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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 

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  • 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.

Reply
  • 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.

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