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1、外文资料Phase-lockedloopTechnology：Aphase-lockedlooporphaselockloop(PLL)isacontrolsystemthatgeneratesasignalthathasafixedrelationtothephaseofa"reference"signal.Aphase-lockedloopcircuitrespondstoboththefrequencyandthephaseoftheinputsignals,automaticallyraisingorloweringthefrequencyofacontrolledoscillato
2、runtilitismatchedtothereferenceinbothfrequencyandphase.Aphase-lockedloopisanexampleofacontrolsystemusingnegativefeedback.IntheorderofthePLListhewayofmadethefrequencystabilityinthesendupwireless,includeVCOandPLLintegratedcircuits,VCOsendupasignal,someofthesignalisoutput,andtheotherthroughthefrequenc
3、ydivisionwithPLLintegratedcircuitsgeneratethelocalsignalmakingcompared.Intheordertoremainthesame,it’smustberemainthephasedisplacementsame.Ifthephasedisplacementhavesomechanges,theoutputofthePLLintegratedcircuitshavesomechangestoo,tocontrolleVCOuntilphasedifferencetorestore,makebothcotrolledoscillat
4、or’sfrequencyandphasewithinputsignalwhichisclose-loopelectroniccircuitkeepfirmrelationship.Phase-lockedloopsarewidelyusedinradio,telecommunications,computersandotherelectronicapplications.Theymaygeneratestablefrequencies,recoverasignalfromanoisycommunicationchannel,ordistributeclocktimingpulsesindi
5、gitallogicdesignssuchasmicroprocessors.Sinceasingleintegratedcircuitcanprovideacompletephase-locked-loopbuildingblock,thetechniqueiswidelyusedinmodernelectronicdevices,withoutputfrequenciesfromafractionofacycleperseconduptomanygigahertz.Earliestresearchtowardswhatbecameknownasthephase-lockedloopgoe
6、sbackto1932,whenBritishresearchersdevelopedanalternativetoEdwinArmstrong'ssuperheterodynereceiver,theHomodyne.Inthehomodyneorsynchrodynesystem,alocaloscillatorwastunedtothedesiredinputfrequencyandmultipliedwiththeinputsignal.Theresultingoutputsignalincludedtheoriginalaudiomodulationinformation.Thei
7、ntentwastodevelopanalternativereceivercircuitthatrequiredfewertunedcircuitsthanthesuperheterodynereceiver.Sincethelocaloscillatorwouldrapidlydriftinfrequency,anautomaticcorrectionsignalwasappliedtotheoscill
