[SI-LIST] Re: Remove Ground underneath Differential signal is deserved or not?


Hello Ratchet man,
Nice to hear from you.  Hope you will be contributing to this group on
regular basis.  I took your class in Boston couple of years ago.
Last week there was a discussion about guard traces and I remember you
had a very strong opinion about them.  Can you please share your
thoughts about the guard traces with this group.

Regards
Ibrahim Khan
-----Original Message-----
From: Ritchey Lee [mailto:leeritchey@xxxxxxxxxxxxx]=20
Sent: Monday, July 29, 2002 11:07 AM
To: jian@xxxxxxxxxx
Cc: binchuan2000@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Remove Ground underneath Differential signal is
deserved or not?


Binchua,

You don't ever want to remove the ground plane from underneath a
differnetial pair.  Many more negative side effects result than the
alleged common mode energy might ever cause.

Lee

Jian X. Zheng wrote:

> Hi, Binchuan:
>
> Removing the ground plane for differential pair will suppress the even

> mode. Basically, the even mode will not be propagating. Its energy=20
> will not be transmitted. The even mode signal, which is considered as=20
> noise, will be reduced in your circuit. Thanks!
>
> Best regards,
>
> ----------------------------------------------------------------------
> -
> Jian-X. Zheng, Ph.D
> Zeland Software, Inc., 48890 Milmont Drive, 105D, Fremont, CA 94538,
U.S.A.
> Tel: 510-623-7162, Fax: 510-623-7135, Web: http://www.zeland.com
> ---------------------------------------------------------------------
>
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx=20
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of binchuan2000
> > Sent: Thursday, July 25, 2002 7:20 PM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Remove Ground underneath Differential signal is=20
> > deserved or not?
> >
> >
> >
> > I am confused that I read some book about remove Ground under=20
> > Differential could reduce the induced Current from Differential=20
> > pair, but the question is how we could control its=20
> > impedance(Differential
> > impedance) although Differential doesn't reference to Ground. If I
> > follow this content to REMOVE Ground under Differential pair how
> > could I control its Zodd impedance and its Zdiff impedance. Does it
> > will generate any other problem and if it does, why some textbook
> > advise it?
> >
> > Remove Ground is worth or not for Differential signal ?
> >
> >
> >
> > Thanks,
> >
> >
> >
> > Binchuan.Wang
> >
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