[time-nuts] How to get 32.768KHz from 10MHz.

Rick Karlquist richard at karlquist.com
Wed Jul 23 19:07:04 EDT 2008

A more practical offshoot of this concept is to subsample the
32 kHz oscillator at 128 Hz (ie a sampling phase detector) and use a slow
loop to tune the 32768 kHz oscillator.  The biggest problem here is that
you have to have a tunable oscillator.  Attempting to get around
this by injection locking a non-tunable oscillator is probably not
going to work very well, since the frequency tolerance is likely
to be larger than the small amount of frequency pulling you can
get with injection locking.  Basically, if the oscillator tolerance
is 0.01%, and it has a Q of >>10,000, it will be hit or miss depending
on luck.

Rick N6RK

Bruce Griffiths wrote:
> Another approach is to divide the 10MHz by 5^7 (78125) and then use an
> injection locked multiplier chain to generate 32768 Hz from the
> resultant 128Hz output.
> It may even be possible to do the 256x multiplication using a single
> injection locked 32768Hz injection locked multiplier.
> When designed correctly the close in phase noise of an injection locked
> oscillator is determined by that of the injection source whereas the
> phase noise floor is determined by that of the oscillator being locked.
> To optimise the performance the oscillator to be injection locked should
> be designed to facilitate injection locking.
> Bruce
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