A 16–22GHz Fractional-N PLL in 8nm FinFET with 68 fsrms Jitter

We present a 16–22 GHz low-jitter fractional-N PLL for 5G mm-wave mobile application. It features an integrated low-cost crystal oscillator (XO) reference at 153.6 MHz and a reconfigurable 19-GHz quad-core VCO and achieves 68-fs rms jitter in fractional-N mode, integrated from 10 kHz to 10 MHz. To minimize inband phase noise (PN), a 153.6-MHz on-chip XO followed by a frequency doubler is employed. The XO achieves -160 dBc/Hz at 1-MHz frequency offset and consumes 4.5 mW. Using a doubler not only reduces the PN amplification of the phase detector and the feedback divider, but also suppresses the PLL inband PN due to the flicker noise of the reference clock buffer. The reconfigurable multi-core VCO occupies the same footprint as a conventional quad-core oscillator and can be programmed to single-core, dual-core, and quad-core three modes to trade off power consumption for PN. Implemented in 8-nm FinFET, the PLL occupies 0.38 mm² and achieves an rms jitter of 120 fs at 18 GHz while consuming 16 mW at single-core VCO mode. Its rms jitter reduces to 88 fs and 68 fs at dual-core and quad-core VCO modes, respectively.