[Arm-netbook] HDMI High-Frequency Layout: Recommendations
Luke Kenneth Casson Leighton
lkcl at lkcl.net
Thu Aug 10 09:18:50 BST 2017
On Thu, Aug 10, 2017 at 9:01 AM, mike.valk at gmail.com
<mike.valk at gmail.com> wrote:
> 2017-08-09 15:23 GMT+02:00 Luke Kenneth Casson Leighton <lkcl at lkcl.net>:
>> next set...
> GND shielding parallel to the differentials is interrupted quite
because there's simply not enough space to do otherwise. if i could
move the entire CPU and RAM up another 0.5mm it would be doable. but
then i would have to re-route 12 signals which go around the top area
of the board and that's (a) risky and (b) not enough space to do it.
> Those GND tracks act as shields, for emission and reception.
> I'd try to put as much parallel GND as possible.
> And trace the parallel GND around the via's, see attachment.
ah, got it - thanks for the tip, i thought i'd done that on all
diffpairs, but i missed one. good call.
yes there's only one, because the layer 1 and layer 6 will be
flood-filled and that will fill the areas that "appear" to be missed.
> Make sure the'res as much solid GND on the layer above and below the
> traces, again shielding.
these are layer 1 and layer 6, and layer 2 and 5 are solid GND.
> Also I'd personally not use curved wriggles. HF signals travel in a
> straight direction. With curves they start diffracting and start
> bouncing cross each other and might start to radiate or echo back.
mmmmm.... *stress*! anyone else feel the curves are "Bad"?
> I see that the community is divided on that stance.
> If tight for space you can use 90% corners with a chamfered outer
> edge. I suppose the chamfer acts like a mirror.
i'd *really* prefer not to do that :)
> Figure 6
wow that's pretty bad-ass.
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