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RE: XAUI experts: Another XAUI issue that crossed my mind - help




Benny,
Valid 8B10B code-groups contauin either 5 "1", 5"0" or 4 1/0 and 6 0/1.
After transmission of one of the later, you're balancing it with one with
opposite polarity, so that on code-group boundary the polarity is +1 or -1
(RD-Running Disparity) at most. This limits the BLW to a very low value.
Boaz

> -----Original Message-----
> From: Christensen, Benny [mailto:benny.christensen@intel.com]
> Sent: Thursday, March 01, 2001 11:55 AM
> To: Serial PMD Ad Hoc Reflector (E-mail) (E-mail)
> Subject: XAUI experts: Another XAUI issue that crossed my mind - help
> 
> 
> 
> Hi XAUI people
> 
> Here is another problem that came across my mind yesterday.
> 
> I was looking at Mysticom's eye diagram simulations and all see quite
> realistic to me with the given set of parameters. However, I  
> assume that
> this has be done with a 50 % transition density signal. (i.e. 
> overall DC
> balanced)
> 
> I wonder if anybody have taken this example into 
> consideration and if my
> assumptions are valid: 
> 
> I have been told that the worst case relative DC voltage 
> (unbalance) could
> be 0.3. I.e. let's assume a 8B10B character (I don't know if 
> it is a valid
> character, but I guess one can find a similar valid example): 
> 01000 11000
> 
> If this character is  repeated infinitely (or at least 
> characters with the 3
> to 7 mark/space ratio) and when the signal is AC coupled (as 
> defined by the
> XAUI channel), this will cause the differential signal to 
> look like this:
> 
>   _   __
> == ===  ===
> ==_===__===
> 
> 00100011000
> 
> ie. the differential swing after the AC coupling has a 
> reduced swing for the
> '0' symbols. In other words: the '0' has a single-ended 
> relative amplitude
> of -0.3 ant the '1' has +0.7 (ie. relative to the DC level of 
> the signal and
> due to the AC coupling). Now the complementary(inverted) 
> signal has the same
> properties ie. its DC values is -.3 and the amplitude of the 
> inverted '0' is
> +0.3 and the amplitude of the '1' is -0.7. So the 
> differential AC coupled
> signal swing at the input of the CDR (or LIA) is  0.6 for the 
> '0' and 1.4
> for '1' symbols. Hey, that is quite amplitude modulation in 
> relation to a DC
> balanced or DC coupled signal.
> 
> This is all due to the AC coupling. For DC coupling the 
> amplitude of all
> signals are 0.5 and the differential swing is 1 for both symbols.
> 
> 
> What is wrong with my conclusion (if it is wrong - I don't think so).
> 
> 
> 
> Benny
> --------------------------------------------
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> 
> GIGA, an Intel company
> Benny Christensen, M.Sc.E.E, Ph.D.
> Mileparken 22, DK-2740 Skovlunde, Denmark
> Tel: +45 7010 1062, Fax: +45 7010 1063
> e-mail: benny.christensen@intel.com, http://www.giga.dk
> 
> 
> 
> 
> 
> 
>