Feedback Amplifiers: Theory and Design

263 Pages·2003·0.73 MB·English

by  Gaetano Palumbo

FEEDBACK AMPLIFIERS
Feedback Amplifiers
Theory and Design
by
Gaetano Palumbo
University of Catania
and
Salvatore Pennisi
University of Catania
KLUWER ACADEMIC PUBLISHERS
NEW YORK,BOSTON, DORDRECHT, LONDON, MOSCOW
eBookISBN: 0-306-48042-5
Print ISBN: 0-7923-7643-9
©2003 Kluwer Academic Publishers
NewYork, Boston, Dordrecht, London, Moscow
Print ©2002 Kluwer Academic Publishers
Dordrecht
All rights reserved
No part of this eBook maybe reproducedor transmitted inanyform or byanymeans,electronic,
mechanical, recording, or otherwise, without written consent from the Publisher
Created in the United States of America
Visit Kluwer Online at: http://kluweronline.com
and Kluwer's eBookstore at: http://ebooks.kluweronline.com
To our families:
Michela and Francesca
Stefania, Francesco, and Valeria
CONTENTS
ACKNOWLEDGEMENTS xi
PREFACE xiii
1. INTRODUCTION TO DEVICE MODELING 1
(byGianluca Giustolisi)
1.1 DOPED SILICON 1
1.2 DIODES 2
1.2.1 Reverse Bias Condition 5
1.2.2 Graded Junctions 6
1.2.3 Forward Bias Condition 7
1.2.4 Diode Small Signal Model 9
1.3 MOS TRANSISTORS 9
1.3.1 Basic Operation 10
1.3.2 Triode orLinearRegion 12
1.3.3 Saturation orActive Region 14
1.3.4 Body Effect 15
1.3.5 p-channel Transistors 16
1.3.6 Saturation Region Small Signal Model 16
1.3.7 Triode Region SmallSignalModel 21
1.3.8 Cutoff Region Small Signal Model 23
1.3.9 Second Order Effects in MOSFET Modeling 24
1.3.10Sub-threshold Region 28
1.4 BIPOLAR-JUNCTIONTRANSISTORS 29
1.4.1 Basic Operation 31
1.4.2 Early Effect or Base Width Modulation 32
1.4.3 Saturation Region 33
1.4.4 Charge Stored in theActive Region 33
1.4.5 Active Region Small Signal Model 34
REFERENCES 36
2. SINGLE TRANSISTOR CONFIGURATIONS 37
2.1 THE GENERIC ACTIVE COMPONENT 37
2.2 AC SCHEMATICDIAGRAM ANDLINEARANALYSIS 39
2.3 COMMON X (EMITTER/SOURCE) CONFIGURATION 41
2.4 COMMON XWITH DEGENERATIVERESISTANCE 42
2.5 COMMON Y(BASE/GATE) 48
2.6 COMMON Z(COLLECTOR/DRAIN) 51
2.7 FREQUENCY RESPONSE OF SINGLE TRANSISTOR 54
CONFIGURATIONS
viii
2.7.1 Common XConfiguration 55
2.7.2 Common Xwith a Degenerative Resistance 56
2.7.3 Common YandCommon ZConfigurations 61
3.FEEDBACK 63
3.1 METHOD OFANALYSIS OFFEEDBACKCIRCUITS 64
3.2 SIGNALFLOWGRAPH ANALYSIS 67
3.3 THE ROSENSTARK METHOD 69
3.4 THE CHOMA METHOD 72
3.5 THE BLACKMANTHEOREM 74
4. STABILITY - FREQUENCY AND STEP RESPONSE 77
4.1 ONE-POLEFEEDBACKAMPLIFIERS 78
4.2 TWO-POLEFEEDBACKAMPLIFIERS 82
4.3 TWO-POLE FEEDBACK AMPLIFIERS WITH A POLE- 92
ZERO DOUBLET
4.4 THREE-POLE FEEDBACK AMPLIFIERS WITH REAL 97
POLES
4.5 THREE-POLEFEEDBACKAMPLIFIERS WITH A PAIROF 98
COMPLEXAND CONJUGATEPOLES
4.6 TWO-POLEFEEDBACK AMPLIFIERSWITHAZERO 100
5. FREQUENCY COMPENSATION TECHNIQUES 103
5.1 DOMINANT-POLECOMPENSATION 104
5.2 MILLER (POLE-SPLITTING)COMPENSATION 106
5.3 COMPENSATION OFTHEMILLER RHPZERO 109
5.3.1 Nulling Resistor 110
5.3.2 Voltage Buffer 111
5.3.3 Current Buffer 114
5.4 NESTED MILLERCOMPENSATION 116
5.4.1 General Features 116
5.4.2 RHP Cancellation withNullingResistors 120
5.5 REVERSED NESTEDMILLER COMPENSATION 126
5.5.1 General Features 126
5.5.2 RHP Cancellation withNullingResistors 130
5.5.3 RHP Cancellation with One Real Voltage Buffer 131
5.5.4 RHP Cancellation with OneRealCurrentBuffer 134
6.FUNDAMENTAL FEEDBACKCONFIGURATIONS 137
6.1 SERIES-SHUNT AMPLIFIER 137
6.1.1 Series-shunt Amplifier with Buffer 146
6.2 SHUNT-SERIESAMPLIFIER 148
6.3 SHUNT-SHUNT AMPLIFIER 155
ix
6.4 SERIES-SERIES AMPLIFIER 158
6.5 A GENERAL VIEW OF SINGLE-LOOP AMPLIFIERS 162
6.6 FREQUENCY COMPENSATION OF THE FUNDAMENTAL 165
CONFIGURATIONS
6.6.1 Frequency Compensation of the Series-Shunt Amplifier 166
6.6.2 Frequency Compensation of the Shunt-Series Amplifier 169
6.6.3 Frequency Compensation of the Shunt- Shunt Amplifier 171
6.6.4 Frequency Compensation of the Series-Series Amplifier 172
7.HARMONIC DISTORTION 173
7.1 HARMONIC DISTORTION AT LOW FREQUENCY 176
7.1.1Nonlinear Amplifier with Linear Feedback 176
7.1.2Nonlinear Amplifier with Nonlinear Feedback 178
7.2 HARMONIC DISTORTION IN THE FREQUENCY DOMAIN 182
7.2.1Open-loop Amplifiers 182
7.2.2Closed-loop Amplifiers 185
7.3 HARMONIC DISTORTION AND COMPENSATION 191
7.3.1 Two-stage Amplifier with Dominant-Pole Compensation 191
7.3.2 Two-stage Amplifier with Miller Compensation 193
7.3.3Single-stage Amplifiers 199
7.4 AN ALTERNATIVE FREQUENCY ANALYSIS 205
8.NOISE 207
8.1 BASIC CONCEPTS 207
8.2 EQUIVALENT INPUT NOISE GENERATORS 209
8.3 NOISE MODELS OF CIRCUIT COMPONENTS 212
8.4 EFFECT OF FEEDBACK 214
9. EXAMPLES OF FEEDBACK IN INTEGRATED CIRCUITS 221
9.1 THE OUTPUT RESISTANCE OF A DIFFERENTIAL 221
AMPLIFIER WITH CURRENT-MIRROR LOAD
9.2 THE WILSON CURRENT MIRROR 224
9.3 THE CASCODE CURRENT MIRROR 228
9.4 THE CURRENT FEEDBACK OPERATIONAL AMPLIFIER 229
AND ITS HIGH-LEVEL CHARACTERISTICS
9.5 TRANSISTOR-LEVEL ARCHITECTURE, SMALL-SIGNAL 232
MODEL, AND FREQUENCY COMPENSATION OF CFOAS
9.6 INTEGRATORS AND DIFFERENTIATORS WITH CFOAS 236
9.7 CFOA VERSUS VOA 238
x
APPENDIX: FREQUENCYANALYSISOFRCNETWORKS 243
A.1 TRANSFERFUNCTIONOFAGENERIC RCNETWORK 243
A.2APPROXIMATED POLES 247
REFERENCES 251
ABOUT THE AUTHORS 263
xi
ACKNOWLEDGEMENTS
The authors wish to thank Massimo Alioto, Walter Aloisi and Rosario Mita
for their help during the correction of the draft.
A special thank is due to Professor John Choma jr., a scientific leader in
feedback theory and feedback amplifiers, for his encouragement and
inspiration in the development of this book.
We would like to thank our families and parents for their endless support and
interest in our careers.
Gaetano Palumbo
Salvatore Pennisi
xiii
PREFACE
Feedback circuits and their related properties have been extensively
investigated since the early days of electronics. From the time scientific and
industrial communities started talking about and working with active
elements like vacuum tubes or transistors, until today, much literature and
many scientific results have been published which reinforce the importance
of feedback. Improved features have been implemented in integrated
circuits, novel techniques of analysis have been proposed which deeply
improve our understanding of the resulting layouts, and new design
strategies have been developed to optimise performance. Nevertheless, the
genuinely complex subject of feedback and its applications in analog
electronics remain obscure even for the majority of graduate electronics
students.
To this end, the main focus of this book will be to provide the reader with
a real and deep understanding of feedback and feedback amplifiers.
Whenever possible and without any loss of generality, a simple and intuitive
approach will be used to derive simple and compact equations useful in
pencil-and-paper design. Complex analytical derivations will be used only
when necessary to elucidate fundamental relationships. Consequently, the
contents of the book have been kept to a reasonably accessible level.
The book is written for use both by graduate and postgraduate students
who are already familiar with electronic devices and circuits, and who want
to extend their knowledge to cover all aspects of the analysis and design of
analog feedback circuits/amplifiers. Although the material is presented in a
formal and theoretical manner, much emphasis is devoted to a design
perspective. Indeed, the book can become a valid reference for analog IC
designers who wish to deal more deeply with feedback amplifier features
and their related design strategies, which are often partially –or even
incorrectly– presented in the open literature. For this purpose (and despite