What is the primary effect of a high Power Supply Rejection Ratio (PSRR) on the performance of an operational amplifier (op-amp) gain in a circuit?

A high Power Supply Rejection Ratio means that changes in the op‑amp’s supply voltage have very little effect on the device’s internal bias currents, so the amplifier’s offset and bias currents stay essentially unchanged. Because the bias currents determine the voltage drop across the input and feedback resistors, keeping them constant preserves the intended voltage division and therefore the exact gain specified by the resistor network. In practice this means that the op‑amp will keep the same closed‑loop gain even when the supply voltage fluctuates or has ripple, preventing the gain from drifting. For example, if a circuit is designed for a 100× gain and the supply voltage rises by 10 mV, a high‑PSRR op‑amp will change its output by only a few microvolts, whereas a low‑PSRR device might shift the gain by several percent. Thus, a high PSRR keeps the op‑amp’s gain stable and accurate under varying supply conditions.