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EMC-Chp.3Chp.3Interferencecouplingmechanismandpreventivemeasures4kindsofinterferencecouplingortransmissionmodes•Electrical,conducted（resistivecoupling）；•Electricfieldcoupling（Capacitivecoupling）；•Magneticfieldcoupling（inductivecoupling）；•Radiation（HFradiatedcoupling）.3.1ResistivecouplingWithexistingcircuitconnectionKeyfactor:CommonimpedanceIncludingtwomodes：•Resistivecouplingbetweenoperatingcircuits；•Resistivecouplingbetweenoperatingcircuitsandgroundingcircuit.1stmodei1i1(I)(II)Unit(I)Z=R+jωLZRjL=+ωUnit(II)Preventivemeasuresfordecouplingsuchinterference•Isolatingbetweenoperatingcircuits.•Decreasethecommonconductorimpedance.Reducingthedistancebetweenthelines,for2lineswithdiameterD,separatedind,L=(μ/π)ln(2d/D)，strandedlines,matchplatelayoutinPCB,etc.•Absorptioncapacitanceatcircuitentrance.•Withseparatedsupply.Butthesupplyinternalimpedancecan’tbeeliminated.•Separateoperatingunitswithsignificantpowerassumption.2ndmodeofconductedcoupling(II)coaxialcable1(I)2u1C(ω)Measuresforreducingsuchcoupling•（1）Cut-offthegroundingcircuit.（2）Applicationofisolatingtransformer.（3）Applicationofchoke.（4）Bypasstechniques.（5）Protectiveshielding.•ForDCandLFeffective.IsolatingtransformersChokeΦProtectiveshielding,principleZL2USDVMZL1UCZIL2CDVMCUSZL1RR1C1UCICR2C2ProtectiveshieldingexamplesIGbacG+RSRXI4I1I2I3IXI5ApplicationinstandardvoltagedividerR3′R3R3R3R2′R2R2RUinUin2UinRR11R1R1′UoutUoutUR0outR0R0′R0Othermethods•Opticalcoupler,opto-coupler,OC.Opticalfiber.Oftenusedforeliminatingcommonmodeinterference.•operationaldifferentialamplifier,运算差分放大器，Lmh730154,NationalSemiconductor.Symmetricsystems.3.2capacitivecoupling•Noticethatthe“capacitor”isnotaconnectedcomponentofthecircuit,butthestraycapacitorbetweentheconductors.•It’sakindofnearelectricfieldeffect.•Withtheincreaseofthevoltagebetweentheconductors,thecapacitivecouplingeffectisincreasingsign
