A Fast Digital Predistortion Algorithm for RF.pdf

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1、374IEEEJOURNALOFSELECTEDTOPICSINSIGNALPROCESSING,VOL.3,NO.3,JUNE2009AFastDigitalPredistortionAlgorithmforRadio-FrequencyPowerAmplifierLinearizationWithLoopDelayCompensationHaoLi,StudentMember,IEEE,DaeHyunKwon,StudentMember,IEEE,DemingChen,Member,IEEE,

2、andYunChiu,Member,IEEEAbstract—Anadaptive,digital,basebandpredistortion(PD)algorithmthatcompensatesforthememorylessnonlinearitiesofradio-frequency(RF)poweramplifiers(PAs)forwirelesssystemsusingnon-constant-envelopmodulationschemesispresented.Comparedw

3、iththeconventional,complex-gainpredistortersbasedonlookuptables(LUTs),theproposeddirect-learning,multilevellookuptable(ML-LUT)approachassistedbyahardware-efficientloopdelaycompensationschemeachievesasignificantreductioninconvergencetimeandanimprovement

4、inlinearizationaccuracyinthepresenceofanunknownloopbackdelay.TheexperimentalresultsinanFPGAprototypingplatformFig.1.SystemblockdiagramofanRFPAlinearizedbyadaptivedigitalpre-showthatthefastadaptationspeedenablesthepredistortertodistortion.Thelowersign

5、alpathfacilitatesthefeedback.tracktime-varyingPAnonlinearitiesasfastasinthetensofkilo-hertzrange,constitutingapotentialsolutionforhighlyefficientPAsinmobilehandsets.nonlinearitiesareusuallymodeledastheAM-AMandAM-PMIndexTerms—Baseband,digitalpredistort

6、ion,lookuptable,distortions[4],whichcanbeexpressedasfollows:loopdelaycompensation.(1)I.INTRODUCTIONwhereisthecomplexbasebandinputsignal,isthecomplexenvelopeofthePA’soutput,andASEBANDdigitalpredistortion(PDorDPD)isawidelyandaretheAM-AMandAM-PMdistorti

7、onBusedlinearity-andefficiency-enhancementtechniqueforfunctions,respectively,bothofwhicharedeterminedsolelybyRFpoweramplifiers(PAs).Atypicalradiofrequency(RF)theamplitudeofthePA’sinputsignal.TypicalsuchdistortiontransmitterwithbasebandPDisshowninFig.1,

8、whereancurvesareshowninFig.2fora5-GHz,two-stage,0.13-adaptivedigitalpredistorterisemployedtopreprocesstheCMOS,Class-BPAfor802.11xOFDMapplications[5].SincebasebandsignaltocanceloutthenonlinearitiesofthePA,thecascadedtransfercharacteristicofthePAandthe