Field of the Invention
The present invention relates to a drive apparatus for a light emitting display panel in which pixels that can emit light are arranged, for example, in a matrix pattern, and particularly relates to a drive apparatus and a drive method for a light emitting display panel, which can prevent a sense of incongruity from arising due to a large change in light-emission luminosity of the panel at the time of the maximum gradation when changing a gamma value of a gradation characteristic.
A display panel in which light emitting pixels are arranged in a matrix pattern has been widely developed.
As an example of such a display panel, a display in which a pixel is constituted by an organic EL (electroluminescence) element using an organic material for its luminescence layer has already been commercialized. This is also because there is a background where an organic compound which can be expected to provide a good luminescence characteristic is used for the luminescence layer of the EL element to allow a high efficiency and a long life, leading to practical use.
As a display panel using such an organic EL element, there have been proposed a passive matrix type display panel in which EL elements are merely arranged in a matrix pattern and an active matrix type display panel in which each of EL elements arranged in a matrix pattern is provided with a TFT (Thin Film Transistor), for example. Compared with the former passive matrix type display panel, the latter active-matrix type display panel can reduce power consumption and has an advantage in that there is less cross talk among pixels, thus being particularly suitable for a high definition display which constitutes a large screen.
It is arranged that a scanning signal Select (also referred to as a write-in pulse) may be supplied to a gate of the above-mentioned data write-in transistor Tr1 through a scanning line 3 connected to a scanning driver. A drain of the above-mentioned data write-in transistor Tr1 is connected to a gate of a lighting and driving TFT i.e., a lighting and driving transistor Tr2 and also connected to one terminal of a capacitor C1 for holding electric charges.
Further, a source of the lighting and driving transistor Tr2 is arranged to be connected with the other terminal of the above-mentioned capacitor C1 and supplied with a drive voltage Vcc via a power supply line 4. A drain of the above-mentioned lighting and driving transistor Tr2 is connected to an anode terminal of an organic EL element E1 as a light emitting element, and a cathode terminal of this organic EL element E1 is connected to a reference potential point (ground).
Furthermore, it is arranged that an erase signal Erase (also referred to as an erase pulse) may be supplied from an erase driver through an erase signal line 5 to a gate of an erase transistor Tr3 as a TFT for erase. A source and a drain of the erase transistor Tr3 are respectively connected to terminals of the above-mentioned capacitor C1.
In addition, in the circuit structure of the pixel 1 as shown in
In the structure of the pixel 1 as shown in
Then, its charge voltage is supplied to the gate of the drive transistor Tr2, the transistor Tr2 passes the current corresponding to the gate voltage and the drive voltage Vcc supplied to the drain, to the above-mentioned EL element E1, so that the EL element E1 emits light.
When application of the above-mentioned write-in pulse to the gate of the above-mentioned control transistor Tr1 is stopped, the transistor Tr1 is so-called cut-off. However, the gate voltage of the drive transistor Tr2 is held by the electric charge accumulated in the capacitor C1, so that the drive current to the EL element E1 is maintained. Therefore, the EL element E1 can continue a lighting state corresponding to the above-mentioned data signal Vdata during the period until the next address operation (i.e., one frame period).
On the other hand, in the middle of a lighting period of the above-mentioned EL element E1 (for example, in the middle of one frame period), the erase pulse Erase which causes the erase transistor Tr3 to turn on is supplied from the above-mentioned erase driver. Thus, the electric charge charged in the capacitor C1 can be instantaneously eliminated (discharged). As a result, the drive transistor Tr2 is in a cut-off state, and the EL element E1 is turned off immediately.
In other words, the lighting period of the EL element E1 is controlled by controlling an output timing of the erase pulse Erase from the erase driver, so that multi-gradation expression can be realized. For example, patent document 1 as indicated below discloses a drive apparatus for the display panel in which the multi-gradation expression is realized by using a pixel structure provided with the above-mentioned erase transistor Tr3.
[Patent Document 1] Japanese Patent Publication (KOKAI) 2001-42822
Incidentally, as an example in which the multi-gradation expression is realized by means of the circuit structure as shown in the above-mentioned patent document 1, there has been proposed a drive method for a display panel in which one frame (period) is divided into a plurality of sub-frames, to control lighting of a pixel on a sub-frame by sub-frame basis.
Now, in order to set the number of gradations, for example, as “10”, the EL element is lit and controlled in 1-10 sub-frames in one frame (period) as shown in
However, it is said that a luminosity characteristic with respect to the gradation is ideally around γ=1.8 to 2.5 in the case of lighting and displaying, for example, inside a room etc. where the circumference is not bright. In other words, as shown in
Then, in the pixel structure as shown in
Incidentally, as described above, when trying to control and change to the gamma value of each value by means of a lighting control means having the pixel structure as shown in
As a result, the luminosity of each pixel especially in the case where the gradation is set as the maximum is different according to the γ value. For example, when it is arranged that the above-mentioned γ value varies according to surrounding brightness, the luminosity of the pixel varies according to the change of the γ value, resulting in giving sense of incongruity to a user. This is because the lighting period of the pixel in each sub-frame is distributed so that light emission duty of the pixel may be the maximum for every γ value, when the γ value of the gradation characteristic is set up for each.
The present invention is made in view of the above-mentioned problem, and provides a drive apparatus and a drive method for a light-emitting display panel which can control luminosity changes generated when switching γ values of gradation characteristics, especially at the time of the maximum gradation, and can reduce degrees of a user's sense of incongruity.
The drive apparatus in accordance with the present invention made in order to solve the above-mentioned problem is a drive apparatus for a light-emitting display panel in which pixels are arranged in intersections where a plurality of data lines intersect with a plurality of scanning lines and each of the above-mentioned pixels is selectively lit and driven, to display an image; the drive apparatus comprises a gradation control means for dividing one frame (period) into a plurality of sub-frames including a lighting period and a non-lighting period for the above-mentioned pixel, to realize gradation control by selecting the above-mentioned sub-frame (period)s and by summing the lighting periods of the pixel within one frame period, and a gamma value selection means for changing proportions of the above-mentioned lighting period and the non-lighting period for every sub-frame, so as to change a gamma value of a gradation characteristic; and a sum of the lighting periods within one frame period of the above-mentioned pixel at the time of setting the maximum gradation by the above-mentioned gradation control means is arranged to be the same at the time of selecting any gamma value selected by the above-mentioned gamma value selection means.
Further, the drive method in accordance with the present invention made in order to solve the above-mentioned problem is a drive method for a light emitting display panel in which pixels are arranged in intersections where a plurality of data lines intersect with a plurality of scanning lines and each of the above-mentioned pixels is selectively lit and driven, to display an image, wherein one frame (period) is divided into a plurality of sub-frames including a lighting period and a non-lighting period for the above-mentioned pixel, gradation control is realized by selecting the above-mentioned sub-frames and by summing the lighting periods of the pixel within one frame period, proportions of the above-mentioned lighting period and the non-lighting period for every sub-frame are changed so as to perform selection operation of a gamma value of a gradation characteristic, and a sum of the lighting periods within one frame period of the above-mentioned pixel at the time of setting the maximum gradation by way of the above-mentioned gradation control is arranged to be the same at the time of selecting any gamma value selected by the above-mentioned gamma value selection operation.
Hereafter, a drive apparatus for a light emitting display panel in accordance with the present invention will be described with reference to preferred embodiments shown in the drawings.
An image signal displayed at the above-mentioned light emitting display panel 10 is supplied to a luminescence control circuit 11. This luminescence control circuit 11 operates so that the inputted image signal is subjected to a sampling process etc. and converted into pixel data corresponding to each pixel, based on a horizontal synchronization signal and a vertical synchronization signal in the image signal, and that the data for each scan may be supplied to a data driver 12. It is arranged that data voltages Vdata corresponding to the above-mentioned pixel data are separately supplied to sources of the data write-in transistors Tr1 which constitute the respective pixels 1 by way of the above-mentioned operation. And the above-mentioned operation is repeated for every scan in the address period.
Further, a scanning clock signal corresponding to the horizontal synchronization signal is supplied from the above-mentioned luminescence control circuit 11 to a scanning driver 13 in the address period. Thus, the above-mentioned write-in pulses Select are arranged to be supplied one by one for every scanning line to the gates of the data write-in transistors Tr1 which constitute respective pixels 1.
Furthermore, a command signal corresponding to the gradation control is transmitted from the above-mentioned luminescence control circuit 11 to an erase driver 14, and the erase driver 14 acts so as to supply the erase pulse Erase which turns on the erase transistor Tr3 in the middle of the lighting period of the pixel 1 (in the middle of one sub-frame period).
Thus, as already described, the electric charge charged in the capacitor C1 as shown in
Further, it is arranged that each of the above-mentioned pixels 1 as shown in
Furthermore, in the preferred embodiment as shown in
Corresponding to the selected γ value, (information about) the lighting period for every sub-frame is stored in the above-mentioned γ table 16 as a parameter. When the sub-frame number to be lit and controlled is supplied from the sub-frame counter 21 to the logical operation unit 22, the logical operation unit 22 accesses the γ table 16 and operates so that the output timing signal of the above-mentioned erase pulse may be generated based on the parameter of the lighting time stored corresponding to the sub-frame number.
This is generated as the output timing signal of the erase pulse for each sub-frame number corresponding to a respective one of the γ values selected as described above. This timing signal is supplied to the above-mentioned erase driver 14 and operates so that, based on the above-mentioned timing signal, the erase pulse may be outputted from the erase driver 14 for each sub-frame as will be described in detail later.
As shown in
In other words, the sums of the lighting periods provided in one frame period as shown in
This is what the luminosity characteristic at each of γ=1.0, γ=1.8, and γ=2.2 is set up so as to be in agreement with the luminosity of the pixel when it is set up as the gradation 15 at γ=2.5 shown in
In the example as shown in
The above-mentioned erase pulse is generated according to the structure shown in
Further, when trying to realize the gradation “15” (for example), a series of lighting patterns as shown in
In the example shown in
When trying to realize the gradation “15” (for example), a series of lighting patterns as shown in
In addition, although
According to the above-mentioned control modes, since the sum of the lighting periods within one frame period of the pixel at the time of setting the maximum gradation is particularly set up so as to be the same at the time of selecting any γ value selected by the γ value selection means, it is possible to solve the problem in that the luminosity of the screen changes considerably as the γ value is changed in a situation where an especially bright image is displayed.
Further, according to the above-mentioned control mode, since the luminescence luminosity value of the pixel at the time of the maximum gradation when the γ value is selected to be small (γ=1.0) can be controlled, it is also possible to reduce the power consumption and ease design criteria, such as current capacity of a power supply circuit, etc.
In addition, as already described, the above-mentioned expression that the sums of the lighting periods are set up so as to be the same at the time of selecting any γ value is carried out based on an idea that a luminescence duty of the pixel at γ=1.0 is brought into agreement with a luminescence duty of the pixel at γ=2.5, Thus, there is a technical feature that the luminosity of the display panel at the time of the maximum gradation changes with changes in the above-mentioned γ value, so that a user's sense of incongruity can be inhibited.
In the preferred embodiments as described above, it is assumed that the light emitting elements (EL elements) which constitute the respective pixels are luminescence drive devices of monochrome displays which emit lights in the same color. On the other hand, in the preferred embodiment as shown in
Also the drive apparatus for the color display panel 10 as shown in this
Then, it is desirable that the drive apparatus for the color display panel as described above is provided with the luminosity characteristic with respect to the gradation as shown in
In addition, although the preferred embodiments as described above illustrate the examples in which the gradation control is carried out with 16 steps, it is not limited thereto. When realizing 32 or 64 steps for the gradation control, the number of sub-frames in one frame period can be increased, and it is possible to employ a similar control mode. Further, in the preferred embodiments as described above, although the examples using the organic EL element as the light emitting element which constitutes each pixel are shown, it is possible to obtain similar operational effects even when it is employed for a drive apparatus of flat panels, such as a light emitting diode and plasma.
Number | Date | Country | Kind |
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2005-274406 | Sep 2005 | JP | national |