A frequency synthesizer has a phase locked loop, a .DELTA..SIGMA. modulator, and a filter. The phase locked loop includes a frequency divider that controls the frequency of the phase locked loop output signal. The output of the .DELTA..SIGMA. modulator is fed through the filter and the output of the filter is used to control a division factor in the frequency divider. Compensation may be performed at the input to the .DELTA..SIGMA. modulator in order to compensate for the filtering performed between the .DELTA..SIGMA. modulator and the frequency divider. The filter may be used to reduce quantization noise in an input to the frequency divider, and thereby reduces phase noise in an output of the phase locked loop.