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Operational amplifier theory and applications

1 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, 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 curve

Figure 2

op-amp input and output terminal map

Figure 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#39;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 asymp; infin;, Ro asymp; 0, A asymp; infin;. By A asymp; infin;, be U asymp; 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 asymp; infin;, we can see that 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. 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.

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 are

Figure 3

the ratio of the reverse circuit schematics

Figure 4

with the ratio of circuit schematics

U_P= U_N= 0 I_P = I_N= 0

Know from Kirchhoff#39;s law:

I_R = I_F U_I - U_N / R = U_N - U_O / R_f

U_O= U_I

Thus know that the output voltage U₀ and the ratio of input voltage U_i said the relationship 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 from

U_P = U_N = U_I I_R = I_F U_N / R = (U_O- U_N) / R_f

SO: U_O = (1 ) U_{I 剩余内容已隐藏，支付完成后下载完整资料}