DelayLocked

Delaylocked refers to concepts and circuits that synchronize timing by locking a signal’s delay to a reference, most commonly through a delay-locked loop (DLL). A DLL uses a chain of programmable delay elements to create taps at different delays relative to a reference clock. A phase detector compares the phase of a chosen tap with the reference and generates control signals that adjust the delay elements. When the loop is in balance, the selected tap edges occur at a defined phase offset from the reference, effectively locking the delay.

In contrast to a phase-locked loop (PLL), a DLL does not attempt to synthesize a different frequency with a voltage-controlled oscillator. The output frequency remains the same as the reference; the objective is to provide deterministic, adjustable timing alignment. DLLs are valued for predictable delay steps, good jitter characteristics, and reduced sensitivity to certain loop dynamics, making them suitable for fine-grained timing adjustment rather than frequency synthesis.

Applications of delay-locked approaches include deskewing data paths in memory interfaces and high-speed I/O, aligning sampling clocks to data streams in synchronous systems, and clock distribution networks where precise phase alignment is crucial. Implementation considerations cover delay-element resolution, the number and spacing of taps, and how the loop is calibrated to compensate for process, voltage, and temperature variations. Proper design aims to maintain a stable lock across operating conditions while meeting target timing requirements.