On Oct 11, 2017, at 18:04, Luke Kenneth Casson Leighton lkcl@lkcl.net wrote:
On Wed, Oct 11, 2017 at 5:58 PM, Richard Wilbur richard.wilbur@gmail.com wrote:
What does PADS currently give as the impedance of the HDMI differential lines?
each line is 90 ohms.
Does it give an impedance for a particular trace?
yes. 90 ohms. or... 89.
(That would likely be the single-ended impedance.)
Those are surprisingly high for single-ended impedance on that board stack and geometry. I would have expected something less than or equal to about 60 Ohm. 89 or 90 Ohm sounds more like what I might expect for our differential impedance (less than twice the single-ended impedance).
Does it offer a differential impedance value for a pair of traces?
no. from what i gather you're expected to read up on diff-pair rules.
What version of PADS Layout are you using? Mentor responded to a question about version 9.2 saying it calculates a general impedance value taking into account:
"PADS uses Diff Pair gap value and the two nearest planes (Cam or Split/Mixed) to calculate trace impedance; if the trace goes between two planes (Stripline), or just one trace to the nearest plane (Micro Stripline) in other case. Cut outs are ignored for both cases."[*]
Reference: [*] https://communities.mentor.com/thread/5743