Power MOSFET characteristics with modified spice modeling

It is suggested that the inclusion of a constant value of r sub s (the bulk series source resistance) is not sufficient to attain a good match to experimental I sub D (the drain current) versus V sub GS (the external gate to source voltage) curves for power MOSFETs. It is noted that a nonlinear source resistance (increasing with increased V sub GS) gives a much better fit. The parameters needed can be readily extracted from device characteristics, and it is shown how the nonlinear resistance can be incorporated when using a standard SPICE program. Another matter briefly examined is the degree to which the SPICE model, as modified by the addition of the nonlinear voltage source, adequately represents the shift of the transfer characteristics with temperature in the range 25-75 C.