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1、APPENDICESSolvingSPICEConvergenceProblemsKeySourcesThefollowingtechniquesonsolvingconvergenceproblemsaretakenfromvarioussourcesincluding:[1]Meares,L.G.,HymowitzC.E.“SIMULATINGWITHSPICE”,Intusoft,1988[2]Muller,K.H.”ASPICECOOKBOOK”,Intusoft,1990[3]Meares,L.G.,HymowitzC.E.“SPICEAPP
2、LICATIONSHANDBOOK”,Intusoft,1990[4]IntusoftNewsletters,variousdatesfrom1986topresent[5]TheDesigner'sGuidetoSPICandSpectre,KennethS.Kundert,KluwerAcademicPublishers,1995[6]TheSPICEBook,AndreiVladimirescu,JohnWiley&SonsInc,,1994[7]InsideSPICE,RonKielkowski,McGraw-Hill,Inc.1994What
3、isConvergence?(orinmycase,Non-Convergence)Theanswertoanonlinearproblem,suchasthoseintheSPICEDCandTransientanalyses,isfoundviaaniterativesolution.Forexample,ISSPICEmakesaninitialguessatthecircuit’snodevoltagesandthen,usingthecircuitconductances,calculatesthemeshcurrents.Thecurren
4、tsarethenusedtorecalculatethenodevoltages,andthecyclebeginsagain.Thiscontinues355WHATISCONVERGENCE?untilallofthenodevoltagessettletovalueswhicharewithinspecifictolerancelimits.Theselimitscanbealteredusingvarious.OptionsparameterssuchasReltol,Vntol,andAbstol.Ifthenodevoltagesdono
5、tsettledownwithinacertainnumberofiterations,theDCanalysiswillissueanerrormessagesuchas“NoconvergenceinDCanalysis”,“SingularMatrix”,or“Gmin/SourceSteppingFailed”.SPICEwillthenterminatetherunbecauseboththeACandtransientanalysesrequireaninitialstableoperatingpointinordertoproceed.D
6、uringthetransientanalysis,thisiterativeprocessisrepeatedforeachindividualtimestep.Ifthenodevoltagesdonotsettledown,thetimestepisreducedandSPICEtriesagaintodeterminethenodevoltages.Ifthetimestepisreducedbeyondaspecificfractionofthetotalanalysistime,thetransientanalysiswillissueth
7、eerrormessage,“Timesteptoosmall,”andtheanalysiswillbehalted.Problemscomeinallshapes,sizes,anddisguises,butconver-genceproblemsareusuallyrelatedtooneofthefollowing:·CircuitTopology·DeviceModeling·SimulatorSetupTheDCanalysismayfailtoconvergebecauseofincorrectinitialvoltageestimate
8、s,modeldiscontinuities,unstable/bistableoperati
