Statistical Static Timing Analysis - Methods of SSTA

Methods of SSTA

There are two main categories of SSTA algorithms - path-based and block-based methods.

A path-based algorithm sums gate and wire delays on specific paths. The statistical calculation is simple, but the paths of interest must be identified prior to running the analysis. There is the potential that some other paths may be relevant but not analyzed so path selection is important.

A block-based algorithm generates the arrival times (and required) times for each node, working forward (and backward) from the clocked elements. The advantage is completeness, and no need for path selection. The biggest problem is that a statistical max (or min) operation that also considered correlation is needed, which is a hard technical problem.

There are SSTA cell characterization tools that are now available such as Altos Design Automation's Variety tool.