Differential pair

A differential pair (or differential signalling) is a way of sending a signal that has a number of advantages:

• It can use lower voltages to achieve a given signal-to-noise ratio
• It is less susceptible to interference
• It produces less interference
• It allows connecting two entities without having to have a common ground

It consists of sending two 'copies' of a signal down a pair of conductors (a balanced pair, for best results); one signal is the inversion of the other. At the destination, the second is subtracted from the first; any noise that has been picked up in common on both conductors is thereby removed.

This reduction in noise allows use of a lower voltage to send a signal. Also, since the return path for the current of the signal in the first conductor is not ground, but the inverse current in the second conductor, this tends to cancel any electro-magnetic radiation from that current.