EFFICIENT CEFF MODEL FOR GATE OUTPUT SLEW COMPUTATION IN EARLY SYNTHESIS

摘要

A slew-based effective capacitance (Ceff) is used to compute gate output slew during early synthesis of an integrated circuit design. A π model is constructed for the gate and reduced to two parameters which are used to compute a slew value for the model, given a slew definition. A capacitance coefficient is then calculated as a function of this slew value. The effective capacitance is the product of the coefficient and the total capacitance of the π model. The output slew of the gate may in turn be computed using the slew-based Ceff. The coefficient may be computed by iteratively solving an equation representing output voltage over time dependent on the first and second parameters, by directly solving a closed-form equation which is a function of the first and second parameters, or by looking up the capacitance coefficient in a table indexed by the first and second parameters.

主权项

1. A method of determining the effective capacitance of a gate in an integrated circuit design comprising:
constructing a π model for the gate which includes an output resistance and a total capacitance, by executing first program instructions in a computer system; reducing the π model to first and second parameters based on the output resistance and the total capacitance, by executing second program instructions in the computer system; providing a slew definition which includes a first voltage level and a second voltage level, by executing third program instructions in the computer system; computing a capacitance coefficient as a function of a slew value of the π model for the slew definition based on the first and second parameters, by executing fourth program instructions in the computer system; and calculating the effective capacitance of the gate as the product of the capacitance coefficient and the total capacitance, by executing fifth program instructions in the computer system.