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Editors' Note—Volume 42, Number 1, 2008
GOOD READING
You’ll find the usual diversity of topics in this issue.
In “Cooking Inductively,” the topic is keeping a heating ring cool while cooking electrically. The key is to let eddy currents in the metal pot produce the heat; the heating ring is just a transformer, driven by a pair of insulated-gate bipolar transistors (IGBTs). One problem in such designs is maintaining electrical isolation between the user interface, the active circuitry, and the IGBTs. Read about an effective, economical approach using ADI’s iCoupler® technology (page 3).
You have a fast, accurate analog-to-digital converter, but it’s not performing as well as you expect. Have you considered the error produced by timing jitter—contributed by the clock source and its signal chain—at the ADC’s convert-start pin? The article on page 6 helps you think about this problem and its remedies.
Accurate high-side current sensing is necessary in applications such as motor control, solenoid control, and power management. The sensing circuitry must reject high common-mode voltages, while providing high gain and accuracy. The article on page 13 compares the pros and cons of two popular sensing-amplifier architectures in such applications.
HIGH-FREQUENCY COMMON MODE
The sea of RF energy in which we are immersed is often the source of mysterious offsets in measurements conducted using conventional instrumentation-amplifier circuitry. Although such amplifiers may be rated at 100 dB or more for low-frequency common-mode rejection, it is possible for ambient RF, picked up on the leads as a high-frequency common-mode signal, to drive amplifier low-level input stages into nonlinear regions, developing mysterious dc- and low-frequency errors.
This matter has been discussed in these pages a number of times, most notably in Analog Dialogue, Volume 37, Number 31 (2003), where we introduced the topic and presented a reader’s observations on Page 2, then offered a set of references on Page 14. A seminal paper on the subject, presented at the 39th Annual Instrumentation Symposium in 1993 by Herman Gelbach—currently a consultant for Scanivalve Corporation—discusses the phenomenon and offers some remedies. Unfortunately, that paper is not available online—but, fortunately, the author has provided us with a revised, updated version, titled “The Contaminator of Signals— High-Frequency Common-Mode Errors,”2 and has given us permission to place it on our website, along with a brief piece entitled “What Is This Third Signal Wire and What Do I Do with It,”3 republished with the permission of Scanivalve Corporation.
Effective analog circuit design requires a strong understanding of linear devices. Linear Circuit Design Handbook4 bridges the gap between component theory and practical circuit design. Providing complete coverage of analog components and showing how to use them effectively, it serves as a useful reference for engineers involved in analog- and mixed-signal design. Analog Dialogue readers can read a sample chapter,5 posted on our website, and get a discount when they order this book directly from Newnes.6 Enter discount code 92222.
Dan Sheingold [ dan.sheingold@analog.com]
Scott Wayne [ scott.wayne@analog.com]
1 www.analog.com/library/analogdialogue/cd/vol37n3.pdf#page=2
2 www.analog.com/library/analogdialogue/archives/42-03/HFCM.pdf
3 www.analog.com/library/analogdialogue/archives/42-03/third_wire.pdf
4 www.elsevierdirect.com/product.jsp?isbn=9780750687034
5 www.analog.com/library/analogdialogue/archives/42-03/CH03-H8703.pdf
6 www.elsevierdirect.com/imprint.jsp?iid=73
