Single-ended signalling

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Single-ended signalling is the simplest 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. This method is the most common means of sending signals down wires.

The main alternative to single-ended signalling is called differential signalling. There is also the historic alternative of ground return, rarely used today.

Single ended signalling is less expensive to implement than differential, but it lacks the ability to reject noise caused by:

1. differences in ground voltage level between transmitting and receiving circuits
2. induction picked up on the signal wire

The main advantage of single-ended over differential signalling 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, plus one for ground. (Differential signalling uses at least 2n wires.) A disadvantage of single-ended signalling 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.

Standards

Single-ended signalling is widely used, and can be seen in numerous common transmission standards, including:

• RS-232 serial communications
• PS/2 mouse and keyboard connectors
• I²C serial bus
• TTL circuits
• CMOS logic circuits
• ECL circuits
• Most parallel computer buses, such as:
  • VMEbus
  • PCI
• VGA video connectors
• SCSI hard disk interfaces
• RCA jacks for audio signals
• TRS connectors for audio signals