Design and Characterization of Power Converters and Amplifiers for Supply-Modulation based ...

216 Pages·2017·33.31 MB·English

Alma Mater Studiorum – Universita` di Bologna
Scuola di Ingegneria e Architettura
Dipartimento di Ingegneria dell’Energia Elettrica e dell’Informazione
Dottorato di Ricerca in Ingegneria Elettronica,
Telecomunicazioni e Tecnologie dell’Informazione Ciclo XXIX
Settore Concorsuale di Afferenza: 09/E3 Elettronica
Settore Scientifico Disciplinare: ING-INF/01 Elettronica
Design and Characterization of
Power Converters and Amplifiers
for Supply-Modulation based
Transmitter Architectures
Presentata da:
Tommaso Cappello
Coordinatore Dottorato: Relatore:
Prof. A. Vanelli Coralli Prof. A. Santarelli
Correlatore:
Dr. C. Florian
Esame Finale Anno 2017

Contents
Abstract i
Acknowledgements iii
List of Figures iv
List of Tables xvii
1 Introduction 1
1.1 Efficiency Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Signal Property Definitions . . . . . . . . . . . . . . . . . . . . . 4
1.3 Characteristics of Modulated Signals . . . . . . . . . . . . . . . . 5
1.3.1 Telecommunication Signals . . . . . . . . . . . . . . . . . 5
1.3.2 Radar Signals . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.4 Architectures for Efficiency-Enhancement . . . . . . . . . . . . . 7
1.4.1 Doherty . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4.2 Outphasing . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.4.3 Envelope Elimination and Restoration . . . . . . . . . . . 10
1.4.4 Envelope Tracking . . . . . . . . . . . . . . . . . . . . . . 11
1.5 Envelope Characteristics . . . . . . . . . . . . . . . . . . . . . . . 12
1.6 Supply-Modulator Architectures . . . . . . . . . . . . . . . . . . 14
1.6.1 Linear-assisted Switching Converters . . . . . . . . . . . . 15
1.6.2 Multi-phase Switching Converters . . . . . . . . . . . . . 15
1.6.3 Multi-level Switching Converters . . . . . . . . . . . . . . 16
1.7 Organization of the Thesis . . . . . . . . . . . . . . . . . . . . . . 18
2 Power-DAC Supply Modulator 22
2.1 Ideal Digital-to-Analog Converter (DAC) . . . . . . . . . . . . . 23
2.2 Power-DAC Topology . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3 Ideal Power-DAC . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4 Switching Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.5 Power-DAC Technology . . . . . . . . . . . . . . . . . . . . . . . 32
2.6 Experimental Prototype . . . . . . . . . . . . . . . . . . . . . . . 34
2.7 Digital Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
2.8 Multi-Output Supply Board . . . . . . . . . . . . . . . . . . . . . 40
2.9 Measurement Results with Resistive Load . . . . . . . . . . . . . 43
2.9.1 Sinusoidal Test . . . . . . . . . . . . . . . . . . . . . . . . 44
2.9.2 Step Response . . . . . . . . . . . . . . . . . . . . . . . . 46
2.9.3 Telecommunications Signals . . . . . . . . . . . . . . . . . 47
2.9.4 Comparison with State-of-Art . . . . . . . . . . . . . . . . 49
2.10 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3 Supply Modulation of RF PAs for Telecommunications 53
3.1 Class-AB L-Band Power-Amplifier . . . . . . . . . . . . . . . . . 54
3.2 ET-PA Connection and Characterization Setup . . . . . . . . . . 56
3.2.1 Digital Baseband (FPGA VI) . . . . . . . . . . . . . . . . 59
3.2.2 Setup Control (Host VI) . . . . . . . . . . . . . . . . . . . 62
3.2.3 PA Drain Voltage and Current Sensing. . . . . . . . . . . 65
3.2.4 DUT Characterization . . . . . . . . . . . . . . . . . . . . 65
3.2.5 DUT Modeling and Pre-Distortion . . . . . . . . . . . . . 67
3.3 Measurement Results with Telecom Signals . . . . . . . . . . . . 69
3.3.1 LTE 1.4-MHz Bandwidth, 7.5-dB PAPR . . . . . . . . . . 69
3.3.2 LTE 10-MHz Bandwidth, 11.65-dB PAPR . . . . . . . . . 72
3.3.3 Experimental Results Discussion . . . . . . . . . . . . . . 72
3.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4 Supply-Modulation of RFPAs for Radars 76
4.1 Radar Transmitter Architectures . . . . . . . . . . . . . . . . . . 79
4.2 Radar Transmitter with Supply Modulation . . . . . . . . . . . . 80
4.2.1 Digital Baseband . . . . . . . . . . . . . . . . . . . . . . . 82
4.2.2 Class-AB X-Band Power-Amplifier . . . . . . . . . . . . . 83
4.3 GaN PA Characterization, Modeling and Pre-Distortion . . . . . 85
4.3.1 PA Characterization . . . . . . . . . . . . . . . . . . . . . 86
4.3.2 PA Modeling and Pre-Distortion . . . . . . . . . . . . . . 90
4.4 Measurement Results with Arbitrary Pulse-Shaped Waveforms . 92
4.4.1 Pulse-to-Pulse Modulation. . . . . . . . . . . . . . . . . . 94
4.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5 Integrated Power-DAC and PA Transmitter 98
5.1 Integrated Power-DAC Supply Modulator . . . . . . . . . . . . . 100
5.1.1 Power-DAC MMIC Design . . . . . . . . . . . . . . . . . 101
5.1.2 Power-DAC PCB Schematic and Manufacturing . . . . . 104
5.1.3 Power-DAC Multi-Output Supply Board . . . . . . . . . . 106
5.1.4 Power-DAC MMIC Functionality Tests . . . . . . . . . . 109
5.1.5 Power-DAC and Power-Amplifier Characterization . . . . 110
5.1.6 Power-Amplifier Characterization . . . . . . . . . . . . . . 112
5.1.7 Power-DAC Characterization . . . . . . . . . . . . . . . . 113
5.1.8 Baseband Digital Part and Pre-Distortion . . . . . . . . . 115
5.2 Experimental Results. . . . . . . . . . . . . . . . . . . . . . . . . 118
5.2.1 Pulsed Radars with Amplitude and Frequency Modulation 118
5.2.2 High Bandwidth, High PAPR Telecom Signal . . . . . . . 120
5.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
6 Supply-Modulation of an Outphasing Chireix PA 125
6.1 Outphasing Chireix X-band PA . . . . . . . . . . . . . . . . . . . 127
6.1.1 Setup for Static Characterization . . . . . . . . . . . . . . 128
6.1.2 Experimental Results . . . . . . . . . . . . . . . . . . . . 129
6.1.3 Setup for Dynamic Characterization . . . . . . . . . . . . 132
6.1.4 Experimental Results . . . . . . . . . . . . . . . . . . . . 136
6.2 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
7 Dynamic Effects of Electron Devices in SMs and PAs 138
7.1 State-of-Art and Commercial I/V Pulsers . . . . . . . . . . . . . 140
7.2 Dynamic R in GaN Switches . . . . . . . . . . . . . . . . . . . 142
ON
7.2.1 Measurement Setup . . . . . . . . . . . . . . . . . . . . . 143
7.2.2 Current Source . . . . . . . . . . . . . . . . . . . . . . . . 144
7.2.3 I and V Sensing and Measurement . . . . . . . . . . 146
DS DS
7.2.4 T Measurement . . . . . . . . . . . . . . . . . . . . . . . 148
C
7.3 Devices Under Tests (DUTs) . . . . . . . . . . . . . . . . . . . . 149
7.3.1 AlGaN/GaN on Si HEMT . . . . . . . . . . . . . . . . . . 149
7.3.2 AlGaN/GaN on SiC HEMT . . . . . . . . . . . . . . . . . 150
7.4 Experimental Results. . . . . . . . . . . . . . . . . . . . . . . . . 151
7.4.1 Dependency of the R on T . . . . . . . . . . . . . . . 151
ON J
7.4.2 Dependency of the R on T and on X(t) . . . . . . . . 154
ON J
7.4.3 Dependency of the R on T and on V . . . . . . . . 156
ON J DD
7.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
7.6 Appendix: Detailed operation of the Setup . . . . . . . . . . . . 159
7.7 Dynamic Effects in LDMOS PAs . . . . . . . . . . . . . . . . . . 162
7.7.1 PA Electro-Thermal Model . . . . . . . . . . . . . . . . . 162
7.7.2 PA Model Identification . . . . . . . . . . . . . . . . . . . 163
7.7.3 Measurement Setup . . . . . . . . . . . . . . . . . . . . . 164
7.7.4 Experimental Results . . . . . . . . . . . . . . . . . . . . 166
7.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
8 ConclusionsandFutureWork 167
8.1 Main Contributions. . . . . . . . . . . . . . . . . . . . . . . . . . 167
8.2 Possible Topics for Future Work . . . . . . . . . . . . . . . . . . 170
8.3 List of Publications . . . . . . . . . . . . . . . . . . . . . . . . . . 172
8.3.1 International Journals . . . . . . . . . . . . . . . . . . . . 172
8.3.2 International Conferences . . . . . . . . . . . . . . . . . . 172
Bibliography 190
Abstract
The rapid evolution of telecommunication systems has strongly influenced our
lives, and the way we communicate and exchange information. Nevertheless,
much progress is expected to happen in the next years with the introduction
of new generations of wireless communications standards, which require signals
with large bandwidth and very high Peak-to-Average Power Ratio (PAPR) in
order to enhance the spectral efficiency and maximize the data rate. However,
suchdevelopmentscanonlytakeplacethroughtheevolutionofRadio-Frequency
(RF) and microwave technology which should be capable of working at higher
frequencies,higherbandwidthandwithhigherefficienciesthanbefore. Inorder
tomeetthesedemandingspecifications,transmitterarchitectureshavetoevolve
from a single linear RF Power-Amplifier (PA) into more complex architectures.
EnvelopeTracking(ET)isoneofthemostpromisingsolutionsfortheefficiency-
enhancement of next generation transmitters. In ET, the performance and the
efficiencyofthesupplymodulatoraffectsdirectlytheoverallperformanceofthe
transmitter.
The research described in this thesis aims to provide solutions to enhance
the efficiency of the RF PA by means of an ET architecture. To this purpose,
a novel discrete level supply modulator is investigated, which is based on a di-
rect digital-to-analog power conversion. This supply modulator is capable of
synthesizingeightvoltagestepsbymeansofthreeisolatedvoltagesources, thus
behavinglikeaPowerDigital-to-AnalogConverter(Power-DAC).Thisfinevolt-
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Abstract ii
age resolution allows for almost continuous tracking, with very small steps, of
theidealsupplyvoltagethatmaximizestheefficiencyofthePA,whilemaintain-
ing the high efficiency typical of a switching converter. A hybrid version of the
Power-DAC exploiting very fast GaN devices is developed and tested with an
L-band PA achieving efficiency improvement up to 13% with 10MHz of band-
width. Furthermore,amonolithicGaNversionofthePower-DACisprototyped
and tested with an X-band PA both with radar and telecommunication signals
achieving efficiency improvement up to 20% and bandwidth of 20MHz. This
supplymodulatoristestedwithevenmorenon-linearPAssuchastheonesused
intheoutphasingarchitectureshowingpromisingresultswithmodulatedsignals
and efficiency improvement up to 9%. Finally, dispersive phenomena, which af-
fectPAsandswitchesinsupplymodulators,areinvestigated,characterizedand
modeled.
Acknowledgements
Firstly,IwouldliketoexpressmysinceregratitudetomyadvisorProf. Alberto
Santarelli for the continuous support during my Ph.D study, for his patience,
motivation, and knowledge. I am also extremely grateful to Dr. Corrado Flo-
rian, basically my co-advisor, who taught me a lot in these years on how to
conduct research and experiments.
I want also to thank Prof. Fabio Filicori for enlightening me the first glance
ofresearchwiththeideaofthethePower-DACandonthesetupforR mea-
ON
surement. I would like also to express my deep gratitude to all my labmates
presentandpastwhomIowemuchofmyprofessionalgrowth. ThereforeIwish
to mention Rudi, Gian Piero, Daniel, Rafael and Pier Andrea. Thank you for
all the support, advises and stimulating discussions in these years.
Besidesmylabmates,Iwouldliketothankmythesiscommittee: Prof. Zoya
Popovi´c and Prof. Dragan Maksimovi´c for their insightful comments and en-
couragement. In particular I want to thank Prof. Zoya Popovi´c to host me for
6monthsinherresearchgroupattheUniversityofColoradoatBoulder. Being
part of that group involved many opportunities and just as many difficulties.
The best aspect was obviously the chance to meet many talented people: Gre-
gor, Tibault, Scott, Parisa, Michael, Ignacio, Yuanzhe and Ali.
Last but not the least, I would like to thank my family for supporting me
throughout this study and my life in general.
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