《电子信息类专业英语》课件-第4章

Unit4ElectronicAmplifiers科技英语中非谓语动词的使用

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

Nowadays,transistorsarethemostimportantdeviceinelectronicamplifiers.WhentheBEjunctionisforwardbiased,andtheBCjunctionisreversebiased,thebasecurrentiBcancontrolthecollectorcurrentiC,representedbytheformulaiC= βiB.Therearethreefundamentalconfigurationsintermsofconnectingtransistorsinacircuit(asshowninFig.4-1):common-emitter,common-collectorandcommon-base,.

Fig.4-1ThreeBasicConfigurationsofTransistorAmplifiers

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.

科技英语中非谓语动词的使用

在句子中只能充当除谓语以外的句子成分的动词形式叫做非谓语动词。非谓语动词分为三种形式：不定式，动名词和分词(分词包括现在分词和过去分词)。非谓语动词虽然有动词的特征，但不能充当谓语，只能起到名词、形容词或副词的语法功能。非谓语动词在句子中可以做主语、宾语、宾语补足语、定语、状语、表语以及其他一些特殊结构。

1.动词不定式to形式

具有名词、形容词或副词的功能,在句子中可以做主语、宾语、宾语补足语、定语、状语、表语等。例如：

(1) Itisnowmuchmoreconvenienttoemployanintegratedcircuit.(动词不定式做主语)

现在采用集成电路更方便。

(2) Allyouhavetodoistoturnonthesystem.(动词不定式做表语)

你所要做的就是打开系统。

(3) Theabilitytojumpfromonedocumenttothenextismadepossiblethroughtheuseofhyperlinks.(动词不定式做定语)

从一个文档跳转到另一个文档是通过超链接来实现的。

(4) Torunasoftwarepackage,yousimplyinsertthediskettecontainingthesoftwareinthediskdrive,thenenterthenameofthefilethatcontainstheapplicationssoftware.(动词不定式做状语)

要运行一个软件包，你只需简单地将含有该软件的软盘插入到磁盘驱动器内，然后输入含有该应用软件的文件名即可。

2.动名词V-ing形式

动名词具有名词的功能,在句子中可以做主语、宾语、定语、表语等。例如：

(1) Findingawaytoexploitthissourceofpowerwouldbeatremendousadvance.(动名词做主语)

找到一种开发这一动力资源的方法将会是一次巨大的进步。

(2) Themostpowerfultoolinprovidingcomputersecurityiscoding.(动名词做介词宾语及表语)

保证计算机安全的最有效的工具是编码。

3.现在分词V-ing形式与过去分词V-ed形式

分词具有形容词或副词的语法功能,在句子中可以做定语、状语、表语、宾语补足语等。例如：

(1) Thecolordependssimplyuponthelengthofthewaveproducingthelight.(现在分词做定语)

颜色是由产生光的波长决定的。

(2)Thisnetworkcouldenhancecommunicationsbetweenteachersandstaff,allowing