Electronics > Altium Designer

Delay Matching Issue in PCIe with Interactive Length Tuning

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electronx:
I want to do delay matching for PCIe, where there are coupling capacitors in between. I clicked on two target pads and defined an xsignal for both UPHY_TX0_N and UPHY_TX0_P.

Then, I defined a rule for intra-pair delay matching and included it in my xsignal. As seen in the picture, the UPHY_TX0_N signal is -3.167ps behind the UPHY_TX0_P signal.

After defining the rule, when I select the interactive length tuning tool and try to extend the UPHY_TX0_N signal, it starts to exceed the UPHY_TX0_P signal. What should I do to resolve this issue?

Pseudobyte:
What picture?

electronx:
thanks for reminder

ajb:
It's been a while since I used the length matching tool, and it looks a little different from what I remember.  It looks like your target length is shorter than the initial length of the track.  What happens if you uncheck "Clip to Target" (in the properties panel in your third screenshot) or increase the target length?

Pseudobyte:
I have only ever seen that popup when I miss-click the wrong net within the diff pair. Try tuning the other one.

Also from your screenshot that shows the entirety of the net it would make sense that you are tuning the wrong one.

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