Sailesh Chittipeddi - EEWeb

EEWeb 

PULSE 

Sailesh Chittipeddi 

President and CEO 

Conexant Systems 

INTERVIEW EEWeb.com 

Issue 62 

September 4, 2012 

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EEWeb PULSE TABLE OF CONTENTS 

Sailesh Chittipeddi 

CONEXANT SYSTEMS 

Interview with Sailesh Chittipeddi - President and CEO 

Featured Products 

Conexant’s Far-Field Voice Input Processing 

BY SAILESH CHITTIPEDDI WITH CONEXANT 

Conexant, market leader in audio with over 300M units shipped over 5 years, enables true far field 

voice input processing and speech recognition capabilities with its latest Skype certified offerings. 

Hidden Hazards in the Sallen-Key 2nd Order 

High Pass Active Filter 

BY MICHAEL STEFFES WITH INTERSIL 

Simple ways to improve performance and fix flatness in the desired signal passband. 

Microampere Current-Sense Amplifiers: 

Redefining a New State-of-the-Art 

BY ADOLFO GARCIA WITH TOUCHSTONE 

How new CSA enhancements enable the next generation of battery-powered, hand-held portable 

instruments addressing power management, motor control, and fixed-platform applications. 

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Visit www.eeweb.com 

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EEWeb PULSE 

Sailesh 

Chittipeddi 

Conexant 

4 

Conexant Systems is a leading provider of solutions 

for imaging, audio, embedded modem and video 

surveillance applications based in Newport Beach, 

California. We spoke with the President and CEO, 

Sailesh Chittipeddi about what it means to be in the 

“true” far-field arena, the company’s rich heritage 

of technology and IP and their plans for long-term 

growth. 

How did you begin your 

engineering career? 

I started my career at Bell 

Laboratories in Allentown, 

Pennsylvania with the CMOS 

technology development group. I 

spent quite a bit of time working on 

process technologies development 

and then on transferring those 

processes into manufacturing. 

When companies owned their wafer 

fabrication facilities, as was the 

case with AT&T Microelectronics 

and subsequently Lucent 

Technologies Microelectronics 

Division, the linkage between 

design engineering and process 

technology development was very 

tightly coupled to drive specific 

customer requirements. During 

this stage in my career, I had an 

opportunity to work with some of the 

best and brightest engineers from 

a process technology as well as 

design perspective. As a result of this 

activity when I was with Bell Labs, I 

was issued 63 U.S. patents and wrote 

about 40 publications. I transitioned 

sometime in the late 90s into the 

operations side of the business. 

EEWeb | Electrical Engineering Community 

In 2001, I took over the wafer 

foundry management responsibility 

for Lucent Technologies 

Microelectronics Division as we 

started the transition to a fabless 

model. Lucent Technologies 

Microelectronics Division was later 

spun-off to become Agere Systems. 

I began working very closely with 

foundries, transferring our process 

technologies to the outside. In 2006, 

I moved over to Conexant Systems 

and became senior vice president 

of global operations. Subsequently, 

I assumed responsibility for the

central engineering efforts and 

took on the role of CTO for a period 

of time, after which I became 

the president and COO prior to 

assuming my current role as CEO. 

What are the main areas 

of technology that your 

company provides? 

Our technology focus and new 

investments are in two primary areas 

– audio and video. One of the areas 

of focus in the audio business is the 

smart television market with voice 

and speech recognition capabilities. 

We bring our far-field voice input 

processing knowledge into this 

market space via our voice input 

processor SoCs. One of the latest 

televisions demonstrated by Korean 

manufacturers uses our voice input 

processor SoC, and it is currently 

selling into the market today. In 

terms of algorithm development, 

far field voice input processing is 

where we have a niche. We are in 

the true far field arena, which means 

if you are sitting in a room and are 

watching television and you tell the 

television to wake up, it basically 

wakes up. We are currently 

developing a new technology called 

“Watch, Live and Talk.” Imagine you 

have your television at full-blast and 

are watching a baseball game when 

you get a Skype conference call 

from the other side. This technology 

will allow you to take the call and 

watch the game at the same time 

without the person on the other side 

hearing what you are watching. 

The second area in which we are 

involved in audio is the unified 

communication headset market. 

We are partnering with every major 

headset manufacturer and have a 

dominant presence in that market. 

The third area is what we broadly 

call integrated mobile audio, 

which includes two specific facets: 

PC audio and mobile audio. Our 

analog and mixed signal design 

together with our firmware enables 

us to provide customers with a 

differentiated audio and voiceinput 

processing experience. It 

is what distinguishes us from the 

competition. 

Video is a significantly smaller 

business for us, but we expect it to 

scale up significantly from current 

levels over the next several years, 

If you step back for 

a moment and ask 

how Conexant is 

different from all of 

the broad-based audio 

suppliers, you’ll see 

that we don’t compete 

on an individual, 

commoditized 

component level 

and take advantage of the move from 

standard-definition to high-definition 

technologies with our new product 

launches. In video, the application 

segments in which we are focused 

include security and monitoring 

and video surveillance. We also 

have a legacy PC-TV business that 

is being adapted for a broader 

application base re-using existing 

IP. The application processor used 

for security and monitoring markets 

can also be adapted for low-cost 

tablets and is currently being used 

by Datawind and other suppliers to 

address emerging market needs. 


INTERVIEW 

In addition to these two investment 

areas, we still have a fairly mature fax 

and embedded modem business, 

where we continue our marketleading 

positions. Unlike some of 

our competitors, we are investing 

in roadmap development to sustain 

our leadership positions and make 

sure our customers’ needs are met. 

Unlike the PC-modem, which is 

largely de-bundled, the continual 

demand for secure point-to-point 

communications keeps the demand 

for these businesses relatively 

healthy. 

The final product line where we had 

made substantial investments in the 

past is the Imaging Systems Group, 

which focuses primarily on SoCs for 

multi-function and single-function 

printers. This unit has successfully 

deployed 11 generations of printer 

SoCs. The combination of its 

unique hardwired imaging pipeline 

combined with superior firmware 

development makes it a market 

leader in the ASSP market for printer 

SoCs. 

Between your audio business 

and video business, which 

would you say is more 

dominant in terms of direction 

of resources you plan to hit? 

Audio is a very resource intensive 

area for us. We are selectively 

investing in video, but not in the 

conventional areas where we would 

run into major SoC participants. 

Rather, we are focused in areas 

where we see more opportunities to 

bring our competencies in design 

and software/firmware to provide 

differentiation. So when you look at it 

in aggregate, audio R&D investment 

is very heavy – we are invested in a 

wider range of applications than 

on the video side, but in the next 

18- 24 months, we expect video to 

contribute to a significant portion of 

our growth. 

5


...our far field 

processing algorithms 

allow us to accomplish 

with one omnidirectional 

microphone 

what most of the 

competition are doing 

with two to four. 

How has Conexant become a 

leading power of solutions for 

imaging, audio, embedded 

modem, and video 

surveillance applications? 

In the imaging area, which is a 

combination of fax and printer 

SoCs, traditionally we have had 

fax datapumps and fax SoCs in 

our pipeline, and the entry barriers 

to newcomers in that market is 

fairly high. In 2008, we acquired 

the Sigmatel (Oasis) Printer SoC 

business from Freescale and have 

invested to make it successful. 

This investment has also led to our 

recent successes in other areas 

such as the low-cost tablet business 

in India. In embedded modems, 

we have a mature business, 

which is expanding into the ePOS 

segment in China. Our significant 

R&D investment moving forward is 

primarily in audio and video areas. 

Specifically, our analog-mixed 

signal capability, coupled with what 

I would characterize as general 

signal processing knowledge and 

firmware/software capabilities, 

allows us to pursue niches that large 

players would typically not pursue 

given the level of support required. 

In the algorithm development area, 

6 

for example, we have differentiated 

technologies in Subband AEC, 

stereo AEC, Phantom Bass 

and Brightsound XV- playback 

processing. 

Conexant sell ICs or is it 

primarily cores for ASICs? 

We sell ICs, but we don’t just 

sell silicon – the ICs will have a 

firmware component to it. We won’t 

compete in a pound-by-pound basis 

with somebody else, so almost 

anything that we do will have some 

differentiated analog and mixed 

signal capabilities with a software 

and firmware element. If you step 

back for a moment and ask how 

Conexant is different from all of 

the broad-based audio suppliers, 

you’ll see that we don’t compete 

on an individual, commoditized 

component level – rather we 

look for something that will have 

a component plus a software 

or firmware play that gives our 

customer a differentiated advantage 

in the end-markets in which they 

compete. 


Photo Credit: CelphImage 

Is Conexant a fabless 

company? 

Yes. Conexant was spun out of 

Rockwell Systems Semiconductor 

Group in 1999. Since that point, 

we’ve gone through a bunch of 

acquisitions like Globespan in 2003 

and have spun off businesses like Jazz 

Semiconductor, Skyworks Solutions, 

Mindspeed Technologies, SiRF and 

Pictos. There is a lot of rich IP in 

this company, so the analogy to Bell 

Labs and AT&T Microelectronics/ 

Lucent Technologies/Agere 

Systems is quite telling because 

both companies have such a rich 

heritage in technology. If one looks 

back at it, the challenge for both 

organizations was the inability 

to capitalize on the tremendous 

knowledge and IP resident in those 

organizations. We are now focused 

on markets and applications where 

we have the engineering and core 

competencies to enable us to be 

successful and resume our growth. 

The advantage we currently have 

since going private in 2011 is that 

we can afford to take a longer-range

view of our investments and take the 

necessary steps consistent with that 

view to be successful. 

How involved are your 

technical resources with the 

customer? Does Conexant 

have a consulting service 

integrated with the product? 

Every headset or television 

opportunity will involve the 

engineers working very closely 

with the customer. The reason is 

pretty simple – every television 

Webcam (external or embedded) 

has a different enclosure design, so, 

forexample, the characteristics that 

are associated with processing are 

going to be very different based on 

how flat or thick your television is and 

on exact speaker placement. The 

same applies for headsets. We have 

to work very closely with customers 

to tune the algorithms that will make 

them successful to give them the 

experience they desire. One thing 

that makes Conexant unique is 

that we are the only certified omni 

directional microphone Skype 

solution on the market today. Before, 

you would have solutions requiring 

a lot of microphones, but our far 

field processing algorithms allow 

us to accomplish with one omnidirectional 

microphone what most 

of the competition are doing with two 

to four uni-directional microphones. 

What are some challenges 

you have faced since being 

named president and CEO last 

year? 

The company has a rich heritage 

of technology and IP in its portfolio. 

However, financially the debt 

overhang from its early existence 

as a public company, coupled with 

a global real-estate footprint of a 

multi-billion dollar company, has 

left the company in a continual 

state of re-engineering without a 

focused investment strategy. What 

we have started doing in the last 18 

months, and continue to do more of 

(since going private has given us 

the flexibility to do so), is focus our 

investments in a few select areas, get 

our financial house in better shape, 

and execute much better both from 

an engineering and operational 

perspective than we ever have 

done before. This has allowed us to 

focus on market niches that are very 

suitable to attack for a company of 

our size and scale. 

What challenges do you 

foresee in the industry? 

The slow-growth in the worldwide 

economy may put a crimp on overall 

industry growth in the near term, in 

the event the economic powers that 

be do not resolve the mounting debt 

crisis enveloping most economies. 

The migration from PCs to tablets 

has reduced semiconductor content 

affecting traditional DRAM, as well 

as more traditional wired component 

players, but it has fueled the growth 

for other applications. Longerterm, 

the increased applicability 

of semiconductors for a variety of 

consumer applications ranging from 

home-entertainment, smart-home, 

medical, security, surveillance, 

connectivity (be it mobile or TV), 

sensors and a variety of industrial 

and automotive applications will 

drive growth of the industry as well 

as for Conexant. Additionally, the 

need for increased storage (both 

from an enterprise and consumer 

perspective), as well as the continual 

demands for increased bandwidth 

and ubiquitous connectivity, will 

ensure the semiconductor industry 

growth over the longer-term 

Can you tell us about some 

other goals for Conexant? 

Our main objective for the next 

five years would be to grow the 


INTERVIEW 

company considerably. One of the 

advantages we have by remaining 

private is that we can take a longer 

term view versus a public company. 

In addition to organic growth, we 

continually assess acquisition 

opportunities that will either provide 

us with the IP or allow for a portfolio 

expansion. While there is pressure 

to deliver results, we are focused 

more on medium/long-term growth 

objectives, as opposed to shortterm 

quarter to quarter targets. 

How many employees are 

there at Conexant? How would 

you describe the culture within 

the company? 

There are about 450 people 

currently working at Conexant. The 

word I used to describe the culture 

in the new Conexant is resilience. I 

would say the company’s culture is 

changing considerably, so our staff 

is certainly adaptable to change, 

and continues to have a desire to 

be a learning organization. The 

employees and engineering teams 

have been through a lot, and 

there is a tremendous desire to 

be successful and turn the place 

around. That’s what keeps me 

here – the fact that the team truly 

wants to succeed. There are a lot of 

competing companies close by, yet 

our extremely talented staff chooses 

to stay with us, because they want to 

move the company forward. ■ 

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9


Conexant’s 

Far-Field 

Voice Input 

Processing 

by Sailesh Chittipeddi 

Think of the advantages of carrying on a telephone 

conversation without having to worry about where 

the microphone is – simply talk and some hidden 

technology will pick up your voice, filter out any 

extraneous noise and send it to the other side. Just like 

talking to someone in the same room. No holding a 

phone to your ear, no headset to wear, no microphone 

to stay close to. And suppose we were able to control 

the gadgets around us simply by talking to them. 

No buttons to push or remote controls to find – we 

simply tell them to do what we want. Truly hands-free 

operation. 

Past attempts at providing this functionality have 

largely failed because of the difficulty with what is 

termed ‘far-field voice input processing’ (FFVIP). 

In near-field voice input processing, where a 

microphone is close to the mouth of a person talking, 

the audio quality tends to be quite good and louder 

than surrounding noise. When there are disturbances, 

several techniques are available to distinguish the 

10 EEWeb | Electrical Engineering Community 

near-field talker from far-away disturbances. Such 

techniques include using spatial differences from 

multiple microphones, as well as taking advantage of 

the level difference to distinguish the higher-level voice 

from the noise, then combining that with statistical 

algorithms to deliver a high-quality voice signal output. 

However, if the microphone is 12-15ft (4-5m) away, 

then the voice signal is part of the far-field and it can 

be buried in a variety of disturbances – for example, 

echo from nearby loudspeakers, noise from traffic or 

appliances, reverberation from the walls of the room, 

and even other voices nearby. In these cases, the voice 

level can be much lower than the noise sources, and 

in the case of sound from a loudspeaker located in the 

same unit as the microphone (e.g. a speakerphone) 

that echo can easily be 100 times louder than the 

desired voice signal. 

To deliver a clear, easily understandable voice signal 

from a far-field source requires a new set of advanced 

algorithms. Conexant’s FFVIP technology addresses 

the following:

Echo Cancellation 

To suppress the echo from a local loudspeaker 

by a factor of a million is extremely challenging. To 

address this, Conexant has developed algorithms that 

use advanced adaptive filters to estimate the echo 

and perform statistical estimation of which frequency 

bands contain echo and which contain the desired 

voice. Sophisticated control algorithms tie these 

together to produce a natural-sounding echo-free 

voice signal. 

Background Noise Suppression 

When trying to provide true FFVIP, there are a variety 

1M 

Near Field 

Experience 


PROJECT 

of background noises that must be eliminated. Not 

just stationary noise from fans and motors but also 

time-varying noise from passing cars, airplanes, 

home appliances and office machines. To eliminate 

background noise, Conexant has developed 

algorithms that analyze the spectral and temporal 

characteristics of the microphone signal and suppress 

anything that is clearly not voice without impacting 

real voice signals. 

De-Reverberation 

When speaking inside a room, the voice signal 

bounces off walls and often takes hundreds of 

milliseconds to die down. Normally the human auditory 

>5M 

Far Field 

Experience 

11


system sorts these reverberations out so they’re not 

noticeable. However, if the sound is recorded by a 

microphone it becomes very pronounced and sounds 

as if the person is speaking from a large empty 

barrel. This reverberation is not only disturbing, but 

affects speech comprehension both for humans and 

speech recognition engines. Conexant’s unique 

de-reverberation algorithm solves the challenge of 

removing the reverberation without adding other 

artifacts. 

Gain Level Adjustment 

Stationary or 

Spatially 

Coherent 

Spatially 

Coherent 

To keep the voice signal at a constant level independent 

of the distance to the microphone, the gain level needs 

to be adjusted without changing the voice signal 

characteristics. Specifically, low-level sounds need 

to stay low and high level sounds need to keep their 


Direct Path 

Non Stationary 

Diffused Reverb 

emphasis. Keeping the voice level too constant will 

make it sound unnatural and it will lose some of its 

characteristics. 

With its collection of audio-processing algorithms 

that enable devices to pick up a clear voice signal, 

even if it’s generated far away in a noisy background, 

Conexant’s FFVIP technology removes a major 

stumbling block for the integration of accurate voice 

control and speech recognition capabilities in today’s 

leading consumer electronic devices. 

FFVIP enabled devices can pick up a clear voice 

signal from a noisy background. This results in good 

hit-rate for the speech recognition algorithms and 

reliable voice control from far away. Without FFVIP, 

voice commands have to be issued very close to the 

appliance, which limits their use significantly.

For example, this year’s high-end smart TVs come 

enabled with two significant new features: they support 

accurate voice recognition and they allow the user to 

make reliable Skype TV calls. Both of these exciting 

features are enabled by Conexant’s revolutionary 

FFVIP technology. 

The effectiveness of Conexant’s FFVIP technology 

has been recognized by many leading consumer 

application manufactures, which have started 

to implement this technology in a wide array of 

consumer products such as smart TVs, notebooks, 

home appliances and more. Some of these products 

are already available in the market and others will be 

available in the near future. 

Conexant’s FFVIP technology can be made available 

in three solutions based on customer needs. The first 

option is for Conexant’s CX 208051 high-performance 

audio DSP with integrated power management and 

CX207082 voice input processor to be used as standalone 

products. 

The second option involves hardware IP on Conexant’s 

DSP core, in which the FFVIP algorithms have been 

ported to Conexant Audio Processing Engine (CAPE), 

a hardware IP core available for integration in SOC 

designs. The CAPE architecture supports the most 

efficient compilation of DSP code written in pure C, 

with minimal use of macros and intrinsics. 

The third option involves software IP, in which the 

algorithms are also available as a software IP package 

that can be ported to the customer’s SOC. 

Conexant Hardware voice input processor and 

algorithms are certified by Skype in both single mic3 

and dual mic4 versions. 

Conclusion 

The challenge with far-field voice input processing 

lies in bringing multiple algorithms to bear on voice 

signals to remove distortion and still provide a clean 

and natural-sounding voice signal. Using its audio 

digital signal processors, Conexant has developed 

a set of advanced algorithms that remove the noise, 

echo and reverberation, and enhance the voice signal 

to deliver high-quality voice through far-field pickup to 

make true hands-free operation a reality. 

References 


PROJECT 

1.)http://eon.businesswire.com/news/ 

eon/20120208005291/en/Conexant/CX20805/Digital- 

Audio-Processor 

2.)http://www.businesswire.com/news/ 

home/20110525005343/en/Conexant-Delivers-Super- 

Wideband-Audio-Chip-Home 

3.)http://developer.skype.com/certification/odmprogram/adc-voice-processing-soc-1-omni-mic 

4.)http://developer.skype.com/certification/odmprogram/adc-beamforming-soc-2-mic-array 

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Adding Touch/Graphics to Your 

Product 

Direct-drive LCD Software 

Integration for the RX62N/RX63N 

Incorporating a Capacitive Touch 

Interface into Your Design 

Industrial Controls GUI Application 

Using emWin 

Display 

Flat Panel Displays: 

LCD Technologies and Trends 

Flat Panel Displays: Touch Panel 

Technologies and Integration 

Flat Panel Displays: Beyond the Basics 

Flat Panel Displays: How to Overcome 

High Ambient Light Conditions 


Exploring a 2D/3D Solution 


Advanced Technology Trends 

M2M and Cloud Solutions 

Energy-efficient Communications 

with Wi-Fi 

Adding Wi-Fi to Embedded 

Applications 

Wireless Connectivity for 

Embedded Systems 

M2M: How to Create Revenuegenerating 

Services and Applications 

Wireless Sensors 

Wireless Transceivers 

M2M: Cloud Connectivity with RX 

and Exosite 

Power 

IGBT vs. Mosfet: 

Which Device to Select? 

How to Make Your House Smarter 

Digital Power: Design and 

Architectural Trade-offs 

Increasing the Performance of PFC 

and LED Driver IC Applications 

Optical Isolation, SSR Switching, 

and Ambient Light Sensing 

in MCU-based Applications 

IGBTs for HEV/EV 

Register Today! Limited Space Available. 

RenesasDevCon.com 

Motor Control 

Power Factor Correction: 

Why and How? 

Sensorless Vector Control and 

Implementation: Why and How 

Know your Precise Position with 

RX600 MCUs 

Field-oriented Control Using a 16-bit 

Low-power MCU 

Operating Systems 

Using ThreadX and IAR Embedded 

Workbench on the RX Processor 

Introduction to RoweBots’ 

Ultra Tiny Linux RTOS 

Embedding USB: Implementation 

Challenges and Limitations 

FreeRTOS Lecture 

Rapid Development on the Renesas 

RX63N RDK using µEZ ® and FreeRTOS 

Introduction to Python 

Software Development with an Open 

Source Real-time Operating System 

HTML5 HMI Development with QNX 

Developing Next-gen Automotive 

User Interface using EB GUIDE 5.3 

w/Windows Embedded Automotive 

7 and Renesas R-Car H1 

Getting Started with Micriµm’s 

µC/OS-III Kernel 

Embedding TCP/IP: Working 

Through uC/TCP-IP Usage 

Introduction to the .NET Micro 

Framework 

System Design 

Technologies 

Are all Batteries Created Equal? 

A/D Converter Fundamentals 

Designing Modern Medical Systems 

Digital Filtering on a MCU 

Infinite Runtime: Energy Harvesting 

with Renesas MCUs 

Moving from 8-bit to 32-bit MCUs 

Battery Management 

ADC Resolution: Myth and Reality 

Exploring the Safety Features of 

the RX210 

Low-power Design 

Increase the Dynamic Range and 

Precision of Digital Filters Using a FPU 

RL78 Project Configuration Tips 

RX Project Configuration Tips 

Sensor Fundamentals 

Extreme Low-power Design: 

Tools, Design Techniques and 

Implementation 

Creating Virtual EEPROM on 

Renesas MCUs 

Implementing Bootloaders on 

Renesas MCUs 

Designing Energy Harvesting 

Applications with the RL78 

Portable Instrumentation 

Applications with the RL78 

Embedded Systems Bootcamp



Hid 

Ha 

in the 

2nd O 

Pass 

Mic 

Inters

hael Steffes 

il - Sr. Applications Manager 

den 

zards 

Sallen-Key 

rder High 

Active Filter 

TECH ARTICLE 

The simple Sallen-Key Filter (SKF) applied 

to high pass requirements appears fairly 

straightforward and simple to implement. 

Latent within the design is a risk of capacitive 

and/or heavy loading for the op amp driving 

into this active filter stage. Most developments 

assume an ideal voltage source for the input 

signal where the effect of a reactive or heavy 

load would be hidden. When multistage 

designs are intended using low power op 

amps, the load presented by a poorly designed 

stage might in fact impair the intended 

signal frequency response above the high 

pass corner. Some of those tradeoffs will be 

exposed here with example designs. Simple 

paths to improved performance will be shown 

where improved flatness in the desired signal 

passband can be achieved. 


17


Vin 

Figure 1: 2nd order, SKF high pass filter 

The SKF High Pass Filter 

The classic Sallen-Key Filter (SKF), also known as a 

voltage controlled voltage source filter ( VCVS), design 

for a 2nd order high pass is shown in Figure 1. This is 

following the numbering of ref. 1, page 399. 

Here, the amplifier acts to convert a passive RC network 

into a design that can offer complex poles in the 

implementation of a high pass filter. The ideal transfer 

function for this network, where K = 1+Rf/Rg, is given 

as Eq. 1. 

V out 

V in = 

C1 

Rf 

K=1+ 

Rg 

C2 

Rg 

s2 

1 1 1 

+ s + R2 C1 C2 

Ks2 

+ 1−K 

 

R1C1 

+ 

The amplifier gain provides the higher frequency gain 

setting for the signal path and is part of the Q setting 

equation. Either Voltage Feedback Amplifier (VFA) or 

Current Feedback Amplifier (CFA) type devices can be 

used in this circuit. 

The characteristic frequency and 1/Q for this transfer 

function is given in equations 2 and 3. 

ω0 = 

R2 

 

1 

Q = 

 

R2 C1 

+ 

R1 C2 

R1 

+ 

– 


1 

R1R2C1C2 

C2 

C1 

 

Rf 

− (K − 1) 

Vout 

1 

R1R2C1C2 

R1C1 

R2C2 

Contrary to the SKF low pass design, the area of 

interest for the signal is actually above the high pass 

corner frequency of the filter. Looking at figure 1, as 

the frequency increases above Fo, the caps short out 

and the source simply sees R2 terminating into a noninverting 

gain stage. But what about the effect of the 

R1 path at frequencies above the intended high pass 

cutoff? Considering a gain of 1 design, the same signal 

that appears at the input to R1 in the passband appears 

at the output of the amplifier -effectively bootstrapping 

out this path from changing the input impedance away 

from just R2. As the frequency continues to increase, the 

propagation delay and rolloff through the amplifier will 

cause R1 to appear as more of a load in parallel with R2. 

It is in fact very possible that this active impedance path 

can dominate the total input impedance presenting a 

load much lower than just the R2 element. Some design 

points are worse than others in this respect. 

Here, the design will begin by constraining R2 to min/ 

max ranges. Increasing R2 will help the loading on the 

prior stage but comes at the cost of the higher noise 

contribution around Fo and possibly added input 

offset consuming signal headroom by the op amp bias 

current times this resistor. One aspect of this design is to 

balance this R2 issue with the resulting R1 to hit the filter 

shape which then also comes into the input impedance 

characteristic. To pursue this, the link between R2 and 

R1 over different design choices must be developed. 

The Resistor Ratio Constraint in the SKF 

High Pass Design. 

All SKF filters achieve their Q as a combination of 

amplifier gain (K), capacitor ratio and then resistor ratio. 

If one of our design goals is to keep R1 from getting too 

low, what might create that condition? If the capacitor 

ratio is swept for a particular amplifier gain and desired 

Q, the required R2/R1 ratio can be generated using the 

relationship of Eq. 4 (ref.2). 

β = 

2Q (1 + α) 

√ 

α 1+ 1+4Q2 

(1 + α)(k − 1) 

Here, K is the amplifier gain, Q is the target for the filter 

poles, with 

α = C2 

C1 

and β = R2 

R1

Most design references assume the gain of 1 design 

is most advantageous for amplifier bandwidth and 

sensitivity reasons. However, it turns out this conditions 

always requires that R11) – and sometimes 

significantly less. Sweeping the C ratio from about 0.2 to 

5 for a gain of 1 and plotting the R2/R1 ratio for different 

target Q’s gives Figure 8. It is desirable that this ratio 

be low. Using equal C gives the minimum but as the 

required Qp goes up, R1 must be much lower than R2 

as shown in the log/log plot of Figure 8. 

R2/R1 Ratio 

Figure 8: Required R2/R1 ratio for swept C2/C1 parametric 

on Q using K=1. 

Getting some of the Q with gain in the amplifier has 

a dramatic effect on this in a desirable direction. 

Using an amplifier gain of 2 and repeating this same 

calculation gives the required R2/R1 ratio of Figure 9. 

Using just a bit of gain has moved the required R1 value 

up significantly if R2 is chosen for loading, noise, and 

input offset voltage reasons. These curves also suggest 

selecting C2/C1>1 might be desirable. 

R2/R1 Ratio 

1000 

100 

10 

10 

1 

R2/R1 Ratio vs C2/C1 Ratio K=1 

Q=.577 Q=.707 Q=1 Q=5.27 

1 

0.1 1 10 

C2/C1 Ratio 

R2/R1 Ratio vs C2/C1 Ratio K=2 

Q=.577 Q=.707 Q=1 Q=5.27 

0.1 

0.1 1 10 

C2/C1 Ratio 

Figure 9: Required R2/R1 ratio for swept C2/C1 parametric 

on Q using K=2. 

Using these two gains of 1 and 2, the difference in input 

impedance will be shown for a Q = 5.27 design (this 

is the approximate highest Q stage required for a 6th 

order 0.25dB Chebychev filter). 

TECH ARTICLE 

Example design for 1kHz 2nd order high 

pass with >1Mhz signal bandwidth for 

K=1 

The lowest R2/R1 ratio in figure 2 is for equal C at K=1. 

Use the ISL28113 (ref.3) to get a signal bandwidth 

exceeding 1Mhz in a μPower design as shown in the 

circuit of figure 4 (ref.4). This device offers a 2MHz Gain 

Bandwidth Product (GBP) using only 90μA (typical, 

130μA max) supply current on a 1.8V to 5.5V supply. 

Use an R2 that adds an input noise approximately equal 

to the amplifier’s 25nV/√Hz and start the design with 

R2=50kΩ. This high Q design will be peaking the input 

noise around Fo quite a lot, so it is best to not let R2 get 

too high. The design of Figure 4 used 50k for R2, but that 

forced R1 down to 457Ω using Eq. 4. 

Vin 

33.3n 

C 1 

33.3n 

C 2 

1.25u 

Figure 10: High Q, K=1 design with 1kHz Fo and 

Q = 5.27 

Figure 11 shows the expected frequency response 

while Figure 12 shows the relatively high noise peaking 

around Fo. The response curve is showing the expected 

peaking at 1kHz, and then a gain of 1 over a broad 

passband with the amplifier rolling off above 2Mhz. 

The output spot noise peaks approximately 60X around 

Fo. This is common for high Q stages but is even higher 

here due to the very high resistor ratio. Since this is 

happening at lower frequencies it should not impact the 

integrated noise too much, but will be degrading the 

loop gain at the lower end of the intended passband. 

Reducing this noise gain peaking for high Q poles is 

desirable and easily achieved by adding some gain in 

the amplifier. 

The added concern in Figure 10 is the several regions of 

capacitive input impedance. Figure 13 shows simulated 

input impedance showing the initial capacitive response 

up to Fo which then recovers to the R2 resistor value. 

The phase response across the R1 resistor comes down 

to approximately 0deg above Fo over a wide frequency 

range effectively bootstrapping out the relatively low R1 

value. However, even a slight phase deviation over the 

457 

R 2 

50k 

20 

Rb ISL28113 

+ 

+ 

– 

– 


R 1 

10k 

R f 

V+ 

V– 

-9.29209u 

19


dbV@VOUT/dB 

10 

0 

-10 

-20 

-30 

-40 

100 

200 400 1k 2k 4k 10k 20k 40k 100k 200k 400k 1M 2M 4M 10M 

Frequency/Hertz 

Figure 11: Gain of 1, 2nd order SKF high pass frequency 

response. 

Output Noise / V/rtHz 

10u 

4u 

2u 

1u 

400n 

200n 

100n 

40n 

20n 

100 



Figure 12: Gain of 1, 2nd order SKF high pass output 

spot noise 

VIN / V 

100k 

40k 

20k 

10k 

4k 

2k 

1k 

400 

200 

100 



Figure 13: Input impedance to the design of Figure 10. 

intended signal frequency span causes the apparent 

input impedance to vary widely and extend to very low 

values as shown in Figure 13. 

This impedance looks roughly like a capacitance again 

above 20kHz. If this stage is then driven from the output 

of another amplifier stage, some impact on the response 

flatness of that device should be expected. Whether this 

V+ 

X1 Vin 

+ 

ISL28136 

– 

+ 

– 

V– 

33.3n 

C 1 

33.3n 

C 2 

1.25u 

R 2 

20 

Rb ISL28113 

+ 

+ 

– 

– 

-9.29209u 

Figure 14: High Q, K=1 HPF driven by another amplifier 

stage. 

457 

R 1 

50k 


10k 

R f 

V+ 

V– 

Vout 

impedance profile impacts the overall performance 

depends strongly on the specific device driving into this 

load. Using an ISL28136 (ref. 5) will give the circuit of 

Figure 14. This slightly lower noise device is faster and 

hence more susceptible to capacitive load peaking 

issues. This is shown as just a buffer stage here, but 

normally this would be another active filter stage to 

implement a multipole high pass filter. 

Running a frequency response and probing the output 

of the first stage (red curve) along with the final output 

gives the desired high pass complex pole filter shape 

but now adds perhaps an undesirable peaking at higher 

frequencies. 

dB 

10 

0 

-10 

-20 

-30 

-40 

-50 

100 200 400 1k 2k 4k 10k 20k 40k 100k 200k 400k 1M 2M 4M 10M 


Figure 15: Buffered 2nd order SKF HPF response showing 

input impedance effects. 

This issue was showing up in the construction of an 

online semi-automatic multi-stage high pass active 

filter design tool. Many amplifier and impedance 

combinations are possible, but using a gain of 1 for 

the higher Q stages introduces a very wide component 

ratio spread that causes other problems as well. While 

increasing the gain for the highest Q stage seems like 

it is going in the wrong direction, it is actually possible 

numerous 2nd order benefits will be seen in physical 

implementations. 

Using K=2 in the SKF HPF to improve the 

input impedance characteristic. 

The parametric R vs. C ratio curves shows a significant 

reduction in required R ratio with that addition of some 

gain in the amplifier. Then, starting from an R2 value that 

does not impact the total noise too much, using a K=2 

will pull up the required R1 value nicely. Continuing 

with the equal C design for simplicity and holding R2 

= 50kΩ adjusts the C values down and the R1 value up 

for 1kHz, Q = 5.27 design as shown in figure 9. With R1 

resolved to 28.6kΩ using eq. 4, the R1C product will be 

given by eq. 5 for k>1 (letting k=1 gives the solution 

for the C in the first example). Dividing this result by R1, 

gives the value for the equal C in this design flow.

Vin 

R1C = 1 

 

1+ 

4ω0Q 

1+8Q2 

(k − 1) 

4.2n 

C 1 

4.2n 

C 2 

1.25u 

28.6k 

R 2 

R 1 

20 

Rb ISL28113 

+ 

+ 

– 

– 

-18.8333u 

Figure 17: K=2 design for Fo = 1kHz, Q = 5.23, low 

power HPF using the ISL28113. 

50k 

The response shows the same high pass poles as the 

unity gain design (shifted up 6dB) but of course lower 

high end cutoff frequency. The frequency response for 

the unity gain design and this K=2 design are shown in 

Figure 18. These responses are not following a strict gain 

bandwidth product profile due the correctly modeled 

open loop phase effects in the ISL28113 macromodel. It 

is not uncommon to see a bit of bandwidth extension in 

VFA based designs operating at lower gains where the 

phase margin is


Summary and Conclusions 

Gain of 1 in the amplifier for a high pass SKF has often 

been the preferred approach in the design and vendor 

literature. Using real amplifiers, or macromodels that 

show the impact of load impedance on response shape, 

can run into response flatness issues driving into the 

reactive load impedance seen at frequencies > Fo. 

Assuming the region of signal interest is actually above 

the high pass corner, this peaking might be totally 

unacceptable in a physical implementation. One path 

to shifting this loading issue in a good direction might 

be to take advantage of the amplifier gain available 

in the design to pull the R ratio much closer. This has 

been shown here to be an effective means of improving 

the response flatness. This issue is very dependent 

on the specific amplifiers chosen for the design but 

simulation tools are readily available to the designer to 

easily evaluate options (ref. 4). If your multi-stage HP 

SKF design has been showing response peaking above 

the high pass corner, perhaps it is this loading issue 

internal to the filter and only a slight design change to 

improve the input impedances can quickly improve 

your response flatness. 

References 

1. “Passive and Active Network Analysis and Synthesis”, 

Dr. Aram Budak, 1974, pp 399 

2. This is essentially the same equation as developed for 

the SKF Low pass with the definition of β and β reversed 

and then each ratio reversed. Contact the author for the 

detailed derivation for the SKF low pass version. 

3. ISL28113, Single General Purpose Micropower, 

RRIO Operational Amplifier, http://www.intersil.com/ 

content/intersil/en/products/amplifiers-and-buffers/allamplifiers/amplifiers/ISL28113.html 

4. These circuits (available from the author) come from 

the free Spice simulator (registration required), iSim PE 

available at http://www.intersil.com/en/tools/isim.html 

5. ISL28136, 5MHz, Single Precision RRIO Op Amp, 

http://www.intersil.com/content/intersil/en/products/ 

amplifiers-and-buffers/all-amplifiers/amplifiers/ 

ISL28136.html 


About the Author 

With 27 years of involvement in high speed amplifier 

design, applications, and marketing, Michael Steffes has 

introduced over 80 products spanning five companies 

while publishing more than 40 technical articles. His 

current focus is on high efficiency high speed ADC 

interfaces, DSL/PLC line interface solutions, and online 

design tool development. ■

Single or Multiple Cell Li-ion Battery Powered 

4-Channel and 6-Channel LED Drivers 

ISL97692, ISL97693, ISL97694A 

The ISL97692, ISL97693, ISL97694A are Intersil’s highly 

integrated 4- and 6-channel LED drivers for display 

backlighting . These parts maximize battery life by featuring 

only 1mA quiescent current, and by operating down to 2.4V 

input voltage, with no need for higher voltage supplies. 

The ISL97692 has 4 channels and provides 8-bit PWM 

dimming with adjustable dimming frequency up to 30kHz. The 

ISL97693 has 6 channels with Direct PWM dimming control. 

The ISL97694A has 6 channels and provides 8-, 10-, or 12-bit 

PWM dimming with adjustable dimming frequency up to 

30kHz, 7.5kHz, or 1.875kHz, respectively, controlled with I 2 C 

or PWM input. 

ISL97692 and ISL97694A feature phase shifting that may be 

enabled optionally, with a phase delay between channels 

optimized for the number of active channels. In ISL97694A, 

phase shifting can multiply the effective dimming frequency by 

6 allowing above-audio PWM dimming with 10-bit dimming 

resolution. 

The ISL97692/3/4A employ adaptive boost architecture, 

which keeps the headroom voltage as low as possible to 

maximize battery life while allowing ultra low dimming duty 

cycle as low as 0.005% at 100Hz dimming frequency in Direct 

PWM mode. 

The ISL97692/3/4A incorporate extensive protection 

functions including string open and short circuit detections, 

OVP, and OTP. 

The ISL97692/3 are offered in the 16 Ld 3mmx3mm TQFN 

package and ISL97694A is offered in the 20 Ld 3mmx4mm 

TQFN package. All parts operate in ambient temperature 

range of -40°C to +85°C. 

VIN: 2.4V~5.5V 

10 

July 19, 2012 

FN7839.2 

1µF 

15nF 

12k 

53k 

291k 

4.7µF 

VIN 

COMP 

ISET 

AGND 

SDA/PWMI 

SCL 

EN 

FPWM 

FSW 

L1 

10µH 

ISL97694A 

D1 

LX 

OVP 

PGND 

CH1 

CH2 

CH3 

CH4 

CH5 

4.7µF 4.7µF 

100pF 470k 

23.7k 

2.2nF 

VOUT: 24.5V, 6 x 20mA 

Features 

TECH ARTICLE 

• 2.4V Minimum Input Voltage, No Need for Higher Voltage 

Supplies 

• 4 Channels, up to 40mA Each (ISL97692) or 6 Channels, up 

to 30mA Each (ISL97693/4A) 

• 90% Efficient at 6P5S, 3.7V and 20mA (ISL97693/4A) 

• Low 0.8mA Quiescent Current 

• PWM Dimming Control with Internally Generated Clock 

- 8-bit Resolution with Adjustable Dimming Frequency up to 

30kHz (ISL97692/4A) 

- 12-bit Resolution with Adjustable Dimming Frequency up 

to 1.875kHz (ISL97694A) 

- Optional Automatic Channel Phase Shift (ISL97692/4A) 

- Linear Dimming from 0.025%~100% up to 5kHz or 

0.4%~100% up to 30kHz (ISL97692/4A) 

• Direct PWM Dimming with 0.005% Minimum Duty Cycle at 

100Hz 

• ±2.5% Output Current Matching 

• Adjustable Switching Frequency from 400kHz to 1.5MHz 

Applications 

• Tablet, Notebook PC and Smart Phone Displays LED 

Backlighting 

Related Literature (Coming Soon) 

• AN1733 “ISL97694A Evaluation Board User Guide” 

• AN1734 “ISL97693 Evaluation Board User Guide” 

• AN1735 “ISL97692 Evaluation Board User Guide” 

0.0001 

143k 

CH6 

0.001 0.01 0.1 1 10 

FIGURE 1. ISL97694A TYPICAL APPLICATION DIAGRAM 

INPUT DIMMING DUTY CYCLE (%) 

FIGURE 2. ULTRA LOW PWM DIMMING LINEARITY 

ILED (mA) 

10 

1 

0.1 

0.01 

0.001 

Get the Datasheet and Order Samples 

http://www.intersil.com 

fPWM : 200Hz 

fPWM : 100Hz 

Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2012 

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


23


24 

Making Wireless 

Truly Wireless: 

Need For Universal 

Wireless Power 

Solution 

Dave Baarman 

Director Of 

Advanced Technologies 

"Sed ut perspiciatis unde omnis 

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laudantium, totam rem aperiam, 

eaque ipsa quae ab illo inventore 

veritatis et quasi architecto beatae vitae 

dicta sunt explicabo. Nemo enim ipsam 

voluptatem quia voluptas sit aspernatur aut odit 

aut fugit, sed quia consequuntur magni dolores eos 

qui ratione voluptatem sequi nesciunt. Neque porro 

quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, 

adipisci velit, sed quia non numquam eius modi tempora incidunt ut 

labore et dolore magnam aliquam quaerat voluptatem. Ut enim ad 

minima veniam, quis nostrum exercitationem ullam corporis suscipit 

laboriosam, nisi ut aliquid ex ea commodi consequatur? Quis autem 

vel eum iure reprehenderit qui in ea voluptate velit esse quam nihil 

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25


26 EEWeb | Electrical Engineering Community

TECH ARTICLE 

Microampere 

Current-Sense 

Amplifiers 

Adolfo Garcia 

Touchstone Semiconductor 

Vice President – Marketing & Applications 

To sense and control supply current flow are 

fundamental requirements in most electronic systems 

from battery-operated, portable equipment to mobile 

or fixed-platform power management and dc motor 

control. High-side current-sense amplifiers (or “CSAs”) 

are useful in these applications especially where power 

consumption is an important design parameter. In 

allowing engineers to save power without sacrificing 

performance, a new breed of CSAs offers even greater 

benefits. 

Design engineers now have even more options for 

high-side current-sensing amplification with the right 

combination of wide operating supply-voltage range, 

low supply-current operation, low input offset voltage 

(VOS) and gain errors, fixed gain options, and small 

form factors. Addressing power management, motor 

control, and fixed-platform applications, new CSA 

enhancements now enable the next generation of 

battery-powered, hand-held portable instruments. 

Uni-directional Current-Sense Amplifiers 

For measuring load currents in the presence of highcommon-mode 

voltages, the internal configuration of 

some uni-directional CSAs is based on a commonly-used 

operational amplifier (op amp) circuit. In the general 

case, a CSA monitors the voltage across an external 

sense and generates an output voltage as a function of 

load current. Featuring Touchstone Semiconductor’s 

TS1100, the inputs of the op-amp-based circuit are 

connected across an external RSENSE as shown in 

the typical application circuit in Figure 1. The applied 

voltage is ILOAD x RSENSE at the RS- terminal. 

Op-amp feedback action forces the inverting input of 

the internal op amp to the same potential (ILOAD x 

RSENSE) since the RS- terminal is the non-inverting 

input of the internal op amp. Therefore, the voltage drop 

across RSENSE (VSENSE) and the voltage drop across 

RGAIN (at the RS+ terminal) are equal. Both RGAIN 

resistors are the same value to minimize any additional 


27


V BATTERY 

2V to 25V 

error because of op-amp input bias current mismatch. 

Bi-directional Current-Sense Amplifiers 

While uni-directional CSAs are primarily used in those 

applications where current is delivered to a load, there 

are many applications where it is necessary to measure 

current in both directions. Some applications where 

bi-directional current-sense monitoring/amplification 

are needed include: smart battery packs and chargers, 

portable computers, super capacitor charging/ 

discharging devices, and general-purpose currentshunt 

measurements. 

Uni-directional CSAs were used prior to the advent of 

bi-directional CSAs; however, two uni-directional CSAs 

are necessary in order to measure current in both 

directions. Whereas the RS+/RS- input pair of CSA #1 

is wired normally for measuring current to the load, the 

RS+/RS- input pair for CSA #2 would be wired antiphase 

with respect to CSA #1 for measuring current 

+ 

R SENSE 

RS+ RS– 

R GAIN 

2nd-Order 

Differential LPF 

f LP ≈ 50kHz 

GND 

Figure 1: A Typical Application for a High-precision Uni-directional Current-sense Amplifier 

(Touchstone Semiconductor’s TS1100). 


– 

M1 

PMOS 

R OUT 

10kΩ 

+ 

R GAIN 

TS1100 

I LOAD 

OUT 

0.047µF 

LOAD 

V DD 

+3.3V 

Microcontroller 

ADC 

back to the source. There are significant disadvantages 

to using this configuration: (a) the cost of two CSAs; (b) 

twice the printed-circuit-board (pcb) area is necessary 

because of the two CSAs; © two ADC inputs are 

consumed; and (d) additional microcontroller coding 

and machine cycles are required. 

A straight-forward modification to the uni-directional 

CSA configuration yields a bi-directional CSA as shown 

in Figure 2 for Touchstone Semiconductor’s TS1101. 

This implementation saves on additional computing 

resources, pcb area, and component costs. 

The internal amplifier was reconfigured for fully 

differential input/output operation and a second lowthreshold 

p-channel FET (M2) was added as shown 

in Figure 2. The operation of this bi-directional CSA is 

identical to that of the uni-directional CSA previously 

discussed when VRS- > VRS+. When M1 is conducting 

current, the internal amplifier holds M2 OFF in the 

implementation shown in Figure 2. The amplifier holds

M1 OFF when M2 is conducting current. The disabled 

FET does not contribute to the resultant output voltage 

in either case. 

For both types of uni-directional or bi-directional CSAs, 

gain error accuracy is a measure of how well-controlled 

is the ratio of ROUT to RGAIN, especially over 

temperature. Gain error accuracy can be 

100μV or more. 

The CSA’s SIGN Output Comparator 

The bi-directional CSA incorporated one additional 

feature as was shown in Figure 2 – an analog comparator 

the inputs of which monitor the internal amplifier’s 

differential output voltage. The SIGN comparator 

output indicates the load current’s direction while the 

voltage at its OUT terminal indicates the magnitude of 

the load current. The SIGN output is a logic high when 

M1 is conducting current (VRS+ > VRS). Alternatively, 

the SIGN output is a logic low when M2 is conducting 

current (VRS+ < VRS-). 

Note that the SIGN comparator exhibits no “dead zone” 

at ILOAD switchover, unlike other bi-directional CSAs 

where hysteresis was purposely introduced to prevent 

comparator output voltage chatter. The load current 

transition band is less than ±0.2mA with respect to a 

50-mΩ external sense resistor. Other types of CSAs 

OUT 

VDD 

LOAD 

SIGN 

0.1µF 

0.047µF 

To AC Wall Cube 

OR Charger 

+3.3V 

Figure 2: A Typical Application for a Bi-directional High-precision Current Sense Amplifier 

(Touchstone Semiconductor’s TS1101). 

V DD 

Microcontroller 

ADC Input 

Digital Input 


29


that also utilize an analog OUT/ comparator SIGN 

arrangement exhibit a SIGN transition band that can 

range up to 2mV (or 40mA referred to a 50mΩ sense 

resistor). Low-transition band, bi-directional CSAs can 

be 200 times more sensitive on this attribute alone. 

Internal Noise Filters 

It’s always been good engineering practice to add 

external low-pass filters (LPFs) in series with the CSA’s 

inputs to counter the effects of externally-injected 

differential and common-mode noise prevalent in any 

load current measurement scheme. Resistors used in 

the external LPFs in the design of discrete CSAs were 

incorporated into the circuit’s overall design so errors 

because of any input-bias current-generated voltage 

and gain errors were compensated. 

Utilizing external LPFs in series with the CSA’s inputs 

only introduces additional offset voltage and gain 

errors with the advent of monolithic CSAs. Higherperformance 

uni-directional and bi-directional CSAs 

incorporate internal LPFs to further save system cost 

and improve overall system performance, thereby 

minimizing/eliminating the need for external LPFs and 

to maintain low offset voltage and gain errors. 

Additional Applications Tips 

All parasitic pcb track resistances to the sense 

resistor should be minimized for optimal VSENSE 

accuracy. Strongly recommended are Kelvin-sense pcb 

connections between RSENSE and the CSAs’ RS+ 

and RS- terminals. The pcb layout should be balanced 

and symmetrical to minimize wiring-induced errors. 

Also, the pcb layout for RSENSE should include good 

thermal management techniques for optimal RSENSE 

power dissipation. 

To form an LPF with the CSAs’ ROUT, a 22nF to 100nF 

good-quality ceramic capacitor should be connected 

from the OUT terminal to GND. The use of a capacitor 

at this terminal minimizes voltage droop (holding VOUT 

constant during the sample interval). Using a capacitor 

on the OUT terminal will also reduce the CSAs’ smallsignal 

bandwidth as well as band-limiting amplifier 

noise. 

A new state of the art in CSA technology has been 

redefined. These new CSAs can resolve charging or 

discharging currents with 12-bit or better resolution, 

exhibit very low VOS and gain match errors, are 

extremely easy to use, are self-powered, and consume 

very little supply current. These higher-performance 


CSAs are specified to operate over wide or extended 

industrial temperature ranges, can operate from 

2V to 25V (and higher) power supplies, and mate 

their electrical performance with pcb-space saving 

packages (such as SOT23-5 and SOT23-6). 

About the Author 

Adolfo Garcia has over 30 years of experience in the 

analog IC business. He has held design, applications, 

marketing, and product line/business unit management 

positions of increasing responsibility at Analog Devices, 

Linear Technology, Micrel, Advanced Analogic 

Technologies, and Leadis Technology. His technical and 

market knowledge spans a broad spectrum of analog 

products and applications, including amplifiers, data 

converters, and power management functions. This 

expertise has led to the definition and market launch 

of over 65 high-performance analog IC products. He 

holds three US Patents and is an accomplished author 

with over 60 publications to his credit.



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