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




Hi Boaz and Ian

Thank for reply. This clears it up.

Benny

> -----Original Message-----
> From: Boaz Shahar [mailto:boazs@mysticom.com]
> Sent: 1. marts 2001 12:07
> To: 'Christensen, Benny'; Serial PMD Ad Hoc Reflector 
> (E-mail) (E-mail)
> Subject: 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
> > --------------------------------------------
> >   llllllll   ii     llllllll     llllll
> > ll                ll           ll      ll
> > ll    llll   ll   ll    llll   llllllllll
> > ll      ll   ll   ll      ll   ll      ll
> >   llllllll   ll     llllllll   ll      ll
> > 
> > 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
> > 
> > 
> > 
> > 
> > 
> > 
> > 
>