[Arm-netbook] HDMI High-Frequency Layout: Recommendations--Taper
richard.wilbur at gmail.com
Mon Dec 18 06:03:17 GMT 2017
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
> 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.
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