2.3.5.3 B-LVDS/M-LVDS

Bus LVDS (B-LVDS) and Multipoint LVDS (M-LVDS) specifications extend the existing LVDS standard to high-performance multipoint bus applications. Multidrop and multipoint bus configurations may contain any combination of drivers, receivers, and transceivers. SoC Products Group LVDS drivers provide the higher drive current required by B-LVDS and M-LVDS to accommodate the loading. The drivers require series terminations for better signal quality and to control voltage swing. Termination is also required at both ends of the bus since the driver can be located anywhere on the bus. These configurations can be implemented using the TRIBUF_LVDS and BIBUF_LVDS macros along with appropriate terminations. Multipoint designs using SoC Products Group LVDS macros can achieve up to 200 MHz with a maximum of 20 loads. A sample application is given in the following figure. The input and output buffer delays are available in the LVDS section in Table 2-66.

Example: For a bus consisting of 20 equidistant loads, the following terminations provide the required differential voltage, in worst-case military operating conditions, at the farthest receiver: R_S = 60Ω and R_T = 70Ω, given Z₀ = 50Ω (2 in) and Z_stub = 50Ω (~1.5 in).