Selfclocking

Selfclocking, or self-clocking, refers to arrangements in which the clock signal is generated, recovered, or implied within a system rather than supplied by a single external source. The approach is used to synchronize components, improve timing robustness, or simplify clock distribution in large or variable environments. Self-clocking can occur through data encoding, handshaking protocols, or local timing circuitry that coordinates operation without a global clock.

In data communication, self-clocking means the data stream carries timing information so the receiver can recover the clock. A classic example is Manchester encoding, where a transition in the middle of each bit period provides a clock edge. Other line codes and high-level schemes embed timing to support clock recovery in serial links, allowing alignment despite transmission delays or jitter.

In digital circuit design, self-timed or asynchronous techniques avoid a global clock. Circuits advance on completion signals from upstream stages, using handshakes and local controllers. This can reduce clock skew and power dissipation, and facilitate modular design or mixed synchronous/asynchronous systems (GALS). However, self-timed designs typically require specialized design methods and verification tools and can have variable performance dependent on load and manufacturing variations.

Applications include high-speed serial interfaces, certain microarchitectures, and low-power embedded systems where clock distribution is challenging. The term is often used interchangeably with self-timed logic or clockless design, though practical use tends to emphasize the balance between clock autonomy and reliable synchronization.