Design of a clock jitter reduction circuit using gated phase blending between self-delayed clock edges

Abstract

Design of a clock jitter reduction circuit that exploits the phase blending technique between the uncorrelated clock edges that are self-delayed by multiples of the clock cycle, nT is presented. By blending uncorrelated clock edges, the output clock edges approach the ideal timing and, thus, timing jitter can be reduced by a factor of √2 per stage. There are three technical challenges to realize this: 1) generating uncorrelated clock edges, 2) phase averaging with small time offset from the ideal center position, and 3) minimizing the error in nT-delay being deviated from ideal nT. The proposed circuit overcomes each of these by exploiting an nT-delay, gated phase blending, and self-calibrated nT-delay elements, respectively. Measurement results with a 180-nm CMOS prototype chip demonstrated an approximately four-fold reduction in timing jitter from 30.2 ps to 8.8 ps in 500-MHz clock by cascading the proposed circuit with four-stages.