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1、AVR040:EMCDesignConsiderationsScope8-bitThisapplicationnotecoversthemostcommonEMCproblemsdesignersencounterMicrocontrollerswhenusingmicrocontrollers.Itwillbrieflydiscussthevariousphenomena.ThereferenceliteraturecoversEMCdesigninmoredetail,andfordesigne
2、rswhoaregoingtobuildproductsthatneedtobeEMCcompliant,furtherstudyishighlyrecommended.AgoodEMCdesignrequiresmoreknowledgethanwhatcanbeApplicationNoteputintoashortapplicationnote.Unlikemanyotherdesignissues,EMCisnotanareawhereitispossibletolistasetofrule
3、s.EMCcompliancecannotbeguaranteedbydesign;ithastobetested.ItisrecommendedthatreadersunfamiliarwithEMCdesignreadthisdocumentPRELIMINARYmorethanonce,assomeofthesubjectsdescribedearlyinthisdocumentaremoreeasilyunderstoodifthereaderhasalreadyreadtherestoft
4、hedocument.1IntroductionElectromagneticcompatibilityisasubjectmostdesignersdidnothavetoworryaboutafewyearsago.Today,everydesignerputtingaproductontheglobalmarkethastoconsiderthis.Therearetwomainreasonsforthis:?Theelectromagneticenvironmentisgettingtoug
5、her.High-frequencyradiotransmitters,likemobiletelephones,arefoundeverywhere.Moreandmoresystemsareusingswitchingpowersuppliesinthepowercircuit,andtheoverallnumberofelectronicappliancesisincreasingeveryyear.?Electroniccircuitsarebecomingmoreandmoresensit
6、ive.Powersupplyvoltagesaredecreasing,reducingthenoisemarginofinputpins.Circuitgeometriesgetsmallerandsmaller,reducingtheamountofenergyrequiredtochangealogiclevel,andatthesametimereducingtheamountofnoiserequiredtoalterthelogicvaluesofsignals.Fromadesign
7、er’spointofview,EMCphenomenahavetobeconsideredintwodifferentways:?Howtheenvironmentmayaffectthedesign(immunity).?Howthedesignmayaffecttheenvironment(emission).Traditionally,theonlygovernmentregulationshavebeenontheemissionside:Anelectronicdeviceisnotal
8、lowedtoemitmorethanacertainamountofradiofrequencyenergytoavoiddisturbingradiocommunicationoroperationofotherRev.1619D-AVR-06/06electronicequipment.Mostcountriesintheworldhaveregulationsonthistopic.Additionaldemandsonnoiseimmunityearlier
