Display device having an integrated sensing device with reduced interference
A processing system for an input device comprises drive circuitry configured to generate a fixed voltage for a common voltage electrode of the input device during a display update period, and generate a sensing signal for the common voltage electrode during an input sensing period, the sensing signal having a duty cycle and a mean value, wherein the duty cycle minimizes a difference between the fixed voltage and the mean value. An input device comprises one or more common voltage electrodes and a coupled processing system. The processing system is configured to drive the one or more common voltage electrodes with a fixed voltage during a display update period, and a sensing signal during an input sensing period. The sensing signal has a duty cycle and a mean value, the duty cycle configured to minimize a difference between the mean value and the fixed voltage.
1. A processing system for an input device, the processing system comprising:
drive circuitry configured to:
generate a fixed voltage to be driven on a common voltage electrode of the input device during a display update period; and
generate a sensing signal to be driven on the common voltage electrode during an input sensing period, the sensing signal having a mean value and a duty cycle, and having a high voltage value during first portions of the sensing period, and a low voltage value during second portions of the sensing period, the duty cycle specifying relative temporal lengths of the first and second portions,
wherein the duty cycle is configured to minimize a difference between the fixed voltage and the mean value.
2. The processing system of claim 1 , wherein the drive circuitry is further configured to drive the common voltage electrode of the input device with the fixed voltage during the display update period.
3. The processing system of claim 1 , wherein the drive circuitry is further configured to drive the common voltage electrode of the input device with the sensing signal during the input sensing period.
4. The processing system of claim 1 , wherein a value of the fixed voltage is a device-specific parameter of the input device.
5. The processing system of claim 4 , wherein the mean value of the sensing signal is set in response to the value of the fixed voltage.
6. The processing system of claim 1 , wherein the sensing signal has a period T, and wherein an amplitude of the sensing signal includes a first segment with a duration of a first fraction of T at a maximum voltage of the drive circuitry, and a second segment with a duration of a second fraction of T at a minimum voltage of the drive circuitry.
7. The processing system of claim 6 , wherein the first fraction is greater than the second fraction when the mean value is greater than one half of a difference between a maximum voltage and a minimum voltage of the sensing signal.
8. The processing system of claim 6 , wherein the second fraction is greater than the first fraction when the mean value is less than one half of a difference between a maximum voltage and a minimum voltage of the sensing signal.
9. The processing system of claim 6 , wherein the duration of each of the first fraction and the second fraction is greater than or equal to a minimum required time for a sensor receiving the sensing signal to acquire a capacitance measurement at a pre-defined signal to noise ratio (SNR).
10. The processing system of claim 1 , wherein the input sensing period is provided between two display update periods of a display frame, and wherein there are a plurality of display update periods and corresponding input sensing periods per display frame.
11. A method for driving a common voltage electrode of an input device, the method comprising:
driving the common voltage electrode of the input device with a fixed voltage during a display update period; and
driving the common voltage electrode with a sensing signal during an input sensing period, the sensing signal having a duty cycle and a mean value, and having a high voltage value for first portions of the sensing period, and a low voltage value for second portions of the sensing period, the duty cycle specifying relative temporal lengths of the first and second portions,
wherein the duty cycle is configured to minimize a difference between the fixed voltage and the mean value, while complying with a minimum settling time of a sensor receiving the sensing signal.
12. The method of claim 11 , wherein a value of the fixed voltage is a device-specific parameter of the input device, and wherein the sensing signal is a waveform with a period T.
13. The method of claim 12 , wherein an amplitude of the waveform includes a first segment, with a duration equal to a first fraction of T, at a maximum voltage, and a second segment, with a duration equal to a second fraction of T, at a minimum voltage.
14. The method of claim 13 , wherein the first fraction is greater than the second fraction when the mean value is greater than one half of the difference between the maximum voltage and the minimum voltage.
15. The method of claim 13 , wherein the second fraction is greater than the first fraction when the mean value is less than one half of the difference between the maximum voltage and the minimum voltage.
16. The method of claim 13 , wherein the duration of each of the first fraction and the second fraction is greater than or equal to a minimum required time for a sensor receiving the sensing signal to acquire a capacitance measurement at a pre-defined SNR.
17. An input device, comprising:
one or more common voltage electrodes; and
a processing system coupled to the one or more common voltage electrodes configured to:
drive the one or more common voltage electrodes with a fixed voltage during a display update period; and
drive the one or more common voltage electrodes with a sensing signal during an input sensing period, the sensing signal having a mean value and a duty cycle, and having a high voltage value for first portions of the sensing period, and a low voltage value for second portions of the sensing period, the duty cycle specifying relative temporal lengths of the first and second portions,
wherein the duty cycle is configured to minimize a difference between the mean value and the fixed voltage, while complying with a minimum settling time of a sensor receiving the sensing signal.
18. The input device of claim 17 , wherein the sensing signal has a period T, and wherein an amplitude of the sensing signal includes a first segment with a duration of a first fraction of T at a maximum voltage, and a second segment with a duration of a second fraction of T at a minimum voltage.
19. The input device of claim 18 , wherein:
the first fraction is greater than the second fraction when the mean value is greater than one half of the difference between the maximum voltage and the minimum voltage of the sensing signal; and
the second fraction is greater than the first fraction when the mean value is less than one half of the difference between the maximum voltage and the minimum voltage of the sensing signal.
20. The input device of claim 18 , wherein the duration of each of the first fraction and the second fraction is greater than or equal to a minimum required time for a sensor receiving the sensing signal to acquire a capacitance measurement at a pre-defined SNR.