Power Grid Analysis in VLSI Designs - SERC

For large T, D(x) becomes time invariant function and hence there is no need to accountfor temporal correlation.Toggle Frequency: If a node x is toggling n(T) times over a time interval of lengthT, then the toggle frequency F(x) is defined as:F(x) = n(T)/(2*T) where T is very huge time (infinite ideally)Example, if the node is switching at 20 MHz, it is expected that the node will switch 2times in 50 ns. As it can be seen, the toggle frequency can be converted to transitiondensity or switching activity by the following equation,Toggle density = #of transitions/Period = Switching ActivityAll the three terms mentioned above are used interchangeably in this document.It should be noted that toggle frequency of a node has no direct relation with the clockdomain(s) in which node (or logic) exists. We have used the clock domain frequency toupper bound the toggle frequency calculated by our approach.Signal Probability: Signal probability P(x) at a node x is defined as the averagefraction of clock period in which the stead state value of x is logichigh.2.2 Toggle Activity EstimationThis section gives overview of Farid Najm’s work.Boolean difference of output is computed with respect to each input pin. Boolean difference offunction y (output) depends on x(each of the input). It is defined as:29