A new method for assigning signal flow directions to MOS transistors

Signal flow directions of MOS transistors have been used in many CAD tools. A graph theoretic approach is presented for determining these directions. A MOS circuit is represented using several undirected graphs called ST-graphs. The direction assignment problem is modeled as a two paths problem in each ST-graph. Necessary and sufficient conditions under which all edges in an ST-graph are unidirectional are derived. A linear time algorithm is presented that assigns directions to all edges in an ST-graph if they all unidirectional. If bidirectional edges exist, the algorithm assigns directions to most edges in the ST-graph, and the remaining edges are resolved by a sequence of additional algorithms. Experimental results validate the performance benefits of this approach.<>