Q.What is loop gain?

Two quantities describe how strongly a feedback loop acts on an amplifier: the feedback factor and the loop gain.

The feedback factor (also called the feedback ratio or feedback fraction), $\beta$, is the ratio of the feedback voltage returned to the input to the total output voltage:

It tells us what fraction of the output is sampled and returned, and it is set by the stable passive elements (resistors, capacitors, inductors) of the feedback network. Because it is fixed by these components, $\beta$ largely controls the closed-loop gain — indeed $A_f \approx 1/\beta$ when the loop gain is large.

The loop gain is the product of the open-loop gain and the feedback factor:

$\text{Loop gain} = A\beta.$ …