Simple and robust microcontroller-based acquisition system for differential capacitive sensors

Differential capacitive sensors, especially if implemented as MEMS (Micro Electro Mechanical Systems) are a widely employed sensor solution, especially after the widespread adoption of the IoT (Internet of things) paradigm. These sensors target very different applications, including accelerometers, gyroscopes, barometers, just to mention a few, because they can take advantage from lower power consumption, better temperature coefficient and manufacturability. The readout circuit plays a central and fundamental role in ensuring optimal overall performance. In this paper, a frontend for interfacing differential capacitive sensors with microcontroller-based systems is discussed and performance is evaluated. In particular, the use of voltage mode is considered and, consequently, the stray capacitance can deeply affect the readouts. The proposed interface evaluates the mismatch between the current flowing in the two sensor equivalent capacitors and estimates the parasitic value. Additionally, the information about the current unbalance is used to improve the measurand estimation. In particular, the proposed approach is able to decrease of one order of magnitude the measurand estimation error, when large stray capacitance affects the sensor.