射频电路设计基础课件.ppt

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1、1射频电路设计基础3B.RFMicrowaveFilters1.0BasicFilterTheoryIntroductionAnidealfilterisalinear2-portnetworkthatprovidesperfecttransmissionofsignalforfrequenciesinacertainpassbandregion,infiniteattenuationforfrequenciesinthestopbandregion,andalinearphaseresponseinthepass

2、band(toreducesignaldistortion).Thegoaloffilterdesignistoapproximatetheidealrequirementswithinacceptabletolerancewithcircuitsorsystemsconsistingofrealcomponents.CategorizationofFiltersLowpassfilter(LPF),highpassfilter(HPF),bandpassfilter(BPF),bandstopfilter(BSF

3、),arbitrarytype,etc.Ineachcategory,thefiltercanbefurtherdividedintoactiveandpassivetypes.Inanactivefilter,therecanbeamplificationofthesignalpowerinthepassbandregion;apassivefilterdonotprovidepoweramplificationinthepassband.Filtersusedinelectronicscanbeconstruc

4、tedfromresistors,inductors,capacitors,transmissionlinesections,andresonatingstructures(e.g.,piezoelectriccrystal,SurfaceAcousticWave(SAW)devices,mechanicalresonators,etc.).Anactivefiltermaycontainatransistor,FET,andanop-amp.FilterLPFBPFHPFActivePassiveActiveP

5、assiveFilterFrequencyResponseFrequencyresponseimpliesthebehaviorofthefilterwithrespecttosteady-statesinusoidalexcitation(e.g.,energizingthefilterwithasinevoltageorcurrentsourceandobservingitsoutput).Therearevariousapproachestodisplayingthefrequencyresponse:Tra

6、nsferfunctionH()(thetraditionalapproach)AttenuationfactorA()S-parameters,e.g.,s21()Others,suchasABCDparameters,etc.FilterFrequencyResponse(cont’d)Lowpassfilter(passive)FilterH()V1()V2()ZLcA()/dB0c31020304050(1.1b)(1.1a)c

7、H()

8、1TransferfunctionArg(H

9、())ComplexvalueRealvalueFilterFrequencyResponse(cont’d)Lowpassfilter(passive)continued...Fortheimpedancematchedsystem,usings21toobservethefilterresponseismoreconvenient,asthiscanbeeasilymeasuredusingavectornetworkanalyzer(VNA).ZcZcZcTransmissionlineisoptiona

10、lc20log

11、s21()

12、0dBArg(s21())FilterZcZcZcVsa1b2ComplexvalueLowpassfilter(passive)continued...FilterFrequencyResponse(cont’d)A()/dB0c31020304050FilterH()V1()V2()ZLPassbandS