《电子信息专业英语》高职配套教学课件

English

forElectronics&Information专业英语特点:specialityvocabulariessentences

目标:专业文献资料的阅读能力(forexample:articles,specifications,datasheet,userguide)公共英语KFCBMWVVTWCDMAWWWLANUnitOneBasicKnowledgeofElectronicsNewWordsandExpressionsresistance

[ri'zistəns]

电阻resistor[ri'zistə] 电阻器capacitor[kə'pæsitə] 电容器capacitance[kə'pæsitəns] 电容inductor[in'dʌktə] 电感器inductance[in'dʌktəns] 电感unit 单位ubiquitous[ju:'bikwitəs]普遍存在的resistivity[ri:zis'tivəti,riz-]

电阻系数alloy['ælɔi,ə'lɔi]

合金prefix[pri:'fiks,'pri:fiks]前缀voltage['vəultidʒ] 电压constant['kɔnstənt]

常数，常量criticalresistance 临界电阻powerrating 额定功率enamelledcopperwire 漆包线ferritecores['ferait] 铁氧体磁芯filtercircuits 滤波电路ferriterod 铁磁棒AC 交流DC 直流charge[tʃɑ:dʒ] 电荷mold[məuld]

模子，模型coil[kɔil] 线圈frequency['frikwənsi] 频率Ohm'slaw欧姆定律electroniccircuits 电子电路timing

circuits 定时电路PassageA

Resistors,capacitorsandinductorsAresistorisatwo-terminalelectroniccomponentthatproducesavoltageacrossitsterminalsthatisproportionaltotheelectriccurrentthroughitinaccordancewithOhm'slaw:V=IR.Resistorsareelementsofelectricalnetworksandelectroniccircuitsandareubiquitousinmostelectronicequipment.Practicalresistorscanbemadeofvariouscompoundsandfilms,aswellasresistancewire(wiremadeofahigh-resistivityalloy,suchasnickel/chrome).Theprimarycharacteristicsofaresistoraretheresistance,thetolerance,maximumworkingvoltageandthepowerrating.Othercharacteristicsincludetemperaturecoefficient,noise,inductanceandcriticalresistance.Theohm(symbol:Ω)isaunitofelectricalresistance.Commonlyusedinelectricalandelectronicusagearethekilohmandmegohm.Capacitorsstoreelectriccharge.Theyareusedwithresistorsintiming

circuitsbecauseittakestimeforacapacitortofillwithcharge.TheyareusedtosmoothDCsuppliesbyactingasareservoirofcharge.TheyarealsousedinfiltercircuitsbecausecapacitorseasilypassAC(changing)signalsbuttheyblockDC(constant)signals.Capacitanceisameasureofacapacitor'sabilitytostorecharge.Alargercapacitancemeansthatmorechargecanbestored.Capacitanceismeasuredinfarads,symbolF.However1Fisverylarge,soprefixesareusedtoshowthesmallervalues.Threeprefixesareused,µ(micro),n(nano)andp(pico).Aninductorisformedbywindingwirearoundasuitablemoldtoformacoil.Itselectricalpropertyiscalledinductanceandtheunitforthisisthehenry,symbolH.1HisverylargesomH(milli-henry)andµH(micro-henry)areused,1000µH

=

1mHand1000mH

=

1H.Ironandferritecoresincreasetheinductance.InductorsaremainlyusedintunedcircuitsandtoblockhighfrequencyACsignals.TheypassDCeasily,butblockACsignals,thisistheoppositeofcapacitors.Inductorsarerarelyfoundinsimpleprojects,butoneexceptionisthetuningcoilofaradioreceiver.Thisisaninductorwhichyoumayhavetomakeyourselfbyneatlywindingenamelledcopperwirearoundaferriterod.Trytomatchthefollowingcolumns:1.two-terminalcomponent电子电路2.Ohm'slaw 额定功率3.electroniccircuits二端元件4.powerrating 欧姆定律5.criticalresistance滤波电路6.electriccharge 漆包线7.enamelledcopperwire电荷8.filtercircuits 临界电阻PassageB

DirectandAlternatingCurrent

NewWordsandExpressionsbattery['bætəri] 电源applications应用components器件、元件series['siəri:z]

串联parallel['pærəlel]并联apparatus[ˌæpə'reitəs]

器件、仪器tandem['tændəm]串联式、双人的divide[di'vaid]

分离、隔开recombining 合并、汇合opposite['ɔpəzit]

相反、不同reciprocal[ri'siprəkəl]

倒数classification分类、类别direct 直流、直接alternating交流、交变current['kʌrənt]

电流abbreviation[əbri:vi'eiʃən]缩写、简写polarity[pəu'lærəti]极性reverse[ri'və:s]反转、倒相constant['kɔnstənt] 恒定、不变、常量regulate['reɡjuleit]控制、调节pulsating 波动的、脉动的unfilter 未滤波的rectifier['rektifaiə] 整流、整流器utility 应用程序、功用periodically[ˌpiəri'ɔdikəli] 周期性地cycle['saikl] 循环、周期frequency['frikwənsi]频率transmission[trænz'miʃən]

传播、传送vast[vɑ:st,væst]

巨大的、广大的majority[mə'dʒɔriti]多数、大多数receiver接收器、接收机provided如果、假如transformer[træns'fɔ:mə]变压、变压器PassageB

DirectandAlternatingCurrentCircuitsconsistingofjustonebatteryandoneloadresistanceareverysimpletoanalyze,buttheyarenotoftenfoundinpracticalapplications.Usually,wefindcircuitswheremorethantwocomponentsareconnectedtogether.Andtherearetwobasicwaysinwhichtoconnectmorethantwocircuitcomponents:seriesandparallel.Seriescircuitisacircuitinwhichtwoormorepiecesofapparatusareconnectedendtoendorintandemwherethecurrentisnotdividedatanypoint.Parallelcircuit,aclosedcircuitinwhichthecurrentdividesintotwoormorepathsbeforerecombiningtocompletethecircuit,istheoppositeofseriescircuit.Andweknowthatiftworesistorswereconnectedinseries.Togetthetotalresistanceoftworesistors,R1andR2,youaddthemtogether.Ontheotherhand,tofindtotalresistanceoftwoinparallelcircuits,youaddthereciprocalsoftheresistancesandtakethereciprocaloftheresult.Capacitorsandinductorinseriescircuitsorinparallelcircuitshasthesimilarcharacters.It’soneofthemainclassificationmethodsaboutcircuitinelectronics.Notbyconnectingmethodsofcomponentsincircuit,itiswellknownthatelectriccircuitisusuallydividedintotwoclasses:directcircuitandalternatingcircuit,bythesignalorcurrentflowingthroughdirectcurrent,abbreviation,dc,isacurrentthatalwaysflowsinthesamedirection(i.e.,thepolarityneverreverses).Thecurrentmightbeconstant,asfromabatteryoraregulatedpowersupply;itmightbepulsating,asfromanunfilteredrectifier.Andthesesystemsareusuallycalleddirectcurrentcircuit.ThefirstutilitysystemsinstalledbyEdisonuseddctechnology.NotlongafterEdisoninstalledhisdirectcurrentsystem,othersrealizedthattheuseofanalternatingcurrentsystemhadadvantagesoverthedc.Everytimeweturnonatelevisionset,aradio,oranyofaotherelectricalappliances,wearecallingonalternatingcurrentstoprovidethepowertooperatethem.But,whatisthealternatingcurrent?Differentfromdirectcurrentmovingthroughaconductororcircuitinonedirectiononly,alternatingcurrent,abbreviation,ac,isacurrentthatperiodicallyreversesitsdirectionofflow.Asfig.1-4showing,inonecycle,analternationstartsatzero,risestoamaximumpositivelevelat90degrees,returnstozeroat180degrees,risestoamaximumnegativelevelat270degrees,andagainreturnstozeroat360degrees.Thenumberofsuchcyclescompletedpersecondistermedtheacfrequency.IntheUnitedStatesandmanyotherareasoftheworld,thefrequencyis60hertzorcyclespersecond.Andinourcountrythecurrentusedforthetransmissionofelectricalenergyandtheoperationofcommonmachineshasafrequencyof50hertz.Aciswidelyusedfortheoperationofthevastmajorityofcircuits.,whichcanbetransmittedoverlongdistances,evenwithoutusingconnectingwiresbetweensourceandreceiver,providedthechangerateofcurrentisfastenough,transformedtovariousvoltagesandeasilytolargerorsmallervaluesusingadeviceknownasatransformer,butdccannot.However,inmanycircuitapplicationssuchasgeneralpurposelightingandheating,eitheracordccanbeused.Wecanconvertdctoacbyusingadc-acconverter,acircuitthatconvertsadcinputvoltageintoanacoutputvoltage,withorwithoutstep-uporstep-down,andactodcbyrectificationcircuitformedbythediode,resistorandcapacitor.Trytomatchthefollowingcolumns:1.step-up 负载2.step-down 直流电路3.dc-acconverter 交流电路4.regulatedpower整流电路5.loadresistance 直流-交流转换器6.Seriescircuit 降压7.Parallelcircuit 稳压电源8.directcircuit升压9.alternatingcircuit并联电路10.rectificationcircuit串联电路Reading:IntegratedCircuitsIn1958,anextremelyimportantdevicewasinventedindependentlybyJackKilby,workingatTexasInstruments,andbyNoyceandMooreatFairchildSemiconductor:theintegratedcircuit(IC),whichcombinesBJTs,MOSFETs,resistors,andcapacitors,aswellastheirinterconnections,intoafunctionalcircuitonasinglechip.IntegratedCircuitsareusuallycalledICsorchips.Theyarecomplexcircuitswhicharecombinationofafewinterconnectedcircuitelementssuchastransistors,diodes,capacitorsandresistorsproducedinasinglemanufacturingprocessononeandthesamebearingstructure,calledthesubstrate,andintendedtoperformadefinitefunctioninvolvedinconvertinginformation.Intheearly1960s,ICscontainedperhaps100devices,andthesmallestfeatureswereabout25micrometers(μm).RealizingthatthecostofcomplexelectronicsystemscouldbereduceddramaticallybytheuseofmorecomplexICs,processengineershaveworkeddiligentlytoincreasethepracticaldimensionsofchipsandtoreducethesizesofthedevices.Today'smostadvancedICscontaininexcessof10milliondevicesandhavefeaturesassmallas0.25μm.(Ahumanhairisabout25μmindiameter.)Thetrendtowardsmallerdevicesisexpectedtocontinue.Inadditiontotheincreasednumberofdevices,thereductioninthesizeoffeaturesresultsinhigherperformance(i.e.,faster)digitalcircuits.Thus,wecananticipateevengreateradvancesinthefieldofelectronics.ThemanufacturingtechniquesusedforICscanbedividedintotwomaintypes:filmtechniqueandmonolithictechnique.AndICscanbeclassifiedbyfunctionintotwo:circuitstobeappliedindigitalsystemsandthosetobeappliedinlinearsystems.ThedigitalICsareemployedmostlyincomputers,electroniccounters,frequencysynthesizersanddigitalinstruments.AndtheanalogorlinearICsoperateoveracontinuousrange,andincludesuchdevicesasoperationalamplifiers.Theseadvanceswillresultfromteamworkbyphysicalelectronicsscientists,processengineers,circuitdesigners,andsystemsdesigners.Althoughthisbookprimarilyconsiderscircuitdesign,itprovidesusefulbackgroundinformationforallengineersintheelectronicsindustry.TheinventionofICisagreatrevolutionintheelectronicindustry.Sharpsize,weightreductionsarepossiblewiththesetechniques;andmoreimportantly,highreliability,excellentfunctionalperformance,lowcostandlowpowerdissipationcanbeachieved.ICsarewidelyusedintheelectronicindustry.Homework翻译TheHistoryofElectricityAsearlyasthelatterpartof16thcentury,experimenterswereexploringthebehaviorofstaticelectricity.WilliamGilbertexperimentedwithelectricchargesanddischarges.In1750,BenjaminFranklinprovedthatlightningwaselectricalinnature.Neitherinvestigatordiscoveredanythingthatwassignificantfromthestandpointofelectricity.Discoveryofthepresenceofmagnetismincertainrocksproceededtheearliestknowledgeofelectricity.UnitTwoAnalogCircuitNewWordsandExpressionsdiode['daiəud] 二极管nonlinear[nɔn'liniə]非线性one-way 单向的valve[vælv]

阀门semiconductor[ˌsemikən'dɔktə] 半导体schematic[ski:'mætik] 原理图symbol['simbəl] 图表arrows 箭头battery['bætəri]电源lamp[læmp] 灯permit[pə'mit] 准许prohibit[prəu'hibit]

禁止polarity[pəu'lærəti]极性Conversely相反switch[switʃ]

开关oddly['ɔdli] 奇怪地invent 发明predominantly占主导地位的conventional

[kən'venʃənəl]

习惯的、传统的notation[nəu'teiʃən]符号、标记metallurgically[ˌmelə'lə:dʒikli]冶金silicon['silikən]

硅n-type N型p-type P型juxtaposed[ˌdʒʌkstə'pəuzd] 紧靠的ohmmeter['əumˌmi:tə] 欧姆表qualitatively['kwɔlitətivli]

定性地purpose 目的expect 期望military['militəri]

军用civilian[si'viljən] 民用peak[pi:k] 峰值clamper['klæmpə] 钳子rectification 整流photic['fəutik] 光decoration[ˌdekə'reiʃən] 装潢、装饰TextDiodeAdiodeisanonlinearelectricaldeviceallowingcurrenttomovethroughitinonedirectionwithfargreatereasethanintheotherandusuallyactingasaone-wayvalveforcurrent.Themostcommonkindofdiodeinmoderncircuitdesignisthesemiconductordiode,althoughotherdiodetechnologiesexist.SemiconductordiodesaresymbolizedinschematicdiagramssuchasFig.2-1.InFig.2-1,arrowsindicatethedirectionofelectroncurrentflow.Whenplacedinasimplebattery-lampcircuit,thediodewilleitheralloworpreventcurrentthroughthelamp,dependingonthepolarityoftheappliedvoltage.(Fig.2-2)(a)Currentflowispermitted;thediodeisforwardbiased.(b)Currentflowisprohibited;thediodeisreversedbiased.Whenthepolarityofthebatteryissuchthatelectronsareallowedtoflowthroughthediode,thediodeissaidtobeforward-biased.Conversely,whenthebatteryis“backward”andthediodeblockscurrent,thediodeissaidtobereverse-biased.Adiodemaybethoughtofaslikeaswitch:“closed”whenforward-biasedand“open”whenreverse-biased.Oddlyenough,thedirectionofthediodesymbol's“arrowhead”pointsagainstthedirectionofelectronflow.Thisisbecausethediodesymbolwasinventedbyengineers,whopredominantlyuseconventionalflownotationintheirschematics,showingcurrentasaflowofchargefromthepositive(+)sideofthevoltagesourcetothenegative(-).Thisconventionholdstrueforallsemiconductorsymbolspossessing“arrowheads”.Thearrowpointsinthepermitteddirectionofconventionalflow,andagainstthepermitteddirectionofelectronflow.oddlyenough：稀奇的是holdstruefor：适用于Onewaytomakeasemiconductordiodeistometallurgicallycreateawaferofsiliconcontainingn-typematerialadjoiningp-typematerial.Inann-channelMOSFET,forexample,then-typedrainjuxtaposedtothep-typechannelregionformsadiode.Anohmmetermaybeusedtoqualitativelycheckdiodefunction.Thereshouldbelowresistancemeasuredonewayandveryhighresistancemeasuredtheotherway.Whenusinganohmmeterforthispurpose,besureyouknowwhichtestleadispositiveandwhichisnegative!Theactualpolaritymaynotfollowthecolorsoftheleadsasyoumightexpect,dependingontheparticulardesignofmeter.Thediodeispopularlyappliedinelectricequipmentwhetherformilitaryuseorcivilianuse.Forexample:peakdetector,clampercircuits,voltagemultipliersandrectificationwhichisthemostpopularapplicationofthediode.AndnowLED（LightEmittingDiode),atypeofdiodewhichcanbedirectlychangetheelectricsignalintothephoticsignal,ispopularlyusedforlighting,display,signalanddecorationinourdailylife.Exercises:Trytomatchthefollowingcolumns:1.MOSFET 正向偏置2.schematicdiagrams施加电压3.forward-biased 高电阻4.reverse-biased电压倍增器5.LED原理图6.voltagemultipliers反向偏置7.highresistance 发光二极管8.appliedvoltage金属氧化物半导体场效管

PassageBNewWordsandExpressionstransistor[træn'sistə] 三极管amplifier['æmplifaiə]放大器response 反应accuracy['ækjurəsi]

精确，准确digital 半导体analog 原理图regulation[reɡju'leiʃən] 图表oscillators['ɔsileitəz]振荡器package 包装，封装individually[indi'vidjuəli]分别地，独立地integrated集成的billion 十亿，数以十亿计的，大量fundamental[fʌndə'mentəl]基本的，必要的govern统治，控制cellular['seljulə]利用电台网通讯的，蜂窝式无线通讯系统的categories['kætiɡəriz]类别bipolar[bai'pəulə]有两极的，双极的；两极世界的junction

['dʒʌŋkʃən]

结点，会合点solid-state使用电晶体的，不用真空管的，researchers 研究人员laboratories[lə'bɔrətəriz]实验室consists 包含，包括sandwich['sænwidʒ] 把……夹在……之间

emitter[i'mitə] 发射极collector 集电极base 基极element['elimənt] 原理，特性conducting 传导condition 状态holes 空穴attract 吸引operation[ɔpə'reiʃən]

工作，运行opposite 相反的connecting 链接common 共有的，公共的electrode[i'lektrəud] 电极configuration[kənfiɡju'reiʃən] 构造，接法wired 连线，以线加强consume[kən'sju:m]

消耗terminals 端子drain[drein]

漏极channel 沟道conductivity[kɔndʌk'tiviti] 导电性potential[pəu'tenʃəl] 电压，电势PassageBTransistorThetransistorisanonlinearsemiconductordevicebeingsimilartothediode,commonlyusedasanamplifieroranelectricallycontrolledswitch.Becauseofitsfastresponseandaccuracy,thetransistormaybeusedinawidevarietyofdigitalandanalogfunctions,includingamplification,switching,voltageregulation,signalmodulation,andoscillators.Transistorsmaybepackagedindividuallyoraspartofanintegratedcircuit,whichmayholdabillionormoretransistorsinaverysmallarea.Sothetransistorisbecomingthefundamentalbuildingblockofthecircuitrythatgovernstheoperationofcomputers,cellularphones,andallothermodernelectronics.Therearetwomajortransistorcategories:ThebipolartransistorAlsocalled“thebipolarjunctiontransistor”(BJT)andthefieldeffecttransistor(FET).Thefirsttypeofsolid-stateelectronictransistorwasmadebyresearchersWilliamShockley,JohnBardeenandWalterBrattainatBellLaboratoriesinDecember1947.And“BipolarJunctionTransistor”wasinventedbyWilliamShocklyin1950whichisthecommonstanderofthecurrenttransistor.Thebipolarjunctiontransistorconsistsofthreeregionsofsemiconductormaterial.Onetypeiscalledan-p-ntransistor,inwhichtworegionsofn-typematerialsandwichaverythinlayerofp-typematerial.Thetwon-typematerialregionsofthen-p-ntransistorarecalledtheemitterandcollectorandthep-typematerialiscalledthebase.n-p-ntransistorsaresymbolizedinschematicdiagramssuchasFig2-3.Whenusedasanamplifyingelement,thebasetoemitterjunctionisina"forward-biased"(conducting)condition,andthebasetocollectorjunctionis"reverse-biased"ornon-conducting.Smallchangesinthebasetoemittercurrent(theinputsignal)causeeitherholes(forpnpdevices)orfreeelectrons(fornpn)toenterthebasefromtheemitter.Theattractingvoltageofthecollectorcausesthemajorityofthesechargestocrossintoandbecollectedbythecollector,resultinginamplification.Theonlyfunctionaldifferencebetweenap-n-ptransistorandann-p-ntransistoristheproperbiasing(polarity)ofthejunctionswhenoperating.Foranygivenstateofoperation,thecurrentdirectionsandvoltagepolaritiesforeachtypeoftransistorareexactlyoppositeeachother.Therearethreewaysofconnectingatransistor,dependingontheusetowhichitisbeingput.Thewaysareclassifiedbytheelectrodethatiscommontoboththeinputandtheoutput.Theyarecalled:(a)common-baseconfiguration(b)common-emitterconfiguration(c)common-collectorconfigurationAlthoughthefirsttransistorsandfirstsiliconchipsusedbipolartransistors,mostchipstodayareFET(fieldeffecttransistors)wiredasCMOSlogic,whichconsumelesspower.AFEThasthreeterminals，asource,adrainandagate.Thesemiconductorregionbetweensourceanddrainiscalledachannelanditsconductivityiscontrolledbythepotentialofthegateterminal.Exercises:Trytomatchthefollowingcolumns:1.signalmodulation 模拟电路2.analogfunctions信号调制3.cellularphones 双极型晶体管4.BJT 共基极5.FET 手机、移动电话6.crossinto场效应晶体管7.properbiasing 共集电极8.common-base 穿过9.common-emitter正确偏置10.common-collector 共发射极ReadingAmplifierMuchasthegateabstractionformsthefoundationofmostofdigitalelectronics,theoperationalamplifierformsthebasisformuchofelectroniccircuitdesign.Theoperationalamplifierisarguablythemostusefulsingledeviceinanalogelectroniccircuitry.Withonlyahandfulofexternalcomponents,itcanbemadetoperformawidevarietyofanalogsignalprocessingtasks.Itisalsoquiteaffordable,mostgeneral-purposeamplifierssellingforunderadollarapiece.Moderndesignshavebeenengineeredwithdurabilityinmindaswell:severalop-ampsaremanufacturedthatcansustaindirectshort-circuitsontheiroutputswithoutdamage.Thenameoperationalamplifieroriginatesfromthebygonedaysoftheanalogcomputer(1940-1960),inwhichtheconstantsindifferentialequationswererepresentedbythegainsofamplifiers.Thustheseamplifiers,constructedfrombalancedpairsofspeciallymanufacturedvacuumtubes,hadtohavereliable,known,fixedgains.Becausetransistorsareinherentlymoretemperature-dependentthanvacuumtubes,itwasatfirstthoughtthatsatisfactorytransistorOpAmpscouldnotbebuilt.Butin1964,itwasdiscoveredthatbyfabricatingbalancedtransistorpairsclosetogetheronasinglesiliconchiptominimizethermalgradients,thetemperatureproblemscouldbeovercome.Andthuswereborninrapidsuccessionthe703,the709,andthentheubiquitous741.OpAmpsarerarelyusedforanalogcomputersnow,butinsteadhavebecomeuniversalbuildingblocksinallaspectsofanalogcircuitry.TheOpAmpisamultistagetwo-inputdifferentialamplifierthatisdesignedtobeanalmostidealcontroldevice,specifically,avoltage-controlledvoltagesource.AnabstractrepresentationoftheoperationalamplifiershowninFig2-4suggestsitisafour-portdevice.Thefourportsareaninputport,anoutputport,andapairofpowerports.A+VS-voltage(forexample,15volts)isappliedatthepluspowerportanda−VS-voltage(forexample,−15volts)isappliedattheminuspowerport.Aninputvoltage(thecontrol)appliedacrossthenon-invertingandinvertinginputterminalsoftheOpAmpisamplifiedbyalargeamountandappearsattheoutputport.Intheoperationalamplifierabstraction,theinputimpedanceacrosstheinputportisinfinity,andtheoutputimpedanceiszero.Thegain,orthefactorbywhichtheinputvoltageisamplified,isalsoinfinity.ThesymbolandstandardlabelingfortheoperationalamplifierareshowninFig2-4(a).Thetworequiredexternalpowersupplieshavebeenexplicitlyshowninthediagram,althoughshowingthemisnottheusualpractice.Allfivecurrentshavebeenlabeled,inadditiontoappropriatenodevoltages,referredtotheindicatedcommongroundterminal.Inthisprimitivecircuit,thevoltageviisusedtocontroltheoutputvoltagevo.Letusexaminethiscontrolfunctionindetailtofindoutboththeextentofthecontrol,andthecostofthecontrol;thatis,howmuchpowermustbeappliedfromsourcevitocontrolagivenamountofpoweratthevoterminal.Toaddressthefirstproblem,wesetupthecircuitexactlyasinFig2-5(a),andmeasuretheoutputvoltagevo,bothasafunctionoftimeandasafunctionofvi,assumingviissomelow-frequencysinusoid.TheresultsareshowninFig2-5(b)and2-5(c).Notethedifferenceinscaleofthevoltageaxes,indicatingthattheoutputvoltageisperhaps300,000timesaslargeastheinputvoltage.Theplotofvoversusvishowsaregionaroundtheoriginwherevoisfairlylinearlyrelatedtovi,butmuchbeyondthisrangethecontrolbecomesineffective,andvostaysatafixedvoltage,orsaturates,atroughlyeither+12voltsor−12volts,dependingonthepolarityofvi.ThecurveswillalsodifferfordifferentsamplesofthesameOpAmptype.Differentdevicesofthesametypemighthavedifferentcharacteristics.Thecharacteristicsmightalsodependontemperature.Onekeytotheusefulnessoftheselittlecircuitsisintheengineeringprincipleoffeedback,particularlynegativefeedback,inwhichaportionoftheoutputsignaloftheOpAmpisfedbacktothev−