IEEE Standard for Low-Voltage Differential Signals (LVDS) for Scalable Coherent Interface (SCI)

Scalable Coherent Interface (SCI), specified in IEEE Std 1596-1992, provides computer-bus-like services but uses a collection of fast point-to-point links instead of a physical bus in order to reach far higher speeds. The base specification defines differential ECL signals, which provide a high transfer rate (16 bits are transferred every 2 ns), but are inconvenient for some applications. IEEE Std 1596.3-1996, an extension to IEEE Std 1596-1992, defines a lower-voltage differential signal (as low as 250 mV swing) that is compatible with low-voltage CMOS, BiCMOS, and GaAs circuitry. The power dissipation of the transceivers is low, since only 2.5 mA is needed to generate this differential voltage across a 100 W termination resistance. Signal encoding is defined that allows transfer of SCI packets over data paths that are 4-, 8-, 32-, 64-, and 128-bits wide. Narrow data paths (4 to 8 bits) transferring data every 2 ns can provide sufficient bandwidth for many applications while reducing the physical size and cost of the interface. The wider paths may be needed for very-high-performance systems.