全套电磁兼容资料10

1ParasiticComponentsOutline•Conductorparasiticelements–resistance–inductance–capacitance•Resistors•Capacitors•Inductors•Ferritebeads•Parasiticcomponentsincircuitlayout•Transformers2RelevantEMI“Components”•OnlyonethirdofthecomponentsaffectingEMIareontheschematics•Anotherthirdareparasiticelementswithincomponents•ThefinalthirdarecreatedbyPCboardtracerouting,andcomponentmounting,placement,andevenorientation•AnypeaceofwireandPCBtracehasanonzeroimpedance3ResistanceofaCylindricalConductor[]m/D4r2WDCΩσπ=DC:(σ=conductivity)DWUniformcurrentdistributioninsidetheconductor4ResistanceofaCylindricalConductorDWNonuniformcurrentdistributioninsidetheconductorduetoskineffectδSkindepthf10σπµ=δ(σ=conductivity)AC:[]m/fD1r0WACΩπσµ≅5ResistanceofaRectangularConductorAveragedepthofcurrentpenetration()[]mfTW21r0AC/Ωσπµ+≅ACresistance:WδT6ACResistanceofaRectangularConductor[]m/fWSW21r0ACΩσπµ+≅WδTS=PCBtracecrosssection0246800.20.40.60.81SWmaxACACrrWideflatconductorshavelessACresistancethanroundorsquarecrosssectionconductors7ConductorInternalInductancerW[]m/H80DC_iπµ=l[]m/Hf1r410WAC_iπσµπ≅lTheinternalinductanceplaysnoroleathighfrequency8ExternalInductancesIIInfinitelengthrWs[]m/Hr2scoshW10eπµ=−l9EquivalentCircuitleLleL(le/2)L(le/2)LLiswirelengthTheexternalinductancecanbeassociatedtoanyofthetwoconductorsIstherearightwaytodothat?10Yes,usePartialInductanceConceptI1I2I3I4Lp22Lp11Lp33Lp44Lp21Lp23Lp24I1I2I3I42134Voltageacrosssegment2:dtdILdtdILdtdILdtdILV424p323p121p222p2−+−=11PartialSelfInductanceSegmentiiBii∞siIiisiiipiiIsdBLi∫=rr12iBij∞siPartialMutualInductanceIjjSegmentjjsiijpijIsdBLi∫=rr13PartialSelfandMutualInductance+−+++πµ=1ss1ssln2L220pijLLLLL+−+++πµ==1rr1rrln2LL2ww2ww0pjjpiiLLLLLTwoparallelcylindricalconductorsofradiusrwijsL14PartialSelfandMutualInductanceIfs/L1+−πµ≈LLLs1s2ln2L0pij+−πµ≈=LLLww0pjjpiir1r2ln2LL15TotalInductanceofaRectangularLoopI1I2I3I4Lp22Lp11Lp33Lp44Lp21Lp23Lp24I1I2I3I42134LsI1=I2=I3=I4=I,Lp11=Lp33=Lpt,Lp22=Lp44=LplLp21=Lp23=Lp41=Lp43=0,Lp24=Lp42=Lml,Lp13=Lp31=Lmt()()mtptmlplLoopLL2LL2L−+−=16TotalInductanceofaRectangularLoopLpl-LmlLpl-LmlLpt-LmtLpt-Lmt−πµ≈−LLsrsln2LLw0mlpl1sL()mlplLoopLL2L−≈17TotalInductanceofaRectangularLoop()mlplLoopLL2L−≈BecausethepartialmutualinductanceLmbetweentwoconductorsincreasesastheirseparationisreduced,whereastheirpartialselfinductanceLpdoesnotchange,thenetpartialinductanceLp-Lmdecreasesastheconductorsarebroughtclosertogether.18FormulaComparison05010015020000.050.10.150.20.25wrL4rsw=6rsw=8rsw=LoopeL1Ll−=εExample:AWG20rw=16mil(406.4µm),L=1cmLLoop=10.88nHleL=9.105nH19PartialSelfInductanceAWGdw[in][nH][nH][µH]AWGdw[in][nH][nH][µH]1cm10cm1m1cm10cm1mLL10.10193,72681,071,26925.01796,999115,641,61611.09073,93283,371,29226.01597,231118,001,64012.08084,14085,651,31527.01427,453120,261,66313.07204,34987,941,33828.01267,688122,651,68714.06414,56290,241,36129.01137,903124,821,70815.05714,77792,541,38530.01008,144127,261,73316.05084,99594,861,40831.00898,374129,591,75617.04535,21197,141,43132.00808,585131,721,77818.04035,43299,461,45433.00718,822134,111,80119.03595,652101,771,47734.00639,059136,491,82520.03205,873104,061,50035.00569,292138,851,84921.02856,096106,361,52436.00509,518141,111,87222.02536,326108,741,54737.00459,727143,221,89323.02266,545110,991,57038.00409,961145,571,91624.02016,773113,331,59320CapacitanceHomogeneousmedium:s++++++------εµ=celInfinitelength[]mFr2scoshcW10e00/επ=εµ=−l21ExternalInductanceandCapacitances++++++------rWsIfs5rW[]mHrslnW0e/πµ≅l[]m/FrslncW0επ≅22ExampleSeriesimpedanceoftwoconductorsAWG20(26x34)at2mmdistance(copper)le≈620nH/mExternalinductance:rDC≈33mΩ/mDCResistance:23ImpedanceperUnitLengthAbovesometensofkHzinductanceisofmajorconcern!01100.010.1[MHz]2040[dB]0.001()DCrfz()DCrfr24ResistorsRideal1)Wirewound2)Filmtype3)CompositionRLpCPLp1Lp2Lp3()ppRCj1RLjjZω++ω=ω25ParasiticInductanceExceptforwirewoundresistors,parasiticinductanceismainlyduetoleadlengthandseparationPCBS=20mmL=8mmLp=12.5nH(Cp=Cpext+Closs=0.06pF+(0.1÷0.5)pF)26Example104106108[Hz]fpf02060100|Z(jω)|dBΩBodeplotofa1MΩresistorwithLp=12nH,Cp=0.5pFfp=318kHzf0=2GHzForhighvalueresistors,parasiticcapacitanceisofmajorconcern27CompositionResistorAttenuationMeasurementSourceReceiverUg+ZgZRZres+-URresRgRgRZZZZUU++=Zg=ZR=50Ω28CompositionResistorR=100kΩ(Ug=100dBµV@50Ω)3WNominalattenuation1/2WCp=0.3pF1/4WCp=0.16pF29CapacitorsRsRpCLRs=seriesresistance(ESR)Rp=parallelresistance(dielectriclosses)L=seriesinductance(ESL)()ZjRjLRjRCsppωωω=+++130ParasiticInductorL=Ls+Li+LwLs=inductanceofthewoundstructureLi=inductanceofinternalleadsLw=inductanceofconnectingwires[]H101r2ln2L7−−=lllw=lengthofconnectingwires[m]rw=radiusofconnectingwires[m]Partialselfinductance31Impedanceofa“Real”CapacitorRRps+Rs1ωC1ωLωoLC=1ω|Z(jω)|RsRpCL32Impedanceofa“Real”CapacitorAttenuationMeasurementSourceUg+ZgZRZC+-URZg=ZR=50ΩReceiverCRgCRgRZ//ZZZ//ZUU+=33Impedanceofa“Real”CapacitorC=100nF,Ceramic(Ug=100dBµV@50