Capacitive sensing device and method

1. A capacitive sensing device, comprising:

n sensing electrodes, wherein n is an integer equal to or larger than two;

a selection register storing a value for selecting m sensing electrodes from the n sensing electrodes, wherein m is an integer satisfying n≧m≧2;

a selection section selecting the m sensing electrodes from the n sensing electrodes based on the value stored in the selection register;

a charging and discharging control section coupled to the m sensing electrodes, wherein controlling charging and discharging capacitors connected to the m sensing electrodes is performed in parallel;

a comparison section coupled to the m electrodes, wherein comparing a reference potential with a potential of each of the m sensing electrodes during the charging is performed by the charging and discharging control section, to generate comparison result signals associated with the m sensing electrodes; and

a determination section coupled to the comparison section, wherein determining a difference between capacitance values of the capacitors coupled to the m sensing electrodes is based on the comparison result signals associated with the m sensing electrodes.

2. The capacitive sensing device according to claim 1 ,

wherein the comparison section comprises m comparators,

wherein the determination section comprises m storage sections each corresponding to the m comparators,

wherein the m storage sections store the comparison result signals obtained from the m comparators at a predetermined timing during the charging, and

wherein the determination section determines the difference between the capacitance values of the capacitors coupled to the m sensing electrodes based on the comparison result signals stored in the m storage sections.

3. The capacitive sensing device according to claim 2 , wherein the determination section further comprises a measurement section,

wherein the measurement section measures a time interval between changing points of the comparison result signals associated with the m comparators, and

wherein the determination section determines the difference between the capacitance values of the capacitors connected to the m sensing electrodes based on the measured time interval and the comparison result signals stored in the m storage sections.

4. The capacitive sensing device according to claim 3 , wherein, the determination section further comprises an exclusive OR calculation section,

wherein the exclusive OR calculation section receives the comparison result signals from the m comparators,

wherein the m storage sections store the m comparison result signals at a first changing point of an output from the exclusive OR calculation section after start of the charging, and

wherein the measurement section measures a time interval between changing points of the output from the exclusive OR calculation section after the start of the charging.

5. The capacitive sensing device according to claim 2 , wherein the predetermined timing comprises a timing at which at least one of the comparison result signals from the m comparators changes.

6. The capacitive sensing device according to claim 2 , wherein the predetermined timing is set as a time between a charging period required for charging up to the reference potential in a case where a human body is not in contact with the m sensing electrodes and a charging period required for charging up to the reference potential in a case where the human body is in contact with at least one of the m sensing electrodes.

7. The capacitive sensing device according to claim 6 , wherein, the determination section further comprises a measurement section, and

wherein the m storage sections store the comparison result signals from the m comparators when a measurement time of the measurement section reaches a time indicated by the predetermined timing.

8. The capacitive sensing device according to claim 1 , wherein the determination section comprises a measurement section;

wherein the measurement section measures time intervals between start of the charging and m changing points of the comparison result signals, and

wherein the determination section determines the difference between the capacitance values of the capacitors coupled to the m sensing electrodes based on a difference between the

measured time intervals.

9. The capacitive sensing device according to claim 8 , wherein the comparison section comprises m comparators,

wherein, the determination section comprises m storage sections each corresponding to the m comparators,

wherein the measurement section causes corresponding one of the m storage sections to store each of the measured time intervals associated with the m changing points of the

comparison result signals, and

wherein the determination section determines the difference between the capacitance values of the capacitors coupled to the m sensing electrodes based on the measured time intervals

stored in the m storage sections.

10. The capacitive sensing device according to claim 1 , wherein the charging and discharging control section connects the m sensing electrodes with a ground potential to discharge the capacitors connected to the m sensing electrodes during a predetermined period, and connects the m sensing electrodes with a power supply potential through resistors to charge the capacitors connected to the m sensing electrodes.

11. The capacitive sensing device according to claim 1 , wherein the determination section comprises a measurement section,

wherein the measurement section measures a time interval between changing points of the comparison result signals associated with the m comparators, and

wherein the determination section determines the difference between the capacitance values of the capacitors connected to the m sensing electrodes based on the measured time interval.

12. The capacitive sensing device according to claim 1 , wherein the determination section refers to the value stored in the selection register to recognize which one of the n sensing electrodes comprises a determination target sensing electrode.

13. The capacitive sensing device according to claim 1 , wherein the charging and discharging control section comprises a plurality of charging and discharging control sections, and

wherein based on said selecting the m sensing electrodes from the n sensing electrodes the m sensing electrodes are connected to respective ones of the charging and discharging control sections through the selection section.

14. A capacitive sensing method of sensing capacitance values of capacitors connected to n sensing electrodes, wherein n is an integer equal to or larger than two sensing electrodes, said method comprising:

setting a value for selecting m sensing electrodes from the n sensing electrodes into a selection register, wherein m is an integer satisfying n≧m≧2;

selecting the m sensing electrodes from the n sensing electrodes based on the value set in the selection register;

discharging capacitors connected to the m sensing electrodes, in parallel, for a predetermined period, and then charging the capacitors connected to the m sensing electrodes;

comparing a reference potential with a potential of each of the m sensing electrodes during the charging, to generate comparison results associated with the m sensing electrodes; and

determining a difference between the capacitance values of the capacitors connected to the m sensing electrodes based on the comparison results associated with the m sensing electrodes,

wherein the selecting, the charging and discharging, the comparing and the determining are performed n/m times.

15. The capacitive sensing method according to claim 14 , wherein the determining comprises obtaining the comparison results at a predetermined timing during the charging, and determining the difference between the capacitance values of the capacitors connected to the m sensing electrodes based on the comparison results.

16. The capacitive sensing method according to claim 15 , wherein the determining further comprises determining the difference between the capacitance values of the capacitors connected to the m sensing electrodes based on the comparison results and a time interval between acquisition times of the comparison results associated with the m sensing electrodes.

17. The capacitive sensing method according to claim 15 , wherein the predetermined timing is set as a time between a charging period required for charging up to the reference potential in a case where a human body is not in contact with the m sensing electrodes and a charging period required for charging up to the reference potential in a case where the human body is in contact with at least one of the m sensing electrodes.

18. The capacitive sensing method according to claim 14 , wherein the determining comprises:

measuring time intervals between a start of the charging and outputs of comparison result signals; and

determining the difference between the capacitance values of the capacitors connected to the m sensing electrodes based on a difference between the measured time intervals.

19. The capacitive sensing method according to claim 14 , wherein the determining comprises determining the difference between the capacitance values of the capacitors connected to the m sensing electrodes based on a time interval between acquisition times of the comparison results associated with the m sensing electrodes.

20. The capacitive sensing method according to claim 14 , wherein the determining comprises:

referring to the value set in the selection register to recognize which one of the n sensing electrodes comprises a determination target sensing electrode.