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

[Richard Wilbur]

On Sun, Dec 17, 2017 at 10:28 PM, Luke Kenneth Casson Leighton
<lkcl at lkcl.net> wrote:
>  aw poop!  i went to all the trouble of writing a parser for PADS :)

That is pretty cool.  Now you have a way to algorithmically generate
traces.  I'm sorry we didn't need it, yet.

>> Are there signals beneath the ESD components on layer 3 or 4?
>
>  it seems i am sensible enough not to have done that :)
>
>>  If not,
>> we could put our ground reference planes on those layers under the ESD
>> components which would move them both one layer deeper.  (We already
>> have several conveniently placed ground vias.)

So it might be easier to just put a ground keepout on layer 2 under
the ESD component on layer 1 and a corresponding ground fill on layer
3.  Likewise a ground keepout on layer 5 under the ESD component(s) on
layer 6 and a corresponding ground fill on layer 4.

(The "otherwise" case below is given in case you feel more comfortable
putting keepouts on layers 2 and 5 than changing layers 3 and 4.)
>>  Otherwise, I would
>> just copy the lands for the ESD pads connected to the high-speed
>> signals and put them as ground keepouts on the normal ground reference
>> planes.
>
>  makes sense to me
>
>>  (In other words, only keep out the copper on the reference
>> plane just under the signal path where it goes through a wide pad for
>> the ESD component.)
>
>  including the 5 mil track *between* the ESD pads, or excluding that?
> so literally just the ESD pads, yeah?

I was recommending just under the ESD pads specifically for the
high-frequency differential signals.

>
>> Likewise with the connector, I would put a ground keep out under the
>> lands on layer 2 (probably best to just draw a keepout under the whole
>> connector on layer 2)
>
>  including for the HSCL, HHPD and even the GND pads? of course there's
> VIAs connecting the tracks in between the diff-pairs

Wouldn't have to I suppose but the idea is to move the ground further
away from the high-frequency pads to reduce the capacitive coupling
thus increasing the impedance.  Thus I think it's probably best to
extend the layer 2 keepout under the whole connector.

>>  but allow layer 5 to provide a full ground
>> shield.  (Provided my assumption is correct that the connector is
>> soldered on layer 1.)
>
>  it is.

Yay!