Long-tail behavior of process variation with application to domino keeper sizing

Designers use Monte Carlo simulations to evaluate the impact of variability on circuits, but such simulations require prohibitive amounts of computation to characterize rare events. In this paper, we propose a method by which the long tail behavior of circuits can be modeled with a reasonable number of simulations. This technique is then applied to the problem of domino keeper sizing to determine the sizing necessary to ensure a reliable circuit. We find that to ensure reliability for a commercial 45 nm process, the width of the keeper must be 0.17 times the effective width of the pull-down stack. Such a wide keeper results in a delay penalty of 9.9% compared to a circuit with no keeper.