[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 Tue, Dec 5, 2017 at 9:15 PM, Richard Wilbur <richard.wilbur at gmail.com> wrote:

> The reason for all the detail is to try and make the changes gradual enough to avoid causing big reflections from the taper itself but also make the geometry symmetric so we avoid turning differential signal into common mode.

 wait... so there's *multiple* of those tiny "wiggles" needed?  what
about... i know: what about doing some of those curves as double-S
double-ended arcs, like in that 1965 paper you found?  i'll draw it
tomorrow

> Notice that all the tracks and keepouts start a move "in" towards TX2 once every 15mil and then stay at that distance for the remainder of that step.  Notice also that all the tracks and keepouts move in except TX2 (since our goal is that it be the shortest--or moreso that TXC be the longest).

 1912 for TX2, 2075 for TX1, 2036 for TX0, 2225 for TXC.

  noo problem about keeping TX2 the longest, even with a *lot* of
taper-wiggling.  keeping TX1 stable (see diagrams i sent) would not be
a problem.

>  At the 5mil-inter-pair-distance end of the taper the manual keepouts become superfluous in light of your 5mil minimum Cu-Cu spacing design rule which then simplifies the connector end of the layout.

 ok that's good

> I threw "step 0" in there to say let's allow things to at least settle a little after making the turn before we start into the taper.
>
> Once we get into that tight bundle then we have to carefully pull the pairs off in order to avoid undoing all our work.  I'll send another drawing later this afternoon.  (I'm waiting for the dental hygienist, right now.)

 ok :)

> The idea is to have the bundle running NE, then simultaneously turn the bottom (southernmost) pair due E while the rest of the bundle turns due N for at least 15mil  before turning back NE.  This makes a 90 degree corner between the bundle and the pair which is leaving and gives enough space to allow ground fill between immediately.

 drawing.  even a rough sketch.  needed definitely