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

[Luke Kenneth Casson Leighton]

On Fri, Aug 4, 2017 at 8:51 AM, mike.valk at gmail.com <mike.valk at gmail.com> wrote:
> 2017-08-04 9:19 GMT+02:00 Luke Kenneth Casson Leighton <lkcl at lkcl.net>:
>> On Thu, Aug 3, 2017 at 11:53 PM, Richard Wilbur
>> <richard.wilbur at gmail.com> wrote:
>>
>>> 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.
>>
> https://e2e.ti.com/cfs-file/__key/communityserver-blogs-components-weblogfiles/00-00-00-03-25/3124.Fig1.jpg
>
> From
> https://e2e.ti.com/blogs_/b/analogwire/archive/2015/06/10/differential-pairs-four-things-you-need-to-know-about-vias
>
> Basically a barrier between a via and a passing layer. Something
> default to prevent shorting.

 oh, ok - just a hole where you'd expect one to be :)  didn't know its
name was "anti-pad".

> With differentals have them combined so there is nothing in between
> them in a horizontal line/z axis as well.

 turns out that the anti-pads from PADS are big enough to create a figure-8.

l.