A multiple modulator fractional divider

Fractional-N frequency synthesis using a phase locked loop (PLL) is considered. Advances in oversampling A/D conversion technology are incorporated into fractional-N synthesis, allowing the spectrum of error energy to be shaped so that fractional synthesis error energy is pushed away from the carrier. Based on this new technology, a CMOS integrated fractional-N divider was successfully developed. A complete fractional-N PLL was constructed utilizing only a CMOS divider, a dual modulus prescaler, a simple loop filter, and a voltage controlled oscillator (VCO). The resulting PLL exhibits no fractional spurs.>