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1、an075_4.0.fmPage1Thursday,November8,20011:48PMHigh-SpeedBoardDesignsNovember2001,ver.4.0ApplicationNote75IntroductionAsuccessfulhigh-speedprintedcircuitboard(PCB)requiresintegrationofthedevice(s),PCB(s),andotherelementsintothedesign.Altera®deviceshavefastI/Opinswithfalltimesaslowas1nsto3ns.Becauseaf
2、astslewratecancontributetonoisegeneration,signalreflection,cross-talk,andgroundbounce,designsmust:■Filterandevenlydistributepowertoalldevicestoreducenoise■Usetherecommendedroutingtechniquesforsignals,includingclockanddifferentialsignals■Matchimpedanceandevaluateterminationschemes■Terminatesignalandt
3、ransmissionlinestodiminishsignalreflection■Minimizecross-talkbetweenparalleltraces■ReducetheeffectsofgroundbouncePowerClean,evenlydistributedpowertoVCConallboardsanddevicescanreducesystemnoise.Filtering&DistributionFilteringNoiseTodiminishthelow-frequency(<1kHz)noisecausedbythepowersupply,filterthen
4、oiseonthepowerlinesatthepointwherethepowerconnectstothePCBandtoeachdevice.Alterarecommendsplacinga100-µFelectrolyticcapacitoradjacenttothelocationwherethepowersupplylinesenterthePCB.Ifusingavoltageregulator,placethecapacitorimmediatelyafterthefinalstagethatprovidestheVCCsignaltothedevice(s).Capacito
5、rsnotonlyfilterlow-frequencynoisefromthepowersupply,butalsosupplyextracurrentwhenmanyoutputsswitchsimultaneouslyinacircuit.Anotherwaytofilterpowersupplynoiseistoplaceanon-resonantsurface-mountferritebead,bigenoughtohandlethecurrent,inserieswithpowersupply.Placea10-µFto100µFbypasscapacitornexttothefe
6、rritebead(seeFigure1).Properterminations,layouts,andfilteringinadesigneliminatetheneedfortheferritebead.Inthiscase,usea0Ωresistorinsteadoftheferritebead.AlteraCorporation1A-AN-75-4.0an075_4.0.fmPage2Thursday,November8,20011:48PMAN75:High-SpeedBoardDesignsFigure1.FilteringNoisewithaFerriteBeadPCBelem
7、entsaddhigh-frequencynoisetothepowerplane.Tofilterhigh-frequencynoiseatthedevice,AlterarecommendsplacingdecouplingcapacitorsascloseaspossibletoeachVCCandgroundpair.Placingthepowerandgroundplanesinpara
