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

[Richard Wilbur]

On Oct 2, 2017, at 19:56, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
> 
> On Mon, Oct 2, 2017 at 10:33 PM, Luke Kenneth Casson Leighton
> <lkcl at lkcl.net> wrote:
> 
>> On Mon, Oct 2, 2017 at 10:15 PM, Richard Wilbur
>> <richard.wilbur at gmail.com> wrote:
>>> The alternative is to use the "U"-shaped with spacing of at least 20mil between facing copper of the same trace.
>> 
>> yyeah that's 4x track width... it's gonna be really really tight to
>> get 20 mil in.  will see.
> 
> it was.   best i could do (attached) - accordion wasn't having any of
> it, had to do them by hand.
> 
> the defaults in PADS for the gap separation btw were set to 2x.  4x
> seems an _awful_ lot, to my eye: i don't believe i've ever seen
> wiggles with such large separation.  are you sure the app note didn't
> mean "4x separation centre-to-centre of the traces"?  or, was the app
> note specifically applying to really *really* high frequency traces
> (above say... 2 or even 3 ghz)?

Toradex, p. 17, section 6.2 as illustrated in figure 13.

It matters more the greater the length of facing copper.  So if you can only get 15mil separation but split it into two or more wiggles, that would be better than having one wiggle at 15mil separation (between facing copper of the same trace).