BACKGROUND NOISE MEASUREMENT AND FREQUENCY SELECTION IN TOUCH PANEL SENSOR SYSTEMS

• US 20120217978A1
• Filed: 02/22/2012
• Published: 08/30/2012
• Est. Priority Date: 02/25/2011
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Maxim Integrated Products, Inc. (Analog Devices, Inc.)
• Inventors: Shen, Guozhong, Erdogan, Ozan E., Mahmud, Syed, Knox, Kenneth W.
• Granted Patent: US 8,860,432 B2
• Time in Patent Office: Days
• US Class Current: 324/601
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means

Abstract

A touch panel sensor system that can dynamically measure noise and automatically switch to a frequency with minimal noise is described. The touch panel sensor system includes a sensor configured to detect a change in capacitance associated with a touch upon a touch panel. The system also includes a drive module configured to generate a drive signal having a first waveform characteristic (e.g., signal having a periodic waveform characteristic) during a first phase (e.g., sensor phase) and a second drive signal having a second waveform characteristic (e.g., constant voltage signal) during a second phase (e.g., noise detection phase). The first and second drive signals are configured to drive the sensor. The system also includes a measuring module coupled to the sensor that is configured to measure noise having the first waveform characteristic (e.g., periodic waveform characteristic) during the second phase.

Claims

1. A system comprising:

a sensor configured to detect a change in capacitance associated with a touch upon a touch panel;

a drive module coupled to the sensor, the drive module configured to generate a first drive signal having a first waveform characteristic during a first phase and a second drive signal having a second waveform characteristic different from the first waveform characteristic during a second phase; and

a measuring module coupled to the sensor, the measuring module configured to measure noise having the first waveform characteristic during the second phase.

2. The system as recited in claim 1, wherein the first drive signal comprises a periodic signal and the second drive signal comprises a constant voltage signal.

3. The system as recited in claim 1, wherein the measuring module comprises an operational amplifier having an integrating capacitor disposed between a non-inverting input and an output of the operational amplifier and a frequency/phase selection module coupled to the output of the operation amplifier, the frequency/phase selection module configured to modify a signal at the measuring module.

4. The system as recited in claim 3, wherein the measuring module further comprises an integrator coupled to the frequency/phase selection module.

5. The system as recited in claim 1, further comprising a control module coupled to the drive module, the control module configured to cause the drive module to generate the first drive signal during the first phase and to generate the second drive signal during the second phase.

6. The system as recited in claim 1, wherein the driver module comprises a digital-to-analog converter coupled to a buffer.

7. The system as recited in claim 1, wherein the capacitive sensor comprises a resistor serially coupled to a mutual capacitor.

8. A system comprising:

a sensor configured to detect a change in capacitance associated with a touch upon a touch panel;

a drive module coupled to the sensor, the drive module configured to generate a first drive signal having a first waveform characteristic during a first phase and a second drive signal having a second waveform characteristic different from the first waveform characteristic during a second phase, the first drive signal and the second drive signal for driving the sensor;

an offset cancellation module coupled to the sensor, the offset cancellation module configured to furnish an adjustable capacitive value for the sensor;

an offset cancellation drive module coupled to the offset cancellation module, the offset cancellation drive module configured to generate a first offset cancellation drive signal having the first waveform characteristic during the first phase and a second offset cancellation drive signal having the second waveform characteristic during the second phase, the first offset cancellation drive signal and the second offset cancellation drive signal for driving the offset cancellation module; and

a measuring module coupled to the sensor and the offset cancellation module, the measuring module configured to detect noise having the first waveform characteristic during the second phase, the noise associated with at least one of the sensor or the offset cancellation module.

9. The system as recited in claim 8, wherein the first drive signal and the first offset cancellation drive signal comprise a periodic signal, and wherein the second drive signal and the second offset cancellation drive signal comprise a constant voltage signal.

10. The system as recited in claim 8, wherein the measuring module comprises an operational amplifier having an integrating capacitor disposed between a non-inverting input and an output of the operational amplifier and a frequency/phase selection module coupled to the output of the operation amplifier, the frequency/phase selection module configured to modify a signal at the measuring module.

11. The system as recited in claim 10, wherein the measuring module further comprises an integrator coupled to the frequency/phase selection module.

12. The system as recited in claim 8, further comprising a control module coupled to the drive module and the offset drive module, the control module configured to cause the drive module to generate the first drive signal during the first phase and to generate the second drive signal during the second phase, the control module further configured to cause the offset cancellation drive module to generate the first offset cancellation drive signal during the first phase and to generate the second offset cancellation drive signal during the second phase.

13. The system as recited in claim 8, wherein at least one of the drive module or the offset cancellation drive module comprise a digital-to-analog converter coupled to a buffer.

14. The system as recited in claim 8, wherein the capacitive sensor is a resistor serially coupled to a mutual capacitor.

15. A method comprising:

initiating a first noise measurement comprising a first waveform characteristic at a measuring module, the first noise measurement associated with a sensor configured to detect a change in capacitance associated with a touch upon a touch panel;

determining whether the first noise measurement exceeds a predetermined threshold; and

initiating a second noise measurement comprising a second waveform characteristic when the first noise measurement exceeds the predetermined threshold, the second waveform characteristic different from the first waveform characteristic, the second noise measurement associated with the sensor.

16. The method as recited in claim 15, further comprising determining whether the second noise measurement exceeds a predetermined threshold;

and initiating a third noise measurement comprising a third waveform characteristic during the first phase when the second noise measurement exceeds the predetermined threshold, the third waveform characteristic different from the second waveform characteristic, the third noise measurement associated with the sensor.

17. The method as recited in claim 16, further comprising determining whether the third noise measurement exceeds a predetermined threshold;

and identifying a frequency associated with at least one of the first waveform characteristic, the second waveform characteristic, or the third waveform characteristic having the least noise measurement of the first noise measurement, the second noise measurement, and the third noise measurement.

18. The method as recited in claim 17, detecting a change in capacitance associated with the touch upon the touch panel, wherein the detection of the change in capacitance is associated with the identified frequency.

19. The method of claim 15, wherein the measuring module comprises an operational amplifier having an integrating capacitor disposed between a non-inverting input and an output of the operational amplifier and a frequency/phase selection module coupled to the output of the operation amplifier.

20. The method of claim 19, wherein the measuring module further comprises an integrator coupled to the frequency/phase selection module.