General 2 voltage levels driving scheme for cholesterical liquid crystal displays
AssigneeEastman Kodak Company
InventorsXiang-Dong Mi, Stanley W. Stephenson
Life of this patent
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Abstract
A driving scheme for chiral nematic (cholesteric) liquid crystal displays comprises a preparation step, a holding-selection step, and an evolution step. The column and row drivers require only 2 voltage levels: U or 0. Duty cycles and phases in the preparation step, the holding-selection step, and the evolution step, are varied to generate optimized contrast, brightness, and gray levels on cholesteric liquid crystal displays.
Claims41
A method of writing pixels in a cholesteric liquid crystal display having opposing rows and columns of electrodes and cholesteric liquid crystal material disposed between said rows and columns of electrodes, the cholesteric liquid crystals having a plurality of reflective states, comprising the steps of:
- a) in a first preparation step, applying row and column voltage pulses, all pulses having the same minimum voltage and the same maximum voltage with a duty cycle of approximately 50% and adjusting the relative phase of the row and column voltage pulses to provide a bipolar field with a duty cycle varying from 90% to 100% across the cholesteric material and sufficient to produce a field that causes the cholesteric material to be in a homeotropic state;
- b) in a second holding-selection step, applying row and column voltage pulses and with the same minimum and maximum voltages, adjusting the duty cycles of the row and column voltage pulses to be the same and adjusting the relative phase between the row and column pulses of selected ON pixels to write ON data into the selected ON pixels and adjusting the relative phases of selected OFF pixels to be in phase to write OFF data into the selected OFF pixels;
- and
- c) in a third evolution step applying row and column voltage pulses at the same minimum and maximum voltages with substantially the same duty cycle and with different relative phases to cause the pixels to evolve to a written reflective state.
A method for writing data to pixels in a cholesteric liquid crystal display having a matrix of electrodes arranged in rows and in columns and a cholesteric liquid crystal material disposed between the rows and columns to form pixels in regions between overlapping row and column electrodes and for displaying image data in the pixels in accordance with electrical voltage applied to the electrodes of the rows and columns, the method comprising:
- a) generating one or more trains of pulses wherein the pulses in each train have a duty cycle, a relative phase with respect to each other, and only one of two amplitudes including a maximum amplitude and a minimum amplitude;
- b) applying one pulse train to the rows and another pulse train to the columns during one or more steps of the group comprising preparation, preparation-holding, pre-holding, selection, post-holding, and evolution;
- and
- c) adjusting duty cycle and relative phases of the pulse trains applied to the row and column electrodes during one or more of the steps for writing image data to a pixel, or adjusting contrast and reflectance of a pixel, or adjusting gray level of a pixel.
A display apparatus for cholesteric liquid crystal display comprising:
- a) a matrix of electrodes arranged in rows and in columns, the regions between overlapping row and column electrodes defining pixels in the display;
- b) a cholesteric liquid crystal material disposed between the rows and columns for assuming a plurality of gray level states in response to the selective application of voltage signals to the rows and columns;
- c) control electronics for generating one or more trains of pulses wherein the pulses in each train have a duty cycle, a relative phase with respect to other pulse trains, and only one of two amplitudes including a maximum amplitude and a minimum amplitude, said control electronics including:
- i) phase control means for adjusting the phase between row and column pulse trains;
- ii) duty cycle control means for adjusting the duty cycle of the row and column pulse trains;
- and
- iii) the phase and duty cycle control means operable during one or more steps of the group comprising steps of preparation, preparation-holding, pre-holding, selection, post-holding and evolution in order to control writing image data to a pixel, or adjusting contrast and reflectance of a pixel, or adjusting gray level of a pixel.
A cholesteric liquid crystal display comprising:
- a) a matrix of electrodes arranged in rows and columns, the regions between overlapping row and column electrodes defining pixels in the display;
- b) a cholesteric liquid crystal material disposed between the rows and columns for assuming one of two stable states in response to the selective application of voltage signals to the rows and columns;
- c) means for generating one or more trains of pulses wherein the pulses in each train have a duty cycle, a phase with respect to each other, and only one of two amplitudes including a maximum amplitude and a minimum amplitude, said control electronics including:
- i) means for controlling phase between row and column pulse trains;
- ii) means for controlling duty cycle of the row and column pulse trains;
- and
- iii) the means for controlling phase and duty cycle operable during one or more steps of the group consisting of preparation, preparation-holding, pre-holding, selection, post-holding and evolution in order to control writing image data to a pixel, or adjusting contrast and reflectance of a pixel, or adjusting gray level of a pixel.
Dependencies are inferred from the claim text.