Transition density: a new measure of activity in digital circuits

Noting that a common element in most causes of runtime failure is the extent of circuit activity, i.e. the rate at which its nodes are switching, the author proposes a measure of activity, called the transition density, which may be defined as the average switching rate at a circuit node. An algorithm is also presented to propagate density values from the primary inputs to internal and output nodes. To illustrate the practical significance of this work, it is shown how the density values at internal nodes can be used to study circuit reliability by estimating the average power and ground currents; the average power dissipation; the susceptibility to electromigration failures; and the extent of hot-electron degradation. The density propagation algorithm has been implemented in a prototype density simulator which is used to assess the validity and feasibility of the approach experimentally. The results show that the approach is very efficient, and makes possible the analysis of VLSI circuits