| Liquid crystal display with color backlighting employing light emitting diodes -> Monitor Keywords |
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Liquid crystal display with color backlighting employing light emitting diodesLiquid crystal display with color backlighting employing light emitting diodes description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060038770, Liquid crystal display with color backlighting employing light emitting diodes. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a continuation of prior application Ser. No. 10/248,037, filed Dec. 12, 2002, the disclosure of which is incorporated herein by reference. BACKGROUND [0002] The following relates to the lighting and display arts. It is especially relates to active matrix liquid crystal display (LCD) devices, and will be described with particular reference thereto. However, it will also find application in other types of LCD displays, and in other types of backlit display devices. [0003] With reference to FIG. 1, a conventional flat screen display 10 includes an active matrix liquid crystal display (LCD) 12 and a backlight 14. The LCD 12 includes a matrix of thin film transistors (TFTs) 16 fabricated on a substrate 18 of glass or another transparent material. A liquid crystal film 20 is disposed over the substrate 18 and the TFTs 16. Addressing of the TFTs 16 by gate lines (not shown) deposited on the substrate 18 during TFT fabrication cause selected TFTs 16 to conduct electrical current and charge the liquid crystal film 20 in the vicinity of the selected TFTs 16. Charging of the liquid crystal film 20 alters the opacity of the film, and effects a local change in light transmission of the liquid crystal film 20. Hence, the TFTs 16 define display cells or pixels 22 in the liquid crystal film 20. Typically, the opacity of each pixel 22 is charged to one of several discrete opacity levels to implement an intensity gray scale, and so the pixel 22 is a gray scale pixel. However, pixel opacity also can be controlled in a continuous analog fashion or a digital (on/off) fashion. [0004] A color-selective filter 26, 28, 30 is disposed over each pixel 22. Specifically, first color filters 26 of a first color component, second color filters 28 of a second color component, and third color filters 30 of a third color component are distributed on pixels 22 across the display area of the LCD 12 to produce a color display. Typically, the first, second, and third colors include red, green, and blue primary colors to produce a red-green-blue (RGB). Preferably, a top matrix 32 of opaque lines separating pixels 22 is arranged between the color filters 26, 28, 30 to improve visual contrast. Specifically, FIG. 1 shows a single color or RGB pixel that includes a first component color (e.g., red output by the pixel 22 covered by the filter 26), a second component color (e.g., green output by the pixel 22 covered by the filter 28), and a third component color (e.g., blue output by the pixel 22 covered by the filter 30) that are selectively combined or blended to generate a selected color. [0005] In operation, the backlight 14, which includes a white compact fluorescent lamp (CFL), an array of white light emitting diodes (LEDs), or other white light source 34, produces a substantially uniform white planar illumination directed toward the LCD 12. A polarizer 36 of the LCD 12 disposed on a backside of the substrate 18 optimizes the light polarization with respect to polarization properties of the liquid crystal film 20. The opacity of the pixels 22 is modulated using the TFTs 16 as discussed previously to create a transmitted light intensity modulation across the area of the display 10. The color filters 26, 28, 30 colorize the intensity-modulated light emitted by the pixels to produce a color output. By selective opacity modulation of neighboring pixels 22 of the three color components, selected intensities of the three component colors (e.g., RGB) are blended together to selectively control color light output. The pixels 22 of a particular color or RGB pixel such as that shown in FIG. 1 are blended. As is known in the art, selective blending of three primary colors such as red, green, and blue can generally produce a full range of colors suitable for color display purposes. Spatial dithering is optionally used to provide further color blending across neighboring color pixels. [0006] Conventional flat screen displays such as the exemplary display 10 suffer certain disadvantages. The light output efficiency is poor due to light absorption within the LCD 12. Typically, the polarizer 36 reduces the light intensity by about 50%. The TFTs 16 produce further shadow losses of a magnitude dependent upon the TFT device area. Typical losses due to TFT shadowing in present active matrix liquid crystal displays are about 15%. The color filters 26, 28, 30 each substantially absorb two of the three color components to produce a pure third color component output, and hence have transmissivities no higher than about 30%. Combining these losses, the light output efficiency for the LCD 12 is about 5%. [0007] Another disadvantage of conventional LCD-based flat screen displays is manufacturing complexity. In particular, for each gray scale pixel 22 one of the color filters 26, 28, 30 is precisely aligned and bonded. Precision in the filter alignment is critical since misalignment can create gaps through which white light can pass. This alignment process is time-consuming and error-prone. [0008] Yet another disadvantage of conventional LCD-based flat screen displays is a relatively large color (RGB) pixel size since each color pixel is comprised of at least three component gray scale pixels 22. In some arrangements, a second green pixel is included to compensate for visual color sensitivity differences, leading to a still larger color pixel size. Increased color pixel size corresponds to reduced display resolution. [0009] The following contemplates an improved apparatus and method that overcomes the above-mentioned limitations and others. BRIEF SUMMARY [0010] According to one aspect, a color display device is disclosed. A backlight cyclically emits at least first, second, and third component color backlighting in turn over a cycle period. The cycle period repeats at a cycling frequency that exceeds a maximum human visual response frequency. A liquid crystal display (LCD) generates a first display during the first component color backlighting, a second display during the second component color backlighting, and a third display during the third component color backlighting. [0011] According to another aspect, a color display is disclosed. A backlight includes an array of backlight elements that produce backlight illumination. Each backlight element includes a plurality of lamps each of which emit illumination of a selected component color when energized. The backlight further includes backlight circuitry communicating with the backlight elements for energizing the plurality of lamps. A liquid crystal film is arranged to receive the backlight illumination. An array of liquid crystal control elements operatively define liquid crystal cells. Each liquid crystal control element is selectively operated to control transmission of the illumination through the liquid crystal cell. The liquid crystal control elements cooperatively produce a color display that selectively blends the selected component colors. [0012] According to another aspect, a display method is provided. A liquid crystal display is configured with a first light transmission pattern. A first illumination of a first color is generated. The first illumination is transmitted through the liquid crystal display configured with the first light transmission pattern. The configuring, generating, and transmitting are repeated for at least two other colors. The above operations are repeated to produce an updateable display. [0013] According to another aspect, a color display device is disclosed, including a light-transmissive liquid crystal display (LCD). A backlight is arranged to illuminate the light-transmissive LCD. The backlight includes at least first color component light emitting diodes (first color component LEDs), second color component light emitting diodes (second color component LEDs), and third color component light emitting diodes (third color component LEDs). LED circuitry cyclically alternates between powering the first color component LEDs to produce first color component backlighting, powering the second color component LEDs to produce second color component backlighting, and powering the third color component LEDs to produce third color component backlighting. LCD circuitry updates a display shown on the LCD. The updates of the LCD are synchronized with color changes of the backlight. [0014] According to yet another aspect, a color display device is disclosed. A backlight emits illumination with a selected temporal sequence of color components. A light-transmissive backlit display includes light-transmissive pixels distributed over a display area. The light-transmissive pixels are backlit by the backlight. The pixels have controlled opacity that is updated synchronously with the selected sequence of color components to effect full-color pixels. [0015] According to still yet another aspect, a color display device is disclosed. A planar light transmissive display includes an array of light-transmissive pixels each having selectable opacity. A backlight includes backlight elements. Each backlight element includes a plurality of light sources. Each light source emits light of a selected color component that is coupled to a selected one pixel. The plurality of light sources and the coupled pixels define a color picture element. [0016] Numerous advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS [0017] The invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. [0018] FIG. 1 shows a cross-sectional schematic view of a conventional color flat screen display including a liquid crystal display (LCD) with color filters and a backlight. [0019] FIG. 2 shows a cross-sectional schematic view of a flat screen display including an LCD coupled with a backlight of light emitting diodes of three component colors, in which each LCD gray scale pixel modulates light output from a light emitting diode of a selected color. [0020] FIG. 3 shows a cross-sectional schematic view of a flat screen display including an LCD coupled with a backlight of light emitting diodes of three component colors, in which each LCD pixel receives light from each of the three component color light emitting diodes in turn. [0021] FIG. 4 shows suitable control circuitry for driving the flat screen display of FIGS. 3, 5, and 6. Continue reading about Liquid crystal display with color backlighting employing light emitting diodes... 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