Second-order clock recovery using three feedback paths

Abstract

An illustrative digital communications receiver and a fractional-N phase lock loop based clock recovery method provide substantially reduced sensitivity to nonlinearities in any included phase interpolators. One receiver embodiment includes: a fractional-N phase lock loop that provides a clock signal; a phase interpolator that applies a controllable phase shift to the clock signal to provide a sampling signal; a sampling element that produces a digital receive signal by sampling an analog receive signal; a timing error estimator that produces a timing error signal; a first feedback path coupling the timing error signal to the phase interpolator to minimize a phase component of the estimated timing error; a second feedback path coupling the timing error signal to the phase interpolator; and a third feedback path coupling the timing error signal to the fractional-N phase lock loop, the second and third feedback paths minimizing a frequency offset component of the estimated timing error.