Directional capacitive sensor system and method

• US 20060238205A1
• Filed: 04/21/2006
• Published: 10/26/2006
• Est. Priority Date: 04/22/2005
• Status: Abandoned Application

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Francis, Mark
• Application Number:
  US11/408,367
• Publication Number:
  US 20060238205A1
• Time in Patent Office: Days
• US Class Current: 324/658
• CPC Class Codes: G01D 5/2405 by varying dielectric
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence
• CPC Class Codes: H03K 17/962 Capacitive touch switches
• CPC Class Codes: H03K 2217/94026 Automatic threshold calibration; e.g. threshold automatically adapts to ambient conditions or follows variation of input
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe

Abstract

A capacitive sensing system (200) can include a sense section (202) and a filter section (206). Sense section (202) can activate logic outputs based on a sensed capacitance from sensors (210-1 and 210-2). A filter section (206) can logically combine logic outputs in different ways to generate output signals (INT_—1 and INT_—2). According to output signals (INT_—1 and INT_—2), different types of movement in a capacitive body (212) can be detected.

Claims

1. A method, comprising:

calibrating a plurality of capacitance measuring circuits, each coupled to a corresponding capacitance sensor, to determine calibration values for the capacitance sensors in a baseline environment;

zeroing out the capacitance sensors with the calibration values to place the capacitance sensors in a non-triggered state absent a change in sensor capacitance from the baseline environment;

configuring at least a sensitivity value for each capacitance sensor, each sensitivity value determining a capacitance change amount that activates a change indication from the capacitance measuring device; and

logically combining change indications from the capacitance measuring devices to activate a trigger indication when an object moves in a particular direction in relation to the capacitance sensors.

2. The method of claim 1, further including:

configuring at least a hysteresis value for each capacitance sensor, each hysteresis value establishing a first limit that activates a change indication from the capacitance measuring device, and a establishing a second limit that de-activates a change indication from the capacitance measuring device.

3. The method of claim 1, wherein:

logically combining change indications from the capacitance measuring devices to prevent activation of a trigger indication when an object moves in a direction perpendicular to the capacitance sensors physical positions.

4. A sensor, comprising:

a first near field capacitive sense circuit having an output that provides a sense indication based on capacitance input value;

a second near field capacitive sense circuit having an output that provides a sense indication based on capacitance input value; and

a detect circuit coupled to the outputs of at least the of the first and second near field capacitive sense circuits that logically combines the sense indications of the first and second near field capacitive sense circuits in at least two different way.

5. The sensor of claim 4, wherein:

the detect circuit logically combines the sense indications with a logical operation selected from the group consisting of a NAND function and an AND function.

6. The sensor of claim 4, wherein:

the detect circuit logically combines the sense indications with a logical operation selected from the group consisting of a NOR function and an OR function.

7. The sensor of claim 6, wherein:

the detect circuit further logically combines the sense indications with a second logical operation selected from the group consisting of a NAND function and an AND function.

8. The sensor of claim 4, wherein:

at least one of the near field capacitive sense circuits activates the sense indication with hysteresis based on changes in the input capacitance value.

9. The sensor of claim 4, wherein:

all of the near field capacitive sense circuits activate the corresponding sense indication with hysteresis based on changes in the input capacitance value.

10. The sensor of claim 4, wherein:

the sense indications are logic signals; and

the detect circuit comprises a logic gate coupled to the outputs of at least the of the first and second near field capacitive sense circuits that logically combines the sense indications.

11. The sensor of claim 4, further including:

a machine readable media storing processing instructions for logically combining sense indications of the near field capacitive sense circuits; and

the detect circuit comprises a processing circuit that executes the processing instructions.

12. The sensor of claim 4, wherein:

the sense indications comprise multi-bit count values.

13. A capacitive sensing method, comprising the steps of:

sensing a capacitance value at each of a plurality of capacitance sensor inputs;

for each capacitance sensor input, activating a corresponding sense signal when the sensed capacitance value is not within a predetermined range;

filtering the sense signals to selectively activate detect signals based on at least two logical combinations of the sense signals.

14. The method of claim 13, wherein:

sensing the capacitance value at each of a plurality of capacitance sensor inputs includes generating a count value corresponding to the rate at which a capacitance at the sensor input can be charged.

15. The method of claim 13, wherein:

filtering the sense signals includes logically combining signals according to any of the logical combinations selected from the group consisting of;

ANDing, NANDin, ORing, NORing.

16. The method of claim 13, wherein:

filtering the sense signals includes applying sense signals as input valued to a look-up table.

17. The method of claim 13, wherein:

filtering the sense signals includes activating a detect signal based on a time difference between activations of same sense signal.

18. The method of claim 13, wherein:

filtering the at least one logic output value includes activating a detect signal based on a time difference between activations of different sense signals.

19. The method of claim 13, further including:

transmitting the detect signal via a wireless transmitter.

20. The method of claim 13, further including:

sensing the capacitance value includes generating a count value corresponding to the rate at which a capacitance at the sensor input can be charged; and

activating the detect signal based on changes in count values for different sensor inputs over time.