Vertical Alignment LCD Optical Compensation for Wide Viewing Angles
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Solution Overview
Problem
Liquid crystal display (LCD) devices operating in vertical alignment mode face a low contrast ratio when viewed from the side due to phase retardation caused by liquid crystal molecules, leading to reduced image quality.
Innovation Solution
The implementation of a display device configuration that includes a display panel with a liquid crystal layer, a first optical unit comprising a C-plate and a polarization plate, and a second optical unit with positive and negative A-plates, which gather the dispersed polarization states of red, green, and blue light into an extinction point on a Poincare sphere, thereby enhancing the contrast ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If liquid crystal molecules are aligned in vertical direction to achieve high contrast ratio in front view, then the contrast ratio of image viewed from front is improved, but the contrast ratio of image viewed from side deteriorates due to phase retardation in thickness direction
Solution Approach 1:
The optical compensation is divided into two independent units: a first optical unit (C-plate) positioned at the bottom of the display panel and a second optical unit (A-plates) positioned at the top. Each unit independently compensates for phase retardation in different directions, collectively resolving the side-viewing angle problem while maintaining front-view contrast.
Solution Approach 2:
Optical compensation films (C-plate and A-plates) are introduced as intermediary elements between the liquid crystal layer and the external environment. These intermediaries compensate for the phase retardation caused by the vertically aligned liquid crystal molecules, enabling both front and side viewing without contrast loss.
2Adaptability or versatility
If optical compensation films are added to improve side viewing angle, then the viewing angle and side contrast ratio are improved, but the device complexity increases
Solution Approach 1:
The C-plate and A-plates are designed to perform multiple functions: they compensate for phase retardation in both thickness and in-plane directions, gather dispersed polarization states into the extinction point, and maintain compatibility with standard vertical alignment liquid crystal modes. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The patent specifies precise parameter ranges for the optical compensation films, including thickness-direction phase retardation value (Rth) and in-plane phase retardation value (Ro), to optimize performance. By controlling these parameters within specific ranges, the system achieves effective compensation without requiring overly complex structures.
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 significantly increases the contrast ratio in side views by aligning the polarization states of light, improving image quality and viewing angles.
Implementation Method 1
The negative A-plate is a phase retardation film having a thickness-direction phase retardation value (Rth) that satisfies a numerical condition of Rth≤0 and nx≠ny. The positive A-plate is a phase retardation film having the thickness-direction phase retardation value (Rth) that satisfies a numerical condition of Rth≥0 and nx≠nym
Data Source
AI summary
A display device includes a display panel, a first optical unit, and a second optical unit. The display panel includes a first substrate, a second substrate, and a liquid crystal layer disposed between the first substrate and the second substrate. The liquid crystal layer is operated in a vertical alignment mode. The first optical unit includes a C-plate and a first polarization plate having a first absorption axis. The second optical unit includes a positive A-plate, a negative A-plate, and a second polarization plate having a second absorption axis substantially perpendicular to the first absorption axis. The positive A-plate and the negative A-plate may gather dispersed polarization states of a colored light.