Differential signal

Elimination of interference when using differential signals. The interference is added to two signals inverted between each other, without changing their difference.

Differential signal - a method of electrical information transmission using two antiphase signals . In this method, one electrical signal is transmitted in the form of a differential pair of signals, each in its own conductor, but one represents the inverted signal of the other, opposite in sign. A pair of conductors can be a twisted pair , a twinaxial cable, or wired on a printed circuit board . A differential signal receiver responds to the difference between two signals, and not to the difference between one wire and ground potential (this principle is used in another transmission method - called asymmetric signaling).

The differential signal is similar to a balanced (symmetrical) signal, providing similar advantages of high-quality high-frequency communication, protected from common mode interference. The high-frequency properties of a balanced connection are partly due to the fact that it is better described as a long waveguide line, the losses in which are mainly determined by the dielectric. At the same time, with a single-wire (unbalanced) connection, losses are determined only by the resistance of the metal, and grow rapidly with frequency due to the skin effect .

The differential signal provides practical convenience for signal connection within a printed circuit board between microcircuits made using similar technology. However, due to its implementation on unipolar output stages of microcircuits, it contains a constant component. As a rule, the output differential port cannot be directly connected to symmetrical transmission lines or antennas without special coordination. In cases where the dimensions and cost of the board are allowed, such coordination and simultaneous balancing are easily achieved using circuits on matching transformers and baluns .

Differential pairs are usually used for high-speed data transmission channels on printed circuit boards , in twisted pair (including shielded ^[1] ), in ribbon cables and connectors. High-speed differential pairs are often connected to SerDes SF units (Serializer / Deserializer).