About tricky differential pair routing

[mulfycrowh]

Hi everyone,

What solution do you implement when the differential pairs you have to route cross each other ?

Thanks for your comment.

[mulfycrowh]

I have a good example there.
I have highlighted the differential pair.
It would be convenient to change the layers using vias to be able to gain access to the balls on the chip.
We speak here about DisplayPort signals.

What is your experience changing the layer on high speed differential pairs ?

[robertferanec]

Cross them when changing layers.

[mulfycrowh]

robertferanec Robert, I know that I can change the layer but changing the layers for differential layers is not a good thing.
You maybe have ideas to avoid this.
In that case modifying the schematic doesn't really help.

[robertferanec]

There is no other way, unless the chip supports polarity swamping.

[robertferanec]

Oh, you mean to change the order of the whole pair? Still the same, you may need to change layers.

[mulfycrowh]

robertferanec Changing the order without changing the layer is quite easy, the true problem comes when you have something to cross.

[mulfycrowh]

I just wanted to show the technique I use to reorder the differential pairs and also to change the polarity (first pair on top).