Method and apparatus for sensing and scanning a capacitive touch panel

• US 8,624,871 B2
• Filed: 07/15/2011
• Issued: 01/07/2014
• Est. Priority Date: 07/15/2011
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Nihei, Tatsuyuki, Uchino, Osamu, Sato, Tatsuro
• Primary Examiner(s): Tzeng, Fred
• Application Number:
  US13/184,321
• Publication Number:
  US 20130016062A1
• Time in Patent Office: 907 Days
• Field of Search: 345/174, 345/173
• 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 3/04182 Filtering of noise external to the device and not generated by digitiser components
• 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 method is provided. A first voltage is applied to a first set of column electrodes within a touch panel during a first interval, and a second voltage is applied to a second set of column electrodes within the touch panel during the first interval. The first and second sets of electrodes are adjacent to one another, and the second voltage has the opposite polarity of the first voltage. During the first interval, a first measurement signal is received from a set of row electrodes in the touch panel, and the first measurement signal is integrated to generate a first integrated signal. The first voltage is applied to the second set of column electrodes within the touch panel during a second interval, and the second voltage is applied to the first set of column electrodes within the touch panel during the second interval. During the second interval, a second measurement signal is received from the set of row electrodes in the touch panel, and the second measurement signal is integrated to generate a second integrated signal. Then, the first and second integrated signals are combined to generate an output signal.

Claims

1. An apparatus comprising:

an interface having a first set of terminals and a second set of terminals,

wherein the first and second sets of terminals are configured to be coupled to a touch panel,

wherein the interface provides a first excitation voltage to a first terminal from the first set of terminals during a first portion of a scan period, and

wherein the interface provides a second excitation voltage to a second terminal from the first set of terminals during the first portion of the scan period, and

wherein the interface provides the first excitation voltage to the second terminal from the first set of terminals during a second portion of the scan period, and

wherein the interface provides the second excitation voltage to the first terminal from the first set of terminals during the second portion of the scan period, and

wherein the second excitation voltage has the opposite polarity of the first excitation voltage, and wherein the interface receives first and second measurement signals from a first terminal from the second set of terminals during the first and second portions of the scan period, respectively; and

an analog front end (AFE) that is coupled to the interface so as to receive the first and second measurement signals, wherein

the AFE integrates the first and second measurement signal to generate first and second integrated signals, and

wherein the AFE combines first and second integrated signals to generate an output signal.

2. The apparatus of claim 1, wherein the interface further comprises:

a multiplexer that is coupled to each terminal from the second set of terminals and that is coupled to the AFE; and

an exciter that is coupled to each terminal from the second set terminals.

3. The apparatus of claim 2, wherein the AFE further comprises:

an integrator that is coupled to the multiplexer;

an analog-to-digital converter (ADC) that is coupled to the integrator; and

a summing circuit that is coupled to the ADC.

4. The apparatus of claim 3, wherein the integrator further comprises:

an amplifier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal of the amplifier receives a reference voltage, and wherein the following input terminal of the amplifier is coupled to the multiplexer, and wherein the output terminal of the amplifier is coupled to the ADC;

a capacitor that is coupled between the second input terminal of the amplifier and the output terminal of the amplifier; and

a switch that is coupled between the second input terminal of the amplifier and the output terminal of the amplifier, wherein the switch is controlled by a sample signal.

5. The apparatus of claim 4, wherein the summing circuit further comprises:

a delay circuit that is coupled to the ADC; and

an adder that is coupled to the ADC and delay circuit.

6. The apparatus of claim 5, wherein the touch panel controller further comprises:

a digital front end (DFE) that is coupled to the AFE; and

control logic that is coupled to the DFE and AFE.

7. An apparatus comprising:

a touch panel having;

a plurality of column sensor electrodes arranged in a plurality of columns;

a first set of strip electrodes, wherein each strip electrode from the first set of strip electrodes is coupled to each column electrode within at least one of the plurality of columns;

a plurality of row sensor electrodes arranged in a plurality of rows; and

a second set of strip electrodes, wherein each strip electrode from the second set of strip electrodes is coupled to each row electrode within at least one of the plurality of rows; and

a touch panel controller having;

an interface that is coupled to each strip electrode from the first and second sets of strip electrodes, wherein the interface provides a first excitation voltage to a first strip electrode from the first set of strip electrodes during a first portion of a scan period, and wherein the interface provides a second excitation voltage to a second strip electrode from the first set of strip electrodes during the first portion of the scan period, and wherein the interface provides the first excitation voltage to the first strip electrode from the first set of strip electrodes during a second portion of the scan period, and wherein the interface provides the second excitation voltage to the second strip electrode from the first set of strip electrodes during the second portion of the scan period, and wherein the second excitation voltage has the opposite polarity of the first excitation voltage, and wherein the interface receives first and second measurement signals from a first strip electrode from the second set of strip electrodes during the first and second portions of the scan period, respectively; and

an analog front end (AFE) that is coupled to the interface so as to receive the first and second measurement signals, wherein the AFE integrates the first and second measurement signal to generate first and second integrated signals, and wherein the AFE combines first and second integrated signals to generate an output signal.

8. The apparatus of claim 7, wherein the interface further comprises:

a multiplexer that is coupled to each strip electrode from the second set of strip electrodes and that is coupled to the AFE; and

an exciter that is coupled to each strip electrode from the second set strip electrodes.

9. The apparatus of claim 8, wherein the AFE further comprises:

an integrator that is coupled to the multiplexer;

an analog-to-digital converter (ADC) that is coupled to the integrator; and

a summing circuit that is coupled to the ADC.

10. The apparatus of claim 9, wherein the integrator further comprises:

an amplifier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal of the amplifier receives a reference voltage, and wherein the second input terminal of the amplifier is coupled to the multiplexer, and wherein the output terminal of the amplifier is coupled to the ADC;

a capacitor that is coupled between the second input terminal of the amplifier and the output terminal of the amplifier; and

a switch that is coupled between the second input terminal of the amplifier and the output terminal of the amplifier, wherein the switch is controlled by a sample signal.

11. The apparatus of claim 10, wherein the summing circuit further comprises:

a delay circuit that is coupled to the ADC; and

an adder that is coupled to the ADC and delay circuit.

12. The apparatus of claim 11, wherein the touch panel controller further comprises:

a digital front end (DFE) that is coupled to the AFE; and

control logic that is coupled to the DFE and AFE.

13. A method comprising:

applying a first voltage to a first set of column electrodes within a touch panel during a first interval;

applying a second voltage to a second sets of column electrodes within the touch panel during the first interval, wherein the first and second sets of electrodes are adjacent to one another, and wherein the second voltage has the opposite polarity of the first voltage;

receiving a first measurement signal from a set of row electrodes in the touch panel during the first interval;

integrating the first measurement signal to generate a first integrated signal;

applying the first voltage to the second set of column electrodes within the touch panel during a second interval;

applying the second voltage to the first set of column electrodes within the touch panel during the second interval;

receiving a second measurement signal from the set of row electrodes in the touch panel during the second interval;

integrating the second measurement signal to generate a second integrated signal; and

combining the first and second integrated signals to generate an output signal.

14. The method of claim 13, wherein the step of combining further comprises:

digitizing the first and second integrated signals to generate first and second digitized signals;

delaying the first digitized signal; and

adding the first and second digitized signals together.

15. The method of claim 14, wherein the method further comprises activating an integrator for a first sample period during the first interval and for a second sample period during the second interval.

16. The method of claim 15, wherein the method further comprises:

repeating for each pair of adjacent sets of column electrodes and each set of column electrodes the steps of applying a first voltage during the first interval, applying the second voltage during the first interval, receiving the first measurement signal, integrating the first measurement signal, applying the first voltage during the second interval, applying the second voltage during the second interval, receiving the second measurement signal, integrating the second measurement, and combining the first and second integrated signals; and

generating a capacitance profile for the touch panel.

17. The method of claim 16, wherein the method further comprises:

scanning the touch panel by repeating for each pair of adjacent sets of column electrodes and each set of column electrodes the steps of applying a first voltage during the first interval, applying the second voltage during the first interval, receiving the first measurement signal, integrating the first measurement signal, applying the first voltage during the second interval, applying the second voltage during the second interval, receiving the second measurement signal, integrating the second measurement, and combining the first and second integrated signals; and

determining a location of a touch event based at least in part on the step of scanning and the capacitance profile.

18. An apparatus comprising:

means for applying a first voltage to a first set of column electrodes within a touch panel during a first interval;

means for applying a second voltage to a second sets of column electrodes within the touch panel during the first interval, wherein the first and second sets of electrodes are adjacent to one another, and wherein the second voltage has the opposite polarity of the first voltage;

means for receiving a first measurement signal from a set of row electrodes in the touch panel during the first interval;

means for integrating the first measurement signal to generate a first integrated signal;

means for applying the first voltage to the second set of column electrodes within the touch panel during a second interval;

means for applying the second voltage to the first set of column electrodes within the touch panel during the second interval;

means for receiving a second measurement signal from the set of row electrodes in the touch panel during the second interval;

means for integrating the second measurement signal to generate a second integrated signal; and

means for combining the first and second integrated signals to generate an output signal.

19. The apparatus of claim 18, wherein the means for combining further comprises:

means for digitizing the first and second integrated signals to generate first and second digitized signals;

means for delaying the first digitized signal; and

means for adding the first and second digitized signals together.

20. The apparatus of claim 18, wherein the apparatus further comprises means for activating an integrator for a first sample period during the first interval and for a second sample period during the second interval.