Via Simplification in ADS Momentum

[big_fudge98]

Hi,

I am using ADS Momentum 2021 in Cadence Virtuoso IC618 environment for EM simulations. My simulations are taking way too long and hence I have turned on via simplifications (local via arrays keeping areas and boundaries). My question is, does this affects my simulation accuracy a lot?
Also, are there any other techniques to speed up EM simulations in Momentum?

(I have set the current mode in vias to 2D distributed type to avoid horizontal current flow in the generated via bars).

 

[volker@muehlhaus]

Via array merging is fine in most cases. The method that you describe sounds fine, you seem to have a good understanding of relevant settings.

You didn't mention what solver mode you use, microwave mode or RF mode. For non-radiating structures you can use RF mode up to pretty high frequencies, that gives massive speed-up compared to µW mode. I use RF mode for most RFIC work, even at 100GHz. The limitation really is: RF mode assumes zero radiation and no parasitic modes from electrically thick substrate.

 

[big_fudge98]

Hi, thanks for the reply. My frequency of interest is 200 GHz-250 GHz. I am using Momentum RF if the structure that I wish to EM simulate is less than half a wavelength. I use momentum microwave only when my structures are large. Also, I do not have any radiating elements on-chip.

 

[volker@muehlhaus]

From my experience, total size isn't really an issue if the coupling is predominantly local. But you can test that yourself.

But back to via array merging: that is safe in most cases. Exceptions are those cases where the "hollow body" of the merged structure creates a signifant change in current path, compared to all the straight paths through all the individual vias. In those cases, merging the array into multiple smaller blocks, instead of one large block, can be a useful compromise.

Best regards
Volker

 

[big_fudge98]

That's a good point. I'll keep that in mind. Thanks. As someone coming from a low-frequency circuit design background, handling return current has been a real pain, haha.