Supply voltage penetration

The power supply rejection ratio , English Power supply rejection ratio , short PSRR in which are electronics , how much the output voltage of an amplifier changes when the supply voltage is changed. In particular, the term is used for operational amplifiers and their technical description in data sheets.

General

Ideally, the output voltage of an operational amplifier should not change if the supply voltage changes in the permissible supply ranges; the supply voltage feedthrough has the same effects as common mode rejection (CMRR). In real operational amplifiers, non-linear interference effects result in a dependency in the form of the supply voltage penetration which, as a rule, is attempted to be kept as small as possible or, as a suppression factor, to be maximal.

The suppression factor for operational amplifiers is defined as the ratio between a change in the supply voltage and the change in the input offset voltage : ${\displaystyle K_{\mathrm {SVR} }}$ ${\displaystyle \Delta U_{\mathrm {cc} }}$ ${\displaystyle \Delta U_{\mathrm {os} }}$

${\displaystyle K_{\mathrm {SVR} }={\frac {\Delta U_{\mathrm {cc} }}{\Delta U_{\mathrm {os} }}}}$

In the case of a symmetrical power supply , it is assumed that the change in the supply voltage is symmetrical.

The suppression factor is infinite for an ideal operational amplifier without supply voltage penetration and in the range of 100,000 for real operational amplifiers. To avoid bulky values, it is expressed as a logarithmic ratio in decibels : ${\displaystyle K_{\mathrm {SVR} }}$

${\displaystyle PSRR(dB)=20\log _{10}\left({\Delta U_{\mathrm {supply} } \over {\Delta U_{\mathrm {out} }}}\cdot A_{v}\right){\mbox{dB}}}$

The supply voltage penetration is particularly important in the case of quasi-stationary and low-frequency supply voltage changes. At higher frequencies, of the order of magnitude from 10 kHz upwards, as occur with DC voltage converters, changes in the supply voltage act like an additional source of noise .

example

In the case of an operational amplifier with a PSRR of 100 dB, which is used in a circuit with a closed-loop gain of 40 dB, the supply voltage may change by a maximum of 1 V so that the maximum error due to the supply voltage penetration at the output of the operational amplifier is below 1 mV remains.

Individual evidence

1. ^ Ron Mancini: Op Amps for Everyone. Design Reference . 2nd Edition. Elsevier, Oxford 2003, ISBN 0-7506-7701-5 ( E-Book - Chapter 11: Understanding Op Amp Parameters ).