Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-04-25
2004-01-27
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S092000, C345S098000, C345S205000, C345S206000
Reexamination Certificate
active
06683596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a data line driving circuit of an electro-optical panel, a control method thereof, an electro-optical device using these, and an electronic apparatus.
2. Description of Related Art
A conventional electro-optical device, for example, an active-matrix-type liquid-crystal display device, mainly includes a device substrate, on which a switching device is provided via pixel electrodes arrayed in a matrix, an opposing substrate, on which color filters, etc., are provided, and a liquid crystal which is provided between these two substrates. In such a structure, when a scanning line signal is applied to the switching device via scanning lines, the switching device is placed in a conducting state. During this conducting state, when an image signal is applied to the pixel electrode via data lines, a predetermined charge is stored in the liquid-crystal layer between the pixel electrode and the opposing electrode (common electrode). After the charge is stored, even if the switching device is turned off, the storage of the charge is maintained by the capacitance of the liquid-crystal layer if the resistance of the liquid-crystal layer is sufficiently high. In this manner, when each switching device is driven to control the amount of charge to be stored, the orientation state of the liquid crystal changes for each pixel, making it possible to display predetermined information.
In this case, since it may only be for a part of a period that the charge is stored in the liquid-crystal layer of each pixel, first, by having a scanning line driving circuit sequentially select each scanning line, and second, by supplying an image signal, obtained by converting image data into a line sequence and by a data line driving circuit performing DA conversion thereon to each data line time-division multiplex driving may be performed in which scanning lines and data lines are made common for a plurality of pixels becomes possible.
Here, the data line driving circuit includes a clock signal supply line, a shift register, an image data supply line, a sampling circuit, a first latch, a second latch, and a DA conversion circuit. The shift register sequentially shifts a transfer start pulse of a horizontal scanning period in accordance with a clock signal supplied via the clock signal supply line in order to generate each sampling signal corresponding to each data line. The sampling circuit samples image data supplied via the image data supply line in accordance with each sampling signal and supplies it to the first latch. The first latch maintains the sampled image data and creates point sequence image data. The second latch latches the point sequence image data in order to create the line sequence image data in accordance with a latch pulse of a horizontal scanning period and supplies this data to each data line.
In the above-described liquid-crystal display device, even if the switching device is turned off, the storage of the charge is maintained by the capacitance of the liquid-crystal layer. Concerning a particular pixel, if the gray scale value to be displayed in the pixel concerned is the same as that one field before, there is no need to supply an image signal to the pixel in the current field in order to newly re-store charge in the liquid-crystal layer. For this reason, by supplying an image signal to only a pixel in which there is a change between fields in order to rewrite the stored charge, reduction of the processing speed is possible, leading to reduced power consumption.
In such a liquid-crystal display device, it is necessary to specify a pixel in which there is a change between fields and to supply an image signal to a corresponding data line in a period in which the pixel concerned is selected by a scanning line signal. In this case, it is necessary to, by using an address decoder, specify the image data concerned by using a row address and a column address and to generate a scanning line signal and a data line signal from these addresses.
However, a problem arises that the circuit scale of the address decoder becomes large, and as a consequence, the power consumption is increased. In particular, a problem arises that even if an attempt to form an address decoder on a device substrate is made by using thin-film transistors (hereinafter referred to as “TFTs”), the circuit scale thereof is too large to be realized.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the above-described circumstances. An object of the present invention is to provide a data line driving method and apparatus suitable for reducing power consumption with a simple structure, an electro-optical device using the data line driving device, and an electronic apparatus in which this electro-optical device is used as a display.
To achieve the above-mentioned object, the data line driving circuit of the present invention is used for an electro-optical panel, which has a plurality of scanning lines, a plurality of data lines, and switching devices, and pixel electrodes arranged in such a manner as to correspond to the intersection of the scanning lines and the data lines and which is divided into blocks in units of a predetermined number of data lines. The data line driving circuit includes: a shift register section having a clock signal supply line that supplies a clock signal, a plurality of shift registers that sequentially shift a transfer start pulse in accordance with the clock signal in order to generate each sampling signal, the plurality of shift registers being provided in such a manner as to correspond to each of the blocks, and a selection circuit that selectively supply the transfer start pulse to each of the shift registers; an image data conversion section that samples image data in accordance with each of the sampling signals and converts the data obtained by performing sampling into line sequence image data after the data is latched; and a DA conversion section that outputs each data line signal obtained by performing DA conversion on the line sequence image data to each of the data lines.
According to the present invention, since the shift register section is divided into blocks by a plurality of shift registers, it is possible to selectively cause a necessary shift register to operate. Consequently, it is possible to reduce power consumption.
In the present invention, the sampling section may perform sampling in accordance with each of the sampling signals only when an enable signal supplied from the outside becomes active. In this case, since sampling is performed in accordance with an enable signal, for example, even if shift registers operate to generate sampling signals for a particular block, it is possible to sample image data only for a necessary dot from these signals.
Furthermore, in a case where the above-described data line driving circuit is controlled, preferably, image data is compared between horizontal lines which are adjacent in a data time-series manner, and supply of the clock signal is stopped for the block in which the data values match. Since the sampled image data is latched by the image data conversion section, when the image data values match between horizontal lines which are adjacent in a data time-series manner, it is not necessary to sample the image data again and to latch it. On the other hand, in order to perform sampling, it is necessary to cause the shift register to operate in order to generate a sampling signal by supplying a clock signal thereto, and parasitic capacitance occurs in the wiring which supplies the clock signal. Since the wiring acts as a capacitive load, in order to supply the clock signal at a sufficient through rate, a large amount of electric power is required. According to the present invention, since supply of the clock signal is stopped for the block in which the data values match, the power consumption can be greatly reduced.
In addition, in a case where the above-described data line driving circuit is controlled, preferably, image data is compa
Leonid Shapiro
Shalwala Bipin
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