Matching2 阻抗匹配2.pdf

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1、Matchbetween100Ωand1000Ω-j333//with1000Ωand+j300inserieswith100Ωwilldoit.FinalCircuitRpQ=Q=−1spRsXsQ=sRsRBpQ==pXGpR=theresistanceintheshuntpbranchofL-networkR=theresistanceintheseriessbranchoftheL-networkXandBmaybeeithercapacitiveorinductivereactance,buteachmustbeofoppositetype.RFMatchin

2、gmethodsTwobasicapproachesinhandlingcompleximpedances(a)Absorptionapproach:Absorbanyreactanceintotheimpedancematchingnetworkbyplacementofeachmatchingelement(shuntcapacitorwithshuntinductor,seriesinductorwithseriescapacitor).(b)Resonanceapproach:Resonateanyreactancewithanyequalandopposite

3、reactanceatthefrequencyofinterest.AfterthatperformmatchingbetweentwopureresistancesSometimeonemethodisnotenoughandyouneedtocombinebothmethods.Example:Useabsorptionapproachtomatchthesourceandtheloadoftheshowncircuit(at100MHz)First:ignorethereactancesandmatchthetworesistorsNow,comparingthe

4、originalcircuittothematchedcircuityoucanfigureoutthematchingcircuitselementsasshownbelow.Example:Usetheresonantapproachforthiscircuitat75MHzFirstweneedshuntinductorwiththecapacitorwhichwillhavethevalue1L==112.6nH2ωCNow,weneedtomatchbetween50Ωand600ΩRp600Q=Q=−=1−=13.32spR50sRpX=QR=166Ω,X=

5、=181ΩssspQpC=1/(ωX)12.78=pF,L=X/ω=384nHspSeriesCShuntCShuntLSeriesLWhatistheimpedancelookingintothenetworkshownbelow?CBBAADCDDesigntwo-elementimpedance-matchingnetworkonaSmithCharttomatchbetweenZ=25-j15ΩandZ=100-j25Ωat60MHz.ThematchingmustactasLsLPfilter.z*szLThreeElementMatchingThedisad

6、vantagesoftheL-shapematchingnetworkisthefixedQvalueofthecircuit.IfweneedsnarrowbandmatchingwithhigherQ,thethreeelementscanprovidethatbychoosingtheQweneeds,whichmustbehigherthanthepossibleQoftheL-network.Thethreeelementnetworkcouldbeπ-networkorT-network.π-networkT-networkπ-networkisatwoba

7、cktobackL-networksconfiguredtomatchRandLRtoaninvisibleresistance(smallersthanRorR)locatedatthejunctionLsbetweenthetwoL-networks.-hereindicatesoppositeelementtypeThedesignissimilartotheL-networktype,buttheinvisibleRmustbesmallerthanRandR.Also,itcanbedefinedbythedesiredload