Importance

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Abstract

A digital phase lock loop synchronizes a first signal to a second signal having a predefined frequency. The first signal usually has an instantaneous frequency greater than the predefined frequency, so that the first signal is constantly gaining phase with respect to the second signal. The digital phase lock loop performs periodic correction cycles by detecting a predefined phase relationship between the first signal and the second signal, and when the predefined phase relationship is detected, expanding the first signal in phase by a predetermined amount. Preferably, the first signal is generated by clocking a frequency divider with a clocking frequency, and the first signal is expanded in phase by inhibiting the clocking of the frequency divider for one clocking cycle for each correction cycle. Preferably, the predetermined phase relationship is detected when the second signal has a predetermined logic state coincident with clocking by the clocking signal and a predetermined state of the frequency divider. The digital phase lock loop can be used in a data processor system for synchronizing data processor clocks to a reference clock at a submultiple of the data processor clocking frequency, by obtaining each data processor clock from an initial stage of the frequency divider in a digital phase lock loop for each processor.

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