Power Grid Analysis in VLSI Designs - SERC

3. The temporal correlation between different inputs influences the characterization data alot. This is due to simultaneous switching. We have used the least affecting combinationi.e. 0 skew between multiple inputs in our analysis – this is worst case also. (Figure 4.8)4.2.2 Current Characterization FlowCurrent Source generation involves time variant current waveform determination for each cell.This is current waveform as it is seen at VDD pin of cell when the cell output is rising or falling.The flow is shown in Figure 4.9. Sample SPICE deck is shown in Appendix D. PERL Programthat takes input from SPICE simulation has following options available. In our case, we tooklast option with 75ps as sampling interval.1. full – Whole current data available in the punch file is given as output in two columnformat, first column giving the simulation time and the second column giving thecurrent value corresponding to each simulation time instance.2. fixed – The total simulation time is divided into 8192 points and the current value atthese 8192 time-values is obtained either directly, if available or by interpolation.3. Interval filtered – An interval in picoseconds is specified and according to that, theprogram obtains the time-values for which the data is expected. Again, the current datacorresponding to these time-values is obtained directly, if available or by interpolation.71