Mixed Analog-digital VLSI Devices and Technology

296 Pages·2002·19.17 MB·English

by  Yannis Tsividis

YannisTsividis
M i x ed
ANALOG-DIGITAL
VLSI Devices and
T E C H N O L O GY
World Scientific
M i x ed
ANALOG-DIGITAL
VLSI Devices and
T E C H N O L O GY
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M i x ed
ANALOG-DIGITAL
VLSI Devices and
T E C H N O L O GY
Yannis Tsividis
Columbia University, USA
US* World Scientific
«• NNeeww J Jeersrseeyy • •L Loonnddoonn • •S Sinineg apore • Hong Kong
Published by
World Scientific Publishing Co. Pie. Ltd.
5 Toh Tuck Link, Singapore 596224
USA office: 27 Warren Street, Suite 401-402, Hackensack, NJ 07601
UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE
British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library.
First published in 1996 by The McGraw-Hill Companies, Inc.
Reprinted 2002, 2005
MIXED ANALOG-DIGITAL VLSI DEVICES AND TECHNOLOGY
Copyright © 2002 by World Scientific Publishing Co. Pte. Ltd.
All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means,
electronic or mechanical, including photocopying, recording or any information storage and retrieval
system now known or to be invented, without written permission from the Publisher.
For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance
Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy
is not required from the publisher.
ISBN 981-238-111-2
Printed in Singapore by Mainland Press
Contents
Preface ix
Chapter 1. Introduction: Mixed Analog-Digital Chips 1
1.1 The Role and Place of Modern Mixed Analog-Digital Chips 1
1.2 Advantages of Mixing Analog and Digital Circuits on the Same Chip 4
1.3 Applications of MAD Chips 4
1.4 Obstacles in the Design of MAD Chips 6
1.5 The Aim and Contents of This Book 10
Chapter 2. The MOSFET: Introduction and Qualitative View 15
2.1 Introduction 15
2.2 MOS Transistor Structure 15
2.3 Assumptions about Terminal Voltages, Currents, and Temperature 18
2.4 A Qualitative Description of MOSFET Operation 19
2.4.1 Effect of V : Level of Inversion 19
GS
2.4.2 Effect of V : The Body Effect 23
SB
2.4.3 Effect of V : Drain Current 24
DS
2.5 A Fluid Dynamical Analog 31
2.6 Complete Set of Characteristics 34
2.7 Form of Functional l -V Dependence: Practical Limits for
0 as
Regions of Inversion 35
2.8 Factors Affecting the Extrapolated Threshold Voltage 41
2.9 Other Factors Affecting the Drain Current 43
Chapter 3. MOSFET DC Modeling 47
3.1 Introduction 47
3.2 DC Model for Weak and for Strong Inversion 48
3.2.1 The Current Equations 50
3.2.2 Model Parameters Influenced by the Body Effect 58
3.2.3 Origin and Validity of the Model 61
3.3 Drain versus Source 63
3.4 Symmetric Models 64
vi Contents
3.5 General Models and Moderate Inversion 66
3.6 Mobility Dependence on Gate and Substrate Bias 70
3.7 Temperature Effects 73
3.8 Small-Dimension Effects 74
3.9 Breakdown 79
3.10 The pMOS Transistor 80
3.11 Device Symbols 82
3.12 Model Accuracy, Parameter Extraction, and Computer Simulation 83
Chapter 4. MOSFET Small-Signal Modeling 99
4.1 Introduction 99
4.2 Small-Signal Conductance Parameters 99
4.3 Expressions for Small-Signal Conductance Parameters in
Weak and in Strong Inversion 103
4.3.1 Gate Transconductance 103
4.3.2 Body Transconductance 106
4.3.3 Drain-Source Conductance 107
4.3.4 Drain-Substrate Conductance 110
4.3.5 Examples 110
4.3.6 Small-Signal Parameters in the Presence of Second-Order
Effects 111
4.4 Capacitance Parameters 111
4.4.1 Extrinsic Capacitances 113
4.4.2 Intrinsic Capacitances in Weak and in Strong Inversion 116
4.5 Intrinsic Cutoff Frequency and Limits of Model Validity 120
4.6 The Transistor at Very High Frequencies 123
4.6.1 Extrinsic Parasitic Resistances 123
4.6.2 Intrinsic Nonquasi-static Effects 123
4.7 Noise 126
4.7.1 Introductory Remarks 126
4.7.2 MOS Transistor Noise 129
4.8 General Models and Moderate Inversion 134
4.9 Parameter Extraction for Accurate Small-Signal Modeling 138
4.10 Requirements for Good CAD Models 140
Chapter 5. Technology and Available Circuit Components 147
5.1 Introduction 147
5.2 The n-Well CMOS Process 148
5.2.1 Basic Fabrication Steps and MOS Transistor Structures 148
5.2.2 Capacitors 158
5.2.3 Resistors 163
5.2.4 Inductors 168
5.2.5 Bipolar Transistors 170
5.2.6 Interconnects 172
5.2.7 Electrical Parameters 174
5.2.8 Input Protection 176
5.2.9 Latch-up 176
5.3 BiCMOS Processes 177
5.3.1 Adding High-Performance Bipolar Transistors to CMOS 177
5.3.2 Bipolar Transistor Models 180
Contents vii
5.4 Other Silicon Processes 191
5.5 Sensors 193
5.6 Trimming 194
5.7 Tolerance and Matching of Electrical Parameters 195
5.8 Chip Size and Yield 197
5.9 The Influence of Pads and Package 199
Chapter 6. Layout 205
6.1 Introduction 205
6.2 Relation of Fabricated Transistors to Layout 206
6.3 Transistor Geometry and Layout 208
6.4 Layout for Device Matching and Precision Parameter Ratios 220
6.4.1 Capacitor Layout 220
6.4.2 Resistor Layout 229
6.4.3 Transistor Layout 231
6.4.4 A Collection of Rules for Good Matching 234
6.5 Layout for Interference Reduction 236
6.6 Integrated-Circuit Design 248
Appendix A Additional MOS Transistor Modeling Information 259
Appendix B A Set of Benchmark Tests for Evaluating
MOSFET Models for Analog Design 261
Appendix C A Sample Spice Input File 269
Index 275
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Preface
Mixed analog-digital chips are now commonplace. They can be found in
a variety of applications, from TV sets and compact disk players to
automobiles, telephony equipment, and the disk drive of personal com
puters. The successful design of such chips requires, in addition to
knowledge of circuits and systems, a background in device models, fab
rication technology, and layout, with the special considerations that
apply to analog and mixed analog-digital circuits. This book has been
written to provide this background. It aims at providing just the infor
mation missing in this respect from digital VLSI textbooks and, in
large part, even from traditional analog IC design textbooks and
courses. The book emphasizes intuition and practical information that
is found to be useful in the development of correctly working chips.
Although the book does not exhaust the subject, it does contain
enough information for a good start. After reading the book, one should
be able to answer questions that keep coming up in design settings in
universities and companies—for example, why simulations disagree
with hand calculations and with experimental results; where common
simulator models, appropriate for digital circuits, fail for analog cir
cuits, why and what to do about it; what are the limits of strong inver
sion in MOS transistors, and what happens outside such limits; how to
model devices at nanoampere levels for low-power design; what are the
frequency limits of validity of common device models found in simula
tors; what devices other than transistors are provided in common fab
rication processes, and what the performance of such devices is; how to
lay out transistors, resistors, and capacitors for good matching; how far
two devices can be on the chip before matching between them deterio
rates; and how to prevent interference from the digital circuits to the
analog circuits on the same chip.
The book can find use in several different settings. It can be used as
a supplement to courses on analog circuit design (usually senior/
graduate level, using, for example, texts by Gray and Meyer, Gregorian
and Temes, Allen and Holberg, or Laker and Sansen), with the mate-
ix