Hello to all,
I was working on a design with some diff pairs and since I had to log a SR for an unrelated topic, I finished writing up this tale.
See if you can enjoy the reading and learn from it, and if you want to joining me (see the mystery section after the end of the tale)
Let's say that I want to design a differential pair.
Armed with the latest HyperLynx release I boldly envision a differential pair of 100 ohms.
I start with the stackup editor, put in a reasonably good stackup and aim at the external layer.
So I start with a "solve for both"
My manufacturer can not do smaller than 120um and an outer layer and the line start to bend at about 150um trace width, so I choose 140um trace width.