Introduction
Analogsignalreferstotheinformationexpressedbycontinuouslychangingphysicalquantities,suchastemperature,humidity,pressure,length,current,voltage,etc.WeusuallycallanalogsignalAsacontinuoussignal,itcanhaveaninfinitenumberofdifferentvalueswithinacertaintimerange.Thedigitalsignalreferstoadiscreteanddiscontinuoussignalinvalue.
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.
Thedigitizationofanalogsignals
Theconversionofanalogsignalstodigitalsignalsrequiresfourbasicsteps:signalsampling,signalholding,signalquantizationandsignalcoding.
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.