A gap detector detects when a phase difference between a feedback signal and a clock signal is larger than a gap threshold. If the phase difference is larger than the gap threshold, then the phase difference is modified by subtracting a gap value from the phase difference. If the phase difference is less than the threshold, the phase difference is not modified. A loop filter receives and filters the modified or unmodified phase difference and controls an oscillator. An accumulator circuit accumulates the modified phase difference and supplies a phase adjust signal. A low pass filter receives the phase adjust signal and supplies a filtered phase adjust signal that is used to slowly adjust the output of the oscillator.