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1、射频电路理论与技术2021/7/30MicrowaveTransistorAmplifierDesign1.IntroductionBasedontheSparametersofthetransistorandcertainperformancerequirements,asystematicprocedureisdevelopedforthedesignofamicrowavetransistoramplifier.Themostimportantdesignconsiderationsinamicrowavetransistoramplifierarestability,pow
2、ergain,bandwidth,noise,anddcrequirements.Adesignusuallystartswithasetofspecificationsandtheselectionofthepropertransistor.Thenasystematicmathematicalsolution,aidedbygraphicalmethods,isdevelopedtodeterminethetransistorloading(i.e.,thesourceandloadreflectioncoefficients)foraparticularstabilityan
3、dgaincriteria.2021/7/30Anunconditionallystabletransistorwillnotoscillatewithanypassivetermination.Ontheotherhand,adesignusingapotentiallyunstabletransistorrequiressomeanalysisandcarefulconsiderationssothatthepassiveterminationsproduceastableamplifier.Itisimportanttoselectthecorrectdcoperatingp
4、ointandtheproperdcnetworktopologyinordertoobtainthedesiredacperformance.2021/7/302.PowerGainEquationstransducerpowergainpowergainavailablepowergain2021/7/30TheexpressionsforGT,Gp,andGAareorand2021/7/30Example2.1TheinputandoutputmatchingnetworksinFig.2.2aredesignedtoproduce(a)DetermineGT,GA,and
5、GpiftheSparametersofthetransistorareFig.2.2(b)CalculatePAVS,PIN,PAVNandPLif(c)Calculate(VSWR)inand(VSWR)out2021/7/30Solution.(a)2021/7/30Comments:(1)Itfollowsthattheinputpowerislessthanthepoweravailablefromthesource.Infact,andsourcemismatchingfactor(2)Thepowerdeliveredtotheloadisclosetothepowe
6、ravailablefromthenetwork.Thatis,GAandGTarefairlyclose.andloadmismatchingfactor2021/7/30(b)ThepoweravailablefromthesourceisThen,theinputpowerisThepowerdeliveredtotheloadorThepoweravailablefromthenetworkor2021/7/30(c)3.StabilityConsiderationsThestabilityofanamplifier,oritsresistancetooscillate,i
7、saveryimportantconsiderationinadesignandcanbedeterminedfromtheSparameters,thematchingnetworks,andtheterminations.Inatwo-portnetwork,oscillationsarepossiblewheneithertheinputoroutputportpresentsanegativeresistance.ororForaunilateraldevic
