Single-ended signaling is the simplest and most commonly used method of transmitting electrical signals over wires. One wire carries a varying voltage that represents the signal, while the other wire is connected to a reference voltage, usually ground.
The main alternative to single-ended signaling is called differential signaling. There is also the historic alternative of ground return, rarely used today.
Single ended signaling is less expensive to implement than differential, but it lacks the ability to reject noise caused by:
The main advantage of single-ended over differential signaling is that fewer wires are needed to transmit multiple signals. If there are n signals, then there are n+1 wires - one for each signal and one for ground. (Differential signaling uses at least 2n wires.) A disadvantage of single-ended signaling is that the return currents for all the signals share the same conductor (even if separate ground wires are used, the grounds are inevitably connected together at each end), and this can sometimes cause interference ("crosstalk") between the signals.
Single-ended signaling is widely used, and can be seen in numerous common transmission standards, including:
Some kinds of connectors, though more often used for balanced pairs, are sometimes used for single-ended operation: