OSC

ReportaboutUsingtheCascadeofINVtoCreateOSCCircuitanditsSimulation,AnalyzingFrequencyResponse,PowerSupplyRejectionRatioandPhaseNoise1.WhatweshouldknowabouttheOSCBeforewemakethecircuit,wehavetoobtaintheworkingprincipleofringoscillator.Firstofall,wehavetoknowthattheworkingperiodoftheoscillatorisrelativetothedelayoftheinputsignalintimedomain,whichisdependedonthedimensionofbothNMOSandPMOSdevice,i.e.,W/L.Furthermore,thenumberofINVtogenerateanoscillatorisodd,atleastthree.Andhence,wechoosetousethreeINVsymbolswebuiltbeforetofigureoutworkingfrequencyofthissimpleOSCcircuit,basedonwhichwecanchangedimensionsofthesetwodifferentdevicestomeetstandardweset.2.1.SimpleOSCcircuitandsimulationAswesaidbefore,weusethreeINVdevicestomakeainitialschematictofigureouttheworkingfrequencyofthiscircuittohelpustochangetheparameters.Regularly,weneedtoopenthecadencesoftwareandinsertdemandedcommandstocreateanewfile--OSCinthelibrarywebuiltinthefirstexperiment--cell_lib_tsmc03,accordingtowhatwediscussedinthefirstsection,weusethethreeoldmodelstogenerateacascadeasdepictedinthefig2.1,andweusethiscircuittomapasymboltomaketest_benchfileinthelibrary--testbench_tsmc03,andhencewegenerateacircuittogetthesimulationofthistypeofcascadingsothatwecanfigureoutworkingfrequency.Inthepicturefig2.2istheschematiccircuit.Fig2.1Fig2.2Intheanalogdesignenvironment(ADE),weplottheoutputnodetoseethewaveformofthisoscillatortogettheperiodasdepictedinthefig2.3,inwhichweconcludethatthiscircuitinthisparametercanonlyreachabout0.5ns,A.K.A.,2GHzwhichisfarawayfromwhatwearerequested--600MHz,sowehavetoneedmorecascadesandasforincreasingtheperiod,weshoulddecreasetheintrinsicparameterssuchasthewidthandlengthofthesetwodevices.Fig2.32.2.FinalOCScircuitandsimulationAfterwehavetriedtochangethevalueoftheparametersfromtheexistingstatetominimumdimensiontocapturethefittingdimension.Wefinallyaccomplishedtomeettherequirement--centralfrequency--600MHz.Andthisachievementofthisfrequencyistocascadingnineoftheseinvertersunderwhichtheparametersare1.275umand0.675umrespectivelyformthepicturefig2.4.Fig2.4WhatwehavetodonextistomapthisschematictoasymbolandrunitintheADEtogeneratesimulation.Andhencewiththetestfiledepictedinthefig2.5,wegetthesimulationinthefig2.6.Andwecanseetheworkingperiodisabout1.672ns,i.e.,600MHz.Fig2.5Fig2.6Aswehavesuccessfullyachievedtheworkingcentralfrequencyoftheexperiment,wehavetomakesurethatwetrulygettherightoutcome,therefore,weneedtousesometoolstogetanaccuratevalueaboutthiscircuit--periodicsteadystateanalysis(PSS),andthenstillintheADEweneedtoaddmoretypesofanalysis,andchangethedefaultvaluestowedemand,asdepictedinthefig2.7tomakesurethescanningrangeisaround600MHz,andlimitthenumberofharmonicbalancetothreesothatwecanlessenthesideeffectsofthem.Furthermoreweneedtoplottheoutputnodeandgroundnodetocapturegraphofthefrequency.,asdepictedinthefig2.8.Andinthispicturewecanclearlyseethevalueoffrequencyisabout600.04MHz,whichmeansthatthisoscillatorissuccessful.Fig2.7Fig2.8Wenowcanthinkaboutdoingthefinalstep--thelayoutdrawing.Sincethesenineinvertersareallinthesamedimensionwecaneasilyjustfinishtheoriginaloneandcopyitbyeight,andhencethisninecascadingringoscillatorisaccomplished,asdepictedinthefig2.9.Inwhichwealreadydefineallthedemandedpinslikeinput,output,vddandgnd.Andthenverifywhetherwematchthelayoutwiththeschematiccircuitwecreatedbeforewonderfully.WithnoerroroccurredintheDRC,andgeneratetherelativefilenamedextractedtodoprecedingworkofLVS,asdepictedinthefig2.10,andthenwerunthebuttonLVStoseeifithasbeenmatched.Withthewindowdisplayedinthefig2.11,wecanfinallydroptheconclusionthatalltheeffortswepaidinthislongprocessaredeserved.Fig2.9Fig2.10