A 1.1 GHz CMOS fractional-N frequency synthesizer with a 3b 3rd-order /spl Delta//spl Sigma/ modulator

Fractional-N frequency synthesis based on /spl Delta//spl Sigma/ modulators offers wide bandwidth with narrow channel spacing and alleviates PLL design constraints for phase noise and reference spur. However, the synthesizer phase noise performance is significantly affected by the high-frequency out-of-band noise, which is difficult to suppress with the finite number of PLL loop filter poles. This work uses a 3b 3rd-order modulator that generates less high-frequency noise and makes the system less sensitive to the phase detector nonlinearity.