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1、Phaselockedloop鎖相回路?Phase-lockedloop鎖相回路2010-04-2723：12Phase-lockedloop"PLL"redirectshere.Forthechemicalsubstancepolylysine,seepolylysine；fortheRubik'sCubePermutationofLastLayer,seeFridrichMethod；forthespinalligament,seePosteriorlongitudinalligament.Aphase-lockedlooporphaselockloop(PLL)isa
2、controlsystemthatgeneratesasignalthathasafixedrelationtothephaseofa"reference"signal.Aphase-lockedloopcircuitrespondstoboththefrequencyandthephaseoftheinputsignals,automaticallyraisingorloweringthefrequencyofacontrolledoscillatoruntilitismatchedtothereferenceinbothfrequencyandphase.Aphase-
3、lockedloopisanexampleofacontrolsystemusingnegativefeedback.Phase-lockedloopsarewidelyusedinradio,telecommunications,computersandotherelectronicapplications.Theymaygeneratestablefrequencies,recoverasignalfromanoisycommunicationchannel,ordistributeclocktimingpulsesindigitallogicdesignssuchas
4、microprocessors.Sinceasingleintegratedcircuitcanprovideacompletephase-locked-loopbuildingblock,thetechniqueiswidelyusedinmodernelectronicdevices,withoutputfrequenciesfromafractionofahertzuptomanygigahertz.AnalogyTuningastringonaguitarcanbecomparedtotheoperationofaphase-lockedloop.Usingatun
5、ingforkorpitchpipetoprovideareferencefrequency,thetensionofthestringisadjustedupordownuntilthebeatfrequencyisinaudible.Thisindicatesthatthetuningforkandguitararevibratingatthesamefrequency.Ifweimaginetheguitarcouldbetunedperfectlytothereferencetuningforkfrequencysothatthestringmovedinexact
6、stepwiththearmofthetuningfork,andmaintainedthatrelationship,theguitarstringwouldbesaidtobeinphase-lockwiththefork.Aphase-lockedloopsmaintainsitsoutputsignalinafixedphaserelationshiptotheinputsignal.StructureandfunctionPhase-lockedloopmechanismsmaybeimplementedaseitheranalogordigitalcircuit
7、s.Bothimplementationsusethesamebasicstructure.BlockdiagramofaPLLBothanaloganddigitalPLLcircuitsincludethreebasicelements：avariableelectronicoscillator,andafeedbackpath(whichoftenincludesafrequencydivider).Digitalphase-lockedloop(DPLL)Adigitalphase-lockedloopop
