[SI-LIST] : Re: Differential impedance

Nirmal Jain ([email protected])
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.



> Thanks for your help,
> Mark Nass

Nirmal Jain       			Ansoft Corporation
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