Capacitive Touch Sensor Guarding Pattern for Negative-Touch Reduction
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Solution Overview
Problem
Capacitive touch screens face challenges in accurately detecting true touches due to negative-touch effects, which are exacerbated by thinner designs and noise interference from displays, particularly in portable devices, and are hindered by the need for rear shielding layers that increase thickness and the inability to use styluses with insulating pen bodies.
Innovation Solution
A capacitive touch screen design featuring a conductive strip pattern and a guarding pattern exposed from each other, where the guarding pattern receives a DC signal, allowing for increased capacitive coupling with external objects and reducing the negative-touch effect by altering the proportion of driving signals flowing into detected conductive strips, thereby eliminating the need for a rear shielding layer and enabling stylus input even with insulating pen bodies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the insulating surface layer is made thinner to reduce device thickness, then the device thickness is reduced, but the negative-touch effect increases causing greater distortion in detected capacitive coupling
Solution Approach 1:
The sensing system is segmented into multiple independent sensing regions (first sensing region and second sensing region) with separate conductive strips. This segmentation allows the system to distinguish between true touches and negative touches by comparing signals from different regions, thereby maintaining detection accuracy even with thinner insulating layers.
Solution Approach 2:
A guard pattern is introduced as an intermediary element between the conductive strips and the display. This guard pattern helps to shield and isolate the sensing regions from external interference, reducing the negative-touch effect while allowing the use of thinner insulating surface layers.
2Object-affected harmful factors
If a rear shielding layer is added to reduce noise interference from the display, then noise resistance is improved, but the device thickness increases
Solution Approach 1:
The shielding function is extracted from a separate rear shielding layer and integrated directly into the sensing structure through the guard pattern. This eliminates the need for an additional thickness-consuming layer while maintaining noise resistance, as the guard pattern is incorporated within the existing sensing architecture.
Solution Approach 2:
The guard pattern serves multiple functions simultaneously: it acts as both a sensing element and a shielding element. By combining these functions into a single structure, the design achieves noise resistance without requiring additional layers that would increase device thickness.
3Adaptability or versatility
If multiple fingers are used for input, then input versatility is improved, but the negative-touch effect increases causing signal cancellation and detection errors
Solution Approach 1:
The touch sensor is divided into multiple independently detectable sensing regions, each with its own conductive strips. When multiple fingers touch the screen, each finger interacts with specific sensing regions, and the system can distinguish between them by analyzing the unique signal patterns from each segmented region, preventing signal cancellation and enabling accurate multi-touch detection.
Solution Approach 2:
The system uses differential signaling and compares capacitive coupling variations across multiple sensing regions to identify true touches versus negative touches. This feedback mechanism allows the system to distinguish between genuine multi-touch inputs and artifacts caused by capacitive coupling, maintaining detection accuracy even when multiple fingers are in use.
4Ease of operation
If an insulating pen body is used for the stylus, then user comfort and isolation are improved, but the ability to detect stylus input is reduced
Solution Approach 1:
The guard pattern acts as an intermediary that enhances the capacitive coupling between the stylus tip and the sensing regions. Even when the stylus has an insulating body, the conductive guard pattern creates a sufficient capacitive pathway that allows the sensing system to detect the stylus input accurately while the insulating body provides user comfort and electrical isolation.
Solution Approach 2:
The sensing system is designed with enhanced local sensitivity at the regions where the stylus is likely to contact. The guard pattern and conductive strip configuration create localized capacitive fields that are optimized to detect the small capacitive changes caused by the stylus tip, enabling accurate detection despite the insulating body reducing overall coupling.
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 design enhances the tolerance to negative-touch effects, reduces the thickness of the touch screen, and allows for accurate detection of multiple true touches and stylus inputs, while maintaining noise resistance and eliminating the need for a rear shielding layer.
Implementation Method 1
the conductive pen head being capacitively coupled to the conductive strip pattern and the guarding pattern, respectively, causing the conductive strip pattern to generate a change in capacitive coupling
Implementation Method 2
the guarding pattern receives a DC signal, allowing for increased capacitive coupling with external objects and reducing the negative-touch effect by altering the proportion of driving signals flowing into detected conductive strips
Data Source
AI summary
The present invention provides a method and device for writing on a capacitive touch screen, which includes a guarding pattern and a conductive strip pattern exposed from each other, and a stylus. The conductive strip pattern includes a plurality of first conductive strips provided with a driving signal and a plurality of second conductive strips that provide mutual capacitive coupling signals, and the guarding pattern is provided with a DC signal. The stylus has a conductive pen head and a pen body. When the human body holding the pen body is not electrically coupled to the conductive pen head, the location of the conductive pen head can be determined by sufficient change in capacitive coupling caused by the conductive pen head capacitively coupling to the guarding pattern and the conductive strip pattern.