LCD Touch Screen Using Capacitance and Photosensors
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Solution Overview
Problem
Liquid crystal displays (LCDs) with built-in touch screens of the photosensor type face operational reliability issues due to low recognition rates in low light conditions and false touch detections in high light conditions, leading to inaccurate multi-touch recognition.
Innovation Solution
The integration of photosensors within the LCD panel, combined with a capacitance type touch screen system, uses a transparent electrode layer and photosensors to measure capacitance variations and calculate touch areas, improving operational reliability by distinguishing between single and multi-touch events through a touch screen driver circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a separate touch screen panel is attached to the LCD panel, then the touch screen can be implemented, but the manufacturing cost increases and the thickness increases
Solution Approach 1:
The patent merges the touch screen panel and LCD panel into a single integrated structure. The touch screen panel is formed directly on the LCD panel by depositing transparent conductive layers (ITO patterns) and encapsulation layers, eliminating the need for separate manufacturing and assembly processes. This integration reduces manufacturing steps, lowers costs, and decreases overall thickness while maintaining touch screen functionality.
2Ease of operation
If photosensors are used to sense touch position, then touch position can be detected, but operational reliability decreases in low light conditions
Solution Approach 1:
The patent employs a composite sensing approach combining photosensors with additional sensing mechanisms. The touch screen includes photosensors for optical detection alongside transparent electrode patterns that can detect touch through capacitance or resistance changes. This composite sensing system compensates for photosensor limitations in low light by providing alternative detection methods, thereby improving overall recognition rate and reliability across varying light conditions.
3Ease of operation
If photosensors are used to sense touch position, then touch position can be detected, but false touch detections occur in high light conditions
Solution Approach 1:
The patent implements a feedback-based touch detection system that uses multiple sensing mechanisms working in conjunction. The transparent electrode patterns provide continuous feedback about touch state through electrical property changes, which complements and verifies photosensor readings. This feedback mechanism helps distinguish actual touches from false detections caused by shadows or lighting changes, improving operational reliability in high light conditions.
4Ease of operation
If photosensors are used to sense touch position, then touch position can be detected, but multi-touch recognition accuracy decreases
Solution Approach 1:
The patent segments the touch detection function across multiple independent sensing elements. The transparent electrode layer is divided into multiple patterned conductive traces that can independently detect touch events at different locations. Combined with an array of photosensors, this segmentation allows the system to simultaneously detect and distinguish multiple touch points with high precision, accurately recognizing multi-touch gestures by analyzing the spatial distribution of electrical and optical signals.
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 enhances the optical characteristics and manufacturing efficiency of LCDs, providing precise touch event recognition and improved reliability by integrating photosensors on the LCD panel and using a capacitance type system to determine touch occurrences.
Implementation Method 1
measure a capacitance variation sensed through a first sensing line connected to the transparent electrode layer
Implementation Method 2
calculate a touch area using optical information sensed through a second sensing line connected to a plurality of photosensors
Data Source
AI summary
A liquid crystal display (LCD) with a built-in touch screen includes: a first substrate including a sensor area having a plurality of photosensors; a second substrate positioned over the first substrate, and including a color filter, a light receiving portion, and a transparent electrode layer and a front polarizing plate; an LCD panel including a liquid crystal layer interposed between the first and second substrates; a touch screen driver circuit to measure a capacitance variation sensed through a first sensing line connected to the transparent electrode layer and to calculate a touch area using optical information sensed through a second sensing line connected to the photosensors when a contact object is in contact with the LCD panel, and to output position information of the contact object, sensed by determining whether a touch occurs and whether a multi-touch occurs using the capacitance variation and the touch area.