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Matching Segmented Differential Pairs...

pcbeng25

 I am using version 16.3 of the Allegro Router, and am trying to figure out how to write rules for matching a bunch of differential traces...however some of them have two segments as there is a small resistor network in the trace.  I need to match two differential segments to a single segment.

 For example:

 (FPGA) NetA --> Resistor --> NetB (Destination)

(FPGA) NetC --> (Destination)

 

So NetA + NetB = NetC

I have defined the pairs for Nets A, B, and C, and looked at creating a group for each fromto, putting them in a set and matching the group length, but it seems I can only include the p or the n side because it adds the total routed length, so if NetA is 2 inches, NetB is 2 inches, and NetC is 4 inches, and I put the p and n side fromto in the group, then the length match will be 4 inches for NetA and NetB and it makes NetC 8 inches.....If I only include the p side fromto in the group, then I get the 2, 2, 4 combination I desire, but I am unsure if this is the proper way to do this.

Using the class rules, I get undesireable results as well because NetA and NetB and both individually made to match the length of NetC which causes that path to be twice as long as the direct path without the resistor.

 Clear as mud...

suggestions?

Parents
  • KoryM

     The idea of the Xnet is that it is an extended net, encompassing both sides of the resistor.  The rule would take both sides into account, even though they are technically two distinct nets.

Reply
  • KoryM

     The idea of the Xnet is that it is an extended net, encompassing both sides of the resistor.  The rule would take both sides into account, even though they are technically two distinct nets.

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