On Sun, 20 Mar 2016 18:26:16 -0000
"Martyn Smith" <[email protected]> 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
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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