On 09/18/2010 04:28 PM, Richard (Rick) Karlquist wrote:
A couple of disclaimers here:
1. Leeson's oscillator model was mentioned. That
doesn't apply much to crystal oscillators. The close
in noise will be limited by the intrinsic noise of
the crystal and the far out noise will be limited by
the buffer amplifier. Leeson's model never comes
into play. BTW, the intrinsic noise of the crystal
is higher than the thermal noise corresponding to
its ESR, at least below 1 kHz or so.
Actually, I did mention the output buffer noise explicitly.
The crystal noise adds ontop of the amplifiers noise, yes... but the
crystal noise will also be feedback to the crystal through the
amplifier, right?
2. Using crystal filters to clean up after the fact
is limited by the intrinsic noise of the crystals in
the filters. Hence, this usually only makes sense
if you multiply a xtal oscillator then filter, as
in the HP8662, and then it only improves the noise
floor.
Essentially only useful as "relatively narrow" filters.
Unless you have access to very low noise crystals,
you are not going to get very far building your
own oscillator.
Agreed. There is a danger in expecting any spare AT-cut crystal laying
around being able to provide the ultra high performance if only
stabilized and "perfect design" of amplifiers. But for the purpose at
hand it may suffice.
Cheers,
Magnus
_______________________________________________
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
