Understanding the Operational Amplifier

Even though the operational amplifier or op-amp is not a discrete component like a resistor or a capacitor, its behavior is described by a few simple rules that are as easy to understand as those of discrete parts.

The ideal op-amp is a 3-terminal device. It has two inputs and one output. One of the inputs is non-inverting, labeled ‘+’, and the other is inverting and labeled ‘−’.

The inputs of the ideal op-amp have infinite impedance, meaning that no current can flow into them.
All the op-amp does is amplify the voltage difference present on its inputs, like this:

Vout = A • (V+ − V−)

When the op-amp is ideal, then the amplification or gain ‘A’ is infinite. In real life ‘A’ is not infinite, of course, but very large, so large that in many circuits it can be considered infinite.

0:00 Intro
0:25 The operational amplifier (op-amp)
2:01 The comparator
2:59 Negative feedback
4:21 The inverting amplifier
5:44 The non-inverting amplifier
6:50 A last question
7:16 Thank you for watching

* John R. Ragazzini et al., “Analysis of problems in dynamics by electronic circuits”, Proceedings of the IRE, vol. 35. p. 444, May 1947.
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