In electronic systems, power supply rejection ratio (PSRR), also supply-voltage rejection ratio[1] (kSVR; SVR), is a term widely used to describe the capability of an electronic circuit to suppress any power supply variations to its output signal.
In the specifications of operational amplifiers, the PSRR is defined as the ratio of the change in supply voltage to the equivalent (differential) output voltage it produces,[2] often expressed in decibels.[3][4][5] An ideal op-amp would have infinite PSRR, as the device should have no change to the output voltage with any changes to the power supply voltage. The output voltage will depend on the feedback circuit, as is the case of regular input offset voltages. But testing is not confined to DC (zero frequency); often an operational amplifier will also have its PSRR given at various frequencies (in which case the ratio is one of RMS amplitudesofsinewaves present at a power supply compared with the output, with gain taken into account). Unwanted oscillation, including motorboating, can occur when an amplifying stage is too sensitive to signals fed via the power supply from a later power amplifier stage.
Some manufacturers specify PSRR in terms of the offset voltage it causes at the amplifiers inputs; others specify it in terms of the output; there is no industry standard for this issue.[6] The following formula assumes it is specified in terms of input:
![{\displaystyle {\text{PSRR}}[{\text{dB}}]=10\log _{10}\left({\frac {\Delta {V_{\text{supply}}}^{2}{A_{v}}^{2}}{\Delta {V_{\text{out}}}^{2}}}\right){\text{dB}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/a6b040511edd46a405ed30c914ff5c96ae70ed15)
where 
For example: an amplifier with a PSRR of 100 dB in a circuit to give 40 dB closed-loop gain would allow about 1 millivolt of power supply ripple to be superimposed on the output for every 1 volt of ripple in the supply. This is because
.And since that's 60 dB of rejection, the sign is negative so:
Note:
