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

Measured MOSFET DC characteristics show monotonically increasing smooth curves for given V_gs (gate-to-source voltage). The authors describe two methods of polynomial approximation to these curves with continuous first-order derivative δI _ds/δV_ds, which is often required for convergence in the circuit simulation. The polynomial coefficients as a function of V_gs are determined to best fit the measured or theoretical curves, and used in calculating the value of I_ds (drain-to-source current) as a function of V _gs, V_ds, and V_bs (bulk bias 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