Zheng You 200809 PhD

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

Queens University

Kingston, Ontario, Canada

(September, 2008)

Copyright You Zheng, 2008

i

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

OTAs 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

ii

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 120 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.

iii

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 Snchez-Sinencio at Texas A&M University gave the permissions to use

iv

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

OFarrell, Fei Chen, and Wei Yang for their kindly helps and useful discussions during

my graduate studies at Queens 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.

v

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

vi

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...............................