Defining rectanular ports in Momentum-Virtuoso environment

[big_fudge98]

Hello everybody,

I am doing some EM simulations using ADS Momentum (ADS 2021) in the Cadence Virtuoso (IC618) layout environment. From what I understand, the way a port is defined (point/edge) can have different impacts on the results, right? Is there any way to define a port as a rectangle?
The particular case I am trying to simulate is as follows: I have a signal line feeding the M6 layer at an edge. This signal is then connected to M1 through a via stack. So, M6 receives excitation along the edge, while the whole M1 sheet receives the excitation. I was wondering how to define the port at M1. I feel some sort of rectangular port definition is required, but I can't seem to find this option anywhere.
Thanks.

 

[BigBoss]

-Point/Edge Port definition impacts definitely the result.No doubt..Unless the metal shape is not larger than minimum wavelength, Point Port or small Edge Port is appropriate otherwise you'll have serious troubles.You can see that Momentum simulation log as warning messages..
-If your structure has been defined on Metal Layer M1 only , you don't have to make it ascend up to M6 because effect of VIAs is not dominant.If you place a PIN on M1 in Virtuoso Layout, Momentum will recognize this PIN as a Port.This can be rectangular or any shape but Momentum will recognize it being as Point Port.

 

[volker@muehlhaus]

One more comment: if your Metal1 is a large solid ground plane, I would recommend to modify the stackup and model M1 as a metal boundary, instead of having the full stackup with M1 as a thick metal model.

For RFIC transmission lines above 50-100 GHz, I had seen some strange dips in transmission which we didn't understand for a long time. They disappeared when using M1 as a boundary, and they also disappeared with 3D solvers that model M1 as a solid volume. It seems that this effect is related to Momentum modelling thick metal as hollow tubes, and my port was only touching the top side of that M1 ground hollow tube. Then, at some frequencies two ground current paths (one on the top side of M1 ground, and the other longer path around the edge to the bottom side of M1 ground) created a resonance that isn't real.

This indirectly solves your ground pin shape issue also, because you don't need an explicit ground pin in that case. M1 defined as a boundary will be used by default, as it is the nearest infinite ground.

 

[big_fudge98]

-Point/Edge Port definition impacts definitely the result.No doubt..Unless the metal shape is not larger than minimum wavelength, Point Port or small Edge Port is appropriate otherwise you'll have serious troubles.You can see that Momentum simulation log as warning messages..
-If your structure has been defined on Metal Layer M1 only , you don't have to make it ascend up to M6 because effect of VIAs is not dominant.If you place a PIN on M1 in Virtuoso Layout, Momentum will recognize this PIN as a Port.This can be rectangular or any shape but Momentum will recognize it being as Point Port.

Thanks. My layout is electrically small. I observed that adding point/edge ports hardly affect anything.
Also, in this case, my objective is to characterize the impact of vias on a FET. (And it is significant at high frequencies). Hence I need to use vias.

--- Updated Feb 13, 2021 ---

One more comment: if your Metal1 is a large solid ground plane, I would recommend to modify the stackup and model M1 as a metal boundary, instead of having the full stackup with M1 as a thick metal model.

For RFIC transmission lines above 50-100 GHz, I had seen some strange dips in transmission which we didn't understand for a long time. They disappeared when using M1 as a boundary, and they also disappeared with 3D solvers that model M1 as a solid volume. It seems that this effect is related to Momentum modelling thick metal as hollow tubes, and my port was only touching the top side of that M1 ground hollow tube. Then, at some frequencies two ground current paths (one on the top side of M1 ground, and the other longer path around the edge to the bottom side of M1 ground) created a resonance that isn't real.

This indirectly solves your ground pin shape issue also, because you don't need an explicit ground pin in that case. M1 defined as a boundary will be used by default, as it is the nearest infinite ground.

Thanks. I'll keep this in mind.