電氣專業(yè)英語教案1

I

Part1

NewWords

diode二極管

electron電子

semiconductor［物］半導(dǎo)體

positive［電］陽的

negative負(fù)的，陰性的

neutralize壓制

junction連接，匯合處

terminal接線端

combine（使）聯(lián)合，（使）結(jié)合

polarity極性

microampere［電］微安培

rectifier整流器

boundary邊界，分界線

anode［電］陽極,正極

emitter發(fā)射器

leakagecurrent漏電流

bipolartransistor雙極晶體管

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不連續(xù)的，離散的

quartz石英

binary二進(jìn)位的

bit［計(jì)］位，比特

relay［電工］繼電器

vacuum真空的

resistor［電］電阻器

capacitor電容器

package包裹，包

dimension尺寸，尺度

dissipation消散，分散

instrumentation使用儀器

synthesis綜合，合成

proportional成比例的

transmit傳輸，轉(zhuǎn)送

immune免疫的

interference沖突，干涉

ample充足的，豐富的

modification更改，修改，修正

pulse脈搏，脈沖

inadequate不充分的，不適當(dāng)?shù)?/p>

digitalcommunication數(shù)字通信系統(tǒng)

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