Stats

  • Locked Locked
  • Replies 7
  • Subscribers 125
  • Views 20505
  • Members are here 0
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Problem in Cadence Virtuoso AC analysis

OneNewBoy

Hi all,

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 ?

 

 

Parents

  • Hi Andrew,

    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 ! 

Reply

  • Hi Andrew,

    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 ! 

Children
No Data

Community Guidelines

The Cadence Design Communities support Cadence users and technologists interacting to exchange ideas, news, technical information, and best practices to solve problems and get the most from Cadence technology. The community is open to everyone, and to provide the most value, we require participants to follow our Community Guidelines that facilitate a quality exchange of ideas and information. By accessing, contributing, using or downloading any materials from the site, you agree to be bound by the full Community Guidelines.