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

[Richard Wilbur]

On Aug 17, 2017, at 14:44, "mike.valk at gmail.com" <mike.valk at gmail.com> wrote:
> 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
(Thank you for the link to another interesting high-frequency circuit and PCB layout reference.  It concentrates on analog circuits but still has good wisdom and recommendations.)

Since we are routing the highest speed signals as a differential pair, and to the extent that we are able to create a differential microstrip transmission line, our biggest return current will be through the neighboring trace of the differential pair.

Since our differential microstrip transmission line will not be perfect, we are using ground vias to provide a low-impedance path for return currents across changes in the associated ground plane.

You bring up an interesting point:  what other current return paths are in the same vicinity?  I have not analyzed that in any detail.  At least there are no other lines from signal source to signal sink that I know of that cross the region of the board where the high-frequency HDMI signals are routed.  Also, to my knowledge we don't have segmented or restricted ground planes that would isolate regions with a higher-impedance reference.