[SI-LIST] : Re: Differential impedance

Nirmal Jain (nirmal@ansoft.com)
Thu, 05 Feb 1998 15:23:48 -0500

Mark Nass wrote:
>
> We are laying out a board that has differential a SCSI bus on it.
> The specs say the that the differential impedance should be 110-135 ohms.
> What is differential impedance? Is this the impedance between
> the 2 traces, or the impedance with respect to the plane?

This is actually the impedance between the two traces. If you
have a geomtery in mind I could do a quick analysis and give
you the differential impedance. In terms of odd mode impedance

Zdiff = 2 * Zodd,

where Zodd is the odd mode impedance. I think there was lively
discussion on differential impedance a while ago on the list.
Let me know if you need more info.

Regards

Nirmal

>
> Thanks for your help,
> Mark Nass

-- 
Nirmal Jain       			Ansoft Corporation
(412)261-3200 X129 (W) 			Four Station Sq., Suite 660
(412)261-471-9427(FAX)			Pittsburgh, PA 15219
_________________________________________________________________________
Check out Ansoft's WWW site at http://www.ansoft.com for product 
information, technical support, employment opportunities, much more...
-------------------------------------------------------------------------