A 16-22 GHz 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 reference at 307.2 MHz and a reconfigurable quad-core VCO and achieves 68-fs rms jitter in fractional-N mode, integrated from 10 kHz to 10 MHz. To lower inband PN, a 153.6 MHz on-chip crystal oscillator followed by a doubler is employed. Using a doubler not only reduces PN amplification of the phase detector, but also suppresses the 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 programed to single-core, dual-core, and quad-core three modes to tradeoff power consumption for PN. The 8-nm PLL achieves 120 fs rms jitter while consuming 16 mW with single-core VCO. Its rms jitter reduces to 88 fs and 68 fs at dual-core and quad-core VCO modes, respectively.