电流源与电压源驱动网络变压器

电流源与电压源驱动网络变压器CurrentandVoltageSourcedrivetransformerContent1.CurrentandVoltageSourcedrive2.BobSmithTermination3.Thefunctionandclassificationoftransform4.Integratedanddiscretemagnetic5.8-Coreand12-CoreMagnetic6.CMC(common-modechoke)onthecableandPHYside21CurrentandVoltageSourcedriveThedrivetypeofPHYcontainsvoltageandcurrentsourcedrive.Thecentertapshouldconnecttocapwhenusevoltagesourcedrive.Meanwhilethecentertapshouldconnecttopowerwhenusecurrentsourcedrive.ButwhichkindofdrivetypetobeusedisdeterminedbythePHY-ic.3CurrentSourceDrive4Centertaptopower:Providetheneededdrivecurrent5VoltageSourceDriveCentertapCap:Providelowimpedancepathforcommon-modecurrentComparisonofPowerConsumption6CurrentSourcepowerconsumptionTodrive1Voutputvoltageand10mAoutputcurrent,PHYhavetosink40mA,10mAgoingdownand30mAgoingdown,currentfromthecentertap.Finallythetransformerhave20mAgoingdowninN/2turnsofcoil,so20mAiswastedThetotalpowerconsumptionof4pairsdifferentialincurrentmodedriver.40mA/ch*4ch*1.8V=288mW/porttodrive+1Vonall4pairs.78VoltageSourcePowerconsumptionTodrive1Voutputvoltageand10mAoutputcurrent,thevoltagesourcehastoapply2Vbecauseoftheseriestermination.Typicallythevoltagesourceisatlest2.5Vassuming1:1turnratiotransformers.Theneededcurrentisonly10mAtooutput10mA.For2.5Voperation:10mA/ch*4ch*2.5V=100mW/porttodrive+1VFor3.3Voperation:10mA/ch*4ch*3.3V=132mW/porttodrive+1V910ConclusionCurrentSourcedriverneeds4timescurrentasmuchasVoltageSourcedriverandmorepowerthanVoltageSourcedriver,sonewergenerationofMarvellPHY-icuseVoltageSourceDrivertoreducepowerconsumption.(Belowforreference).Forexample,88E1318usescurrentsourcedriver,butnewerPHY-ic88E1543and88E1518usevoltagesourcedriver.Note:Itdescribesthebasicdifferencebetweencurrentsourcedrivervsvoltagesourcedriverandthedifferenceintermofthevoltage,current,andpowerbetweenthetwoapproaches.Itonlydescribesthetheorynotactualsituation.11TransformandBobSmithTermination123BobSmithTerminationRobertW.(Bob)Smith’spatentedideaproposesthewaytoreducethecommonmodecurrentsonamulti-pairsystem(e.g.CAT5networkcable).Itisbasedonthefactthatthepair-to-pairrelationshipsofaCAT5cableformtransmissionlinesinthemselves.DuetotheapproximatesymmetryintheconstructionoftheCAT5cable,eachpairhasthesamerelation(150Ω)withanyotherpair.FunctionofBobSmithTerminationProvidingthosepair-to-pairtransmissionlineswithterminationmatchingtheircharacteristicimpedanceinordertoabsorbthereflectedwaveandpreventstandingwavefromoccurringsignificantlylowersparasiticinterferenceradiation.ThehighvoltagecapacitorbetweenthecommonpointofallthefourresistorsandtheChassisgroundisnotapartofBobSmithterminationbuthelpsinfilteringthenoiseresiduemanagingtoleakoutthroughthetransformer.13TransformFunction:ConnectPHYandRJ45forisolatingcableinterfaceandlowcommonmodeemissions,protectPHYICfromhighvoltage,strengthensignalforfartherdistance,andEMC(Electro-MagneticCompatibility)Classification:Integratedanddiscrete8-coreand12-core144IntegratedandDiscrete15IntegratedDiscreteIntegratedAdvantages:LowercomponentcountandcostBetterEMCSmallerfootprint,easyforlayoutDisadvantages:Higherproductioncost,hardtoreworkduringproductiontest.Duetothespacelimitations,themagneticcoresaresmallerandclosertoeachotherthusdegradingcrosstalkandEMCcharacteristics,increasingnon-lineardistortionandlosses.16LayoutforDiscreteLayoutrequirementsareslightlydifferentwhenusingdiscretemagnetics.Theseinclude:GroundcutforHVinstallation(notrequiredforintegratedmagnetics)AmaximumoftwoviasTurnslessthan45°Discreteterminators(BobSmithtermination)Thegroundplanebeneathamagneticsmoduleshouldbesplit.TheRJ45connectorsideofthetransformermoduleshouldhavechassisgroundbeneathit.Aminimumof50-milspacingfromhighvoltage(1500pF/2KVor1000pF/3KV)capacitortotracesandcomponentsshouldbemaintained.1718Areferencelayoutfordiscretemagnetics198-CoreMagneticsTransformer+CMC=2-Corefor1pairFor4pairs=8-Core20512-CoreMagneticsTransformer+CMC+Autotransformer=3-Corefor1pairFor4pairs=12-Core12-coreand8-coreMagneticscomparisonThe8-coremagneticarecheaper,butriskierinmanycasesandcautiouslyrecommendedtoskilleddesignerstomeetstricterEMCguidelines.TheBobSmithterminationbecomeslesseffectiveforcommonmodenoiseduetothehighimpedanceinsertedbetweenthecableandtheimpedance-matchingresistor.The12-coreonesmakethedesignprocessmucheasierwithoutdemandingextremeexperienceinthelayoutart,especiallyiftheEthernetmoduleisapartofasystemwithabigdigitalsectiongeneratingalotofinterferencenoise.212268-coreMagneticswithCMConcableside238-coreMagneticswithCMConPHYsideCMConthecablesideandPHYsidecomparisonCMConthecablesideadvantages:Attenuatesanycommon-modenoisethatisgeneratedbyeitherthecentertapsnoiseofthetransformerorbythetransformerwindingsimbalance.FiltersthenoiseinthesystemswheretheChassisgroundisconnectedtothedigitalground,evenbeingconnectedtoEarthgroundthroughthepowersupplycircuit,isstillnoisyenoughtoinjectnoisethroughthehighvoltagecapacitor.Disadvantages:TheBobSmithterminationbecomeslesseffectiveforcommonmodenoiseduetothehighimpedanceinsertedbetweenthecableandthei