Multichannel capacitive sensor device

1. A capacitive sensor device comprising a capacitance-measuring circuit, a plurality of sense inputs and a reference input, each sense input being connectable to a sense electrode, the capacitive sensor device being configured, in a first measurement mode, for driving the reference input to be equipotential with one of the sense inputs that is measured by the capacitance-measuring circuit and determine a value of the capacitance seen by the sense input that is measured unaffected by any capacitance between the sense input that is measured and the reference input, and, in a second measurement mode, for measuring the capacitance seen at the reference input with the capacitance-measuring circuit while holding one sense input to ground and driving other sense inputs to be equipotential with the reference input, determining a value of the reference capacitor connected between the reference input and the sense input that is held to ground unaffected by any capacitance between the reference input and sense inputs that are driven to be equipotential to the reference input.

2. The capacitive sensor device of claim 1 , the capacitive sensor device being configured to set selectively sense inputs and reference input in a ground state or in a shield state or in a measure state, whereby inputs in the ground state are connected to a low impedance node that could be the ground, inputs in the measure state are read by the capacitance-measuring circuit, and inputs in the shield state are held at the same potential as inputs in the measure state, wherein the capacitive sensor device is configured, in the second measurement mode, to select a sense input, set the selected sense inputs in the ground state, set other sense inputs in the shield state set the reference input in the measure state and measure with the capacitance-measuring circuit a reference capacitance seen at the reference input and, in the first measurement mode, set the reference input in the shield state and the selected sense input in the measure state and measure with the capacitance-measuring circuit an uncorrected capacitance seen at the selected sense input.

3. The capacitive sensor device of claim 1 , further configured to generate a corrected capacitance for the selected sense input based on the uncorrected capacitance and the reference capacitance.

4. The capacitive sensor device of claim 1 , wherein the generation of a corrected capacitance comprises multiplying the reference capacitance by a predetermined factor and subtracting the resulting value from the uncorrected capacitance.

5. The capacitive sensor device of claim 1 , configured to select the sense inputs repeatedly and in turn and generate corrected capacitances for each of the sense inputs.

6. The capacitive sensor device of claim 1 , comprising a processing unit, the sense inputs having a controllable input unit that is configured to accept a command from the processing and, based on said command, set the corresponding sense input in a ground state, in the shield state or in the measure state.

7. The capacitive sensor device of claim 6 , the reference input having a controllable input unit that is configured to accept a command from the processing and, based on said command, set the reference input in the shield state or in the measure state.

8. The capacitive sensor device of claim 1 , wherein each of the sense input is coupled through an external reference capacitor with the reference input.

9. The capacitive sensor device of claim 8 , wherein the sense inputs are coupled with capacitive sense electrodes, whose self-capacitance changes at an approach of a conductive body, and the external reference capacitors have a temperature coefficient that is same or proportional to the temperature coefficient of the capacitive sense electrodes.

10. The capacitive sensor device of claim 9 , wherein the capacitive sense electrodes are conductor areas on a printed circuit board, and the external reference capacitors include tracks and/or conductor areas on the same board or on a bord of same characteristics, and the capacitances of the external sense electrodes is less affected by the approach of the conductive body.

11. The capacitive sensor device of claim 1 , wherein the capacitance-measuring circuit determines the capacitance seen at an input by connecting the input to a variable voltage source and measuring the corresponding variation of electric charge.

12. The capacitive sensor device of claim 1 and a portable electronic device, wherein the capacitive sensor device is configured to generate a proximity signal based on a corrected capacitance, and the portable electronic device is configured to activate a predetermined action when the proximity signal is generated and/or when the proximity signal is extinguished.

13. The capacitive sensor device and portable electronic device of claim 12 , wherein the action is one of: change a power of a radio transmitter, switch on or off a display backlight, enable or disable a tactile input interface.

14. The capacitive sensor device and portable electronic device of claim 12 , wherein at least one of the sense inputs is coupled with a radiofrequency antenna whose self-capacitance changes at an approach of a conductive body.