Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1994-12-27
2001-11-20
Wu, Xiao (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S096000, C345S090000
Reexamination Certificate
active
06320568
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. 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 rotate the polarization of light when an electric field is applied across it between the circuit panel and a ground affixed to the filter plates. Thus, when a particular pixel of the display is turned on, the liquid crystal material rotates polarized light being transmitted through the material so that it 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 large area 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.
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.
A continuing, need exists for systems and methods of controlling pixel of a panel displays having the desired speed and providing for ease, and reduced cost, of fabrication.
SUMMARY
The invention is a control system for a liquid crystal display panel. A control apparatus is fabricated with the active matrix as a monolithic SOI structure. After the SOI structure is fabricated on a silicon substrate, the structure is removed from the silicon substrate using a lift-off process and transferred to a glass substrate as a single substrate. The single structure provides improved processing speeds and the fabrication process reduces the difficulty and cost of manufacturing display panels.
In a preferred embodiment, a control apparatus for a liquid crystal display device comprises a video interface, a left select scanner, a right select scanner, a video polarity switch, and a data scanner. The video interface converts video signals from a video source into active matrix control signals. In response to the active matrix control signals, the left and right select scanners simultaneously drive opposite sides of the matrix select lines. The video polarity switch generate an even column video signal and an odd column video signal from the video source signal, the even column signal being of the opposite polarity of the odd column signal. The polarities of the even and the odd column signals are reversed on each sequential video frame. In response to the active matrix control signals, the data scanner drives the active matrix columns with the even and the odd column signals.
The data scanner comprises an odd column shift register array and an even-column shift register array. The odd column array driving the odd columns of the active-matrix and the even column array driving the even columns of the active matrix.
An encoder may be coupled between the video source and the video polarity switch. The encoder generating a superposed analog video signal from a video source RGB data signal. The RGB data signal may be mapped to a superposed color analog signal. The RGB data signal may also be mapped to a gray-scale analog signal. Preferably, the encoder may map to either of the color or gray-scale signal in response to a control signal.
In a preferred embodiments, the control apparatus adjusts the gray-scale video signal level to compensate for changes in the transmittance of the liquid crystal material. A sensor is fabricated within the SOI structure. The sensor generates a data signal in response to the temperature of the active matrix and the light transmittance of the liquid crystal material. The sensor data is processed by a measurer, which generates a feedback signal in response to the sensor data. An amplifier gain is adjusted by the feedback signal, the amplifier amplifying the video signal by the gain. The gain may be linear or nonlinear. The sensor may comprise at least one real-time light sensor and at least one real-time temperature sensor. At least one other light sensor is provided that generates a signal representing light transmittance through a black pixel. The black pixel signal may be generated by permanently grounding the black pixel light sensor. At least one other light sensor is provided that generates a signal representing light transmittance through a white pixel. The white pixel signal may be generated by permanently connecting the white pixel light sensor to a DC voltage. The black and white pixel light sensors define the end points of the active matrix transmittance curve.
In a preferred embodiment, the video source generates a video signal having variable synchronization frequencies. The active matrix display has a fixed pixel resolution. The video interface generates a dot clock signal from the variable synchronization frequencies for driving the display at the fixed resolution. The video interface allows the display panel to function as a multiple-frequency scanning display device.
The video interface comprises a control processor and dot clock regenerator. The control processor is responsive to video mode changes on the video signal as reflected by the synchronization frequencies. In response to mode changes, the control processor signals the dot clock regenerator. The dot clock regenerator is responsive to the control processor signal. The dot clock regenerator comprises a digitally programmable phase-locked loop that tracks changes on the synchronization frequencies such that the dot clock signal is centered over the correct pixel and does not drift. The video interface providing compatibility with VGA and XVGA adapters.
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Hamilton Brook Smith & Reynolds P.C.
Kopin Corporation
Wu Xiao
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