Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2002-07-26
2003-09-02
Wu, Xiag (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S100000, C345S204000
Reexamination Certificate
active
06614417
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a driving circuit for an electrooptical device in which the driving circuit performs high definition display while preventing an unnecessary region from being generated in a formation region, to the electrooptical device including the driving circuit, and to an electronic apparatus using the electrooptical device.
2. Description of Related Art
A driving circuit for a conventional electrooptical device, for example, a liquid crystal device, includes a data-line driving circuit, a scanning-line driving circuit, and a sampling circuit that supply video signals, scanning signals, etc., with predetermined timing, to data lines, scanning lines, etc., provided in an image display region. Among the circuits, the data-line driving circuit includes, in general, a plurality of latch circuits (shift-register circuit), and outputs sampling-control signals by sequentially shifting transfer signals supplied in the beginning of a horizontal scanning period in accordance with a clock signal. The scanning-line driving circuit similarly includes a plurality of latch circuits, and outputs a scanning signal by sequentially shifting transfer signals supplied in the beginning of a vertical scanning period in accordance with a clock signal. The sampling circuit, which includes sampling switches provided corresponding to the data lines, samples externally supplied video signals in accordance with sampling-control signals, and supplies the sampled signals to the data lines.
Also, a construction is employed that provides buffer circuits between latch circuits and a sampling circuit so that transfer signals are processed by wave shaping to generate the sampling-control signals and that can sufficiently cope with a load on the sampling switches, even if the driving ability of the latch circuits is insufficient for driving sampling switches.
In addition, an electrooptical device with built-in driving circuits has been developed in which the above-described driving circuits are provided on a substrate included in the electrooptical device. In this type of electrooptical device, devices constituting the driving circuits are fabricated in a common process, with switching devices, in view of, for example, increasing the efficiency of the fabrication process. For example, in a liquid crystal device using liquid crystal as an electrooptical material, devices constituting driving circuits include thin-film transistors (hereinafter referred to as “TFTs”) which drive liquid crystal pixels. This type of electrooptical device with built-in driving circuits are advantageous in achieving a reduction in the overall size and cost reduction, compared with a type of electrooptical device in which driving circuits, formed on a separate substrate, are externally provided.
Recently, not only in electrooptical devices but also in display units in general, high definitions, such as XGA (1024×768 dots), SXGA (1280×1024 dots), and UXGA (1600×1200 dots) standards, are in great demand. In accordance with the demand, it is required that a dot frequency in an electrooptical device be increased. When the dot frequency is increased in the type of electrooptical device with built-in driving circuits, insufficiency in the sampling performance of sampling switches, delays in the operations of devices constituting the driving circuit, etc., occur, so that, by way of example, as a result of writing, video signals that must originally be written in the next data line, as well as in the previous data line, a so-called “ghost” or “crosstalk” is generated, reducing the definition of a displayed image. As a solution, the performance itself of the sampling switches and devices constituting the driving circuits can be enhanced, but this results in a remarkable increase in the cost.
Accordingly, a technique has recently been developed in which video signals on a route are distributed to a plurality of routes while being expanded (serial-to-parallel converted) in a time domain and in which a sampling circuit simultaneously samples video signals on a plurality of routes and simultaneously supplies the sampled signals to a plurality of data lines. According to this technique, in accordance with the number of data lines being simultaneously driven, the sampling time of each sampling switch is multiplied by the number of data lines being simultaneously driven. Thus, a driving frequency in a driving circuit decreases substantially with the reciprocal of the number of data lines being simultaneously driven. Therefore, it is possible to cope with an increased dot frequency without improving the performance of the sampling switches, devices constituting driving circuits, devices for driving pixels, etc.
In the case where a plurality of data lines are simultaneously driven as described above, it is required that a plurality of sampling switches be supplied with sampling-control signals at the same time or of the same type. Accordingly, it is required that the driving ability of buffer circuits provided between latch circuits and the sampling switches be enhanced in accordance with a total load on the sampling switches.
Concerning measures for enhancing the driving ability of the-buffer circuit, it is possible that logic circuits constituting the buffer circuit, for example, devices constituting an inverter, be enlarged in size. In the measures, simple enlargement of the component devices generates the need for enhancing the driving ability of the latch circuit, causing a result which contradicts a general demand in the technical field of the electrooptical device, such as reduction in power consumption of the shift-register circuit including a plurality of latch circuits. Accordingly, a construction is employed in which a buffer circuit is formed by connecting a plurality of inverters in series so as to have a plurality of stages, whereby the driving ability of the buffer circuit is enhanced step-by-step in each stage. In other words, a construction is employed in which the size of devices constituting inverters in stages on the side of the latch circuits is small and in which the size of devices constituting inverters on the side of the sampling switches is large.
If each buffer circuit including inverters connected in series so as to have a plurality of stages is provided in the above-described electrooptical device with built-in driving circuits, each buffer circuit is enlarged in a substrate region, so that a problem occurs in that an area occupied by each buffer circuit and an ineffectively used area increase. In particular, since a region in which the buffer circuits are formed is normally a region provided between video-signal lines and a shift-register circuit, it is longitudinal in a direction intersecting with a direction in which data lines extend. Accordingly, in a simple construction in which inverters in each stage are formed from devices longitudinally extending along the direction in which data lines extend and in which the inverters are connected in series so as to have a plurality of stages, the proportion of an ineffectively used area of the region is remarkably large. Finally, a data-line driving circuit is formed in an outermost part of an image-display region. Thus, a non-image-display region expands, causing a result contradicting general demands on the electrooptical device, such as size and weight reduction of the entire electrooptical device, and enlargement of an image display region in the same device size.
SUMMARY OF THE INVENTION
The present invention provides a driving circuit for an electrooptical device including the driver circuit, such as a liquid crystal device simultaneously driving a plurality of data lines in which the driving circuit efficiently uses a substrate region to enable reduction in the size of the entire electrooptical device, an electrooptical device including the driving circuit, and an electronic apparatus including the electrooptical device.
To achieve the foregoing, the present invention provides a drivi
Seiko Epson Corporation
Wu Xiag
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