Bus-LVDS Emulated (BLVDSE25) Output Mode

BLVDS is used in multipoint, bidirectional, and heavily-loaded backplane applications. The effective impedance of these systems is lower than a typical pair of PCB traces due to the backplane capacitance, the connectors on the backplane, and the line stubs. The following illustration shows an example of BLVDS implementation using 90 Ω stub resistors at every drop and 55 Ω stub resistors on either side of the bus. The termination values at the end of the bus, which can range anywhere between 45 Ω and 90 Ω, must be optimized to match the effective differential impedance of the bus. In this example, the two parallel 55 Ω stub resistors yield an effective 27 Ω differential termination.

Figure 1. Bus-LVDSE System Diagram