DC Analysis模电的DC仿真

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1、Chapter2DCAnalysis2.1IntroductionManyoftheanalysesavailableforSPICEandSpectrecomputeop-eratingpoints.Forexample,SPICE’s.opanalysiscomputesandoutputsinformationabouttheoperatingpointsuchasthevoltage,current,power,etc.ateachcomponent.The.dcanalysiscomputestheoperatingpointasafunctionofsome

2、independentvariable.Thelinearsmallsignalsanalyses,suchas.acand.noise,firstcomputetheoperatingpointandthenlinearizethecircuitaboutthatoperat-ingpointbeforecomputingthesmall-signalbehaviorofthecircuit.Finally,thetransientanalysiscomputesanoperatingpointfortheinitialstateofthecircuit.Clearl

3、ytheabilitytoreliablycomputeanaccurateoperatingpointisveryimportant.Ingeneraloperatingpointsaresimplysnap-shotsofsomesolutiontrajectory.InDCanalysis,theoperatingpointsarealsoassumedtobeequilibriumpoints.Equilibriumpointsareconstant-valuedoper-atingpoints.Inotherwords,equilibriumpointsare

4、solutionsthatdonotchangewithtime.Acircuitcannotreachanequilibriumpointifthestimulusisstillchanging,sothefirststepofaDCanalysisistoconfiguretheindependentsourcessotheyareconstant.Inaddi-tion,sinceallwaveformsareconstant-valuedatequilibriumpoints,andandsocapacitorsactasopencircuitsandinduc

5、torsactasshortcircuits.Thereinliesthebasicalgorithmforcomputinganequilibriumpoint.16Chapter2.DCAnalysis1.Configureallindependentsourcestobeconstantvalued.2.Replaceallcapacitorswithopencircuits.3.Replaceallinductorswithshortcircuits.Solvingtheequationsthatdescribetheresultingsystemgivesan

6、equilibriumpoint.Thissystemofequationsisnonlinearandalge-braic(notimederivativesorintegrals).Solvinglargenonlinearsys-temsofalgebraicequationsisadifficultchallenge.TheonlywaytosolvegeneralnonlinearequationsistouseiterativemethodssuchasNewton’smethod.However,eventhesemethodsarenotguarante

7、edtowork.Infact,thereisnopracticalalgorithmthatalwaysworks.Whenaniterativemethodfails,itdoessobynotconvergingtoaso-lution.ConvergenceissuesaretheprimaryconcernwhenusingDCanalysisbecauseconvergenceisproblematicforcircuitsimulators,es-peciallyonlargecircuits.Theaccuracyofth