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Combination Reflective Transmissive Liquid Crystal Display

IP.com Disclosure Number: IPCOM000078462D
Original Publication Date: 1973-Jan-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 3 page(s) / 29K

Publishing Venue

IBM

Related People

Young, WR: AUTHOR

Abstract

In liquid crystal displays wherein there are contained relatively few alphanumeric characters (20 or less), operation can be in either the reflective or transmissive mode. The reflective mode is advantageous since display brightness increases with ambient brightness thereby eliminating display washout in bright light conditions. Also, the reflective mode eliminates the need for an internal light source, thereby saving a power drain. However, the use of the reflective mode of operation presents the disadvantage in that, in a dark or dimly-lit area, the display is not bright enough to be read. For example, for such applications as wristwatches, ambient light may be intense enough for 90-95% of the viewing occasions.

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Combination Reflective Transmissive Liquid Crystal Display

In liquid crystal displays wherein there are contained relatively few alphanumeric characters (20 or less), operation can be in either the reflective or transmissive mode. The reflective mode is advantageous since display brightness increases with ambient brightness thereby eliminating display washout in bright light conditions. Also, the reflective mode eliminates the need for an internal light source, thereby saving a power drain. However, the use of the reflective mode of operation presents the disadvantage in that, in a dark or dimly-lit area, the display is not bright enough to be read. For example, for such applications as wristwatches, ambient light may be intense enough for 90-95% of the viewing occasions. However, a viewing problem exists in the other 5-10% of the instances of viewing where reflective displays are employed.

There is described a liquid crystal display cell, which is characterized by a combination reflective/transmissive mode of operation. Such combination mode of operation is accomplished in the cell by incorporating therein a partially-coated mirror and an internal light source for transmissive operation. Figs. 1 and 2 are different illustrative examples of the display cell.

Referring to Fig. 1, the structure 10 is a transparent electrode and the structure 12 is a partially-coated mirror electrode, there being disposed therebetween a liquid crystal material 14. Electrode 10 can suitably comprise tin oxide or indium oxide on a glass substrate, and electrode 12 may suitably comprise chromium or aluminum on a glass substrate. For operation in the normal-reflective mode (passive operation), ambient light is employed. Most of such light will be either scattered or reflected from mirror-electrode 12, thereby producing a normal reflective display. For operation in the transmissive mode, there is provided an internal light source 16 which has a switch associated therewith that can be suitably located on an external part of the display cell. When light source 16, which can be for example a light-emitting diode, electroluminescent body, etc., and which is suitably located behind and possibly to the side of the electrodes is provided, the resultant light produced thereby passes into a plastic body 18 suitably a plas...