Cumulative drive scheme and method for a liquid crystal display
First Claim
1. A method for changing a reflective state of picture elements that make up a flat-panel liquid crystal display comprising the steps of:
- a) arranging a voltage control addressing electrodes in relation to a layer of liquid crystal material that makes up the flat panel liquid crystal display for applying a control voltage across controlled picture element locations of the liquid crystal material;
b) defining a first voltage level for a application to a picture element of the display for converting said picture element from a relatively high reflective initial state to a relatively low reflective final stage;
said first voltage level of a size to maintain a picture element in a low reflective state if said picture element is initially in a low reflective state;
c) defining a second voltage level for application to a picture element of the display for converting said picture element from a relatively low reflective initial state of a relatively high reflective final state;
said second voltage level of a size to maintain a picture element in the high reflective state if said picture element is initially in a high reflective state;
d) defining a third voltage level for application to those picture element that are not subject to application of said first voltage level or said second voltage level, said third voltage level of an amplitude sufficiently low to retain said picture elements in their respective present reflective states; and
e) converting control signals indicating a reflective state of all picture elements into said first, second and third voltage levels and applying said first, second and third voltage levels to said voltage control addressing electrodes in a synchronized manner to refresh said liquid crystal display at at least a near video rate;
1) said first voltage level applied to a picture element as a series of short duration pulses of the first voltage level, a duration of a voltage pulse, defined as ton1, being such that a plurality of voltage pulses are required to convert the picture element from the relatively high reflective initial state to the relatively low reflective final state wherein a time between positive going edges of successive voltage pulses, defined as T1, is greater that ton1;
2) said second voltage level applied to a picture element as a series of short duration pulses of the second voltage level, a duration of a voltage pulse, defined as ton2, being such that a plurality of voltage pulses are required to convert the picture element from the relatively low reflective initial state of the relatively high reflective final state wherein a time between positive going edges of successive voltage pulses, defined as T2, is greater than ton2; and
3) said third voltage level applied to said picture elements that are not subject to application of said first voltage level or said second voltage level.
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Accused Products
Abstract
A liquid crystal display including driver circuitry which applies a series of voltage pulses at a frequency of approximately 60 Hz. to cumulatively change a reflectance state of a pixel in an array of pixels at a near video updating rate. The display includes a near video rate updating portion, while the remainder of the display has a slower updating frequency or rate. The display is comprised of a bistable cholesteric liquid crystal material sandwiched between an electrode array having a plurality of row and column electrodes. In one operating embodiment, the driver circuitry generates a unipolar row and column waveforms, the row waveforms being applied to the row electrodes and the column waveforms being applied to the column electrodes of the near video rate updating portion. Approximately every 16 milliseconds, a pixel in the near video rate updating portion receives a control voltage pulse corresponding to the difference between the row and column waveforms. Application of six to seven control voltage pulses is sufficient to change the reflectance state of the pixel. In a second operating embodiment, the driver circuitry generates bipolar row and column waveforms. In alternate embodiments, dual column driver circuitry is provided and interlacing schemes are used to increase the number of rows in the near video rate updating portion of the display.
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Citations
42 Claims
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1. A method for changing a reflective state of picture elements that make up a flat-panel liquid crystal display comprising the steps of:
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a) arranging a voltage control addressing electrodes in relation to a layer of liquid crystal material that makes up the flat panel liquid crystal display for applying a control voltage across controlled picture element locations of the liquid crystal material; b) defining a first voltage level for a application to a picture element of the display for converting said picture element from a relatively high reflective initial state to a relatively low reflective final stage;
said first voltage level of a size to maintain a picture element in a low reflective state if said picture element is initially in a low reflective state;c) defining a second voltage level for application to a picture element of the display for converting said picture element from a relatively low reflective initial state of a relatively high reflective final state;
said second voltage level of a size to maintain a picture element in the high reflective state if said picture element is initially in a high reflective state;d) defining a third voltage level for application to those picture element that are not subject to application of said first voltage level or said second voltage level, said third voltage level of an amplitude sufficiently low to retain said picture elements in their respective present reflective states; and e) converting control signals indicating a reflective state of all picture elements into said first, second and third voltage levels and applying said first, second and third voltage levels to said voltage control addressing electrodes in a synchronized manner to refresh said liquid crystal display at at least a near video rate; 1) said first voltage level applied to a picture element as a series of short duration pulses of the first voltage level, a duration of a voltage pulse, defined as ton1, being such that a plurality of voltage pulses are required to convert the picture element from the relatively high reflective initial state to the relatively low reflective final state wherein a time between positive going edges of successive voltage pulses, defined as T1, is greater that ton1; 2) said second voltage level applied to a picture element as a series of short duration pulses of the second voltage level, a duration of a voltage pulse, defined as ton2, being such that a plurality of voltage pulses are required to convert the picture element from the relatively low reflective initial state of the relatively high reflective final state wherein a time between positive going edges of successive voltage pulses, defined as T2, is greater than ton2; and 3) said third voltage level applied to said picture elements that are not subject to application of said first voltage level or said second voltage level. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 33, 34, 39, 40, 41, 42)
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10. Display apparatus for displaying an image comprising:
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a) a chiral nematic liquid crystal display material that forms a sheet which extends over an image area for presenting a viewing image; b) confining structure for encapsulating the sheet of liquid crystal display material that includes electrode structure for imposing a selection field across a thickness of the liquid crystal display material for applying the selection field across individually controllable pixels that make up the image area; and c) drives circuitry for updating the pixels at a video refresh rate by applying a first voltage level across the thickness of the liquid crystal display material to those pixels to be converted from a relatively high reflective initial state to a relatively low reflective final state and to those pixels to be maintained in a low reflective state, the first voltage level being applied as a series of short duration pulses of the first voltage level, a duration of a voltage pulse, defined as ton1, being such that a plurality of voltage pulses are required to convert a pixel from the relatively high reflective initial state to the relatively low reflective final state wherein a time between leading edges of successive voltage pulses, defined as T1, is greater than ton1 and by applying a second voltage level across the thickness of the liquid crystal display material to those pixels to be converted from a relatively low reflective initial state to a relatively high reflective final state and to those pixels to be maintained in a high reflective state, the second voltage level being applied as a series of short duration pulses of the second voltage level, a duration of a voltage pulse, defined as ton2, being such that a plurality of voltage pulses are required to convert a pixel from the relatively low reflective state to the relatively high reflective final state wherein a time between leading edges of successive voltage pulses, defined as T2, is greater than ton2 and by applying a third voltage level across the thickness of the liquid crystal display material to those pixels not subject to application of said first voltage level or said second voltage level, said third voltage level of an amplitude sufficiently low to retain said pixels in their respective present reflective states. - View Dependent Claims (35, 36)
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11. Driver circuitry for changing a reflective state of an array of picture elements that make up a flat-panel liquid crystal display, a picture element being defined by an intersection of a first row electrode segment of a set of row electrode segments and a first column electrode segment of a set of column electrode segments, the sets of row and column electrode being spaced apart by a layer of liquid crystal material, the driver circuitry comprising:
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a) row driver circuitry electrically coupled to the set of row electrode segments and generating a row waveform; b) column driver circuitry electrically coupled to the set of column electrode segments and generating a column waveform; c) control circuitry coupled to the row driver circuitry and the column driver circuitry for synchronizing generation and application of the row waveform and the column waveform to the first row electrode segment and the first column electrode segment to generate a resultant voltage across the picture element, which changes the reflective state of the picture element; and d) the resultant voltage being a first voltage level if the picture element is to be converted from a relatively high reflective initial state to a relatively low reflective final state or is to be maintained in a low reflective state, the first voltage level being applied as a series of short duration of the first voltage level, a duration of a voltage pulse, defined as ton1, being such that a plurality of voltage pulses are required to convert the picture element from the relatively high reflective initial state to be relatively low reflective final state wherein a time between leading edges of successive voltage pulses, defined as T1, is greater than ton1, the resultant voltage being a second voltage level if the picture element is to be converted from a relatively low reflective initial state to a relatively high reflective final state or is to be maintained in a high reflective state and the resultant voltage being a third voltage level which is applied to those picture elements not subject to application of said first voltage level or said second voltage level, said third voltage level of an amplitude sufficiently low to retain said picture elements in their respective present reflective states. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 37, 38)
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28. Driver circuitry for changing a reflective state of an array of picture elements that make up a flat-panel liquid crystal display, a picture element being defined by an intersection of a first row electrode segment of a set of row electrode segments and a first column electrode segment of a set of column electrode segments, the sets of row and column electrode segments being spaced apart by a layer of liquid crystal material, the driver circuitry comprising:
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a) row driver circuitry electrically coupled to the set of row electrode segments and generating a row waveform; b) column driver circuitry electrically coupled to the set of column electrode segments and generating a column waveform; c) control circuitry coupled to the row driver circuitry and the column driver circuitry for synchronizing generation and application of the row waveform and the column waveform to the first row electrode segment and the first column electrode segment to generate a resultant voltage across the element which changes the reflective state of the picture element; and d) the resultant voltage being a first voltage level if the picture element is to be converted from a relatively low reflective initial state to a relatively high reflective final state or is to be maintained in a high reflective state, the first voltage level being applied as a series of short duration pulses of the first voltage level, a duration of a voltage pulse, defined as ton2, being such that a plurality of voltage pulses are required to convert the picture element from the relatively low reflective initial state to the relatively high reflective final state wherein a time between leading edges of successive voltage pulses, defined as T2, is greater than ton2, the resultant voltage being a second voltage level if the picture element is to be converted from a relatively high reflective initial state to a relatively low reflective final state or is to be maintained in a low reflective state and the resultant voltage being a third voltage level which is applied to those picture elements not subject to application of said first voltage level or said second voltage level, said third voltage level of an amplitude sufficiently low to retain said picture elements in their respective present reflective states. - View Dependent Claims (29, 30, 31, 32)
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Specification