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1、Chapter2ElectronicsSection1IntroductionTextNewWordsandExpressionsExercisesEndVocabularyCharacteristicIIISection1IntroductionTosaythatweliveinanageofelectronicsisanunderstatement.Fromtheomnipresentintegratedcircuittotheequallyomnipresentdigitalcomputer,weencounterelectronicdevicesa
2、ndsystemsonadailybasis.Ineveryaspectofourincreasinglytechnologicalsociety—whetheritisscience,engineering,medicine,music,maintenance,orevenespionage—theroleofelectronicsislarge,anditisgrowing.Ingeneral,allofthetaskswithwhichweshallbeconcernedcanbeclassifiedas"signal-processing"Sect
3、ion1Introductiontasks.Letusexplorethemeaningofthisterm.SignalAsignalisanyphysicalvariablewhosemagnitudeorvariationwithtimecontainsinformation.Thisinformationmightinvolvespeechandmusic,asinradiobroadcasting,aphysicalquantitysuchasthetemperatureoftheairinaroom,ornumericaldata,suchas
4、therecordofstockmarkettransactions.Thephysicalvariablesthatcancarryinformationinanelectricalsystemarevoltageandcurrent.Whenwespeakof"signals",therefore,Section1Introductionwereferimplicitlytovoltagesorcurrents.However,mostoftheconceptswediscusscanbeapplieddirectlytosystemswithdiff
5、erentinformation-carryingvariables.Thus,thebehaviorofamechanicalsystem(inwhichforceandvelocityarethevariables)orahydraulicsystem(inwhichpressureandflowratearethevariables)canoftenbemodeledorrepresentedbyanequivalentelectricalsystem.Anunderstandingofthebehaviorofelectricalsystems,t
6、herefore,providesabasisforunderstandingamuchbroaderrangeofphenomena.Section1IntroductionAnalogandDigitalsignalsAsignalcancarryinformationintwodifferentforms.Inananalogsignalthecontinuousvariationofthevoltageorcurrentwithtimecarriestheinformation.Anexample,inFig.2-l,isthevoltagepro
7、ducedbyathermocouplepairwhenthetwojunctionsareatdifferenttemperatures.Asthetemperaturedifferencebetweenthetwojunctionsvaries,themagnitudeofthevoltageacrossthethermocouplepairalsovaries.Thevoltagethusprovidesananalogrepresentationofthetemperaturedifference.Section1IntroductionTheot
8、herkindofsignalisadigitalsignal.A
