operational transconductance amplifiers for gigahertz applications

159 Pages·2008·8.34 MB·English

OPERATIONAL TRANSCONDUCTANCE AMPLIFIERS
FOR GIGAHERTZ APPLICATIONS

by

You Zheng

A thesis submitted to the
Department of Electrical and Computer Engineering
In conformity with the requirements for
the degree of Doctor of Philosophy

Queen’s University
Kingston, Ontario, Canada
(September, 2008)

Copyright ©You Zheng, 2008
Abstract

A novel CMOS operational transconductance amplifier (OTA) is proposed and
demonstrated in this thesis. Due to its feedforward-regulated cascode topology, it breaks
the previous OTA frequency limit of several hundred MHz and operates at frequencies up
to 10 GHz with a large transconductance. This is confirmed by an in-depth high-
frequency analysis, simulations, and experimental demonstrations using purpose-built
circuits. Experimental results also show that the proposed OTA has high linearity and low
intermodulation distortion, which is of particular interest in microwave circuits. The
OTA’s noise behavior and the effects of process variations, device mismatch, and power
supply noise on the transconductance are also studied. To the best of our knowledge, the
noise analysis here is the first of its kind on regulated cascode circuits, which can be
applied to other regulated cascodes with minor changes.
Three microwave applications of this OTA are explored in this thesis: 1) an active
bandpass filter with a wide tuning range, 2) a 2.4-GHz ISM-band variable phase shifter,
and 3) a microwave active quasi-circulator, which are all in CMOS MMIC form. These
three circuits can be easily integrated with other chip components for System-on-Chip
(SoC) realizations. The use of the OTA makes these three applications super compact: the
active filter is at least 5 times smaller than previous circuits with a similar topology, and
the phase shifter and quasi-circulator are at least 3 times smaller than previous works in
that frequency range. Furthermore, the tunability of the developed OTA on its
transconductance gives its applications extra freedom in tuning their frequencies and
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gains/losses electronically. In the first application, the active bandpass filter has a novel
narrowband-filtering topology and has a wide tuning-range of 28% around 1.8 GHz,
which makes it very suited for reconfigurable multi-band wireless systems. In the second
and third applications, the active variable phase shifter has a comparable variable phase
shift range of 120º in the 2.4-GHz ISM band and the active quasi-circulator has
transmissions close to 0 dB and directivities over 24 dB from 1.5 GHz to 2.7 GHz.
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Acknowledgements

Deep thanks are owed to many people who contributed to the creation of this thesis.
Without their invaluable supports, this thesis would never come true.
I would like to first thank my supervisor, Prof. Carlos E. Saavedra for his enthusiasm
and inspiration in providing supervision, encouragement and sound advices throughout
all the stages of my thesis project. I also cherish all the leisure time we spent together on
tennis, movie, and lunch. With his invaluable knowledge, insights and friendliness, he
helped to make research fun for me.
CMC Microsystems offered numerous financial and technical supports for this thesis
project, including IC designs, fabrications, and tests. Many thanks to its Silicon
Allocation Review Committee (SARC) for granting the IC areas of this thesis project and
also its technical support team including Jian Wang, Jim Quinn and Feng Liu for their
great patience in answering my endless questions and explaining the design and
fabrication details to me. Thanks are also owed to Mariusz Jarosz in the CMC
Engineering Department and Patricia Greig in the CMC Photonics Testing Collaboratory
for providing me the most convenience in using their instruments for the tests.
I would also like to thank Prof. Brian M. Frank, who gave me a lot of invaluable
instructions with his excellent knowledge and deep insights in RF CMOS technologies.
His friendliness and his willingness to help people strongly impressed me.
Prof. Edgar Sánchez-Sinencio at Texas A&M University gave the permissions to use
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some figures in this thesis from his previous distinguished works. His kindly help is
greatly appreciated.
Thanks are also given to Brad Jackson, Ahmed El-Gabaly, Gideon Yong, Stanley Ho,
John Carr, Ryan Bespalko, Yang Zhang, Mridula Das, Francesco Mazzilli, Michael
O’Farrell, Fei Chen, and Wei Yang for their kindly helps and useful discussions during
my graduate studies at Queen’s University.
Furthermore, I want to thank my parents and my wife, Yonghong Yang, for their
encouragement and understanding over years. Thanks are also given to my little baby,
Angela Y. Zheng, for her company during this thesis writing.

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Table of Contents

Abstract............................................................................................................i
Acknowledgements........................................................................................iii
Table of Contents.............................................................................................v
List of Figures..............................................................................................viii
List of Tables................................................................................................xii
Abbreviations and Symbols.........................................................................xiii

Chapter 1 General Introduction.......................................................................1
1.1 High Frequency OTAs..............................................................................................1
1.2 OTA Concept............................................................................................................2
1.3 CMOS OTA History.................................................................................................4
1.4 Thesis Contributions and Overview..........................................................................4

Chapter 2 OTA Review...................................................................................6
2.1 CMOS OTAs.............................................................................................................6
2.1.1 Single input/output OTAs...................................................................................6
2.1.2 Differential OTAs...............................................................................................8
2.2 OTA Trends.............................................................................................................11
2.2.1 High Frequency................................................................................................12
2.2.2 High Linearity...................................................................................................13
2.2.3 Low power........................................................................................................17
2.3 OTA Applications...................................................................................................19
2.3.1 Variable Resistors.............................................................................................20
2.3.2 Active Inductors ...............................................................................................22
2.3.3 Filters................................................................................................................25
2.3.3.1 OTA-C Filters............................................................................................25
v
2.3.3.2 High-Frequency Filters..............................................................................29
2.3.4 Oscillators.........................................................................................................30
2.4 Summary.................................................................................................................31

Chapter 3 High-Frequency OTAs................................................................. 32
3.1 Introduction.............................................................................................................32
3.2 Cascoding Techniques.............................................................................................34
3.3 Feedforward-Regulated Cascode OTA...................................................................39
3.4 OTA Theoretical Analyses......................................................................................42
3.4.1 High-Frequency Analysis.................................................................................42
3.4.2 Noise Analysis..................................................................................................49
3.5 Microwave Performance.........................................................................................51
3.5.1 Transconductance and Frequency Response....................................................51
3.5.2 Power and Intermodulation Distortion.............................................................57
3.5.3 Demonstration Circuits.....................................................................................61
3.5.3.1 Active Inductor...........................................................................................61
3.5.3.2 Microwave Oscillator.................................................................................65
3.6 Summary.................................................................................................................71

Chapter 4 Wide Tuning-Range Bandpass Filter — OTA Application I...... 72
4.1 Introduction...................................................................................................................................72
4.2 Topology Considerations..........................................................................................................74
4.2.1 Ladder Filter Topology......................................................................................................74
4.2.2 Coupled-Resonator Filter Topology.................................................................79
4.3 Active Bandpass Filter Design................................................................................84
4.4 Experimental Demonstration...................................................................................89
4.5 Summary.................................................................................................................94

Chapter 5 ISM-Band Variable Phase Shifter — OTA Application II.......... 95
5.1 Introduction.............................................................................................................95
5.2 Overview of MMIC Phase Shifting Techniques.....................................................97
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5.3 OTA-based Active Variable Phase Shifter............................................................101
5.3.1 Phase Shifter Design.......................................................................................101
5.3.2 Simulation and Experimental Demonstrations...............................................105
5.4 Summary...............................................................................................................113

Chapter 6 Active MMIC Quasi-Circulator — OTA Application III ......... 114
6.1 Introduction...........................................................................................................114
6.2 Quasi-Circulator Design........................................................................................116
6.3 Experimental Demonstration.................................................................................119
6.4 Summary...............................................................................................................124

Chapter 7 Conclusions................................................................................ 125
7.1 Thesis Summary and Contributions......................................................................125
7.2 Future Work..........................................................................................................127

References................................................................................................... 129

Appendix..................................................................................................... 141
A-1. Derivation of i and i ..........................................................................................141
p n
A-2. Derivation of Z and Z .......................................................................................142
p n
A-3. Computation of Butterworth and Chebyshev Filters..........................................143

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List of Figures

1-1. Three types of OTAs and their equivalent circuit models: (a) single-
input/output, (b) differential-input single-output, and (c) differential
input/output........................................................................................................3

2-1. Single-input/output OTAs from [16] with permission: (a) a common-
source transconductor, (b) a cascode transconductor, (c) a folded-
cascode transconductor, (d) a regulated-cascode transconductor, and (e)
a positive transconductor...................................................................................7
2-2. Differential-input single-output CMOS OTAs from [16] with permission:
(a) a simple OTA, and (b) a balanced OTA.......................................................9
2-3. Differential-input/output CMOS OTAs from [16] with permission................11
2-4. Source-degeneration linear techniques from [16] with permission.........15
2-5. Linear techniques using nonlinear-term sum cancellation from [16] with
permission: (a) multiplication-sum technique, and (b) squaring-sum
technique (V = -V ).........................................................................................16
1 2
2-6. A complex combined linear technique from [26] with permission.................17
2-7. (a) Simplified class-AB amplifier and (b) level-shifter............................19
2-8. OTA variable resistors (a) single-ended variable resistor (b) floating
variable resistor after [2]..................................................................................20
2-9. (a) OTA negative variable resistor, and (b) its application in a loss
compensation for a LC tank circuit.............................................................21
2-10. (a) single-ended active inductor, and (b) floating active inductor after [2].....23
2-11. Two-transistor active inductors using CS-CD and CG-CS topologies
after [41]...........................................................................................................24
2-12. OTA integrator.................................................................................................26
2-13. Four second-order OTA-C filter structures after [2]........................................27
2-14. OTA-C oscillators after [46]: (a) 2OTA3C, (b) 3OTA2C, and (c) their
unified equivalent circuit model......................................................................30

3-1. Cascode OTAs from [16] with permission: (a) basic cascode
transconductor, and (b) regulated cascode transconductor..............................34
3-2. Output resistance model of the basic cascode OTA........................................36
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3-3. Equivalent circuit model of the regulated cascode transconductor. ................38
3-4. Regulated cascode OTAs using different feedback regulation topologies:
(a) a common-source amplifier (T ) after [54] and (b) a common-source
3
amplifier plus an additional OTA (g ) after [50].............................................38
m
3-5. (a) Proposed CMOS fully-differential OTA using negative feedforward-
regulated cascodes, (b) one pair of cross-connected cascodes. .......................40
3-6. (a) High-frequency half equivalent circuit model of the OTA in Fig.3-5,
(b) high-frequency MOSFET transistor model, (c) simplified circuit
model of the proposed OTA.............................................................................43
3-7. Thermal noise model of the proposed OTA....................................................50
3-8. (a) Block diagram and (b) microphotograph of the fabricated OTA
synthetic resistor (outlined by the black ring)..................................................52
3-9. Proposed OTA’s transconductance (V =-0.55V)............................................55
C
3-10. Input/output parasitic capacitance of the proposed OTA (V =-0.55V)...........55
C
3-11. Distributions of the transconductance and the input/output parasitic
capacitance with 1% deviations of W/L for all transistors in the Monte
Carlo simulation (@2GHz)..............................................................................56
3-12. (a) Schematic and (b) microphotograph of the single-stage differential
amplifier...........................................................................................................58
3-13. Measured P1dB compression point of the test amplifier in Fig. 3-12(a).........60
3-14. Measured IP3 intermodulation of the test amplifier in Fig. 3-12(a) with
two-tone signal inputs......................................................................................60
3-15. (a) Schematic and (b) microphotograph of the fabricated active inductor
(outlined by the black ring)..............................................................................62
3-16. Inductance of the active inductor (Vc=-0.55V)...............................................63
3-17. Series resistance of the active inductor (Vc=-0.55V)......................................64
3-18. Distribution of the active inductance in Fig. 3=16 with 1% deviations of
W/L for all transistors in the Monte Carlo simulation (@2GHz)....................65
3-19. (a) Schematic and (b) microphotograph of the fabricated active-inductor-
based oscillator.................................................................................................67
3-20. Measured output fundamental spectrum of the oscillator at V =-0.55V.........68
C
3-21. Measured output harmonic spectra of the oscillator at V =-0.55V.................68
C
3-22. Measured harmonic output powers and frequency versus the OTA
control voltage.................................................................................................69
3-23. Measured phase noise of the oscillator at 2.89 GHz........................................70

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