Method and apparatus for spur reduction in a frequency synthesizer

Abstract

A frequency synthesizer includes: a frequency source generating a reference signal that includes a plurality of pulses having periodicity based on a reference frequency; a feedback loop that includes, a phase detector circuit, a loop filter, a controlled oscillator that generates an output signal at an output, and a loop divide circuit; a non-linear circuit element at an input of the phase detector circuit, which generates intermodulation distortion that causes at least one spurious signal at the output; and a controller controlling the loop divide circuit and the non-linear circuit element. The frequency synthesizer further includes a dither circuit that adjusts the timing of some of the pulses of the reference signal based on a parameter provided by the controller to the non-linear circuit element, thereby, providing a jittered reference signal to the non-linear circuit element for attenuating the at least one spurious signal at the output.