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

Magnus Danielson magnus at rubidium.dyndns.org
Wed Oct 22 16:10:00 EDT 2014

Which is why the new style instruments sampling the waveforms with a 
common clock and then downsampling digitally until churning out phase 
data for further processing can achieve such a good measurement floor.

See Sam Steins papers.

For some applications the DDMTD approach is pretty amazing precision for 
it's simplicity. For some you can get more.


On 10/22/2014 08:09 PM, WarrenS via time-nuts wrote:
> 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
>>> -------------------------------------------------------------------------------
>>> 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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