Single-ended signaling

Single-ended signaling is the simplest and most com-monly used method of transmitting electrical signals overwires. One wire carries a varying voltage that representsthe signal, while the other wire is connected to a referencevoltage, usually ground.The main alternative to single-ended signaling is calleddifferential signaling. There is also the historic alternativeof ground return, rarely used today.Single ended signaling is less expensive to implement thandifferential, but it lacks the ability to reject noise causedby:

1. differences in ground voltage level between trans-mitting and receiving circuits

2. induction picked up on the signal wire

The main advantage of single-ended over differential sig-naling is that fewer wires are needed to transmit multiplesignals. If there are n signals, then there are n+1 wires -one for each signal and one for ground. (Differential sig-naling uses at least 2n wires.) A disadvantage of single-ended signaling is that the return currents for all the sig-nals share the same conductor (even if separate groundwires are used, the grounds are inevitably connected to-gether at each end), and this can sometimes cause inter-ference ("crosstalk") between the signals.

1 Standards

Single-ended signaling is widely used, and can be seen innumerous common transmission standards, including:

RS-232 serial communications

PS/2 mouse and keyboard connectors

IC serial bus

TTL circuits

CMOS logic circuits

ECL circuits

Most parallel computer buses, such as:

VMEbus PCI

VGA video connectors

SCSI interfaces for hard drives and other peripherals

Parallel ATA interfaces for hard drives and other pe-ripherals

Some kinds of connectors, though more often used forbalanced pairs, are sometimes used for single-ended op-eration:

RCA jacks for audio signals

TRS phone connectors for audio signals

2 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 sig-nal. The high voltage levels give the signals some immu-nity from noise, since few naturally occurring signals cancreate a voltage of such magnitude. They also have theadvantage of requiring only one wire per signal. However,they also have a serious disadvantage: they cannot run athigh speeds. The effects of capacitance and inductance,which filter out high-frequency signals, limit the speed.Large voltage swings driving long cables also require sig-nificant power from the transmitting end. This problemcan be reduced by using smaller voltages, but then thechance of mistaking random environmental noise for asignal becomes much more of a problem.

1

https://en.wikipedia.org/wiki/Electrical_signalhttps://en.wikipedia.org/wiki/Wirehttps://en.wikipedia.org/wiki/Voltagehttps://en.wikipedia.org/wiki/Ground_(electricity)https://en.wikipedia.org/wiki/Differential_signalinghttps://en.wikipedia.org/wiki/Single-wire_earth_returnhttps://en.wikipedia.org/wiki/Current_(electricity)https://en.wikipedia.org/wiki/Crosstalkhttps://en.wikipedia.org/wiki/RS-232https://en.wikipedia.org/wiki/IBM_Personal_System/2https://en.wikipedia.org/wiki/I%C2%B2Chttps://en.wikipedia.org/wiki/Transistor-transistor_logichttps://en.wikipedia.org/wiki/CMOShttps://en.wikipedia.org/wiki/Emitter_coupled_logichttps://en.wikipedia.org/wiki/VMEbushttps://en.wikipedia.org/wiki/Peripheral_Component_Interconnecthttps://en.wikipedia.org/wiki/Video_Graphics_Arrayhttps://en.wikipedia.org/wiki/SCSIhttps://en.wikipedia.org/wiki/Parallel_ATAhttps://en.wikipedia.org/wiki/RCA_jackhttps://en.wikipedia.org/wiki/Phone_connector_(audio)https://en.wikipedia.org/wiki/RS-232https://en.wikipedia.org/wiki/Capacitancehttps://en.wikipedia.org/wiki/Inductance

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