I had a test recently and one of the problems was pretty basic. It gave you a table with the voltages at the gate, source, and drain of the device. Vt (Threshold voltage) was also provided, which was +1V. From there we were supposed to find Vgs, Vov(Overdrive voltage), Vds and the region of operation of the device. So for one part of the table I was provided with Vs (voltage at the source) is +1V, Vg (voltage at the gate) is +1V, and Vd (Voltage at the drain) is +2V. I know Vgs is Vg-Vs which in this case is 0V. And Vds is Vd-Vs which is +1V. However for Vov I got -1V which is solved by the equation (Vgs-Vt) so that would be 0-1=-1. This was wrong on my test. Does this mean the overdrive voltage can never be less than zero? Please help!