Capacitive Touch Panel Shielding for Higher S/N Detection
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Solution Overview
Problem
Electrostatic-capacitance-type touch panels face challenges in achieving a high signal-to-noise ratio due to varying capacitance between X and Y directions, leading to inconsistent detection sensitivity and potential erroneous operations.
Innovation Solution
A shield electrode is formed on the back surface of the touch panel with a constant voltage supply, and the area of Y electrodes is reduced relative to X electrodes, with floating electrodes added to equalize capacitance, and the intersection of lines on the flexible printed circuit board is minimized to reduce line capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the area of electrodes on one line is increased to elevate signal level, then detection sensitivity is improved, but capacitance to ground increases and noise is easily detected
Solution Approach 1:
A shield electrode is introduced as an intermediary component between the electrode and the display device. This shield electrode acts as a mediator that blocks electromagnetic interference from the display device, preventing noise from reaching the electrode while allowing the electrode to maintain its signal-generating area
Solution Approach 2:
The shield electrode is positioned in advance to counteract noise before it can affect the electrode. By placing the shield electrode between the display device and the electrode, the system preemptively blocks harmful electromagnetic interference, preventing noise contamination of the detection signal
2Object-affected harmful factors
If a transparent conductive film is formed on the back surface of the touch panel substrate as a shield layer, then noise suppression is improved, but it becomes necessary to supply voltage to the back surface
Solution Approach 1:
The shielding function is extracted from the back surface of the touch panel substrate and relocated to the front surface. Instead of forming a shield layer on the back surface that requires voltage supply, the patent uses the existing electrode structure on the front surface to generate the shielding effect, eliminating the need for additional voltage supply infrastructure
Solution Approach 2:
The shielding effect is achieved by utilizing the electrode's own electromagnetic field characteristics rather than creating a separate active shield layer. The electrode structure itself is configured to produce the necessary shielding effect, copying the protective function without requiring a duplicate active component
3Measurement precision
If signals are supplied to X electrodes and Y electrodes from both ends of each electrode, then S/N ratio is enhanced, but line capacitance increases due to lateral line extension and intersections
Solution Approach 1:
The signal supply approach transitions from a two-dimensional planar routing with intersections to a three-dimensional layered structure. By routing signals through multiple layers and using vertical connections, the patent eliminates lateral line intersections, reducing line capacitance while maintaining the benefit of dual-end signal supply
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 configuration enhances the signal-to-noise ratio, improving detection sensitivity and reducing noise interference, resulting in a more reliable touch panel operation.
Implementation Method 1
it is found that the fluctuation of a signal voltage which is generated when a display device performs a display is detected as noises by the electrode of the touch panel positioned directly above the display device
Implementation Method 2
an electrostatic-capacitance-type touch panel detects a capacitance change which occurs when a finger of a person or the like touches the touch panel
Data Source
AI summary
A highly reliable electrostatic-capacitive-type display device with a touch panel which allows a user to perform finger touch inputting and exhibits excellent detection sensitivity is provided. A transparent conductive film is formed above a back surface of an electrostatic-capacitive-type touch panel so as to block noises generated by a display device. A conductive member is provided to supply a voltage to a transparent conductive film formed above a back surface of the touch panel. An electrode which is formed on the electrostatic-capacitive-type touch panel is divided in accordance with a ratio between the number of X electrodes and the number of Y electrodes. A floating electrode is formed in a gap defined between the electrodes so as to adjust an area of the electrode. Due to the shrinkage of the area of the electrode, it is possible to lower a noise level to a level equal to or lower than a signal level. Accordingly, an S/N ratio is increased thus enhancing detection sensitivity. Further, lines are branched on a flexible printed circuit board and intersecting lines are formed on a back surface of the flexible printed circuit board, and the intersecting lines are made to orthogonally intersect with lines formed on a front surface of the flexible printed circuit board thus lowering line capacitance.