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

  • From: Wen Fred-Q16099 <fred.wen@xxxxxxxxxxxx>
  • To: "'jian@xxxxxxxxxx'" <jian@xxxxxxxxxx>, binchuan2000@xxxxxxxxxxxx,si-list@xxxxxxxxxxxxx
  • Date: Sat, 27 Jul 2002 15:05:15 +0800

Binchuan & Dr. Zheng,

My two cents:

Generally, you'll introduce more radiated emission from (the odd mode of ) the 
differential pair and more odd mode noise on the differential pair receiver by 
removing the ground, even you can keep the differential impedance, I think. A 
differential pair receiver does care the odd mode noise, but not the even mode 
noise, unless the even mode noise has much high level (e.g. Surge).

Regards,
Fred Wen

> -----Original Message-----
> From: Jian X. Zheng [mailto:jian@xxxxxxxxxx]
> Sent: Saturday, July 27, 2002 12:38 AM
> To: binchuan2000@xxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Remove Ground underneath Differential 
> signal is deserved or not?
> 
> 
> 
> 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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