Delay locked loop circuits and methods preventing erroneous transition from coarse lock to fine lock due to noise or jitter

Abstract

Delayed locked loop (DLL) circuits and methods using a coarse-fine lock structure which prevent malfunction due to jitter or noise that causes erroneous transitions from a coarse-lock to a fine-lock delay. A phase detector uses two feedback signals to detect a phase of an external clock signal (or reference signal) based on a phase difference between the two feedback signals, thereby enabling a more accurate determination as to when to transition from a coarse-lock to a fine-lock delay. The phase difference of the two feedback signals can be regulated by using frequency information to set a phase difference between the first and second feedback signals to renders the detection process more robust against noise or jitter over a wide frequency band from a low frequency to a high frequency, for determining when to transition from the coarse-lock to the fine-lock.