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1、PCBLayout中的专业走线策略，三大误区要注意PCBLayoutisaprofessionallinestrategy,threemistakesshouldbenoticedLayoutisoneofthebasicskillsofPCBdesignengineers・Walklineisgoodorbadwilldirectlyaffecttheperformanceofthewholesystem,mostofthehighspeeddesigntheorywilleventuallypassbyLayoutimpleme
2、ntedandvalidation,thus,wiringinhigh-speedPCBdesigniscritica1.Inthispaper,wewillanalyzesomepossiblesituationsintheactualwiring,analyzeitsrationality,andgivesomeoptimalroutingstrategies・Thispapermainlyexpoundsthefollowingthreeaspects:rightAnglewalking,differentialwalking
3、,andserpentine.1.Right-anglewalkinglineRectangulsrwalklineisusuallyaskedtoavoidPCBwiring,alsoalmostbecomeoneofthecriteriaformeasuringwiring,thenrightgolinewillhowmuchimpactonthesignaltransmission?Inprinciple,arightAnglecanchangethelinewidthofthetransmissionline,causing
4、thediscontinuityoftheimpedance・Infact,it'snotjusttherightAngle,thecornet,thesharpAngleofthelinethatcancausethechangeofimpedance・Theinfluenceofright-anglewalkingsignalsismainlyreflectedinthreeaspects:oneisthatthecornercanbeequivalenttothecapacityloadonthetransmissionlin
5、e,whichcans1owtherisetime;Thesecondisthattheimpedancediscontinuitycausesthereflectionofthesignal;ThethirdistheEMIproducedattherightAngle・TheparasiticcapacilaneeoftherightAngleofthetransmissionlinecanbecalculatedbythefollowingempiricalformula:Intheaboveequation,Creferst
6、otheequivalentcapacitanceofthecorner(unit:pF),Wreferstothewidthofthewalkingline(unit:inch),thedielectricconstantoftheepsilonr,andZOisthecharacteristicimpedanceofthetransmissionline.Forexample,fora4Mils50-ohmtransmissionline(epsilonris4.3),arightAngleisabout0.0101pF,whi
7、chcanthenestimatetheamountoftimechangecausedbythis:ItcanbeseenfromthecalculationthatthecapacitiveeffectoftherightAnglelineisextremelysmalLDuetotherectangulargoline,linewidthincreaseitsimpedancewilldecrease,sowillproducecertainsignalreflectionphenomenon,wecanaccordingto
8、theimpedanceofthetransmissionlinesectionmentionedintheformulatocalculatethelinewidthincreasingaftertheequivalentimped
