Computer graphics processing and selective visual display system – Display driving control circuitry
Reexamination Certificate
2003-04-14
2004-07-13
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display driving control circuitry
C345S080000
Reexamination Certificate
active
06762754
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention belongs to the technological fields of a driving circuit including a data line driving circuit for driving an electro-optical device, such as a liquid-crystal apparatus of an active-matrix transistor driving method, such as a thin-film transistor (hereinafter referred to as a “TFT” where appropriate), and an electro-optical device of a type incorporating such a driving circuit. More particularly, the present invention belongs to the technological fields of a driving circuit for an electro-optical device, which adopts a driving method for driving plural data lines simultaneously in order to support high dot frequencies and color image signals, and an electro-optical device of a type incorporating such a driving circuit.
2. Description of Related Art
This type of driving circuit for an electro-optical device includes a data line driving circuit, a scanning line driving circuit, and a sampling circuit and the like, which are used to supply image signals and scanning signals at a predetermined timing to data lines and scanning lines wired in an image display area of an electro-optical device.
Such a driving circuit is constructed so that when a line sequential driving method is adopted, image signals which are supplied to one image signal line from an external source are sampled by plural sampling switches provided in such a manner as to correspond to each data line, respectively, in accordance with a sampling control signal which is supplied in sequence in such a manner as to correspond to each data line from the data line driving circuit, and are supplied to each data line based on the line sequence. Also, generally, the data line driving circuit includes a shift register circuit including plural arranged latch circuits which output a transfer signal in sequence according to a reference clock. Furthermore, the construction is formed in such a way that a buffer circuit is interposed between this latch circuit and the sampling circuit, and the waveform of the transfer signal is shaped to become the sampling control signal, and even if the driving performance of the latch circuit is not sufficient to drive the sampling switch, the load of the sampling switch can be sufficiently dealt with by the buffer circuit.
Here, in response to the demand for higher quality of display images in recent years, the dot frequency in an electro-optical device, such as a liquid-crystal device, is becoming increasingly higher, for example, as in an XGA method, an SXGA method, or an EWS method. When the dot frequency is increased in this manner, the sampling performance in the sampling switch becomes insufficient, and the delay time in each TFT, which is an element of the driving circuit, exerts an adverse influence upon the quality of the display image. For example, a problem arises in that an image signal for the previous data line is written into the next data line, causing ghost or crosstalk. However, if the performance of the sampling switch and each TFT is increased to deal with this problem, a substantial increase in cost will occur.
For this reason, recently, a technology described below has been developed. For example, an image signal is converted from serial into parallel form in advance so that the image signal is divided into plural parallel image signals, or the image signal is divided into parallel image signals for each color in the case of a color image signal, after which the image signals are supplied to plural image signal lines provided in an electro-optical device. In the sampling circuit, plural parallel image signals which are converted from serial into parallel form are sampled simultaneously, and are supplied to a plurality (for example, 6, 12, 24 lines, and the like) of data lines at the same time. According to this technology, since the time each sampling switch performs sampling can be increased about n times according to the number of data lines n which are driven simultaneously, the driving frequency in the driving circuit can be substantially decreased to about 1
. That is, there is no need to improve the performance itself of the sampling switches and each TFT as described above, and it is possible to cope with a high dot frequency.
In a case in which plural data lines are driven simultaneously in this manner, since a sampling control signal is supplied simultaneously or the same sampling control signal is supplied to plural sampling switches, the data line driving circuit requires driving performance capable of withstanding a total of loads of the plural sampling switches. That is, the driving performance of the buffer circuit interposed between the latch circuit and the sampling switch must be increased according to the total of loads of the plural sampling switches. For this purpose, the size of the TFT which is an element of the inverter included in the buffer circuit need only be increased. However, if the size of the TFT is simply increased, there occurs the need to increase the driving performance in the latch circuit for driving this TFT by a transfer signal, causing the power consumption in the shift register circuit in which, in particular, the large amount of the power consumption is conventionally deemed to be problematical in the field of the relevant electro-optical device, to be increased even more. Accordingly, a construction is generally adopted in which the buffer circuit is formed of inverters of plural stages which are connected in series so that the driving performance in the buffer circuit is increased in a stepped manner for each inverter. That is, a construction is adopted in which the size of the TFT which is an element of an inverter of a stage on the side of the latch circuit of the buffer circuit is small and the size of the TFT which is an element of an inverter of a stage on the side of the sampling switch of the buffer circuit is large.
On the other hand, an electro-optical device of a driving circuit built-in type has been developed in which a driving circuit such as that described above is provided on a substrate which is an element of the main unit of an electro-optical device, such as a liquid-crystal device. This electro-optical device of a driving circuit built-in type is advantageous in achieving an overall reduction in size of the device and a decrease in cost in comparison with an electro-optical device of a type in which a driving circuit is formed on a separate substrate and is provided externally.
However, if the above-mentioned buffer circuit formed of plural stages is provided in the above-mentioned liquid-crystal device of a driving circuit built-in type, an increase in the occupied area by the buffer circuit having a larger size on the substrate of a liquid-crystal device, and the like, becomes a problem. In particular, as in the above-mentioned conventional liquid-crystal apparatus of a line sequential driving method, if each inverter is formed of TFTs extending in a longitudinal direction along the data lines and this is connected in series in a longitudinal direction at plural stages along the data lines, conventionally, there is the problem in that the ratio of the ineffective use area by the buffer circuit, which occupies an area on a horizontally elongated substrate along the scanning lines present between the image signal lines and the shift register circuit, is increased. Ultimately, a non-image display area for forming a data line driving circuit in the upper or lower portion of the image display area is extended, resulting in a problem in that a situation is brought about which is contrary to a general demand for a smaller size and a lighter weight of the overall device and a larger area of the image display area of the same device size in the technological field of the relevant electro-optical device.
SUMMARY OF THE INVENTION
The present invention has been achieved in view of the above-described problems. A driving circuit for an electro-optical device is provided, which is capable of achieving a smaller size of the device or a larger size o
Anyaso Uchendu O.
Oliff & Berridg,e PLC
Saras Steven
Seiko Epson Corporation
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