Getting a match to output characteristic plots from data sheet values can be difficult, and involves some trial and error. Our datasheet parameterization gets the most important part right i.e. the characteristics at the on-state working point. To match
characteristic curves away from this point, you can fine tune the following:
1. Gate-source threshold voltage, Vth: Don't necessarily put exactly the datasheet value - the datasheet will typically quote a maximum value for the threshold, as this is worst-case if you're trying to ensure the device is fully turned on. Characteristic plots on the other hand will be for some nominal/typical value.
2. Ohmic resistance values Rd and Rs: These shape the curve at higher currents i.e. when they become straight lines, the I-V gradient being inversely proportional to the resistance.
3. Channel modulation, L: This affects the slope of the I-V curve at high Vds and low Ids.
If tuning these parameters proves insufficient, you can use the SPICE MOSFET block in the Additional Components Library. This has many more things you can tune, but, you'll need a good understanding of the underlying models to do this effectively. The following is a link to the aforementioned block:
<http://www.mathworks.com/help/releases/R2011a/toolbox/physmod/elec/ref/spicenmos.html>
