蒙特卡洛分析.ppt

MonteCarlosimulationforbetteryieldandperformance,-Atutorial,start,Systemrequirement,Statisticalanalysisincludeprocess,mismatcheffects,Initialdesign,Designmeetsthegoal?,end,NO,YES,MonteCarlosimulationforbetteryieldandperformance,SomedesignmaydegradeinperformanceOveralldesignyieldcouldbeunexpectedlylow,Iffabricationprocessparameteranddevicemismatcheffectonsamediearenottakenintoaccountthen,Hencestatisticalanalysismustfindahighplaceindesigncycle,WewillperformMonteCarloanalysisonanRF-frontendLNAandcomparetheresultifnostatisticalanalysisisdone.WewillalsoseehowtoanalyzeyieldandscalardatainMonteCarlowiththehelpofLowpassfilterexample.,MonteCarlosimulation,MonteCarlosimulation(example),Linearity,Inputmatching,BiasN/W,Outputmatching,Cascodearch.toreducefeedbackcapacitance,RF-frontend(LNA),KnowingSystemrequirementInitialdesignbasedonrequirementlikenoise,gain,narroworwideband.,MonteCarlosimulation,Cadencesimulationsetup(Normal),Choosingaffirmaanalogartist,2.ChoosingSpectresimulator,Choosingmodelfile,whichcontainsallMOS,reg.,capmodelparameters.,MonteCarlosimulation,1.Choosesetupmodellibraries,2.Browseandchoosemodelfileinthedirectory,Cadencesimulationsetup(Normal),Setupanalysis(dc,ac,spetc.),createnetlistandrunsimulator,MonteCarlosimulation,1.Chooseanalysistorun,2.Chooseoutputtoplot,3.Createnetlistandrun,Cadencesimulationsetup(Normal),Plottingresults,MonteCarlosimulation,1.Choosedirectplotforanalysis,2.Clicktoviewthedesiredresult,3.Analyzewaveform,Cadencesimulationsetup(Normal),MonteCarlomodelinginCadencespectresimulator,ProcessSection-describesmanufacturingparameter,theirstatisticalvariationandamodelfordevicethatcalculatesits(width,length,cap,res.Etc.)accordingtoprocessparameter.Design-SpecificSectiondesigneraccordingtohisneedcanspecifyMonteCarloanalysis.Forexampleinacurrentmirrorcircuit,matchedtransistorsareusedanddesignercangivesomecorrelationfactorbetweenthesematchedtransistor.,MonteCarlosimulation,Cadencesimulationsetup(MonteCarlo),TypicalModelFile,ProcessSection,Allparametersetstotheirnominalvalue,nostatisticalvariationdefinedModel(NMOSsRg)iscalculatedusingnominalparametervalue,2,1,MonteCarlosimulation,Cadencesimulationsetup(MonteCarlo),Definingprocess,mismatchparameterasstatisticallyassignedvalue,Assessesthedevicemismatchondifferentdie,whichcouldhavegonethroughsomedifferentprocessparametersduringfabrication.,Assessesthedevicemismatchonsamedie,whichcouldhavegonethroughsomedifferentprocessparameter.,Variationdefinedasadistributedfunction,MonteCarlosimulation,ProcessSection,Cadencesimulationsetup(MonteCarlo),DesignSpecificSection,Thisincludesthecircuitconnectivity(tworesistors,andcorrespondingcurrentsourcesthatfeedthem),Definingcorrelationbetweentwodevices(R1,R2),Note:AlternativelythisinformationcanalsobeinsertedthroughArtistMonteCarloTool.,MonteCarlosimulation,Cadencesimulationsetup(MonteCarlo),MonteCarlosimulation,ModelfileusedforLNAexample,NoteThisisnotbasedonfoundrydatabutmodeledforillustrativepurposes.,Cadencesimulationsetup(MonteCarlo),MonteCarlosimulation,AfterInitialdesignthatmeetsthesystemrequirement,statisticalanalysismusthavetobecarriedout.,Makesuretheadditionofprocessandmismatchparametersectioninmodelfile.Makecertaintoincludetheparticularsection(forexa.Statsinspectre)insimulationmodellibraryGototoolMonteCarloinaffirmaanalogartist,Cadencesimulationsetup(MonteCarlo),MonteCarlosimulation,Choosenoofiteration(default=100),1.ChoosewhichvariationtoincludeProcessdevicemismatcheffectontwodiff.dieMismatchdevicemismatcheffectonsamedie,2.Clickifyouwanttoseethefamilyofcurvei.e.curvefromeachiteration,3.Definetheexpressions/signalsonwhichMonteCarloanalysiswillbeperformed.,Note:calculatorcanalsobeusedtogettheseexpression,Finallyruntheanalysis,Cadencesimulationsetup(MonteCarlo),MonteCarlosimulation,(Analyzingwaveform),Matching,Normalsimulation(withoutstatisticalvariation),MonteCarloSimulation(withstatisticalvariation),Processparameterandmismatcheffect,Input&OutputmatchingN/W,DEGRADES,Overalldesignperformance(noise,gainetc.),DEGRADES,S11,S22,MonteCarlosimulation,(Analyzingwaveform),Matching(VSWR):IttellshowwellinputandoutputN/Warematched.,MonteCarlosimulation,Normalsimulation,VSWR1,VSWR2,VariationsinVSWR,MonteCarlosimulation,(Analyzingwaveform),Matching(forwardandreversetransmissiongain),Ithasdeterioratedtheperformancesignificantly,asaminimumS12andmaximumS21valueisdesirable.,Normalsimulation,MonteCarlosimulation,S12,S21,MonteCarlosimulation,(Analyzingwaveform),Normalsimulation,MonteCarlosimulation,Stability:AKfvalue1,isdesiredforanstableamplifier,Kfvaluehasbecome1,andconsequentlycreatingapotentialunstability,hencealargemarginisrequiredatinitialdesignphase.,Stabilityfactor,MonteCarlosimulation,(Analyzingwaveform),Normalsimulation,MonteCarlosimulation,NoisePerformance,Asvisible,designhasarobustnoiseperformanceatdesiredband(2.4-2.5GHz)BUT.,Noisefigure,PeriodicOutputnoise,MonteCarlosimulation,(Analyzingwaveform),ButLNAasanRF-frontendhastoprovideenoughgainwithmaximumnoisesuppressiontomaintainanallowableSNRatdemodulatorsinput.,Itfailstomeetthegainrequirement,Gain,MonteCarlosimulation,WewillquicklygooveranotherexampleoflowpassfilterandseehowtoanalyzescalardataandyieldthroughMonteCarlosimulation,MonteCarlosimulation,InitialDesign:Circuitdesigningaccordingtosystemrequirement,Low-PassFilter,MonteCarlosimulation,1.Runningnormalanalysis,2.Specifyingstatisticalvariationinmodelfile,3.RunningMonteCarloanalysis,1,2,3,Cadencesimulationsetup(MonteCarlo),MonteCarlosimulation,Simulationshowsdb20andphasevaluesaregreatlyaffectedbystatisticalvariationsintroducedintransistor.Hencetheneedforredesigningthecircuit,(Analyzingresults),MonteCarlosimulation,(AnalyzingScalardata),1.ChooseresultsplotHistogram,2.Chooseparameterstoplot,3.Analyzethehistogramappearedinwaveformwindow,MonteCarlosimulation,1.Chooseresultsspecificationlimits,2.Setboundsandlimits,3.ChooseResultsyieldsimpleinanalysiswindow,4.Setsuppressionvalueforyield,5.Analyzeyield,Only64%iterationspassesthespecifiedlimitsforbandwidthandymax,(AnalyzingYield),MonteCarlosimulation(PLLComponents),Overview,Referenceclock,Detectoroutput,Loopfilterresponse,Oscillatoroutput,Clockdivideroutput,Phase/frequencydetectordeterminesthedifferencebetweenthephaseorfrequencyoftwosignalsTheloopfilterremovesthehigh-frequenciesfromthevoltage-controlledoscillator(VCO)controllingvoltageTheVCOproducesandoutputfrequencycontrolledbyavoltage,MonteCarlosimulation(PLLComponents),NoiseSources,Detectornoise,VCOnoise,-Quantizationnoise,InPLLdesignitishighlydesirabletobeabletoseetheimpactofallnoisesources,whichinturnaffectstheoverallPLLperformance.,Duetoreferencejitter,Duetovariationincontrolvoltage,Duetouncertaintyinvolvedindiscretization,MonteCarlosimulation(VCO),Anoscillatorisacircuitcapableofmaintainingelectricoscillations.,Frequencyofoscillation=1/(LC)1/2Controlledbyvoltagedependentcapacitance(varactor),Powerefficientsincebiascurrentissharedbetweenthetwotransconductors.,ComplimentaryCross-CoupledLCVCO,equivalent,Foroperationincurrent-limitedregime:VO=(4/).Ibias.Req(Idealswitching)VO(apx)=Ibias.Req(Highfrequency),Causesofspectralpuritydegradation(phasenoise):1.)Randomnoiseinthereferenceinput,thePFD,loopfilterandVCO(alsodividersifthePLLisafrequencysynthesizer)2.)Spurioussidebandshighenergysidebandswithnoharmonicrelationshiptothegeneratedoutputsignal.Itissystematicinorigin.Whyisspectralpurityimportant?,MonteCarlosimulation(VCOPhaseNoise),Phasenoiseproducesadjacentchannelinterference,Phasenoisecandegradethesensitivityofareceiverduetoreciprocalmixing,MonteCarlosimulation(VCOPhaseNoise),Howdotheprocessandmismatchvariationaffectphasenoise?,-wewillperformmontecarloanalysistoassessthis.Step1VaryingtheprocessparameteronlyStep2investigatingthedevicemismatch(indiffVCOonesidemismatchedtotheother)inpresenceofprocessvariation,Thestatisticsblockcontainsthedistributionsforparameters:DistributionsspecifiedintheprocessblockaresampledonceperMonteCarlorun,areappliedatglobalscope,andareusedtypicallytorepresentbatch-to-batch(process)variations.Distributionsspecifiedinthemismatchblockareappliedonaper-subcircuitinstancebasis,aresampledoncepersubcircuitinstance,andareusedtypicallytorepresentdevice-to-device(onchip)mismatchfordevicesonthesamechip.,CadenceSpectremodeling:,MonteCarlosimulation(VCOPhaseNoise)modelfile,Definestatisticalblocksinthemodelfile(ideallyitshouldbeprovidedfromthefoundry),Processsection,Mismatchsection,MonteCarlosimulation(VCOPhaseNoise)STEP-1,RunningMonteCarloforprocessvariationonly,Normalsimulation,MonteCarlosimulation,Withappliedstatisticalvariation(inmodelfile)anincreaseinnoisecanbeobserved,andatthisrunresultednoiseisworstandunacceptable.,MonteCarlosimulation(VCOPhaseNoise)STEP-2,RunningMonteCarloformismatchin2sidesofDiff.VCO,Normalsimulation,MonteCarlosimulation,Againsimilarlookingbutnotthesameresultsappearsandnoiseatthisrunisunacceptable.,Note:Whenthesameparameterissubjecttobothprocessandmismatchvariations,thesampledprocessvaluebecomesthemeanforthemismatchrandomnumbergeneratorforthatparticularparameter.,MonteCarlosimulation(VCOPhaseNoise)-moreinsight,Togetmoreinsightwewillvaryonlyfewparameterandcheckhowvaluesareassignedfordifferentrunaswellasthesimulationresult,Definingvariationforonlytwoparametersinthemodelfile-Vth-tox,MonteCarlosimulation(VCOPhaseNoise)-moreinsight,Herebothnmos(pmos)transistorshavebeenassignedsameprocessvariation.Ineachruntheytakeondifferentparameteraccordingtodistributiondefined,Processvariationonly,NM0,NM1,PM1,PM0,MonteCarlosimulation(VCOPhaseNoise)-moreinsight,ProcessandMismatchbothvariationtogether,withcorrelationof0.2betweenthetwonmos(pmos)transistor,Asconspicuouseachnmos(pmos)transistorisgettingdifferentparametervalueineachrun.,MonteCarlosimulation(VCOPhaseNoise)-moreinsight,Processvariationonly,Process&mismatchvariation,Asvisibleinthecaseofprocessvariationwithdevicemismatchnoisehasbeenincreased.,MonteCarlosimulation(PLLataglance),InaPLLalltheseprocessvariationcandegradeitsoverallperformancesignificantly.Toseetheimpactofprocessvariationweprobetheoutputaftertheloopfilter.,MonteCarlosimulation,Asclearinonecasecontrolvoltage(i.e.loopfilteroutput)isrampingrapidlycomparetootherandthuswillresultindifferentperformance.,MonteCarlosimulation,InourdesignPLLhasasettlingtimeof65us.Tosimplyruntheanalysis(transistorlevel)forthismuchperiodmaytake2-3daysonasinglemachine.Todomontecarlosimulationevenfor10runwillmakethesituationworse.,TospeedupMonteCarloanalysestomakethemruninminutesasopposedtodays-WeneedtoreducetheruntimeandcanutilizeParallelsimulation.-Suchasvariancereductiontechniquecanbeemployed.,MonteCarlosimulation(Seedno¶llelsimulation),Note:(1)Inputfileshouldhave.scsextension(forexa.input.scs)(2)InspectreonecannotspecifydifferentseedfromGUI(bydefaultitalwaystakesseed=1).,IfMonteCarlosimulationfordifferentseedisrequiredthen.,Step1.Createnetlist(inputfile)a)Eitherfromanalogartistorb)Toolsmontecarlosimulationcreate_input_files,Seed,MonteCarlosimulation,MonteCarlosimulation(Seedno¶llelsimulation),Step2.Editinput.scsfilemanuallyeditSEED=?line(numberyouwant),Seed,MonteCarlosimulation,MonteCarlosimulation(Seedno¶llelsimulation),Step3.Runspectrefromcommandlinewithoptionforexample.spectre-envartist4.4.6+log./psf/spectre.out-formatpsfbin-raw./psfinput.scs,Hereoneshouldexecutespectrecommand(orexecutablefile)fromthenetlistdirectory.,Forexampleonewantstosimulate“PLL”designfromcommandlineThengotoyoursimulationdirectorycd/simulation/pll/spectre/schematic/netlistandhereexecutespectrecommand,Seed,MonteCarlosimulation,MonteCarlosimulation(Seedno¶llelsimulation),Step4.ResultscanbeplottedwitheitherfromcalculatororfromMonteCarlotool.,Seed=1,Seed=11,Seed=3,Fig:Plotsfordifferentseedvaluesimulation,Seed,MonteCarlosimulation(Seedno¶llelsimulation),Anotherwayofdoingsimilarthing(givingdifferentseedvalue)fromGUIwouldbetostartsimulationfromdifferentrun,orsaytoskipsomeinitialrunasshowninthefig.,Butbewareskippingtheserunscouldtakemuchlongertimeforacomplexdesign,Hereitwillskipfirst10runsandsimulatefrom11thto110thrunfor100iterationThisisquitesimilartoassigningdifferentseedvalue.,AwayaroundfromGUI,MonteCarlosimulation(Seedno¶llelsimulation),Runningmultipleanalysisfromonefile,Thiscanbedonebydefiningmultiplemontecarloanalysisstatementintheinputfileasshownbelow,Note:Foreachanalysisadifferentnametochildanalysis(forexampleac,dc,tran)an