Lvds Introduction - Aaeon VIA Eden Series User Manual

LVDS Introduction

Low Voltage Differential Signaling is a low noise, low power, low amplitude
method for high-speed (gigabits per second) data transmission over
copper wire.
LVDS differs from normal input/output (I/O) in a few ways: Normal digital
I/O works with 5 volts as a high (binary 1) and 0 volts as a low (binary 0).
When you use a LVDS, you add a third option (-5 volts), which provides
an extra level with which to encode and results in a higher maximum data
tranfer rate.
A higher data transfer rate means fewer wires are required, as in UW (Ultra
Wide) and UW-2/3 SCSI harddrive, which use only 68 wires. These
devices require a high transfer rate over short distance. Using standard I/
O transfer, SCSI hard drives would require a lot more than 68 wires. Low
voltage means that the standard 5 volts is replaced by either 3.3 volts or
1.5 volts. LVDS uses a dual wire system, running 180 degrees of each
other. This enables noise to travel at the same level, which in turn can get
filtered more easily and effectively.
With standard I/0 signaling, data storage is contingent upon the actual
voltage level. Voltage level can be affected by wire length (longer wires
increase resistance, which lowers voltage). But with LVDS, data storage is
distinguished only by positive and negative voltage values, not the
voltage level. Therefore, data can travel over greater length of wire while
maintaining a clear and consistent data stream.
Chapter 1 General Information 3