[SOLVED] NMOS IV characteristic completely different with 2 similar setup

[henry kissinger]

I am plotting the IV characteristics of the NMOS of 2 similar setups.

Here I sweep the Vg from -13 to 13V and vdd from 0 to 50.

note that the only difference is that vdd is positive for one but negative for the other. both grounded at the other end.

But why I am getting 2 different IV characteristic results? should't they be the same? Shouldn't that Id curve should be only related to difference in drain and source voltages when nmos is turned on with same Vg?

 

[BigBoss]

\[ V_{gs} > 0 \] condition must be maintained.
MOS Transistors may be symmetric on layout but not in model.Therefore they remarked "Source" and the others.
We also don't know that the MOS transistors are Depletion Mode or Enhancement Mode ?

 

[FvM]

Switching Vds polarity means switching drain and source. Respectively Vgs is not the same for both setups.

 

[henry kissinger]

Switching Vds polarity means switching drain and source. Respectively Vgs is not the same for both setup

ｔｈａｎｋ　ｙｏｕ．　ｕｎｄｅｒｓｔａｎｄ　ｎｏｗ！