Capacitive Readout System for Micro Sensors and Actuators with Automatic Parasitic Cancellation

In this article, a capacitive readout system with automatic parasitic capacitance cancellation function is designed and implemented. The readout system is implemented with discrete components on a board level. The parasitic cancellation is realized by matching a digital programmable capacitor to the parasitic capacitance using a PI controller. The function of the readout system is verified by using standard ceramic capacitors and a MEMS micromirror device. Capacitance measurements up to 35 pF for ceramic capacitors are performed, the maximum error between the measurement results of the circuit and an LCR meter is 0.07 pF. For MEMS micromirror, the circuit cancels the parasitic capacitance of 32.63 pF and realizes a measurement error within 0.06 pF. The proposed system can be used as a proof-of-concept platform demonstrating the feasibility of the generic parasitic cancellation method for MEMS sensors and actuators.