Principles of T ransistor Circuits This Page Intentionally Left Blank Principles of Transistor Circuits Ninth Edition Introduction to the Design of Amplifiers, Receivers and Digital Circuits S. W. Amos, BSc, CEng, MIEE M. R. James, BSc, CEng, MIEE Newnes OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI Newnes An imprint of Newnes Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier plc group First published by Iliffe Books Ltd 1959 Second edition 1961 Third edition 1965 Fourth edition 1969 Fifth edition 1975 Sixth edition 1981 Seventh edition 1990 Eighth edition 1994 Ninth edition 2000 © S. W. Amos and M. R. James 2000 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 9HE. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data Amos, S. W. Principles of transistor circuits. – 9th ed. 1. Transistor circuits 2. Electronic circuit design I. Title 621.3815Ј30422 TK7871.9 ISBN 0 7506 4427 3 Library of Congress Cataloguing in Publication Data Amos, S. W. (Stanley William) Principles of transistor circuits/S. W. Amos. – 9th ed. p. cm. ISBN 0 7506 4427 3 1. Transistor circuits. I. Title TK7871.9A45 1994 621.381Ј528–dc20 93–50682 Composition by Genesis Typesetting, Laser Quay, Rochester, Kent Printed in England by Clays Ltd, St Ives plc Contents Preface to the ninth edition vi 1 Semiconductors and junction diodes 1 2 Basic principles of transistors 22 3 Common-base and common-gate amplifiers 53 4 Common-emitter and common-source amplifiers 65 5 Common-collector and common-drain amplifiers (emitter and source followers) 78 6 Bias and d.c. stabilisation 90 7 Small-signal a.f. amplifiers 112 8 Large-signal a.f. amplifiers 134 9 D.C. and pulse amplifiers 158 10 R.F. and I.F. amplifiers 180 11 Sinusoidal oscillators 205 12 Modulators, demodulators, mixers and receivers 227 13 Pulse generators 255 14 Sawtooth generators 281 15 Digital circuits 293 16 Further applications of transistors and other semiconductor devices 328 Appendix A The manufacture of transistors and integrated circuits 369 Appendix B Transistor parameters 381 Appendix C The stability of a transistor tuned amplifier 387 Appendix D Semiconductor letter symbols 390 Index 397 Preface to the ninth edition This ninth edition was introduced to bring the material up-to-date and to render all of the diagrams to the same standard. Some of the information from previous editions has been left out; either because it was obsolete or because it is not relevant to modern electronics. Most students are taught discrete component circuit analysis and design with silicon npn transistors as the main active devices. Although a flexibility of approach is important (i.e. to be able to use both npn and pnp devices of any semiconductor type), the redrawn diagrams have been changed to conform to the npn silicon arrangement so that the learning process does not involve unfamiliar configurations. Some of the abbreviations have been modernised, and the gate turn off thyristor introduced along with optically coupled devices. Much of the section on digital techniques has been reworked to reflect current practice. S. W. Amos M. R. James This Page Intentionally Left Blank Chapter 1 Semiconductors and junction diodes Introduction The 1950s marked the beginning of a revolution in electronics. It started with the invention by William Shockley of the transistor, a minute three- terminal device which could switch, amplify and oscillate yet needed only a few microwatts of power; it was also robust and virtually everlasting. Inevitably the transistor replaced the electron tube (valve) in all except very high power applications. The pace of the revolution was accelerated a decade later by the development of the integrated circuit or i.c. (popularly known as the silicon chip) in which transistors and other components are manu- factured and interconnected by the planar process (see Appendix A) to form amplifiers, signal stores and other functional units on a single silicon slice. The miniaturisation now possible is such that several million transistors can be accommodated on an i.c. less than 1 cm 2 . The applications of i.c.s seem boundless. They feature in activities as diverse as satellite communication and control of model railways. They are widely used in audio, video and radio equipment and they made possible the computers and microprocessors now universally employed in commerce and industry. Perhaps their most familiar applications are in digital watches, calculators and toys. This book describes the properties of the various types of transistor and shows how they can be used in the design of electronic circuits. The principles described apply to circuits employing discrete transistors and those embodied in i.c.s. To explain the properties of transistors it is useful to begin with an account of the physics of semiconductors because all transistors, irrespective of type, depend on semiconducting material for their action. 2 Principles of Transistor Circuits Mechanism of semiconduction As the name suggests a semiconducting material is one with a conductivity lying between that of an insulator and that of a conductor: that is to say one for which the resistivity lies between, say 10 12 ⍀-cm (a value typical of glass) and 10 –6 ⍀-cm (approximately the value for copper). Typical values for the resistivity of a semiconducting material lie between 1 and 100 ⍀-cm. Such a value of resistivity could, of course, be obtained by mixing a conductor and an insulator in suitable proportions but the resulting material would not be a semiconductor. Another essential feature of a semiconducting material is that its electrical resistance decreases with increase in temperature over a particular temperature range which is characteristic of the semiconductor. This behaviour contrasts with that of elemental metallic conductors for which the resistance increases with rise in temperature. This is illustrated in Fig. 1.1, which gives curves for a conductor and a semiconductor. The resistance of the conductor increases linearly, whereas that of the semiconductor decreases exponentially, as temperature rises. Over the significant temperature range the relationship between resistance and temperature for a semiconductor could be written R t = ae bT where R t is the resistance at an absolute temperature T, a and b are constants characteristic of the semiconductor material and e is the base of the natural logarithms, i.e. 2.81828 . . . The two curves in Fig. 1.1 are not to the same vertical scale of resistance. Fig. 1.1. ResistanceÐtemperature relationship for a conductor and a semiconductor