Digital loop filter for all-digital phase-locked loop design

Abstract

A digital loop filter installed in an all-digital phase-locked loop (PLL) receives a digitally controlled oscillator (DCO) control code transmitted from a PLL controller in the all-digital PLL, and calculate an average value, such that the PLL controller can produce another DCO control code by the average value for controlling and adjusting an output signal of a digitally controlled oscillator (DCO) in the neighborhood of the average value to maintain compensating a phase/frequency difference with an input signal, so as to minimize the jitter effect of the input signal on the all-digital PLL, reduce the jitter effect of the output signal, and keep tracking and locking the frequency and the phase of the input signal.