Study on Signal Detection Techniques for the Capacitive Micromachined Inertial Sensors

A capacitance to voltage conversion circuit based on charge amplifier and coherent detection method for the capacitive micromachined inertial sensors was presented. Charge amplifier based on operational amplifier was used to eliminate influences of the parasitic capacitance. Two differential bridges were simulated using SPICE program to show the influences of asymmetry of the bridges. Then single-carrier differential bridge was chosen to minimize zero drift while enhance the circuit's sensitivity. Furthermore, the coherent detection method was used for demodulation to suppress the electronic noises. The principles of routing, ground and decoupling in the printed circuit board were also discussed to improve the circuit's performance further. The scheme can achieve 195 V/pF sensitivity and 1 fF minimum detectable capacitance variance, which can satisfy the capacitive micromachined inertial sensors with ordinary precision.