Touch Detection Circuit Water Discrimination via Capacitance Segmentation
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Solution Overview
Problem
Existing touch input devices using electrostatic capacitance detection methods face challenges in distinguishing between water droplets and touches, and in detecting multi-touch inputs, with self-capacitance methods being sensitive but unable to differentiate water and touches, and mutual-capacitance methods being less sensitive but capable of multi-touch detection.
Innovation Solution
A touch detection circuit that includes a first electrode, a second electrode adjacent to the first, a capacitance sensing circuit to measure both self-capacitance and mutual-capacitance, and a signal processor to differentiate between water and touch inputs by analyzing the difference in electrostatic capacitance between the two electrodes, with a cancel circuit to adjust voltage and correct for sensitivity differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the self-capacitance method is used, then detection sensitivity is improved, but the ability to distinguish water droplets from touches deteriorates
Solution Approach 1:
The patent divides the detection task into separate measurement phases: first measuring capacitance with the second electrode at a first voltage level, then measuring again with the second electrode at a second voltage level. This segmentation allows the system to distinguish water droplets from touches by analyzing capacitance changes across different voltage conditions, resolving the contradiction between high sensitivity and water-touch differentiation.
Solution Approach 2:
The patent changes the voltage parameter of the second electrode between measurements. By varying the voltage level of the second electrode and observing how capacitance values respond to different voltage conditions, the system can identify whether a detected object is water or a touch, maintaining high sensitivity while eliminating false detections.
2Adaptability or versatility
If the mutual-capacitance method is used, then the ability to detect multi-touch is improved, but detection sensitivity deteriorates
Solution Approach 1:
The patent segments the detection process into multiple measurement steps with different voltage configurations. This allows the system to first establish baseline capacitance values and then detect additional touches by analyzing changes in the capacitance matrix, enabling multi-touch detection while maintaining high sensitivity through systematic measurement division.
Solution Approach 2:
The patent adds a voltage dimension to the capacitance measurement. Instead of measuring capacitance at a single voltage level, the system measures capacitance values at different voltage levels of the second electrode, creating a multi-dimensional detection space that enables both high sensitivity and accurate multi-touch identification.
3Adaptability or versatility
If both self-capacitance and mutual-capacitance methods are used, then comprehensive detection capability is improved, but device complexity increases
Solution Approach 1:
The patent makes the existing electrode structure serve multiple functions: the first and second electrodes are used for both self-capacitance measurement and mutual-capacitance measurement by varying the voltage applied to the second electrode. This multi-functionality approach enables comprehensive detection capability without adding separate dedicated circuits for each measurement method.
Solution Approach 2:
The system uses its own electrodes and existing circuitry to perform both self-capacitance and mutual-capacitance measurements. By controlling the voltage of the second electrode and measuring capacitance changes, the system leverages its existing components to achieve comprehensive detection functionality, avoiding the need for additional external equipment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate detection of water and touch inputs, including multi-touch, by effectively distinguishing between water droplets and finger touches, improving sensitivity and accuracy in touch input detection.
Implementation Method 1
sense first electrostatic capacitance formed by the first electrode in a space with a periphery including the second electrode
Implementation Method 2
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
Data Source
AI summary
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.