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DatasheetJitterSpecificationsforCypressTimingProducts001-71968Rev.
*BSeptember2017IntroductionThisnotedescribeshowCypressSemiconductordefinesjitterforclockproductdatasheetspecifications.
Thereareseveralmotivationsforthis.
First,thereisnoaccepteduniversalspecificationdefiningjitterforallapplications.
Therefore,eachindustrystandardmustdefinejitterfortheirneeds.
However,thesestandardsdonotalwayssharethesamedefinitions.
Also,someapplicationsdonothaveassociatedstandardsgoverningthem.
Secondly,thegrowingimportanceofjitterintraditionallynon-jittersensitiveapplicationshasledtojitterterminologybeingusedlooselyintheindustry,causingadditionalconfusion.
Thedefinitionssetinthisnoteonlyapplytothoseproductsspecificallyreferringtothisdocumentintheirrespectivedatasheets.
Allotherproductscontaintherelevantjitterdefinitionswithinthebodyoftheirdatasheet.
Unlessotherwisenoted,thejitterdefinitionsprovidedbelowapplytoperiodicclockwaveforms.
TypesversusComponentsofJitterToclarifythediscussionofjitter,wemustfirstdifferentiatebetween"types"ofjitterversus"components"ofjitter.
Thetypeofjitteridentifiesthespecificmeasurementthatismade.
Thecomponentofjitteridentifiesthestatisticalcompositionofjitterpresent.
Examplesoftypesofjitterinclude(butarenotlimitedto)periodjitterandcycle-to-cyclejitter.
Componentsofjittermaybeeitherrandomordeterministic.
Thus,alltypesofjittermaybebrokendownintorandomanddeterministiccomponentsofjitter.
However,sinceitisonlypossibletodirectlymeasurethetotaljitter(andnotitsrandomanddeterministiccomponentsseparately),Cypressonlyspecifiestotaljitterondatasheets.
Whileitispossibletoapplyamathematicalalgorithmtodecomposetotaljitterintoitsrandomanddeterministiccomponents,thereisnoindustryagreed-uponmethodologyforthemechanicsofthisalgorithm(thatiscoveringsuchthingsastimescales,samplingdomains,andthemultitudeofseeminglytrivialminutiaspecifictotheimplementationofthealgorithm,eachhavingsignificantimpactonthefinaldecomposedvalues).
Forthisreason,andsincethejitterseenbyanyhardwaresystemissimplythetotaljitter,ourdatasheetspecificationsdonotapplymathematicalalgorithmstodecomposejitterintorandomanddeterministiccomponents.
WHITEPAPERChrisMartinCypressSemiconductorCorp.
AbstractThisdocumentservestooutlinethemostcommontypesofjitteralongwithcleardefinitionsofeachtypeandhowitisspecifiedinCypressclockproductdatasheets.
DatasheetJitterSpecificationsforCypressTimingProductsDatasheetJitterSpecificationsforCypressTimingProducts001-71968Rev.
*BSeptember20172CypressSemiconductorCorp.
InputJitterAlldatasheetjitterspecificationsarebasedonmeasuredcharacterizationdata(plusmargin)andguaranteedbydesign.
Themeasureddataisnotmathematicallyprocessedtosubtracttheinputjitter.
Jitterisacomplexcompositionofstatisticalvariables,whosecorrelationbetweeneachotherandtheirinteractionwiththeproduct'sbandwidthisverydifficulttoaccuratelymodel.
Applyingmathematicalpostprocessingtothemeasuredjittercompromisestheintegrityofthedatabyincreasingtheuncertaintyoftheresult.
Cypress'sstrategyformeasuringthemostaccurateintrinsicjitterthereforereliesuponminimizingtheinputjitter.
Asaresult,ourjitterspecificationsincludeinputjitterwithintrinsicjitter,andarethereforeconservative(totheextentthattheinputjitterinfluencestheoutputjitter).
DatasheetFormatforSpecifyingJitterSpecificationsguaranteeingjitterappearonthedatasheetasshowninFigure1.
Thistableillustratestheformatforspecifyingjitteronthedatasheet.
Thedatasheetmayhaveoneormoreoftherowsshowninthistable.
Figure1.
FormatforSpecifyingJitterFigure2.
GenericHistogram(example)IllustratingtheRelationshipbetweenPeakandPeak-to-PeakThefollowingterminology,asshowninFigure1andFigure2,isusedinthenextsectionfordefiningjitterspecifications.
maxpeak-peakjitter=A=D–Cminpeakjitter=Cmaxpeakjitter=D,ifminpeakjitter(C)isspecifiedonthedatasheet,otherwisemaxpeakjitter=B,whichisthelargerof|C|orD,ifminpeakjitter(C)isnotspecifiedonthedatasheetRMSjitter=EDefinitionsforVariousTypesofJitterThissectiondefinesthefollowingtypesofjitter.
1.
Periodjitter2.
Half-periodjitter3.
Cycle-to-cyclejitter4.
N-cyclejitter5.
N-cycle-to-cyclejitter6.
Half-periodcycle-to-cyclejitter7.
Phasejitter8.
Dynamic-phaseoffsetDatasheetJitterSpecificationsforCypressTimingProducts001-71968Rev.
*BSeptember20173CypressSemiconductorCorp.
PeriodJitterInaccordancewithJEDECstandardJESD65B,periodjitterisdefinedasthedeviationincycletimeofasignalwithrespecttotheaverageperiodoverarandomsampleofcycles.
Mathematically,periodjitterisdefinedasEquation1Wherefoistheaverage(thatis,arithmeticmean,referredtoas"mean"below)outputfrequencyfromthemeasureddataandtcyclenisanyperiodmeasuredoncontrollededges.
Figure3.
PeriodJitterMeasurementAtleast1000periodsaremeasured(n>1000).
Thedistributionoftheseperiodsischaracterizedbyameanof1/fo,astandarddeviation,andminimum(min)andmaximum(max)periods.
Thedatasheetmayreportanyofthefollowingparameters.
maxpeak-peakperiodjitter=max–minminpeakperiodjitter=min–meanmaxpeakperiodjitter=max–mean,ifminpeakperiodjitterisspecifiedonthedatasheet,otherwisemaxpeakperiodjitter=thelargerof(max-mean)or(mean-min),ifminpeakperiodjitterisnotspecifiedonthedatasheetRMSperiodjitter=standarddeviationHalf-PeriodJitterInaccordancewithJEDECstandardJESD65B,half-periodjitterisdefinedasthemagnitudeofthedeviationintimedurationbetweenhalf-cyclethresholdcrossingsofasinglehalf-cycleoverarandomsampleofhalfcycles.
Mathematically,half-periodjitterisdefinedas,Equation2Wherethpnisthenthhalf-periodmeasured,andfoistheaveragefrequencyfromthemeasureddata.
Figure4.
HalfPeriodMeasurementAtleast1000half-periodsaremeasured(n>1000).
Thedistributionoftheseperiodsischaracterizedbyameanof1/fo,astandarddeviation,andminimum(min)andmaximum(max)half-periods.
Thedatasheetmayreportanyofthefollowingparameters.
maxpeak-peakhalf-periodjitter=max–minminpeakhalf-periodjitter=min–meanmaxpeakhalf-periodjitter=max–mean,ifminpeakhalf-periodjitterisspecifiedonthedatasheet,otherwisemaxpeakhalf-periodjitter=thelargerof(max-mean)or(mean-min),ifminpeakhalf-periodjitterisnotspecifiedonthedatasheetRMShalf-periodjitter=standarddeviationDatasheetJitterSpecificationsforCypressTimingProducts001-71968Rev.
*BSeptember20174CypressSemiconductorCorp.
Cycle-to-Cycle(C2C)JitterInaccordancewithJEDECstandardJESD65B,C2Cjitterisdefinedasthevariationincycletimeofasignalbetweenadjacentcycles,overarandomsampleofadjacentcyclepairs.
Mathematically,C2Cjitterisdefinedas,Equation3Wheretcyclenandtcyclen+1areanytwoadjacentperiodsmeasuredoncontrollededges.
Figure5.
Cycle-to-CycleJitterMeasurementAtleast1000C2Cjittermeasurementsaremade(n>1000).
ThedistributionofC2Cjitterisone-sided,asdictatedbytheabsolutevalueinthedefinition.
Thisdistributionischaracterizedbyitsroot-mean-squarevalue,andamaximumC2Cjitter.
Thedatasheetmayreportanyofthefollowingparameters.
peakC2Cjitter=maximummeasuredvalueoftjit(c2c)RMSC2Cjitter=root-mean-squareofthedistributionfortjit(c2c)OthercompaniesmightdefineC2Cjitterwithoutanabsolutevaluesign.
Figure6a)showshowthedistributionchangesforthisalternatedefinition(CurveB).
However,ourdefinition'sRMSvalue(CurveA)ismathematicallyequaltoCurveB'sstandarddeviation.
ThisisbecausetheequationforstandarddeviationsimplifiestotheequationforRMSwhenthemeanofthedistribution(thedistributionthatisusedtocalculatethestandarddeviation)iszero.
Therefore,RMSAandthestandarddeviationfromB)areequivalentmeasuresofC2Cjitter,asshowninFigure6(b).
Note,however,thattheRMSvalueofCurveAdoesnotequalitsstandarddeviation(Figure6(c)),sincethemeanofCurveAisnotzero.
AlthoughaGaussiancurveisdrawnforsimplicityinFigure6,thecurveinrealitymayormaynotbeGaussian.
Figure6.
IllustrationoftheRelationshipbetweenStandardDeviationandRMSValuesforourDefinitionofC2CJitter(CurveA)VersusanAlternateDefinition(CurveB)DatasheetJitterSpecificationsforCypressTimingProducts001-71968Rev.
*BSeptember20175CypressSemiconductorCorp.
N-CycleJitterN-cyclejittermeasuresthevariationbetweentheoutputclocks'sfirstandN-thrisingedges.
TheexactvalueofNdependsontheapplication.
ForPCmotherboardandgraphicsapplications,theN-thcycleusuallyoccursaround10–20microseconds.
Otherapplicationsmaydiffer.
Mathematically,N-cyclejitterisdefinedas,Equation4WheretNandtoaretheinstantaneousandmeantimedifferences,respectively,betweenthefirstandN-thrisingedges.
Figure7.
N-CycleJitterMeasurementAtleast1000N-cyclejittermeasurementsaremade.
Thedistributionofthesemeasurementsischaracterizedbyastandarddeviation,amostnegativetimedeviation(nmax),andamostpositivetimedeviation(pmax).
Thedatasheetmayreportanyofthefollowingparameters.
maxpeak-peakN-cyclejitter=pmax–nmaxminN-cyclejitter=nmaxmaxpeakN-cyclejitter=pmax,ifminpeakN-cyclejitterisspecifiedonthedatasheet,otherwisemaxpeakN-cyclejitter=thelargerof|nmax|orpmax,ifminpeakN-cyclejitterisnotspecifiedonthedatasheetRMSN-cyclejitter=standarddeviationN-Cycle-to-Cycle(N-C2C)JitterN-C2Cjitterisdefinedasthevariationintimeofasignalbetweenadjacentintervals,whereeachintervalisNcycles(i.
e.
,periods)long,overarandomsampleofadjacentintervalpairs.
Mathematically,N-C2Cjitterisdefinedas,Equation5WheretNcyclenandtNcyclen+1areanytwoadjacentintervalsoftime,eachequaltoNcycleslong,measuredoncontrollededges.
Figure8.
N-Cycle-to-CycleJitterMeasurementAtleast1000N-C2Cjittermeasurementsaremade(n>1001).
ThedistributionofN-C2Cjitterischaracterizedbyitsstandarddeviation,amostnegativetimedeviation(nmax),andamostpositivetimedeviation(pmax).
Thedatasheetmayreportanyofthefollowingparameters.
maxpeak-peakN-C2Cjitter=pmax–nmaxminN-C2Cjitter=nmaxDatasheetJitterSpecificationsforCypressTimingProducts001-71968Rev.
*BSeptember20176CypressSemiconductorCorp.
maxpeakN-C2Cjitter=pmax,ifminpeakN-C2Cjitterisspecifiedonthedatasheet,otherwisemaxpeakN-C2Cjitter=thelargerof|nmax|orpmax,ifminpeakN-C2CjitterisnotspecifiedonthedatasheetRMSN-C2Cjitter=standarddeviationHalf-PeriodCycle-to-Cycle(HP-C2C)JitterHalf-periodcycle-to-cyclejitterisdefinedasthevariationintimeofasignalbetweenmatchinghalf-periodsbetweenadjacentperiodsoverarandomsampleofadjacentmatchinghalf-periodpairs.
Mathematically,HP-C2Cjitterisdefinedas,tjit(herc2c)=thpn+1(–)–thpn(–)andtjit(hperc2c)=thpn+1(+)–thpn(+)Equation6Wherethpn+1(–)andthpn(–)areanytwoadjacentperiods'negative-polarityhalf-periods,andthpn+1(+)andthpn(+)areanytwoadjacentperiods'positive-polarityhalf-periods,measuredoncontrollededges.
Figure9.
HPCycle-to-CycleJitterMeasurementAtleast1000HP-C2Cjittermeasurementsaremade(n>1001).
ThedistributionofHP-C2Cjitterischaracterizedbyitsstandarddeviation,amostnegativetimedeviation(nmax),andamostpositivetimedeviation(pmax).
Thedatasheetmayreportanyofthefollowingparameters.
maxpeak-peakHP-C2Cjitter=pmax–nmaxminHP-C2Cjitter=nmaxmaxpeakHP-C2Cjitter=pmax,ifminpeakHP-C2Cjitterisspecifiedonthedatasheet,otherwisemaxpeakHP-C2Cjitter=thelargerof|nmax|orpmax,ifminpeakHP-C2CjitterisnotspecifiedonthedatasheetRMSHP-C2Cjitter=standarddeviationPhaseJitterPhasejitteriscalculatedbyfilteringthemeasuredphase-noisedatawithanindustry-standarddefinedfilter,andintegratingtheresultacrossoffsetfrequencytoderiveanRMSphase-jittervalue.
Figure10.
PhaseJitterThedatasheetreportsphasejitterinunitsoftime,ataspecificcarrierfrequency.
Thevaluesoff1andf2(androll-offcharacteristics,ifappropriate)asdictatedbytheend-marketspecificationarealsoprovidedinthedatasheet.
Itisnotpossibletodirectlymeasurepeakvaluesfromaphase-noisegraph.
DatasheetJitterSpecificationsforCypressTimingProducts001-71968Rev.
*BSeptember20177CypressSemiconductorCorp.
DynamicPhaseOffsetDynamicphaseoffset(DPO)isatypeofPLLjitterthatdefinesthevariationintimedifferencebetweentheinputreferenceclockandthePLLfeedbackinputsignalwithrespecttothemeanforarandomsampleofcycles,whenthePLLislockedandtheinputreferencefrequencyisstable.
DPOistheaccounterparttostatic-phaseoffset.
Figure11.
(a)ApplicationDiagram,and(b)WaveformsusedintheCalculationofDynamicPhaseOffsetMathematically,DPOisdefinedas,Equation7Wheretoisthetimedifferencebetweenreferenceandfeedbackinputs,andtomeanisitsaveragevalue.
Atleast1000DPOmeasurementsaretaken.
Thedistributionofthesemeasurementsischaracterizedbyastandarddeviation,amostnegativephaseoffset(nmax)andamostpositivephaseoffset(pmax).
Thedatasheetmayreportanyofthefollowingparameters.
maxpeak-peakDPO=pmax–nmaxminpeakDPO=nmaxmaxpeakDPO=pmax,ifminpeakDPOisspecifiedonthedatasheet,otherwisemaxpeakDPO=thelargerof|nmax|orpmax,ifminpeakDPOisnotspecifiedonthedatasheetRMSDPO=standarddeviationDatasheetJitterSpecificationsforCypressTimingProducts001-71968Rev.
*BSeptember20178CypressSemiconductorCorp.
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