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 where the two conductors carry signals equal in magnitude but of opposite electric polarity.
Single-ended signaling is less expensive to implement than differential, but it has a distinct disadvantage: a single-ended system requires a power supply voltage equal to the maximum amplitude of the signal to be received whereas a differential system only requires a voltage half of the signal amplitude to be received. For a given power supply voltage then, a differential system produces signals of twice the amplitude and therefore has twice as good noise immunity (6 dB higher signal-to-noise ratio) as a single-ended system.
