全套电磁兼容资料8

1CouplingOutline•Capacitivecoupling:–frequencydomain–timedomain•Inductivecoupling:–frequencydomain–timedomain2CapacitiveCoupling•Wherevertherearetwocircuits,thereismutualcapacitance.Voltagesinonecircuitcreateelectricfieldswhichaffectthesecondcircuit.•Amutualcapacitivecouplingbetweentwocircuits1and2issimplyaparasiticcapacitorC12connectedfromcircuit1tocircuit2.•AmutualcapacitanceC12injectsacurrentintocircuit2proportionaltotherateofchangeofvoltageincircuit13CapacitiveCoupling:FrequencyDomainC12=parasiticcapacitancebetweenconductors1and2U2NC12C2GRU1Conductor1Conductor24CapacitiveCoupling:FrequencyDomain+U2NU1C12RC2GEquivalentcircuit()UUjjRCCCCCNGG21122121221=++⋅+ωωVoltagenoiseU2Ninducedinconductor25CapacitiveCoupling:FrequencyDomainUUN21ωCCCG12122+VoltagenoiseU2Ninducedinconductor2()G212cCCR1+=ω6CapacitiveCoupling:TimeDomainAssumptions:•ThecoupledcurrentflowinginC12ismuchsmallerthantheprimarysignalcurrentincircuit1.•Thecoupledsignalvoltageincircuit2issmallerthanthesignaloncircuit1.•AcapacitorC12hasalargeimpedancecomparedtotheimpedancetogroundofcircuit2.•Theimpedancetogroundofcircuit2isR7CapacitiveCoupling:TimeDomain123ns0U1(t)Tr=1ns∆U1Maxdv/dtofdrivingwaveform:r11TUdtdU∆=Injectedcurrentincircuit2:r112CTUCI∆=r121N2TRCUUCrosstalk=∆=8CapacitiveCoupling:TimeDomainExample:∆U1=1V,Tr=1ns,C12=1pF,R=50Ω050TRCUUCrosstalkr121N2.==∆=9CapacitiveCoupling:TimeDomain10⋅U2N0123456789[ns]00.10.20.30.40.50.60.70.80.91U1EstimationofC12frommeasurednoisevoltage:pF1150105URAreaC11112=⋅⋅=∆=−10CapacitiveCoupling:TimeDomain10⋅U2NU1U2Npk10.90.70.80123456789[ns]00.10.20.30.40.50.605080UUCrosstalkMeasured1Npk2.=∆=11CapacitiveCoupling:ExampleCgdCgsRGRDriveruDS+-100200ns0uDS(t)trv=100nsUOFF=100VFora100V,20AdeviceCgs≈1nF,Cgd≈100pFA1.0tUCdtduCIrvOFFgdgdgdN=≈=12CapacitiveCoupling:Example100200UOFF=100Vt[ns]IN=0.1Atrv=100nsEquivalentcircuit:uDS(t)CgsiN(t)uGS+-RTt[ns]iN(t)()−=−gsTCRtNTGSe1IRtuDriverGTRRR+=0uGS(t)UTH=5VRT50Ω13ParasiticCapacitancesinTransistorPackageEBCBHeat-sink&chassisMicainsulationMetalliccaseairgapCEFornormalthicknessmicainsulationCparasitic≈100pFforTO-3≈80pFforTO-5≈30pFforTO-220Forisolatepackage,Cparasiticdependsonchiparea.Fora600V,75AIGBT,C≈25pF.14InductiveCoupling•Wherevertherearetwoloops,thereismutualinductance.Currentinoneloopcreatesamagneticfieldwhichaffectsthesecondloop.•Amutualinductivecouplingbetweentwocircuits1and2issimplyaparasiticmutualinductanceLMbetweencircuit1andcircuit2.•AmutualinductanceLMinjectsanoisevoltageintocircuit2proportionaltotherateofchangeofcurrentincircuit115InductiveCouplingLoop1loop2U2N(t)+-I1(t)•Currentinloop1producesapatternofmagneticfieldenergy•Thetotalmagneticfieldstrengthovertheareaofloop2(magneticflux)isafunctionofthedistance,physicalproportions,andrelativeorientationsoftheloopsaswellasofthecurrentinloop116InductiveCouplingLoop1loop2U2N(t)+-I1(t)()∫⋅−=φ−=2area12N2sdBdtddtdtUrrFaraday’slaw:Mutualinductance:112MILφ=()dtdILtU1MN2=17InductiveCouplingU2NLMi1R2RL2+u1+18InductiveCoupling:FrequencyDomainU2NLMI1R2RL2+Equivalentcircuit-I2TN22N221M22N2RURRUIILjILjU−=+−=ω+ω=VoltagenoiseU2Ninducedinconductor21T2MN2IRLj1LjUω+ω=19InductiveCouplingUiN21ω2TLRMLjω2TMLRL20InductiveCoupling:TimeDomainAssumptions:•TheinducedvoltageacrossLMismuchsmallerthantheprimarysignalvoltageincircuit1.•Thecoupledsignalcurrentincircuit2issmallerthanthecurrentincircuit1.•Thesecondaryimpedanceissmallcomparedtotheimpedancetogroundofcircuit2.•Theimpedancetogroundofloop1isR121InductiveCoupling:TimeDomain123ns0I1(t)Tr=1ns11RU∆Maxdi/dtofdrivingwaveform:r111TRUdtdI∆=Injectedvoltageincircuit2:r11MN2TRULU∆=r1M1N2TRLUUCrosstalk=∆=22InductiveCoupling:TimeDomainExample:∆U1=1V,Tr=1ns,LM=10nH,R1=50Ω2.0TRLUUCrosstalkr1M1N2==∆=Amonghigh-speeddigitalcircuits,mutualinductanceisoftenaworseproblemthanmutualcapacitance23Summary•Highsignalriseandfalltimesincreasebothcapacitiveandinductivenoisecoupling•Ahighreceptorimpedancetogroundincreasesitssusceptibilitytocapacitivenoisecoupling•Magneticcouplingdependsonloopareas(mutualinductance)•Capacitivecouplinginjectsanoisecurrentintothereceptorcircuit•Inductivecouplinginjectsanoisevoltageintothereceptorcircuit•Unlikemutualcapacitivecoupling,mutualinductivecouplingiscapableofinducingcrosstalkwithapolarityoppositethatofthedrivingsignal.