EK
Erik Kaashoek
Tue, Oct 25, 2022 10:54 AM
Hi Carsten,
In my DMTD I use a PLL to lock the LO of the analog down mixers to the
reference input. In the digital domain the I/Q mixer has a fixed LO
converting to an fb of zero Hz (kept at zero with the PLL) and the
output of the mixer is averaged as decimation.
This should (I hope) also avoid spectral leakage, just like you did with
the NCO. I've tested this by adding/removing a window function and this
did not make any difference, as long as the fb was kept at zero Hz. The
further processing is done as you describe in the second part of your
reaction.
The problem with my DMTD seems to be not spectral leakage but the
limited isolation between the two inputs (only about 80dB isolation) so
the DUT input leaks into the REF input and because the frequency
difference is small the downconverted DUT leakage is not filtered out by
the averaging. Adding/removing the windowing did not make any difference
for this DUT leakage.
But as the leakage is linear it may be possible to model the leakage and
compensate for it.
Erik.
On 25-10-2022 9:43, Carsten Andrich wrote:
Hi Erik,
spectral leakage only occurs with the DFT due to its implicit
rectangular window applied to the input samples. The appeal of the
digital down conversion (DDC) implemented with the NCO is that
coherence does not matter and spectral leakage does not occur. It's
simply a perfect, digital implementation of the down mixing you
perform in the analog domain. Its purpose is to shift the frequency of
the signal to enable reduction of the sample rate to reasonable levels
(a few kSa/s instead of >= 25 MSa/s) via decimation. The decimation
can also be seen as averaging, so this approach also uses every
available sample.
Additionally, the use of complex down-conversion enables
straightforward phase estimates. Relative to the sampling clock by
taking the phase angle of the complex samples of a single channel.
Between two channels by taking the phase angle of fraction of two
channels' complex samples. If you unwrap the phase angles and apply
linear regression, you can compute the average frequency difference.
Best regards,
Carsten
Hi Carsten,
In my DMTD I use a PLL to lock the LO of the analog down mixers to the
reference input. In the digital domain the I/Q mixer has a fixed LO
converting to an fb of zero Hz (kept at zero with the PLL) and the
output of the mixer is averaged as decimation.
This should (I hope) also avoid spectral leakage, just like you did with
the NCO. I've tested this by adding/removing a window function and this
did not make any difference, as long as the fb was kept at zero Hz. The
further processing is done as you describe in the second part of your
reaction.
The problem with my DMTD seems to be not spectral leakage but the
limited isolation between the two inputs (only about 80dB isolation) so
the DUT input leaks into the REF input and because the frequency
difference is small the downconverted DUT leakage is not filtered out by
the averaging. Adding/removing the windowing did not make any difference
for this DUT leakage.
But as the leakage is linear it may be possible to model the leakage and
compensate for it.
Erik.
On 25-10-2022 9:43, Carsten Andrich wrote:
>
> Hi Erik,
>
> spectral leakage only occurs with the DFT due to its implicit
> rectangular window applied to the input samples. The appeal of the
> digital down conversion (DDC) implemented with the NCO is that
> coherence does not matter and spectral leakage does not occur. It's
> simply a perfect, digital implementation of the down mixing you
> perform in the analog domain. Its purpose is to shift the frequency of
> the signal to enable reduction of the sample rate to reasonable levels
> (a few kSa/s instead of >= 25 MSa/s) via decimation. The decimation
> can also be seen as averaging, so this approach also uses every
> available sample.
>
> Additionally, the use of complex down-conversion enables
> straightforward phase estimates. Relative to the sampling clock by
> taking the phase angle of the complex samples of a single channel.
> Between two channels by taking the phase angle of fraction of two
> channels' complex samples. If you unwrap the phase angles and apply
> linear regression, you can compute the average frequency difference.
>
> Best regards,
> Carsten
>
>
EK
Erik Kaashoek
Fri, Oct 28, 2022 12:49 PM
Hi John,
Thanks for the practical advice and the measurements.
After ironing out some problems the measurement noise with two equal
inputs and a tau of 0.1 s is now below 100 fs.
Long term phase stability has also improved and typical slow phase
variations over an hour, when measured on a desktop in a room with
people, are now within 4 ps
The next step may be to replace the current plastic enclosure with a
decommissioned fridge, but that would defeat the idea of having a small
battery powered portable device.
Erik.
On 24-10-2022 21:49, John Miles via time-nuts wrote:
You should see similar sub-picosecond drift figures from your own
DMTD, given similar conditions. If not, there will be a reason, one that is
probably not too hard to address.
Hi John,
Thanks for the practical advice and the measurements.
After ironing out some problems the measurement noise with two equal
inputs and a tau of 0.1 s is now below 100 fs.
Long term phase stability has also improved and typical slow phase
variations over an hour, when measured on a desktop in a room with
people, are now within 4 ps
The next step may be to replace the current plastic enclosure with a
decommissioned fridge, but that would defeat the idea of having a small
battery powered portable device.
Erik.
On 24-10-2022 21:49, John Miles via time-nuts wrote:
> You should see similar sub-picosecond drift figures from your own
> DMTD, given similar conditions. If not, there will be a reason, one that is
> probably not too hard to address.
>
>
BK
Bob kb8tq
Fri, Oct 28, 2022 1:16 PM
Hi
A beach towel tossed over the device may improve things quite a bit.
Next step up from that would be a die cast metal enclosure. They are
pretty cheap from a number of sources, Hammond is one, but there are
others.
Bob
On Oct 28, 2022, at 8:49 AM, Erik Kaashoek via time-nuts time-nuts@lists.febo.com wrote:
Hi John,
Thanks for the practical advice and the measurements.
After ironing out some problems the measurement noise with two equal inputs and a tau of 0.1 s is now below 100 fs.
Long term phase stability has also improved and typical slow phase variations over an hour, when measured on a desktop in a room with people, are now within 4 ps
The next step may be to replace the current plastic enclosure with a decommissioned fridge, but that would defeat the idea of having a small battery powered portable device.
Erik.
On 24-10-2022 21:49, John Miles via time-nuts wrote:
You should see similar sub-picosecond drift figures from your own
DMTD, given similar conditions. If not, there will be a reason, one that is
probably not too hard to address.
Hi
A beach towel tossed over the device may improve things quite a bit.
Next step up from that would be a die cast metal enclosure. They are
pretty cheap from a number of sources, Hammond is one, but there are
others.
Bob
> On Oct 28, 2022, at 8:49 AM, Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>
> Hi John,
> Thanks for the practical advice and the measurements.
> After ironing out some problems the measurement noise with two equal inputs and a tau of 0.1 s is now below 100 fs.
> Long term phase stability has also improved and typical slow phase variations over an hour, when measured on a desktop in a room with people, are now within 4 ps
> The next step may be to replace the current plastic enclosure with a decommissioned fridge, but that would defeat the idea of having a small battery powered portable device.
> Erik.
>
> On 24-10-2022 21:49, John Miles via time-nuts wrote:
>
>> You should see similar sub-picosecond drift figures from your own
>> DMTD, given similar conditions. If not, there will be a reason, one that is
>> probably not too hard to address.
>>
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
AK
Attila Kinali
Mon, Nov 14, 2022 4:37 PM
During the testing of a DMTD there appears to be a "large" sensitivity
to temperature variations.
Opening a door in the room with the DMTD causes changes in the phase
difference in the order of 1 ps
Blowing cold air over the encased DMTD causes phase variations up to 10 ps.
I would like to add a few things that have not been mentioned already:
Most electronics seem to have a tempco of 1-10ps/K. It is not clear
where this tempco comes from, i.e. nobody fully explained it. It
is remarkable, though, that the range is pretty narrow and quite
stable over various technologies. Of course, analog filters have
a larger variation of tempco.
My guess (read: totally unscientific assumption, not backed by
any data or experiments) is that a major source of tempco are
mechanical stresses due to different linear expansion coefficients.
How exactly mechanical stresses affect delay in electronics is
not quite as simple as it would seem at a first glance. So it's
difficult to come up with a decent model that can be tested in
experiments.
Summa summarum: The few-ps tempco you are seeing is what I would
expect. See also [1] where they measured the tempco of a mixer
setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
a way how to measure and compensate the drift.
I also recommend having a look at [2] for a more general treatment
of the issue of temperature coefficients in time/frequency measurement
systems.
On Mon, 24 Oct 2022 14:43:43 +0200
Erik Kaashoek via time-nuts time-nuts@lists.febo.com wrote:
The PTFE cables have been replaced with semi-rigid coax cables and the
stability, both mechanical and temperature, have improved.
Please keep in mind that the problem with PTFE is not the external
insulation of the coax cables, but the dielectric between the core
and the screen. A lot of semi-rigid still uses PTFE because it's
reasonably cheap and gives good performance. See [3-5] for more
information on this topic.
On Mon, 24 Oct 2022 10:10:27 +0200
Carsten Andrich via time-nuts time-nuts@lists.febo.com wrote:
only the ADC clock should matter and the used ADC should be of the
simultaneous sampling type. If it's not, its multiplexer may have a
detrimental temperature-dependent effect on the phase measurement.
It's a bit more complicated than that, unfortunately.
The mixer and their LO already add already some temperature dependence
due to inevitable asymmetries. The ADC themselves have a tempco too.
And it's not just direct temperature effect on the circuitry but also
indirect effect from power supplies. Even if using a dual-channel ADC
there are effects that affect the two channels differently. If you look
at Sherman and Jördens' paper [6], who looked at phase stability in SDR
systems for frequency / stability measurements, then you see that there
is a lower limit of a few 10's of fs in ADC sample timing. My guess is
that at least some of that is due to noise on the power grid in the
chip that causes IR drop [7]. Which is, by its nature, not symmetric.
It is also very likely that even small mechanical stresses due to minute
temperature variations at short time scales already cause timing differences
and phase shifts in the 10s of fs.
Figuring out where all these small temperature coefficients come from
is difficult, to say the least, and very tedious. Once you reach <10ps/K
I would, personally, call it a day and do the rest by proper enclosure
design and keeping everything at a stable temperature. This way it is
easier to reduce the tempco than to hunt for it in the electronics.
Attila Kinali
[1] "2π Low Drift Phase Detector for High-Precision Measurements"
by Jablonski, Czuba, Ludwik and Schlarb, 2015
https://doi.org/10.1109/TNS.2015.2425733
[2] "Environmental Effects in Mixers and Frequency Distribution Systems",
by Nelson and Walls, 1992
[3] "Current Innovations In Phase Stable Coaxial Cable Design",
by Times Microwave Systems
https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
[4] "Understanding Phase Versus Temperature Behavior",
by Micro-coax
http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
[5] "Temperature Stability of Coaxial Cables",
by Czuba and Sikora, 2011
http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
[6] "Oscillator metrology with software defined radio",
by Jeff A. Sherman and Robert Jördens, 2016
http://dx.doi.org/10.1063/1.4950898
[7] https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
--
In science if you know what you are doing you should not be doing it.
In engineering if you do not know what you are doing you should not be doing it.
-- Richard W. Hamming, The Art of Doing Science and Engineering
Good afternoon,
On Sun, 23 Oct 2022 18:05:40 +0200
Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
> During the testing of a DMTD there appears to be a "large" sensitivity
> to temperature variations.
> Opening a door in the room with the DMTD causes changes in the phase
> difference in the order of 1 ps
> Blowing cold air over the encased DMTD causes phase variations up to 10 ps.
I would like to add a few things that have not been mentioned already:
Most electronics seem to have a tempco of 1-10ps/K. It is not clear
where this tempco comes from, i.e. nobody fully explained it. It
is remarkable, though, that the range is pretty narrow and quite
stable over various technologies. Of course, analog filters have
a larger variation of tempco.
My guess (read: totally unscientific assumption, not backed by
any data or experiments) is that a major source of tempco are
mechanical stresses due to different linear expansion coefficients.
How exactly mechanical stresses affect delay in electronics is
not quite as simple as it would seem at a first glance. So it's
difficult to come up with a decent model that can be tested in
experiments.
Summa summarum: The few-ps tempco you are seeing is what I would
expect. See also [1] where they measured the tempco of a mixer
setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
a way how to measure and compensate the drift.
I also recommend having a look at [2] for a more general treatment
of the issue of temperature coefficients in time/frequency measurement
systems.
On Mon, 24 Oct 2022 14:43:43 +0200
Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
> The PTFE cables have been replaced with semi-rigid coax cables and the
> stability, both mechanical and temperature, have improved.
Please keep in mind that the problem with PTFE is not the external
insulation of the coax cables, but the dielectric between the core
and the screen. A lot of semi-rigid still uses PTFE because it's
reasonably cheap and gives good performance. See [3-5] for more
information on this topic.
On Mon, 24 Oct 2022 10:10:27 +0200
Carsten Andrich via time-nuts <time-nuts@lists.febo.com> wrote:
> only the ADC clock should matter and the used ADC should be of the
> simultaneous sampling type. If it's not, its multiplexer may have a
> detrimental temperature-dependent effect on the phase measurement.
It's a bit more complicated than that, unfortunately.
The mixer and their LO already add already some temperature dependence
due to inevitable asymmetries. The ADC themselves have a tempco too.
And it's not just direct temperature effect on the circuitry but also
indirect effect from power supplies. Even if using a dual-channel ADC
there are effects that affect the two channels differently. If you look
at Sherman and Jördens' paper [6], who looked at phase stability in SDR
systems for frequency / stability measurements, then you see that there
is a lower limit of a few 10's of fs in ADC sample timing. My guess is
that at least some of that is due to noise on the power grid in the
chip that causes IR drop [7]. Which is, by its nature, not symmetric.
It is also very likely that even small mechanical stresses due to minute
temperature variations at short time scales already cause timing differences
and phase shifts in the 10s of fs.
Figuring out where all these small temperature coefficients come from
is difficult, to say the least, and very tedious. Once you reach <10ps/K
I would, personally, call it a day and do the rest by proper enclosure
design and keeping everything at a stable temperature. This way it is
easier to reduce the tempco than to hunt for it in the electronics.
Attila Kinali
[1] "2π Low Drift Phase Detector for High-Precision Measurements"
by Jablonski, Czuba, Ludwik and Schlarb, 2015
https://doi.org/10.1109/TNS.2015.2425733
[2] "Environmental Effects in Mixers and Frequency Distribution Systems",
by Nelson and Walls, 1992
[3] "Current Innovations In Phase Stable Coaxial Cable Design",
by Times Microwave Systems
https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
[4] "Understanding Phase Versus Temperature Behavior",
by Micro-coax
http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
[5] "Temperature Stability of Coaxial Cables",
by Czuba and Sikora, 2011
http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
[6] "Oscillator metrology with software defined radio",
by Jeff A. Sherman and Robert Jördens, 2016
http://dx.doi.org/10.1063/1.4950898
[7] https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
--
In science if you know what you are doing you should not be doing it.
In engineering if you do not know what you are doing you should not be doing it.
-- Richard W. Hamming, The Art of Doing Science and Engineering
EK
Erik Kaashoek
Mon, Nov 14, 2022 8:44 PM
Antilla
Using a narrow tube and a soure of cold air the biggest contributor has
been identified as the Gilbert cell active mixers used in the first stage.
In the current HW they are not used in a balanced way so a common mode
change, e.g. temperature change, is very visible.
I will read the the documents you referred to.
Erik
On Mon, Nov 14, 2022, 21:00 Attila Kinali via time-nuts <
time-nuts@lists.febo.com> wrote:
During the testing of a DMTD there appears to be a "large" sensitivity
to temperature variations.
Opening a door in the room with the DMTD causes changes in the phase
difference in the order of 1 ps
Blowing cold air over the encased DMTD causes phase variations up to 10
ps.
I would like to add a few things that have not been mentioned already:
Most electronics seem to have a tempco of 1-10ps/K. It is not clear
where this tempco comes from, i.e. nobody fully explained it. It
is remarkable, though, that the range is pretty narrow and quite
stable over various technologies. Of course, analog filters have
a larger variation of tempco.
My guess (read: totally unscientific assumption, not backed by
any data or experiments) is that a major source of tempco are
mechanical stresses due to different linear expansion coefficients.
How exactly mechanical stresses affect delay in electronics is
not quite as simple as it would seem at a first glance. So it's
difficult to come up with a decent model that can be tested in
experiments.
Summa summarum: The few-ps tempco you are seeing is what I would
expect. See also [1] where they measured the tempco of a mixer
setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
a way how to measure and compensate the drift.
I also recommend having a look at [2] for a more general treatment
of the issue of temperature coefficients in time/frequency measurement
systems.
On Mon, 24 Oct 2022 14:43:43 +0200
Erik Kaashoek via time-nuts time-nuts@lists.febo.com wrote:
The PTFE cables have been replaced with semi-rigid coax cables and the
stability, both mechanical and temperature, have improved.
Please keep in mind that the problem with PTFE is not the external
insulation of the coax cables, but the dielectric between the core
and the screen. A lot of semi-rigid still uses PTFE because it's
reasonably cheap and gives good performance. See [3-5] for more
information on this topic.
On Mon, 24 Oct 2022 10:10:27 +0200
Carsten Andrich via time-nuts time-nuts@lists.febo.com wrote:
only the ADC clock should matter and the used ADC should be of the
simultaneous sampling type. If it's not, its multiplexer may have a
detrimental temperature-dependent effect on the phase measurement.
It's a bit more complicated than that, unfortunately.
The mixer and their LO already add already some temperature dependence
due to inevitable asymmetries. The ADC themselves have a tempco too.
And it's not just direct temperature effect on the circuitry but also
indirect effect from power supplies. Even if using a dual-channel ADC
there are effects that affect the two channels differently. If you look
at Sherman and Jördens' paper [6], who looked at phase stability in SDR
systems for frequency / stability measurements, then you see that there
is a lower limit of a few 10's of fs in ADC sample timing. My guess is
that at least some of that is due to noise on the power grid in the
chip that causes IR drop [7]. Which is, by its nature, not symmetric.
It is also very likely that even small mechanical stresses due to minute
temperature variations at short time scales already cause timing
differences
and phase shifts in the 10s of fs.
Figuring out where all these small temperature coefficients come from
is difficult, to say the least, and very tedious. Once you reach <10ps/K
I would, personally, call it a day and do the rest by proper enclosure
design and keeping everything at a stable temperature. This way it is
easier to reduce the tempco than to hunt for it in the electronics.
Attila Kinali
[1] "2π Low Drift Phase Detector for High-Precision Measurements"
by Jablonski, Czuba, Ludwik and Schlarb, 2015
https://doi.org/10.1109/TNS.2015.2425733
[2] "Environmental Effects in Mixers and Frequency Distribution Systems",
by Nelson and Walls, 1992
[3] "Current Innovations In Phase Stable Coaxial Cable Design",
by Times Microwave Systems
https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
[4] "Understanding Phase Versus Temperature Behavior",
by Micro-coax
http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
[5] "Temperature Stability of Coaxial Cables",
by Czuba and Sikora, 2011
http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
[6] "Oscillator metrology with software defined radio",
by Jeff A. Sherman and Robert Jördens, 2016
http://dx.doi.org/10.1063/1.4950898
[7]
https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
--
In science if you know what you are doing you should not be doing it.
In engineering if you do not know what you are doing you should not be
doing it.
-- Richard W. Hamming, The Art of Doing Science and Engineering
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
Antilla
Using a narrow tube and a soure of cold air the biggest contributor has
been identified as the Gilbert cell active mixers used in the first stage.
In the current HW they are not used in a balanced way so a common mode
change, e.g. temperature change, is very visible.
I will read the the documents you referred to.
Erik
On Mon, Nov 14, 2022, 21:00 Attila Kinali via time-nuts <
time-nuts@lists.febo.com> wrote:
> Good afternoon,
>
> On Sun, 23 Oct 2022 18:05:40 +0200
> Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>
> > During the testing of a DMTD there appears to be a "large" sensitivity
> > to temperature variations.
> > Opening a door in the room with the DMTD causes changes in the phase
> > difference in the order of 1 ps
> > Blowing cold air over the encased DMTD causes phase variations up to 10
> ps.
>
> I would like to add a few things that have not been mentioned already:
>
> Most electronics seem to have a tempco of 1-10ps/K. It is not clear
> where this tempco comes from, i.e. nobody fully explained it. It
> is remarkable, though, that the range is pretty narrow and quite
> stable over various technologies. Of course, analog filters have
> a larger variation of tempco.
>
> My guess (read: totally unscientific assumption, not backed by
> any data or experiments) is that a major source of tempco are
> mechanical stresses due to different linear expansion coefficients.
> How exactly mechanical stresses affect delay in electronics is
> not quite as simple as it would seem at a first glance. So it's
> difficult to come up with a decent model that can be tested in
> experiments.
>
> Summa summarum: The few-ps tempco you are seeing is what I would
> expect. See also [1] where they measured the tempco of a mixer
> setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
> a way how to measure and compensate the drift.
>
> I also recommend having a look at [2] for a more general treatment
> of the issue of temperature coefficients in time/frequency measurement
> systems.
>
> On Mon, 24 Oct 2022 14:43:43 +0200
> Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>
> > The PTFE cables have been replaced with semi-rigid coax cables and the
> > stability, both mechanical and temperature, have improved.
>
> Please keep in mind that the problem with PTFE is not the external
> insulation of the coax cables, but the dielectric between the core
> and the screen. A lot of semi-rigid still uses PTFE because it's
> reasonably cheap and gives good performance. See [3-5] for more
> information on this topic.
>
> On Mon, 24 Oct 2022 10:10:27 +0200
> Carsten Andrich via time-nuts <time-nuts@lists.febo.com> wrote:
>
> > only the ADC clock should matter and the used ADC should be of the
> > simultaneous sampling type. If it's not, its multiplexer may have a
> > detrimental temperature-dependent effect on the phase measurement.
>
> It's a bit more complicated than that, unfortunately.
> The mixer and their LO already add already some temperature dependence
> due to inevitable asymmetries. The ADC themselves have a tempco too.
> And it's not just direct temperature effect on the circuitry but also
> indirect effect from power supplies. Even if using a dual-channel ADC
> there are effects that affect the two channels differently. If you look
> at Sherman and Jördens' paper [6], who looked at phase stability in SDR
> systems for frequency / stability measurements, then you see that there
> is a lower limit of a few 10's of fs in ADC sample timing. My guess is
> that at least some of that is due to noise on the power grid in the
> chip that causes IR drop [7]. Which is, by its nature, not symmetric.
> It is also very likely that even small mechanical stresses due to minute
> temperature variations at short time scales already cause timing
> differences
> and phase shifts in the 10s of fs.
>
> Figuring out where all these small temperature coefficients come from
> is difficult, to say the least, and very tedious. Once you reach <10ps/K
> I would, personally, call it a day and do the rest by proper enclosure
> design and keeping everything at a stable temperature. This way it is
> easier to reduce the tempco than to hunt for it in the electronics.
>
> Attila Kinali
>
>
> [1] "2π Low Drift Phase Detector for High-Precision Measurements"
> by Jablonski, Czuba, Ludwik and Schlarb, 2015
> https://doi.org/10.1109/TNS.2015.2425733
>
> [2] "Environmental Effects in Mixers and Frequency Distribution Systems",
> by Nelson and Walls, 1992
>
> [3] "Current Innovations In Phase Stable Coaxial Cable Design",
> by Times Microwave Systems
> https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
>
> [4] "Understanding Phase Versus Temperature Behavior",
> by Micro-coax
>
> http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
>
> [5] "Temperature Stability of Coaxial Cables",
> by Czuba and Sikora, 2011
> http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
>
> [6] "Oscillator metrology with software defined radio",
> by Jeff A. Sherman and Robert Jördens, 2016
> http://dx.doi.org/10.1063/1.4950898
>
> [7]
> https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
>
> --
> In science if you know what you are doing you should not be doing it.
> In engineering if you do not know what you are doing you should not be
> doing it.
> -- Richard W. Hamming, The Art of Doing Science and Engineering
> _______________________________________________
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MD
Magnus Danielson
Tue, Nov 15, 2022 9:59 PM
Hi,
Somewhere in the NIST T&F archive, there is reference to how mixers
cause a reflection of energy and temperature coefficients then change
phase and working-point. They use 3 dB damper on the mixer to stabilize
that and reduce the tempco situation. The signal degradation is
compensated for but improvement in stability significant. As I recall
it, they refer to the cable phase stability with regard to temperature
to be part of the culprit.
Now, DBM isn't perfect in terms of balance and nor is the Gilbert cell
mixers that Erik is using, so milage may vary, but one should look at
multiple aspects. Alteration of operating points, alteration of
dielectric with temperature etc. is things to be aware of and then try
to figure out which is the major driver for your setup and measurement
needs and aims.
I am sure someone have attempted to temperature stabilize a mixer at
some time.
When building synths for music, we end up temperature compensating the
expo-converters or even ovenize them to achieve needed stability. That
is not far from what a mixer does. Also, it is what got me into this
time and frequency thing in the first place.
Cheers,
Magnus
On 2022-11-14 17:37, Attila Kinali via time-nuts wrote:
Good afternoon,
On Sun, 23 Oct 2022 18:05:40 +0200
Erik Kaashoek via time-nuts time-nuts@lists.febo.com wrote:
During the testing of a DMTD there appears to be a "large" sensitivity
to temperature variations.
Opening a door in the room with the DMTD causes changes in the phase
difference in the order of 1 ps
Blowing cold air over the encased DMTD causes phase variations up to 10 ps.
I would like to add a few things that have not been mentioned already:
Most electronics seem to have a tempco of 1-10ps/K. It is not clear
where this tempco comes from, i.e. nobody fully explained it. It
is remarkable, though, that the range is pretty narrow and quite
stable over various technologies. Of course, analog filters have
a larger variation of tempco.
My guess (read: totally unscientific assumption, not backed by
any data or experiments) is that a major source of tempco are
mechanical stresses due to different linear expansion coefficients.
How exactly mechanical stresses affect delay in electronics is
not quite as simple as it would seem at a first glance. So it's
difficult to come up with a decent model that can be tested in
experiments.
Summa summarum: The few-ps tempco you are seeing is what I would
expect. See also [1] where they measured the tempco of a mixer
setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
a way how to measure and compensate the drift.
I also recommend having a look at [2] for a more general treatment
of the issue of temperature coefficients in time/frequency measurement
systems.
On Mon, 24 Oct 2022 14:43:43 +0200
Erik Kaashoek via time-nuts time-nuts@lists.febo.com wrote:
The PTFE cables have been replaced with semi-rigid coax cables and the
stability, both mechanical and temperature, have improved.
Please keep in mind that the problem with PTFE is not the external
insulation of the coax cables, but the dielectric between the core
and the screen. A lot of semi-rigid still uses PTFE because it's
reasonably cheap and gives good performance. See [3-5] for more
information on this topic.
On Mon, 24 Oct 2022 10:10:27 +0200
Carsten Andrich via time-nuts time-nuts@lists.febo.com wrote:
only the ADC clock should matter and the used ADC should be of the
simultaneous sampling type. If it's not, its multiplexer may have a
detrimental temperature-dependent effect on the phase measurement.
It's a bit more complicated than that, unfortunately.
The mixer and their LO already add already some temperature dependence
due to inevitable asymmetries. The ADC themselves have a tempco too.
And it's not just direct temperature effect on the circuitry but also
indirect effect from power supplies. Even if using a dual-channel ADC
there are effects that affect the two channels differently. If you look
at Sherman and Jördens' paper [6], who looked at phase stability in SDR
systems for frequency / stability measurements, then you see that there
is a lower limit of a few 10's of fs in ADC sample timing. My guess is
that at least some of that is due to noise on the power grid in the
chip that causes IR drop [7]. Which is, by its nature, not symmetric.
It is also very likely that even small mechanical stresses due to minute
temperature variations at short time scales already cause timing differences
and phase shifts in the 10s of fs.
Figuring out where all these small temperature coefficients come from
is difficult, to say the least, and very tedious. Once you reach <10ps/K
I would, personally, call it a day and do the rest by proper enclosure
design and keeping everything at a stable temperature. This way it is
easier to reduce the tempco than to hunt for it in the electronics.
Attila Kinali
[1] "2π Low Drift Phase Detector for High-Precision Measurements"
by Jablonski, Czuba, Ludwik and Schlarb, 2015
https://doi.org/10.1109/TNS.2015.2425733
[2] "Environmental Effects in Mixers and Frequency Distribution Systems",
by Nelson and Walls, 1992
[3] "Current Innovations In Phase Stable Coaxial Cable Design",
by Times Microwave Systems
https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
[4] "Understanding Phase Versus Temperature Behavior",
by Micro-coax
http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
[5] "Temperature Stability of Coaxial Cables",
by Czuba and Sikora, 2011
http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
[6] "Oscillator metrology with software defined radio",
by Jeff A. Sherman and Robert Jördens, 2016
http://dx.doi.org/10.1063/1.4950898
[7] https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
Hi,
Somewhere in the NIST T&F archive, there is reference to how mixers
cause a reflection of energy and temperature coefficients then change
phase and working-point. They use 3 dB damper on the mixer to stabilize
that and reduce the tempco situation. The signal degradation is
compensated for but improvement in stability significant. As I recall
it, they refer to the cable phase stability with regard to temperature
to be part of the culprit.
Now, DBM isn't perfect in terms of balance and nor is the Gilbert cell
mixers that Erik is using, so milage may vary, but one should look at
multiple aspects. Alteration of operating points, alteration of
dielectric with temperature etc. is things to be aware of and then try
to figure out which is the major driver for your setup and measurement
needs and aims.
I am sure someone have attempted to temperature stabilize a mixer at
some time.
When building synths for music, we end up temperature compensating the
expo-converters or even ovenize them to achieve needed stability. That
is not far from what a mixer does. Also, it is what got me into this
time and frequency thing in the first place.
Cheers,
Magnus
On 2022-11-14 17:37, Attila Kinali via time-nuts wrote:
> Good afternoon,
>
> On Sun, 23 Oct 2022 18:05:40 +0200
> Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>
>> During the testing of a DMTD there appears to be a "large" sensitivity
>> to temperature variations.
>> Opening a door in the room with the DMTD causes changes in the phase
>> difference in the order of 1 ps
>> Blowing cold air over the encased DMTD causes phase variations up to 10 ps.
> I would like to add a few things that have not been mentioned already:
>
> Most electronics seem to have a tempco of 1-10ps/K. It is not clear
> where this tempco comes from, i.e. nobody fully explained it. It
> is remarkable, though, that the range is pretty narrow and quite
> stable over various technologies. Of course, analog filters have
> a larger variation of tempco.
>
> My guess (read: totally unscientific assumption, not backed by
> any data or experiments) is that a major source of tempco are
> mechanical stresses due to different linear expansion coefficients.
> How exactly mechanical stresses affect delay in electronics is
> not quite as simple as it would seem at a first glance. So it's
> difficult to come up with a decent model that can be tested in
> experiments.
>
> Summa summarum: The few-ps tempco you are seeing is what I would
> expect. See also [1] where they measured the tempco of a mixer
> setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
> a way how to measure and compensate the drift.
>
> I also recommend having a look at [2] for a more general treatment
> of the issue of temperature coefficients in time/frequency measurement
> systems.
>
> On Mon, 24 Oct 2022 14:43:43 +0200
> Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>
>> The PTFE cables have been replaced with semi-rigid coax cables and the
>> stability, both mechanical and temperature, have improved.
> Please keep in mind that the problem with PTFE is not the external
> insulation of the coax cables, but the dielectric between the core
> and the screen. A lot of semi-rigid still uses PTFE because it's
> reasonably cheap and gives good performance. See [3-5] for more
> information on this topic.
>
> On Mon, 24 Oct 2022 10:10:27 +0200
> Carsten Andrich via time-nuts <time-nuts@lists.febo.com> wrote:
>
>> only the ADC clock should matter and the used ADC should be of the
>> simultaneous sampling type. If it's not, its multiplexer may have a
>> detrimental temperature-dependent effect on the phase measurement.
> It's a bit more complicated than that, unfortunately.
> The mixer and their LO already add already some temperature dependence
> due to inevitable asymmetries. The ADC themselves have a tempco too.
> And it's not just direct temperature effect on the circuitry but also
> indirect effect from power supplies. Even if using a dual-channel ADC
> there are effects that affect the two channels differently. If you look
> at Sherman and Jördens' paper [6], who looked at phase stability in SDR
> systems for frequency / stability measurements, then you see that there
> is a lower limit of a few 10's of fs in ADC sample timing. My guess is
> that at least some of that is due to noise on the power grid in the
> chip that causes IR drop [7]. Which is, by its nature, not symmetric.
> It is also very likely that even small mechanical stresses due to minute
> temperature variations at short time scales already cause timing differences
> and phase shifts in the 10s of fs.
>
> Figuring out where all these small temperature coefficients come from
> is difficult, to say the least, and very tedious. Once you reach <10ps/K
> I would, personally, call it a day and do the rest by proper enclosure
> design and keeping everything at a stable temperature. This way it is
> easier to reduce the tempco than to hunt for it in the electronics.
>
> Attila Kinali
>
>
> [1] "2π Low Drift Phase Detector for High-Precision Measurements"
> by Jablonski, Czuba, Ludwik and Schlarb, 2015
> https://doi.org/10.1109/TNS.2015.2425733
>
> [2] "Environmental Effects in Mixers and Frequency Distribution Systems",
> by Nelson and Walls, 1992
>
> [3] "Current Innovations In Phase Stable Coaxial Cable Design",
> by Times Microwave Systems
> https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
>
> [4] "Understanding Phase Versus Temperature Behavior",
> by Micro-coax
> http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
>
> [5] "Temperature Stability of Coaxial Cables",
> by Czuba and Sikora, 2011
> http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
>
> [6] "Oscillator metrology with software defined radio",
> by Jeff A. Sherman and Robert Jördens, 2016
> http://dx.doi.org/10.1063/1.4950898
>
> [7] https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
>
EK
Erik Kaashoek
Wed, Nov 16, 2022 6:41 AM
Magnus,
One of the articles referenced by Attila mentioned inserting a second
known calibration input signal into both channels with a frequency
offset big enough so it becomes invisible in the regular DSP phase
measurement channel but by adding a second DSP phase measurement channel
at the offset of the inserted signal they had a real-time measurement of
the drift and where able to compensate for it.
Its rather compute intensive and I'm not sure what the offset has to be
to become invisible but could you imagine this could work in a rather
limited HW?
Maybe I should test it by inserting a calibration signal and see the
impact, but I can not imagine the short "FFT length" I'm using to be
long enough to give 100dB or more suppression of the calibration signal.
Erik.
On 15-11-2022 22:59, Magnus Danielson via time-nuts wrote:
Hi,
Somewhere in the NIST T&F archive, there is reference to how mixers
cause a reflection of energy and temperature coefficients then change
phase and working-point. They use 3 dB damper on the mixer to
stabilize that and reduce the tempco situation. The signal degradation
is compensated for but improvement in stability significant. As I
recall it, they refer to the cable phase stability with regard to
temperature to be part of the culprit.
Now, DBM isn't perfect in terms of balance and nor is the Gilbert cell
mixers that Erik is using, so milage may vary, but one should look at
multiple aspects. Alteration of operating points, alteration of
dielectric with temperature etc. is things to be aware of and then try
to figure out which is the major driver for your setup and measurement
needs and aims.
I am sure someone have attempted to temperature stabilize a mixer at
some time.
When building synths for music, we end up temperature compensating the
expo-converters or even ovenize them to achieve needed stability. That
is not far from what a mixer does. Also, it is what got me into this
time and frequency thing in the first place.
Cheers,
Magnus
On 2022-11-14 17:37, Attila Kinali via time-nuts wrote:
During the testing of a DMTD there appears to be a "large" sensitivity
to temperature variations.
Opening a door in the room with the DMTD causes changes in the phase
difference in the order of 1 ps
Blowing cold air over the encased DMTD causes phase variations up to
10 ps.
I would like to add a few things that have not been mentioned already:
Most electronics seem to have a tempco of 1-10ps/K. It is not clear
where this tempco comes from, i.e. nobody fully explained it. It
is remarkable, though, that the range is pretty narrow and quite
stable over various technologies. Of course, analog filters have
a larger variation of tempco.
My guess (read: totally unscientific assumption, not backed by
any data or experiments) is that a major source of tempco are
mechanical stresses due to different linear expansion coefficients.
How exactly mechanical stresses affect delay in electronics is
not quite as simple as it would seem at a first glance. So it's
difficult to come up with a decent model that can be tested in
experiments.
Summa summarum: The few-ps tempco you are seeing is what I would
expect. See also [1] where they measured the tempco of a mixer
setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
a way how to measure and compensate the drift.
I also recommend having a look at [2] for a more general treatment
of the issue of temperature coefficients in time/frequency measurement
systems.
On Mon, 24 Oct 2022 14:43:43 +0200
Erik Kaashoek via time-nuts time-nuts@lists.febo.com wrote:
The PTFE cables have been replaced with semi-rigid coax cables and the
stability, both mechanical and temperature, have improved.
Please keep in mind that the problem with PTFE is not the external
insulation of the coax cables, but the dielectric between the core
and the screen. A lot of semi-rigid still uses PTFE because it's
reasonably cheap and gives good performance. See [3-5] for more
information on this topic.
On Mon, 24 Oct 2022 10:10:27 +0200
Carsten Andrich via time-nuts time-nuts@lists.febo.com wrote:
only the ADC clock should matter and the used ADC should be of the
simultaneous sampling type. If it's not, its multiplexer may have a
detrimental temperature-dependent effect on the phase measurement.
It's a bit more complicated than that, unfortunately.
The mixer and their LO already add already some temperature dependence
due to inevitable asymmetries. The ADC themselves have a tempco too.
And it's not just direct temperature effect on the circuitry but also
indirect effect from power supplies. Even if using a dual-channel ADC
there are effects that affect the two channels differently. If you look
at Sherman and Jördens' paper [6], who looked at phase stability in SDR
systems for frequency / stability measurements, then you see that there
is a lower limit of a few 10's of fs in ADC sample timing. My guess is
that at least some of that is due to noise on the power grid in the
chip that causes IR drop [7]. Which is, by its nature, not symmetric.
It is also very likely that even small mechanical stresses due to minute
temperature variations at short time scales already cause timing
differences
and phase shifts in the 10s of fs.
Figuring out where all these small temperature coefficients come from
is difficult, to say the least, and very tedious. Once you reach <10ps/K
I would, personally, call it a day and do the rest by proper enclosure
design and keeping everything at a stable temperature. This way it is
easier to reduce the tempco than to hunt for it in the electronics.
Attila Kinali
[1] "2π Low Drift Phase Detector for High-Precision Measurements"
by Jablonski, Czuba, Ludwik and Schlarb, 2015
https://doi.org/10.1109/TNS.2015.2425733
[2] "Environmental Effects in Mixers and Frequency Distribution
Systems",
by Nelson and Walls, 1992
[3] "Current Innovations In Phase Stable Coaxial Cable Design",
by Times Microwave Systems
https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
[4] "Understanding Phase Versus Temperature Behavior",
by Micro-coax
http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
[5] "Temperature Stability of Coaxial Cables",
by Czuba and Sikora, 2011
http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
[6] "Oscillator metrology with software defined radio",
by Jeff A. Sherman and Robert Jördens, 2016
http://dx.doi.org/10.1063/1.4950898
[7]
https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
Magnus,
One of the articles referenced by Attila mentioned inserting a second
known calibration input signal into both channels with a frequency
offset big enough so it becomes invisible in the regular DSP phase
measurement channel but by adding a second DSP phase measurement channel
at the offset of the inserted signal they had a real-time measurement of
the drift and where able to compensate for it.
Its rather compute intensive and I'm not sure what the offset has to be
to become invisible but could you imagine this could work in a rather
limited HW?
Maybe I should test it by inserting a calibration signal and see the
impact, but I can not imagine the short "FFT length" I'm using to be
long enough to give 100dB or more suppression of the calibration signal.
Erik.
On 15-11-2022 22:59, Magnus Danielson via time-nuts wrote:
> Hi,
>
> Somewhere in the NIST T&F archive, there is reference to how mixers
> cause a reflection of energy and temperature coefficients then change
> phase and working-point. They use 3 dB damper on the mixer to
> stabilize that and reduce the tempco situation. The signal degradation
> is compensated for but improvement in stability significant. As I
> recall it, they refer to the cable phase stability with regard to
> temperature to be part of the culprit.
>
> Now, DBM isn't perfect in terms of balance and nor is the Gilbert cell
> mixers that Erik is using, so milage may vary, but one should look at
> multiple aspects. Alteration of operating points, alteration of
> dielectric with temperature etc. is things to be aware of and then try
> to figure out which is the major driver for your setup and measurement
> needs and aims.
>
> I am sure someone have attempted to temperature stabilize a mixer at
> some time.
>
> When building synths for music, we end up temperature compensating the
> expo-converters or even ovenize them to achieve needed stability. That
> is not far from what a mixer does. Also, it is what got me into this
> time and frequency thing in the first place.
>
> Cheers,
> Magnus
>
> On 2022-11-14 17:37, Attila Kinali via time-nuts wrote:
>> Good afternoon,
>>
>> On Sun, 23 Oct 2022 18:05:40 +0200
>> Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>>
>>> During the testing of a DMTD there appears to be a "large" sensitivity
>>> to temperature variations.
>>> Opening a door in the room with the DMTD causes changes in the phase
>>> difference in the order of 1 ps
>>> Blowing cold air over the encased DMTD causes phase variations up to
>>> 10 ps.
>> I would like to add a few things that have not been mentioned already:
>>
>> Most electronics seem to have a tempco of 1-10ps/K. It is not clear
>> where this tempco comes from, i.e. nobody fully explained it. It
>> is remarkable, though, that the range is pretty narrow and quite
>> stable over various technologies. Of course, analog filters have
>> a larger variation of tempco.
>>
>> My guess (read: totally unscientific assumption, not backed by
>> any data or experiments) is that a major source of tempco are
>> mechanical stresses due to different linear expansion coefficients.
>> How exactly mechanical stresses affect delay in electronics is
>> not quite as simple as it would seem at a first glance. So it's
>> difficult to come up with a decent model that can be tested in
>> experiments.
>>
>> Summa summarum: The few-ps tempco you are seeing is what I would
>> expect. See also [1] where they measured the tempco of a mixer
>> setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
>> a way how to measure and compensate the drift.
>>
>> I also recommend having a look at [2] for a more general treatment
>> of the issue of temperature coefficients in time/frequency measurement
>> systems.
>>
>> On Mon, 24 Oct 2022 14:43:43 +0200
>> Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>>
>>> The PTFE cables have been replaced with semi-rigid coax cables and the
>>> stability, both mechanical and temperature, have improved.
>> Please keep in mind that the problem with PTFE is not the external
>> insulation of the coax cables, but the dielectric between the core
>> and the screen. A lot of semi-rigid still uses PTFE because it's
>> reasonably cheap and gives good performance. See [3-5] for more
>> information on this topic.
>>
>> On Mon, 24 Oct 2022 10:10:27 +0200
>> Carsten Andrich via time-nuts <time-nuts@lists.febo.com> wrote:
>>
>>> only the ADC clock should matter and the used ADC should be of the
>>> simultaneous sampling type. If it's not, its multiplexer may have a
>>> detrimental temperature-dependent effect on the phase measurement.
>> It's a bit more complicated than that, unfortunately.
>> The mixer and their LO already add already some temperature dependence
>> due to inevitable asymmetries. The ADC themselves have a tempco too.
>> And it's not just direct temperature effect on the circuitry but also
>> indirect effect from power supplies. Even if using a dual-channel ADC
>> there are effects that affect the two channels differently. If you look
>> at Sherman and Jördens' paper [6], who looked at phase stability in SDR
>> systems for frequency / stability measurements, then you see that there
>> is a lower limit of a few 10's of fs in ADC sample timing. My guess is
>> that at least some of that is due to noise on the power grid in the
>> chip that causes IR drop [7]. Which is, by its nature, not symmetric.
>> It is also very likely that even small mechanical stresses due to minute
>> temperature variations at short time scales already cause timing
>> differences
>> and phase shifts in the 10s of fs.
>>
>> Figuring out where all these small temperature coefficients come from
>> is difficult, to say the least, and very tedious. Once you reach <10ps/K
>> I would, personally, call it a day and do the rest by proper enclosure
>> design and keeping everything at a stable temperature. This way it is
>> easier to reduce the tempco than to hunt for it in the electronics.
>>
>> Attila Kinali
>>
>>
>> [1] "2π Low Drift Phase Detector for High-Precision Measurements"
>> by Jablonski, Czuba, Ludwik and Schlarb, 2015
>> https://doi.org/10.1109/TNS.2015.2425733
>>
>> [2] "Environmental Effects in Mixers and Frequency Distribution
>> Systems",
>> by Nelson and Walls, 1992
>>
>> [3] "Current Innovations In Phase Stable Coaxial Cable Design",
>> by Times Microwave Systems
>> https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
>>
>> [4] "Understanding Phase Versus Temperature Behavior",
>> by Micro-coax
>> http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
>>
>>
>> [5] "Temperature Stability of Coaxial Cables",
>> by Czuba and Sikora, 2011
>> http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
>>
>> [6] "Oscillator metrology with software defined radio",
>> by Jeff A. Sherman and Robert Jördens, 2016
>> http://dx.doi.org/10.1063/1.4950898
>>
>> [7]
>> https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
AK
Attila Kinali
Wed, Nov 16, 2022 10:13 AM
Its rather compute intensive and I'm not sure what the offset has to be
to become invisible but could you imagine this could work in a rather
limited HW?
Before you go into your digital down mixer or CIC, you will have some form
of anti-aliasing filter. This filter's bandwidth is your first indication
how far you should be away. Later filters in the signal chain then filter
out the remaining components.
If you want to minimize the influence of the probe signal, you can,
and IMHO should, add a notch filter into the signal path. That should
give you some 80-100dB of additional damping and remove the probe signal
for all intents and purposes.
It is still a good idea to check for some kind of modulation in the
(processed) output at the difference frequency and its multiples.
BTW: I recommend having a look at [1], which is a very hands on book
on signal processing. It gives examples of what kind of structures to
use for different signal processing tasks and discusses their advantages
and disadvantages.
Attila Kinali
[1] "Understanding Digital Signal Processing",
by Richard Lyons, 3rd edition, 2011
--
In science if you know what you are doing you should not be doing it.
In engineering if you do not know what you are doing you should not be doing it.
-- Richard W. Hamming, The Art of Doing Science and Engineering
On Wed, 16 Nov 2022 07:41:30 +0100
Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
> Its rather compute intensive and I'm not sure what the offset has to be
> to become invisible but could you imagine this could work in a rather
> limited HW?
Before you go into your digital down mixer or CIC, you will have some form
of anti-aliasing filter. This filter's bandwidth is your first indication
how far you should be away. Later filters in the signal chain then filter
out the remaining components.
If you want to minimize the influence of the probe signal, you can,
and IMHO should, add a notch filter into the signal path. That should
give you some 80-100dB of additional damping and remove the probe signal
for all intents and purposes.
It is still a good idea to check for some kind of modulation in the
(processed) output at the difference frequency and its multiples.
BTW: I recommend having a look at [1], which is a very hands on book
on signal processing. It gives examples of what kind of structures to
use for different signal processing tasks and discusses their advantages
and disadvantages.
Attila Kinali
[1] "Understanding Digital Signal Processing",
by Richard Lyons, 3rd edition, 2011
--
In science if you know what you are doing you should not be doing it.
In engineering if you do not know what you are doing you should not be doing it.
-- Richard W. Hamming, The Art of Doing Science and Engineering
MD
Magnus Danielson
Wed, Nov 16, 2022 12:05 PM
Erik,
The side-channel to track the side-carrier can be made much simpler. You
do not need to FFT it, but you can do a direct PLL lock setup in
software and with that relate the clocks to each other. It consumes a
few cycles per sample, but really not much.
Cheers,
Magnus
On 2022-11-16 07:41, Erik Kaashoek via time-nuts wrote:
Magnus,
One of the articles referenced by Attila mentioned inserting a second
known calibration input signal into both channels with a frequency
offset big enough so it becomes invisible in the regular DSP phase
measurement channel but by adding a second DSP phase measurement
channel at the offset of the inserted signal they had a real-time
measurement of the drift and where able to compensate for it.
Its rather compute intensive and I'm not sure what the offset has to
be to become invisible but could you imagine this could work in a
rather limited HW?
Maybe I should test it by inserting a calibration signal and see the
impact, but I can not imagine the short "FFT length" I'm using to be
long enough to give 100dB or more suppression of the calibration signal.
Erik.
On 15-11-2022 22:59, Magnus Danielson via time-nuts wrote:
Hi,
Somewhere in the NIST T&F archive, there is reference to how mixers
cause a reflection of energy and temperature coefficients then change
phase and working-point. They use 3 dB damper on the mixer to
stabilize that and reduce the tempco situation. The signal
degradation is compensated for but improvement in stability
significant. As I recall it, they refer to the cable phase stability
with regard to temperature to be part of the culprit.
Now, DBM isn't perfect in terms of balance and nor is the Gilbert
cell mixers that Erik is using, so milage may vary, but one should
look at multiple aspects. Alteration of operating points, alteration
of dielectric with temperature etc. is things to be aware of and then
try to figure out which is the major driver for your setup and
measurement needs and aims.
I am sure someone have attempted to temperature stabilize a mixer at
some time.
When building synths for music, we end up temperature compensating
the expo-converters or even ovenize them to achieve needed stability.
That is not far from what a mixer does. Also, it is what got me into
this time and frequency thing in the first place.
Cheers,
Magnus
On 2022-11-14 17:37, Attila Kinali via time-nuts wrote:
Good afternoon,
On Sun, 23 Oct 2022 18:05:40 +0200
Erik Kaashoek via time-nuts time-nuts@lists.febo.com wrote:
During the testing of a DMTD there appears to be a "large" sensitivity
to temperature variations.
Opening a door in the room with the DMTD causes changes in the phase
difference in the order of 1 ps
Blowing cold air over the encased DMTD causes phase variations up
to 10 ps.
I would like to add a few things that have not been mentioned already:
Most electronics seem to have a tempco of 1-10ps/K. It is not clear
where this tempco comes from, i.e. nobody fully explained it. It
is remarkable, though, that the range is pretty narrow and quite
stable over various technologies. Of course, analog filters have
a larger variation of tempco.
My guess (read: totally unscientific assumption, not backed by
any data or experiments) is that a major source of tempco are
mechanical stresses due to different linear expansion coefficients.
How exactly mechanical stresses affect delay in electronics is
not quite as simple as it would seem at a first glance. So it's
difficult to come up with a decent model that can be tested in
experiments.
Summa summarum: The few-ps tempco you are seeing is what I would
expect. See also [1] where they measured the tempco of a mixer
setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
a way how to measure and compensate the drift.
I also recommend having a look at [2] for a more general treatment
of the issue of temperature coefficients in time/frequency measurement
systems.
On Mon, 24 Oct 2022 14:43:43 +0200
Erik Kaashoek via time-nuts time-nuts@lists.febo.com wrote:
The PTFE cables have been replaced with semi-rigid coax cables and the
stability, both mechanical and temperature, have improved.
Please keep in mind that the problem with PTFE is not the external
insulation of the coax cables, but the dielectric between the core
and the screen. A lot of semi-rigid still uses PTFE because it's
reasonably cheap and gives good performance. See [3-5] for more
information on this topic.
On Mon, 24 Oct 2022 10:10:27 +0200
Carsten Andrich via time-nuts time-nuts@lists.febo.com wrote:
only the ADC clock should matter and the used ADC should be of the
simultaneous sampling type. If it's not, its multiplexer may have a
detrimental temperature-dependent effect on the phase measurement.
It's a bit more complicated than that, unfortunately.
The mixer and their LO already add already some temperature dependence
due to inevitable asymmetries. The ADC themselves have a tempco too.
And it's not just direct temperature effect on the circuitry but also
indirect effect from power supplies. Even if using a dual-channel ADC
there are effects that affect the two channels differently. If you look
at Sherman and Jördens' paper [6], who looked at phase stability in SDR
systems for frequency / stability measurements, then you see that there
is a lower limit of a few 10's of fs in ADC sample timing. My guess is
that at least some of that is due to noise on the power grid in the
chip that causes IR drop [7]. Which is, by its nature, not symmetric.
It is also very likely that even small mechanical stresses due to
minute
temperature variations at short time scales already cause timing
differences
and phase shifts in the 10s of fs.
Figuring out where all these small temperature coefficients come from
is difficult, to say the least, and very tedious. Once you reach
<10ps/K
I would, personally, call it a day and do the rest by proper enclosure
design and keeping everything at a stable temperature. This way it is
easier to reduce the tempco than to hunt for it in the electronics.
Attila Kinali
[1] "2π Low Drift Phase Detector for High-Precision Measurements"
by Jablonski, Czuba, Ludwik and Schlarb, 2015
https://doi.org/10.1109/TNS.2015.2425733
[2] "Environmental Effects in Mixers and Frequency Distribution
Systems",
by Nelson and Walls, 1992
[3] "Current Innovations In Phase Stable Coaxial Cable Design",
by Times Microwave Systems
https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
[4] "Understanding Phase Versus Temperature Behavior",
by Micro-coax
http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
[5] "Temperature Stability of Coaxial Cables",
by Czuba and Sikora, 2011
http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
[6] "Oscillator metrology with software defined radio",
by Jeff A. Sherman and Robert Jördens, 2016
http://dx.doi.org/10.1063/1.4950898
[7]
https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
time-nuts mailing list -- time-nuts@lists.febo.com
To unsubscribe send an email to time-nuts-leave@lists.febo.com
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To unsubscribe send an email to time-nuts-leave@lists.febo.com
Erik,
The side-channel to track the side-carrier can be made much simpler. You
do not need to FFT it, but you can do a direct PLL lock setup in
software and with that relate the clocks to each other. It consumes a
few cycles per sample, but really not much.
Cheers,
Magnus
On 2022-11-16 07:41, Erik Kaashoek via time-nuts wrote:
> Magnus,
> One of the articles referenced by Attila mentioned inserting a second
> known calibration input signal into both channels with a frequency
> offset big enough so it becomes invisible in the regular DSP phase
> measurement channel but by adding a second DSP phase measurement
> channel at the offset of the inserted signal they had a real-time
> measurement of the drift and where able to compensate for it.
> Its rather compute intensive and I'm not sure what the offset has to
> be to become invisible but could you imagine this could work in a
> rather limited HW?
> Maybe I should test it by inserting a calibration signal and see the
> impact, but I can not imagine the short "FFT length" I'm using to be
> long enough to give 100dB or more suppression of the calibration signal.
>
> Erik.
>
>
> On 15-11-2022 22:59, Magnus Danielson via time-nuts wrote:
>> Hi,
>>
>> Somewhere in the NIST T&F archive, there is reference to how mixers
>> cause a reflection of energy and temperature coefficients then change
>> phase and working-point. They use 3 dB damper on the mixer to
>> stabilize that and reduce the tempco situation. The signal
>> degradation is compensated for but improvement in stability
>> significant. As I recall it, they refer to the cable phase stability
>> with regard to temperature to be part of the culprit.
>>
>> Now, DBM isn't perfect in terms of balance and nor is the Gilbert
>> cell mixers that Erik is using, so milage may vary, but one should
>> look at multiple aspects. Alteration of operating points, alteration
>> of dielectric with temperature etc. is things to be aware of and then
>> try to figure out which is the major driver for your setup and
>> measurement needs and aims.
>>
>> I am sure someone have attempted to temperature stabilize a mixer at
>> some time.
>>
>> When building synths for music, we end up temperature compensating
>> the expo-converters or even ovenize them to achieve needed stability.
>> That is not far from what a mixer does. Also, it is what got me into
>> this time and frequency thing in the first place.
>>
>> Cheers,
>> Magnus
>>
>> On 2022-11-14 17:37, Attila Kinali via time-nuts wrote:
>>> Good afternoon,
>>>
>>> On Sun, 23 Oct 2022 18:05:40 +0200
>>> Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>>>
>>>> During the testing of a DMTD there appears to be a "large" sensitivity
>>>> to temperature variations.
>>>> Opening a door in the room with the DMTD causes changes in the phase
>>>> difference in the order of 1 ps
>>>> Blowing cold air over the encased DMTD causes phase variations up
>>>> to 10 ps.
>>> I would like to add a few things that have not been mentioned already:
>>>
>>> Most electronics seem to have a tempco of 1-10ps/K. It is not clear
>>> where this tempco comes from, i.e. nobody fully explained it. It
>>> is remarkable, though, that the range is pretty narrow and quite
>>> stable over various technologies. Of course, analog filters have
>>> a larger variation of tempco.
>>>
>>> My guess (read: totally unscientific assumption, not backed by
>>> any data or experiments) is that a major source of tempco are
>>> mechanical stresses due to different linear expansion coefficients.
>>> How exactly mechanical stresses affect delay in electronics is
>>> not quite as simple as it would seem at a first glance. So it's
>>> difficult to come up with a decent model that can be tested in
>>> experiments.
>>>
>>> Summa summarum: The few-ps tempco you are seeing is what I would
>>> expect. See also [1] where they measured the tempco of a mixer
>>> setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
>>> a way how to measure and compensate the drift.
>>>
>>> I also recommend having a look at [2] for a more general treatment
>>> of the issue of temperature coefficients in time/frequency measurement
>>> systems.
>>>
>>> On Mon, 24 Oct 2022 14:43:43 +0200
>>> Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>>>
>>>> The PTFE cables have been replaced with semi-rigid coax cables and the
>>>> stability, both mechanical and temperature, have improved.
>>> Please keep in mind that the problem with PTFE is not the external
>>> insulation of the coax cables, but the dielectric between the core
>>> and the screen. A lot of semi-rigid still uses PTFE because it's
>>> reasonably cheap and gives good performance. See [3-5] for more
>>> information on this topic.
>>>
>>> On Mon, 24 Oct 2022 10:10:27 +0200
>>> Carsten Andrich via time-nuts <time-nuts@lists.febo.com> wrote:
>>>
>>>> only the ADC clock should matter and the used ADC should be of the
>>>> simultaneous sampling type. If it's not, its multiplexer may have a
>>>> detrimental temperature-dependent effect on the phase measurement.
>>> It's a bit more complicated than that, unfortunately.
>>> The mixer and their LO already add already some temperature dependence
>>> due to inevitable asymmetries. The ADC themselves have a tempco too.
>>> And it's not just direct temperature effect on the circuitry but also
>>> indirect effect from power supplies. Even if using a dual-channel ADC
>>> there are effects that affect the two channels differently. If you look
>>> at Sherman and Jördens' paper [6], who looked at phase stability in SDR
>>> systems for frequency / stability measurements, then you see that there
>>> is a lower limit of a few 10's of fs in ADC sample timing. My guess is
>>> that at least some of that is due to noise on the power grid in the
>>> chip that causes IR drop [7]. Which is, by its nature, not symmetric.
>>> It is also very likely that even small mechanical stresses due to
>>> minute
>>> temperature variations at short time scales already cause timing
>>> differences
>>> and phase shifts in the 10s of fs.
>>>
>>> Figuring out where all these small temperature coefficients come from
>>> is difficult, to say the least, and very tedious. Once you reach
>>> <10ps/K
>>> I would, personally, call it a day and do the rest by proper enclosure
>>> design and keeping everything at a stable temperature. This way it is
>>> easier to reduce the tempco than to hunt for it in the electronics.
>>>
>>> Attila Kinali
>>>
>>>
>>> [1] "2π Low Drift Phase Detector for High-Precision Measurements"
>>> by Jablonski, Czuba, Ludwik and Schlarb, 2015
>>> https://doi.org/10.1109/TNS.2015.2425733
>>>
>>> [2] "Environmental Effects in Mixers and Frequency Distribution
>>> Systems",
>>> by Nelson and Walls, 1992
>>>
>>> [3] "Current Innovations In Phase Stable Coaxial Cable Design",
>>> by Times Microwave Systems
>>> https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
>>>
>>> [4] "Understanding Phase Versus Temperature Behavior",
>>> by Micro-coax
>>> http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
>>>
>>>
>>> [5] "Temperature Stability of Coaxial Cables",
>>> by Czuba and Sikora, 2011
>>> http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
>>>
>>> [6] "Oscillator metrology with software defined radio",
>>> by Jeff A. Sherman and Robert Jördens, 2016
>>> http://dx.doi.org/10.1063/1.4950898
>>>
>>> [7]
>>> https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
>>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@lists.febo.com
>> To unsubscribe send an email to time-nuts-leave@lists.febo.com
> _______________________________________________
> time-nuts mailing list -- time-nuts@lists.febo.com
> To unsubscribe send an email to time-nuts-leave@lists.febo.com
EK
Erik Kaashoek
Wed, Nov 16, 2022 3:58 PM
Magnus,
As often with your advice, I'm not smart enough to understand.
The digital down mixing to zero Hz is done with I/Q mixers where sin/cos
of the internal LO is multiplied with the input signals and then average
over some samples to get I and Q of the signal vector as the output
frequency is zero Hz.
I would expect I would need a separate set of I/Q mixers for the side
channel and by summing over many samples the noise would be reduced
sufficiently to get a relevant I and Q signal even if the side channel
has 40dB lower amplitude. I may have used the word FFT to describe the
operation of the I/Q mixers as computationally they look a lot like a
single bucket FFT
Erik.
On 16-11-2022 13:05, Magnus Danielson via time-nuts wrote:
Erik,
The side-channel to track the side-carrier can be made much simpler.
You do not need to FFT it, but you can do a direct PLL lock setup in
software and with that relate the clocks to each other. It consumes a
few cycles per sample, but really not much.
Cheers,
Magnus
On 2022-11-16 07:41, Erik Kaashoek via time-nuts wrote:
Magnus,
One of the articles referenced by Attila mentioned inserting a second
known calibration input signal into both channels with a frequency
offset big enough so it becomes invisible in the regular DSP phase
measurement channel but by adding a second DSP phase measurement
channel at the offset of the inserted signal they had a real-time
measurement of the drift and where able to compensate for it.
Its rather compute intensive and I'm not sure what the offset has to
be to become invisible but could you imagine this could work in a
rather limited HW?
Maybe I should test it by inserting a calibration signal and see the
impact, but I can not imagine the short "FFT length" I'm using to be
long enough to give 100dB or more suppression of the calibration signal.
Erik.
On 15-11-2022 22:59, Magnus Danielson via time-nuts wrote:
Hi,
Somewhere in the NIST T&F archive, there is reference to how mixers
cause a reflection of energy and temperature coefficients then
change phase and working-point. They use 3 dB damper on the mixer to
stabilize that and reduce the tempco situation. The signal
degradation is compensated for but improvement in stability
significant. As I recall it, they refer to the cable phase stability
with regard to temperature to be part of the culprit.
Now, DBM isn't perfect in terms of balance and nor is the Gilbert
cell mixers that Erik is using, so milage may vary, but one should
look at multiple aspects. Alteration of operating points, alteration
of dielectric with temperature etc. is things to be aware of and
then try to figure out which is the major driver for your setup and
measurement needs and aims.
I am sure someone have attempted to temperature stabilize a mixer at
some time.
When building synths for music, we end up temperature compensating
the expo-converters or even ovenize them to achieve needed
stability. That is not far from what a mixer does. Also, it is what
got me into this time and frequency thing in the first place.
Cheers,
Magnus
On 2022-11-14 17:37, Attila Kinali via time-nuts wrote:
During the testing of a DMTD there appears to be a "large"
sensitivity
to temperature variations.
Opening a door in the room with the DMTD causes changes in the phase
difference in the order of 1 ps
Blowing cold air over the encased DMTD causes phase variations up
to 10 ps.
I would like to add a few things that have not been mentioned already:
Most electronics seem to have a tempco of 1-10ps/K. It is not clear
where this tempco comes from, i.e. nobody fully explained it. It
is remarkable, though, that the range is pretty narrow and quite
stable over various technologies. Of course, analog filters have
a larger variation of tempco.
My guess (read: totally unscientific assumption, not backed by
any data or experiments) is that a major source of tempco are
mechanical stresses due to different linear expansion coefficients.
How exactly mechanical stresses affect delay in electronics is
not quite as simple as it would seem at a first glance. So it's
difficult to come up with a decent model that can be tested in
experiments.
Summa summarum: The few-ps tempco you are seeing is what I would
expect. See also [1] where they measured the tempco of a mixer
setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
a way how to measure and compensate the drift.
I also recommend having a look at [2] for a more general treatment
of the issue of temperature coefficients in time/frequency measurement
systems.
On Mon, 24 Oct 2022 14:43:43 +0200
Erik Kaashoek via time-nuts time-nuts@lists.febo.com wrote:
The PTFE cables have been replaced with semi-rigid coax cables and
the
stability, both mechanical and temperature, have improved.
Please keep in mind that the problem with PTFE is not the external
insulation of the coax cables, but the dielectric between the core
and the screen. A lot of semi-rigid still uses PTFE because it's
reasonably cheap and gives good performance. See [3-5] for more
information on this topic.
On Mon, 24 Oct 2022 10:10:27 +0200
Carsten Andrich via time-nuts time-nuts@lists.febo.com wrote:
only the ADC clock should matter and the used ADC should be of the
simultaneous sampling type. If it's not, its multiplexer may have a
detrimental temperature-dependent effect on the phase measurement.
It's a bit more complicated than that, unfortunately.
The mixer and their LO already add already some temperature dependence
due to inevitable asymmetries. The ADC themselves have a tempco too.
And it's not just direct temperature effect on the circuitry but also
indirect effect from power supplies. Even if using a dual-channel ADC
there are effects that affect the two channels differently. If you
look
at Sherman and Jördens' paper [6], who looked at phase stability in
SDR
systems for frequency / stability measurements, then you see that
there
is a lower limit of a few 10's of fs in ADC sample timing. My guess is
that at least some of that is due to noise on the power grid in the
chip that causes IR drop [7]. Which is, by its nature, not symmetric.
It is also very likely that even small mechanical stresses due to
minute
temperature variations at short time scales already cause timing
differences
and phase shifts in the 10s of fs.
Figuring out where all these small temperature coefficients come from
is difficult, to say the least, and very tedious. Once you reach
<10ps/K
I would, personally, call it a day and do the rest by proper enclosure
design and keeping everything at a stable temperature. This way it is
easier to reduce the tempco than to hunt for it in the electronics.
Attila Kinali
[1] "2π Low Drift Phase Detector for High-Precision Measurements"
by Jablonski, Czuba, Ludwik and Schlarb, 2015
https://doi.org/10.1109/TNS.2015.2425733
[2] "Environmental Effects in Mixers and Frequency Distribution
Systems",
by Nelson and Walls, 1992
[3] "Current Innovations In Phase Stable Coaxial Cable Design",
by Times Microwave Systems
https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
[4] "Understanding Phase Versus Temperature Behavior",
by Micro-coax
http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
[5] "Temperature Stability of Coaxial Cables",
by Czuba and Sikora, 2011
http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
[6] "Oscillator metrology with software defined radio",
by Jeff A. Sherman and Robert Jördens, 2016
http://dx.doi.org/10.1063/1.4950898
[7]
https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
Magnus,
As often with your advice, I'm not smart enough to understand.
The digital down mixing to zero Hz is done with I/Q mixers where sin/cos
of the internal LO is multiplied with the input signals and then average
over some samples to get I and Q of the signal vector as the output
frequency is zero Hz.
I would expect I would need a separate set of I/Q mixers for the side
channel and by summing over many samples the noise would be reduced
sufficiently to get a relevant I and Q signal even if the side channel
has 40dB lower amplitude. I may have used the word FFT to describe the
operation of the I/Q mixers as computationally they look a lot like a
single bucket FFT
Erik.
On 16-11-2022 13:05, Magnus Danielson via time-nuts wrote:
> Erik,
>
> The side-channel to track the side-carrier can be made much simpler.
> You do not need to FFT it, but you can do a direct PLL lock setup in
> software and with that relate the clocks to each other. It consumes a
> few cycles per sample, but really not much.
>
> Cheers,
> Magnus
>
> On 2022-11-16 07:41, Erik Kaashoek via time-nuts wrote:
>> Magnus,
>> One of the articles referenced by Attila mentioned inserting a second
>> known calibration input signal into both channels with a frequency
>> offset big enough so it becomes invisible in the regular DSP phase
>> measurement channel but by adding a second DSP phase measurement
>> channel at the offset of the inserted signal they had a real-time
>> measurement of the drift and where able to compensate for it.
>> Its rather compute intensive and I'm not sure what the offset has to
>> be to become invisible but could you imagine this could work in a
>> rather limited HW?
>> Maybe I should test it by inserting a calibration signal and see the
>> impact, but I can not imagine the short "FFT length" I'm using to be
>> long enough to give 100dB or more suppression of the calibration signal.
>>
>> Erik.
>>
>>
>> On 15-11-2022 22:59, Magnus Danielson via time-nuts wrote:
>>> Hi,
>>>
>>> Somewhere in the NIST T&F archive, there is reference to how mixers
>>> cause a reflection of energy and temperature coefficients then
>>> change phase and working-point. They use 3 dB damper on the mixer to
>>> stabilize that and reduce the tempco situation. The signal
>>> degradation is compensated for but improvement in stability
>>> significant. As I recall it, they refer to the cable phase stability
>>> with regard to temperature to be part of the culprit.
>>>
>>> Now, DBM isn't perfect in terms of balance and nor is the Gilbert
>>> cell mixers that Erik is using, so milage may vary, but one should
>>> look at multiple aspects. Alteration of operating points, alteration
>>> of dielectric with temperature etc. is things to be aware of and
>>> then try to figure out which is the major driver for your setup and
>>> measurement needs and aims.
>>>
>>> I am sure someone have attempted to temperature stabilize a mixer at
>>> some time.
>>>
>>> When building synths for music, we end up temperature compensating
>>> the expo-converters or even ovenize them to achieve needed
>>> stability. That is not far from what a mixer does. Also, it is what
>>> got me into this time and frequency thing in the first place.
>>>
>>> Cheers,
>>> Magnus
>>>
>>> On 2022-11-14 17:37, Attila Kinali via time-nuts wrote:
>>>> Good afternoon,
>>>>
>>>> On Sun, 23 Oct 2022 18:05:40 +0200
>>>> Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>>>>
>>>>> During the testing of a DMTD there appears to be a "large"
>>>>> sensitivity
>>>>> to temperature variations.
>>>>> Opening a door in the room with the DMTD causes changes in the phase
>>>>> difference in the order of 1 ps
>>>>> Blowing cold air over the encased DMTD causes phase variations up
>>>>> to 10 ps.
>>>> I would like to add a few things that have not been mentioned already:
>>>>
>>>> Most electronics seem to have a tempco of 1-10ps/K. It is not clear
>>>> where this tempco comes from, i.e. nobody fully explained it. It
>>>> is remarkable, though, that the range is pretty narrow and quite
>>>> stable over various technologies. Of course, analog filters have
>>>> a larger variation of tempco.
>>>>
>>>> My guess (read: totally unscientific assumption, not backed by
>>>> any data or experiments) is that a major source of tempco are
>>>> mechanical stresses due to different linear expansion coefficients.
>>>> How exactly mechanical stresses affect delay in electronics is
>>>> not quite as simple as it would seem at a first glance. So it's
>>>> difficult to come up with a decent model that can be tested in
>>>> experiments.
>>>>
>>>> Summa summarum: The few-ps tempco you are seeing is what I would
>>>> expect. See also [1] where they measured the tempco of a mixer
>>>> setup (the numbers boiled down to 1-2ps/K IIRC) and proposed
>>>> a way how to measure and compensate the drift.
>>>>
>>>> I also recommend having a look at [2] for a more general treatment
>>>> of the issue of temperature coefficients in time/frequency measurement
>>>> systems.
>>>>
>>>> On Mon, 24 Oct 2022 14:43:43 +0200
>>>> Erik Kaashoek via time-nuts <time-nuts@lists.febo.com> wrote:
>>>>
>>>>> The PTFE cables have been replaced with semi-rigid coax cables and
>>>>> the
>>>>> stability, both mechanical and temperature, have improved.
>>>> Please keep in mind that the problem with PTFE is not the external
>>>> insulation of the coax cables, but the dielectric between the core
>>>> and the screen. A lot of semi-rigid still uses PTFE because it's
>>>> reasonably cheap and gives good performance. See [3-5] for more
>>>> information on this topic.
>>>>
>>>> On Mon, 24 Oct 2022 10:10:27 +0200
>>>> Carsten Andrich via time-nuts <time-nuts@lists.febo.com> wrote:
>>>>
>>>>> only the ADC clock should matter and the used ADC should be of the
>>>>> simultaneous sampling type. If it's not, its multiplexer may have a
>>>>> detrimental temperature-dependent effect on the phase measurement.
>>>> It's a bit more complicated than that, unfortunately.
>>>> The mixer and their LO already add already some temperature dependence
>>>> due to inevitable asymmetries. The ADC themselves have a tempco too.
>>>> And it's not just direct temperature effect on the circuitry but also
>>>> indirect effect from power supplies. Even if using a dual-channel ADC
>>>> there are effects that affect the two channels differently. If you
>>>> look
>>>> at Sherman and Jördens' paper [6], who looked at phase stability in
>>>> SDR
>>>> systems for frequency / stability measurements, then you see that
>>>> there
>>>> is a lower limit of a few 10's of fs in ADC sample timing. My guess is
>>>> that at least some of that is due to noise on the power grid in the
>>>> chip that causes IR drop [7]. Which is, by its nature, not symmetric.
>>>> It is also very likely that even small mechanical stresses due to
>>>> minute
>>>> temperature variations at short time scales already cause timing
>>>> differences
>>>> and phase shifts in the 10s of fs.
>>>>
>>>> Figuring out where all these small temperature coefficients come from
>>>> is difficult, to say the least, and very tedious. Once you reach
>>>> <10ps/K
>>>> I would, personally, call it a day and do the rest by proper enclosure
>>>> design and keeping everything at a stable temperature. This way it is
>>>> easier to reduce the tempco than to hunt for it in the electronics.
>>>>
>>>> Attila Kinali
>>>>
>>>>
>>>> [1] "2π Low Drift Phase Detector for High-Precision Measurements"
>>>> by Jablonski, Czuba, Ludwik and Schlarb, 2015
>>>> https://doi.org/10.1109/TNS.2015.2425733
>>>>
>>>> [2] "Environmental Effects in Mixers and Frequency Distribution
>>>> Systems",
>>>> by Nelson and Walls, 1992
>>>>
>>>> [3] "Current Innovations In Phase Stable Coaxial Cable Design",
>>>> by Times Microwave Systems
>>>> https://www.timesmicrowave.com/downloads/tech/phasearticle.pdf
>>>>
>>>> [4] "Understanding Phase Versus Temperature Behavior",
>>>> by Micro-coax
>>>> http://www.micro-coax.com/wp-content/themes/micro_coax/includes/pdf/applications_notes/13-MIC-0012.Phase_vs_Temp_Behavior_FINAL.pdf
>>>>
>>>>
>>>> [5] "Temperature Stability of Coaxial Cables",
>>>> by Czuba and Sikora, 2011
>>>> http://przyrbwn.icm.edu.pl/APP/PDF/119/a119z4p17.pdf
>>>>
>>>> [6] "Oscillator metrology with software defined radio",
>>>> by Jeff A. Sherman and Robert Jördens, 2016
>>>> http://dx.doi.org/10.1063/1.4950898
>>>>
>>>> [7]
>>>> https://semiengineering.com/knowledge_centers/low-power/architectural-power-issues/ir-drop/
>>>>
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