A Wideband Fractional-N PLL With Suppressed Charge-Pump Noise and Automatic Loop Filter Calibration

Abstract

This paper explores a new topology of charge-pump PLL intended for ΔΣ-fractional-N frequency synthesis. Thanks to the adoption of a bang-bang phase detector and a two-path analog loop filter, the impact of charge-pump noise on PLL phase noise is reduced to negligible levels with no penalty on power dissipation. Additionally, the proposed topology enables an efficient cancellation of the ΔΣ quantization error, a novel scheme for the calibration of the loop filter parameters and a low-sensitivity VCO, which is beneficial in lowering the reference-spur level. The 3.0-to-4.0-GHz fractional-N synthesizer integrated in a 65-nm CMOS technology consumes 5 mW from a 1.2-V voltage supply. The flat phase noise is -105 dBc/Hz over the 5.5-MHz PLL bandwidth with a 40-MHz crystal reference.