On Mon, Aug 14, 2017 at 10:37 PM, Richard Wilbur richard.wilbur@gmail.com wrote:
I have some time today to continue this discussion.
awesome.
So if we were to remove the ground shield traces from between differential pairs we could meet the inter-pair spacing recommendations without moving anything else. This may explain the design by the wits-tech senior engineer you mentioned which worked without ground shield traces between the differential pairs.
yehyeh. i could then move them slightly away from the edge of the board.
Another interesting reference on high-speed HDMI PCB layout is TI's SLLA324[2].
nnniiiiiice. i love it. that's exactly the same connector being used. hmmm iinteresting, they bring the vias up from underneath on all 4 diff-pairs...
So, for the HDMI differential signals' sake, we don't necessarily need:
- Ground guard traces between neighboring differential pairs
- Ground guard traces between HDMI differential pairs and other circuits
- Multiple ground vias riveting along the side of the board to block emissions
- Perfectly matched inter-pair lengths
hmmm....
On the other hand:
- Ground guard traces can be important in reducing noise radiated from single-ended circuits and coupled into other single-ended circuits on the board.
- Ground fences, traces riveted with multiple ground vias, can help even more with the goals of "reducing noise radiated from and coupled into other single-ended circuits on the board" as above.
In other words, if we had more board space there are several things we could do differently: increase differential pair trace width and spacing, ground shield trace spacing.
But as it stands I believe it will likely work fine. Without changing anything else we could drop the ground shield traces which would serve to increase our differential impedance.
i think i will do that.
We would want to retain the ground vias near signal vias.
yehyeh.