Arrangement to calibrate a capacitive sensor interface

A capacitive sensor interface circuit comprising:

• a bias circuit coupleable to a charge storing circuit having a changeable capacitance and to a capacitive sensor, the bias circuit configured to apply a bias voltage to the charge storing circuit and to the capacitive sensor when the bias circuit is coupled to the capacitive sensor and to the charge storing circuit;
• a test circuit coupleable to the charge storing circuit and to the capacitive sensor, the test circuit configured to apply a test signal to the charge storing circuit and to the capacitive sensor when the test circuit is coupled to the capacitive sensor and the charge storing circuit;
• an amplifier circuit having a first input coupleable to the capacitive sensor and a second input coupleable to the charge storing circuit, wherein the amplifier circuit is configured to provide an output signal (Vout) at an output of the amplifier circuit in response to application of the test signal to the capacitive sensor and the charge string circuit;
• a detection circuit configured to detect a level of the output signal (Vout);
• a control circuit coupled to the detection circuit and configured to trim the capacitance of the charge storing circuit such that the level of the output signal (Vout) tends to zero when the test signal is applied to the charge storing circuit and to the capacitive sensor.

A method in a capacitive sensor interface circuit, the method comprising:

• generating a bias signal for application to a capacitive sensor and to a charge storing circuit;
• generating a test signal for application to the capacitive sensor and the charge storing circuit when under bias;
• generating a differential output signal based on input signals received from the capacitive sensor and the charge storing circuit in response to applying the test signal to the capacitive sensor and to the charge storing circuit;
• detecting the differential output signal;
• trimming a capacitance of the charge storing circuit using a control signal based on the detected differential output signal, wherein the control signal tends to reduce the differential signal to zero.