资源描述
单击此处编辑母版标题样式,Unit 2 Semiconductor Devices,Unit 2 Semiconductor Devices,Text,Key words,Technical terms,Expressions,Notes to the text,TextSemiconductors are the substances whose ability to conduct electricity ranks between that of a conductor and that of a nonconductor, or insulator. The basic building block of most semiconductor devices is the diode. A semiconductor diode consists of a PN junction and has two terminals, an anode(+) and a cathode(-). However, the diode has an important property: it is unidirectional. In a diode, current flows in only one direction across the junction from p- to n-type material, and then only when the p-type material is at a higher voltage than the n-type material.,The voltage applied to the diode to create this condition is called the forward bias shown in Fig.2-1, in this condition, current flows from anode to cathode within the diode. The opposite voltage, for which current will not flow, is called reverse bias. An ideal diode is like a light switch in your home. When the switch is closed, the circuit is completed and the light turns on. When the switch is open, there is no current and the light is off. Fig. 2-2 shows an ideal diode characteristic.,I,F,is forward current,U,F,is forward voltage,U,R,is reverse voltage,I,R,is reverse current.,Fig.2-1 Forward bias,Transistors are the most widely used semiconductor device in electronics today. Transistors are three-terminal devices and there are two basic types of standard transistors, NPN and PNP, with different symbol shown in Fig. 2-3. Most transistors used today are NPN because this is the easiest type to make from silicon. If you are new to electronics it is best to start by learning how to use NPN transistors. The letters refer to the layers of semiconductor material used to make the transistor. The leads are labeled base(B), collector(C), and emitter(E). These terms refer to the internal operation of a transistor. A transistor has two PN junctions: the base-emitter(BE) junction and the base-collector junction.,Both of them should behave like a diode and conduct one way only. Current from a power source enters the emitter, passes through the very thin base region, and leaves via the collector. Current flow is always in this direction. This current can be made to vary in amplitude by varying the current flowing in the base circuit. It takes only a small change of base current to control a relatively large collector current. It is this ability that enables the transistor to amplify.,Fig.2-3 Transistor circuit symbols,Key wordssemiconductor n. 物半导体substance n. 物质，实质，主旨electricity n. 电流，电，电学insulator( =nonconductor) n. 绝缘体device n. 装置,设备anode n. 电阳极，正极cathode n. 阴极unidirectional adj. 单向的，单向性的property n. 性质，特性material n. 材料，原料,bias n. 偏置opposite adj. 相对的，相反的switch n. 开关，转换characteristic n. 特性，特征transistor n. 电子晶体管silicon n. 化硅，硅元素layer n. 层base n. 基极collector n. 集电极emittern. 发射极powern. 物功率,Technical termssemiconductor device半导体器件PN junctionPN结p-/n-type materialp/n型材料forward bias正向偏置reverse bias反向偏置ideal diode理想二极管three-terminal device三端器件base-emitter(BE) junction发射结base-collector junction集电结power source功率源；电源the current gain电流增益DC current直流电,Notes to the text1Semiconductors are the substances whose ability to conduct electricity ranks between that of a conductor and that of a nonconductor, or insulator.,半导体是一种导电性能介于导体和绝缘体之间的物质。,句中，“whose”引导的定语从句修饰“substances”；不定式“to conduct electricity”作后置定语修饰“ability”；两个“that”指代“ability”。,2The voltage applied to the diode to create this condition is called the forward bias.,加在二极管上的满足这一条件的电压称正向偏压。,句中的“applied to the diode to create this condition”为过去分词短语作定语，修饰前面的“voltage”。3Current from a power source enters the emitter, passes through the very thin base region, and leaves via the collector.,电流从电源流入发射极，穿过很薄的基区，再由集电极流出。,句中“enters”、“passes”、“leaves”为并列成分作谓语。,
展开阅读全文