Methods and systems for detecting noise in a position sensor using minor shifts in sensing frequency

• US 20080040079A1
• Filed: 03/22/2006
• Published: 02/14/2008
• Est. Priority Date: 12/14/2004
• Status: Active Grant

• Current Assignee: Medical College of Wisconsin Incorporated, Synaptics Incorporated
• Original Assignee: Medical College of Wisconsin Incorporated
• Inventors: Hargreaves, Kirk
• Granted Patent: US 7,451,050 B2
• Time in Patent Office: Days
• US Class Current: 702/191
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment

Abstract

Methods, systems and devices are described for detecting noise in a touchpad or other sensor that produces an output in response to a stimulus that is applied at or near a sensing region. According to various embodiments, a carrier signal is applied to the sensing region at two or more frequencies to thereby produce an output from the sensing region at each frequency. Each of the outputs is demodulated and filtered by a demodulation filter having a demodulation filter bandwidth. The various frequencies applied to the carrier signal are selected such that a difference between the frequencies is less than the demodulation filter bandwidth. At least some of the effects of the stimulus are removed from the outputs produced by the various carrier frequencies to produce two or more filtered outputs. The filtered outputs are then added, combined or otherwise processed to detect noise contained therein. If noise contained in one or more of the filtered outputs reaches an unacceptable level, the carrier signal may be shifted to a new sensing frequency for subsequent operation of the sensor.

Claims

1. A method of detecting noise in an output provided by a sensor configured to modulate a carrier signal in response to the proximity of a stimulus, wherein the output is synchronously demodulated with the carrier signal and filtered by a demodulation filter having a demodulation filter bandwidth, the method comprising the steps of:

sequentially applying the carrier signal to the sensor at a plurality of different frequencies comprising at least a first frequency and a second frequency to thereby produce at least a first output and a second output, respectively, wherein a difference between the first and second frequencies is less than the demodulation filter bandwidth;

filtering an effect produced by the stimulus from at least the first and second outputs to thereby produce at least one filtered output; and

determining noise contained within the at least one filtered output.

2. The method of claim 1, wherein the at least one filtered output is based on a combination of at least the first and second outputs.

3. The method of claim 1, wherein the at least one filtered output is based on a combination of at least the first filtered output and a second filtered output.

4. The method of claim 1, further comprising the step of subsequently avoiding the frequency of the carrier signal if the at least one filtered output is determined to be noisy.

5. The method of claim 4, wherein the noise determining step comprises comparing at least one of the first and second filtered outputs to a threshold.

6. The method of claim 1, further comprising the step of repeating the applying, filtering and determining steps.

7. The method of claim 6, wherein the applying step and the determining step are each repeated for a differing number of repetitions.

8. The method of claim 6, wherein the applying step and the determining step are both repeated for an equal number of repetitions.

9. A position sensor configured to execute the method of claim 1.

10. A processor configured to execute the method of claim 1.

11. A touchpad configured to execute the method of claim 1.

12. A digital storage medium having computer-executable instructions stored thereon, wherein the instructions are configured to execute the method of claim 1.

13. An apparatus configured to detect noise in an output of a capacitive sensor, wherein the capacitive sensor is configured to respond to a stimulus provided in proximity to a sensing region, wherein the output is filtered by a demodulation filter having a demodulation filter bandwidth, the apparatus comprising:

means for directing the sequential application of the carrier signal to the sensor at a plurality of different frequencies comprising at least a first frequency and a second frequency to thereby produce at least a first output and a second output, wherein a difference between the first and second frequencies is less than the demodulation filter bandwidth;

means for filtering an effect produced by the stimulus from at least the first and second outputs to thereby produce at least one filtered output; and

means for determining noise contained within the least one filtered output.

14. The apparatus of claim 13, wherein the means for directing comprises means for continuously varying the frequency of the carrier signal.

16. A position sensor comprising the apparatus of claim 13.

17. A touchpad comprising the apparatus of claim 13.

15. An input device comprising the apparatus of 13.

18. An input device for detecting a user input, the input device comprising:

a sensor configured for detecting the user input and for providing an output in response thereto;

a signal generator configured to produce a carrier signal having a sensing frequency;

a demodulator configured for demodulating the output of the sensor with the carrier signal;

a demodulation filter associated with the demodulator and having a demodulation filter bandwidth; and

a processor in communication with the signal generator and the demodulation filter, wherein the processor is configured;

to communicate with the signal generator to direct sequential application of the carrier signal to the sensing region at a plurality of different frequencies comprising at least a first frequency and a second frequency to thereby produce at least a first output and a second output, respectively, wherein a difference between the first and second frequencies is less than the demodulation filter bandwidth;

to filter at least some of an effect produced by the stimulus from at least the first and second outputs to thereby produce at least one filtered output; and

to determine noise contained within the at least one filtered output.

19. The input device of claim 18, wherein the input device is a position sensing device.

20. The input device of claim 18, wherein the sensing region is defined by a capacitive touch sensor.

21. A method of detecting noise in an output provided by a sensor configured to modulate a carrier signal in response to the proximity of a stimulus, wherein the output is synchronously demodulated with the carrier signal and filtered by a demodulation filter having a demodulation filter bandwidth, the method comprising the steps of:

adjusting a frequency of a carrier signal across a plurality of different frequencies on a substantially continuous basis, wherein the plurality of different frequencies comprises at least a first frequency and a second frequency that differ by an amount that is less than the demodulation filter bandwidth;

applying the carrier signal to the sensor at each of the plurality of different frequencies to thereby produce sensor outputs;

filtering an effect produced by the stimulus from the sensor outputs to thereby produce at least one filtered output; and

determining noise contained within the at least one filtered output.

22. The method of claim 21, further comprising the step of subsequently avoiding the frequency of the carrier signal if the at least one filtered output is determined to be noisy.

23. The method of claim 21, wherein the noise determining step comprises comparing the at least one filtered output to a threshold.

24. A position sensor configured to execute the method of claim 21.

25. A processor configured to execute the method of claim 21.

26. A touchpad configured to execute the method of claim 21.

27. A digital storage medium having computer-executable instructions stored thereon, wherein the instructions are configured to execute the method of claim 21.