A 1.8-GHz CMOS fractional-N frequency synthesizer with randomized multiphase VCO

A 1.8-GHZ fractional-N frequency synthesizer implemented in 0.6-mum CMOS with an on-chip multiphase voltage-contiolled oscillator (VCO) exhibits no spurs resulting from phase interpolation. The proposed architecture-randomly selects output phases of a multiphase VCO for fractional frequency division to eliminate spurious tones. Measured phase noise at 1.715 GHz is lower than -80 dBc/Hz within a 20-kHz loop bandwidth and -118 dBc/Hz at 1-MHz offset with no fractional spurs above -70 dBc/Hz. The synthesizer has a frequency resolution step,smaller than 10 Hz. The chip consumes 52 mW at 3.3 V and occupies 3.7 min x 2.9 min.