raja.cedt wrote on May 21st, 2009, 12:19pm:hi buddy poor,
in the first what i mean to say for finding dc gain both methods has to give same answer, how capacitive coupling will effect? or could you please explain how to find dc gain?
for second question i derived expression for output impedance and substituted all small signal parameters (gm,gds) from .op result and i have same operation point in both cases?
Thanks,
Rajasekhar.
During dc analysis all capacitors are neglected (set to zero Farad).
Therefore, if caps are there, results of dc and ac analyses are different.
Regarding the output impedance, I would trust the simulation results.
Probably your calculations using formulas are not correct.
Which formula did you use ? Is the circuit a simple common source amp without any feedback?