2023學(xué)年完整公開課版Analogueanddigitalsignals

Chapter20

AnalogueanddigitalsignalsAnanaloguequantity:itcanhaveanyvalueAndigitalquantity:itonlyhaveafewvalues,usuallyjusttwoWeseeanalogueimages,hearandmakeanaloguesounds,anddriveanaloguecars.So,whyisthereafussaboutdigital?The

voltagesignalgeneratedbyamicrophoneisananaloguesignal.Adigitalsignalconsistsofaseriesofzeroesandones.1:thepresenceofavoltagepulse0:theabsenceofapulseAdvantagesofdigitalsignalsDealwith“noise”CompatiblewithmoderntechnologyandcanbestoredandprocessedmoreeasilyMorereliableandeasiertodesignandbuildBuildinsafeguardsDigitalsignalsdopickupnoiseandareattenuatedjustlikeanaloguesignals.Thedifferenceisthatthedigitalversioncanbecanberegeneratedandthenoiseeliminated.AttenuationAmplifythesignalNoiseAregeneratorshouldbeconsideredasdistinctfromarepeateramplifier,whichamplifiesthenoiseaswellasthesignal.RegenerateAdvantagesofdigitalsignalsDealwith“noise”CompatiblewithmoderntechnologyandcanbestoredandprocessedmoreeasilyMorereliableandeasiertodesignandbuildBuildinsafeguardsSAQ12EOC2SAQ12EOC2Paper43,Nov2013,Q11(a)Paper42,Nov2012,Q11(a)Paper43,Nov2010,Q12(a)AssignmentThankyou!ReviewActivity20.1Homeworkquestions1–3SAQ10–12EOC2,9Analogvs.DigitalTransmissionAnalogtransmissionisamethodofconveyingvoice,data,image,signal,orvideoinformation.Itusesacontinuoussignalvaryinginamplitude,phase,oranotherpropertythatisinproportiontoaspecificcharacteristicofavariable.Analogtransmissioncouldmeanthatthetransmissionisatransferofananalogsourcesignalwhichusesananalogmodulationmethod(oravarianceofoneormorepropertiesofhighfrequencyperiodicwaveform,alsoknownasacarriersignal).FMandAMareexamplesofsuchamodulation.Thetransmissioncouldalsousenomodulationatall.Itismostnotablyaninformationsignalthatisconstantlyvarying.Datatransmission(alsoknownasdigitaltransmissionordigitalcommunications)isaliteraltransferofdataoverapointtopoint(orpointtomultipoint)transmissionmedium–suchascopperwires,opticalfibres,wirelesscommunicationsmedia,orstoragemedia.Thedatathatistobetransferredisoftenrepresentedasanelectro-magneticsignal(suchasamicrowave).Digitaltransmissiontransfersmessagesdiscretely.Thesemessagesarerepresentedbyasequenceofpulsesviaalinecode.However,thesemessagescanalsoberepresentedbyalimitedsetofwaveformsthatalwaysvary.Eitherway,theyarerepresentedusingadigitalmodulationmethod.Analogtransmissioniscapableofbeingconveyedinanofewerthanfourways:throughatwistedpairorcoaxcable,throughafibreopticcable,throughtheair,orthroughwater.Thereare,however,onlytwobasictypesofanalogtransmission.Thefirstisknownasamplitudemodulation(orAM).Thisisatechniqueusedinelectroniccommunicationandworksbyalternatingthestrengthofatransmittedsignalinrelationtotheinformationthatisbeingsent.Thesecondisknownasfrequencymodulation(orFM).Thistypeofcommunicationconveysinformationoveracarrierwave,justasAMtransmission.However,FMcommunicationalternatesthefrequencyofthetransmittedsignal.Datathatistransmittedviadigitaltransmissionmaybedigitalmessagesthathaveoriginsforadatasource(acomputerorakeyboard,forexample).However,thistransmitteddatamayalsobefromananalogsignal(aphonecalloravideosignal,forexample).Itmaythenbedigitizedintoabitstreamusingpulsecodemodulation(orPCM)–orevenmoreadvancedsourcecodingschemes.Thecodingofthedataiscarriedoutusingcodecequipment.Summary:

1.Analogtransmissionconveysvoice,data,image,signal,orvideoinformationusinganinformationsignalthatiscontinuouslyvarying;digitaltransmissiontransfersdataoveratransmissionmediumdiscretely.

2.Analogtransmissioncanbeconveyedinfourways:atwistedpairorcoaxcable,afibreopticcable,theair,orwater;digitaltransmissionmaybetransmittedviaanelectro-magneticsign