On determining sensitization criterion in an iterative gate sizing process

Since only sensitizable paths contribute to the delay of a circuit, false paths must be excluded in optimizing the delay of the circuit. However, just identifying sensitizable paths in the first place is not sufficient since during the optimization process, false paths may become sensitizable, and sensitizable paths false. In addition, some paths may shuttle frequently as false paths and sensitizable ones. That is, a thrashing phenomenon may occur. To lessen the thrashing phenomenon of critical paths, a loose sensitization criterion is proposed in this paper to identify both exact sensitizable paths and shuttle paths. Moreover, the selection of sensitization criterion should be related to the specified delay constraint of a given circuit. Taking into account the tightness of sensitization criterion and delay constraint together, we define in this paper a thrashing coefficient which is used to guide the selection of sensitization criterion in the performance optimization process. Moreover, to save time for path sensitizability analysis in the optimization process, we find a special type of false paths, function-false paths, which can be put aside since they never become sensitizable during the process.