Hi all,

I barely dealt with MOS devices in weak inversion condition before, and now I'm facing such problem. I have a basic question concerning the differences (if any) between weak inversion condition and sub-threshold.

From what I know, weak inversion could be achieved under the following conditions:

1) if VG < VTH (subthreshold)
2) if  VG > VTH and both VS and VD are higher than the pinch-off voltage

From my standpoint, scenario #2 is different than #1 since the channel was previously well stablished (strong inversion) and afterwards the pinch-off condition is reached. On the other hand in #1 there are some free minority carriers which comprise the sub-threshold current, which is mainly a diffusion current.

I also know both conditions are well modeled by ID being exponentially dependent on the gate voltage, but not sure if the parameters are the same (I would expect they are different).

Could anyone enlighten me about the differences about these two operating conditions for a MOS device?

Many thanks
tosei

Hi Vivek,

Thanks much for your answer. However, I'm still a little bit confused:
In which case you are saying that VTH is higher? I understand that there is no channel in both cases; so I guess I'm getting confused with the references I'm using.

Thanks & Regards
Tosei