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Analog Dialogue

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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.

Part 4 of the “Four Quick Steps to Production: Using Model Based Design for Software Defined Radio” concludes the article series by introducing the final step in a SDR design - generating C and HDL code out of the Simulink model and integrating the code into the SDR platform’s software and HDL infrastructure.  This article highlights three very useful and powerful tools: MATLAB Coder and HDL Coder provided by MathWorks and Board Support Package provided by Analog Devices. By reading this article, you will learn how these tools work together to complete the final production.


When it comes to content, Part 4 walks through the steps of partitioning the ADS-B model presented in the previous parts of the series into hardware and software components, optimizing the model for code generation, generating C and HDL code using MATLAB Coder and HDL Coder and finally deploying the code onto the SDR system.  Then it introduces the Analog Devices HDL Workflow Advisor Board Support Package (BSP) that provides seamless integration of Simulink generated IPs into the Analog Devices AD9361 SDR platforms HDL reference designs. The end result is a fully functional SDR platform capable of decoding live commercial aircraft ADS-B traffic. This example system shows that the Model-Based Design workflow in combination with the Analog Devices AD9361/AD9364 integrated RF Agile Transceiver programmable radio hardware can help design teams develop working radio prototypes more quickly and less expensively than using the traditional design methodologies.


Please check out Part 4 of the article series to learn more about the final steps of taking a SDR system from simulation to production.

In Part 3 of the Four Quick Steps to Production: Using Model-Based Design for Software-Defined Radio article series we employ two very useful tools provided by ADI. These two tools not only help us verify the ADSB algorithm with live data, but also have been well received and widely adopted by ADI partners and customers.


First is the MATLAB and Simulink IIO System Object. The IIO System Object is based on the libiio library and is designed to exchange data over Ethernet with an ADI hardware system connected to a FPGA/SoC platform running the ADI Linux distribution. With this tool, the users can easily stream the data from ADI hardware to MATLAB, and then the post processing will happen inside MATLAB. Before this tool was developed, in order to verify the data from real hardware, the users had to first save some data on the Linux side, and then import the data into MATLAB. Based upon this interface, we have created several MATLAB and Simulink models for users to try out the hardware in the loop simulation, which is an important step in model-based design.


The AD9361 filter design wizard helps you design the 128-tap FIR filter on the Tx and Rx paths of AD9361. This digital FIR filter is very much required to maximize the system performance, but designing it is quite complicated, since there are various combinations on the signal paths, consisting of analog filters, as well as several digital half band filters. Before this tool was developed in late 2013, customers who needed to design an FIR filter had to ask for help from the ADI designers, which was not a very efficient way to solve each individual problem. Nowadays, with this tool, the users only needs to input the basic filter specifications, and the tool will make the design for them, so that everyone can easily implement their own design and change it as often as they want. So far, this tool has been a required dependency by two MathWorks hardware support packages: Zynq SDR Support from Communications System Toolbox and Analog Devices RF Transceivers Support from MATLAB and Simulink.


Please check out the Part 3 article to see how to use the MATLAB/Simulink IIO System Object to perform hardware in the loop simulation, and how the AD9361 filter design wizard is used to improve the SNR on receiver path.

In this new article, the single-ended to differential circuit is even made more versatile with adjustable common-mode and greater output dynamic range. The article discusses how it is accomplished, the considerations in choosing the right amplifiers, and the stability and bandwidth of the configuration. With the versatility of a simple single-ended to differential circuit, high performance and precision, this circuit can have wide applications in the analog front end of data acquisition circuits.


Versatile, Precision Single-Ended-to-Differential Signal Conversion Circuit with Adjustable Output Common Mode Boosts Sy…

In the November issue of Analog Dialogue we present Part 3 of our ongoing series on software-defined radio, covering validation of the system algorithm using live data as input and some powerful software and system development tools provided by ADI, MathWorks, and Avnet. If you’ve read Parts 1 & 2, you’ve seen this SDR system steadily progress from initial prototyping toward a production design. This radio will soon be ready for its real-world test drive, so stay tuned (pardon the pun). The second article revisits an earlier design of a versatile, low power single-ended–to–differential converter circuit. This time around, this useful converter circuit is made even more versatile. The authors have addressed using the circuit in applications that require greater output dynamic range, such as in signal conditioning temperature and pressure sensor outputs. They also explain how to implement an adjustable common mode which is very convenient when interfacing signals to some ADCs where the reference determines its full-scale range.


Check out the November Analog Dialogue here



In the  October issue of Analog Dialogue is online and we continue the series on model-based software-defined radio system design with the objective of building a platform that will receive and decode the automatic dependent surveillance broadcast (ADS-B) transmissions from commercial aircraft. This month, our designers analyze the Mode S Extended Squitter format used in ADS-B signal transmissions and explain how to capture these Mode S signals with a receiver platform based on the AD9361 RF agile transceiver IC.
The authors then use MATLAB and Simulink tools to develop an algorithm that can decode the messages. We’re one step closer…


Our second article explains that when external overvoltage conditions are applied to an amplifier, ESD diodes can be the last line of defense between your amplifier and the catastrophic damage that can result from electrical over stress. Our expert shows us how ESD cells are implemented in an amplifier device, discusses their characteristics, and shows how they can improve the robustness of a
design. This article will interest everyone who wants and needs to enhance the survival factor of their amplifier circuit.


Okay now, so how diverse can two articles be?


Really, they’re as diverse as ADI’s customer base. Looking back through the Analog Dialogue archives, I saw an interesting note written a few years back by then editor Dan Sheingold on the history of Analog Dialogue, where he points out that its original 1967 subtitle was A journal for the exchange of operational amplifier technology. I think you’d agree that this suggests a pretty limited focus. And now, as evidenced by the two articles in this issue, Analog Dialogue addresses a wide variety of engineering concerns — from designing a complete SDR system that pulls air traffic control communications out of the ether, down to a very specific amplifier hardware refinement technique that protects an amplifier from overstress. My apologies that I’ve yet to come across an article on protecting engineers from overstress. That really might be just ahead of what’s possible.


ADI’s product diversity has greatly expanded over the years but one thing hasn’t changed: the need for us to provide peer-to-peer technical forums where engineers exchange design ideas, suggest improvements, discuss design techniques, demystify new technologies and, yes, even analyze full-blown reference designs and source code. Analog Dialogue will continue to diversify and evolve to meet that need.


Check out the October Analog Dialogue here.

The September 2015 issue of Analog Dialogue contains…


The first of a four-part article series that explores a model-based design technique for wireless software-defined radio systems. This article tackles the complete system design: the RF signal chain, the digital processing, and the system software. The series, jointly written by ADI and two of our systems resource partners, Xilinx and MathWorks, presents a more holistic view of system design than what you might expect from Analog Devices, especially if you consider us just a component supplier. The authors will walk through the SDR system design process utilizing reference hardware and operating software, functional device models, and system code development tools. This design journey will demonstrate a working radio programmed to receive and decode automatic dependent surveillance broadcast (ADS-B) signals from commercial aircraft in the vicinity — and fully discerning the aircraft’s position, altitude, and velocity.


A second article on energy harvesting systems explores the technique of capturing and storing energy from a host of ambient sources such as solar, mechanical vibrations, temperature, movement, and RF signals. Energy harvesting technology has advanced such that now it’s feasible and economical to capture this “free” energy even though it contains very small quantities of power, and use it to perform periodic functions and supplement replace batteries in some electric equipment. This article looks at the block diagrams and design considerations involved with the highly efficient power regulators required for managing the periodic and varying energy levels of captured energy and converting it to stable and usable output power.

Contemplating these two articles brought to mind the crystal AM radios I had as a kid in the early 1960s. These sets could be considered the lowest form of radio receiver technology (outside of some folk’s alleged AM radio reception via loose tooth fillings). These simple radio circuits harvested their audio power by rectifying the modulation envelope of the received AM signal. I remember having a couple of sets resembling rocket ships and one fashioned as a Coca-Cola® vending machine. I’d venture to say that a fair number of us budding “radiomen” who were totally intrigued by these primitive radio receivers went on to become the design engineers who ultimately contributed to the development of software-defined radio technology.

Soon, SDR and energy harvesting will undoubtedly cross paths as the demands of The Internet of Things (IoT) will require self-powered networks and radio transceivers. So energy harvesting radios will once again rule, although software-defined, not cat whisker-defined. And they will likely not resemble Coke machines, but will most certainly be embedded in them.

Check out the September Analog Dialogue  here.

Engineers that must design for very high temperature environments -- such as down-hole oil and gas, avionics, heavy industrial, and under-hood automotive -- face quite a challenge when it comes to making high precision circuits that are also reliable, compact and low power.  After all, 210°C/410°F is a great temperature to cook a pizza, but standard electronic circuits are not going to fare very well!  At these temperatures there are multiple physical phenomena working against you when it comes to the performance and reliability of integrated circuits.  Gustavo.Castro and I described many of these factors in our 2012 article  "High-Temperature Electronics Pose Design and Reliability Challenges", which I would recommend reading for a good overview of the applications, challenges, solutions and best practices.


Since 2012 a lot of progress has been made in this space.  Analog Devices has released several new products for high temperature environments, enabling a signal chain for "sensor-to-bits", including sensor signal conditioning, analog-to-digital conversion and MEMS inertial sensors.  To that end, we are excited to introduce our first reference design for high temperature precision data acquisition, based around the new AD7981 High Temperature 600 kSPS SAR ADC:




In the August 2015 edition of Analog Dialogue, Maithil Pachchigar (maithil) and I present a new reference design for high temperature data acquisition, characterized from room temperature to 175°C. This circuit is intended to be a complete data acquisition circuit building block that will take an analog sensor input, condition it, and digitize it to an SPI serial data stream. It is versatile enough to be used as a single channel, or it can be scaled for multiple channel simultaneous sampling applications. Recognizing the importance of low power consumption, the power consumption of the ADC scales linearly with the sample rate. The ADC can also be directly powered from the voltage reference, eliminating the need for an additional power rail and the associated power conversion inefficiencies. This reference design is available off the shelf (CN0365) to facilitate testing by designers and includes all schematics, bill of materials, PCB artwork, and test software.  You can read the full text of the article at "A Low Power Data Acquisition Solution for High Temperature Electronics Applications"


You can see this board in action in a demo that we made that incorporates the data acquisition reference design along with the eval board for our high temp MEMS gyroscope, the ADXRS645:



For more information on high temperature products from Analog Devices, visit

One of the more difficult aspects of PLL synthesizer applications is dealing with spurious signals and using frequency planning to avoid unwanted interference. This article details a simple, yet very effective optimization technique for avoiding spurious signals from the Analog Devices family of integrated PLLVCO products. The article also introduces our new, free frequency planning software: ADIsimFrequencyPlanner.



For more information on this application, please read, Analyzing, Optimizing, and Eliminating Integer Boundary Spurs in Phase-Locked Loops with VCOs at up to 13.6 GHz, which was recently published in the August 2015 issue of Analog Dialogue. We hope that you find this useful and look forward to your feedback.