An Ultra-Low-Noise Capacitive Readout Circuit for Gyroscopes

Inhalt:
In this paper, we present an ultra-low noise readout circuit for capacitive micro-electro-mechanical system (MEMS) sensors, which is used to detect and amplify the capacitive signal of the gyroscope with an amplitude range of 0~0.2 pF and a frequency range of 5~10 kHz. The capacitance readout circuit is composed of two sub-modules, a C/V (Capacitance to Voltage) conversion circuit and a capacitively-coupled chopper gain amplifier circuit. According to the circuit characteristics of the two sub-modules, different technical means are used to achieve the overall low-noise design goal. Based on SMIC.18 CMOS process, 3.3 V power supply voltage, and 1.65 V common-mode voltage, the C/V conversion circuit can convert the capacitance signal of the gyroscope into a voltage signal and achieve good linearity fitting. To meet the optimal range requirements of the subsequent analog-to-digital converter, the voltage signal output by the C/V conversion circuit is adjusted and amplified to a preset value of 2 V through a capacitively-coupled chopper gain amplifier circuit. Finally, the output noise of the overall capacitance readout circuit is as low as 89.27 nV/√Hz@5kHZ, and the capacitance resolution also reaches the design goal of 0.1 aF.