
Operational amplifier
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An operational amplifier (opamp) is an electronic amplifier of direct current, with a differential input and usually one output. Such an amplifier has a very high gain.
History
The operational amplifier was originally developed in the 1930s. The operational amplifier was designed to perform mathematical operations (hence the name  operational amplifier) as part of the first analog electronic computers (with mathematical operations  addition, subtraction, integration, differentiation, etc.) In the 60s an American Fairchild Semiconductor company developed the world's first opamp in the form of a microcircuit.
Operating principle
The differential input (from the Latin differentia  "difference") of the device consists of a noninverting (V_{in+}) and inverting (V_{in}) inputs. See Fig. 1.
Fig. 1. Operational amplifier  conventional graphic designation
An ideal opamp amplifies the difference in voltage at the inputs of the operational amplifier, while the commonmode signal (that is, coinciding in magnitude and phase at both inputs) does not affect the resulting voltage.
To calculate the output voltage V_{out} at the output of an ideal operational amplifier, the formula is used:
V_{out} = K × (V_{1} − V_{2})
where:
 V_{1} and V_{2} are the voltage at the noninverting and inverting inputs, respectively;
 K is the gain in the absence of feedback.
In practice, such a circuit (without feedback) is not used, with the exception of the comparator circuit. Most commonly used in 741 and LM308 chips.
Comparison of parameters of ideal and real operational amplifier
Parameter

Ideal operational amplifier

Real operational amplifier

Operational amplifier gain without feedback (K)

Equals infinity

Is in the range 10^{4} ÷ 10^{5}

Output voltage (V_{out})

In the range from minus infinity to plus infinity

Vout is limited by the supply voltage range

Input resistance

Equals infinity

The resistance is very high and has little effect on the input signal

Input current and offset voltage

The zeros

They have small but real meanings

Bandwidth

Infinitely large

It is impossible to implement this in practice

Output voltage slew rate

Infinitely large

It is impossible to implement this in practice

Intrinsic noise

Complete absence of own noise

It is impossible to implement this in practice

Common mode rejection ratio

Infinitely large

It has great importance, but not infinite

Influence of power supply noise and ripple

Complete absence

Little influence

Output resistance

Equals zero

In a real op amp the output resistance is not zero, so the output current affects the output voltage (as the load resistance decreases, the output voltage decreases)

Typical circuits for using an operational amplifier are:
 Comparator
 Voltage follower
 Differential amplifier
 Inverting amplifier
 Summing amplifier  inverting amplifiersummer
 Noninverting amplifier
 Integrator
 Differentiator
 Selfoscillating generator (multivibrator) of rectangular pulses
 Peak detector
 Analog signal sampleandhold circuit
 Instrumentation amplifier
Use our online Operational Amplifier Gain Calculator.
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