 Common-mode voltage

For a differential signal pair, the common-mode voltage is the average potential of the two conductors relative to a specified local reference:It is the component shared by both inputs. With $V_{+}=2.6$ V and $V_{-}=2.4$ V, the common component is 2.5 V and the differential component is 0.2 V. A 1 V change of the receiver's reference changes both measured conductor potentials equally and therefore changes $V_c$, while leaving $V_d$ unchanged.^[ref]

This decomposition is useful when a small sensor difference sits on a large shared offset. Even a receiver with excellent common-mode rejection ratio has a finite permitted common input range. A practical test therefore varies the average input while holding the difference fixed and checks when the output stops following its differential-gain calibration.