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

Jeff Seeger (jseeger@appliedcad.com)
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