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1、TheDohertyPowerAmplifierThecurrentwirelesscommunicationsystemshavemadesignificantprogresstowardincreasedbandwidthandnumberofcarriersforhigh-data-rateapplications.Memoryeffects,however,makeitverydifficulttodesignahigh-poweramplifierwithawideinstantaneousbandwidth.Inadditiontobandwidthco
2、ncerns,theinstantaneoustransmitpowersofthewirelesscommunicationsystems,suchasCDMA-2000,wide-bandcodedivisionmultipleaccess(WCDMA),orthogonalfrequencydivisionmultiplexity(OFDM)andsoon,varywidelyandrapidly,carryinghighpeak-to-averageratio(PAR)signals.Thebasestationpoweramplifiersforthesy
3、stemsrequireahighlinearitytoamplifythehighPARsignalsourcewithoutdistortion.Tosatisfylinearityrequirements,thepoweramplifiersareusuallybiasedatclassAorABmodeandmustoperateatalargeamountofback-offfromthepeakoutputpower.Anotherrequirementofthebasestationpoweramplifierforthemodernwirelessc
4、ommunicationsystemsishighefficiency.Asthecommunicationsystemsarereducedinbothsizeandcost,thecoolingsystemshouldbesimpleandsmall,requiringapoweramplifierwithhighefficiency.Becausethebasestationpoweramplifiershavealowefficiencyduetotheback-offoperation,efficiencyenhancementtechniquesbeco
5、meveryimportant.Thedesigntechniqueofthebasestationpoweramplifierswithhighefficiencyandlinearityacrossawideinstantaneousbandwidthhasbecomeahotissue.Inthisarticle,weshowthattheDohertyamplifieriscapableofdeliveringthestringentrequirementsofthebasestationpoweramplifiers.Weexplaintheoperati
6、onprinciples,includingbothlinearityandefficiencyimprovements,andthebasiccircuitconfigurationoftheamplifier.Advanceddesignmethodstooperateacrosswidebandwidthandimprovethelinearityarealsodescribed.Forverification,theDohertyamplifierisimplementedusinglaterallydiffusedmetaloxidesemiconduct
7、or(LDMOS)transistorsandmeasuredusingaWCDMA4FAsignal.TheseresultsshowthattheDohertyamplifierisapromisingcandidateforbasestationpoweramplifierswithwidebandwidth,highefficiency,andlinearity.DohertyAmplifierOperationFigure1.(a)OperationaldiagramoftheDohertyamplifier.(b)Fundamentalcurrent
