Touch Sensing Circuit Water Detection via Segmented Capacitance
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Solution Overview
Problem
Conventional touch sensing circuits in in-cell touch displays fail to accurately differentiate between large-area touch events caused by wet fingers and erroneous touches, often misidentifying meaningful user interactions as errors due to parasitic capacitances and water interference.
Innovation Solution
The implementation of a touch sensing circuit that performs both self-capacitance and mutual-capacitance touch detection on sensing electrodes, using the same driving signal in different periods to determine whether a touch event is triggered by water, thereby distinguishing between wet finger interactions and erroneous touches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the touch sensing circuit uses conventional single-mode capacitance detection, then the device complexity is low, but the measurement precision of touch events is insufficient to differentiate between wet finger and erroneous touch
Solution Approach 1:
The patent segments the capacitance detection process into two distinct modes: self-capacitance detection mode and mutual-capacitance detection mode. Each mode serves a specific purpose - self-capacitance for detecting touch events and mutual-capacitance for detecting water presence. This segmentation allows the system to achieve high measurement precision for differentiating touch events without requiring a completely complex sensing circuit, as each mode can be implemented with relatively simple circuitry.
Solution Approach 2:
The patent implements periodic switching between self-capacitance detection mode and mutual-capacitance detection mode. The control unit alternates between these modes in a periodic manner, first performing self-capacitance detection to identify touch events, then switching to mutual-capacitance detection to verify whether water is present. This periodic action enables the system to maintain high measurement precision while using a relatively simple circuit structure that can be reused across both detection modes.
2Reliability
If the touch sensing circuit applies driving signals to all sensing electrodes simultaneously during touch sensing, then parasitic capacitances between VCOM and data/scan lines are eliminated, but the ability to detect water-induced touch events is reduced
Solution Approach 1:
The patent segments the sensing electrode activation into two phases: during self-capacitance detection, driving signals are applied to all sensing electrodes simultaneously to eliminate parasitic capacitance effects and ensure reliable touch sensing. During mutual-capacitance detection, the control unit selectively activates only specific sensing electrodes while others remain unactivated, allowing the circuit to detect water presence through capacitance changes without the interference of simultaneous driving signals. This segmentation resolves the contradiction by applying different signal strategies to different detection phases.
Solution Approach 2:
The patent implements dynamic control of driving signal application to sensing electrodes based on the current detection mode. The control unit dynamically adjusts which electrodes receive driving signals - all electrodes are activated during self-capacitance detection for reliable touch sensing, while only specific electrodes are activated during mutual-capacitance detection to enable water detection. This dynamic adaptation allows the system to optimize performance for each specific detection task, eliminating water interference while maintaining touch sensing reliability.
3Reliability
If the touch sensing circuit ignores large-area touch events, then erroneous touches are filtered out, but meaningful wet finger touch events are mistakenly rejected
Solution Approach 1:
The patent implements a feedback mechanism where the control unit uses the results of mutual-capacitance detection to verify and correct self-capacitance detection results. After detecting a touch event through self-capacitance detection, the control unit switches to mutual-capacitance detection mode to check for water presence. Based on this feedback, the control unit determines whether to accept or reject the touch event - accepting it if water is detected (indicating a meaningful wet finger touch) or rejecting it if no water is present (indicating an erroneous touch). This feedback loop resolves the contradiction by providing additional verification that prevents both erroneous touches and meaningful wet finger touches from being incorrectly rejected.
Solution Approach 2:
The patent introduces water detection as an intermediary verification step between touch detection and final touch event recognition. The mutual-capacitance detection mode acts as an intermediary that detects the presence of water on the touch surface. This intermediary mechanism allows the system to differentiate between true touch events and erroneous touches by checking for water presence, thereby preventing the rejection of meaningful wet finger touch events while still filtering out erroneous touches.
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
This approach effectively prevents misidentification of large-area touch events caused by wet fingers, ensuring that meaningful user interactions are recognized and reported correctly, while reducing parasitic capacitance effects.
Implementation Method 1
the touch sensing circuit applies a driving signal to the sensing electrodes at the same time, and the touch sensing circuit performs self-capacitance touch detection on the sensing electrodes
Implementation Method 2
parasitic capacitances may be generated between the common electrode layer and the data lines and between the common electrode layer and the scan lines
Data Source
AI summary
A touch apparatus and a sensing method and a touch sensing circuit thereof are provided. The touch apparatus includes a touch panel and the touch sensing circuit. In a first period, the touch sensing circuit applies the same driving signal to a plurality of sensing electrodes of the touch panel at the same time, and performs self-capacitance touch detection on the sensing electrodes to obtain a self-capacitance detection result. In a second period, the touch sensing circuit performs mutual-capacitance touch detection on at least one of the sensing electrodes to obtain a mutual-capacitance detection result. The touch sensing circuit determines whether a touch event of the touch panel is triggered by water based on the mutual-capacitance detection result and the self-capacitance detection result.