Stats

  • Locked Locked
  • Replies 9
  • Subscribers 127
  • Views 18194
  • 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

Why gm is not zero even when iDS is a constant DC current?

BaaB

I am trying to plot transconductance gm of M0 in the picture below. However, what I am supprised here is why gm is not zero when iDS is a constant DC current (1uA).

gm = diDS/dvGS

So according to this, gm should be zero when iDS is a constant.

As seen from the picture below, gm is not zero.

Could anyone explain why and how gm is calculated by the simulator?

Thank you.

Parents
  • BaaB

    Thank you very much for the help.
    I think I misunderstood how transconductance is calculated by DC analysis.
    I thought that firstly it would plot large signal iD = f(vGS, vDS, vBS) and then derivative the curve, evaluate the value of the derivatived function at operating point to get gm.
    For transconductance formula, I think this is what you referred to.
    I am familiar with these formulations too.

    I would like to see the formula for gm in Virtuoso® Simulator Components and Device Models Reference. (cdnshelp)
    I tried to find it there but couldn't locate it. There is a transconductance parameter formula but it is a totally different parameter.
    If possible, could you tell me where in the manual should I find it?

Reply
  • BaaB

    Thank you very much for the help.
    I think I misunderstood how transconductance is calculated by DC analysis.
    I thought that firstly it would plot large signal iD = f(vGS, vDS, vBS) and then derivative the curve, evaluate the value of the derivatived function at operating point to get gm.
    For transconductance formula, I think this is what you referred to.
    I am familiar with these formulations too.

    I would like to see the formula for gm in Virtuoso® Simulator Components and Device Models Reference. (cdnshelp)
    I tried to find it there but couldn't locate it. There is a transconductance parameter formula but it is a totally different parameter.
    If possible, could you tell me where in the manual should I find it?

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.