Detection of a conductive object during an initialization process of a touch-sensing device

• US 8,941,393 B2
• Filed: 08/25/2011
• Issued: 01/27/2015
• Est. Priority Date: 01/14/2011
• Status: Expired due to Fees

• Current Assignee: Monterey Research, LLC (Vector Capital Corporation)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Young, Kristopher L.
• Primary Examiner(s): Koval, Melissa
• Assistant Examiner(s): MILLER, DANIEL R
• Application Number:
  US13/218,090
• Publication Number:
  US 20120212240A1
• Time in Patent Office: 1,251 Days
• Field of Search: 178/18.06, 178/19.03, 324658-690, 341/33, 345/173, 345/174
• US Class Current: 324/679
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: G06F 2203/04101 2.5D-digitiser, i.e. digitiser detecting the X/Y position of the input means, finger or stylus, also when it does not touch, but is proximate to the digitiser's interaction surface and also measures the distance of the input means within a short range in the Z direction, possibly with a separate measurement setup
• CPC Class Codes: G06F 2203/04106 Multi-sensing digitiser, i.e. digitiser using at least two different sensing technologies simultaneously or alternatively, e.g. for detecting pen and finger, for saving power or for improving position detection
• CPC Class Codes: G06F 2203/04108 Touchless 2D- digitiser, i.e. digitiser detecting the X/Y position of the input means, finger or stylus, also when it does not touch, but is proximate to the digitiser's interaction surface without distance measurement in the Z direction
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/04186 Touch location disambiguation
• CPC Class Codes: G06F 3/044 by capacitive means

Abstract

A method and system for detecting a presence of a conductive object proximate to a capacitive sense element during an initialization process of a touch-sensing device. A reference sense element is calibrated to produce a sensing parameter value. A capacitance of a plurality of capacitive sense elements is measured based on the sensing parameter value, and compared to a baseline capacitance value stored in a non-volatile memory of the touch-sensing device. The presence of a conductive object proximate to a capacitive sense element is detected when a difference between the measured capacitance and the stored baseline capacitance value is greater than a threshold value.

Claims

1. A method, comprising:

during an initialization process of a touch-sensing device;

measuring a capacitance of a reference sense element disposed on a second side of a printed circuit board of the touch-sensing device, wherein the measured capacitance is responsive to an environmental condition and is not responsive to a conductive object,

comparing the measured capacitance of the reference sense element to a target measurement output value, and

calibrating a capacitance measurement of the reference sense element to produce a sensing parameter value;

comparing a capacitance measured on each of a plurality of capacitive sense elements disposed on a first side of the printed circuit board based on the sensing parameter value to a baseline capacitance value for each of the plurality of capacitive sense elements to determine a capacitance difference value; and

detecting a presence of the conductive object proximate to a capacitive sense element when the capacitance difference value for the capacitive sense element is greater than a threshold value.

2. The method of claim 1, wherein calibrating the capacitance measurement of the reference sense element further comprises adjusting a sensing parameter to the sensing parameter value to set the measured capacitance of the reference sense element to the target measurement output value.

3. The method of claim 2, wherein the sensing parameter is a current of a current source connected to a capacitance sensor of the touch-sensing device.

4. The method of claim 2, wherein the sensing parameter is a voltage of a voltage source connected to a capacitance sensor of the touch-sensing device.

5. The method of claim 2, wherein the sensing parameter is programmable by a processing device.

6. The method of claim 1, wherein the presence of the conductive object proximate to the capacitive sense element is detected during the initialization process of the touch-sensing device.

7. The method of claim 1, wherein the baseline capacitance value for each of the plurality of capacitive sense elements is stored in a non-volatile memory.

8. A system, comprising:

a processing device coupled to a capacitance sensor, the capacitance sensor comprising;

a printed circuit board comprising a first side including a plurality of capacitive sense elements disposed thereon, and a second side including a reference sense element disposed thereon, and

a sensing parameter,

wherein the processing device is to;

measure a capacitance of the reference sense element, wherein the measured capacitance is responsive to an environmental condition and is not responsive to a presence of a conductive object,

compare the measured capacitance of the reference sense element to a target measurement output value,

adjust the sensing parameter to a sensing parameter value to set a measured capacitance of the reference sense element to the target measurement output value,

compare a capacitance of each of the plurality of capacitive sense elements to a baseline capacitance value for each of the plurality of capacitive sense elements to determine a capacitance difference value, and

detect a presence of the conductive object proximate to a capacitive sense element when the capacitance difference value for the capacitive sense element is greater than a threshold value.

9. The system of claim 8, wherein the capacitance sensor is to measure the capacitance of each of the plurality of capacitive sense elements based on the sensing parameter value.

10. The system of claim 8, wherein the baseline capacitance value for each of the plurality of capacitive sense elements is stored in a non-volatile memory of the touch-sensing device.

11. The system of claim 8, wherein the presence of the conductive object proximate to the capacitive sense element is detected during an initialization process of the touch-sensing device.

12. The system of claim 8, wherein the reference sense element is not responsive to the presence of the conductive object during an initialization process of the touch-sensing device.

13. The system of claim 8, wherein the sensing parameter is a programmable current.

14. The system of claim 8, further comprising a printed circuit board comprising an overlay covering the reference sense element such that the reference sense element is not responsive to a presence of a conductive object proximate to the reference sense element during an initialization process of the touch-sensing device.

15. A non-transitory computer-readable medium including data that, when accessed by a processing device, causes the processing device to perform operations comprising:

during an initialization process power up of a touch-sensing device, measuring a capacitance of a reference sense element disposed on a second side of a printed circuit board of the touch-sensing device, wherein the measured capacitance is responsive to an environmental condition and is not responsive to a presence of a conductive object, comparing the measured capacitance of the reference sense element to a target measurement output value, and calibrating a measurement of a reference sense element to produce a sensing parameter value;

comparing a capacitance measured on each of a plurality of capacitive sense elements disposed on a first side of the printed circuit board based on the sensing parameter value to a baseline capacitance value stored in a non-volatile memory for each of the plurality of capacitive sense elements to determine a capacitance difference value; and

detecting a presence of the conductive object proximate to a capacitive sense element during the initialization process power up of the touch-sensing device when the capacitance difference value for the capacitive sense element is greater than a touch threshold value.

16. The non-transitory computer-readable medium of claim 15, wherein the operations further comprise adjusting a sensing parameter to a sensing parameter value to set a capacitance of the reference sense element to a target measurement output value.

17. The non-transitory computer-readable medium of claim 16, wherein the sensing parameter is a current of a current source connected to a capacitance sensor of the touch-sensing device.

18. The non-transitory computer-readable medium of claim 15, wherein the capacitance on the capacitive sense element is measured by a capacitance sensor.