DC impedance values (history)

Alvin.Cox at seagate.com Alvin.Cox at seagate.com
Tue Dec 12 09:23:06 PST 2006

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I have found no reference to DC in the existing specification of impedance 
values. The original SAS work included the following with regards to 
impedance measurement:
All impedance measurements shall be TDR measurements except where the 
receiver termination being tested includes inductive components such as 
transformers.  When inductive components exist in the receiver 
termination, a swept frequency Return Loss or VSWR measurement may be more 
appropriate.  The frequency sweep shall cover the range Bit rate/10 to Bit 
As far as I can tell from the SAS perspective, the term DC is first used 
in Kevin's proposal. It may have resulted from the issue that we have not 
specifically stated how the measurements are to be made (an item that 
Kevin Witt has indicated that we need in the SAS-2 specification) or it 
may be a carry-over from another specification (non-SAS). Appendix B is 
very general in its measurement descriptions.
Alvin Cox
Seagate Technology, LLC
Tel 405-350-7424
Cell 405-206-4809

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