Conditional-capture flip-flop for statistical power reduction

This paper describes a family of novel low-power flip-flops, collectively called conditional-capture flip-flops (CCFFs). They achieve statistical power reduction by eliminating redundant transitions of internal nodes. These flip-flops also have negative setup time and thus provide small data-to-output latency and attribute of soft-clock edge for overcoming clock skew-related cycle time loss. The simulation comparison indicates that the proposed differential flip-flop achieves power savings of up to 61% with no impact on latency while the single-ended structure provides the maximum power savings of around 67%, as compared to conventional flip-flops. With a typical switching activity of 0.33, the power consumption is reduced by as much as 23-30% with comparable minimum data-to-output latency. It is also indicated that the proposed single-ended structure provides power comparable to the fully static master-slave design with significantly reduced data-to-output latency. An eight-bit counter was fabricated using a 0.35-μm CMOS technology, and the experimental results indicate that the counter using the differential CCFF saves the overall power consumption by about 30% as compared to that using the conventional flip-flop.