电磁兼容入门（英文版）ppt课件.ppt

《电磁兼容入门（英文版）ppt课件.ppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、RadiatedElectromagneticInterference(EMI)NoiseAnalysisandSuppressionRadiatedEMIfromDigitalCircuitsRadiatedEMISuppressionConceptsPowerSupplyDecouplingRadiatedEMIfromDigitalCircuitsManydigitalcircuitdesignersdesignhigh-speeddigitalcircuits.But,manyofthemareunawarethatdigitalcircuits,ifnotpr

2、operlydesignedwithEMCconsideration,canradiatesignificantlevelsofelectromagneticfieldsoccupyingawidefrequencyspectrum.Thesewide-bandunintentionalelectromagneticemissionscaninterferewithotherintentionalcommunications,suchasAM/FMradio,iftheirlevelsarenotcontrolledandregulated.Hence,manycoun

3、trieshaveimposedradiatedEMIlimitstoalldigitaldevices,usuallyfrom30MHzto1GHz.WewillprovideinsightsonhowradiatedEMIisgeneratedfromadigitalcircuitandproposeseffectivecountermeasurestokeepradiatedemissionsfromthedigitalcircuitbelowtherequiredEMIlimit.Fig.4-1RadiationMechanismofaDigitalCircui

4、t1RadiationMechanismofDigitalCircuitsFig.4-1showsaverysimpleCMOSinverterconnectedtoaDCpowersupply.Asaninverter,itperformslogictransitionfromeitherhigh-to-low(10)orlow-to-high(01).Fig.4-1RadiationMechanismofaDigitalCircuitTherateoftransitionisdeterminedbythefrequencyoftheclocksignalappl

5、iedtoitsinput.Whenitsoutputchangesfromhigh-to-low,thelowertransistorturnsonandtheuppertransistorturnsoff.Thechargestoredattheoutputloadcapacitancedischargestothegroundconductorthroughthelowertransistor.Whenitsoutputswitchesfromlow-to-high,thelowertransistorturnsoffandtheuppertransistortu

6、rnson,currentwillbedrawnfromtheDCpowersupplytochargeuptheloadcapacitanceviatheuppertransistor.Duringthelogictransition,thetransistorcannotturnonoroffinstantly.Therefore,therewillbeashortperiodoftimewherebothtransistorsarepartiallyonandalargecurrentcalled“cross-overcurrent”isexpectedtobed

7、rawnfromtheDCpowersupply.Fig.4-1RadiationMechanismofaDigitalCircuitTherefore,averysimpleinvertercircuitthatprovidesinvertingfunctionhasalreadycreatedthreeclosedloops.Eachoftheseclosedloopscarriestimevaryingcurrent,di/dt,switchingatveryhighrate.FromanRFdesigner’sview,these