Can you also explain the differences between PMOS and NMOS characteristics? This

Question

Can you also explain the differences between PMOS and NMOS characteristics?

This is how I try to solve it:

I was taught to always assume it is in saturation and solve. Then, see if it makes sense, if not, try to solve for the triode equations. So,

I first "assume" it is in saturation and apply the formula:

ID=(1/2)?k??(W/L)?(vGS?Vtp)2

which gives:

.1mA=(1/2)(.08mA/v2)(25)(vGS?(?1))2

AndvGS=?.6837

Therefore, since in a NMOS it is in cut-off whenevervGS<=Vt

-.6837 > -1, and this NMOS would be in cut-off mode no matter what the resistance is.

Therefore, I know I am doing something wrong, but don't know what it is.

Explanation / Answer

In the saturation current equation, within the squared term, instead of (VGS - VTP), it will be (VSG + VTP)

For a p-MOS, the threshold voltage VTP is negative. Its -1V in your case, so when its value is put in the equation, you get (VSG - 1), instead of (VSG + 1).

When you solve this, you get VSG = 1.316 V, which is perfectly okay

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