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Analoginen signaali



Johdanto

Analoginen signaali viittaa jatkuvasti muuttuvien fyysisten määrien, kuten lämpötilan, kosteuden, paineen, pituuden, virran, jännitteen jne., ilmaisemaan tietoon.Soimme tavallisesti analogista signaalia jatkuvana signaalina, sillä voi olla eriarvoinen aika-arvo. erillinen ja epäjatkuva signaaliarvo.

Variousphysicalquantitiesinactualproductionandlife,suchasimagestakenbycameras,pressure,flowrate,speed,humidity,etc.recordedintheworkshopcontrolroom,areallanalogsignals.Thedigitalsignalisformedbysampling,quantizingandcodingonthebasisoftheanalogsignal.Specifically,samplingistoobtainthesamplevalueofeachmomentoftheinputanalogsignalatanappropriatetimeinterval.Quantizationistousethebinarycodesystemtorepresentthevalueofeachmomentmeasuredbysampling,andtheencodingistogeneratethequantizationBinarynumbersarearrangedtogethertoformasequentialpulsetrain.

Intheprocessofanalogsignaltransmission,theinformationsignalisfirstconvertedintoalmost"identical"fluctuatingelectricalsignals(hencethename"analog"),andthentransmittedthroughwiredorwirelessmeans,andtheelectricalsignalsarereceivedAfterthat,itisrestoredtoaninformationsignalthroughthereceivingdevice.

Fornearlyahundredyears,whetheritisawiredtelephoneoraradioandtelevisionthatissentwirelessly,analogsignalshavebeenusedtotransmitsignalsforalongtime.Itcanbesaidthattheanalogsignalisalmost"exactlythesame"astheoriginalsignal,anditseemsthatitshouldachieveagoodtransmissioneffect.However,thefactisonthecontrary.Inthepast,weoftenencounteredunintelligiblephenomenawhencalling;radiostationsalwayshavetheeffect.Largershortcomings;snowflakesflickeronTVimagesfromtimetotime.Thisisbecausethesignalhastoundergoalotofprocessingandtransmissionduringthetransmissionprocess,andthesedeviceswillinevitablyproducesomeinterference;inaddition,ifitiswiredtransmission,electricalequipmentnearthelinewillalsoproduceelectromagneticinterference;ifitiswirelesstransmission,itisevenmore""Open",allkindsofinterferenceintheairaresimplyirresistible.Theseinterferencescaneasilycausesignaldistortionandsomenoise.Thesedistortionsandadditionalnoisewillalsoaccumulateasthetransmissiondistanceincreases,whichwillseriouslyaffectthecommunicationquality.Inthisregard,peoplethoughtofmanyways.Oneistotakevariousmeasurestoresistinterference,suchasimprovingthequalityofinformationprocessingequipmentandminimizingitsinterference;anotherexampleistoshieldthetransmissionline;anotherexampleistouseafrequencymodulationcarrierinsteadofanamplitudemodulationcarrier.However,noneofthesemethodscanfundamentallysolvetheproblemofinterference.Anotherwayistotrytoremovethenoiseinthesignalandrecoverthedistortedsignal.However,foranalogsignals,sincetheoriginalundistortedsignalcannotbemoreaccuratelyinferredfromthedistortedsignal,thismethodisveryuseful.Itisdifficulttobeeffective,andsomeevengetworse.

Analogsignalsaremainlycontinuoussignalsrelativetodiscretedigitalsignals.Analogsignalsaredistributedinallcornersofthenaturalworld,suchastemperaturechanges,whiledigitalsignalsareartificiallyabstractedintermsofamplitudevalues.Discontinuoussignal.Electricalanalogsignalsmainlyrefertoelectricalsignalswithcontinuousamplitudeandphase.Thissignalcanbeusedbyanalogcircuitstoperformvariousoperations,suchasamplification,addition,andmultiplication.

Analogisten signaalien digitalisointi

Fanalogisten signaalien muuntaminen digitaalisiksi signaaleiksi edellyttää neljää perusvaihetta: signaalin näytteenotto, signaalinpidätys, signaalin kvantisointi ja signaalin koodaus.

Samplingistodiscretethecontinuoussignalintime,thatis,collecttheinstantaneousvaluepointbypointontheoriginalanalogsignalaccordingtoaspecifictimeinterval.Fromtheeffectpointofview,thehigherthesamplingfrequency,theclosertheobtaineddiscretesignalistotheoriginalanalogsignal,butthehigherthesamplingfrequency,thehighertherequirementsfortheactualcircuit,whichwillalsobringalotofcalculationandstorage.Ifthesamplingfrequencyistoolow,itwillcauselossofinformation.Aftertakingitsinstantaneousvalue,itshouldbekeptintheoriginalpositionforaperiodoftime,andthesawtoothwavesignalformedinthiswayisprovidedforsubsequentsignalquantization.

Toquantizethecollecteddiscretesignalistoconvertasignalofaspecificamplitudeintoanintegermultipleofthesmallestunitoftheanalog-to-digitalconverter.Thissmallestunitisalsocalledthequantizationunitoftheanalog-to-digitalconverter.Eachsampledvaluerepresentstheinstantaneousamplitudeoftheanalogsignalobtainedbyonesample.Usuallythequantizationunitisamultipleof2.Themorequantizationbits,thesmallerthequantizationerror,andthebettertheresultofquantization.Intheactualquantizationprocess,approximateprocessingisrequired,sotheremustbeaquantizationerror.Thiserrorwillbereproducedinthefinaldigital-to-analogconversion.Thiserrorisusuallycalledquantizationnoise.Thisquantizationerrorcanusuallybereducedbyincreasingthenumberofquantizationbits,butwhenthesignalamplitudeisreducedtoacertainvalue,thecorrelationbetweenthequantizationnoiseandtheoriginalanalogsignalbecomesmoreobvious.

Encodingthequantizeddiscretesignalisthefinalstepofconvertinganalogsignalsintodigitalsignals.Itiscommonlyimplementedbyparallelcomparisonandsuccessiveapproximationcircuits.Withthehelpofcertaincircuits,thequantizedThediscretesignalisconvertedtothecorrespondingdigitalsignal.

Signaladvantages

Themainadvantageofanalogsignalsistheirpreciseresolution.Underidealconditions,ithasinfiniteresolution.Comparedwithdigitalsignals,analogsignalshavehigherinformationdensity.Sincethereisnoquantizationerror,itcandescribethetruevalueofthephysicalquantityinnatureascloseaspossible.

Anotheradvantageofanalogsignalsisthatwhenthesameeffectisachieved,analogsignalprocessingissimplerthandigitalsignalprocessing.Theprocessingofanalogsignalscanbeimplementeddirectlythroughanalogcircuitcomponents(suchasoperationalamplifiers,etc.),whiledigitalsignalprocessingofteninvolvescomplexalgorithmsandevenrequiresspecializeddigitalsignalprocessors.

SignalDisadvantages

Themaindisadvantageofanalogsignalsisthattheyarealwaysaffectedbynoise(undesiredrandomchangesinthesignal).Afterthesignalisduplicatedmanytimes,orafterlong-distancetransmission,theinfluenceoftheserandomnoisesmaybecomeverysignificant.Inelectricity,theuseofgroundedshields,goodlinecontact,andtheuseofcoaxialcablesortwistedpairscanalleviatethesenegativeeffectstoacertainextent.

Noiseeffectscancausesignalloss.Itisalmostimpossibletorestorethedamagedanalogsignalagain,becausetheamplificationofthedesiredsignalwillamplifythenoisesignalatthesametime.Ifthereisalargegapbetweenthenoisefrequencyandthefrequencyofthedesiredsignal,anelectronicfiltercanbeintroducedtofilteroutthenoiseofaspecificfrequency,butthissolutioncanonlyreducetheimpactofnoiseasmuchaspossible.Therefore,undertheinfluenceofnoise,althoughtheanalogsignaltheoreticallyhasinfiniteresolution,itisnotnecessarilymoreaccuratethanthedigitalsignal.

Althoughthedigitalsignalprocessingalgorithmisrelativelycomplex,theexistingdigitalsignalprocessorcanquicklycompletethistask.Inaddition,thegradualpopularizationofcomputersandothersystemshasmadethespreadandprocessingofdigitalsignalsmoreconvenient.Devicessuchascamerashavegraduallyrealizeddigitalization,althoughtheymustinitiallyreceiveinformationofrealphysicalquantitiesintheformofanalogsignals,andfinallytheywillbeconvertedintodigitalsignalsbyanalog-to-digitalconverterstofacilitatecomputerprocessingortransmissionviatheInternet.

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