Four clock buffer ICs provide reference clocks for PCI Express Gen2 at 5 Gbits/s, and FBDIMM memory modules. The devices include the PI6C20400S with four differential outputs; the PI6C20800S with eight differential outputs, each with one spread-spectrum-compatible PLL; and the PI6C21900 (18+1) and PI6C21900S (17+2) with 19 total differential outputs, using two spread-spectrum-compatible PLLs and offering separate frequency domains for FBDIMM and PCIe applications.