbyists

discussions

power

microcontroller

students

industry experts

community

wireless

technical documents

lighting

sensor

resources

application notes

white papers

links

reference designs

latest innovations. The forum is divided into fi ve separate sections, or communities:

Lighting, Microcontroller, Power, Sensors, and Wireless. A General Community is also

available if your question does not fi t easily into a specifi c category. Each section is

moderated by approved subject matter specialists who are ready and able to answer

any questions that are posted in the forum. Users are also encouraged to share their

expertise and reply to posted questions.

Each of the TechXchange sections coincides with a corresponding TechZone SM on the

Digi-Key website. These TechZones are invaluable resources that go hand-in-hand with

TechXchange by providing product guides, application notes, reference designs, white

papers, product training modules and more for the over two million products that are

available on the Digi-Key website from over 470 electronic component suppliers.

Users also have direct access to TechZone SM Interactive via the link at the top of the

section with which the publication corresponds.

TechXchange includes a fully-searchable discussion archive. Every discussion that

appears on TechXchange will be available via search. The value of this feature will

only grow as the content of the site increases day by day.

To ensure users are getting quality answers from reliable sources, Digi-Key has

implemented a rating system for TechXchange. This system indicates those individuals,

whether Digi-Key staff or not, who have the highest level of accuracy and participation

within the community. These people are given special recognition for their commitment

in a special box on each section page.

As TechXchange grows, so will the diversity of opinions that are given through the

community experience, making it a valuable resource for important information.

So, when that seemingly insurmountable problem arises during your next project,

remember that Digi-Key is always here to help, and that TechXchange should be

your fi rst stop in your quest for information.

Become a member today!

www.digikey.com/techxchange

Wireless Solutions | TZ W 112.US


Making Choices in Wireless Networks:

To Each Application Its Own

Sub-GHz proprietary protocols are often the best

choice for low power, low data rate wireless

networks due to their extended range, ease of

implementation, and small code size.

Designers know there are a myriad of choices for sending data

wirelessly. These include simple command and control schemes,

such as Remote Keyless Entry (RKE) and garage door openers, and

the more complex WLAN. This article presents various options and

their limitations as they pertain to choosing a wireless network for

industrial applications.

RKE systems are used in automobiles to lock and unlock doors,

offering an excellent example of simple command and control

applications. In an RKE application, a command is sent from a key

fob to a car receiver. In response to a properly received command,

the car is either locked or unlocked.

Receivers in similarly made automobiles can theoretically accept

packets sent from any similar model key fob. However, the car will

only accept commands from the unique key fob assigned to it. Security

protocols like rolling code generators and security encryption are

utilized to transmit a unique ID from the key fob to the car. In this way,

a driver’s key fob is not able to unlock a similar model car.

In the case of automobile RKE, the key fob operator typically hears the

locks being engaged. If this audible feedback “click” is not heard, the

operator simply presses the button again, completing the feedback loop.

by Vince Stueve, Micrel, Inc.

To put it in simple terms, if you don’t hear the car unlock, you press the

button again until you do.

uC

Figure 1: RKE application.

RF

Transmitter

Typical RKE Application

Passing of Command and Control

The sending of a temperature reading from a sensor to a host

computer is an example of command and control type data useful in

industrial applications. The difference between industrial applications

and RKE is that there is no human involved to decide if the temperature

indication was actually received.

The need for this type of acknowledged receipt of data dictates that a

two-way network be used. The level of system complexity immediately

goes up as the need for more actuators, switches, and motors

become necessary. Thus, the use of simple one way RKE networks is

usually not implemented for industrial networks, due to the need for

acknowledgment that the data sent actually got through.

Article Resources

Product Information

• Frequency Hopping

Techniques

• MICRF505/506 Basic:

Handling the Control

Interface

• MICRF505/506 Basic:

Handling the Data

Interface

• MICRF505/506/600/

610/620 User Guide

• MICRF50x/6x0 RF Test

Bench User Guide

Related Products

• MICRF505YML TR

• MICRF505DEV1

Online Resources

Additional Links

• Component Reference

Guide

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• Future Editions

23

Wireless Solutions | TZ W 112.US


Each node of an industrial wireless solution utilizes a microcontroller.

The microcontroller then interfaces to real world devices such as

temperature sensors and actuators to read or write to them. At the

same time, the microcontroller manages an RF network protocol. The

protocol chosen depends upon a number of factors. Range, data rate,

power consumption, and the complexity of the network protocol stack

are the issues that determine which solution will work best.

ZigBee ® has received a lot of attention. As a standard, ZigBee or IEEE

802.15.4 initially appears to be an excellent choice for many low

power, low data rate wireless communication applications. However,

ZigBee is not a one-size-fi ts-all technology. There are circumstances

where 802.11 WLAN will work well with high data rate traffi c. Further,

there are applications that require longer range and more battery life.

In short, specifi c architectures will drive the type of wireless network

chosen for any given application.

In wireless networks, as the data rate increases, there is a

corresponding increase in system resources. For example, with respect

to 802.11 WLAN, these protocols will not work for most embedded

applications due to power consumption and the code size needed

for a network. A typical 802.11 WLAN node requires up to 1 MByte of

program memory and a higher functioning processor to make even a

single functioning node.

The relatively low-power consumption of the 802.11 WLAN radio plus

a system processor make it well suited to computing applications and

the backhaul of information on an industrial network. However, portable

nodes suffer from the amount of power required and system resources

necessary to realize a functioning node of 802.11 WLAN. Tasks, such

as remote monitoring of temperatures, pressures, and actuation cannot

allow for the large power consumption, code size, and expense of

802.11 WLAN.

ZigBee protocols are relatively modest with respect to code space

(32 to 70 KByte), and they enable a moderate range (10 to 100

meters). These attributes make ZigBee a good fi rst choice for industrial

networking. One of the major benefi ts of ZigBee is its “mesh”

capability. Mesh networks pass messages from node to node. If any

of the nodes fail or drop out, the message can still reach its intended

destination. Mesh networks require sophisticated handling of packets

and therefore more program memory. Figure 2 illustrates the relative

code size of several different wireless networking protocols.

1000

100

10

1

8 KByte

ISM Band

“Proprietary

Networks”

315,433,

915 MHz

32-70 KByte

ZigBee TM

2.4 GHz WW

915 MHz NA

868 MHz Europe

Figure 2: System resources required for various RF networks.

Bluetooth ® is another option that is considered for industrial

applications. However, the short range and the sizeable code

requirements, along with the fact that Bluetooth is a point-to-point

communication scheme, remove it from the list of possibilities.

Then there are proprietary networks, operating independent of

standards, to consider. These typically fall in the 915 MHz and

2.4 GHz ISM bands. Occasionally, 315 MHz or 433 MHz are also used

for command and control applications. Local regulatory requirements

often dictate which frequency can be used.

As an RF signal travels through the air, its power level decreases at a

rate inversely proportional to the distance traveled and proportional to

the frequency. The free space path loss equation is shown below along,

with a corresponding graph of path loss versus distance for various

frequencies, in Figure 3.

Where d = distance in meters

λ = wavelength in meters

250 KByte

Bluetooth

2.4 GHz

1 MByte

WLAN

2.4 GHz,

5.6 GHz

Article Resources

Product Information

• Frequency Hopping

Techniques

• MICRF505/506 Basic:

Handling the Control

Interface

• MICRF505/506 Basic:

Handling the Data

Interface

• MICRF505/506/600/

610/620 User Guide

• MICRF50x/6x0 RF Test

Bench User Guide

Related Products

• MICRF505YML TR

• MICRF505DEV1

Online Resources

Additional Links

• Component Reference

Guide

Wireless Solutions,

March 2011

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• TechXchange

• Future Editions

24

Wireless Solutions | TZ W 112.US


120.0

100.0

80.0

60.0

40.0

Path Loss Versus Distance for Various Frequencies

20.0

Distance (Meters)

Figure 3: Path loss versus distance for various frequencies.

2.4 GHz

915 MHz

433 MHz

At 100 meters, the following path loss is present for a transmission in

free space:

2.4 GHz, 80 dB

915 MHz, 72 dB (8 dB less path loss than 2.4 GHz)

433 MHz, 65 dB (15 dB less path loss than 2.4 GHz)

In RF systems, the received signal is the sum of the transmitted power

plus the antenna gain of the system less the path loss, as shown in the

following equation:

Where R = Received Signal Strength

P t

= Power Transmitted

G ant

= Antenna Gain

L = Path Loss

For a system that puts out 10 dBm of power and has an antenna

system gain of zero, one would calculate the received signal at 100

meters of ideal free space to be:

2.4 GHz, -70 dB

915 MHz, -62 dB

433 MHz, -55 dB

This means that the receiver for a 2.4 GHz system must have at

least -70 dB sensitivity in order to detect signals in the ideal free

space environment.

In addition to free space path loss, the transmitted signal also

has attenuation due to buildings, vegetation, and other objects.

Additional challenges, such as multipath and signal dispersion, are

factors as the receiver attempts to decode the incoming RF signal.

Other path loss models, such as the Hata Model, take into account

the distance of the antenna above the ground and losses due to

the effects of being in an urban area; these models yield more

realistic indications of path loss. Actual path loss numbers are

considerably higher for most applications than what is depicted

in Figure 3. Interestingly, as the frequency increases, so does the

path loss. This is one reason that 2.4 GHz systems exhibit less

range than comparable 915 MHz or 433 MHz systems.

A commonly used rule of thumb in RF engineering is that a 6 dB

increase in the link budget will roughly double transmission distance.

With this in mind, a 915 MHz system will have twice the transmission

distance of a comparable 2.4 GHz system, and a 433 MHz system will

again have twice the distance of one operating at 915 MHz. Thus the

lower frequency systems provide longer distance transmission of data.

Data rate also plays an important role when choosing the frequency

and modulation for an industrial network. As previously discussed,

remote temperature monitoring and actuation applications function

best when constructed with proprietary networks running small

software stacks at low power. The ability to customize the data

packet for the intended application can greatly simplify these

proprietary networks.

The range, or reach, of wireless solutions using ISM band proprietary

networks is often much better than what can be realized with ZigBee,

Bluetooth, or WLAN. In addition to the reduced path loss of proprietary

networks operating at lower frequencies, other factors can increase

the range of such networks. Smaller data packets, lower data rates,

and the ability to send multiple copies of the data are all reasons that

proprietary networks often outperform standards-based networks.

Figure 4 shows a comparison of reach versus technology for different

wireless networks.

Article Resources

Product Information

• Frequency Hopping

Techniques

• MICRF505/506 Basic:

Handling the Control

Interface

• MICRF505/506 Basic:

Handling the Data

Interface

• MICRF505/506/600/

610/620 User Guide

• MICRF50x/6x0 RF Test

Bench User Guide

Related Products

• MICRF505YML TR

• MICRF505DEV1

Online Resources

Additional Links

• Component Reference

Guide

Wireless Solutions,

March 2011

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• TechXchange

• Future Editions

25

Wireless Solutions | TZ W 112.US


1000

100

10

Up to 200 Kbps

ISM Band

“Proprietary

Networks”

315,433,

915 MHz

20-250 bps

ZigBee TM

2.4 GHz WW

915 MHz NA

868 MHz Europe

Figure 4: Reach versus technology for various RF networks.

1-3 Mbps

Bluetooth

2.4 GHz

11-54 Mbps

WLAN

2.4 GHz,

5.6 GHz

The power consumption of ZigBee and ISM band proprietary networks

is more in line with the expectations of industrial networks for remote

monitoring of temperatures, pressures, and actuation data. A ZigBee

node can be expected to survive about a year on a pair of AA batteries,

while nodes utilizing proprietary ISM band protocols can easily last a

decade using the same power source. The reason for extended battery

life of ISM band solutions is the ability of the designer to choose the

duty cycle of the data and thus customize the solution to the situation.

The worldwide accepted frequency for ZigBee 802.15.4 systems is

2.4 GHz, using direct sequence, spread spectrum (DSSS) O-QPSK as a

modulation scheme. ZigBee radios are also allowed at 915 MHz DSSS

in the Americas and 868 MHz DSSS in Europe; these frequencies use

BPSK as a modulation scheme. The majority of ZigBee solutions to date

operate at 2.4-GHz. The 2.4-GHz band has become overcrowded due

to its worldwide usage for many wireless devices, including microwave

ovens. The more sparsely populated ISM bands of 915, 868 or

433 MHz offer a viable alternative to crowded 2.4 GHz wireless

solutions and should be considered.

The 2.4 GHz band requires a shorter antenna than does 915 MHz or

lower frequencies. This is the reason that many WLAN routers require

two antennas (three for 802.11g at 5.6 GHz). Refl ections and multipath

cause nulls in the 2.4 GHz transmissions. Networks realized using lower

frequencies such as 915 MHz do not demonstrate as much multipath and

associated nulling, and therefore work very well with a single antenna.

Many applications at 915 MHz or below will do well with an onboard

stripline PCB antenna. This reduction of antennas helps diminish overall

system cost and provides another reason that networks outside of 2.4

GHz are often chosen for low cost and longer range industrial networks.

Other options available in the ISM band include proprietary RF

networks using on-off keying (OOK), amplitude shift keying (ASK), and

frequency shift keying (FSK) modulation schemes. These networks

often have benefi ts that engineers simply cannot overlook. Micrel

presently offers transceivers in the 310 MHz to 950 MHz bands which

can perform many of the RKE and two-way wireless network functions

in the ISM band. The challenging aspect of a wireless network is the

software stack used by the microcontroller. This last bit of engineering

is where many RF designs get derailed.

Micrel has made available as generic C source code an FCC

15.247-compliant protocol for frequency hopping, spread spectrum

(FHSS) utilizing the MICRF505 FSK transceiver chip. This software is

called MicrelNet and provides for FHSS modulation in a

250 KHz bandwidth utilizing 25 frequency hops. The MICRF505 chip

has an onboard power amplifi er which allows for -3 dBm to +10

dBm transmission to an antenna without an external transmit/receive

switch. With the onboard PA of the MICRF505 set to 10 dBm, ranges of

up to 200 meters are easily achieved for data rates of 9.6 Kbps.

Figure 5 illustrates the multiple carrier frequencies in an FHSS system.

All nodes are synchronized to allow for hopping. If there is a bad or

used frequency, the system simply hops to the next frequency to

get the information. The software stack is ultimately responsible for

reassembling packets that are sent between nodes. An IP addressing

scheme in MicrelNet allows for easily recognizable source address and

destination address formatting of data packets. Software CRCs ensure

data delivery.

FCC 15.247 allows FHSS radios at 915 MHz to have an output power of

up to 250 mW, which equates to 24 dBm into a 50 Ω antenna. With the

addition of an external PA and transmit/receive switch, power levels of

250 mW are possible with the MICRF505 transceiver chip. At 250 mW

output power, the MICRF505 has demonstrated ranges of up to 2 Km

for data rates of around 10 Kbps in line-of-sight applications.

Article Resources

Product Information

• Frequency Hopping

Techniques

• MICRF505/506 Basic:

Handling the Control

Interface

• MICRF505/506 Basic:

Handling the Data

Interface

• MICRF505/506/600/

610/620 User Guide

• MICRF50x/6x0 RF Test

Bench User Guide

Related Products

• MICRF505YML TR

• MICRF505DEV1

Online Resources

Additional Links

• Component Reference

Guide

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Wireless Solutions | TZ W 112.US


25-50 Hops

Figure 5: Frequency Hop Spread Spectrum (FHSS).

The MicrelNet code stack can run in 8 KBytes of memory on an

8-bit microcontroller. Many industrial wireless networks are added

to enhance existing RS232 type networks controlled by small,

low-power MCUs at each node. The ability to add large sections of

code is often not an option, due to the restricted fl ash memory size of

small, low-power MCUs. The 8-Kbyte code size of MicrelNet is much

smaller than a corresponding 802.11 WLAN (1 MByte) or ZigBee

(32 K to 70 KByte) stack.

MicrelNet operates in a cluster tree network, with one central master

capable of communicating with other masters in a network of up to

65,000 slave nodes. This is similar to ZigBee, except that ZigBee is

a mesh network where any node can fi nd a way to talk to any other

node. Mesh networks are possible with the MICRF505, but require

additional software resources, similar to those discussed for ZigBee

implementations. Figure 6 illustrates various wireless network

topologies and the number of nodes supported by each.

In wireless industrial networks, the application and environment

ultimately dictate what type of network makes the most sense.

The choices of frequency, protocol, and power consumption are

key elements in the decision process as they affect range, system

resources, and ultimately, the cost of the solutions.

f

Zigbee TM

30 Nodes Per Router

802.11 WLAN

Reduced

Function

Node

Network

Coordinator

Full

Virtual

Function

Link

Node

65,000 Nodes Possible

Figure 6: Network topologies and nodes.

ISM Band

MicrelNET TM

Gateway Controller

10/100 Copper Ethernet,

RS232 or RS485

Central

Master

Master

Slave

65,000 Nodes Possible

User Defined

Protocols such as 802.11 WLAN, ZigBee, and proprietary schemes

such as MicrelNet can all co-exist. The emergence of “gateway

controllers”, as shown in Figure 6, enable various wireless networks

to communicate on the most common of all networks, 10/100 copper

Ethernet. A good example of such a gateway controller has been

assembled and proven at http://www.micrel.com/wirelessgateway

and is available to view and download.

Article Resources

Product Information

• Frequency Hopping

Techniques

• MICRF505/506 Basic:

Handling the Control

Interface

• MICRF505/506 Basic:

Handling the Data

Interface

• MICRF505/506/600/

610/620 User Guide

• MICRF50x/6x0 RF Test

Bench User Guide

Related Products

• MICRF505YML TR

• MICRF505DEV1

Online Resources

Additional Links

• Component Reference

Guide

Wireless Solutions,

March 2011

• TechZone Library

• TechXchange

• Future Editions

27

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WIRELESS

HEALTH &

FITNESS

The potential for wireless to impact the health care market is

extraordinary, but the undertaking to deliver on this potential does

not have to be. The medical industry is embracing wireless standards

to better enable freedom and mobility, while creating an ecosystem

of simple-to-use data measuring devices that can be used in making

medical decisions. The applications in TeleHealth are far-reaching,

but the idea of wireless sensors that interface seamlessly to an

online portal or your smartphone, once prevalent only in R&D labs,

is now a reality. The adoption of Bluetooth, Zigbee, the IEEE 802.11

standards, NFC (Near-Field Communications), and RFID enables an

interface to a large installed base and interaction with the computing

and smartphone platforms available today. Fitness and Sports

monitoring devices have been around for more than three decades,

but the capability of today’s technology provides a unique stepping

stone for a far richer, more interactive experience.


WIRELESS HEALTH AND FITNESS: Wellness Without Wires

Medical Systems

Go Wireless

Both in the hospital and in the home, wireless

technology is revolutionizing healthcare as new

applications appear all the time.

Wireless connectivity is sweeping through the healthcare industry,

giving patients more mobility and giving doctors more real-time, realistic

information by allowing patients to move around rather than trap them

in a bed, encased in a “rat’s nest” of wires. There is no single wireless

standard adopted by the medical industry. Rather, the industry seems

to be embracing all the wireless standards – Bluetooth ® , ZigBee ® ,

Wi-Fi ® (IEEE 802.11a, b, g, n), RFID, Near-Field Communications (NFC),

and more. This article provides an overview of the various approaches

to wireless system implementations for a wide variety of healthcare

monitoring systems.

In the hospital, the doctor’s offi ce, and at home, medical products are

going wireless, giving patients more mobility, giving doctors access

to records wherever they happen to be, and allowing nurses, doctors,

and other healthcare providers to collect and record data while making

their rounds (see Figure 1). To link the various data collection tools,

data capture tools, and diagnostic systems, designers have a variety

of wireless connectivity options. Each option comes with a different

set of data transfer speeds, power consumption levels, and operating

frequencies. Depending on the application scenario, each wireless

standard – Bluetooth, ZigBee, Wi-Fi, NFC, RFID, or simple schemes

such as amplitude-shift keying (ASK) or on-off keying (OOK) – has its

place in the medical and fi tness infrastructure.

To Ethernet

Connection

by Dave Bursky, PRN Engineering Services

Wireless Router

Notebook Computer

Desktop Computer

Blood Pressure Monitor ECG/EKG Monitor Infusion Pump

Figure 1: Wireless communications have made many inroads into medical systems. (Source:

Microchip Technology. Used with permission.)

Which standard to choose

For low-cost applications such as “smart” running shoes, simple

heart-rate monitors, and other equipment which only require a

transmission distance of several yards for the sensor to send a signal

to a nearby receiver, low-power schemes like ASK, OOK, or the new

low-power Bluetooth or ZigBee schemes would be a good fi t.

Article Resources

PTM and Another Geek Moment

• Freescale Semiconductor,

Inc. - ZigBee Technology

Overview

Product Information

• MAX1472A Datasheet

• Automotive Product Guide

• EM357 System-on-Chip

Platforms

• InSight Dev Kit Fact Sheet

Related Products

• MAX1472AKA+T

• MRF24J40-I/ML

• EM351-RTR

• EM357-RTR

• EM35X-DEV

Online Resources

Additional Links

• Component Reference

Guide

Wireless Solutions,

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

However, in a hospital environment, Wi-Fi can be used to keep the

doctors connected via date-entry/retrieval tablets or other hand-held

devices that can be kept in charging cradles when not in use.

In the emerging area of home-care and remote diagnostics,

a combination of wireless approaches can be employed to achieve the

best coverage while minimizing cost and power. Market researchers at

Parks Associates estimate that 7.2 million customers in North America

and Europe will be using remote health monitoring by 2012

(up from 500,000 in 2008).

For most medical monitoring and diagnostic tools, data usually comes

in small bursts rather than a long, continuous stream. Thus, the more

small-packet-oriented wireless approaches, such as Bluetooth and

ZigBee, will deliver the desired performance at low-power consumption

levels. For very short range applications, ASK and OOK can also

transfer data while consuming very little power.

Other RF schemes such as NFC and RFID are also being used to track

supplies and medication. For example, inexpensive passive RFID tags

can be added to medication bottles or various disposable supplies to

track usage and ensure that the correct medications are dispensed.

A simple RFID reader or NFC reader is all that is needed to capture

the information.

Let’s take a look at some of the equipment being designed to take

advantage of the various wireless standards, and at some of the chips

that designers have implemented to eliminate the cables and give

patients more freedom. Blood-oxygen measurements are common

for hospital patients and for many people using home-based remote

monitoring. Some of the latest pulse oximetery systems are smaller

than a smart phone, can run from standard AAA batteries, and

incorporate NFC or a Bluetooth wireless interface to transfer collected

data to a host system such as a tablet computer, smart phone, or

full PC. Recent announcements by Google and NXP Semiconductors

have stated that the next generation of Android ® smart phones will

include NFC capability so that the phones can be used as electronic

wallets. However, by just running a different application, the same NFC

interface could also be used to collect medical data.

Photodiode

RED

LED

AC/DC

Adapter

Sensor

IR

LED

1-Wire

Memory

Battery

Charger

Line

Prot.

TIA PGA ADC

System Monitoring

MUX

Voltage

Reference

LED

Drivers

Battery Management

Fuel

Gauge

Battery

Authentication

MCU/

DSP

Blacklight

The basic functions required in a pulse oximeter are shown in the system

block diagram in Figure 2. In such a system, the designers can implement

the wireless interface using any of several standards – Bluetooth, Wi-Fi,

or NFC. One of the larger suppliers of NFC chips is NXP Semiconductors,

offering transceiver chips that operate at 13.56 MHz — the PN511 and

the PN512 (see Figure 3). To create a full NFC subsystem, however, the

PB511/512 chips are typically combined with a microcontroller, and

NXP offers several modules – the PN531, 532, 533, and 544 – that

contain both the MCU and the NFC transceivers. Simply by bringing two

NFC-enabled devices close together, they automatically initiate network

communications without requiring the user to confi gure the setup.

NFC-enabled devices make it easy for users to connect and transfer data.

ADC

Voltage

Monitor

DAC

Touch-Screen

Controller

Data

Interface

Audio

DAC

Data

Storage

User

Interface

Wireless

Link

Bluetooth or

WiFi

Speaker

AMP

Display

Power Management

Boost LDO Inverter

Converter

Figure 2: A typical pulse oximetry system, such as defi ned by Maxim Integrated Products, contains

many blocks to sense, collect and display the blood-oxygen levels. A small but important piece of the

system is the wireless link implemented using a Bluetooth or WiFi radio. In future generations, NFC

wireless interfaces will also be available. (Souce: Maxim. Used with permission.)

Antenna

Analog

Interface

Contactless

UART

FIFO

Buffer

Register Bank

Serial UART

SPI

1 2 C-BUS

Figure 3: Simplifi ed diagram of the PN512 Near-Field Communications transceiver developed by

NXP Semiconductors. (Source: NXP Semiconductors. Used with permission.)

Host

Article Resources

PTM and Another Geek Moment

• Freescale Semiconductor,

Inc. - ZigBee Technology

Overview

Product Information

• MAX1472A Datasheet

• Automotive Product Guide

• EM357 System-on-Chip

Platforms

• InSight Dev Kit Fact Sheet

Related Products

• MAX1472AKA+T

• MRF24J40-I/ML

• EM351-RTR

• EM357-RTR

• EM35X-DEV

Online Resources

Additional Links

• Component Reference

Guide

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

The transceiver chip includes an 8-bit parallel interface, an SPI

serial port, a serial UART (similar to RS232 with voltage levels set by

the pad voltage supply), and an I 2 C interface, any of which can be

used to connect the transceiver to the host microcontroller. On-chip

analog circuits demodulate and decode responses, and buffered

output drivers allow an antenna to be connected with a minimum of

external components. The typical operating distance in the read/write

mode is up to 50 mm, depending on the antenna size and tuning.

The integrated RF interface can transfer data at up to 424 kbits/s in

the NFCIP-1 operating mode, and at either 212 or 424 kbits/s in the

FeliCa and ISO/IED 14443A transfer modes.

Maxim employs a simple ASK transmitter/receiver in a

heart-rate/fi tness monitoring system. Designers at Maxim decided on

this approach because it offers better sensitivity than a

frequency-shift keying approach, and requires little power for data

transmission (see Figure 4). Used to link a sensor in an exercise shoe

(a running shoe, for example), the transmitter sends its signal less

than two meters to a receiver typically worn on the person’s waist.

A transmitter in a wireless chest-band can also be set up to measure

breathing and transmit readings to the receiver. When the exercise

period is fi nished, the receiver can be linked to the PC host via a

Bluetooth dongle, or a Bluetooth-capable cell phone or tablet

(see Figure 5).

50 Ω

Antenna

220 pF 680 pF

*

XTAL1

GND

PAGND

PAOUT

MAX1472

XTAL2

VDD

DATA

ENABLE

3.0 V

Data Input

Standby or

Power-Up

*Optional power-adjust resistor

Figure 4: The MAX1472 delivers a serial data stream using OOK/ASK modulation. (Source: Maxim.

Used with permission.)

Wristwatch Display

USB

Connector

AC/DC

Adapter

Data

Storage

RF

Interface

USB

Interface

Heart-Rate Chest Strap

Cardiac

Transducer

Temperature

Transducer

MCU

Battery Management

Battery Fuel

Charger Gauge

OP

AMP

ADC

LED/EL

Backlight

Buzzer

Battery

Coin-Cell or

Rechargeable

Battery

Power Management

RF

Interface

MCU

Accelerometer

Another example of wireless technology that is becoming popular in

medical systems is the hearing aid. Rather than build in hard-to-access

switches that change modes, designers are now creating hearing

aids with wireless interfaces such as Bluetooth. Through the wireless

interface, the hearing specialists can tune the algorithms while the

hearing aid is in the patient’s ear, thus ensuring that the hearing aid’s

performance can be optimized for the patient without removing and

re-inserting the device in the ear.

In a typical digital hearing aid, the digital signal processor (DSP) can

be tuned via the wireless interface to optimize the performance of the

hearing aid to the patient. A PC or smart phone running an application

can be used by the doctor. If the patient needs several performance

profi les and wishes to switch between them, the patient could also

control the wireless link to adjust the algorithm (see Figure 6).

LDO

Food-Pod Shoe Insert

RF

Interface

ADC

MCU

PC Dongle

RF

Interface

MCU

USB

Interface

USB Connector

Battery

Battery

Figure 5: The heart-rate monitor contains several sections-a sensor and transmitter for the

running shoe (lower right), a sensor and transmitter for the chest strap (lower left), a receiver

that collects all the data and then sends it on to a host computer or a smart phone/tablet

(upper left), and host-PC dongle that converts the RF data into a USB data stream

(upper right). (Source: Maxim. Used with permission.)

Article Resources

PTM and Another Geek Moment

• Freescale Semiconductor,

Inc. - ZigBee Technology

Overview

Product Information

• MAX1472A Datasheet

• Automotive Product Guide

• EM357 System-on-Chip

Platforms

• InSight Dev Kit Fact Sheet

Related Products

• MAX1472AKA+T

• MRF24J40-I/ML

• EM351-RTR

• EM357-RTR

• EM35X-DEV

Online Resources

Additional Links

• Component Reference

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

TELECOIL

User Interface

AC/DC

Adapter

MIC PREAMP

MUX

MIC PREAMP

Line Protection

Battery

Charger

Fuel Gauge

Battery

Management

Audio

Codec

EEPROM

RF

Interface

Voltage

Supervisor

Linear

Regulator

Switching

Regulator

Power

Management

The ZigBee wireless standard is also an ideal option for many medical

systems since the protocol allows multiple transceivers to form a simple

mesh network. In addition, ZigBee devices are very low power since they

spend most of their time in a standby or sleep state, typically waking up

to transmit a burst of data and then going back to sleep.

One example of a ZigBee transceiver chip is the MRF24J40 from

Microchip. The transceiver is compliant with the IEEE 802.15.4 standard

and operates at 2.4 GHz. The chip integrates both the PHY and MAC

functions, but an external low-power microcontroller is typically paired

with the transceiver to complete the node (see Figure 7).

DSP

Speaker

Amplifier

Figure 6: A typical hearing aid can leverage a wireless interface to adjust the DSP algorithms.

(Source: Maxim. Used with permission.)

Antenna

Matching

Circuitry

RFP

RFN

PHY

Power

Management

MRF24J40

MAC

Memory

CS

SDI

SDO

SCK

INT

WAKE

RESET

PIC ® MCU

I/O

SDO

SDI

SCK

INTx

I/O

I/O

20 MHz

Crystal

Figure 7: The MRF24J40 ZigBee transceiver just requires a low-power MCU to form a complete

ZigBee node. (Source: Microchip Technology. Used with permission.)

The MRF24J40 and MCU form a low-cost, low-power, low-data-rate

(250 or 625 kbps) wireless personal area network (WPAN) node.

The MRF24J40 interfaces with many of Microchip’s PIC ® family

microcontrollers via a 4-wire serial SPI interface with interrupt,

wake, and reset pins. There are many other vendors offering ZigBee

solutions, both at the chip level and at the module level.

Several vendors combine the transceiver and MCU on the same chip

to further reduce component count. One such solution is the EM351

from Ember. Their chip integrates a programmable ARM ® Cortex-M3

processor along with the RF transceiver, 128 kbytes of fl ash memory,

and 12 kbytes of RAM. Another version of the chip, the EM357,

is optimized for applications that require more memory.

Bluetooth solutions, both in chip and module form, are also on the

market and available for medical applications. The recently released

low-power profi le lowers the power consumption of the Bluetooth

interface and allows it to compete better in the market for

battery-powered systems.

One Bluetooth-based solution, the Saelig Co. CM-500W3, is a small

barcode scanner, ideal for nurses and other healthcare providers to use

to capture the codes from supplies and medications. The CM-500W is

compact (5 x 1.5 x 0.7 in.), lightweight (2 oz.), and features two keys

(scan/clear) plus a beeper and LEDs to indicate read status. With a USB

cable attached, it becomes a plug & scan scanner. Without the USB

cable, it functions as a memory or wireless scanner. As a Bluetooth

device, it can be programmed as a master or slave device to allow

communication between a Windows PC, a mobile phone, or a PDA for

instant or delayed data entry. The CM-500W3’s built-in Li-polymer

battery pack (3.7 V, 420 mAH) can be recharged via any USB port,

and the unit can read up to 15,000 scans before requiring a recharge.

For information regarding the wireless standards, go to:

www.Bluetooth.org

www.ZigBee.org

www.Wi-Fi.org

Article Resources

PTM and Another Geek Moment

• Freescale Semiconductor,

Inc. - ZigBee Technology

Overview

Product Information

• MAX1472A Datasheet

• Automotive Product Guide

• EM357 System-on-Chip

Platforms

• InSight Dev Kit Fact Sheet

Related Products

• MAX1472AKA+T

• MRF24J40-I/ML

• EM351-RTR

• EM357-RTR

• EM35X-DEV

Online Resources

Additional Links

• Component Reference

Guide

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Bluetooth ® Modules Exceed Expectations

Panasonic Electronic Components provides powerful, highly fl exible, costeffective

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New Bluetooth RF Modules. Bluetooth, which is based on IEEE 802.15.1, was developed

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33

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

Comparing Low-Power

Wireless Technologies

by Phil Smith, CSR PLC

Article Resources

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Other Resources

• ZigBee Specification

• RF4CE Specification

This article compares Bluetooth low-energy, ANT,

ANT+, ZigBee, ZigBee RF4CE, Wi-Fi, Nike+, IrDA,

and the near-field communications (NFC) standard,

detailing the features, benefits, and shortcomings of

each protocol in various applications.

Many innovative new use cases are now being made possible with

the introduction of ultra-low-power wireless chipsets. Until recently,

the only way to achieve data transfer between a sensor and a client

has been to use wires, or manually collect data from a logging device.

Wireless technologies have been available for decades. However,

they tend to use signifi cant amounts of power and need specialized

equipment to establish communications.

Most target markets are characterized by periodic transfer of

small amounts of sensor information between sensor nodes and a

central device. Some identifi ed end products which may implement

a low-power radio system include cell phones, health and fi tness

devices, home automation, heating, ventilating, and air conditioning

(HVAC), remote controls, gaming, human interface devices (HID), smart

meters, payment, and many others.

These applications are all constrained by the following critical key

requirements: ultra-low-power, low cost, and physical size.

The ultra-low-power requirement is mainly due to the need of targeted

devices to operate for extended periods of time from coin cells or energy

scavenger technology. Apart from the obvious advantages of a low

chipset cost, overall product expense is largely affected by the power

source. For example, if a shopping mall has a wireless beacon in every

shop and batteries need replacing regularly, the maintenance cost will

soon outweigh the advantages of such a technology being deployed.

This article analyzes the pros and cons of various low-power wireless

technologies and leaves it up to the reader to decide which technology

is most suitable for their intended product.

Background on Bluetooth low energy

Bluetooth ® low energy (LE) started life as a project in the Nokia

Research Centre with the name Wibree. In 2007, the technology was

adopted by the Bluetooth Special Interest Group (SIG) and renamed

Bluetooth Ultra-Low-Power and then Bluetooth low energy.

The aim of this technology is to enable power sensitive devices to be

permanently connected to the Internet. LE sensor devices are typically

required to operate for many years without needing a new battery.

They commonly use a coin cell, for example, the popular CR2032.

LE technology is primarily aimed at mobile telephones, where it is

envisaged that a star network topology, similar to Bluetooth, will often

be created between the phone and an ecosystem of other devices.

LE is also known as Bluetooth v4.0 and is part of the public Bluetooth

specifi cation. As a result of being a standard, LE benefi ts from all the

advantages of conformance and extensive interoperability testing at

unplug fests. A device that operates Bluetooth v4.0 may not necessarily

implement other versions of Bluetooth; in such cases it is known as a

single-mode device. Most new Bluetooth chipsets from leading Bluetooth

silicon manufacturers will support Bluetooth and the new LE functionality.

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

What is ANT

ANT is a low-power proprietary wireless technology which operates

in the 2.4 GHz spectrum. It was established in 2004 by the sensor

company Dynastream. Typically, the ANT transceiver device is treated

as a black box and shouldn’t require much design effort to implement

into a network. Its primary goal is to allow sports and fi tness sensors to

communicate with a display unit, for example a watch or cycle computer.

It also typically operates from a coin cell. ANT+ has taken the ANT

protocol and made the devices interoperable in a managed network,

thereby guaranteeing that all ANT+ branded devices work seamlessly.

Similar to LE, ANT devices may operate for years on a coin cell.

ANT devices are not subject to the extensive conformance and

interoperability testing applied to other standardized technologies.

ANT+ is introducing a new certifi cation process in 2011 which will be

chargeable and a prerequisite for using ANT+ branding.

What about ZigBee

ZigBee ® is a low-power wireless specifi cation based on the Institute

of Electrical and Electronics Engineers (IEEE) Standard 802.15.4-2003

and was established in 2002 by a group of 16 companies. It introduces

mesh networking to the low-power wireless space and is targeted

towards applications such as smart meters, home automation, and

remote control units. Unfortunately, ZigBee’s complexity and power

requirements do not make it particularly suitable for unmaintained

devices that need to operate for extensive periods from a limited

power source. ZigBee channels are similar to those for LE in that they

are 2 MHz wide. However, they are separated by 5 MHz, thus wasting

spectrum somewhat. ZigBee is not a frequency hopping technology,

therefore and requires careful planning during deployment in order to

ensure that there are no interfering signals in the vicinity.

Does RF4CE tick all the boxes

Radio Frequency for Consumer Electronics (RF4CE) is based on

ZigBee and was standardized in 2009 by four consumer electronics

companies: Sony, Philips, Panasonic, and Samsung. Two silicon vendors

support RF4CE: Texas Instruments and Freescale Semiconductor, Inc.

RF4CE’s intended use is as a device remote control system,

for example for television set-top boxes. The intention is that

it overcomes the common problems associated with infrared:

interoperability, line-of-sight, and limited enhanced features.

How does Wi-Fi compare

In recent years, a number of improvements have been made to the

wireless-fi delity (Wi-Fi ® ) IEEE Standard 802.11 wireless networking

standard, which may be able to reduce its power consumption,

including IEEE Standard 802.11v and other proprietary standards.

Although Wi-Fi is a very effi cient wireless technology, it is optimized

for large data transfer using high-speed throughput and is not really

suitable for coin cell operation. Some companies are attempting to use

Wi-Fi for HUD devices. Special propreitary driver software is required,

however, and only limited functionality can be achieved.

What is NIKE+

Nike+ ® is a proprietary wireless technology developed by Nike and

Apple to allow users to monitor their activity levels while exercising.

Its power consumption is relatively high, returning only 41 days of

battery life from a coin cell. Being a proprietary radio, it will only work

between Nike and Apple devices. Nike+ devices are shipped as a

single unit: processor, radio, and sensor. In this article, we therefore

evaluate this technology as a single entity. The design is a two-chip

solution, consisting of a processor and a Nordic nRF2402 radio

transceiver integrated circuit (IC).

Doesn’t IrDA solve the problems already

The Infrared Data Association (IrDA) is a SIG consisting of 36 members.

IrDA has recently announced an ultra-high-speed connectivity version,

yielding 1 Gbps. However, it only works over a distance of less than

10 cm. One of the main problems with infrared (IR) is its line-of-sight

requirement, which RF4CE was established to overcome. IrDA ® is also

not particularly power effi cient (power per bit) when compared against

radio technologies. By its very nature, it is a two-component solution as

an absolute minimum because it needs a processor and a transceiver.

Is NFC going to take over

This is unlikely, as near fi eld communication (NFC) is signifi cantly

different from the other low-power wireless technologies discussed

in this article. It only works up to a range of approximately 5 cm and

consumes relatively more power. Passive NFC tags can be completely

Article Resources

PTM and Another Geek Moment

• EPCOS, Inc. - SAW Filters

Other Resources

• ZigBee Specification

• RF4CE Specification

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• Component Reference

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

unpowered, only becoming active when an NFC fi eld is present.

That eliminates NFC from many of the use cases discussed here.

NFC is a perfect fi t for its intended use cases, and is likely to be

integrated alongside the other technologies discussed in this article.

It has few competing technologies.

Network topologies

Five main network topologies exist when discussing personal

low-power radio networks:

Key:

• Broadcast: A message is sent from a device in the hope that it

is received by a receiver within range. The broadcaster doesn’t

receive signals.

• Mesh: A message can be relayed from one point in a network to

any other by hopping through multiple nodes.

• Star: A central device can communicate with a number of

connected devices – Bluetooth is a common example.

• Scanning: A scanning device is constantly in receive mode,

waiting to pick up a signal from anything transmitting within range.

• Point-to-Point: In this mode, a one-to-one connection exits, where

only two devices are connected, similar to a basic phone call.

Which technology supports which topology

Table 1 shows which wireless technologies, support which

network topologies.

Table 1: Network topologies supported by wireless technologies.

LA A A+ Zi RF Wi Ni Ir NF

Broadcast √ √ 1 √ 1 x x x x x x

Mesh √ 2 √ √ √ √ x x x x

Star √ √ √ √ √ √ x x x

Scanning √ √ 3 √ √ √ x √ x x

Point-to-Point √ √ √ √ √ √ √ √ √

Notes:

LE (Bluetooth low energy), A (ANT), A+ (ANT+), Zi (ZigBee),

RF (RF4CE), Wi (Wi-Fi), Ni (Nike+), Ir (IrDA), NF (NFC)

1

Not just broadcasting, it also needs to listen.

2

An application can be put on LE to enable meshing.

3

All connections stop and power consumption is high.

Is Bluetooth low energy easy to implement

Based on the amount of software that would be required to

implement a simple program and hardware requirements, it is

possible to estimate how much effort may be required to implement

a simple connectivity application.

LE chipsets come in two categories: single-mode and Bluetooth + LE.

Single-mode confi gurations are shipped as a single chip that contains

the host processor and radio. The protocol stack is integrated in the

silicon and exposes some simple application programming interfaces

(API) for a developer to use. As a result, there is little effort required

by the developer when creating a new product. Single-mode LE

devices are often shipped from silicon vendors as pre-certifi ed units.

This means original end manufacturers (OEM) do not need to spend

resources qualifying their new products. If the developer decides to

deviate signifi cantly from a given reference design, then it is possible

that some features may need retesting. The hardware for a

single-mode LE device is very simple, as shown in Figure 1.

C2032 Battery Holder

1

+ +

2

1206

-

C1

BAT1

100 u

GND

GND

ANT1

0402

0402

C13

47 n

0402

GND

7

C11

RF

NF

C16

470 n

C12

47 n

0402

VDD BAT

L1

4u7

C2

2u2

C3

470 n

Bluetooth low

energy radio

including host

processor

X1

16 MHz

C7

15 p

0402 0402

C8

8p2

Figure 1: A complete Bluetooth low energy beacon schematic.

X2

C4 C5

470 n NF R7

0402

0402

0402 0R0 GND

U2

CSR1000

12C_SDA

29

12C_SCL

28

PIO[2]

27

VDD BAT

SPI_PIO#_SEL 26

PIO[5] 18

PIO[6] 19

PIO[7] 20

PIO[8]

22

14

PIO[0] 15

PIO[1]

PIO[9] 23

PIO[3] 16

PIO[4] 17

PIO[10] 24

PIO[11] 25

AIO[2] 11

AIO[1] 12

AIO[0] 13

C9

10 p

0402 0402

0402 0402

32.768 kHz

C10

10 p

1 A0 VCC 8 23 A1 WP 765

4 A2 SCL

GND SDA

GND SO-8

AT24C512BN-SH

0402

C6

1u0

GND

Article Resources

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• ZigBee Specification

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

Figure 2 shows a real device implementing Bluetooth v4.0. This unit

consists of the schematic in Figure 1, a buzzer, a Light-Emitting Diode

(LED) and a switch.

Figure 2: A real Bluetooth low energy device.

Antenna

16 MHz Xtal

A bill of materials (BOM) for the real LE device is shown in Table 2.

Notes:

1

Electrically Erasable Programmable Read-Only Memory.

Component costs will be lower in mass production.

32 KHz Xtal

EEPROM

CSR1000

Test Connector

Table 2: A BOM for a Bluetooth low energy device.

Component Quantity Cost ($)

Battery 1 0.325

Antenna 1 0 (Printed Antenna)

EEPROM 1 1 0.89

Decoupling Cap 6 0.002

Signal Cap 5 0.0.02

Resistor 4 0.0001

Crystal 2 0.243

Bluetooth low energy IC 1 Approx $1

Total $2.72

Dual-mode Bluetooth chipsets, as used in a mobile handset, have a

host processor present. Silicon vendors normally ship a protocol stack

which executes on the host processor and provides a simple API to

access Bluetooth and LE. Dual-mode Bluetooth chips may also contain

their own application processor. Such devices have the sensitive

protocol stack burnt into Read-Only Memory (ROM) and expose an API

as a virtual machine. These types of chips are often found in consumer

electronics, like headsets, where more than just sensing applications

are necessary.

RF4CE is also an easy technology to implement, but requires

approximately 64 Kbytes of protocol stack to be ported to the host

processor. Some RF4CE chips contain an application processor,

which may simplify the hardware effort required.

ANT is often a two-chip solution, where developers need to choose

which radio and host processor to use. SensRcore ® chips are a

single-chip solution that offers a power saving over regular ANT

devices, but they are typically only suitable for the sensor end of a link

and require a proprietary scripting language. Certifi cation for ANT+

is compulsory and costs are still being fi nalized. There are some ANT

development kits on the market which ship with various modules and

all required software. This makes life easier for the developer. The

protocol stack is intended to be treated as a black box, implying that

ANT-based products should be easy to develop. It is worth noting that

device profi les are a collaborative effort between the ANT+ team and

application developers. They are likely to require some effort to write

and verify as interoperable with other technologies.

IrDA has some simple protocols that can be obtained in a simple

microprocessor IC + LED and receiver. Complexity increases when

higher data rates are required, because a full IrDA protocol stack and

powerful processor are needed. Plastic IR transmission windows are

also a requirement for end products using IR. They must ensure IR

intensity is within specifi cation. Certifi cation is compulsory and needs

to be carried out at an IrDA authorized test lab.

NFC integration has recently been simplifi ed with the release of an

open source protocol stack from Inside Contactless. Some porting

effort is required to implement NFC in a system and signifi cant

Article Resources

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• RF4CE Specification

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

thought needed when designing an optimal antenna. NFC requires at

least two chips (a radio and a processor) and a power supply.

Certifi cation is not compulsory for NFC, but standard radio emission

testing should be performed to ensure it remains in the 13.56 MHz

band. A new certifi cation program has been established which offers

manufacturers the opportunity to prove their device is fully interoperable.

Wi-Fi is probably the most complicated technology to integrate

into a system. It requires various drivers and a full protocol stack.

The hardware also needs to be designed with tight tolerances to

ensure that radio specifi ed performance is achieved. Certifi cation is

not compulsory. However, the Wi-Fi logo cannot be obtained unless

the device is certifi ed. Certifi cation costs are high, relative to the

other technologies discussed here because of the amount of testing

that is required at a specialist test facility. Most new power-saving

specifi cations are still being written, or are not in mass production yet,

thereby lengthening the time-to-market of such advancements.

What does it cost to manufacture low-energy devices

Some of the main costs associated with a low-power sensor are the

processor, radio, antenna, battery, battery connector, sensor, regulator,

and the printed circuit board (PCB). Table 3 shows typical costs for

different technologies.

Note:

It is assumed that battery, battery connectors, and sensors are

equal across all platforms and therefore not included.

Crystals can also contribute a signifi cant portion of cost to a small

sensor device. In wireless technologies, a high quality crystal is

often required to meet strict regulatory requirements. Typical crystal

tolerances are:

Least Expensive

• NFC 500 ppm (parts per million): NFC provides data clocking,

a crystal is only required keep the radio in band.

• LE 250 ppm

• Nike+ 60 ppm

• ANT 50 ppm

• RF4CE 40 ppm

Most Expensive

Table 3: Bluetooth low energy device manufacturing costs.

Processor Radio Antenna Regulator PCB Size

LE N/A $2.95/1 k (1) Printed 8mm (2) N/A 20 mm 2(3)

A $low $3.95/10 k Printed ‘F’ 15 mm N/A 125 mm 2

A+ N/A $3.33/1 k Printed ‘F’ 15 mm N/A 306 mm 2

Zi N/A $3.20/1 k Printed ‘F’ 15 mm N/A 305 mm 2

RF N/A $2.75/1 k Printed ‘F’ 15 mm N/A 305 mm 2

Wi $high $3 Printed 8 mm (2) $1.50 (4) 60 mm 2

Ni $low $1.60/10 k Metal 2 cm N/A 300 mm 2

Ir N/A $1.97/10 k 8 mm N/A 21 mm 2 +CPU

NF $high $1 50 mmx 30 mm $0.33 (5) 100 mm 2

Key: LE (Bluetooth low energy), A (ANT), A+ (ANT+), Zi (ZigBee),

RF (RF4CE), Wi (Wi-Fi), Ni (Nike+), Ir (IrDA), NF (NFC)

Notes:

1

If used as part of a Bluetooth design, the cost would be less than a

20 percent addition.

2

Cambridge Silicon Radio (CSR) patented printed antenna design may be used with

CSR chips.

3

Bluetooth and LE. LE only is aimed at medium cost PCB technologies, therefore

modules are approximately 96mm 2 including antenna.

4

Wi-Fi requires 1.8 V @200 mA and 3.3 V @400 mA = £0.86. At an exchange rate

of £1.75 to $1 => $1.50.

5

NFC requires 50 mA @ 3.3 V = £0.194. At an exchange rate

of £1.75 to $1 => $0.33.

Efficiency

Protocol

A wireless transmission consists of two main components: payload and

overhead. These are used to ensure that packets are delivered reliably.

The effi ciency of the protocol can be measured as the ratio of payload

to total packet length. If a protocol is very ineffi cient and spends most

of its time transferring non-payload information, it will soon discharge

the battery and transfer very little data. Alternatively, a protocol close to

100 percent effi ciency will transfer signifi cantly more data on a single

charge. There is a trade-off between reliability and effi ciency when

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looking at extremes. Consider an ultra-effi cient protocol that does not

incorporate a reasonable checksum or error corrections. Each packet

could easily be corrupted by interference in the 2.4 GHz band, resulting

in virtually no payload being realized. By analyzing on-the-air packets,

it is possible to determine the effi ciency of a protocol.

ANT

An ANT packet consists of an 8-byte payload wrapped by various other

components. Without any public evidence, due to its proprietary blackbox

nature, the effi ciency of ANT is stated to be 47 percent.

Bluetooth low energy

LE, being an open standard, has the breakdown of packets published.

Figure 3 shows a typical packet.

Overhead

Overhead

Figure 3: Bluetooth low-energy packet.

Preamble = 1 octet

Access Address = 4 octets

PDU (Protocol Data Unit (packet or message)) =

39 octets

Advertising Header = 1 octet

Payload length = 1 octet

Advertiser Address = 6 octets

Payload = 31 octets

CRC (Cyclic Redundancy Check) = 3 octets

From these fi gures, it is possible to show the following LE protocol

effi ciency: Payload/Total length = 31/47 = 0.66 > 66 percent effi cient.

Power efficiency

Power effi ciency is often queried by customers who are interested in

prolonging the battery life of their devices while still achieving good

user experience.

For example, when a mobile handset needs to synchronize email,

the handset’s battery (with a fi xed mAh) must last long enough to allow

all emails (a fi xed quantity) to be downloaded and read by the user.

PDU

Which wireless technology on the handset would be most

effi cient - Wi-Fi or cellular

Similar questions need to be answered for remote sensor devices.

The quantity derived is the power per bit measurement.

ANT

An ANT device is confi gured to transmit 32 bytes/second and

consumes 61 µA.

• A byte consists of 8 bits, therefore 32 x 8 = 256 bits/second

• Power = VI = 3 V x 61 µA = 0.183 mW

• Power per bit = 0.183 mW / 256 bits = 0.71 µW/bit

Bluetooth low energy

Connectable advertising packets (adverts) are broadcast every 500 ms.

Each packet has 20 bytes of useful payload and consumes 49 µA at

3 V. For this particular setup, adverts are spread across all three

channels, with the positive side effect of increasing robustness over a

single-channel technology.

• Power consumption = 49 µA x 3 V = 0.147 mW

• Bytes per second = 20 x (1 second/500 ms) x 3 channels =

120 bytes/second

• Bits per second = 120 bytes/second x 8 = 960 bits/second

• Power per bit = 0.147 mW/960 = 0.153 µW/bit

It should be noted that this confi guration uses connectable packets.

Therefore, the advertising device is also scanning after each advert.

This consumes signifi cant power, but is still lower than its nearest

competitor. By increasing the payload to 31 bytes per packet and

confi guring for broadcast only, power per bit effi ciency would be

improved further. This would occur due to the increase in protocol

effi ciency from 20 payload bytes to 31 for the same overhead.

IrDA

A television remote control sends a 14-bit payload. This is

implemented with an ultra-low-power processor (consuming 0.1 µA

during sleep, allowing for its negligible power consumption to be

ignored for this calculation). The transaction takes 1.5 ms at 170 µA,

then 114 ms at 55 µA.

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• Power = 0.163 mW

• Bits = 14

• Power per bit = 0.163 mW/14 bits = 11.7 µW/bit

Nike+

A foot pod lasts 1000 hours and transmits its payload every second.

The payload is 34 bytes. A typical CR2032 has 225 mAh.

• Current drawn = 225 mAh/1000 hours = 0.225 mA

• Power = 3 x 0.225 mA = 0.675 mW

• Bits per second = 34 x 8 = 272 bits/second

• Power per bit = 0.675 mW / 272 = 2.48 µW/bit

Wi-Fi

Wi-Fi consumes approximately 116 mA at 1.8 V when transmitting

a 40 Mbps User Datagram Protocol (UDP) payload. Unfortunately,

current consumption does not reduce when throughput is reduced in

a Wi-Fi chipset.

• Power = 116 mA x 1.8 V = 0.210 W

• Power per bit = 0.210/40,000,000 = 0.00525 µW/bit

Zigbee

A Zigbee device consumes 0.035706 W when transferring 24 bytes

of data.

• Bits per second = 24 x 8 = 192 bits

• Power per bit = 0.035706/192 = 185.9 µW/bit

From the above calculations it is clear that Wi-Fi is the most

power effi cient technology and would be ideally suited to large fi le

downloads. Unfortunately, its peak current consumption is far beyond

the capabilities of a coin cell and would need to be provided with a

large battery. Work is being conducted in Wi-Fi groups to lower power

consumption, enabling use with HID devices. Currently, proprietary

drivers are needed, with the technology only applicable to the personal

computer market where receiver power budgets are higher. LE is

second, requiring approximately a quarter of the power of its closest

competitor, ANT. It is surprising to see how much energy is wasted by

infrared remote controls currently in wide global use.

Performance

Range

The range of a wireless technology is often thought of as being

proportional to the radio frequency (RF) sensitivity of a receiver and

the power of a transmitter. This is true to some extent. However,

there are many other factors that affect the real range of wireless

devices. For example, the environment, frequency of carrier, design

layout, mechanics, and coding schemes. For sensor applications,

range can be an important factor. Range is usually stated for an ideal

environment, but devices are often used in a congested spectrum and

shielded environments. For example, Bluetooth is quoted as a 10 meter

technology, but can struggle to provide a reliable Advanced Audio

Distribution Profi le (A2DP) stream from a pocket to headset due to

cross-body shielding. Similar problems can be observed in the health

and fi tness space, where users have body-mounted gadgets and move

continuously. It is worth noting that 2.4 GHz is easily attenuated by

human bodies.

The following list shows typical ranges that can be expected from

ultra-low powered technologies in an open environment:

• NFC – 5 cm

• IrDA – 10 cm

• Nike+ – 10 m

• ANT(+) – 30 m

• ZigBee – 100 m

• RF4CE based on ZigBee – 100 m

• Wi-Fi – 150 m

• LE – 280 m

Robustness

Reliable packet transfer has a direct infl uence on battery life and the

user experience. Generally speaking, if a data packet is undeliverable

due to suboptimal transmission environments, accidental interference

from nearby radios, or deliberate frequency jamming, a transmitter will

keep trying until the packet is successfully delivered. This comes at

the expense of battery life. If a wireless system is restricted to a single

channel, its reliability may deteriorate in congested environments.

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A proven method to assist in overcoming interference is to use channel

hopping, as implemented in Bluetooth. Channel hopping has been

carried forward to LE. Bluetooth devices use Adaptive Frequency

Hopping (AFH), which allows each node to map out frequently

congested areas of the spectrum to be avoided in future transactions.

ANT is specifi ed to operate over eight channels. However, it is often the

case that sensor-node chipsets only operate on a single channel. ANT

employs a Time Division Multiplexing (TDM) system, which increases

reliability. A technique is used in an ANT network known as bursting.

Bursting uses the available spectrum aggressively and is known to

block other ANT devices in the vicinity. ANT+ recognizes this and

recommends that fi le transfers only be conducted on a clear channel.

ZigBee PRO implements a technique known as frequency agility

(not hopping). A network node is able to scan for clear spectrum and

communicate its fi ndings back to the ZigBee coordinator so that a new

channel can be used across the network. While this method will work

most of the time, it will not always be possible for the scan reports to

migrate across the mesh under severe congestion/interference.

Can these technologies be jammed

As already mentioned, ANT is susceptible to bursting and continuous

interference on its assigned channel. ZigBee is easy to block with a

Wi-Fi access point, so networks must be planned to avoid placing

the two technologies together. As Wi-Fi output power increases with

advances in technology, it will be increasingly diffi cult for a ZigBee

network to coexist.

Jamming an LE network is particularly diffi cult. Advertising channels

can be blocked with a strong continuous carrier. However, tests in the

lab, using high-power signal generators, have shown such jamming

to only be effective if the node and signal generator are within a

few centimeters of each other. LE adverts are spread across three

channels, therefore requiring three signal generators to be used at

high power. When data channels hop (adaptively) across 37 different

frequencies, it becomes much more diffi cult to inhibit data transfer

during a connection.

Throughput

Throughput of a wireless network can be measured in two ways:

• On air signaling rate, which is often quoted on packaging

(for example, Wi-Fi at 54 Mbps).

• Measuring how quickly useful payload data can be transferred,

which is the more useful method.

For the intended monitoring use cases, it is unlikely that ultra-high data

rates will be needed regularly. The following fi gures show how different

technologies’ payload throughputs compare:

• IrDA ~1 Gbps

• Wi-Fi (lowest power 802.11b mode) ~6 Mbps

• NFC ~424 kbps

• LE ~305 kbps

• ZigBee ~100 Vkbps

• RF4CE (same as ZigBee)

• ANT+ ~20 kbps

• Nike+ ~272 bps

Latency

The latency of a wireless system can be defi ned by a user action sent

to a receiving device. A common scenario is gaming, where a user hits

a button on the controller and the effect is perceived to be instant at

the console. It is not acceptable that a user presses the trigger and

must wait for a bullet to appear. Latency is also critical in applications

such as HID (mice and keyboards), sports and fi tness (instantaneous

body readings), and security devices.

The list below describes some of the typical latencies of low-power

wireless network technologies:

• ANT ~zero

• Wi-Fi ~1.5 ms

• LE ~2.5 ms

• ZigBee ~20 ms

• IrDA ~25 ms

• NFC ~polled typically every second, this is manufacturer specifi c

• Nike+ ~1 second

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Although ANT and Wi-Fi have possible low latencies, they require the

receiving device to listen continuously and therefore use considerable

power. The previous references show that this low latency is often only

achieved on devices that do not have strict power budgets.

Peak power consumption

Peak power consumption is a critical fi gure when designing long-life,

low-power sensor devices. The main reason for this is that certain

types of battery technology are not able to source high currents

instantaneously. The common CR2032 coin cell is a popular choice for

long life sensor gadgets. However, it can only source about

15 mA peaks without damage. If the peak current exceeds 15 mA,

battery life may be degraded. Demanding 30 mA peaks would reduce

realized capacity by about 10 percent of manufacturers’ stated fi gures.

Acceptable continuous standard loads are typically 2 mA or less, in

order to achieve published capacity fi gures.

Other alternative forms of energy source are available from energy

harvesting technologies. Energy harvesters are likely to be used in

conjunction with mass deployment, ultra-low energy radios, to reduce

ongoing maintenance costs of battery replacement. Solar cells are a

well known example of an energy harvester, but they are notorious

for low effi ciency when converting ambient light into useful electrical

energy. An amorphous solar cell of similar dimensions to a CR2032

(3cm 2 ) would yield 1.5 V x 8 µA = 12 µW. With such small amounts of

power available, it is critical that a radio is selected that does not have

high current demands.

Table 4 shows typical peak current consumption for wireless

technologies which can operate from Manganese Dioxide Lithium coin

batteries such as the CR2032.

Table 4: Peak power consumption for wireless technologies.

• IrDA peak current draw ~ 10.2 mA

• Nike+ peak current draw ~ 12.3 mA

• LE peak current draw ~ 12.5 mA

• ANT peak current draw ~ 17 mA

• RF4CE peak current draw ~ 40 mA

• NFC ~ 50 mA

• Wi-Fi peak current draw ~ 116 mA (@1.8 V)

CR2032 OK

Too much current demand

Coexistence

Coexistence means different things to different people. Coexistence is

sometimes thought of as the ability of technologies to operate in the

presence of other radios in the same room or building. However, others

would defi ne coexistence as the collocating of radios on the same PCB

with little radio separation. A standard approach between Bluetooth and

Wi-Fi is to use a signaling scheme between two ICs. This often consists

of a number of wires to inform each IC when its radio is clear to

transmit/receive. For the purpose of this article, we will refer to

coexistence schemes as active and passive, where passive is an

interference avoidance system and active is chip-to-chip signaling.

When added to Bluetooth chips, LE will be able to use existing

coexistence features available in Bluetooth Wi-Fi coexistence schemes.

LE also implements passive interference avoidance schemes.

For example, adaptive frequency hopping can be used to keep clear of

channels where interference is detected. LE advertising channels are

also specifi cally chosen to be in the least congested regions of the

2.4 GHz ISM band.

Wi-Fi has active coexistence technology implemented, when

integrated with a device containing Bluetooth, and a mechanism to

reduce its data rates, when interferers are detected from neighboring

wireless technology.

IrDA does not implement any form of coexistence technology. However,

it is only likely to be affected by bright background light. A positive side

effect of IR being short range and line-of-sight is that it is unlikely that

IR devices will interfere with each other.

NFC implements a form of coexistence where the reader is able to

select a particular tag from a wallet containing many NFC cards. NFC is

similar to IR in that its range is very short and unlikely to interfere with

other NFC devices. It is worth noting that 13.56 MHz has harmonics in

the frequency modulation (FM) band that are particularly strong at 81.3

MHz and 94.9 MHz. This can potentially cause clicking noises in a colocated

FM receiver. However, FM interference effects may be reduced

in a handset by implementing anti-collision techniques – for example,

by skewing or clean up.

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ANT devices normally operate over a single channel; 8-channel

chipsets are available but are often only implemented in the hub

device. Because the sensor device only operates on a single

channel, it limits any form of frequency agility. ANT+ is defi ned as

a single-frequency system, where each sensor transmits at one

particular RF frequency. ANT implements a Time Division Multiple

Access (TDMA) system where it attempts to detect and avoid regular

interferers by informing a remote device to offset its timing. If the

used channel is fully occupied, an ANT network doe not have the

ability to hop to a clear part of the spectrum. This halts data transfer.

ANT burst mode uses the assigned channel in an aggressive manner

and can quite easily absorb a channel’s entire bandwidth. This halts

communications between other ANT devices in the vicinity.

One would assume other continuous interferers, Wi-Fi or household

mobile phones, would also cause similar problems to an ANT network.

ZigBee does not implement a coexistence scheme, but it does have the

ability to continuously listen for clear time on its channel. If the channel

is heavily used, ZigBee throughput and latency are adversely affected,

eventually halting. ZigBee PRO has a feature known as frequency agility

(not the same as hopping) where it may be possible to search for a clear

channel (of the 16 channels defi ned) and then re-establish the network.

Placing a ZigBee node in close proximity to a wide band (Wi-Fi) device

causes severe problems to the ZigBee network.

It is unclear whether Nike+ implements any form of coexistence

scheme. It can evidently operate in the same vicinity as other

Nike+ devices, because it works in crowded gyms. The likelihood of

discovering a regular interferer while exercising outdoors is minimal,

therefore reducing the need for 100 percent reliable packet transfer.

Figure 4 and Figure 5 show spectrum usage for LE and ZigBee.

Each channel is 2 MHz wide, but the spacing and placement of ZigBee

channels implies that only four are likely to be free in the presence of

average Wi-Fi network settings. Typically, channels 1, 6, and 11 are

defaults. With an on-air signaling data rate of only 250 kbps and the

inability to implement hopping, ZigBee is at high risk of non-delivery

of its packets. LE makes much more effi cient use of the spectrum and

employs adaptive frequency hopping as proven by Bluetooth.

Figure 4: Bluetooth low energy channel allocations.

Note: Each channel is 2 MHz wide with no wasted spectrum.

Ch

Wi-Fi Ch. 1 Wi-Fi Ch. 6 Wi-Fi Ch. 11

Wi-Fi Ch. 1 Wi-Fi Ch. 6 Wi-Fi Ch. 11

Figure 5: ZigBee channel allocations.

Note: Each channel is 2 MHz wide with a wasteful 5 MHz spacing. In the presence of

Wi-Fi, only four channels are likely to be available.

How long will my battery last

As mentioned previously, the most common preference for remote

sensor devices is the Lithium coin cell. These cells are typically found

in wrist watches and sports accessories because of their low cost,

size, and weight. Lithium coin cells are very sensitive to the amount of

current that is demanded from them. If treated correctly, they have a

relatively high capacity relative to physical size.

Lifetime fi gures for this type of battery can be obtained in two ways.

From earlier in this article, we know how much power is required to

transmit a wanted payload bit using each technology.

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This would enable us to determine how much data the sensor can

offl oad in a single charge. Alternatively, it is possible to look at

average power consumption while a sensor device is operating.

The ANT website provides a handy calculator for estimating current

draw. The scenario modeled is the most effi cient chipset (AT3),

which sends 120 bytes/second. Each page in ANT is 8 bytes long

and therefore needs to transmit at 120/8 = 15 Hz to achieve

120 bytes/second throughput. The unit is switched on continuously

throughout the day with a 225 mAh battery. Average current is

175.5 µA and a battery would last 52.64 days.

Achieving the same data rate of 120 bytes/second with LE, draws an

average current of 49 µA as described in earlier calculations.

A 225 mAh battery should support this current draw for

225 mAh/49 µA = 4592 hours = 191 days.

Nike+ devices are specifi ed to operate for 1000 hours, which

equates to 42 days. It should be noted that the data rate is fi xed, and

is only 34 bytes/second.

In reality, desired throughputs would be much lower, resulting in

years of battery life with a similar ratio of lifetime.

Target markets

The low-power wireless technologies described in this article are

targeted towards specifi c market segments, some of which overlap.

Table 5 shows examples of these identifi ed target markets.

Summary

The research in this article has shown a number of technologies

competing for the same market space.

ANT is a good example of a technology that is already in mass

production and has begun to establish itself as the “sports

and fi tness” technology. However, it has only managed to sell

approximately 15 million chips to date, beginning in 2004 and has

only been integrated into three mobile handsets. ANT makes a good

attempt at operating from limited power sources and has built a

niche ecosystem.

Table 5: Low-power wireless technology target markets.

LE A A+ RF Zi Wi Ni Ir NF

Remote Control √ x x √ x √ x √ x

Security √ x x x √ √ x x √

Health and Fitness √ √ √ x x x √ x x

Smart Meters √ x x x √ √ x x x

Cell Phones √ x √ x x √ x √ √

Automotive √ x x x x √ x x √

Heart Rate √ x √ x x x x x x

Blood Glucose √ x √ x x x x x x

Positioning √ x x x √ √ x x x

Tracking √ x x x √ x x x √

Payment x x x x x x x x √

Gaming √ x x x x x x √ x

Key Fobs √ x x √ x x x √ √

3D TV √ x x x x x x √ x

Smart Applications √ x x x √ x x x x

Intelligent Transport Systems √ √ √ x √ x x x x

PCs √ x x x x √ x √ √

TVs √ x x √ x √ x √ x

Animal Tagging √ x x x √ x x x √

Assisted Living √ √ √ x x x x x √

Key:

LE (Bluetooth low energy), A (ANT), A+ (ANT+), RF (RF4CE),

Zi (ZigBee), Wi (Wi-Fi), Ni (Nike+), Ir (IrDA), NF (NFC).

LE is the closest competitor and will be competing in the same markets

and many others, offering mobile handset manufacturers a route to a

larger ecosystem. LE also provides the best power per bit requirements

of the personal space technologies, beaten only by Wi-Fi.

Wi-Fi is normally intended for bulk traffi c transfer at high speed.

Work is in progress to enable special Wi-Fi chips to operate in HID

equipment. However, currently available chipsets for HID over Wi-Fi

are proprietary and require a special driver to be installed on Microsoft

Windows ® 7 PCs. In addition, such systems are likely to consume

signifi cant power at the PC end of the link to minimize latency.

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ZigBee and RF4CE are virtually the same technology and

appear positively power hungry compared with the other

radio technologies.

NFC is not seen as a competitor to most low-power wireless

technologies, because it brings new use cases to the mobile scene.

It is a short range (~5 cm) radio which is ideally suited to “Touch to

” applications.

The cost of implementing IR transmit-only is very cheap and may

still remain a viable option in low-end televisions for the near future.

IR has been around for a long time and is being replaced in most

areas by non-line-of-sight radio technology. It is also relatively

power hungry. By switching to radio, running costs for traditional

IR products will be reduced considerably. In an increasingly

environmentally conscious world, this reduction in power

consumption is a good thing – it’s ‘Green.’

General-Purpose RF Switches

Skyworks Solutions offers a select group of radio frequency

(RF) switches from its diverse switch offering that are in stock

and ready for immediate design into various markets including

handsets, infrastructure, automotive, CATV/Satcom, smart

energy, medical, military, RFID, test and measurement, and

WLAN/WiMAX/WiFi.

Features

• Low insertion loss

• High isolation

• High linearity and low

distortion

• High power handling

• Broad frequency range:

20 MHz to 8 GHz

• Low bias and control logic

voltage

• Low current operation

Applications

• Tx/Rx and diversity

• WCDMA handsets and data

cards

• 3G/4G wireless networks

• LNB/DBS matrix

• Microwave applications up to

8 GHz

• Multi-antenna switching

BUY NOW!

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• RF4CE Specification

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

Full Signal Path Solution for

Portable Ultrasound Systems

by Suresh Ram, National Semiconductor

Article Resources

Product Information

• LM96570 Datasheet

• LM96530 Datasheet

• LM96511 Ultrasound AFE

Demo

Medical ultrasound is a sophisticated signal

processing system whose non-invasive nature

enables a wide range of applications.

There is a rising demand for accessible medical care. The world

population is rapidly growing and aging, increasing the cost of healthcare.

Medical practitioners need small, energy effi cient, and cost effective

diagnostic devices. Portable diagnostic equipment that will improve the

quality of healthcare in a cost effective manner is highly desirable.

In addition to addressing traditional imaging applications in

obstetrics, gynecology, radiology, cardiology, and vascular

applications, portable ultrasound imaging allows for deployment at

the point-of-care. System designers are fi nding that simply shrinking

a console into a portable or handheld unit does not guarantee

adequate battery life or diagnostic image quality.

Beamforming technique

Innovations in system architecture, coupled with analog and mixed

signal electronics, FPGA-based algorithms and control, or CPU and

GPU-based image processing enable compact systems with high

diagnostic relevance. Ultrasound systems use focal imaging techniques

to achieve performance far beyond what can be achieved through

a single-channel approach. Using an array of transmitters and

receivers, a high-defi nition image can be built by time shifting, scaling,

coherently summing echo energy, and phasing as seen in the phased

array ultrasound system in Figure 1. The concept of shifting, phasing,

and scaling of transmit and receive signals, generally from the same

reciprocal transducer array, is known as beamforming. It provides the

ability to form an image by dynamically focusing and concentrating

energy sequentially in points of the scan region.

A Gate Array based solution like National Semiconductor’s

eight-channel ultrasound trasmit/receive chipset has many advantages

compared to a DSP based solution. The most important ones are higher

fl exibility, lower cost, and signifi cantly less power consumption.

The transmit beamformer provides the delay patterns and profi les to set

the desired focal point of the transducer. The LM96570 [1] confi gurable

transmit beamformer provides a seamless interface between the

master control engine and the pulser, allowing programmable pulse

pattern profi les with fi ne delay resolution. Delay resolution of

1 µs/1280 µs provides an order-of-magnitude better jitter performance

over traditional FPGA beamforming.

LM96530

T/R Switch

LM96550

Pulser

LM96570

Tx Beamformer

Registers

TX Control

µWire

Clock Engine FPGA

DVGA

CT∑∆

LNA DVGA ADC

CW

Doppler

LM96511 Analog Front End

Clock

Figure 1: Phased array ultrasound system.

Power

RX

Beamformer

PCI/

USB

Image

Processing

Micro

Processor

Doppler

Processing

Related Products

• LM96570SQE/NOPB

• LM96530SQE/NOPB

Online Resources

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• Component Reference

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

The pulser needs to deliver high voltage pulses to the transducer.

Ringing during positive and negative signal transitions affects image

quality. Symmetrical square wave pulses improve second harmonic

imaging. Often times, it may not suffi ce to simply visualize abnormal

tissue. Harmonic imaging improves spatial resolution and the resultant

diagnosis of the abnormality.

The LM96550’s [2] symmetric pulses can be used in either B-mode or

the Continuous Wave (CW) Doppler mode. An on-chip active damper

minimizes ringing. A transmit receive (T/R) switch is required to protect

the receive path amplifi er from the high voltage transmit pulses.

The LM96530 [3] T/R switch allows independent control of each channel

through a daisy-chained SPI interface. Only three pins are required

from the FPGA to control any channel in the system. This simplifi es

the system design signifi cantly where otherwise dedicated pins are

required for each chip. Bias current adjustment allows either highperformance

or low-power mode.

Time gain control

Low receiver noise fl oor is desired for deep penetration with high

spatial resolution. In a well designed system, the low noise amplifi er

(LNA) sets each channel’s performance. The purpose of the variable

gain amplifi er (VGA) is to map the LNA output signal to the full scale

range of the analog-to-digital converter (ADC) as return signals from

the body become weaker with depth and time. This process is called

Time Gain Control (TGC) or Depth Gain Control (DGC). High resolution

digital variable gain amplifi ers (DVGAs) offer better gain matching,

gain fl atness, and close-in phase noise than log amps or

piecewise-linear analog VGAs. In addition, gain errors of DVGAs are

relatively low and consistent throughout the entire variable gain range.

Analog VGAs often have gross errors at the lower and higher gain

extremes, reducing the amount of usable range.

As shown in Figure 2, the DVGA’s improved close-in noise

performance facilitates visualization of low velocity blood fl ow deep

in an organ like the liver. Small signals are readily discerned when

they are not buried in the high close-in noise fl oor of a traditional

analog VGA.

-20

-30

-40

-50

-60

-70

-80

-90

Freq Domain

Analog VGA:

Higher Noise

Digital VGA:

Lower Noise

Tones Difficult to

See with AVGA

-100

1.3 MHz 1.5 MHz 1.7 MHz 1.9 MHz 2.1 MHz 2.3 MHz 2.5 MHz

Figure 2: Close-in noise performance.

The ADC digitizes the signals for further processing. The Xignal CT∑∆

is a highly oversampled system. The high rate of oversampling spreads

the quantization noise. The on-board modulator shapes noise and

moves it out of band. The on-chip brick wall digital fi lter then creates

an alias-free Nyquist sample range (see Figure 3). The elimination of

anti-aliasing fi lters, and power hungry sample-and-hold amplifi ers,

inclusion of an on-chip clock, and low jitter PLL simplify the receive

path front end design.

ADC

Kf s

Oversampled

Quantization Noise

Kf s Kf

2 2

s

Shaped Noise

Kf s Oversampling

+ Noise Shaping

∑∆

MOD

f s

Kf s

Kf

Oversampling

2 2

s

+ + Digital Decimation

Filter

Digital Filter

Kf s Removed Noise

∑∆

MOD

Figure 3: CT∑∆ principle.

Digital

Filter

f s

DEC

f s

f s

2

Kf s

2

Kf s

Article Resources

Product Information

• LM96570 Datasheet

• LM96530 Datasheet

• LM96511 Ultrasound AFE

Demo

Related Products

• LM96570SQE/NOPB

• LM96530SQE/NOPB

Online Resources

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• Component Reference

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WIRELESS HEALTH AND FITNESS: Wellness Without Wires

In CW Doppler systems used to measure blood fl ow velocity,

a continuous sine wave is broadcast into the body, and the phase

shift of the returning signals is measured. Dynamic range (DNR)

requirements of the CW Doppler analog signal path are very high,

since small signal refl ections from deep in the body are summed with

large close-in signals. Any nonlinearity creates cross-products that are

diffi cult, if not impossible to remove.

Multiple channel I and Q components are summed and highpass

fi ltered to minimize stationary clutter, vessel wall returns, and slow

sonographer hand movement. Highpass fi lter outputs are presented in

both audible and visual formats.

The LM96511 [4] Receive Analog Front End (AFE) combines the benefi ts

of a DVGA and CT∑∆ ADC with CW Doppler to provide a total

input-referred noise of 0.9 nV/rtHz across a gain range of 58 dB,

a DVGA step resolution of 0.05 dB, 110 mV/channel B-mode power

consumption, a CW Doppler phase rotation resolution of 22.5 degrees,

-144 dBc/Hz phase noise at 5 KHz offset, a -161 dB/Hz dynamic range,

and 208 mW/channel CW Doppler power consumption in a small

footprint package.

Summary

In summary, medical ultrasound is a sophisticated signal processing

system. It is the least invasive diagnostic tool, fi nding widespread use

in many applications. The portable system designer is challenged with

numerous tradeoffs to achieve an optimal balance between power

consumption, performance, and size. National’s 8-channel Transmit &

Receive chipset comprising the Programmable Transmit Beamformer,

Pulser, T/R Switch, and Receive AFE provides a comprehensive

subsystem solution designed with system level features to pack console

performance within a small form factor portable or handheld system.

References:

1

LM96570, Programmable Transmit Beamformer data sheet

www.national.com/ultrasound

2

LM96550, Pulser data sheet www.national.com/ultrasound

3

LM9530, T/R Switch data sheet www.national.com/ultrasound

4

LM96511, Receive Ultrasound Analog Front End datasheet

www.national.com/ultrasound

KwiQMAte Series Connectors

Emerson’s

KwiQMAte series

designed for higher

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Emerson Network

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Connector bodies are offered with a tri-alloy as a standard fi nish

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Article Resources

Product Information

• LM96570 Datasheet

• LM96530 Datasheet

• LM96511 Ultrasound AFE

Demo

Related Products

• LM96570SQE/NOPB

• LM96530SQE/NOPB

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New Design Database Gives Digi-Key

Customers a Competitive Edge

Digi-Key’s Reference Design Library is a new

online tool for electronic design engineers.

This interactive web-based library consists of proven designs

contributed by reliable sources and a fi ltering capability based on

each design’s measured performance.

Digi-Key’s Reference Design Library was created for the convenience

of engineers and electronics designers. Creators of this resource

understood the need for valuable, proven design blueprints from

leading component suppliers to be available in one organized,

searchable repository.

By clicking into categories, users of the Reference Design Library

can search for designs based on voltage in, current out, outputs and

types, and effi ciency in certain conditions.

Digi-Key’s Reference Design Library currently houses 400+

designs regarding AC/DC and DC/DC conversion, audio amplifi ers,

motor control, power management, sensor solutions, lighting, and

wireless communication.

Instead of searching countless manufacturer websites and contacting

companies to fi nd needed designs, users can browse the Reference

49

Design Library based upon category and subcategory. Currently,

the lighting and AC/DC conversion categories are the most expansive,

but new designs are frequently added.

This addition to Digi-Key’s website is located on the homepage at

www.digikey.com under the “Resources” section or by visiting

www.digikey.com/referencedesign. Visit Digi-Key’s Reference

Design Library often to view the newest design additions.

www.digikey.com/referencedesign

Reference

Design Library

Browse by Category

• AC/DC and DC/DC

Conversion

• AC/DC, SMPS - Multi Output

• AC/DC, SMPS - Single Output

• DC/DC SMPS

• Audio Amplifiers

• Lighting

• CFL Ballasts

• Color Mixing LED Controllers

• LED Camera Flash Drivers

• LED Drivers/Constant Current

Sources

• Motor Control

• Power Management

• Battery Chargers

• Energy Metering

• OR-ing Controllers

• POE - Power Over Ethernet

• Power Factor Correction

• Sensor Solutions

Wireless Communication

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Considerations for Sending

Data over a Wireless Link

Implementing a robust RF communications link

clearly begins at the design stage. Anticipate a host

of problems, customize your protocol accordingly,

choose a capable RF module, and your wireless link

should work as planned.

Linx Technologies modules are designed to create a robust wireless

link for the transfer of data. Since they are wireless devices, they

are subject to external infl uences which are not present in wired

communications. These infl uences are capable of interrupting and

corrupting the data that is being sent by the transmitter, causing the

output at the receiver to be incorrect. The designer should implement a

noise-tolerant protocol to correct for this possible interference.

The goals of the protocol are to synchronize communications between

the transmitting and receiving ends, identify valid data packets, verify

that the data packets are correct, and correct any bad data in a packet.

One common misconception is that a digital address can be sent

to distinguish one transmitter from another, even when multiple

transmitters are on at the same time. RF is an analog domain, so the

digital content does not matter. For an analogy, think of a crowded room.

If only one person is talking, everyone will be able to hear that person.

If everyone talks at once, it becomes diffi cult to hear any single person.

A protocol can help reduce noise in a multiple transmitter system and

help the receiver pick out the valid data in a noisy environment.

contributed by Linx Technologies

Except for the encoder/decoder pair, Linx modules do not place any

constraints on the type or format of the data being sent. This freedom

allows for more versatility in the types of applications that can use the

modules, but it also places the protocol design burden on the customer.

This article is intended to help engineers design a suitable protocol for

their application.

To better understand the requirements for such a protocol, we will fi rst

examine all of the potential sources of data corruption which create

the need for the protocol. We will develop a general model for the

communications channel from the transmitter to the receiver through

which the data must travel. Using this model, we can account for all of

the external and internal infl uences on the data stream.

Communications basics

A communications channel is the path that data travels from the

transmitter to the receiver, and is made up of all of the components

required to generate the data stream, encode it, transmit it (including

the propagation path), receive it, decode it, and interpret it. Figure 1

shows a generic model of a communications channel.

DATA

SOURCE

DATA

RECEPTION

DATA

ENCODING

PROPAGATION

PATH

DATA

DECODING

DATA

TRANSMISSION

DATA

INTERPRETATION

Article Resources

Product Information

• ES Series Transmitter

Data Guide

• ES Series Master Dev

User Guide

• ES Series Receiver

Data Guide

• ES Series Master

Development System

User’s Guide

Related Products

• TXM-916-ES_

• RXM-916-ES_

• MDEV-916-ES-USB

• MDEV-916-ES-RS232

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Figure 1: Generic communications channel.

50

Wireless Solutions | TZ W 112.US


Data source

The data source can be anything. It could be an ADC reading a

temperature, a fi le on a computer hard disk, or a key press on a keypad.

Data corruption at this stage in the communication channel is unlikely and

can usually be traced to a bug in the hardware or software of the device.

Data encoding

The data coming from the data source is generally raw and

unprotected. Encoding the data provides a structure, security, and a

form of error correction that can ensure data integrity. Data corruption

at this stage in the communications channel is unlikely and can usually

be traced to a bug in the hardware or software of the device.

Data transmission

All Linx transmitters are fully tested at the factory. However, external

factors such as power supply noise and improper modulation voltage can

corrupt the data stream. A transmitter that is operated as recommended

by its data sheet should not contribute to data corruption.

Propagation path

The propagation path is the path that the radio waves take through

free space from the transmitter to the receiver. It is in this stage that

data corruption is most likely to occur. Corruption is most commonly a

result of either in-band interference or desensitization from unwanted

RF sources present in the propagation path. Interference can manifest

itself in many ways. Low-level interference will produce noise and

hashing on the output, reducing the link’s overall range.

Another type of interference can be caused by higher powered devices

such as frequency hopping spread-spectrum devices. Since these

devices move rapidly from frequency to frequency, they will usually

cause short, intense losses of information. Such errors are referred to

as bursting errors and will generally be dealt with through a protocol.

High-level interference is caused by products sharing the same

frequency or from near-band, high-power devices. Fortunately,

this type of interference is less common than those mentioned

previously, but in severe cases, it can prevent useful functioning of the

affected device. It is in these cases that the frequency agility offered by

the Linx Technologies HP3 Series RF modules is especially useful.

Although technically it is not interference, multipath propagation is also

a factor to be understood. Multipath is a term used to refer to the signal

cancellation effects that occur when RF waves arrive at the receiver

in different phase relationships. This is particularly a factor in interior

environments where objects provide many different refl ection paths.

Multipath results in lowered signal levels at the receiver, and thus

shorter useful distances for the link.

All of these effects can cause continuous or periodic data corruption.

It must be recognized that many bands are widely used, and the potential

for confl ict with other unwanted sources of RF is very real.

In a wired application, the propagation path is a wire instead of free

space and tends to introduce few, if any, errors into the data stream.

This fundamental difference between a wired and a wireless link dictates

the need for some type of data-transfer protocol. Later in this article, we

will discuss how such a protocol can help deal with these issues.

Data reception

All Linx receivers are fully tested at the factory to ensure that they

function to all of the specifi cations set forth in the receiver data guide.

There are several conditions, however, that can cause data corruption

in the receiver stage. If another transmitter turns on with suffi cient

power, it can interfere with the desired signal, causing the data output

to become noisy. Furthermore, in-band interference and desensitization

can cause the receiver to corrupt the data stream. Finally, the receiver

can corrupt the data stream if the data source violates the minimum or

maximum baud rate specifi cation of the receiver.

The method of signal modulation also has an impact on the receiver’s

ability to capture a signal in the presence of interference. FM/frequency

shift keying (FSK) modulation systems are generally superior to

AM/on-off keying (OOK) systems in this respect.

Data decoding

The received data is decrypted and checked for errors. If implemented,

error correction is performed to correct any mistakes detected in the

data. Data corruption at this stage in the communications channel is

unlikely and can usually be traced to a hardware or software bug.

Article Resources

Product Information

• ES Series Transmitter

Data Guide

• ES Series Master Dev

User Guide

• ES Series Receiver

Data Guide

• ES Series Master

Development System

User’s Guide

Related Products

• TXM-916-ES_

• RXM-916-ES_

• MDEV-916-ES-USB

• MDEV-916-ES-RS232

Online Resources

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• Component Reference

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Data interpretation

Data interpretation is usually accomplished in software and involves

doing something useful with the information received. Data corruption

at this stage in the communications channel is unlikely and can usually

be traced to a hardware or software bug.

What is a protocol

Every time two people communicate, there is always a potential for

misunderstanding. In some cases the risk is acceptable; other times,

such as during negotiations, a misunderstanding can cause severe

repercussions. When the accuracy of communications is vital, rules

for communication are established prior to negotiations to ensure

that both sides are “speaking the same language.” These rules are

referred to as protocols. Since the communications between the

transmitter and receiver can be corrupted, a protocol is required

to ensure that the receiver can “understand” the data from the

transmitter, and also determine if the data that was received is

correct or if there were any errors.

Packetization

A protocol will generally cut the main data into smaller pieces that are

easier to handle. It will wrap the data with special information needed

by the protocol to put the data back together at the reception end.

This process is called packetization. At the reception end, the protocol

strips the extra data from the packet and reassembles the original

data. This process is called depacketization.

Minimum overhead

A wireless data transfer protocol should be effi cient. A protocol must

add information to the main data, such as packet identifi cation codes,

error checking, encryption, etc. The amount of information added

should be the minimum amount required to achieve all of the goals of

the wireless data transfer.

Reliability

A protocol is said to be reliable if it can separate good data from errant

data. Reliability is usually achieved by embedding some form of error

detection in the data stream. Parity, checksums, and cyclic redundancy

checks (CRC) are all forms of error detection codes.

Robustness

A protocol is said to be robust if it can correct errant data. Robustness is

usually achieved by embedding forward error correction (FEC) codes in

the data stream. There are several methods of forward error correction,

though the more complete the system, the more overhead required.

Security

A protocol is said to be secure if it can prevent unauthorized access to

the data. Since the data is transferred over a wireless link, anyone with

a receiver can see the transmission. Encryption is used to make the

data useless to anyone without the correct access code.

Uniqueness

A protocol is said to be unique if it can distinguish the correct

transmission in the vicinity of several transmitters. This is usually

accomplished by placing address bits in each packet, enabling the

receiver to tell which packets came from the correct transmitter.

Optimum radio performance

A wireless protocol should operate in a way that takes maximum

advantage of the transmitter and receiver, while staying within the legal

requirements for operation.

Selecting the features you really need

The preceeding features are the most important features of a good

protocol. There must be a compromise between the error detection,

error correction, encryption, and overhead. The more strongly the data

is encoded, the more overhead will be required from the processor to

do the required calculations. This will add time to the transmissions,

as the processors encode the data and then decode it on the receiving

end. The designer should choose only the features that the project

really needs and no more. This will strike a balance between protocol

strength and product performance.

Packetization

It is a good idea to structure the data being sent into small packets so

that errors can be managed without affecting large amounts of data.

Typically, a packet would begin with a start sequence so that the receiver

can identify the beginning of valid data. This sequence would then be

followed by the data and any error detection or correction information.

Article Resources

Product Information

• ES Series Transmitter

Data Guide

• ES Series Master Dev

User Guide

• ES Series Receiver

Data Guide

• ES Series Master

Development System

User’s Guide

Related Products

• TXM-916-ES_

• RXM-916-ES_

• MDEV-916-ES-USB

• MDEV-916-ES-RS232

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A stop sequence can end the packet so that the receiver knows when to

stop accepting information. After receiving the stop sequence,

the receiver must see a valid start sequence before accepting any more

data. Otherwise, the receiver can count the number of bits it receives,

or time out after not receiving valid data for a certain time.

Start codes and noise

The fi rst thing any protocol must be able to do is identify the difference

between noise and valid data. Noise appears as random bytes of

information with no obvious pattern. An ideal noise source has the

ability to generate any combination of bytes with the same probability

as any other combination of bytes. This property of noise makes it very

diffi cult to fi nd a combination of bytes to signify the start of a valid

packet. Fortunately, in the real world, noise is rarely ideal.

Wake-up sequence

The transmitter has no way of knowing the state of the receiver, so the

protocol must place the receiver into a known state prior to sending

data. Failure to do this could cause the receiving processor to miss the

fi rst few bits of data potentially corrupting the entire packet.

The protocol should use a start sequence that begins with two

transitions to pull the receiver out of squelch and into a known state.

The order of the transitions, either 010 or 101, is up to the designer.

Noise filter

Next, there needs to be a way for the receiving processor to qualify

the start of the packet as valid data and not noise. A good way to

implement a noise fi lter is with bit sampling. The transmitter would

send a high marking period and a low marking period of specifi c

lengths determined by the baud rate and processing power at the

receiver. The receiving processor will repeatedly sample the bit as

fast as possible, looking for level changes. If no changes are seen

within the specifi ed period, then the receiver can accept the data as

valid. Using more than two pulses would give a higher probability that

the transmission is valid, but would need more overhead from the

processor and require a longer transmission length.

The order of the initial wake-up sequence described above will

determine the order of the sampled bits. For example, if the wake-up

sequence is 010, then the fi rst sampled bit should be a one. The order

of the pulses doesn’t matter, just that at least two bits are measured

since the probability of random noise producing one bit of the correct

length may be fairly good.

The length of the sampled bits will generally depend on the baud

rate chosen for the application. If possible, make the sampled bit

longer than a bit at the chosen baud rate to prevent the receiver from

detecting the start sequence in the middle of the data. Also, some

margin should be built into the front and back of the pulse. Some

transmitters and receivers can cause pulse stretching or shortening as

a result of start-up times and modulation methods, so the radios used

should be tested to determine the appropriate margin.

This method must be performed at the bit level, which may not be

possible for some applications. It works well for removing random

noise, but it may pass structured data from other, undesired

transmitters. A method for detecting the correct data should also

be used.

Digital logic filter

To remove the chance that an undesired data transmission will be

verifi ed, a digital logic fi lter should be implemented. This is a series

of bits that are not likely to appear in the transmitted data, but must

appear in the correct position in order for the packet to be valid. This

has the advantage of being able to be implemented at the byte level. For

example, any valid text transmission must be preceded by one of the

ASCII characters. This method is not good for removing random noise.

Combining the two fi lter methods will help to create a robust start

sequence that will help to qualify a valid packet. The designer can

combine them in whatever manner is appropriate for the application,

though the following order will generally work the best:

[Wake-Up][Noise Filter][Logic Filter][Data]

The receiver can only hold a specifi c level for a certain amount of

time, resulting in the minimum baud rate and maximum time between

transition specifi cations. If the length of time between transmissions

exceeds this time, then data integrity cannot be guaranteed and the

start sequence should be resent.

Article Resources

Product Information

• ES Series Transmitter

Data Guide

• ES Series Master Dev

User Guide

• ES Series Receiver

Data Guide

• ES Series Master

Development System

User’s Guide

Related Products

• TXM-916-ES_

• RXM-916-ES_

• MDEV-916-ES-USB

• MDEV-916-ES-RS232

Online Resources

Additional Links

• Component Reference

Guide

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Error detection

Error detection is achieved by performing some type of analysis on the

data prior to transmission and adding the results of this analysis to the

data packet. The same analysis is then performed at the reception end

and compared to the results embedded in the packet. If the two are

different, the packet is errant. There are three common types of error

detection: parity check, checksum, and cyclic redundancy check.

Parity check

The simplest form of error detection is the parity check. A parity check

is accomplished by adding all of the 1s in a string of bits. For even

parity, if the number is even, then the parity bit is set. For odd parity, if

the number is odd, then the parity bit is set.

Example 1:

In this example, we will calculate the parity of a byte that is to be

transmitted using even parity. During transmission, one of the bits gets

reversed. The receiver catches this through the parity check at the

reception end.

Transmitter:

10101010

There is an even number of 1s, so the parity bit is set and the byte is

transmitted as follows:

101010101

Receiver:

001010101

The last bit is not used in the parity calculation since it is the parity

bit from the transmitter. Calculating parity on the received byte yields

an odd number of 1s and the parity is 0. Since the receiver’s parity

calculation does not match the transmitter’s calculation, the byte is

determined to be errant and is thrown out.

The parity check is the easiest to implement, but is also the most

unreliable. It can only catch an odd number of errors in the bit stream.

If the number of errors is even, then the parity calculation will incorrectly

indicate that the byte is good. Thus, there is a 50 percent chance of the

parity check catching an error, which is less than optimal.

Checksum

A checksum is calculated based on a series of bytes by adding the

values of the bytes together and truncating the result to the desired bit

length. For example:

4 data byte 1

109 data byte 2

65 data byte 3

204 data byte 4

126 8-bit checksum

A checksum will catch many more errors than the parity check.

However, by simply transposing data bytes 2 and 3, the data packet

becomes errant, but the checksum would provide the same result.

The checksum only gives weight to the value of the bytes, not their

order. Thus, errors of ordering cannot be caught with the checksum.

Cyclic redundancy check

The most popular form of error checking is the cyclic redundancy

check (CRC). A CRC is more reliable than the checksum because every

bit can individually contribute to the checksum. This makes it much

less likely that multiple errors will cancel each other out.

The idea behind the CRC is fairly straightforward. The math, however,

is more complicated. Essentially, the data is considered a large binary

number. This number is divided by another fi xed binary number (called

the generator) and the remainder is used as the checksum.

This checksum is appended to the end of the data and transmitted.

While the individual bits do not affect the quotient very much, they do

have a large effect on the remainder. This is why division is much more

robust than addition.

The receiver can then do one of two things:

1. Remove the checksum from the received data, recalculate the

checksum, and then compare the received and calculated versions.

2. Calculate the checksum for the entire received message and see if

it comes out to zero.

Both of these methods work, but the second option is a little cleaner

and faster.

Article Resources

Product Information

• ES Series Transmitter

Data Guide

• ES Series Master Dev

User Guide

• ES Series Receiver

Data Guide

• ES Series Master

Development System

User’s Guide

Related Products

• TXM-916-ES_

• RXM-916-ES_

• MDEV-916-ES-USB

• MDEV-916-ES-RS232

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Both the data stream and the fi xed number are generally described in

terms of polynomials, and are written in the form of aXy, where “a” is

either 1 or 0 and “y” is the bit position. For example:

10011

would be represented as:

1X4 + 0X3 + 0X2 + 1X1 + 1X0

Since anything times zero is zero, you can remove all of the

exponentials with a coeffi cient of zero and simplify the equation.

1X4 + 1X1 + 1X0

This seems ineffi cient and confusing if the generator polynomial is

small, but when dealing with 32-bit polynomials, it is actually easier

to understand.

The generator polynomial is chosen so that it has the greatest chance

of detecting the kinds of errors most likely to be found in the real

world. This includes one or two bit errors through bursting errors. Some

popular generator polynomials are:

16 bits: (16,12,5,0) [X25 standard]

(16,15,2,0) [“CRC-16”]

32 bits: (32,26,23,22,16,12,11,10,8,7,5,4,2,1,0) [Ethernet]

These polynomials all have a leading 1. This means that the 16-bit

polynomial is actually 17 bits long with the leading 1 (bit 17) and then

the other bits listed in the above set. This leading 1 is called the implicit

top bit, while the remaining bits are called active bits.

There are two ways of performing this operation. The most basic

method is to feed the data into a shift register one bit at a time. This is

shown in the Figure 2 for an 8-bit generator polynomial.

OUT

7 6 5 4 3 2 1 0

1 1 0 1 1 1 0 0 1

Figure 2: CRC shift register.

BIT NUMBER

DATA

GENERATOR

Since the generator is eight bits long, eight 0s are appended to the end

of the data. This data is then fed into the shift register one bit at a time.

Every time a 1 comes out the other end, the generator polynomial is

XORed (exclusive OR) with what is in the shift register. What is left in

the shift register at the end of the data is the checksum.

This is a fairly slow way of computing the checksum, though it requires

very little overhead. The faster way of computing it is to use a look-up

table. It turns out that a full byte can be computed at a time. More

than that, most of the necessary calculations can be pre-computed

and stored in a table. What happens here is that the registers shift out

a byte and this byte is used to reference a location in a table of 256

values. The number at this location is then XORed with the values in

the registers. This is repeated until all of the data bytes are shifted

out. The value method is faster, however it requires the table to be

generated and stored in memory.

This is a glossed-over description of a complicated scheme, but it

covers the basic idea.

Forward error correction

The goal of error correction is to embed redundant data in the packet

at the transmitter end so that the receiver can correct the data if the

error detection mechanism indicates that the data recevied is errant.

A simple error correction algorithm

A very simple method of forward error correction has been developed

at Linx that is suitable for many wireless data links. The data to be sent

is duplicated two times (for a total of three copies) in the packet at the

transmission end. At the reception end, the fi rst copy of the data in

the packet is checked for errors. If there is an error, the two redundant

copies of the data in the packet are used to generate one correct

version of the data.

The correction is achieved by comparing the bits of each of the three

copies of the data. If two or more bits are set, the corrected version has

that bit set: 0 0 0 0 1 0 1 1 copy 1 (errant byte)

1 0 1 0 1 0 1 0 copy 2

1 0 1 1 1 0 1 0 copy 3 (errant copy)

--------------------

1 0 1 0 1 0 1 0 corrected byte

Article Resources

Product Information

• ES Series Transmitter

Data Guide

• ES Series Master Dev

User Guide

• ES Series Receiver

Data Guide

• ES Series Master

Development System

User’s Guide

Related Products

• TXM-916-ES_

• RXM-916-ES_

• MDEV-916-ES-USB

• MDEV-916-ES-RS232

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Once all of the bytes are corrected, they should be resubmitted to the

error checking procedure to verify that the corrected bytes are valid.

If they are not, then that data packet is uncorrectable; otherwise, the

data can be used.

Hamming code

Hamming codes use a modifi cation of the parity check to correct a

single errant bit or detect two errant bits in a byte; they are used with

great success in computer memory applications. In wireless data

links, though, the noise tends to be ‘bursty’ and can corrupt several

concurrent bits. Hamming cannot correct these types of errors, so it

is probably not the best choice for use in the 900 MHz band where

high-power, spread-spectrum devices can cause frequent interference.

It should be good enough for short-range links, especially remote

control applications that register a key press. Combined with repeated

transmission of the packet, Hamming can make a fairly reliable link.

Implementing Hamming is fairly straightforward. We will look at the

case of eight data bits in a byte for this example.

First, all of the bit positions that are powers of two are marked as the

parity bit positions. All of the other bit positions are for the data bits.

For example, suppose we have the data byte:

10100101

Spaces for the parity bits are added in the positions that are a power

of two.

Position 12 11 10 9 8 7 6 5 4 3 2 1

Bit 1 0 1 0 0 1 0 1

The parity is calculated by using modulus arithmetic (XOR logic) on the

decimal number for the bit location of all of the data bits that are 1.

So in this example it would be:

3 XOR 6 XOR 10 XOR 12 = 3 = 0011

This gives us the fi nal code word.

Position 12 11 10 9 8 7 6 5 4 3 2 1

Bit 1 0 1 0 0 0 1 0 0 1 1 1

The receiver would then XOR the bit positions of all of the 1s:

1 XOR 2 XOR 3 XOR 6 XOR 10 XOR 12 = 0

Since the result is zero there are no errors. Now, suppose position six

was switched during transmission, making the word:

Position 12 11 10 9 8 7 6 5 4 3 2 1

Bit 1 0 1 0 0 0 0 0 0 1 1 1

The receiver calculates the parity as:

1 XOR 2 XOR 3 XOR 10 XOR 12 = 6

So position six is in error. This bit is fl ipped and the byte is corrected.

The receiver then removes the parity bits and the data is recovered.

If more than two data bits are wrong, the byte cannot be corrected

and must be discarded. More data and parity bits can be used, but

the (12,8) code shown is a good compromise between code integrity

and overhead.

Manchester encoding

Manchester encoding is a way of combining the clock and the data of a

synchronous bit stream into one serial data stream. In this method, the

bits are transmitted as a level change in the middle of the data bit.

A 1 data bit is transmitted as a 0 to 1 transition, and a 0 data bit is

transmitted as a 1 to 0 transition. This is essentially an exclusive XOR

between the clock and the data as seen in Figure 3.

CLOCK

DATA

MACHESTER

ENCODED

DATA

Figure 3: Manchester encoding.

1 0 1 0 0 1 1 1

Article Resources

Product Information

• ES Series Transmitter

Data Guide

• ES Series Master Dev

User Guide

• ES Series Receiver

Data Guide

• ES Series Master

Development System

User’s Guide

Related Products

• TXM-916-ES_

• RXM-916-ES_

• MDEV-916-ES-USB

• MDEV-916-ES-RS232

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This is advantageous because regardless of what happens at the bit

edges, there will always be a level change at the center of each bit.

A series of 1s or Os will not result in the receiver seeing just a DC level.

It also helps the receiver synchronize with the transmitter by having a

level change at predictable intervals. The downside is that the frequent

level changes require more bandwidth than the original signal. So, for

a given data rate the clock can operate at the maximum rate, but the

data will be half that rate. An advantage of Linx AM RF modules is that

a 50 percent duty cycle will draw less current than a higher duty cycle,

and the output power, which is averaged over time, may be increased

and still comply with FCC limits.

Reed-Solomon encoding

Reed-Solomon codes have the capability of identifying and

correcting strings of errant bits. They are used in everything from

satellite transmission to CD players to compensate for interference

and physical deformities – for example, a scratch on a CD. Turbo

codes are a way of encoding the data twice to allow for more error

correction power. These codes are very math intensive and are

generally overkill for the applications using Linx modules, so they will

not be discussed in detail here.

Encryption

Encryption is used to scramble a message in such a way that anyone

without the correct key will be unable to decipher the message

and understand the content. This is done based on very complex

mathematical equations that can only be solved in one way using a

number called a key.

The key is known at the transmitter and receiver, but is not transmitted

and is kept secret, since without the key the transmission cannot

be decrypted. Due to the variety, sophistication, and mathematical

complexity of encryption methods, it is often best to utilize encoder and

decoder chips, such as those offered by Linx for on-off applications.

For data applications, a method suitable to the processing resources

should be chosen.

Creating a serial link to the modules

There are several ways to create a serial link to Linx RF modules.

The modules themselves do not require any programming or data

manipulation, but instead act like a virtual wire and will simply send

along whatever is presented to them. This means that the data source

will do all of the protocol generation, setting the baud rate, etc. Typically

the data source will be one of two things: a PC or a microcontroller.

Interfacing to a PC will happen one of two ways: through an RS232

serial port or through a USB cable. The RS232 specifi cation uses large

positive and negative voltage swings to send data over long distances.

These voltage levels can damage the RF modules, so a level converter,

such as a Maxim MAX232, must be used to reduce the voltages to

levels appropriate for digital logic (see Figure 4). Level converters

are common in the industry and are made by manufacturers such as

Maxim, National Semiconductor, and Sipex.

4.7 uF

4.7 uF

4.7 uF +

+

+

VCC

4.7 uF

+

4.7 uF

4.7 uF

VCC

4.7 uF

+

+

+

4.7 uF

+

MAX232

1 C1+ VCC 16

23 V+ GND 15

C1-

4

T1OUT

C2+ R1IN 13

14

567

C2- R1OUT

12

V- T1IN 10

11

8 T2OUT T2IN 9

R2IN R2OUT

VCC

RXM-916-ES

1

2 ANT NC

345 GND NC

NC PDN

GND RSSI

6

VCC DATA 12

13

14

15

16

NC AUDIO 11

7 NC AREF 10

8 NC NC 9

1

2

3

4

5

6

7

8

MAX232

C1+

V+

C1-

C2+

C2-

V-

T2OUT

R2IN

VCC

GND

T1OUT

R1IN

R1OUT

T1IN

T2IN

R2OUT

Figure 4: ES Series RF modules and MAX232.

Transmitter

TXM-916-ES

1 PDN ANT

10

VCC 2 LVL ADJ GND

VCC 3 VCC LOW V DET

89

4 GND /CLK SEL 7

+ 5 DATA /CLK 6

4.7 uF

Receiver

16

15

13

14

12

10

11

9

VCC

+

4.7 uF

1 62738

4 95

1 62738

4 95

Article Resources

Product Information

• ES Series Transmitter

Data Guide

• ES Series Master Dev

User Guide

• ES Series Receiver

Data Guide

• ES Series Master

Development System

User’s Guide

Related Products

• TXM-916-ES_

• RXM-916-ES_

• MDEV-916-ES-USB

• MDEV-916-ES-RS232

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Since most new computers, especially laptops, do not have serial ports,

Linx has developed a USB module. This module can interface to a PC

via a USB cable and the RF module via a PCB trace (see Figure 5).

Transmitter

TXM-916-ES

1

VCC

PDN ANT

10

2 LVL ADJ GND

3 VCC LOW V DET

89

4 GND /CLK SEL 7

5 DATA /CLK 6

USB Type B

Connector

GND 4 SDM-USB-QS-S

DAT+

USBDP

RI

DAT -

5 V 1 23 1 16

23456

USBDM DCD

15

GND

DSR

14

VCC DATA_IN 13

VCC 220 SUSP_IND DATA_OUT 12

RX_IND RTS

7 TX_IND CTS 10

11

8 485_TX DTR 9

Receiver

1 RXM-916-ES

2 ANT NC

345 GND NC

NC PDN

VCC GND RSSI

6

VCC DATA 12

13

14

15

16

NC AUDIO 11

7 NC AREF

8 NC NC 10

9

USB Type B

Connector

GND

SDM-USB-QS-S

DAT+ 1

16

USBDP

RI

DAT -

5 V 1234 2

USBDM DCD

15

3456

GND

DSR

14

VCC DATA_IN 13

SUSP_IND DATA_OUT 12

VCC RX_IND RTS

7 TX_IND CTS 10

11

220

8 485_TX DTR 9

Figure 5: ES Series RF modules and QS Series USB module.

In either case, application software running on the transmitter PC will

generate the packet according to whatever protocol is used and send

the data to the transmitter. The receiving PC will receive the data and

decode it according to the same protocol.

Using a microcontroller provides some challenges but offers a great

deal of fl exibility. The microcontroller will create the packet and then

send the data to the RF module, which will receive it and decode it.

Microcontrollers with a built-in UART can send data to the RF module

via a Print statement (or similar depending on the programming

language used) and can receive from it via a Get statement; the UART

will perform all of the necessary functions. The actual operation may

vary based on the type of microcontroller used.

Controllers without a UART can do what is called “bit banging” to an

output line. This occurs when an output line is toggled for a specifi c

time to send a bit at a specifi c baud rate. For example, to send a 1 at

2400 bps, the microcontroller will pull the line high, wait 417 µS,

and pull the line low. This would be done for each bit in the packet.

The wait time can change to vary the baud rate.

One thing that the RF modules cannot do is transmit actual voltage

levels since there is no physical connection to a common reference

point. Sending sensor telemetry, for instance, would be a reason to

transmit voltage levels. Sensors often represent pressure, temperature,

fl ow, acceleration, etc., as a voltage level. Since the modules will not

be able pass this voltage, it must be represented by either a frequency

(analog) or a number (digital).

A voltage-to-frequency converter may be used to send the level

information in an analog form, or a microcontroller with an

analog-to-digital converter (ADC) can be used to convert the level to a

digital number. A microcontroller is most commonly used since it can

be more accurate, and many products need to have some intelligence

onboard anyway.

The ADC will convert the analog voltage level to a digital number which

can then be packetized and sent to the RF module. Another advantage

to using an MCU is that it can convert the ADC number into a number

that represents what is being measured. Since the sensor, voltage,

and ADC values are all typically related linearly, the processor can use

linear interpolation to come up with the temperature or pressure that

was measured rather than just sending the ADC value. The receiving

controller would then be able to display the actual measurement,

which would be easier to understand than the ADC value.

Article Resources

Product Information

• ES Series Transmitter

Data Guide

• ES Series Master Dev

User Guide

• ES Series Receiver

Data Guide

• ES Series Master

Development System

User’s Guide

Related Products

• TXM-916-ES_

• RXM-916-ES_

• MDEV-916-ES-USB

• MDEV-916-ES-RS232

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Putting it all together

The designer has a great deal of freedom when creating a protocol,

so it can be tailored to meet the requirements and resources of a

given application. There is no magic sequence that will work for

all applications since each project will have different baud rates,

processing speeds, and available overhead. It is up to the designer to

decide what will work best for the project and write it into software.

While there are many other methods of encoding and decoding

transmissions, those covered here are some of the most common and

should give the designer a good starting point for the development of

the designer’s own protocol.

RF Coaxial Board-to-Board Connectors

TE Connectivity’s compression

coaxial board-to-board RF

connector product line meets

the space and cost effi ciency

necessities of a growing range of

applications. Before compression

coaxial technology, board-to-board

RF connections were achieved

by incorporating either two cable

connectors or two connectors and

a third bullet spacer.

TE Connectivity’s board-to-board,

low profi le coaxial connector

consists of a single-piece,

blind-mating connector with a

spring-loaded contact to achieve

simplicity in Printed Circuit Board

(PCB) organization and to lower

applied product costs.

Article Resources

Product Information

• ES Series Transmitter

Data Guide

• ES Series Master Dev

User Guide

• ES Series Receiver

Data Guide

• ES Series Master

Development System

User’s Guide

Related Products

• TXM-916-ES_

• RXM-916-ES_

• MDEV-916-ES-USB

• MDEV-916-ES-RS232

Features

• Available in four sizes for varied

board spacing: 14 mm, 10 mm,

6.65 mm and 4 mm

• Large radial and axial

misalignment; for positioning both

boards and for gap between boards

• Gold plated phosphor bronze

and brass contacts, stainless

steel springs

• Easy connection and no

mechanical stress when mating

or un-mating, without the risk

of breaking either soldering

or connector

Applications

• Modular parallel board-to-board

blind mate applications

• Base station / sub station systems

• PDA / PCS / cellular handset

applications

Wireless communications systems

(GSM, PCS, WCDMA, UMTS)

BUY NOW!

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Right-Sizing Your Wireless

Design for Power and Cost

Wireless solutions are popping up everywhere,

but in the case of portable consumer devices in

particular, power consumption and cost represent

some serious constraints.

Designing with RF is no longer the mysterious and diffi cult challenge

it used to be. Advances in process technology, coupled with the

availability of system-on-chip (SoC) architectures, have brought the

price of RF down while signifi cantly simplifying design. As a result,

wireless technology is being integrated into nearly every type of

application, including healthcare equipment, lighting control, security,

energy management, gaming, and many other embedded and

industrial applications.

Often, the application defi nes the topology, protocol, and RF

technology that will be required. For example, a wireless heart

monitor would likely use a point-to-point topology. If the monitor

needs to speak to a conventional network, ZigBee ® may be the best

protocol to use. However, if the monitor is paired to a specifi c piece

of exercise equipment, a proprietary protocol utilizing a sub-GHz

radio may be appropriate and more cost-effective. In many cases,

the primary design challenge remaining is selecting the

implementation that provides the performance required while

minimizing cost and power use.

by Nicholas Cravotta

The system-on-chip approach

Today’s SoC architectures are able to combine an RF radio with an

MCU with suffi cient processing capacity to handle the appropriate

protocol stack and still have enough headroom to run an application

(see Figure 1). Texas Instruments (TI), for example, offers SoCs which

support nearly every wireless technology available, including:

CC2530: ZigBee plus 8051 MCU

CC2560: Bluetooth ® plus MSP430 controller

CC2540: Bluetooth Low Energy plus 8051 MCU

CC430: Sub-GHz radio plus MSP430 controller

Clocks, Power

Management

Unified Clock

System

Supply

Supervisors

Brownout

CPU/Memory

Flash RAM

RISC CPU DMA

16-Bit Controller

Enhanced System

Eumulation Control/

Module Watchdog

JTAG

Spy-Bi-Wire

Interface

RF

Transceiver

Packet

Handler

Digital

RSSI

Carriet

Sense

PQI/LQI

CCA

Sub-1 GHZ

Radio

CPU

Interface

Modem

Timing &

Control

General-

Purpose

Timers

Capture/

Compare

PWM

Ouputs

Basic

Timer +

RTC

Operational

Amplifers

Communication

Universal

Serial

Communication

Interfaces

SPI, USART

I2C USB

2.0 (Full

Speed)

Display

General-

Purpose

I/O

Pull-Up,

Pull-

Down,

Drive

Frequency

Synthesizer

RF/Analog

TX & RX

Figure 1: The TI CC430 combines an RF radio with an MCU. (Source: Texas Instruments. Used

with permission.)

ADC

DAC

High-

Performance

Analog

AES

I/O &

Segment

LCD

Static,

Muxed

Article Resources

PTM and Another Geek Moment

• STMicroelectronics -

M24LR64 Dual Interface

EEPROM

Related Products

• CC2530F128RHAT

• CC2530EMK

• CC2530DK

• EZ430-RF2560

• CC2540F128RHAR

• CC2540F256RHAR

• CC2540DK-MINI

• CC430F6137IRGCR

• EZ430-CHRONOS-915

• MRF24J40MA-I/RM-ND

• MRF24WB0MB/RM

• AC164136-4

• M24LR64-RMN6T/2

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With an SoC, an entire RF application can be implemented with a single

processor. To accommodate the different requirements of each protocol

and application, each SoC family offers products with varying degrees

of integration so that developers can select a device optimized for

their particular system. With several choices of processor speed and

memory depth, developers have the option of supporting advanced

features such as security or hub/mesh capabilities. Many devices

offer optional analog peripherals, enabling the SoC to integrate sensor

functionality to handle low frequency tasks such as monitoring a

system’s temperature, up to high frequency sensing such as is required

to manage a capacitive touch screen. A variety of interfaces may also

be available, including USB, so that these SoCs can communicate with

other system components. Some devices even integrate an LCD driver

to enable single-chip design of portable devices such as glucometers.

Many SoCs have features which allow developers to add advanced

features and, as a consequence, signifi cant value to devices.

In addition, these SoCs have already been optimized for performance

and power effi ciency. Designing around an SoC architecture

simplifi es RF design to the point of enabling engineers with little to

no RF experience to introduce wireless capabilities into a system.

It provides a production-ready subsystem that signifi cantly reduces

time-to-market. In many cases, especially when a company does not

have RF expertise in-house, an SoC can come at a lower total cost of

ownership when factors such as hardware and software development

costs, along with time-to-market delays, are already addressed.

TI also provides a variety of resources to accelerate RF design.

Its SmartRF ® Studio, for example, enables developers to easily

change radio settings such as sensitivity and output power to

facilitate system optimization (see Figure 2). With a wide range of

application-specifi c development kits – including the RF2560 EZ

430 Bluetooth EVM and Chronos wireless development kit with a

wristwatch form factor [1] – developers can assess different wireless

technologies in less than a few hours. In addition, pads or pins on the

EVMs allow for real-time power measurements to enable accurate

profi ling of power consumption.

Figure 2: SmartRF Studio from TI. (Source: Texas Instruments. Used with permission.)

TI also offers radio-only transceivers which connect to an external

processor via a standard embedded interface. If a system is extremely

simple and does not require an LCD or ADC, a transceiver interfaced to

a small MCU will be the most cost-effective approach. However, many

of today’s embedded and medical applications require a high level of

intelligence, and this approach would require developers to perform

much of the heavy lifting behind RF design.

STMicroelectronics’ approach to wireless is its STM32W SoC

processor which integrates an IEEE 802.15.4 WPAN-based

2.4 GHz radio with a Cortex-M3 processor. Also a single-chip

implementation, the STM32W offers 128 K of code space, providing

ample room for a ZigBee protocol stack and full application.

The STM32W offers several low-power modes (see Table 1) and

integrates a variety of features that together increase the power

effi ciency of wireless applications:

Built-In Voltage Regulator: This allows the STM32W to run off of a

single lithium coin cell battery.

Dynamic Voltage Regulation: The system can be disconnected from

power, leaving only the clock functioning with wake-up capabilities

Programmable Frequency: The STM32W can be clocked slower to

conserve power.

Full Peripheral Control: Each peripheral can be turned off when it

is not being used.

Article Resources

PTM and Another Geek Moment

• STMicroelectronics -

M24LR64 Dual Interface

EEPROM

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• CC430F6137IRGCR

• EZ430-CHRONOS-915

• MRF24J40MA-I/RM-ND

• MRF24WB0MB/RM

• AC164136-4

• M24LR64-RMN6T/2

Online Resources

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RAM Retention: When a processor goes to deep sleep, RAM must

fi rst be saved in non-volatile memory. This can create issues, such

as startup latency as a system reloads the LCD display memory or

needs to read a sensor. The STM32W offers a low-power mode that

retains RAM, enabling fast wake-up responsiveness.

Table 1: The STM32W low-power modes. (Source: STMicroelectronics. Used with permission.)

Mode Regulators Lowfrequency

10 kHz RC

oscillator

Deep

sleep 2

Deep

sleep 1

32 kHz

cyrstal

oscillator

Highfrequency

12 MHz RC

oscillator

24 MHz

cyrstal

oscillator

off off off off off 0.4 µA

power

consumption

off on optional off off 0.7 µA

Standby on on optional off off 2 mA

Active at on on optional off on 6 mA

12 MHz

Active Mode Sensitivity Rx current Tx current Tx current

dBm mA mA at 0 mA at -32 d Bm

Radio Peripheral

dBm

-100 20 24 15

Table 2: Microchip RF modules. (Source: Microchip Technology. Used with permission.)

IEEE 802.15.4 Transceivers/Modules

Device Pin count Frequency

Range

Sensitivity

Power

output

Taking a modular approach

Offering an even higher level of integration are RF modules. Microchip’s

approach to RF, for example, is to offer PCB-based modules supporting

different RF technologies ranging from 2.4 GHz to sub-GHz frequencies

that provide the entire RF subsystem except for the MCU (see Table 2).

The MCU implements the protocol stack – i.e., Wi-Fi ® , ZigBee,

Bluetooth, and Microchip’s proprietary MiWi – and connects to the

radio with SPI. Depending upon the technology, base modules cost

between $10 and $20 and have a small form factor of roughly 1” x 1”

(see Figure 3).

RSSI Tx power Rx power Clock Sleep MAC MAC

feature

Encryption Interface Packages

MRF24J40 40 2.405 - 2.48 -95 0 yes 23 19 yes yes yes CSMA-CA AES128 4-wire SPI 40-QFN

MRF24J40MA 12 2.405 - 2.48 -95 0 yes 23 19 yes yes yes CSMA-CA AES128 4-wire SPI 12/Module

MRF24J40MB 12 2.405 - 2.475 -102 20 yes 130 25 yes yes yes CSMA-CA AES128 4-wire SPI 12/Module

Sub-GHz Transceivers/Modules

Device Pin count Frequency Sensitivity Power RSSI TX power RX power Clock Sleep Interface Packages

output

MRF49XA 16 433/868/915 -110 7 yes 15 mA @ 0 dBm 11 10 MHz yes 4-wire SPI 16-TSSOP

MRF89XAM8A 12 868 -113 12.5 yes 25 mA @ 10 dBm 3 12.8 MHz yes 4-wire SPI 12/Module

IEEE 802.11 Module

Device Pin

count

Frequency

range

Sensitivity

Power

output

MRF24J40MA

2.4 GHz FCC-Certified Module

RSSI Tx power Rx power Clock Sleep MAC MAC

feature

IEEE 802.11

Embedded Wi-Fi ® Module

Figure 3: The MRF24J40MA RF module (a) is a 2.4 GHz module that has already been certifi ed by

the FCC while the MRF24WB0MB RF module (b) provides Wi-Fi connectivity. (Source: Microchip

Technology. Used with permission.)

Encryption Interface Packages

MRF24WB0MB 36 2.412 - 2.484 -91 10 yes 156 85 25 MHz 0.1 yes 802.11 WPA, WPA-2, WEP 4-wire SPI 36/Module

Article Resources

PTM and Another Geek Moment

• STMicroelectronics -

M24LR64 Dual Interface

EEPROM

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• CC430F6137IRGCR

• EZ430-CHRONOS-915

• MRF24J40MA-I/RM-ND

• MRF24WB0MB/RM

• AC164136-4

• M24LR64-RMN6T/2

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The advantage of this approach, compared to placing the MCU on

the module, is that developers can select any of Microchip’s 700+

PIC ® MCUs, giving full fl exibility in terms of performance, memory,

and peripheral options. Devices range from simple 8-bit MCUs to

32-bit MCUs which can run a wireless protocol stack, application, and

high-speed interface like USB. Advanced features, such as capacitive

sensing, can be added to existing designs by upgrading the MCU.

Since the protocol stacks are implemented in C, developers can

transparently migrate between MCU architectures without having to

rewrite applications. This allows the MCU to be the right size for each

application, as well as providing a platform upon which a full line

of products can be based using a single code base. Developers can

also easily change RF technologies, such as offering proprietary and

ZigBee-based devices, to address the requirements of specifi c markets

with minimal code changes.

For applications in which a proprietary protocol can be used to reduce

product cost, Microchip offers its MiWi protocol and development

tools. Because MiWi offers a common API, developers can switch

between wireless technologies without code modifi cation. In addition,

no product-level certifi cation is required. Several of the 2.4 GHz

and sub-GHz modules are footprint compatible to simplify hardware

migration as well.

Modules also accelerate initial product development. Rather than

working with an EVM and having to develop hardware in parallel

to software, developers are able to work with the fi nal production

hardware from the start, even if they have no RF experience. Modules

also serve well in applications where there is an ASIC or host

processor. Rather than burden the system with TCP/IP processing,

RF capabilities can be easily added by using the interface the PIC plus

RF module to the ASIC/host via a UART or SPI channel.

In terms of system cost and power, the more design a manufacturer

takes on internally, the more effi cient the RF system can be because

each component can be optimized to the application. SoCs do add

some ineffi ciency due to the fact that RF and analog circuitry are

implemented more effi ciently in different process technologies.

Specifi cally, when an MCU is implemented on the same die as an RF

subsystem, this increases the cost of the MCU. Designing with an SoC,

however, eliminates many RF design concerns that would challenge

engineers and delay a product’s launch.

The same logic applies to going with an RF module. Modules reduce

RF design headaches down to a matter of connecting an MCU to a

standard interface port. The cost is a little higher than it would be for a

design based on an SoC, but there is very little thinking required.

It is important to note that deciding whether to use a module, SoC,

or design your own RF subsystem is not as simple as it used to be.

A decade ago, the breakeven point for using a module was fi ve

thousand units/year or less. If your volumes were any higher, it made

sense to build your own. Today, however, advances in technology and

manufacturing effi ciencies have changed this number signifi cantly.

Microchip, for example, estimates that the make-your-own breakeven

point for its modules approaches one hundred thousand units. Again,

more than just the bill-of-materials cost of the module has to be taken

into account. The RF design of a module is fi eld-proven and all agency

certifi cations are complete (although individual product certifi cation,

such as is required for Wi-Fi, may still be necessary). For many

manufacturers, the ability to outsource this part of the production chain

reduces risk and investment.

Power optimization

The key to power effi ciency in RF systems is to limit, in this order,

scan time, transmit time, and receive time. Scan time refers to when

a device listens across the spectrum to discover if another device is

trying to communicate with it. As the device must listen over every

available channel, it consumes more power than when it is actually

communicating. With Wi-Fi, for instance, this difference needs to be

considered when evaluating whether to put the RF system into sleep

or hibernate mode between transmissions. Hibernate mode enables a

system to run at leakage current levels, but the device must reestablish

a link with the access point when it wakes, requiring extra time and

power compared to the fast wake up ability of sleep mode.

For all these modes, power effi ciency is a factor of time; the less time

the radio is active, the better.

Article Resources

PTM and Another Geek Moment

• STMicroelectronics -

M24LR64 Dual Interface

EEPROM

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• CC2530DK

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• CC2540DK-MINI

• CC430F6137IRGCR

• EZ430-CHRONOS-915

• MRF24J40MA-I/RM-ND

• MRF24WB0MB/RM

• AC164136-4

• M24LR64-RMN6T/2

Online Resources

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Collecting data and burst transmitting is preferred, as one long

transmission is better than many short ones. Also, the footprint and

effi ciency of the stack will come into play, since the faster the MCU

can turn on, stabilize, transmit, and go back to sleep, the more power

effi cient the system.

After minimizing radio time, wireless systems are designed to

maximize sleep time. This means that the MCU’s power consumption,

both in sleep and while active, can represent a signifi cant portion of

the total power consumption. The ability to right-size the processor to

match the radio and application, as well as have full control over which

peripherals are powered up, can be the difference between months

and years of operation for battery-operated devices like glucometers

and heart monitors.

Using a SoC approach also improves power effi ciency since data does

not need to be transmitted over an external interface between the

transceiver and processor. Rather, it can be sent straight to memory.

This reduces latency, which enables the system to go back to sleep

sooner, and further reduces power consumption.

The integrated aspect is also important for applications such as

medical equipment where reliability is important. RF can be challenging

to design, and integration reduces the number of components, as well

as points of failure.

Many RF systems need to wake for system events such as a key press.

Ideally, the system is set to wake on an interrupt that is triggered when

a GPIO pin is turned on. The number of pins dedicated to this task can

be reduced to one by multiplexing several GPIO into one signal. This

is a power-effi cient approach to monitoring a capacitive sensor touch

screen, for example.

RFID: An attractive alternative

One of the keys to reducing power consumption is to eliminate or

power down circuitry a system is not currently using. Given that the

wireless transceiver is one of the major power consumers in a system,

signifi cant improvements in battery operating life can be achieved by

limiting transmit and receive time. However, even more substantial

gains can be achieved by eliminating the wireless transceiver

altogether using RFID technology.

For many medical and embedded applications, the value a wireless

interface brings to the system is the ability to transmit data to

a centralized location where it is processed and correlated with

data from other devices. This is especially true for sensor-based

applications. The transceiver enables the sensor node to receive a

request for data and then transmit the data. From a power standpoint,

such a system needs to continuously scan the spectrum for a request.

This, for many systems, is the activity that single-handedly consumes

the most power.

Dual Interface EEPROM

Two Worlds Connected

Figure 4: ST’s M24LR64 dual-interface EEPROM has an RFID interface on one side of the chip and

an I 2 C interface on the other. (Source: STMicroelectronics. Used with permission.)

RFID technology provides a mechanism for reducing power

consumption for the wireless link to zero by eliminating the transceiver

altogether. For example, the M24LR64 from ST is a dual-interface

EEPROM with an RFID interface on one side of the chip and an I 2 C

interface on the other (see Figure 4). The MCU controlling the sensor

node stores data in the dual-interface EEPROM. When a user wants to

collect and analyze the data, an RF reader powers the RFID interface

and reads off the data without requiring any power from the sensor

node’s battery. Because the device is an EEPROM, no power is required

to hold the data over long periods. The only time power required from

the battery is to write sensor data that has just been collected.

In fact, data can be read from a device even when it is turned off.

The M24LR64 has a 64-Kbit capacity, supports password security

(see Figure 5).

Article Resources

PTM and Another Geek Moment

• STMicroelectronics -

M24LR64 Dual Interface

EEPROM

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• CC2530DK

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• CC430F6137IRGCR

• EZ430-CHRONOS-915

• MRF24J40MA-I/RM-ND

• MRF24WB0MB/RM

• AC164136-4

• M24LR64-RMN6T/2

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I 2 C Interface

-industry standard

- 1.8 V to 5.5 V, 400 kHz

ISO 15693 RF Interface

-industry standard

-passive RFID technology

-high-speed mode

(up to 53 Kbit/s)

VCC

GND

SCL

SDA

E1

E0

AC1

AC0

PC

Protocol

RF

Protocol

Power

extraction

Power

management

and PC/RF

arbitration unit

EEPROM

Password

Protection

Scheme

I 2 C/RF

Arbitration

64-Kbit

EEPROM

Figure 5: The M24LR64 has a 64 Kbit capacity, supports password security. (Source: STMicroelectronics.

Used with permission.)

Consider a pedometer embedded in a shoe based on RFID technology.

The pedometer captures movement data and records it for later

collection. The complexity of this system lies not in the capture of

data, but in how the data is interpreted. When data interpretation is

implemented in the collector rather than the node, evolution of analysis

algorithms does not require any modifi cation of nodes; the actual

process of measuring impact in the shoe stays the same regardless

of how the data is used. Code upgrading is therefore unnecessary,

eliminating one of the key reasons for implementing receive

capabilities in a node. This results in lower node complexity and cost,

which is especially important for multi-node systems (e.g., a person

wears two shoes). In addition, because the cost per node is so low

compared to a wireless transceiver, both in terms of dollars and power,

more nodes can be introduced to a system to provide more accurate

and reliable coverage.

Since the RFID cannot receive transmissions, it needs to be able to

collect data in a way that always makes data available. The sensor

node, each shoe in this case, collects data and stores it in a circular

list that overwrites the oldest data entry. The use of timestamps

enables the data collection device to determine what data has been

added since the last the time the device was read. However, if the time

between data collections is too long, data may be lost. This may not

be an issue for systems in which data becomes too old to be useful

anyway. Alternatively, the sensor node can employ techniques that

compress data to enable longer periods of time between reads.

For example, rather than record the temperature every second

(60 samples per minute), only the highest and lowest temperature

during the past minute are stored (2 samples per minute), resulting in

a reading frequency 30 times longer.

With RFID technology, a device does not need to scan, transmit,

or receive, thereby eliminating the major power factors of an RF

subsystem. As RF is a primary source of battery drain, this approach

can extend the operating life of a battery-based system signifi cantly.

Finally, RFID technology deployment in the past was limited by the

ability of applications to absorb the high cost of an RFID reader.

However, as reader technology continues to enter mainstream

applications – for example, the new Google Nexus S cell phone has an

embedded RFID reader – the volumes are increasing and leading to

lower cost.

With the availability of modules and SoCs, RF has become a component

like any other that can be added to a system. The actual RF signal

chain can be transparent to developers, making the most diffi cult

design decision how to size the power consumption and data rate of

the RF subsystem to the actual use cases of an application. Introducing

RF to a system is not yet quite as simple as adding an antenna and

reading data off a SPI port. Developers still need to understand the

limitations of the particular implementation they choose. They also

have to know enough about how to implement the RF link to manage

power consumption. However, with the tremendous number of SoC and

modular choices, as well as the availability of alternative technologies

like RFID, RF capabilities can be added in a cost-effective manner to

nearly every type of system.

References

1. “Introducing MEMS to Personal and Consumer Electronics”, TechZone Magazine,

May 6, 2011, Page 26.

Article Resources

PTM and Another Geek Moment

• STMicroelectronics -

M24LR64 Dual Interface

EEPROM

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• CC2530DK

• EZ430-RF2560

• CC2540F128RHAR

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• CC2540DK-MINI

• CC430F6137IRGCR

• EZ430-CHRONOS-915

• MRF24J40MA-I/RM-ND

• MRF24WB0MB/RM

• AC164136-4

• M24LR64-RMN6T/2

Online Resources

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8-bit Wireless Development Kit –

2.4 GHz MRF24J40

SUPPORT FOR

ENGINEERS

8-bit Wireless Development Kit – 2.4 GHz MRF24J40 is an easy-to-use

evaluation and development platform for IEEE 802.15.4 application

designers. This kit includes Microchip’s MRF24J40 transceiver module

and also features Microchip’s PIC18 eXtreme Low Power (XLP)

microcontroller family and is pre-programmed with MiWi protocol stack.

Key Features

• MiWi stack support – MiWi, MiWi P2P and MiWI Pro

• PIC18F46J50 MCU featuring XLP Technology for extreme low power

• MRF24J40MA FCC/IC/ETSI certifi ed module with 25AA02E48 EUI Node

Identity serial EEPROM on PICtail daughter board

• MCP9700A Temperature sensor

• LCD display to develop interactive wireless demos (removable for

lower power)

• Board can be powered by either AA batteries, 9 V power supply, external

power supply, or USB

• RS-232 Serial Accessory board – for debug purposes

• Support other radios – both in 2.4 GHz and Sub-GHz frequencies through

PICtail connector

Design Support Services Team

• Provides in-depth application assistance

and advice on system design

• Assists with product selection

and development tools

• Produces application notes,

webinars, and instructional videos

• DSS website: www.digikey.com/design

• Contact: design@digikey.com

Technical Support Team

• Available 24/7 via telephone, email,

and live web chat

• Provides customers with productspecific

information, cross-reference,

and component recommendations

• Contact: techs@digikey.com

BUY NOW!

www.digikey.com

66

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Innovations in Connectivity:

The Digi-Key Weather

Center Smart Charger

by Brandon Tougas, Digi-Key Corporation

The Digi-Key Weather Center utilizes the best in electronic

components to test conditions in an environment where conditions

vary greatly. The diagram below depicts the process in which

Digi-Key’s Weather Center conveys the data collected to computers

and mobile devices.

Node

(Wired/Wireless)

Drivers

Gateway

(Cellular, WiFi,

Ethernet, Satellite)

Drivers

iDigi Server

Internet

(Cloud)

Digi-Key Server

Ethernet, WiFi,

Cellular

WiFi, Cellular

Computer

HTML,

Gadgets, Widgets

Cell Phone

Android, iPhone,

Blackberry Apps

This article focuses on the Smart Charger technology used, engaging

alternative energies to allow power and data collection. Information

collected from and about the design of the Weather Center can be

found on eeWiki.net, sponsored by Digi-Key Corporation.

Designed to utilize alternative energy sources such as a solar panel or

a wind turbine to charge a sealed lead acid battery, the Smart Charger

is based around an Atmel MEGA1281 AVR. It is at the heart of the

Digi-Key Weather Center’s design to monitor and control the charging

circuits for the energy inputs. Figure 1a shows a block diagram of the

Smart Charger system and its functionality. Figure 1b is an image of

the Smart Charger prior to its installation in the Weather Center.

Article Resources

List of Products

• ATMEGA1281 (1)

• XBP24BZ7WIT-004 (1)

• BQ24450 (1)

• V7803-1000 (1)

• IPS7091 (14)

• ZXCT1010 (2)

• WSLG-.25CT-ND (3)

• LM4140 (1)

• EMHSR-0002C5 (5)

• A98333-ND (12)

Related Links

• www.eewiki.net

• connectivity.digikey.com

Online Resources

ZigBee

Remote Communication

VAC

Test and Monitor

AC-DC

VDC Charging

System

Test and

Monitor

MCU

Charging

System

13.5 v - 14.9 VDC

Test and Monitor

13.5 v - 14.9 VDC

12 VDC

Power Rail

12 VDC Sealed

Lead Acid

Battery

Additional Links

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Figure 1a: Block diagram of the Smart Charger system.

Figure 1b: The Smart Charger.

67

Wireless Solutions | TZ W 112.US


Smart Charger circuits

The two alternative energy sources are connected to two separate,

though similarly designed charging circuits. The charging circuits

are based on the Texas Instruments’ BQ24450, a linear-designed

regulator which monitors the battery voltage with a voltage divider

circuit. In conjunction with the charging IC, some additions to the

solar charging circuit (Figure 2) have been made, including the Zetex

ZXCT1010 to measure the current through a sense resistor, and a

series of resistors IPS7091 arranged in a voltage divider confi guration.

5 VCC OUT 4

These two modifi cations allow the controller to measure the input

DC

6 VCC

7 VCC

8 VCC

DG 3

IN 2

GND 1

S0

Rin

15K

4 Vsennce+

6 Vsennce-

voltage and current from the solar panels. Secondly, fi ve IPS6031

high side switches from International Rectifi er were added to allow

the controller to connect or disconnect various inputs in and out of

the circuit for a couple of different reasons. The fi rst reason is to

control the solar inputs individually in order to get maximum solar

power, and the second reason is to allow testing of each solar panel

individually for maximum life and performance. Lastly, fi ve Ultra

capacitors from NESSCAP were added to the input of the circuit

to allow intermittent solar inputs to have a minimal effect on the

charging of the battery.

Z XCT1010E5TA

Iout 3

GND 2

NC 1

Rout

1K

ADC0

Article Resources

List of Products

• ATMEGA1281 (1)

• XBP24BZ7WIT-004 (1)

• BQ24450 (1)

• V7803-1000 (1)

• IPS7091 (14)

• ZXCT1010 (2)

• WSLG-.25CT-ND (3)

• LM4140 (1)

• EMHSR-0002C5 (5)

• A98333-ND (12)

Related Links

• www.eewiki.net

• connectivity.digikey.com

IPS7091

5 VCC OUT 4

6 VCC DG 3

RSENSE

. 25 5W

IPS7091

5 VCC OUT 4

6 VCC DG 3

Risns

. 250 5W

BQ24450DWTR

TIP32C

Qex t

ICH G

1N4001

VBAT

DC

7 VCC

8 VCC

IN 2

GND 1

Rin

15K

S1

2. 5F 5v

150K

1. 00M

49. 9K

ADC1

7 VCC

8 VCC

IN 2

GND 1

Rin

15K

1 ISNS

2 ISNSM

3 ISNSP

4 IF B

DRVC 16

DRVE 15

COMP 14

VF B 13

475 RT

365

RP

Ccomp

. 1uF 50v

215K

RA

S3

5 IN

CE 12

17. 4K RB

DC

IPS7091

5 VCC OUT 4

6 VCC DG 3

7 VCC IN 2

8 VCC GND 1

Rin

15K

S2

2. 5F 5v

2. 5F 5v

2. 5F 5v

2. 5F 5v

150K

150K

150K

150K

VCC

VCC

VCC

IPS7091

GND

IN

DG

Rin

15K

S4

8

7

6

1

2

3

4 OUT VCC 5

RLOAD

50 10W

6 GND

7 PGOOD

8 BSTOP

PRE- CH G 11

STAT1 10

STAT2 9

590K

RD

46. 4K

RC

Online Resources

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Figure 2: Solar Charging circuit.

68

Wireless Solutions | TZ W 112.US


The wind turbine charging circuit (Figure 3) is designed around

the same BQ24450 with the same voltage and current monitoring

additions along with two switches to control an input load, but with

only one DC input from a 3-phase wind turbine which has already been

rectifi ed into DC.

Battery monitoring

Monitoring of the Smart Charger battery (Figure 4) is accomplished

with a simple voltage divider to monitor the voltage across the battery,

Z XCT1010E5TA

and a current sensor ZXCT1010E5TA from Zetex to monitor the charge

4 Vsennce+ Iout 3

ADC4

and discharge current of the battery.

Z XCT10E5TA

1 NC Vsennce- 6

2 GND

3 Iout Vsennce+ 4

1. 00M

49. 9K

6 Vsennce-

GND 2

NC 1

Rout

1K

VBAT

ADC2

Rout

1K

ADC3

RSENSE

. 25 5W

Load

Article Resources

List of Products

• ATMEGA1281 (1)

• XBP24BZ7WIT-004 (1)

• BQ24450 (1)

• V7803-1000 (1)

• IPS7091 (14)

• ZXCT1010 (2)

• WSLG-.25CT-ND (3)

• LM4140 (1)

• EMHSR-0002C5 (5)

• A98333-ND (12)

Figure 4: Battery monitoring system circuit.

Related Links

• www.eewiki.net

• connectivity.digikey.com

DC- WIND

RSENSE

. 25 5W

IPS7091

5 VCC OUT 4

6 VCC DG 3

Risns

. 250 5W

BQ24450DWTR

TIP32C

Qex t

ICH G

1N4001

VBAT

1. 00M

ADC5

49. 9K

7 VCC

8 VCC

IN 2

GND 1

Rin

15K

1

2

3

4

ISNS

ISNSM

ISNSP

IF B

DRVC 16

DRVE 15

COMP 14

VF B 13

475 RT

365

RP

Ccomp

. 1uF 50v

215K

RA

VCC

VCC

IPS7091

GND

IN

8

7

1

2

VCC

VCC

DG

OUT

Rin

15K

6

5

3

4

RLOAD

50 10W

S5

5

6

7

8

IN

GND

PGOOD

BSTOP

CE 12

PRE- CH G 11

STAT1 10

STAT2 9

590K

RD

17. 4K RB

46. 4K

RC

Online Resources

Additional Links

• Component Reference

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Figure 3: Wind turbine charging circuit.

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Smart Charger control

The microcontroller used in this design is the AVR ATMEGA1281

from Atmel. This microcontroller was selected for various reasons,

including personal familiarity with programming and debugging tools

which allowed for rapid development and testing of the program and

circuit. The numerous analog and digital I/Os (Figure 5) on the device

are integral in the monitoring and control of the entire board. The

multiple digital I/Os allow the controller to have full control over the

high-side switches used to control various parts of the circuit board,

and the analog I/Os allow the controller to monitor the voltage and

current of both the inputs and outputs. Along with monitor and control

capabilities, the controller has multiple communication ports which

allow other devices to be connected. In particular, the circuit board is

using the UART to communicate through an XBee module to a remote

Ethernet gateway, giving remote access to the board. The controller

has 128 KB of Flash memory for program code, which is more than

enough for this implementation and allows for future program updates

or additions.

ZigBee communication

The XBee module (Figure 6) from Digi International provides a wireless

connection to the Smart Charger, utilizing the ZigBee protocol over the

2.4 GHz frequency band. By using the XBee with the ZigBee protocol,

the Smart Charger functions like another node on the network. Using

the module in a data pass-through mode the controller does not have

to deal with the ZigBee protocol. This allows the controller to pass data

as it would through a wired RS232 communication network. Finally, the

ZigBee network is equipped with a ZigBee enabled Ethernet gateway

device. This device is able to communicate over the Internet via the

Ethernet port and relay any information through the ZigBee network,

making the Smart Charger accessible over the Internet for control and

monitoring.

Load control

Each load attached to the charger can be controlled individually by

the MCU using an IPS6031 high side driver (Figure 7) as a switch.

This gives the MCU fl exibility to monitor each load independently in

order to determine the impact each one has on the system or monitor

the entire load.

PDI

PDO

VCC3

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

PG5

64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49

PE0/RXD0/PDI

PE1/TXD0/PDO

PE2

PE3

PE4

PE5

PE6

PE7

PB0/SS

PB1/SCK

PB2/MOSI

PB3/MISO

PB4

PB5

PB6

AVCC

PB7

ADC0

GND

PG3

ADC1

AREF

PG4

ADC2

PF 0/ADC0

RESET

ADC3

AF 1/ADC1

VCC

ADC4

PF 2/ADC2

GND

ADC5

PF 3/ADC3

PF 4/ADC4/TCK

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

PF 5/ADC5/TMS

PF 6/ADC6/TDO

PF 7/ADC7/TDI

ATMEGA1281

XTAL2

SCL

ADC6

XTAL1

SDA

DOUT

Figure 5: Numerous analog and digital I/Os.

ADC7

PD0/SCL

DIN

PD1/SDA

PD2/RXD1

GND

PD3/TXD1

VCC

PD4

PA0/AD0

PD5

PA1/AD1

PD6

SLEEP

VCC

PA2/

AD2

PA3/AD3

PA4/AD4

PA5/AD5

PA6/AD6

PA7/AD7

PG2/ALE

PC7/A15

PC6/A14

PC5/A13

PC4/A12

PC3/A11

PC2/A10

PC1/A9

PC0/A8

PG1/RD

PG0/WR

PD7

SLEEP_RQ

SS0

SS1

48

47

46

45

44

43

42

41

40

39

38

37

36

35

34

33

XRESET

SS2

SS3

SS4

SS5

SS6

SS7

LS0

LS1

LS2

LS3

LS4

LS5

LS6

LS7

Article Resources

List of Products

• ATMEGA1281 (1)

• XBP24BZ7WIT-004 (1)

• BQ24450 (1)

• V7803-1000 (1)

• IPS7091 (14)

• ZXCT1010 (2)

• WSLG-.25CT-ND (3)

• LM4140 (1)

• EMHSR-0002C5 (5)

• A98333-ND (12)

Related Links

• www.eewiki.net

• connectivity.digikey.com

Online Resources

Additional Links

• Component Reference

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XRESET

VCC3

DOUT

DIN

SLEEP_RQ

Figure 6: The XBee module.

1

2

3

4

5

6

7

8

9

VCC

DOUT

DIN

DIO12

RESET

RSSI PWM

DIO11

NC

SLEEP_RQ

10 GND

Commisioning Button 20

AD1/DIO1 19

AD2/DIO2 18

AD3/DIO3 17

RTS 16

Associate 15

NC 14

SLEEP 13

CTS 12

DIO4 11

After installing the Smart Charger on the Digi-Key Weather Center

(Figure 8), the solar voltage, current input, current output, and load

voltage are measured and collected by the AVR, and then sent to a data

base via the XBee module and ZigBee network. The most recent data can

be viewed on connectivity.digikey.com. For schematics, source code,

and diagrams please visit www.eewiki.net/display/WeatherCenter.

RTS

SLEEP

CTS

Figure 8: The Smart Charger mounted in the control panel.

Article Resources

List of Products

• ATMEGA1281 (1)

• XBP24BZ7WIT-004 (1)

• BQ24450 (1)

• V7803-1000 (1)

• IPS7091 (14)

• ZXCT1010 (2)

• WSLG-.25CT-ND (3)

• LM4140 (1)

• EMHSR-0002C5 (5)

• A98333-ND (12)

Related Links

• www.eewiki.net

• connectivity.digikey.com

Figure 7: Individual control of IPS6031 high side driver.

Online Resources

Additional Links

• Component Reference

Guide

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How New Antenna-Matching Technology

Helps HF-RFID Designs Perform

Reliably in Difficult Environments

Electronics manufacturers everywhere constantly

strive to automate basic processes. RFID antenna

tuning is another manual process that should soon

become history.

One of the principal difficulties in the design of RF circuits is

maintaining a good match between the antenna and the transceiver.

Tuning a system in the laboratory might be convenient, but conditions

in the lab rarely reflect the conditions that the system will experience

in the real world. After installation, system performance can be

greatly impaired by environmental conditions, such as the proximity

of the design to metal or water.

High-Frequency RFID (HF-RFID) applications are vulnerable to this

effect. Unfortunately, conventional HF-RFID components provide

no means for the user to adjust the device to compensate for

environmental conditions. Trimming is a time-consuming,

manual, and expensive process carried out at the factory.

HF-RFID systems, which operate at 13.56 MHz, are governed by

globally accepted standards:

• ISO 14443 A/B (4,5) – Proximity or short range up to

approximately 75 mm.

• ISO 15693 (6,7) – Vicinity or mid-range up to approximately 1 m.

by Brian Zachrel, austriamicrosystems

• ISO 18092 (8) – Near Field Communications (NFC). Used for

communicating reader-to-reader or reader-to-NFC device.

Each standard defines the characteristics of the tag, including:

• Physical characteristics

• Radio frequency interface (ISO 14443)

• Initialization and anti-collision (ISO 14443)

• Air interface and initialization (ISO 15693)

• Transmission protocols (ISO 14443)

• Other protocols (ISO 15693)

• Registration of applications/users (ISO 15693)

It is possible to design a multi-standard reader to communicate

with any HF-RFID transponders (also known as tags). A reader will

be capable of reading and writing to the tag. In ISO 14443 and ISO

15693 systems, the tag will be powered by the energy of the RF field

broadcast by the reader (see Figure 1).

The variety of standards for HF-RFID has evolved in response to the

diversity of ways in which organizations wish to utilize it. For instance,

RFID can be used both in fixed and mobile applications. In fixed

installations, readers must be able to function in the presence of many

different materials.

Article Resources

Related Products

• AS3910-BQFT

Other Resources

• ISO/IEC 14443-1:2008

• ISO/IEC 14443-2:2010

• ISO/IEC 14443-3:2011

• ISO/IEC 14443-4:2008

• ISO/IEC 15693-1:2010

• ISO/IEC 15693-2:2006

• ISO/IEC 15693-3:2009

• ISO/IEC 18092:2004

Online Resources

Additional Links

• Component Reference

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T3

T2

T1

Energy from RF field

Commands

Responses

Responses

Reader

Commands

The purpose of the resistor is to determine the bandwidth, and “Q”,

of the tank circuit. “Q” merits careful attention. If the value selected

is too small, then the signal will suffer from excessive attenuation. If

the value is too large, then noise can be a problem. For ISO 14443 for

example, a Q of 13 is a good choice. This is because the bandwidth

required is 848 kHz (Fb). This is defined by the equation:

The actual calculation results a Q of 16. The extra margin is desirable

to minimize the attenuation of the signal.

The value of R can now be calculated. The desired value will be

determined by:

Article Resources

Related Products

• AS3910-BQFT

Other Resources

• ISO/IEC 14443-1:2008

• ISO/IEC 14443-2:2010

• ISO/IEC 14443-3:2011

• ISO/IEC 14443-4:2008

• ISO/IEC 15693-1:2010

• ISO/IEC 15693-2:2006

• ISO/IEC 15693-3:2009

• ISO/IEC 18092:2004

Figure 1: Simplified architecture of typical RFID application.

In access control systems, for instance, the reader is generally located

at a doorway. It could be adjacent to metal, glass, wood, or composites

and each of these has different RF characteristics. Clearly, the reader’s

RF circuit needs a way to compensate for the effect of these materials

to ensure proper performance in every location. The environment

might be different for handheld readers (as used in payment terminals,

livestock tracking systems, etc.), as they must cope, for instance, with

rain, humidity, and the proximity of human and animal bodies. However,

the requirement for antenna trimming is the same.

The basic building blocks of an RFID reader are the antenna,

the RF section, and the controller. Good system performance

requires a match between the RF section and the antenna.

Since HF-RFID systems use an RLC tank circuit (See Figure 2) for the

antenna system, antenna tuning is required.

The frequency of the tank circuit is defined by the equation:

))

Application

Since this is a parallel circuit, the effective resistances of the

inductor and capacitor must be taken into consideration, so R can be

calculated by:

Due to the tolerances of each of the components, the resonant

frequency has to be calibrated before the reader can be used.

This is normally done by adjusting a variable capacitor designed into

the circuit. This tuning process is time consuming. Manufacturing

engineers dislike manual processes, because they are costly and

vulnerable to human error. Further, the environment in the production

line is likely to be different from the environment in its final location,

so the system might need to be retuned after installation. This requires

more time and money before the system goes online. Lastly, adjustable

capacitors drift over time and can take the system off-frequency.

A reader IC that automates the antenna tuning process as part of

an easy-to-use, software-controlled system eliminates all of

these problems.

Online Resources

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• Component Reference

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A good example of an integrated solution for a reader with automatic

antenna management is the AS3910 HF-RFID reader IC from

austriamicrosystems. Its main advantage for the system designer is

that system tuning is performed digitally via a command sent from the

system controller. Not only does software control simplify tuning,

it also allows the user to easily retune the system to improve

performance in the field when needed.

Digital tuning is simple to implement. When the tuning sequence

begins, an initial measurement is taken with the tuning capacitors

disabled. If the system is not in resonance, then the capacitance is

increased. This process continues until antenna resonance is achieved.

In the AS3910, this process is implemented with just two commands,

Check Antenna Resonance and Calibrate Antenna Resonance,which

are hard-coded into the device. A phase detector is used to measure

the phase shift between the transmitter output signals and the

receiver input. When a phase shift of 90 degrees is achieved, the

system is properly matched. The low-impedance output driver can

be configured to direct-drive a single-ended or differential antenna

system (see Figure 2).

TRIM 1_0

TRIM 1_1

TRIM 1_2

TRIM 1_3

RF01

RF02

RFI1

RFI2

TRIM 2_3

TRIM 2_2

TRIM 2_1

TRIM 2_0

Antenna

TRIM 1_0

TRIM 1_1

TRIM 1_2

TRIM 1_3

RF01

RF02

RFI1

RFI2

TRIM 2_3

TRIM 2_2

TRIM 2_1

TRIM 2_0

Figure 2: AS3910 can be configured to drive a single-ended or differential antenna.

1/2 Antenna

1/2 Antenna

The Calibrate Antenna Resonance command lets the user optimize

antenna performance in a way that both simplifies the manufacturing

process and allows some compensation for detuning in the field.

When the command is first executed (with the trim capacitors disabled)

the measured frequency will be higher than 13.56 MHz. Next,

the device switches in Trim1_0 and measures the resonant frequency.

Each switch-and-test step takes approximately 10 µs. Next,

the AS3910 will switch in the trim capacitors until a resonant frequency

of 13.56 MHz is achieved.

Ideally, this will be achieved with trim capacitors two and three

inserted. This allows for adjustment either higher or lower should the

antenna become detuned. The positions of the trim capacitors used

for resonance are stored in the antenna calibration register. If, after

switching in all the trim capacitors, resonance cannot be achieved,

the antenna calibration register displays an error flag alerting the user

that a calibration error has occurred and that the system should be

checked.

Lowering cost and improving performance

Digital calibration of the RF circuit in HF-RFID readers has the virtue of

improving RF performance in environments that are hostile to RF, and at

the same time, lowering the manufacturing cost of the product. As the

AS3910 shows, it is possible to implement digital trimming with elegant

and simple software controls. Electronics manufacturers everywhere

constantly strive to automate basic processes. RFID antenna tuning, is

surely another manual process that should soon become history.

For more information about austriamicrosystems’ products for RFID

applications, including the AS3910 IC, visit

www.austriamicrosystems.com.

References

1. Applications for HFRFID – http://www.rfid.averydennison.com/products.php#1

2. Applications for HFRFID – http://en.wikipedia.org/wiki/Radio-frequency_identification

3. Applications for RFID – http://www.rfidjournal.com/article/articleview/4111

4. Standards – http://www.rfid-handbook.de/rfid/standardization. html#iso14443

5. Standards – http://en.wikipedia.org/wiki/Proximity_cards

6. Standards – http://en.wikipedia.org/wiki/ISO/IEC_15693

7. Standards – http://www.rfid-handbook.de/rfid/standardization. html#iso15693

8. Standards – http://www.rfid-handbook.de/rfid/standardization.html

Article Resources

Related Products

• AS3910-BQFT

Other Resources

• ISO/IEC 14443-1:2008

• ISO/IEC 14443-2:2010

• ISO/IEC 14443-3:2011

• ISO/IEC 14443-4:2008

• ISO/IEC 15693-1:2010

• ISO/IEC 15693-2:2006

• ISO/IEC 15693-3:2009

• ISO/IEC 18092:2004

Online Resources

Additional Links

• Component Reference

Guide

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Passive Mixers in

Downconverter Applications

by Tom Schiltz, Bill Beckwith, Xudong Wang, and Doug Stuetzle, Linear Technology

Article Resources

Product Information

• LT5557 Datasheet

• LTC5540 Datasheet

• LTC5542 Datasheet

• LT5527 Datasheet

While most downconverting mixer designs typically

use an active or current-commutating topology,

new passive mixer ICs can deliver markedly better

performance with comparable linearity.

The LTC554x family of passive downconverting mixers covers

frequencies from 600 MHz to 4 GHz and delivers high conversion gain

and low noise fi gure (NF) with high linearity. These mixers are targeted

at wireless infrastructure receivers which require a high gain mixer

to overcome the high insertion loss of today’s high-selectivity IF SAW

fi lters. While legacy passive mixers typically have 7 dB of conversion

loss, the new LTC554x mixers have integrated IF amplifi ers, as shown

in Figure 1, which produce 8 dB of overall conversion gain. This allows

an additional 15 dB of IF fi lter loss, while still enabling the receiver to

meet sensitivity and spurious-free dynamic range requirements.

V CCIF

3.3 V OR 5 V

RF 1920 MHz TO

1980 MHz

1 µF 22 pF

LNA

IMAGE BPF

2.2 pF

SHDN

(O V/3.3 V)

V CC

3.3 V

Figure 1: LTC554x passive mixer in a receiver application.

RF

SHDN

IF +

1 nF

150 nH 150 nH

IF

IF -

190 MHz SAW

1 nF

LTC5541

LO

IF AMP

190 MHz BPF

22 pF

LO2

22 pF

BIAS

V CC2

V CC1

V CC3

LOSEL

LO1

LO SELECT

(O V/3.3 V)

ADC

SYNTH 2

ALTERNATE LO FOR

FREQUENCY-HOPPING

SYNTH 1

LO

1760 MHz

Active versus passive mixers

Most integrated-circuit mixers are based on an active or currentcommutating

topology. Linear Technology has a wide portfolio of active

mixers, such as the LT5527 and LT5557, which are widely accepted due

to their ease of use and low power consumption. Nevertheless, their 2 dB

to 3 dB of conversion gain is not enough for some wireless infrastructure

designs. Furthermore, active mixers typically exhibit higher NF than

passive mixers with comparable linearity. LTC554x mixers employ a

passive mixer core to achieve the lowest NF with high linearity. Table 1

compares the performance of the LTC5541 passive mixer to the LT5557

active mixer. As shown in the table, the passive mixer has approximately

5 dB higher gain, 2 dB lower NF, and 1.7 dB higher IIP3. The LT5557,

however, has much lower DC power consumption.

Table 1: Active versus passive mixer comparison at 1.95 GHz.

PART

GAIN

(DB)

NF (DB) IIP3 (DBM) INPUT P1DB

(DBM)

LTC5541 (passive) 7.8 9.6 26.4 11.3 630

LT5557 (active) 2.9 11.7 24.7 8.8 270

DC POWER

(MW)

Large-signal noise figure

Another important mixer performance parameter is large-signal noise

fi gure. The NF of a mixer is the ratio of the input S/N to the output S/N,

as in an amplifi er. All mixers suffer from increased NF when driven with

high level RF signals. This phenomenon is also referred to as “noise

fi gure under blocking” in receiver applications, where the “blocking”

signal is a high-amplitude signal in an adjacent channel. The elevated

noise fi gure occurs because the mixer’s output noise fl oor is proportional

to the RF input amplitude multiplied by the LO path noise (A RF

• N LO

).

Related Products

• LT5557EUF#PBF

• LTC5540IUH#PBF

• LTC5542IUH#PBF

• LT5527EUF#PBF

Online Resources

Additional Links

• Component Reference

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There are many times when a receiver needs to detect a weak signal

in the presence of strong blocker. If the blocker causes the noise fl oor

to rise suffi ciently, then the desired weak signal could be lost in the

noise. Figure 2 shows NF versus RF input power for the LTC5540.

The NF approaches the small-signal value at low input levels, but as

the RF signal power is increased, the A RO

• N LO

contribution becomes

dominant, and the NF increases. With a high RF input level of +5 dBm,

and a nominal LO power of 0 dBm, the NF increases only 6 dB from the

small-signal value to 16.2 dB. It is also apparent from the graph that

the large-signal noise improves with higher LO power level, thus even

better performance can be realized if necessary.

24

22

20

18

16

14

12

10

PLO = -3 dBm

PLO = 0 dBm

PLO = +3 dBm

PLO = +6 dBm

8

-20 -15 -10 -5 0 5 10

RF BLOCKER POWER (dBm)

Figure 2: LTC5540 noise fi gure versus RF blocker level.

RF = 900 MHz

BLOCKER = 800 MHz

While elevation of the noise fi gure cannot be totally eliminated,

performance can be improved through careful design. All of the parts in

the LTC554x family exhibit excellent large-signal noise fi gure behavior,

as shown in Table 2.

Table 2: LTC554x large-signal noise fi gure with +5 dBm blocker.

Part

RF Frequency

(MHZ)

LO Injection

Small-Signal

NF (DB)

LTC5540 900 High-Side 9.9 16.2

LTC5541 1950 Low-Side 9.6 16.0

LTC5542 2400 Low-Side 9.9 17.3

LTC5543 2500 High-Side 10.2 17.5

Large-Signal NF

(DB)

Calculated performance comparison in a receiver chain

The benefi ts of these new passive mixers are demonstrated in the

following receiver chain analysis. A typical, single-conversion base

station receiver line-up is shown in Figure 3, and is used to compare

the overall system performance when the LT5557 active mixer is used

to the same receiver using the new LTC5541 passive mixer

(see Table 3). The LTC6400-26 IF amplifi er, with 26 dB of gain, is

used with the LT5557-based line-up, and LTC6400-20, with 20 dB of

gain, is used with the LTC5541-based line-up. This keeps the overall

receiver gain nearly the same for both cases. A high-selectivity SAW

fi lter is used at the mixer’s output in each case, as required by the

high-performance base station. As shown in Table 3, the receiver

line-up using the LTC5541 passive mixer has 0.76 dB lower NF and 1.6

dB higher IIP3. This results in higher signal-to-noise ratio (SNR) and

spurious-free dynamic range (SFDR) for the LTC5541-based receiver.

Antenna

LNA1

1950 MHz

Antenna

1950 MHz

G = 17.5 dB

NF = 0.6 dB

IIP3 = 15 dBm

LNA1

G = 17.5 dB

NF = 0.6 dB

IIP3 = 15 dBm

G = -2.1 dB

G = -2.1 dB

LNA2

G = 14.9 dB

NF = 2.7 dB

IIP3 = 33 dBm

LNA2

G = 14.9 dB

NF = 2.7 dB

IIP3 = 33 dBm

G = -2.1 dB

G = -2.1 dB

LT5557

IF SAW

LTC6400-26

ADC DRIVER

G = 2.9 dB

G = -20 dB

G = 26 dB

NF = 11.7 dB

NF = 6.6 dB

IIP3 = 24.7 dBm IIP3 = 22 dBm

LTC5541

IF SAW

LTC6400-26

ADC DRIVER

G = 7.8 dB

G = -20 dB

G = 20 dB

NF = 9.6 dB

NF = 6.5 dB

IIP3 = 26.4 dBm IIP3 = 22 dBm

190 MHz

190 MHz

Figure 3: Typical wireless base station receiver line-up comparison of an LT5557-based receiver

and an LTC5541-based receiver.

Article Resources

Product Information

• LT5557 Datasheet

• LTC5540 Datasheet

• LTC5542 Datasheet

• LT5527 Datasheet

Related Products

• LT5557EUF#PBF

• LTC5540IUH#PBF

• LTC5542IUH#PBF

• LT5527EUF#PBF

Online Resources

Additional Links

• Component Reference

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Table 3: Cascaded receiver performance summary.

LINE-UP GAIN (dB) NF (dB) IIP3 (dBm)

LT5557-Based 35.0 4.03 -1.6

LTC5541-Based 33.9 3.27 0.0

Measured performance comparison in a

transmitter DPD application

In its simplest form, a single-conversion digital receiver consists

of a downconverting mixer, a lowpass or bandpass fi lter, and an

analog-to-digital converter (ADC). This type of receiver can be used

as a digital pre-distortion (DPD) receiver in high linearity base station

transmitters. In this application, the most important performance

parameters are linearity, gain fl atness, wide IF bandwidth and,

of course, simplicity. Unlike the receiver application described earlier,

NF is not critical in DPD applications due to the high-amplitude signal

coupled from the transmitter output. The LTC554x mixers are ideal

candidates for use in DPD receiver applications due to their high linearity,

high conversion gain, and fl at IF output response versus frequency.

A prototype DPD receiver using the LTC5541 is shown in Figure 4. This

receiver was built and tested for a 1.95 GHz application with a wideband

IF of 185 MHz ± 60 MHz. For comparison, another receiver was built

using the LT5557 active mixer. The LT5557-based DPD receiver required

an external IF amplifi er preceding the bandpass fi lter to make up for

the 5dB lower gain of the active mixer. The primary advantage of the

LTC5541 is that it eliminates the need for this IF amplifi er. Furthermore,

as summarized in Table 4, the LTC5541-based DPD receiver delivered a

higher SNR, higher IIP3, and lower harmonic distortion.

Table 4: Prototype DPD receiver measured results (RF = 1950 MHz, IF = 185 MHz).

Mixer

0.5 DB if

BW

Input Level

at -1 DBFS

SNR at -1

DBFS

LTC5541 126 MHz -0.6 dBm 63.4 dB

(120 MHz)

LT5557 130 MHz -1.8 dBm 62.8 dB

(120 MHz)

HD2 at -7 DBFS IM3 at -7

DBFS

-54.5 dBc -64.8 dBc

@ 123 MHz

-78.2 dBc

@ 184 MHz

-69.5 dBc

@ 243 MHz

-52.4 dBc -58.0 dBc

@ 123 Mhz

-63.1 dBc

@ 184 MHz

-67.4 dBc

@ 243 MHz

Conclusion

The new LTC554x family of passive downconverting mixers delivers

the high performance needed for today’s wireless infrastructure

receivers. The mixers’ combination of high conversion gain, low NF,

excellent NF under blocking, and high linearity can improve overall

system SNR and SFDR. The excellent performance also contributes

to improved DPD receiver performance while the 600 MHz to 4 GHz

frequency coverage of the LTC554x family makes them useful in a

wide variety of receiver applications.

Article Resources

Product Information

• LT5557 Datasheet

• LTC5540 Datasheet

• LTC5542 Datasheet

• LT5527 Datasheet

Related Products

• LT5557EUF#PBF

• LTC5540IUH#PBF

• LTC5542IUH#PBF

• LT5527EUF#PBF

Online Resources

RF IN

1950 MHz ±60 MHz

LTC5541

LO IN

1765 MHz

Figure 4: Prototype DPD receiver block diagram.

L-C

BPF

LTC2242-12

12-BIT ADC

CLOCK

250 MHz

Additional Links

• Component Reference

Guide

Wireless Solutions,

March 2011

• TechZone Library

• TechXchange

• Future Editions

77

Wireless Solutions | TZ W 112.US


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