Method and apparatus for driving reflective bistable cholesteric displays

Inactive Publication Date: 2001-08-23
THE HONG KONG UNIV OF SCI & TECH
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  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

0031] In the preferred embody the reset voltage V.sub.r may be the maximum high voltage required. This may generally fall in the range of 40 V to 25 V depending on the reset pulse duration required. For a 40 V reset pulse, the reset pulse duration can be as small as 10 ms. For a 25 V reset pulse, the reset pulse duration ha

Problems solved by technology

A number of voltage levels are needed for matrix driving of the display making the invention rather cumbersome.
However, this scheme has the disadvantage of a high voltage requirement and the relative slowness in scanning.
A further drawback in the dynamic scheme of Yang et al. is the appearance of a dark band in the d

Method used

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  • Method and apparatus for driving reflective bistable cholesteric displays
  • Method and apparatus for driving reflective bistable cholesteric displays
  • Method and apparatus for driving reflective bistable cholesteric displays

Examples

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Embodiment Construction

[0032] To implement the method in a preferred embodiment, a low voltage cell has to be made. Several test cells were made. In a particular preferred embodiment, the cell gap of the sample LCD cell was 5 .mu.m. The liquid crystal was provided with a homogeneous alignment and a mixture of a chiral dopant and ZLI 6204 were used in the sample cells. Although these are provided in the preferred embodiment, other nematic liquid crystals can also be used.

[0033] The response of the BCD cell to pulses of various voltages was measured using the following procedure, First the cell was driven to the reflective P state by a refresh pulse. The stabilized reflectance of the cell was measured as a function of the voltage of a switching pulse. This procedure was repeated with the cell in the FC state initially. Both the width of the applied switching pulse and the refresh pulse were 10 ms in this measurement. The pulse duration was changed in other measurements taken.

[0034] In this particular experi...

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PUM

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Abstract

This invention provides a method and apparatus for driving bistable cholesteric liquid crystal displays. The method and apparatus provided a display in which all the pixels are initially driven to the P state. Selected pixels for the display are then driven to the FC state to provide the desired message. The state of the pixels is then maintained for a viewing period prior to any resetting of the display to the P state. The switching from the P state to the FC state allows faster addressing times and lower voltages to be used ha driving the display.

Description

[0001] 1. Field of the Invention[0002] This invention relates to bistable cholesteric displays and, in particular, although not necessarily solely, a method and apparatus for driving reflective bistable cholesteric displays.[0003] 2. Description of the Prior Art[0004] Bistable cholesteric liquid crystal displays "BCD" are already well known and utilized in a number of applications. The bistable cholesteric display usually consist of two pieces of glass forming a thin liquid crystal cell. The liquid crystal material is usually composed of twisted nematic liquid crystal heavily doped with a chiral dopant to give the liquid crystal a strong twist sense or chirality. Such cholesteric liquid crystal displays exhibit two stable states at a zero driving voltage. The first of these is the reflective planar "P" state and, as the name suggests, is reflective in normal usage. The second state is the scattering / transparent focal conic (FC) state. In normal usage, the FC state is transparent.[00...

Claims

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Application Information

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IPC IPC(8): G02F1/137G09G3/36
CPCG02F1/13718G09G3/3629G09G2300/0486G09G2310/063
Inventor KWOK, HOI-SINGYU, FEI-HONGLI, QING-CHENGYIP, WING CHIU
Owner THE HONG KONG UNIV OF SCI & TECH
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