This invention relates to a liquid crystal display device driven by a switching element using amorphous silicon, polycrystalline silicon or the like for each pixel, an electroluminescent-type display device, and a display device provided with a light emitting element such as a light emitting diode and the like for each pixel. In particular, this invention relates to a display device that performs blanking processing.
Liquid crystal display devices have been widely used as display devices that retain light emitted from each of a plurality of pixels in a desired amount within a predetermined period of time (e.g., a period of time corresponding to 1 frame period) on the basis of video data inputted for each 1 frame period. In the liquid crystal display device of active matrix scheme, each of a plurality of pixels arranged in a two-dimensional form or in a matrix form is provided with a pixel electrode and a switching element (e.g., a thin film transistor) for supplying a video signal to the pixel electrode. The video signal is supplied from one of a plurality of data lines (also called video signal lines) extending in the longitudinal direction of a picture, for example, to a pixel electrode through the switching element. The switching element receives scanning signals at predetermined intervals (e.g., for each frame period) from one of a plurality of gate lines (also called scanning signal lines) intersecting the plurality of data lines and extending (e.g., in a horizontal direction in a picture) and supplies a video signal from one of the plurality of data lines to a pixel electrode. Accordingly, the switching element keeps the pixel electrode at a potential based on the video signal supplied to this pixel electrode in response to the previous scanning signal until it receives the next scanning signal, so that the pixel provided with this pixel electrode is maintained at a desired brightness level.
Such an operation stands in contrast to an impulse emission operation of a cathode-ray tube represented by a Braun tube where a phosphor arranged for each pixel is caused to emit light at the instant of receiving the video signal. Unlike the impulse light emission, the video displaying operation of the active matrix type liquid crystal display device as described above is also called sometimes hold-type light emission. In addition, such video display as performed by the active matrix type liquid crystal display device is also employed in the electroluminescent type (abbreviated as EL type) or a light emission diode array type display device and those operations can be described by replacing the aforesaid voltage control of the pixel electrode with the control of carrier injection to the electroluminescent element or the light emission diode.
Since the display device using such a hold-type light emission displays an image by retaining a brightness level of each of the pixels within a predetermined period of time to display the image, when the image to be displayed by the display device is replaced with a different image, for example, between a pair of the successive aforesaid frame periods, the pixel sometimes does not provide a sufficient response. This phenomenon can be explained by the fact that the pixel set to a predetermined brightness level in a certain frame period (e.g., a first frame period) keeps the brightness level associated with the previous frame period (the first frame period) in the next frame period (e.g., a second frame period) subsequent to the first frame period until the brightness level associated with the second frame period is set. In addition, this phenomenon can also be explained by the so-called hysteresis of the image signal in each of the pixels, in which part of the image signal (or an amount of electric charge corresponding to the image signal) sent to the pixel in the aforesaid certain frame period (the first frame period) interferes with the image signal (or an amount of electric charge corresponding to the image signal) to be sent to the pixel in the aforesaid next frame period (the second frame period). The technology for resolving such a problem as above in regard to the response performance of the image display in the display device using the hold-type light emission has been disclosed by Japanese Patent Publication Nos. 06-016223 and 07-044670, and Japanese Patent Laid-open Nos. 05-073005 and 11-109921, for example.
Among them, Japanese Patent Laid-Open No. 11-109921 makes a reference to the so-called blurring phenomenon in which a contour of an object becomes vague as compared with that of a cathode ray tube for light emitting the pixel in an impulse manner when moving images are reproduced by the liquid crystal display device (one example of the display device using the hold-type light emission). To obviate the blurring phenomenon, Japanese Patent Laid-open No. 11-109921 discloses the liquid crystal display device in which a pixel array (a group of pixels arranged in a two-dimensional manner) in a liquid crystal display panel is divided into two, upper and lower, segments in a picture (an image display area) and each of the divided pixel arrays is provided with a data line drive circuit. This liquid crystal display device performs the so-called dual scanning operation in which a video signal is supplied from the data line drive circuits arranged the respective pixel arrays while selecting a gate line of each of the upper and lower pixel arrays one by one, i.e. two, upper and lower, gate lines in total.
An upper phase and a lower phase are displaced while this dual scanning operation is being carried out in 1 frame period, a signal (the so-called video signal) corresponding to a displayed image at one phase and a signal of blanking image (e.g., a black image) at the other phase are inputted from the associated data line drive circuits to the pixel array. Accordingly, a period in which the image is displayed and a period in which a blanking display is carried out are given to both upper and lower pixel arrays in 1 frame period, whereby a period for holding an image in the entire picture area is shortened. With such an arrangement, the liquid crystal display device can also provide moving image display performance comparable to that of a Braun tube.
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