Static timing: Back to our roots

Existing static timing methodologies apply various techniques to address increasingly larger process variations. The techniques include multi-corner timing, on-chip variation (OCV) derating coefficients, and path-based common path pessimism removal (CPPR) procedures. These techniques, however, destroy the benefits of linear run-time and incrementality possessed by classical static timing. The major contribution of this work is an efficient statistical timing methodology with comprehensive modeling of process variations, while at the same time retaining those key benefits. Our methodology is compatible with existing characterization methods and scales well to large chip designs. To achieve this goal, three techniques are developed: (1) building the statistical delay model based on existing multi-corner library characterization; (2) modeling spatial correlation in a scalable manner; and (3) avoiding the time-consuming CPPR procedure by removing common path pessimism in the clock network by an incremental block-based technique. Experimental results on industrial 90 nm ASIC designs show that the proposed timing methodology correctly handles all types of process variation, achieves high correlation with traditional multi-corner timing with more than 4x speedup, and is a vehicle for pessimism reduction.