Issue 91, February 1998
Choosing the Right Crystal For Your Oscillator

Start •Why Quartz Crystals • Timing Budget & Accuracy • Frequency Tolerance • Frequency Stability • Aging • Load Capacitance • Series and Parallel Resonance • Frequency Tolerance and Load Capacitance • AT vs. BT Cut • Mode of Operation • Package Considerations • Crystal Placement • Crystal Clear • References

AT vs. BT CUT

If you take a look at the two temperature coefficient curves for the AT- and BT-cut crystals (see Figure 1), you find that the AT cut is preferable. For the BT, temperature changes always cause a resonant frequency decrease.

Unfortunately, you may not have a choice. For low-frequency crystals below 1 MHz, BT cuts dominate. Oscillators using these style cuts may not perform well in environments with large temperature fluctuations. But, if you have the choice, pick the AT cut.