Derivation of Signal Flow Direction in MOS VLSI

This paper presents two sets of rules for deriving the direction of signal flow in MOS circuits. The first set works for a wide range of circuit designs in both nMOS and CMOS technologies because it is based on basic electrical and logical principles of circuit design. The second set contains design and technology specific heuristics. Together these rules yield the direction of signal flow through more than 99.9 percent of the transistors in four VLSI chips constructed in four different design styles. The application of derived signal directions in a timing verifier and electrical rules checker is also discussed