差分滤波器设计

ApplicationReportSLWA053B–November2007–RevisedApril2010DesignofDifferentialFiltersforHigh-SpeedSignalChainsKenChan.......................................................................................HighSpeed-WirelessInfrastructureABSTRACTDifferentialfiltershavemanydesirableattributes.Thetaskofdesigningdifferentialfilterscanseemdauntingatfirst.Single-endedfiltersdesignedinanyfilterdesignpackagecanbeconvertedtoadifferentialimplementation.Thisapplicationreportexploressimpleconversiontechniquesforlow-pass,high-pass,andband-passLCfilters.1IntroductionDifferentialsignalshavemanydesirableattributesinhigh-speedsignalchains:namely,common-moderejectionfromabalancedsignalpathandmatchedfilterresponse,immunityfromsingle-endedcomponentparasiticeffects,decouplingthesignalfromrequiringagroundreference,andrejectionofeven-orderharmonics.However,mostLCfilterdesigninformation,techniques,andsoftwareareforsingle-endedsystems.Thisapplicationreporthighlightssomesimpletranslationsthatcanbemadetoconvertthesingle-endeddesignstofullydifferentialdesigns.Someexamplesareusedtodemonstratethesetranslations.Thedesignofsingle-endedpassiveanalogLCfiltershasbeensimplifiedgreatlybyvariouspiecesofsoftwarethatcanbeobtainedfreelyontheInternet.AnInternetsearchforLCfilterdesignyieldsmanyresults,anyofwhichcanbeusedforthistutorial.ThisapplicationreportusesELSIE(i.e.,LC)whichisfreelyavailablefordownloadfromthefollowinglinkasatrialversionwithsomelimitationsonfilterorderandusage.Forcommercialapplications,thefullversionshouldbepurchased.Forpurposesofthisapplicationreport,thefreeversionissufficient.://focus.ti.com/docs/toolsw/folders/print/tina-ti.htmlThefullTINAversioncanbepurchasedfromitsvendorforaccesstoitsfullfeatureset.2Single-EndedtoDifferential-EndedFilterTranslation:2.1Low-Pass,High-Pass,andBand-PassFilterImplementationsTheprocessofdesigningadifferentialfilterrequiresthedesignofasingle-endedfilterthatmeetsthefilterrequirements.Freelyavailabletoolsmaybeusedtogenerateasingle-endedfilterwiththedesirablefrequencyresponse.Thelow-pass,high-passandband-passdifferentialfilterimplementationsarediscussedinthefollowingsections.Thesingle-endedLClow-passfiltercanbeconvertedtoadifferentialfilterbyrepeatingandfoldingthedesignaroundGNDtocreatetheVin+andVin-.TheGNDisremovedandthecentercapacitorvaluesarerecalculated:theCishalf-value(sumoftwoseriesC).TheLinthehorizontalparallelseriespathsarekeptthesameandtheloadresistorisdoubled(sumoftwoseriesR).TheprocessisillustratedinFigure1.1SLWA053B–November2007–RevisedApril2010DesignofDifferentialFiltersforHigh-SpeedSignalChainsCopyright©2007–2010,TexasInstrumentsIncorporatedVinR26100WL2522HmC272.2nFR25100WVoutR28100WL2622HmC292.2nFR33100WVin+C282.2nFR29100WL2722HmR27100WVout+Vout-R31100WL2822HmC311.1nFVin+R32100WL2922HmR34200WVout+Vout-Vin-Vin-R3100WL322HmC42.2nFR10100WVINVOUTVINVIN-R2100WL122HmL222HmC11.1nFR1200WVOUTVOUT-R4100WR3100WL322HmC42.2nFR10100WVINVOUTVINVIN-R2100WL122HmL222HmC11.1nFR1200WVOUTVOUT-R4100WSingle-EndedtoDifferential-EndedFilterTranslation:–November2007–RevisedApril2010Copyright©2007–2010,TexasInstrumentsIncorporatedR3100WL311HmC21.1nFR10100WVINVOUTVINVIN-R2100WL122HmC11.1nFR1200WVOUTVOUT-R4100WC31.1nF–November2007–RevisedApril2010DesignofDifferentialFiltersforHigh-SpeedSignalChainsCopyright©2007–2010,TexasInstrumentsIncorporatedR5100WL211HmC41.1nFR6100WVINVOUTVINVIN-R8100WL422HmC51.1nFR7200WVOUTVOUT-R9100WC61.1nFSingle-EndedtoDifferential-EndedFilterTranslation:–November2007–RevisedApril2010Copyright©2007–2010,TexasInstrumentsIncorporatedR11100WL718.3HmC101.64nFR12100WVINVOUTL5617nHC755.5pFC111.64nFL8617nHR13200WL918.3HmC9821pFR14100WVINVOUTL61.23HmC855.5pFL131.23HmVIN-VOUT-R16100WL1218.3HmC12821pFC1355.5pF