Capacitive sensing device and method

• US 8,125,232 B2
• Filed: 03/23/2009
• Issued: 02/28/2012
• Est. Priority Date: 03/27/2008
• Status: Active Grant

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: Renesas Electronics Corporation
• Inventors: Ozawa, Naofumi
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): Baldridge, Benjamin M
• Application Number:
  US12/382,724
• Publication Number:
  US 20090243632A1
• Time in Patent Office: 1,072 Days
• Field of Search: 324/679
• US Class Current: 324/679
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/960715 Rc-timing; e.g. measurement of variation of charge time or discharge time of the sensor

Abstract

In a capacitive sensing device for detecting a change in capacitance of an electrode which is caused by contact with a human body, the improvement of determination speed may be enabled. M (m is an integer satisfying n≧m≧2) electrodes are selected from n (n is an integer equal to or larger than two) electrodes. Capacitors connected to the m electrodes are discharged in parallel during a predetermined period, and then charged. During the charging period, a potential of each of the m electrodes is compared with a reference potential. A difference between capacitance values of the capacitors connected to the m electrodes is determined based on a result obtained by the comparison between the m electrodes.

Claims

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.