[SI-LIST] Re: Is a copper plane not tied to any net a referenceplane?
- From: Lei Luo <lluo3@xxxxxxxxxxxxxx>
- To: eric steimle <ericsilist@xxxxxxxxx>
- Date: Tue, 4 May 2004 17:33:53 -0400 (EDT)
Eric,
If you have microstrip TLs on SIG1, you can measure Z0 of this TL by
TDR. Without copper layer on top, it's a microstrip line. With it, it's
a strip line. You will find different Z0 for these 2 cases.
I have similar experiences. The copper layer above it(even not tied to
any references) will change the Z0 a lot.
Hope this helps,
Lei
ECE - NCSU
On Tue, 4 May
2004, eric steimle
wrote:
> I=92m trying to settle an argument without saying which
> side I=92m 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:
> =09=09//www.freelists.org/archives/si-list
> or at our remote archives:
> =09=09http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> =09=09http://www.qsl.net/wb6tpu
>
>
>
Lei Luo
Electrial & Computer Department
NC State University
Room438 EGRC, Centennial Campus,
Office: 1.919.513.2015 Mobile: 1.919.749.9262
Welcome to my webpage: http://www4.ncsu.edu/~lluo3
------------------------------------------------------------------
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:
