Operational amplifier theory and applications1 the principle of op-ampOp 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, intermediate-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 circuit (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 closer 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, open-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 differential-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 differential-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 signals, 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 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.Output: U0 = A (U +-U-); A known as the op amp's 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 ideal, 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 thatsimilar 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 AmplifiersHere only the application of the ideal operational amplifier, the actual op amp can be seen as similar to an ideal operational amplifier. Application 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 including 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 divided 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 areFigure 3 the ratio of the reverse circuit schematicsFigure 4 with the ratio of circuit schematicsU P =U N =0 I P =I N =0Know from Kirchhoff's law:I R =I F （U I -U N ）/R =（U N -U O ）/R fU O =I F U RR - Thus know that the output voltage U0 and the ratio of input voltage Ui said therelationship between the opposite direction, changing the ratio of coefficients, namely, two resistors of resistance to change can change 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 circuit is essentially similar, apart from a section of ground in the same direction is the reverse input fromU P =U N =U I I R =I F 得：U N /R =(U O -U N )/R fSO: U O =I F U R R ）（+1 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 circuit 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):U O =)(121I I F U U R R - Input signal, respectively, added to the RP-phase input and input, the specific steps and not in the first two are derived almostAnd 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 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 Figure7. By Kirchhoff's current law, reverse summation circuit output voltage and input voltage relationship,U O =)(332211R U R U R U R I I I F ++-Figure 5 the proportion of the circuit differential circuitFigure 6 Reverse summation circuit schematicsFigure 7 with the circuit diagrams and circuitWith the summation circuit output voltage and the relationship between the input voltage as follows:U O =)(321CI B I A I F R U R U R U R ++ 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 veryconvenient for the input resistance of a circuit to change the relationship between the 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 circuit: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:U O =)(22114433R U R U R U R U R I I I I F --+Figure 8 and the differential 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 secondaryoperational amplifier integrated circuit and poor. Its circuit diagram as shown in Figure 9, it's the relationship between input and output voltage is:U O =)(22114433R U R U R U R U R I I I I F --+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 differential 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 computing, 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:U O =dt U RC I ⎰-1 One: that the initial capacitor voltage at both ends. 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 output voltage and input voltage relations showed differential. Circuit diagram shown in Figure 11: its input and output voltage relationship:U O =I U dt d CR -Circuit schematics Figure 10 pointFigure 11 Differential circuit schematics4. And the index calculation on the number of circuits:Circuit used for a number of 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:U O =ri u U s i T ln - Logarithm computing circuit output voltage and input voltage was logarithmicfunction. 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 computing 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:U O =R e I T iU u SIndex calculation on the number of circuits and circuit computing the difference 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 relationshipUse 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，其特性都是一样的。
