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LVDS (Low-Voltage Differential Signaling)

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LVDS is an industry standard that defines a high-speed, low-power, data-signaling technique that is implemented in a variety of connection technologies. The fastest and longest SCSI disk interfaces implement LVDS. LVDS is also used in new high-speed switching fabrics such as InfiniBand, and in system area networks. LVDS is also used in digital camera interfaces and has even been used to drive LCD displays in laptop computers. LVDS is defined by ANSI/TIA/EIA-644 (EIA-644), which specifies electrical characteristics of the driver output and receiver input. Guidelines for bus configuration, cables, and termination are given, but protocols, connectors, and bus structures are not defined in the standards.

LVDS overcomes some of the limitations of more traditional signaling standards such as RS-422. LVDS cuts down on noise and boosts data rates by using extremely low voltage levels (350 mV compares to 2.4 V), which translates to low radiation and less power consumption. Most important, differential signaling allows the receiver to filter out noise. This is done by sending signals across two wires simultaneously, each with opposing current and voltage swings. The actual data is read as the difference in amplitude between the signals on the two wires. If noise is induced, it will appear on both lines, but the signal information remains unchanged. Since the signal has improved noise immunity, voltage can be reduced and data rate can be increased.

LVDS is ideal for building high-speed multipoint switching fabrics directly onto backplanes. The current trend is to move away from parallel buses like PCI to high-speed switching fabrics that allow simultaneous point-to-point transmissions between multiple components and devices. Normally, the close spacing in such a design would create noise and signal interference. BLVDS (bus LVDS), developed by National Semiconductor, supports low-power, high-speed multipoint switching with low noise and interference. According to Texas Instruments, LVDS drivers and receivers can support speeds up to 400 Mbps, consume 1/8 the power of RS-422, and radiate 1/10 the EMI of the best single-ended input/output (I/O).

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