《電子信息類專業(yè)英語》課件-第3章

Unit3SemiconductorDevices科技英語詞匯特點

Semiconductorsarethesubstanceswhoseabilitytoconductelectricityranksbetweenthatofaconductorandthatofanonconductor,orinsulator.Thebasicbuildingblockofmostsemiconductordevicesisthediode.

AsemiconductordiodeconsistsofaPNjunctionandhastwoterminals,ananode(+)andacathode(-).However,thediodehasanimportantproperty:itisunidirectional.Inadiode,currentflowsinonlyonedirectionacrossthejunctionfromp-ton-typematerial,andthenonlywhenthep-typematerialisatahighervoltagethanthen-typematerial.ThevoltageappliedtothediodetocreatethisconditioniscalledtheforwardbiasshowninFig.3-1,inthiscondition,currentflowsfromanodetocathodewithinthediode.

Theoppositevoltage,forwhichcurrentwillnotflow,iscalledreversebias.Anidealdiodeislikealightswitchinyourhome.Whentheswitchisclosed,thecircuitiscompletedandthelightturnson.Whentheswitchisopen,thereisnocurrentandthelightisoff.Figure3-2showsanidealdiodecharacteristic.IFisforwardcurrent,UFisforwardvoltage,URisreversevoltage,IRisreversecurrent.Fig.3-1ForwardbiasFig.3-2Idealdiodecharacteristic

Transistorsarethemostwidelyusedsemiconductordeviceinelectronicstoday.Transistorsarethree-terminaldevicesandtherearetwobasictypesofstandardtransistors,NPNandPNP,withdifferentsymbolshowninFigure3-3.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.3-3Transistorcircuitsymbols

科技英語詞匯特點

詞匯是構(gòu)成句子、語篇的基石,詞匯的學(xué)習(xí)與研究是學(xué)好科技英語的一個重要環(huán)節(jié)。初學(xué)者往往感到專業(yè)詞匯較難理解記憶，其實專業(yè)英語詞匯的記憶還是有章可循的，下面讓我們來研究一下科技英語的詞匯特點。

1.專業(yè)術(shù)語與縮略詞多

由于專業(yè)術(shù)語、縮略語能使文章更加簡潔、準(zhǔn)確，因而在科技英語中大量使用,這也是科技英語區(qū)別于普通英語的重要特征。例如：

2.合成詞多

例如：

firewall防火墻troubleshooting故障排除

microfarad微法

modem(modulation+demodulation)調(diào)制解調(diào)器

3.音譯轉(zhuǎn)換多

例如：(1)?ampere安培volt伏特ohm歐姆hertz赫茲?coulomb庫侖farad法拉

(2)?radar雷達engine引擎(發(fā)動機)

4.派生詞多

所謂派生，就是在詞根的基礎(chǔ)上加上詞綴形成新詞的方法。詞綴分為前綴和后綴。很多專業(yè)英語詞匯是