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

[Richard Wilbur]

On Aug 22, 2017, at 08:13, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:

Looking at your cool diagram from 22 Aug, the ground trace at the bottom of the board looks like it is 5mil wide as it appears the same width as HTXCN et al.  That assumption together with the dimensions you provide leads me to believe that we can nearly have our cake and eat too!
distance from ground trace to closest differential trace = 37mil from board edge to closest differential trace - 18mil from board edge to ground trace - 5mil ground trace width = 14mil

I notice that the via copper extends to 13mil from board edge.  Thus, if we were to move the ground trace down 1mil, we would have 15mil spacing to the closest differential trace without breaking the 11.84mil board edge clearance.  (Vias would extend to 12mil from board edge.)

This is good for impedance on the differential pair next to the board edge, HTXC = HDMI transmit clock.  The vias will encroach closer.  Can we trim the pad on the side towards the differential trace to reduce the encroachment?