Re: [time-nuts] A simple sampling DMTD

[Bob Martin]

Timing Solutions Corp had several products that might be of interest.

Designed around 20 years ago. The TSC5110 was mixer based.
The TSC5120 and successors were A/D based.

The block diagram in the TSC52120A datasheet may be of interest:

https://www.axiomtest.com/documents/models/MicroSemi%205120A%20DataSheet.pdf


In the TSC5120A manual, Appendix B has some theory:

https://deki.mpifr-bonn.mpg.de/@api/deki/files/4701/=TSC-5120A-MAN-Rev-G.pdf

For you history buffs, Timing Solutions was bought by Symmetricom, 
which was bought by Microsemi which was bought by Microchip. The
location and many of the key employees at TSC have remained  despite 
all the ownership changes.


Cheers,

Bob

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Re: [time-nuts] A simple sampling DMTD

[Jan-Derk Bakker]

Dear Joe,

Thank you for your mail; always happy with the dialogue.

In a way we have come full circle; the Sherman/Jördens NIST paper was one
of my primary references for the design I made last summer. (It would have
been helpful had I linked to it upthread; I could have sworn I had done so,
but I cannot find the post.)

The arctan-based approach in the NIST paper is computationally infeasible
on an 8-bit processor. Even so, back in November I have dumped raw samples
over USB to a PC to see how much improvement can be seen over a simple
least squares linear ZCD. As was discussed before, bandpass filtering and
more advanced phase estimation are complementary in their results: with
ideal band pass filtering, the phase detection becomes much less critical
(and vice versa). The best balance I could find at the time was a tracking
loop which runs a 501-point BPF FIR kernel on three points of the period of
both channels (expected on-time, ~1/6th period early, ~1/6th period late)
and then uses the arctangens to determine the phase. This produced ADEV
results about 1dB worse than running the FIR+arctan on all samples, and
about 1dB better than the simple ZCD with cascaded
differentiators/integrators as computationally inexpensive filters. This
gave me a workable baseline for the DMTD with reduced sampling rate and
reduced computational effort.

(One of the limiting factors with the arctan-approach was that the quality
of the amplitude estimator plays a large role in the accuracy of the end
result. With arctan2 on I/Q data this is less of an issue; a FPGA can
efficiently do both in one go with a CORDIC)

Inspired by the NIST paper my sampling DMTD was designed to take an FPGA
daughterboard (the two rows of headers visible on
http://www.lartmaker.nl/time-nuts/dmtd-proto.jpg ). Last February I have
designed such a daughterboard (see attached image). Sadly, due to the
COVID-19 crisis my lab has closed for the foreseeable future; as I don't
have facilities to reliably populate 0402 parts and QFN packages at home,
this will have to wait for now.

(@Luciano: Yes, having this available as a solution accessible to amateurs
has always been one of my goals)

Sincerely,

JDB.
[I've been working on other mildly time-nutty things that *can* be soldered
at home lately; hope to have a post in a week or two]

[image: timenuts-dmtd-fpga.png]

On Fri, May 29, 2020 at 6:07 PM Joseph Gwinn  wrote:

> On Sun, 01 Dec 2019 01:01:34 -0500, time-nuts-requ...@lists.febo.com
> wrote:
> Re: time-nuts Digest, Vol 185, Issue 1
>
> -
> >
> > Message: 1
> > Date: Sat, 30 Nov 2019 12:23:07 -0500
> > From: Joseph Gwinn 
> > To: time-nuts@lists.febo.com
> > Subject: Re: [time-nuts] A simple sampling DMTD
> > Message-ID: <20191130122307326859.fc045...@comcast.net>
> > Content-Type: text/plain; charset=us-ascii
> >
> > Re: time-nuts Digest, Vol 184, Issue 40
> > On Fri, 29 Nov 2019 20:37:02 -0500, time-nuts-requ...@lists.febo.com
> > wrote:
> >
> > [snip]
> >> Message: 6
> >> Date: Fri, 29 Nov 2019 20:37:16 +0100
> >> From: Gerhard Hoffmann 
> >> To: time-nuts@lists.febo.com
> >> Subject: Re: [time-nuts] A simple sampling DMTD
> >> Message-ID: 
> >> Content-Type: text/plain; charset=utf-8; format=flowed
> >>
> [snip]
> > The fundamental problem to be solved is to estimate the phases of two
> > beatnotes, one per channel (ref, signal under test), the phase
> > difference being converted into a relative time delay.  So, we are
> > estimating phase twice, against an unknown but common internal
> > reference, and the key question here is how best to measure those two
> > phases.  Detection of zero crossings is one way, but there are others.
>
> FYI, while looking for something unrelated, I recently ran across a
> relevant article from the NIST of Japan, published in 2007:
>
> "Frequency-Stability Measurement System Using High-Speed ADCs and
> Digital Signal Processing", Ken Mochizuki, Masaharu Uchino, and Takao
> Morikawa, IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL.
> 56, NO. 5, OCTOBER 2007, pages 1887-1893, Digital Object Identifier
> 10.1109/TIM.2007.895588.
>
> This can be implemented using a modern Software Defined Radio system.
>
> No zero-crossing detecter is used.  Computation of the time difference
> is detailed in reference [16] therein:
>
> [16] M. Uchino and K. Mochizuki, "Frequency stability measuring
> technique using digital signal processing," Electron. Commun. Jpn.,
> vol. 87, no. 1, pp. 21–33, 2004.   IEEE Xplore has it.
>
> Searching for Uchino et al led me to the following:
>
> "Oscillator metrology with software defined radio, Jeff A. Sherman and
> Robert Jördens (of NIST),  Review of Scientific Instruments 87, 054711
> (2016); https://doi.org/10.1063/1.4950898.  (Open version:
> )
>
> Joe Gwinn
>
>
> > We know the frequencies of the beatnotes quite accurately, and that the
> > waveforms are sine waves (which we will have band-pass filtered in
> > ha

Re: [time-nuts] A simple sampling DMTD

[timeok]

   It looks very interesting.

   The TICC which has similar performance to the HP53132A, has a residual of 6 
e-11 @ 1s while the two-channel version described in the document is around 5 e 
-14.

   It would be extremely interesting if someone turned this into a solution 
accessible to amateurs.

   Luciano

   Luciano P. S. Paramithiotti
   tim...@timeok.it
   www.timeok.it

   Da "time-nuts" time-nuts-boun...@lists.febo.com
   A time-nuts@lists.febo.com
   Cc
   Data Fri, 29 May 2020 12:06:41 -0400
   Oggetto Re: [time-nuts] A simple sampling DMTD
   On Sun, 01 Dec 2019 01:01:34 -0500, time-nuts-requ...@lists.febo.com
   wrote:
   Re: time-nuts Digest, Vol 185, Issue 1

   -
   >
   > Message: 1
   > Date: Sat, 30 Nov 2019 12:23:07 -0500
   > From: Joseph Gwinn 
   > To: time-nuts@lists.febo.com
   > Subject: Re: [time-nuts] A simple sampling DMTD
   > Message-ID: <20191130122307326859.fc045...@comcast.net>
   > Content-Type: text/plain; charset=us-ascii
   >
   > Re: time-nuts Digest, Vol 184, Issue 40
   > On Fri, 29 Nov 2019 20:37:02 -0500, time-nuts-requ...@lists.febo.com
   > wrote:
   >
   > [snip]
   >> Message: 6
   >> Date: Fri, 29 Nov 2019 20:37:16 +0100
   >> From: Gerhard Hoffmann 
   >> To: time-nuts@lists.febo.com
   >> Subject: Re: [time-nuts] A simple sampling DMTD
   >> Message-ID: 
   >> Content-Type: text/plain; charset=utf-8; format=flowed
   >>
   [snip]
   > The fundamental problem to be solved is to estimate the phases of two
   > beatnotes, one per channel (ref, signal under test), the phase
   > difference being converted into a relative time delay. So, we are
   > estimating phase twice, against an unknown but common internal
   > reference, and the key question here is how best to measure those two
   > phases. Detection of zero crossings is one way, but there are others.

   FYI, while looking for something unrelated, I recently ran across a
   relevant article from the NIST of Japan, published in 2007:

   "Frequency-Stability Measurement System Using High-Speed ADCs and
   Digital Signal Processing", Ken Mochizuki, Masaharu Uchino, and Takao
   Morikawa, IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL.
   56, NO. 5, OCTOBER 2007, pages 1887-1893, Digital Object Identifier
   10.1109/TIM.2007.895588.

   This can be implemented using a modern Software Defined Radio system.

   No zero-crossing detecter is used. Computation of the time difference
   is detailed in reference [16] therein:

   [16] M. Uchino and K. Mochizuki, "Frequency stability measuring
   technique using digital signal processing," Electron. Commun. Jpn.,
   vol. 87, no. 1, pp. 21–33, 2004. IEEE Xplore has it.

   Searching for Uchino et al led me to the following:

   "Oscillator metrology with software defined radio, Jeff A. Sherman and
   Robert Jördens (of NIST), Review of Scientific Instruments 87, 054711
   (2016); https://doi.org/10.1063/1.4950898. (Open version:
   )

   Joe Gwinn


   > We know the frequencies of the beatnotes quite accurately, and that the
   > waveforms are sine waves (which we will have band-pass filtered in
   > hardware before conversion to digital data). Here, I will assume that
   > the frequencies are the same. The only free variables are thus
   > amplitude and phase; these can be estimated using least squares applied
   > to successive batches of I&Q samples. Windowing is still useful to
   > reduce end splice effects, as previously discussed. Given that we are
   > working in the numerical domain, it's probably adequate to apply the
   > window function to the product of the proposed match and the actual
   > data, and then sum the windowed products.
   >
   > As a quality check, if the estimated amplitude is too small (or too
   > large), reject the phase estimate and try again. If this condition
   > persists too long or becomes too common, something is broken.
   >
   > I doubt that anything of the 8-bit class is practical for this, and
   > certainly not for a small-volume product, because programming effort
   > increases sharply if the chosen processor is too limited. Ardinuo and
   > maybe StrawberryPi seem more like it.
   >
   > As for emulation of floating point, the least-squares algorithm defined
   > above can certainly be implemented in fixed-point arithmetic, called
   > fractional integers above.
   > 
   >
   > In the extreme, this kind of algorithm will work with data clipped to a
   > few bits per sample. The underwater sonar folk are masters of this,
   > especially back in the days when signal processors were necessarily
   > bespoke hardware. The search term is "one-bit correlator" (without the
   > quotes).
   >
   > --
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