Hi,
     What exactly do you mean by Volt-Amperic characterstics of a MOS ?

      1.  Are you referring to input-output transfer characterstics (id vs. vgs) ?
OR 2.  Are you referring to output transfer characterstics (id vs. vds for diff vgs )  ??

Anyways for both, you have two variables vds & vgs....In your schematic, place two voltage sources so as to vary these two variables....say, you keep your source voltage fixed...place one b/w source & drain & other b/w Source & gate.....Do a nested sweep....Obtain all characterstics that you want....

hope it helps,
mayank.