Differential signalling
The pair of conductors can be wires in a twisted-pair or ribbon cable or traces on a printed circuit board.
Electrically, the two conductors carry voltage signals which are equal in magnitude, but of opposite polarity.
The electronics industry, particularly in portable and mobile devices, continually strives to lower supply voltage to save power.
Differential signalling helps to reduce these problems because, for a given supply voltage, it provides twice the noise immunity of a single-ended system.
Another difficulty is the electromagnetic interference that can be generated by a single-ended signalling system that attempts to operate at high speed.
[citation needed] When transmitting signals differentially between two pieces of equipment it is common to do so through a balanced interface.
In theory, it can reject any interference so long as it is common-mode (voltages that appear with equal magnitude and the same polarity in both conductors).
[3] There exists great confusion as to what constitutes a balanced interface and how it relates to differential signalling.
[3] The technique minimizes electronic crosstalk and electromagnetic interference, both noise emission and noise acceptance, and can achieve a constant or known characteristic impedance, allowing impedance matching techniques important in a high-speed signal transmission line or high-quality balanced line and balanced circuit audio signal path.
Differential signalling often uses length-matched wires or conductors which are used in high speed serial links.
Single-ended signalling is typically used with coaxial cables, in which one conductor totally screens the other from the environment.
All screens (or shields) are combined into a single piece of material to form a common ground.
A balanced pair of microstrip lines is a convenient solution because it does not need an additional PCB layer, as a stripline does.
Low crosstalk is important when many lines are packed into a small space, as on a typical PCB.
SCSI-1 variations included a high voltage differential (HVD) implementation whose maximum cable length was many times that of the single-ended version.
Low-voltage differential signalling (LVDS), on the other hand, is a specific system defined by a TIA/EIA standard.
This can be utilized to simplify or improve the routing of high-speed differential pairs of traces on printed circuit boards in hardware development, to help to cope with common cabling errors through swapped wires, or easily fix common design errors under firmware control.
