Power estimation in combinational modules is addressed from a probabilistic point of view. The zero-delay hypothesis is considered and under highly correlated input streams, the activities at the primary outputs and all internal nodes are estimated. For the first time, the relationship between logic and probabilistic domains is investigated and two new concepts - conditional independence and isotropy of signals - are brought into attention. Based on them, a sufficient condition for analyzing complex dependencies is given. In the most general case, the conditional independence problem has been shown to be NP-complete and thus appropriate heuristics are presented to estimate switching activity. Detailed experiments demonstrate the accuracy and efficiency of the method. The results reported here are useful in low power design.
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