1.2 Signal Gain and Noise Gain

When working with operational amplifiers, a common term used is A_V, also known as gain. Specifically, A_V refers to Signal Gain, which is equal to the ratio of the output signal over the input signal:

A_{v} = \frac{V_{O U T}}{V_{I N}}

Another term sometimes used with operational amplifiers is called Noise Gain (NG). NG is the gain seen by the small, parasitic voltage sources in series with the device inputs. By analyzing the NG response with frequency, the stability of the operational amplifier's circuit can be determined.

Another use of NG is to predict the change in the Signal-to-Noise Ratio (SNR) with frequency. Some configurations of the operational amplifier have a flat response between Av and NG, such as in unity gain or non-inverting amplifier.

However, in other cases, the NG may increase faster than A_V, which implies a reduction of the SNR at higher gains.