On Aug 10, 2017, at 23:12, Luke Kenneth Casson Leighton lkcl@lkcl.net wrote:
On Fri, Aug 11, 2017 at 12:37 AM, Richard Wilbur richard.wilbur@gmail.com wrote:
On Wed, Aug 9, 2017 at 7:23 AM, Luke Kenneth Casson Leighton lkcl@lkcl.net wrote:
next set...
wiggles.jpg is the layer 6 length-matching area: HX2N/P is the one that's the longest, it snakes back on itself. i length-matched all 3 signal pairs to 56.413, and left the CK lines at 57.134 just to give the tiniest bit of delay (TI recommendations iirc).
Very nicely done! 57.134mm - 56.413mm = 721um => T(delay) = 721um / 150um/ps = 4.8ps
That is a very tiny delay!
I would need to do more research to make a meaningful recommendation. Sorry for bringing up a topic I wasn't prepared to discuss intelligently. Let's go with what you've done.
According to my calculations you could get away without any inter-pair skew compensation on the board whatsoever and still meet the HDMI specification for the transmitter budget. What you have done regarding inter-pair skew compensation reserves nearly all of the transmitter inter-pair skew budget from the HDMI standard for the connector and the rest of the system. This will serve to accommodate less than optimal inter-pair skew imposed by the cable and/or receiver.
Now that we have achieved such close synchronization, I'm suggesting we go for the next goal where we design a certain amount of inter-pair skew into the layout for purposes of lowering the strength of our synchronized pulsing data lines to a more diffuse chatter.
*deep breath*.... aaaaaaaa! :)
well.... that actually happens for the majority of the length in the middle (starting layer 6)
but.... if i simply *take out* the intermediary wiggles on layer 6....
Ill-founded proposal for which I don't presently have the time to improve.
no - not even enough space to do 5.1mil / 5.0 clearance... just... too much.
I understand. We might end up with more room--see discussion below.
which has probably been truncated...
Turns out we don't have the room to change the trace width or spacing without having a deleterious effect on impedance.