《電子信息類專業(yè)英語(yǔ)》課件-第4章

Unit4ElectronicAmplifiers科技英語(yǔ)中非謂語(yǔ)動(dòng)詞的使用

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.

科技英語(yǔ)中非謂語(yǔ)動(dòng)詞的使用

在句子中只能充當(dāng)除謂語(yǔ)以外的句子成分的動(dòng)詞形式叫做非謂語(yǔ)動(dòng)詞。非謂語(yǔ)動(dòng)詞分為三種形式：不定式，動(dòng)名詞和分詞(分詞包括現(xiàn)在分詞和過(guò)去分詞)。非謂語(yǔ)動(dòng)詞雖然有動(dòng)詞的特征，但不能充當(dāng)謂語(yǔ)，只能起到名詞、形容詞或副詞的語(yǔ)法功能。非謂語(yǔ)動(dòng)詞在句子中可以做主語(yǔ)、賓語(yǔ)、賓語(yǔ)補(bǔ)足語(yǔ)、定語(yǔ)、狀語(yǔ)、表語(yǔ)以及其他一些特殊結(jié)構(gòu)。

1.動(dòng)詞不定式to形式

具有名詞、形容詞或副詞的功能,在句子中可以做主語(yǔ)、賓語(yǔ)、賓語(yǔ)補(bǔ)足語(yǔ)、定語(yǔ)、狀語(yǔ)、表語(yǔ)等。例如：

(1)?Itisnowmuchmoreconvenienttoemployanintegratedcircuit.(動(dòng)詞不定式做主語(yǔ))

現(xiàn)在采用集成電路更方便。

(2)?Allyouhavetodoistoturnonthesystem.(動(dòng)詞不定式做表語(yǔ))

你所要做的就是打開(kāi)系統(tǒng)。

(3)?Theabilitytojumpfromonedocumenttothenextismadepossiblethroughtheuseofhyperlinks.(動(dòng)詞不定式做定語(yǔ))

從一個(gè)文檔跳轉(zhuǎn)到另一個(gè)文檔是通過(guò)超鏈接來(lái)實(shí)現(xiàn)的。

(4)?Torunasoftwarepackage,yousimplyinsertthediskettecontainingthesoftwareinthediskdrive,thenenterthenameofthefilethatcontainstheapplicationssoftware.(動(dòng)詞不定式做狀語(yǔ))

要運(yùn)行一個(gè)軟件包，你只需簡(jiǎn)單地將含有該軟件的軟盤插入到磁盤驅(qū)動(dòng)器內(nèi)，然后輸入含有該應(yīng)用軟件的文件名即可。

2.動(dòng)名詞V-ing形式

動(dòng)名詞具有名詞的功能,在句子中可以做主語(yǔ)、賓語(yǔ)、定語(yǔ)、表語(yǔ)等。例如：

(1)?Findingawaytoexploitthissourceofpowerwouldbeatremendousadvance.(動(dòng)名詞做主語(yǔ))

找到一種開(kāi)發(fā)這一動(dòng)力資源的方法將會(huì)是一次巨大的進(jìn)步。

(2)?Themostpowerfultoolinprovidingcomputersecurityiscoding.(動(dòng)名詞做介詞賓語(yǔ)及表語(yǔ))

保證計(jì)算機(jī)安全的最有效的工具是編碼。

3.現(xiàn)在分詞V-ing形式與過(guò)去分詞V-ed形式

分詞具有形容詞或副詞的語(yǔ)法功能,在句子中可以做定語(yǔ)、狀語(yǔ)、表語(yǔ)、賓語(yǔ)補(bǔ)足語(yǔ)等。例如：

(1)?Thecolordependssimplyuponthelengthofthewaveproducingthelight.(現(xiàn)在分詞做定語(yǔ))

顏色是由產(chǎn)生光的波長(zhǎng)決定的。

(2)Thisnetworkcouldenhancecommunicationsbetweenteachersandstaff,allowing