Senseline data adjustment method, circuit, and system to reduce the detection of false touches in a touch screen

• US 9,041,684 B2
• Filed: 08/14/2012
• Issued: 05/26/2015
• Est. Priority Date: 08/14/2012
• Status: Active Grant

• Current Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Asia Pacific Pte Limited (STMicroelectronics NV)
• Inventors: Santos, Maria Rhea, Ningrat, Kusuma Adi, Soe, Wah Wah
• Primary Examiner(s): Haley, Joseph
• Assistant Examiner(s): ILUYOMADE, IFEDAYO B
• Application Number:
  US13/585,749
• Publication Number:
  US 20140049501A1
• Time in Patent Office: 1,015 Days
• Field of Search: None
• US Class Current: 345/174
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• 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 touch controller processes a captured data frame and detects the presence of touch points in the data frame. The data frame includes a plurality of digital capacitance values organized as groups of sense line data and the touch controller determines for each digital capacitance value in a group of sense line data the difference between the digital capacitance value and an associated no-touch threshold to generate a baseline delta value for each digital capacitance value in the group. The touch controller selects the minimum baseline delta and adjusts each digital capacitance value in the group by the minimum baseline delta to generate adjusted sense line data. The touch control generates adjusted sense line data for each group of sense line data in the data frame and thereafter processes the groups of adjusted sense line data to detect the presence of touch points in the data frame.

Claims

1. A touch controller operable to;

determine, for each one of a plurality of digital capacitance values in a group of sense line data, a baseline delta value as being a difference between the digital capacitance value and an associated no-touch threshold;

select a minimum baseline delta value;

adjust each digital capacitance value in the group by the minimum baseline delta value to generate corresponding groups of adjusted sense line data; and

process the groups of adjusted sense line data to detect touch points in the data frame by comparing each adjusted digital capacitance value in the adjusted sense line data to a touch-in threshold, and detect the presence of a touch point when the adjusted digital capacitance value reaches or exceeds the touch-in threshold,

wherein the touch-in threshold is a constant value to which every adjusted digital capacitance value is compared.

2. The touch controller of claim 1, wherein the touch controller adjusts each digital capacitance value in the group by subtracting the minimum baseline delta value from the digital capacitance value.

3. The touch controller of claim 1, wherein the data frame comprises an N×

M array of digital capacitance values where N corresponds to the number of force lines and M to the number of sense lines in a touch sensor array, and wherein each group of sense line data corresponds to N digital capacitance values associated with a corresponding sense line of the touch sensor array.

4. The touch controller of claim 3 further comprising a conversion circuit coupled to receive signals on the sense lines and convert each of these received signals to a corresponding digital capacitance value.

5. The touch controller of claim 4 further comprising a switch circuit coupled to the force lines and operable to sequentially apply a clock signal on each of the force lines.

6. An electronic device, comprising:

a touch sensor array including a plurality of sensor nodes operable to detect the presence of touch points;

processing circuitry operable to execute applications;

a touch controller coupled to the touch sensor array and to the processing circuitry, the touch controller operable to;

sequentially scan each sensor node of the touch sensor array;

generate a corresponding digital capacitance value for each sensor node, the digital capacitance values of a given scan collectively forming a data frame and digital capacitance values being organized as groups of sense line data;

determine for each digital capacitance value in a group of sense line data the difference between the digital capacitance value and an associated no-touch threshold to generate a baseline delta value for each digital capacitance value in the group;

select the minimum baseline delta value and adjust each digital capacitance value in the group by the minimum baseline delta value to generate adjusted sense line data,

generate adjusted sense line data for each group of sense line data in the data frame; and

process the groups of adjusted sense line data to detect the presence of touch points in the data frame by comparing each adjusted digital capacitance value in the adjusted sense line data to a touch-in threshold, and detect the presence of a touch point when the adjusted digital capacitance value reaches or exceeds the touch-in threshold,

wherein the touch-in threshold is a constant value to which every adjusted digital capacitance value is compared.

7. The electronic device of claim 6, wherein the touch sensor array comprises:

a plurality of sense lines

a plurality of orthogonally arranged force lines;

a plurality of sensor nodes at the overlap portions of sense and force lines.

8. The electronic device of claim 7, where each sense line and each force line comprises a conductive line having a plurality of diamond-shaped conductive sense pads arranged along a length of the sense line or force line.

9. The electronic device of claim 7, wherein the ouch controller comprises:

a switch circuit including,

a buffer circuit having an input adapted to receive a clock signal and an output;

a switch matrix coupled to the output of the buffer circuit and coupled to the force lines, the switch circuit operable to sequentially provide the clock signal at the output of the buffer circuit on respective force lines; and

a conversion circuit including,

a capacitance-to-digital converter operable to generate a digital capacitance value from a coupled signal provided on an input of the capacitance-to-digital converter;

a switch matrix coupled to the sense lines and coupled to the input of the capacitance-to-digital converter, the switch matrix operable to couple a selected sense line to the input of the capacitance-to-digital converter and thereby provide the coupled signal on the selected sense line to the capacitance-to-digital converter for generation of corresponding digital capacitance values.

10. The electronic device of claim 7, wherein the processing circuitry comprises smart phone processing circuitry.

11. The electronic device of claim 9, wherein the touch controller adjusts each digital capacitance value in the group by subtracting the minimum baseline delta value from the digital capacitance value.

12. A method of processing data frames to detect the presence of touch points, each data frame including a plurality of sense node values arranged as groups of sense node values, the method comprising:

for each group of sense node values,

determining the difference between each sense node value and an associated no touch threshold to provide a baseline delta value for each sense node value in the group;

determining the minimum baseline delta value; and

subtracting the corresponding minimum baseline delta value from each of the sense node values in the group to provide adjusted sense node values for the group; and

processing the adjusted sense node values to detect the presence of touch points by comparing each adjusted sense node value to a corresponding touch-in threshold and detecting the presence of a touch point when the adjusted sense node value reaches or exceeds the threshold,

wherein the touch-in threshold is a constant value to which every adjusted digital capacitance value is compared.

13. The method of claim 12, wherein each sense node value includes a digital capacitance value.

14. The method of claim 13, wherein each data frame includes an N×

M array of digital capacitance values where N corresponds to the number of force lines and M to the number of sense lines in a touch sensor array, and wherein each group corresponds to N digital capacitance values associated with a corresponding sense line of the touch sensor array.

15. A touch controller operable to:

determine, for each one of a plurality of digital touch sensor values in a group of sense line data, a baseline delta value as being a difference between the digital touch sensor value and an associated no-touch threshold;

select a minimum baseline delta value;

adjust each digital touch sensor value in the group by the minimum baseline delta value to generate corresponding groups of adjusted sense line data; and

process the groups of adjusted sense line data to detect touch points in the data frame by comparing each adjusted digital touch sensor value in the adjusted sense line data to a touch-in threshold and detects the presence of a touch point when the adjusted digital touch sensor value reaches or exceeds the touch-in threshold,

wherein the touch-in threshold is a constant value to which every adjusted digital touch sensor value is compared.