Modelling of a diode

so i have a SPICE simulation where i put a 1 volt sawtooth wave through a diode in the following circuit with the following graph Then i can then plot the V-I graph, and then i've tried to use a curve fitting program in order to find the value of the saturation current, ideality factor and the other terms given by the diode equation,the problem is that the values don't make any sense as i get a value of 7.713E-08 for the saturation current and 0.15 for the ideality factor. letting S be saturation current, and n being the ideality factor. thermal voltage is assumed to be 0.25 I've also tried the circuit without the resistor so the I-V graph takes into account the whole voltage drop of the circuit, but nothing seems to help. i've also tried using different diodes in SPICE(I'm using Partsim)

Am i doing something fundamentally wrong? and can this method be used in order to get the diode equation or not?

thanks

• thermal voltage (kT/q) is about 25 mV , 0.25 is 250mV – JIm Dearden Feb 12 '17 at 20:52