Capacitive sensor device and method for calibrating a capacitive sensor device

1. A capacitive sensor device for approach and/or contact detection, comprising at least one generator electrode, at least one measurement electrode and at least one calibration electrode, wherein the at least one calibration electrode is arranged in a predefined distance adjacent to the at least one measurement electrode, wherein the at least one measurement electrode and the at least one calibration electrode are assigned to the at least one generator electrode, wherein the at least one generator electrode receives an alternating generator voltage and the at least one calibration electrode receives an alternating calibrating voltage, and wherein the at least one calibration electrode may be operated at least in a first operating mode and a second operating mode, wherein

in each of the operating modes the calibrating voltage is equal to or smaller than the generator voltage, and

the calibrating voltage is different in each operating mode;

and further comprising an evaluation device which is configured to measure a capacitance between the measurement electrode (M) and ground while the calibration electrode is operated in the first and second operating mode, respectively and to determine a difference between the measurements, wherein the evaluation device furthermore compares the difference between the measurements with a threshold value to determine whether a calibration can be performed.

2. The capacitive sensor device of claim 1 , wherein the evaluation device is configured

to load the calibration electrode with a first calibrating voltage in the first operating mode and to detect a first capacitance between the measurement electrode and the ground of the sensor device, and

to load the calibration electrode with a second calibrating voltage in the second operating mode and to detect a second capacitance between the measurement electrode and the ground of the sensor device.

3. The capacitive sensor device of claim 1 , wherein the shape of the calibration electrode substantially is adapted to the shape of the measurement electrode.

4. The capacitive sensor device of claim 1 , wherein the measurement electrode and the calibration electrode are arranged on a printed circuit board and wherein the printed circuit board comprises a cut-out in the region between the measurement electrode and the calibration electrode.

5. The capacitive sensor device of claim 1 , wherein one calibration electrode is assigned to a number of measurement electrodes.

6. The capacitive sensor device of claim 1 , wherein the generator electrode is arranged at a bottom side of a printed circuit board, and the at least one measurement electrode and the at least one calibration electrode are arranged at an upper side of the printed circuit board.

7. A method for determining whether an instant is suitable for calibrating a capacitive sensor device, wherein the sensor device comprises at least one generator electrode, at least one measurement electrode and at least one calibration electrode, wherein the at least one measurement electrode and the at least one calibration electrode are arranged in a predefined distance adjacent to each other and are assigned to the at least one generator electrode, the method comprising:

feeding an alternating generator voltage to the at least one generator electrode,

for a first measurement, feeding a first alternating calibration voltage to the calibration electrode and measuring a capacitance between the first measurement electrode (M) and ground as a first sensor signal,

for a second measurement, feeding a second alternating calibration voltage to the calibration electrode and measuring a capacitance between the first measurement electrode (M) and ground as a second sensor signal, wherein the first calibrating voltage is chosen to be different from the second calibrating voltage and both calibrating voltages are chosen such that they are equal to or less than the generator voltage;

determining a difference between the first sensor signal and the second sensor signal, and

carrying out the calibration of the capacitive sensor device, when the difference in its absolute value is greater than a predefined threshold value.

8. The method of claim 7 , wherein the measurement electrode and the calibration electrode are arranged on a printed circuit board, wherein the printed circuit board comprises a cut-out in the region between the measurement electrode and the calibration electrode.

9. The method of claim 7 , wherein the shape of the calibration electrode substantially is adapted to the shape of the measurement electrode.

10. The method of one of claim 9 , wherein the measurement electrode and the calibration electrode are arranged on a printed circuit board, wherein the printed circuit board comprises a cut-out in the region between the measurement electrode and the calibration electrode.

11. The method of one of claim 7 , wherein a preliminary calibration of the capacitive sensor device is carried out, when the difference in its absolute value is smaller than the predefined threshold value, wherein a distance of an object from the measurement electrode is derived and estimated, respectively, from the first and the second sensor signal and the sensor data of the capacitive sensor device are calibrated with the estimated distance.

12. The method of one of claim 7 , wherein the first sensor signal and the second sensor signal each comprise sensor raw data.

13. A handheld device, comprising a capacitive sensor device for approach and/or contact detection, comprising at least one generator electrode, at least one measurement electrode and at least one calibration electrode, wherein the at least one calibration electrode is arranged in a predefined distance adjacent to the at least one measurement electrode, wherein the at least one measurement electrode and the at least one calibration electrode are assigned to the at least one generator electrode, wherein the at least one generator electrode receives an alternating generator voltage and the at least one calibration electrode receives an alternating calibrating voltage, and wherein the at least one calibration electrode is operated at least in a first operating mode and a second operating mode, wherein

in each of the operating modes the calibrating voltage is equal to or smaller than the generator voltage, and

the calibrating voltage is different in each operating mode;

and further comprising an evaluation device which is configured to measure a capacitance between the measurement electrode (M) and ground while the calibration electrode is operated in the first or second operating mode, respectively and to determine a difference between the measurements, wherein the evaluation device furthermore compares the difference between the measurements with a threshold value to determine whether a calibration can be performed.

14. The handheld device of claim 13 , wherein the evaluation device is configured

to load the calibration electrode with a first calibrating voltage in the first operating mode and to detect a first capacitance between the measurement electrode and the ground of the sensor device, and

to load the calibration electrode with a second calibrating voltage in the second operating mode and to detect a second capacitance between the measurement electrode and the ground of the sensor device.

15. The handheld device of claim 13 , wherein the shape of the calibration electrode substantially is adapted to the shape of the measurement electrode.

16. The handheld device of claim 13 , wherein the measurement electrode and the calibration electrode are arranged on a printed circuit board and wherein the printed circuit board comprises a cut-out in the region between the measurement electrode and the calibration electrode.

17. The handheld device of claim 13 , wherein one calibration electrode is assigned to a number of measurement electrodes.

18. The handheld device of claim 13 , wherein the generator electrode is arranged at a bottom side of a printed circuit board, and the at least one measurement electrode and the at least one calibration electrode are arranged at an upper side of the printed circuit board.

19. A method for operating a handheld device, comprising a capacitive sensor device for approach and/or contact detection, comprising at least one generator electrode, at least one measurement electrode and at least one calibration electrode, wherein the at least one calibration electrode is arranged in a predefined distance adjacent to the at least one measurement electrode, wherein the at least one measurement electrode and the at least one calibration electrode are assigned to the generator electrode, wherein the at least one generator electrode is loaded with a generator voltage and the at least one calibration electrode is loaded with a calibrating voltage, and wherein the at least one calibration electrode is operated at least in a first operating mode and a second operating mode, wherein in each of the operating modes the calibrating voltage lies between a ground voltage and the generator voltage, and the calibrating voltage is different in each operating mode, the method comprising:

loading the at least one generator electrode with an alternating generator voltage,

for a first measurement, loading the calibration electrode with a first alternating calibration voltage and measuring a capacitance between the first measurement electrode (M) and ground as a first sensor signal,

for a second measurement, loading the calibration electrode with a second alternating calibration voltage and measuring a capacitance between the first measurement electrode (M) and ground as a second sensor signal, wherein the first calibrating voltage is chosen to be different from the second calibrating voltage and both calibrating voltages are chosen such that they are equal to or less than the generator voltage;

determining a difference between the first sensor signal and the second sensor signal, and

carrying out the calibration of the capacitive sensor device, when the difference in its absolute value is greater than a predefined threshold value.

20. The method of claim 19 , wherein the measurement electrode and the calibration electrode are arranged on a printed circuit board, wherein the printed circuit board comprises a cut-out in the region between the measurement electrode and the calibration electrode.