Op-Amp

Op-Amp - The basic applications of operational...

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The basic applications of operational amplifier(op-amp) 1/7 The basic applications of operational amplifier(op-amp) Sheng Bao 1. Ideal op-amp An ideal op-amp is such an op-amp that has infinite gain ,infinite input impedance and zero output impedance. The gain is so high that the output attempts to do whatever is necessary to make the voltage difference between the inputs zero.So we can consider the voltage of two input terminal is the same,thus,virtual short.This is the voltage rule of the socalled op-amp golden rules. In many conditions we connect an ideal op-amp in a negative feedback network.The effect of feedback is so big that we consider the inputs draw is zero.This is the current rule of the op-amp golden rules. This two golden rules is the base of our following study. Generally speaking, there is no problem with ideal op-amp that can’t be solved with these two rules. 2. Inverting amplifier and noninverting amplifier This two applications are the basic usage of op-amp.Finally you will find that the gain of these two circuit is not depent on the performance of your amplifier but the resistors that connected with the op-amp. Fig.1 shows the schematic of an inverting amplifier.The input signal is send to inverting terminal.We can conclude that the close-loop gain is 2 1 O I vR A == eq.(1) According to eq(1) the inverting amplifier actually multiplies v I with A and outputs the result v O . So we can see that this circuit can do time operation. Based on this result, the summing amplifier was invented.The output voltage v o is given by 123 12 3 () ff f OI I I RRR vv v v RR R =− + + eq .(2) If R 1 =R 2 =R 3 =R,we obtain f I I R v v R + + eq.(3)
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The basic applications of operational amplifier(op-amp) 2/7 It is obviously a sum operation. To reduce the error, a resistor, R eq is required.The resistance of R eq is given by 12 3 // // / eq f R RR R R = eq.(4) Next, we will talk about the noninverting amplifier.
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This note was uploaded on 01/25/2012 for the course EE 3220 taught by Professor Audiffred during the Spring '06 term at LSU.

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Op-Amp - The basic applications of operational...

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