Advantages & Disadvantages of the TPLL Method
subject: Advantages & Disadvantages of the TPLL Method.
Here is a new and unique Idea that may be useful for many.
Rather than focusing on what some members may or may not already know,
or how good or bad one specific working BB configuration is.
How about focusing on what the TPLL method can and can not do well.
If someone will make a place to post and compile a couple of list,
I can start it off with what I've learned so far:
DISADVANTAGES of the TPLL method:
#1) The TPLL method is limited by it's reference OSC.
The ref osc (or the DUT) needs to have an Analog &/or Digital EFC control input with a bandwidth that is wider than the desired Tau0
#2) It basically measures Freq and not Phase differences, and few understand how and why it works so well or it's many advantages.
#3) TBD
ADVANTAGES of the TPLL method:
1 thru 30) same as I've posted several times before.
I'm sure others will find many more if they try it or at least understand it better.
WarrenS wrote:
subject: Advantages& Disadvantages of the TPLL Method.
Here is a new and unique Idea that may be useful for many.
Rather than focusing on what some members may or may not already know,
or how good or bad one specific working BB configuration is.
How about focusing on what the TPLL method can and can not do well.
If someone will make a place to post and compile a couple of list,
I can start it off with what I've learned so far:
DISADVANTAGES of the TPLL method:
#1) The TPLL method is limited by it's reference OSC.
This isn't necessarily correct, one could use a pair of tight PLL loops
and use correlation techniques to reduce the contribution of the
reference oscillator noise.
The ref osc (or the DUT) needs to have an Analog&/or Digital EFC control input with a bandwidth that is wider than the desired Tau0
#2) It basically measures Freq and not Phase differences, and few understand how and why it works so well or it's many advantages.
This is not true, there is no inherent SNR advantage in measuring
frequency changes as opposed to measuring phase differences.
When the phase measurement system and the frequency measurement systems
being compared have the same noise bandwidth then the measurement floors
are comparable.
For example, the TSC5120A is a narrow band system based on measuring
phase differences with a comparable or lower noise floor than your
implementation of the tight PLL.
The common technique of using a time interval counter to measure the
phase difference between 2 RF signals once ever second or so is a
wideband technique with severe undersampling, consequently the system
noise floor is much higher than for narrow bandwidth techniques. If the
phase difference between the 2 signals were measured more frequently and
digitally low pass filtered the noise will be much lower.
Since one has to calculate average frequency from the frequency samples
by integration/averaging this is mathematically equivalent to
reconstructing the phase change between the start and end of the
averaging time (Tau0).
One effect of undersampling is to convert (in the sampled data) a
proportion of any flicker phase noise (and other non white phase noise
components) to white phase noise.
The effect of this is to change the ADEV vs Tau plots from their true shape.
With a single pole RC filter the required minimum sampling rate to
ensure that such effects are acceptably small cannot be known unless the
phase noise spectra of the 2 oscillators being compared is known.
However the extra phase noise filtering due to the finite PLL bandwidth
(including any EFC filtering built in to the reference oscillator)
allows an estimate of the maximum sampling rate likely to be required to
ensure that such phase noise whitening effects are acceptably small.
#3) TBD
ADVANTAGES of the TPLL method:
1 thru 30) same as I've posted several times before.
I'm sure others will find many more if they try it or at least understand it better.
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Bruce
On 06/12/2010 11:29 PM, Bruce Griffiths wrote:
WarrenS wrote:
subject: Advantages& Disadvantages of the TPLL Method.
Here is a new and unique Idea that may be useful for many.
Rather than focusing on what some members may or may not already know,
or how good or bad one specific working BB configuration is.
How about focusing on what the TPLL method can and can not do well.
If someone will make a place to post and compile a couple of list,
I can start it off with what I've learned so far:
DISADVANTAGES of the TPLL method:
#1) The TPLL method is limited by it's reference OSC.
This isn't necessarily correct, one could use a pair of tight PLL loops
and use correlation techniques to reduce the contribution of the
reference oscillator noise.
True. The same technique is being used for LPLL phase noise
measurements. The reference oscillator will still be a limit, but wither
you can go below the reference oscillator noise or not is what makes the
difference. Such a setup costs about twice of a single-channel TPLL.
Usually there is two ADC channels available.
The cross-correlation processing isn't too hard to achieve and is
efficiently performed using FFTs and a little support-processing. FFTW
is a good tool to toss the FFT processing to. The remaining wrapping is
in a few ten lines of codes or so. Going down the FFT path will give the
frequency plot for free, getting it back into the time-domain cost extra.
The ref osc (or the DUT) needs to have an Analog&/or Digital EFC
control input with a bandwidth that is wider than the desired Tau0
#2) It basically measures Freq and not Phase differences, and few
understand how and why it works so well or it's many advantages.
This is not true, there is no inherent SNR advantage in measuring
frequency changes as opposed to measuring phase differences.
When the phase measurement system and the frequency measurement systems
being compared have the same noise bandwidth then the measurement floors
are comparable.
For example, the TSC5120A is a narrow band system based on measuring
phase differences with a comparable or lower noise floor than your
implementation of the tight PLL.
The common technique of using a time interval counter to measure the
phase difference between 2 RF signals once ever second or so is a
wideband technique with severe undersampling, consequently the system
noise floor is much higher than for narrow bandwidth techniques. If the
phase difference between the 2 signals were measured more frequently and
digitally low pass filtered the noise will be much lower.
Using time-stamping counters at high rate would be possible if being
able to cope with the rate of samples. You want a frontend to do that if
you want to run continously.
As for digital filtering. When doing measurements in the 0,1 - 1000 s
range for the G.813 measurements, a 10 Hz low-pass filter is being required.
Since one has to calculate average frequency from the frequency samples
by integration/averaging this is mathematically equivalent to
reconstructing the phase change between the start and end of the
averaging time (Tau0).
Depends on the details. Some counters (SR620 for instance) can have
biases for frequency data which their time-difference measures do not
have. A TPLL does not suffer from that particular problem, as it cranks
out its frequency estimation by a different method.
One effect of undersampling is to convert (in the sampled data) a
proportion of any flicker phase noise (and other non white phase noise
components) to white phase noise.
The effect of this is to change the ADEV vs Tau plots from their true
shape.
Care to hand a reference or two for this statement?
Regardless, care must be taken to ensure high enough bandwidth compared
to the tau for the measurements not to be affected.
Cheers,
Magnus
Magnus Danielson wrote:
On 06/12/2010 11:29 PM, Bruce Griffiths wrote:
WarrenS wrote:
subject: Advantages& Disadvantages of the TPLL Method.
Here is a new and unique Idea that may be useful for many.
Rather than focusing on what some members may or may not already know,
or how good or bad one specific working BB configuration is.
How about focusing on what the TPLL method can and can not do well.
If someone will make a place to post and compile a couple of list,
I can start it off with what I've learned so far:
DISADVANTAGES of the TPLL method:
#1) The TPLL method is limited by it's reference OSC.
This isn't necessarily correct, one could use a pair of tight PLL loops
and use correlation techniques to reduce the contribution of the
reference oscillator noise.
True. The same technique is being used for LPLL phase noise
measurements. The reference oscillator will still be a limit, but
wither you can go below the reference oscillator noise or not is what
makes the difference. Such a setup costs about twice of a
single-channel TPLL. Usually there is two ADC channels available.
Yes the cost of the reference oscillator dominates the system cost, the
additional $10 (omitting the cost of the phase detector) to implement
the tight PLL is relatively insignificant.
The cross-correlation processing isn't too hard to achieve and is
efficiently performed using FFTs and a little support-processing. FFTW
is a good tool to toss the FFT processing to. The remaining wrapping
is in a few ten lines of codes or so. Going down the FFT path will
give the frequency plot for free, getting it back into the time-domain
cost extra.
If one is calculating the FFT then it is possible to calculate ADEV
directly from the FFT (of the frequency samples) with little additional
effort, for the relevant formulae see:
http://hal.archives-ouvertes.fr/docs/00/37/63/05/PDF/alaa_p1_v4a.pdf
Note such processing doesn't increase the cost of the system as one
needs a PC to calculate frequency stability measures, unless one
wants/needs to do it in real time.
One disadvantage of a tight PLL system is that finite EFC range and EFC
non linearity may preclude its application to noisier sources.
Linearising the EFC transfer function will help but the reference
oscillator EFC range will ultimately provide an upper limit to the
measurable noise.
The ref osc (or the DUT) needs to have an Analog&/or Digital EFC
control input with a bandwidth that is wider than the desired Tau0
#2) It basically measures Freq and not Phase differences, and few
understand how and why it works so well or it's many advantages.
This is not true, there is no inherent SNR advantage in measuring
frequency changes as opposed to measuring phase differences.
When the phase measurement system and the frequency measurement systems
being compared have the same noise bandwidth then the measurement floors
are comparable.
For example, the TSC5120A is a narrow band system based on measuring
phase differences with a comparable or lower noise floor than your
implementation of the tight PLL.
The common technique of using a time interval counter to measure the
phase difference between 2 RF signals once ever second or so is a
wideband technique with severe undersampling, consequently the system
noise floor is much higher than for narrow bandwidth techniques. If the
phase difference between the 2 signals were measured more frequently and
digitally low pass filtered the noise will be much lower.
Using time-stamping counters at high rate would be possible if being
able to cope with the rate of samples. You want a frontend to do that
if you want to run continously.
As for digital filtering. When doing measurements in the 0,1 - 1000 s
range for the G.813 measurements, a 10 Hz low-pass filter is being
required.
Since one has to calculate average frequency from the frequency samples
by integration/averaging this is mathematically equivalent to
reconstructing the phase change between the start and end of the
averaging time (Tau0).
Depends on the details. Some counters (SR620 for instance) can have
biases for frequency data which their time-difference measures do not
have. A TPLL does not suffer from that particular problem, as it
cranks out its frequency estimation by a different method.
Yes, but I thought that we were calculating the required averages from
the frequency (EFC) samples by approximating the required integrals.
One effect of undersampling is to convert (in the sampled data) a
proportion of any flicker phase noise (and other non white phase noise
components) to white phase noise.
The effect of this is to change the ADEV vs Tau plots from their true
shape.
Care to hand a reference or two for this statement?
References for the whitening effect of undersampling:
http://www.obs-besancon.fr/tf/publis/metrologia98a.pdf
http://www.obs-besancon.fr/tf/publis/metrologia98b.pdf
The change in shape of the ADEV vs Tau plot is a consequence of the
whitening of the phase noise.
Regardless, care must be taken to ensure high enough bandwidth
compared to the tau for the measurements not to be affected.
Cheers,
Magnus
Bruce
Here are a couple of really good articles that describe many
methods of phase/frequency measurement, including TPLL.
You'll see some nice "advantage/disadvantage" lists in several
of these documents, which is why I'm posting the links.
Warren & Bruce, please look at the first five documents at least.
John too. Lots of TPLL info. This is all worth reading. I don't
know why I didn't find some of these papers six months ago.
System Phase Noise Calculation and Measurement Techniques
http://www.mpdigest.com/issue/Articles/2009/sept/spectrum/Default.asp
-- short article, nice summary.
PN9000 Automated Phase Noise Measurement System Application Note #1
http://www.aeroflex.com/ats/products/prodfiles/appnotes/12/app1.pdf
-- see section 2; TPLL is section 2.2.
Oscillator Phase Noise Measurements using the Phase Lock Method
http://ravoltek.net/dippa/dippa_rajala_olli.pdf
-- TPLL, equations, graphs, error analysis, photos, schematics, parts list.
An investigation into the phase noise of quartz crystal oscillators
http://etd.sun.ac.za/bitstream/10019/337/1/BentleyB.pdf
-- see chapter 4 or at least section 4.3; TPLL is 4.3.3.2.
PN9000 Automated Phase Noise Measurement System Application Note #2
http://smartdata.usbid.com/datasheets/usbid/2000/2000-q4/app2.pdf
http://www.datasheetarchive.com/pdf/Datasheet-010/DSA00173368.pdf
-- theory of operation, TPLL
A General Theory of Phase Noise in Electrical Oscillators
http://www.chic.caltech.edu/Publications/general_full.PDF
-- too deep for me.
Phase Noise Measurement. Using the Phase Lock Technique
http://www.chem.duke.edu/~boris/datasheets/AN1639_phase_noise.pdf
http://www.lansdale.com/Articles/an1639.pdf
-- might be applicable.
Correlation-based phase noise measurements
http://www.femto-st.fr/~rubiola/pdf-others/correl-report.pdf
-- for John Miles
Practical Problems Involving Phase Noise Measurements
http://tycho.usno.navy.mil/ptti/ptti2001/paper42.pdf
-- also for John.
/tvb
All of these are in my collection of papers that I have read.
Bruce
Tom Van Baak wrote:
Here are a couple of really good articles that describe many
methods of phase/frequency measurement, including TPLL.
You'll see some nice "advantage/disadvantage" lists in several
of these documents, which is why I'm posting the links.
Warren & Bruce, please look at the first five documents at least.
John too. Lots of TPLL info. This is all worth reading. I don't
know why I didn't find some of these papers six months ago.
System Phase Noise Calculation and Measurement Techniques
http://www.mpdigest.com/issue/Articles/2009/sept/spectrum/Default.asp
-- short article, nice summary.
PN9000 Automated Phase Noise Measurement System Application Note #1
http://www.aeroflex.com/ats/products/prodfiles/appnotes/12/app1.pdf
-- see section 2; TPLL is section 2.2.
Oscillator Phase Noise Measurements using the Phase Lock Method
http://ravoltek.net/dippa/dippa_rajala_olli.pdf
-- TPLL, equations, graphs, error analysis, photos, schematics, parts
list.
An investigation into the phase noise of quartz crystal oscillators
http://etd.sun.ac.za/bitstream/10019/337/1/BentleyB.pdf
-- see chapter 4 or at least section 4.3; TPLL is 4.3.3.2.
PN9000 Automated Phase Noise Measurement System Application Note #2
http://smartdata.usbid.com/datasheets/usbid/2000/2000-q4/app2.pdf
http://www.datasheetarchive.com/pdf/Datasheet-010/DSA00173368.pdf
-- theory of operation, TPLL
A General Theory of Phase Noise in Electrical Oscillators
http://www.chic.caltech.edu/Publications/general_full.PDF
-- too deep for me.
A fairly easy paper to read and one of a series by Ali Hajimiri, but one
should also read papers gexpressing contrary views on cyclostationary
noise etc.
Phase Noise Measurement. Using the Phase Lock Technique
http://www.chem.duke.edu/~boris/datasheets/AN1639_phase_noise.pdf
http://www.lansdale.com/Articles/an1639.pdf
-- might be applicable.
Correlation-based phase noise measurements
http://www.femto-st.fr/~rubiola/pdf-others/correl-report.pdf -- for
John Miles
Practical Problems Involving Phase Noise Measurements
http://tycho.usno.navy.mil/ptti/ptti2001/paper42.pdf
-- also for John.
/tvb
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
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and follow the instructions there.
Bruce
Correlation-based phase noise measurements
http://www.femto-st.fr/~rubiola/pdf-others/correl-report.pdf
-- for John Miles
Practical Problems Involving Phase Noise Measurements
http://tycho.usno.navy.mil/ptti/ptti2001/paper42.pdf
-- also for John.
I've got these in my collection, but it never hurts to go back over them.
Both these papers, of course, end their exploration of averaged correlation
by saying "and here a dynamic signal analyzer is typically used." :-P
It turns out that the common OCXO I was using has a higher PN floor than I
thought (about -154 dBc/Hz) so I'll probably switch to independent OCXOs
before delving into this too much further.
-- john, KE5FX
John,
On 06/13/2010 10:00 AM, John Miles wrote:
Correlation-based phase noise measurements
http://www.femto-st.fr/~rubiola/pdf-others/correl-report.pdf
-- for John Miles
Practical Problems Involving Phase Noise Measurements
http://tycho.usno.navy.mil/ptti/ptti2001/paper42.pdf
-- also for John.
I've got these in my collection, but it never hurts to go back over them.
Both these papers, of course, end their exploration of averaged correlation
by saying "and here a dynamic signal analyzer is typically used." :-P
Which is how they say "problem solved by somebody else".
It turns out that the common OCXO I was using has a higher PN floor than I
thought (about -154 dBc/Hz) so I'll probably switch to independent OCXOs
before delving into this too much further.
You where kind of measuring the noise floor of your setup.
Cheers,
Magnus
Tom,
I took the liberty of converting your post into an entry in my Time-Nuts
Wiki:
http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:phase_frequency_m
easurement_methods
Please note anyone can edit this Wiki or create new pages.
Didier
-----Original Message-----
From: time-nuts-bounces@febo.com
[mailto:time-nuts-bounces@febo.com] On Behalf Of Tom Van Baak
Sent: Sunday, June 13, 2010 1:35 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Advantages & Disadvantages of the TPLL Method
Here are a couple of really good articles that describe many
methods of phase/frequency measurement, including TPLL.
You'll see some nice "advantage/disadvantage" lists in
several of these documents, which is why I'm posting the links.
Warren & Bruce, please look at the first five documents at least.
John too. Lots of TPLL info. This is all worth reading. I
don't know why I didn't find some of these papers six months ago.
System Phase Noise Calculation and Measurement Techniques
http://www.mpdigest.com/issue/Articles/2009/sept/spectrum/Default.asp
-- short article, nice summary.
PN9000 Automated Phase Noise Measurement System Application
Note #1
http://www.aeroflex.com/ats/products/prodfiles/appnotes/12/app1.pdf
-- see section 2; TPLL is section 2.2.
Oscillator Phase Noise Measurements using the Phase Lock
Method http://ravoltek.net/dippa/dippa_rajala_olli.pdf
-- TPLL, equations, graphs, error analysis, photos,
schematics, parts list.
An investigation into the phase noise of quartz crystal
oscillators http://etd.sun.ac.za/bitstream/10019/337/1/BentleyB.pdf
-- see chapter 4 or at least section 4.3; TPLL is 4.3.3.2.
PN9000 Automated Phase Noise Measurement System Application
Note #2
http://smartdata.usbid.com/datasheets/usbid/2000/2000-q4/app2.pdf
http://www.datasheetarchive.com/pdf/Datasheet-010/DSA00173368.pdf
-- theory of operation, TPLL
A General Theory of Phase Noise in Electrical Oscillators
http://www.chic.caltech.edu/Publications/general_full.PDF
-- too deep for me.
Phase Noise Measurement. Using the Phase Lock Technique
http://www.chem.duke.edu/~boris/datasheets/AN1639_phase_noise.pdf
http://www.lansdale.com/Articles/an1639.pdf
-- might be applicable.
Correlation-based phase noise measurements
http://www.femto-st.fr/~rubiola/pdf-others/correl-report.pdf
-- for John Miles
Practical Problems Involving Phase Noise Measurements
http://tycho.usno.navy.mil/ptti/ptti2001/paper42.pdf
-- also for John.
/tvb
time-nuts mailing list -- time-nuts@febo.com To unsubscribe,
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and follow the instructions there.
Didier
On 13 June 2010 21:51, Didier Juges didier@cox.net wrote:
Tom,
I took the liberty of converting your post into an entry in my Time-Nuts
Wiki:
http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:phase_frequency_m
easurement_methods
Just to let you know that your link got busted by a line-wrap
somewhere so it is not clickable and has to be cut and pasted into
place.
But it could be just the World hating me again :)
Cheers,
Steve
Please note anyone can edit this Wiki or create new pages.
Didier
-----Original Message-----
From: time-nuts-bounces@febo.com
[mailto:time-nuts-bounces@febo.com] On Behalf Of Tom Van Baak
Sent: Sunday, June 13, 2010 1:35 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Advantages & Disadvantages of the TPLL Method
Here are a couple of really good articles that describe many
methods of phase/frequency measurement, including TPLL.
You'll see some nice "advantage/disadvantage" lists in
several of these documents, which is why I'm posting the links.
Warren & Bruce, please look at the first five documents at least.
John too. Lots of TPLL info. This is all worth reading. I
don't know why I didn't find some of these papers six months ago.
System Phase Noise Calculation and Measurement Techniques
http://www.mpdigest.com/issue/Articles/2009/sept/spectrum/Default.asp
-- short article, nice summary.
PN9000 Automated Phase Noise Measurement System Application
Note #1
http://www.aeroflex.com/ats/products/prodfiles/appnotes/12/app1.pdf
-- see section 2; TPLL is section 2.2.
Oscillator Phase Noise Measurements using the Phase Lock
Method http://ravoltek.net/dippa/dippa_rajala_olli.pdf
-- TPLL, equations, graphs, error analysis, photos,
schematics, parts list.
An investigation into the phase noise of quartz crystal
oscillators http://etd.sun.ac.za/bitstream/10019/337/1/BentleyB.pdf
-- see chapter 4 or at least section 4.3; TPLL is 4.3.3.2.
PN9000 Automated Phase Noise Measurement System Application
Note #2
http://smartdata.usbid.com/datasheets/usbid/2000/2000-q4/app2.pdf
http://www.datasheetarchive.com/pdf/Datasheet-010/DSA00173368.pdf
-- theory of operation, TPLL
A General Theory of Phase Noise in Electrical Oscillators
http://www.chic.caltech.edu/Publications/general_full.PDF
-- too deep for me.
Phase Noise Measurement. Using the Phase Lock Technique
http://www.chem.duke.edu/~boris/datasheets/AN1639_phase_noise.pdf
http://www.lansdale.com/Articles/an1639.pdf
-- might be applicable.
Correlation-based phase noise measurements
http://www.femto-st.fr/~rubiola/pdf-others/correl-report.pdf
-- for John Miles
Practical Problems Involving Phase Noise Measurements
http://tycho.usno.navy.mil/ptti/ptti2001/paper42.pdf
-- also for John.
/tvb
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Steve Rooke - ZL3TUV & G8KVD
The only reason for time is so that everything doesn't happen at once.
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