If we compare AT-cut and SC-cut resonators having the same frequency and overtone, the motional inductance (L₁) and motional resistance (R) of the SC-cut resonator will be significantly higher than for the AT-cut resonator, while the motional capacitance (C₁) will be lower in the same proportion.  The static capacitance (C₀), however, will be nearly the same for the two.  For oscillator applications, high impedance is desirable if aging is important, because it reduces the effect of the sustaining circuit on the oscillator frequency.  The trade-off is that high resonator impedance reduces the tuning range of the oscillator frequency, limiting corrections for manufacturing tolerance and for aging.  In VCXOs, aging is, at most, a secondary consideration, so that the required tuning range will determine the highest practical overtone.  For either cut, the impedance level increases roughly as the square of the overtone for a given frequency, but also depends upon details of the resonator design.

Size:

    For most applications, the sizes of the AT-cut and SC-cut resonator packages are the same.

Cost:

     Because of tighter orientation tolerances, the SC-cut is more expensive to manufacture than the AT-cut, but for high-performance applications this cost is more than offset by savings in oven complexity, and for many applications the SC-cut is the only choice.  For some applications where thermal transient characteristics are less important, a modified (near) SC-cut may be used.  This provides essentially the same f - T curve as the true SC-cut but allows looser orientation tolerances, thereby providing some cost savings at the expense of thermal transient performance.  Normally, cuts having T_o much removed from 92°C will not provide the thermal transient performance for which the true SC-cut is noted.

Quartz Turning Folk Resonators / Watch Crystal

       The requirements of quartz resonators for wristwatch are: small size, low power dissipation (including the oscillator), low cost, and high stability (temperature, aging, shock, attitude).  These requirements can be met with 32.768 kHz quartz turning fork resonators.  It is interesting to know that 32768 = 2¹⁵ or 1 Hz = 32768/2¹⁵.  In an analog watch, a stepping motor receives one impulse per second which advances the second pin by 6, i.e., 1/60^th of a circle every second.  The 32.768 kHz is a compromise among size, power requirement (i.e., batter life) and stability.

    Quartz wristwatches are sufficiently accurate, usually, while worn as intended, i.e., on the wrist for ~16 h and off the wrist for ~8 h each day. The accuracies degrade when the watch is off the wrist for extended periods. The further the storage temperature is from the optimum temperature, the faster the watch loses time.  At temperature extremes, e.g., in a freezer at - 55°C, or at the temperature of boiling water, wristwatches lose about 20 s per day.

       The angle of cut of the resonator used in wristwatches is such that the zero temperature coefficient is at ~ 25°C, as shown in the following f – T curve. This has been found to provide the highest probability of accuracy, based on the typical durations and temperatures while the watch is on the wrist and while it is off the wrist.

Type of Seal for Quartz Crystal Resonators

Solder Seal

     Solder seal packages have several advantages.  They have lower lead-to-case capacitance than other types and therefore used in some filter designs that require minimal junction capacitance.  In addition, the packages can be opened for rework that is sometimes helpful in meeting difficult filter requirements.  Their main disadvantage is that they cannot be sealed without introducing contamination, and therefore they tend to have relatively poor frequency stability.

Resistance Weld

      These packages require more sophisticated sealing equipment than solder seal, but the sealing process introduces less contamination, resulting in better frequency stability.  Resistance weld packages are available in a wide range of styles, and all are economical choices for long-term performance

Seam Weld

     Seam weld sealing is the most widely used method today in producing ceramic base/metal cover low profile SMD crystals and oscillators. Performance and cost are similar to those resistance weld packages.