[time-nuts] 74AC gates phase noise

Rick Karlquist richard at karlquist.com
Thu Feb 25 21:33:57 UTC 2010


Martyn Smith wrote:
> Garry,
>
> Are you also saying your 100 MHz OXCO is making -178 dBc/Hz?
>
> Unless your 100 MHz OXCO is some special $10k type, there's no way your
> OXCO
> has a -178 dBc/Hz floor noise?
>
> Regards
>
> Martyn

Can you explain this further?

It isn't clear to me that there is any fundamental reason
why this noise floor is not possible, especially if other
specs (like aging) can be relaxed.  Also, the noise floor
tends to be limited by issues having to do with physics,
not economics.  How would having $10,000 to spend get
around the physics issues?

I think I could approach this noise floor by taking a 10811
and bringing the signal directly out of the grounded base
buffer, and then readjusting the ALC to double or triple
the crystal current.  The biggest unknown is at what point
the crystal sustains damage.  The 10811 is definitely not
optimized for phase noise floor.  The designers were well
aware of this.  But phase noise floor isn't everything.

Rick Karlquist N6RK




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