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1、Operational amplifier theory and applications1 the principle of op-amp Op amp is the most widely used of a device, although the different structure of different operational amplifier, but the external circuit, its characteristics are the same. Op amp is usually 4 parts, bias circuits, input stage, i
2、ntermediate-level, output level, which is generally used input stage differential amplifier circuit (inhibitory power), the middle class in general the use of active load circuit loads the total radio (increase the magnification), the complementary output stage generally symmetrical output stage cir
3、cuit (drive circuit to increase the capacity of the load), here is a brief introduction about the realization of the specific complex. Industries, an operational amplifier used to measure the performance of many of the indicators, the actual operational amplifier is generally believed that the close
4、r the ideal op amp, the better, the classroom involved, we are only asking the equivalent input resistance of infinity, infinite open-loop gain, In fact, there are many other indicators, I will, are you a brief introduction, the performance of operational amplifiers including the five indicators, op
5、en-loop differential-mode voltage amplification factor, the maximum output voltage, differential-mode input resistance, output resistance, common mode rejection ratio CMRR. (Open-loop differential-mode is the magnification on the integrated delivery without additional feedback loop in case of differ
6、ential-mode voltage amplification. Maximum output voltage is saying that it refers to a certain voltage, the integrated operational amplifier is not the largest output voltage distortion peak - peak. differential-mode input resistance reflects the size of integrated operational amplifier input diffe
7、rential-mode input signal to obtain the current size of the source. requiring the greater the better. reflect the size of the output resistance of an integrated transport on the small-signal output load capacity. CMRR shown on the integrated operational amplifier common-mode rejection of input signa
8、ls, which is defined with the differential amplifier circuit. CMRR the better.)Figure 1 op-amp characteristic curveFigure 2 op-amp input and output terminal mapFigure 1 is the characteristic curve of amplifier is generally used only the linear part of curve. As shown in Figure 2. U-corresponding to
9、the terminal -, when the importation of Canadian U-separate from the terminal, the output voltage and input voltage U-RP, the RP-call input. U + corresponding to the terminal +, when the input U + separate from the client to join, the output voltage and U + with the phase, so called in-phase input.
10、Output: U0 = A (U +-U-); A known as the op amps open loop gain (open-loop voltage amplification factor) In the practical application of often idealized op amp, this is because generally speaking, the input resistance OPAMP great open-loop gain, output resistance is very small, can be regarded as ide
11、al, it can be : Ri , Ro 0, A . By A , be U + U-, a result similar to the two inputs can be seen as a short-circuit (referred to as the virtual short), if the input termination in the same direction, the reverse input and almost the same potential (referred to as virtual land). By Ri , we can see tha
12、t similar to the input circuit is equal to 0, it can be seen as the input circuit (known as the virtual shutdown).2 Application of Operational Amplifiers Here only the application of the ideal operational amplifier, the actual op amp can be seen as similar to an ideal operational amplifier. Applicat
13、ion of operational amplifiers is very broad, here we only talk about the op-amp with some focus on other components of the computing circuit. Application of circuit operation in terms of comparison with other more extensive, and easy to understand some of them. Computing the ratio of the circuit inc
14、luding the circuit, and differential circuit, integro-differential circuit, and the index of the number of computing circuit. 1. The proportion of the circuit: The proportion of the so-called circuit is proportional to the input signal amplification circuit, the ratio of the reverse circuit is divid
15、ed into the proportion of the circuit, the circuit with the phase ratio, the ratio of differential circuit. (1) reverse the ratio of the circuit: Reverse the ratio of the circuit shown in Figure 3, the input signal input by adding RP, there are Figure 3 the ratio of the reverse circuit schematicsFig
16、ure 4 with the ratio of circuit schematics=0 =0Know from Kirchhoffs law:= （-）/=（-）/=Thus know that the output voltage U0 and the ratio of input voltage Ui said the relationship between the opposite direction, changing the ratio of coefficients, namely, two resistors of resistance to change can chang
17、e the value of output voltage. Reverse the ratio of operational amplifier circuits for the performance of a certain performance requirements, such as the input signal to a certain load capacity requirements.(2) the ratio of the circuit in the same direction (Figure 4): With the reverse ratio of the
18、circuit is essentially similar, apart from a section of ground in the same direction is the reverse input from= =得：/=(-)/SO: =So as long as the coefficient of change in the proportion of the output voltage can be changed, and U0 and Ui the same direction, of course, with the proportion of the circui
19、t is to have a certain requirements, such as the integrated operational amplifier of the common mode rejection ratio requirements. (3) the ratio of differential circuit (Figure 5):=Input signal, respectively, added to the RP-phase input and input, the specific steps and not in the first two are deri
20、ved almost And in the end be: From this we can see that it is actually completed: two of the input differential signal operation. 2. And the difference circuit: And poor use of the circuit is a relatively wide range of circuits, where the three circuits on the move: Reverse summation circuit to sum
21、the same circuit, and differential circuits. (1) reverse summation circuit and summation circuit in the same direction: Only difference is that the input signal by adding a reversed-phase input with input phase difference, reverse-sum circuit in Figure 6, with the summation circuit in Figure 7. By K
22、irchhoffs current law, reverse summation circuit output voltage and input voltage relationship,= Figure 5 the proportion of the circuit differential circuit Figure 6 Reverse summation circuit schematicsFigure 7 with the circuit diagrams and circuitWith the summation circuit output voltage and the re
23、lationship between the input voltage as follows:=Although the comparison between the two similar, but different, the reverse sum of the characteristics of the circuit with the same RP-circuit ratio. It can be very convenient for the input resistance of a circuit to change the relationship between th
24、e proportion of the circuit without affecting the relationship between the proportion of other routes. And with the application to the summation circuit is not very extensive, mainly because of its better regulation of RP-sum circuit, and its large common-mode input signal. (2) and the difference ci
25、rcuit:Its circuit diagram is shown in Figure 8. The function of this circuit is Ui1, Ui2 carried out by RP-summation of Ui3, Ui4 sum to the same direction, and then superimposed the results obtained and the poor, and his relationship between input and output voltage as follows:=Figure 8 and the diff
26、erential circuit schematicsAs the use of an integrated circuit operational amplifier, and its calculation and the circuit resistance is not easy to adjust, so we used the composition of the secondary operational amplifier integrated circuit and poor. Its circuit diagram as shown in Figure 9, its the
27、 relationship between input and output voltage is:= Figure 9 composed of two integrated operational amplifier circuit schematics and poorIts former level after the level does not affect (in the ideal of integrated operational amplifier), which is very convenient calculation. 3. Integral and differen
28、tial circuit: The above components used are basically resistive element, if one side of the resistor capacitor replaced, then the results will become integral circuits and differential circuits. (1) integral circuit: The circuit shown in figure 10, it can achieve integration and production of comput
29、ing, such as triangular waveform. Integral operation is: the output voltage and input voltage relations were integral. It is the use of capacitive charge and discharge operations to achieve integration, and its input and output voltage relationship:=One: that the initial capacitor voltage at both en
30、ds. If the circuit input voltage waveform is a square, then have a triangular waveform output. (2) differential circuit: Differential circuits and the difference between circuit points just swap the location of resistors and capacitors. Differential is the integral of the inverse operation, its outp
31、ut voltage and input voltage relations showed differential. Circuit diagram shown in Figure 11: its input and output voltage relationship:=Circuit schematics Figure 10 point Figure 11 Differential circuit schematics4. And the index calculation on the number of circuits: Circuit used for a number of
32、diodes, diode characteristics of the most important is one-dimensional conductivity. In the circuit, the current only flows from the diode cathode, anode flow, it is the realization of the characteristics and indicators of the number of circuits. (1) of the number of operation circuits:=Logarithm co
33、mputing circuit output voltage and input voltage was logarithmic function. RP we use the ratio of Rf diode circuit that is formed instead of the number of operations on the circuit. Circuit diagram shown in Figure 12. He relationship between the output of the input voltage isFigure 12 Logarithm comp
34、uting circuit schematicsFigure 13 Index computation circuit schematicsIn fact, transistor can also be used in place of diodes, the principle is the same, in addition to a multi-line connections. (2) index operation circuits:=Index calculation on the number of circuits and circuit computing the diffe
35、rence is only diodes and resistors to each other location, the index is the number of operation circuits computing inverse operation, the index of the diode operation circuits (three tubes) and the resistance R of the exchange can be. Circuit as shown in 13 Its input and output voltage relationshipU
36、se of computing as well as index number and the proportion of poor operation and circuit can be composed of multiplication or division operation circuits and other non-linear operation circuit, will no longer be described here.中文翻译：运算放大器的原理和应用1 运算放大器的原理 运算放大器是目前应用最广泛的一种器件，虽然各中不同的运放结构不同，但对于外部电路而言，其特性
37、都是一样的。运算放大器一般由4个部分组成，偏置电路，输入级，中间级，输出级，其中输入级一般是采用差动放大电路（抑制电源），中间级一般采用有源负载的共射负载电路（提高放大倍数），输出级一般采用互补对称输出级电路（提高电路驱动负载的能力），这里只是简单的介绍一下，具体的实现比较复杂。工业上，用来衡量一个运算放大器的性能的指标有很多，一般认为实际运算放大器越接近理想运放就越好，课堂上我们涉及到的只是要求输入端等效电阻无穷大，开环增益无穷大，其实还有很多其他的指标，我就简要介绍下吧，运算放大器的性能指标包括5个，开环差模电压放大倍数，最大输出电压，差模输入电阻，输出电阻，共模抑制比CMRR。（开环差模
38、放大倍数是指集成运放在无外加反馈回路的情况下的差模电压的放大倍数。最大输出电压是指它是指一定电压下，集成运放的最大不失真输出电压的峰-峰值。差模输入电阻的大小反映了集成运放输入端向差模输入信号源索取电流的大小。要求它愈大愈好。输出电阻的大小反映了集成运放在小信号输出时的负载能力。共模抑制比放映了集成运放对共模输入信号的抑制能力，其定义同差动放大电路。CMRR越大越好。） 图1是运算放大器的特性曲线，一般用到的只是曲线中的线性部分。如图2所示。U-对应的端子为“-”，当输入U-单独加于该端子时，输出电压与输入电压U-反相，故称它为反相输入端。U+对应的端子为“”，当输入U+单独由该端加入时，输出
39、电压与U+同相，故称它为同相输入端。输出：U0= A(U+-U-) ； A称为运算放大器的开环增益（开环电压放大倍数） 在实际运用经常将运放理想化，这是由于一般说来，运放的输入电阻很大，开环增益也很大，输出电阻很小，可以将之视为理想化的，这样就能得到：Ri，Ro0，A。由 A,得到U+U-，于是两个输入端可以近似看作短路（称为“虚短”），如果同向输入端接地，反向输入端与地几乎同电位（称为“虚地”）。由Ri可知，输入端电路近似等于0，故可把输入端看作是断路（称之为“虚断”）。2 运算放大器的应用 这里只谈理想运放的应用，实际运放可以近似看作是理想运放。运算放大器的应用很广泛，这里我们只谈谈由运算
40、放大器加上其他一些集中性元件组成的运算电路。运算电路的应用相对其他而言更加广泛，而且理解起来方便一些。运算电路包括比例电路，和差电路，积分微分电路，对数和指数运算电路。1比例电路： 所谓的比例电路就是将输入信号按比例放大的电路，比例电路又分为反向比例电路、同相比例电路、差动比例电路。（1） 反向比例电路： 反向比例电路如图3所示，输入信号加入反相输入端，有=0 =0由基尔霍夫定律知：= 即（-）/=（-）/得： =由此知道，输出电压U0与输入电压Ui称比例关系，方向相反，改变比例系数，即改变两个电阻的阻值就可以改变输出电压的值。反向比例电路对于运放的性能也有一定的性能要求，比如对输入信号的负载
41、能力有一定的要求.。（2） 同向比例电路（图4）： 跟反向比例电路本质上差不多，除了同向接地的一段是反向输入端，由= =得：/=(-)/即 =于是只要改变比例系数就能改变输出电压，且Ui与U0的方向相同，当然同向比例电路也是有一定要求的，比如对集成运放的共模抑制比要求高. （3） 差动比例电路（图5）： =输入信号分别加在反相输入端和同相输入端，具体的步骤和前两个差不多就不在推导了，最后得到： 由此我们可以看出它实际完成的是：对输入两信号的差运算。 2和差电路： 和差电路也是一种运用比较广泛的电路，这里就举三个电路：反向求和电路，同向求和电路，和差电路。（1） 反向求和电路与同向求和电路： 两
42、者差别只在于输入信号加入了反相输入端与同相输入端的差别，反向求和电路如图6，同向求和电路如图7。由基尔霍夫电流定律，反向求和电路的输出电压和输入电压的关系为: =图5 差动比例电路电路图 图6 反向求和电路电路图同向求和电路的输出电压和输入电压的关系为：=虽然两者比较类似，但还是有区别的，反向求和电路的特点与反相比例电路相同。它可十分方便的某一电路的输入电阻，来改变电路的比例关系，而不影响其它路的比例关系。而同向求和电路的应用不是很广泛，主要由于它的调节不如反相求和电路，而且它的共模输入信号大。（2） 和差电路： 它的电路图如图8所示。此电路的功能是对Ui1、Ui2进行反相求和，对Ui3、Ui
43、4进行同相求和，然后进行的叠加即得和差结果，他的输入输出电压关系为：=图8 和差电路电路图由于该电路用一只集成运放，它的电阻计算和电路调整均不方便，因此我们常用二级集成运放组成和差电路。它的电路图如图9所示，它的输入输出电压的关系是：=它的后级对前级没有影响（采用的是理想的集成运放），它的计算十分方便。3积分和微分电路： 以上用到的元件基本上都是电阻元件，如果其中端的电阻换成电容，那么结果就会变成积分电路和微分电路。 （1） 积分电路： 如图10所示的电路，它可实现积分运算及产生三角波形等。积分运算是：输出电压与输入电压呈积分关系。它是利用电容的充放电来实现积分运算，它的输入、输出电压的关系为
44、：=其中:表示电容两端的初始电压值。如果电路输入的电压波形是方形，则产生三角波形输出。（2） 微分电路： 微分电路与积分电路的区别只是电阻和电容位置互换。微分是积分的逆运算，它的输出电压与输入电压呈微分关系。电路图如图11所示：它的输入、输出电压的关系为：=4对数和指数运算电路： 对数电路使用了二极管，二极管最重要的特性就是单方向导电性。在电路中，电流只能从二极管的正极流入，负极流出，正是利用这个特性而实现了对数和指数电路。（1） 对数运算电路： =对数运算电路输出电压与输入电压呈对数函数。我们把反相比例电路中Rf用二极管代替即组成了对数运算电路。电路图如图12所示。于是他的输出输入电压关系是其实也可以用三极管代替二极管，原理是一样的，除了要多连接一条线路。 （2） 指数运算电路： =指数运算电路与对数运算电路差别仅仅只是把二极管和电阻互相位置，指数运算电路是对数运算的逆运算,将指数运算电路的二极管(三级管)与电阻R对换即可。电路图如13所示它的输入、输出电压的关系为利用对数和指数运算以及比例，和差运算电路，可组成乘法或除法运算电路和其它非线性运算电路，此处就不再介绍了。17