Noise gain of an operational amplifier
= Noise gain of an operational amplifier
{title2=$G_{\rm n}=1/\beta$}
The closed-loop gain from an equivalent differential input-<voltage> disturbance to the output is the noise gain. For an ideal-input <inverting amplifier>, $\beta=R_1/(R_1+R_2)$ and $G_{\rm n}=1+R_2/R_1$, although the <voltage gain> is $-R_2/R_1$. A dominant-pole amplifier has approximate closed-loop <bandwidth> $f_T/G_{\rm n}$ when loop gain is large at low frequency and the circuit is stable.