[time-nuts] Question about DDMTD deglitching

Robert Darby bobdarby at triad.rr.com
Sat Feb 22 12:30:46 EST 2014


In August 2011 there was a brief mention on Time-Nuts of DDMTD's which 
led me to The P. Moreira  and I. Darwazeh  paper "Digital femtosecond 
time difference circuit for CERN’s timing system".  I'm hoping that 
someone can explain one item mentioned in this paper for me.   For those 
not familiar with this work, it is part of a sub-nanosecond network 
synchronization scheme know as White Rabbit.

One of the elements of the DDMTD is a deglitching system and the authors 
describe three possible deglitching strategies.  The first two are quite 
straightforward but the third method  described as "Zero Count – counts 
the numbers of “1” and “0” and selects as the best edge the time 
position where the number of zeros is the same as the number of ones." 
seems totally ambiguous.  If I take the statement quite literally, there 
must be dozens or hundreds of times when the number of 1's and 0's in a 
glitch are equal.   Can anyone familiar with this work explain what I am 
missing? I realize that the answer to my question is probably at hand in 
the FPGA code but that's well beyond my pay grade.

This paper is available at:
http://www.ee.ucl.ac.uk/lcs/previous/LCS2011/LCS1136.pdf
A list of White Rabbit papers is available at:
http://www.ohwr.org/projects/white-rabbit/wiki/WRpublications

Thanks,
Bob Darby




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