BUFGs

BUFGs, or global clock buffers, are specialized primitives in many field-programmable gate arrays (FPGAs) designed to distribute clock signals across the device with minimal skew and jitter. A BUFG takes a clock source—such as an input clock pin, a phase-locked loop (PLL) output, or a clock management tile output—and fans it out into the FPGA’s global clock routing network. From there, the clock is delivered to a large portion of flip-flops, latches, and other synchronous elements, helping ensure that clock arrival times are as uniform as possible across the fabric.

BUFGs are implemented as dedicated resources separate from the general routing fabric to isolate clock paths from data paths and reduce routing-induced skew. In practice, a design typically uses one BUFG or a small number for each distinct clock domain; the global clock network can supply multiple destinations with low skew relative to the other destinations on the same network.

Variants and control: Some FPGA families provide variants such as BUFGCE (clock enabling), BUFGMUX (source multiplexing), and BUFGCTRL (advanced control). These allow gating, selecting between sources, or additional configuration without interrupting the global clock distribution.

Constraints and best practices: Clock nets should be constrained as clocks in design tools, and BUFGs should be used for primary clocks that drive a large portion of the design. Do not route user signals through BUFGs; ensure proper clock domain crossing when multiple clocks exist.

See also: clock tree synthesis, clock domain crossing, clock routing, global clock buffer.