A 2.9-4.0-GHz Fractional-N Digital PLL With Bang-Bang Phase Detector and 560-fsrms Integrated Jitter at 4.5-mW Power

This paper introduces a Delta Sigma fractional-N digital PLL based on a single-bit TDC. A digital-to-time converter, placed in the feedback path, cancels out the quantization noise introduced by the dithering of the frequency divider modulus and permits to achieve low noise at low power. The PLL is implemented in a standard 65-nm CMOS process. It achieves 102-dBc/Hz phase noise at 50-kHz offset and a total absolute jitter below 560 fs(rms) (integrated from 3 kHz to 30 MHz), even in the worst-case of a -42-dBc in-band fractional spur. The synthesizer tuning range spans from 2.92 GHz to 4.05 GHz with 70-Hz resolution. The total power consumption is 4.5 mW, which leads to the best jitter-power trade-off obtained with a fractional-N synthesizer. The synthesizer demonstrates the capability of frequency modulation up to 1.25-Mb/s data rate.