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

Luke Kenneth Casson Leighton lkcl at lkcl.net
Sun Aug 13 13:09:24 BST 2017

On Fri, Aug 11, 2017 at 6:15 PM, Richard Wilbur
<richard.wilbur at gmail.com> wrote:

>> 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. But
>> I see that the community is divided on that stance.
> I also prefer 45 degree corners to the curves.  Looks like they only
> occur in one section.

 yes - i was trying to save space.  ok i managed to get some 45-corner
wiggles in, instead.  and also got the GND separation in between the
CK lines up to the via.

 i'd *really* like to get this done and into test, particularly the
DC3 connector test PCB (first).

 ok. so wiggles1.jpg is the beginning part.  track-pairs remain
slightly offset, if you take the difference betweeen each pair it's
nearly... 8 mm because the clock lines have to go down (3mm) then
right-angle (2mm) then right (2mm) just to catch up with TX2.

 so they _stay_ up to 8mm out until they get to the right end.. then
they wiggle again to get match-lengthed.

 BUT... it just occurred to me that on the *other* side of those ESD
rclamp0524p protectors the diff-pairs are all *different lengths*.

 so on the other side of the rclamp0524p components all four
diff-pairs will be different lengths.

 would that be sufficient, do you think, richard, to satisfy the
"spread spectrum" style you were thinking of?

 short lengths to the RIGHT of the rclamp0524p:

 TXC: 3.11mm
 TX0: 1.23mm
 TX1: 3.23mm
 TX2: 1.14mm

 total lengths:

 TX2: 56.401mm

so the signal pairs are all eever so slightly different, and they're
all around 0.85mm shorter than CK.

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