This article introduces a new method for temperature-compensated capacitance-frequency converter with a single quartz crystal oscillating in the switching oscillating circuit. The novelty of this method lies in the use of additionally connected capacitances in series with JFET switching transistors to the shunt capacitance of the quartz crystal bringing a considerable reduction of the temperature influence of AT-cut crystal frequency change in the temperature range between 0 and 50°C. The oscillator switching method and parallel switching stray capacitances connected to the quartz crystal do not only compensate crystal's natural temperature characteristics but also any other influences on the crystal such as aging of both the crystal and other oscillating circuit elements. In addition, they also reduce the output frequency measurement error. The experimental results show that through high temperature compensation improvement of the quartz crystal characteristics, this switching method enables 20 zF resolution capacitance to frequency transduction in the range 0-4 pF to 2-45 kHz.
Matko, V., & Milanović, M. (2014). Temperature-compensated capacitance-frequency converter with high resolution. Sensors and Actuators, A: Physical, 220, 262–269. https://doi.org/10.1016/j.sna.2014.09.022