Capacitive Touch Detection in Liquid Crystal Display Devices
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Solution Overview
Problem
Existing liquid crystal display devices with integrated touch panels face challenges in thinning, design flexibility, and circuit integration due to the need for conductive films to be grounded and closely positioned, limiting their application in mobile devices and design freedom.
Innovation Solution
A display device configuration with pixel electrodes, counter electrodes, and detection electrodes that utilize A.C. drive scanning and write drive scanning to detect changes in electrostatic capacitance for touch input, allowing for thinner designs and improved integration of circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a conductive film for the touch panel is provided between the observation side substrate and the polarizing plate to form an electrostatic capacitance type touch panel, then the liquid crystal element can be thinned, but the conductive film must be set at the same potential as the user requiring proper grounding which limits mobile device application
Solution Approach 1:
The patent changes the electrical parameter of the touch panel by eliminating the requirement for the conductive film to be at the same potential as the user. Instead, it uses a conventional liquid crystal display structure where the touch panel electrodes are driven by standard liquid crystal drive circuits, allowing operation without user grounding while maintaining thin profile and mobile device compatibility.
2Measurement precision
If the conductive film for the touch panel is positioned very close to the finger of the user to ensure proper operation, then touch detection sensitivity is improved, but the degree of freedom of design is reduced and the conductive film cannot be disposed in deeper portions
Solution Approach 1:
The patent resolves the positioning constraint by utilizing the liquid crystal layer itself as the detection medium. Instead of requiring the conductive film to be positioned close to the finger in the thickness direction, the system detects touch by measuring changes in the liquid crystal orientation caused by the finger's proximity, allowing electrodes to be positioned in conventional locations while maintaining detection capability.
3Adaptability or versatility
If separate circuit portions for touch panel driving and coordinate detecting are provided in addition to the display driving circuit, then touch functionality is achieved, but circuit integration becomes difficult
Solution Approach 1:
The patent merges the touch panel drive circuit with the liquid crystal display drive circuit by using the same liquid crystal drive circuit to drive both the liquid crystal and the touch panel electrodes. The coordinate detection is performed by analyzing the capacitance changes in the liquid crystal layer itself, eliminating the need for separate touch detection circuitry and achieving full integration.
4Device complexity
If an electrostatic capacitance type touch panel is formed with the polarizing plate outer surface as the touch surface, then the liquid crystal element structure is simplified, but the conductive film must be very close to the finger limiting disposition options
Solution Approach 1:
The patent makes the liquid crystal layer serve dual functions: as the display medium for liquid crystal modulation and as the detection medium for touch input. By detecting changes in liquid crystal orientation caused by finger proximity, the system eliminates the need for a separate conductive film positioned close to the finger, allowing the polarizing plate to serve as the touch surface while maintaining conventional electrode positioning.
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
Enables a thinner display device configuration with enhanced design flexibility and integrated circuits, enabling effective touch input detection without the need for separate grounding, suitable for mobile applications.
Implementation Method 1
detection electrodes having respective electrostatic capacitances between the n counter electrodes and the detection electrodes; a detecting portion for detecting a change in voltage for the A.C. drive caused in each of the detection electrodes due to an influence of an external capacitance
Data Source
AI summary
A display device including: a plurality of pixels; pixel electrodes; n (n≧2) counter electrodes; a display functional layer; a write drive scanning portion; detection electrodes; an alternate current drive scanning portion; and a detecting portion.