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Multiplexing for Large Matrix, Dynamic Scattering, Liquid Crystal Cells

IP.com Disclosure Number: IPCOM000079985D
Original Publication Date: 1973-Oct-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 49K

Publishing Venue

IBM

Related People

Alt, PM: AUTHOR

Abstract

Limitations on the number of lines that might be scanned in a dynamic scattering liquid crystal (LC) display have recently been reviewed. See A. R. Kmetz, "Experimental Comparison of Multiplexing Techniques for Liquid Crystal Displays," 1972 SID Digest p. 66, June 1972. Those limits are, for conventional addressing: For a 2:1 selection scheme - 2 lines scanned; for a 3:1 selection scheme - 4 lines scanned. To overcome these severe limitations, a two-frequency addressing scheme is suggested where 10 to 20 lines may be scanned.

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Multiplexing for Large Matrix, Dynamic Scattering, Liquid Crystal Cells

Limitations on the number of lines that might be scanned in a dynamic scattering liquid crystal (LC) display have recently been reviewed. See A. R. Kmetz, "Experimental Comparison of Multiplexing Techniques for Liquid Crystal Displays," 1972 SID Digest p. 66, June 1972. Those limits are, for conventional addressing: For a 2:1 selection scheme - 2 lines scanned; for a 3:1 selection scheme - 4 lines scanned. To overcome these severe limitations, a two- frequency addressing scheme is suggested where 10 to 20 lines may be scanned.

Conventional dynamic scattering cells are used. Homogeneous or homeotropic alignment can be used, the latter being preferred for large scanning capability, the former preferred for moderate scanning and human factors considerations. The doping level depends on the number of lines to be scanned. The multiplexing scheme is illustrated and described below: a) A 3:1 amplitude selection scheme is employed. A 2:1 scheme can be used at a reduced scanning capability. b) Scanning and information pulses, as seen by the cells, consist of one period of a sinusoidal signal of frequency fp having zero average value. Other waveshapes of zero average value per period may be used but are less desirable. c) The frequency fp is chosen to be near, but less than, the cut-off frequency fc. Under these conditions, the worst case "off" element sees a cw sinusoidal signal of zero average value...