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.
Cheers,
Magnus
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: >
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
