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

[Luke Kenneth Casson Leighton]

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


On Fri, Dec 22, 2017 at 9:37 PM, Richard Wilbur
<richard.wilbur at gmail.com> wrote:
> On Dec 22, 2017, at 07:51, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
>> On Fri, Dec 22, 2017 at 8:54 AM, Luke Kenneth Casson Leighton
>> <lkcl at lkcl.net> wrote:
> […]
>>> this is a pain!  i might see if i can set a clearance to GND on
>>> individual tracks / connections as opposed to NETs.
>>
>> ok that worked.  just uploading a video here:
>>
>> https://youtu.be/LfQc89CS4m0
>>
>> turns out that there's a feature i'd not used before, called
>> "conditional rules".  you can specify that *if* GND meets HDMI Group,
>> clearance rules shall be different.  ordinarily you have to forcibly
>> set the *entire* GND plane to specific clearances (to ALL objects), or
>> the *entire* HDMI group to specific clearances (to ALL objects)...
>> this "conditional" rule does the trick.
>
> Nice work!  That certainly simplifies things!

 tell me about it.  and also makes for much cleaner / accurate separation.

> I believe that the right thing is to not extend the layer 5 ground
> keepout under the differential nets on their way out to the connector
> because it is the ground plane for layer 6.

 that makes sense.

> The reason for dropping the ground plane under the connector pins
> (layer 1) from layer 2 to layer 5 is that the pins are so close to each other.

 yyeahhh but so are the pins on the bottom layer ESD... which are
covered by the layer 5 GND keepout hole... it was under the connector
i was concerned about, with the VIAs on pins 4 10 and 16 (right-hand
row of 9) being guard VIAs that are within 5mil of HTX1P/N and
THXCP/N...


> But we are still interested in the shielding effect of ground plane
> below the high-frequency signals (on the differential pairs) on
> layer 1 and between the signals on layer 1 and those sneaking
> under on layer 6.

 yehyeh.

> That's my reason for keeping layer 5 ground fill everywhere
> except under the layer 6 high-frequency pads of the ESD
> (where he drop to ground on layer 4).

 yehyeh, with you.

l.