Clk

CLK is an abbreviation that can refer to several concepts, most commonly the clock signal in digital electronics. A clock signal is a periodic electrical waveform used to coordinate the timing of circuits and systems. It is typically produced by an oscillator or crystal and distributed to synchronous elements such as flip-flops, registers, counters, and memory interfaces. The clock’s frequency, duty cycle, and jitter determine timing performance, and designs may employ single-clock or multi-clock domains. Clock distribution networks, or clock trees, are optimized to minimize skew and latency; timing analysis tools verify that data meet setup and hold requirements relative to the active clock edge. In hardware description languages and schematics, the clock input is usually labeled CLK or clk and serves as the primary timing reference that triggers edge-sensitive devices on a defined edge, commonly the rising edge.

In biology, CLK commonly denotes the CLOCK gene or CLOCK protein, a transcription factor that is central to the molecular circadian clock. In circadian biology, CLOCK forms a transcriptional activator complex with BMAL1 and drives rhythmic expression of clock-controlled genes. Variants or dysregulation of CLK activity can affect sleep timing, metabolism, and other physiological processes.

Outside these domains, clk is also a common variable name for a clock signal in hardware description language code and schematic annotations, reflecting its role as the timing reference in digital designs.