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RE: XAUI Related Issues




Ali,
Differential skew can be measured in presence of both DCD and jitter.
The Fibre Channel method that Tom Lindsay reported seems to be
robust. My concerns with the differential skew are more concerning
consistency of the standard. It is the only one out of a whole 
range of signal balance quality numbers that are otherwise left
outside the standard. Rather than adding all that, I suggest we
remove the differential skew spec.

Best Regards
Tord.


-----Original Message-----
From: Ali Ghiasi [mailto:aghiasi@broadcom.com]
Sent: Wednesday, February 28, 2001 01:19
To: Kesling, Dawson W
Cc: Serial PMD reflector (E-mail); Anthony Sanders (E-mail); Ali Ghiasi
Subject: 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.