Methods and apparatus for a capacitive touch sensor
Various embodiments of the present technology may comprise methods and apparatus for a touch sensor. The capacitive touch sensor may comprise a plurality of drive electrodes and a reception electrode, wherein two capacitors are formed. Under various conditions, the capacitive touch sensor may be configured to trigger a touch event in the presence of a human finger and trigger a non-touch event in the presence of water.
1. A capacitive touch sensor, comprising:
a touch panel comprising:
an input electrode;
a first drive electrode; and
a second drive electrode;
wherein:
the input electrode and the first drive electrode form a first capacitor; and
the input electrode and the second drive electrode form a second capacitor; and
a detection circuit coupled to the touch panel and configured to generate:
a feedback voltage, wherein the feedback voltage is greater than zero when there is a change in capacitance of the first capacitor and a capacitance of the second capacitor remains constant; and
an output voltage according to the feedback voltage.
2. The capacitive touch sensor according to claim 1 , wherein the detection circuit comprises:
an operational amplifier comprising a first input terminal and an output terminal, and coupled to the touch panel via the first input terminal; and
a feedback capacitor coupled between the first input terminal and the output terminal.
3. The capacitive touch sensor according to claim 1 , wherein an initial capacitance of the first capacitor is equal to an initial capacitance of the second capacitor.
4. The capacitive touch sensor according to claim 1 , wherein the detection circuit is further configured to measure a change in capacitance of the first capacitor and a change in capacitance of the second capacitor.
5. The capacitive touch sensor according to claim 1 , wherein:
the second drive electrode and the detection circuit form a third capacitor; and
an initial capacitance of the first capacitor is different from an initial capacitance of the second capacitor.
6. The capacitive touch sensor according to claim 5 , wherein the detection circuit sums a change in capacitance of the second capacitor with an initial capacitance of the third capacitor.
7. The capacitive touch sensor according to claim 1 , wherein the feedback voltage is equal to zero when there is a change in capacitance of the first capacitor and a change in capacitance of the second capacitor.
8. The capacitive touch sensor according to claim 1 , where a non-touch event is generated when one of:
the feedback voltage is equal to zero; and
the feedback voltage is greater than zero and less than a threshold voltage.
9. The capacitive touch sensor according to claim 1 , wherein a touch event is generated when the feedback voltage is greater than a threshold voltage.
10. A method for operating a capacitive touch sensor, comprising:
detecting a first capacitance of a first capacitor during a first phase, wherein the first capacitor is formed in a touch panel between an input electrode and a first drive electrode;
detecting a second capacitance of a second capacitor during a second phase, wherein the second capacitor is formed in the touch panel between the input electrode and a second drive electrode; wherein the input electrode, the first drive electrode, and the second drive electrode are arranged in parallel with each other;
generating, with a detection circuit coupled to the touch panel, a feedback voltage according to the detected first and second capacitances; and
generating, with the detection circuit, an output voltage according to the feedback voltage, wherein the output voltage corresponds to one of: a touch event and a non-touch event;
wherein:
during the first phase, the first drive electrode is connected to a supply voltage and the second drive electrode is connected to a ground voltage; and
during the second phase, the first drive electrode is connected to the ground voltage and the second drive electrode is connected to the supply voltage.
11. The method for operating a capacitive touch sensor according to claim 10 , wherein the feedback voltage is equal to zero when there is a change in capacitance of the first capacitor and a change in capacitance of the second capacitor.
12. The method for operating a capacitive touch sensor according to claim 10 , wherein the feedback voltage is greater than zero when there is a change in capacitance of the first capacitor and a capacitance of the second capacitor remains constant.
13. The method for operating a capacitive touch sensor according to claim 10 , wherein:
the touch event corresponds to a feedback voltage greater than a threshold voltage; and
the non-touch event corresponds to one of:
a feedback voltage equal to zero; and
a feedback voltage greater than zero and less than the threshold voltage.
14. The method for operating a capacitive touch sensor according to claim 10 , wherein:
the non-touch event occurs when a change in capacitance of the second capacitor cancels a change in capacitance of the first capacitor.
15. A capacitive touch sensor, comprising:
a touch panel comprising:
an input electrode;
a first drive electrode positioned in parallel with and adjacent to a first side of the input electrode; and
a second drive electrode positioned in parallel with and adjacent to a second side, directly opposite the first side, of the input electrode;
wherein:
the input electrode and the first drive electrode form a first capacitor;
the input electrode and the second drive electrode form a second capacitor; and
the first and second electrodes are selectively connected to a supply voltage and a ground voltage; and
a detection circuit coupled to the touch panel and configured to generate:
a feedback voltage according to the first and second capacitors; and
an output voltage according to the feedback voltage;
wherein the output voltage corresponds to one of: a touch event and a non-touch event.
16. The capacitive touch sensor according to claim 15 , wherein:
the touch event corresponds to a feedback voltage greater than a threshold voltage; and
the non-touch event corresponds to one of:
a feedback voltage equal to zero; and
a feedback voltage greater than zero and less than the threshold voltage.
17. The capacitive touch sensor according to claim 15 , wherein the feedback voltage is equal to zero when there is a change in capacitance of the first capacitor and a change in capacitance of the second capacitor.
18. The capacitive touch sensor according to claim 15 , the feedback voltage is greater than zero when there is a change in capacitance of the first capacitor and a capacitance of the second capacitor remains constant.