CMOS Current Amplifiers: Speed versus Nonlinearity

293 Pages·2003·14.09 MB·English

by  Kimmo Koli

CMOS CURRENT 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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CMOS CURRENT
AMPLIFIERS
Speed versus Nonlinearity
by
Kimmo Koli
Nokia Research Center, Finland
and
Kari Halonen
Helsinki University of Technology, Finland
KLUWER ACADEMIC PUBLISHERS
NEW YORK,BOSTON, DORDRECHT, LONDON, MOSCOW
eBookISBN: 0-306-48003-4
Print ISBN: 1-4020-7045-4
©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
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Contents
1 Introduction to current-mode circuit techniques 1
1.1 Development of integration technologies 1
1.2 Motivation for current-mode circuit design 2
1.3 Evolution of current-mode building blocks 3
1.4 Adjoint principle 4
1.5 Scope of this book 6
2 Basic current amplifiers 11
2.1 Current-mirror 12
2.1.1 Nonidealities due to the channel length modulation 13
2.1.2 Nonidealities due the mismatch 16
2.1.3 High frequency nonidealities 18
Linear effects 18
Nonlinearity in limited frequency ranges 20
Mirror as a feedback amplifier 22
2.1.4 Distortion reduction methods 27
Transconductance linearisation 27
Nonlinear current reduction 28
Nonlinear current cancellation 28
2.1.5 Noise and dynamic range 31
2.1.6 Other mirror topologies 33
Accurate current-mirror topologies for large signal amplitudes 33
Resistively compensated mirror 35
2.2 Current buffer 38
2.2.1 Linear nonidealities 39
2.2.2 Nonlinearity 40
2.2.3 Noise 41
2.2.4 Alternative topologies 41
vi Contents
3 Open-loop current amplifiers 45
3.1 First generation current-conveyor CCI 45
3.1.1 Linear nonidealities 46
3.1.2 Nonlinearity 49
3.1.3 Applications of the CCI 49
3.1.4 Push-pull CCI topologies 50
3.1.5 Low voltage CCI topologies 54
3.2 Second generation current-conveyor CCII 55
3.2.1 Linear nonidealities 57
3.2.2 CCII macromodel 59
3.2.3 Applications of the CCII 61
3.2.4 Nonlinearity of the class-A CCII 67
3.2.5 Alternative class-A CCII topologies 68
3.2.6 Push-pull CCII topologies 72
Basic operation of a push-pull CCII+ 72
Basic operation of a push-pull CCII- 74
X-terminal impedance 75
Current gain nonlinearity 76
3.3 Third generation current-conveyor CCIII 80
4 Current-mode feedback amplifiers 85
4.1 Current-feedback operational amplifier 85
4.1.1 Closed loop bandwidth 87
4.1.2 Integrator implementations 90
4.1.3 Self-compensation of voltage followers 92
4.1.4 Common-mode rejection 93
4.1.5 CMOS implementations 95
4.2 Operational floating conveyor 97
4.2.1 Applications 98
4.2.2 Composite conveyors 99
4.3 Current-mode operational amplifiers 101
4.3.1 Distortion 102
4.3.2 Slew rate and full power bandwidth 104
4.3.3 Alternative topologies 105
4.4 High-gain current-conveyor 107
4.4.1 Linear nonidealities 108
4.4.2 Applications 110
4.4.3 Distortion 113
4.4.4 Design example 115
Contents vii
5 System aspects of current-mode circuits 123
5.1 Input voltage-to-current conversion 123
5.2 Output current-to-voltage conversion 126
5.3 Differential voltage input structures 129
5.3.1 CMRR enhancement techniques 130
Common-mode bootstrapping 131
Output current subtraction 131
Composite conveyors 135
5.4 Differential current input structures 137
5.5 Single-ended to differential conversion 138
5.6 Noise in current-mode circuits 141
5.6.1 Class-A CMOS CCII+ 141
5.6.2 Other low-gain conveyor topologies 145
5.6.3 High-gain current-conveyor 145
5.6.4 Other current-mode feedback amplifiers 148
5.6.5 General notes on current amplifier noise 149
6 Current-mode continuous-time filters 153
6.1 Integrator quality factor 154
6.2 Voltage-mode active-RC integrators 155
6.3 OTA-based integrators 157
6.3.1 The effects of process variation and temperature drift 158
6.3.2 Transconductance linearity 160
6.4 Integrators with MOS-resistors 162
6.5 Current-conveyor based filters 163
6.6 Current-mirror based filter 167
6.7 High-gain current-conveyor based filters 172
6.8 Multi-output current integrator with a linearised transconductor 176
6.8.1 Linearization by drain current difference 177
6.8.2 Linearisation by dynamic biasing 181
6.9 Design case: A 1 MHz current-mode low-pass filter 183
6.9.1 Filter building blocks 183
The transimpedance driver amplifier 184
Multiple-output linearised transconductance element 187
Temperature drift compensation of the integrator time constant 187
6.9.2 The first filter realisation 190
Integrator Q-enhancement 192
Experimental results 195
6.9.3 The second test chip 198
viii Contents
Alternate driver implementation 201
Experimental results 205
6.10 Final remarks 208
7 Current-mode logarithmic amplifiers 213
7.1 Diode-feedback logarithmic amplifiers 214
7.1.1 Voltage-mode operational amplifier based realizations 214
7.1.2 Design case: based logarithmic peak detector 216
BiCMOS implementation of a 217
Logarithmic peak detector implementation 217
Post processing of the logarithmic output voltage 222
Final remarks on the design 229
7.2 Pseudologarithmic amplifiers 230
7.2.1 Limiting CMOS voltage amplifiers 231
7.2.2 Limiting CMOS current amplifiers 233
7.2.3 Accuracy of the pseudologarithmic amplifier 235
7.2.4 Amplitude detection in pseudologarithmic amplifiers 236
CMOS rectifiers 236
CMOS squarers 238
CMOS peak detectors 238
7.2.5 Design case: A 2.5 V CMOS pseudologarithmic current am-
plifier 242
Limiting amplifier 243
Current reference 245
Current peak detector 247
Experimental results 247
7.3 Other approaches 252
Current peak detector with enhanced discharging time con-
stant adjustment 252
Conclusions 259
A Basic distortion definitions 261
A.1 Harmonic distortion 261
A.2 Intermodulation distortion 262
A.3 Distortion in feedback amplifiers 263
A.3.1 Distortion in quasi-static feedback amplifiers 263
A.3.2 Distortion in dynamic feedback amplifiers 264
Contents ix
B Distortion in push-pull current amplifiers 269
B.1 Class-A operation 269
B.2 Class-AB operation 271
C Distortion in CMOS operational amplifiers 275
C.1 Miller-compensated unbuffered operational amplifier 275
C.2 Folded cascode operational transconductance amplifier 279
D Distortion in a dual current-mirror integrator 283
D.1 Single-ended integrator 283
D.2 Differential integrator 286
Chapter 1
Introduction to current-mode
circuit techniques
1.1 Development of integration technologies
The development of modern integration technologies is normally driven by the needs
of digital CMOS circuit design. As the sizes of integrated devices decrease, so maxi-
mum voltage ratings also rapidly decrease. Although decreased supply voltages do not
restrict the design of digital circuits, it is harder to design high performance analogue
integrated circuits using new processes.
In digital integration technologies, there are fewer integrated devices available for
circuit design. In a worst case situation, this means that only transistors are available
for analogue circuit design. There may occasionally bee capacitances and resistors
but their values may be small and there are significant parasitic components present.
Thus, if we want to utilise the fastest integration technologies available, we are usually
restricted to active components in the design of integrated analogue circuits.
Since the introduction of integrated circuits, the operational amplifier has served
as the basic building block in analogue circuit design. Since then, new integrated
analogue circuit applications have emerged and the performance requirements for ana-
logue circuits have changed. Voltage-mode operational amplifier circuits have limited
bandwidth at high closed-loop gains due to the constant gain-bandwidth product. Fur-
thermore, the limited slew-rate of the operational amplifier affects the large-signal,
high-frequency operation.
When wide bandwidth, low power consumption and low voltage operation are
needed simultaneously, the voltage-mode operational amplifier easily becomes too
complex and has characteristics that are not needed, for example DC-accuracy. On
the other hand, circuit techniques used in radio frequency applications are usually too