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Analog Dialogue

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I'm selecting an op amp for a high-precision signal path and need to choose the best gain-bandwidth product. Isn't faster always better?


Determining which op amp has the right gain-bandwidth product for our application is like Goldilocks choosing which bowl of porridge to eat. We want to choose one that is not too fast and not too slow but gives us just the right trade-offs between speed, accuracy, and stability.

August RAQ Goldilocks.jpg

For a closer look at these considerations, see "Choosing a Precision Op Amp? Trust Goldilocks" in the August 2016 issue of Analog Dialogue.


We welcome your feedback. What other topics would you like us to discuss? Are you interested in more information?


Best regards,
Daniel Burton

August always makes me a little anxious—I think it’s a flashback from school days: summer’s almost over and it will soon be time to hit the books. That got me thinking about today’s electrical/electronics engineering students. I’ve heard comments and opinions about how engineering students aren’t interested in analog design anymore, and how schools don’t teach the analog/linear fundamentals like they used to.


I did an informal online survey of the curricula at a number of the major engineering schools in the US, and it sure looks like analog/mixed signal engineering is alive and well there. Stanford has the Murmann Mixed-Signal Group, innovating analog-to-digital interface circuits. From the photo on their site, it looks like they have a healthy group of grad students. Texas is apparently a hotbed of analog design learning and research, with the Texas Analog Center of Excellence at the University of Texas, Dallas. They claim to be “the largest international, university-based analog technology center,” creating design innovations to improve health care, energy efficiency, and public safety. About 200 miles to the south, Texas A&M has their Analog and Mixed-Signal Center, for “the education and training of highly qualified engineers for design and manufacturability of analog and mixed-signal integrated systems.” And of course MIT weighs in. According to the online description of their EE curriculum, “a focus is digital and analog signal processing with emphasis on design and practical implementation.” All of the university curricula I looked at—and it was a lot of them—still have the  analog/linear circuit fundamentals, along with numerous specialized analog/mixed-signal design courses at both the undergrad and graduate levels. I found that reassuring. We here at Analog Devices know that analog technology is a flourishing, vital, and exciting field—we just need to make sure that fact is communicated to today’s students. Attention EE students: analog rocks!


Speaking of state-of-the-art analog electronics, the article in this month’s issue by Umesh Jayahoman explains how the high bandwidth sampling core and the digital downconverter options contained in the new generation of RF ADCs (aka GSPS ADCs) enable design innovation in communications infrastructure. This mixed-signal technology offers a flexible pathway to rethink and redefine the radio architectures that will cater to the growing demands of consumers. The Capacitive Programmable-Gain Amplifier device is the subject of the second article by Miguel Usach and Gerard Mora. Our two engineers provide a look into the circuit architecture, describe the amplifier’s advantages in certain applications over the resistive PGA, and compare some of the critical specifications of the two amplifier topologies. Daniel Burton tells us we "must trust Goldilocks" when choosing a precision op amp in his RAQ article. You can read it all here.


So happy reading and please enjoy the rest of your summer, and if you’re an EE student, get ready to dive into those (hopefully) analog and mixed-signal design courses. The real world anxiously awaits your innovation.


In order to fill the needs of many customers today the sample rate of our ADCs at ADI is getting pushed higher and higher.  Customers desire to sample frequencies in the GHz range which comes with a stiff penalty of higher bandwidth in the digital data transmission.  High frequency is needed but typically not high bandwidth.  Generally about 100-200MHz at most is required but the operating frequency may be up at 1.5 GHz or higher.  Here come DDCs to the rescue.  With a DDC, input frequencies in the GHz range can be sampled by the ADC and then tuned and filtered by the DDC to select the 100-200MHz of required bandwidth.  This allows the digital output bandwidth to be reduced to a manageable level resulting in less challenging layout and cheaper FPGAs.  This all sounds great, but how does this DDC actually work.  Take a look at my latest article on Analog Dialogue titled "What's Up with Digital Downconverters Part 1" to learn more.  You can find it here:

Stay tuned for the second part of the article coming up in Analog Dialogue in November of this year.  I welcome any feedback and questions you may have.

Welcome to the exciting new frontiers in high-performance data conversion: GHz bandwidths, giga-samples-per-second, and direct RF conversion. As CMOS process technology has advanced, speeds have increased and the addition of signal processing to data converters has become commonplace. The lines continue to blur between analog and digital as the trend toward software-defined systems and broad-band signal conversion grows. Our two  feature articles this month both deal with design details of ADI’s latest RF data converters. These blazingly fast embodiments of devices that used to be considered mostly analog now incorporate just as much digital functionality. In fact, these devices, with output data that is processor-ready, are more like  integrated data conversion systems than components.


Jonathan Harris provides an in-depth look at the digital down conversion function in a couple of ADI’s high-speed ADC devices. This digital signal processing function obviates the need to implement multiple analog down conversion stages in a GHz RF signal chain, and it has the added advantage of improving dynamic range within selected bands. This article explains the signal-tone flow through a DDC block and introduces an online Frequency Folding Tool that aids in the analysis of the sampled spectrum.


The second article addresses the transmit side of the radio  signal chain. Dan Fague describes how a new breed of RF DAC can directly synthesize GHz signals, eliminating the need for entire stages of analog frequency upconversion, thus simplifying frequency planning, and reducing power consumption and the size of the radio. Advancements in CMOS process, innovations in DAC architectures, and implementation of JESD204B serial interface, have come  together to enable a practical high-performance GHz DAC. Dan explores the  functionality and performance of this remarkable product.


With more and more digital processing and frequency translation being done inside the direct RF data converter solution itself, and the output data seamlessly interfacing to an FPGA, the radio system designer’s IP can largely reside in the digital domain. This  unprecedented flexibility in system  architecture is helping designers reach the next level in truly software-defined radio platforms. All of which enables many innovative applications that couldn’t have been considered even a few years ago. Or as we like to say around here, “Ahead of what’s possible.”

Last month, a horse named Nyquist won the 142nd Kentucky Derby. Of course, I immediately thought of the groundbreaking engineer and communications theorist Harry Nyquist, whose work is fundamental to data conversion
applications. He’s a true engineering celebrity of the sort that I wrote aboutin an earlier Editor’s Note. It was a thrill to see the name of one of our engineering heroes being honored in the mainstream international media.


Harry Nyquist came to the US from Sweden in 1907 at the age of 18, and promptly earned BSEE and MSEE degrees from the University of North Dakota and then a Ph.D. in physics from Yale. He went on to do amazing things at AT&T and Bell Labs, and his name lives on today most notably  in the Nyquist sampling theorem, also known as the Nyquist–Shannon sampling theorem. So when I saw the horse Nyquist, my mind immediately started to think up engineering jokes: I wonder if Nyquist will run twice as fast as the next fastest horse…How do we know that the horse we see is real and not an aliased image…Will his lane at the starting gate be the Nyquist Zone?  Then I discovered Nyquist the horse is actually named for a hockey player. My short-lived excitement was crushed.


In this issue, our feature article authors Colm Slattery and Ke Li take a look at a particularly timely issue, as more and more environmental regulations to control and monitor liquid waste are appearing worldwide.  Electromagnetic flow technology is the choice for this particular application, and the trend is toward an oversampled approach, which challenges the ADC requirements. In addition to oversampling design considerations, their detailed article discusses the significant power
challenges involved in the application.


In the 141st running of the Preakness, Nyquist came in third, so no Triple Crown bid for this horse. But those of you involved with  mixed-signal system design, know that Nyquist, the sampling theorem, can never really be beaten. It is also known to occasionally bite you.


The data sheet for the amplifier that I've chosen for my application specifies a small signal bandwidth along with a large signal bandwidth, and they are quite different specs. How do I determine if my signal qualifies as small or large?


Whether you consider your signal small or large, proper selection of an amplifier requires (among other things) knowledge of how fast it needs to be. And the larger the signal at the output, the harder it gets a good, high-fidelity reproduction of the input signal.


Learn more in "Citius, Altius, Fortius" as published in the April 2016 issue of Analog Dialogue.




We welcome your feedback in the comments section. Has this article been useful or helped you in your design? Would you like more information on this topic?


Best regards,

Gustavo Castro

When designing a motion control system that uses a gyroscope as it feedback sensing element, understanding the system's dependence on the gyroscope's noise behaviors has a number of rewards.  Most notably, these insights can help system architects establish application-relevant performance requirements, which will help them focus early evaluation efforts and resources on the most appropriate class of device.  While we all want our designs to be as small and as inexpensive as possible, they also need to perform appropriately, through all relevant environmental conditions.


A wise man once offered that "a problem that has been well defined, is already half-solved." With that thought process in mind, we present, Designing for Low-Noise Feedback Control with MEMS Gyroscopes, which describes some of the key attributes of noise in MEMS Gyroscopes, while describing how they impact a simplified application that tightens a camera's pointing angle error from red to green (see below).  I hope that this helps you and I look forward to your comments!  Thank you for visiting our blog and for checking out the latest issue of Analog Dialogue. To gain access to this new article, just click here.

Our company bills itself as “bridging the physical and  digital.” For those of you working on circuits and systems that cross that bridge, both of our feature articles this month include hard hitting design information for you.


Mark Looney offers practical insights for using MEMS gyroscopes as feedback sensing elements in motion control systems. MEMS gyros are a booming tech area, with both gyros and accelerometers essentially taken
for granted in smartphones, tablets and game systems nowadays. Of course, they have many applications beyond consumer electronics, such as automobiles, space, and industry. Mark probes a bit further beyond simply designing for “low noise” and looks at quantifying how gyroscope angular rate noise will directly affect system level behaviors. I don’t know about you, but the word “gyroscope” brings to mind one of my favorite mystifying toys as a kid—a flywheel combined with a gimbal that, when given a good spin, would balance and stay somewhat upright for a little while on just about anything, including a piece of taut string or the tip of a pencil. The gyroscope technology that Mark Looney writes about doesn’t contain microscopic spinning flywheels, which is comforting to me, because if a gyroscope is going to be driving my car of the future, I’d just as soon not have a toy at the wheel.


Daniel Burton’s article discusses classic vs. integrated solutions for protecting high-precision op amps from those nasty, real-world overvoltage conditions that can ruin the op amp’s performance, or even take it out altogether. The trick is to protect the signal path adequately without creating an unacceptable loss in performance. Daniel does a good job of
describing the always present real-world phenomena that can cause a harmful overvoltage event on the op amp’s input. There’s danger crossing that bridge between the digital and real worlds, and you have to protect your circuit
“babies” so they can keep doing the jobs they’re designed for. It’s a lot like sending your kids out into the world—a notion which currently is at the top of my mind, because my triplets are all graduating from college this month. This
life-event has my mind going down some weird paths, both celebratory and anxiety-ridden. With kids, as with your circuit and system designs, you do all you can to anticipate the real-world dangers ahead and prepare them adequately—as Daniel clearly points out. Do this well, and for years to come your designs will help protect, inform and entertain our world.


Lastly, I want to thank those of you who participated in our March survey. We appreciate you taking time from your no doubt very busy schedules to offer some feedback. Your comments were overwhelmingly positive and it’s gratifying to hear that Analog Dialogue content helps you do your job. It’s clear that many of you use our publication to help solve some of your technical design problems and to find new design ideas, and we aim to keep it that way. Your feedback is helping us make the magazine’s content more accessible in today’s varied media while still remaining true to its engineer-to-engineer roots, a commitment we'll carry forth into our next 50 years.

Analog design engineers often throw around names like Chebyshev and Butterworth and Bessel when referring
to types of filter designs and most of us probably get an immediate mental image of the amplitude vs. frequency response when we hear these common filter designations. But, one might wonder, who are these folks who’ve lent their names to famous filters?
Read about them and their relative levels of fame in the Note from the Editor in the April 2016 issue of Analog Dialogue.

Sometimes you just can’t beat having a reference book on your office shelf for quick access to those formulas, graphs, concepts, circuits, and general technical knowledge that you occasionally need, but maybe don’t want to commit the brain cells to memorize. Technical books are alive and well and ADI has been a fairly prolific publisher over the last 50 years. Read about what’s available and where in the Note from the Editor in the March 2016 issue of Analog Dialogue here.

Moore’s Law, just like Analog Devices, has recently celebrated its 50th anniversary. Moore’s Law, as you probably know, is essentially the principle that the number of transistors on a chip doubles every 18 to 24 months. This breathtaking scaling has worked well for the digital world—i.e., memories and microprocessors—but not totally for interfacing with the actual physical world, which is of course analog. Read more in A Note from the Editor in the February 2016 issue of Analog Dialogue.

An increased number of applications in industrial, instrumentation, optical communication, and healthcare industries use multichannel data acquisition systems that result in increased printed circuit board (PCB) density and thermal power dissipation challenges. These applications also demand precision measurements, reliability, affordability, and portability. System designers make trade-offs among performance, thermal stability, and PCB density to maintain optimum balance and they are continually pressed to find innovative ways to tackle these challenges while minimizing overall bill of material (BOM) cost.


You can read the entire article titled: "Integrated Multiplexed Input ADC Solution Alleviates Power Dissipation and Increased Channel Density Challenges" as published in the January 2016 issue of Analog Dialogue. This article highlights the design considerations for multiplexed data acquisition systems and focuses on an integrated multiplexed input 4-channel/8-channel, 16-bit, 250 kSPS PulSAR® ADCs AD7682/AD7689 solution to address these technical challenges for space constrained applications such as optical transceivers and wearable medical devices.


We welcome your feedback in the comments section. Has this article been useful or helped you in your design? Would you like more information on this topic?


Best regards,



Are you kidding me — it’s 2016 already? It seems like just yesterday the world was stressing over the Y2K bug. Anyone remember that? Folks were worried that our dependence on computer technology would be civilization’s demise, when the calendar rolled over to the new millennium and every computer would crash. After we got safely past that apocalyptic hurdle, it seemed like the dam broke in terms of technology dependence — i.e., embedded computing — PDAs and smartphones took off around that time, and the rest is technological history. Virtually every major industry has been revolutionized by technological breakthroughs in the past 16 years, or maybe you hadn’t noticed.


Way before the Y2K non-disaster, I remember the predictions of the death of analog, as digital gradually took over. But analog and mixed-signal design is alive and well today especially since these complex embedded high-speed and low-power computing systems that we’re so dependent on need to connect to, communicate with, or sense the real world. And the real world speaks analog. 


In this issue the integrated multi-channel data acquisition solution article by Maithil Pachchigar, discusses how to solve the analog interface challenge in power- and space-constrained applications, such as wearable devices and the internet of things. These are fast-moving markets on the edge of what’s possible, and analog interface design solutions like those discussed in the article are essential to making the products work. Whether we’re talking home automation, medical technology, automotive mechanics, fitness, smart clothing—or some new market concept that we currently aren’t aware of—they all require a degree of real-world interfacing along with masterful analog design techniques, design tools (also addressed in this issue), parts, and systems.


I don’t think our society is at all nostalgic for those days 16 years ago when we feared that our growing dependence on computers would ruin everything. I never thought my wife would become addicted to smart technology, but it’s happened. It’s just way too much fun. Not to mention that it saves lives, keeps us safer and healthier, and, well, it makes life interesting since we never know what innovation is coming next. So, thanks to our readers for the amazing designs, products, and systems that you all have created over the years. Here’s to a new year of continued creativity and design excellence. We hope you continue to stay in touch with Analog Dialogue through the New Year, (note that this issue begins our 50th volume set – more to come on that milestone) and let us know how we can better help you to keep innovating. 


Read the January 2016 issue of Analog Dialogue here.


Jim Surber, editor

Why is the effect of common-mode signals at the output of an instrumentation amplifier larger than the CMRR specification? Even if you haven't run into this type of issue but normally work with differential signals, it is worth taking a couple minutes to make sure you're not misplacing your expectations regarding common-mode errors.

Learn more in "O CMRR, CMRR! Wherefore Art Thou CMRR?" as published in the January 2016 issue of Analog Dialogue.



We welcome your feedback in the comments section. Has this article been useful or helped you in your design? Would you like more information on this topic?

Best regards,

Gustavo Castro

In the December issue of Analog Dialogue we conclude the four-part series on software-defined radio design. The authors bring the algorithm and hardware together, and to life, and take their radio for a real-world test drive. This is the culmination of a journey that has taken us from simulation to prototyping to production-worthy design, and now we see it in action. This issue also features an article on the critical role that precision bipolar DACs serve in calibration and control functions in a multitude of applications from motor control to industrial automation. Several system block diagrams are explored with a focus on the design considerations for the DAC functions involved therein.