Do-Young Lee

Contrast ratio of twisted nematic liquid crystal cells and its improvement

The light leakage of twisted nematic (TN) liquid crystal displays is investigated. While the TN mode has a robust structure in regard to light scattering, due to thermal fluctuations of the liquid crystals and light leakage from imperfect rubbing defects, it maintains significant residual retardation of the liquid crystal layer in the black state. The residual retardation is induced by the azimuthally twisted liquid crystal alignment near substrate surfaces and causes major light leakage in the black state. We investigated several methods to compensate for the residual retardation, and the methods include the adjustment of the helical power of the liquid crystal material, the increase of driving voltage, the control of rubbing direction and a newly designed compensation film with a small angle twist. Though all these methods improve the contrast ratio by about 30%, each method has its own weaknesses and limitations. The development of a new compensation film would provide a good chance for future TN applications.

Procedure-based development platform for communication protocol stack software

This paper presents a novel approach for developing a communication protocol stack efficiently. In this approach, a communication protocol stack is implemented directly from the message sequence chart (MSC) describing its behavior. To verify the proposed approach, we implemented a procedure-based development platform composed of MSC design tool, protocol stack framework, test framework, and MSC extractor. Procedures and their dependencies are specified through the MSC design tool during the design phase. They are translated into data structures and template codes which the protocol stack framework can handle during the implementation phase. These are further reused in the test framework with test configuration at the test phase. The test framework also supports reproduction tests with extracted MSCs from the test logs. This approach enables users to examine the system behavior by comparing MSCs — one drawn during the design phase and the other collected under the test phase, which makes it easier for the users to revise the design based on the test result. Finally, a virtuous development cycle is accomplished for the development process of protocol stack from the design to the test. We show that our platform is superior to FSM-based framework in terms of traceability, maintainability, and productivity by implementing LTE RRC protocol using both frameworks.

P-160: Improvement of the Contrast Ratio in Twisted Nematic LCD

Mainly due to the twisted directors near surface in dark state, the decreased contrast ratio of TN mode has been observed. Here we describe the investigation of the contrast ratio of twist nematic liquid crystal display (TN-LCD) with an optical compensation film, WV-film, by using computational simulation and suggest new method to improve the contrast ratio significantly. Our results indicated that by optimizing the pitch of liquid crystal with chiral dopant, the contrast ratio was improved about 20%, but the reverse twisted region of the liquid crystal occurs. By adopting twisted WV-Film, the contrast ratio was increased about 19% without the reverse twisted region.