CONTROLLER AND METHOD FOR CONTROLLING A CAPACITIVE TOUCH SCREEN OR THE LIKE

• US 20130169584A1
• Filed: 01/03/2012
• Published: 07/04/2013
• Est. Priority Date: 01/03/2012
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Konradi, Vadim, Dorris, Parker, Welland, David R., Franklin, Michael
• Granted Patent: US 9,727,159 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• 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 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes

Abstract

A controller for a capacitive touch screen includes a touch resolve subsystem and a processor. The touch resolve subsystem, in response to a trigger input, measures a plurality of capacitance values using a plurality of input pins. The processor controls the touch resolve subsystem to acquire a baseline capacitance in a calibration mode, to acquire a frame comprising the plurality of capacitance values in a normal operation mode, and to update the baseline capacitance to a new baseline capacitance in the normal operation mode in response to the frame without entering the calibration mode.

Claims

1. A controller for a capacitive touch screen, comprising:

a touch resolve subsystem that in response to a trigger input measures a plurality of capacitance values using a plurality of input pins; and

a processor that controls said touch resolve subsystem to acquire a baseline capacitance in a calibration mode, to acquire a frame comprising said plurality of capacitance values in a normal operation mode, and to update said baseline capacitance to a new baseline capacitance in said normal operation mode in response to said frame without entering said calibration mode.

2. The controller of claim 1 wherein said processor acquires said baseline capacitance in said calibration mode by causing said touch resolve subsystem to measure said plurality of capacitance values using said plurality of input pins when the capacitive touch screen is in an untouched condition.

3. The controller of claim 1 wherein said processor updates said baseline capacitance in said normal operation mode in response to changing a value of a parameter used to acquire said frame.

4. The controller of claim 1 wherein said processor determines a touch location in said normal operation mode in response to both said baseline capacitance and each of said plurality of capacitance values.

5. The controller of claim 1 wherein during said calibration mode said processor acquires at least one of a plurality of baseline capacitances corresponding to each of a plurality of values of a parameter, and during said normal operation mode uses both said parameter and a first baseline capacitance corresponding to a selected value of said parameter to determine a touch location.

6. The controller of claim 5 wherein said parameter comprises a scan frequency.

7. The controller of claim 5 wherein said parameter comprises a number of scan pulses per scan line.

8. The controller of claim 7 wherein said processor determines said new baseline capacitance when changing said number of scan pulses per scan line by adjusting said baseline capacitance by a ratio of a new number of scan pulses per scan line to a current number of scan pulses per line.

9. The controller of claim 5 wherein during said calibration mode said processor acquires said plurality of baseline capacitances and builds a table of baseline offsets indicating, for each of said plurality of values of said parameter, a difference between said baseline capacitance and a reference baseline capacitance at a second value of said parameter, and wherein said processor, when changing said value of said parameter to said new desired value during said normal operation mode, adjusts said baseline capacitance by said baseline offset.

10. A controller for a capacitive touch screen, comprising:

a touch resolve subsystem that in response to a trigger input measures a plurality of capacitance values using a plurality of input pins; and

a processor that controls said touch resolve subsystem to acquire a frame comprising said plurality of capacitance values, determines a level of interference in said frame, and uses said frame to determine a touch location if said level of interference is less than a first threshold.

11. The controller of claim 10, wherein said plurality of capacitance values comprises capacitance values for each of a plurality of row values.

12. The controller of claim 10, wherein said processor further acquires a baseline capacitance in an untouched condition, and uses said frame to determine said touch location by subtracting said baseline capacitance from each of said plurality of capacitance values.

13. The controller of claim 12, wherein said processor further uses said frame to update said baseline capacitance if said level of interference is less than a second threshold.

14. The controller of claim 10, wherein said processor further determines said level of interference in said frame by measuring a difference between each of said plurality of capacitance values of said frame and each of a corresponding plurality of capacitance values of a prior frame.

15. The controller of claim 10, wherein said processor further determines that interference in said frame is negative interference if at least one of said plurality of capacitance values exceeds a negative interference threshold compared to a baseline capacitance in a direction opposite a touch signal, and determines that said interference in said frame is positive interference if a number of said plurality of said capacitance values exceeding a positive interference threshold is greater than a touch signature threshold in a direction the same as said touch signal.

16. A method for acquiring information from a capacitive touch screen comprising:

acquiring a baseline capacitance using a plurality of input pins in a calibration mode;

acquiring a frame comprising a plurality of capacitance values using said plurality of input pins in a normal operation mode; and

updating said baseline capacitance to a new baseline capacitance in said normal operation mode in response to said frame without entering said calibration mode.

17. The method of claim 16 wherein said acquiring said baseline capacitance comprises:

acquiring said baseline capacitance in an untouched condition of the capacitive touch screen.

18. The method of claim 16 wherein said acquiring said baseline capacitance comprises:

updating said baseline capacitance in said normal operation mode in response to changing a value of a parameter used in said acquiring said frame.

19. The method of claim 16 further comprising:

determining a touch location in said normal operation mode in response to both said baseline capacitance and each of said plurality of capacitance values.

20. The method of claim 16 wherein said acquiring said baseline capacitance comprises:

acquiring a plurality of baseline capacitances corresponding to each of a plurality of values of a parameter; and

using both said parameter and a first baseline capacitance corresponding to a selected value of said parameter to determine a touch location.