Diff Amp Biasing

Discussion in 'General Electronics Chat' started by mr_ivoryz, Nov 19, 2011.

  1. mr_ivoryz

    Thread Starter New Member

    Nov 19, 2011
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    I am trying to figure out why there is 2.55mA running through the drain of M1? Its seems way too high....

    The currents out of the Source of M1 & M2 are negative, due to LTspice's definition, but they are flowing the correct way.

    Does anybody know why M1's drain current is so high? is their something wrong with my circuit design/DC Biasing?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Did you check your gate and substrate currents?
    Probably not. That current has to be going somewhere.

    You didn't post your cmosedu_models.txt file. Sometimes people put ground references in subcircuits, which can cause unexpected problems in a simulation.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Your mystery missing current is in the substrate.

    Try connecting the substrate and drain together.
     
  4. mr_ivoryz

    Thread Starter New Member

    Nov 19, 2011
    8
    0
    Thanks for the response Sgt Wookie. I tried connecting the substrate to the drain, and the drain current went down, but now the source currents are not in unison. (See Attached Photos)

    Do you think I need to use a diffrernt NMOS model? I have included the txt file with the parameters. I am using the N_50, which I got from Jake Baker's website. (I also included the DC Parameters from the original circuit)

    Any other other insight you might have on how to fix this mystery current? Or if anyone else knows how to fix this problem, please jump in.
     
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