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What's the definition of "Ref node" in QRC extraction?

greatqs

I know from the user guide it says "Ref node" specify the reference node (net) that QRC will use for decoupling capacitors during a run.

But what's the physical meaning for this "decoupling capacitors"? I think every parasitic capacitor should be explicitly specified by schematic/layout net names without specify this magic "Ref node". 

 

  • If you choose "decoupled" as how capacitors are extracted, instead of getting capacitors from one node to another, all the capacitors on each node will be lumped and connected to "ground". This reduces the number of capacitors in the circuit, but of course does not capture the effects of coupling one node another. In addition, even if you pick "coupled", if the capacitances are small (below the minC value), then they get decoupled to "ground" to ensure that any resulting simulation matrix remains sparse and not full of tiny capacitances.

    The "Ref node" defines the ground node that should be used for any capacitor to be decoupled to.

    Regards,

    Andrew.

  •  Andrew,

     

    Thanks for your detaled explanation.

     

    Thanks,

    QS

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