SMART SCANNING FOR A CAPACITIVE SENSE ARRAY

• US 20120050216A1
• Filed: 02/25/2011
• Published: 03/01/2012
• Est. Priority Date: 08/24/2010
• Status: Active Grant

• Current Assignee: Parade Technologies, Ltd.
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Kremin, Victor, Pirogov, Oleksandr, Ryshtun, Andriy
• Granted Patent: US 9,013,441 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G06F 3/041661 using detection at multiple resolutions, e.g. coarse and fine scanning; using detection within a limited area, e.g. object tracking window
• CPC Class Codes: G06F 3/044 by capacitive means
• 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 and apparatus scan a plurality of scan groups in a capacitive sense array to generate signals corresponding to a mutual capacitance between the electrodes. Each of the plurality of scan groups is formed from a subset of the plurality of electrodes. A processing device identifies a scan group where the generated signal is affected by a presence of a conductive object. The processing device individually scans the subset of the plurality of sense elements in the identified scan group to determine a location of the conductive object.

Claims

1. A method, comprising:

scanning, by a processing device, a plurality of scan groups in a capacitive sense array to generate signals corresponding to a mutual capacitance at sense elements of the capacitive sense array, wherein each of the plurality of scan groups comprises a plurality of sense elements;

identifying a scan group where the generated signal is affected by a presence of a conductive object; and

individually scanning the plurality of sense elements in the identified scan group to determine a location of the conductive object.

2. The method of claim 1, wherein scanning the plurality of scan groups comprises:

driving one or more transmit electrodes with a transmit signal; and

measuring a receive signal from a number of receive electrodes that form each of the plurality of scan groups.

3. The method of claim 2, wherein a number of receive electrodes that form each of the plurality of scan groups is based on a level of charge that the receive electrodes can handle.

4. The method of claim 1, further comprising:

measuring a baseline capacitance value for each of the plurality of scan groups in the capacitive sense array; and

measuring a baseline capacitance value for each of the sense elements in the capacitive sense array.

5. The method of claim 4, wherein identifying a scan group comprises:

comparing a value corresponding to the mutual capacitance for the scan group to the baseline capacitance value for the scan group to determine a differential value; and

determining if the differential value is greater than a touch threshold value.

6. The method of claim 1, wherein individually scanning the plurality of sense elements comprises:

sequentially driving one or more transmit electrodes in the identified scan group with a transmit signal; and

measuring a receive signal from each of a plurality of receive electrodes that form the identified scan group.

7. The method of claim 1, wherein a first scan group of the plurality of scan groups overlaps a second adjacent scan group by at least one electrode.

8. An apparatus, comprising:

a capacitive sense array having a plurality of sense elements; and

a processing device coupled to the capacitive sense array, the processing device configured to;

scan a plurality of scan groups in the capacitive sense array to generate signals corresponding to a mutual capacitance at the sense elements, wherein each of the plurality of scan groups comprises a subset of the plurality of sense elements;

identify a scan group where the generated signal is affected by a presence of a conductive object; and

individually scan the subset of the plurality of sense elements in the identified scan group to determine a location of the conductive object.

9. The apparatus of claim 8, wherein when the processing device scans the plurality of scan groups, the processing device is configured to:

drive one or more transmit electrodes with a transmit signal; and

measure a receive signal from a number of receive electrodes that form each of the plurality of scan groups.

10. The apparatus of claim 9, wherein a number of receive electrodes that form each of the plurality of scan groups is based on a level of charge that the receive electrodes can handle.

11. The apparatus of claim 8, wherein the processing device is further configured to:

measure a baseline capacitance value for each of the plurality of scan groups in the capacitive sense array; and

measure a baseline capacitance value for each of the sense elements in the capacitive sense array.

12. The apparatus of claim 11, wherein in order to determine if a conductive object is present, the processing device is configured to:

compare a value corresponding to the mutual capacitance for a scan group to the baseline capacitance value for the scan group to determine a differential value; and

determine if the differential value is greater than a touch threshold value.

13. The apparatus of claim 8, wherein when the processing device individually scans the subset of the plurality of sense elements, the processing device is configured to:

sequentially drive one or more transmit electrodes in the identified scan group with a transmit signal; and

measure a receive signal from each of a plurality of receive electrodes that form the identified scan group.

14. The apparatus of claim 8, wherein a first scan group of the plurality of scan groups overlaps a second adjacent scan group by at least one electrode.

15. An apparatus comprising:

a touch-sensor device, the touch-sensor device comprising an array of capacitive sense elements, the array comprising a plurality of transmit electrodes and a plurality of receive electrodes;

a transmit selection circuit coupled to the touch-sensor device, the transmit selection circuit to selectively apply a transmit signal to one or more of the transmit electrodes;

a receive selection circuit coupled to the touch-sensor device, the receive selection circuit to selectively measure a signal from one or more of the receive electrodes, wherein the measured signal corresponds to a mutual capacitance value between a transmit electrode and a receive electrode; and

a processing device coupled to the touch-sensor device, the processing device configured to;

scan a scan group of the capacitive sense array to determine if a conductive object is present on the touch-sensor device in an area corresponding to the scan group, wherein the scan group comprises at least one transmit electrode and a plurality of receive electrodes; and

if a conductive object is present on the touch-sensor device in the area corresponding to the scan group, individually scan the plurality of sense elements in the scan group to determine a location of the conductive object.

16. The apparatus of claim 15, wherein when the processing device scans the scan group, the processing device is configured to:

apply the transmit signal to the at least one transmit electrode of the scan group through the transmit selection circuit; and

measure a single signal from all of the receive electrodes in the scan group through the receive selection circuit.

17. The apparatus of claim 15, wherein a number of receive electrodes that form the scan group is based on a level of charge that the receive electrodes can handle.

18. The apparatus of claim 15, wherein when the processing device individually scans the plurality of sense elements in the scan group, the processing device is configured to:

sequentially apply the transmit signal to each transmit electrode of the scan group through the transmit selection circuit; and

measure a signal from each of the sense elements in the scan group through the receive selection circuit.

19. The apparatus of claim 15, wherein when the processing device determines the location of the conductive object, the processing device is configured to:

determine a coordinate value corresponding to the location of the conductive object; and

provide the coordinate value to a host machine.

20. The apparatus of claim 15, wherein the capacitive sense array comprises and plurality of scan groups and wherein a first scan group of the plurality of scan groups overlaps a second adjacent scan group by at least one sense element.