NOISE FILTERING DEVICES, SYSTEMS AND METHODS FOR CAPACITANCE SENSING DEVICES

• US 20120200524A1
• Filed: 09/28/2011
• Published: 08/09/2012
• Est. Priority Date: 02/07/2011
• Status: Active Grant

• Current Assignee: Parade Technologies, Ltd.
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Kremin, Victor, Maharyta, Andriy, Boychuk, Yuriy, Karpin, Oleksandr, Grivna, Edward, Vallis, Darrin, Konovalov, Anton, Musijchuk, Ihor, Klein, Hans
• Granted Patent: US 9,128,570 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G01R 29/26 Measuring noise figure; Measuring signal-to-noise ratio
• CPC Class Codes: G01R 35/005 Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence
• 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
• CPC Class Codes: H04B 1/0475 with means for limiting noise, interference or distortion H04B1/0483 takes precedence

Abstract

A capacitance sensing system can filter noise that presents in a subset of electrodes in the proximity of a sense object (i.e., finger). A capacitance sensing system can include a sense network comprising a plurality of electrodes for generating sense values; a noise listening circuit configured to detect noise on a plurality of the electrodes; and a filtering circuit that enables a filtering for localized noise events when detected noise values are above one level, and disables the filtering for localized noise events when detected noise values are below the one level.

Claims

1. A capacitance sensing system, comprising:

a sense network comprising a plurality of electrodes for generating sense values;

a noise listening circuit configured to detect noise on a plurality of the electrodes; and

a filtering circuit that enables a filtering for localized noise events when detected noise values are above one level, and disables the filtering for localized noise events when detected noise values are below the one level.

2. The capacitance sensing system claim 1, wherein:

the filtering circuit includes a median filter that is enabled when detected noise values are above one level, and disabled when detected noise values are below the one level.

3. The capacitance sensing system claim 1, further including:

a mutual capacitance sensing circuit that senses a mutual capacitance between at least one transmit (TX) electrode and individual receive (RX) electrodes; and

the noise listening circuit is configured to sense noise on at least multiple RX electrodes.

4. The capacitance sensing system claim 1, further including:

a mutual capacitance sensing circuit that senses a mutual capacitance between at least one transmit (TX) electrode and individual receive (RX) electrodes; and

the noise listening circuit is configured to sense noise on both TX and RX electrodes simultaneously.

5. The capacitance sensing system claim 1, wherein:

a mutual capacitance sensing circuit that senses capacitance values with a first sense time when detected noise values are below one level, and senses capacitance values with a second sense time, greater than the first sense time, when detected noise values are above the one level.

6. The capacitance sensing system claim 1, further including:

switching circuits configurable to couple at least one device connection to a transmit signal and sequentially couple multiple device connections to the capacitance sensing circuit in a sense mode, and configurable to couple multiple device connections simultaneously to the noise listening circuit in a noise listening mode.

7. The capacitance sensing system of claim 1, wherein:

the noise listening circuit and filtering circuit comprise a processor and corresponding first instructions stored in an instruction memory.

8. The capacitance sensing system of claim 1, further including:

an alarm circuit that generates an alarm condition when detected noise values are above a second level, corresponding to greater noise than the first level.

9. The capacitance sensing system of claim 1, further including:

the noise detected by the noise listening circuit is coupled to the sense network by an object being sensed.

10. The capacitance sensing system of claim 1, further including:

a display;

the sense network overlays the display; and

the noise listening circuit is configured to detect noise from a charging device coupled to the capacitance sensing system.

11. A method, comprising:

detecting noise with a plurality of capacitance sense electrodes;

if noise is determined to be below a first threshold, scanning the electrodes for capacitance sense values a first number of times, while disabling a local noise filter for sensed values; and

if noise is determined to be above the first threshold, scanning the electrodes for capacitance sense values a second number of times, greater than the first number of times, and enabling the local noise filter for sensed values.

12. The method of claim 11, wherein:

detecting noise with the plurality of electrodes includes connecting a plurality of electrodes simultaneously to a capacitance sensing circuit; and

scanning the electrodes includes sequentially connecting one of the electrodes to the capacitance sensing circuit.

13. The method of claim 11, wherein:

detecting noise with the plurality of electrodes includes

while scanning electrodes to acquire a set of digital noise detect values, filtering a previously acquired set of noise detect values for common noise, and determining if the filtered noise detect values exceed the first threshold.

14. The method of claim 11, wherein:

if noise is determined to be above the first threshold,

determining a main value for an electrode based on its sensed capacitance versus other sensed capacitances for a group of electrodes;

scaling values from electrodes physically adjacent to the main value prior to applying the local noise filter.

15. The method of claim 11, further including:

disabling the detecting of noise if a charging device is not connected to a device.

16. The method of claim 11, wherein:

the local noise filter comprises a median filter.

17. A capacitance sensing system, comprising:

a touchscreen;

a listening circuit configure to detect at least one noise source;

a capacitance sensing circuit coupled to the touchscreen; and

a processor configured by instructions to execute at least one of a plurality of operations selected from;

varying a scanning time of the touchscreen apparatus, applying a local noise filter to an output of the capacitance sensing circuit, and applying a common mode filter to the output of the capacitance sensing circuit.

18. The capacitance sensing system of claim 17, wherein:

the processor is configured by instructions to vary a scanning time in response to a noise level value generated by the listening circuit.

19. The capacitance sensing system of claim 18, wherein:

the listening circuit determines if noise from the at least one noise source exceeds at least a first threshold; and

the processor is configured by instructions to apply the local noise filter in response to a noise level exceeding the first threshold, and to not apply the local noise filter in response to the noise level being below the first threshold.

20. The capacitance sensing system of claim 18, wherein:

the local noise filter comprises a median filter.