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

[Richard Wilbur]

On Oct 11, 2017, at 18:08, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
> On Wed, Oct 11, 2017 at 6:18 PM, Richard Wilbur
> <richard.wilbur at gmail.com> wrote:
>> Afterthought:  If PADS does give impedance values, please include the
>> values for each of the HDMI differential traces and a URL to images of
>> the top and bottom layers of that layout.
> 
> they're all 89 ohms, single-line.
> 
> 
>> That way I'll be able to make recommendations and markup the picture
>> to hopefully make everything clear.
> 
> appreciated... there's no differences: they're all 89 ohms.  i'm
> assuming that's calculated from track width and board / layer widths.
> 
> capacitance is slightly different: the shorter traces (TX2) are
> 3.06pF, the longer ones (CK) are 3.55pF - i would imagine that the
> extra length results in a directly-proportionally larger capacitance?

I think you are probably correct here.  I think the capacitance has to do with length of trace near other copper (same layer or not) and separation distance between the trace in question and the other copper.  Also the area of the trace and other copper which are facing each other.

Which layout are these measurements coming from?  Is it pictured at a publicly available URL?