A Self-Calibrated 2-bit Time-Period Comparator-Based Synthesized Fractional-N MDLL in 22-nm FinFET CMOS

This article describes a synthesized fractional-N multiplying delay-locked loop (MDLL) implemented in Intel 22-nm FFL FinFET technology. A 2-bit time-period comparator (TPC) is proposed to adjust the ring oscillator frequency to suppress the spurs without introducing errors due to its inherent phase offset. A programmable delay is used to compare the periods of the MDLL output in time domain, reducing power consumption and making the design synthesizable. TPC 2-bit output achieves fast and robust locking without any initial calibration. The fractional multiplication ratio is achieved by using a digital-to-time converter (DTC) in the reference path with a replica of the digitally controlled oscillator (DCO) to automatically achieve a range of one DCO period. Any variation in DTC delay due to gain mismatch is corrected by a digital loop operating in the background. A detailed analysis of the small-signal model and noise of the proposed MDLL has also been presented. The core area of the synthesized design is 0.0052 mm
²
while operating over the frequency range from 1.2 to 3.8 GHz. The integrated rms jitter is 2.74 ps, and the spurs are below -47 dBc measured at 3.6175 GHz. Fractional-N MDLL power consumption is 3.19 mW with the figure of merit (FOM) of -226.3 dB.