cheap 5V OCXO in 14DIP has about 1E-9 drift per day
My question about these regenerative filters is that while I know F1 +
F2 = Fin I'm still wondering how stable it is and how you know your
divider will not do something like
10.0001 + 15.9999 = 26.000 for a few hours and then drift over to
9.9999 + 16.0001 = 26.000. In other words I can see how the filter
keeps the sum locked to the 26.000 reference but I don't see how it
keeps the 10Mhz component stable.
On Sun, Apr 17, 2011 at 3:16 AM, Magnus Danielson
magnus@rubidium.dyndns.org wrote:
On 04/16/2011 10:50 PM, Bruce Griffiths wrote:
Bruce Griffiths wrote:
Oz-in-DFW wrote:
On 4/9/2011 11:29 AM, Greg Broburg wrote:
I expect that I am missing something obvious here
a little nudge may help.
Regards;
Greg
What you are missing is that the concept only applies to small integer
(2 or 3) division ratios and won't work as speculated here. It's sort
of (long stretch here) like injection locking in reverse. If you want
I'll try and post some links to papers later.
Nonsense, its already been done for much larger ratios and they need
not be integers.
Try simulating it.
Bruce
One counter example to the simplistic statement about the operating mode
of a regenerative divider being restricted to division by small integers
only, is that such analysis appears to preclude the possibility of using
a regenerative divider to produce a frequency comb. Unfortunately a
regenerative divider has already been used to produce a low noise
frequency comb where the comb frequency spacing is f/n(where f is the
input frequency and n is an integer). Its possible to extract a
frequency that is a rational fraction (m/n where m and n are integers)
of the input frequency from such a regenerative frequency comb. Thus
there is at least one method of using a regenerative divider to produce
a 10MHz signal from a 26MHz signal.
As I recall it, in the generalized regenerate divider where two frequencies
is filtered these match up
http://tf.nist.gov/general/pdf/1800.pdf
The two frequencies f1 and f2 has the sum of the input. This has the
side-consequence that
f1 = fin - f2
f2 = fin - f1
which is also the conversion steps that the phase will experience over two
turns around the loop. For synchronous operation the aggregate phase becomes
0 degrees (modulus 360 degrees).
Considering that fin = 26 MHz and f1 = 10 MHz we can conclude that f2 needs
to be 16 MHz.
As for avoiding asynchronous operations the above NIST articles gives some
addtional hints on page 3, among which keeping the loop short is among the
important onces, essentially that the electrical delay length doesn't
support many modes. Keeping all traces on a normal PCB for 10 MHz and 26 MHz
should avoid that issue completely.
This would form a 5f/13 - 8f/13 system since 2 MHz is the common frequency
for all of these. Keeping phase solutions unique for 2 MHz separation should
not be too hard.
Cheers,
Magnus
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--
Chris Albertson
Redondo Beach, California
As long as the divisor isnt too large such behaviour doesnt happen.
When the divisor is too large and the filters detune too far then stable
operation may not be possible.
Until recently the reason for the demonstrated stability of regenerative
dividers has been poorly understood.
Non linear analysis is required as a linear analysis can lead to
conclusions that conflict with the observed characteristics of a
regenerative divider.
To understand the stability requirements one has to examine the
transient response and the phase portrait of the signals involved:
http://www.its.caltech.edu/~kaushiks/KS_RFIC.pdf
http://www.its.caltech.edu/%7Ekaushiks/KS_RFIC.pdf
http://www.its.caltech.edu/~kaushiks/KS_TCAS.pdf
http://www.its.caltech.edu/%7Ekaushiks/KS_TCAS.pdf
In practice the behaviour of regenerative dividers is sufficiently
stable and well established that they are being considered for use in
various atomic frequency standards by NIST and others.
Bruce
Chris Albertson wrote:
My question about these regenerative filters is that while I know F1 +
F2 = Fin I'm still wondering how stable it is and how you know your
divider will not do something like
10.0001 + 15.9999 = 26.000 for a few hours and then drift over to
9.9999 + 16.0001 = 26.000. In other words I can see how the filter
keeps the sum locked to the 26.000 reference but I don't see how it
keeps the 10Mhz component stable.
On Sun, Apr 17, 2011 at 3:16 AM, Magnus Danielson
magnus@rubidium.dyndns.org wrote:
On 04/16/2011 10:50 PM, Bruce Griffiths wrote:
Bruce Griffiths wrote:
Oz-in-DFW wrote:
On 4/9/2011 11:29 AM, Greg Broburg wrote:
I expect that I am missing something obvious here
a little nudge may help.
Regards;
Greg
What you are missing is that the concept only applies to small integer
(2 or 3) division ratios and won't work as speculated here. It's sort
of (long stretch here) like injection locking in reverse. If you want
I'll try and post some links to papers later.
Nonsense, its already been done for much larger ratios and they need
not be integers.
Try simulating it.
Bruce
One counter example to the simplistic statement about the operating mode
of a regenerative divider being restricted to division by small integers
only, is that such analysis appears to preclude the possibility of using
a regenerative divider to produce a frequency comb. Unfortunately a
regenerative divider has already been used to produce a low noise
frequency comb where the comb frequency spacing is f/n(where f is the
input frequency and n is an integer). Its possible to extract a
frequency that is a rational fraction (m/n where m and n are integers)
of the input frequency from such a regenerative frequency comb. Thus
there is at least one method of using a regenerative divider to produce
a 10MHz signal from a 26MHz signal.
As I recall it, in the generalized regenerate divider where two frequencies
is filtered these match up
http://tf.nist.gov/general/pdf/1800.pdf
The two frequencies f1 and f2 has the sum of the input. This has the
side-consequence that
f1 = fin - f2
f2 = fin - f1
which is also the conversion steps that the phase will experience over two
turns around the loop. For synchronous operation the aggregate phase becomes
0 degrees (modulus 360 degrees).
Considering that fin = 26 MHz and f1 = 10 MHz we can conclude that f2 needs
to be 16 MHz.
As for avoiding asynchronous operations the above NIST articles gives some
addtional hints on page 3, among which keeping the loop short is among the
important onces, essentially that the electrical delay length doesn't
support many modes. Keeping all traces on a normal PCB for 10 MHz and 26 MHz
should avoid that issue completely.
This would form a 5f/13 - 8f/13 system since 2 MHz is the common frequency
for all of these. Keeping phase solutions unique for 2 MHz separation should
not be too hard.
Cheers,
Magnus
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On 04/17/2011 09:13 PM, Bruce Griffiths wrote:
As long as the divisor isnt too large such behaviour doesnt happen.
When the divisor is too large and the filters detune too far then stable
operation may not be possible.
Until recently the reason for the demonstrated stability of regenerative
dividers has been poorly understood.
Non linear analysis is required as a linear analysis can lead to
conclusions that conflict with the observed characteristics of a
regenerative divider.
To understand the stability requirements one has to examine the
transient response and the phase portrait of the signals involved:
http://www.its.caltech.edu/~kaushiks/KS_RFIC.pdf
http://www.its.caltech.edu/%7Ekaushiks/KS_RFIC.pdf
http://www.its.caltech.edu/~kaushiks/KS_TCAS.pdf
http://www.its.caltech.edu/%7Ekaushiks/KS_TCAS.pdf
In practice the behaviour of regenerative dividers is sufficiently
stable and well established that they are being considered for use in
various atomic frequency standards by NIST and others.
Thanks for the good links. The TCAS paper contains the goodies.
Cheers,
Magnus
I asked the question because I might want to build one of there but I
could not see how they coud be stable with just an RC filter. So the
answer is "they just are".
OK, so they are stable but why would it run at 10+16=26 and not 10.01+15.99=29
And what happens if I want to build a 10.01 reference clock? Could I
do that with a regenerative filter?
On Sun, Apr 17, 2011 at 12:13 PM, Bruce Griffiths
bruce.griffiths@xtra.co.nz wrote:
As long as the divisor isnt too large such behaviour doesnt happen.
When the divisor is too large and the filters detune too far then stable
operation may not be possible.
--
Chris Albertson
Redondo Beach, California
I prophet:
Chris Albertson schrieb:
I asked the question because I might want to build one of there but I
could not see how they could be table with just an RC filter. So the
answer is "they just are".
Mixing generates two frequencies and a DC phase shift response.
If RC filtered you get the lower of both frequencies.
OK, so they are stable but why would it run at 10+16=26 and not 10.01+15.99=29
And what happens if I want to build a 10.01 reference clock? Could I
do that with a regenerative filter?
Is have a natural tendency to lock to the lowest n/m ratio.
- Henry
--
ehydra.dyndns.info
On 04/18/2011 01:06 AM, Chris Albertson wrote:
I asked the question because I might want to build one of there but I
could not see how they coud be stable with just an RC filter. So the
answer is "they just are".
OK, so they are stable but why would it run at 10+16=26 and not 10.01+15.99=29
As I look around, the non-linearity provides a sample/injection lock
effect which creates the asynchronous mode. I haven't read the papers
through, not the time, but that's the concept I gather from the quick
browsing thru.
And what happens if I want to build a 10.01 reference clock? Could I
do that with a regenerative filter?
The capture range would be narrow while the 10.00 mode would capture it
as it would have a wider capture range.
As far as I have gathered the knowledge.
Cheers,
Magnus