In op-amps, which statement best describes PSRR?

• A. PSRR is the ratio of output change to input under all conditions.
• B. PSRR is the ratio of differential gain to common-mode gain.
• C. PSRR is how much output changes with supply variation.
• D. PSRR measures temperature stability of the input stage.

Answer: (C)

PSRR, or Power Supply Rejection Ratio, measures how much the output of an op-amp changes when the supply voltage varies. The best description is that PSRR tells you how much the output shifts due to supply fluctuations, since a higher PSRR means the circuit rejects those supply changes more effectively and keeps the output stable. In practice PSRR is often expressed as a ratio (or in dB) of supply variation to the resulting output variation, so the direct idea—output change caused by supply variation—captures the concept. Other options describe different notions: a general output-to-input ratio under all conditions isn’t specific to supply rejection, the ratio of differential to common-mode gain is CMRR, and temperature stability of the input stage concerns how temperature affects the input circuitry rather than supply-induced output changes.