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

Luke Kenneth Casson Leighton lkcl at lkcl.net
Fri Aug 4 08:19:05 BST 2017

crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68

On Thu, Aug 3, 2017 at 11:53 PM, Richard Wilbur
<richard.wilbur at gmail.com> wrote:

> We can still take some of the recommendations to heart:
> 1.  Use minimal size vias for high-frequency traces to reduce
> parasitic capacitance.[23]

 yep.  0402 all the way round.  can't go smaller as it risks the drill
hitting the edge of the ring.

> 2.  Place the two vias of the differential pair in close proximity to
> increase capacitive coupling between the signals.(smaller via pitch)

 yep.  doing that.

> 3.  Instead of using two separate anti-pads on signal vias, combine
> them into an oval shared antipad (on every layer) to reduce parasitic
> capacitance.

 oo.  never heard of this practice.   never heard of "anti-pads"
either!  so sorry, if you put some references i missed them.

> 4.  Place ground vias next to signal vias to provide low-impedance
> ground-return paths.[22, Figure 2]

 yep doing that.


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