common-mode rejection ratio (CMRR)
PrintA measure of an instrument's ability to reject an undesired signal that is common to both input terminals.
Also, CMRR describes the ability of a differential amplifier to reject interfering signals common to both inputs, and to amplify only the difference between the inputs. A differential-input instrumentation amplifier has both normal-mode (differential) gain and common-mode gain. The normal-mode gain is the amplification of the difference between the positive and negative inputs, and ideally has such values as 1, 10, or 100. The common-mode gain refers to signals appearing at the output of the amplifier resulting from the same (that is, common) signals appearing at both of the inputs. Because the amplifier is expected to ignore common-mode signals, the common-mode gain is usually very low and is ideally zero. The CMRR is the ratio of the normal-mode gain to the common-mode gain and is usually expressed in dB. The higher the CMRR, the better the amplifier can extract differential signals in the presence of common-mode noise. Click for a demo of CMRR using the LabVIEW Player.
Units:
dB
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