以太网设备PCB布线参考

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1、RTL8208REALTEKRTL8208DESIGNANDLAYOUTGUIDE1.IntroductionThisdocumentprovidesdetaileddesignandlayoutguidelinestoachievethebestperformanceforimplementinga2-layerboarddesignwiththeRTL8208OctalPHY.TheRTL8208isthesmallestOct-PHYintheindustry,havingthesmallestfoot-print.Tob

2、enefitBOMcosts,oneexternalPNPtransistorisusedtogeneratea2.5Vpowersource.Careneedstobetaken,however,topreventsignalsfromcross-talkandinterferenceduetothesmallpackage,andmostimportantly,tosupportastable2.5Vpowerplanewhichdeterminestheperformanceofdatarecoveryandtransmi

3、tjitter.CRS_DV[7:0]CRS_DV[7:0]RXD0[7:0]RXD0[7:0]RXD1[7:0]RXD1[7:0]TX_EN[7:0]8-portTX_EN[7:0]8-portRTL8208RTL8208TXD0[7:0]MACTXD0[7:0]MACX1TXD1[7:0]X1TXD1[7:0]REFCLKREFCLKX225MHz50MHzoscillatorRMIISignalDiagramRMIISignalDiagram50MHzOscillatorSolution25MHzCrystalSoluti

4、on2002/1/29Rev.1.11RTL82082.GeneralDesignandLayoutGuideInordertoachievemaximumperformancewiththeRTL8208,gooddesignattentionisrequiredthroughoutthedesignandlayoutprocess.Thefollowingrecommendationswillhelpimplementahighperformancesystem.2.1GeneralGuidelines•Createagoo

5、dpowersource,minimizingnoisefromswitchingpowersupplycircuits(<50mV).•Verifythequalityofthecomponents,suchasclocksourceandtransformer,tomeettheapplicationrequirements.•Keeppowerandgroundnoiselevelsbelow50mV.•Usebulkcapacitors(4.7uF-10uF)betweenthepowerandgroundplanes.

6、•Use0.1uFdecouplingcapacitorstoreducehigh-frequencynoiseonthepowerandgroundplanes.•KeepdecouplingcapacitorsascloseaspossibletotheRTL8208.•Provideterminationonallhigh-speedswitchingsignals.2.2DifferentialSignalLayoutGuidelines•Keepdifferentialpairsascloseaspossibleand

7、routebothtracesasidenticallyaspossible,meaningwidth,lengthandlocation.•Avoidviasandlayerchangesifpossible.•Keepthetransmitandreceivepairsasfarfromeachotheraspossible.Runthemorthogonallyorseparatedbyagroundplaneifpossible.•Avoidright-anglesignaltraces88AA220088BBbad!g

8、ood!2.3ClockCircuit•Theclockshouldbe25M/50MHz/125MHz100ppmwithjitterlessthan0.5ns.•ThelengthoftheclockpathtotheRTL8208shouldbeequal