[SI-LIST] Re: Remove Ground underneath Differential signal is deserved or not?
- From: Ritchey Lee <leeritchey@xxxxxxxxxxxxx>
- To: Ibrahim Khan <ikhan@xxxxxxxxxxxxxxxxxxx>
- Date: Mon, 29 Jul 2002 17:07:22 -0700
Ibrahim,
I read most of the mail that goes by with this group. When I have time I
answer some. As to guard traces, I'd rather not be though of as having
opinions about them, but rather science that demonstrates that they are not
useful as a way to separate transmission lines from each other. As always,
opinion is for politicians, science is for engineers.
What I show in my class is that guard traces are always LC networks that
resonate at some frequency and can and do turn into bandpass filters at some
frequencies. I demonstrate this will actual failed circuits.
Hope this helps.
Lee
Ibrahim Khan wrote:
> 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]
> 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
> > will not be transmitted. The even mode signal, which is considered as
> > 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
> > > [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
> > > deserved or not?
> > >
> > >
> > >
> > > I am confused that I read some book about remove Ground under
> > > Differential could reduce the induced Current from Differential
> > > pair, but the question is how we could control its
> > > 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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