# MOSFET problem

#### chintu84

Joined Oct 18, 2006
6
Parameters: VTn = 0.75, Kn = 25 uA/V2, lambda = 0.05 V-1, Vdd = 10 V.
Calculate the output impedance (the total impedance as seen from the node labeled Vo) of this circuit, if IDS is 1.2 mA.
I have attached the circiut for this problem and i have been tring to solve this problem for 4days, and i hav got the answer as 2/gm, but the answer was wrong when i substituted the values.
can any one help me to solve this problem.
i have tried using small signal analysis.

#### n9352527

Joined Oct 14, 2005
1,198

#### Dave

Joined Nov 17, 2003
6,970
Posting your attempts at the small signal analysis would help. I take it you have modelled M2 as a resistor in the small signal model?

Dave

#### chintu84

Joined Oct 18, 2006
6
i got the out put impedance to be

Ro=Rs+ro(1+(gms+gmbs)Rs)

Rs=Vs/Ids

ro=1/lambda*gms*vs

#### Dave

Joined Nov 17, 2003
6,970
Sorry to be picky, but can you post the small-signal model circuit that you performed the above analysis on? The suitability of your equations is dependant on the circuit you perform the analysis on.

Dave