电磁兼容资料第二部分1

1RLCNetwork()()utVQesintCot=−+1142αβϕQ2oω−=α2oQ411−ω=β()1Q4tg2−=ϕQZRo=12ZLCo=ωoLC=1R+CLuC(0)=Vouc2RinginginaRLCNetworkuCVotVeoQto−ω2πLCQ1142−21142πLCQ−−−−VeoQπ412Worst-caseovershoot3RinginginaRLCNetworkInresponsetoaperfectstepinput:W.C.Overshoot=16%Q=1Q=2W.C.Overshoot=44%Theworst-caseovershoothappensonlyifthestepinputgeneratorcantransmitsignificantenergyatfrequenciesabovetheringingfrequencyfo4Example:realstepsignal10%90%TrfTrmax=12(forarandomgaussianpulsesignal)Iffmax=foactualovershootisaboutonehalfofworst-caseovershoot5ExampleWire-wrapwire(AWG30)oflengthL=2.25in(57mm),withheighth=0.2in(5.08mm)aboveagroundplaneconnectingaTTLdriver(Rout=25Ω)toatypicalload(C=10pF)Wirediameter:dinAWG==−−100011020.6ExampleExternalinductance(capacitance)ofaconductoroveragroundplaneisonehalf(twice)oftheinductance(capacitance)correspondingtotheconductorplusitsimageconductor.GROUNDhrwhImageconductor[]m/Hrh2ln2rhcosh2W0W10eπµ≈πµ=−lHoldsforh/rw17ExampleParasiticinductance:nH50rh2ln2Lw0=πµ=LQZRo==283.Qualityfactor:fLCMHzo==122252π.Resonancefrequency:8ResponsetoaFiniteRise-TimeStepInputSignalUUoin1Tr=1nsTr=2nsTr=4ns010201.50.5Time[ns]9RatiobetweenRealandWorst-CaseOvershootsasaFunctionofNormalizedInputStepSignalRise-Time050.20.40.60.84321TToscrOvsOvsWC10EstimationofL-CParametersfromaStepResponseknowingInputSignalRise-TimeandDriverOutputResistance•Measureovershootandoscillationperiodfromthestepresponse•Findworst-caseovershootfrompreviousdiagram•CalculateQfactor•Calculatenaturaloscillationfrequencyfo•CalculateLandC11EstimationofL-CParametersfromaStepResponse1)MeasureovershootandoscillationperiodUUoin10.210201.20.600.40.8Ovs=0.19ns2932Tosc.=Time[ns]12EstimationofL-CParametersfromaStepResponseTToscr050.20.40.60.84321OvsOvsWC2.190.53192TTrosc.=Inputsignalrise-timeTr=3ns13EstimationofL-CParametersfromaStepResponse2)Findworst-caseovershootOvsOvsWC==0530358..3)FindQfactor()611Ovsln121Q2WC.=π−+=OvseWCQ=−−π41214EstimationofL-CParametersfromaStepResponseωπooscTQ=−2111424)Findnaturaloscillationfrequency5)FindL,C(DriveroutputresistanceR=30Ω)ZQRo==483.ΩLZnHCZpFoooo====ωω481206.(L=50nH,C=20pFusedinsimulation)15Example:TTLLogicDrivingaCapacitiveLoadL+5V-CLRcLgng+LoadQ1Q2+UgngULILTTLoutputstage16Example:TTLLogicDrivingaCapacitiveLoadIgndttUgnd-CLRcLgng+LoadL+5VQ1Q2+UgngULILTTLoutputstage2L2LgndLgndgnddtUdCLdtdILU==2fLgndtU59.1CL∆tULtf∆U