[Arm-netbook] EOMA68-A20 2.7.4 pre-production prototypes received and working

mike.valk at gmail.com mike.valk at gmail.com
Fri Jun 16 11:06:11 BST 2017

2017-06-16 9:33 GMT+02:00 mike.valk at gmail.com <mike.valk at gmail.com>:

> 2017-06-16 8:55 GMT+02:00 mike.valk at gmail.com <mike.valk at gmail.com>:
> To the left I see that all HDMI tracks are routed trough some chips. What
> are those? Magnetics, impedance matchers? I mention that because on the
> blue tracks the'res a log of extra track for matching track length. maybe
> that should that be done before those chips.

Just a design thought on track length. Because of impedance matching HF
tracks should be of equal length. And to minimize their EM emission the
need to run parallel. But when changing direction you get an inner and
outer track where the outer track becomes longer. To mitigate that you have
those curly lines scattered around, usually at the end. Those cost a lot of

Since the schematics already show two layers with HF signal tracks why not
place the Tx and Rx track on top of each other. Result: Parallel tracks.
And very close to each other. Equal lengths on "curves". And minimize the
curly tacks.

I know that this introduces issue when you need tracks crossing. But that
could be solved by cross bridging... Hmm how am I going to visualize that
in text....

             T  R
             x  x
             |  |
          /  |  | \
         /   |  |  o
Tx/Rx---<    |  |   >----Rx/Tx
         o   |  |  /
             |  |
             |  |

ASCII art needs monospace font...

Tx/Rx on the left come in stacked. Before the bridge they split Rx passes a
via to the Tx layer. leaving the Rx layer free for other tracks to pass on
the Rx layer. After the bridge Tx passes the via the the previous Rx layer
and Rx continues on the Tx layer, The swapped layers. Both Rx and Tx have
passed a keeping a match via count for impedance matching.

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