Frequency-temperature characteristics
       The frequency-temperature characteristics vary with the vibration mode which may vary considerably different, Figure 5 shows the theoretical relationship between the frequency-temperature characteristic curve of the type commonly used in cutting. Crystal resonator used primarily AT-cut and BT-cut, because the AT-cut frequency difference is easier to control the temperature, and therefore require more stringent temperature frequency difference more choice of AT-cut crystals, Figure 6 shows a relatively complete set of AT frequency-temperature characteristic curve of the theoretical cut crystal. These curves show that a certain angle may be selected to obtain a predetermined range to ensure that the temperature within a predetermined range performance. In fact, due to the design and manufacture of a variety of restrictions, such as guiding theoretical curve for information. It should be noted that the choice to pay a higher price for a smaller temperature difference frequency. For general use as digital circuits (eg PC) applications clock, ± 30 × 10-6 ,, temperature ± 50 × 10-6 of the frequency difference is enough, only when the communication system and precise timing reference applications will consider more stringent temperature frequency difference. Figure 7 shows the cost of AT-cut crystal frequency when the provisions are very small temperature difference takes. Too strict frequency difference can lead to an increase in manufacturing costs, designers should fully assess the scope of the desired frequency difference.

Figure 7 AT-cut crystal element frequency tolerance / temperature range of difficult situations