Logic clause analysis for delay optimization

Abstract

In this paper, we present a novel method for topological delay optimization of combinational circuits. Unlike most previous techniques, optimization is performed after technology mapping. Therefore, exact gate delay information is known during optimization. Our method performs incremental network transformations, specifically substitutions of gate input or output signals by new gates. We present new theory which relates incremental network transformations to combinations of global clauses, and show how to detect such valid clause combinations. Employing techniques which originated in the test area, our method is capable to globally optimize large circuits. Comprehensive experimental results show that our method reduces the delay of large standard cell netlists by 23% on average. In contrast to most other delay optimization techniques, area reductions are achieved concurrently.