What this clock buffer does on a PCIe board
The Cypress CY2304NZZXI-1T is a zero-delay clock buffer designed for PCI Express reference clock distribution. It takes one LVCMOS or LVTTL input and delivers four identical LVCMOS outputs at up to 140 MHz, with a 1:4 fanout ratio. There is no PLL inside — this is a buffer, not a synthesizer, so the output frequency equals the input frequency with added deterministic delay.
The 140 MHz maximum output frequency covers the 100 MHz reference clock used by PCIe Gen1, Gen2, and Gen3. Gen4 and Gen5 run at higher data rates but still use a 100 MHz reference, so this buffer is fine for those too — the limiting factor is the edge rate and jitter on the output, not the frequency. Because it is a zero-delay buffer (not a PLL), the output tracks the input phase with minimal skew, which simplifies timing closure in a multi-load clock tree.
It is surface-mount only.