Integrated Audio Amplifiers in BCD Technology

220 Pages·1997·6.27 MB·English

by  Marco Berkhout (auth.)

INTEGRATED AUDIO AMPLIFIERS IN BCD TECHNOLOGY
INTEGRATED
AUDIO AMPLIFIERS IN
BCD TECHNOLOGY
by
Marco Berkhout
MESA Research Institute,
University of Twente,
and
Philips Semiconductors
"~
Springer Science+Business Media, B.V.
A C.I.P. Catalogue record for this book is available from the Library of Congress
ISBN 978-1-4613-7787-0 ISBN 978-1-4615-6083-8 (eBook)
DOI 10.1007/978-1-4615-6083-8
Printed on aeid-free paper
Ali Rights Reserved
@ 1997 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 1997
Softcover reprint of thc hardcover Ist cdition 1997
No part of the material protected by this copyright noticc may be reproduced or
utilized in any form or by any means, electronic or mechanical,
including photocopying, recording or by any information storage and
retrieval system, without written permission from the copyright owner.
"Sounds like art, • the instructor says.
"WeU, it is art, • I say. "This divorce oj artjrom
technology is completely Wlnatural. It'sjust that it's
gone on so long you have to be an archeologist to find
out where the two separated. •
Robert M. Pirsig
Zen and the Art oj Motorcycle Maintenance
Contents
Foreword
xi
Preface
xiii
1 Introduction 1
1. 1 Integrated Audio Amplifiers 1
1.1.1 Output Power and Dissipation 2
1.1.2 Amplifier Classes 4
1. 1.3 Amplifier Requirements 10
1.2 BCD Technology 11
1.2.1 DMOS versus Bipolar 12
1.2.2 DMOS Output Stage 13
1.3 Outline of this Thesis 14
1.4 References 15
2 DMOS Technology 17
2.1 Introduction 17
2.1.1 Historical Perspective 17
2.1.2 Introduction to DMOS 18
2.1.3 Application Areas 22
2.2 DMOS Device Structures 23
2.2.1 Lateral DMOS 23
2.2.2 Vertical DMOS 27
2.2.3 VMOS and UMOS 32
vii
Contents
2.2.4 Comparison of DMOS Structures 35
2.3 DMOS Device Properties 36
2.3.1 Transfer Charactertstics 36
2.3.2 Parasitic Elements 38
2.4 DMOS Process Technology 41
2.4.1 Isolation Techniques 41
2.4.2 Device Termination Techniques 44
2.4.3 BCD Technology 45
2.5 DMOS Versus Bipolar 52
2.5.1 Second Breakdown 52
2.5.2 Bipolar /DMOS Hybrtds 55
2.6 Conclusion 57
2.7 References 57
3 Chargepump Circuits 63
3.1 Introduction 63
3.1.1 Switching Voltage Regulators 64
3.1.2 Voltage Multiplication 64
3.1.3 Application Areas of Chargepumps 66
3.2 Voltage Multipliers 67
3.2.1 Marx Voltage Multiplier 68
3.2.2 Cockcroft-Walton Voltage Multiplier 70
3.2.3 Dickson Voltage Multiplier 72
3.2.4 Comparison of Voltage Multipliers 73
3.3 Chargepump Operation 73
3.3.1 Normal Mode 75
3.3.2 Double Phase Mode 75
3.3.3 Current Drtven Mode 77
3.3.4 Double Phase Current Driven Mode 78
3.3.5 Simulation Results 80
viii
3.4 Voltage Control 80
3.4.1 Output Voltage Clipping 81
3.4.2 Amplitude Control 81
3.4.3 Frequency Control 82
3.4.4 Active Stage Control 82
3.5 Chargepump Implementation 82
3.5.1 Diodes and Switches 82
3.5.2 Driver Circuits 84
3.5.3 Output Voltage Detection 85
3.5.4 Realization Example 86
3.6 Conclusion 88
3.7 References 89
3.8 Appendix: Down Conversion 91
3.8.1 Voltage Division 91
3.8.2 References 96
4 Chargepump Modeling 97
4.1 Introduction 97
4. 1.1 Chargepump Models 98
4.2 Extended Chargepump Model 100
4.2.1 Some Notation Conventions 101
4.2.2 Transient Modeling 103
4.2.3 Steady-State Modeling 107
4.2.4 Transient Behavior 109
4.3 Modeling of ParaSitic Effects III
4.3.1 Current Leakage 112
4.3.2 Series Resistance 114
4.3.3 Stray Capacitance 119
4.3.4 Parallel Capacitance 122
4.3.5 Body-Effect 127
ix
Contents
4.3.6 Combination of Parasitic Effects 131
4.4 Conversion Efficiency 132
4.4.1 Power Consumption and Efficiency 132
4.4.2 Influence of Parasitics 134
4.5 ConcluSion 136
4.6 References 136
5 BCD Audio Amplifiers 137
5.1 Introduction 137
5.1.1 Sources of Distortion 138
5.1.2 Output Resistance 142
5.1.3 Circuit Design in BCD Technology 145
5.2 Output Stage Topologies 146
5.2.1 Common Drain Stages 147
5.2.2 Common Source Stages 154
5.2.3 Comparison of Output Stages 161
5.3 A BCD Amplifier Design 163
5.3.1 Amplifier Topology 163
5.3.2 Signal Splitter 169
5.3.3 Input Stage 184
5.3.4 Output Drivers 185
5.3.5 Complete Amplifier 196
5.4 ConclUSion 200
5.5 References 201
6 Conclusion 203
6.1 Conclusions 203
6.2 Recommendations 206
Index
x
Foreword
Audio power amplifiers were among the first analog circuits available as
integrated circuits. Early on. there was a lot of similarity with operational
amplifiers. but during its evolution. the audio power amplifier increasingly
became a special art of analog electronics. The modem integrated audio
amplifier can deliver an audio output power up to 100 Watt and is robust
against almost any kind of mishandling such as a short circuit across the
load or to the supply lines. Besides this. it has a very high ratio between
quiescent current and maximum output current. very good linearity and
the ability to handle almost any complex load without oscillation. Audio
amplifiers are often the last link in the audio chain. directly connected to
the loudspeaker. and therefore common mode input signals. supply voltage
variations and switch-on should not give any audible output from the
loudspeaker.
Until recently almost all integrated audio amplifiers were designed in
bipolar processes. Although it is possible to design very good bipolar
amplifiers. there are some drawbacks that limit the performance for future
generations of audio amplifiers. The first limitation is in the bipolar power
transistor. For high voltage and high power the Safe Operating ARea
(SOAR) of the bipolar transistor is a serious limitation to the design of a
robust integrated high power audio amplifier. BeSides the bipolar process
is not well suited to the integration of digital and mixed signal circuits
such as buses for control and diagnoses and digital to analog converters.
In a world where digital audio signals have become standard. integrating
these functions with the audio amplifier is a logical chOice. especially
where the submicron CMOS processes for the DSP elements is not
particularly suitable for high performance analog audio signals. To
overcome the limitations of the bipolar process a new process technology
needs to be used. Marco Berkhout's book concentrates on the design of the
analog part of a integrated audio power amplifier in a Bipolar CMOS DMOS
(BCD) process. The DMOS power transistor. with its very good SOAR. offers
a robust. compact alternative for the bipolar power transistor. Besides the
CMOS opens the way to the addition of digital and mixed-signal circuits.
The DMOS power transistor has a large and small signal behavior that
differs considerably from that of the bipolar power transistor. Furthermore.
xi
Foreword
in the small signal part of the amplifier the bipolar transistor is non
preferred because its quality becomes inferior in newer BCD processes.
Another particularity is that the upper output transistor needs a boosted
supply voltage to realize a rail to rail output voltage. For maximum output
power the DMOS power transistor is used in its saturated and in its non
saturated region resulting in an extra source of non linearity that is
unknown in bipolar amplifiers. All these differences between bipolar and
BCD amplifiers gave rise to the challenge to design new basic circuits that
satisfy the high standards of audio power amplifiers. A number of the basic
circuits get special attention in this book.
The book starts with an extensive discussion of the properties of the DMOS
transistor. Then the theory and the design of the charge pump that is
needed for the boosted supply voltage is considered. The new solutions
that are found can also be used for many applications where DC-DC
conversion with low output ripple is needed. The design of the amplifier
concentrates on a new quiescent control circuit with very high ratio
between quiescent current and maximum output current and on the
output stage topologies. The problem of controlling the DMOS output
transistors over a wide range of currents either saturated or non saturated
requires a completely new design of the driving circuits that utilize of the
special properties of the DMOS transistor. All of this is explained in a clear
way and it will certainly help the reader to set foot down the difficult path
of audio amplifier design in BCD technology.
Ed van Tuijl
xii