A capacitive accelerometer is an accelerometer device which measures accelerations (on a surface) using capacitive sensing techniques. It has the ability to sense and record acceleration on equipment or devices and converts this acceleration into electrical currents or voltage. Capacitive accelerometers are also sometimes referred to as vibration sensors. They comprise a capacitive micro-electro-mechanical system (MEMS) element connected to an electronic circuitry. When supplied by an electronic circuitry, the MEMS element will convert the resulting force due to its acceleration into an electrical signal, which in turns is amplified by the electronic circuitry, and converted to a useful signal for a given application (for example a digital representation of the acceleration). In capacitive MEMS accelerometers, the signal is due to the change of the MEMS capacitance in presence of the acceleration. Capacitive accelerometers are widely implemented in computational and commercial applications, such as airbag deployment sensors in automobiles, human computer interaction devices and smartphones.
Capacitive accelerometers typically have some manufacturing imperfections due to a non-perfect manufacturing process. For instance, the capacitive accelerometers typically comprise some parasitic capacitance values which vary from one capacitive accelerometer to another. Furthermore, when measuring the capacitance generated by the acceleration, electrostatic forces are often generated which have a negative impact on the precision of the measured acceleration value. The cancellation of the electrostatic force effect without degrading the MEMS output useful signal is one of the key challenges to be addressed. The purpose of this invention is to allow electrostatic force effect cancellation when using a MEMS excitation strategy that optimizes the signal over noise ratio.
USPTO Backgrounds
USPTO Backgrounds