Patent ID: 6600378
Filing Date: 2003-07-29
Classification: H03L

Abstract:
A delta-sigma fractional-N frequency synthesizer comprising:a phase locked loop including a phase frequency detector, a loop filter, a voltage-controlled oscillator and a multi-modulus frequency divider in a feedback loop between the voltage-controlled oscillator output and an input of the phase frequency detector; a delta-sigma modulator having an input for receiving a fractional control word and an output coupled to the multi-modulus frequency divider for controlling the division ratio of the multi-modulus frequency divider in response to the input fractional control word; a generator for producing a signal in accordance with and related to a frequency compensation loop error signal from the multi-modulus frequency divider; and means for adding said generator signal output to a fractional input control word to produce a zero average dither fractional control word as the input to the delta-sigma modulator to generate a multi-modulus input control signal whereby the division ratio is changed without generation of fractional spurious frequencies.