CMOS RFIC substrate ground

Hi

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

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: http://muehlhaus.com/support/ads-application-notes/inductor-em-ports:Dr. Mühlhaus Consulting & Software GmbH » Inductor EM simulation: 1-port or 2-port?

Best regards

Volker

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