Capacitive Touch Detection Linearity via Level Shift Control
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Solution Overview
Problem
Conventional capacitive touch screen panels face challenges in achieving linearity in touch capacitance measurement, leading to increased system complexity, cost, and reduced precision in detecting touch coordinates due to the need for high-frequency capacitance detection and complex statistical processing.
Innovation Solution
A capacitive touch detection apparatus featuring a sensor pad, operational amplifier, level shift detection unit, and switching unit that controls voltage variations to establish a linear relationship between level shift values and touch capacitance, eliminating the need for additional circuitry to improve linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional capacitive touch detection is used with additional ITO patterns and insulating layers, then touch detection capability is achieved, but the thickness of the touch screen panel increases
Solution Approach 1:
The patent combines the sensor pattern layers and ITO patterns into a single integrated structure. The first and second sensor pattern layers are formed using the same ITO material without requiring separate ITO pattern layers, thereby merging multiple functional layers into one while maintaining touch detection capability and reducing overall thickness
Solution Approach 2:
The ITO patterns serve multiple functions simultaneously: they act as both the sensor pattern layers for touch detection and as the conductive patterns for signal transmission. This multi-functionality eliminates the need for separate ITO pattern layers and insulating layers, reducing the panel thickness while maintaining detection capability
2Measurement precision
If high-frequency capacitance detection is used to accumulate small capacitance changes, then touch detection sensitivity is improved, but the operation and processing complexity increases
Solution Approach 1:
The patent applies an alternating voltage signal at a specific frequency (e.g., 60Hz) to the sensor patterns, causing the capacitance to oscillate. By detecting the amplitude of this oscillation, the system can measure small capacitance changes caused by touch without requiring high-frequency detection or complex statistical processing, thereby maintaining sensitivity while reducing operational complexity
Solution Approach 2:
The system uses periodic alternating voltage signals to excite the sensor patterns and measures the periodic response. This periodic action allows for simple amplitude-based detection of capacitance changes, avoiding the need for complex high-frequency analysis or statistical processing while maintaining detection sensitivity
3Measurement precision
If metal interconnection is used to maintain low resistance for capacitance accumulation, then capacitance detection accuracy is improved, but the bezel thickness and manufacturing complexity increase
Solution Approach 1:
The patent extracts the metal interconnection layer from the touch panel structure and replaces it with transparent conducting material (ITO) patterns that serve the same electrical function. This extraction eliminates the need for thick metal interconnections and associated mask processes, reducing bezel thickness while maintaining low resistance for capacitance detection
Solution Approach 2:
The patent substitutes metal interconnections with transparent conducting material patterns (ITO) that provide the same electrical connectivity function. This substitution eliminates the need for thick metal layers and complex mask processes, reducing bezel thickness while maintaining the low resistance required for accurate capacitance detection
4Reliability
If additional mask process is used for metal interconnection, then electrical connectivity is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the ITO pattern formation process with the sensor pattern layer formation process. Both are created in the same sputtering step using the same material, eliminating the need for separate mask processes for metal interconnections and reducing manufacturing complexity while maintaining electrical connectivity
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 solution allows for precise calculation of touch coordinates and area with reduced system complexity and cost by ensuring linearity in capacitance measurement, enhancing the accuracy and efficiency of touch detection.
Implementation Method 1
A capacitive touch screen panel converts a contact position into an electric signal by detecting change in capacitance formed between a conductive detection pattern and nearby another detection pattern or a ground electrode when a hand or an object makes contact with the touch screen panel
Data Source
AI summary
A touch detection apparatus includes a sensor pad to output a signal based on a touch state in response to an alternating voltage in a floating state after being charged, an operational amplifier including a first input connected to an output of the sensor pad and a second input to receive the alternating voltage, a level shift detection unit to detect a touch signal based on a difference between a voltage variation at an output end of the operational amplifier caused by the alternating voltage and a voltage variation at the output end of the operational amplifier caused by occurrence of a touch, and a switching unit including a first switch to control an electric potential between a first input and the output end of the operational amplifier and a second switch to connect or not the sensor pad and the first input of the operational amplifier.