[time-nuts] Dumb question about SC-cut crystals

Rick Karlquist richard at karlquist.com
Mon Oct 22 17:32:51 EDT 2007

A lot of work has been done in this area under the
designator "Microprocessor Controlled Crystal Oscillator"
MCXO, which is probably not a really great name.
Anyway, they are non ovenized and use SC cuts.  I believe
the original FCS paper on them was around 1990.

Regarding turnover specifically:  many 10811 crystals
do not have turnovers.  Instead they have a broad range
of very low (but not zero) tempco.  There is nothing
magic about being at a turnover other than zero tempco.

Rick Karlquist N6RK

Murray Greenman wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+richard
> Hi,
> When comparing with AT-cut, we all know that the SC-cut crystal gives
> better warmup without overshoot, better 2nd order temperature performance,
> fewer dips, lower acceleration sensitivity and better short-term
> stability. However, nothing's been said in any of the literature I've seen
> whether this depends on running the crystal at/near a turnover point, or
> whether these advantages APPLY AT ALL TEMPERATURES.
> I am particularly interested in post-correction by electronic means in low
> power applications, rather than temperature compensation (TCXO), as an
> uncompensated oscillator tends to have lower phase noise and is cheaper to
> make. In some applications (such as the one of interest here), absolute
> oscillator frequency is unimportant, but knowing all about its
> environmental behaviour is important. The biggest problem with using a
> polynomial temperature fit approach is that with an AT-cut crystal, it is
> very difficult to mathematically correct for the second order temperature
> effects.
> Would using an SC-cut crystal in this type of application provide a
> measure of freedom from second order temperature and acceleration effects
> over a wide (-40°C to +85°C) temperature range, or does it only apply at
> or near turnover?
> Regards,
> Murray Greenman
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

More information about the time-nuts mailing list