Timing Analysis Using Functional Analysis

The usual block-oriented timing analysis for logic circuits does not take into account functional relations between signals. If functional relations are taken into consideration, it could be found that a long path is never activated. This results in more accurate delays. A comparison is made of three arrival time functions, A, B, and R. A is the arrival time as given by exhaustive simulation; B is the arrival time as calculated by a usual block-oriented algorithm; and R is the arrival time, that does functional analysis. It is shown that B contained in R contained in A. The first relation means that R is never more conservative than B and whenever the containment is proper, R is an improvement over B. The second relation means that R is correct in the sense that it will never assert a signal to be valid when it is not valid according to the ideal A. Experimental results showing how often R is an improvement over B are presented.