The analysis of circuit switching activity is a fundamental step towards dynamic power estimation of CMOS digital circuits. In this paper, a probabilistic method for switching activity estimation of VHDL-RTL combinatorial designs is presented. Switching activity estimation is performed through the propagation of input signals probabilities and switching activities by means of BDDs (Binary Decision Diagrams). In order to avoid the BDD memory explosion of large circuits, an automatic circuit partition is performed taking advantage of the specific characteristics of some VHDL statements that permit the circuit division in exclusive regions. In addition, a reduced representation of switching activity BDDs is proposed. The method is implemented in a CAD tool, which, besides the signal probabilities and switching activities, offers abundant information and means for circuit exploration.
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