DEVICE AND METHOD FOR DETERMINING TOUCH POSITION ON SENSING AREA OF CAPACITIVE TOUCH PANEL

• US 20090058818A1
• Filed: 08/29/2007
• Published: 03/05/2009
• Est. Priority Date: 08/29/2007
• Status: Active Grant

• Current Assignee: eGalax_eMPIA Technology Inc.
• Original Assignee: eGalax_eMPIA Technology Inc.
• Inventors: LEE, CHENG-HAN, CHANG, CHIN-FU
• Granted Patent: US 7,808,490 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• 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 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/0444 using a single conductive element covering the whole sensing surface, e.g. by sensing the electrical current flowing at the corners

Abstract

Described is a device and a method for determining a touch position on a sensing area of a capacitive touch panel. In the device and method, an alternating current (AC) scan signal having a frequency and a current value is supplied to each of four corners of the capacitive touch panel. Next, the frequencies of the AC scan signals are each rapidly switched among a group of specific frequencies. The current values of the AC scan signals detected. In response, a group of selected frequencies is selected according to a noise filtering procedure from the group of specific frequencies based on the current values. Final current values are obtained by calculating the current values of the AC scan signals of the group of selected frequencies. Finally, the touch position on the capacitive touch panel is determined based on the final current values.

Claims

1. A device for determining a touch position on a sensing area of a capacitive touch panel, comprising:

a signal providing unit alternatively providing an alternating current (AC) scan signal having a frequency and a current value to each of four corners of the capacitive touch panel, respectively;

a frequency switching unit rapidly switching the frequency of the AC scan signal associated with each of the four corners among a group of specific frequencies;

a voltage driving and current detecting unit driving the capacitive touch panel by alternatively using the AC scan signal associated with each of the four corners, respectively, and detecting the current value of the AC scan signal of each of the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively;

a valid frequency selecting unit receiving the current value of the AC scan signal of each of the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively, and selecting a group of selected frequencies according to a noise filtering procedure from the group of specific frequencies associated with each of the four corners of the capacitive touch panel based on the current value of each of the group of specific frequencies, respectively;

a valid current value selecting unit obtaining a final current value by calculating the current value of the AC scan signal of each of the group of selected frequencies associated with each of the four corners of the capacitive touch panel, respectively; and

a position coordinate calculation unit calculating a coordinate value of the touch position on the capacitive touch panel based on the final current value associated with each of the four corners of the capacitive touch panel, respectively.

2. The device as claimed in claim 1, wherein the noise filtering procedure comprises the steps of:

determining one or more of the group of specific frequencies having the current value having a variation larger than a threshold as one or more to-be-filtered frequencies associated with each of the four corners of the capacitive touch panel, respectively; and

filtering out the one or more to-be-filtered frequencies from the group of specific frequencies as the group of selected frequencies for each of the four corners of the capacitive touch panel, respectively, and

the step of calculating the current value is a step of summing the current value associated with each of the group of selected frequencies for each of the four corners of the capacitive touch panel, respectively.

3. The device as claimed in claim 1, wherein noise filtering procedure comprises the steps of:

determining one or more noise frequencies causing a noise to the four corners of the capacitive touch panel, respectively, resulted from an ambient environment and a user of the capacitive touch panel by detecting a variation of the current value of each of the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively; and

filtering out one or more noise frequencies each equal to one of the one or more noise frequencies from the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively, and

the step of calculating the current value is a step of summing the current values associated with the group of selected frequencies for each of the four corners of the capacitive touch panel; and

the noise filtering procedure is performed only at a specific condition.

4. The device as claimed in claim 3, wherein the specific condition is one of the following conditions:

the capacitive touch panel is set up, the capacitive touch panel is powered on, and a specific work task begins on the capacitive touch panel.

5. The device as claimed in claim 1, wherein the noise filtering procedure comprises the steps of:

detecting a variation of the current value of each of the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively; and

selecting a least-variation frequency corresponding to a minimum of the variation of the current value of each of the group of specific frequencies, respectively, and taking the least-variation frequency as the group of selected frequency and the group of specific frequency, respectively, and

the step of calculating the current value is a step of summing the current values associated with the group of selected frequencies for each of the four corners of the capacitive touch panel; and

the noise filtering procedure is performed only at a specific condition.

6. The device as claimed in claim 5, wherein the specific condition is one of the following conditions:

the capacitive touch panel is set up, the capacitive touch panel is powered on, and a specific work task begins on the capacitive touch panel.

7. The device as claimed in claim 1, wherein each of the group of specific frequencies is less than 200 kHz.

8. The device as claimed in claim 1, wherein the AC scan signal for each of the four corners of the capacitive touch panel is one of a square-wave signal and a sinusoidal or cosine-wave signal.

9. A method for determining a touch position on a sensing area of a capacitive touch panel, comprising the steps of:

alternatively providing an alternating current (AC) scan signal having a frequency and a current value to each of four corners of the capacitive touch panel, respectively;

rapidly switching the frequency of the AC scan signal associated with each of the four corners among a group of specific frequencies;

driving the capacitive touch panel by alternatively using the AC scan signal associated with each of the four corners, respectively, and detecting the current value of the AC scan signal of each of the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively;

receiving the current value of the AC scan signal of each of the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively, and selecting a group of selected frequencies according to a noise filtering procedure from the group of specific frequencies associated with each of the four corners of the capacitive touch panel based on the current value of each of the group of specific frequencies, respectively;

obtaining a final current value by calculating the current value of the AC scan signal of each of the group of selected frequencies associated with each of the four corners of the capacitive touch panel, respectively; and

calculating a coordinate value of the touch position on the capacitive touch panel based on the final current value associated with each of the four corners of the capacitive touch panel, respectively.

10. The method as claimed in claim 9, wherein the noise filtering procedure comprises the steps of:

determining one or more of the group of specific frequencies having the current value having a variation larger than a threshold as one or more to-be-filtered frequencies associated with each of the four corners of the capacitive touch panel, respectively; and

filtering out the one or more to-be-filtered frequencies from the group of specific frequencies as the group of selected frequencies for each of the four corners of the capacitive touch panel, respectively, and

the step of calculating the current value is a step of summing the current value associated with each of the group of selected frequencies for each of the four corners of the capacitive touch panel, respectively.

11. The method as claimed in claim 9, wherein the noise filtering procedure comprises the steps of:

determining one or more noise frequencies causing a noise to the four corners of the capacitive touch panel, respectively, resulted from an ambient environment and a user of the capacitive touch panel by detecting a variation of the current value of each of the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively; and

filtering out one or more noise frequencies each equal to one of the one or more noise frequencies from the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively, and

the step of calculating the current value is a step of summing the current values associated with the group of selected frequencies for each of the four corners of the capacitive touch panel; and

the noise filtering procedure is performed only at a specific condition.

12. The method as claimed in claim 11, wherein the specific condition is one of the following conditions:

the capacitive touch panel is set up, the capacitive touch panel is powered on, and a specific work task begins on the capacitive touch panel.

13. The device as claimed in claim 9, wherein the noise filtering procedure comprises the steps of:

detecting a variation of the current value of each of the group of specific frequencies associated with each of the four corners of the capacitive touch panel, respectively; and

selecting a least-variation frequency corresponding to a minimum of the variation of the current value of each of the group of specific frequencies, respectively, and taking the least-variation frequency as the group of selected frequency and the group of specific frequency, respectively, and

the step of calculating the current value is a step of summing the current values associated with the group of selected frequencies for each of the four corners of the capacitive touch panel; and

the noise filtering procedure is performed only at a specific condition.

14. The method as claimed in claim 13, wherein the specific condition is one of the following conditions:

the capacitive touch panel is set up, the capacitive touch panel is powered on, and a specific work task begins on the capacitive touch panel.

15. The method as claimed in claim 9, wherein each of the group of specific frequencies is less than 200 kHz.

16. The method as claimed in claim 9, wherein the AC scan signal for each of the four corners of the capacitive touch panel is one of a square-wave signal and a sinusoidal or cosine-wave signal.