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:
differences in ground voltage level between transmitting and receiving circuits
induction picked up on the signal wire
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. A disadvantage of single-ended signaling is that the return currents for all the signals use the same conductor, and this can sometimes cause interference between the signals.
Standards
Single-ended signaling is widely used, and can be seen in numerous common transmission standards, including:
Parallel ATA interfaces for hard drives and other peripherals
Some kinds of connectors, though more often used for balanced pairs, are sometimes used for single-ended operation:
RCA jacks for audio signals
TRS phone connectors for audio signals
Example
The widely used RS-232 system is an example of single-ended signaling, which uses ±12 V to represent a signal, and anything less than ±3 V to represent the lack of a signal. The high voltagelevels give the signals some immunity from noise, since few naturally occurring signals can create a voltage of such magnitude. They also have the advantage of requiring only one wire per signal. However, they also have a serious disadvantage: they cannot run at high speeds. The effects of capacitance and inductance, which filter out high-frequency signals, limit the speed.
