Computer graphics processing and selective visual display system – Display driving control circuitry – Display power source
Reexamination Certificate
1997-09-30
2004-01-13
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Display driving control circuitry
Display power source
C345S102000, C345S088000, C348S333010, C348S333130, C396S374000
Reexamination Certificate
active
06677936
ABSTRACT:
BACKGROUND OF THE INVENTION
Flat-panel displays are being developed which utilize liquid crystals or electroluminescent materials to produce high quality images. These displays are expected to supplant cathode ray tube (CRT) technology and provide a more highly defined television picture or computer monitor image. The most promising route to large scale high quality liquid crystal displays (LCDs), for example, is the active-matrix approach in which thin-film transistors (TFTs) are co-located with LCD pixels. The primary advantage of the active matrix approach using TFTs is the elimination of cross-talk between pixels, and the excellent grey scale that can be attained with TFT-compatible LCDs.
Flat panel displays employing LCDs generally include five different layers: a white light source, a first polarizing filter that is mounted on one side of a circuit panel on which the TFTs are arrayed to form pixels, a filter plate containing at least three primary colors arranged into pixels, and finally a second polarizing filter. A volume between the circuit panel and the filter plate is filled with a liquid crystal material. This material will allow transmission of light in the material when an electric field is applied across the material between the circuit panel and a ground affixed to the filter plate. Thus, when a particular pixel of the display is turned on by the TFTs, the liquid crystal material rotates polarized light being transmitted through the material so that the light will pass through the second polarizing filter.
The primary approach to TFT formation over the large areas required for flat panel displays has involved the use of amorphous silicon, which has previously been developed for large-area photovoltaic devices. Although the TFT approach has proven to be feasible, the use of amorphous silicon compromises certain aspects of the panel performance. For example, amorphous silicon TFTs lack the frequency response needed for high performance displays due to the low electron mobility inherent in amorphous material. Thus the use of amorphous silicon limits display speed, and is also unsuitable for the fast logic needed to drive the display.
As the display resolution increases, the required clock rate to drive the pixels also increases. In addition, the advent of colored displays places additional speed requirements on the display panel. To produce a sequential color display, the display panel is triple scanned, once for each primary color. For example, to produce color frames at 20 Hz, the active matrix must be driven at a frequency of 60 Hz. In order to reduce flicker it is desirable to drive the active matrix at 180 Hz to produce a 60 Hz color image. At over 60 Hz, visible flicker is reduced.
Owing to the limitations of amorphous silicon, other alternative materials include polycrystalline silicon, or laser recrystallized silicon. These materials are limited as they use silicon that is already on glass, which generally restricts further circuit processing to low temperatures.
Integrated circuits for displays, such as, the above referred color sequential display, are becoming more and more complex. For example, the color sequential display is designed for displaying High Definition Television (HDTV) formats requiring a 1280-by-1024 pixel array with a pixel pitch, or the distance between lines connecting adjacent columns or rows of pixel electrodes, being in the range of 15-55 microns, and fabricated on a single five-inch wafer.
SUMMARY OF THE INVENTION
In accordance with the invention, the cost and complexity of high resolution displays is significantly reduced by fabricating multiple integrated displays of reduced size on a single wafer and then dicing the wafer to produce a plurality of display devices.
The displays are then assembled with appropriate magnifying optics to form a portable display system of low cost and reduced size. Included in the optics is a magnification system which compensates for the small image size by magnifying and projecting the image at an appropriate distance for viewing.
In preferred embodiments, the microdisplay, because of its small size and weight, can be used as a hand-held communication system such as a pager, a wireless mobile telephone, or alternatively, as a head-mounted display, video camcorder, digital camera or a card reader display system. The display can provide a visual display suitable for data, graphics or video and accommodate standard television or high definition television signals. The system can optionally include circuitry for cellular reception and transmission of facsimile communications, can be voice activated, can include a mouse operated function, provide Internet access, and can have a keyboard or touch pad for numeric or alphabetic entry. The system can have, such as in a card reader display system, a housing with a port or aperture to receive a card, and a card reader for reading information from the card and displaying the information on the micro-display.
The telephone or hand-held unit can be equipped with a camera or solid state imaging sensor so that images can be generated and transmitted to a remote location and/or viewed on the display. Also the telephone user can call to access a particular computer at a remote location, present the computer screen on the microdisplay, access specific files in the computer memory and download data from the file into a memory within the telephone or a modular memory and display unit connected to the telephone. The telephone can be connected to a local computer or display and the data from the file can be loaded into the local memory.
The video camcorder or digital camera has a microdisplay for a viewfinder. Either an image as seen through the lens or as previously recorded can be seen through the viewfinder, depending on what is selected.
In a preferred embodiment of the invention, a light emitting diode (LED) device is used to illuminate the display. For transmission displays the LED device operates as a backlight and can include a diffuser. An LED device can also be used as a light source for a reflective display in another preferred embodiment of the invention. The displays are preferably liquid crystal displays using a twisted nematic liquid crystal material. Consequently, controlling the time domain is not necessary to obtain grey scale.
For the purposes of this application, a microdisplay is defined as a display having at least 75,000 pixel electrodes and an active area of less than 160 mm
2
, where the active area of the display is the area of the active matrix circuit that generates an image, including all of the pixel electrodes but not including the driver electronics and the border area for bonding and sealing of the liquid crystal display. For example, the array can be at least 320×240, 640×480 or higher. A preferred embodiment of the microdisplay has an active area of 100 mm
2
or less, and is preferably in the range between 5 mm
2
and 80 mm
2
. The pixel pitch for these displays is in the range of 5-30 microns and preferably in the range between 5 and 18 microns. By utilizing pixel pitches of less than 18 microns smaller high resolution displays are now possible. For an embodiment utilizing a high definition format such as 1280×1024, and utilizing a pixel pitch of 12 microns or less, the active area of the display is less than 200 mm
2
.
For displays of this size and resolution to be read by a user at distances of less than 10 inches (25.4 cm) there are specific lighting and magnification requirements. For a 0.25 inch (6.35 mm) diagonal display, for example, the LED device preferably includes a plurality of LEDS coupled to a diffuser. The lens used to magnify the display image has a field of view in the range of 10-60 degrees, and preferably at least about 16 degrees-22 degrees, an ERD in the range of about 25 mm-100 mm and an object distance of between about 1.5 and 5 feet (152.4 cm). A color field sequentially operated LED backlight system can use a plurality of LEDS with a two or four sided reflector assembly to concentrate the ligh
Bumgardner Rodney
Chern Wen-Foo
Fan John C. C.
Jacobsen Jeffrey
Pombo Stephen A.
Kopin Corporation
Wu Xiao
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