Patent ID: 6848317

Claim:
A method for uniformizing output signal levels of MEMS capacitive sensors uniform, each including a microstructure being displaced by a certain force and a fixed electrode for detecting capacitance variations caused by gap size variations between the microstructure and the fixed electrode, comprising the steps of: a) initializing a reference value used for adjusting an output AC level of the MEMS capacitive sensor, and setting a target RMS level of the output AC level of the MEMS capacitive sensor; b) applying an actuating current of a predetermined frequency to the microstructure and detecting a voltage from the fixed electrode; c) detecting an RMS level of the voltage detected from the fixed electrode; d) comparing the RMS level detected in the step c) with the target RMS level; e) in the case that a result of the step d) indicates that there is an error between the detected RMS level and the target RMS level, adjusting the reference value by adding proportional integral value of the error to the reference value or subtracting the proportional integral value of the error from the reference value, thereby outputting the adjusted current reference value as an offset voltage of the fixed electrode, and repeating the steps b) to e); and f) in the case that the detected RMS level is the same as the target RMS level in the step d), setting the offset voltage of the fixed electrode to the adjusted current reference value which is obtained at the time when no error is detected in the step e).