A 2.8–4.3GHz wideband fractional-N sub-sampling synthesizer with −112.5dBc/Hz in-band phase noise

Abstract

A 2.8-4.3GHz low noise fractional-N subsampling frequency synthesizer in 40nm CMOS technology is presented in this paper. The reference sampling clock is modulated by a 10-bit edge modulator to achieve fractional phase lock. A novel fast two-step background calibration is used to correct gain errors in the edge modulator, reducing fractional spurs. For a 3.75GHz carrier, the synthesizer achieves 376fs rms jitter with a worst case fractional spur of -48.3dBc. The in-band phase noise at 200kHz offset is -112.5dBc/Hz. The system consumes a total power of 9.18mW from a 1.1V supply and occupies an area of 0.41mm2.