National Semiconductor Corporation

Keith James Mueller

Gary W Tietz

A digital logic level signal indicates whether a first signal in a phase-locked loop is locked in phase and frequency with a second signal provided to the loop. The digital logic level signal is provided from the sequentially last stage of a counter having a predetermined number of stages. The counter counts cycles in an input signal corresponding to one of the first signal and the second signal. A reset signal pulse having a first predetermined duration is provided to the counter from a pulse width discriminator when the pulse width discriminator detects a phase difference between the first and second signals of greater than a second predetermined duration. The reset signal pulse resets the counter. The digital logic level signal is in a state indicating an in-lock condition when a predetermined number of input signal cycles occur without the counter being reset.

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Keith James Mueller