[Arm-netbook] HDMI High-Frequency Layout: Impedance

[Luke Kenneth Casson Leighton]

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crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68


On Thu, Aug 3, 2017 at 2:59 PM, Richard Wilbur <richard.wilbur at gmail.com> wrote:

> What I said earlier is that I would recommend the following geometry
> for the transmission lines:
> trace width = 6.5mil

 there's not enough space.  when i said "there's not enough space" i
*really meant*, "there's not enough space".  it *might* be possible to
increase to 5.1 mil but i think you'd agree it would not be worth it.

 the reason that there's not enough space is because:

 the processor is only about 4.5mm away from the edge of the board.
this used to be only 3.5mm.

 there is no way to further increase the width of the board.

 there is no way that i am moving the processor.  or the DDR3 RAM ICs.

 the 24mhz XTAL is *right* next to the damn HDMI signals.  as it's
that close, it blocks layer 1.

 moving the XTAL to layer 6 is a bad idea (vias) but even if you did
that it *still* would not help... because the PMIC components are in
the way on layer 1 further down the board.

 the space that would normally be used to drop the HDMI signals onto
layer 6 immediately they come out the vias is not available because
there are tracks on both layer 3 and layer 6 which are in the way (and
cannot be routed anywhere else)

 ok i did a video explaining: https://youtu.be/vFbzAmLSHPY

l.