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

Richard Wilbur richard.wilbur at gmail.com
Mon Aug 28 22:13:46 BST 2017

On Aug 22, 2017, at 08:13, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
> On Tue, Aug 22, 2017 at 2:43 PM, Richard Wilbur
> <richard.wilbur at gmail.com> wrote:
>> How much intra-pair skew do we incur at each of those bends?
> very little.  it's a 45 degree bend in each case so.... can probably
> work out the maths... 15mil separation...

Between traces of the same differential pair (intra-pair) I would have expected 5mil separation.

I'm not entirely sure how PADS does the trace length calculation:
1.  Is it measuring the inside edges of the differential pair traces?  Then the intra-pair skew from one 45° corner would be 5mil.
2.  Is it measuring the centers of the 5mil wide traces?  If so I'd expect the intra-pair skew to be 10mil.
3.  It may be measuring in a different way of which I'm not thinking.

> attached diagram is probably a lot easier.  i also checked the
> Design Rules: board-to-everything-and-anything is set to 11.84 mil,
> everything-else-to-anything-else is set to 5mil.
> so in the attached diagram those traces i put right at the bottom
> will be overwritten by about... 1.2 mil to make up to the 11.84
> board-to-copper clearance.

Does that mean that flood fill will cover out from 13mil off the board edge (as noted in the diagram) up to the 11.84mil board-to-copper clearance?

> so, actually very simple.  everything-to-everything-but-board: 5mil.
> board-to-everything: 11.84mil.

Simple is good--only as complicated as it needs to be.

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