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

[Luke Kenneth Casson Leighton]

On Mon, Dec 18, 2017 at 5:16 AM, Richard Wilbur
<richard.wilbur at gmail.com> wrote:

> On Sun, Dec 17, 2017 at 9:05 PM, Luke Kenneth Casson Leighton
> <lkcl at lkcl.net> wrote:
>>  so... ah.... key question here... is the taper needed or not? :)
>
> The taper is a nice idea for changing the context smoothly but it
> requires enough space that we can't return to our original context
> before the cable connector (which is specified to be 100 Ohms).  So I
> think we're better off living with the small, brief discontinuities
> due to incursions into our design geometrical constraints, than
> introducing a hulking change in our design geometrical constraints to
> cover up the incursions (with the likely effect of changing our
> impedance) and having no space left to taper the new impedance to 100
> Ohm at the connector.

 aw poop!  i went to all the trouble of writing a parser for PADS :)

>> should i instead be just setting 15mil clearance all round?  (and put
>> a GND keepout underneath the ESD)?
>
> 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.)  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?

> 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


>  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.

l.
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