Quartz crystal oscillator used as temperature sensor

A method for obtaining temperature data from a quartz crystal is described. To implement it, the first and third overtones of AT- and SC-cut crystal behavior with temperature have been studied. The AT-cut crystal shows instabilities at unpredictable temperature point while the SC-cut crystal has no activity dips in its c mode of vibration. A circuit to obtain a frequency very sensitive to and linear with temperature changes from the crystal fundamental and third overtone has been developed. Crystal design ideas obtaining the optimum frequency vs. temperature compensation are also explained. The goal of this technique is to compensate frequency vs. temperature variations of a quartz crystal oscillator, obtaining a factor-of-ten improvement over others that use thermistors as temperature sensors