IP101G-PHY-to-PHY-ap-20120831

IP101GPHYtoPHYApplicationNoteAugust31,201211.Settinga.Hardwarecircuit30ohm30ohm0.1uF0.1uFIP101GOtherVendor'sPHY_BTx+orRx+VDD_BorunconnectedRx+orTx+OriginalPHY-to-PHYCircuitPointBACBypassCapacitorR2R4PointCPointDPointEPointFTx-orRx-Rx-orTx-Attheleftside,pointCandpointEofIP101Gshouldnotbeconnectedtoneitheranyresistornoranypowersource.Attherightside,thereare2possibilitiesforthepowersourceofpointB—NoconnectionorVDD_B,dependingonthevendor’sdesign.Ifothervendor’sPHYrequiresasupplyvoltageonthecentraltapofthetransformer,thenVDD_BshouldbeappliedtoPointB;otherwisePointBdoesnotneedapowersource.Note.TheACBypassCapacitorshouldbeadded.2.DCSpecinRXofIP101GPHYtoPHYDCtypical:1.65VPeaktoPeak:minimum=+-0.45V,maximum=+-0.65V3.SimplifiedPHYtoPHYcircuitNomatterwhatthedesignarchitectureis,PointBareatthestableDCvoltage.FromtheviewpointoftheACcoupledsignal,allstableDCvoltagepointscanbetreatedasshortcircuit.ThesimplifiedcircuitfromtheTxsideofIP101GtoRxsideofothervendor’sPHYcanberepresentedbythefollowingfigure.IP101GPHYtoPHYApplicationNoteAugust31,2012212mAcurrentsourceRxsideLoad30ohm0.1uF50ohmThiscapacitorcanbebypassedforcalculatingACcoupledsignalAssumahighimpedanceload.0V+Vp-VpSimplifiedPHY-to-PHYCircuitR1R24.AmplitudeCalculationModelBecauseourconcernistheACcoupledsignal,wecanmakethecapacitorshortandignoretheloadingeffectofRxdifferentialload.Thefinalsimplifiedcircuitcanberepresentedbythefollowingfigure.12mAcurrentsource30ohm50ohmAmplitudeCalculationModel0V+Vp-VpR1R2ThemaxdifferentialvoltagecrossingR2is300mV.Intheotherword,+Vpand–Vpare300mVand–300mVrespectively.Therealmeasuredvaluewillbelessthanthis,becausewebypassthelossofcapacitorinthecalculation.BecausewecalculatesingleendvoltagecrossingR2intheabovecase,theactualdifferentialvoltagebetweenRx+andRx-isthedoublevalueof300mV.i.e.it’sshouldbe0.6V.ThefollowingfigureisthemeasureddifferentialvoltageonbothPHY’sRxside.VerticalAmplitude=0.600VppIP101GPHYtoPHYApplicationNoteAugust31,20123Thistheorycanbeappliedtoothervendor’sPHY,iftheothervendor’sPHYalsoprovidesacurrentsource.5.HowtoTunetheTx/Rxperformance•ResistorInordertoachievethebetterRxperformanceofIP101G,werecommendthedesignertosettheseresistorsasR2=R4=25ohm~30ohm.Theoreticallythedesignerdoesnotneedtotunetheseresistors,aslongastheseresistorsarewithintherange.WecanderivethedifferentialvoltageonRx+-iswithintherangebetween450mV(min)and650mV(max).Buttheactualmeasuredvalueshouldbealittlesmallerthanthis,becauseweignorethelossofACcoupledcapacitorinthecalculation.6.ConnecttoIP175C/DIP101GconnectstoIP175C/Dasthefollowingapplicationcircuit.30ohm30ohm0.1uF0.1uFIP101GIP175C/DTx+orRx+1.8V~1.9VRx+orTx+IP101GPHY-to-PHYIP175C/DCircuitPointBACBypassCapacitorR2R4PointCPointDPointEPointFTx-orRx-Rx-orTx-7.ConnecttoIP178G/IP175GIP101GconnectstoIP178G/IP175Gasthefollowingapplicationcircuit.0.1uF0.1uFIP101GIP178G/IP175GTx+orRx+Rx+orTx+IP101GPHY-to-PHYIP178G/IP175GCircuitPointCPointDPointEPointFTx-orRx-Rx-orTx-(~ABOVE~)