Method for reducing pessimism in coupled noise analysis with disjoint clock domains (01-Oct-2009)

Method for reducing pessimism in coupled noise analysis with disjoint clock domains

To quickly calculate the impact of coupled noise on delay and slew, a typical approach is to compute Miller factors, which are used to scale the capacitance on a wire, and thus affect the delay and slew. To do this in a way which produces acceptable compute times, a single pair of Miller factors is calculated for each victim/aggressor combination (the pair reflects the early-mode scaling factor and the late-mode scaling factor). With multiple clock domains, this means all victim clock phases are equally affected by the Miller factors. However, a given victim clock phase may not be susceptible to coupling by one or more of its aggressors, due to clock exclusions defined by the user (for instance, a scan phase and a data phase cannot be active at the same time). In summary, the current state-of-the-art provides acceptable tool run times at the expense of excessive timing pessimism. This invention provides a quick-running solution to this problem, and gives credit back for these particular victim clock phases.

The main idea of the invention is to look at each victim clock phase and determine if it is eligible for credit (based on user-defined clock exclusions). We then calculate both delay and slew credit to avoid having that victim phase unfairly penalized during the timing analysis. This reduces pessimism in the coupling analysis step. It also provides a computationally cheap solution, compared to the brut...