Self-capacitance measurement using compensation capacitor
View Patent ↗In one embodiment, a method includes dividing a first amount of charge between a measurement capacitance and a sample-and-hold capacitor resulting in a voltage at the measurement capacitance being a first voltage. The division of the first amount of charge is based at least in part on a configuration of a compensation capacitor relative to the measurement capacitance and the sample-and-hold capacitor. The configuration being determined based at least in part on an output without the compensation capacitor. The method also includes determining a first difference between the first voltage at the capacitance and a reference voltage; and determining whether a touch input to the touch sensor has occurred based at least in part on the first difference.
1. A method comprising:
configuring a compensation capacitor relative to a measurement capacitance based at least in part on a value of a calibration voltage relative to a reference value, wherein configuring the compensation capacitor comprises coupling the compensation capacitor in parallel with the measurement capacitance in response to the calibration voltage being lower than the reference value;
dividing an amount of charge between the measurement capacitance, a sampling capacitor, and the compensation capacitor resulting in a voltage at the measurement capacitance being a measurement voltage, the division of the amount of charge being based at least in part on the configuration of the compensation capacitor relative to the measurement capacitance;
determining a measurement difference between the measurement voltage at the measurement capacitance and a reference value; and
determining whether a touch input to a touch sensor has occurred based at least in part on the measurement difference.
2. The method of claim 1 , further comprising determining the configuration at least in part by a value of a calibration voltage relative to the reference value, the calibration voltage being measured without the touch input and the compensation capacitance.
3. The method of claim 2 , further comprising reconfiguring the compensation capacitor relative to the measurement capacitance, wherein reconfiguring the compensation capacitor comprises coupling the compensation capacitor in series with the measurement capacitance in response to the calibration voltage becoming higher than the reference value by least a pre-determined value.
4. The method of claim 1 , wherein the determination of whether a touch input has occurred comprises comparing the measurement difference to a measurement difference without the touch input.
5. The method of claim 1 , further comprising sampling the measurement voltage through an analog-to-digital converter (ADC).
6. The method of claim 1 , further comprising pre-charging the measurement capacitance based at least in part on the configuration of the compensation capacitor relative to the measurement capacitance.
7. A computer-readable non-transitory storage medium embodying logic configured when executed to:
configure a compensation capacitor relative to a measurement capacitance based at least in part on a value of a calibration voltage relative to a reference value, wherein configuring the compensation capacitor comprises coupling the compensation capacitor in parallel with the measurement capacitance in response to the calibration voltage being lower than the reference value;
divide an amount of charge between the measurement capacitance, a sampling capacitor, and the compensation capacitor resulting in a voltage at the measurement capacitance being a measurement voltage, the division of the amount of charge being based at least in part on the configuration of the compensation capacitor relative to the measurement capacitance;
determine a measurement difference between the measurement voltage at the measurement capacitance and a reference value; and
determine whether a touch input to a touch sensor has occurred based at least in part on the measurement difference.
8. The medium of claim 7 , wherein the logic is further configured to
determine the configuration at least in part by a value of a calibration voltage relative to the reference value, the calibration voltage being measured without the touch input and the compensation capacitance.
9. The medium of claim 8 , wherein the logic is further configured to reconfigure the compensation capacitor relative to the measurement capacitance, wherein reconfiguring the compensation capacitor comprises coupling the compensation capacitor in series with the measurement capacitance in response to the calibration voltage becoming higher than the reference value by least a pre-determined value.
10. The medium of claim 7 , wherein the logic is further configured to compare the measurement difference to a measurement difference without the touch input.
11. The medium of claim 7 , wherein the logic is further configured to sample the measurement voltage through an analog-to-digital converter (ADC).
12. The medium of claim 7 , wherein the logic is further configured to pre-charge the measurement capacitance based at least in part on the configuration of the compensation capacitor relative to the measurement capacitance.
13. A device comprising:
a measurement circuit; and
a computer-readable non-transitory storage medium coupled to the measurement circuit and embodying logic configured when executed to:
configure a compensation capacitor relative to a measurement capacitance based at least in part on a value of a calibration voltage relative to a reference value, wherein configuring the compensation capacitor comprises coupling the compensation capacitor in parallel with the measurement capacitance in response to the calibration voltage being lower than the reference value;
divide an amount of charge between the measurement capacitance, a sampling capacitor, and the compensation capacitor resulting in a voltage at the measurement capacitance being a measurement voltage, the division of the amount of charge being based at least in part on the configuration of the compensation capacitor relative to the measurement capacitance;
determine a measurement difference between the measurement voltage at the measurement capacitance and a reference value; and
determine whether a touch input to a the touch sensor has occurred based at least in part on the measurement difference.
14. The device of claim 13 , wherein the logic is further configured to
determine the configuration at least in part by a value of a calibration voltage relative to the reference value, the calibration voltage being measured without the touch input and the compensation capacitance.
15. The device of claim 14 , wherein the logic is further configured to reconfigure the compensation capacitor relative to the measurement capacitance, wherein reconfiguring the compensation capacitor comprises coupling the compensation capacitor in series with the measurement capacitance in response to the calibration voltage becoming higher than the reference value by least a pre-determined value.
16. The device of claim 13 , wherein the logic is further configured to compare the measurement difference to a measurement difference without the touch input.
17. The device of claim 13 , wherein the logic is further configured to pre-charge the measurement capacitance based at least in part on the configuration of the compensation capacitor relative to the measurement capacitance.