email@example.com on 05/06/98 10:29:25 AM
cc: (Chris Heard/US/3Com)
Subject: [SI-LIST] : Propagation velocity / discontinuous reference plane
Whilst trawling through the si-list archive, I came across the following
throw-away comment (Mike Jenkins, "+3.3,5-board stackup problem", 7 July
> Regarding mesh power planes, one caveat: If the plane uses a diagonal
> mesh (i.e., lines at 45 degrees to signal lines), then the ground
> current can't follow the signal path directly. This can substantially
> reduce the velocity of propagation.
The reasoning seems to suggest that whenever a return current is unable
to follow the signal path closely, then the propagation delay will
increase. This will occur in many circumstances, such as a power-plane
split, a poorly placed bypass cap, or even when there is no appropriate
return plane available.
Can anyone provide any more theory on this phenomenon?