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

[Murray Greenman]

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