《电子信息专业英语》-Chapter 1 Fundamentals of Electronics

Althoughresistors，capacitorsandinductorsformimportantelementsinelectroniccircuitry，itisessentialtoknowsomethingaboutresistance，capacitanceandinductance.ResistanceAresistorisatwo-terminalelement.Betweenitsterminalsitexhibitsavoltagedropwhichisdirectlyproportionaltothecurrentpassingthroughit.Wespecifythesizeoftheresistorinohms(Ω)，whichistheratioofvoltagetocurrent.Thisrelationshipbetweenvoltageandcurrent，calledOhm'sLaw，canbestatedinanequationV=IR.Resistorsmaybeclassifiedasfixedorvariableintheirtypeandalsoaslinearandnonlinear.下一页返回Text1Rsistance,CapacitanceandInductanceResistanceistheoppositiontotheflowofcurrentandisrepresentedbythelettersymbolR.Theunitofresistanceistheohm，expressedbyusing(Ω).Oneohmisdefinedasthatamountofresistancethatwilllimitthecurrentinaconductortooneamperewhenthevoltageappliedtotheconductorisonevolt.Largeramountofresistancearecommonlyexpressedinkilo-ohm(kΩ)andinmega-ohm(MΩ).CapacitanceElectricalenergycanbestoredinanelectricfield.Thedevicetobecapableofdoingthisiscalledacapacitororacondenser.下一页返回上一页Text1Rsistance,CapacitanceandInductanceAsimplecondenserconsistsoftwometallicplatesseparatedbyadielectric.Ifacondenserisconnectedtoabattery，theelectronswillflowoutofthenegativeterminalofthebatteryandaccumulateonthecondenserplateconnectedtothatside.Atthesametime，theelectronswillleavetheplateconnectedtothepositiveterminalandflowintothebatterytomakethepotentialdifferencejustthesameasthatofthebattery[asshowninFig.1-1(a)].Thusthecondenserissaidtobecharged.下一页返回上一页Text1Rsistance,CapacitanceandInductanceThecapacitanceisdirectlyproportionaltothedielectricconstantofthematerialandtotheareaoftheplatesandinverselytothedistanceoftheplates.Itismeasuredinfarads(F).Whenachangeofonevoltpersecondacrossitcausesthecurrentofoneamperetoflow，thecondenserissaidtohavethecapacitanceofonefarad.However，faradistoolargeaunittobeusedinradiocalculation，somicrofarad(onemillionthofafarad)andthepicofaradaregenerallyused.Theamountofthestoredenergyofachargedcondenserisproportionaltotheappliedvoltageanditscapacitance.Thecapacitanceofacondenserisdeterminedbythreeimportantfactors，namely，theareaoftheplatesurface，thespacebetweenthemanddielectricmaterial.下一页返回上一页Text1Rsistance,CapacitanceandInductanceOneofthecondenserstobeusedinradioreceiverisavariablecondenser,whosecapacitancecanbevariedbyturningtheplates.Itisusedinthereceiverfortuningandvaryingcapacitanceinthecircuitsoastopickupthedesiredsignalsofdifferentwavelengths.InductanceItiswellknownthatinductorsareoneofthemainbuildingblocksinelectroniccircuits.AninductorissimplyacoilofwirewithorwithoutamagneticcoredasshowninFig.1-1(b)].Allcoilshaveinductance.Inductanceisthepropertyofopposinganychangeofcurrentflowingthroughacoil.Ifacoiloffersalargeoppositiontothecurrentflowingthroughitatacertainfrequency，itissaidtohavelargerinductance.下一页返回上一页Text1Rsistance,CapacitanceandInductanceWhenane.m.fisappliedtoacoil，thereisaninducede.m.finit.Thepolarityoftheinducede.m.fisalwayssuchastoopposeanychangeinthecurrentinthecircuit.Thismeansthatthepropertyofinductanceopposeanincreaseincurrentjustasmuchasitopposesadecreasemcurrent.Acoilofmanyturnswillhavemoreinductancethanoneoffewturns.Alsoifacoilisplacedonanironcore，itsinductancewillbegreaterthanitwaswithoutthemagneticcore.Theunitofinductanceishenry.Acoilhasaninductanceofonehenryifaninducede.m.fofonevoltisinducedinthecoilwhenthecurrentthroughitchangesattherateofoneamperepersecond.Valuesofinductanceusedinradioequipmentvaryoverawiderange.下一页返回上一页Text1Rsistance,CapacitanceandInductanceNOTES1.Betweenitsterminalsitexhibitsavoltagedropwhichisdirectlyproportionaltothecurrent

passingthroughit.在它的两端间所呈现的电压降和通过它的电流成正比。该句为复合句，关系代词which引导定语从句，passingthroughit是现在分词短语作定语，修饰thecurrent，意为:流过它的电流。2.Atthesametime,theelectronswillleavetheplateconnectedtothepositiveterminalandflow

intothebatterytomakethepotentialdifferencejustthesameasthatofthebattery.同时，电子从与电池正极相连的金属平板流进电池，由此产生电位差，其值等于电池的电压值。下一页返回上一页NOTESatthesametime同时，相当于meanwhile不定式短语tomake...thatofthebattery是结果状语，其中that指thedifference。3.Thecapacitanceisdirectlyproportionaltothedielectricconstantofthematerialandtothearea

oftheplatesandinverselytothedistanceoftheplates.电容器的电容量与介质的介电常数及平板的面积成正比，与平板间的距离成反比。bedirectlyproportionalto与……成正比beinverselyproportionalto与……成反比下一页返回上一页NOTES4.Whenane.m.fisappliedtoacoil，thereisaninducede.m.finit.当电动势加在线圈上时，线圈中就会产生感应电动势。5.Valuesofinductanceusedinradioequipmentvaryoverawiderange.用于无线电设备的电感值在很大范围内变化。usedinradioequipment是过去分词短语，作后置定语，修饰valuesofinductance下一页返回上一页ReadingResistorAresistorisatwo-terminalelectroniccomponentdesignedtoopposeanelectriccurrentby

producingavoltagedropbetweenitsterminalsinproportiontothecurrent,thatis,inaccordance

withOhm'sLaw:V=IR.TheresistanceRisequaltothevoltagedropVacrosstheresistor

dividedbythecurrentlthroughtheresistor.Resistorsareusedaspartofelectricalnetworksandelectroniccircuits.Fig.1-2

shows

resistorsymbols.下一页返回上一页ReadingUnitsTheohm(symbol:Ω)istheSIunitofelectricalresistance,namedafterGeorgOhm.The

mostcommonlyusedmultiplesandsubmultiplesinelectricalandelectronicusagearethe

milliohm,ohm,kilohm,andmegohm.Oncircuitdiagramsthevaluemaybewrittenin“SINotation"withthemultiplierreplacing

thedecimalpoint,so"2k5”means2.5kiloohms.PowerDissipationThepowerdissipatedbyaresistoristhevoltageacrosstheresistormultipliedbythecurrentthroughtheresistor:下一页返回上一页ReadingAllthreeequationsareequivalent.ThefirstisderivedfromJoule'sLaw，andtheothertwoarederivedfromthatbyOhm'sLaw.Thetotalamountofheatenergyreleasedistheintegralofthepowerovertime:Iftheaveragepowerdissipatedismorethantheresistorcansafelydissipate,theresistormaydepartfromitsnominalresistance，andmaybedamagedbyoverheating.Excessivepowerdissipationmayraisethetemperatureoftheresistortoapointwhereitburnsout，whichcouldcauseafireinadjacentcomponentsandmaterials.下一页返回上一页ReadingSeriesandParallelResistorsResistorsinaparallelconfigurationeachhavethesamepotentialdifference(voltage)(Fig.1-3).Tofindtheirtotalequivalentresistance(Req):Theparallelpropertycanberepresentedinequations

by

twoverticallines“||”(asin

geometry)

tosimplifyequations.Fortworesistors,下一页返回上一页ReadingThecurrentthroughresistorsinseriesstaysthesame(Fig.1-4)，butthevoltageacrosseachresistorcanbedifferent.Thesumofthepotentialdifferences(voltage)isequaltothetotalvoltage.Tofindtheirtotalresistance:Aresistornetworkthatisacombinationofparallelandseriescansometimesbebrokenup

intosmallerpartsthat

are

eitheroneortheother(Fig.1-5).Forinstance,下一页返回上一页ReadingFour-BandResistors(Fig.1-6)Four-bandidentificationisthemostcommonlyusedcolor-codingschemeonallresistors.It

consistsoffourcoloredbandsthatarepaintedaroundthebodyoftheresistor.Thefirsttwobands

encodethefirsttwosignificantdigitsoftheresistancevalue,thethirdisapower-of-tenmultiplier

ornumber-of-zeroes,andthefourthisthetoleranceaccuracy,oracceptableerror,ofthevalue.Sometimesafifthbandidentifiesthethermalcoefficient,butthismustbedistinguishedfromthe

true5-colorsystem,with3significantdigits.下一页返回上一页ReadingForexample,green-blue-yellow-redis56x104Ω±2%=560kΩ±2%.Aneasier

descriptioncanbeasfollows:Thefirstband,green,hasavalueof5andthesecondband,blue,hasavalueof6,andiscountedas56.Thethirdband,yellow,hasavalueof104,whichadds

four0'stotheend,creating560000Ωat±

2%toleranceaccuracy.560000Ωchangesto

560kΩ

±2%(asakilois103).Eachcolorcorrespondstoacertaindigit,progressingfromdarkertolightercolors,asshown

inthechartbelow.下一页返回上一页Reading下一页返回上一页ReadingSMTResistorsSurfacemountedresistorsareprintedwithnumericalvaluesinacoderelatedtothatusedonaxialresistors.StandardtoleranceSurfaceMountTechnology(SMT)resistorsaremarkedwithathree-digitcode，inwhichthefirsttwodigitsarethefirsttwosignificantdigitsofthevalueandthethirddigitisthepoweroften(thenumberofzeroes).Forexample:下一页返回上一页ReadingResistanceslessthan100ohmsarewritten:100,220,470.Thefinalzerorepresentstentothepowerzero，whichis1.Forexample:Sometimesthesevaluesaremarkedas“10"or“22"to

preventamistake.Resistancesless

than10ohmshave“R"toindicatethe

positionofthedecimalpoint(radix

point).Forexample:下一页返回上一页ReadingPrecisionresistorsaremarkedwithafour-digitcode,inwhichthefirstthreedigitsarethesignificantfiguresandthefourthisthepoweroften.Forexample:下一页返回上一页ReadingCapacitorAcapacitorisapassiveelectricalcomponentthatcanstoreenergyintheelectricfieldbetweenapairofconductors(called“plates").Acapacitor'sabilitytostorechargeismeasuredbyitscapacitance,inunitsoffarads.Fig.1-7showsvariouscapacitorexamplesandcircuitsymbol.Capacitorsareoftenusedinelectricandelectroniccircuitsasenergystoragedevices.Theycanalsobeusedtodifferentiatebetweenhigh-frequencyandlow-frequencysignals.Thispropertymakesthemusefulinelectronicfilters.下一页返回上一页ReadingCapacitanceAcapacitor'sabilitytostorechargeismeasuredbyitscapacitanceC,theratiooftheamountofchargestoredoneachplatetothevoltage:q=CvForanidealparallelplatecapacitorwithaplateareaAandaplatedseparation:

InSIunits,acapacitorhasacapacitanceofonefaradwhenonecoulombofchargestoredon

eachplatecausesavoltagedifferenceofonevoltbetweenitsplates.Sincethefaradisaverylarge

unit,capacitanceisusuallyexpressedinmicrofarads(uF),nanofarads(uF),orpicofarads

(pF).下一页返回上一页ReadingElectricCircuitsWhenacapacitorisconnectedtoacurrentsource，chargeistransferredbetweenitsplatesataratei(t)=dq(t)/dt.Conversely，ifacapacitorisconnectedtoavoltagesource，theresultingdisplacementcurrentisgivenby:Forexample,ifoneweretoconnecta1000uFcapacitortoavoltagesource,thenincreasethesourcedvoltageatarateof2.5voltspersecond,thecurrentflowingthroughthecapacitorwouldbe:下一页返回上一页ReadingSeriesorParallelArrangementsCapacitorsinaparallelconfigurationeachhavethesamepotentialdifference(voltage)(Fig.1-8).Theirtotalcapacitance(Ceq)isgivenby:Ceq=C1+C2+…+CnThereasonforputtingcapacitorsinparallelistoincreasethetotalamountofchargestored.Inotherwords，increasingthecapacitancealsoincreasestheamountofenergythatcanbestored.Thecurrentthroughcapacitorsinseriesstaysthesame(Fig.1-9)，butthevoltageacrosseachcapacitorcanbedifferent.Thesumofthepotentialdifferences(voltage)isequaltothetotalvoltage.下一页返回上一页ReadingTheirtotalcapacitanceisgivenby:Inparallel，theeffectiveareaofthecombinedcapacitorhasincreased，increasingtheoverallcapacitance.However，inseries，thedistancebetweentheplateshaseffectivelybeenincreased，reducingtheoverallcapacitance.Capacitors

areusedinseriesforhigherworkingvoltage,forexample,forsmoothinginahighvoltagepowersupply.Three“600voltmaximum"capacitorsin

seriescanheusedat1800volts.下一页返回上一页ReadingApplicationsEnergystorageAcapacitorcanstoreelectricenergywhendisconnectedfromitschargingcircuit，soitcanbeusedlikeatemporarybattery.Capacitorsarecommonlyusedinelectronicdevicestomaintainpowersupplywhilebatteriesarebeingchanged.Incaraudiosystems，largecapacitorsrangingfrom0.5toover100faradsareusedtostoreenergyfortheamplifiertouseondemand.FilteringBecausecapacitorspassACbutblockDCsignals，theyareoftenusedtoseparatetheACandDCcomponentsofasignal.下一页返回上一页ReadingSignalprocessingTheenergystoredinacapacitorcanbeusedtorepresentinformation，eitherinbinaryform，asinDRAMS，orinanalogueform，asinanaloguesampledfiltersandCCDs.Capacitorscanbeusedinanaloguecircuitsascomponentsofintegratorsormorecomplexfiltersandinnegativefeedbackloopstabilization.Signalprocessingcircuitsalsousecapacitorstointegrateacurrentsignal.TunedcircuitsCapacitorsandinductorsareappliedtogetherintunedcircuitstoselectinformationinparticularfrequencybands.Forexample，radioreceiversrelyonvariablecapacitorstotunethestationfrequency.Speakersusepassiveanaloguecrossovers，andanalogueequalizersusecapacitorstoselectdifferentaudiobands.下一页返回上一页ReadingTheresonantfrequencyfofatunedcircuitisafunctionoftheinductance(L)andcapacitance(C)inseries，andisgivenby:whereLisinhenriesandCisinfarads.SensingMostcapacitorsaredesignedtomaintainafixedphysicalstructure.However,variousfactorscanchangethestructureofthecapacitor;theresultingchangeincapacitancecanbe

usedtosensethosefactors.返回上一页Text2DiodeandItsCircuitBothP-typeandN-typesiliconwillconductelectricityjustlikeanyconductor;however,ifapieceofsiliconisdopedP-typeinonesectionandN-typeinanadjacentsection，currentwillflowinonlyonedirectionacrossthejunctionbetweenthetworegions.Thisdeviceiscalledadiodeandisoneofthemostbasicsemiconductordevices.AdiodeiscalledforwardbiasedifithasapositivevoltageacrossitfromtheP-typetoN-typematerial.Inthiscondition，thediodeactsratherlikeagoodconductor，andcurrentcanflow，asshowninFig.1-10.Therewillbeasmallvoltageacrossthediode，about0.6voltsforSi，andthisvoltagewillbelargelyindependentofthecurrent，verydifferentfromaresistor.下一页返回Text2DiodeandItsCircuitIfthepolarityoftheappliedvoltageisreversed，thenthediodewillbereverselybiasedandwillappearnonconducting(asshowninFig.1-11).Almostnocurrentwillflowandtherewillbealargevoltageacrossthedevice.ConnectingandSolderingDiodesmustbeconnectedthecorrectwayround，thediagrammaybelabelled“a"or“+”foranodeand“k"or“-”forcathode(Yes，itreallyis“k"，not“c"，forcathode!).Thecathodeismarkedbyalinepaintedonthebody.Diodesarelabelledwiththeircodeinsmallprint，youmayneedamagnifyingglasstoreadthisonsmallsignaldiodes，asshowninFig.1-12.下一页返回上一页Text2DiodeandItsCircuitSmallsignaldiodescanbedamagedbyheatwhensoldered，buttheriskissmallunlessyouareusingagermaniumdiode(codesbeginningOA...)，inwhichcaseyoushoulduseaheatsinkclippedtotheleadbetweenthejointandthediodebody.Astandardcrocodileclipcanbeusedasaheatsink.Rectifierdiodesarequiterobustandnospecialprecautionsareneededforsolderingthem.TestingDiodesYoucanuseamultimeterorasimpletester(battery，resistorandLED)tocheckthatadiodeconductsinonedirectionbutnottheother.Alampmaybeusedtotestarectifierdiode，butNOTasignaldiodebecausethelargecurrentpassingbythelampwilldestroythediode!下一页返回上一页NOTES1.IfapieceofsiliconisdopedP-typeinonesectionandN-typeinanadjacentsection，currentwillflowinonlyonedirectionacrossthejunctionbetweenthetworegions.Thisdeviceiscalledadiodeandisoneofthemostbasicsemiconductordevices.如果一块硅片在一个区域掺杂为P型，在临近区域掺杂为N型，则电流仅朝一个方向流过这两个区域之间的结合处。这种装置被称为二极管，是最基本的半导体器件之一。2.AdiodeiscalledforwardbiasedifithasapositivevoltageacrossitfromtheP-typetoN-typematerial.下一页返回上一页NOTES如果一个正的电压从一个二极管的P型材料经过N型材料，我们称二极管正偏。3.Smallsignaldiodescanbedamagedbyheatwhensoldered，buttheriskissmallunlessyouareusingagermaniumdiode(codesbeginningOA...)，inwhichcaseyoushoulduseaheatsinkclippedtotheleadbetweenthejointandthediodebody.焊接时的热度会导致小信号二极管的损坏，但是这种危险是很小的，除非你用的是锗二极管(编号以OA开头)。用锗二极管时需要在焊接点和二极管之间放置一个散热片。下一页返回上一页ReadingDiodeInelectronics,adiodeisatwo-terminaldevice.Fig.1-13shows

varioussemiconductordiodes.Diodeshavetwoactiveelectrodesbetweenwhichsignalsofinterestmayflow,andmostareusedfortheirundirectionalelectriccurrentproperty.Thevaricapdiodeisusedasanelectricallyadjustablecapacitor.Thedirectionalityofcurrentflowmostdiodesexhibitissometimesgenericallycalledtherectifyingproperty.Themostcommonfunctionofadiodeistoallowanelectriccurrenttopassinonedirection(calledtheforwardbiasedcondition)andtoblockthecurrentintheoppositedirection(thereversebiasedcondition).下一页返回上一页ReadingRealdiodesdonotdisplaysuchaperfecton-offdirectionalitybuthaveamorecomplexnon-linearelectricalcharacteristic,whichdependsontheparticulartypeofdiodetechnology.Diodes

alsohavemanyotherfunctionsinwhichtheyarenotdesignedtooperateinthison-offmanner.MostmoderndiodesarebasedonsemiconductorP-Njunctions.InaP-Ndiode,conventionalcurrentcanflowfromtheP-typeside(theanode)totheN-typeside(thecathode),butcannotflowintheoppositedirection.Anothertypeofsemiconductordiode,theSchottkydiode,isformedfromthecontactbetweenametalandasemiconductorratherthanbyaP-Njunction.下一页返回上一页ReadingAdiode'sl一Vcharacteristiccanbeapproximatedbyfourregionsofoperation(Fig.1-14).TypesofSemiconductorDiodeThereareseveraltypesofjunctiondiodes(Fig.1-15).Fig.1-16showssomediodesymbols.ApplicationsRadiodemodulationThefirstuseforthediodewasthedemodulationofamplitudemodulated(AM)radiobroadcasts.Thehistoryofthisdiscoveryistreatedindepthintheradioarticle.下一页返回上一页ReadingInsummary,anAMsignalconsistsofalternatingpositiveandnegativepeaksofvoltage,whoseamplitudeor“envelope"isproportionaltotheoriginalaudiosignal.Thediode(originally

acrystaldiode)rectifiestheAMradiofrequencysignal,leavinganaudiosignalwhichistheoriginalaudiosignal.Theaudioisextractedusingasimplefilterandfedintoanaudioamplifierortransducer,whichgeneratessoundwaves.PowerconversionRectifiersareconstructedfromdiodes,wheretheyareusedtoconvertalternatingcurrent(AC)electricityintodirectcurrent(DC).Automotivealternatorsareacommonexample,wherethediode,whichrectifiestheACintoDC,providesbetterperformancethanthecommutatorofearlierdynamo.下一页返回上一页ReadingSimilarly,diodesarealsousedinCockcroft-WaltonvoltagemultiplierstoconvertACintohigherDCvoltages.Over-voltageprotectionDiodesarefrequentlyusedtoconductdamaginghighvoltagesawayfromsensitiveelectronicdevices.Theyareusuallyreverse-biased(non-conducting)undernormalcircumstances.Whenthevoltagerisesabovethenormalrange,thediodesbecomeforward-biased(conducting).Forexample,diodesareusedinmotorcontrollerandrelaycircuitstode-energizecoilsrapidlywithoutthedamagingvoltagespikesthatwouldotherwiseoccur.下一页返回上一页ReadingMany

integratedcircuitsalsoincorporatediodesontheconnectionpinstopreventexternalvoltagesfromdamagingtheirsensitivetransistors.Specializeddiodesareusedtoprotectfromover-voltagesathigherpower.LogicgatesDiodescanbecombinedwithothercomponentstoconstructANDandORlogicgates.Thisisreferredtoasdiodelogic.TemperaturemeasuringAdiodecanbeusedasatemperaturemeasuringdevice,sincetheforwardvoltagedropacrossthediodedependsontemperature.返回上一页Text3TransistorandItsCircuitTransistorsarethemostimportantdeviceinelectronicstoday.Notonlyaretheymadeasdiscrete(separate)componentsbutintegratedcircuits(ICs)maycontainseveralthousandonatinysliceofsilicon.Atransistorconsistsofthreelayersofsemiconductormaterial:athinlayerofonetypewiththeothertwotypesoneachside.Therearetwopossiblearrangements:N-typeinthemiddlewithP-typeoneachside(PNP)andP-typeinthemiddlewithN-typeoneachside(NPN).Thecenteriscalledbase，oneoutsidelayeriscalledtheemitter,andtheotherisknownasthecollector(asshowninFig.1-17).下一页返回Text3TransistorandItsCircuitAtransistorisanelectronicallydevicethatregulatesthecurrentflowingthroughit.Currentfromapowersourceenterstheemitter,passesthroughtheverythinbaseregion,andleavesviathecollector.Currentflowisalwaysinthisdirection.Thiscurrentcanbemadetovaryinamplitudebyvaryingthecurrentflowinginthebasecircuit.Ittakesonlyasmallchangeofbase

currenttocontrolarelativelylargecollectorcurrent.Itisthisabilitythatenablesthetransistortoamplify.下一页返回上一页Text3TransistorandItsCircuitTherearethreebasicwaysofconnectingtransistorsinacircuit:common-base,common-emitter,andcommon-collector(asshowninFig.1-18).Inthecommon-baseconnection,the

signalisintroducedintotheemitter-basecircuitandextractedfromthecollector-basecircuit.Inthecommon-emitterconnection,thesignalisintroducedintothebase-emittercircuitandextracted

fromthecollector-emittercircuit.Thethirdtypeofconnectionisthecommon-collectorcircuit.Inthisconfiguration,thesignalisintroducedintothebase-collectorcircuitandextractedfromtheemitter-collectorcircuit.下一页返回上一页Text3TransistorandItsCircuitAtransistormaybeusedasaswitch(eitherfullyonwithmaximumcurrent，orfullyoffwithnocurrent)andasanamplifier(alwayspartlyon).Transistorshavethreeleadswhichmustbeconnectedthecorrectwayround.Pleasetakecarewiththisbecauseawronglyconnectedtransistormaybedamagedinstantlywhenyouswitchon.Transistorscanbedamagedbyheatwhensolderedorbymisuseinacircuit.Ifyoususpectthatatransistormaybedamagedthereisoneeasywaytotestit:下一页返回上一页Text3TransistorandItsCircuitUseamultimeterorasimpletester(battery，resistorandLED)tocheckeachpairofleadsforconduction.Setadigitalmultimetertodiodetestandananaloguemultimetertoalowresistancerange.Testeachpairofleadsbothways(sixtestsintotal):Thebase-emitter(BE)junctionshouldbehavelikeadiodeandconductonewayonly.Thebase-collector(BC)junctionshouldbehavelikea

diodeandconductonewayonly.Thecollector-emitter(CF)shouldnotconducteither

way.Fig.1-19showshowthejunctionsbehaveinaNPN

transistor.ThediodesarereversedinaPNPtransistorbutthe

same

testprocedurecanbeused.下一页返回上一页NOTES1.Therearetwopossiblearrangements:N-typeinthemiddlewithP-typeoneachside(PNP)andP-typeinthemiddlewithN-typeoneachside(NPN).可以有两种排列方式:N型在中间，P型在两边(PNP);P型在中间，N型在两边(NPN)。N-type...oneachside(PNP)和P-type...oneachside(NPN)是arrangements的同位语。下一页返回上一页NOTES2.Ittakesonlyasmallchangeofbasecurrenttocontrolarelativelylargecollectorcurrent.基极电流只需很小的变化，就会引起集电极电流很大的变化。重要句型Ittakes...todosth.:指花费多少时间(金钱等)来做某事。3.Itisthisabilitythatenablesthetransistortoamplify.正是这种能力使晶体管能起放大作用。此句是强调句型，强调thisability。下一页返回上一页ReadingTransistorInelectronics，atransistorisasemiconductordevicecommonlyusedtoamplifyorswitchelectronicsignals.Atransistorismadeofasolidpieceofasemiconductormaterial，withatleastthreeterminalsforconnectiontoanexternalcircuit.Avoltageorcurrentappliedtoonepairofthetransistor‘sterminalschangesthecurrentflowingthroughanotherpairofterminals.Becausethecontrolled(output)powercanbemuchlargerthanthecontrolling(input)power,thetransistorprovidesamplificationofasignal.Thetransistoristhefundamentalbuildingblockofmodernelectronicdevices，andisusedinradio，telephone，computerandotherelectronicsystems.下一页返回上一页ReadingSometransistorsarepackagedindividuallybutmostarefoundinintegratedcircuits.Fig.1-20showstransistorexamplesandcircuitsymbols.ImportanceThetransistorisconsideredbymanytobethegreatestinventionofthetwentiethcentury.Itisthekeyactivecomponentinpracticallyallmodernelectronics.Itsimportanceintoday'ssociety

restsonitsabilitytobemassproducedusingahighlyautomatedprocess(fabrication)thatachievesastonishinglylowper-transistorcosts.Althoughseveralcompanieseachproduceoverabillionindividually-packaged(knownasdiscrete)transistorseveryyear,下一页返回上一页Readingthevastmajorityoftransistorsproducedareinintegratedcircuits

(oftenshortenedtoIC,microchipsorsimplychips)alongwithdiodes,resistors,capacitorsandotherelectroniccomponentstoproducecompleteelectroniccircuits.Alogicgateconsistsofabout

twentytransistorswhereasanadvancedmicroprocessor,asof2006,canuseasmanyas1.7billiontransistors(MOSFETs).“About60milliontransistorswerebuiltthisyear(2002),for[each]man,woman,andchildonEarth.”Thetransistor'slowcost,flexibilityandreliabilityhavemadeitaubiquitousdevice.Transistorizedmechatroniccircuitshavereplacedelectromechanicaldevicesincontrollingappliancesandmachinery.下一页返回上一页ReadingItisofteneasierandcheapertouseastandardmicrocontrollerandwriteacomputer

progra