The recent discussions about the simple digital mixer got me thinking about
the performance vs. complexity trade offs when measuring accurate, high
resolution, phase drift differences between two oscillators.
It would seem to me, that using both the positive and negative slope edges
of the high freq sinewave signal is a better way to go.
Is using just one edge, acceptable for a 'state of the art' Phase drift
measurements?
I am not suggesting the KISS approach is the wrong solution for Simon.
I am questioning if the paper posted, is the best way for CERN to make a
state of the art femtosecond DDMDT?
Here is an extreme example of throwing away useful data for the sake of
simplicity:
When measuring phase drift of a 10 MHz osc using just a 1PPS signal,
19,999,999 other possible data points are being discarded.
Using all possible data points could decrease the noise floor considerably.
(by ~5,000 to 1)
ws
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Tom Posted
Re: [time-nuts] Digital Mixing with a BeagleBone Black and D Flip
Hi Simon,
Some additional info. I first heard about the D-FF method of frequency
comparison in the late 90's (from Rick Hambly, I think) on the old gps
mailing list. It sounded really interesting. Since then, the subject has
turned up every few years on this list. But each time, the topic seems to
go away quietly with little or no data, plots or explanation. In
addition, none of the commercial products I've taken apart appear to use
this approach. Hmm. So that begs the question -- what's really going on,
and why.
I'm enjoying this thread because you've shown both technical competence
and optimistic persistence. Perhaps once and for all, with your efforts,
we can settle this matter. You will either find a working combination
with excellent performance, or you will uncover enough uncontrolled
variables that you never want to try it again. Either way, we all learn a
lot. Keep the photos, data, and plots coming.
Thanks,
/tvb
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Re: [time-nuts] Digital Mixing with a BeagleBone Black and D Flip Flop
Bruce posted
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/36903/1/01-2617.pdf
among other things illustrates a modified approach to the offset
generator by replacing the intermediate phase locked VCXO with a bandpass
filter.
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Re: [time-nuts] Digital Mixing with a BeagleBone Black and D Flip Flop
Simon posted www.ee.ucl.ac.uk/lcs/previous/LCS2011/LCS1136.pdf ...
The idea is based on the following article which describes creating a
digital DMTD with an FPGA for clocks @ 125mhz: >
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