THE CALCULATION OF SIGNAL STABLE RANGES IN COMBINATIONAL-CIRCUITS

The estimation of signal stable ranges in a combinational circuit is a n important issue for determining clock time in a synchronous system. An optimal clocking period time highly depends on the accuracy of the shortest path length as well as the longest path length in a combinati onal circuit. In this paper, a sensitization criterion for the short p ath is first proposed. Based on this sensitization criterion, an accur ate model for calculation of signal stable range can be created. This will allow the output stable range of a gate to be the union of its in puts when the input leads hold a controlling value, rather than to be always the intersection as the previous approach [3] did. Then, an LS- algorithm for calculation of signal stable ranges is presented in whic h both the sensitizable shortest path and the sensitizable longest pat h are considered. It avoids the exhaustive search by tracing the path sensitization and eliminates some conservative restriction to get more accurate results in a more efficient way, compared to the previous ap proaches. The speedup and the improved accuracy of the proposed LS-alg orithm showed promising experimental results.