Magnus Danielson 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
Attenuating the sum frequencies fin + f2 (36MHz) and fin + f1(42MHz)
sufficiently (~10dB or so) is also required.
The 10MHz and 16MHz bandpass filters in the feedback loop should easily
accomplish this.
Its also possible to use a cross coupled pair of mixers where
the first mixer has 26MHz and 10MHz inputs producing a bandpass filtered
output at 16MHz
the second mixer has 26MHz and 16MHz inputs producing a bandpass
filtered output at 10MHz.
The 10MHz output from the first mixer drives one of the 2nd mixers
inputs whilst the 16MHz output from the second mixer dries one of the
first mixers inputs.
This can simplify the filtering.
Another variant uses a pair of cross coupled lower sideband mixers.
Bruce
Bruce
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