Capacitive sensor

A capacitive sensor, comprising:

• a first MEMS capacitive element having a capacitance value changing in accordance with reflection of a change in a physical quantity;
• a second MEMS capacitive element having a capacitance value changing in accordance with reflection of the change in the physical quantity;
• a first variable capacitor connected with the first MEMS capacitive element;
• a second variable capacitor connected with the second MEMS capacitive element;
• a CV conversion circuit that includes a first input terminal, a second input terminal, a first output terminal, and a second output terminal, and generates a voltage in which a change in the capacitance value of the first MEMS capacitive element and a change in the capacitance value of the second MEMS capacitive element are reflected;
• a detection circuit that detects an average voltage of input voltages of the first input terminal and the second input terminal of the CV conversion circuit or an average voltage of output voltages of the first output terminal and the second output terminal of the CV conversion circuit;
• an analog digital converter that converts the average voltage into a digital average voltage signal;
• and
• a control circuit that changes the capacitance values of the first variable capacitor and the second variable capacitor on the basis of the digital average voltage signal,
• wherein a connection point of the first MEMS capacitive element and the first variable capacitor is connected to the first input terminal, and
• a connection point of the second MEMS capacitive element and the second variable capacitor is connected to the second input terminal.

A capacitive sensor, comprising:

• a sensor unit that includes a pair of capacitors configured with a fixed electrode and a movable electrode, applies a voltage to one of the fixed electrode and the movable electrode, extracts charges accumulated in the pair of capacitors from the other electrode, and obtains two output signals;
• a CV converting unit that receives the two output signals as an input, reflects the charges extracted from the sensor unit in a capacitance value of a feedback capacitor, converts a voltage signal, and obtains a differential output;
• an AD converter that converts the differential output of the CV converting unit into a digital signal;
• and
• a variable capacitor having a capacitance value which is controlled on the basis of the digital signal;
• and
• a voltage-dividing resistive circuit that extracts a common mode output potential of the differential output,
• wherein one electrode of the variable capacitor is connected to the other electrode from which the accumulated charges are extracted, and the common mode output potential of the differential output is controlled by controlling a capacitance value of the variable capacitor,
• an output of the voltage-dividing resistive circuit is input to a first terminal of the AD converter,
• a fixed potential is input to a second terminal of the AD converter,
• a difference signal between an input of the first terminal and an input of the second terminal is the digital signal, and
• the capacitive sensor further comprises a digital control unit that generates a control signal for controlling the capacitance value of the variable capacitor on the basis of a result of comparing the digital signal with a reference signal.