Comparative Analysis and Study of Metastability on High-Performance Flip-Flops

David Li,  Pierce Chuang,  Manoj Sachdev
University of Waterloo


In this paper, we analyze and characterize the metastability of 11 previously proposed high-performance flip-flops, reduced clock-swing flip-flops, and level-converting flip-flops. From extensive simulation results in 65nm CMOS technology, the main metastability parameters of tau and T0 are extracted and analyzed at both nominal and reduced supply voltage. Our simulation results indicate that these flip-flops exhibit a wide range (up to few orders of magnitudes) of metastability windows. In particular, flip-flops with differential and positive feedback configuration such as the sense-amplifier based flip-flops demonstrate the most optimal metastability. Based on this finding, a novel pre-discharge flip-flop (PDFF) with positive feedback configuration is proposed. Extensive simulation results reveal that PDFF achieves better metastability than the previous proposed flip-flops at both nominal voltage supply and nominal voltage supply with reduced clock-swing.