In the field of industrial measurement, capacitive sensors are widely used. In many types of capacitive sensors, the output capacitance value range of many sensors is very small, generally between 10pF to 1000pF, but accuracy is usually required to be more than one thousandth. The conventional method of detecting capacitance value is generally the capacitor charge and discharge. By charging and discharging time statistics and calculations, capacitance values are deduced finally. The inherent disadvantages of this method are: (1) Temperature drift of the measurement circuit is large. (2) The spatial magnetic field under special circumstances impact on measurement circuit. (3) Long-term stability of the device will deteriorate. In this paper, a "capacitance measurement method with reference and comparison" is summed up through a lot of measurement experiments of humidity capacitance, that method can eliminate three kinds of defects in the capacitor charging and discharging process.
A Baseband Ultra-Low Noise SiGe:C BiCMOS 0.25μm Amplifier and its Application for an On-Chip Phase-Noise Measurement Circuit