Operational Amplifier
The operational amplifier is a basic analog building block
common to a number of electronic functions performed in instrumentation,
computation and control. Op-amp is basically a differential amplifier whose
function is to amplify the difference between two input signals. Op-amp is
available in IC form.
Ideal Op Amp Characteristics
The ideal operational amplifier is shown in the below fig, and
its equivalent circuit. A signal appearing at the negative terminal V1
is inverted at the output, a signal at the positive terminal V2
appears at the output with no change in sign.
Hence the negative terminal is called the “inverting terminal” and the positive terminal the “non-inverting terminal.” In general the output voltage is directly proportional to the difference of the input voltage. The constant of proportionality, - A; is the voltage gain of the amplifier.
Hence the negative terminal is called the “inverting terminal” and the positive terminal the “non-inverting terminal.” In general the output voltage is directly proportional to the difference of the input voltage. The constant of proportionality, - A; is the voltage gain of the amplifier.
(a) Symbol (b) Equivalent Circuit
Characteristics
The ideal op-amp has the following characteristics.
1. Infinite gain A = ∞
2. I1 = I2 = 0 of
infinite input impedance Zi = ∞
3. Zero output impedance ZO =
0
4. Zero output voltage for Vd
= 0 i.e. zero offset
5. Infinite bandwidth Bw = ∞
6. Infinite common mode refection ratio
CMRR = ∞
From the above, it is clear that slightest voltage at the
input will cause it to go into saturation at the output. Hence it is necessary
to apply feedback to obtain finite voltage gain.
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