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VXL: Setup Vias for Shield Constraints?

JoeyT

Hi All,

I've been exploring the shield constraints for routing in VXL. One thing though that I can't find a setup a for is the vias for the shield lines. Everytime I change metal layers, the shields follow, but somehow they don't create vias for themselves to stay connected. is there a way to set it up that the shields run along the 'net' they are protecting like normal routing? the picture below describes my question. basically I prefer the image on the right, but all I get is the one on the left. is there a setup for this? I really appreciate the help. thanks in advance :)

  • skillUser

    Hi Joseph,

    I've certainly seen this in the past, that the shields are not fully connected when changing metal layer.  I have a feeling that this is a known limitation of the shielded net routing, however, my information is probably old - are you using the latest version of virtuoso (IC617/ICADV12.2) ? It is probably worth filing a service request with Cadence to request that this is improved (if they have not done so already).

    Cheers,

    Lawrence.

  • JoeyT

    Hi Lawrence,

    Thanks for the reply. I'm currently on IC616 but will soon be upgrading to 617. I think this shield constraint is a great feature and has potential. it would be a great improvement if Cadence can add an option to connect these shields.

    Cheers

    Joey

  • ColinSutlieff

    Hi Joey,

    there is, in fact a feature: Menu "route"->"tie shield" that is available in 616 and 617.

    You may want to try it out.

    If you don't get the results you want there are some alternatives that may want to try out.

    If you have overlapping shields try out the auto via command (create->via, auto,create "connected shapes on the same net" on) followed by Middle-Mouse Button drag over the whole area where the net is.

    Another option could be to simply use the create->wiring->bus and route the 3 wires together.

    Regards

    Colin

  • JoeyT

    Hi Colin,

    Thanks, I've looked at the 'Tie shield' but from what I understand, it's a feature to tie shields to closest power/ground. It doesn't seem to have any other options to get the shields connected. Your other two suggestions I've already tried before. The bus wire 'alternative' is actually also one of my strategies for manually creating shields. This shield constraint has some potential though and I'd like to explore it more.

    Thanks for your suggestions.

    Regards

    Joey

  • ColinSutlieff

    Hi Joey,

    O.K. Just one more thing ..

    Your shield nets should have the property power or ground for this to work.

    In the Navigator, select the shield nets.

    In the Property Editor, change the signal type to power/ground.

    Regards

    Colin

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