Improved delay and current models for estimating maximum currents in CMOS VLSI circuits

Excessive voltage drops in power and ground (P&G) buses of CMOS VLSI circuits can severely degrade both design reliability and performance. Maximum current estimates are needed in the circuit to accurately determine the impact of these problems. In a previous paper by the authors (see Design Automation Conf., p. 2-7, June 8-12, 1992), a pattern-independent, linear time algorithm (iMax) is described that is very effective in estimating the maximum current waveforms at various contact points in the circuit. In the aforementioned paper, the algorithm was demonstrated for simple gate delay and current models. In this paper, we first derive expressions for modeling delays and current waveforms for a general gate and then describe how the algorithm can be extended under more general models