# MOSFET problem

Discussion in 'Homework Help' started by chintu84, Nov 15, 2006.

1. ### chintu84 Thread Starter New Member

Oct 18, 2006
6
0
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.
Express your answer in Ohm, accurate to 1 Ohm.
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.

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2. ### n9352527 AAC Fanatic!

Oct 14, 2005
1,198
4
Could you post your attempt in steps please?

3. ### Dave Retired Moderator

Nov 17, 2003
6,960
145
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

4. ### chintu84 Thread Starter New Member

Oct 18, 2006
6
0
i got the out put impedance to be

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

Rs=Vs/Ids

ro=1/lambda*gms*vs

5. ### Dave Retired Moderator

Nov 17, 2003
6,960
145
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