Low-voltage Differential Signaling - Multipoint LVDS

Multipoint LVDS

The original LVDS standard only envisioned driving a digital signal from one transmitter to one receiver in a point-to-point topology. However, engineers using the first LVDS products soon wanted to drive multiple receivers with a single transmitter in a multipoint topology. As a result NSC invented Bus LVDS (BLVDS) as the first variation of LVDS designed to drive multiple LVDS receivers. It uses termination resistors at each end of the differential transmission line to maintain the signal integrity. Double termination is necessary because it is possible to have one or more transmitters in the center of the bus driving signals toward receivers in both directions. The difference from standard LVDS transmitters was increasing the current output in order to drive the multiple termination resistors. In addition, the transmitters need to tolerate the possibility of other transmitters simultaneously driving the same bus.

Bus LVDS and LVDM (by TI) are de facto multipoint LVDS standards. Multipoint LVDS (MLVDS) is the TIA standard (TIA-899). The AdvancedTCA standard specified MLVDS for clock distribution across the backplane to each of the computing module boards in the system.

MLVDS has two types of receivers. Type-1 is compatible with LVDS and uses a +/- 50 mV threshold. Type-2 receivers allow Wired-Or signaling with M-LVDS devices. For MLVDS: