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
<mag...@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:
<deletia>
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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