Fractional phase locked loop (pll) with digital control driven by clock with higher frequency than pll feedback signal

Abstract

A phase locked loop (PLL) method includes generating a first signal based on a comparison of a phase of a reference clock or signal to a phase of a feedback clock; generating an output clock based on the first signal; generating an intermediate feedback clock including frequency dividing the output clock; fractionally frequency dividing the intermediate feedback clock based on a digital control signal to generate the feedback clock; and generating the digital control signal based on a sampling clock having a frequency greater than a frequency of the feedback clock. In one implementation, a PLL includes a frequency multiplier to generate the sampling clock based on the feedback clock. In another implementation, a PLL uses the intermediate feedback clock as the sampling clock.