I am facing an often discussed problem while simulating a differential pair in cadence virtuoso.
Though I have biased the transistors through DC (though they are in subthreshold mode), yet when I try do do ac analysis (I follow all regular steps) I get a zero magnitude at output. Ths schematic is attached.
Can someone help me in debugging this ?
I had a little doubt on what parameters are explicitly needed for ac analysis. This is because I am using verilog -A based models and hence want to be sure if I am doing the right thing.
As far as I know, AC analysis first computes the DC operating point: so I must define current at each operating/gate voltage.
Now at that particular operating point, I expect that spectre automatically computes all variables like transconductance/output resistance etc., which it will use in the linearized model representation of the circuit.
So I wish to know if I need to provide these variables explicitly at each operating point and somehow include them in building a small signal model, to get MOSFET drain current as function of small signal inputs ?
Thanks a lot !