Power supply rejection ratio

The supply voltage feedthrough, English Power supply rejection ratio, PSRR short, in electronics indicates how much the output voltage of an amplifier changes when changing the supply voltage. In particular, the term is used in amplifiers and their technical description in data sheets.

General

Ideally, the output voltage of an operational amplifier should not change when the supply voltage changes in the permitted areas of care, the supply voltage feedthrough has it the same effect as the common-mode rejection ratio (CMRR ). In real operational amplifiers According occurs not ideal parasitics to a dependency in the form of the supply voltage penetration, which is usually attempted to keep as small as possible or as a suppression factor should be maximum.

The suppression factor is defined as the ratio between the operational amplifiers in a change in the supply voltage and the change in input offset voltage:

For a symmetrical voltage supply is provided that the change in the supply voltage is symmetrical.

The suppression factor is infinite for an ideal operational amplifier without power penetration and real operational amplifiers in the order of 100,000. To avoid unwieldy large values ​​, it is expressed as a logarithmic ratio in decibels:

The supply voltage feedthrough is mainly in the quasi-stationary and low supply voltage changes of meaning. At higher frequencies, the size from 10 kHz upwards as they occur in DC-DC converters to supply voltage changes affect as an additional noise source.

Example

In an operational amplifier with a PSRR of 100 dB, which is used in a circuit having a loop gain of 40 dB, the power supply voltage is allowed to change by no more than 1 V, so that the maximum error, according to the supply voltage through the handle at the output of the operational amplifier is less than 1 mV.