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 and passive parts.

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 and passive parts.

Understanding the Operational Amplifier

The ideal op-amp is a 3-terminal device (ignoring its power supply pins and other feature pins it may have). It has two inputs and one output. One of the inputs is non-inverting, labeled ‘+’ (plus), and the other is inverting and labeled ‘−’ (minus).

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:

V_out = 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. This strange and impractical (at first sight) property is what makes the device such a useful component for circuit designers.

In this video Clemens shows how to use the op-amp equation above to understand circuits that use negative feedback (as do most op-amp circuits).