Re: [SI-LIST] : Differential Signals

Mike Jenkins ([email protected])
Wed, 21 Oct 1998 15:37:12 -0700

This is a multi-part message in MIME format.
--------------303D33535332BF74D333E880
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

Susan,

Since dif'l signals carry their own return current, they survive
the trip across split planes much better than single-ended signals.
What ground currents are induced (depending on the distance between
the dif'l pair lines and their spacing to the ground plane) loop
back on themselves when a split in the ground plane is encountered,
and another such "racetrack of ground current" forms on the far
side of the split.

To look at it another way, the dif'l mode impedance goes up from
the case of the pair's cross section WITH the ground plane to the
case of the pair's cross section WITHOUT a groundplane. This
increase is usually small and applies only for the distance across
the split. The common mode impedance, of course has the same
large increase, EMI problems, etc., as single-ended signals do
when they encounter a split ground plane.

Others may have a less sanguine view of the consequences, but
that's my opinion based on a number of applications.

Regards,
Mike

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Mike Jenkins               Phone: 408.433.7901            _____     
 LSI Logic Corp, ms/G750      Fax: 408.433.2840        LSI|LOGIC| (R)   
 1525 McCarthy Blvd.       mailto:[email protected]        |     |     
 Milpitas, CA  95035         http://www.lsilogic.com      |_____|    
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--------------303D33535332BF74D333E880
Content-Type: text/x-vcard; charset=us-ascii; name="vcard.vcf"
Content-Transfer-Encoding: 7bit
Content-Description: Card for Mike Jenkins
Content-Disposition: attachment; filename="vcard.vcf"

begin: vcard fn: Mike Jenkins n: Jenkins;Mike org: LSI Logic Corporation adr: 1551 McCarthy Blvd;;MS G-750;Milpitas;CA;95035;USA email;internet: [email protected] title: Senior Design Engineer tel;work: 408.433.7901 tel;fax: 408.433.2840 x-mozilla-cpt: ;0 x-mozilla-html: FALSE version: 2.1 end: vcard

--------------303D33535332BF74D333E880--

**** To unsubscribe from si-list: send e-mail to [email protected]. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****