Method and apparatus for calculating slew rates and signal propagation times for signal waveforms

摘要

A signal propagation time in an integrated circuit can be calculated based on a signal delay time in each of the cells composing the integrated circuit. The signal delay time in each cell can be calculated from the load capacity of a wire connected to an output terminal of the cell and from the slew of the waveform of an input signal. To calculate the slew of the waveform of the input signal, it is required to trace back the path of the input signal. When a feedback loop exists in the integrated circuit, the process of tracing back the path of the input signal may result in an endless loop. To prevent the occurrence of the endless loop, if an input terminal for a clock signal is present in a cell having an output terminal at which a signal waveform is not calculated, the signal waveform at the output terminal is calculated based on the waveform of the clock signal. In addition, a directory in which the correspondence of the output terminal and the input terminal is recorded is produced so that the signal waveform at the output terminal can be calculated based on the signal waveform at the corresponding input terminal recorded in the directory.