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Parasitic exclusion

manudupouy

Hello,

I was using parasitic filter from an extracted view to discover the worst influences. I understood that I could add some parasitics or include all parasitics of an extracted view. So, if I want to simulate my circuit with all parasitic excluding a net, I have to include all parasitics in my constraint window and deactivate the one I don't want. Logic. But, it would be more simple in this case, by default activating all parasitics (without including the long list of parasitcs) and only put in my constraint window the net I don't want the parasitics.

Is it possible?

Emmanuel

  • Andrew Beckett

    Hi Emmanuel,

    This can be done with a combination of parasitic filters (I'm assuming you're using the Parasitic Filters in the constraint view - selected via the Parasitics/LDE menu in ADE XL?).

    The idea is that you add a parasitic cell filter for C and R which means that it will include all parasitics by default, and then you'd add a normal parasitic filter for R and C where you turn off the parasitics for the specific nets. In the picture below I've done this (just for excluding the resistances on a particular net):

    Hope that's clear?

    Regards,

    Andrew.

  • manudupouy
    in reply to Andrew Beckett

    Yes, it is clear. Thank you very much Andrew.

    I had tried this option but I was unsuccessful because, for caps, I only selected one net to deactivate all caps connected to that net. It didn't work. So, I concluded that was the wrong way.

    But you showed me it was the right way. And to deactivate caps, I have to select the two nets where the caps are connected.

    Whatever, it is fine now.

    Thanks again.

    Regards,

    Emmanuel

  • manudupouy

    Hi,

    One year later. I am back with another problem related to parasitic filter. So, I put it on the same post.

    I don't obtain the same result when I simulate the schematic and the extracted layout where I filtered all parasitics.

    So, could you explain me why such a difference please Andrew?

    It's a real problem for me because I optimized my schematic and was looking for problematic tracks on my layout. My initial step was to begin to simulate the extracted layout without parasitic and add influence of tracks one after one.

    Emmanuel

  • Andrew Beckett
    in reply to manudupouy

    Hi Emmanuel,

    When you are using parasitic filters to filter all parasitics, you are still using the designed devices from the extracted view. This means that any parameters extracted for those devices, such as ad, as, pd, ps, length-of-diffusion effects, well proximity effects and so on, will have been extracted by your LVS tool. With the schematic, you would (at best) have estimates of those parameters - but they will be different, almost certainly.

    So I wouldn't expect the results to be the same, even if you'd filtered all the parasitic Rs and Cs.

    Regards,

    Andrew.

  • manudupouy
    in reply to Andrew Beckett

    Hi Andrew,

    Understood. Thanks a lot for your answer.

    Emmanuel

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