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

Dr. Zheng,

I think it is more precise to say that you will suppress the even mode that
flows on the ground plane.  Since the even mode is caused by characteristics
of the signal (imbalance), it cannot be done away with.  It will find a path
for propagation, just not on the ground plane.

My two cents,

Jim


Jim Knighten, Ph.D.
Teradata, a Division of NCR             http://www.ncr.com
17095 Via Del Campo
San Diego, CA 92127
USA
Tel: 858-485-2537
Fax: 858-485-3788
jim.knighten@xxxxxxx

 -----Original Message-----
From:   Jian X. Zheng [mailto:jian@xxxxxxxxxx] 
Sent:   Friday, July 26, 2002 9:38 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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