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1、电气工程气工程专业英英语section_2-4Section 4 Operational Amplifiersn Textn New Words and Expressionsn Exercisesn Endn Translation of Long SentencesSection 4 Operational Amplifiers Introduction Operational amplifiers are high-gain difference amplifiers,which were perfected during World War II.They became the fou
2、ndation of analog computers,at one time analog computers were called differential analyzers because they are used to solve differential equations.运算放大器是一种高增益的差分放大器,它在第二次世界大战期间得到完善,并成为 模拟计算机的基础.由于运算放大器被用来 解差分方程,因此一段时期内模拟计算机被 称为差分分析器.运算放大器也是很多 重要仪器的主要组成部分.Operational amplifiers are also the basis of m
3、any important instruments.Section 4 Operational Amplifiers The analog amplifier consists of a basic difference amplifier,implemented by feedback and other compensating amplifying circuits to give linear response,stability,freedom from drift,and other desirable properties.Thus it is more difficult to
4、 isolate the long-term changes that arise from variations in temperature and power-supply voltage and from other effects that cause the output voltage to drift.模拟放大器由基本的差分放大器组成,通过反馈以及其它补偿放大电路实现线性反应,稳定性,来自漂移的自由度以及其它 我们所期望的性能.我们要求它具有复杂性,因为运算放大器放大直流以及交流信号,在 放大阶段不允许有容性耦合.The complexity is required becau
5、se operational amplifiers amplify dc as well as ac signals,capacitive coupling between amplifying stages is not permitted.因此我们很难 隔离由温度的变化和电源电压以及其它引起 输出电压漂移的因素而产生的长效变化.Section 4 Operational Amplifiers After the invention of the transistor,solid-state operational amplifiers were introduced as integrat
6、ed circuits.Now operational amplifiers are used to make high-quality,low-power analog amplifier,and it is possible to avoid designing individual transistor amplifier stages for many application.For most amplifying purposes and for many measuring and control applications,simple arrangements of operat
7、ional amplifiers with feedback circuits will meet the designers needs.在发明了晶体管后,固态运算放大器被 引入成为集成电路.现在运算放大器被用来 制造高品质,低功率的模拟放大器,因而我 们可以在很多应用场合免去了设计单个的晶 体管放大器的过程.对于大多数要求放大和 很多测量和控制应用的场合,具有反馈电路 的简单的运算放大器将满足设计者的需要.Section 4 Operational Amplifierspackages(DIPs)or in other compact forms makes the solution of
8、 analog signal problems analogous in many respects to the solution of digital logic problems,that is,through the interconnection of integrated circuits.The availability of operational amplifiers as integrated circuits in the form of dual in-lineOperational Amplifier Fig.2-5 shows the symbol for an o
9、perational amplifier.There are two inputs:the one marked with a plus sign is the noninverting input,and the one marked with a minus sign is the inverting input.以双列直插式封装或以其它密封形式出现的 运算放大器做成的集成电路的可用性使模拟 信号问题在很多方面类似数字逻辑问题那样 得到解决,也就是通过集成电路的相互连接 得到解决.运算放大器运算放大器 图2-5显示了运算放大器的符号.它有 两个输入端:标有正号的为非倒向输入端,而标有负号的
10、为倒向输入端由运算放大器 放大的电压是两个输入端之间的电压The voltage amplified by the operational amplifier is the voltage difference between the two inputs.Section 4 Operational AmplifiersThe open-circuit gain is so large,l05 to l06,that a voltage difference of only a few microvolts will give an appreciable output.Because the
11、 operational amplifier is a difference amplifier,connections must always be made to both input terminals for proper operation.Fig.2-5 A symbol for an operational amplifier 由于 开始增益是如此大,从l05到l06,所以仅仅 是几微伏的电压差将产生相当大的输出电压.由于运算放大器是一种差分放大器,因此,在两个输入端必须都连接电压才能使之正常 工作.Section 4 Operational Amplifiers If two
12、different positive voltages are applied separately to the two inputs,the output of the operational amplifier will be at the maximum(saturated)value if the voltage at the noninverting input is larger than the voltage at the inverting input.If the voltages exchange their relative valuesthat is,if the
13、inverting input exceeds the noninverting inputthe operational amplifier will switch to a minimum output,which is the saturated negative voltage.如果两个不同的正电压分别被加在两 个输入端,而且非倒向输入端的电压大于倒 向输入端的电压,那么运算放大器的输出端 电压将处于最大值(饱和值)The switching occurs very quickly whenever the relative values of the voltages change.
14、如果电压 进行相互交换其相对值也就是,如果倒 向输入端的电压大于非倒向输入端的电压 运算放大器将产生一个最小的输出,即为 饱和负电压.每当相对电压值改变时这种转 换就会很快地发生.Section 4 Operational Amplifiers We will see that an operational amplifier is an excellent voltage comparator because it produces a large voltage swing at the instant of crossing,when an earlier relation in vol
15、tage magnitudes is reversed by only a few microvolts.If the operational amplifier is to operate in its linear range,a very small voltage difference must exist between the inverting and the noninverting inputs.我们将看到运算器是非 常好的电压比较器,因为它在瞬间电压变换 时产生很大的电压起伏.此时仅仅几微伏的 电压将使先前的电压大小关系产生逆转.如果运算放大器工作在其线性范围内,在 其倒向
16、输入端和非倒向输入端之间必须存在非 常小的电压差.In analyzing operational amplifying circuits,we assume,because of the large open-circuit gain,that the voltage difference across the inputs is negligible.在分析运算放大电路时,我们 假设由于存在很大的开路电压增益,所以输入 端两端的电压差可以忽略不计.Section 4 Operational AmplifiersIn some cases we will set the voltage to
17、 zero.When a portion of the output signal is returned to the input as negative feedback,the voltage difference cannot grow large because the output changes to minimize the voltage difference between the inputs.Two additional properties are present in operational amplifiers.They are a very high input
18、 impedance,approximately l06,and a low output impedance,approximately l00.在某些场合我 们将把电压设为零.当输出信号的一部分返回 输入端作为负反馈,电压差就无法增大因为输 出改变使输入端的电压差减小.另外两个性质也存在于运算放大器,它们 是非常高的输入阻抗,大约l06,以及很小的 输出阻抗,大约l00.Section 4 Operational AmplifiersThese properties contribute to the usefulness of operational amplifiers by allo
19、wing signal sources with small current capabilities to drive operational amplifiers directly.In turn,operational amplifiers may drive devices that have severe signal requirements.To summarize,a good operational amplifier is characterized by a very large open-circuit gain of a million or so,an extrem
20、ely small difference voltage between the inverting and the noninverting input terminals,a very high input impedance,and a small output impedance.An ideal operational amplifier,however,would have an infinite gain,这些性质使运算放大 器变得有用因为它可以允许信号源用非常小的 电流来驱动放大器,反过来,运算放大器可以 驱动具有很高信号要求的器件.概括起来,一个好的运算放大器具有以下 特性:
21、非常大的大约一百万的开路增益,倒向输入 端和非倒向输入端之间相当小的电压差;很高 的输入阻抗以及很小的输出阻抗.而一个理想 的运算放大器将会有一个无穷大的增益.Section 4 Operational Amplifiersa zero difference voltage between inputs,an infinite input impedance,and a zero output impedance.Many operational amplifiers require two equal but opposite supply voltages,one positive and
22、 one negative.Typical values are l2V or 15V.输入端之间的一个零电位差,一个无穷大的输 入阻抗以及一个零输出阻抗.With a two-sided power supply of l5 V,the output signal is restricted to about l2V.Other operational amplifiers may be operated with a single-ended power source,such as+15V.The useful range of the output voltage in an oper
23、ational amplifier is approximately 80 percent of the supply voltages.很多运算放大器要求两个数值相等但符号相 反的供电电压,一个为正而另一为负,典型的 值是12V或15V.其它运算放大器可能工 作在单端输入电源,比如说15V.运算放大 器的有用的输出电压范围等于大约80%的供电 电压对于具有双边电源电压15V的运算放 大器,输出信号被限制在大约12V.Section 4 Operational Amplifiers Many operational amplifiers have limitations,two of whic
24、h need to be mentioned.One is that the gain decreases rapidly as the frequency increases.At small frequenciesas low as l0 Hzthe voltage gain begins to drop.(Power begins to drop at-20 dB per decade.)The gain-versus-frequency limitation is offset by the use of negative feedback to expand the frequenc
25、y band.The other limitation is the rate at which most operational amplifiers can respond to a step change in the input signal.Compared to digital gates,operational amplifiers are poor in this respect;common operational amplifiers change at a rate of approximately l V/s.很多运算放大器都有其局限性,其中有 两点需要在这里提到一个局
26、限性是随着频 率的增加其增益下降得很快.在低频阶段 如象10Hz那么低电路增益就开始下降(功率在-20分贝处开始以每10分贝的速度 减小).增益-相对-频率的局限性通过负 反馈的补偿作用而使频带得以增宽.另外一 个局限是大多数运算放大器对输入信号的改 变所能起反应的速率.与逻辑门相比较,运 算放大器在这个方面的性能不算好,普通运 算放大器在大约1v/us的速率时可以改变状 态.Section 4 Operational AmplifiersA TTL digital gate changes from one state to the other nearly 500 times faster
27、.ReturnThe importance of operational amplifiers lies in the advantages of using negative feedback networks.Operational amplifiers and digital logic gates used together allow data to be processed and analyzed with the greatest advantages of both technologies.而一个TTL数字逻辑门从一个状态到另 一个状态的翻转大约比这个速度快500倍.运算放
28、大器的重要性在于使用负反馈网 络的优点.同时应用运算放大器和逻辑门的 电路因为具有两种技术优势而允许进行数字 处理和分析.New Words and Expressionsoperational amplifier 运算放大器difference amplifier差动放大器differential a.微分的，差动的，差分的，差别的；n.微分，差动，差分，差别feedback n.反馈，回复，反应stabilityn.稳定性，稳定度，安定性，复原性 耐性，耐久性capacitive a.电容性的，电容的，容性的 coupling n.耦合,偶合,连接；a.耦合的,连接的 New Words and Expressionslong-terma.长期的，远期的power-supplyn.电源solid-statea.固态的microvoltn.微伏saturatev.使饱和；a.饱和的，浸透的comparatorn.比较器swingv.;n.摇摆，摆动 New Words and Expressionssingle-endeda.单端的two-sided a.双边的，双侧的，两边的，两方面的frequency band 频带 ReturnChapter 2Section 4 End谢谢观赏谢谢观赏