Surya,

  This should have been posted to the circuit simulation since your
question is tool related. You also refer to the tool that you seeking
help with ADE, Spectre, ...

  Have you connecting an ac current voltage source at the target
node and forced an ac current, mag=1?  Note: the other sources
need to be disabled for this test.

  Question for you, how would you calculate the conductance from
the response?

                                                                 Best Regards

                                                                    Sheldon

saam wrote on Sep 22^nd, 2010, 1:27am:
Your approach based on S-parameter Analysis is appropriate if "port" never affects DC operation point of circuits.
See http://www.designers-guide.org/Forum/YaBB.pl?num=1240334878/16#16

If not, your approach is not appropriate.