Reducing Interconnect Delay Uncertainty via Hybrid Polarity Repeater Insertion

Abstract

Capacitive crosstalk between adjacent signal wires has significant effect on performance and delay uncertainty of point-to-point on-chip buses in deep submicrometer (DSM) VLSI technologies. We propose a hybrid polarity repeater insertion technique that combines inverting and non-inverting repeater insertion to achieve constant average effective coupling capacitance per wire transition for all possible switching patterns. Theoretical analysis shows the superiority of the proposed method in terms of performance and delay uncertainty compared to conventional and staggered repeater insertion methods. Simulations at the 90-nm node on semi-global METAL5 layer show around 25% reduction in worst case delay and around 86% delay uncertainty minimization compared to standard bus with optimal repeater configuration. The reduction in worst case capacitive coupling reduces peak energy which is a critical factor for thermal regulation and packaging. Isodelay comparisons with standard bus show that the proposed technique achieves considerable reduction in total buffers area, which in turn reduces average energy and peak current. Comparisons with staggered repeater which is one of the simplest and most effective crosstalk reduction techniques in the literature show that hybrid polarity repeater offers higher performance, less delay uncertainty, and reduced sensitivity to repeater placement variation.