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noise summary parameters and noise simualtions

Jeni

Hi,

I have 2 questions:

1. When I use a NEGATIVE resistor to in schematic the noise simulations and noise summary ADD noise - why is that? 

2.In the noise summary there is a noise contributor described as .rg with parameter rn. I understand that  this is the gate resistance noise contribution, but what is the exact calculation of this?

After some investigation, I think that this does not come from the bsim model , since in my bsim model file, the gate resistance is not modeled. I think that it is coming from the simulator itself.

If someone could point me to the exact equation/calculation of this noise it would be fantastic! 

Thanks

Jenia 

  • Andrew Beckett

    Answers to your questions:

    1. Noise analyses compute the output noise power spectral density (in V^2/Hz) and sum up the noise power contributions from each device. Since it's in V^2/Hz, negative noise voltages end up being a positive noise power - so I expect that's the reason. If you think about it, noise is random and can't subtract from the noise of the output, unless it's correlated with another noise source. At least I assume this is the reason without doing any investigation.
    2. I expect your model is actually a subcircuit model and has components other than just the bsim device. It probably has an explicit resistor for the gate. The simulator won't just make stuff up.

    Regards,

    Andrew.

  • Jeni

    Hi Andrew,

    Thank you for replying.

    Regarding the model, do you know how or where should I look for this explicit gate resistance you mentioned, which is not part of the BSIM model?

    I tried to change the rgx parameter inside the subcircuit model in the .scs file, but it had no effect on simulation results, therefore I suspect the simulator takes the resistance value from some other palce..  

    Thanks

    Jenia  

  • Andrew Beckett

    Hi Jenia,

    I'd say there's little chance of knowing what the problem is without seeing the model and what you've changed. You can't post it here (without breaking an NDA agreement), so the only viable possibility is to contact customer support, I think.

    Regards,

    Andrew.

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