[SI-LIST] Re: Is a copper plane not tied to any net a reference plane?
- From: steve weir <weirsp@xxxxxxxxxx>
- To: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- Date: Wed, 05 May 2004 11:09:09 -0700
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
> >
> >
> >
> >
> >
> >__________________________________
> >Do you Yahoo!?
> >Win a $20,000 Career Makeover at Yahoo! HotJobs
> >http://hotjobs.sweepstakes.yahoo.com/careermakeover
> >------------------------------------------------------------------
> >To unsubscribe from si-list:
> >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> >or to administer your membership from a web page, go to:
> >//www.freelists.org/webpage/si-list
> >
> >For help:
> >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> >List FAQ wiki page is located at:
> > http://si-list.org/wiki/wiki.pl?Si-List_FAQ
> >
> >List technical documents are available at:
> > http://www.si-list.org
> >
> >List archives are viewable at:
> > //www.freelists.org/archives/si-list
> >or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages
> >Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
> >
>
>
>------------------------------------------------------------------
>To unsubscribe from si-list:
>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
>or to administer your membership from a web page, go to:
>//www.freelists.org/webpage/si-list
>
>For help:
>si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
>List FAQ wiki page is located at:
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
>List technical documents are available at:
> http://www.si-list.org
>
>List archives are viewable at:
> //www.freelists.org/archives/si-list
>or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
>Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
