The NB4N121K is a Clock differential input fanout distribution 1 to 21 HCSL level differential outputs, optimized for ultra low propagation delay variation. The NB4N121K is designed with HCSL clock distribution for FBDIMM applications in mind. Inputs can accept differential LVPECL, CML, or LVDS levels. Single-ended LVPECL, CML, LVCMOS or LVTTL levels are accepted with the proper VREFAC supply (see Figures 5, 10, 11, 12, and 13). Clock input pins incorporate an internal 50 W on die termination resistors.