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Baseline wander modelling (Read 4411 times)
currant
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Baseline wander modelling
Aug 03rd, 2010, 7:24am
 
Hello,
 I am trying to simulate baseline wander effect in the ethernet 100 Mbit/s transmit path. I use test pattern from TP-PMD standart doc, scrambler with seed=390, ideal transformer with first winding
inductance 350uH on transmit and load ends and transmition line in the form of 2wire mtline.
 When I do AC analysis, I see second order HPF response with f3db≈65 kHz.
But I can't see any big and long base line offset. I see only little (no more than 50 mV) and short (1-3 us) offset.
Did anybody simulate this effect? With what problem could I confront?
 Many Thanks.
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love_analog
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Re: Baseline wander modelling
Reply #1 - Aug 7th, 2010, 1:35pm
 
you may have tested too short a pattern. Remember the worst case will be a long string of 1s and thats when you see the max effect. Simulate with that input stream and you will surely see the issue
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currant
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Re: Baseline wander modelling
Reply #2 - Feb 9th, 2011, 6:57am
 
Hello,
after a long work on another theme, I returned to the 100 Mbit/s Ethernet project.
  I corrected binary-to-MLT-3 converter, and after applying BLW worst-case test pattern to the input of 4b/5b converter I saw a 53 bit time zero on output of scrambler. But I see baseline drift  only  if scrambler out connects directly to bin-to-MLT-3 converter.
  In my structure after scrambler there is a NRZ-to-NRZI converter, as in datasheet of NS  DP83816 and when I apply output of NRZ-to-NRZI block to input of bin-to-MLT-3 there is no any significant baseline drift.
Does anybody know,   Do I need a NRZ-to-NRZI converter between  scrambler and bin-to-MLT-3 converter?
Many Thanks.
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