Re: +3.3,5-board stackup problem / return currents...

Jeff Seeger ([email protected])
Mon, 07 Jul 1997 17:28:44 -0400

Mike Jenkins wrote:
> 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.

This point brings to (my) mind related questions:

If a signal crosses supply domain, is there any possiblity
of return currents trying to flow on power planes?

I would think that 5v > 3.3v and the complement would have
an overwhelming proportion of return current forced to the
ground layer alone, as long as these signals are routed such
that a reference ground layer is available.

Can the power-vs-ground as return mechanism be predicted,
if so, is there any simplistic rule of thumb (for physical
design folks with many thumbs, such as myself)?

Many thanks in advance,

      Jeff Seeger                             Applied CAD Knowledge Inc
      Chief Technical Officer                      Tyngsboro, MA  01879
      jseeger "at" appliedcad "dot" com                    508 649 9800