电子信息类专业英语第3章

1、Unit 3 Electronic Amplifiers Unit 3 Electronic Amplifiers TextKey wordsTechnical termsExpressionsNotes to the textUnit 3 Electronic Amplifiers TextElectronic amplifiers are used mainly to increase the voltage, current, or power of a signal. A liner amplifier provides signal amplification with little

2、 or no distortion, so that the output is proportional to the input. A nonlinear amplifier may produce a considerable change in the waveform of the signal. Linear amplifiers are used for audio and video signals, whereas nonlinear amplifiers find use in oscillators, power electronics, modulators, mixe

3、rs, logic circuits, and other applications where an amplitude cutoff is desired. Today either discrete transistor circuits or integrated circuits are mostly used.Unit 3 Electronic Amplifiers Nowadays, transistors are the most important device in electronic amplifiers. When the BE junction is forward

4、 biased, and the BC junction is reverse biased, the base current iB can control the collector current iC, represented by the formula iC=iB. There are three fundamental configurations in terms of connecting transistors in a circuit (as shown in Fig.3-1): common-emitter, common-collector and common-ba

5、se.Unit 3 Electronic Amplifiers Fig. 3-1 Three Basic Configurations of Transistor AmplifiersUnit 3 Electronic Amplifiers In the common-base connection, as the input current iE is approximately equal to the output current iC, it is called the current follower. In this configuration, the circuit has l

6、ow input impedance and high output impedance. The voltage gain Au0, that means the output and the input is in-phase. The CB configuration circuit is mainly used in high frequency and wide band circuits.Unit 3 Electronic Amplifiers For the transistor voltage amplifier, often it is a small alternating

7、 voltage that has to be amplified. A bipolar junction transistor in the common-emitter mode can act as a voltage amplifier if the transistor has a proper bias and a suitable resistor, called the load, is connected in the collector circuit. This configuration has more moderate input and output impeda

8、nce than the common-base circuit. It provides both current gain and voltage gain, moreover Au0. Unit 3 Electronic Amplifiers The third type of connection is the common-collector circuit. In this configuration, the input impedance of the transistor is very high and the output impedance is low, the vo

9、ltage gain is slightly less than one, represented by Au1，and the power gain is usually lower than that obtained in a common-base or a common-emitter circuit. On the other hand, electronic amplifiers contain audio amplifiers, video amplifiers and radio frequency amplifiers according to the frequency

10、of the signal to be operated. Unit 3 Electronic Amplifiers Audio amplifiers, such as are found in radios, television sets, are generally operated at frequencies below 20 kilohertz. They amplify the electrical signal, which then is converted to sound in a loudspeaker. Video amplifiers are used mainly

11、 for signals with a frequency spectrum range up to 6 megahertz. A video amplifier must operate over a wide band and amplify all frequencies equally and with low distortion.Radio frequency amplifiers are used to deal with the signals that their frequencies generally range from 100 kHz to 1 GHz, and c

12、an extend well into the microwave frequency range. Unit 3 Electronic Amplifiers Key wordselectronic adj. 电子的increase vt. 增加，加大signal n. 信号amplification n. 扩大distortion n. 失真proportional adj. 比例的，成比例的considerable adj. 相当大(或多)的，值得考虑的，相当可观的waveform n. 波形audio adj. 音频的，声频的Unit 3 Electronic Amplifiers vi

13、deo n. 电视，录像，视频oscillator n. 振荡器modulator n. 调节器amplitude n. 振幅discrete adj. 不连续的，离散的integrated adj. 综合的，完整的configuration n. 构造，结构，配置，外形approximately adv. 近似地，大约impedance n. 电阻抗alternate adj. 交替的，轮流的Unit 3 Electronic Amplifiers bipolar adj. 有两极的，双极的load n. 负载moderate adj. 中等的，适度的，适中的kilohertz n. 千赫l

14、oudspeaker n. 扩音器，喇叭spectrum n. 频谱microwave n. 微波Unit 3 Electronic Amplifiers Technical termselectronic amplifier 电子放大器a liner/nonlinear amplifier 线性/非线性放大器logic circuits逻辑电路integrated circuit(IC)集成电路the BE /BC junction发射结/集电结common-base/emitter/collector 共基/共射/共集the current follower电流跟随器input/outpu

15、t impedance 输入/输出阻抗voltage gain电压增益Unit 3 Electronic Amplifiers in-phase同相high frequency高频a bipolar junction transistor(BJT)双极型晶体管television set电视机frequency spectrum频谱low distortion低失真Unit 3 Electronic Amplifiers Expressionsbe proportional to与成比例eitheror或者或者be represented by用表示in terms of根据；按照bothan

16、d既又on the other hand另一方面according to根据be converted to转换为deal with处理Unit 3 Electronic Amplifiers Notes to the text1A liner amplifier provides signal amplification with little or no distortion, so that the output is proportional to the input.线性放大器可以进行无失真的信号放大或失真很小，线性放大器可以进行无失真的信号放大或失真很小，因此，其输出与输入是成正比的

17、。因此，其输出与输入是成正比的。句中，“so that”引导结果状语从句；“be proportional to”意为与成正比。Unit 3 Electronic Amplifiers 2A bipolar junction transistor in the common-emitter mode can act as a voltage amplifier if the transistor has a proper bias and a suitable resistor, called the load, is connected in the collector circuit.若晶体管加正确的偏置且在集电极回路中接合适的电若晶体管加正确的偏置且在集电极回路中接合适的电阻作为负载，则共射极方式下的双极型结型晶体管可用作阻作为负载，则共射极方式下的双极型结型晶体管可用作电压放大器。电压放大器。句中“if”引导条件状语从句；“called the load”为插入语，定义前面的“a suitable resistor”。Unit 3 Electronic Amplifiers 3Radio frequency amplifiers are used to d