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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