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High resolution, high brightness light emitting diode display and method and producing the same    
United States Patent5724062   
Link to this pagehttp://www.wikipatents.com/5724062.html
Inventor(s)Hunter; C. Eric (Chapel Hill, NC)
AbstractA high resolution, high brightness, full color display is provided having a liquid crystal pixel selectably addressable during a predetermined time period, a set of at least one red, one green, and one blue color light emitting diodes positioned adjacent the liquid crystal pixel for emitting light through the liquid crystal pixel, and means connected to the liquid crystal pixel for addressing the liquid crystal pixel a plurality of times during the predetermined time period for each color so as to provide persistence when changes in color are perceived by the human eye. A method of producing a high resolution, full color display is also provided by lighting a set of one red, one green, and one blue light emitting diodes by lighting the respective colored light sources for a predetermined time period for each color and shuttering the set of light sources with a liquid crystal pixel for at least a portion of the predetermined time period to thereby emit light from the shuttered pixel for a selected time period so as to provide persistence when changes in color are perceived by the human eye.
   














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Drawing from US Patent 5724062
High resolution, high brightness light emitting diode display and method

     and producing the same - US Patent 5724062 Drawing
High resolution, high brightness light emitting diode display and method and producing the same
Inventor     Hunter; C. Eric (Chapel Hill, NC)
Owner/Assignee     Cree Research, Inc. (Durham, NC)
Patent assignment
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Publication Date     March 3, 1998
Application Number     08/310,260
PAIR File History     Application Data   Transaction History
Image File Wrapper   Patent Term   Fees
Litigation
Filing Date     September 21, 1994
US Classification     345/102 345/83
Int'l Classification     G09G 003/36
Examiner     Liang; Regina D.
Assistant Examiner    
Attorney/Law Firm     Attorney; Philip Summa, Patent
Address
Parent Case     RELATED APPLICATION This application is a continuation-in-part of copending U.S. patent application Ser. No. 07/926,035 filed on Aug. 5, 1992, U.S. Pat. No. 5,359,345.
Priority Data    
USPTO Field of Search     345/102 345/46 345/82 345/83 345/207 359/48 359/39 359/49
Patent Tags     high resolution, high brightness light emitting diode display method
   
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 U.S. References
 
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5394167
Migny
345/690
Feb,1995

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5359345
Hunter
345/102
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Sarraf
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Nakamura
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Frett
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Kaise
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Hatano
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Niina
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Numao
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Bull
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 Technical Review Submit all comments and votes
 Claims Submit all comments and votes
 


That which is claimed is:

1. A high resolution, full color display, comprising:

a liquid crystal pixel selectably addressable during a predetermined time period wherein said liquid crystal pixel comprises an array of individual portions of a liquid crystal pixel and wherein each individual portion of said pixel is individually addressable over the predetermined time period;

an interspersed set of at least one red, one green, and one blue color light emitting diodes positioned adjacent said liquid crystal pixel and adapted for emitting light through said liquid crystal pixel; and

means connected to said liquid crystal pixel for selectably addressing the liquid crystal pixel a plurality of times during the predetermined time period so as to provide persistence when changes in color occur.

2. A high resolution, high brightness, full color display as defined by claim 1, wherein said liquid crystal pixel is selectably addressable for an amount of time generally less than the amount of time that the human eye can detect changes in colors.

3. A high resolution, high brightness, full color display as defined by claim 1 further comprising:

means connected to safe interspersed set of LEDs for lighting said interspersed set of LEDs by respective red, green, and blue colors for a predetermined time period for each color.

4. A high resolution, high brightness, full color display according to claim 1, further comprising:

means connected to said set of LEDs and said liquid crystal pixel for synchronizing the lighting of said interspersed set of LEDs with the means for addressing said individual liquid crystal pixel a plurality of times during the predetermined time period.

5. A high resolution, high brightness, full color display according to claim 1, further comprising means positioned between said LEDs and said LCD for measuring the intensity of said LEDs during a time interval.

6. A high resolution, high brightness, full color display according to claim 1, further comprising means positioned between said set of LEDs and said liquid crystal pixel for diffusing the light emitted from said set of LEDs to said liquid crystal pixel.

7. A high resolution, high brightness, full color display as defined by claim 1, wherein said blue LED is formed of gallium nitride.

8. A high resolution, high brightness, full color display as defined by claim 1, wherein said array of LEDs are formed in a single semiconductor substrate.

9. A method of producing a high resolution, high brightness, full color display that is particularly useful for a flat display, comprising the steps of:

lighting a set of one red, one green, and one blue LEDs by lighting the respective LEDs in the set for a predetermined time period for each LED in which one cycle is defined by the sum of the predetermined time periods, and in which one cycle is a time period less than that for which the sequential lighting of the LEDs can be detected by the human eye; and

shuttering the set of LEDs with a liquid crystal pixel which comprises an array of individual portions of a liquid crystal pixel for at least a portion of the predetermined time periods to thereby emit light from the shuttered pixel for a selected time period from each of the red, green, and blue LEDs so that the light emitted from the pixel is an emission of red, green, and blue light, each for a time period less than or up to the predetermined time period so that the emission from the pixel during each cycle is defined by the amount of time a light pulse from each LED is shuttered and will normally be perceived by a human eye as a blend of the colors emitted by the respective LEDs.

10. A method as defined by claim 9, further comprising the step of:

selectably addressing the liquid crystal pixel a plurality of address times during each predetermined time period.

11. A method as defined by claim 10, further comprising the step of:

synchronizing the addressing of the liquid crystal pixel with the lighting of the set of red, green, and blue LEDs.

12. A method as defined by claim 9, wherein one cycle is less than the amount of time that the human eye can detect changes in colors.

13. A method as defined by claim 9, wherein one cycle is generally less than 1/60th of a second.

14. A method as defined by claim 9, wherein the predetermined time period is generally less than 1/180th of a second.

15. A method of producing a high resolution, high brightness, full color display that is particularly useful for a flat display, comprising the steps of:

transmitting data to the display to be represented during a predetermined time period;

receiving the data to be represented for display during the predetermined time period;

sequentially and cyclically lighting an interspersed set of red, green, and blue LEDs in response to the received data by lighting the respective LEDs in the set for a predetermined time period for each color, in which one cycle is defined by the sum of the predetermined time periods, and in which one cycle is a time period less than that for which the sequential lighting of the LEDs can be detected by the human eye;

addressing individually the liquid crystal pixels in a set of liquid crystal pixels wherein at least one of said liquid crystal pixels comprises an array of individual portions of a liquid crystal pixel and wherein a liquid crystal pixels in the set of liquid crystal pixels is addressed individually a plurality of address times during each sequential predetermined time period in response to said received data;

synchronizing the addressing of the individual liquid crystal pixels with the sequentially and cyclically lighting of the set of red, green, and blue LEDs; and

shuttering the set of LEDs with individual pixels in the set of liquid crystal pixels for at least a portion of the sequential predetermined time periods in response to said received data to thereby emit light from the shuttered pixels for a selected time period from each of the red, green, and blue LEDs so that the light emitted from the pixel is a sequential emission of red, green, and blue light, each for a time period less than or up to the predetermined time period so that the emission from the pixels during each cycle is defined by the amount of time a light pulse from each LED is shuttered and will normally be perceived by a human eye as a blend of the colors emitted by the respective LEDs rather than as a sequential appearance of those colors.

16. A method as defined by claim 15, wherein one cycle is generally less than 1/60th of a second.

17. A method as defined by claim 15, wherein said predetermined time period is generally less than 1/180th of a second.
 Description Submit all comments and votes
 


FIELD OF THE INVENTION

This invention generally relates to display devices and more particularly to an array of light emitting diodes in combination with a liquid crystal display for producing a high resolution, high brightness, full color display.

BACKGROUND OF THE INVENTION

For many years, the cathode ray tube ("CRT") dominated the display market for numerous applications. CRTs provided high resolution, graphics, full color, and real-time animation. CRT displays, however, have several associated problems such as bulkiness, high voltage requirements, high heat generation, and sensitivity to vibration and shock.

Because of the problems associated with CRT displays, other display technologies such as the light emitting diode ("LED"), liquid crystal display ("LCD"), vacuum fluorescent ("VF"), plasma, and electroluminescence have been replacing CRT displays for many applications, especially for flat panel display applications. These technologies have various advantages in specific applications, depending on such factors as environmental conditions, voltage requirements, and size.

LED displays have been used for many years and have been popular because of their ruggedness, fast switching speeds, and wide range of sizes. These advantages, however, were somewhat diminished by the fact that blue LEDs were difficult to develop and were expensive. Without the blue LED, a full color LED display was impossible.

The lack of a blue LED slowed the development and marketability of LED display technology, especially for multi-color applications such as personal computers, computer aided design ("CAD"), and video imaging. The need for a blue LED encouraged the development of the inventions described in U.S. Pat. Nos. 4,918,497 and 5,027,168 by Edmond titled "Blue Light Emitting Diode Formed In Silicon Carbide." The silicon carbide blue LED technology, in turn, has opened the field for the development of multi-color LED displays.

LCDs have been popular for many applications, primarily in low power areas such as battery-powered systems (e.g., wrist watches, portable computers) or small size applications. LCDs, however, have suffered from several problems over the years. LCDs, for example, are difficult to view in low ambient light environments because they transmit rather than emit light. In addition, LCDs have a limited viewing angle and poor contrast.

For full color displays, supertwist LCD technology has been developed to allow a wide variety of colors and improved contrast. Supertwist technology, for example, bends light 270 degrees instead of the 90 degrees provided by conventional LCD technology. The supertwist color LCDs still lack the clarity and brightness achieved by CRT displays and LED displays.

More recently, due to the problems with LED and LCD technology, LCDs have been used in combination with LEDs to attempt to achieve better clarity and brightness for flat panel displays over the full-color spectrum, especially for three-dimensional, multi-color, high resolution applications. To overcome the need for a blue LED, various filters and other devices have been used to produce the blue color when needed. Most of these alternative blue color techniques, however, added additional circuitry and expense and, therefore, were still not adequate for commercial applications.

One such method for producing a full color, flat panel display is to form a display with three colored filters (e.g., red, green, blue) for each LCD pixel. A mixture of the filtered light shines through the LCD pixel to display the desired color for that particular pixel. An example of this filter method is seen in U.S. Pat. No. 4,716,403 to Morozumi titled "Liquid Crystal Display Device." Although this is a theoretically simple solution, the filter system fails to allow the intensity of individual colors of light for an individual pixel to be controlled.

Another method is to use fewer LED sources and to project or scan the light sources over a large number of LCD pixels. As the light source is directed to a particular pixel, it lights the pixel with the appropriate color. As long as the entire display is covered in one-sixtieth (1/60th) of a second or less--a rate above which the human eye generally cannot detect the individual changes taking place--an appropriate image can be maintained. An example of such a device may be seen in U.S. Pat. No. 4,978,952 to Irwin titled "Flat Screen Color Video Display."

In the scanning method, as shown in U.S. Pat. No. 4,978,952 to Irwin, LEDs are used as individual light sources, and LCDs are used as shutters that define each pixel. The LCD pixels are opened and closed a row or column at a time in an appropriate manner to allow the LED light source to emit through the pixels and thereby define the overall display. The intensity of color transmitted is varied by varying the output of the source LEDs.

One problem with the scanning method, however, is a lack of power output which from a practical standpoint results in a lack of brightness, clarity, and overall resolution. The fundamental difficulty is that a row or column of LCD pixels at a time is illuminated from its source. Even if that time period for illuminating an entire row or column of LCDs is very short and refreshed very rapidly, the brightness is greatly affected. Therefore, the overall power output of the display is roughly limited by the ratio of sources to pixels in that row.

Other similar attempts at addressing this problem have been made by transferring the color to the screen a lattice or group of pixels at a time. An example of this may be seen in U.S. Pat. No. 5,093,652 to Bull et al. titled "Display Device." Because this device also controls blocks of pixels at a time, instead of individual pixels, it fails to produce the desired high resolution needed for video imaging applications. Also, the original patent application for this device was filed in a foreign country on Dec. 4, 1987, prior to the develo