Targeted transcapacitance sensing for a matrix sensor

1. An input device comprising a display device having an integrated capacitive sensing device, the input device comprising:

a plurality of sensor electrodes arranged in a matrix, each sensor electrode comprising one or more common electrodes that are configured for both touch sensing and display updating; and

a processing system configured to be coupled to the plurality of sensor electrodes, wherein the processing system is configured to:

modulate each of the plurality of sensor electrodes to determine changes in absolute capacitance;

select a subset of the plurality of sensor electrodes based on the determined changes in absolute capacitance, wherein the subset is less than the plurality of sensor electrodes and includes a first sensor electrode and a second sensor electrode;

drive the first sensor electrode and receive with the second sensor electrode to determine changes in transcapacitance between the first sensor electrode and the second sensor electrode; and

determine positional information for an input object in a sensing region of the capacitive sensing device based on the changes in transcapacitance.

2. The input device of claim 1 , wherein each of the plurality of sensor electrodes has a common shape and size.

3. The input device of claim 1 , wherein driving the first sensor electrode and receiving with the second sensor electrode comprises driving a substantially constant voltage onto the first sensor electrode and modulating the second sensor electrode with a modulated signal, wherein an input object couples the substantially constant voltage with the modulated signal.

4. The input device of claim 1 , wherein driving the first sensor electrode and receiving with the second sensor electrode comprises driving a transmitter signal on the first sensor electrode and receiving a resulting signal with the second sensor electrode.

5. The input device of claim 1 , wherein the processing system is configured to drive the common electrodes with a display update signal for display updating, wherein the display update signal is based on a modulated reference signal having a first frequency; and

wherein driving the first sensor electrode and receiving with the second sensor electrode comprises driving the first sensor electrode with a transmitter signal and receiving a resulting signal with the second sensor electrode, wherein the transmitter signal comprises a second frequency that is substantially orthogonal to the first frequency.

6. The input device of claim 1 , wherein the processing system is further configured to modulate each of the plurality of sensor electrodes to determine changes in absolute capacitance in a time period, wherein the time period is selected from a group consisting of a time period that at least partially overlaps with display updating and a time period that is non-overlapping with display updating.

7. A processing system configured to drive a capacitive sensing device, the capacitive sensing device having a plurality of sensor electrodes arranged in a matrix, each sensor electrode comprising one or more common electrodes that are configured for both capacitive sensing and display updating, the processing system comprising:

a sensor module having sensor circuitry configured to modulate each of the plurality of sensor electrodes to determine changes in absolute capacitance, and configured to select a subset of the plurality of sensor electrodes based on determined changes in absolute capacitance, wherein the subset being less than the plurality of sensor electrodes and includes a first sensor electrode and a second sensor electrode;

wherein the sensor module is further configured to drive onto the first sensor electrode and receive with the second sensor electrode to determine changes in transcapacitance between the first sensor electrode and the second sensor electrode; and

a determination module configured to determine positional information for an input object in a sensing region of the capacitive sensing device based on the changes in transcapacitance.

8. The processing system of claim 7 , wherein driving the first sensor electrode and receiving with the second sensor electrode comprises driving a substantially constant voltage onto the first sensor electrode and modulate the second sensor electrode with a modulated signal, wherein an input object couples the substantially constant voltage with the modulated signal.

9. The processing system of claim 7 , driving the first sensor electrode and receiving with the second sensor electrode comprises driving a transmitter signal on the first sensor electrode and receive a resulting signal with the second sensor electrode.

10. The processing system of claim 7 , wherein the processing system is configured to drive the common electrodes with a display update signal for display updating, wherein the display update signal is based on a modulated reference signal having a first frequency; and

wherein driving the first sensor electrode and receiving with the second sensor electrode comprises driving the first sensor electrode with a transmitter signal and receiving a resulting signal with the second sensor electrode, wherein the transmitter signal comprises a second frequency that is substantially orthogonal to the first frequency.

11. The processing system of claim 7 , wherein the sensor circuitry of the sensor module further comprises:

a first plurality of analog front ends configured to modulate each of the plurality of sensor electrodes to determine changes in absolute capacitance; and

a second plurality of analog front ends configured to receive resulting signals with the second sensor electrode to determine changes in transcapacitance.

12. The processing system of claim 11 , wherein the sensor circuitry of the sensor module are configured to multiplex the second plurality of analog front ends to select the subset of the plurality of sensor electrodes.

13. The processing system of claim 7 , wherein the sensor module is further configured to:

select a second subset of the plurality of sensor electrodes based on the determined changes in absolute capacitance, wherein the second subset is less than the plurality of sensor electrodes and includes a third sensor electrode and a fourth sensor electrode; and

drive the third sensor electrode and receive with the fourth sensor electrode to determine changes in transcapacitance between the third sensor electrode and the fourth sensor electrode; and

wherein the determination module is further configured to determine positional information for a second input in the sensing region based on the changes in transcapacitance between the third sensor electrode and the fourth sensor electrode.

14. The processing system of claim 13 , wherein driving the first sensor electrode and receiving with the second sensor electrode and driving the third sensor electrode and receiving with the fourth sensor electrode occur simultaneously.

15. The processing system of claim 7 , further comprising:

a display driver module configured to couple to the common electrodes and configured to drive the common electrodes for display updating; and

an integrated controller comprising the sensor module and the display driver module.

16. The processing system of claim 7 , further comprising:

a display driver module configured to couple the common electrodes and configured to drive the common electrodes for display updating;

a first integrated controller comprising at least a portion of the sensor module; and

a second integrated controller comprising the display driver module.

17. The processing system of claim 7 , wherein the sensor module is further configured to modulate each of the plurality of sensor electrodes to determine changes in absolute capacitance in a time period, wherein the time period is selected from a group consisting of a time period that at least partially overlaps with display updating and a time period that is non-overlapping with display updating.

18. A method for detecting an input object in a sensing region of a capacitive sensing device, the capacitive sensing device having a plurality of sensor electrodes arranged in a matrix, the method comprising:

modulating each of the plurality of sensor electrodes with electrical signals to determine changes in absolute capacitance;

selecting a subset of the plurality of sensor electrodes based on the determined changes in absolute capacitance, wherein the subset is less than the plurality of sensor electrodes and includes a first sensor electrode and a second sensor electrode; and

driving the first sensor electrode and receiving with the second sensor electrode to determine changes in transcapacitance between the first sensor electrode and the second sensor electrode.

19. The method of claim 18 , further comprising:

determining positional information based on the changes in transcapacitance.

20. The method of claim 18 , further comprising driving a plurality of common electrodes for display updating, wherein each sensor electrode of the plurality of sensor electrodes comprises at least one common electrode of the plurality of common electrodes.