电子信息类专业英语318

Unit1Current,VoltageandResistanceTextKeywordsTechnicaltermsExpressionsNotestothetextText

Theprimarypurposeofanelectriccircuitistomoveortransferchargesalongspecifiedpaths.Thismotionofchargesconstitutesanelectriccurrent.CurrentflowisrepresentedbythelettersymboliorI,anditisthetimerateofchangeofcharge,givenbyi=dq/dt.Thebasicunitinwhichcurrentismeasuredistheampere(A).Anampereofcurrentisdefinedasthemovementofonecoulomb(6.28×1018electrons)pastanypointofaconductorduringonesecondoftime.Themilliampere(mA)andthemicroampere(mA)unitsarealsousedtoexpressamagnitudeofcurrentmuchsmallerthantheampere.Onemilliampereisequivalenttoone-thousandthofanampere,andonemicroampereisequivalenttoone-millionthofanampere.

Weshalldefinevoltage“across”anelementastheworkdoneinmovingaunitcharge(+1C)throughtheelementfromoneterminaltotheother.Thetermvoltage(representedbythelettersymbolU)iscommonlyusedtoindicatebothapotentialdifferenceandanelectromotiveforce.Theunitinwhichvoltageismeasuredisthevolt(V).Onevoltisdefinedasthatmagnitudeofelectromotiveforcerequiredcauseacurrentofoneamperetopassthroughaconductorhavingaresistanceofoneohm.Besidesthevolt,smallerorlargermagnitudeofvoltageareexpressedinmillivolts(mV),microvolts(μV)orkilovolts(kV).

Resistorsrestricttheflowofelectriccurrent,forexample,aresistorisplacedinserieswithalight-emittingdiode(LED)tolimitthecurrentpassingthroughtheLED.ThevalueofresistoriscalledresistanceandisrepresentedbythelettersymbolR.Resistanceismeasuredinohms;thesymbolforohmisanomegaΩ.Oneohmisdefinedasthatamountofresistancethatwilllimitthecurrentinaconductorisoneamperewhenthevoltageappliedtotheconductorisonevolt.1 Ωisquitesmallsoresistorvaluesareoftengiveninkiloohm(kΩ)ormegohm(MΩ).“Ohm’sLaw”isoneofthefundamentallawsofelectronics,andpertainstotherelationshipbetweencurrent,voltageandresistanceinanelectricalconductor.Thisrelationshipstatesthat“Current=Voltage/Resistance”.Ohm’sLawstatesthattheratioofthevoltagebetweentheendsofawireandthecurrentflowinginitisequaltotheresistanceofthewire.Theusualwayofexpressingthisinmathematicaltermsis“I=U/R”,and“U=IR”or“R=U/I”arealsoused.Keywords

current n.电流

voltage

n.电压

resistance n.电阻，阻抗

electric adj.电的，电动的

circuit n.电路

transfer vt.转移，移动

charge n.电荷

specify vt.指定

path

n.路线，轨道

motion

n.运动，动作

symbol n.符号；象征

ampere

n.安培

milliampere

n. [电]毫安(培)

microampere

n. [电]微安(培)

coulomb n. [电]库仑

conductor n. [电]导体

magnitude

n.数量，大小

element n.元素，元件

terminal

n.终端，接线端

ohm n. [电]欧姆

kiloohm n. [电]千欧(姆)

megohm n. [电]兆欧(姆)

millivolt n. [电]毫伏(特)(=1/1000伏(特),略作mV)

microvolt n. [电]微伏(等于1伏特的百万分之一)

kilovolt n.千伏(特)

resistor n. [电]电阻器

diode n.二极管

limit vt.限制，限定

fundamental adj.基础的，基本的

electronics n.电子学

pertain v.适合，属于

ratio n.比，比率

mathematical adj.数学的，精确的Technicalterms

electriccircuit 电子线路

electriccurrent 电流

potentialdifference 电位差

electromotiveforce 电动势

light-emittingdiode(LED) 发光二极管

Ohm’sLaw 欧姆定律Expressions

berepresentedby 用…表示

bedefinedas 被定义为

beequivalentto 等于

inserieswith 和…串联

pertainto 适合于Notestothetext

1．Theprimarypurposeofanelectriccircuitistomoveortransferchargesalongspecifiedpaths.

电路的主要功能是沿着特定路径移动或传送电荷。句中“to”引导的不定式作表语，这是一个表语从句。

2．Theunitinwhichvoltageismeasuredisthevolt(V).

度量电压的单位是伏特(V)。句中“inwhichvoltageismeasured”是定语从句，修饰“unit”。

3．Onevoltisdefinedasthatmagnitudeofelectromotiveforcerequiredcauseacurrentofoneamperetopassthroughaconductorhavingaresistanceofoneohm.

使1安培电流流过电阻为1欧姆的导体所需的电动势定义为1伏特。句中，过去分词“required”充当后置定语，修饰“electromotiveforce”；“havingaresistanceofoneohm”是现在分词短语，充当后置定语，修饰“conductor”。

4．Oneohmisdefinedasthatamountofresistancethatwilllimitthecurrentinaconductorisoneamperewhenthevoltageappliedtotheconductorisonevolt.

1欧姆的定义是：1伏特的电压施加在导体上产生了1安培的电流，此时该导体的电阻值为1欧姆。句中，“that”引导定语从句，修饰“amountofresistance”，其中“when”引导时间状语从句。Unit2SemiconductorDevicesTextKeywordsTechnicaltermsExpressionsNotestothetextText

Semiconductorsarethesubstanceswhoseabilitytoconductelectricityranksbetweenthatofaconductorandthatofanonconductor,orinsulator.Thebasicbuildingblockofmostsemiconductordevicesisthediode.

AsemiconductordiodeconsistsofaPNjunctionandhastwoterminals,ananode(+)andacathode(-).However,thediodehasanimportantproperty:itisunidirectional.Inadiode,currentflowsinonlyonedirectionacrossthejunctionfromp-ton-typematerial,andthenonlywhenthep-typematerialisatahighervoltagethanthen-typematerial.ThevoltageappliedtothediodetocreatethisconditioniscalledtheforwardbiasshowninFig.2-1,inthiscondition,currentflowsfromanodetocathodewithinthediode.Theoppositevoltage,forwhichcurrentwillnotflow,iscalledreversebias.Anidealdiodeislikealightswitchinyourhome.Whentheswitchisclosed,thecircuitiscompletedandthelightturnson.Whentheswitchisopen,thereisnocurrentandthelightisoff.Fig.2-2showsanidealdiodecharacteristic.IF

isforwardcurrent,UFisforwardvoltage,URisreversevoltage,IRisreversecurrent.Fig.2-1ForwardbiasFig.2-2Idealdiodecharacteristic

Transistorsarethemostwidelyusedsemiconductordeviceinelectronicstoday.Transistorsarethree-terminaldevicesandtherearetwobasictypesofstandardtransistors,NPNandPNP,withdifferentsymbolshowninFig.2-3.MosttransistorsusedtodayareNPNbecausethisistheeasiesttypetomakefromsilicon.IfyouarenewtoelectronicsitisbesttostartbylearninghowtouseNPNtransistors.Thelettersrefertothelayersofsemiconductormaterialusedtomakethetransistor.Theleadsarelabeledbase(B),collector(C),andemitter(E).Thesetermsrefertotheinternaloperationofatransistor.AtransistorhastwoPNjunctions:thebase-emitter(BE)junctionandthebase-collectorjunction.Bothofthemshouldbehavelikeadiodeandconductonewayonly.Currentfromapowersourceenterstheemitter,passesthroughtheverythinbaseregion,andleavesviathecollector.Currentflowisalwaysinthisdirection.Thiscurrentcanbemadetovaryinamplitudebyvaryingthecurrentflowinginthebasecircuit.Ittakesonlyasmallchangeofbasecurrenttocontrolarelativelylargecollectorcurrent.Itisthisabilitythatenablesthetransistortoamplify.Fig.2-3Transistorcircuitsymbols

Transistorsamplifycurrent,forexampletheycanbeusedtoamplifythesmalloutputcurrentfromalogicchipsothatitcanoperatealamp,relayorotherhighcurrentdevice.Atransistormayalsobeusedasaswitch.Theamountofcurrentamplificationiscalledthecurrentgain,symbolhFE.Somemultimetershavea“transistortest”functionwhichprovidesaknownbasecurrentandmeasuresthecollectorcurrentsoastodisplaythetransistor’sDCcurrentgainhFE.Keywords

semiconductor

n.[物]半导体

substance n.物质，实质，主旨

electricity n.电流，电，电学

insulator(=nonconductor)

n.绝缘体

device

n.装置,设备

anode n.[电]阳极，正极

cathode

n.阴极

unidirectional

adj.单向的，单向性的

property n.性质，特性

material n.材料，原料

bias n.偏置

opposite adj.相对的，相反的

switch n.开关，转换

characteristic n.特性，特征

transistor n.[电子]晶体管

silicon n.[化]硅，硅元素

layer n.层

base n.基极

collector n.集电极

emitter

n.发射极

power

n.[物]功率

relatively

adv.相关地

amplify

vt.放大，增强

output n.输出，输出量

logic n.逻辑，逻辑学，逻辑性

chip n.芯片

relay n.[电工]继电器

multimeter n.[物]万用表

gain n.[电]增益Technicalterms

semiconductordevice 半导体器件

PNjunction

PN结

p-/n-typematerial

p/n型材料

forwardbias 正向偏置

reversebias 反向偏置

idealdiode 理想二极管

three-terminaldevice 三端器件

base-emitter(BE)junction 发射结

base-collectorjunction 集电结

powersource 功率源；电源

thecurrentgain 电流增益

DCcurrent 直流电Expressions

applyto 将…应用于

turnon 打开

makefrom… 由…制成(看不出原材料)

referto 提到，指

sothat 以便于

beusedas 用作Notestothetext

1．Semiconductorsarethesubstanceswhoseabilitytoconductelectricityranksbetweenthatofaconductorandthatofanonconductor,orinsulator.

半导体是一种导电性能介于导体和绝缘体之间的物质。句中，“whose”引导的定语从句修饰“substances”；不定式“toconductelectricity”作后置定语修饰“ability”；两个“that”指代“ability”。

2．Thevoltageappliedtothediodetocreatethisconditioniscalledtheforwardbias.

加在二极管上的满足这一条件的电压称正向偏压。句中的“appliedtothediodetocreatethiscondition”为过去分词短语作定语，修饰前面的“voltage”。

3．Currentfromapowersourceenterstheemitter,passesthroughtheverythinbaseregion,andleavesviathecollector.

电流从电源流入发射极，穿过很薄的基区，再由集电极流出。句中“enters”、“passes”、“leaves”为并列成分作谓语。

4．Transistorsamplifycurrent,forexampletheycanbeusedtoamplifythesmalloutputcurrentfromalogicchipsothatitcanoperatealamp,relayorotherhighcurrentdevice.

晶体管能放大电流，例如它们可用于放大逻辑芯片很小的输出电流，以使它能操控一盏灯、继电器或其它高电流设备。句中“canbeusedto”为被动语态；“sothat”引导目的状语从句；“it”在该句中指代“current”。Unit3ElectronicAmplifiersTextKeywordsTechnicaltermsExpressionsNotestothetextText

Electronicamplifiersareusedmainlytoincreasethevoltage,current,orpowerofasignal.Alineramplifierprovidessignalamplificationwithlittleornodistortion,sothattheoutputisproportionaltotheinput.Anonlinearamplifiermayproduceaconsiderablechangeinthewaveformofthesignal.Linearamplifiersareusedforaudioandvideosignals,whereasnonlinearamplifiersfinduseinoscillators,powerelectronics,modulators,mixers,logiccircuits,andotherapplicationswhereanamplitudecutoffisdesired.Todayeitherdiscretetransistorcircuitsorintegratedcircuitsaremostlyused.

Nowadays,transistorsarethemostimportantdeviceinelectronicamplifiers.WhentheBEjunctionisforwardbiased,andtheBCjunctionisreversebiased,thebasecurrentiBcancontrolthecollectorcurrentiC,representedbytheformulaiC=βiB.Therearethreefundamentalconfigurationsintermsofconnectingtransistorsinacircuit(asshowninFig.3-1):common-emitter,common-collectorandcommon-base.Fig.3-1ThreeBasicConfigurationsofTransistorAmplifiers

Inthecommon-baseconnection,astheinputcurrentiEisapproximatelyequaltotheoutputcurrentiC,itiscalledthecurrentfollower.Inthisconfiguration,thecircuithaslowinputimpedanceandhighoutputimpedance.ThevoltagegainAu＞0,thatmeanstheoutputandtheinputisin-phase.TheCBconfigurationcircuitismainlyusedinhighfrequencyandwidebandcircuits.

Forthetransistorvoltageamplifier,oftenitisasmallalternatingvoltagethathastobeamplified.Abipolarjunctiontransistorinthecommon-emittermodecanactasavoltageamplifierifthetransistorhasaproperbiasandasuitableresistor,calledtheload,isconnectedinthecollectorcircuit.Thisconfigurationhasmoremoderateinputandoutputimpedancethanthecommon-basecircuit.Itprovidesbothcurrentgainandvoltagegain,moreoverAu＜0.

Thethirdtypeofconnectionisthecommon-collectorcircuit.Inthisconfiguration,theinputimpedanceofthetransistorisveryhighandtheoutputimpedanceislow,thevoltagegainisslightlylessthanone,representedbyAu≈1，andthepowergainisusuallylowerthanthatobtainedinacommon-baseoracommon-emittercircuit.

Ontheotherhand,electronicamplifierscontainaudioamplifiers,videoamplifiersandradiofrequencyamplifiersaccordingtothefrequencyofthesignaltobeoperated.

Audioamplifiers,suchasarefoundinradios,televisionsets,aregenerallyoperatedatfrequenciesbelow20kilohertz.Theyamplifytheelectricalsignal,whichthenisconvertedtosoundinaloudspeaker.

Videoamplifiersareusedmainlyforsignalswithafrequencyspectrumrangeupto6megahertz.Avideoamplifiermustoperateoverawidebandandamplifyallfrequenciesequallyandwithlowdistortion.

Radiofrequencyamplifiersareusedtodealwiththesignalsthattheirfrequenciesgenerallyrangefrom100kHzto1GHz,andcanextendwellintothemicrowavefrequencyrange.Keywords

electronic adj.电子的

increase vt.增加，加大

signal n.信号

amplification n.扩大

distortion n.失真

proportional adj.比例的，成比例的

considerable adj.相当大(或多)的，值得考虑的，相当可观的

waveform n.波形

audio adj.音频的，声频的

video n.电视，录像，视频

oscillator n.振荡器

modulator n.调节器

amplitude n.振幅

discrete adj.不连续的，离散的

integrated adj.综合的，完整的

configuration n.构造，结构，配置，外形

approximately adv.近似地，大约

impedance n. [电]阻抗

alternate adj.交替的，轮流的

bipolar adj.有两极的，双极的

load n.负载

moderate adj.中等的，适度的，适中的

kilohertz n.千赫

loudspeaker n.扩音器，喇叭

spectrum

n.频谱

microwave n.微波Technicalterms

electronicamplifier 电子放大器

aliner/nonlinearamplifier 线性/非线性放大器

logiccircuits 逻辑电路

integratedcircuit(IC) 集成电路

theBE/BCjunction 发射结/集电结

common-base/emitter/collector 共基/共射/共集

thecurrentfollower 电流跟随器

input/outputimpedance 输入/输出阻抗

voltagegain 电压增益

in-phase 同相

highfrequency 高频

abipolarjunctiontransistor(BJT) 双极型晶体管

televisionset 电视机

frequencyspectrum 频谱

lowdistortion 低失真Expressions

beproportionalto… 与…成比例

either…or… 或者…或者…

berepresentedby… 用…表示

intermsof 根据；按照

both…and… 既…又…

ontheotherhand 另一方面

accordingto 根据

beconvertedto 转换为

dealwith 处理Notestothetext

1．Alineramplifierprovidessignalamplificationwithlittleornodistortion,sothattheoutputisproportionaltotheinput.

线性放大器可以进行无失真的信号放大或失真很小，因此，其输出与输入是成正比的。句中，“sothat”引导结果状语从句；“beproportionalto”意为与…成正比。

2．Abipolarjunctiontransistorinthecommon-emittermodecanactasavoltageamplifierifthetransistorhasaproperbiasandasuitableresistor,calledtheload,isconnectedinthecollectorcircuit.

若晶体管加正确的偏置且在集电极回路中接合适的电阻作为负载，则共射极方式下的双极型结型晶体管可用作电压放大器。句中“if”引导条件状语从句；“calledtheload”为插入语，定义前面的“asuitableresistor”。

3．Radiofrequencyamplifiersareusedtodealwiththesignalsthattheirfrequenciesgenerallyrangefrom100kHzto1GHz,andcanextendwellintothemicrowavefrequencyrange.

射频放大器用于处理频率范围在100千赫到1吉赫的信号，并能较好地扩展至微波频率范围。句中，“areusedto…”为被动语态；“that”引导定语从句，修饰前面的“signals”；“and”前后为并列成分。Unit4IntegratedCircuitTextKeywordsTechnicaltermsExpressionsNotestothetextText

Firstly,let’sseethedevelopmentofIntegratedCircuit(IC).

Before1947,theheartoftheelectroniccircuitwasvacuumtubeinventedin1904byaBritishengineer,thoughthisdeviceunderwentconstantimprovement,inrealityforitscomplexdesign,thevacuumtubeisinherentlyunstable,power-hungry,andsubjecttoburnoutsandinternalshortcircuits.Italsotakesupalotofspace.TheseareamongtheshortcomingsofthevacuumtubethatledtothedevelopmentofthetransistorbyBellTelephoneLaboratoriesengineers.Thekeytothetransistor’srapiddevelopmentwastheuseofsiliconinsteadofwireasthebasicconductivematerial.Thiselement,whichcomprises28percentoftheearth’scrust,isnotonlystableoverawiderangeoftemperatures,butalsooffersdependablemanufacturingcontrol.

Itwasduringtheearly1950’sthattheneedforeversmallerelectroniccomponentsbecamereallyinsistent.Spacetechnologywasonefactor.Largecomputerscalledupontoperformhundredsmillionsofcalculationsasecond,andsoon.TheresultwasIC,combiningforthefirsttimethemultiplefunctionsoftransistors,capacitors,andresistorsinonecompleteunitallonasingle,tinybitofmaterial.ExpertsnowpredictthattheIChasbroughtinaneraofchangesofundamentalandwide-sweepingthatitalreadyhasthecharacteristicofasecondindustrialrevolution.Moreover,very-large-scaleintegrated(VLSI)circuitsthatcontainseveralhundredthousandcomponentsonasinglechiphavebeendeveloped.

Then,whatisIC?

Integratedcircuits,orICisacombinationofafewinterconnectedcircuitelementssuchastransistors,diodes,capacitors,andresistorsproducedinasinglemanufacturingprocessononeandthesamebearingstructure,calledthesubstrate,andintendedtoperformdefinitefunctioninvolvedinconvertinginformation.

TheelectricallyinterconnectedcomponentsthatmakeupanICarecalledintegratedelements.Ifanintegratedcircuitincludesonlyonetypeofcomponents,suchasonlydiodeorresistors,itissaidtobeanassemblyorsetofcomponents.

Theprincipleofintegratedcircuitelementsliesinthefollowing.Agreatnumberof“set”areproducedsimultaneouslyonawafer.Eachsetcontainsallthecomponentssuchastransistors,diodes,andresistorswhichareinterconnectedwithshortfinemetallicstripesdepositedonthewafersurface.Theymakeupafunctionalblock.EachICsofcomponentsisareadyintegratedcircuit.AllICsareregularlydistributedonthewafersurface.

ICscanbeclassifiedbyfunctionintotwo:circuitstobeappliedindigitalsystemsandthosetobeappliedinlinearsystems.ThedigitalICsareemployedmostlyincomputers,electroniccounters,frequencysynthesizersanddigitalinstruments.AndtheanalogorlinearICsoperateoveracontinuousrange,andincludesuchdevicesasoperationalamplifiers.

Thedevelopmentofintegratedcircuitshasrevolutionizedthefieldsofcommunications,informationhandling,andcomputing.Integratedcircuitsreducethesizeandtheweightofdevicesandlowermanufacturingandsystemcosts,whileatthesametimeprovidinghighspeed,excellentfunctionalperformance,lowpowerdissipationandincreasedreliability.ICsarewidelyusedintheelectronicindustry.Keywords

development

n.发展

vacuum

n.真空；adj.真空的

engineer

n.工程师，技师

undergo

vt.经历，遭受，忍受

reality n.真实，事实

inherently adv.天性地，固有地

burnout n.燃尽，烧光，歇火

shortcoming n.缺点，短处

conductive adj.传导的

comprise v.包含，由…组成

crust n.外壳

manufacture vt.制造，加工; n.制造，制造业，产品

component n.成分；元件

insistent adj.坚持不懈的

factor n.因素，要素

calculation n.计算

multiple adj.多样的，多重的

function n.功能，作用

capacitor n.(=capacitator)电容器

predict v.预知，预言

revolution n.革命

combination n.结合，联合

substrate n.(=substratum)底层，下层

assembly n.集合，装配

principle n.原则，原理

simultaneously adv.同时地

wafer n. [无]晶片

deposit vt.存放，堆积

digital adj.数字的；n.数字

employ vt.雇用，用，使用

synthesizer n. [电子]合成器

instrument n.工具，手段，器具

analog n.模拟

performance n.履行，性能

dissipation n.消散，浪费Technicalterms

vacuumtube 真空管

shortcircuit 短路

electroniccomponent 电子元器件

very-large-scaleintegrated(VLSI)circuit超大规模集成电路

electroniccounters 电子计数器

frequencysynthesizer 频率合成器

digitalinstrument 数字仪器

operationalamplifier 运算放大器

lowpowerdissipation 低功耗Expressions

subjectto 遭受

takeup 占有

leadto 导致

callupon 号召

suchas 比如

makeup 形成

liein... 位于…，在于…

beclassifiedbyfunctioninto按功能分类为Notestothetext

1.Thiselement,whichcomprises28percentoftheearth’scrust,isnotonlystableoverawiderangeoftemperatures,butalsooffersdependablemanufacturingcontrol.

这种覆盖地壳表面28%的硅元素，不但温度稳定性高，而且制造技术完善。句中，“whichcomprises28percentoftheearth’scrust”为非限制性定语从句，修饰“element”；“notonly…butalso…”意为不但…而且…，前后为并列成分。

2.Itwasduringtheearly1950’sthattheneedforeversmallerelectroniccomponentsbecamereallyinsistent.

20世纪50年代初，人们对电子元器件微型化的要求更加强烈。此句“Itwas…that…”是强调句型，强调“duringtheearly1950’s”。

3.ExpertsnowpredictthattheIChasbroughtinaneraofchangesofundamentalandwide-sweepingthatitalreadyhasthecharacteristicofasecondindustrialrevolution.

专家预言集成电路带来的如此根本而广泛的划时代的变化，使它具备第二次工业革命的特征。句中，“that”引导宾语从句；“so…that…”意为如此…以至于…，引导结果状语从句。

4.Integratedcircuits,orICsisacombinationofafewinterconnectedcircuitelementssuchastransistors,diodes,capacitors,andresistorsproducedinasinglemanufacturingprocessononeandthesamebearingstructure,calledthesubstrate,andintendedtoperformdefinitefunctioninvolvedinconvertinginformation.

集成电路缩写为IC，是一些互相连接的电路元件的组合，如晶体管、二极管、电容器和电阻等电路元件的组合。它们是在同一个基底结构上，同时是在一个单独制造过程中生产出来的，这个基底结构叫做衬底。集成电路可用在信息转换中执行一定的功能。句中“producedinasinglemanufacturingprocessononeandthesamebearingstructure,calledthesubstrate,andintendedtoperformdefinitefunctioninvolvedinconvertinginformation”为过去分词短语作定语，修饰前面的“circuitelements”，其中“produced”与“intendedto”为并列部分，而“calledthesubstrate”为过去分词短语作定语，修饰前面的“thesamebearingstructure”，同时“involvedinconvertinginformation”也为过去分词短语作定语修饰前面的“function”。

5.Eachsetcontainsallthecomponentssuchastransistors,diodes,andresistorswhichareinterconnectedwithshortfinemetallicstripesdepositedonthewafersurface.

每个组包含诸如晶体管、二极管和电阻之类的全部元件，各元件用沉积在晶片表面上的短细金属条互相连接起来，组成一个功能模块。句中“whichare…thewafersurface”为定语从句，修饰前面的“transistors,diodes,andresistors”，而定语从句中的“depositedonthewafersurface”为过去分词短语作定语，修饰前面的“metallicstripes”。Unit5DigitalLogicCircuitTextKeywordsTechnicaltermsExpressionsNotestothetextText

Thephrase“digitalelectronics”isusedtodescribethosecircuitsystemswhichprimarilyoperatewiththeuseofonlytwodifferentvoltagelevelsortwootherbinarystates.Thetwodifferentstatesbywhichdigitalcircuitsoperatemaybeofseveralforms.Theycan,inthesimplestform,consistoftheopeningandclosingofaswitch.Inthiscase,theclosed-switchstatecanberepresentedby1andtheopen-switchstateby0.

Averycommonmethodofdigitaloperationisachievedbyusingvoltagepulses.Thepresenceofapositivepulsecanberepresentedby1andtheabsenceofapulseby0.Withasquare-wavesignal,thepositivepulsescanrepresent1andthenegativepulsescanrepresent0.

Asmentionedabove,“digitallogic”isarationalprocessformakingsimple“true”or“false”decisionsbasedontherulesofBooleanalgebra.“True”canberepresentedbya1and“false”bya0,andinlogiccircuitsthenumeralsappearassignalsoftwodifferentvoltages.Logiccircuitsareusedtomakespecifictrue-falsesignalsattheinputs.Thesignalsmaybegeneratedbymechanicalswitchesorbysolid-statetransducers.Oncetheinputsignalhasbeenacceptedandconditioned(toremoveunwantedelectricalsignals,or“noise”),itisprocessedbythedigitallogiccircuits.Thevariousfamiliesofdigitallogicdevices,usuallyintegratedcircuits,performavarietyoflogicfunctionsthroughlogicgates,including“OR”,“AND”,and“NOT”,andcombinationsofthese(suchas“NOR”,whichincludesbothORandNOT).Onewidelyusedlogicfamilyisthetransistor-transistorlogic(TTL).Anotherfamilyisthecomplementarymetaloxidesemiconductorlogic(CMOS),whichperformssimilarfunctionsatverylowpowerlevelsbutatslightlyloweroperatingspeeds.

Integratedcircuitscontainingmanytransistorsaremostcommonlyusedasswitchingdevicesindigitalelectronicslogicgates.ThethreebasictypesofdigitallogicgatesaretheANDgate,theORgate,andtheNOTgate.TheoperationofanANDgateismathematicallyexpressedbytheequationA·B=C.Thiscanbereadas“inputAandinputBequalsoutputC”.AnANDgatehastwoormoreinputsandasingleoutput.TheoutputofanANDgateistrueonlyifalltheinputsaretrue.TheoperationofanORgateisoftenexpressedbytheequationA+B=C.Thiscanbereadas“eitherinputAorinputB(orboth)equalsoutputC”.AnORgatealsohastwoormoreinputsandasingleoutput.TheoutputofanORgateistrueifanyoneoftheinputsistrueandisfalseifalloftheinputsarefalse.AnINVERTERhasasingleinputandasingleoutputterminalandcanchangeatruesignaltoafalsesignal,thusperformingtheNOTfunction.Morecomplicatedlogiccircuitsarebuiltupfromelementarygates.Anylogicfunctioncanbeperformedbythethreebasicgatesthathavebeendescribed.Eveninalargescaledigitalsystem,suchasacomputer,control,ordigital-communicationsystem,thereareonlyafewbasicoperations,whichmustbeperformed.Thethreebasictypesofdigitallogicgatesandtheflip-floparethefourcircuitsmostcommonlyemployedinsuchsystems.Keywords

system n.系统，体系

primarily adv.首先，起初，主要地

level n.水平，标准

binary adj.二进制的

method n.方法

pulse n.脉搏，脉冲

positive adj.肯定的，积极的；[数]正的；[电]阳的

negative adj.否定的，消极的；负的；阴性的

algebra n.代数学

transducer n.传感器，变频器，变换器

complementary adj.补充的，补足的

metal n.金属

oxide n. [化]氧化物

inversion n.倒置，反相

opposite adj.相反的

elementary adj.初步的，基本的

communication n.传达，信息，通信Technicalterms

digitalelectronics 数字电