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Quantus Coupled vs Decoupled Parasitic Extraction Results

Aida

Hi all,

I extracted the parasitic capacitances of my layout (Charge Pump) using both the coupled and decoupled modes using Quantus Pegasus. The coupled result gives me closer result to the pre-simulation than the decoupled mode. In some of my designs (all charge pumps) the decoupled mode result is significantly lower than the coupled mode result. I am a bit confused because I read that the coupled extraction gives a  more accurate extraction with higher complexity and inclusion of cross coupling while the decoupled mode is against one node (VSS) and less accurate. I am wondering if such case happens or if i am missing some settings on the Quantus Setup? I have also attached a picture of the Quantus setup and extraction menu that I used below .

Thanks

  • Hi,

    In both coupled and decoupled modes of extraction, Quantus extracts the coupling caps between the nets. However, in decoupled mode, Quantus removes the parasitic coupling capacitor between two nets (or net nodes), and produces two decoupled caps, attaching one decoupled cap to each of the two nets (or nodes). These decoupled caps are reported to the reference net (VSS in your case), but were actually extracted between signal nets.

    Coupled RC netlists can be slower to simulate, but some sensitive circuits might need coupled cap extraction to yield accurate results. This is probably the case for you. If you are concerned about the results you get with decoupled extraction, please contact Cadence customer support so they can take a closer look at your results.

    Regards,

    Saloni

  • in reply to Saloni Chhabra

    Thank you for your response! Yes i am concerned about the results because the coupled extraction gave me higher result that matches my pre-extraction simulation while the results from decoupled extraction where significantly lower. I will contact customer support. Thank you!

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