Recently there have been increasing demands for high precise information of humidity. The realization of driving circuit of a humidity sensor to satisfy them have been desired.
We produced a high precise and sensitive driving circuit of a capacitive humidity sensor used both a negative-capacitor-circuit and a capacitance-scaling-circuit on the basis of a Wien bridge oscillator as an experiment.
In detecting small capacitance change, removing unnecessary offset capacitance by the negative-capacitor-circuit leads to increasing capacitance sensitivity. The combined capacitance was amplified up to fit the Wien bridge oscillator by the capacitance-scaling-circuit and we detected a frequency change which the capacitance change converted into through its oscillator.
We investigated three circuits, our proposed new circuit, Wien bridge oscillator, and astable multivibrator one. As a result of experiment, the frequency stability, the capacitance resolution, and the temperature coefficient of a new circuit is -5.6×10-3, 0.0015pF (at 100pF), and -0.005pF/°C (at 100pF), respectively. These values were improved to be about one order magnitude better than that of the conventional circuits.
J-STAGEがリニューアルされました! https://www.jstage.jst.go.jp/browse/-char/ja/
