Dynamic Flip-Flop Conversion: A Time-Borrowing Method for Performance Improvement of Low-Power Digital Circuits Prone to Variations

Abstract

Dynamic flip-flop (FF) conversion is a method of time borrowing (TB) for improving the performance of digital systems prone to variations. The first type of this method (Type A), which was previously presented, suffers from a large inefficient transparency window. In this brief, we present an improved structure for this method (Type B) that mitigates this problem by automatically closing the window after the arrival of late data at timing critical FFs. This method was compared with soft edge FF and dynamic clock stretching through simulations on different ITC'99 benchmarks. We defined a parameter called improvement efficiency, which is the ratio of the timing yield improvement to the power overhead of TB. According to the simulation results, the efficiency of Type A is on average 269% more than the best results of other methods when considering only the setup time violations. But, when taking both the setup time and the hold time violations into account, Type B is on average 46% more efficient than the best results of other methods. The simulations also show that the yield improvement of this method increases in higher clock frequencies and it remains the most efficient method when reducing the voltage down to near-threshold region.