MEASUREMENT OF SMALL CAPACITANCE VARIATIONS

In this paper a new technique to measure low frequency and low level capacitance variations is proposed. It is based on a "lock-in detection" circuit with a feedback loop, containing an integrator and a modulator, to zero the capacitance mean value. This method provides good signal-to-noise ratio and high sensitivity. Capacitance variations can be in the order of 100 ppm of the mean value while the frequency of the variations can be as low as 0.1 Hz. Stray capacitances and drift due to the environmental conditions are automatically compensated. A description of the measurement technique and of the experimental apparatus is reported together with a first set of experimental results.