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Assura QRC extraction

Jinsung
Hi, I have a question about Assura QRC extraction.

When I have multiple ground nodes, which nodes do I need to set as a ‘Ref Node’ in the ‘Extraction’  tap of QRC parasitic extraction run form? Otherwise, do I need to just set the ‘Ref Node’ to the backside metal such as ‘wafer!’?

The reason I started to have a question was that the QRC simulation results varied depending on which ground node I set as a reference node.

Thanks,

Jinsung

  • Hi Jinsung

    May I know if you are using "coupled" or "decoupled" cap extraction mode? You can set ref node to the main ground net in the design. If you are currently using decoupled mode, you should switch to coupled mode as it gives more realistic results.

    Best regards
    Quek

  • Hi Quek,

    It was "decoupled" cap extraction mode. I switched to "coupled" mode as you recommend, and now the problem is cleared.

    For anybody reading this post, I recommend to refer the QRC extraction user manual (page 169/170) for this issue. There are examples showing the different extraction results with "coupled" and "decoupled" mode.

    Thanks,

    Jinsung

  • Hi Jinsung

    It is good to know that your problem has been resolved. Decoupled mode will allow faster simulation but the results might be slightly optimistic because cross-talk problems caused by coupling parasitic caps cannot be detected. It is usually best to just use coupled mode. I would also like to highlight that for critical nets such as clock nets, you can use the built-in field solver to do the extraction so that you can have more accurate cap values. Extraction time will be much longer as field solver takes longer time to do the calculations.

    Best regards
    Quek

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