DIFF pairs

[peter408]

Okay, I have some diff pairs that I need to keep loosely coupled. I need the gap to be the same most of the way between 2 points, but at some point I need to tune one of them so it will match the other in length by .005". I can set the gap and it will route fine, but I cannot figure out a method to uncouple one of the traces to tune it. Any ideas?

[Skip Yutkus]

You'll find a set of values in setup - constraints - electrical constraints. In there will be uncoupled + and - values as well as max uncoupled length, you must be carefull if you are autorouting - what will happen is 1/2 of the pair will uncouple, then length equalize for any distance it deems necessary and then recouple at your limit, obviously to us this violates the rule but Specctra doesn't seem to think so, you can end up with an inch of the pair uncoupled but recoupling back to the other leg at your limit tolerance.

I hope that made sense!

Skip