Which choice best describes common mode rejection?

Common mode rejection refers to the ability of a differential amplifier to reject signals that are present simultaneously on both the positive and negative inputs. This is crucial in many applications, particularly in medical equipment such as electrocardiograms (ECGs), where it's essential to amplify the desired signals (like heart activity) while minimizing interference and noise that might be common to both input channels.

By focusing on rejecting these common signals, a differential amplifier enhances the quality of the desired output by ensuring that only the differential signal, which represents the actual information of interest, is amplified. This ability is quantified by the common mode rejection ratio (CMRR), which measures how effectively the amplifier suppresses these unwanted signals.

In contrast, the other choices do not accurately define common mode rejection. The first option relates to signal-to-noise ratios, which focuses on distinguishing useful signals from random noise rather than specifically on the commonality of those signals across inputs. The second option is more related to harmonic analysis rather than common mode interference. The third option speaks to measurements of waveform characteristics that do not pertain directly to how input signals are processed in terms of commonality.

Thus, the choice that encapsulates the concept of common mode rejection's functionality is the one identifying its role in rejecting