CMOS readout electronics for capacitive acceleration sensors

In this contribution we will present a readout electronics for a capacitive acceleration sensor, both fabricated in silicon. The sensor is formed by an arrangement of a sensing capacitor and a reference capacitor. The capacitance of the sensing capacitor is inversely proportional to the active acceleration of the sensing capacitor. The readout electronics uses a switched-capacitor amplifier for determining the ratio of the reference capacitance and the sensing capacitance. The output signal of the system, which consists of the readout electronics and the acceleration sensor, is linearly proportional to the active acceleration. Since the output signal is symmetrical with respect to the ground, it has the same sign dependence as the measured acceleration. Using two external adjustable voltages the electronics makes it possible to trimm the sensitivity and the offset. The smallest detectable change of capacitance is about 7fF.