1、Chapter 2ElectronicsSection 4 Operational Amplifiersn Textn New Words and Expressionsn Exercisesn Endn Translation of Long SentencesSection 4 Operational AmplifiersIntroductionOperational amplifiers are high-gain difference amplifiers, which were perfected during World War II. They became the founda
2、tion 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
3、 basis of many important instruments. Section 4 Operational AmplifiersThe 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 mo
4、re difficult to 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 com
5、plexity is required because 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 AmplifiersAfter the invention of the transistor, solid-state operational amplifiers
6、 were introduced as integrated 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 applicatio
7、ns, simple arrangements of operational 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 i
8、n other compact forms makes the solution of 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-lineOperationa
9、l AmplifierFig.2-5 shows the symbol for an operational 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
10、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 mi
11、crovolts will give an appreciable output. Because the 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 ,
12、在两个输入端必须都连接电压才能使之正常 工作 .Section 4 Operational AmplifiersIf two 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 i
13、nput. If the voltages exchange their relative valuesthat is, if the 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 switchin
14、g occurs very quickly whenever the relative values of the voltages change. 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 AmplifiersWe will see that an operational amplifier is an excellent voltage comparator because it produces a
15、 large voltage swing at the instant of crossing, when an earlier relation in voltage 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
16、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
17、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 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
18、inputs.Two additional properties are present in operational amplifiers. They are a very high input 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.
