A 0.0056-mm2 −249-dB-FoM All-Digital MDLL Using a Block-Sharing Offset-Free Frequency-Tracking Loop and Dual Multiplexed-Ring VCOs

This paper describes an ultra-compact all-digital multiplying delay-locked loop (MDLL) featuring a low-power block-sharing offset-free frequency-tracking loop (FTL) to calibrate the process–voltage–temperature variations of the voltage-controlled oscillator (VCO) frequency. Such FTL utilizes a digital-controlled delay line (DCDL)-based low-power time-interval comparator and an adjacent-edge selector, to precisely detect the static phase offset (SPO) caused by the VCO frequency drifting in the presence of reference injection. The block-sharing-based SPO detection aids nullifying the circuit-mismatch- and offset-induced deterministic error. Also, for the adjacent edge selector, block sharing between its control generation circuits and the coarse FTL further reduces the power consumption. The varactor-tuned dual multiplexed-ring VCOs (MRVCOs) serve to reduce jitter variation while extending the frequency tuning range. Fabricated in a 28-nm CMOS with a core area of 0.0056 mm
²
, the proposed MDLL covers a tuning range from 1.55 to 3.35 GHz, and exhibits a root-mean-square (rms) jitter of 292 fs at 3-GHz output, under a 200-MHz reference clock. The power consumption is 1.45 mW at a 0.8-V supply, resulting in an FoM of −249 dB favorably comparable with the state of the art.