《电子信息类专业英语》课件-第3章

Unit3SemiconductorDevices科技英语词汇特点

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

科技英语词汇特点

词汇是构成句子、语篇的基石,词汇的学习与研究是学好科技英语的一个重要环节。初学者往往感到专业词汇较难理解记忆，其实专业英语词汇的记忆还是有章可循的，下面让我们来研究一下科技英语的词汇特点。

1.专业术语与缩略词多

由于专业术语、缩略语能使文章更加简洁、准确，因而在科技英语中大量使用,这也是科技英语区别于普通英语的重要特征。例如：

2.合成词多

例如：

firewall防火墙troubleshooting故障排除

microfarad微法

modem(modulation+demodulation)调制解调器

3.音译转换多

例如：(1) ampere安培volt伏特ohm欧姆hertz赫兹 coulomb库仑farad法拉

(2) radar雷达engine引擎(发动机)

4.派生词多

所谓派生，就是在词根的基础上加上词缀形成新词的方法。词缀分为前缀和后缀。很多专业英语词汇是