A 22.5–27.7-GHz Fast-Lock Bang-Bang Digital PLL in 28-nm CMOS for Millimeter-Wave Communication With 220-fs RMS Jitter

We present a 22.5–27.7-GHz fast-lock low-phase-noise bang-bang digital phase-locked loop (PLL) for mm-wave communication. The fast lock is achieved with the help of the proposed gear-shift algorithm, scaling up the PLL bandwidth for faster settling, and orderly reducing it for jitter performance. A digitally controlled oscillator (DCO), based on transformer feedback with a tunable source-bridged capacitor, exhibits low phase noise (PN) over a wide tuning range (FoM of −184 dBc/Hz and FoMT of −191 dBc/Hz). The PLL occupies 0.09-mm² core area and exhibits 220-fs RMS jitter while consuming 25 mW, giving FoMRMS of −239 dB. Its settling time improves from 780 to 45 µs with our gear-shift algorithm. For 60-GHz communication, with a frequency multiplication factor of 2.5, this PLL covers all six channel frequencies of IEEE-802.11ad and is capable of supporting 128 QAM and beyond.