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

[mike.valk at gmail.com]

2017-12-12 9:33 GMT+01:00 Luke Kenneth Casson Leighton <lkcl at lkcl.net>:
> On Tue, Dec 12, 2017 at 8:10 AM, mike.valk at gmail.com
>
>  so by doing this series of steps the inter-pair impedance changes
> from its (appx).... 110 ohms by virtue of the distance being 15mil to
> each pair and also to the keep-out area, down to something closer to
> 50 ohms by the time we get to the end of the set of 8 steps, by which
> point the inter-pair spacing is 5mil, as you have to have, because of
> the distance between the pads on the ESD and the JAE DC-3 HDMI
> connector.
>
>  if we followed the "straight line" inter-pair approach that you're
> advocating, the change from the 110 ohms to 50 ohms using linear
> spacing between 45-turn steps OR a straight 1-line arbitrary-angle
> taper is *GUARANTEED* to result in reflections back down the line(s).
>

We'll I'm not convinced on the reflections in inter pair matching. But
indeed my "linear" might not be the best and results in unequal
impedance transitions and thus in signal degradation. But you can stil
do gradual corners. See the "transitioned" attachment.

But without a, 3d, simulation or a real world test this is all very theoretical.

>  btw numbers (110, 50) above are not wholly accurate, richard
> calculated them correctly, i am just substituting convenient
> indicative numbers from my vague and non-specific memory.
>
> l.
>
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