Patent ID: 6442741
Filing Date: 2002-08-27
Classification: G06F

Abstract:
A method of deriving one of timing margin or signal skew information from relevant ones of a plurality of connected logic cells and waveforms from the relevant logic cells of a circuit described by using a simulation tool, the waveforms including input and output waveforms to and from each logic cell, the simulation tool describing a transition and a transition time point when the transition occurs for each waveform, said method comprising the steps of:selecting an output waveform and a transition time point of the selected output waveform delivered from a selected logic cell; identifying a predictive input waveform and a transition time of the predictive input waveform to the selected logic cell which causes the transition of the output signal from the selected logic cell at the selected transition time; identifying a predictive logic cell connected to the selected logic cell which supplies the output waveform to the selected logic cell which constitutes the predictive input waveform identified in the preceding step; performing the aforesaid three steps as a repetition; performing at least one new repetition to accomplish the selecting and identifying steps under circumstances where the predictive logic cell identified in a previous repetition becomes the selected logic cell for the new repetition and the transition time point of the predictive input waveform to the selected logic cell of the previous repetition becomes the selected transition time of the output waveform of the selected logic cell for the new repetition; defining a logic cone formed from each of the logic cells selected and identified by performing the repetitions; selecting magnitudes for variables influencing performance of the circuit under best case circumstances and worst case circumstances; using the best case variable magnitudes when defining a first instance of the logic cone; using the worst case variable magnitudes when defining a second instance of the logic cone; and deriving the one of timing margin or signal skew information from any difference in transition times of the predictive input waveforms in the first and second instances of the defined logic cone.