Electronic Devices and Circuits

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1 Electronic Devices and Circuits I.J. Nagrath

2 Electronic Devices and Circuits I.J. NAGRATH Adjunct Professor Former Deputy Director Birla Institute of Technology & Science Pilani New Delhi

3 ELECTRONIC DEVICES AND CIRCUITS I.J. Nagrath 2007 by PHI Learning Private Limited, New Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN The export rights of this book are vested solely with the publisher. Sixth Printing º º º October, 2012 Published by Asoke K. Ghosh, PHI Learning Private Limited, M-97, Connaught Circus, New Delhi and Printed by Rajkamal Electric Press, Plot No. 2, Phase IV, HSIDC, Kundli , Sonepat, Haryana.

4 Contents Preface ix 1. Semiconductors, Diodes and Diode Circuits Introduction to Electronics Typical Electronic Systems Classification of Electronic Systems and Devices The Future Conduction in Solids Doped Semiconductors Junction Diodes DC Analysis of Diode Circuits Zener Diode as Voltage Regulator Diode Circuits with Time-Varying Sources Transition and Diffusion Capacitances Switching Characteristics of a Diode Special Purpose Diodes Rectifiers and Power Supplies Filters Some Diode Wave Shaping Circuits Additional Examples 61 Problems Transistors and Other Devices Introduction Bipolar Junction Transistor (BJT) Junction Field Effect Transistor (JFET) and Metal Oxide Semiconductor Field Effect Transistor (MOSFET) 94 iii

5 iv Contents 2.4 Manufacturing Integrated Devices and Circuits Four-Layer Devices Thyristors Additional Examples 114 Problems Small-Signal Models, Amplification and Biasing Introduction Small-Signal Transistor Models Hybrid-p Model h-parameter Model Transistor Biasing Constant Current and Current Mirror Circuits Bias Design, AC Gain, Input Output Impedances Some Special Circuits Darlington Pair Feedback Pair Emitter Coupled Pair CMOS Circuits Additional Examples 191 Problems Small-Signal Amplifiers Frequency Response Introduction Single-Stage RC-Coupled Amplifier Frequency Response Tuned Amplifier Gain Bandwidth Product Multistage Amplifiers Cascode Amplifier (CE-CB Configuration) Additional Examples 256 Problems Large-Signal Amplifiers Amplifier Classes Class-A Power Amplifiers Transformer-Coupled Power Amplifier Class-B Power Amplifiers Complementary Symmetry Circuits Distortion in Amplifiers Class-AB Amplifiers Class-C Power Amplifiers 306

6 Contents v 5.9 New Power Transistors Additional Examples 314 Problems Feedback Amplifiers and Oscillators Feedback Concepts Types of Feedback Circuits Block Diagram Representation of Feedback Amplifiers Effect of Feedback on Impedances Some Negative Feedback Circuits Properties of Negative Feedback Stability in Feedback Amplifiers Oscillator Operation Phase Shift Oscillator Wein Bridge Oscillator Tuned Oscillators Crystal Oscillators Unijunction Oscillator Phase-Locked Loop (PLL) Additional Examples 350 Problems Operational Amplifiers Introduction Basic Operational Amplifier Differential Amplifier Basic Operational Amplifier Circuit Applications of OPAMPs Linear Applications of OPAMPs OPAMP Filters (Active Filters) Nonlinear Applications of OPAMPs Analog Simulation Additional Examples 400 Problems Multivibrators and Switching Regulators Multivibrators Analog Multivibrators Timer Power Supplies and Regulators 429 Problems 442

7 vi Contents 9. Integrated Circuits Fabrication Introduction Pre-Fabrication Stage IC Fabrication The Planar Processes Illustration A Simple IC Fabrication Monolithic Transistors Bipolar Fabrication of MOSFET Monolithic Diodes Integrated Resistors Integrated Capacitors Metal Semiconductor Contact Characteristics of IC Components Monolithic Circuit Layout Levels of Integration 469 Problems Circuit Theory Introduction Voltage and Current Sources Resistance The Basic Laws of Electric Circuits Resistances in Series and Parallel General Methods of Network Analysis Network Theorems Step Response of RC Circuits Duality of Networks Sinusoidal Steady-State Circuit Analysis Resonance Miller s Theorem Two-Port Networks Frequency Response 512 Problems Cathode Ray Oscilloscope (CRO) Introduction Cathode Ray Tube CRO Applications 530

8 Contents vii Appendix The Ebers-Moll Model of the BJT References Answers to Problems Index

9 Preface This book is designed to be course-specific for the undergraduate students pursuing courses in Electronics and Electrical Engineering and its related disciplines. The topics are presented to meet the standards and syllabi of various universities. The background material required for the study of the characteristics and applications of the electronic devices and circuits is covered in the first chapter. It includes introduction to semiconductors both intrinsic and doped (extrinsic) the concept of electrons and holes, drift and diffusion currents and pn-junction behaviour. The devices treated in Chapter 2 are diodes (including special purpose diodes), transistors BJTs, JFETs, and MOSFETs and also fourlayered devices, i.e. thyristors. These chapters acquaint the students with theory, characteristics, and construction of the electronic devices covered. Chapter 3 contains the presentation of smallsignal modelling of transistors, dc biasing of transistors, and some special circuits. The circuitry and analysis of small signal amplifiers, power amplifiers, feedback amplifiers, and oscillators are covered in Chapters 4 6. The circuits of both types of transistors are treated together in each of these chapters. Operational amplifiers and their parameters, differential amplifiers, and their linear and nonlinear applications form the contents of Chapter 7. Special circuits (multivibrators and switching regulators) and compound configurations of various kinds find a detailed treatment in Chapter 8. Chapter 9 is devoted to IC fabrication technology. A short but comprehensive presentation on circuit theory is offered in Chapter 10, primarily for quick reference or for teaching purposes where it forms part of the courseware. Finally, the concluding Chapter 11 offers a brief treatment of Cathode Ray Oscilloscope, so often required for practical measurements. The treatment of the topics throughout is succinct, to the point, yet well-explained and rigorous. The author acknowledges with thanks the efforts of the editorial and production teams of Prentice-Hall of India towards bringing out this book in excellent form. The feedback from the readers towards improvement of the book will be gratefully acknowledged by the author. I.J. NAGRATH ix

10 1 Semiconductors, Diodes and Diode Circuits 1.1 INTRODUCTION TO ELECTRONICS Electronics is a very wide field embracing almost all walks of human endeavour. In a way, electronics is the branch of electrical engineering which employs devices in which current flow is due to the controlled flow of charge carriers in a gas, in vacuum or in semiconductors. Electronic devices came into existence in the beginning of twentieth century. These devices used gaseous or vacuum medium for the flow of negatively charged particles, electrons. These devices were widely used for communications, controls and computers. A major breakthrough was achieved in the field of electronics when it became possible to use semiconductors such as silicon and germanium for making electronic devices. The semiconductor devices are smaller, cheaper, more reliable and consume less power than the vacuum or the gaseous devices. Further developments in the semiconductor technology made it possible to integrate a large number of devices in a small silicon chip, known as Integrated Circuit (IC). Today, the number of devices on a chip has gone well beyond ten million. The integrated circuits have revolutionized the field of electronics and it will not be unrealistic to call the present age as the electronics age. The impact of developments in electronics can be gauged from the availability of personal computers, which have tremendous capabilities as compared to computers in 1950s and 1960s, which occupied large space, consumed large power and costed millions of dollars. The major areas of application of electronics are communication, controls and computers, although it has invaded almost every field in our modern living. 1.2 TYPICAL ELECTRONIC SYSTEMS As human beings, we are interested in communicating with people around us. If the persons with whom we want to have communication are closeby, such as in a small classroom, we can 1

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