A Pseudo-Differential Capacitive MEMS Accelerometer Analog Front-End Design

Abstract

Based on the current design and application of the chip and the research status at home and abroad, we proposed a silicon micro-accelerometer analog front-end integrated circuit with high resolution and wide capacitance application range by using SMIC 0.18μm CMOS technology. The circuit is composed of a capacitive readout circuit, a demodulator, and a low-pass filter. To detect the weak capacitive signal, the capacitor readout circuit of this paper adopts the continuous-time voltage mode charge amplifier structure and combines with the signal modulation technology and the optimization of the MOS transistor size to achieve low noise and high resolution. With the application of the signal modulation technology, the low-frequency capacitance sensor signal is shifted from 2-12 kHz to high-frequency 800 kHz. The signal modulation technology modulates the low-frequency capacitive sensor signal of 2~12 kHz at the high frequency of 800 kHz, and the signal is converted into voltage through the capacitive readout circuit. The simulation results show that the designed analog front-end circuit can convert the accelerometer capacitance signal with the frequency of 2~12 kHz, the dynamic capacitance peak is 0.108 pF, and the static capacitance is 10 pF into the expected voltage signal. In addition, the output noise can be as low as 556 nV/√Hz in the capacitive frequency range of the accelerometer, which meets the requirement of 2.5 aF capacitive resolution. Therefore, the silicon micro-accelerometer analog front-end circuit designed in this paper has the characteristics of a wide capacitor application range, low noise, and high resolution, and can be widely used.