every injection locked oscillator has jitter, since the oscillator
slowly --depend on the "tank circuit"s Q will return to it's original
frequency, what will be interrupted by the next injection, therefore the
oscillator will have a larger phase jump during the interaction with the
pulse.
"how fare the oscillator could get" is depend on the "tank circuit"-'s
Q, therefor the jitter in worst case could be a whole period of the
oscillator, which is 1/100kHz = 10usec
in case the locking pulse does not let the oscillator go to fare away
the jitter will be less, but the jitter will be always a dependence of
the Q of the oscillator's "tank circuit in this case the crystal, also
the length of the synchronizing pulse -- the energy of the pulse is
dependon it's length -- will influence the phase of the synchronized
oscillator.
there was a very good paper written on injection locking: R. Adler, “A
study of locking phenomena in oscillators,”Proc. IEEE, vol. 61, no. 10,
pp. 1380–1385, Oct. 1973
73
KL6UHN
Alex
On 3/21/2016 6:00 AM, Attila Kinali wrote:
On Sun, 20 Mar 2016 18:26:16 -0000
"Martyn Smith" <mar...@ptsyst.com> wrote:
I have a real time clock calendar chip that requires a 32.768 kHz crystal.
I want to feed it with 10 MHz signal instead, so it is synchronised to my
main 10 MHz in a frequency standard I am designing.
Currently, all that has been discussed were digital solutions.
But what about using an analog approach?
If you have a 32kHz crystal oscillator, you can injection lock it
to the 10MHz signal, by dividing the 10MHz down to 128Hz, then use this
to form short (as in a couple of ns) pulses, which you then couple
to the crystal using a small (a couple of pF) capacitor.
Given that the crytsal has an accuracy of better than 100ppm, then
even a very weak coupling at 128Hz should be enough to keep it locked.
Upper bound on the jitter is 1/128Hz*100ppm=781ps (very simplified
calculation, but it should be definitly less than 1-2ns)
Attila Kinali
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