Color fluorescent liquid crystal display

• US 5,402,143 A
• Filed: 05/18/1994
• Issued: 03/28/1995
• Est. Priority Date: 12/23/1991
• Status: Expired due to Fees

• Current Assignee: PixTech, Inc.
• Original Assignee: Panocorp Display Systems
• Inventors: Liang, Jemm, Ge, Shichao
• Primary Examiner(s): BRIER, JEFFERY A
• Application Number:
  US08/245,454
• Time in Patent Office: 314 Days
• Field of Search: 345/4, 345/5, 345/74, 345/75, 345/102
• US Class Current: 345/102
• CPC Class Codes: G02F 1/133621 providing coloured light G02F1/133617, G02F1/133533 take precedence
• CPC Class Codes: G02F 1/133622 Colour sequential illumination
• CPC Class Codes: G02F 1/133625 Electron stream lamps
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/024 Scrolling of light from the illumination source over the display in combination with the scanning of the display screen
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 3/2025 the sub-frames having all the same time duration
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: H01J 29/467 Control electrodes for flat display tubes, e.g. of the type covered by group H01J31/123

Abstract

An electronic fluorescent device (EFD) is used as the back light source for a black/white LCD. Where the EFD provides red, green and blue light, the LCD displays multi-color or full-color images. The EFD includes a number of cathodes disposed in a vacuum chamber, an anode, phosphor strips near the anode, and grid electrodes for controlling the timing of the light generation and sequential color addressing. The control system may be such that the transmission rate of the LCD is proportional to the amplitude of the input signal forming an analog system; the EFD then simply provides sequential red, green and blue light pulses of constant intensity. Alternatively, selected pixels of the LCD may be addressed digitally to be either on or off, and the intensities of the red, green and blue pulses provided by the EFD are varied. In both instances, full scale gray tone monochromatic, multi-color or full-color images can be achieved.

Claims

1. A method for image display employing an apparatus comprising:

a front end unit including;

(a) an array of row electrodes and an array of column electrodes transverse to the row electrodes;

(b) a layer of liquid crystal material placed between and overlapping the two arrays at a pixel plane, wherein the row electrodes intersect the column electrodes over areas of intersection of the layer at the pixel plane to define a spatial sequence of a first through nth linear arrays of pixels, n being a positive integer, said n arrays arranged spatially consecutively in the plane from the first array to the nth array;

a back light unit adjacent to the front end unit and having an array of elongated light emitting elements arranged in a light emitting plane alongside the pixel plane so that each light emitting element is spatially aligned and corresponds to at least one array of pixels, said elements including at least elements that emit light of a first color defining first color elements, and elements that emit light of at least one additional color defining additional color elements, wherein the total thickness of the apparatus is less than 2 cm;

said method comprising;

applying electrical signals to the two arrays of electrodes to cause each of the n arrays of pixels to modulate their light transmittance and one at a time during a corresponding scanning cycle defining the scanning of each such pixel array and so that the pixel arrays are sequentially scanned from the first to the nth array to sequentially modulate their light transmittance, said applying step applying a first sequence of first color data signals to modulate the light transmittance of the pixels for displaying and controlling the brightness of images of the first color, said applying step applying at least one additional sequence of other color data signals to modulate the light transmittance of the pixels for displaying images of said at least one additional color, said at least one additional sequence of signals being applied subsequent to or preceding the application of the first sequence of signals;

during the application of the first sequence, causing each of the first color elements aligned with and corresponding to at least one pixel array to emit light at a time delay after electrical signals are applied to the electrodes during the scanning cycle for such at least one pixel array to modulate the light transmittance of the corresponding at least one array of pixels for displaying and controlling the brightness of images of the first color; and

during the application of the at least one additional sequence, causing each of the additional color elements aligned with and corresponding to at least one pixel array to emit light at a time delay after electrical signals are applied to the electrodes during the scanning cycle for such at least one pixel array to modulate the light transmittance of the corresponding at least one array of pixels for displaying and controlling the brightness of images of said at least one additional color, so that different elements emitting light of the same color are caused to emit light sequentially over time and sequentially spatially across the light emitting plane;

said time delay or delays being such that each element emits light substantially at or near the end of the corresponding scanning cycle of the corresponding at least one array of pixels.

2. The method of claim 1, wherein the causing steps cause the elements to emit light pulses that are short in duration compared to the duration of the scanning cycles.

3. The method of claim 1, further comprising performing sequentially and repeatedly said applying step for applying said first sequence and said at least one additional sequence and performing sequentially and repeatedly said causing steps to cause the elements to emit sequentially light of the first color and said additional color, for a full color or multicolor display.

4. The method of claim 1, wherein said first color elements are grouped into groups of elements, and said additional color elements are grouped into groups of elements, the elements in each group being adjacent to one another and overlapping a corresponding group of array of pixels, said causing steps being such that they cause the elements in each group to emit light at the same time after electrical signals are applied to the electrodes to change the light transmittance of the arrays of pixels in the corresponding group of arrays of pixels to become light transmitting.

5. The method of claim 1, wherein said back light unit includes:

a housing defining a vacuum chamber therein, said light emitting elements being in said chamber;

an anode in the chamber, said anode overlapping entirely a plurality of arrays of pixels;

a plurality of cathodes in the chamber; and

a plurality of control electrodes in the chamber, said control electrodes aligned with and corresponding to the light emitting elements, wherein said causing steps include applying electrical signals to the anode, cathodes, and control electrodes.

6. The method of claim 5, wherein at least one of the cathodes does not spatially overlap at least one of the light emitting elements, said method further comprising causing the cathodes to generate electrons, wherein said step of applying electrical signals to the anode, cathodes, and control electrodes is such that electrons generated by said at least one cathode are directed towards said at least one of the elements to cause light emission therefrom.

7. The method of claim 6, wherein said step of applying electrical signals to the anode, cathodes, and control electrodes is such that electrons generated by said cathodes are spread out laterally before they are directed towards the elements.

8. The method of claim 5, wherein said elements are phosphor strips that generate light of a first, second or third color, and wherein said set of control electrodes comprises a plurality of subsets of control electrodes, each subset being aligned with and corresponding to a phosphor strip, said causing steps comprising applying a time sequence of predetermined voltages to said subsets of control electrodes to direct electrons sequentially towards phosphor strips that generate sequentially light of a first color, light of a second color, and then light of a third color.

9. The method of claim 5, wherein each of the first or additional sequence comprises a time sequence of first color or other color LCD data pulses and other data signals wherein said causing steps include applying a time sequence of electrical pulses, each electrical pulse being applied at a first time delay after the application of and corresponds to a first color or other color LCD data pulse,

wherein each electrical pulse is applied at a second predetermined time period preceding the LCD data pulse that succeeds the LCD data pulse corresponding to such electrical pulse to reduce crosstalk.

10. The method of claim 9, wherein the LCD data pulses are applied at a scanning speed, and wherein said second time period is greater than kd(tan0), where d is the distance between the elements in the light emitting plane and the liquid crystal layer, 0 the liquid crystal viewing angle, and k a constant inversely proportinal to the scanning speed of the LCD data pulses.

11. The method of claim 9, wherein said first predetermined time delay is such that each electrical pulse is applied when the transmission rate of the selected pixels through which light transmission is modulated exceeds about 50% of the light transmittance of such pixels upon settlement.

12. The method of claim 8, wherein said array of row or column electrodes includes M row or column electrodes divided into p groups of n rows or columns each, wherein said phosphor strips are divided into p groups each aligned and corresponding with one of the p groups of row or column electrodes, wherein the step for applying signals to the row or column electrodes and the step for applying voltages to the subsets of control electrodes are such that when such signals are applied to electrodes in a group, electrons destined for the strips of the corresponding group are not directed towards the strips until the transmission rate of the selected pixels corresponding to the selected group of row or column electrodes exceeds 50% of the light transmittance of such pixels upon settlement.

13. The method of claim 1, wherein said causing steps generate and direct sequentially red, blue and green light towards each pixel, so that when any pixel is light transmitting, red, blue or green light is permitted to pass through the entire pixel area to display multi-color or full color images.

14. An apparatus for image display comprising:

a front end unit including;

(a) an array of row electrodes and an array of column electrodes transverse to the row electrodes;

(b) a layer of liquid crystal material placed between and overlapping the two arrays at a pixel plane, wherein the row electrodes intersect the column electrodes over areas of intersection of the layer at the pixel plane to define a spatial sequence of a first through nth linear arrays of pixels, n being a positive integer, said n arrays arranged spatially consecutively in the plane from the first array to the nth array;

a flat panel back light-unit adjacent to the front end unit and defining a vacuum chamber therein and an array of elongated light emitting elements in the chamber arranged in a light emitting plane alongside the pixel plane so that each light emitting element is spatially aligned and corresponds to at least one array of pixels, said elements including at least elements that emit light of a first color defining first color elements, and elements that emit light of at least one additional color defining additional color elements, wherein the total thickness of the front end and back light units is less than 2 cm;

a first device applying electrical signals to the two arrays of electrodes to cause each of the n arrays of pixels to modulate their light transmittance one at a time during a corresponding scanning cycle defining the scanning of each such pixel array and so that the pixel arrays are sequentially scanned from the first to the nth array to sequentially modulate their light transmittance, said first device applying a first sequence of first color data signals to modulate the light transmittance of the pixels for displaying and controlling the brightness of images of the first color, said first device applying at least one additional sequence of other color data signals to modulate the light transmittance of the pixels for displaying images of said at least one additional color, said at least one additional sequence of signals being applied subsequent to or preceding the application of the first sequence of signals;

a second device causing each of the first color elements aligned with and corresponding to at least one pixel array to emit light at a time delay after electrical signals are applied to the electrodes during the scanning cycle for such at least one pixel array and during the application of the first sequence, to modulate the light transmittance of the corresponding at least one array of pixels for displaying and controlling the brightness of images of the first color; and

wherein during the application of the at least one additional sequence, said second device causes each of the additional color elements aligned with and corresponding to at least one pixel array to emit light at a time delay after electrical signals are applied to the electrodes during the scanning cycle for such at least one pixel array to modulate the light transmittance of the corresponding at least one array of pixels for displaying and controlling the brightness of images of said at least one additional color, so that elements emitting light of the same color are caused to emit light sequentially over time and sequentially spatially across the light emitting plane;

said time delay or delays being such that each element emits light at a time substantially at or near the end of the scanning cycle of the corresponding at least one array of pixels.

15. The apparatus of claim 14, wherein said back light unit includes:

a housing defining said vacuum chamber therein, said light emitting elements being in said chamber;

an anode in the chamber;

a plurality of elongated cathodes in the chamber, wherein at least one of said cathodes does not spatially overlap at least one light emitting element; and

a plurality of control electrodes in the chamber, said control electrodes aligned with and corresponding to the light emitting elements, wherein said causing steps include applying electrical signals to the anode, cathodes including said at least one cathode, and control electrodes.

16. The apparatus of claim 15, further comprising a third device causing the cathodes to generate electrons, wherein said first device applies electrical signals to the anode, cathodes including said at least one cathode, and control electrodes such that electrons generated by said at least one cathode are directed towards said at least one of the elements to cause light emission therefrom.

17. The apparatus of claim 16, wherein said first device applies electrical signals to the anode, cathodes, and control electrodes such that electrons generated by said cathodes are spread out laterally before they are directed towards the elements.

18. The apparatus of claim 15, wherein said elements are phosphor strips that generate light of a first, second or third color, and wherein said set of control electrodes comprises a plurality of subsets of control electrodes, each subset being aligned with and corresponding to a phosphor strip, said second device applying a time sequence of predetermined voltages to said subsets of control electrodes to direct electrons sequentially towards phosphor strips that generate sequentially light of a first color, light of a second color, and then light of a third color.

19. The apparatus of claim 15, wherein each of the first or additional sequence comprises a time sequence of first color or other color LCD data pulses and other data signals wherein said causing steps include applying a time sequence of electrical pulses, each electrical pulse being applied at a first time delay after the application of and corresponds to a first color or other color LCD data pulse,

wherein each electrical pulse is applied at a second predetermined time period preceding the LCD data pulse that succeeds the LCD data pulse corresponding to such electrical pulse to reduce crosstalk.

20. The apparatus of claim 19, wherein the LCD data pulses are applied at a scanning speed, and wherein said second time period is greater than kd(tan0), where d is the distance between the elements in the light emitting plane and the liquid crystal layer, 0 the liquid crystal viewing angle, and k a constant inversely proportinal to the scanning speed of the LCD data pulses.

21. A flat panel display apparatus comprising:

a layer of liquid crystal material;

a first device for addressing locations on said layer to cause said layer to modulate the intensity of light transmitted through said layer at selected pixel locations, said locations arranged in linear pixel arrays; and

a back light source comprising;

a plurality of cathodes disposed in a chamber;

a second device for causing the cathodes to emit electrons;

an anode in the chamber overlapping entirely a plurality of the arrays of pixels;

at least a first and a second set of control electrodes in the chamber substantially parallel to the layer, said two sets of control electrodes being on different planes between the anode and cathodes;

elements disposed in the chamber at or near the anode and responsive to said electrons for generating and directing light towards the layer of liquid crystal material, said elements arranged in arrays aligned with and corresponding to the linear pixel arrays, at least one of said cathodes not overlapping or aligned with any element; and

a third device for applying electrical signals to the anode, cathodes and control electrodes, causing the electrons emitted by the cathodes to travel towards the anode, and electrons emitted by said at least one cathode to travel toward an element;

wherein the electrical signals applied to the first or the second set of control electrodes are such that electrons emitted by the cathodes are caused to spread out laterally in the chamber and the cathodes and control electrodes and the electrical signals are such that electrons from different cathodes are directed towards a selected element to cause light emitted by the selected element to be directed to the corresponding pixel array to generate images.

22. The apparatus of claim 21, said elements generating and directing sequentially red, blue and green light towards each pixel, so that when any pixel is light transmitting, red, blue or green light is permitted to pass through the entire pixel area to display multi-color or full color images.

23. The apparatus of claim 21, wherein said elements comprises phosphor strips that emit light in one of three colors, said colors including red, blue and green, towards the anode in response to electrons, said strips being substantially parallel to the contol electrodes.

24. The apparatus of claim 23, wherein said set of control electrodes comprises a plurality of subsets of grid electrodes, each subset overlapping and corresponding to a phosphor strip, said third device applying a time sequence of predetermined voltages to said subsets of grid electrodes to direct electrons sequentially towards phosphor strips that generate sequentially light of a first color, light of a second color, and then light of a third color.

25. The apparatus of claim 23, said strips being arranged in an array where strips for emitting light of the three colors alternate periodically.

26. The apparatus of claim 21, wherein said back light source includes a housing comprising a face plate facing the liquid crystal layer and a back plate, said two plates defining between them the chamber, said housing further comprising a plurality of elongated spacers between the two plates dividing the chamber into a number of subchambers.

27. The apparatus of claim 26, wherein said spacers extend between the two plates to support the plates against atmospheric pressure, said spacers being wedge-shaped with thicker and thinner sides, their thinner sides being attached to the face plate to reduce any dark areas caused thereby.

28. The apparatus of claim 26, said spacers having diffusive light reflecting surfaces.

29. The apparatus of claim 21, said first device comprising an array of row electrodes and an array of column electrodes transverse to the row electrodes, said layer of liquid crystal material placed between and overlapping the two arrays at a pixel plane, wherein the row electrodes intersect the column electrodes over areas of intersection of the layer at the pixel plane to define a spatial sequence of a first through nth linear arrays of pixels, n being a positive integer, said n arrays arranged spatially consecutively in the plane from the first array to the nth array;

said first or second set of control electrodes divided into groups of control electrodes with each group corresponding to and aligned with a group of elements, wherein during at least one cycle of a scanning operation;

said first device applying scanning pulses to a selected electrode in the row or column electrode array and LC data pulses to the electrodes in the remaining electrode array to select pixels of the pixel array corresponding to said one selected electrode, through which transmission of light is modulated, and

said third device applying electrical data potential pulses to the group of control electrodes corresponding to and aligned with said selected electrode for sequentially emitting light of one or more colors through said selected pixels in the pixel row, said electrical data potential pulses being of predetermined time relationship with the scanning pulses for displaying monochromatic, multi-color or full color data in said pixel row.

30. The apparatus of claim 29, wherein selected pixels corresponding to the selected electrode during said at least one cycle are not in the nth array, and wherein during the next cycle of the scanning operation,

said first device applies additional LCD scanning pulses to the selected electrode adjacent to the electrode scanned in the previous cycle and LCD data pulses to the remaining electrode array to select pixels of the corresponding next pixel array through which transmission of light is permitted, and

said third device applies data potential pulses to the group of control electrodes corresponding to and aligned with said next row electrode for sequentially emitting light of one or more colors through said selected pixels in the next pixel array, said data potential pulses being of predetermined time relationship with the additional scanning pulses for displaying monochromatic, multicolor or full color data in said next pixel array.

31. The apparatus of claim 30, wherein the third device applies each data potential pulse at a first predetermined time delay after the previous scanning LCD pulse and at a second predetermined time period preceding the next LCD scanning pulse to reduce crosstalk.

32. The apparatus of claim 31, wherein said second time period is greater than kd(tan0), where d is the distance between the phosphor strips and the liquid crystal layer, 0 the liquid crystal viewing angle, and k a constant inversely proportinal to the scanning speed.

33. The apparatus of claim 31, wherein said first predetermined time delay is such that the transmission rate of the selected pixels through which light transmission is permitted exceeds about 50% of the transmission rate at settlement when each data potential pulse is applied.

34. The apparatus of claim 29, said elements including phosphor strips, wherein one of said arrays includes M row or column electrodes divided into p groups of n rows or columns each, wherein said phosphor strips are divided into p groups each aligned and corresponding with one of the p groups of row or column electrodes, wherein the third device is such that when the voltages are applied to electrodes in a group, electrons destined for the strips of the corresponding group are not directed towards the strips until the transmission rate of the selected pixels corresponding to the selected group of row or column electrodes reach 50% of the transmission rate upon settlement.

35. The apparatus of claim 21, wherein said second device includes means for heating the cathodes.

36. The apparatus of claim 35, wherein said cathodes include an array of elongated oxide coated filaments arranged substantially parallel to one another.

37. The apparatus of claim 21, said cathodes comprising cone-shaped field electron emitting structures, one of said sets of control electrodes including at least one set of grid electrodes substantially parallel to said row or column electrodes, wherein said grid electrodes define holes therein, said cone-shaped cathodes being located in said holes with their tips exposed for emitting electrons.

38. The apparatus of claim 21, said anode being located between the cathodes and the liquid crystal layer, said anode being substantially transparent, wherein said control electrodes have light reflecting surfaces facing the layer for reflecting light towards the layer.

39. The apparatus of claim 21, said cathodes being located between the anode and the liquid crystal layer, said anode having a light reflecting surface facing the layer for reflecting light towards the layer.

40. The apparatus of claim 21, back light source including a housing having a face plate adjacent to the liquid crystal layer so that light emitted by the elements passes through said face plate before it travels to the layer, said face plate having an internal surface in the chamber and an external surface outside the chamber, wherein the internal or external surface or both surfaces are light diffusive to evenly distribute light transmitted from the back lighting source to the layer.