Fundamentals of RFand MicrowaveTransistor AmplifiersInder J. Bahl

A John Wiley & Sons, Inc., Publication

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Fundamentals of RFand MicrowaveTransistor Amplifiers

Fundamentals of RFand MicrowaveTransistor AmplifiersInder J. Bahl

A John Wiley & Sons, Inc., Publication

Copyright 2009 by John Wiley & Sons, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New JerseyPublished simultaneously in Canada.

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Library of Congress Cataloging-in-Publication Data:

Bahl, I. J.Fundamentals of RF and Microwave Transistor Amplifiers / Inder Bahl.

p. cm.Includes bibliographical references and index.ISBN 978-0-470-39166-2 (cloth)

1. Amplifiers, Radio frequency. 2. Microwave amplifiers. 3. Transistor amplifiers. I.Title.

TK6565.A55B26 2009621.381535dc22

2008049895

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

http://www.copyright.comhttp://www.wiley.com/go/permissionhttp://www.wiley.com

Contents in Brief

1. Introduction 1

2. Linear Network Analysis 17

3. Amplifier Characteristics and Definitions 33

4. Transistors 61

5. Transistor Models 91

6. Matching Network Components 125

7. Impedance Matching Techniques 149

8. Amplifier Classes and Analyses 185

9. Amplifier Design Methods 211

10. High-Efficiency Amplifier Techniques 259

11. Broadband Amplifier Techniques 295

12. Linearization Techniques 331

13. High-Voltage Power Amplifier Design 363

14. Hybrid Amplifiers 399

15. Monolithic Amplifiers 419

16. Thermal Design 453

17. Stability Analysis 479

18. Biasing Networks 507

19. Power Combining 527

20. Integrated Function Amplifiers 557

21. Amplifier Packages 585

22. Transistor and Amplifier Measurements 613

Contents

Foreword xviiPreface xix

1. Introduction 1

1.1. Transistor Amplifier 11.2. Early History of Transistor Amplifiers 31.3. Benefits of Transistor Amplifiers 31.4. Transistors 41.5. Design of Amplifiers 51.6. Amplifier Manufacturing Technologies 71.7. Applications of Amplifiers 71.8. Amplifier Cost 121.9. Current Trends 121.10. Book Organization 13References 14

2. Linear Network Analysis 17

2.1. Impedance Matrix 182.2. Admittance Matrix 202.3. ABCD Parameters 212.4. S-Parameters 23

2.4.1. S-Parameters for a One-Port Network 292.5. Relationships Between Various Two-Port Parameters 29References 31Problems 31

3. Amplifier Characteristics and Definitions 33

3.1. Bandwidth 333.2. Power Gain 343.3. Input and Output VSWR 383.4. Output Power 383.5. Power Added Efficiency 393.6. Intermodulation Distortion 40

3.6.1. IP3 403.6.2. ACPR 413.6.3. EVM 41

3.7. Harmonic Power 43

viii CONTENTS

3.8. Peak-to-Average Ratio 433.9. Combiner Efficiency 443.10. Noise Characterization 46

3.10.1. Noise Figure 473.10.2. Noise Temperature 473.10.3. Noise Bandwidth 483.10.4. Optimum Noise Match 483.10.5. Constant Noise Figure and Gain Circles 493.10.6. Simultaneous Input and Noise Match 51

3.11. Dynamic Range 513.12. Multistage Amplifier Characteristics 53

3.12.1. Multistage IP3 533.12.2. Multistage PAE 543.12.3. Multistage NF 54

3.13. Gate and Drain Pushing Factors 563.14. Amplifier Temperature Coefficient 573.15. Mean Time to Failure 58References 59Problems 59

4. Transistors 61

4.1. Transistor Types 614.2. Silicon Bipolar Transistor 63

4.2.1. Figure of Merit 654.2.2. High-Frequency Noise Performance of Silicon BJT 664.2.3. Power Performance 67

4.3. GaAs MESFET 684.3.1. Small-Signal Equivalent Circuit 714.3.2. Figure of Merit 724.3.3. High-Frequency Noise Properties of MESFETs 75

4.4. Heterojunction Field Effect Transistor 774.4.1. High-Frequency Noise Properties of HEMTs 784.4.2. Indium Phosphide pHEMTs 79

4.5. Heterojunction Bipolar Transistors 804.5.1. High-Frequency Noise Properties of HBTs 834.5.2. SiGe Heterojunction Bipolar Transistors 85

4.6. MOSFET 86References 88Problems 90

5. Transistor Models 91

5.1. Transistor Model Types 915.1.1. Physics/Electromagnetic Theory Based Models 915.1.2. Analytical or Hybrid Models 925.1.3. Measurement Based Models 92

5.2. MESFET Models 995.2.1. Linear Models 995.2.2. Nonlinear Models 102

5.3. pHEMT Models 1055.3.1. Linear Models 105

CONTENTS ix

5.3.2. Nonlinear Models 1065.4. HBT Model 1095.5. MOSFET Models 1105.6. BJT Models 1115.7. Transistor Model Scaling 1125.8. Source-Pull and Load-Pull Data 113

5.8.1. Theoretical Load-Pull Data 1135.8.2. Measured Power and PAE Source Pull and Load Pull 1165.8.3. Measured IP3 Source and Load Impedance 1185.8.4. Source and Load Impedance Scaling 118

5.9. Temperature-Dependent Models 120References 121Problems 123

6. Matching Network Components 125

6.1. Impedance Matching Elements 1256.2. Transmission Line Matching Elements 125

6.2.1. Microstrip 1266.2.2. Coplanar Lines 134

6.3. Lumped Elements 1346.3.1. Capacitors 1356.3.2. Inductors 1366.3.3. Resistors 139

6.4. Bond Wire Inductors 1416.4.1. Single Wire 1416.4.2. Ground Plane Effect 1426.4.3. Multiple Wires 1436.4.4. Maximum Current Handling of Wire 145

6.5. Broadband Inductors 145References 147Problems 147

7. Impedance Matching Techniques 149

7.1. One-Port and Two-Port Networks 1497.2. Narrowband Matching Techniques 150

7.2.1. Lumped-Element Matching Techniques 1507.2.2. Transmission Line Matching Techniques 156

7.3. WideBand Matching Techniques 1637.3.1. GainBandwidth Limitations 1647.3.2. Lumped-Element Wideband Matching Techniques 1697.3.3. Transmission Line Wideband Matching Networks 1727.3.4. Balun-Type Wideband Matching Techniques 1777.3.5. Bridged-T Matching Network 180

References 182Problems 183

8. Amplifier Classes and Analyses 185

8.1. Classes of Amplifiers 1858.2. Analysis of Class-A Amplifiers 188

x CONTENTS

8.3. Analysis of Class-B Amplifiers 1908.3.1. Single-Ended Class-B Amplifier 1918.3.2. PushPull Class-B Amplifier 1928.3.3. Overdriven Class-B Amplifier 194

8.4. Analysis of Class-C Amplifiers 1968.5. Analysis of Class-E Amplifiers 1978.6. Analysis of Class-F Amplifiers 2018.7. Comparison of Various Amplifier Classes 204References 207Problems 208

9. Amplifier Design Methods 211

9.1. Amplifier Design 2119.1.1. Transistor Type and Fabrication Technology 2129.1.2. Transistor Size Selection 2129.1.3. Design Method 2139.1.4. Circuit Topology 2139.1.5. Circuit Analysis and Optimization 2149.1.6. Stability and Thermal Analyses 215

9.2. Amplifier Design Techniques 2159.2.1. Load-Line Method 2169.2.2. Low Loss Match Design Technique 2189.2.3. Nonlinear Design Method 2219.2.4. Taguchi Experimental Method 222

9.3. Matching Networks 2269.3.1. Reactive/Resistive 2269.3.2. Cluster Matching Technique 228

9.4. Amplifier Design Examples 2309.4.1. Low-Noise Amplifier Design 2309.4.2. Maximum Gain Amplifier Design 2329.4.3. Power Amplifier Design 2349.4.4. Multistage Driver Amplifier Design 2399.4.5. GaAs HBT Power Amplifer 244

9.5. Silicon Based Amplifier Design 2489.5.1. Si IC LNA 2489.5.2. Si IC Power Amplifiers 249

References 255Problems 257

10. High-Efficiency Amplifier Techniques 259

10.1. High-Efficiency Design 25910.1.1. Overdriven Amplifier Design 26110.1.2. Class-B Amplifier Design 26310.1.3. Class-E Amplifier Design 26910.1.4. Class-F Amplifier Design 274

10.2. Harmonic Reaction Amplifier 28210.3. Harmonic Injection Technique 28210.4. Harmonic Control Amplifier 28310.5. High-PAE Design Considerations 284

CONTENTS xi

10.5.1. Harmonic Tuning Bench 28410.5.2. Matching Network Loss Calculation 28710.5.3. Matching Network Loss Reduction 289

References 290Problems 294

11. Broadband Amplifier Techniques 295

11.1. Transistor Bandwidth Limitations 29511.1.1. Transistor Gain Roll-off 29511.1.2. Variable Device Input and Output Impedance 29611.1.3. PowerBandwidth Product 297

11.2. Broadband Amplifier Techniques 29711.2.1. Reactive/Resistive Topology 29811.2.2. Feedback Amplifiers 30311.2.3. Balanced Amplifiers 30711.2.4. Distributed Amplifiers 31011.2.5. Active Matching Broadband Technique 32011.2.6. Cascode Configuration 32411.2.7. Comparison of Broadband Techniques 325

11.3. Broadband Power Amplifier Design Considerations 32511.3.1. Topology Selection 32611.3.2. Device Aspect Ratio 32611.3.3. Low-Loss Matching Networks 32711.3.4. Gain Flatness Technique 32711.3.5. Harmonic Termination 32711.3.6. Thermal Design 327

References 328Problems 328

12. Linearization Techniques 331

12.1. Nonlinear Analysis 33212.1.1. Single-Tone Analysis 33212.1.2. Two-Tone Analysis 334

12.2. Phase Distortion 33712.3. Linearization of Power Amplifiers 339

12.3.1. Pulsed-Doped Devices and Optimum Match 33912.3.2. Predistortion Techniques 34212.3.3. Feedforward Technique 343

12.4. Efficiency Enhancement Techniques for Linear Amplifiers 34412.4.1. Chireix Outphasing 34512.4.2. Doherty Amplifier 34512.4.3. Envelope Elimination and Restoration 34712.4.4. Bias Adaptation 348

12.5. Linear Amplifier Design Considerations 34912.5.1. Amplifier Gain 34912.5.2. Minimum Source and Load Mismatch 350

12.6. Linear Amplifier Design Examples 350References 358Problems 361

xii CONTENTS

13. High-Voltage Power Amplifier Design 363

13.1. Performance Overview of High-Voltage Transistors 36313.1.1. Advantages 36613.1.2. Applications 366

13.2. High-Voltage Transistors 36613.2.1. Si Bipolar Junction Transistors 36713.2.2. Si LDMOS Transistors 36713.2.3. GaAs FieldPlate MESFETs 36813.2.4. GaAs FieldPlate pHEMTs 37013.2.5. GaAs HBTs 37013.2.6. SiC MESFET 37113.2.7. SiC GaN HEMTs 371

13.3. High-Power Amplifier Design Considerations 37213.3.1. Thermal Design of Active Devices 37313.3.2. Power Handling of Passive Components 374

13.4. Power Amplifier Design Examples 38213.4.1. HV Hybrid Amplifiers 38213.4.2. HV Monolithic Amplifiers 386

13.5. Broadband HV Amplifiers 38813.6. Series FET Amplifiers 390References 394Problems 397

14. Hybrid Amplifiers 399

14.1. Hybrid Amplifier Technologies 39914.2. Printed Circuit Boards 39914.3. Hybrid Integrated Circuits 401

14.3.1. Thin-Film MIC Technology 40514.3.2. Thick-Film MIC Technology 40614.3.3. Cofired Ceramic and GlassCeramic Technology 406

14.4. Design of Internally Matched Power Amplifiers 40814.5. Low-Noise Amplifiers 410

14.5.1. Narrowband Low-Noise Amplifier 41014.5.2. Ultra-wideband Low-Noise Amplifier 41114.5.3. Broadband Distributed LNA 412

14.6. Power Amplifiers 41314.6.1. Narrowband Power Amplifier 41314.6.2. Broadband Power Amplifier 416

References 416Problems 417

15. Monolithic Amplifiers 419

15.1. Advantages of Monolithic Amplifiers 41915.2. Monolithic IC Technology 420

15.2.1. MMIC Fabrication 42015.2.2. MMIC Substrates 42115.2.3. MMIC Active Devices 42215.2.4. MMIC Matching Elements 423

CONTENTS xiii

15.3. MMIC Design 42815.3.1. CAD Tools 42815.3.2. Design Procedure 42815.3.3. EM Simulators 429

15.4. Design Examples 43115.4.1. Low-Noise Amplifier 43115.4.2. High-Power Limiter/LNA 43115.4.3. Narrowband PA 43215.4.4. Broadband PA 43415.4.5. Ultra-Wideband PA 43715.4.6. High-Power Amplifier 44015.4.7. High-Efficiency PA 44115.4.8. Millimeter-Wave PA 44115.4.9. Wireless Power Amplifier Design Example 442

15.5. CMOS Fabrication 448References 449Problems 452

16. Thermal Design 453

16.1. Thermal Basics 45416.2. Transistor Thermal Design 456

16.2.1. Cooke Model 45616.2.2. Single-Gate Thermal Model 45716.2.3. Multiple-Gate Thermal Model 458

16.3. Amplifier Thermal Design 46116.4. Pulsed Operation 46416.5. Heat Sink Design 467

16.5.1. Convectional and Forced Cooling 47016.5.2. Design Example 471

16.6. Thermal Resistance Measurement 47216.6.1. IR Image Measurement 47216.6.2. Liquid Crystal Measurement 47316.6.3. Electrical Measurement Technique 475

References 476Problems 477

17. Stability Analysis 479

17.1. Even-Mode Oscillations 48017.1.1. Even-Mode Stability Analysis 48017.1.2. Even-Mode Oscillation Suppression Techniques 487

17.2. Odd-Mode Oscillations 49017.2.1. Odd-Mode Stability Analysis 49117.2.2. Odd-Mode Oscillation Suppression Techniques 49917.2.3. Instability in Distributed Amplifiers 500

17.3. Parametric Oscillations 50017.4. Spurious Parametric Oscillations 50117.5. Low-Frequency Oscillations 502

xiv CONTENTS

References 503Problems 504

18. Biasing Networks 507

18.1. Biasing of Transistors 50718.1.1. Transistor Bias Point 50718.1.2. Biasing Schemes 509

18.2. Biasing Network Design Considerations 51318.2.1. Microstrip Biasing Circuit 51418.2.2. Lumped-Element Biasing Circuit 51618.2.3. High-PAE Biasing Circuit 51918.2.4. Electromigration Current Limits 520

18.3. Self-Bias Technique 52018.4. Biasing Multistage Amplifiers 52318.5. Biasing Circuitry for Low-Frequency Stabilization 52418.6. Biasing Sequence 524References 525Problems 526

19. Power Combining 527

19.1. Device-Level Power Combining 52719.2. Circuit-Level Power Combining 530

19.2.1. Graceful Degradation 53219.2.2. Power Combining Efficiency 534

19.3. Power Dividers, Hybrids, and Couplers 53719.3.1. Power Dividers 53719.3.2. 90 Hybrids 54019.3.3. Coupled-Line Directional Couplers 541

19.4. N -Way Combiners 54519.5. Corporate Structures 54619.6. Power Handling of Isolation Resistors 55019.7. Spatial Power Combiners 55119.8. Comparison of Power Combining Schemes 553References 553Problems 555

20. Integrated Function Amplifiers 557

20.1. Integrated Limiter/LNA 55720.1.1. Limiter/LNA Topology 55820.1.2. Limiter Requirements 55920.1.3. Schottky Diode Design and Limiter Configuration 56020.1.4. 10-W Limiter/LNA Design 56220.1.5. Test Data and Discussions 565

20.2. Transmitter Chain 56720.2.1. Variable Gain Amplifier 56920.2.2. Variable Power Amplifier 57120.2.3. Amplifier Temperature Compensation 57320.2.4. Power Monitor/Detector 57520.2.5. Protection Against Load Mismatch 580

CONTENTS xv

20.3. Cascading of Amplifiers 581References 581Problems 583

21. Amplifier Packages 585

21.1. Amplifier Packaging Overview 58521.1.1. Brief History 58721.1.2. Types of Packages 590

21.2. Materials for Packages 59221.2.1. Ceramics 59221.2.2. Polymers 59221.2.3. Metals 592

21.3. Ceramic Package Design 59321.3.1. Design of RF Feedthrough 59321.3.2. Cavity Design 59521.3.3. Bias Lines 59721.3.4. Ceramic Package Construction 59721.3.5. Ceramic Package Model 599

21.4. Plastic Package Design 59921.4.1. Plastic Packages 60021.4.2. Plastic Package Model 600

21.5. Package Assembly 60121.5.1. Die Attach 60221.5.2. Die Wire Bonding 60321.5.3. Assembly of Ceramic Packages 60521.5.4. Assembly of Plastic Packages 60621.5.5. Hermetic Sealing and Encapsulation 607

21.6. Thermal Considerations 60821.7. CAD Tools For Packages 60921.8. Power Amplifier Modules 609References 611Problems 611

22. Transistor and Amplifier Measurements 613

22.1. Transistor Measurements 61322.1.1. IV Measurements 61422.1.2. S-Parameter Measurements 61522.1.3. Noise Parameter Measurements 61922.1.4. Source-Pull and Load-Pull Measurements 620

22.2. Amplifier Measurements 62322.2.1. Measurements Using RF Probes 62422.2.2. Driver Amplifier and HPA Test 62522.2.3. Large-Signal Output VSWR 62622.2.4. Noise Figure Measurements 626

22.3. Distortion Measurements 62722.3.1. AMAM and AMPM 62722.3.2. IP3/IM3 Measurement 62822.3.3. ACPR Measurement 62922.3.4. NPR Measurement 63022.3.5. EVM Measurement 630

xvi CONTENTS

22.4. Phase Noise Measurement 63022.5. Recovery Time Measurement 632References 635Problems 636

Appendix A. Physical Constants and Other Data 637

Appendix B. Units and Symbols 639

Appendix C. Frequency Band Designations 641

Appendix D. Decibel Units (dB) 643

Appendix E. Mathematical Relationships 647

Appendix F. Smith Chart 649

Appendix G. Graphical Symbols 651

Appendix H. Acronyms and Abbreviations 653

Appendix I. List Of Symbols 657

Appendix J. Multiple Access and Modulation Techniques 661

Index 663

Foreword

It has been a pleasure to review a book manuscript called Fundamentals of RF andMicrowave Transistor Amplifiers and to reflect on the career of the author, my friendand colleague of more than 25 years, Dr. Inder Bahl.

Dr. Bahl is a man who is passionate about microwaves. Microwaves are his workand his play. I recall a time when those of us working with Dr. Bahl could tellwhen he was on vacation because as he sat at his desk working his latest microwaveproject, he wasnt wearing a tie! Dr. Bahl has been a prodigious contributor to themicrowave art, authoring or coauthoring over 150 papers, 12 books, serving as theeditor of International Journal of RF and Microwave Computer-Aided Engineering,and successfully completing literally hundreds of low noise, power, and control MMICdesigns. Beyond the science, engineering, and the math, Dr. Bahl has a canny intuitivefeel for how microwave circuits behave. It is almost as though Dr. Bahl can surfthe microwaves through the circuit, feeling the gains and losses, experiencing thediscontinuities, and uncovering the hidden gremlins!

The writing of this text is a gift from Dr. Bahl to the microwave community.Authoring a text of the scope and magnitude of Fundamentals of RF and MicrowaveTransistor Amplifiers is a monumental task the success of which is a tribute to Dr.Bahls broad and extensive experience in the field, and to his dedication. His goal isto support and encourage others to participate in the microwave art to which Dr. Bahlhas dedicated his life, and to share his excitement!

In this book, Dr. Bahl has outlined for his readers the keys to successful transistoramplifier design. In the following text, you will get the opportunity to see the worldof solid-state RF and microwave amplifiers through the eyes of a master. What doeshe think about? Whats important? How does he proceed with a design? Sit back,read, enjoy, and get prepared for what the future will bring. The excitement is justbeginning!

Dr. Edward L. Griffin

Roanoke, VirginiaDecember 2008

Preface

Amplifiers have played a vital role in the development of high-performance andlow-cost solutions for front-end RF and microwave systems. Numerous articles scat-tered in a wide array of technical journals and conference proceedings, book chapters,and even books have been published on amplifiers. However, no comprehensive textdedicated to this topic covering both theory and practical aspects exists. Thus there isan urgent need to bring out a book on this subject to fill the void.

This book evolved basically with my transistor amplifier design experience overthe past 28 years. I have been actively involved with numerous amplifier designs fromthe concept level to the end products. The present book provides a comprehensivetreatment of RF and microwave low-noise and power amplifier circuits including, lownoise, narrowband, broadband, linear, high power, high efficiency, and high voltage.The topics discussed include modeling, analysis, design, packaging, and thermal andfabrication considerations. The elements of the book are self-contained and cover prac-tical aspects in detail. The book also includes extensive design information in the formof equations, tables, graphs, and examples and has a unique integration of theory andpractical aspects of amplifier circuits. Amplifier related design problems range frommatching networks to biasing and stability. Practical examples (over 80 fully solved)make it simple to understand the concepts of amplifier design.

Simple design equations are also included to help the reader understand designconcepts. In addition to the solved examples, over 160 problems are provided to helpreaders test their basic amplifier and circuit design skills. With its emphasis on the-ory, design, and practical aspects geared toward day-to-day applications, this bookis intended for students, teachers, scientists, and practicing engineers. Students arerequired to have prior knowledge of topics such as solid state device basics, theoryof transmission lines, basic circuit theory, and electromagnetics taught at the under-graduate level. It is hoped that through this book, readers will benefit in their quest tounderstand RF and microwave transistor amplifier circuit design.

The unique features of this book include in-depth study of transistor amplifiers,extensive design equations and figures, treatment of the practical aspects of amplifiercircuits, and description of fabrication technologies. It provides a broad view of solidstate transistor amplifiers. It has dedicated chapters on topics such as stability analysis,high-efficiency amplifiers, broadband amplifiers, monolithic amplifiers, high-voltagedesign, biasing of amplifiers, thermal design, power combining, integrated functionamplifiers, and amplifier measurements. This book is not intended to cover any spe-cific application, however; its purpose is to present essential background material in thefundamentals of amplifier design including both theoretical and practical aspects. RFand microwave circuits using Si bipolar and CMOS technologies have made tremen-dous progress and an enormous number of papers have been published in recent years.

xx PREFACE

This topic is covered in a limited scope because there are several excellent booksavailable on this subject and amplifier designs are largely based on analog designconcepts.

The book is divided into 22 chapters, with the material treated precisely and thor-oughly and covering various aspects of amplifiers in each chapter. These chapterspresent the basic principles, analysis, techniques, and designs used in transistor ampli-fiers and provide the foundation for the analysis and design of RF and microwavetransistor amplifiers. Design procedures and examples are provided in each chapter.The step-by-step procedures help to eliminate any doubts and help the student sharpenhis/her design skills. In addition, technical information and remarks on various com-ponents, devices, and circuits update the reader on the most widely used microwavetechniques. It is hoped that the selection of topics and their presentation will meetthe expectations of the readers. Like any other comprehensive book, the work ofother researchers is included or cited for further reading. This book also includes acomprehensive list of references. Finally, most chapters have a set of problems.

Chapter 1 provides an introduction to transistor amplifiers and their applicationsin both commercial and military systems. Chapter 2 establishes the basic amplifieranalysis parameters and representation of RF and microwave networks. Fundamentalnetwork analysis tools such as impedance, admittance, ABCD , and scattering matrixtechniques are introduced together with the properties of multiport networks. Rela-tionships between the commonly used matrix representation forms are established topermit the researcher or designer to work in the system of his/her preference.

Chapter 3 deals with the definition of amplifier terms and characterization of ampli-fiers. Fundamental amplifier parameters are defined, together with a brief introductionto reliability. The intent of this chapter is to define amplifier characteristics at one placefor quick reference. Chapter 4 deals with transistors, including Si bipolar, GaAs FETs,GaAs pHEMTs, GaAs HBTs, Si MOSFETs, and SiGe HBTs. The treatment is limitedto emphasize characteristics that will be of interest to students and design engineers.Chapter 5 deals with linear and nonlinear transistor models. These models are the back-bone of amplifier designs and are based on equivalent circuit formulations. The devicemodels included are for low-noise and low-power applications. The devices includedare MESFETs, pHEMTs, HBTs, and MOSFETs. The EC model, model scaling, andsource-pull and load-pull characterizations are also detailed in this chapter.

In Chapter 6, the fundamentals of transmission lines and lumped elements areconsidered, including their characteristics. Since the book is primarily devoted to pla-nar circuits, the characteristics of commonly used planar transmission media such asmicrostrip line and coplanar waveguide are described. Discontinuities and couplingaspects in the microstrip line are also covered. The design of lumped elements suchas capacitors, inductors, and resistors is treated at the end of the chapter. All of thisleads naturally into Chapter 7 on impedance matching networks that are fundamentalto any microwave circuit or system. Impedance matching circuits for narrowband andwideband applications and their design techniques are discussed. Finally, their practicalrealization aspects are considered.

Analyses of most commonly used amplifier classes are discussed in Chapter 8. Italso provides a comparison of the various amplifier classes used for high-efficiencyapplications. High-efficiency operation of the power amplifiers can be obtained byoperating the transistor in class B or C as well as using load impedances for class Eor F. The switched-mode class-E tuned power amplifiers are widely used at low RF

PREFACE xxi

frequencies while class-F amplifiers are realized up to microwave frequencies. Practicalaspects of high-efficiency amplifiers are provided in greater detail in later chapters.

The next five chapters describe amplifier designs, beginning with Chapter 9 onamplifier design methods. The fundamental design methods for amplifiers, includinglinear, nonlinear, and statistical, are described. Nonlinear circuit analysis, employingtime and frequency domain simulations, is a powerful CAD tool for design and opti-mization of power amplifiers developed for different applications. The advantages ofsuch tools include accurate design predicting nonlinear behavior, first-pass success forMMICs, and reduced product development time and cost. Design procedures and typ-ical design examples are presented for GaAs FETs, pHEMTs, and HBTs, and for SiCMOS and SiGe HBT amplifiers. Using the material in Chapter 8 as background,high-efficiency amplifier design techniques are discussed in Chapter 10. This criticalcomponent is treated in depth, starting with an overdriven class-A amplifier and con-cluding with harmonic tuning techniques for high PAE. Design examples are providedand important design considerations for high PAE are discussed.

The design of broadband amplifiers is described in Chapter 11. Bandwidth foramplifiers is always an important consideration, and several methods used in broad-banding amplifiers are presented. This includes reactive/resistive, feedback, balanced,and distributed amplifiers. Critical design considerations for the broadband amplifiersare discussed. These circuits are seeing widespread use, particularly in electronic war-fare, countermeasures, and support systems. The design of linear amplifiers is presentedin Chapter 12. As in previous chapters, the emphasis is on the design of these compo-nents and thus different circuit possibilities for each component, design considerations,limitations of design, and so on are presented. Linearization techniques are discussedtogether with design techniques, realization aspects, and special design considerations.

Chapter 13 covers the fast evolution of high-voltage transistors, which are gain-ing widespread acceptance and application. Pros and cons of high-voltage transistorbased amplifies are described. Si bipolar and LDMOS, GaAs MESFET, pHEMT, andHBT and SiC MESFET and GaN HEMT devices are considered, and their designtechniques are presented. Both the hybrid and monolithic high-voltage amplifiers aredescribed. High-voltage operation employing several low-voltage transistors in seriesis also discussed.

Using the material presented in the previous chapters, it is naturally hoped that thereader will embark on the design and fabrication of microwave integrated circuit (MIC)amplifiers. While mastering the complexity of the manufacture of these circuits canonly come from years of practical experience, Chapters 14 and 15 expose one to thetypes of hybrid and monolithic MIC amplifiers, along with their design considerations,fabrication procedures, and design criteria. Adequate material is presented to allow thedesigner to make a good choice of substrates and materials for design and fabrication,for both hybrid MICs and monolithic MICs. Examples of hybrid MIC amplifiers areillustrated. Chapter 15 deals with monolithic microwave integrated circuit (MMIC)amplifiers. Several types of amplifiers are discussed and MMIC examples are presented.

The next four chapters are devoted to the practical design aspect of various typesof amplifiers. These include thermal design, stability analyses, biasing networks, andpower combining. Chapter 16 deals with the thermal design of power amplifiers. Ther-mal models for channel temperature calculation for both transistors and amplifiers aredescribed. Practical methods for thermal resistance determination are also discussed.Amplifier stability is the topic of Chapter 17. A comprehensive treatment is given oftheoretical and practical aspects of amplifier stability with several examples.

xxii PREFACE

Biasing is another important aspect for successful amplifier design, which is treatedin Chapter 18. The biasing of transistors is discussed first, followed by a detaileddescription of biasing networks. Biasing of multistage amplifiers as well as biasingfor low-frequency stabilization of power amplifiers are discussed. Chapter 19 givesan overview of power combining techniques. After the basics of power combiningare described, the fundamental differences between the device and circuit combiningtechniques are presented. Power combiners are also covered in this chapter togetherwith the methods for design and analysis for both hybrids and couplers. Practicalexamples of multichip MMIC based combined HPAs are included.

Applications of amplifiers in modern commercial and military systems requirecost-effective solutions. A popular technique to achieve product cost goals is to inte-grate more functions into a single MMIC amplifier chip or into a package or module.For example, a high level of integration at the MMIC chip level reduces the numberof chips and interconnects and results in low test and assembly costs, which in turnincreases the reliability and reduces the subsystem cost. Chapter 20 includes examplesof this type of integration such as a limiter/LNA, transmitter chains with several stages,amplifiers with variable gain and output power, amplifiers with built-in power monitors,temperature compensation for gain, and output mismatch protection.

Chapter 21 deals with amplifier packaging issues. Both plastic and ceramic pack-ages are described. Design of the feed and cavity for ceramic packages is treated indetail. Brief descriptions of die attach and wire bonding techniques are also included.Measurements of transistor and amplifiers are covered in the last chapter. The char-acterization of transistors is described first, followed by amplifier testing includingS -parameters, noise figure, source-pull and load-pull characterization, VSWR, outputpower versus input power, PAE, harmonics, distortion, phase noise, and recovery time.At the end, several appendix are included to facilitate the designs of readers.

This book contains enough material for a one-year course at the senior or graduatelevel. With judicious selection of specific topics, one can use the book for one-semester,two-semester, or two-quarter courses. Problems are given at the end of most chapters.They have been tested to ensure that their level of difficulty and complexity is suitablefor the student.

This book is dedicated to all my colleagues who have done pioneer work in theadvancement of microwave engineering. I am also indebted to Dr. Edward L. Griffinwho introduced me to the wonderful field of microwave amplifiers. He reviewed themanuscript and made excellent suggestions. Many friends and colleagues, at TycoElectronics and elsewhere, have significantly contributed to improvements in this book.I particularly want to thank George Studtmann for critically reviewing and editing thecomplete manuscript, making numerous suggestions to greatly enhance the text, andalso providing HBT amplifier examples. I wish to thank Mark Dayton, Andy Peake,Tom Winslow, Jain Zhao, James Perdue, and Gordon Tracy for providing criticalreviews of chapters and for their support. The preparation of this book has dependedon my organization and a number of very supportive individuals, including DavidConway, Michael Rachlin, Janice Blackwood, and Neil Alls. I owe a special note ofthanks to Linda Blankenship for expertly transforming some of my handwritten textinto word-processing documents. I would like to thank Tyco Electronics managementfor its support and encouragement. This book became a reality only because of thegreat support I received from George Telecki and his staff including Lucy Hitz andLisa Morano Van Horn at John Wiley & Sons.

PREFACE xxiii

Finally, I want to express my deep appreciation to my wife, Subhash Bahl, for herlove, encouragement, enduring unselfishness, and support. Her patience allowed me towork during many evenings, holidays, and weekends to complete this gigantic task.Especially, I wish to thank my daughter, Preeti, my son-in-law, Ashutosh, my son,Puneet, and my grandsons, Karan and Rohan, for their love, support, and patience.They all truly deserve much of the credit.

Inder J. BahlRoanoke, VirginiaMarch 2009

Chapter 1

Introduction

Among electronic circuits, signal amplification is one of the most importantradiofrequency (RF) and microwave circuit functions. The introduction of radarduring World War II provided the first significant application requiring amplificationof microwave signals. In recent times, the wireless communication revolution hasprovided an explosion of RF and microwave amplification applications. During the lasttwo decades, amplifier technology has made tremendous progress in terms of devices(low noise and power), circuit computer-aided design (CAD) tools, fabrication,packaging, and applications. Low-cost power amplifiers for wireless applications area testament to this explosion.

Early microwave amplifiers were the exclusive province of vacuum tube devicessuch as Klystrons [13], traveling-wave tube (TWT) amplifiers [24], and magnetrons[2, 3]. Today, microwave amplification is dominated by solid state amplifiers exceptfor applications at high output powers (100 watts). Today, the most common vacuumtube application is the 900-watt microwave oven using a 2.45-GHz magnetron. Thepower levels achievable for tube amplifiers are on the order of 103 higher than achiev-able for solid state amplifiers. The microwave oven magnetron, with a manufacturingcost of about $10 ($0.01/watt), has no solid state competition in sight. Likewise,todays $0.50/watt 900-MHz to 2-GHz cell phone solid state transistor amplifier and$0.30/watt 200500-W L/S-band base station transistor power amplifiers have no tubecompetition.

Solid state amplifiers are of two general classes: those based on two-terminalnegative resistance diode devices, and those based on three-terminal devices knownas transistors. Early solid state amplifiers were dominated by two-terminal devicesbecause diodes are typically much easier to fabricate than transistors. Quite an array oftwo-terminal amplifier designs have been introduced, including parametric amplifica-tion (varactor diodes) [58], tunneling diodes [79], transferred electron diodes (Gunnand LSA diodes) [8, 10, 11], and avalanche transit-time diodes (IMPATT, TRAPATT,and BARITT) [8, 12]. Such diodes are used only for special amplifier functions.

1.1 TRANSISTOR AMPLIFIER

Today, solid state amplification is dominated by use of three-terminal transistors[1336]. Using a small voltage applied at the input terminal of the device, onecan control, in an efficient manner, a large current at the output terminal when the

Fundamentals of RF and Microwave Transistor Amplifiers. By Inder J. BahlCopyright 2009 John Wiley & Sons, Inc.

1

2 Chapter 1 Introduction

common terminal is grounded. This is the source for the name transistor , which is aunification of the words transfer resistor .

Solid state transistors may be grouped into two categories: bipolar and unipolardevices. The bipolar devices are comprised of silicon (Si) bipolar junction transis-tors (BJTs) and silicon germanium (SiGe) and gallium arsenide (GaAs) heterojunctionbipolar transistors (HBTs). The unipolar devices include Si metal oxide semiconductorfield effect transistors (MOSFETs), GaAs metal semiconductor field effect transistors(MESFETs), and pseudomorphic high electron mobility transistors (pHEMTs). Theswitchover to three-terminal devices was largely due to cost. Diodes are typically lessexpensive to manufacture than transistors but the associated circuitry to achieve gainfrom a two-terminal device is much more expensive than that for a three-terminaldevice. For example, a transistor (without any matching network) connected between50-ohm input and output terminals can provide 1520 dB gain at radiofrequencies and68 dB at 20 GHz. In addition, design of three-terminal amplifiers for stable operationand routine high-yield manufacturing is exceedingly simple.

Signal amplification is a fundamental function in all RF and microwave systems.When the strength of a weak signal is increased by a device using a direct current(DC) power supply, the device along with its matching and biasing circuitry is knownas an amplifier. Here the DC power from the power supply is converted into RFpower to enhance the incoming signal strength. If a device is a transistor, the signal isapplied to the input terminal (gate/base) and the amplified signal appears at the output(drain/collector) and the common terminal (source/emitter) is usually grounded. Thematching networks help in exciting the device and collecting the output signal moreefficiently. Figure 1.1 shows a schematic representation of a single-stage transistoramplifier. Basic constituents are a transistor, input and output matching networks, biascircuitry, and input and output RF connections. The DC bias and RF connections maybe made to connectors if housed in a fixture or to lead frame if assembled in a packagedepending on the amplifier fabrication scheme.

There are various types of amplifiers used at RF and microwave frequencies.Basic types consist of low-noise, buffer, variable gain, linear power, saturatedhigh-power, high-efficiency, narrowband, and broadband amplifiers. The design of

Input matchTransistor

Input to connector orlead frame

Carrier or heat sink

Output match

Output to connector orlead frame

Bias to connector orlead frame

Bias to connector or lead frame

Substrate

Wire bond

Via sourceground

Figure 1.1 Schematic representation of a transistor amplifier.

1.3 Benefits of Transistor Amplifiers 3

amplifiers requires essentially device models/S-parameters, CAD tools, matching andbiasing networks, and fabrication technology. Each type mandates additional insightsto meet required amplifier specifications. For example, a low-noise amplifier (LNA)needs a low-noise device and a low-loss input matching network while a poweramplifier (PA) requires a power device and low-loss output matching network.

RF and microwave amplifiers have the following characteristics:

Band-limited RF response Less than 100% DC to RF conversion efficiency Nonlinearity that generates mixing products between multiple signals RF coupled and no DC response Power-dependent amplitude and phase difference between the output and input Temperature-dependent gain, higher gain at lower temperatures and vice versa

1.2 EARLY HISTORY OF TRANSISTOR AMPLIFIERS

The use of Si based bipolar transistors and GaAs based MESFET for amplifiers havebeen reported since the mid-1960s and early 1970s, respectively. Most of the ini-tial work on Si based bipolar transistor amplifiers was below C-band frequencies,whereas GaAs based MESFET amplifiers were designed above L-band frequencies(see Appendix C for frequency band designations). Low-noise HEMTs were reportedin the early 1980s. Internally matched narrowband MESFET power amplifiers workingfrom S- through X-band were available during the 1980s and Ku-band amplifiers wereintroduced in the early 1990s.

The GaAs monolithic microwave integrated circuit (MMIC) amplifier was reportedin 1976 and since then there has been tremendous progress in both LNAs and PAs.Some of the early development milestones in MMIC amplifiers are as follows:

X-band low-power GaAs MESFET amplifier in 1976 X-band GaAs MESFET power amplifier in 1979 K-band GaAs MESFET LNA in 1979 Q-band GaAs MESFET power amplifier in 1986 V-band GaAs HEMT LNA in 1988 X-band GaAs HEMT power amplifier in 1989 W-band HEMT LNA/power amplifier in 1992

1.3 BENEFITS OF TRANSISTOR AMPLIFIERS

Major benefits of transistor amplifiers versus tube amplifiers are smaller size, lighterweight, higher reliability, high level of integration capability, high-volume andhigh-yield production capability, greater design flexibility, lower supply voltages,reduced maintenance, and unlimited application diversity. Transistors have muchlonger operating life (on the order of millions of hours) and require much lowerwarming time. Solid state amplifiers also do not require adjustment in the bias or thecircuit, as required in tubes, over long periods of operation.

4 Chapter 1 Introduction

In comparison to solid state diode amplifiers, transistor amplifiers have greaterflexibility in terms of designing matching networks, realizing high-stability circuits,and cascading amplifier stages in series for high gain. The outstanding progress madein monolithic amplifiers is attributed to three-terminal transistors, especially on GaAssubstrates. Monolithic amplifiers are fabricated on wafers in batches, and hundreds orthousands can be manufactured at the same time. For example, over 15,000 amplifiers,each having a chip size of 1 mm2, can be obtained on a single 6-inch diameter GaAswafer. Thus monolithic amplifiers have a great advantage in terms of the manufacturingcost per unit. In general, monolithic amplifiers will have advantage in terms of size andweight over hybrid integrated techniques. It is worth mentioning that the weight of anindividual or discrete chip resistor or a chip capacitor or an inductor is typically morethan an entire monolithic amplifier chip. Many of todays high-volume applicationsusing amplifiers are in hand-held gadgets. Both hybrid and monolithic MIC technolo-gies are used and considered reliable. However, a well-qualified MMIC process canbe more reliable because of the much lower part counts and far fewer wire bonds.

1.4 TRANSISTORS

During the past two decades outstanding progress has been made in microwave andmillimeter-wave transistors. The low-noise and power performance as well as theoperating voltages have significantly been advanced. Among low-noise devices, thepHEMT is the most popular due to its low noise figure and high gain characteristics.Other devices for small-signal applications are MESFETs, MOSFETs, and SiGe HBTs.Today, a designer has several different types of power transistors available as discretedevices (in chip or packaged form) or as part of a foundry service to design poweramplifier MMICs. Several solid state devices are being used to develop power amplifier(PA) circuits including BJTs, laterally diffused metal oxide semiconductor (LDMOS)transistors, MESFETs, or simply FETs, both GaAs and indium phosphide (InP) basedHEMTs, GaAs based HBTs and silicon carbide (SiC) based FETs, and gallium nitride(GaN) HEMTs. Each device technology has its own merits, and an optimum technol-ogy choice for a particular application depends not only on technical issues but also oneconomic issues such as cost, power supply requirements, time to develop a product,time to market a product, and existing or new markets.

HEMTs have the highest frequency of operation, lowest noise figure, and highpower and PAE capability. Due to the semi-insulating property of GaAs substrates,the matching networks and passive components fabricated on GaAs have lower lossthan on Si. The GaAs FET as a single discrete transistor has been widely used inhybrid microwave integrated circuit (MIC) amplifiers for broadband, medium-power,high-power, and high-efficiency applications. This wide utilization of GaAs FETs canbe attributed to their high frequency of operation and versatility. However, increasingemphasis is being placed on new devices for better performance and higher frequencyoperation. HEMT and HBT devices offer potential advantages in microwave andmillimeter-wave IC applications, arising from the use of heterojunctions to improvecharge transport properties (as in HEMTs) or pn-junction injection characteristics (asin HBTs). HEMTs have a performance edge in ultra low-noise, high-linearity, andhigh-frequency applications. The MMICs produced using novel structures such aspseudomorphic and lattice matched HEMTs have significantly improved power andpower added efficiency (PAE) performance and high-frequency (up to 280 GHz)operation. The pHEMTs that utilize multiple epitaxial IIIV compound layers have