A lock detection circuit operatively associated with a phase-locked loop indicates when a feedback clock signal is locked to a reference clock signal. The lock detection circuit counts the number of rising and falling edges of the feedback clock signal that are detected between rising edges of the reference...http://www.google.com/patents/US20050162199?utm_source=gb-gplus-sharePatent US20050162199 - PLL lock detection circuit using edge detection and a state machine
