24PCBDesignforRealworldEMIControl

PCBDesignforReal-WorldEMIControlPreparedByJiaWu2003-11-202019/8/22PCBDesignforReal-WorldEMIControlThecontents1.IntroducetheEMC2.AbouttheBasicEMCDesignIntention3.IntroducetheElectromagneticInduction4.TheMythoftheGround5.IntroducetheReturnCurrentRoute6.TheConclusions2019/8/231.IntroducetheEMC1.1EMIandEMCconcepts1.2ThesourceofEMI1.3IntroducetheInductance1.4IntroducetheGround1.5IntroducetheShielding2019/8/241.1.1EMIconceptsEMI:ElectromagneticInterferenceAnyelectromagneticdisturbancethatinterrupts,obstructs,orotherwisedegradesorlimitstheeffectiveperformanceofelectronics/electricalequipment.Itcanbeinducedintentionallyandunintentionally,asaresultofspuriousemissionsandresponses,intermodulationproducts,andthelike.2019/8/25EMC:ElectromagneticCompatibilityTheconditionwhichprevailswhenequipmentisperformingitsindividuallydesignedfunctioninacommonelectromagneticenvironmentwithoutcausingorsufferingunacceptabledegradationduetounintentionalelectromagneticinterferencetoorfromotherequipmentinthesameenvironment.Theabilityofsystems,equipment,anddevicesthatutilizetheelectromagneticspectrumtooperateintheirintendedoperationalenvironmentswithoutsufferingunacceptabledegradationorcausingunintentionaldegradationbecauseofelectromagneticradiationorresponse.1.1.2EMCconcepts2019/8/26ElectromagneticCompatibilityEMCInterference(EMI)Susceptibility(EMS)ConductedEmissionRadiatedEmissionConductedImmunityRadiatedImmunityEMCStructureChart1.1.2EMCconcepts(Continue)2019/8/271.2TheSourceofEMIHighspeedclockgenerator;Highspeedbussignal;Powernode;DigitalandAnalogGND;I/OCableandConnector2019/8/281.3IntroducetheInductanceTheinductancehereisnotonlyfortheinductor.Inductanceiscriticalforhighspeedsignals.AvoltagedecreasewillcausethechangeofElectromagneticfield.ThischangeofintensityandshapeisasourceofEmission.2019/8/291.4IntroducetheGroundGround:Thereferencepoint.DifferentkindsofGroundshouldbeseparatedfromeachothers.SuchasEarthreference,Powerreference,Chassisreference.Thiscanmitigatetheinterferencebetweendifferentsignalsandkeepthempure.2019/8/2101.5IntroducetheShieldingShieldingisausefulwaytolimitEMI.Themagnitudeofreflectionlossdependsontheratioofbarrierimpedancetowaveimpedance,whichinturndependsonitsdistancefromthesourceandwhetherthefieldiselectricormagneticorwhetheritisaplanewave.Foraslotwithadimensionequaltoorlessthanahalf-wavelength,theshieldingeffectivenessis:Wherelismaximumdimensionofslot.)2log(20lS2019/8/2111.5IntroducetheShielding(Continue)2019/8/2122.BasicEMCDesignIntention2.1TheimportanceforEMCdesign2.2CouplingMechanisms2.3IntroducetheSignalSpectra2.4IntroducetheResonanceEffect2.5PotentialInterferenceSource2019/8/2132.1TheImportanceofEMCdesign1.EMCDesignisimportantforcost-down.2.Needcertificatestoenterintodifferentcountriesandregions,commonmarks:CCC-ChinaCE-EuropeanUnionVCCI-JapanBSMI-TaiwanFCC-UnitedStates2019/8/2142.2CouplingMechanismsElectricalFieldCoupling2019/8/215MagneticFieldCoupling2.2CouplingMechanisms(Continue)2019/8/2162.3SignalSpectra2019/8/2172.4ResonanceEffectsMostEMIisnarrowband,notbroadband.Theresonancefrequencyincavityis:2221()()()2mnpmnpfabcThea,bandcisthedimensionofthecavity.Them,nandpisinteger,andbebothorallzero.2019/8/2182.5PotentialInterferenceSourceShieldedproducts:Viasandholes,connectors,I/Ocables…UnshieldedproductsPCboard,radiators,externalcables,wirelessantennas…2019/8/2193.TheInductance3.1IntroducetheInductance3.2ElectromagneticInduction3.3IntroducetheMutualinductance3.4IntroducetheSelf-Induction3.5IntroducethePartialInduction2019/8/2203.1IntroducetheInductanceTheinfluenceofinductanceisextremelyimportantinhighfrequencyspectra.Theinductancecanbeanywhereinallcomponentssuchascapacitorsresistors,lines,andplanes.2019/8/2213.2ElectromagneticInductionTheelectromagneticinductanceformulainFaraday’slaw:BEdldStInasmallareaA,the:BVAt2019/8/222EffectofPower/GroundInductanceTheinductivereactanceofaconductorisusuallymoresignificantthantheimpedanceresistance.Atime-varyingcurrentpassingthroughaninductorcausesavoltagedrop.Thecurrentwhenacapacitordischarging:Thevoltagewhenachangingcurrentpassingthroughainductance:|dtdvCIdtdILV3.2ElectromagneticInduction(Continue)2019/8/2233.3IntroducetheMutualInductance2201222322()llMlr2019/8/224TheMutualInductancebetweentwoparallellines3.3IntroducetheMutualInductance(Continue)2019/8/2253.4IntroducetheSelf-inductance2019/8/2263.5IntroducethePartialInductanceThePartialInductanceistheinductanceonapartoftheloopcircuit,itcanbesubstitutetotheinductanceofsmallparts.Thisinductancecombinesthemutualandselfinductancesamongtheseresistors.2019/8/2274.TheMythoftheGround4.1TheMeaningofGround4.2IntroducetheReferencePoint4.3PCBtoAccessoriesConnection4.4PCBtoGroundConnection2019/8/2284.1TheMeaningofGroundGround-isaplacewherepotatoesandcarrotsthrive.--PCBDesignforRealWorldEMIControlbyB.R.ArchambeaultTheKeytomitigateEMI.Anywhereinthesocalled‘ground’onthePCBdohasvoltagedecrease,foritismetal.ThiscausetheEMI.2019/8/229Aproperdesignforlowfrequencycurrent.4.1TheMeaningofGround(Continue)201