Electronic CircuitsFor Computer Engineers

Electronic CircuitsFor Computer Engineers

U. B. Mahadevaswamy V. Nattarasu Assistant Professor Assistant Professor

Department of Electronics and CommunicationSri Jayachamarajendra College of Engineering,

Mysore 570 006, India

Sanguine Technical PublishersBangalore - 560016

2008

Price:Rs. 295.00 US $ 19.99

9 7 8 8 1 8 8 8 4 9 5 2 9

ISBN 978 81 88849 52 9

Title: Electronic Circuits: For Computer EngineersU. B. Mahadevaswamy, V. Nattarasu

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© 2008 by Sanguine Technical Publishers, Bangalore – 560 016.

Published by Lal M Prasad for SANGUINEProduction Editor: R.SubramanianTypeset in Times New Roman by Sigma Publishing Solutions, Chennai – 600 033.Printed in India at Viralam Graphics, Bangalore – 560 018.

Submitted at the lotus feet ofParama poojya Lingaikya Jagadguru

Shree Shree Shree Shivaratri Rajendra Mahaswamigalavaru,Founder president

J. S. S. Mahavidyapeeta Mysore.

In fond memory of my Grand mother Late Smt. M. S. Basamma

and My father

Late Shri T. N. Basavaraju who are responsible for what I am today.

— U. B. Mahadevaswamy

In fond memory of my ParentsLate Smt. V. Eshwari

AndLate Sri. S. M. Venkataraman

— V. Nattarasu

FOREWORD

It is a matter of immense pleasure that my colleagues Mr. U. B Mahadevaswamy and Mr. V. Nattarasu from the Department of Electronics and Communication have been able to bring out another successful book in the area of Electronics, entitled ‘Electronic Circuits’. Both the authors have been my students with vast experience in teaching and training. The topics of the book have been arranged carefully in a graded manner, with numerous examples to support the concepts. The book begins with diode circuits and covers topics in transistor amplifi ers, feedback circuits, MOSFETs , frequency response of amplifi ers, oscillators and regulated power supplies. The concepts are explained in a easy-to-understand way through illustrative examples. This book refl ects the rich experience of the authors in teaching Electronics for over two decades. I am very sure that the students will fi nd this book very easy to follow and understand.

I wish the authors all success in this new Endeavour and hope that many more publications would come out of their vast experience.

Dr. B. G. Sangameshwara Principal,

SJCE, Mysore.

PREFACE

This book is the offshoot of our rich experience of teaching a number of subjects in the area of Electronics for two decades. In this book, the various concepts of the subject are arranged logically and explained in a simple reader friendly language for proper understanding of the subject. A large number of problems with their step by step solution are provided for every concept. Illustrative examples are discussed to emphasize on conceptual clarity and typical applications are highlighted to strengthen them.

This book takes you from simple diode circuits through the analysis and design of a variety of transistor amplifi ers. Analyses of various feedback amplifi ers, principle of working and applications of MOSFETs, IC Timers, PLLs and Function generation ICs have also been covered. This book concludes with Regulated power supplies wherein different types of voltage regulators and their analysis have been presented elaborately. This book provides a simplifi ed and systematic approach to diffi cult theoretical concepts in Electronic Circuits. It can serve as an excellent reference material for design engineers. Those of you who enjoyed reading our previous book titled ‘Electronic Circuits’ would certainly enjoy this book too.

Despite the delight taken by many reviewers in fi nding mistakes, a few typo errors have managed to slip through the sieve. This suggests that more await discovery by you. We suppose that is what second editions are for.

U. B. Mahadevaswamy V. Nattarasu

ACKNOWLEDGMENTS

Our sincere pranamas at the lotus feet of his Holiness Parama Poojya Jagadguru Shree Shree Shree Shivaratri Deshikendra Mahaswamigalavaru, President, J.S.S Mahavidyapeeta, Mysore, whose divine blessings inspired us to take up and successfully complete this project.

We are grateful to Prof. M. H. Dhananjaya, Director (Technical), JSS Mahavidyapeeta who is a constant source of inspiration for us. We gratefully acknowledge all the encouragement from Dr. B. G. Sangameshwara, Principal, SJCE, Mysore in providing all the facilities and resources in drafting this book. We sincerely thank our beloved HOD Dr. R. D. Sudhaker Samuel who encouraged us to take up this project. His support and invaluable suggestions at each and every stage of drafting this book are unforgettable. We hope without his support and encouragement, this book would hardly be in its present form.

Our sincere thanks are due to Dr. D. Ganesh Rao who encouraged us to pen this book. We whole heartedly thank Mr. R. Subramanian of Sanguine Technical Publishers, who has meticulously reviewed this book and gave invaluable inputs to bring this book to its present form.

Nattarasu wishes to thank his wife Malarkodi. N for her modesty and extreme patience shown during the preparation of the draft. He greatly acknowledges the support rendered by his two Engineer daughters, Archana. N and Abirami. N and his son-in-law Mukesh Sagar. N

U. B. Mahadevaswamy gratefully acknowledges the support rendered during this project, by his teacher and well wisher Mr. C. Chamaraju, Assistant Professor, Mathematics department, SJCE, Mysore. His sincere thanks are due to Ms. Sheethal M. J and Ms. Swetha M.J, software Engineers, for their timely technical inputs, support and encouragement throughout this project. He appreciates the relentless efforts of his nephew Mr. Shashidharamurthy .G, software Engineer and his niece Ms. Indumathi, for fi nding mistakes and typo errors through several readings. He also appreciates the help rendered by Ms. K.S.Sindhu, who patiently checked the solutions of all numerical examples. He greatly acknowledges all the encouragement and support from his wife K. S. Umadevi in making this project a success. The timely support of his brother B. Chandra Shekara Murthy, Quality Control Engineer, Muscat and his mother K. P. Leelavthi and all his family members needs a very special mention.

We must thank our colleagues in the department of Electronics and Communication, SJCE, Mysore for all their suggestions towards improving the material presented.

We express our sincere gratitude to Mr. Lal M Prasad, M/s. Sanguine Technical Publishers, Bangalore for continuing to make our dreams a reality. We also thank Mr. R. Mohan and his team, M/s. Sigma Business Processing, Chennai for typesetting the material in a nice format.

Please feel free to contact the publisher at sanguine_publishers@vsnl.net for further assistance. We sincerely thank all the persons who have supported us at the right time to make this work truly marvelous.

U. B. Mahadevaswamy V. Nattarasu

CONTENTS

Diode Circuits and Special Purpose Diodes 1.1 Volt-ampere Characteristics of Diode 1 1.2 Diode Equivalent Circuit 2 1.3 Equivalent Circuit of Ideal Diode [First Approximation] 2 1.4 The Second Approximation of Diode 3 1.5 The Third Approximation of Diode 5 1.6 Clipping and Limiting Circuits 8 1.7 Positive Clipper 8 1.8 Negative Clipper 10 1.9 Biased Clipper 16 1.10 Biased Positive Clipper 17 1.11 Biased Negative Clipper 20 1.12 Combination Clipper [Biased Positive-negative Clipper] 23 1.13 Other Clipping Circuits 27 1.14 Clipping Circuit with Two or More Series Connected Diodes 27 1.15 Clipping Circuit using Voltage Divider Bias 28 1.16 Clipping Circuit with Zero Knee Voltage 29 1.17 Clamping Circuits 37 1.18 Positive Clamper 39 1.19 Negative Clamper 42 1.20 Peak-to-peak Detector 52 1.21 Light Emitting Diodes 57 1.22 Photo Diode 60 1.23 Opto Coupler 61 1.24 Laser Diode 62 1.25 The Schottky [Hot-carrier] Diode 68 1.26 Varactor Diodes 72 1.27 Varistors 75 1.28 Current-regulator Diodes 75 1.29 Step Recovery Diodes 76 1.30 Back Diodes 77 1.31 Tunnel Diodes 78 1.32 Pin Diodes 79

Transistor AC Models 2.1 Notation in Amplifi er Analysis 85 2.2 Biasing Circuits 85

2.3 Base-biased Amplifi er 89 2.4 Emitter-biased Amplifi er 96 2.5 Voltage-divider Bias (VDB) Amplifi er 96 2.6 Two Supply Emitter Bias (TSEB) Amplifi er 98 2.7 Large Signal Operation 103 2.8 Reducing Distortion using Small Signal Operation 104 2.9 AC Current Gain (AC Beta) 106 2.10 Graphical Determination of AC Beta 106 2.11 AC Resistance of the Emitter Diode (AC Emitter Resistance) 107 2.12 Graphical Determination of AC Emitter Resistance 107 2.13 Formula for AC Emitter Resistance 108 2.14 Transistor Models 114 2.15 The T Model of Transistor 114 2.16 Input Impedance of the Base 115 2.17 The π model of Transistor 116 2.18 Comments on T and π models of a Transistor 117 2.19 Analysis of Transistor Amplifi er 117 2.20 DC Equivalent Circuit 118 2.21 AC Equivalent Circuit 118 2.22 Basic Transistor Amplifi er Confi gurations 134 2.23 The h-model of Transistor 135 2.24 Relation between r′ and h Parameters 136 2.25 Variation of h-parameters 136

Voltage Amplifiers 3.1 Expression for Voltage Gain of Single Stage CE Amplifi er (VDB Amplifi er) 147 3.2 Expression for the Voltage Gain of Base-Biased Amplifi er 150 3.3 Expression for the Voltage Gain of TSEB Amplifi er 151 3.4 Loading Effect of Input Impedance 158 3.5 Multistage Amplifi er 165 3.6 Two Stage CE Amplifi er 165 3.7 Swamped Amplifi er 170 3.8 Two Stage Feedback 180 3.9 Trouble Shooting 184

CC and CB Amplifiers 4.1 Common Collector (CC) Amplifi er (Emitter Follower) 191 4.2 Circuit Operation 192 4.3 AC Equivalent Circuit of Emitter Follower 192 4.4 Negative Feedback in Emitter Follower 194 4.5 Expression for Voltage Gain 194 4.6 Current Gain in Emitter Follower 195

4.7 Input Impedance of Emitter Follower 195 4.8 Output Impedance of Emitter Follower 197 4.9 Emitter Follower with Collector Resistor RC 209 4.10 Representation of Amplifi er by Thevenin Equivalent at Input and Output Sides 209 4.11 Cascading of CE and CC Amplifi ers 211 4.12 Darlington Pair 216 4.13 Darlington Emitter Follower 218 4.14 Analysis of Darlington Emitter Follower 219 4.15 The Common-base Amplifi er 222 4.16 Analysis of CB amplifi er 224 4.17 Loading of Signal Source 227 4.18 Important Characteristics of CB Amplifi er 228 4.19 Applications of CB Amplifi er 228 4.20 Summary of the Transistor Amplifi er Confi gurations 234

Power Amplifier 5.1 Classifi cation of Amplifi ers 239 5.2 Classes of Operation 239 5.3 Types of Interstage Coupling 242 5.4 Frequency Range of Operation 243 5.5 Signal Level 244 5.6 The DC and AC Load Lines 245 5.7 Power Gain 257 5.8 To Express Power Gain in Terms of Voltage and Current Gains 257 5.9 Class A Power Amplifi er 259 5.10 Impedance Matching using Transformer Coupling 268 5.11 Transformer Coupled Class A Power Amplifi er 271 5.12 Emitter-follower Class A power Amplifi er 274 5.13 Merits and Demerits of Class A Power Amplifi er 279 5.14 Class B Push-pull Power Amplifi er 280 5.15 Advantages and Disadvantages of Class B Push-pull Power Amplifi er 281 5.16 Class B Push-pull Emitter Follower 281 5.17 Cross Over Distortion 287 5.18 Biasing Class B/AB Amplifi ers 293 5.19 Class B/AB Driver 297 5.20 Class C Power Amplifi er 300 5.21 AC Collector Resistance 306 5.22 Bandwidth 308 5.23 Current Dip at Resonance 309 5.24 Duty Cycle 310 5.25 Transistor Power Dissipation 312 5.26 Stage Effi ciency 313

5.27 Transistor Power Rating 318 5.28 Summary of Characteristics and Applications of Power Amplifi ers 323

MOSFETs 6.1 Depletion-mode MOSFET 331 6.2 D-MOSFET Characteristic Curves 333 6.3 Transconductance, gm and AC Equivalent Circuit of D-MOSFET 336 6.4 Depletion-mode MOSFET Amplifi ers 337 6.5 Voltage Gain of Common-source D-MOSFET Amplifi er 339 6.6 Dual Gate D-MOSFETs 340 6.7 Enhancement-mode MOSFET 342 6.8 Drain Characteristics of E-MOSFET 343 6.9 Transconductance Characteristics 344 6.10 Schematic Symbol of E-MOSFET 344 6.11 Maximum Gate-source Voltage and MOSFET Handling 345 6.12 The Ohmic Region of E-MOSFET 346 6.13 Static Drain-source On-state Resistance 346 6.14 To Determine Whether the MOSFET is Biased in the Ohmic Region 347 6.15 Digital Switching 355 6.16 CMOS 362

Frequency Effects 7.1 Frequency Response of an Amplifi er 371 7.2 Decibel Power Gain, AP(dB) 378 7.3 Decibel Voltage Gain, AV(dB) 380 7.4 Impedance Matching 385 7.5 Decibels above a Reference 388 7.6 Bode Plots 390

Negative Feedback 8.1 Types of Negative Feedback 397 8.2 Equivalent circuits of Negative Feedback Amplifi ers 398 8.3 VCVS or Voltage amplifi er 400 8.4 Effect of Negative Feedback on the Characteristics of VCVS 403 8.5 ICVS or Transresistance Amplifi er 409 8.6 VCIS or Transconductance Amplifi er 414 8.7 ICIS or Current Amplifi er 418 8.8 Band Width of Negative Feedback Amplifi ers 421

Nonlinear Op-amp Circuits 9.1 Comparators with Zero Reference Voltage 429 9.2 Comparators with Non-zero References 439

9.3 Comparator with Hysterisis 447 9.4 Window Comparator 452 9.5 Integrator 455 9.6 Waveform Conversion with Op-amp 459 9.7 Waveform Generation using Op-amp 466

Oscillators 10.1 The 555 Timer 475 10.2 Operating Modes of 555 Timer 475 10.3 Functional Block Diagram of 555 Timer 477 10.4 Monostable Operation of 555 Timer 478 10.5 Astable Operation of 555 Timer 482 10.6 Voltage Controlled Oscillator (VCO) 486 10.7 555 Circuits 489 10.8 Phase Locked Loop 498 10.9 Function Generation ICs 501

Regulated Power Supplies 11.1 Power Supply Characteristics 509 11.2 Shunt Regulators 513 11.3 Series Regulators 520 11.4 Linear IC Voltage Regulators 536 11.5 Current Boosters 546 11.6 DC-to-DC Converters 547 11.7 Switching Regulators 550

Bibliography 563

Index 565

Chapter 1

DIODE CIRCUITS AND SPECIAL PURPOSE DIODES

Diodes are semiconductor devices which conduct only in one direction. Their behaviour depends on the value and polarity of the applied voltage. This chapter begins with the volt-amper characteristics of diode and takes the reader through several diode applications. Analysis of each diode circuit is presented, backed by numerous illustrative examples.

1.1 VOLT-AMPERE CHARACTERISTICS OF DIODE

Fig. 1.1(a) shows the semiconductor diode biased in the forward region. The dc supply VS forward biases the diode and the series resistor R is used to limit the forward current.

R

IDVD

R

VDVSVS

+

–

+

–

(a) (b)

Fig. 1.1 (a) Forward biased diode (b) Reverse biased diode

Fig. 1.2 shows the V-I characteristics of the diode. In the forward region, the diode current begins to increase rapidly when the diode voltage equals the knee voltage, VK . The knee voltage equals the barrier potential. For silicon diode the knee voltage is approximately 0.7 V.

There is a sharp increase in the diode current above the knee voltage. The only opposition to the flow of forward current is the bulk resistance, RB , of the diode. It is given by the sum of the ohmic resistances of the p and n regions. Typically it is in the order of a few ohms.

Fig. 1.1(b) shows the diode biased in the reverse region. From the V-I characteristics, we find that the reverse current is very small as long as the applied reverse voltage is less than the Break down voltage. The reverse current is in the order of few micro amperes and the reverse breakdown

2 Electronic Circuits

voltage is hundreds of volts. It is important to note that the reverse break down is destructive and therefore the applied reverse voltage should not exceed the reverse break down voltage of the diode.

ID

VD

Break down

voltageReverse

current

Reverse

region

Forward

region

VK

Fig. 1.2 V-I Characteristics of diode

1.2 DIODE EQUIVALENT CIRCUIT

The equivalent circuit of a diode is a circuit that closely approximates the diode behavior under forward and reverse biased conditions. The analysis of circuits using diode can be performed by simply replacing the diode by its equivalent circuit.

1.3 EQUIVALENT CIRCUIT OF IDEAL DIODE [FIRST APPROXIMATION]

The equivalent circuit of ideal diode is obtained by making the following idealistic assumptions.

1. The knee voltage of the diode is zero. As a result the diode begins to conduct for VD ≥0.

2. The bulk resistance of the diode is zero. As a result the diode current rises abruptly to a large value soon after, VD exceeds zero volts.

3. The reverse current is zero.

To summarize• Under forward bias, the diode acts as a short circuit since the diode voltage is zero.• Under reverse bias, the diode acts as an open circuit since the diode current is zero.• Therefore a conducting diode can be represented by a closed switch and a non conducting

diode by an opened switch.Fig. 1.3 shows the V-I characteristics and equivalent circuits of ideal diode.

Diode Circuits and Special Purpose Devices 3

ID

VDVK = 0

Ideal

Reverse bias

Forward bias

(a) (b)

Slope = = ∞RB

1

Fig. 1.3 (a) V-I Characteristics of ideal diode (b) Equivalent circuit of ideal diode

Example 1.1

For the circuit shown below calculate the load current IL and the load voltage VL assuming ideal diode.

IL

VL

RL12 V1.5 kΩ

Ideal

SolutionThe dc voltage 12 V forward biases the diode. The diode can be replaced by a short circuit as shown below.

IL = ID

IDVL

12 V 1.5 kΩIL

VL12 V 1.5 kΩ

+

–

≡

IL = 12V

1.5kΩ = 8 mA = ID

VL = IL (1.5 kΩ) = (8 mA) (1.5 kΩ) = 12 V

1.4 THE SECOND APPROXIMATION OF DIODE

In the second approximation of diode, the effect of barrier potential is included but the bulk resistance is taken as zero, same as in the case of ideal diode. Since the barrier potential opposes

4 Electronic Circuits

the current flow in the diode, till it is overcome by external forward bias, the knee voltage VK is placed in series so as to reverse bias the ideal diode a shown in Fig. 1.4. The V-I characteristics for second approximation is shown in Fig. 1.5.

≡

≡

(a)

(b)

(c)

Second approximation Ideal VK

VK

VK

Fig. 1.4 (a) Second approximation of diode (b) Equivalent circuit under reverse bias (c) Equivalent circuit under forward bias

ID

VD

∞

VK

Slope = RB

1=

Fig. 1.5 V-I Characteristics for second approximation

Example 1.2

Using second approximation for the diode calculate the load current, load voltage and power dissipated in the diode.

15 V

VL

RL1 kΩIL

Electronic Circuits For ComputerEngineers

Publisher : Sanguine Publishers ISBN : 9788188849529Author : U. B.Mahadevaswamy And V.Nattarasu

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