Fast-Locking and High-Resolution Mixed-Mode DLL with Binary Search and Clock Failure Detection for Wide Frequency Ranges in 3-nm FinFET CMOS

Abstract

This paper presents a mixed-mode delay-locked loop (MM-DLL) with binary search (BS) locking, designed to cover a broad frequency range from 533 MHz to 4.26 GHz. The BS locking scheme optimizes the locking time, reducing it from a linear to a logarithmic function, completing in B+1 cycles, where B represents the digital-to-analog (DAC) resolution controlling the voltage-controlled delay line (VCDL). At the start of the BS process, large step sizes can cause significant bias overshoots, potentially leading to clock failure conditions (i.e., clocks fail to propagate through the VCDL). To address this issue, a toggle detector is introduced to monitor clock activity and adjust the binary search controller. Upon detecting a stalled clock, the controller reverts the DAC code to the previous working code and resumes the BS with a reduced step size. Fabricated in a 3-nm FinFET CMOS process, the proposed MM-DLL achieves a locking time of under 10.5 ns while consuming 5.4 mW from a 0.75 V supply at 4.26 GHz. The measured performance includes a high resolution of 0.73 ps, with a static phase error of 0.73 ps, RMS jitter of 1.2 ps, and peak-to-peak jitter of 4.9 ps. The proposed MM-DLL achieves state-of-the-art power figure of merit (FoM) of 0.82 pJ and DLL locking FoM of 0.01 $pJ\cdot ns^2$.