電子信息類專業(yè)英語第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. 電子的increase vt. 增加，加大signal n. 信號amplification n. 擴大distortion n. 失真proportional adj. 比例的，成比例的considerable adj. 相當(dāng)大(或多)的，值得考慮的，相當(dāng)可觀的waveform n. 波形audio adj. 音頻的，聲頻的Unit 3 Electronic Amplifiers vi

13、deo n. 電視，錄像，視頻oscillator n. 振蕩器modulator n. 調(diào)節(jié)器amplitude n. 振幅discrete adj. 不連續(xù)的，離散的integrated adj. 綜合的，完整的configuration n. 構(gòu)造，結(jié)構(gòu)，配置，外形approximately adv. 近似地，大約impedance n. 電阻抗alternate adj. 交替的，輪流的Unit 3 Electronic Amplifiers bipolar adj. 有兩極的，雙極的load n. 負載moderate adj. 中等的，適度的，適中的kilohertz n. 千赫l

14、oudspeaker n. 擴音器，喇叭spectrum n. 頻譜microwave n. 微波Unit 3 Electronic Amplifiers Technical termselectronic amplifier 電子放大器a liner/nonlinear amplifier 線性/非線性放大器logic circuits邏輯電路integrated circuit(IC)集成電路the BE /BC junction發(fā)射結(jié)/集電結(jié)common-base/emitter/collector 共基/共射/共集the current follower電流跟隨器input/outpu

15、t impedance 輸入/輸出阻抗voltage gain電壓增益Unit 3 Electronic Amplifiers in-phase同相high frequency高頻a bipolar junction transistor(BJT)雙極型晶體管television set電視機frequency spectrum頻譜low distortion低失真Unit 3 Electronic Amplifiers Expressionsbe proportional to與成比例eitheror或者或者be represented by用表示in terms of根據(jù)；按照bothan

16、d既又on the other hand另一方面according to根據(jù)be converted to轉(zhuǎn)換為deal with處理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.線性放大器可以進行無失真的信號放大或失真很小，線性放大器可以進行無失真的信號放大或失真很小，因此，其輸出與輸入是成正比的

17、。因此，其輸出與輸入是成正比的。句中，“so that”引導(dǎo)結(jié)果狀語從句；“be proportional to”意為與成正比。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.若晶體管加正確的偏置且在集電極回路中接合適的電若晶體管加正確的偏置且在集電極回路中接合適的電阻作為負載，則共射極方式下的雙極型結(jié)型晶體管可用作阻作為負載，則共射極方式下的雙極型結(jié)型晶體管可用作電壓放大器。電壓放大器。句中“if”引導(dǎo)條件狀語從句；“called the load”為插入語，定義前面的“a suitable resistor”。Unit 3 Electronic Amplifiers 3Radio frequency amplifiers are used to d