A Fully Synthesizable Fractional-N MDLL with Zero-Order Interpolation-Based DTC Nonlinearity Calibration and Two-Step Hybrid Phase Offset Calibration

Abstract

In this paper, a fully-synthesizable digital-to-time (DTC)-based fractional- {N} multiplying delay-locked loop(MDLL) is presented. Noise and linearity of synthesizable DTCs are analyzed, and a two-stage synthesizable DTC is proposed in which a path-selection DTC is used as the coarse stage and a variable-slope DTC is used as the fine stage. To calibrate the DTC nonlinearity, a highly robust zero-order interpolation based nonlinearity calibration is proposed. Besides, the static phase offsets (SPO) between bang-bang phase detector (BBPD) and multiplexer (MUX) are calibrated by a proposed hybrid analog/digital phase offset calibration, while the dynamic phase offsets (DPO) are removed by a proposed complementary switching scheme. The co-design of the analog circuits and digital calibrations enable excellent jitter and spur performance. The MDLL achieves 0.70 and 0.48ps root-mean-square (RMS) jitter in fractional- {N} and integer- {N} modes, respectively. The fractional spur is less than -59.0dBc, and the reference spur is -64.5dBc. The power consumptions are 1.85mW and 1.22mW, corresponding to figures of merit (FOM) of -240.4dB and -245.5dB.