[SI-LIST] Re: Is a copper plane not tied to any net a referenceplane?
- From: Jean Audet <jaudet@xxxxxxxxxx>
- To: weirsp@xxxxxxxxxx
- Date: Wed, 5 May 2004 16:05:33 -0400
There is a good paper about that... (floating plane)
Name of article is ''Influence of a floating plane on effective ground
plane inductance in multilayer packages"" wrote in May 1999 by J.L PRince
and A.Cangellaris
Jean Audet
Electrical Analysis
World Wide Packaging & Test
IBM Burlington
Tel: 802-769-0835, tie line: 446-0835
Tel: 450-534-6317, tie line: 552-6317
E-mail: jaudet@xxxxxxxxxx
steve weir
<weirsp@xxxxxxxxx To: "Loyer, Jeff"
<jeff.loyer@xxxxxxxxx>
t> cc:
<si-list@xxxxxxxxxxxxx>
Sent by: Subject: [SI-LIST] Re: Is a
copper plane not tied to any net a reference plane?
si-list-bounce@fr
eelists.org
05/05/2004 03:45
PM
Please respond to
weirsp
Jeff, no, and I don't know where you get that idea. Lambda will be at
about 1/500MHz, lambda/2 at 250MHz, and lambda/4 at about 125MHz. A Tr of
2ns has a knee at about 250MHz, which coincides with lambda/2.
Regards,
Steve.
At 12:39 PM 5/5/2004 -0700, Loyer, Jeff wrote:
>If I understand you correctly, you predict that if I ran a trace on a
>12" board and performed VNA on that trace, I should expect to see a
>"resonance" at 100MHz. If I took that same trace and ran it on a 24"
>board, I would see a resonance at 200MHz, and so on.
>
>If this is the prediction, I am respectfully skeptical.
>
>If this isn't the prediction, could you articulate how the phenomenon
>would be reproduced, and how it would manifest itself?
>
>Perhaps you're talking about power distribution (where my experience is
>admittedly limited)? In that case, could you answer the same questions?
>
>Thanks,
>Jeff Loyer
>
>-----Original Message-----
>From: steve weir [mailto:weirsp@xxxxxxxxxx]
>Sent: Wednesday, May 05, 2004 11:09 AM
>To: Loyer, Jeff
>Cc: si-list@xxxxxxxxxxxxx
>Subject: RE: [SI-LIST] Re: Is a copper plane not tied to any net a
>reference plane?
>
>Jeff, sure it is just the propagation velocity of the wavefront. A 12"
>
>board at Er of 4 is 2nS 1 way delay. The round trip directly aligns on
>a
>2nS Tr/Tf.
>
>Regards,
>
>
>Steve.
>At 07:25 AM 5/5/2004 -0700, Loyer, Jeff wrote:
> >Steve,
> >Could you clarify what you meant about "the half-wave resonance of a
>12"
> >board"? Do you mean to say that you think a 12" board (I assume you're
> >talking about a height or width dimension) will be susceptible to
> >resonances at ~100MHz? If so, I'd like to understand that better.
> >
> >
> >Jeff Loyer
> >
> >
> >-----Original Message-----
> >From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]
> >On Behalf Of steve weir
> >Sent: Tuesday, May 04, 2004 3:59 PM
> >To: ericsilist@xxxxxxxxx; si-list@xxxxxxxxxxxxx
> >Subject: [SI-LIST] Re: Is a copper plane not tied to any net a
>reference
> >plane?
> >
> >Eric, I believe Dr. Green provided a nice explanation for what happens
> >to
> >the current in your trace. However, that is hardly the end of the
> >story. When you reference a signal, intentionally, or unintentionally
> >against anything other than ground, you would be wise to consider what
> >happens to that other reference. For your example case, it is pretty
> >close
> >to the half-wave resonance of a 12" board, resulting in efficient
> >broadcasts to Zontar and other points East. Resonant cavities excited
> >with
> >substantial energy are generally not a good thing.
> >
> >Steve.
> >At 02:16 PM 5/4/2004 -0700, eric steimle wrote:
> > >I'm trying to settle an argument without saying which
> > >side I'm on, and I was hoping someone could give a
> > >quick and easy example to prove this.
> > >
> > >You have a four layer board that looked like this
> > >
> > >SIG1
> > >GND
> > >VCC
> > >SIG2
> > >
> > >And the maximum rise time on the board was about 2ns
> > >(say a 100MHz clock), then if I ran a trace from one
> > >IC to another on SIG1 the return current would flow
> > >along the GND plane (assuming no splits in the plane
> > >etc.)
> > >
> > >What if I covered SIG1 with a plane of copper say
> > >hovering 5 mil above SIG1, and then made the distance
> > >between SIG1 and GND 100mil so..
> > >
> > >Plane sheet of Copper
> > >5 mil of air
> > >SIG1
> > >100 mil FR4
> > >GND
> > >VCC
> > >SIG2
> > >
> > >Now that plane sheet is not GND and it has no
> > >association to any net it is just a continuous sheet
> > >of copper about the size of the board. One of us
> > >argues that the return current will continue to flow
> > >along the GND plane as it did before. The other
> > >argues that the return current will instead flow
> > >mostly along that sheet of copper unitl it jumps back
> > >to the GND plane as it gets closer to the IC. Any
> > >help in this would be much appreciated.
> > >
> > >Thanks
> > >
> > >
> > >
> > >
> > >
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