Feedforward Amplifiers for Wideband Communication Systems

187 Pages·2006·3.12 MB·English

by  Jon Legarda

FEEDFORWARDAMPLIFIERS FOR WIDEBAND
COMMUNICATION SYSTEMS
Feedforward Amplifiers for
Wideband Communication Systems
by
JON LEGARDA
CEIT and TECNUN (University of Navarra), San Sebastian,
Spain
AC.I.P. Catalogue record for this book is available from the Library of Congress.
ISBN-10 0-387-35137-X (HB)
ISBN-13 978-0-387-35137-7 (HB)
ISBN-10 0-387-35138-8 (e-book)
ISBN-13 978-0-387-35138-4 (e-book)
Published by Springer,
P.O. Box 17, 3300 AADordrecht, The Netherlands.
www.springer.com
Printed on acid-free paper
All Rights Reserved
© 2006 Springer
No part of this work may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, microfilming, recording
or otherwise, without written permission from the Publisher, with the exception
of any material supplied specifically for the purpose of being entered
and executed on a computer system, for exclusive use by the purchaser of the work.
Dedication
This book is dedicated to my
mom, dad, brothers and my
girlfriend Oihane. Thank you
all for everything.
Contents
Preface xiii
Acknowledgments xvii
1. Introduction 1
1. Radio-Electric transmitters - Historical overview 1
1.1 Arc and spark transmitters 1
1.2 Multi-polar alternators 3
1.3 Thermoionic vacuum tubes 3
1.4 Discrete transistors 5
1.5 Integrated transistors 6
2. Digital communication systems 6
2.1 Analog signal 6
2.2 Discrete signal 7
2.3 Digital signal 7
2.4 Digital transmission 7
2.5 Electromagnetic spectrum 9
2.6 Modulation techniques 10
2.7 Signal degradation 12
2.7.1 Attenuation 12
2.7.2 Noise 13
2.7.3 Distortion 13
2.8 Basic architectures of wireless transmitters 14
2.8.1 Analog I/Q modulator vs. digital IF 15
2.8.2 Other implementations 15
vii
viii Contents
3. Digital modulation 16
3.1 Applications 17
3.2 Phase Shift Keying 18
3.3 Frequency Shift Keying 19
3.4 Minimum Shift Keying 20
3.5 Quadrature Amplitude Modulation 20
3.5.1 I/Q offset modulation 22
3.5.2 Differential modulation 22
3.6 Broadband wireless access techniques 23
2. Nonlinear distortion 25
1. Harmonic distortion 27
1.1 Nth harmonic distortion coefficient 29
1.2 Global harmonic distortion 30
2. Intermodulation analysis 30
2.1 2 tone intermodulation 30
2.2 3 tone intermodulation 33
3. Cross modulation (X ) 34
mod
3.1 Cross modulation (m<<1) 36
3.2 Cross modulation (m>>1) 37
4. Distortion measurement techniques 39
4.1 Harmonic distortion measurement 39
4.2 Third order distortion measurement 40
4.2.1 Two tone procedure 40
4.2.2 Third order intercept point (IP) 41
3
4.3 Second order distortion measurement 45
4.4 Cross modulation (X ) measurement 47
mod
5. Measurements of wideband digital signals 49
5.1 Peak to average power ratio and CCDF curves 49
5.2 Modulation quality measurements 51
5.3 Code domain power 52
5.4 Adjacent Channel Leakage Ratio (ACLR) 53
3. RF power amplifiers 55
1. Classification of power amplifiers 56
2. Power amplifiers parameters 57
2.1 The efficiency rate 57
2.2 The back-off 58
2.3 Power utilization factor (PUF) 58
3. Class A 59
4. Class B 61
5. Class AB (outphasing) 63
6. Class C 65
Contents ix
7. Switching amplifiers 67
7.1 Class D 68
7.2 Class E 70
7.3 Class F 72
8. More operating modes 73
4. Linearization techniques 75
1. Classification of the linearization techniques 75
2. Feedback 76
2.1 RF Feedback 76
2.2 Envelope Feedback 77
2.3 Envelope and phase Feedback 78
2.4 Polar Loop 78
2.5 Cartesian Loop 79
3. Predistortion 80
3.1 RF Predistortion 81
3.1.1 Simple analog Predistortion 81
3.1.2 Compound Predistortion 83
3.2 Envelope Predistortion 83
3.3 Baseband Predistortion 84
4. Feedforward 86
5. Efficiency enhancement techniques 87
5.1 Bypassing 87
5.2 Envelope Elimination and Restoration 89
5.3 Bias Adaptation 90
5.4 LINC 90
5.5 Doherty Method 92
5.6 CALLUM 93
6. Comparison of linearization techniques 94
5. Feedforward amplifiers 97
1. Feedforward linearization technique 97
1.1 Frequency dependence 101
1.2 Amplitude and phase adjustments 105
1.3 Error amplifier distortion 107
1.4 Isolation lack 108
1.5 Main signal path loss 109
2. Feedforward in wideband communications systems 110
6. Implementation of Feedforward amplifiers 115
1. Simulation of the Feedforward architecture 116
1.1 Simulation models 116
1.2 Simulation of the error loop 117
x Contents
1.3 Simulation of the distortion cancellation loop 119
1.4 The isolation effect 120
2. Selection of the error amplifier 122
3. The adjustment of the cancellation loops 124
3.1 Delay lines 124
3.1.1 Configuration 125
3.1.2 Length tolerances 125
3.1.3 Packaging 125
3.1.4 System design 126
3.2 An adjustment method for delay lines 126
4. Distortion enhanced measurement techniques 130
4.1 Spectrum analyzer mixer level optimization 131
4.1.1 Mixer level 131
4.1.2 Signal to noise ratio versus mixer level 132
4.1.3 Signal to noise ratio with external noise 134
4.1.4 Signal to distortion ratio versus mixer level 135
4.1.5 The dynamic range chart 135
4.1.6 Spectrum analyzer distortion 136
4.2 Enhanced ACLR measurements 137
4.2.1 Signal to noise ratio 137
4.2.2 Spectral regrowth 139
4.2.3 Phase noise influence 140
4.2.4 Dynamic range chart for wideband signals 141
5. Improvements of Feedforward amplifier 142
5.1.1 OIP improvement 143
3
5.1.2 ACLR improvement 144
7. Adaptive Feedforward amplifiers 145
1. Adaptive adjusting methods for Feedforward amplifiers 145
1.1 Maximum cancellation method 146
1.1.1 Error signal minimization 146
1.1.2 Distortion cancellation 147
1.1.3 Maximum cancellation 147
1.2 Maximum output method 148
2. Distortion monitoring architectures 150
2.1 Signal correlation 150
2.2 Pilot signal detection 152
2.3 Power minimization 153
3. An output signal monitoring architecture 156
3.1 Switched RF receiver 156
3.2 Frequency down-conversion 158
3.3 Amplitude equalization 160
Contents xi
4. The adaptive Feedforward amplifier 162
5. Conclusions 165
References 167
Index 175
Preface
This work has been possible thanks to the research carried out throughout
several years in the field of the linearization techniques applied to digital
communication systems, particularly to those with high frequency-efficient
modulation techniques.
The wireless telecommunications are more and more demanded for the
Information Society. Such requirements are reflected as a great many of
communication standards with specific coverage applications and, above all,
with higher and higher data transmission rates.
The electromagnetic spectrum, nevertheless, is a scarce asset that can not
be spread and despite the increasingly tendency to transmit in higher
frequencies, the bandwidths assigned to each application are always
exploited to the limit.
This context merges in the need of developing frequency-efficient
modulations with widespread codification techniques that result in wideband
communication systems, with strict regulations in the usable frequency
bandwidths and tight restrictions in the spurious emissions over the
remaining spectrum.
The radio frequency transmitters do not remain impassive to those
changes, especially the power amplifiers, which efficiency and linearity
directly determines the correct performance of the entire transmission
system. The linearity specifications are commonly fixed by the
telecommunication standards while the efficiency rates directly strikes the
commercial viability of those devices.
This work tries to put into practice the Feedforward linearization
technique, aimed at improving either the linearity or efficiency parameters of
power amplifiers, just intended for achieving a trade-off between the
xiii