Linear CMOS RF Power Amplifiers: A Complete Design Workflow

191 Pages·2014·4.98 MB·English

by  Hector Solar Ruiz

Hector Solar Ruiz · Roc Berenguer Pérez
Linear CMOS RF
Power Amplifiers
A Complete Design Workflow
Linear CMOS RF Power Amplifiers
Hector Solar Ruiz Roc Berenguer Pérez
•
Linear CMOS RF
Power Amplifiers
A Complete Design Workflow
123
HectorSolarRuiz
RocBerenguer Pérez
Electronics andCommunication Department
Centre of Technical Research (CEIT)
and Universityof Navarra (Tecnun)
San Sebastian
Spain
ISBN 978-1-4614-8656-5 ISBN 978-1-4614-8657-2 (eBook)
DOI 10.1007/978-1-4614-8657-2
SpringerNewYorkHeidelbergDordrechtLondon
LibraryofCongressControlNumber:2013945144
(cid:2)SpringerScience+BusinessMediaNewYork2014
Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof
the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations,
recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor
informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar
methodology now known or hereafter developed. Exempted from this legal reservation are brief
excerpts in connection with reviews or scholarly analysis or material supplied specifically for the
purposeofbeingenteredandexecutedonacomputersystem,forexclusiveusebythepurchaserofthe
work. Duplication of this publication or parts thereof is permitted only under the provisions of
theCopyright Law of the Publisher’s location, in its current version, and permission for use must
always be obtained from Springer. Permissions for use may be obtained through RightsLink at the
CopyrightClearanceCenter.ViolationsareliabletoprosecutionundertherespectiveCopyrightLaw.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this
publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexempt
fromtherelevantprotectivelawsandregulationsandthereforefreeforgeneraluse.
While the advice and information in this book are believed to be true and accurate at the date of
publication,neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityfor
anyerrorsoromissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,with
respecttothematerialcontainedherein.
Printedonacid-freepaper
SpringerispartofSpringerScience+BusinessMedia(www.springer.com)
You have had the good fortune to find real
teachers, authentic friends, who have taught
you everything you wanted to know without
holding back. You have had no need to
employ any tricks to steal their knowledge,
because they led you along the easiest path,
even though it had cost them a lot of hard
work and suffering to discover it… Now, it is
your turn to do the same, with one person,
and another—with everyone
Saint Josemaría Escrivá
Founder of the University of Navarra
To our families
Preface
Thegreatspreadofwirelesstechnologiesthatisnowobservedreflectstheinterest
in greater connectivity and pushes the development of portable devices that are
able to connect to these emerging wireless technologies. Portable devices, then,
need to offer increasing connectivity capabilities while maintaining their perfor-
mance in terms of size and autonomy. Therefore, portable devices must further
reduce not only their power consumption but also the size of their electronics. In
other words, high performance, low cost, and highly integrated Radio Frequency
IntegratedCircuits(RFICs)areincreasinglyrequiredbytheconsumerelectronics
industry.
CMOS integrated technology has played an important role in this wireless
explosion due to its high functionality, integration capabilities, and low cost.
Consequently,poweramplifiers(PAs)implementedinstandardCMOSprocesses,
whichofferperformanceclosetothatfoundinmoreexpensivetechnologies,such
as GaAs, are highly attractive. This is not only because CMOS technologies are
extensively currently used in RF ICs implementations but also because CMOS
PAs may offer low cost and high integration characteristics.
However, the PA is still an RF component that has not been completely inte-
grated within the whole transceiver due to the existing trade-off between high-
performance and high integration characteristics. If high-performance PAs are
required, designers focus on expensive processes that prevent PAs from being
implementedinlowcost,highlyintegrateddevices.Conversely,ifhighintegration
is desired, achieving high-linearity and high-efficiency CMOS PAs is still a
challenge.Inadditiontothis,PAshaveadirectimpactontransceiverperformance
becausethePApowerconsumptionmayeasilymakeup50%oftheoverallpower
consumption of the transceiver, meaning that a high-performance PA is crucial.
This work, then, focuses on design techniques for high-performance, fully
integrated linear CMOS PAs for wireless applications. The work provides a
complete flow for the design of the CMOS PA by describing the steps from the
very beginning of the design process. The book provides an overview of the
metrics that quantify the performance of the PA in order to obtain the PA
requirements.InChap.3,thelinearityandefficiencymetricsofPAscanbefound
along with the metrics of PAs that handle digitally modulated channels. Stability
and power capability parameters have been also included.
vii
viii Preface
Once the specific requirements of the PA have been established, this work
providesdesignerswithaPAmodeltohelpanticipatetheexpectedperformanceof
the PA. Based on the most important design parameters such as biasing, supply
voltage,inductorqualityfactors,currentconsumption,etc.,themodelprovidesthe
expected metrics of the PA in terms of efficiency, linearity, and output power
levels. This model proves, then, to be a useful starting point in the first design
steps. The model description can be found in Chap. 6.
Once parameters such as current consumption, supply voltage, or the required
inductor quality factors have been quantified, the book discusses the optimization
process of all the PA stages. Based on a linear CMOS PA example, the output
matching network, output, and driver amplifying stages, the input matching net-
work, and the interstage matching network are detailed. In addition, the main
issues that must be considered in the PA layout design process in order to avoid
performancedegradationarealsopresented. Specialattentionispaidtotheissues
of integrated inductors in PAs, along with the extra considerations that designers
must know inorder to optimize inductor performance. Thedetailsfor the PAand
the integrated inductor optimization process are also found in Chap. 6.
The test setups and procedures required to characterize a PA are described in
Chap. 7. In order to fully characterize PA performance, single-tone test and tests
based on digital channels should be performed. The book presents both types of
tests,alongwithresultsbasedontheaforementionedlinearCMOSPAexample.In
addition,testsetupsandproceduresformeasuringinductorsforPAsareincluded.
ThebookalsoprovidesanintroductoryoverviewoftheimpactofthePAinthe
transceiverquantified for modern communicationstandardsinChap. 1.Chapter2
addressestheissuesandlimitationsthatCMOSprocessesimposeonthedesignof
high-performance linear PAs such as the low supply voltage that is available in
modern submicron CMOS processes or low transistor transconductance. This
chapter also details several other aspects of CMOS processes, such as substrate
losses, impedance transformation, or stability and reliability issues.
Fundamentals of PAs, i.e., the classification of PAs into different classes, as
current source oras switch-typePAs, are also presented inChap.4. Thepractical
uses of the different PA classes in implementing a linear PA architecture are also
presented; examples might be using class C PAs in linear Doherty PAs or com-
bining class D PAs to implement an outphasing PA architecture.
Finally, Chap. 5 is devoted to PA architectures that are of interest for building
fully integrated PAs in order to achieve higher output power levels, enhanced
linearity, or better efficiency. Power combined PAs and the Doherty architecture,
along with dynamic supply, adaptive biasing or digital predistortion techniques,
andtheuseofcascodetransistorsareallinterestingsolutionstoboostPAlinearity,
efficiency,oroutputpowerlevelsinCMOSprocesseswithlimitedsupplyvoltage.
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The Power Amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Impact of PA on Integrated Transceivers . . . . . . . . . . . . . . . . . . . . . 1
Requirements of Modern Wireless Standards . . . . . . . . . . . . . . . . 2
CMOS Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Organization of the Book. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2 Power Amplifier Fundamentals: Metrics. . . . . . . . . . . . . . . . . . . . 11
AM–AM Distortion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Saturated Power and One dB Compression Point . . . . . . . . . . . . . 11
Third-Order Intercept Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
AM–PM Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Digital Channel Metrics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Spectral Regrowth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Error Vector Magnitude. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Efficiency Metrics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Drain Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Power-Added Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Power Back-Off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Transmit Power Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Stability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Power Capability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3 Power Amplifier Fundamentals: Classes. . . . . . . . . . . . . . . . . . . . 29
Current Source PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Transconductance Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Knee Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
Class A PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Class AB PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Class B PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Class C PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
ix
x Contents
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Switch-Type PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Class D PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Class E PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Harmonic Tuning: Class F PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4 CMOS Performance Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Low Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Effect of the Knee Voltage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Load Transformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Reliability Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Oxide Breakdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Hot Carrier Degradation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Reliability Projection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Reliability Under RF Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Transistor Parasitics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Substrate Issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Stability Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5 Enhancement Techniques for CMOS Linear PAs . . . . . . . . . . . . . 75
Cascode PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Thick Oxide Cascode PAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Self-Biased Cascode PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Multiple Stacked Cascode PAs. . . . . . . . . . . . . . . . . . . . . . . . . . 79
Combined PAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
Integrated Transformer Power Combining . . . . . . . . . . . . . . . . . . 80
Simple Parallel Combination . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Doherty PAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Predistorted PAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Dynamic Supply or Envelope Tracking . . . . . . . . . . . . . . . . . . . . . . 88
Adaptive Biasing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
6 Power Amplifier Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
A Model for the Power Amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . 101
Model Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Output Power, Drain Efficiency and PAE . . . . . . . . . . . . . . . . . . 111
Model-Based Analyses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Starting Point Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Contents xi
Measurement Comparisons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Power Amplifier Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Schematic Circuit Description. . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Design Flow. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Power Inductor Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Top Metal Layer Width Considerations . . . . . . . . . . . . . . . . . . . . 130
Multiple Metal Layer Considerations. . . . . . . . . . . . . . . . . . . . . . 131
Inductor Geometry Considerations. . . . . . . . . . . . . . . . . . . . . . . . 132
Accuracy Analysis of the Electromagnetic Simulator. . . . . . . . . . . 133
Power Inductor Design Flow . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Layout Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Circuit Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Differential Design Considerations . . . . . . . . . . . . . . . . . . . . . . . 141
Passive Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
Stage Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Pad Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
7 Test Setups and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Inductor Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Test Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
Prior Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Calibration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
De-Embedding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
PA Characterization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
Single-Tone Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
Digital Channel Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
Reliability and Maximum Rating . . . . . . . . . . . . . . . . . . . . . . . . 175
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
8 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Highlights. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Main Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
A Complete Design Flow for a CMOS Linear PA. . . . . . . . . . . . . 181
Useful Enhancement Techniques for Linear CMOS PAs . . . . . . . . 181
Design and Characterization of Power Inductors. . . . . . . . . . . . . . 181
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183