1. A computer-readable medium embodying instructions that when executed by a computer system, perform steps for modeling a driver cell, wherein when an output capacitance of the driver cell is equal to a first output capacitance and an input signal having a first input slew is applied to the driver cell, the driver cell generates a first output current signal and a first voltage signal, the steps comprising: segmenting the first output current signal along a plurality of time intervals, wherein for each of the plurality of time intervals, an expected output voltage change based on an integral of the first output current signal over the time interval matches an actual change in the first voltage signal over the time interval within a predetermined tolerance; storing beginning and ending output current values and time values from each of the plurality of time intervals as a first piecewise linear representation of the first output current signal, the first piecewise linear representation being referenced by the first input slew and the first output capacitance; and outputting a model of the driver cell based on the first piecewise linear representation.