Display guarding techniques
Embodiments described herein mitigate the effect of a coupling capacitance between a sensor electrode in a touch sensor and a display electrode in a display screen. An input device, which includes the touch sensor and display screen, may transmit a guarding signal on the display electrodes when performing capacitive sensing. In one embodiment, the guarding signal may have similar characteristics as a modulated signal (e.g., similar amplitude and/or phase) driven on the sensor electrode to detect interaction between the input device and an input object. By driving a guarding signal that is similar to the modulated signal onto the display electrodes, the voltage difference between the sensor electrode and display electrode remains the same. Accordingly, the coupling capacitance between the sensor electrode and the display electrode does not affect a capacitance measurement used to detect the user interaction.
1. A processing system for a display device comprising an integrated capacitive sensing device, the processing system comprising:
sensor circuitry configured to be coupled to a plurality of sensor electrodes and configured to drive a first sensor electrode of the plurality of sensor electrodes and a second sensor electrode of the plurality of sensor electrodes for absolute capacitive sensing during a first period by driving the first sensor electrode and the second sensor electrode with a modulated signal, the plurality of sensor electrodes are disposed in a rectangular array and each sensor electrode of the plurality of sensor electrodes comprises at least one common electrode of a plurality of common electrodes of the display device,
wherein the plurality of common electrodes are configured for capacitive sensing and updating a display of the display device; and wherein during the first period a first gate electrode and a second gate electrode of the display device are driven with a gate voltage modulated with a guard signal having at least one of a similar amplitude, frequency, and phase as the modulated signal.
2. The processing system of claim 1 , wherein driving the first gate electrode and the second gate electrode with the gate voltage modulated with the guard signal mitigates an effect of a coupling capacitance between the first sensor electrode and the first and second gate electrodes and between the second sensor electrode and the first and second gate electrodes.
3. The processing system of claim 1 , wherein the first gate electrode and the second gate electrode are driven with the (late voltage modulated with the guard signal such that a voltage difference between the first gate electrode, the second gate electrode, and the first sensor electrode remains substantially constant during the first period, and wherein the voltage difference between the first gate electrode, the second gate electrode, and the second sensor electrode remains substantially constant during the first period.
4. The processing system of claim 1 , wherein a first source electrode and a second source electrode of the display device are electrically floated during the first period.
5. The processing system of claim 1 , wherein a first source electrode and a second source electrode of the display device are driven with the guard signal during the first period.
6. The processing system of claim 1 , wherein driving the first gate electrode and the second gate electrode with the gate voltage modulated with the guard signal comprises modulating at least one of a power signal and a control signal.
7. The processing system of claim 1 , wherein a third sensor electrode of the plurality of sensor electrodes is driven with the guard signal during the first period.
8. The processing system of claim 1 , wherein modulating the gate voltage with the guarding signal comprises modulating an output of a power converter with the guarding signal.
9. A display device comprising:
a plurality of common electrodes configured for capacitive sensing and updating a display of the display device;
a plurality of gate electrodes;
a plurality of sensor electrodes disposed in a rectangular array, each of the plurality of sensor electrodes comprising at least one common electrode of the plurality of common electrodes; and
a processing system coupled to the plurality of sensor electrodes and the gate electrodes, the processing system configured to:
drive a first sensor electrode of the plurality of sensor electrodes and a second sensor electrode of the plurality of sensor electrodes with a modulated signal for absolute capacitive sensing during a first period, and
drive at least one gate electrode of the plurality of gate electrodes with a gate voltage modulated with a guard signal during the first period, the guard signal has at least one of a similar amplitude, frequency, and phase as the modulated signal.
10. The display device of claim 9 , wherein driving the at least one gate electrode with the gate voltage modulated with the guard signal mitigates an effect of a coupling capacitance between the first sensor electrode and the at least one gate electrode and between the second sensor electrode and the at least one gate electrode.
11. The display device of claim 9 , wherein the at least one gate electrode is driven with the gate voltage modulated with the guard signal such that a voltage difference between the at least one gate electrode and the first sensor electrode remains substantially constant during the first period, and wherein a voltage difference between the at least one gate electrode and the second sensor electrode remains substantially constant during the first period.
12. The display device of claim 9 , wherein the processing system is configured to drive the first sensor electrode and the second sensor electrode with the modulated signal to determine a first change of absolute capacitance for the first sensor electrode and a second change in absolute capacitance for the second sensor electrode.
13. The display device of claim 12 , wherein the processing system is further configured to determine a capacitive image based on the first change of absolute capacitance and the second change in absolute capacitance.
14. The display device of claim 13 , wherein the first sensor electrode corresponds to a first pixel of the capacitive image and the second sensor electrode corresponds to a second pixel of the capacitive image.
15. The display device of claim 9 , further comprising a plurality of source electrodes, wherein the processing system is configured to electrically float at least one source electrode of the plurality of source electrodes during the first period.
16. The display device of claim 9 , further comprising a plurality of source electrodes, wherein the processing system is configured to drive at least one source electrode of the plurality of source electrodes during the first period with the guard signal during the first period.
17. The display device of claim 9 , wherein driving the at least one gate electrode with the gate voltage modulated with the guard signal comprises modulating a power signal for the at least one gate electrode.
18. The display device of claim 9 , wherein driving the at least one gate electrode with the gate voltage modulated with the guard signal comprising modulating a control signal for the at least one gate electrode.
19. A method for capacitive sensing, the method comprising:
driving a first sensor electrode of a plurality of sensor electrodes and a second sensor electrode of the plurality of sensor electrodes with a modulated signal for absolute capacitive sensing during a first period, the plurality of sensor electrodes are disposed in a rectangular array and each sensor electrode of the plurality of sensor electrodes comprises at least one common electrode of a plurality of common electrodes of a display device, wherein the plurality of common electrodes are configured for capacitive sensing and updating a display of the display device; and
driving at least one gate electrode of a plurality of gate electrodes with a gate voltage modulated with a guard signal having at least one of a similar amplitude, frequency, and phase as the modulated signal.
20. The display device of claim 9 , wherein modulating the gate voltage with the guarding signal comprises modulating an output of a power converter with the guarding signal.
21. The method of claim 19 further comprising electrically floating at least source electrode of a plurality of source electrodes during the first period.
22. The method of claim 19 further comprising driving at least source electrode of a plurality of source electrodes with the guard signal during the first period.