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

[Luke Kenneth Casson Leighton]

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


On Wed, Aug 30, 2017 at 9:34 PM, Richard Wilbur
<richard.wilbur at gmail.com> wrote:
> On Wed, Aug 23, 2017 at 5:27 AM, Luke Kenneth Casson Leighton
> <lkcl at lkcl.net> wrote:
>> damn.  i just noticed:  the via transition here is at 90 degrees.
>> i've been switching off except 1 layer at a time so didn't notice.
>> arse.
>>
>> i'll need to shift all but the TX2 via set down a fixed amount so i
>> can get a second wiggle in the right-hand one one layer 1, to make the
>> track come in to the top right corner (1 o clock). rather than as they
>> do now: from right side (3 o clock).
>
> Not necessarily bad on the same scale as you might think.  Our board
> is ~47mil thick while the copper is ~1mil thick, so when a signal
> plunges into a via from top to bottom it's already making a 90 degree
> turn into and out of the via.
>
> I'm not criticizing your attempt to straighten out some corners we
> have control over in the signal path, just pointing out that vias
> themselves present the signal with a couple 90 degree turns.

 understood.  which would be why they're best minimised and you're
also supposed to keep them as close together as possible.

 i did however hear somewhere that it's really really bad to make via
tracks turn 180 back on themselves, and in the same vein it makes
sense not to turn them too much other than being a sort-of
"continuation" of "as if" they were on the same layer...

 thx about the other responses.

l.