Doherty功率放大器英文资料Word文件下载.docx

Doherty功率放大器英文资料Word文件下载.docx

《Doherty功率放大器英文资料Word文件下载.docx》由会员分享，可在线阅读，更多相关《Doherty功率放大器英文资料Word文件下载.docx（7页珍藏版）》请在冰豆网上搜索。

Doherty功率放大器英文资料@#@ @#@@#@Doherty功率放大器（英文）@#@TheDohertyPowerAmplifier@#@Thecurrentwirelesscommunicationsystemshavemadesignificantprogresstowardincreasedbandwidthandnumberofcarriersforhigh-data-rateapplications.Memoryeffects,however,makeitverydifficulttodesignahigh-poweramplifierwithawideinstantaneousbandwidth.Inadditiontobandwidthconcerns,theinstantaneoustransmitpowersofthewirelesscommunicationsystems,suchasCDMA-2000,wide-bandcodedivisionmultipleaccess（WCDMA）,orthogonalfrequencydivisionmultiplexity（OFDM）andsoon,varywidelyandrapidly,carryinghighpeak-to-averageratio（PAR）signals.ThebasestationpoweramplifiersforthesystemsrequireahighlinearitytoamplifythehighPARsignalsourcewithoutdistortion.Tosatisfylinearityrequirements,thepoweramplifiersareusuallybiasedatclassAorABmodeandmustoperateatalargeamountofback-offfromthepeakoutputpower.Anotherrequirementofthebasestationpoweramplifierforthemodernwirelesscommunicationsystemsishighefficiency.Asthecommunicationsystemsarereducedinbothsizeandcost,thecoolingsystemshouldbesimpleandsmall,requiringapoweramplifierwithhighefficiency.Becausethebasestationpoweramplifiershavealowefficiencyduetotheback-offoperation,efficiencyenhancementtechniquesbecomeveryimportant.Thedesigntechniqueofthebasestationpoweramplifierswithhighefficiencyandlinearityacrossawideinstantaneousbandwidthhasbecomeahotissue.@#@Inthisarticle,weshowthattheDohertyamplifieriscapableofdeliveringthestringentrequirementsofthebasestationpoweramplifiers.Weexplaintheoperationprinciples,includingbothlinearityandefficiencyimprovements,andthebasiccircuitconfigurationoftheamplifier.Advanceddesignmethodstooperateacrosswidebandwidthandimprovethelinearityarealsodescribed.Forverification,theDohertyamplifierisimplementedusinglaterallydiffusedmetaloxidesemiconductor（LDMOS）transistorsandmeasuredusingaWCDMA4FAsignal.TheseresultsshowthattheDohertyamplifierisapromisingcandidateforbasestationpoweramplifierswithwidebandwidth,highefficiency,andlinearity.@#@DohertyAmplifierOperation@#@Figure1.（a）OperationaldiagramoftheDohertyamplifier.（b）Fundamentalcurrents.（c）Loadimpedances.@#@TheDohertyamplifierwasfirstproposedbyW.H.Dohertyin1936.TheoriginalDohertyamplifierconsistedoftwotubeamplifiersandanimpedanceinvertingnetwork.TheefficiencyofanRFpoweramplifierisincreasedusingtheRFDohertyamplifiertechnique,asdescribedindetailin.Thisamplifierconsistedofacarrieramplifierandapeakingamplifier.Theoutputloadisconnectedtothecarrieramplifierthroughanimpedanceinverter（aquarter-wavetransmissionline）anddirectlytothepeakingamplifier.Figure1（a）showsanoperationaldiagramtoanalyzetheDohertyamplifiercircuit.Twocurrentsourcesrepresenttheamplifiers.Itisassumedthateachcurrentsourceislinearlyproportionaltotheinputvoltagesignal,operatingasaclassABorclassBamplifierwithharmonicshortcircuitsafteritisturnedon,andtheefficiencyanalysiscanbecarriedoutusingthefundamentalanddccomponentsonly.AsshowninFigure1（b）,thepeakingamplifierturnsonatone-halfthemaximuminputvoltage.@#@TheDohertyamplifiertechniqueisbasedontheloadimpedancechangeofeachamplifier,referredtoasloadmodulation,accordingtotheinputpowerlevel.Figure1（b）showsthefundamentalcurrentsfromtheamplifiers.Theloadimpedancesoftwoamplifiersaregivenby@#@ @#@@#@whereZListheloadimpedanceoftheDohertyamplifier;@#@ICandIPrepresentthefundamentalcurrentsofthecarrierandpeakingamplifiers,respectively;@#@andZCandZParetheoutputloadimpedancesofthecarrierandpeakingamplifiers,respectively,andaredepictedinFigure1（c）.@#@Inthelow-powerregion（0∼Vin,max/2）,thepeakingamplifierremainsinthecut-offstate,andtheloadimpedanceofthecarrieramplifieristwotimeslargerthanthatoftheconventionalamplifier.Thus,thecarrieramplifierreachesthesaturationstateattheinputvoltage（Vin,max）/2sincethemaximumfundamentalcurrentswingishalfandthemaximumvoltageswingreachesVdc.Asaresult,themaximumpowerlevelishalfofthecarrieramplifier’sallowablepowerlevel（aquarterofthetotalmaximumpoweror6dBdownfromthetotalmaximumpower）,andtheefficiencyoftheamplifierisequaltothemaximumefficiencyofthecarrieramplifierasshowninFigure2.@#@Inthehigh-powerregion（Vin,max/2∼Vin,max）,wherethepeakingamplifierisconducting,thecurrentlevelofthepeakingamplifierplaysanimportantroleindeterminingtheloadmodulationoftheDohertyamplifier[see

（1）and

（2）].Assumingthatgmofthepeakingamplifieristwiceaslargeasthatofthecarrieram