Fast-locking delay locked loop

Abstract

A fast locking delay-locked loop (DLL), which can also operate as a clock data recovery circuit (CDR), includes a delay chain, a sampling circuit and a transition detector. An input signal and delayed versions of the input signal generated by the delay chain are sampled by the sampling circuit. The outputs of the sampling circuit are provided to a transition detector which selects one of the input signal and its delayed versions determined to have signal transitions most closely aligned with a sampling edge of a clock. The selected signal and the clock are provided as inputs to a phase discriminator which generates an error signal representing a level of phase mismatch between the inputs. The error signal is fed back to the sampling circuit to maintain phase lock between the clock signal and the input bit stream.