subject: Improve aging time up to 2 to 3 times with SC-cut crystal [print this page] Improve aging time up to 2 to 3 times with SC-cut crystal
Advantages of the SC-cut crystals:
Improved aging For a given frequency and overtone (e.g. 10 MHz, 3rd overtone), the SC-cut crystal provides 2 to 3 times aging improvement relative to AT-cut. Thermal transient compensated - Allowing faster warm-up in OCXOs Phase noise For a given oscillator design for a particular crystal frequency and overtone, the SC-cut crystal provides higher Q and associated improved phase noise characteristics. Planar stress compensated - Smaller changes in frequency due to edge forces and bending. Far fewer activity dips Lower drive level sensitivity Lower sensitivity to radiatio. These Sc-cut crrystals are widely used in crystal oscillators. They are used in especially in OCXOs nad TCXOs.
Drawback of the SC-cut crystals:
Cost - Because of difficulties associated with tightly-controlled angle rotations around two axes in the manufacture of SC crystals vs one axis for the AT, the SC crystal is significantly higher in cost than that of an AT of the same frequency and overtone. Pull ability - The motional capacitance of an SC crystal is several times less than that of an AT of the same frequency and overtone, thus reducing the ability to "pull" the crystal frequency. This restricts the SC crystal from being used in conventional TCXOs and VCXOs, or even in oven controlled oscillators requiring the ability to deviate the frequency of oscillation by any significant degree. The suitability of double rotated crystals for use in crystal oscillators is essentially restricted to those oven controlled applications where the improved aging, warm-up, and close-in phase noise characteristics justify a significant cost increase.
