[Arm-netbook] HDMI High-Frequency Layout: Recommendations
Richard Wilbur
richard.wilbur at gmail.com
Tue Aug 22 16:30:21 BST 2017
On Aug 18, 2017, at 20:13, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
>
> On Fri, Aug 18, 2017 at 5:51 PM, Richard Wilbur
> <richard.wilbur at gmail.com> wrote:
>
>> You bring up an interesting point: what other current return paths are in the same vicinity? I have not analyzed that in any detail. At least there are no other lines from signal source to signal sink that I know of that cross the region of the board where the high-frequency HDMI signals are routed. Also, to my knowledge we don't have segmented or restricted ground planes that would isolate regions with a higher-impedance reference.
>
> CEC etc. all follow roughly the same path, on layer 3 (separated by GND).
>
> i just noticed that SD0 runs round the back of the HDMI 1st set of
> VIAS (with no GND separation) on layer 3 - i've removed the SATA power
> (not being used) so i can shift them up a bit
>
> some GPIOs cross on layer 3 as well, just near the GND shielding near
> those first vias...
>
> not much.
Layer 3 always has ground separation from layer 1 in the intervening ground plane on layer 2 and likewise from layer 6 by layers 4 and 5. So I'm not worried about those signals.
Regarding the SATA power: Is it an important part of providing a SATA interface? If so, I would suggest not limiting our options on this card. My understanding is that SATA is significantly more efficient for harddisk data interface than USB.
Regarding SD0: To what interface does it belong? What is the maximum data rate on this line?
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