Thermal hysteresis in quartz crystal resonators and oscillators

Data are presented on the hysteresis of quartz crystal resonators and oscillators. The dual-c-mode self-temperature sensing technique is used for thermometry. Temperature measurement inaccuracies are eliminated with this technique because the resonator and the thermometer are one and the same. Measurements were made using both a passive pi network/vector voltmeter system, and dual-mode oscillators of two designs. The experimental variables investigated are the end point temperatures, the rate of change of temperature, the sequence of temperatures (i.e. low-high-low, high-low-high, or mid-low-high-mid, etc.), and the drive level. Resonators are measured over several different cycles in both a pi network and a dual-mode oscillator. The results show that the thermal hysteresis of the crystal resonators studied is independent of temperature sequence and drive level but is dependent on the temperature extremes. The contribution to the thermal hysteresis from a poorly designed oscillator may be larger than the contribution from the resonator. Resonators from several different manufacturers and different lots from the same manufacturer exhibit thermal hysteresis signatures