DESIGNING WITH FIELD-EFFECT TRANSISTORS DESIGNING WITH FIELD-EFFECT TRA~SISTORS SILICONIX INC. Editor in Chief Arthur D. Evans McGRAW-HILL BOOK COMPANY New York St. Louis San Francisco Auckland Bogota Hamburg Johannesburg London Madrid Mexico Montreal New Delhi Panama Paris Sao Paulo Singapore Sydney Tokyo Toronto Library of Congress Cataloging in Publication Data Siliconix Incorporated. Designing with field-effect transistors. Includes index. 1. Field-effect transistors. 2. Transistor cir­ cuits. 3. Electronic circuit design. I. Evans, Arthur D. II. Title. TK7871.95.S54 1981 621.3815'284 80-15690 ISBN 0-07-057449-9 Copyright ® 1981 by McGraw-Hill, Inc. All rights reserved. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. 567890 KPKP 89876543 The editors for this book were Tyler G. Hicks and Geraldine Fahey, the designer was Elliot Epstein, and the production supervisor was Sally Fliess. It was set in Baskerville by The Kingsport Press. Printed and bound by The Kingsport Press. CONTENTS Preface lX 1 FIELD-EFFECf TRANSISTOR THEORY 1 2 PARAMETERS AND SPECIFICATIONS 25 3 LOW-FREQUENCY CIRCUITS 61 4 HIGH-FREQUENCY CIRCUITS 137 5 ANALOG SWITCHES 193 6 VOLTAGE-CONTROLLED RESISTORS AND FET CURRENT SOURCES 233 7 POWERFETs 255 8 FETs IN INTEGRATED CIRCUITS 281 INDEX 289 v I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I CONTRIBUTORS Written by the Applications Engineering Staff of Siliconix Incorporated Editor in Chief ARTHUR D. EVANS Contributors Arthur D. Evans (Chapters 1, 2, and 5) Walt Heinzer (Chapters 3 and 6) Ed Oxner (Chapter 4) Lee Shaeffer (Chapters 7 and 8) vii PREFACE The purpose of this book is to aid the electronics circuit designer in the utilization of the field-effect transistor (FET). Since its emergence from the development laboratory in about 1962, the FET has become an important and widely used component in the electronic industry. With its importance increasing annually, both as a discrete component and in integrated circuits, it is essential that the serious circuit designer have an insight into how the FET behaves under different circuit and environmental conditions. It is also helpful to understand how its physi­ cal and electrical characteristics are interrelated. This book goes just deep enough into FET theory to provide that insight. Mter the introductory chapter describing how the device works, the interrelationship of the various FET characteristics and how they relate to typical data sheet specifications is discussed. Subsequent chapters deal with various categories of circuit applica­ tions of the FET. The order of these application chapters is rather arbi­ trary; each chapter stands on its own. Detailed circuit design examples are given to illustrate applications. As this book was being readied for publication, the availability of FETs designed for power applications was expanding rapidly. The chap­ ter on Power FETs spotlights this relatively new field. Art Evans ix 1 FIELD-EFFECT TRANSISTOR THEORY 1-1 Introduction 1-2 The Junction FET 1-3 The MOSFET (Insulated-Gate FET) 1-4 FET Symbols 1-5 Physical Characteristics of FETs 1-6 Summary 1-1 INTRODUCTION This handbook is designed principally for the FET user. The primary emphasis has been placed on allowing the reader to learn necessary information quickly, without becoming bogged down in complicated analyses. The first two chapters provide sufficient background informa­ tion to answer many questions asked by FET circuit design engineers. The aim of these chapters is to give design engineers an intuitive sense of how to manipulate the circuits presented in the remaining chapters, which contain both theory and "cookbook" applications. Some knowl­ edge by the reader of semiconductor theory is assumed. A prior under­ standing of the concept of conduction by electrons and holes, of the "forward" and "reverse" characteristics of a p-n junction, and of the "depletion" region at a p-n junction will be helpful in understanding FET theory. There are two general types of transistors: bipolar and unipolar. The unipolar, more commonly called the "field-effect transistor" (FET), is the subject of this book. The concept of controlling the electronic con­ duction in a solid by an electric field predates the invention of the bipolar transistor. J. E. Lilienfeld filed for a patent on such a device in 1925, as shown in Fig. 1-1. W. Shockley presented a comprehensive theory 1 2 DESIGNING WITH FIELD EFFECT TRANSISTORS P.tented Jaa. 28, 1930 1,745,175 UNITED STATES PATENT OFFICE .JUI.I'O'8 EllOAB LILIElI'J'ELD, OJ' BROOnYlI, NEW YOBlt xmBOD AlrII APPARATUS rOB CONTROLLING ELECTRIC C11l1.BEl1'TS .6»Jl,:Atloa lied Octo.er " 1828, 8eriall1'o. 140,383, aad. ia. Cu.ada Octoltel' It, 1915. The invention relates to a method of and receiving circuit in which the novel ampli­ apparatus for controlling tho flow of IlR clec- fier is em ' ·· ..1 for two st."". n' ·.<lio ire­ tric current between two terminals of an clec- quency a trically conducting solid by establishing a cation. M • third I?otcntial between said terminals; and Refe., is partIcularly adaptable to the amplification a hase II of oscillating current. such as prcvail, for rill I. for eDlllple, in radio communication. Hereto- sllrfnce fore, thermionic tubes or vah'es ha,·. been thereof a.1====j..J 10 generally e!'lploy~ for thi~ ,.. (~ . j'. - ~ II the present Invention has for 'oY"'" .L..____ .....I pense entirely with dev: .~t7' • transmission of pl. space and p' INVENTOR 1. aetcrwr an jr rlul,;us Ed!fJr ldl"enleld &.- BY • ~ oy 14 in the • two pieces .11e said piece •• "kness appro:.i- 18 .1 rart of an inch . -~l--------------tlll 1 II I-::....-~ foi is arranged to • -- - !.... ~i'per surface of the glass 80 . both of the coatings 11 and 12, the .medinte upper surface portion of the .. IS" 10. nnd the e.l!!e of the foil l:l is pro­ vided a film or coating 15 of a compound II ing menns at .. predetemline~C -p~t;nti~i h'!o\"ing ~he property of acting in conjnnction s;; which is to be substantially in e:.cess of a With Sll1d metal foil electrode as an element potel ..•. •. -. .' aid of uni-directional conductivih·. That is to eire. Although the word "TRANSISTOR" had say•. this conting is to be electrically con­ TI .ill ductl~e and pos...,ss also the property, when 40 best not been coined yet, it appINITS that the lec~ tlssorintt'd with other snituhlp ron,luctors. of ::to tion "Field Effect" Tran,isror concept pre- io estahlishing at the surface of contact a con­ Whit sidereble drop of potential. The thickness Fi dates the inwmtion of the Bipolar Ltly of the film, morco"er, is minute and of such wa, the a de/n'ee that the elrticnl conductivity +­ " Dove Junction TranliJltor by a few yeafS. of therethru would he in !lenccd by applying ~5 thereto An electrostatic force A suitable es;; (say about 23 yearsO i ng material for this film and especblly suitable the voltall'! characteristics of an amplifier in conjunction with aluminum foil, is a com~ as .hown in Fig. 1. pound of copper and sulphllr. A com·enient· N Fig. 3 is a diagrammatic view of a radio way of pro"iding the film onr the coatinll:s 100 FIGURE 1-1 "FET" patent. FIELD-EFFECT TRANSISTOR THEORY 3 of the field-effect transistor in 1952.2 However, the commercial availabil­ ity of the FETin the early 1960s followed the bipolar transistor by 8 or 10 years. The superior performance of the FET in many circuit appli­ cations previously utilizing bipolar transistors or vacuum tubes resulted in a rapid growth in its acceptance as an important electronic component. Several types of semiconductor materials have been used for making FETs: silicon, germanium, gallium arsenide, and others. By far the most widely used is silicon, and unless otherwise specified all device types discussed in this book are silicon types. The field-effect transistor (FET) is a class of electronic semiconductor device in which the conduction of a "channel" between source (S) and drain (D) terminals is controlled by an electric field impressed upon the channel via a gate (G) terminal. The conducting channel may utilize n-type carriers (electrons) or p-type carriers (holes). The electric field which controls the channel conduction may be introduced via a p-n junc­ tion (for a 'junction" FET), a metal plate separated from the semicon­ ductor channel by an oxide dielectric (for a metal-oxide-semiconductor FET), or a combination of the two methods. The polarity of the control­ ling electric field is a function of the type of carriers in the channel. A FET "family tree" is shown in Fig. 1-2. Junction Insulated gate Depletion Depletion Enhancement FIGUR.E 1-2 FET family tree. 4 DESIGNING WITH FIELD EFFECT TRANSISTORS 1-2 THE JUNCTION FET A section view of a junction field-effect transistor UFET) is shown in Fig. 1-3. This structure contains, between the source and the drain con­ tacts, an n-type "channel" embedded in a p-type silicon substrate. If it is assumed that the p-n junction forms a barrier to current flow, then it can be seen that channel conduction is a function of the channel width, length, and thickness and of the density and mobility of the carri­ ers.