Performance Investigation of a High-Precision Charge-Discharge Differential Capacitance Sensor

Capacitive sensing circuit is one of the key technologies in the development of a series of deep space exploration instruments, such as inertial sensors in space gravitational wave detection mission and seismometers in planetary/lunar exploration programs. Space exploration missions require high-precision, low-power, and high-reliable capacitive sensing circuits. Although the traditional bridge-based capacitive detection circuits widely used currently behave high accuracy, they have a relatively complex structure and higher power consumption. In this article, a charge-discharge differential capacitive sensing circuit based on high stability square-wave generator, ring diode switch, and low-noise transimpedance amplifier is proposed and investigated systematically. The system noise model is presented based on detailed analysis and measurement of the main noise sources. Low-noise design optimization scheme is proposed based on the noise model. A prototype circuit is developed and tested. The sensitivities with several different excitation frequencies are calibrated. The measured noise is compared to the theoretical model and demonstrates a good consistency. The experimental results show that the noise equivalent capacitance resolution of this circuit reaches 0.24 aF/Hz $^{{1}/{2}}$ at 0.1 Hz and 0.028 aF/Hz $^{{1}/{2}}$ at 100 Hz. Benefiting from its simple structure and high measurement accuracy, it is highly suitable for space exploration instruments and other applications.