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

Luke Kenneth Casson Leighton lkcl at lkcl.net
Fri Jan 5 10:53:04 GMT 2018

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

On Fri, Jan 5, 2018 at 8:25 AM, Richard Wilbur <richard.wilbur at gmail.com> wrote:
> On Fri, Jan 5, 2018 at 12:44 AM, Luke Kenneth Casson Leighton
> <lkcl at lkcl.net> wrote:
>> On Fri, Jan 5, 2018 at 7:32 AM, Richard Wilbur <richard.wilbur at gmail.com> wrote:
>>> Any
>>> chance we could use another trace to even up the little dimples that
>>> are left in the edge facing the differential pairs?
>>  always best to screenshot / arrow-mark it, richard.  round-trip
>> delays getting critical here, we're up to 5th january already.
> I have attached a screenshot with red arrows.  It is taken from the
> long straight differential microstrip transmission lines on layer 6.
> These are otherwise so clean and straight.

 gooot it.  yehyeh there's signals (3V3) and stuff close by
(unavoidably), and i have to put manual GND tracks in because the
flood-fill won't blotch in to spaces narrower than 10mil... it's a
setting somewhere and i kinda prefer it that way, otherwise flood-fill
tends to get into some really small spaces and creates awkward-looking
tiny shapes.

>> attached green arrows, i am guessing you mean, i remember you said
>> that causes... something-or-other... capacitance-related?
> The ones you marked weren't the ones I was looking at.  I think they
> are probably fine as they aren't too sharp, they mind the 15mil
> clearance, and we are turning 90 degrees out of some signal vias onto
> the top of the board.  (If they were pointing at a straight side I'd
> be more worried.)

 with you.

>>  there's a few more like that back at the source diff-pair vias, i'll
>> think about whether to drop a plain square keepout in place (to
>> preserve 15mil) or a straight manual track.  track would cut clearance
>> to around 12mil.  thoughts?
> It is kind of tumultuous with the pairs coming from close quarters on
> layer 1 and still to be sorted through the intra-pair
> skew-compensating wiggles.  What you've done at that end looks much
> better.

 yay :)

>>> I glanced at parts of the rest of the board but it would be much more
>>> straightforward with the schematics.
>>  not so concerned about the rest of the board, it's mainly the HDMI.
>> PDF version of schematics should be here
>> http://hands.com/~lkcl/eoma/DS113-V2.7-2017-02-17.pdf
> I'll concentrate on the HDMI, then.

 yes please


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