Piecewise polynomial models for MOSFET DC characteristics with continuous first order derivative

The measured DC characteristics of MOSFET show monotonically increasing smooth curves for given gate-to-source voltage. The authors describe two methods of polynomial approximation to these curves with continuous first order derivative of drain current with respect to drain-to-source voltage, which is often required for convergence in the circuit simulation. The polynomial coefficients, as a function of gate-to-source voltage, are so determined as to best fit the measured or theoretical curves and are used in calculating the value of drain current as a function of gate-to-source voltage and drain-to-source voltage, without any interpolation in actual circuit simulation. The required storage for the coefficients is minimal, the fitting is excellent, and the computational efficiency improves by a factor of up to eight over the SPICE simulation in the DC transfer curve generation