HYSTERESIS IN QUARTZ RESONATORS - A REVIEW

The frequency versus temperature and pressure versus temperature characteristics of quartz crystal resonators do not repeat exactly upon temperature cycling, i.e., resonators exhibit "hysteresis." The subject of hysteresis is reviewed. The subject has been studied only sporadically until recently. A search of the literature has revealed only about a dozen papers in the Proceedings of the Annual Symposium on Frequency Control, a couple of contract reports, and a few other papers that deal with the subject. Books dealing with oscillators either do not mention the subject at all, or devote only a few sentences to the phenomenon. The causes of hysteresis are not well understood. The evidence to date is inconclusive. The mechanisms that can cause hysteresis include: strain changes, changes in the quartz, contamination redistribution, oscillator circuitry hysteresis, and apparent hysteresis due to thermal gradients.