Differential pair spacing

[eric_engineer]

How do I set my differential pair spacing?  I see a width option but no spacing option. I hope this is not one of those things that's missing or can be fixed by modifying a DRC rule that affects everything else.  It's amazing to me that Fusion sells a Ansys high-speed design option, but lacks so many basic differential pair and other high speed routing functions. We can't route any of our high-speed stuff with 360 but I'd like to.

[Evert_2N3055]

This is controlled via DRC setting and through NET classes. So I would set special net class to DP and set appropriate rules.

[marcocipriani01 · Accepted solution]

This is probably the single stupidest thing about doing high-speed designs in Fusion Electronics. You can only set the minimum spacing between two wires of the same net class, using the "Clearance Matrix" in the "Net Class" settings. There is no way of setting a fixed spacing between two signals in a differential pair...

In the following example, I've set the spacing between USB_D_P and USB_D_N by creating a USB net class and defining a 0.254mm clearance between the USB net class and itself (look on the diagonal of the matrix).

The Fusion team should definitively improve differential routing, IMHO. The Meanders tool is awful to use.

[eric_engineer]

Oh, I forgot about this. Thanks.  Yeah, high-speed support in general is pretty awful I feel. I'm remembering now that last design I had to do groups of length matched diff pairs and I had to do all the matching slowly by hand.

[jorge_garcia]

Hi everyone,

Thank you for your comments, this stuff is actually being addressed in the near term so expect some improvements soon. 

Our developers ran into this thread before I had a chance to report it so your feedback is very much of interest to our team.

One thing to help in the mean time. When you are routing the meanders you can enter a length in the CLI and press enter. So once you know what the longest diff pair is you can meander all the other to that length by entering the length in the command line.

Another thing that will help is starting meanders from one end of a segment and working your way towards the other end. In the DRC set your Gap Factor to 1 in the Misc tab. Those things will help.

All of this is being addressed, but the above can help for now.

Let me know if there's anything else I can do for you.

Best Regards,