Method and apparatus to improve noise immunity of a touch sense array

• US 9,645,690 B1
• Filed: 07/28/2015
• Issued: 05/09/2017
• Est. Priority Date: 04/19/2011
• Status: Active Grant

• Current Assignee: Parade Technologies, Ltd.
• Original Assignee: Parade Technologies, Ltd.
• Inventors: Konovalov, Anton, Ogirko, Roman, Pirogov, Oleksandr, Sharamaga, Roman, Maharyta, Andriy, Kremin, Viktor, Yarosh, Andriy
• Primary Examiner(s): LEE, NICHOLAS J
• Application Number:
  US14/811,174
• Time in Patent Office: 651 Days
• Field of Search: None
• 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 method for improving noise immunity of capacitive sensing circuit associated with a touch sense array is disclosed. The capacitive sensing circuit receives a response signal from a touch sense array. The capacitive sensing circuit measures a noise component of the response signal. When a level of noise of the noise component within a passband of the capacitive sensing circuit is greater than a threshold, the capacitive sensing circuit changes at least one parameter of capacitive sensing circuit to move the passband substantially outside the frequency spectrum of the noise component.

Claims

1. A method, performed at a capacitive sensing circuit for a touch sense array, comprising:

scanning the touch sense array using a first sensing frequency passband;

during a noise detection state in which transmit TX signals are absent on TX electrodes;

receiving a response signal on an RX channel;

measuring a noise component of the response signal; and

when a level of noise of the noise component within the first sensing frequency passband is greater than a threshold, selecting a second sensing frequency passband having a lower level of noise from among a plurality of alternative sensing frequency passbands; and

scanning the touch sense array using the second sensing frequency passband.

2. The method of claim 1, further comprising while selecting the second sensing frequency passband, changing at least one parameter of the capacitance sensing circuit.

3. The method of claim 1, wherein selecting the second sensing frequency passband comprises forcing synchronization of the second sensing frequency passband to cause the frequency spectrum of the noise component to substantially match a passband of the capacitive sensing circuit.

4. The method of claim 2, wherein changing at least one parameter includes at least one of changing an integration time, changing a driving signal, changing a number of subconversions per conversion cycle, and changing a number of TX cycles applied in an individual subconversion.

5. The method of claim 1, wherein determining whether the level of noise is greater than the threshold comprises analyzing raw counts levels during several conversions around a touch area of a conductive object proximate to the touch sense array.

6. The method of claim 1, wherein determining whether the level of noise is greater than the threshold comprises analyzing touch position jitter history of a touch position of a conductive object proximate to the touch sense array.

7. The method of claim 1, wherein determining whether the level of noise is greater than the threshold comprises measuring a level of noise when all receive (RX) electrodes are tied together in a single channel.

8. The method of claim 7, further comprising alternating between listening to the level of noise and performing a full panel scan of the touch sense array.

9. The method of claim 7, further comprising interleaving between listening to the level of noise and performing a partial scan of the touch sense array.

10. A circuit comprising:

a capacitive sensing circuit for a touch sense array, wherein the capacitive sensing circuit is configured to;

scan the touch sense array using a first sensing frequency passband;

during a noise detection state in which transmit TX signals are absent on TX electrodes;

receive a response signal on an RX channel;

measure a noise component of the response signal; and

when a level of noise of the noise component within the first sensing frequency passband is greater than a threshold, select a second sensing frequency passband having a lower level of noise from among a plurality of alternative sensing frequency passbands; and

scan the touch sense array using the second sensing frequency passband.

11. The circuit of claim 10, wherein the capacitive sensing circuit comprises a circuit for forcing synchronization of a sensing frequency passband to cause the frequency spectrum of the noise component to substantially match the passband of the capacitive sensing circuit.

12. The circuit of claim 11, wherein the circuit for forcing synchronization of the sensing frequency passband comprises a clocking circuit.

13. The circuit of claim 12, wherein the capacitive sensing circuit further comprises a pair of current sources each coupled to the clocking circuit and a one shot coupled between the clocking circuit and one of the current sources to determine whether the level of noise is above the threshold.

14. The circuit of claim 12, wherein the capacitive sensing circuit further comprises a current source coupled to the clocking circuit and a delay circuit coupled between the clocking circuit and the current source to determine whether the level of noise is above the threshold.

15. A processing device, comprising:

a capacitive sensing circuit for a touch sense array, wherein the capacitive sensing circuit is configured to;

scan the touch sense array using a first sensing frequency passband;

during a noise detection state in which transmit TX signals are absent on TX electrodes;

receive a response signal on an RX channel;

measure a noise component of the response signal; and

when a level of noise of the noise component within the first sensing frequency passband is greater than a threshold, select a second sensing frequency passband having a lower level of noise from among a plurality of alternative sensing frequency passbands; and

scan the touch sense array using the second sensing frequency passband; and

processing logic coupled to the capacitive sensing circuit and configured to detect a conductive object proximate to the touch sense array using the response signal.

16. The processing device of claim 15, wherein the processing device further comprises a circuit for forcing synchronization of a sensing frequency passband to cause a frequency spectrum of the noise component to substantially match the passband of the capacitive sensing circuit.

17. The processing device of claim 15, wherein the processing logic is configured to interleave between listening to the level of noise and performing a partial panel scan.