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1、电子印制电路板设计技巧IntroductionThisinformationispresentedasguidelinestothepreliminarydesignanddevelopmentstagesofelectroniccircuitsforthepurposeofpreventingpotentialelectromagneticinterferenee(EMI)andelectromagneticcompatibility(EMC)problems・Thetipsarerepresentativeofgoodprintedcircu
2、itboard(PCB)designpracticesandarerecommendedasachecklistforevaluatingandselectingEMI/EMCsoftwaremodelingtools.TheEMIsimulationofcircuitboardsrequirestheevaluationofmanydetailssuchasclockfrequencies,switchingrates,rise/falltimes,signalharmonics,datatransferrates,impedances,tra
3、celoadingandconsiderationofthetypesandvaluesofthevariouscircuitcomponents.ThephysicallayoutofthePCboardanditsassociatedmetalliccomponentsareimportantconsiderations.Specialattentionshouldbegiventotheplacementandcharacteristicsofsignalsourcecomponents,vias,traces,pads,boardstac
4、k-up,shieldedenclosures,connectorsandcables.Forexample,assignalfrequenciesandclock/switchingratesincrease,PCboardtracecharacteristicscanbecomesimilartothoseoftransmissionlinesandradiators.APCboardtraceorcomponentcanbecomeanefficientantennaatalengthassmallasonetwentiethofawave
5、length.EMI/EMCproblemsmaybeapproachedatthecomponent,PCboardorenclosurelevels.However,itismuchmoreefficienttodealwiththeseproblemsasclosetothesourceorsusceptiblevictimaspossible・Therefore,itisimportanttoconsiderthesetipsasguidelinesforPCBdesignandlayoutsothatproblemsmaybeident
6、ifiedandpreventedpriortoactualfabricationoftheequipment.General(1)EMIcontrolsshouldbeappliedatthecircuitandboxlevelspriortoaddressingEMIattheinterconnectedandsystemlevels.(2)Digitalcircuitsaremorelikelytobethesourceofemissionsduetothehandlingofperiodicwaveformsandthefastclock
7、/switchingrates.Analogcircuitsaremorelikelytobethesusceptiblevictimsduetohighergainfunctions.(3)ThesourceorsusceptiblevictimofmostEMIproblemsistypicallyanelectroniccomponent.AlthoughactivecomponentsareusuallythesourcesofEMI,passivecomponentsoftencontributetoit,dependingonthes
8、ignalfrequenciesandcomponentscharacteristics.Forexample,aninductorca
