XAUI Related Issues
Hi Dawson
I was looking at D2.1 and I found several potential issue:
- In Tampa meeting we agreed the RX amplitude will be fixed to
1600 mV and TX need to be determined. Here you need some margin
and as allowing some reflection. Probably maximum TX need to be
lowered.
- Return loss originally was intended only for receiver (10 dB
diff, and 5 dB common mode). It would very difficult to meet
to meet transmit return loss. In the IB we added Zdiff,
ZSingle_Ended, 10% matching, but not the return loss.
- Differential Skew can't be measured separately from DJ even if
you are sending 1010, you still may have DCD. The total DJ
already include the Diff_Skew so I would propose removing it
since it can't be measured.
- We need to have better definition of how much skew you can
have lane to lane. Chapter 48 says you can have 1 UI allocated
to the PMA, but we need to allocated like 0.5 UI to the electrical
XAUI portion.
- It seems to me the connector loss is lumped as part of interconnect
loss resulting in 7.5 dB of loss. Under some cases where the 7.5 dB
is just ISI some implementation may not work. We should try to
separate
ISI loss from connector+misc+croasstalk loss.
- Fig 47-4 assuming measured with an ideal load does not include
4% cross talk which equates to 63 mV under worst case scenario of
1600 mV and 200 mV. Loss allocation in the table 47-6 specifies 4.5 dB
for others but according to eye diagram Fig 47-4 some one may introduce
more loss. The 4% crosstalk results in 31% additional eye closure with
an actual XAUI receiver. Return loss penalty associated with a XAUI
receiver gets absorbed in to the SerDes effective sensitivity, but the
crosstalk may not. As the biggest source of the crosstalk is the
connector.
Thanks,
--
Ali Ghiasi
Broadcom Corp.
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