General framework for removal of clock network pessimism

The paper presents a simple yet powerful general theoretical framework and efficient implementation for removal of clock network timing pessimism. We address pessimism in static timing analysis (STA) tools caused by considering delay variation along common segments of clock paths. The STA tools compute setup (hold) timing slack based on conservative combinations of late (early) launching and early (late) capturing arrival times. To avoid exponential-time path-based analysis the STA tools use both early and late arrival times on gates common to both launching and capturing paths. It is impossible in a real circuit and is observed as the clock network pessimism in STA. Our approach supports any kind of delay variation though the typical causes of the pessimism are process, voltage, and temperature on-chip variation, and reconvergence in clock network. We propose a new theoretical framework that allows one to apply known graph algorithms instead of time consuming forward and backward multi-pass tracing algorithms and heuristics that are limited to some network topologies. The new graph-based framework supports clock networks of virtually any size and type, e.g., tree, mesh, hybrid, clock gating, chains of multipliers and dividers, loops in such chains, etc.