Noise reduction in fractional-N frequency synthesizers with multiphase VCO

A novel noise reduction technique for a fractional-N frequency synthesizer using a multiphase voltage-controlled oscillator (VCO) is presented in this paper. It is shown that both in-band and out-of-band noise can be reduced by 6 dB for every two-fold increase in the number of phases. A reduced complexity multi-input multi-modulus delta-sigma modulator controlled frequency divider is proposed which combines the functions of frequency division and phase selection. Its power and area consumption are much less than those of conventional multi-phase frequency dividers. Simulation results confirm the analytical predictions.