To SAS PHY WG: Reference Channel for 12G SAS
alvin.cox at seagate.com
Fri Nov 19 13:48:40 PST 2010
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The drive connector mated pair was identified as an issue at 12G due to the
crosstalk peaking near 6GHz. Simulations from multiple connector suppliers
indicate that this peak can be moved to a higher frequency and thus, result
in a connector mated pair enhanced to work at 12G.
Channel simulations on existing s-parameter files indicate that not all 6G
channels are acceptable for 12G operation. I dont consider this an
unexpected result. 12G brings new challenges and it should be expected that
optimization is needed to double the transfer rate. In an ideal world, all
of these 6G channels should work at 12G, however, the added complexity,
power, and expense of implementation does not necessarily support that goal
We have been looking at the 10 meter Mini SAS HD cable as the possible
reference channel. There is confusion as to what the correct version is
since there have been a few iterations of the HD connector design.
SAS 3.0 needs the reference channel defined so that we can move forward.
Based on where we are at in the development and with the progress we have
made as a group, I see the following as a minimum set of items we need to
work on to move forward:
1. Post a fresh set of Mini SAS HD cable s-parameters for 10 meter, 8
meter, and 6 meter cables. This will make sure that the same set of
parameters is being used and let us know if 10 meters is achievable. Some
early investigation indicated that we may need to reduce the length to 8
meters. This will give us the data available to determine what the
capabilities and trade-offs are.
2. The drive connector mated pair simulations appear to be very similar.
The means to achieve this performance has not been openly shared. If IP is
involved, that can be resolved as a separate issue. We need to see actual
test data that supports the simulation data. This means that real
s-parameters from real hardware needs to be supplied. We should move
with the simulated data in parallel with actual connectors being built to
provide verification that the simulation results are actually achieved.
3. The channel requirements should include more information than
currently used for 6G. One thing mentioned during the last meeting was a
crosstalk to insertion loss spec. Crosstalk is definitely a major
consideration, but in simple terms, are we not talking about SNR? How
we address this? I believe it is the right direction, but what would be
best way to approach it from a specification standpoint?
Comments are welcome and encouraged.
Seagate Technology, LLC
E-Mail alvin.cox at seagate.com
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