Statistical logic cell delay analysis using a current-based model

A statistical model for the purpose of logic cell timing analysis in the presence of process variations is presented. A new current-based cell delay model is utilized, which can accurately compute the output waveform for input waveforms of arbitrary shapes subjected to noise. The cell parasitic capacitances are pre-characterized by lookup tables to improve the accuracy. To capture the effect of process parameter variations on the cell behavior, the output voltage waveform of logic cells is modeled by a stochastic Markovian process in which the voltage value probability distribution at each time instance is computed from that of the previous time instance. Next the probability distribution of a % V/sub dd/ crossing time, i.e., the hitting time of the output voltage stochastic process is computed. Experimental results demonstrate the high accuracy of our cell delay model compared to Monte-Carlo-based SPICE simulations.