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How can I make one track of the differential pair jump to the bottom layer while the other track stays in top layer ? Currently I only know that when using differential interactive routing in Altium and trying to use vias, it is not possible to do it separately for a track, but both. How can do it then?

enter image description here

asterix
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  • this is a question that is really easily answerable by doing a bit of google research, and there's also sufficient video tutorials out there, and there's also very many questions about differential pairs on this site; you really didn't do your part of the research. Not to mention that the thing you circled doesn't match your description. – Marcus Müller Jun 24 '19 at 21:17
  • @marcus-müller the question is not well written but the marked part is what he describes: it's a cross over between the two lines of a USB data pair – asdfex Jun 24 '19 at 22:30
  • Possible duplicate of [USB signal routing - Swap data lines using vias?](https://electronics.stackexchange.com/questions/209236/usb-signal-routing-swap-data-lines-using-vias) – asdfex Jun 24 '19 at 22:32
  • sorry my question was wrong. The exact question is the photo attached. I know there are videos, no for this cross between layers – asterix Jun 25 '19 at 02:31
  • Route the traces as single ended when you do that. – Wesley Lee Jun 25 '19 at 16:14
  • but I can not do impedance control I guess. – asterix Jun 25 '19 at 17:01

1 Answers1

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You can manually route parts of differential pairs using the standard routing tool. Just exit the differential routing command and start the regular route command to complete the segment of track that's on the bottom layer. Then re-start the differential routing tool to continue.

That being said, generally you should keep both tracks on the same layers. If you have to drop one through a via, then you should drop the other one through a via as well. Normally you should try to avoid vias in high-speed routing altogether because it can cause discontinuities and result in reflections that could distort the signals. I see in your case all you need to do is swap the positions of the conductors in the pair. There are a couple of tricks you might try to reverse their positions. The first is to use SMD resistors (R19 and R20 in your design) as "bridges", and route the track of one conductor between the pads of the resistor on the other line. See the light blue "trace" in the graphic below for a suggestion. You may need to use a larger resistor package size, depending on whether or not your trace will fit between the pads of the one you are currently using.

enter image description here

Another idea might be to route around connector or IC pads (though I don't see a practical way to do this in your particular situation). I think your best bet is to use resistors as a jumper to cross the traces over each other. That way you keep both pairs on the same layer and you minimize discontinuities.

DerStrom8
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  • Thanks for your great answer, Really. It is not my design, It is a eagle file of Arduino Due I downloaded from official page pf arduino. – asterix Jun 26 '19 at 02:34