Capacitive sensing apparatus that uses a combined guard and sensing electrode

• US 7,583,092 B2
• Filed: 07/30/2007
• Issued: 09/01/2009
• Est. Priority Date: 07/30/2007
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Reynolds, Joseph K., Dattalo, Tracy S.
• Primary Examiner(s): NGUYEN, HOAI AN D
• Application Number:
  US11/888,170
• Publication Number:
  US 20090033343A1
• Time in Patent Office: 764 Days
• Field of Search: 324/688, 324/686, 324/658, 324/649, 324/600, 324/661, 324/662, 324/663, 324/671, 324/548, 340/562, 340/545.4, 73/17.9, 737/80, 737/18, 737/24, 738/623.37, 738/626.26, 735/143.2, 702/47, 702/52, 702/150
• US Class Current: 324/688
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2017/9604 characterised by the number of electrodes
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
• CPC Class Codes: H03K 2217/960765 Details of shielding arrangements
• CPC Class Codes: H03K 2217/960775 Emitter-receiver or "fringe" type detection, i.e. one or more field emitting electrodes and corresponding one or more receiving electrodes

Abstract

A capacitive sensing apparatus includes capacitive sensor electrodes, and a combined guard and sensing electrode that is disposed proximate to the capacitive sensor electrodes. The combined guard and sensing electrode has at least a first operating mode and a second operating mode. In the first operating mode, the combined guard and sensing electrode can detect an object at a distance that is greater than the distance at which the object can be sensed by the capacitive sensor electrodes. In the second operating mode, the combined guard and sensing electrode can electrically guard the capacitive sensor electrodes.

Claims

1. A capacitive sensing apparatus comprising:

a plurality of capacitive sensor electrodes that are operable for sensing an object that is within a first distance of said plurality of sensor electrodes; and

a combined guard and sensing electrode disposed proximate to said plurality of sensor electrodes and having associated therewith at least a first operating mode and a second operating mode, wherein in said first operating mode said combined guard and sensing electrode is operable for detecting said object at a second distance that is greater than said first distance, and wherein in said second operating mode said combined guard and sensing electrode is operable for electrically guarding at least one of said capacitive sensor electrodes.

2. The apparatus of claim 1 wherein said combined guard and sensing electrode is configured to switch from said first operating mode to said second operating mode in response to detecting said object.

3. The apparatus of claim 1 wherein said combined guard and sensing electrode is configured to switch from said second operating mode to said first operating mode in response to determining absence of said object.

4. The apparatus of claim 1 further comprising a guard electrode in proximity to said combined guard and sensing electrode and operable for electrically guarding said combined guard and sensing electrode.

5. The apparatus of claim 1 wherein said plurality of capacitive sensor electrodes is selected from the group consisting of:

buttons;

one-dimensional sensors; and

two-dimensional sensors.

6. The apparatus of claim 1 wherein said plurality of capacitive sensor electrodes is disabled when said combined guard and sensing electrode is in said first operating mode and enabled when said combined guard and sensing electrode is in said second operating mode.

7. The apparatus of claim 1 wherein said combined guard and sensing electrode transitions from an enabled state to a disabled state in response to said combined guard and sensing electrode detecting presence of said object while in said first operating mode, and wherein said combined guard and sensing electrode transitions from said first operating mode to said second operating mode in response to said plurality of capacitive sensor electrodes sensing presence of said object.

8. The apparatus of claim 1 wherein said plurality of capacitive sensor electrodes is enabled when said combined guard and sensing electrode is in said first operating mode and enabled when said combined guard and sensing electrode is in said second operating mode.

9. The apparatus of claim 1 wherein said plurality of capacitive sensor electrodes guards said combined guard and sensing electrode when said combined guard and sensing electrode is in said first operating mode.

10. The apparatus of claim 1 wherein, in said first operating mode, said plurality of capacitive sensor electrodes and said combined guard and sensing electrode are driven by current excitation and measured with voltage sensing circuitry.

11. The apparatus of claim 1 wherein, in said first operating mode, said plurality of capacitive sensor electrodes and said combined guard and sensing electrode are driven by voltage excitation and measured with current sensing circuitry.

12. The apparatus of claim 1 wherein said combined guard and sensing electrode encompasses a majority of a perimeter of at least one of said capacitive sensor electrodes.

13. A capacitive sensing apparatus comprising:

a combined guard and sensing electrode that has associated therewith a first operating mode and a second operating mode; and

a plurality of capacitive sensor electrodes disposed proximate to said combined guard and sensing electrode and having associated therewith a function that can be transitioned between a first state and a second state depending on whether an object is within sensing range of said combined guard and sensing electrode;

wherein, when said function is placed in said first state, said combined guard and sensing electrode is transitioned from said second operating mode to said first operating mode in which said combined guard and sensing electrode is operable for detecting an object within sensing range of said combined guard and sensing electrode; and

wherein, in response to said combined guard and sensing electrode detecting an object, said function is transitioned to said second state and said combined guard and sensing electrode is transitioned from said first operating mode to said second operating mode in which said combined guard and sensing electrode is operable for electrically guarding said plurality of capacitive sensor electrodes.

14. The apparatus of claim 13 wherein said combined guard and sensing electrode is configured to switch from said first operating mode to said second operating mode in response to detecting said object.

15. The apparatus of claim 13 wherein said combined guard and sensing electrode is configured to switch from said second operating mode to said first operating mode in response to determining absence of said object.

16. The apparatus of claim 13 wherein said combined guard and sensing electrode is configured to switch from said second operating mode to said first operating mode after a prescribed period of time.

17. The apparatus of claim 13 further comprising a guard electrode in proximity to said combined guard and sensing electrode and operable for electrically guarding said combined guard and sensing electrode.

18. The apparatus of claim 13 wherein said plurality of capacitive sensor electrodes is selected from the group consisting of:

buttons;

one-dimensional sensors; and

two-dimensional sensors.

19. The apparatus of claim 13 wherein said first state is a disabled state and wherein said second state is an enabled state.

20. The apparatus of claim 19 wherein said plurality of capacitive sensor electrodes guard said combined guard and sensing electrode when said combined guard and sensing electrode is in said first operating mode.

21. The apparatus of claim 13 wherein, in said first operating mode, said plurality of capacitive sensor electrodes and said combined guard and sensing electrode are driven by current excitation and measured with voltage sensing circuitry.

22. The apparatus of claim 13 wherein, in said first operating mode, said plurality of capacitive sensor electrodes and said combined guard and sensing electrode are driven by voltage excitation and measured with current sensing circuitry.

23. The apparatus of claim 13 wherein said combined guard and sensing electrode encompasses a majority of a perimeter of at least one of said capacitive sensor electrodes.

24. A method of operating a capacitive sensing apparatus, said method comprising:

placing a combined guard and sensing electrode of said apparatus in a first operating mode if a signal that indicates an object is within sensing range of said apparatus is absent for a prescribed length of time, wherein in said first operating mode said combined guard and sensing electrode is operable for detecting an object within said sensing range and wherein said combined guard and sensing electrode remains in said first operating mode until an object is detected; and

placing said combined guard and sensing electrode in a second operating mode in response to detecting an object, wherein in said second operating mode said combined guard and sensing electrode is operable for electrically guarding a plurality of capacitive sensor electrodes of said apparatus.

25. The method of claim 24 further comprising:

disabling said plurality of capacitive sensor electrodes when said combined guard and sensing electrode is in said first operating mode; and

enabling said plurality of capacitive sensor electrodes when said combined guard and sensing electrode is in said second operating mode.

26. The method of claim 24 further comprising enabling said plurality of capacitive sensor electrodes when said combined guard and sensing electrode is in said first operating mode, wherein said plurality of capacitive sensor electrodes remains enabled when said combined guard and sensing electrode is in said second operating mode.

27. The method of claim 24 further comprising:

disabling said plurality of capacitive sensor electrodes when said combined guard and sensing electrode is in said first operating mode; and

using said plurality of capacitive sensor electrodes to guard said combined guard and sensing electrode.

28. The method of claim 24 further comprising:

disabling said plurality of capacitive sensor electrodes when said combined guard and sensing electrode is in said first operating mode; and

using said plurality of electrodes to determine a state of said combined guard and sensing electrode.