Touch detection circuit with detection of water
A touch detection circuit has a first terminal and a second terminal which are respectively coupled to a first electrode and a second electrode located adjacent to each other. The capacitance sensing circuit (i) senses first electrostatic capacitance formed by the first electrode in a space with a periphery including the second electrode, and (ii) senses, by a self-capacitance method, second electrostatic capacitance formed by the first electrode in a space with a periphery in a state where voltage of the second terminal is made to follow voltage of the first terminal. A signal processor detects water over the first electrode and the second electrode on the basis of a difference between the first electrostatic capacitance and the second electrostatic capacitance.
1. A touch detection circuit comprising:
a first terminal to which a first electrode is to be coupled;
a second terminal to which a second electrode located adjacent to the first electrode is to be coupled;
a capacitance sensing circuit structured to: (i) sense first electrostatic capacitance formed by the first electrode in a space with a periphery including the second electrode; and (ii) sense, by a self-capacitance method, second electrostatic capacitance formed by the first electrode in a space with a periphery in a state where voltage of the second terminal is made to follow voltage of the first terminal; and
a signal processor structured to detect, on the basis of a difference between the first electrostatic capacitance and the second electrostatic capacitance, water over the first electrode and the second electrode,
wherein the capacitance sensing circuit comprises:
a self-capacitance sensor coupled to the first terminal; and
a cancel circuit having an input node coupled to the first terminal and an output node coupled to the second terminal, and structured to drive the second terminal such that the voltage of the second electrode follows the voltage of the first electrode when it is enabled,
and wherein the first electrostatic capacitance is sensed when the cancel circuit is disabled and the second electrostatic capacitance is sensed when the cancel circuit is enabled.
2. The touch detection circuit according to claim 1 , wherein the signal processor is structured to correct an error between sensitivity of the capacitance sensing circuit for the first electrostatic capacitance and sensitivity of the capacitance sensing circuit for the second electrostatic capacitance.
3. The touch detection circuit according to claim 1 , wherein the signal processor is structured to determine presence/absence of a touch on the first electrode on the basis of the second electrostatic capacitance.
4. The touch detection circuit according to claim 3 , wherein for touch determination for a certain frame, the signal processor is structured to generate a correction value on the basis of the second electrostatic capacitance measured in a past frame, to correct at least one of a threshold value for touch detection and the second electrostatic capacitance of a current frame on the basis of the correction value, and to determine presence/absence of a touch on the first electrode on the basis of a comparison result between the second electrostatic capacitance and the threshold value after the correction.
5. The touch detection circuit according to claim 1 , wherein a determination condition to determine presence/absence of a touch on the first electrode is changed in accordance with a detection result of the water.
6. The touch detection circuit according to claim 5 , wherein a determination condition to determine presence/absence of a touch on the first electrode in a certain frame is changed in accordance with a detection result of the water in a frame prior to the certain frame.
7. The touch detection circuit according to claim 1 , wherein the capacitance sensing circuit is structured to sense (iii) third electrostatic capacitance formed by the second electrode in a space with a periphery including the first electrode, and (iv) to sense, by the self-capacitance method, fourth electrostatic capacitance formed by the second electrode in a space with a periphery in a state where the voltage of the first terminal is made to follow the voltage of the second terminal, in addition to the first electrostatic capacitance and the second electrostatic capacitance.
8. The touch detection circuit according to claim 7 , further comprising a selector provided between the capacitance sensing circuit and a portion including the first terminal and the second terminal, and structured to switch a coupling relation of the capacitance sensing circuit between the first terminal and the second terminal.
9. The touch detection circuit according to claim 1 , wherein the touch detection circuit is integrated on one semiconductor integrated circuit.
10. An input device comprising a touch detection circuit according to claim 1 .
11. An electronic apparatus comprising an input device according to claim 10 .
12. The touch detection circuit according to claim 1 , wherein the cancel circuit comprises:
a buffer having an input node coupled to the first terminal;
a drive auxiliary circuit coupled to the second terminal and structured to change the voltage at the second terminal; and
a first switch coupled between an output node of the buffer and the drive auxiliary circuit.
13. The touch detection circuit according to claim 12 , wherein the drive auxiliary circuit comprises a second switch coupled between the second terminal and a ground line.
14. The touch detection circuit according to claim 13 , wherein the drive auxiliary circuit further comprises a third switch coupled between the second terminal and a power supply line.