电子信息类专业英语市公开课一等奖百校联赛获奖课件.pptx

Unit 3 Electronic Amplifiers Unit 3 Electronic Amplifiers TextKey wordsTechnical termsExpressionsNotes to the text第1页Unit 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 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,mixers,logic circuits,and other applications where an amplitude cutoff is desired.Today either discrete transistor circuits or integrated circuits are mostly used.第2页Unit 3 Electronic Amplifiers Nowadays,transistors are the most important device in electronic amplifiers.When the BE junction is forward 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-base.第3页Unit 3 Electronic Amplifiers Fig.3-1 Three Basic Configurations of Transistor Amplifiers第4页Unit 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 low 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.第5页Unit 3 Electronic Amplifiers For the transistor voltage amplifier,often it is a small alternating 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 impedance than the common-base circuit.It provides both current gain and voltage gain,moreover Au0.第6页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 voltage 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 of the signal to be operated.第7页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 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 can extend well into the microwave frequency range.第8页Unit 3 Electronic Amplifiers Key wordselectronic adj.电子increase vt.增加，加大signal n.信号amplification n.扩大distortion n.失真proportional adj.百分比，成百分比considerable adj.相当大(或多)，值得考虑，相当可观waveform n.波形audio adj.音频，声频第9页Unit 3 Electronic Amplifiers video n.电视，录像，视频oscillator n.振荡器modulator n.调整器amplitude n.振幅discrete adj.不连续，离散integrated adj.综合，完整configuration n.结构，结构，配置，外形approximately adv.近似地，大约impedance n.电阻抗alternate adj.交替，轮番第10页Unit 3 Electronic Amplifiers bipolar adj.有两极，双极load n.负载moderate adj.中等，适度，适中kilohertz n.千赫loudspeaker n.扩音器，喇叭spectrum n.频谱microwave n.微波第11页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/output impedance 输入/输出阻抗voltage gain电压增益第12页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低失真第13页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bothand既又on the other hand其次according to根据be converted to转换为deal with处理第14页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.线性放大器能够进行无失真信号放大或失真很小，所以，线性放大器能够进行无失真信号放大或失真很小，所以，其输出与输入是成正比。其输出与输入是成正比。句中，“so that”引导结果状语从句；“be proportional to”意为与成正比。第15页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.若晶体管加正确偏置且在集电极回路中接适当电阻作为若晶体管加正确偏置且在集电极回路中接适当电阻作为负载，则共射极方式下双极型结型晶体管可用作电压放大器。负载，则共射极方式下双极型结型晶体管可用作电压放大器。句中“if”引导条件状语从句；“called the load”为插入语，定义前面“a suitable resistor”。第16页Unit 3 Electronic Amplifiers 3Radio frequency amplifiers are used to deal with the signals that their frequencies generally range from 100 kHz to 1 GHz,and can extend well into the microwave frequency range.射频放大器用于处理频率范围在射频放大器用于处理频率范围在100千赫到千赫到1吉赫信号，吉赫信号，并能很好地扩展至微波频率范围。并能很好地扩展至微波频率范围。句中，“are used to”为被动语态；“that”引导定语从句，修饰前面“signals”；“and”前后为并列成份。第17页