The principle is: twist two insulated wires together, and the interference signal acts on the two twisted wires in the same way (this interference signal is called common mode signal), in the differential circuit that receives the signal The common mode signal can be eliminated to extract the useful signal (differential mode signal). The function of the twisted pair is to make the noise generated by external interference on the two wires (in the professional field, the useless signal is called noise) the same, so that the subsequent differential circuit can extract the useful signal. The differential circuit is a subtraction circuit. The in-phase signals (common-mode signals) of the two input terminals cancel each other (m-n), and the anti-phase signals are equivalent to x-(-y) and are enhanced.