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CMOS RFIC substrate ground

Question asked by engrvip on Sep 12, 2017
Latest reply on Sep 13, 2017 by volker_muehlhaus

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I want to simulate a RFIC inductor layout in CMOS technology. During EM simulation which layer will be used as a GROUND, since in RFIC several metal layers and substrate itself can be assigned a ground?

I have seen some places where infinite ground is defined at bottom of substrate ? What kind of applications determine this approach of assigning ground at bottom of substrate ?

Regards

Vipul

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volker_muehlhaus Sep 13, 2017 12:17 AM
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Hi Vipul,
- If you have not assigned a terminal for the port, Momentum will use the nearest infinite ground.
- We want to see the effects of substrate on inductor. We want to have a substrate node in results, for possible common mode effects to the substrate. Placing the infinite ground at the substrate surface is a bad idea, because that would shield the substrate and give results that are not real. So indeed, we place the infinite ground at the bottom of the substrate.
- If you are interested in purely differential operation of the inductor, and don't need to include the common mode response, you can also use an explicit terminal. I wrote an appnote on that topic: Dr. Mühlhaus Consulting & Software GmbH » Inductor EM simulation: 1-port or 2-port?
Best regards
Volker
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