Predict-PLL-Behavior-Accurately-Using-SpectreRF

INVENTIVEUsingSpectreRFNoise-AwarePLLMethodologytoPredictPLLBehaviorAccuratelyHeleneThibierozCustomerSupportCICSeptember17,20072UsingSpectreRFNoise-AwarePLLMethodologytoPredictPLLBehaviorAccurately•Introduction•SpectreRFNoise-AwarePLLFlowandNon-LinearVCOModeling•Advantagesofthisflowversusothercommercialapproaches•Experimentalresults•ConclusionSeptember17,20073Introduction•Phaselockedloopsareessentialblocksinmostanalogmixed-signalandradiofrequency(RF)applicationstoday.•BecauseofthecomplexityofPLLs,thedifferenttimeconstantsinvolved(twowidely-spacedtimeconstants),andthefactthatthevoltage-controlledoscillator(VCO)frequencyoftenoscillatesseveralorderofmagnitudefasterthanthereferencefrequency,simulatingPLLsatatransistorlevelpresentsmultiplechallengesandisextremelytimedemanding.•CadenceSpectreRFNoise-awarePLLflowenablesdesignerstoefficientlyandaccuratelypredictPLLresponseusinganon-linearmodelapproachtocapturetheVCOdynamicbehaviorSeptember17,20074ChallengesofPLLSimulation•PLLare“stiff”circuits–Containtwowidely-spacedtimeconstants–Forwirelesssystems,theVCOoftenoscillatesordersofmagnitudefasterthanthereferencefrequencyfreffrefPFDLPFVCODividebyNN*frefCPRefDivOutSeptember17,20075ChallengesofPLLSimulation•Behavioralmodelbasedsimulationapproachesacceleratesimulationspeed,allowingdesignerstotrade-offblockcharacteristicsandPLLperformance.•Cadencehasdevelopedanewnon-linearmodelthatallowsdesignerstoaccuratelysimulatethedynamicbehavioroftheVCO,suchasinjectionlockingandpower-supplyinterference.freffrefPFDLPFVCODividebyNN*frefCPRefDivOutSeptember17,20076UsingSpectreRFNoise-AwarePLLMethodologytoPredictPLLBehaviorAccuratelyIntroductionSpectreRFNoise-AwarePLLFlowandNon-LinearVCOModelingAdvantagesofthisflowversusothercommercialapproachesExperimentalresultsConclusionSeptember17,20077SpectreRFNoise-AwarePLLSimulationVRPFDCPVCON÷VFClosedLoopPLLNoise100nV/√Hz200nV/√Hz500nV/√Hz1μV/√Hz2μV/√Hz5μV/√Hz10μV/√Hz20μV/√Hz50μV/√Hz1kHz10kHz100kHz1MHz10MHz100MHzVerilog-A–TransientAnalysisAutomaticallygeneratemodelComputePSS-PNoiseADETestBenchandAnalysis•AutomatedflowforclosedloopPLLnoiseanalysis•ADEtestbenchandanalysisforallPLLblocks•Automaticgenerationofbehavioralmodels•SpectreRFenhanceddirectintegrationSeptember17,20078SpectreRFNoise-AwarePLLSimulationFlow1.InSpectreRF,aPLLcircuitispartionedasaPFDblockandaVCOblocksincetheyhavedifferentworkfrequencies(OtherblockssuchasCP,LPFandDIVIDERarebeingmergedinthosetwoblocks).2.SpectreRFsolvesthetwotestbenchesatdifferentfrequencieswithPSS(usingeithertimedomainandharmonicbalancesolvers)andgetthelargesignaloperationpoints.3.ThePerturbationProjectionVector(PPV)isextractedintheVCOtestbench.ThenaPLLtestbenchcombinesthePFDandVCOmacromodels.4.PLLbehavioristhensimulatedwithaTRANanalysis.SincePPVisusedtoprovidethephasechanges,theoutputofVCO/DIVIDERistracingthereferencefrequency.Alsonoiseinformation(representedbyJitter)couldbeaddedandsimulatedwiththesametestbench.September17,20079PLLModelExtractionFlow•Placetheblocktobetestedintothetestbenchschematic•InvokeADE,setupsimulationandenablemodelextraction•RunPSSandPNOISEanalysis–PSScalculatesthePPVoftheVCOandthetransferfunctionoftheotherblocks–PNOISEcalculatesthenoisecharacteristicsoftheblock•Spectreautomaticallygeneratesthemodel–Modelisgeneratedintwoformats:CMIandVerilog-AmodelsPlaceDUTinTestbenchStartADEandSetupTestSimulatePSS/PNOISEAutomaticallyGenerateModelSeptember17,200710PLLSimulationFlow•CreatenewPLLTestbenchbyplacingtheextractedmodelsinaPLLtestbench•StartADEandsetuptestsimulation•RunTransientAnalysis–Designershaveanoptiontosimulateeitherwithorwithoutnoise–SimulatewithoutnoiseforPLLlargesignalcharacteristicssuchaslockTime–SimulatewithnoiseforphasenoiseandjitterCreatePLLTestbenchStartADEandSetupTestSimulateTransientAnalyzeResultsSeptember17,200711PLLtestbenchusingthePPVmodelCell:pll_bench(customveriloga)(PPVmodel)(schematic)(utilityforfreqoutputandsavingperiods.txtforphasenoise/jittercalculation)(powersupplynoiseinjection)(LCtanknoiseinjection)September17,200712ModelOverview•Noise-AwarePLLflowsupportsextractionandmodelingofVoltageControlledOscillator,Phase/FrequencyDetector,ChargePump,Divider•VCOModelsupports–Single-endedVCOoutputs.–SensitivitytoTuningVoltage,PositivePowerSupply,andNegativePowerSupply.•Phase/FrequencyDetectorandChargePump–P/FDandCParemerged..•Dividermodel–Dividernoiseisnotextracted.–ThedividerismergedintotheVCOforfastersimulation.•Modelsaresingle-ended,voltageoutputlevels•Twotypesofmodelsaregenerated–CMImodelwillnotbeeditable.–Verilog-Amodelwillbeeditableanddesignerswillbeabletoextendthemodelthemselves.September17,200713Non-LinearVCOModeling•Whydoweneednonlinearoscillatormodels?–Oscillatorsarefundamentallynonlinearsystems.–Linearoscillatormodelsoftenfailtoaccuratelypredictoscillationamplitudeandphasedeviationsunderperturbations[1].•Nonlinearoscillatormodelscancapturethenonlineardynamicsofoscillatorssuchasinjectionlocking,powersupplyinterference,cycleslipping,…September17,200714Non-LinearVCOModeling•Twomainapproachesareavailableandprovidethesameinfor