Williams 06 - 1995 - EDN - A designer's guide to Innovative Linear Circuits.pdf - Książki - neo666x

INTRODUCTION

Writing about applications, like all engineering tasks, involves compromises and limitations. An author

must, for example, consider the editorial standards of the publication he writes for, his readers' interests,

his employer's commercial aspirations, and the time available. And then, the author must simply desire

to do the work. Without this drive, there's no point in even starting.

Balancing these sometimes conflicting considerations can be difficult, but not unduly so. You can, for

example, balance a publication's needs, its readers' interests, and your employer's needs. After all, a

successful publication must reflect its readers' interests. An astute employer will understand that serv-

ing the readers' interests can benefit the company as well. Such an employer realizes that the true value

of publishing an applications article can't be measured in the immediate sales the article generates.

Instead, a stream of useful articles sponsored by a certain company lets readers know that the compa-

ny can provide solutions to engineering problems. Such articles are a subtle and effective form of adver-

tising. Instead of generating immediate sales, applications articles establish credibility. They become

powerful long-term sales tools because they win customers' confidence by portraying the company as

a problem-solving ally.

Of course, producing an applications article takes a lot of time. Typically, I need more than 100 hours

to complete each article, and some articles take 200 to 300 hours. The actU'al writing takes up less than

10% of all the time I spend developing an article. The bulk of my article-development time is consumed

by the lab work that I write the article around.

Because engineers are basically skeptical, a good author must address them in the language of work-

ing circuits and systems: The author must use laboratory-based material that's worked out and document-

ed. Too, it's important to know when to stop. The author should work out his material well, but he doesn't

have to refine it to the highest possible degree. An article's primary function is to be a catalyst-to

start the reader thinking.

Finally, an author must simply desire to do the work. Applications work allows more freedom and

flexibility than almost any other engineering job. And conceiving ideas and developing them into cir-

cuits is an enjoyable way to spend one's time.

Doing applications work has allowed my hobby and my vocation to become an indivisible entity, hope-

fully to the benefit of EDN and its readers. This state of affairs is made possible by you, EDN's readers,

and I appreciate your support.

VJ. ·,lliJv~-

James M Williams

Linear Technology Corp

Milpitas, CA

PREFACE

Analog design is not dead. Neither is interest in it. Although digital design techniques have become

the primary focus of most electronics trade journals and design magazines, the need for linear applica-

tions material remains strong. Designers continue to make significant advances in linear ICs, and using

these new devices is anything but a trivial task.

EDN has regularly published design features that help readers get the most from the latest, most

sophisticated linear ICs. And EDN's readers have written time and time again to thank us for continu-

ing to print linear-design articles as well as for introducing the latest digital techniques.

Among all the contributors of linear-design features to EDN, one author stands out, both because

of the large volume of material he's written for EDN and because of the originality and usefulness of

his ideas. This man is Jim Williams. Since he first wrote for EDN in the mid 1970s, Jim has become

a regular contributor and a favorite with readers. In fact, many readers have requested that we publish

a compilation of his work. This book is a direct result of such requests.

In this preface, EDN would like to thank Jim for the time and effort he's invested in the many articles

he's written for us. We hope that you find this material useful; we know that by reading it, you'll gain

a similar appreciation for this man's talents.

EDN Staff

This book is dedicated

to the memory of

EDN Associate Editor George Huffman

EON, a Cahners Publication, Cahners Building, 275 Washington St, Newton, MA 02158

TABLE OF CONTENTS

GENERAL ANALOG CIRCUIT DESIGN

Test your analog-design IQ ............................................................. 3

Use comparator ICs in new and useful ways .............................................. 13

AUDIO

Use off-the-shelf linear ICs for sophisticated audio designs ................................... 23

CONTROL

Analog design techniques suit process-control needs ........................................ 28

Apply sample-and-hold techniques for elegant design solutions ............................... 35

Current-source alternatives increase design flexibility ........................................ 43

Designer's Guide to: Temperature control ................................................ 49

Employ pulse-width modulators in a wide range of controllers ................................ 59

Expand linear circuit functions with nonlinear design schemes ................................ 64

Exploit D/A converters in unusual controller designs ....................................... 69

ISOLATION TECHNIQUES

Piezoceramics plus fiber optics boost isolation voltages ...................................... 7 6

Transformers and optocouplers implement isolation techniques ............................... 81

SENSING

Designer's Guide to: Temperature sensing ................................................ 89

Exotic-transducer interfacing calls for proven techniques ..................................... 97

Increase your design options with analog-MUX ICs ...................................... . 103

Interface nonstandard sensors using standard circuit methods ............................... . 109

SIGNAL CONVERSION

Conversion techniques adapt voltages to your needs ...................................... . 115

Heavy-duty power supply regulates either voltage, current or power ......................... . 127

High-powered booster circuits enhance op-amp output ................................... . 131

Low-cost, linear AID conversion uses single-slope techniques ............................... 138

SIGNAL SOURCES

A few proven techniques ease sine-wave-generator design ................................... 143

Low-cost dual, quad FET op amps implement complex functions ............................ 153

TEST AND MEASUREMENT

An elegant 6-IC circuit gauges relative humidity ...................... .

Designer's Guide to: Temperature measurement ...................... .

Low-cost instrument measures 4-decade power ...................... .

161

165

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