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The University Of Cincinnati College of Engineering
WidebandReconfigurableHarmonicallyTunedGaN SSPAforCognitiveRadios
Seth W. WaldsteinThe University of Cincinnati-Main Campus
Miguel A. Barbosa KortrightUniversity of Puerto Rico, Mayagüez Campus
Rainee N. SimonsNASA Glenn Research Center
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Introduction - MotivationBenefits&ChallengesWide-BandReconfigurableHarmonically TunedPowerAmplifier
• InverseClass-FDesign• AmplifierFabricationandResults• ThermalManagement• Dual-BandMulti-NetworkDesign
PowerVariability• HybridCoupler• BalancedAmplifier
Conclusions andAcknowledgements
Outline
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Whatcapabilities doweneedfromatransmitpoweramplifiertoenableacognitivecommunication system?I. Re-configurability
• Highoutputpower;withoutsacrificing efficiency• Operatingfrequency;withoutsacrificing efficiency
II. Linearity
Introduction- Motivation• Congestion,causedbyagrowingusercommunity attheX-Bandspace-to-grounddatalinkfrequencyrange,iscreatingtheneedforcognitiveradiocapabilities.
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BenefitsHigherEfficiencyMeans
• SavedDCpower• DecreasedExcessHeat
• Efficiency islostprimarilythroughpowerdissipationwithinthetransistorjunctionandconductorlosses.
• ImprovedThermalReliabilityOurproposedinnovationhasthepotentialtoenablelowcostCognitiveCommunicationSystems:
• AvoidstheneedformultipleTx andRx modulesApplicationsinclude:
• NASAMissions• SmallSatellitesandSpacecraft• MilitaryUnmannedAirVehicles• Commercial/AmateurCubesats
DecreaseinHeatSinkMass
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Challenges
WidebandDevices• Class-FtypewidebandharmonictuningtechniquesusedatlowerfrequenciesareunrealizableatX-band
PowerVariability• Amplifiersefficiencydropswhenbackedofffromsaturation
GaN TransistorFrequencyLimitation• AchievingmaxPAEwithClass-FtypeamplifiersrequiresFT >3rd harmonic• CurrentcommerciallyavailabletransistorshaveanFT of18GHz(≈ 2nd Harmonic at X-Band)
• HighFT ofGaN HEMTscomesattheexpenseoffeaturesizeandpowerdensity
Efficiency• HighEfficiencySSPA’srequireharmonictuning- suchasClass-FandInverseClass-Fdesigns.Matchingcircuitiscomplexandinherentlynarrowband.
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CircuitWithinthisareacanberealizedusinglowcostCMOS
technology
*IMN(InputMatchingNetwork)*OMN(OutputMatchingNetwork)*ISW(InputSwitch)*OSW(OutputSwitch)
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Wide-BandReconfigurableHarmonicallyTunedPA
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Lowfrequencydampingcircuit
2nd harmonicshort
λ/4@fundamental
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InverseClass-FGaN SSPAatX-Band
Harmonicsarereflectedtoreshapethevoltageandcurrentwaveformatthedrain
Current(mA)
Voltage(V
)
Transistor
X-Bandisselectedbecausethe8.0-8.5GHzfrequencyrangeisdesignatedforNEN
space-groundlinks
OurtargetisPout >4-WwithPAE>35%
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FabricatedInverseClass-FAmplifier
Substrate height, h = 0.02 inch & 𝝴r = 3.0
Tran
sist
or: C
ree
CG
HV1
F006
S 6W
, DC
-18
GH
z, 4
0V, G
aNH
EMT
RF Output
Low Freq. Stability Circuit
Parallel RL Gate Bias
Choke
GaNTransistor
RF Input
DC Drain Bias
DC Gate Bias
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TuningofInverseClass-FAmplifier
SchematicoftheinverseClass-Famplifierdesign.
SimulatedandMeasured(Γopt-in)parametersofIMNaftertuningfrom8.4to16.8GHz.
SimulatedandMeasured(Γopt-out)parametersofOMNaftertuningfrom8.4to16.8GHz.
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Maximum Pout = 5.14-W, PAE = 38.6% with DE = 48.9%
MeasuredPout andPAEvs.Pin VDS=40V,VGS=-3.2Vandfrequency=8.45GHz.
MeasuredgainandVSWRvs.Pin ;VDS=40V,VGS=-3.2V,andfrequency=8.45GHz
InverseClass-FPout,PAE,GainandVSWR
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InverseClass-FBandwidth
70 MHz bandwidth where Pout > 36 dBm and PAE >
35%8.315 - 8.385 GHz
PAE and Pout vs. Frequency VDS = 40 V, VGS = -3.2 V; Pin ranges 21.5-30.35 dBm, VSWR ranges 2.4 -33
70 MHz
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Freq. (GHz) Pin (dBm) VDS (V) Gain(dB) PAE(%) Temp(°C) Pout (W)8.36 29.9 32 6.3 37.3 95 4.2
ThermalManagement
CW operation required direct contact between
transistor belly and heat sink
Operating conditions of measured package temp = 95°C :DC Power Dissipation ≈ 7 W
• Data sheet indicates for package temperature of 95°C, the max allowed power dissipation is ≈ 9 W.
Hence, achieved thermal safety margin of ≈ 22%.
Operating conditions observed
through thermal imaging
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Switch1(GaAs)
X-BandMN
S-BandMN
Switch#2(PIN
Diode)
X-BandMN
S-BandMN
DiplexerInputPort
⊪
GaNHEMT
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DualBandMulti-NetworkDesign
Reconfigurableconceptcanbeappliedtodual-band transmitters
Diplexer
DualBandAntenna
CONTROLLER
COGNITIVERADIO
PROCESSOR
DC BIAS SUPPLY
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Amp#1
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Amp#2
3-dB Hybrid Coupler 3-dB Hybrid Coupler
Output
Isolated
Input
Isolated
Port#1
Port#2
Port#3
Port#4
PowerVariability- BalancedAmplifier
BalancedAmplifierCircuitTopology
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Microstrip Branch Line 3-dB Hybrid Coupler
InputPort #1
IsolatedPort #2
OutputPort #3
OutputPort #4
Substrate height, h = 0.02 inch & 𝝴r = 3.0
Measured vs Simulated Results
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InputPort #1
OutputPort #4
IsolatedPort #3
IsolatedPort #2
MMICAmplifiers
Substrate height, h = 0.02 inch & 𝝴r = 3.0 16
Hybrid Couplers
FabricatedBalancedAmplifier
Mini-Circuits GVA-123+, GaAs
HBTs
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Pin vs. Pout for Single & Balanced MMIC Amplifiers
-10
-5
0
5
10
15
20
25
-19.
3-1
7.3
-15.
3-1
3.3
-11.
3-9
.3-7
.3-5
.3-3
.3-1
.3 0.7
2.7
4.7
6.7
8.7
10.7
12.7
14.7
Pou
t(d
Bm
)
Pin (dBm)
Frequency = 8.546 GHz
Balanced Amplifer Single Amplifier
+3dB
Balanced amplifier provides a 3dB increase in output power over a single
MMIC
MeasuredPout vs.Pin withVD=5 Vandfrequency =8.546GHz.
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Conclusion• Challenges have been presented for achieving the desiredhigh efficiency wide-band operation of a transmit poweramplifier at X-band
• A reconfigurable harmonically tuned SSPA has beenproposed as being a solution to enabling wideband highefficiency needed for a cognitive system
• An inverse Class-F GaN SSPA operating at 8.4 GHz has beenshown to achieve 5.14-W of output power with 38.6% PAEand a 70 MHz bandwidth of Pout > 36 dBm and PAE >35%.
• A balanced amplifier has been presented for additionalconsideration in reconfigurable power topologies.