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SNP with internal ports

Question asked by SCHAEFFNER.HARALD.DA on Jun 7, 2007
Latest reply on Feb 10, 2008 by ALEPEREZ

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Hello - as described in a previous post the SNP component for momentum data only work with internal or single ports. For a substrate with ground plane no problem - but I use no ground plane. So i wounder to what point the impedance of a internal port is referenced to?

Thanks for support!
Harald:P

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ALEPEREZ Jun 21, 2007 3:41 AM
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Internal ports without an infinite ground plane and without a ground reference use the concept of "ground at infinity". These S-parameters tend to be quite unphysical in nature, but can be recombined to give physically valid results using Circuit simulator with Layout Components properly wired.
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ASWIN Jan 17, 2008 2:55 PM
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As the problem I face is similar to the question in this thread, I thought I would re-open this thread.

I am trying to simulate a Top-C coupled filter where the coupling capacitors are implemented as overlapped capacitors. To give a better idea, this is the substrate definition I use.

----Copper layer1
Substrate
----Copper layer2

Electrical Schematic:

--||---shunt resonator---||---

As there is no physical ground plane for the overlapped caps, it would be helpful if someone could clarify the following questions:
1. The best way to simulate overlapped capacitors in Momentum and
2. The best way to get these results into circuit simulators (Co-Simulation).

Thanks
Aswin
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ALEPEREZ Feb 10, 2008 8:20 PM
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Even if you have two capacitor plates with some feedline extensions (or no feedline), you usually have a ground plane somewhere. You can then use two single or internal ports on each plate edge to run the simulation. Sometimes, capacitor plates need to be seeded a bit denser than the default if the capacitor parasitics at very high frequencies are of interest (e.g., self-resonance). Later, when you tie the cap in series with the rest of the circuit, the ground plane is effectively taken out of the picture. If you simulate the cap without any ground plane using 2 internal ports, the recombined SPs in the schematic may still be valid, but might suffer some accuracy loss.
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SNP with internal ports

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