Viewing angle dependence contrast

The number of addressable lines in a multiplexed LCD with acceptable contrast and viewing angle dependency is limited, although to a much lesser extent than using direct addressing. The maximum number of addressable lines (AO is given by (see Figure 2.15) ... 

A more sophisticated retardation plate is a film consisting of the perpendicular arranged combination of two optical uniaxial materials, e g., uniaxially stretched polycarbonate foil with a homeotropic oriented LC siloxane layer [18]. The purpose of such a foil is the improvement of the optical properties of LC displays, especially the viewing angle dependence of the contrast. 

In order to obtain images with a high contrast and to reduce the viewing-angle dependence, all STN displays need at least one retarder film which compensates the optical retardation of the switchable cell filled with a low-molecular-weight hquid-crystalline mixture. The conventional polymer retardation films used in these displays have a nearly constant optical retardation as a function of temperature. Its retardation value is usually adapted to the retardation of the STN cell at room temperature. However, the cell s retardation decreases with increasing temperature due to the thermal motion of the LC molecules in the cell. This leads to a mismatch between the retarder film... 

Temperature Dependence of Threshold Voltage Threshold Sharpness, Viewing Angle Dependence of Vf Viewing Angle ( Contrast ) Response Time... 

To improve the viewing angle dependence and contrast ratio of the twist cell, phase retardation plates are used [116]. Sometimes a second twist cell is placed after the first one with a 90° twist in the opposite sense. The two cells optically compensate for each other when place so that their directors are perpendicular on the facing surfaces. Thus the double-layered twisted device appears black between crossed polars for all wavelengths and has better viewing characteristics at oblique incidence [117]. 

Improvement of Viewing Angle Dependence of the Contrast Ratio... 

Pig. 4.5.1 Viewing angle dependence of the contrast ratio of the VA mode (a) TN mode (b) VA mode (c) VA mode with two retardation films (d) MVA mode [1]. 

The viewing angle dependence of the MVA-mode is wider than 160° from left to right and from up to down and the contrast is more than 10 to 1. For any viewing angle, no inversion of the grey scale can be observed. The MVA mode was commercialized in December 1997, and the specification of an MVA LCD is shown in Table 4.5.1 [5]. 

In the case of a helical pitch shorter than the wavelength of visible light, colouration due to selective reflection from the helical structure disappears and the rotation of the optical axis by deformation of the helical structure can be used for optical switching. This mode is called the Deformed-Helix Ferroelectric (DHF) liquid crystal mode. The DHF mode can realize stable continuous grey scale. Moreover, the viewing angle dependence of the contrast is small even in... 

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