High speed length tuning. Need help to know which measurement to go with

Layout
1

Hello all.

This is somewhat of a continuation of what my high speed signals checking. I have everything the way that I want. I setup my DRC to get the lengths of the high speed traces. However, for like 4 pairs, the length from the DRC differs from when I highlight the net. I have been spending some time on this issue, but I can’t seem to figure out why there is a discrepancy with this. How I know? When I tune the net to what the DRC says, the net length went highlighting is not what the DRC says. When I tune the length to match what the values are when highlighting the net, I get the DRC errors.

I don’t want to waste much time on this now (I think that I need to investigate what is going on). But which measurement should I tune the lengths to? The one reported in the DRC? Or the one reported when highlighting the net?

2

Hello all,

Could use some feedback on this one

3

It is a known issue at the moment unfortunately

However, there are a couple of forum post detailing some work arounds, all of them manually until the issue gets fixed (Look for post from JamesJ, he appears to been dealing with those lately)

I hope this helps

4

It is a known issue, but it’s not related to the thread / bug you shared I’m afraid. This issue is that the various places which show length use slightly different calculation methods. I’ve fixed this for the next version, so it’s sorted in the testing builds:

For now, in this instance I’d go with the DRC lengths.

1 Like
5

Thank you for this. Just for the record, this is the DRC rule that I created for the length tuning. Even though they are separate netclasses, I decided to separate them out for future revisions

(version 1)
(rule "Diff_90R intra-pair length matching"
    (constraint skew (within_diff_pairs)(min 0mm)(max 0.127mm))
    (condition "A.Netclass == 'Diff_90R'"))

(rule "Diff_100R intra-pair length matching"
    (constraint skew (within_diff_pairs)(min 0mm)(max 0.127mm))
    (condition "A.Netclass == 'Diff_100R'"))
1 Like