电气专业英语教案1

I

Part1

NewWords

diode二极管

electron电子

semiconductor［物］半导体

positive［电］阳的

negative负的，阴性的

neutralize压制

junction连接，汇合处

terminal接线端

combine（使）联合，（使）结合

polarity极性

microampere［电］微安培

rectifier整流器

boundary边界，分界线

anode［电］阳极,正极

emitter发射器

leakagecurrent漏电流

bipolartransistor双极晶体管

Part2

Reading

PNJunction(Diode)

Whenafreeelectronmeetsamovingholeinasemiconductormaterial,theelectron

occupiesthefreespaceandapositiveornegativechargenolongerexists;thatis,

thechargeisneutralized.WhenaP-typeandaN-typecrystalarejoinedtomakea

singlesemiconductor,asshowninFig.1-1,currentwillflowinonedirectiononly.As

anexample,whenapowersourceisconnectedtothesemiconductorasshownin

Fig.1-2,thesemiconductorissaidtobeforwardbiased.

symbol

+=holes

-=electrons

Fig.1-1Thebasiccrystaljunction

+=holes

—=electrons

Theholeswillberepelledtowardthejunctionbythepositivelychargedbattery

terminal,whereastheelectronsarepushedtowardthejunctionbythebattery's

negativeterminal.

Atthejunction,theelectronscombinewiththehole.Electronsenterthe

semiconductorattheNterminaltoreplacetheelectronsthathavecombinedwith

theholes.Likewise,electronsleavethePterminalbyattractionofpositivevoltage

andcreatenewholes.Thismovementofelectrons,fromthenegativevoltagesource

throughthejunctionandfromthepositiveterminalofsemiconductortopositive

voltagesource,createsacurrentflow.Thuscurrentwillflowinasemiconductor

whenthesemiconductorisforwardbiased

Whenthepolarityofthepowersourceisreversed,thesemiconductorissaidtobe

reversebiased.Theholesaremovedawayfromthejunctionbythenegativevoltage,

whereastheelectronsaredrawnthejunctionbythepositivevoltage.Thusthereis

littleornocombiningofelectronsandholesatthejunction,andnocurrentwillflow.

Inpracticalterms,therewillalwaysbeafewelectronsandholesnearthejunction,

allowingaverysmallcurrenttopass.Thissmallcurrentisknownasleakagecurrent

andisusuallyintheorderofafewmicroamperes(orpossiblypicoamperes).

WhenP-typeandN-typeregionsareformedinsamecrystal,thesemiconductoris

knownasadiodeorrectifier.Theboundarybetweenthetworegionsistermeda

junction.TheP-regionterminaliscalledtheanode,whereastheN-regionterminalis

calledthecathode.

Usually,whensuchsemiconductorsareusedwithsignals,thesemiconductorsare

calleddiodesorsignaldiodes.Whenthedeviceisusedforconversionofalternating

current(AC)todirectcurrent(DC),thesemiconductoriscalledarectifier.

2.BasicTwo-junctionorBipolarTransistor

Likeadiode,atransistorcanbeusedtoprevent(orlimit)theflowofcurrentin

onedirection,Theprimeuseforatransistor,however,istocontroltheamountof

currentinacircuit,Thisisdonebyaddingasecondjunctiontothebasicdiode

junction,discussedintheabovesection.Forthisreason,suchtransistorsarecalled

two-junctiontransistorsor,possibly,bipolartransistors.Theauthorprefersthe

formertermbutrecognizesthatthelattertermisalsoincommonuse.

Therearetwopossiblearrangementsforthetwo-junctionintransistors:NPN,

whereapositivesemiconductormaterial(holes)isplacedbetweentwonegative

semiconductormaterials(electrons),andPNP,wherethenegativematerial

(electrons)isplacedbetweentwopositivematerials(holes).

Witheitherjunctionarrangement,thebasictwo-junctiontransistorwillhavethree

elements.Theseelements,showninFig.1-3asanNPNarrangementaretheemitter,

whichemitselectrons;thecollector,whichcollectselectrons;andabase,which

controlstheflowofelectronsbycontrollingthechargeconcentrationatthetwo-

junctiononeithersideofthebase.

junctionjunction

emitterbasecollectoremitterbasecollector

Fig.1-4showshowtwo-junctiontransistoroperatesinitsbasiccircuit.Asshown,the

emitter-basejunctionwillpasscurrenteasilybecausethejunctionisforwardbiased.

Thecollector-basejunctionwillnotpasscurrent(exceptforasmallleakagecurrent)

sincethejunctionisreversebiased(Thetermbackisoftenusedinplaceofreverse

bias).

emitterbasecollectorbc

NPN

—I——I1

forwardbiasreversebiasforwardbiasreversebias

Fig.1-3NPNandPNPtwo-junctiontransistorarrangements

Fig.1-4showshowtwo-junctiontransistoroperatesinitsbasiccircuit.Asshown,the

emitter-basejunctionwillpasscurrenteasilybecausethejunctionisforwardbiased.

Thecollector-basejunctionwillnotpasscurrent(exceptforasmallleakagecurrent)

sincethejunctionisreversebiased(Thetermbackisoftenusedinplaceofreverse

bias).

emitterbasecollector

NPN

—l——i1

forwardbiasreversebias

Fig.1-4Basictwo-junctiontransistorbiascircuit

ItshouldbenotedthatthepolaritiesofbiasvoltageforanNPNtransistordifferfrom

thoseofaPNPtransistor;however,thenetresultsarethesame.Forexample,as

showninFig.1-4,theemitterisnegativewithrespecttothebase(NPN)toproducea

forwardbias.InFig.1-4,theemitterispositivewithrespecttobase(PNP)toproduce

thesameforwardbias.Similarly,thecollectorhasareversebiasforbothNPNand

PNP,eventhoughthepolaritiesarerevered.Also,itshouldbenotedthatfornormal

operationanNPNhasitsbasebiasedpositivelywithrespecttoitsemitter.

Conversely,aPNPbaseisnegativewithrespecttoitsemitter.

n

Part1

Discrete不连续的，离散的

quartz石英

binary二进位的

bit［计］位，比特

relay［电工］继电器

vacuum真空的

resistor［电］电阻器

capacitor电容器

package包裹，包

dimension尺寸，尺度

dissipation消散，分散

instrumentation使用仪器

synthesis综合，合成

proportional成比例的

transmit传输，转送

immune免疫的

interference冲突，干涉

ample充足的，丰富的

modification更改，修改，修正

pulse脉搏，脉冲

inadequate不充分的，不适当的

digitalcommunication数字通信系统

Part2

Reading

Anelectronicsystemisanorderlycollectionofinteractingelectronicbuildingblocks

thatperformsadesiredtask.Adigitalelectronicsystemperformsthetasksby

dealingwithdiscretequantities.Discretequantitiesareintegral,fractional,ormixed

numbersthatrepresent,tothenearestleastsignificantdigit,somequantitiesinthe

realworldsuchastemperature,pressure,ordistance.Incontrastthereareanalog

electronicsystemsthatrepresentthesequantitiesonacontinuousscale.

•Manymeasurementsmayberepresentedineitherdigitaloranalogform.For

example,timehasbeenrepresentedoverthecenturiesinananalogformtheangle

subtendedbythesmallandlargehandsoftheclockprovidedalltheinformation

abouttimethatwasdesired.Forbetterresolutionintime,asecondhandwasadded.

Inthelastseveralyearsatotallynewmethodwasdevelopedtomeasureanddisplay

time.Themethodisbasedontheoscillationfrequencyofaquartzcrystalthatin

conjunctionwithdigitalcircuitryanddigitaldisplaytechnologypresentsthetime

informationindigitalformasanumber.

•Manymeasurementsmayberepresentedineitherdigitaloranalogform.For

example,timehasbeenrepresentedoverthecenturiesinananalogformtheangle

subtendedbythesmallandlargehandsoftheclockprovidedalltheinformation

abouttimethatwasdesired.Forbetterresolutionintime,asecondhandwasadded.

Inthelastseveralyearsatotallynewmethodwasdevelopedtomeasureanddisplay

time.Themethodisbasedontheoscillationfrequencyofaquartzcrystalthatin

conjunctionwithdigitalcircuitryanddigitaldisplaytechnologypresentsthetime

informationindigitalformasanumber.

•Digitalprocessingofinformationhasindeedbecomewidespreadinthisdecade;

inadditiontodigitalwatches,clocks,andcalculators,therearenumerousdigital

controllers(microcomputers)usedinhomeappliancesandautomobiles.

•Indigitalelectronicsystems,informationisrepresentedbybinarydigits,bits.Abit

mayassumeeitheroneoftwovalues:0or1.Amathematicalsystemthatusesonly

twodigitsiscalledabinarysystem.ItsfoundationswerelaidbytheBritish

MathematicianGeorgeBoole(1815~1864)inhisclassictreatiseAnInvestigationof

theLawsofThought(1854).

•Theinventionofthetransistormaybeviewedasanothermajorbreakthroughin

digitalinformationprocessing.Thevolumeoccupiedbyatransistorisaboutone

hundredthofthatoccupiedbyeitherarelayoravacuumtube,andasimilarratio

holdsforthepowerdissipatedbythedevicesundercomparison.Thetransistoralso

providethetechnologicalbaseforthedevelopmentofintegratedcircuits,an

ensembleofmanytransistorthatareinterconnectedtoperformaspecifiedfunction.

•Thefirstintegratedcircuitwasdevelopedin1958,whichisastartofa

revolutionarychangeintheartofelectronicsdesign.Intheinitialstagesof

semiconductortechnologydevelopment,thedeviceswereclassifiedaseitherdiscrete

orintegrated.Adigitalintegratedcircuitconsistedofseveraltransistorsand

sometimesalsoofpassivecomponents(resistorsandcapacitors)onasemiconductor

substratethatwereinterconnectedtoperformalogicalfunction.Suchlogical

functionimplementingsimplelogicoperationsprovidedthebuildingblocksforthe

realizationofswitchingnetworks.Furtheradvancesintechnologyenabledfabrication

ofmanytransistorsononesemiconductorsubstrate.Thelevelofcomplexity

increased,broadeningthescopeofcircuitscontainedinonepackage.Thesenew

circuitscouldcount,performaddition,subtraction,ormultiplicationoftwobinary

digits,comparetheirbinaryvalues,andrealizemorecomplexlogicaloperations.

•Scientistsandengineersengagedinthedevelopmentofthetransistortechnology

metthechallengeofthenextlevelofcomplexity.Theindividualcomponentsona

semiconductorsubstratewerefurtherdecreasedindimensionsandsimilarlytheir

powerdissipationwasreduced.Deviceswithsome100,000transistorsonone

substratebecameareality,andpracticallimitationswerenowsetprimarilybythe

inputandoutputterminalstothe''outsideworldz,ratherthanbythecomplexityand

numberoftransistorsonasubstrate.

•Digitalcircuitsarebeingusedinsuchdiversefieldsasinformationstorage,medical

instrumentation,processcontrol,calculatorsandcomputers,airtraffic,digital

communications,andinvoiceandtonesynthesis.

Digitaltechniquesarealsobeginningtobeusedinareasthattraditionallyapplied

analogtechniques.Forexample,assumewedesiretosendtemperatureinformation

frompointAtopointBinanindustrialplant.Alsoassumethattheinformationisin

formofa