[SI-LIST] Re: Some reference on reference planes
- From: Julia Nekrylova <fialka113@xxxxxxxxx>
- To: Mark Grobman <markgrobman@xxxxxxxxx>, Rick Collins <gnuarm.2006@xxxxxxxxx>
- Date: Thu, 10 Nov 2011 17:08:45 -0800 (PST)
Mark,
If the interface is not that wide what you could do is to cut copper on layers
Power2 and Power3, i.e. above and under your signals, to effectively provide
referencing to Power1 and Power4 but that might create problems on it's own
like tandem (broad-side coupled) xtalk to Signal1 and Signal3 or impedance
discontinuities for signals on Signal1 and Signal3 layers.
From: Mark Grobman <markgrobman@xxxxxxxxx>
To: Rick Collins <gnuarm.2006@xxxxxxxxx>
Cc: si-list@xxxxxxxxxxxxx
Sent: Monday, November 7, 2011 1:40 PM
Subject: [SI-LIST] Re: Some reference on reference planes
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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