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Editors' NotesVolume 39, Number 4, 2005



We’re winding down the celebration of the 40th anniversary of Analog Devices, Inc., but inspection of your calendar will confirm that—by the time you receive these printed pages—Analog Dialogue will be launched well into its 40th year of existence (and eighth year on line) As a final reminder of ADI’s 40th, if you’re interested in the high points

of our corporate history, the spread on pages 10-11 of the last issue, Volume 39, Number 3, depicts the contents page of a time line accessible on the Web (www.analog.com/timeline); in it you can click on any year to access a brief audiovisual clip reviewing some of that year’s major corporate events.

This publication has served its several generations of readers well—offering in-depth articles on design, technology, and applications of ADI’s many innovative products, brief introductions to hundreds of significant new products, and a growing potpourri of useful information of all kinds, from data-sheet revisions and links to articles in the trade press to book reviews and patent grants.

Interestingly, the arrival of the Company’s 40th anniversary showed us an unheralded additional value of Analog Dialogue: its usefulness to us as a cumulative history of our products and technologies—a fount of information for nurturing the retrospective activities of the celebration (for example, the above-mentioned timeline). Although it also reminded us of the occasional lost opportunity and no-go setback, it is a remarkable chronicle of progress. In the coming year, part of our celebration will be to share the early parts of the story with those of you who were too young to experience it and to refresh the memory of those who enjoy nostalgia.


In this growingly “digital” age, the lay world has increasingly come to believe that “analog is antique.” We sometimes are asked “When are you going to change your name to something more modern?” In actuality, everything we make is an analog device; analog is the tangible world of time, space, matter, and energy—even a “digital” processor has concerns about power supply, heat dissipation, speed, and threshold levels. Digital signal processing is the processing of analog signals by applying programs, logic, and symbols to analog variables in a physical system (such as a radio, camera, CAT scanner) comprising such analog devices as amplifiers, converters, and DSPs.

So, if the digital world grows, the future must also look bright for analog. But don’t take our word for it. As a precursor to the Dialogue’s fortieth year of celebration, we asked our sage and analog champion, Dr. Barrie Gilbert, ADI Fellow, to look into his crystal ball and give us a vision of the future. In the pages that follow, you will experience a futuristic story he has woven, imagining the pervasiveness and ever-bright possibilities of analog technologies and designs—and their human designers.

Dan Sheingold (dan.sheingold@analog.com)



No signal chain would be complete without sensors or actuators, and the generic signal chains shown on our four 40th anniversary commemorative covers are no different. The first quarterly issue featured digital signal processors; the second featured A/D and D/A converters; and the third featured amplifiers and linear circuits. This, the fourth and final issue, features the input- and output circuitry.

Few circuits simply crunch numbers—instead they process real-world signals, such as voice, music, or video; or data, such as temperature, pressure, or acceleration. Furthermore, circuits must also communicate with other circuits that may operate in remote locations or hazardous environments. Thus, this issue discusses system considerations encountered in industrial measurement and control, laboratory instrumentation, communications, computers, and other signal-processing applications.

The first article in this issue shows how digital isolators can enable safe transmission of serial data between systems that may be separated by long distances. Galvanic isolation is often required to break ground loops, protect the system from high-voltage transients, reduce signal distortion, and enhance physical safety. The digital isolation technology described here uses chip-scale transformers made from CMOS metal layers, plus a gold layer that is placed on top of the passivation. A high breakdown polyimide layer underneath the gold layer insulates the top transformer coil from the bottom. High-speed CMOS circuits connected to the top and bottom coils provide the interface between each transformer and its external signals.

The second article shows how a dual-axis accelerometer can sense an impending crash and protect a personal media player from being destroyed. It describes a novel technique that calculates differential acceleration and—if excessive—parks the read/write head of a hard disk drive, thus protecting the head and the platter from damage. The acceleration is sensed by a polysilicon, surface-micromachined structure built on top of a silicon wafer. Polysilicon springs suspend the structure over the surface of the wafer and provide resistance against acceleration forces. Deflection of the structure is measured using a differential capacitor formed by fixed independent plates in relation to plates attached to the moving mass. The complete single-chip accelerometer includes the sensor and all of the signal-conditioning circuitry required to measure acceleration.

The third article shows how implementing a precision weigh scale may not be as easy as it first seems. Typical weigh scale resolution is only 1:3,000 to 1:10,000, so a 12- to 14-bit ADC would seemingly be adequate. A closer examination, however, shows that a 20-bit ADC is really required. Designers must consider weigh-scale system specifications including noise, dynamic range, offset drift, gain drift, and filtering. The most common weigh-scale implementation uses a bridge-type load-cell sensor, with voltage output directly proportional to the weight placed on it. A typical load-cell is a 4-resistor bridge circuit with at least two variable arms, where the resistance changes with the weight applied, creating a differential voltage at a common-mode level of one-half the supply voltage.


By the end of 2006 we plan to have every issue of Analog Dialogue available in our online archives, including all of the rare and long-out-of-print volumes from 1967 on. Also, be on the lookout for a searchable index and perhaps some contests and promotions for you, our loyal readers, to help us celebrate 40 years of Analog Dialogue. We welcome your suggestions.

Scott Wayne (scott.wayne@analog.com)


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