Rick Collins wrote: >> Question 2: In this a reasonable assignment, or am I missing something? >> That's the stackup I use. In general, you want the ground plan near >> the signal plane with the most signals. For surface mount, that's the >> top. For through-hole it might be the bottom. > > I took an excellent class in high speed digital design by Lee > Ritchey. One of the things he covered was using ground planes and > controlling impedance. Turns out that for the purpose of impedance > (which is why you want your traces close to the plane) a power plane > is exactly the same as a ground plane. So it does not matter if your > signals are next to the power or the ground plane, they are both at AC ground. > > Just thought I would chime in with my two cents worth.
If my traces were carrying ground referenced analog signals I wouldn't want the power plane being my "ground" plane. And yes, I've seen a real life case with some rather frustrating behavior that the correct stackup totally fixed. There was a moment of clarity when a bypass cap way on the other end of the board made a much larger than expected difference. -Dan _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user