Continuous Mode High Efficiency Power Amplifier Design for X Band

247 Pages·2014·32.19 MB·English

Continuous Mode High Efficiency
Power Amplifier Design for X Band
A thesis submitted to Cardiff University
In candidature for the degree of
Doctor of Philosophy
Author: Tim Canning
Date: March 2014
I

Summary
Thisthesisisfocusedontheinvestigationandimplementationofnoveltechniquesforthe
designofXband(8 12GHz)poweramplifiers.
−
Oneofthemaintopicsistheexpansionandnovelimplementationofcontinuousmode
theory, with the intention of improving the bandwidth and efficiency of X band power
amplifiers. This work builds upon the Class B/J continuous mode theory to incorporate
cases where [Z ] = R , not described by the original Class B/J theory, with a tool
F0 L
(cid:60) (cid:54)
calledthe“clippingcontour”.
The clipping contour tool shows a graphical representation on the Smith chart of
the boundary between impedances generating a voltage waveform which will modulate
or “clip” the current waveform, and a voltage waveform which will leave the current
waveform unaltered. This non-clipping space is shown, with measured load pull and
amplifierdata,torepresentthemaximumefficiencycaseforagivenZ ,thustheclipping
F0
contour tool thus gives designers the ability to predict the areas of highest efficiency and
powergivenanyZ ,withouttheneedtousecostly,timeconsumingmultiharmonicload
F0
pulltechniques.
Push pull amplifiers using quarter wave coupled line baluns are proposed as an ideal
matching topology to exploit this new tool. Various balun topologies are studied using
a novel extended transmission line model. This model is shown to predict accurately
and explain the “trace separation” effect seen in planar baluns and not their 3D coaxial
cable equivalents. It also forms the basis of analysis which results in a powerful new
equation capable of guaranteeing the elimination of trace separation completely, without
compromising performance. This equation is used to design an optimal balun which
possesses the largest fractional bandwidth (130%) of any balun ever published on single
layerthinfilmAlumina,whilstsimultaneouslyeliminatingtraceseparation.
The optimised Alumina baluns are used to construct push pull output demonstrator
circuitswhichshowefficienciesof40%overgreaterthananoctavebandwidth,asignificant
advancementofanyothercomparablepublishedwork. Thesetechniquesdemonstratethe
potential to exceed double octave bandwidths with efficiencies greater than 40% once
optimised. Initial investigations on MMIC and 2.5D processes show the potential to
replicatetheAluminaperformanceoveroctaveanddecadebandwidthsrespectively.
III
Acknowledgements
This thesis and the past 3 years would not have been possible without the help, support
and inspiration of many. Many thanks to my friends and family, for their support, prayer
andpatience,especiallywhenItryandexplainmythesissubjecttothem.
Thanks also to my industrial sponsor SELEX ES, my industrial supervisor Dr Angus
McLachlan and the team at SELEX Edinburgh for their technical and financial support,
andtheirpatienceinenduringmyprogresspresentations.
To my colleagues at Cardiff university, for patiently listening to my grumblings and
the many excellent titbits of advice, suggested long after my patience with the particular
measurement or piece of equipment had evaporated, I will miss you all. Thanks must go
toProfPaulTaskerforaccesstomeasurementequipment,ideasandassistancenavigating
thedangerousworldofnon-linearmeasurements. SpecialthankstomycolleagueDrJeff
Powellforhiscontinuedcollaboration,patiencewithmymanyquestionsandremarkable
layout skills, his contribution to this work has been invaluable. Special thanks also to
my supervisor Prof Steve Cripps, a gold mine of novel ideas, common sense and legacy
measurementequipment.
Lastly I thank my wife Johanna Canning. I cannot imagine any scenario where this
thesiswouldhavebeencompletedwithoutherunwaveringloveandsupport. Idedicateit
toher.
IV
Contents
1 Motivation&Objectives XIII
1.1 ThesisObjectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XVII
1.2 KeyContributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XVII
2 TheoryandLiteratureReview 1
2.1 AreviewofXBandBroadbandPAs . . . . . . . . . . . . . . . . . . . . 1
2.1.1 GaAsFETDevelopment . . . . . . . . . . . . . . . . . . . . . . 2
2.1.2 DevelopmentsinSolidStateBroadbandXBandPAs . . . . . . . 3
2.2 MicrowaveTransistorsandAmplifierTheory . . . . . . . . . . . . . . . 6
2.2.1 AmplifierEfficiencyandLoading . . . . . . . . . . . . . . . . . 6
2.2.2 MicrowaveTransistorTechnology . . . . . . . . . . . . . . . . . 9
2.2.3 ParasiticsandModelling . . . . . . . . . . . . . . . . . . . . . . 13
2.2.4 AmplifierModesofOperation . . . . . . . . . . . . . . . . . . . 15
2.2.5 MatchingTechniques . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2.6 AlternativeMatchingTechniques . . . . . . . . . . . . . . . . . 29
2.3 LinearMicrowaveMeasurements . . . . . . . . . . . . . . . . . . . . . . 31
2.3.1 TwoandN-portLinearNetworkParameters . . . . . . . . . . . . 32
2.3.2 Balanced/MixedModeSparameters . . . . . . . . . . . . . . . . 33
2.4 Non-linearMicrowaveMeasurements . . . . . . . . . . . . . . . . . . . 34
2.4.1 WaveformMeasurements . . . . . . . . . . . . . . . . . . . . . . 36
2.5 BalunsandPush-PullAmplifiers . . . . . . . . . . . . . . . . . . . . . . 37
2.5.1 CoupledLine/TransmissionLineTransformerBaluns . . . . . . . 39
2.5.2 Electricalgroupings . . . . . . . . . . . . . . . . . . . . . . . . 43
2.5.3 Physicalgroupings . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.5.4 BalunsinAmplifiers(Push-Pull) . . . . . . . . . . . . . . . . . . 51
2.6 Particleswarmoptimisation(PSO) . . . . . . . . . . . . . . . . . . . . . 52
2.6.1 BasicAlgorithm . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.6.2 Advancedversions . . . . . . . . . . . . . . . . . . . . . . . . . 54
3 InputHarmonicShorting 55
3.1 SimulatedGateVaractorEffects . . . . . . . . . . . . . . . . . . . . . . 55
3.2 MMICTestCells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.3 WaveformMeasurements . . . . . . . . . . . . . . . . . . . . . . . . . . 60
V
3.3.1 XbandClassB/JWaveforms . . . . . . . . . . . . . . . . . . . . 64
3.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4 ClippingContours 66
4.1 ExpandingClassB/JintoClippingContours . . . . . . . . . . . . . . . . 68
4.2 SecondHarmonicClippingContours . . . . . . . . . . . . . . . . . . . . 72
4.2.1 ClosedFormSolution . . . . . . . . . . . . . . . . . . . . . . . 72
4.2.2 PlottingandAnalysis . . . . . . . . . . . . . . . . . . . . . . . . 74
4.2.3 PredictingtheminimumVmax: UnityBoundaryCrossing . . . . 78
4.3 FundamentalHarmonicClippingContours . . . . . . . . . . . . . . . . . 79
4.3.1 ClosedFormSolutiontoFundamentalHarmonicClippingContours 80
4.3.2 PlottingAndAnalysis . . . . . . . . . . . . . . . . . . . . . . . 81
4.4 CurrentWaveformInfluenceonClippingContours . . . . . . . . . . . . 84
4.4.1 ClippedHalfWaveArbitrarilyRectifiedSinusoid . . . . . . . . . 85
4.4.2 EvenModeMaximallyFlatWaveform . . . . . . . . . . . . . . . 90
4.5 WaveformMeasurementVerification . . . . . . . . . . . . . . . . . . . . 92
4.6 10WS-BandGaNDemonstrators . . . . . . . . . . . . . . . . . . . . . 93
4.6.1 TopologyChoice . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.6.2 DemonstratorA:De-embeddingandOptimumNetworkDesign . 95
4.6.3 DemonstratorA:MeasuredResults . . . . . . . . . . . . . . . . 99
4.6.4 DemonstratorB:ViolatingtheClippingContour . . . . . . . . . 102
4.7 ThirdHarmonic(ClassF/J)ClippingContours . . . . . . . . . . . . . . . 102
4.7.1 LoadPullVerification . . . . . . . . . . . . . . . . . . . . . . . 108
4.8 ConclusionsandFutureWork . . . . . . . . . . . . . . . . . . . . . . . . 111
5 PlanarBalunsforPush-PullAmplifiers 113
5.1 ModellingPlanarBaluns . . . . . . . . . . . . . . . . . . . . . . . . . . 114
5.1.1 CompensatingforZinner . . . . . . . . . . . . . . . . . . . . . . 116
5.2 AluminaBalunTopologyStudy . . . . . . . . . . . . . . . . . . . . . . 120
5.2.1 “Zhang”Balun . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
5.2.2 LangeCouplerBalun . . . . . . . . . . . . . . . . . . . . . . . . 122
5.2.3 “Via”Balun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
5.2.4 Basic3-wireBalun . . . . . . . . . . . . . . . . . . . . . . . . . 125
5.2.5 FullMarchandBalun . . . . . . . . . . . . . . . . . . . . . . . . 127
5.2.6 MarchandLiteBalun . . . . . . . . . . . . . . . . . . . . . . . . 129
5.3 OptimalAluminaBalun . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
5.4 FutureWork . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
VI
5.4.1 MMICBalun . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
5.4.2 2.5DBaluns . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
6 Push-PullAmplifiers 142
6.1 GaAsAluminaAmplifier(MLiteBalun) . . . . . . . . . . . . . . . . . . 142
6.1.1 GaAsTransistors . . . . . . . . . . . . . . . . . . . . . . . . . . 143
6.1.2 AmplifierBalun . . . . . . . . . . . . . . . . . . . . . . . . . . 145
6.1.3 Amplifiersimulationsandmeasurements . . . . . . . . . . . . . 145
6.2 GaNAluminaAmplifier(5FBalun) . . . . . . . . . . . . . . . . . . . . 152
6.2.1 GaNTransistors . . . . . . . . . . . . . . . . . . . . . . . . . . 152
6.2.2 AmplifierBalun . . . . . . . . . . . . . . . . . . . . . . . . . . 153
6.2.3 Amplifiersimulationsandmeasurements . . . . . . . . . . . . . 155
6.3 GaAsMMICMediumBandwidth . . . . . . . . . . . . . . . . . . . . . 161
6.3.1 GaAsMMICTransistors . . . . . . . . . . . . . . . . . . . . . . 162
6.3.2 AmplifierBalun . . . . . . . . . . . . . . . . . . . . . . . . . . 164
6.3.3 Amplifiersimulationsandmeasurements . . . . . . . . . . . . . 165
6.3.4 Redesignwithoptimalbalun . . . . . . . . . . . . . . . . . . . . 170
6.4 ConclusionsandFutureWork . . . . . . . . . . . . . . . . . . . . . . . . 172
7 Conclusionsandfuturework 175
Appendices 179
A MicrowaveOfficeClippingContoursDemo . . . . . . . . . . . . . . . . 179
B CreeCGH40010Fdeembeddingnetwork . . . . . . . . . . . . . . . . . 181
C Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
VII
List of Abbreviations
j Thecomplexoperatorj = √ 1
−
RF RadioFrequency
OC OpenCircuit
SC ShortCircuit
OCSS OpenCircuitShuntStub
SCSS ShortCircuitShuntStub
PA/RFPA PowerAmplifier/RFPowerAmplifier
LNA Low Noise Amplifier - An amplifier with high gain and a low
noise figure that usually amplifies very low amplitude signals
fromdetectiondevicessuchasantennas
VNA Vector Network Analyser. Used primarily to measure S
parameters.
LO LocalOscillator.
Balun Balanced to unbalanced transformer. Converts a single ended
signaltoabalancedsignal.
DLL Dynamic load line. The dynamic current and voltage
trajectory, typically plotted drain current versus drain voltage,
ataspecifiedfrequency.
DCIV DirectCurrent,CurrentandVoltagepropertiesofatransistor.
DUT Device under test. Refers to the circuit or component under
testinthecurrentmeasurement.
MMIC MonolithicMicrowaveIntegratedCircuit.
VIII
LCP Liquid Crystal Polymer. Plastic substrate material which can
be used to fabricate low cost, 2.5D “stacked” microwave
circuits.
Z Impedance at the Xth harmonic, where 0-DC, 1-Fundamental
XF0
etc. 1
Γ Reflection coefficient at the Xth harmonic, where 0-DC,
XF0
1-Fundamentaletc.
V Fourier Voltage component of a waveform at the Xth
XF0
harmonic,where0-DC,1-Fundamentaletc.
I Fourier Current component of a waveform at the Xth
XF0
harmonic,where0-DC,1-Fundamentaletc.
P PowerofaharmonicpowersourceattheXthharmonic,where
XF0
0-DC,1-Fundamentaletc.
dB Decibels. A logarithmic scale used to compare two figures,
dB = 10log(A/B). 3dB is a ratio of 1/2, 6dB a ratio of 1/4
andsoon.
dBm Decibels referenced to 1mW - A logarithmic measure of
power,referencedto1mW
MAG Maximum Available Gain. The ratio of available power from
theDUTtothepowerinputtotheDUT.
PowerGain The ratio of the power delivered to the load over the power
inputtotheDUT.
S21 The scattering parameter often associated with gain (where 1
is the input port). Typically defined as b2/a1, where all other
portsarepassivelyterminated.
η Drain Efficiency. The ratio of DC power successfully
converted to RF power at the DUT output (P /P ),
RFout DC
usuallydisplayedasapercentage.
1Wherenonumberisgiven,1isoftenassumedfortheseharmonicmetrics.
IX
PAE Power Added Efficiency. The proportion of DC power
successfully converted to the additional RF power generated
at the DUT output, i.e. minus the required drive power
((P P )/P ). Differs to η in that it requires high
RFout RFin DC
−
gainaswellasgoodconversionefficiency.
f Unity current gain frequency. The frequency at which the
t
currentgainofthetransistorreachesunity.
f Unitypowergainfrequency. Thefrequencyatwhichthepower
max
gainofthetransistorreachesunity,orthemaximumfrequency
atwhichthetransistorwilloscillate. Typicallylowerthanf .
t
P1dB Point of 1dB compression. The output power at which the
gainoftheamplifieris1dB belowitsextrapolatedsmallsignal
response.
IMx Intermodulation product. The Xth order product produced by
the mixing of an amplifiers harmonics. Usually only the odd
numbered harmonics are of interest (3,5,7,9,..) as these reside
very close to the fundamental frequency and are very difficult
tofilterout.
IPx Intermodulation Point. The power at which the magnitude of
the Xth order intermodulation product would equal the power
of the fundamental tone at the output, assuming neither signal
enteredcompression.
PUF PowerUtilisationFactor. Theamountofpowergeneratedbya
setofvoltageandcurrentwaveforms,ascomparedtotheClass
Acondition(sinusoidalvoltageandcurrent).
ACPR Adjacent Channel Power. A measure of the power leaked into
anadjacentchannel,relativetothecarrierpower(dBc).
Igen Current generator. Typically used to refer to the theoretical
intrinsic output current in transistors which can be accessed
usingde-embeddingtechniques.
Vmin/Imin Waveform minimum voltage/current. The global minimum
valueforagivenwaveform.
X