Dynamic Offset Compensated CMOS Amplifiers

1. Dynamic Offset Compensated CMOS Amplifiers

2. ANALOG CIRCUITS AND SIGNAL PROCESSING SERIES
Consulting Editor: Mohammed Ismail. Ohio State University
For other titles published in this series, go to
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3. Dynamic Offset Compensated
CMOS Amplifiers
Delft University of Technology, the Netherlands
Springer
Boston/Dordrecht/London
Johan F. Witte, Kofi A.A. Makinwa, Johan H. Huijsing

4. Dr. Johan F. Witte Prof. Kofi A.A. Makinwa
Delft University of Technology Delft University of Technology
Dept. Electrical Engineering Dept. Electrical Engineering
Mekelweg 4 Mekelweg 4
2628 CD Delft 2628 CD Delft
Netherlands Netherlands
frerik.witte@nsc.com k.a.a.makinwa@tudelft.nl
Prof. Johan H. Huijsing
Delft University of Technology
Dept. Electrical Engineering
Mekelweg 4
2628 CD Delft
Netherlands
j.h.huijsing@tudelft.nl
ISBN 978-90-481-2755-9 e-ISBN 978-90-481-2756-6
DOI 10.1007/978-90-481-2756-6
Springer Dordrecht Heidelberg London New York
Library of Congress Control Number: 2009926941
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5. Preface ...................................................................................................
Acknowledgements .......................................................................
1. Introduction ......................................................................................... 1
1.1 Motivation .............................................................................................. 1
1.2 Offset ...................................................................................................... 3
1.2.1 Drain current mismatch ................................................................. 4
1.2.2 Folded cascode amplifier offset ..................................................... 5
1.2.3 Minimizing offset .......................................................................... 6
1.3 Challenges .............................................................................................. 7
1.4 Organisation of the book ........................................................................ 8
1.5 References ............................................................................................ 10
2. Dynamic Offset Compensation Techniques ............... 13
2.1 Introduction .......................................................................................... 13
2.2 Auto-zero amplifiers ............................................................................. 14
2.2.1 Output offset storage ................................................................... 14
2.2.2 Input offset storage ...................................................................... 16
2.2.3 Auxiliary amplifier ...................................................................... 17
2.2.4 Noise in auto-zero amplifiers ...................................................... 19
2.3 Chopper amplifiers ............................................................................... 23
2.3.1 Noise in chopper amplifiers ......................................................... 25
2.3.2 Chopped operational amplifier in a feedback network ................ 26
2.3.3 Charge injection effects in chopper amplifiers ............................ 27
2.4 Chopped auto-zeroed amplifier ............................................................ 29
2.5 Switching non-idealities ....................................................................... 31
2.5.1 Charge injection reduction tactics ............................................... 33
2.5.2 Charge injection suppression circuits .......................................... 36
2.6 Conclusions .......................................................................................... 40
2.7 References ............................................................................................ 40
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6. 3. Dynamic Offset Compensated Operational
Amplifiers .............................................................................................................. 43
3.1 Introduction .......................................................................................... 43
3.2 Ping-pong operational amplifier .......................................................... 44
3.3 Offset-stabilized amplifiers .................................................................. 45
3.3.1 Auto-zero offset-stabilized amplifiers ......................................... 47
3.3.2 Chopper offset-stabilized amplifiers ........................................... 48
3.3.3 Frequency compensation ............................................................. 50
3.3.4 Chopper stabilized amplifiers with ripple filters ......................... 55
3.3.5 Chopper and auto-zero stabilized amplifiers ............................... 58
3.4 Chopper offset-stabilized chopper amplifiers ...................................... 59
3.4.1 Iterative offset-stabilization ........................................................ 61
3.5 Conclusions .......................................................................................... 63
3.6 References ............................................................................................ 64
4. Dynamic Offset Compensated Instrumentation
Amplifiers .............................................................................................................. 67
4.1 Introduction .......................................................................................... 67
4.1.1 Current-feedback instrumentation amplifiers ............................. 69
4.2 Dynamic offset compensated instrumentation amplifiers .................... 74
4.2.1 Chopper instrumentation amplifier ............................................. 75
4.2.2 Auto-zeroed instrumentation amplifier ....................................... 76
4.2.3 Ping-pong instrumentation amplifier .......................................... 78
4.2.4 Ping-pong-pang instrumentation amplifier ................................. 78
4.2.5 Offset-stabilized instrumentation amplifiers ............................... 79
4.2.6 Chopper offset-stabilized chopper instrumentation amplifier ..... 82
4.3 Conclusions .......................................................................................... 82
4.4 References ............................................................................................ 82
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7. 5. Realizations of Operational Amplifiers ........................ 85
5.1 Introduction .......................................................................................... 85
5.2 Chopper offset-stabilized operational amplifier ................................... 86
5.2.1 Topology ...................................................................................... 86
5.2.2 Circuits ........................................................................................ 91
5.2.3 Measurement results .................................................................... 98
5.3 Chopper and auto-zero offset-stabilized operational amplifier .......... 104
5.3.1 Topology .................................................................................... 104
5.3.2 Circuits ...................................................................................... 107
5.3.3 Measurement results .................................................................. 112
5.4 Conclusions ........................................................................................ 115
5.5 References .......................................................................................... 116
6. Realizations of Instrumentation Amplifiers ............ 117
6.1 Introduction ........................................................................................ 117
6.2 Low-offset indirect current-feedback instrumentation amplifier ....... 118
6.2.1 Introduction ............................................................................... 118
6.2.2 Topology .................................................................................... 118
6.2.3 Circuits ...................................................................................... 122
6.2.4 Measurement results .................................................................. 124
6.3 High-side current-sense amplifier ...................................................... 129
6.3.1 Current-sensing .......................................................................... 129
6.3.2 Topology .................................................................................... 133
6.3.3 Circuits ...................................................................................... 138
6.3.4 Measurement results .................................................................. 143
6.4 Conclusions ........................................................................................ 147
6.5 References .......................................................................................... 149
7. Conclusions and Future Directions ................................ 151
7.1 Conclusions ........................................................................................ 151
7.2 Future directions ................................................................................. 151
7.3 References .......................................................................................... 153
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8. viii
A. Layout Issues ................................................................................... 155
A.1 Introduction ......................................................................................... 155
A.2 Chopper layout .................................................................................... 157
A.3 Clock shielding .................................................................................... 160
A.4 Conclusion ........................................................................................... 162
A.5 References ........................................................................................... 162
About the Authors ....................................................................... 163
Index ...................................................................................................... 167

9. Preface
CMOS amplifiers suffer from relatively poor offset specifications. Since the
1980s techniques have been explored to calibrate for this offset, or to let the
amplifier itself compensate for its offset in some way or another. This latter
approach is often done dynamically during operation of the amplifier, hence
the name “dynamic offset compensation”. This thesis describes the theory,
design and realization of dynamic offset compensated CMOS amplifiers.
It focuses on the design of general-purpose broadband operational amplifiers
and instrumentation amplifiers.
Two distinguishable offset compensation techniques are described in
chapter 2: auto-zeroing and chopping. Several topologies are discussed, in chapter
3 which can be used to design broadband dynamic offset-compensated
operational amplifiers as well as instrumentation amplifiers, which are described
in chapter 4. Four implementations are discussed in this book: two low-offset
broadband operational amplifiers in chapter 5, and chapter 6 discusses a
low-offset instrumentation amplifier, and a low-offset current-sense amplifier,
which can sense battery currents at a 28V rail.
J.F. Witte
K.A.A. Makinwa
J.H. Huijsing
Delft, December 2008
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10. Acknowledgements
This book started as a Ph.D. thesis written at the Electronic
Instrumentation Laboratory of Delft university of technology, where I spent
an productive, learningfull period of more than 6 years obtaining both my
M.Sc. and Ph.D. degrees. I would start by thanking a lot of people, to whom I
am indebted.
Firstly, I would like to thank my inspirators Han Huijsing and Kofi
Makinwa. I am grateful to Han for introducing me into the field of precision
amplifiers. I want to thank Kofi for giving me good advice and proofreading
my publications.
Secondly, I would like to thank the people who in my opinion keep the
university’s wheels turning. Money makes the world go round and I would
like to thank Willem van der Sluys for guiding every person of the laboratory
through the financial bureaucracy. He even does it with a smile on his face.
Without tools an engineer would only be a philosopher, and, therefore, I
thank Antoon Frehe for keeping the computer servers in the air, despite
failing and leaking air conditioners. My thanks also go to Evelyn, Ingeborg,
Inge, Trudie, Pia, Helly and Joyce whose administrative support kept the
group running through the first years of my M.Sc. and Ph.D. projects, and my
thanks go to Ilse and Joyce who continue to keep the group running thanks to
their ongoing administrative support.
Thirdly, I would really like to thank all the people who helped me
during the design and measurements of my amplifiers. I want to thank Ger de
Graaf, who has also defeated me quite often in our regular tennis matches. I
want to thank Maureen Meekel, who even saw me crying once. Special
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11. Acknowledgements
thanks go to Piet, Jeff, Jeroen and Zu-Yao for helping me with various
measurement problems. I also want to thank Harry Kerkvliet, who sadly
enough passed away during my project, but he used to be a great help when a
student needed equipment.
Special thanks also go to my former roommates Vladimir and Peter, and
my fellow roommates Davina, Gayathri and Eduardo. Thanks also go to
Michiel, Martijn, and Paulo with whom I have also enjoyed some vacations as
well as tough technical discussions. I also have to thank the current group
members Mahdi Kashmiri, Caspar van Vroonhoven, Rong Wu, and Andre
Aita for many interesting discussions.
I would also like to thank all the people from Maxim semiconductor,
who helped me with the implementation of the current-sense amplifier. I
thank Paul and Bill for getting the project started, Matt Kolluri for helping me
through my first real product design cycle, Jennifer for her layout efforts,
Ray, Mike and Brian for their help in testing, and Rich for keeping the project
going.
I also thank my former house-mate, Rob. I really thank him for
maintaining a social circle. He taught me to drink whisky. We have brewed
some mead and together with Martijn, Bas and Marc we slayed a dragon or
two. Fun and friendship are necessary parts of life.
I also want to thank my family members. I especially want to thank my
father for supporting me in my education. My aunt Corry for giving me
advice over the years. I also would like to thank my mother. If you are able to
raise a child to become an engineer, or even a doctor, then you really haven’t
been a bad mother after all.
Finally I want to thank my girlfriend Sophie with whom I have struggled
through the last parts of this long and hard quest. Doing a Ph.D. is also a
burden on your most loved ones. She has carried that burden.
J.F. Witte
Delft, December 2008
xii