[SI-LIST] Re: MGB/s pair crossing on adajent layers
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Hirshtal Itzhak <ihirshtal@xxxxxxxxxx>
- Date: Wed, 02 Jun 2010 03:54:23 -0700
True perpendicular routing should not introduce any significant
cross-talk. If you are autorouting, I would be more concerned with
keeping the number of layer swaps and their associated vias / via stubs
in check.
On the other hand, if you have significant parallelism between offset
stripline layers then you can manually estimate or better use a field
solver to figure out how much cross-talk you are going to get. It
should come as little surprise that if you have 4 mils to your return
plane and 4 mils to parallel victim traces that you can couple a
significant amount of energy into the victim traces. You would want to
review that carefully to see if it is enough.
Steve
Hirshtal Itzhak wrote:
> Hi Experts!
>
>
> I use double-stripline layers for MGb (PCI-Ex, sRIO) pair routing. I
> ordered the PCB Designer not to route such pairs on adjacent layers,
> close to each other, not even PERPENDICULAR to each other.
>
>
>
> Now it seems I can't avoid it any more. My PCB Designer seems to run out
> of real-estate.
>
>
>
> I have 4-mil separation between the 2 layers and 4-mil from each one to
> a GND layer on each side.
>
>
>
> The pairs are running at 2.5 to 3.125 Gb/s
>
>
>
> What risks, if any, I run into, if I do permit routing the pairs
> perpendicular to each other? Are there any precautions I should take
> while doing it?
>
>
>
> Thanks
>
>
>
> Itzhak Hirshtal
>
>
>
> Elta
>
>
>
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--
Steve Weir
IPBLOX, LLC
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