Ic phase detector with re-timed reference clock controlling switches

Abstract

A phase detector includes a counter to generate the integer portion of a number of complete cycles of an output clock at each active edge of a reference clock. A time to digital converter in the phase detector generates the fractional portion of the number of complete cycles of the output clock at each active edge of the reference clock. The sum of the fractional portion and the integer portion is subtracted from an accumulated value obtained by accumulating a pre-determined number to generate an error signal as the output of the phase detector. The counter is read at an active edge of one of two re-timed clocks derived from the reference clock. Each of the two re-timed clocks is generated based on a comparison of the fractional portion with a pair of thresholds. Errors due to metastability in reading the counter are thereby avoided.