hiya richard, so how you getting on? --- crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68
On Fri, Oct 13, 2017 at 1:56 AM, Luke Kenneth Casson Leighton lkcl@lkcl.net wrote:
On Thu, Oct 12, 2017 at 9:16 PM, Richard Wilbur richard.wilbur@gmail.com wrote:
whoops.... :) 89 ohm... 50 ohm. 89 ohm... 50 ohm. oops... :)
Well, if the reported impedance is the single-ended impedance of those lines we have considerable margin to burn and should aggressively pursue the taper structure and bring in the keepouts at each end.
i sort-of understand that. am i right in thinking: at the ends we have to treat them as single-ended, and achieve a sngle-ended impedance of 50 ohms, but 100 ohms for the diff-pairs.
For the geometry that fit our constraints, we calculated a single-ended impedance of ~72 Ohm and differential impedance of ~111 Ohm (which corresponds to a tolerance of 11%).
ok so 72's not really very close to 50 ohms... interested to learn how that can be achieved.
l.