[time-nuts] Phase, One edge or two? (was Digital mixing with a D Flip Flop)

WarrenS warrensjmail-one at yahoo.com
Wed Oct 22 14:09:11 EDT 2014

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

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
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)


>> -------------------------------------------------------------------------------
>> 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
>> ------------------------------------------------------------------
>> 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.
>> ------------------------------------------------------------------
> 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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