Switch-Level Delay Models for Digital MOS VLSI

This paper presents fast, simple, and relatively accurate delay models for large digital MOS circuits. Delay modeling is organized around chains of switches and nodes called stages, instead of logic gates. The use of stages permits both logic gates and pass transistor arrays to be handled in a uniform fashion. Three delay models are presented, ranging from an RC model that typically errs by 25% to a slope-based model whose delay estimates are typically within 10% of SPICE's estimates. The slope model is parameterized in terms of the ratio between the slopes of a stage's input and output waveforms. All the models have been implemented in the Crystal timing analyzer. They are evaluated by comparing their delay estimates to SPICE, using a dozen critical paths from two VLSI designs.