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

[mike.valk at gmail.com]

2017-08-17 18:30 GMT+02:00 Richard Wilbur <richard.wilbur at gmail.com>:
> On Aug 16, 2017, at 23:28, "mike.valk at gmail.com" <mike.valk at gmail.com> wrote:
>>
>> 2017-08-17 1:01 GMT+02:00 Richard Wilbur <richard.wilbur at gmail.com>:
>>>> On Aug 15, 2017, at 23:31, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
>>>> if i just take *out* the ground intermediary traces that would do the
>>>> trick of bringing the impedance back up, is that right?
>>>
>>> Should be a major step in the right direction.

After thinking it through I have to agree. Each GND trace would become
coupled with the diff pairs. Effectively creating a link between two
pairs. Which we do not want.

>>>
>>
>> How about the ground plane below the traces... That's a major stray
>> capacitance and closer than the "narrow" surrounding GND traces?
>
> The ground plane would be stray except we designed it into the single-ended and differential impedance.  At this point it is integral to our differential microstrip geometry.  (See my original post in the thread "HDMI High-Frequency Layout:  Impedance".)

I'll read that again.

I guess we just need to make sure that no other GND loop crosses the
HDMI plane. Perhaps create a barrier on the GND that follows the outer
HDMI traces. To prevent unwanted GND loops

http://www.ti.com/lit/ml/slyp173/slyp173.pdf