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 Net pairs on same layer 

Last post Wed, Jun 10 2009 9:13 AM by Jamez. 4 replies.
Started by Jamez 09 Jun 2009 03:17 PM. Topic has 4 replies and 1679 views
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  • Tue, Jun 9 2009 3:17 PM

    • Jamez
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    • Joined on Tue, Jun 9 2009
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    • Points 110
    Net pairs on same layer Reply

    Hello, I am trying to find a way to have pairs of nets follow the rules of a "diff. pair" except I do not want them to follow the same path. I prefer them to be separated from each other and can actually have other nets between them. They do need to be an the same layer however and be equal length. I would prefer not to assign them to a specific layer, rather let Specctra pick the layer. Any Ideas?

    Thanks

     

    • Post Points: 35
  • Tue, Jun 9 2009 11:00 PM

    • Khurana
    • Top 25 Contributor
    • Joined on Thu, Aug 14 2008
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    • Points 3,300
    Re: Net pairs on same layer Reply
    Put the nets in same class (in Constraint Manager).
    • Post Points: 20
  • Wed, Jun 10 2009 8:33 AM

    • redwire
    • Top 10 Contributor
    • Joined on Thu, Jul 17 2008
    • Allen, TX
    • Posts 875
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    Re: Net pairs on same layer Reply

    Unfortunately if you call them a diff pair you will get the "tightly coupled" version of the diff pair (you can make them edge or broadside).

    But you just want two equally matched 50 ohm lines and push your signal and its complement down each one and have them arrive at the receiver in unison?  Simple, just set them up as a matched group (relative propagation delay).  All the same benefits.  You can add multiple nets to this group -- if they all need the same distance rule.

    • Post Points: 20
  • Wed, Jun 10 2009 8:48 AM

    • Jamez
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    • Joined on Tue, Jun 9 2009
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    Re: Net pairs on same layer Reply

    Hi Khurana,  Thanks for replying. It is my understanding that if I puts the nets in the same class, I can get the = length I want, but not the layer assignment unless I specifically tell each net which layer I want it to route on otherwise the nets could end up on different layers. This limits Specctras ability to untangle. The other option I know of is to assign them as DIFFERENTIAL_PAIRs. This option makes the pairs route on the same layer and gives me the = length but one net always follows its pairs path at a set spacing gap. What I am really looking for is all the rules DIFFERENTIAL_PAIR has except I want to get rid of the Gap so that each net can take its own path but stay on the same layer. Thanks again.

    • Post Points: 5
  • Wed, Jun 10 2009 9:13 AM

    • Jamez
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    • Joined on Tue, Jun 9 2009
    • Posts 7
    • Points 110
    Re: Net pairs on same layer Reply

    Thanks redwire. I would like to let Specctra pick the layer (not assign the pair to 1 specific layer). I have 12 routing layers with 245 "pairs". I believe the matched group will put the nets on any of the 12 layers and not consider the pair requirments of being on the same layer unless I assign each pair to a specific layer. If I am wrong, could you please explain more on this. Thanks.

    • Post Points: 5
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Started by Jamez at 09 Jun 2009 03:17 PM. Topic has 4 replies.