3 ms·

A few of these rules are outright not true or are missing a greater picture of things. 90 degree vs 45 degree bends do not matter. Ground planes are not a nec

A few of these rules are outright not true or are missing a greater picture of things. 90 degree vs 45 degree bends do not matter. Ground planes are not a necessity for high speed digital, you just need either a power OR a ground plane referenced to the digital. They're both identical when talking about high speed. Generally speaking (although almost no one seems to do this), you would prefer to have differential pairs NOT be tightly coupled. Tightly coupled pairs means impedance goes down, which drives very small traces on high speed signals (which, screws you if you have single-ended signals... because the traces need to be fat in comparison). Overall not a horrible start, but it's pretty surface-level for high speed design.

jeffbee 4y ago
> 90 degree vs 45 degree bends do not matter. The book "Right The First Time" devotes a whole chapter to debunking 90-degree bends as problematic, except under extraordinary circumstances like transmission lines > 50GHz. But ask yourself: have you ever seen something like a DDR4 length-matching snake that used 90-degree bends? Why are beveled corners absolutely universal? Is there some manufacturability problem with right angles in traces? Or are there weird problems caused by dozens of equally-spaced right angles on the same trace?
- Kirby64 4y ago
  I suspect 45 degree bends are due to two main reasons: * Institutional misinformation or cargo cult behavior * Ease of layout based on convention. If you need to match differential trace lengths, 90 degree angles are going to give you pretty big difference length wise, so you need more squiggles to compensate. My point on 90 vs 45 is that some people seem to take the opinion that the 'ideal' trace is some sort of sweeping trace with absolutely no angles, and a 45 degree is a compromise. It's really not. It does not matter. Electrons don't 'bunch up' in corners like some people claim.

jeffbee 4y ago

> 90 degree vs 45 degree bends do not matter. The book "Right The First Time" devotes a whole chapter to debunking 90-degree bends as problematic, except under extraordinary circumstances like transmission lines > 50GHz. But ask yourself: have you ever seen something like a DDR4 length-matching snake that used 90-degree bends? Why are beveled corners absolutely universal? Is there some manufacturability problem with right angles in traces? Or are there weird problems caused by dozens of equally-spaced right angles on the same trace?

Kirby64 4y ago
I suspect 45 degree bends are due to two main reasons: * Institutional misinformation or cargo cult behavior * Ease of layout based on convention. If you need to match differential trace lengths, 90 degree angles are going to give you pretty big difference length wise, so you need more squiggles to compensate. My point on 90 vs 45 is that some people seem to take the opinion that the 'ideal' trace is some sort of sweeping trace with absolutely no angles, and a 45 degree is a compromise. It's really not. It does not matter. Electrons don't 'bunch up' in corners like some people claim.