[SI-LIST] Re: Some reference on reference planes

  • From: Mark Grobman <markgrobman@xxxxxxxxx>
  • To: Rick Collins <gnuarm.2006@xxxxxxxxx>
  • Date: Mon, 7 Nov 2011 23:40:06 +0200

Thanks for the quick reply's.
Paul - I read in Bogatain's book that this method is not effective -It was
mentioned under what happens when you run over a gap in the return plane
but as I understand the physics is essentilay the same. To the best of my
understanding the current will "find it's way back" in a radiative manner
so that as long as the capacitance between the relevent planes is suffiecnt
it should be ok above a certain rise time - I just don't know the numbers.
Is this method effective from your experince? what's the range of Rt for
which it works.

Rick - Your absoulty right. I've been a bit vauge. The setup I'm talking
> about is something like this:
>
Power 1(Real Ref.)
Signal 1
Power 2
Signal 2
Power 3
Signal 3
Power 4(GND)

And the relevent Signal layer is "Signal 2". The distance between different
layers is 5 mil on each side.

Mark

>
On Mon, Nov 7, 2011 at 11:24 PM, Rick Collins <gnuarm.2006@xxxxxxxxx> wrote:

> I recall from a course I took that if the plane of the stripline is
> tightly coupled to the reference plane, you should not have a
> problem.  But "tightly coupled" may not be what you have.  I think
> the context of what I learned was when there was a separation in a
> power plane or even a signal passing across a gap between two
> separate power planes, but in both cases the power planes were
> opposite a ground plane and so were "tightly coupled" acting just
> like the ground plane.
>
> Where is your driver's "reference plane" that it does not interact
> with the signal?  Can you give us a better picture of what you are
> designing rather than talking in the abstract?
>
>
> At 04:15 PM 11/7/2011, Mark Grobman wrote:
> >Hello experts,
> >I require some help on the subject of reference planes. I'm designing a
> >board and despite my best efforts i'm stuck with a situation where I'm
> >forced to conduct a signal using a stripline neither of whose planes are
> >the reference planes of the signal's driver (not the driver's ground or
> >VCC).
> >
> >Now I know from various App. notes and books that this sort of situation
> >should be avoided and that I have been a bad engineer indeed.
> >
> >Still, assuming the situation cannot be avoided  I was hoping to get
> >some quantitative approximation to how bad of an idea this is.Sadly
> >speaking I don't have access to a 3d simulator which can give me exact
> >results so I'm going for best effort design methods. I would love to get
> >your input on the following issues:
> >
> >1. Does the interference caused by not using the correct ref. planes carry
> >throughout the transmission line or does it occur only at the edges where
> >the current "jumps" back to the correct ref. planes?
> >2. Is there a merit figure of RiseTime/planes capacitance/????  for which
> >the situation isn't problematic?
> >3. Will using diff. lines improve the situation?
> >4. Suggested reading on the matter.
> >5. Highly insightful remarks which will blow my mind.
> >
> >Cheers,
> >Mark
> >
> >
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