Robin McCarty - EEWeb

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Robin McCarty - EEWeb

EEWeb

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Robin McCarty

Senior R&D Engineer

EEWeb.com

Issue 27

January 3, 2012

Electrical Engineering Community


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technical documents

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TABLE OF CONTENTS

Robin McCarty 4

Senior R&D Engineer

Interview with Robin McCarty - Marlow Industries

Timing ICs Keep Beat with Needs

of Today’s Embedded Market

BY ELIE AYACHE WITH SILICON LABS

Innovations in timing technology that will help improve performance.

Millimeter Scale Energy Harvesting 16

Based Sensors

BY STEVE GRADY WITH CYMBET

How to create millimeter scale intelligent sensors using ambient energy harvesting to

power the device autonomously.

RTZ - Return to Zero Comic 21

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9

TABLE OF CONTENTS


INTERVIEW

Robin

McCarty

Senior R&D Engineer

How did you get into

electronics/engineering and

when did you start?

Looking back on my childhood, I

was very mechanically inclined. I

put together model cars, planes and

ships. I also took apart my sewing

machine and put it back together. I

always enjoyed math and science

and went straight into mechanical

engineering as an undergraduate.

Once I took thermodynamics, I was

hooked on heat and energy. I went

on to further develop these skills in

my master’s and Ph.D. programs. I

worked on the master’s as I worked

Robin McCarty - Member of Technical Staff, R&D Engineer at Marlow Industries

full-time for a laser level company.

After five years, I went back to

school full-time for the Ph.D.

Do you have any tricks up

your sleeve?

I love to model complex thermal and

energy systems using a combination

of analytical simplifications and

numerical methods—I usually

write my own programs to predict

the performance of these systems.

I also love developing new test

methods to acquire experimental

data to further understand these

systems. There is nothing better

than developing a brand new model

for a system, along with a new test

fixture and method, and seeing the

two results match.

What has been your favorite

project?

During the Ph.D. program, I

designed a test stand to measure

the efficiency of thermoelectric

generators (TEGs). It took a year

to design and improve, but then I

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FEATURED INTERVIEW


INTERVIEW

used it for years to take data. When

Marlow hired me, they asked me

to design a similar but enhanced

fixture. It was a great opportunity to

start fresh and incorporate all of the

new ideas I had.

What are you currently

working on?

We are targeting higher temperature

energy harvesting applications.

I think this is a niche for

thermoelectric generators (TEG)

where other energy harvesting

technology can’t compete. In order

to move our technology to higher

temperatures, we have to target

higher temperature materials, new

device structures and fabrication

methods, new test fixtures and new

models. My focus is on the next

generation TEG models and test

fixtures.

Can you tell us more about

Marlow Industries?

Marlow was founded in 1973.

The core business has been

thermoelectric coolers and

systems, but in recent years

thermoelectric power generation

has emerged. A thermoelectric

cooler (TEC) uses current input

and produces heat pumping while

a thermoelectric generator (TEG)

takes a temperature difference and

produces current. Marlow is the

premier supplier of TECs, TEGs

and systems. We are also among

the world leaders in developing TE

materials, technologies and new

products.

How did the idea of EverGen

come about?

Until a year ago, the existing

thermoelectric technology that

was used in energy harvesting

applications for low-power

wireless sensors used thinfilm

thermoelectric materials.

Because most energy harvesting

applications will use a passive

natural convection heat sink, a bulk

thermoelectric material and device

is a better thermal and mechanical

match for these bulky, high thermal

resistance heat sinks. Bottom line, I

knew our devices would outperform

the competition.

With the introduction of the low

voltage DC-DC converters, our

low electrical resistance, low cost,

and high volume thermoelectric

generators could be used for energy

harvesting.

Marlow will

continue to expand

our thermoelectric

technology into

new and emerging

markets for both

cooling and power

generation.

What are the goals of this

project?

Produce more power and start

working at lower temperature

differences than the competition.

Throughout the project, we

investigated what makes an optimal

thermoelectric energy harvesting

system. Depending on the DC-DC

converter technology used, the

optimal TEG design (based on

pure math and science) can be very

similar to Marlow’s high volume,

low cost thermoelectric coolers. It

was a natural extension to use these

types of TE devices for low cost,

optimal thermal energy harvesting

applications enabling Marlow to

provide a cost effective thermal

power source to replace batteries

for wireless sensors.

How is this energy source able

to power wireless sensors for

the lifetime of the harvester?

The EverGen series takes advantage

of small, naturally occurring

temperature differences that our

customers encounter every day and

converts it into small, sustaining

power sources. The unique quality

of our products is that it starts to

produce power with as little as a

2°C temperature difference, much

less than the current competition.

This opens up a wide variety of

applications such as providing

power for sensors and actuators

incorporated into smart buildings.

With a perpetual power source, our

customers do not need to worry

about replacing batteries or other

maintenance. The TEGs operating

in their typical temperature

ranges will be very reliable

and virtually maintenance-free.

Marlow leverages its long history

producing extremely high reliability

products for defense, space,

telecommunications, medical and

automotive applications.

What does the EverGen series

kit offer?

Each system integrates a Marlow

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FEATURED INTERVIEW


INTERVIEW

electrically-matched, thermallyoptimized

custom thermoelectric

generator and heat sink with

an ultra-low voltage DC-DC

step-up converter to provide

the customer with the tools and

flexibility necessary to evaluate

a wide range of test conditions.

Customers can choose one of four

regulated voltages depending

on their application needs. It also

has a 2.2V, 3mA LDO to power the

external microprocessor. The kits

have provisions for external energy

storage. It also has a PGOOD

logic out indicating output voltage

is within regulation. And finally,

it has built-in power and charge

management prioritizing power

to VOUT. When there is excess, it

directs it to VSTORE.

Can you tell us about the

different types of kit?

Each kit was designed to interface

with common heat sources and heat

sinks. One of the kits, EHA-PA1AN1-

R02-L1, is designed to harvest heat

from a hot solid surface such as

a compressor to monitor if it is

overheating. It dumps this heat to

cooler ambient air through a natural

convection heat sink. Two of our

kits, the EHA-L50AN1-R02-L1 and

EHA-L37AN1-R02-L1, harvest heat

from hot pipes to cooler ambient air.

An example of where these could be

used is in our factory where we have

warm waste fluid leaving our dicingsaw

during machining. One could

envision monitoring the temperature

or pressure of this fluid if it is critical

and wirelessly send this data. Our

final two kits, EHA-L50L50-R01-L1

and EHA-L37L37-R01-L1, harvest

heat between warm and cool

pipes. Because this is in essence

Figure 1: Liquid-to-Air Kit

Figure 2: Liquid-to-Liquid Kit

Figure 3: Solid-to-Air Kit

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FEATURED INTERVIEW


INTERVIEW

a water-to-water heat exchanger,

the thermal resistance is quite low

and we are able to pull much more

heat through the TEG, therefore

producing more power at lower

temperature differences. These

devices could be used wherever

the customer has a warm and cold

water pipe in near proximity to each

other, such as the water pipes going

to any commercial sink.

What are some benefits that

the customers will see using

this technology?

Customers will be able to produce

small amounts of maintenancefree

power wherever they have

small temperature differences.

By using EverGen products, our

customers will see more power at

smaller temperature differences,

opening up a variety of applications

previously not possible.

Where do you hope to see this

technology implemented?

Because our bulk thermoelectric

technology is so scalable, we can

scale up our liquid-to-air harvester

to address remote sensing

applications for applications such

as oil and gas monitoring that

require Watts of power generation,

multiple TEGs and heat sinks.

This technology can be used as

a stand-alone power source or

work with other energy harvesting

technologies.

What direction do you see

your business heading in the

next few years?

Marlow will continue to expand

our thermoelectric technology

into new and emerging markets

for both cooling and power

generation. For energy harvesting,

we will be targeting higher power

systems ranging from hundreds of

microwatts to multiple Watts and

pushing our technology to higher

operating temperatures.

What can we expect to see

from Marlow Industries in the

near future?

EverGen (liquid-to-air systems)

will be expanding to higher power

output (multiple Watts) and higher

temperature harvesting (up to

500°C) for process plants and oil

and gas sensing. These assemblies

will utilize very similar TEG and

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converter technology but will be

“super-sized” to include multiple

TEGs and larger natural convection

heat sink areas to accommodate

pipes up to 12 inches in diameter.

What challenges do you

foresee in our industry?

Most customers will need a

custom thermoelectric solution to

maximize the power or efficiency

of their systems. Thermoelectrics

require specialized expertise to

successfully incorporate them into

systems. Educating our customers

that these TEGs need to be

electrically and thermally optimized

for their systems is difficult. Most

electrica engineers understand

electrical matching but don’t

appreciate thermal design; and most

mechanical engineers understand

thermal design but might not

understand electrical matching.

How do we create standardized

solutions that engineers from

diverse backgrounds can easily

implement? ■

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FEATURED INTERVIEW


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Timing

ICs

Keep Beat with Needs of

Today’s Embedded Market

Elie Ayache

Timing Products

Timing devices represent

a substantial, steadily

growing multi billion-dollar

market that encompasses both

clock generator and buffer ICs, as

well as frequency control devices.

The large size of the timing market

is not surprising if you consider

that virtually all electronic devices

contain a timing IC. Given the

importance of timing products to the

electronics industry, it’s surprising

how slowly timing technology has

evolved in recent years. In fact,

over the past two decades, timing

device suppliers have delivered

clocking and frequency control

products with a surprisingly slow

rate of innovation. However, recent

trends in the embedded market

and the entry of new suppliers in

that segment are driving innovation

in timing technology that will

help designers improve system

performance, simplify their designs

and decrease their reliance on

timing devices with historically long

lead times.

A Snapshot of Timing

Devices in Embedded

Applications

Classic embedded designs

historically have focused on such

applications as network and storage

systems, industrial automation and

controls, point of sale (POS) systems,

test and measurement equipment,

home and building automation,

and medical systems. (See Figure

1 for an example of a clock IC

used in a storage application

with PCI-Express connectivity.)

Mainstream x86 PC chipsets,

or slightly modified versions of

these chipsets, are generally

used in embedded applications.

To meet the requirements of

embedded systems, x86 chipsets

have to achieve industrial grade

compliance, and they typically have

life spans of more than six years.

If legacy chipset architectures

required modifications to the main

system clock, the changes would be

infrequent and relatively minor, and

it often made sense to accommodate

these clock changes by adding

discrete components to the board.

To a great degree, this trend has

kept the timing requirements of

embedded systems very similar to

their mainstream PC predecessors.

Differences were mainly associated

with the longer production life

spans of certain products and their

conformity to industrial grades.

In short, embedded systems

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TECHNICAL ARTICLE

have not required frequent or

significant changes to timing device

architectures. (See Figure 1)

In the past seven or eight years,

however, the basic computation

architecture of CPUs, graphics/

VGA controllers, memory

controllers and I/O interfaces has

become overwhelmingly pervasive

in a multitude of emerging end

products that require an operating

system and only a limited number of

applications. This market dynamic

has broadened the embedded

market from being primarily

industrial to include a wider

range of consumer and enterprise

systems, as well as small-formfactor

processing modules. Timing

devices have evolved accordingly to

address the changing requirements

of today’s embedded systems.

A New Generation of

Timing Devices

To understand how timing

technology is evolving to meet the

needs of embedded applications, it

is helpful to understand three recent

trends in main system design.

• The first factor to consider

is the recent integration of

basic timing functions in

mainstream PC chipsets that

historically would have been

provided externally as part of

the total timing solution. The

embedded version of these

chipsets might require smaller

timing components, often in

the form of expansion buffers

or standalone complementary

clock generators.

• A second factor is the

introduction of new chipsets

133 MHz

100 MHz

96 MHz

Clock IC

33 MHz

48 MHz

Controller

SL28504-2

100 MHz

focused exclusively on

embedded applications and

relying primarily on external

main system clock generators.

These timing devices would

have the flexibility to address

a multitude of form factors

ranging from tiny processor

modules to large-scale main

boards.

• A third factor is the increased

dissemination of processing

architectures beyond x86 that

present somewhat different

system clocking requirements,

mainly in the consumer and

enterprise segments of the

embedded applications.

These market trends are impacting

clock IC suppliers that have

traditionally derived a major part

of their revenues from the PC

industry. Clock IC vendors that

have dominated the PC timing

device market are now finding

themselves facing rapidly declining

revenue in the PC clock market,

coupled with an under investment

in other key growth markets, such

as communications and consumer

electronics.

To satisfy the requirements of

today’s embedded systems, new

players in the timing industry have

introduced highly customizable

clock generator ICs that integrate

non-volatile technology. These

timing devices address a wide

range of customer requirements

by providing application-specific

clocking solutions customized

to meet the frequency, type of

output, jitter, phase, skew and

other interface requirements for a

particular application.

Perhaps the most significant

limitation of traditional

programmable clock solutions

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PCIe Mini

PCIe

Processor

PCIe

Hub

USB

PCI

Memory

(DDR II 667)

LVDS

6x USB

SATA

Figure 1: Storage Area Network System Using a Clock IC Optimized for Embedded

Applications.

TECHNICAL ARTICLE


TECHNICAL ARTICLE

is that they require I2C-based

firmware or BIOS development.

In many applications, an I2C

interface is either not available or

not desirable. New generations of

configurable timing devices are now

available to address the deficiencies

associated with traditional I2C

programmability solutions. These

new timing products can be

customized entirely at the factory or

by using Web-based utilities. This

customizable approach benefits

the system design by alleviating

the burden of using BIOS memory

space and allocation of scarce

firmware resources, as well as by

assisting in boot time reduction.

Once the device is customized,

I2C programming may still be used

for post-boot features such as hot

swapping where the clock would

need to be enabled on the fly at

detection of a hardware card plugin.

Another emerging trend in

timing device technology is to

provide flexibility in frequency

generation and tuning capabilities

of the clock signals. This latter

capability has recently become

important to developers due to

the increased dissemination of

differential signaling in embedded

applications. In addition, the

ability to provide features to help

embedded designers minimize

power consumption for mobile

applications and green initiatives

as well as conformity with

governmental regulations, such

as FCC regulations in the United

States, have become common

requirements.

And finally, timing devices are now

offered in a variety of package types

that were not available a decade

ago. These packages—some as

tiny as 1.2 mm x 1.4 mm—are

now available to address varying

requirements for small form factors

and manufacturability in today’s

embedded applications.

Using Clock ICs to

Combat EMI

Clock generator and buffer ICs are

now available with built-in features,

such as programmable edge

rates, programmable impedance,

programmable skew and spread

spectrum technology, that can be

used to combat electromagnetic

interference (EMI) in embedded

applications. These features can

also be used to reduce radio

frequency interference (RFI) in

applications where interference with

3G/4G radios must be optimized to

File Control Setup Measure Analyze Utilities Help

More

(2 of 2)

Clear

All

8.00 GSa/s

1

On

Measurements

Frequency (3•)

Rise time (3•)

Fall time (3•)

Duty cycle (3•)

Scales

current

33.192 MHz

1.736 ns

1.268 ns

48.7 %

improve device operation.

Slowing the edge rate, as shown

in Figure 2, is the quickest method

to reduce EMI. For many clock

vendors, edge rate control typically

applies to the entire bank, which

limits the ability to tune each signal

for its particular load. If one receiver

requires a fast edge rate, all other

receivers in the same output bank

will have that same fast edge rate,

resulting in higher EMI. Timing

devices with programmable edge

rate controls for each individual

output allow board designers to

customize each output to its own

load and trace length.

When multiple outputs of the same

frequency are switching at the

same point in time, the end result

is large EMI spurs at harmonics

of the clock frequency as well

H 5.00 ns/div 7.750 ns 0 T 800 mV

mean

33.271 MHz

2.390 ms

1.945 ns

48.4%

10:53 AM

EEWeb | Electrical Engineering Community Visit www.eeweb.com 11

On

3 500 mV/div 4 (3 & 4 Combined)

std dev

81.92034 kHz

1.417 ns

1.211 ns

1.03%

min

33.192 MHz

1.029 ns

720 ps

47.2%

Figure 2: Edge Rate Control Is an Effective Technique for Controlling EMI.

max

33.356 MHz

4.323 ns

3.458 ns

49.7%

T

3

TECHNICAL ARTICLE


TECHNICAL ARTICLE

• Products • Applications • Support • Buy or Sample

Silicon Labs > Products > Clocks & Oscillators > ClockBuilder

ClockBuilder Utility

Step 1: Specify Requirements > Step 2: Preview Configuration > Step 3: Initiate Request

Specify your custom clock by selecting parameters below. Need help? View the ClockBuilder video tutorial.

Input

Block Diagram

Input Type: Crystal + VCX

Crystal Frequency: 27 MHz

Internal Load

Capacitance (CL):

VCXO Pull Range:

Optional Control Pins

The Si5350 has programmable input pins that can be factorycustomized

to support any of the following functions.

You may choose up to 1 optional control pin functions:

Output Enable (OEB) Pins: 0

Modulation: Down Spread

Modulation Rate: 31.5 kHz

Powerdown (PDN) Pins: 0

Output Clocks

as increased noise at the power

supplies due to the combined

amount of switching current. By

programming each clock output

skew to be delayed relative to other

outputs, the spur energy is spread

out, which reduces peak EMI and

power supply switching noise.

Most of today’s embedded systems

implement differential clocking

approaches for higher bandwidth;

many board designers neglect the

effects that these signal formats

can have on EMI and system

performance. Mismatch in the

edge slew rate and skew between

true and complement signals will

Package: 10-MSOP

XA

XB

Vc

P0

Crystal VC

Oscillator

Control

Logic

PLL

VCXO

Output Frequency: 0.008 to 133 MHz

Any Si5350 output clock can be connected to either the crystal or the analog control voltage input.

Any OE pin can be mapped to control any output clock. Use the table below to assign OE control to specific

output clocks. The device pinout will be assigned based on the selected frequency configuration.

Enable

Channel

10 pf

+/- 120ppm

Spread Spectrum

Clocking (SSC): Disabled

Percentage: 1.0 (-0.1% to -2.5%)

Output

Frequency

(MHz) OE Control Pin Reference

Crystal VC

Crystal VC

Enable

SSC

Home | About Us | News | Investor Relations

Multi

Synth

0

Multi

Synth

1

Multi

Synth

2

Si5350B

Figure 3: Web-Based Utilities Enable Rapid Customization of Timing Devices.

create common mode energy

that radiates EMI, as well as an

unstable cross-point that causes

data loss. Because clock trees in

these systems commonly drive

multiple buses with differential

outputs, any differential clock

misalignments can generate a large

amount of common mode energy.

By using the I2C-programmable

or factory-configurable skew

and edge rate features, each I/O

can be individually tuned to the

PCB environment for cross-point

optimization and EMI reduction.

Programmable impedance

also allows board designers to

optimally match load impedance

without having to modify discrete

termination networks or PCB

trace design. Mismatched trace

impedance causes reflections

that generate clock overshoot and

undershoot, resulting in increased

EMI and glitches in the clock

circuitry of the receiving device.

Time for Mass

Customization

Frequency customization has

become a given, but what about

addressing other parameters

that developers care about when

designing their systems and

meeting their milestones, such as

signal optimization or end product

compliance with federal regulatory

requirements? It’s still hard to

convince system designers that

there is such a thing as “mass”

customization in timing, enabling the

best-fit timing solution regardless of

the application without months of

lead times or a lot of non-recurring

engineering (NRE) expenses.

Now that embedded designs have

expanded beyond classic industrial

systems and have migrated into

faster-paced consumer and

enterprise markets, there is a

greater sense of urgency to get

products to market quickly. Today’s

timing device suppliers must be

able to respond quickly to the

developer’s customization needs.

Until recently, custom configurations

were achieved through changes

in the IC design, layout, masks

and new wafer developments.

This customization process often

required lengthy lead times of three

to four months to deliver working

products to the customer.

EEWeb | Electrical Engineering Community Visit www.eeweb.com 12

CLK0

CLK1

CLK2

TECHNICAL ARTICLE


TECHNICAL ARTICLE

Factory and web-customization

of timing devices represents a

significant advantage by enabling

the embedded developer to avoid

having to develop BIOS subroutines

for the sole purpose of configuring

the clock. The developer gets an

added bonus of receiving clock

samples in a couple of weeks

instead of months—60 percent

faster than mask-customized clocks.

Perhaps the most significant benefit

to embedded developers provided

by web-customized, programmable

timing devices is that they are

no longer only available for the

highest volume applications. Using

web-based clock configuration

utilities such as Silicon Labs’

ClockBuilder (shown in Figure 3),

BeStar®

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Leisure

embedded designers can now

expect platform-specific timing

solutions with lead times as short as

two weeks regardless of the size of

their project. Now, anyone with an

Internet connection can configure

timing devices online and enjoy the

benefits of having fully customized,

application-specific clocks and

oscillators with lead times as short

as two weeks.

About the Author

Elie Ayache manages Silicon Labs’

high-volume clock IC business.

Offering more than 20 years of

experience in the timing industry,

Mr. Ayache joined Silicon Labs

in 2011 following the company’s

acquisition of SpectraLinear,

where he served as vice president

of marketing. Previously, he

was the marketing director of

the computation clock business

Unit at Cypress Semiconductor.

Before joining Cypress, he served

as director of marketing and

applications engineering at IMI

where he pioneered numerous

launches of innovative products.

Mr. Ayache also spent several years

in the area of mixed-signal ASIC

design where he patented the linear

frequency shift doze mode for green

applications as well as the powerup

bidirectional I/O, which are still

widely used in the industry today.

Mr. Ayache has a BSEE degree

from Santa Clara University. ■

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EEWeb | Electrical Engineering Community Visit www.eeweb.com 13

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TECHNICAL ARTICLE


Low-Noise 24-bit Delta Sigma ADC

ISL26132, ISL26134

The ISL26132 and ISL26134 are complete analog front ends

for high resolution measurement applications. These 24-bit

Delta-Sigma Analog-to-Digital Converters include a very

low-noise amplifier and are available as either two or four

differential multiplexer inputs. The devices offer the same

pinout as the ADS1232 and ADS1234 devices and are

functionally compatible with these devices. The ISL26132 and

ISL26134 offer improved noise performance at 10Sps and

80Sps conversion rates.

The on-chip low-noise programmable-gain amplifier provides

gains of 1x/2x/64x/128x. The 128x gain setting provides an

input range of ±9.766mVFS when using a 2.5V reference. The

high input impedance allows direct connection of sensors such

as load cell bridges to ensure the specified measurement

accuracy without additional circuitry. The inputs accept signals

100mV outside the supply rails when the device is set for unity

gain.

The Delta-Sigma ADC features a third order modulator

providing up to 21.6-bit noise-free performance.

The device can be operated from an external clock source,

crystal (4.9152MHz typical), or the on-chip oscillator.

The two channel ISL26132 is available in a 24 Ld TSSOP

package and the four channel ISL26134 is available in a 28 Ld

TSSOP package. Both are specified for operation over the

automotive temperature range (-40°C to +105°C).

ISL26134

Only

September 9, 2011

FN6954.1

AIN1+

AIN1-

AIN2+

AIN2-

AIN3+

AIN3-

AIN4+

AIN4-

INPUT

MULTIPLEXER

AVDD

A0 A1/TEMP AGND

PGA

1x/2x/64x/

128x

GAIN0 GAIN1

CAP

CAP

Features

• Up to 21.6 Noise-free bits.

• Low Noise Amplifier with Gains of 1x/2x/64x/128x

• RMS noise: 10.2nV @ 10Sps (PGA = 128x)

• Linearity Error: 0.0002% FS

• Simultaneous rejection of 50Hz and 60Hz (@ 10Sps)

• Two (ISL26132) or four (ISL26134) channel differential

input multiplexer

• On-chip temperature sensor (ISL26132)

• Automatic clock source detection

• Simple interface to read conversions

• +5V Analog, +5 to +2.7V Digital Supplies

• Pb-Free (RoHS Compliant)

• TSSOP packages: ISL26132, 24 pin; ISL26134, 28 pin

Applications

• Weigh Scales

• Temperature Monitors and Controls

• Industrial Process Control

• Pressure Sensors

DGND

VREF+

NOTE for A1/TEMP pin: Functions as A1 on ISL26134; Functions as TEMP on ISL26132

FIGURE 1. BLOCK DIAGRAM

INTERNAL

CLOCK

ADC

VREF-

Get the Datasheet and Order Samples

http://www.intersil.com

DVDD

EXTERNAL

OSCILLATOR

DGND

DGND

XTALIN/CLOCK

XTALOUT

SDO/RDY

SCLK

PWDN

SPEED

Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2011

All Rights Reserved. All other trademarks mentioned are the property of their respective owners.


Millimeter Scale

Energy

Harvesting

Based Sensors

Steve Grady

VP Marketing

This article introduces several new concepts for

creating millimeter scale intelligent sensors using

ambient energy harvesting to power the device

autonomously. Using the energy surrounding the sensor

can provide life-of-product powering. Energy harvesting

techniques are used in large scale applications like

solar panel installations and wind farms. But energy

harvesting can also be used in extremely small scale

devices as is demonstrated in this article. Light is

converted to electricity, stored in rechargeable solid

state batteries and delivered to the sensor system. There

are no traditional batteries to change out and devices

can be placed anywhere.

This article is based on the sensor presented in the 2011

ISSCC paper, A Cubic-Millimeter Energy-Autonomous

Wireless Intra-Ocular Pressure Monitor by authors

Gregory Chen, Hassan Ghaed, Razi-ul Haque, Michael

Wieckowski, Yejoong Kim, Gyouho Kim, David Fick,

Daeyeon Kim, Mingoo Seok, Kensall Wise, David Blaauw

and Dennis Sylvester from the University of Michigan,

Ann Arbor, MI.

Figure 1: Millimeter Scale Computer Wireless Sensor Photo.

The actual paper can be found here.

This University of Michigan ISSCC paper describes an

Intra-Ocular Pressure Monitor (IOPM) device that is

implanted in the eye of a glaucoma patient. The most

suitable implantation location is the anterior chamber

EEWeb | Electrical Engineering Community Visit www.eeweb.com 15


TECHNICAL ARTICLE

of the eye, which is surgically accessible and out of

the field of vision. The IOPM volume is limited to 1.5

cubic millimeters. This aggressive IOPM size constraint

creates major challenges for achieving high-resolution

capacitance measurements, wireless communication,

and multi-year device lifetime. Little energy can be stored

on the tiny IOPM system, calling for ultra-low power

operation and energy harvesting. The required millimeter

antennas or inductors result in lower received power and

higher transmission frequency, both increasing microsystem

power. The IOPM harvests solar energy that

enters the eye through the transparent cornea to achieve

energy autonomy. The IOPM contains an integrated solar

cell, EnerChip thin-film Li battery, MEMS capacitive

sensor, and integrated circuits vertically assembled in

a biocompatible glass housing as shown in Figure 1.

The circuits include a wireless transceiver, capacitance

to digital converter (CDC), DC-DC switched capacitor

network (SCN), microcontroller (μP), and memory

fabricated in 0.18μm CMOS.

Why Millimeter Scale?

As in the case of the Intra-Ocular Pressure Monitor, it

is often desirable to place microelectronic systems in

very small spaces. New advances in ultra-low power

Integrated Circuits, MEMS sensors and Solid State

Batteries are making these systems a reality. Miniature

wireless sensors, data loggers and computers can now

be embedded in hundreds of new applications and

millions of locations.

Ultra-Low Power Management is Key

The desired IOPM lifetime is years to converge on a

suitable glaucoma treatment. However, the anterior

chamber volume limits lifetime by constraining the size

and capacity of the micro-system’s power sources.

The IOPM uses a 1μAh EnerChip solid state battery

from Cymbet. The lifetime is 28 days with no energy

harvesting!

To extend lifetime, the IOPM harvests light energy

entering the eye with an integrated 0.07 square millimeter

solar cell that recharges the battery. Given the ultra-small

solar cell size, energy autonomy requires average power

consumption of less than 10nW. For the majority of its

lifetime, the IOPM is in a 3.65nW standby mode where

mixed-signal circuits are disabled, digital logic is powergated,

and 2.4fW/bitcell SRAM retains IOP instructions

and data. The average system power with pressure

measurements every 15 minutes and daily wireless

data transmissions is 5.3nW. When sunny, the solar cells

supply 80.6nW to the battery. The combination of energy

harvesting and low-power operation allows the IOPM

to achieve zero-net energy operation in low light. The

IOPM requires 10 hours of indoor lighting or 1.5 hours of

sunlight per day to achieve energy-autonomy.

EH Wireless Sensor Components

The Intra-Ocular Pressure Monitor is an example

of a wireless sensor that uses Energy Harvesting

techniques to power the device. With the availability

of low-cost integrated circuits to perform the sensing,

signal processing, communication and data collection

functions, coupled with the versatility that wireless

networks afford, we can move away from fixed, hardwired

network installations in both new construction

as well as retrofits of existing installations (such as the

eye!). The IOPM block diagram is shown in Figure 2.

The IOPM as shown in Figure 2 consists of five basic

elements:

1. A pressure sensor to detect and quantify the pressure

in that area of the eye.

2. A solar energy harvesting transducer that converts

ambient light to electricity.

3. An ultra-low power management device and Solid

State Battery to collect, store and deliver electrical

energy to the IOPM.

4. A microcontroller to receive the signal from the

sensor, convert data into a useful form for analysis,

and communicate with the radio link.

5. A specialized radio link at the sensor node to transmit

the information from the processor on a periodic

basis to a receiver held in front of the patient’s eye.

Building Millimeter Scale

EH-based Computers

The IOPM millimeter wireless sensor shown in the

Figure 1 photo is shown diagrammatically in Figure

3. The device is a 4-layer stack encapsulated in a biocompatible

glass enclosure. The first layer is the MEMS

pressure sensor, with a 1uAh rechargeable EnerChip

EEWeb | Electrical Engineering Community Visit www.eeweb.com 16

TECHNICAL ARTICLE


TECHNICAL ARTICLE

Light

solid state battery sitting on top. The processor with

memory, power management and sensor A/D converter

sits on the EnerChip. The top layer is the solar cell and

wireless transceiver. All the layers in this case were wire

bonded together for electrical connectivity.

Permanent Power Using Solid

State Rechargeable Batteries

EH Transducer

Photovoltaic

Using incident

light hitting

the eye

Energy Processor

Power Conversion

Energy Storage

Power Management

Figure 2: IOPM Wireless Sensor Block Diagram.

One drawback to moving toward wide-spread wireless

sensor installation has been the poor reliability and

limited useful life of batteries needed to supply the

energy to the sensor, radio, processor, and other

electronic elements of the system. This limitation has

to some extent curtailed the proliferation of wireless

networks, especially with small devices. Legacy battery

technology can be eliminated through the use of Energy

Wireless Transceiver

Solar Cell

Sensor A/D Conv.

Processor/Memory

CymbetEnerChip

MEMS Pressure

Sensor

Figure 3: IOPM Layers Block Diagram.

Microcontroller and Radio Link

Ultra Low Power

RF Wireless

Optimized Protocol

1.5mm

Solid State

Energy Storage

Microcontroller

Pressure Sensor

Harvesting techniques which use an energy conversion

transducer tied to an integrated rechargeable solid

state battery. This mini “power plant” lasts the life of the

wireless sensor.

Cymbet has commercialized a solid state rechargeable

battery based on a silicon substrate called the EnerChip.

The photo in Figure 4 shows the 1uAH EnerChip used

in the IOPM. The EnerChips are used as bare die

or packaged in a standard semiconductor package.

Mounted on tape and reel, the EnerChips are placed on

circuit boards using Surface Mount Technology and then

can be reflow soldered to the board. The EnerChips are

treated like the other IC packages on the final board.

Using the EnerChip bare die has unique advantages for

internal energy storage from a packaging perspective,

EEWeb | Electrical Engineering Community Visit www.eeweb.com 17

2mm

0.5mm

TECHNICAL ARTICLE


TECHNICAL ARTICLE

Figure 4: EnerChip 1uAh battery on US Dollar for size reference.

as they are small and can be co-packaged in many ways

with other ICs or micro devices. The devices are wire

bonded to each other. EnerChip bare die co-packaged

in “wedding cake” die stack look like this diagram:

Figure 5

EnerChip bare die can be co-packaged side-by side

with an IC, as is the case with the Cymbet CBC3105,

CBC3112 and CBC3150:

Figure 6

EnerChip Bare Die

µController, Sensor, RTC

Rechargeable solid state battery bare die can be

attached to a substrate with other devices in System on

Chip module:

Figure 7

An important attribute of EnerChip batteries built on a

silicon wafer is that they can be solder attached to the

circuit board surface using a “flip chip” technique.

The flip chip attach mechanism opens up many new

miniature packaging options.

Solder

Bump

Figure 8

Designing and Deploying

Millimeter Scale Sensors

This article demonstrated that existing technologies

can be used to build millimeter-scale energy harvesting

based computing systems and wireless sensors. One of

the key enablers for long life operation is rechargeable

solid state batteries. There are solid state batteries, ultra

low power electronics and Energy Harvesting evaluation

kits available today from Cymbet and our Distributors that

can be used to design and deploy the concepts discussed

in this article. Reference schematics, application notes,

and ultra low power design techniques can be found at

http://www.cymbet.com.

About the Author

Steve Grady is responsible for all strategic messaging,

product roadmap, CRM, e-initiatives, collateral and

lead generation at Cymbet. He has more than two

decades of domestic and international experience

in marketing, sales, business development, product

management, engineering, and general management

in the networking, hardware, and software industries.

Steve has been in both startup and large company

environments with global scope. Prior to joining Cymbet,

Steve held senior management and technical positions

at ADC, Marconi, TimeSys, Reltec, and AT&T Bell Labs.

He holds BSEE and MSEE degrees from the University

of Illinois Champaign-Urbana. ■

EEWeb | Electrical Engineering Community Visit www.eeweb.com 18

PASSIVES

Mold Compound

Die

Sn/Pb or Sn

Lead

Solder

Bump

FLIPCHIP

Mold Compound

Die

Lead

TECHNICAL ARTICLE


EEWeb

Electrical Engineering Community

Contact Us For Advertising Opportunities

1.800.574.2791

advertising@eeweb.com

www.eeweb.com/advertising


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