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  3. Noise simulation wrong

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Noise simulation wrong

LukiLeu
LukiLeu over 7 years ago

Hi,

Since today I have a strange behaviour in the ADE Explorer. I perform different simulations in order to get some specifications for a fully differential opamp which I designed. All these simulations worked fine until today.

I changed something in the schematic of the opamp and since then the noise simulation is wrong when I simulate only one corner or perform a Monte Carlo simulation. If I simulate multiple corners the noise simulations calculates a correct result.

EG. I simulate for example the Nominal Corner, the noise simulation gives me a result of around 50uV/sqrt(Hz) (at a frequency of 200kHz) (way too much).
If i simulate the nomial corner and for example a corner with a different ambient temperature, the reported noise is around 10nV/sqrt(hz) (in the range of the expected value).

If I then open a debug environment and simulate the noise there it is again around 50uV/sqrt(Hz) (for the nominal corner and also for the other corners).

I tried to revert my opamp schematic to the point where it worked but the strange behaviour stays.

Do you have any ideas what is happening here and how to resolve this issue?

Kind regards

Lukas

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  • LukiLeu
    LukiLeu over 7 years ago

    I have now found a backup which works correct. I visualy compare the not-working and the working schematic but could not find any differences. However the file of the not working schematic is around 100kB bigger than the working one. I can provide the two schematics if that would be of any help.

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  • LukiLeu
    LukiLeu over 7 years ago

    I have now found a backup which works correct. I visualy compare the not-working and the working schematic but could not find any differences. However the file of the not working schematic is around 100kB bigger than the working one. I can provide the two schematics if that would be of any help.

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  • Marc Heise
    Marc Heise over 7 years ago in reply to LukiLeu

    You  have a higher chance to find the difference if you compare the netlists. Might be a device, might be a simulator statement.

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  • Andrew Beckett
    Andrew Beckett over 7 years ago in reply to Marc Heise

    This behaviour sounds very odd indeed, and doesn't like something I've seen reported before. Please contact customer support so that you can provide the data for an application engineer to look at in more detail to try to identify the problem.

    Marc is absolutely right though - maybe the difference in the netlists (input.scs files, since maybe it's a difference in the analysis setup) will make it clearer as to what is going on.

    Regards,

    Andrew.

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  • LukiLeu
    LukiLeu over 7 years ago in reply to Andrew Beckett

    The idea with the netlist just showed the difference between the working and the not-working schematic. There are two transistors which were added, however they should not have any influence on the noise. Especially as it is calculated correct when simulating multiple corners.

    Unfortunately I am not able to contact customer support direct, as I am taking part in the europractice programm. I will see if they can provide access to the customer support.

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  • Andrew Beckett
    Andrew Beckett over 7 years ago in reply to LukiLeu

    You can certainly contact EuroPractice support (via their web site) and then if they can't solve it, they will contact us (we work with EuroPractice closely). Please reference this discussion and let them know I'm happy for them to contact us to help with this issue.

    Regards,

    Andrew.

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