Driving sensor electrodes for absolute capacitive sensing

1. A processing system, comprising:

a sensor module comprising sensor circuitry, the sensor module configured to:

drive sensor electrodes with a capacitive sensing signal to measure first changes of capacitance between each of the sensor electrodes and at least one input object; and

drive at least one sensor electrode in a first set of the sensor electrodes with a reference signal and at least one sensor electrode in a second set of the sensor electrodes with a capacitive sensing signal to measure second changes of capacitance between the at least one sensor electrode in the second set and the at least one input object; and

a capacitive measurer module configured to determine a capacitive image based at least in part on the first and second changes of capacitance.

2. The processing system of claim 1 , wherein the first set of the sensor electrodes is disposed orthogonal to the second set of the sensor electrodes.

3. The processing system of claim 1 , wherein the sensor module is configured to drive the at least one sensor electrode in the first set of the sensor electrodes with a reference signal and the at least one sensor electrode in the second set of the sensor electrodes with a capacitive sensing signal to measure the second changes of capacitance by:

driving a first sensor electrode in the first set with a reference signal while driving the at least one sensor electrode in the second set with a capacitive sensing signal; and

driving a second sensor electrode in the first set with a reference signal while driving the at least one sensor electrode in the second set with a capacitive sensing signal.

4. The processing system of claim 1 , wherein the capacitive measurer module is configured to determine the capacitive image by differencing the first changes of capacitance and the second changes of capacitance.

5. The processing system of claim 1 , wherein the sensor module is configured to drive the sensor electrodes with a capacitive sensing signal to measure the first changes of capacitance by driving the sensor electrodes concurrently with a capacitive sensing signal.

6. The processing system of claim 1 , wherein the sensor module is configured to drive the sensor electrodes with a capacitive sensing signal to measure the first changes of capacitance by:

driving the first set of the sensor electrodes with a capacitive sensing signal while driving the second set of the sensor electrodes with a guard signal during a first time period; and

driving the first set of the sensor electrodes with a guard signal while driving the second set of the sensor electrodes with a capacitive sensing signal during a second time period.

7. The processing system of claim 1 , wherein the sensor module is configured to drive the at least one sensor electrode in the first set of the sensor electrodes with a reference signal and the at least one sensor electrode in the second set of the sensor electrodes with a capacitive sensing signal to measure the second changes of capacitance by:

obtaining a first capacitive profile along an axis defined by a first plurality of the sensor electrodes and a second capacitive profile along an axis defined by a second plurality of sensor electrodes; and

selecting the first set of the sensor electrodes as either the first plurality of the sensor electrodes or the second plurality of the sensor electrodes based on numbers of local maxima in the first and second capacitive profiles.

8. The processing system of claim 1 , wherein the sensor module is configured to drive the at least one sensor electrode in the first set of the sensor electrodes with a reference signal and the at least one sensor electrode in the second set of the sensor electrodes with a capacitive sensing signal to measure the second changes of capacitance by:

obtaining a capacitive profile along an axis defined by the first set of sensor electrodes; and

selecting the at least one electrode in the first set to be driven with a reference signal based on the capacitive profile.

9. The processing system of claim 1 , wherein the sensor module is configured to drive the at least one sensor electrode in the first set of the sensor electrodes with a reference signal and the at least one sensor electrode in the second set of the sensor electrodes with a capacitive sensing signal to measure the second changes of capacitance by:

driving a plurality of sensor electrodes in the first set with a reference signal while driving at least one sensor electrode in the second set with a capacitive sensing signal.

10. The processing system of claim 1 , wherein the sensor module is configured to:

drive at least one sensor electrode in the second set of the sensor electrodes with a reference signal and at least one sensor electrode in the first set of the sensor electrodes with a capacitive sensing signal to measure third changes of capacitance between the at least one sensor electrode in the first set and the at least one input object; and

wherein the capacitive measurer module is configured to determine the capacitive image based at least in part on the first changes of capacitance and an average of the second changes of capacitance and the third changes of capacitance.

11. A method of driving sensor electrodes for capacitive sensing, comprising:

driving the sensor electrodes with a capacitive sensing signal to measure first changes of capacitance between each of the sensor electrodes and at least one input object;

driving at least one sensor electrode in a first set of the sensor electrodes with a reference signal and at least one sensor electrode in a second set of the sensor electrodes with a capacitive sensing signal to measure second changes of capacitance between the at least one sensor electrode in the second set and the at least one input object; and

determining a capacitive image based at least in part on the first and second changes of capacitance.

12. The method of claim 11 , wherein the step of determining the capacitive image comprises:

differencing the first changes of capacitance and the second changes of capacitance.

13. The method of claim 11 , wherein the step of driving the sensor electrodes with a capacitive sensing signal to measure the first changes of capacitance comprises:

driving the sensor electrodes concurrently with a capacitive sensing signal.

14. The method of claim 11 , wherein the step of driving the sensor electrodes with a capacitive sensing signal to measure the first changes of capacitance comprises:

driving the first set of the sensor electrodes with a capacitive sensing signal while driving the second set of the sensor electrodes with a guard signal during a first time period; and

driving the first set of the sensor electrodes with a guard signal while driving the second set of the sensor electrodes with a capacitive sensing signal during a second time period.

15. The method of claim 11 , wherein the step of driving the at least one sensor electrode in the first set of the sensor electrodes with a reference signal and the at least one sensor electrode in the second set of the sensor electrodes with a capacitive sensing signal to measure the second changes of capacitance comprises:

obtaining a first capacitive profile along an axis defined by a first plurality of the sensor electrodes and a second capacitive profile along an axis defined by a second plurality of sensor electrodes; and

selecting the first set of the sensor electrodes as either the first plurality of the sensor electrodes or the second plurality of the sensor electrodes based on numbers of local maxima in the first and second capacitive profiles.

16. The method of claim 11 , wherein the step of driving the at least one sensor electrode in the first set of the sensor electrodes with a reference signal and the at least one sensor electrode in the second set of the sensor electrodes with a capacitive sensing signal to measure the second changes of capacitance comprises:

obtaining a capacitive profile along an axis defined by the first set of the sensor electrodes; and

selecting the at least one electrode in the first set to be driven with a reference signal based on the capacitive profile.

17. The method of claim 11 , wherein the step of driving the at least one sensor electrode in the first set of the sensor electrodes with a reference signal and the at least one sensor electrode in the second set of the sensor electrodes with a capacitive sensing signal to measure the second changes of capacitance comprises:

driving a plurality of sensor electrodes in the first set with a reference signal while driving at least one sensor electrode in the second set with a capacitive sensing signal.

18. The method of claim 11 , further comprising:

driving at least one sensor electrode in the second set of the sensor electrodes with a reference signal and at least one sensor electrode in the first set of the sensor electrodes with a capacitive sensing signal to measure third changes of capacitance between the at least one sensor electrode in the first set and the at least one input object;

determining the capacitive image based at least in part on the first changes of capacitance and an average of the second changes of capacitance and the third changes of capacitance.

19. An input device, comprising:

sensor electrodes; and

a processing system coupled to the sensor electrodes, the processing system configured to:

drive the sensor electrodes with a capacitive sensing signal to measure first changes of capacitance between each of the sensor electrodes and at least one input object;

drive at least one sensor electrode in a first set of the sensor electrodes with a reference signal and at least one sensor electrode in a second set of the sensor electrodes with a capacitive sensing signal to measure second changes of capacitance between the at least one sensor electrode in the second set and the at least one input object; and

determine a capacitive image based at least in part on the first and second changes of capacitance.

20. The input device of claim 19 , wherein the first set of the sensor electrodes is disposed orthogonal to the second set of the sensor electrodes.