Suppression of Low-Frequency Noise From Diode Forward Voltage Based on Chopper Stabilization in a Charge-Discharge Capacitive Sensing Circuit

Abstract

Charge-discharge capacitive sensing circuit has the advantages of high precision, simple structure and low power consumption. However, its low-frequency noise performance is limited by the fluctuations of the forward voltage of the switching diodes in the ring-diode circuit. In this brief, a chopper stabilization circuit is designed by periodically interchanging the positions of the four diodes to suppress the low-frequency noise introduced by the ring-diode circuit. The principle is analyzed and the noise performance is validated. Experimental results show that this method can significantly suppress the low-frequency noise of the sensing circuit. At a carrier frequency of 2.5 MHz, the equivalent capacitance resolution of the sensing circuit at 0.01 Hz is improved from about 1.1 aF/Hz ${}^{\mathrm {1/2}}$ to about 0.12 aF/Hz ${}^{\mathrm {1/2}}$ . The optimized sensing circuit can promote the application in fields with high requirements for low-frequency performance, such as space inertial sensors and planetary seismometers.