Research And Design Of Low-Pass Filter In MEMS Capacitive Accelerometer Sensor Readout Circuit

MEMS sensor is a current research focus, and the low-pass filter is the important part of the signal processing in the readout circuit. Research and development of the easy-integration, high performance and applied to MEMS sensor readout circuit will be great significant.This paper is to research and design the low-pass filter of the MEMS capacitive accelerometer sensor readout circuit. In order to adapt to different MEMS capacitive accelerometer sensor's needs, the low-pass filter will be designed to be adjustable bandwidth, and the bandwidth ranges are 100Hz~10 kHz. When the signal frequency is below 500Hz, using the adjustable bandwidth switched-capacitor low-pass filter; and when the signal frequency is higher than 500Hz, using the adjustable bandwidth continuous-time low-pass filter.In this paper, the biquadrate switched-capacitor low-pass filter is designed by using the switched capacitor analog resistance to substitute the resistance of the active filter. The in-phase integrator and reverse-phase integrator which are both not sensitive to parasitic capacitor are chosen in the filter design. The CMOS two-stage operational amplifier which has the high DC gain and unity gain bandwidth is used to form the integrator. The non-ideal factors, such as the MOS switch conducted resistance and charge injection, and clock feed through will be analyzed in detail. Using the two-phase non-overlapping and an optimized falling edge asynchronous clock to control the switch timing can reduce the impact of the non-ideal factors. In the continuous-time filter design, using two first-order cascade continuous-time low-pass filter circuits to achieve a second-order low-pass filter.Finally, using the TSMC 0.18 Mixed Signal SALICIDE CMOS process model to simulate the entire filter module. The maximum bandwidth of the biquadrate switched-capacitor low-pass filter is 500Hz, and the smallest bandwidth of the second-order continuous-time low-pass filter is 902Hz, its maximum bandwidth is up to 64Hz. The results meet the 100~10kHz bandwidth design requirements, and the entire filter module is suitable for the small-signal readout processing and noise filtering of the MEMS capacitive accelerometer sensor.