In a non-inverting amplifier configuration using an operational amplifier, how does the common-mode rejection ratio (CMRR) influence the performance of a voltage follower circuit?

In a voltage follower, the op‑amp’s output is meant to copy the input voltage exactly, so any noise or unwanted signals that appear on both the inverting and non‑inverting inputs should be cancelled. The common‑mode rejection ratio, or CMRR, tells us how well the amplifier can ignore a signal that is present on both inputs at the same time; a higher CMRR means the follower will reject that common‑mode noise more effectively. If the CMRR is low, the follower will let some of that noise leak into the output, degrading the fidelity of the copied voltage. For example, if a 1 V common‑mode voltage appears on both inputs and the CMRR is 80 dB, only about 0. 1 mV of that noise will appear at the output, whereas a CMRR of 40 dB would let about 10 mV leak through.