Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-04-10
2002-11-19
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S098000, C345S100000
Reexamination Certificate
active
06483493
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to a technical field of an electro-optical apparatus such as an active matrix driving liquid crystal apparatus driven by thin film transistors (hereinafter also referred to as TFTs) or the like, and also to an electronic device using the same. More particularly, the present invention relates to an electro-optical apparatus in which data lines are driven at a high frequency by a data line driving circuit provided on a TFT array substrate in response to a control signal such as a clock signal, and also an electronic device using the same.
2. Description of Related Art
In conventional electro-optical apparatuses such as an active-matrix driving TFT liquid crystal apparatus, a great number of scanning lines and data lines are formed in horizontal and vertical directions, respectively, on a TFT array substrate, and a great number of pixel electrodes are formed at respective intersections of the scanning lines and the data lines. In some cases, in addition to the above elements, other elements are also formed on the TFT array substrate, such as data signal supply means including a data line driving circuit and a sampling circuit or the like and serving to supply a data signal to the data lines, and also a scanning signal supply means including a scanning line driving circuit or the like and serving to supply a scanning signal to the scanning lines.
In this case, a control signal such as a data line side reference clock signal which activates a data line driving circuit indicating a time reference for supplying a data signal, an image signal which corresponds to the content of images to be displayed and which is used as a basis on which the data signal is produced, and positive and negative constant electric potential power-supply or the like are supplied to the data signal supply means via external input terminals and wiring provided on the TFT array substrate, respectively. Similarly, a scanning line side reference clock signal which activates a scanning line driving circuit indicating a time reference for supplying a scanning signal, and positive and negative constant electric potential power-supply are supplied to the scanning signal supply means via external input terminals and wiring provided on the TFT array substrate. In the scanning signal supply means, for example, the scanning line driving circuit supplies a scanning signal over the scanning lines on the line-by-line basis in accordance with the scanning line side reference clock signal In response, in the data signal supply means, the data line driving circuit drives the sampling circuits, which serve to sample the input image signal, one by one in accordance with the timing indicated by the data line side reference clock signal. As a result, a data signal is supplied from the sampling circuits over the data lines. The respective TFTs whose gate is connected to one of the scanning lines turn on in response to receipt of the scanning signal supplied via the scanning lines. As a result, the data signal is supplied to the pixel electrodes via the corresponding TFTs and thus an image is displayed on the respective pixels.
In recent liquid crystal apparatuses, in particular in those for use in a liquid crystal projector, the frequency of serial image signals becomes increasingly high with the increase in the resolution of the image displayed. For example, the dot frequency of the image signal in the XGA display mode or SXGA display mode employed in recent high-resolution displays for personal computers is about 65 MHZ and 135 MHZ, respectively, which are much higher than the dot frequency in the conventional VGA mode (about 30 MHZ). As a result, a very high frequency is also required for the data line side reference clock signal supplied to the data signal supply means.
SUMMARY OF THE INVENTION
The increase in the frequency of the reference clock signals results in generation of high-frequency clock noise, which cannot be neglected, to achieve a high-quality display image. With the conventional technique of supplying a relatively low-frequency data line side reference clock signal to the data line driving circuit to drive the sampling circuit, if the frequency of the clock signal is simply increased, high-frequency clock noise intrudes into the image signal input to the sampling circuit or into the data signal output from the sampling circuit, and thus the data signal supplied to the data lines is degraded by the noise. The degradation in the data signal input to the respective pixels results in degradation in the image displayed by the respective pixels. For example, when a halftone image is displayed by the respective pixels, if noise as small as about 10 mV intrudes into the image signal, then visual noise appears in the displayed image. This is because, in the case of the halftone image, unlike the two-level display in which only white and black levels are displayed by applying a highest or lowest driving voltage (for example, 5 and 0 V) to a liquid crystal, the transmittance of the liquid crystal is very sensitive to the change in the voltage applied to the liquid crystal. Therefore, high-frequency clock noise is an important problem which has to be solved to realize a high-precision multi-level gray scale display.
If the number of phases into which the original image signal is serial-to-parallel converted is increased, it is possible to reduce the frequency of the image signals supplied to the sampling circuit. However, in this case, it is required to increase the number of external input terminals, which are provided on a substrate of a liquid crystal apparatus so as to input an image signal, depending on the number of phases of the serial-to-parallel-converted image signal. For example, when the serial-to-parallel conversion is performed into six phases, six external input terminals for inputting the image signal are required. In the case where the serial-to-parallel conversion is performed into twelve phases, twelve external input terminals are required. Furthermore, it is also required that there be as many wirings for transferring the image signal, input via the external input terminals, to the sampling circuit as there are serial-to-parallel conversion phases. As a result, the wirings for the image signal occupy a large area on the substrate of the liquid crystal apparatus. This makes it difficult to allocate a proper area on the substrate for forming the data signal supply means including the sampling circuit, the data line driving circuit, or the like. If wirings for control signals such as a clock signal are formed on a substrate in such a manner that they extend from an edge of the substrate where external input terminals are formed to one side of the data line driving circuit, and many wirings for image signals are formed on a substrate in such a manner that they extend to the other side if the data line driving circuit as is employed in the conventional technique, then the number of wirings extended to each side becomes very different between two sides of the data line driving circuit, so that the wiring balance in the surrounding of the data line driving circuit becomes quite bad (that is, wirings are concentrated on only one side). It is possible to increase the size of the substrate of the liquid crystal apparatus so that the wiring area and the data line driving circuit are disposed in the increased area. However, the increase in the size does not meet the requirement in the art of the liquid crystal apparatus for achievement of a large image display area using a limited size of substrate.
In view of the above, it is an object of the present invention to provide an electronic device including an electro-optical apparatus capable of displaying a high-quality image according to an input image signal or a data signal generated from the image signal with suppressed high-frequency clock noise.
It is another object of the present invention to provide a liquid crystal apparatus capable of displaying a high-quality image and also
Hjerpe Richard
Laneau Ronald
Oliff & Berridg,e PLC
Seiko Epson Corporation
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