Modeling the Effective Capacitance of Interconnect Loads for Predicting CMOS Gate Slew

Zhangcai HUANG
Yasuaki INOUE

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E88-A    No.12    pp.3367-3374
Publication Date: 2005/12/01
Online ISSN: 
DOI: 10.1093/ietfec/e88-a.12.3367
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on VLSI Design and CAD Algorithms)
Category: Prediction and Analysis
static timing analysis,  gate slew,  CMOS inverter,  effective capacitance,  interconnect loads,  

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In deep submicron designs, predicting gate slews and delays for interconnect loads is vitally important for Static Timing Analysis (STA). The effective capacitance Ceff concept is usually used to calculate the gate delay of interconnect loads. Many Ceff algorithms have been proposed to compute gate delay of interconnect loads. However, less work has been done to develop a Ceff algorithm which can accurately predict gate slew. In this paper, we propose a novel method for calculating the Ceff of interconnect load for gate slew. We firstly establish a new expression for Ceff in 0.8Vdd point. Then the Integration Approximation method is used to calculate the value of Ceff in 0.8Vdd point. In this method, the integration of a complicated nonlinear gate output is approximated with that of a piecewise linear waveform. Based on the value of Ceff in 0.8Vdd point, Ceff of interconnect load for gate slew is obtained. The simulation results demonstrate a significant improvement in accuracy.