Frequency Compensation Techniques for Low-Power Operational Amplifiers

255 Pages·1995·7.92 MB·English

by  Rudy G. H. Eschauzier

FREQUENCY COMPENSATION TECHNIQUES
FOR LOW-POWER
OPERATIONAL AMPLIFIERS
THE KLUWER INTERNATIONAL SERIES
IN ENGINEERING AND COMPUTER SCIENCE
ANALOG CIRCUITS AND SIGNAL PROCESSING
Consulting Editor
Mohammed Ismail
Ohio State University
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FREQUENCY COMPENSATION TECHNIQUES
FOR LOW-POWER
OPERATIONAL AMPLIFIERS
by
Rudy G. H. Eschauzier
Philips Semiconductors, Sunnyvale, CA, U.S.A.
and
Jo han H. Huijsing
Deljt University ofTechnology, Deljt, The Netherlands
Springer-Science+Business Media, B.Y.
A C.I.P. Catalogue record for this book is available from the Library of Congress
ISBN 978-1-4419-5154-0 ISBN 978-1-4757-2375-5 (eBook)
DOI 10.1007/978-1-4757-2375-5
Printed on acid-free paper
All Rights Reserved
© Springer Science+ Business Media Dordrecht 1995
Originally published by K1uwer Academic Publishers in 1995.
Softcover reprint ofthe hardcover 1st edition 1995
No part of the material protected by this copyright notice may be reproduced or
utilized in any form or by any means, electronic or mechanical,
incIuding photocopying, recording or by any information storage and
retrieval system, without written permission from the copyright owner.
Preface
"Frequency Compensation Techniques for Low-Power OperationaJ
Amplifiers" is intended for professional designers of integrated amplifiers
and graduate students in this field. It serves as a guide to the frequency
compensation of integrated amplifiers, emphasizing low-voltage and low
power solutions.
The basis of this text was written as a dissertation at the Delft Uni
versity ofTechnology. The aim ofthe Ph.D. project was to investigate ne\\
frequency compensation techniques that were suited for the new genera
tion low-voltage, low-power integrated amplifiers. During the four years
of research it soon became apparent that, although frequency compensa
ti on is a subject that every integrated-circuit designer is likely to come
across, surprisingly few attempts have been made to systematically
address this subject.
The book aims at bridging the gap between the professional
designer's needs and available techniques for frequency compensation. It
does so in the first place by explaining existing techniques. Furthermore,
the text covers several new techniques which are the direct results of the
Ph.D. study. Examples of the latter are Hybrid Nested Miller compensa
tion (Sect. 5.4), Multipath Miller Zero cancellation (Sect. 6.4) and Multi
path Conditionally Stable compensation (Sect. 6.5). All compensation
techniques are treated in a stage-number based order, progressing from a
single transistor to circuits with six stages and more. Apart from discuss-
vii
Preface
ing the mathematical basis of the compensation methods, the book pro
vides the reader with the factual information that is required for practicing
the design of integrated feedback amplifiers and many worked out exam
pIes. What is more, many bipolar and CMOS operational amplifier realiza
tions, along with their measurement results, prove the effectiveness of the
compensation techniques in real-life circuits.
In li ne with the current trends in analog circuit design, the text
focuses on low-voltage, low-power integrated amplifiers. Many of the pre
sented bipolar circuits operate at supply voltages down to 1 V, while sev
eral CMOS amplifiers that function correctly just slightly above this
voltage are demonstrated. The lowest measured power consumption
amounts to 17flW for a dass AB CMOS opamp with 120dB gain. Despite
this attention to low-voltage and low-power, the frequency compensation
strategies provided are universally applicable. The fundamental approach
followed leads to efficient compensation strategies that are wen guarded
against the parameter variations inherent to the mass-fabrication of inte
grated circuits.
The book is divided into three main parts. The first part (chapters
1,2 and 3) is optional. The interested reader will find the basic theory of
negative feedback amplifiers here. The second and the third parts, span
ning chapters 4 through 7, establish the core of the work. Of these, the sec
ond part (chapters 4 through 6) introduces the various compensation
techniques, induding the theory and several simple examples, while the
third (chapter 7) discusses the worked-out silicon realizations and the mea
surement results. Although the last two parts build upon the theory of part
one, they are intended to be usable without prior reading of the first.
Ruud G.H. Eschauzier
Johan H. Huijsing
Delft, January 4,1995.
viii Frequency Compensation Techniques for Low-Power Operational Amplifiers
Contents
Preface vii
List of Symbols xiii
1.
Introduction 1
1.1. Low voltage and low power 2
1.2. Low-power frequency compensation 3
1.3. Organization of the work 4
2.
Properties of Feedback Circuits 7
2.1. Feedback in linear networks 11
2.1.1. The solution of a linear network 12
2.1.2. Return differenee and sensitivity 14
2.1.3. The impedanee off eedback cireuits 17
2.2. Non-linear distortion and noise 18
2.2.1. Harmonie distortion 18
2.2.2. Harmonie distortion and non-linearity 19
2.2.3. 1ntermodulation distortion 21
2.2.4. An example of distortion in a non-linear network 24
2.2.5. Modeling ofnon-linear distortion in linear networks 26
2.2.6. Noise infeedbaek cireuits 27
2.3. Conc1usions 28
3.
Stability of Feedback Circuits 29
3.1. Stability analysis 31
3.1.1. Open-loop requirementsfor stability 32
3.1.2. Cauehy's theorem 32
3.1.3. The Nyquist criterion 34
ix
Contents
3.1.4. Conditional stability 37
3.1.5. Gain and phase margin 38
3.2. Maximum obtainable feedback 39
3.2.1. MaximumJeedback absolutely stable amplijiers 40
3.2.2. Optimal Jrequency response Jor integrated amplijiers 49
3.2.3. Conditional stability 53
3.3. Conclusions 55
4.
Basic Frequency Compensation of Integrated
Circuits 57
4.1. The single-stage case 58
4.2. Two-stage parallel compensation 60
4.3. Miller compensation 67
4.3.1. Optimal dimensioning oJthe output stage and Miller capacitor 73
4.3.2. Current-mode Miller compensation 75
4.4. Parallel VS. Miller compensation 76
4.4.1. Bandwidth-to-power ratio 76
4.4.2. Noise 83
4.4.3. Distortion 88
4.5. Conclusions 93
5.
Multistage Compensation Techniques 95
5.1. Multi-stage parallel compensation 99
5.1.1. Bandwidth reduction oJ parallel compensation 103
5.2. Nested Miller compensation 105
5.2.1. Dimensioning oJNMC with more than three stages 115
5.2.2. Current-mode Nested Miller compensation 117
5.3. Reversed Nested Miller compensation 118
5.3.1. Eliminating the loading caused by the Miller capacitors 123
5.3.2. Cascode based Reversed Nested Miller compensation 126
5.4. Hybrid Nested Miller compensation 131
5.4.1. Hybrid Nested Miller compensation Jor more than Jour stages 137
5.5. Merging of compensation techniques 138
5.6. Conclusions 140
x Frequency Compensation Techniques tor Low-Power Operational Amplitiers
6.
Multipath Compensation Techniques 143
6.1. Multipath Nested Miller compensation 144
6.1.1. MultipathDarlington 150
6.2. Pole-zero doublets and settling time 153
6.3. Multipath Hybrid Nested Miller compensation 157
6.4. Multipath Miller Zero Cancellation 160
6.4.1. Multipath Miller Zero Cancellationjor more than two stages 165
6.5. Multipath Conditionally Stable compensation 166
6.5.1. Conditionally stable compensationjor more thanjour stages 169
6.6. Conclusions 171
7.
Realizations 175
7.1. Precision operational amplifiers with NMC and MNMC 176
7.1.1. Introduction 176
7.1.2. Circuit description 177
7.1.3. Realizations and experimental results 182
7.1.4. Conclusions 192
7.2. Opamp with Multipath Miller Zero Cancellation 193
7.2. J. 1ntroduction 193
7.2.2. Multipath Miller Zero Cancellation 195
7.2.3. Realizations 196
7.3. Low-voltage opamps with HNMC and MHNMC 201
7.3.1. Introduction 201
7.3.2. Principle oj operation 207
7.3.3. The ultimate low-voltage opamps 210
7.3.4. The bipolar MHNMC opamp 213
7.3.5. Realizations and measurement results 217
7.3.6. Conclusions 222
7.4. Multipath Conditionally Stable amplifier 224
7.5. Conclusions 227
Bibliography 231
xi