Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-01-11
2003-03-11
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S100000, C345S087000, C345S092000
Reexamination Certificate
active
06531996
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an electro-optical-apparatus such as an active matrix type liquid crystal device which is driven by thin-film transistors (hereinafter referred to as TFTs) and to an electronic apparatus using such an electro-optical apparatus. More particularly, the present invention relates to an electro-optical apparatus including at least one of a sampling circuit and a precharging circuit formed on a TFT array substrate and to an electronic apparatus using such an electro-optical apparatus.
2. Description of Related Art
In a conventional active matrix liquid crystal device driven by TFTs, a great number of scanning lines and data lines are disposed on a TFT array substrate in such a manner that they extend in vertical and horizontal directions, respectively, and a great number of pixel electrodes are disposed on the TFT array substrate at intersections of the scanning and data lines. In some cases, in addition to the above elements, various peripheral circuits composed of TFTs, such as a sampling circuit, a precharging circuit, a scanning line driving circuit, and a data line driving circuit, are also formed on the TFT array substrate.
Of these peripheral circuits, the sampling circuit serves to sample an image signal and output, in sychronization with a scanning signal, sampled image signal at a high frequency over respective data lines.
The precharging circuit supplies a precharging signal (auxiliary image signal) over the data lines before the image signal is supplied from the data line driving circuit via the sampling circuit or directly over the data lines so as to improve the contrast, stabilize the voltage level on the data lines, and improve the line-to-line uniformity in intensity of the image displayed on the screen. That is, the precharging circuit facilitates writing a high-quality image signal on the data lines. In particular, when the polarity of the voltage applied on the data lines is inverted at a predetermined frequency so as to drive a liquid crystal in an AC mode, as is the case with the so-called 1H inverting driving technique, it is possible to greatly reduce the charge required to write an image signal on the data lines if a precharging signal is written on the data lines before the image signal is written on the data lines. A specific example of a precharging circuit is disclosed for example in Japanese Unexamined Patent Publication No. 7-295520.
As described above, if peripheral circuits such as a sampling circuit and a precharging circuit are formed on the TFT array substrate, it becomes possible to display a high-quality image and it is also possible to reduce the load exerted on the hardware resource such as a driving circuit.
However, when the TFTs of the precharging circuit or the sampling circuit are turned on, the precharging signal line or the image signal line used to transmit the precharging signal or the image signal is connected, via TFTs of the precharging circuit or the sampling circuit, to a great number of data lines having an extremely large interconnection capacitance. Besides, because the precharging signal or the image signal is supplied only from one end of the precharging signal line or the image signal line, the signal propagation delay increases with the location along the precharging signal line or the image signal line toward the opposite end.
According to the conventional technique, the precharging signal line or the image signal line are formed in such a manner that they extend over the TFT array substrate, starting at a contact connected to an external terminal on the TFT array substrate, in a direction parallel to the great number of data lines and generally perpendicular to the direction in which the scanning line extends, for example, from left to right, wherein the end of the precharging signal line or the image signal line is connected to a TFT, and connected to a data line at the extreme right of the precharging circuit or the sampling circuit. In particular, in the case where a precharging signal is supplied at the same time to a great number of data lines, or in the case where phase expansion is employed and thus an image signal is supplied at the same time to a great number of data lines, the great number of data lines are connected to the precharging signal line or the image signal line via TFTs of the precharging circuit or the sampling circuit. As a result, the increase in the interconnection capacitance becomes greater with the location along the precharging signal line or the image signal line toward its end.
Therefore, the precharging signal or the image signal supplied from the external terminal has a propagation delay which increases along the precharging signal line or the image signal line toward its end, and the charge written on the data lines in accordance with the precharging signal or the image signal varies depending on the location of the data lines from left to right. As a result, the contrast becomes different between the left and right portions of the image displaying area.
In particular, in the case of a liquid crystal device having a great number of pixels arranged at small intervals to display a high-precision image, a greater number of data lines are required and thus the circuit is required to supply a precharging signal to a greater load. As a result, the propagation delay and the associated degradation become greater.
The variation in the contrast is not so serious when only a single liquid crystal device is used. However, when two or three liquid crystal devices are combined and only one of them is inverted in the scanning direction of the data line driving circuit as is the case in a multipanel liquid crystal projector, one liquid crystal device has a variation in contrast in the opposite direction to that of the other liquid crystal devices and thus perceptible non-uniformity in color occurs.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a liquid crystal device capable of displaying a high-quality image including no non-uniformity in contrast or color even when the scanning direction is inverted. It is another object of the invention to provide an electronic apparatus including such a liquid crystal device.
As described above, the present invention provides an electro-optical apparatus in which at least either an image signal line or a precharging signal line extends on a substrate such that at least either the image signal line or the precharging signal line is connected to the sampling circuit or the precharging circuit from two sides of an arrangement of a plurality of data lines along a direction in which data lines are arranged side by side thereby preventing non-uniformity in contrast. A plurality of electro-optical apparatus can be employed as liquid crystal devices to realize a liquid crystal projector capable of displaying a high-quality image including no non-uniformity in color.
To achieve the above objects, according to an aspect of the invention, there is provided an electro-optical apparatus including a plurality of data lines for supplying an image signal, a plurality of scanning lines for supplying a scanning signal, first switching means connected to the respective data lines and the respective scanning lines, and pixel electrodes connected to the corresponding first switching means, the electro-optical apparatus comprising:
a sampling circuit including second switching means for sampling the image signal supplied to an image signal line and supplying the resultant signal to the data lines; and
a precharging circuit including third switching means for supplying a precharging signal supplied to a precharging signal line, to the data lines, according to a driving signal supplied from a precharging circuit driving signal line, before a sampling period in which the image signal is supplied to the data lines;
the precharging signal line extending over the substrate along the direction in which the data lines are arranged side by side so as to be conne
Alphonse Fritz
Oliff & Berridge PLC.
Saras Steven
Seiko Epson Corporation
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