Patent Application
20100177086
The present application claims priority from Japanese application JP2009-004590 filed on Jan. 13, 2009, the content of which is hereby incorporated by reference into this application.
1. Field of the Invention
This invention relates to an image display device that performs display control of pixels by causing light emitting elements such as organic electroluminescence elements to emit light.
2. Description of the Related Art
Image display devices that display an image by controlling the luminance on a pixel basis include ones that perform display control of pixels by causing light emitting elements of the respective pixels to emit light, for example, organic electroluminescence display devices (hereinafter referred to as organic EL display devices) which include organic electroluminescence elements (hereinafter referred to as organic EL elements) as light emitting elements.
In those image display devices, a brighter screen (higher luminance) is generally desirable. Higher luminance, however, necessitates more power consumption, which goes against the request for reduction in power consumption. As a solution, techniques have been proposed which pay attention to the fact that what is important in terms of screen brightness to human sight is the luminance around the center of the screen (e.g., JP 06-282241 A and JP 2008-158399 A). One of the techniques improves the apparent brightness while preventing an increase in power consumption by enhancing the luminance in the central part of the screen. Another keeps power consumption low without sacrificing the apparent brightness by lowering the luminance along the edges of the screen.
In the above-mentioned image display devices that perform display control of pixels by causing light emitting elements to emit light, the ratio of power supplied for making the light emitting elements emit light to the overall power consumption of the device is large. The conventional techniques described above, which lower the luminance along the edges of the screen but allow pixels in the central part of the screen to emit high luminance light, are unable to lower the voltage applied to the light emitting elements of the respective pixels itself, and are unlikely to be helpful in keeping power consumption necessary to make light emitting elements emit light at a satisfactorily low level.
Also, light emitting elements of the respective pixels in the above-mentioned image display devices emit light at a brightness level that corresponds to the magnitude of current and/or voltage supplied from a power supply line. This means that fluctuations among pixels in terms of magnitude of power supplied from power supply lines may make the overall brightness of the display screen uneven. However, power supply from a power supply line is usually shared by a plurality of pixels. In addition, when to execute light emission control of pixels is common to a plurality of pixels, so that the light emission control is executed at once for the entire screen or executed on a pixel row basis. The consequence is that, when a plurality of pixels are to emit light simultaneously, a current flows from the same power supply line into a plurality of light emitting elements at once and the magnitude of power supplied to each pixel is accordingly reduced. Further, the resistance of the power supply line and other factors make the degree of this power reduction vary depending on how far along the power supply line a pixel in question is from the power source. The variation may cause a luminance gradient within the screen (luminance shading) in which each pixel has a brightness level that varies depending on the pixel's location in the screen.
This invention has been made in view of the circumstances described above, and it is therefore an object of this invention to provide an image display device capable of controlling power that is supplied to each pixel to make a light emitting element emit light based on the pixel's location in a display area.
A representative aspect of the invention disclosed in this patent application is briefly summarized as follows.
(1) An image display device for displaying an image by causing a light emitting element contained in each of a plurality of pixels that are arranged in a display area to emit light, including: power supply paths for supplying electric power to each of a plurality of partial areas, which are created by dividing the display area, independently of other partial areas to make the light emitting element of each pixel that belongs to the partial area emit light; and a power control unit for controlling electric power to be supplied from each of the power supply paths to the associated partial area, in which at least some of the partial areas have an area that overlaps with other adjacent partial areas.
(2) The image display device according to item (1), in which the power control unit controls power that is supplied from each of the power supply paths to the associated partial area based on a location of the partial area.
(3) The image display device according to item (2), in which the power control unit controls power that is supplied from each of the power supply paths to the associated partial area based on a distance of the partial area from a center of the display area.
(4) The image display device according to item (1), in which the power control unit controls power that is supplied from each of the power supply paths to the associated partial area based on what image is to be displayed in the partial area.
(5) The image display device according to item (4), in which the power control unit controls power that is supplied from each of the power supply paths to the associated partial area based on an index value that indicates brightness of an image to be displayed in the partial area.
(6) The image display device according to item (1), in which at least some of the partial areas each include a plurality of small areas which are apart from one another within the display area.
(7) The image display device according to item (1), in which the light emitting element is an organic electroluminescence element, and the organic electroluminescence element emits light by allowing a current supplied from at least one of the power supply paths to flow into the organic electroluminescence element.
In the accompanying drawings:
Hereinafter, embodiments of this invention are described in detail below with reference to the drawings. The following description takes as an example a case of applying this invention to an organic EL display device, which is one of modes of image display devices.
An image display device according to a first embodiment of this invention is described first.
The display panel 2 includes a glass substrate, a sealing substrate, a front frame FF, and a back frame BF. A plurality of pixel circuits each containing an organic EL element, which is a light emitting element, are formed in a matrix pattern on the glass substrate. The sealing substrate is bonded to the glass substrate to seal the organic EL element. The front frame FF frames the sealing substrate, leaving a part of the display panel 2 that serves as a display area open. The back frame BF frames the opposite side of the glass substrate and is fixed to the front frame FF by snap fit. A polarizing plate PP is bonded to the open part of the front frame FF which corresponds to the display area.
A thin film transistor (TFT) is formed on the glass substrate. The light emission of an organic EL element is controlled through the thin film transistor, to thereby perform display control on a pixel basis.
As illustrated in
Each data signal line DAT is connected at one end to a data signal output circuit 12, and each lighting switch control line ILM and each reset switch control line RES are connected at one end to a scanning circuit 14. The data signal output circuit 12 and the scanning circuit 14 may be formed from polycrystalline silicon TFT elements or the like on the glass substrate, as is the case for other components of the display panel 2 including a switch that is a constituent of each pixel circuit 10. Alternatively, the data signal output circuit 12 and the scanning circuit 14 may each be constituted of a single or a plurality of driver IC chips or the like mounted onto the glass substrate, or a combination of a driver IC chip and a circuit element such as a polycrystalline silicon TFT element. Each power supply line PWR is connected at one end to one of a plurality of main power supply lines Pm. In this embodiment, the plurality of main power supply lines Pm are arranged on the glass substrate to apply a voltage for making light emitting elements emit light to the respective pixels through the power supply lines PWR. The arrangement of the main power supply lines Pm is described later.
A reset switch 28 constituted of an n-type TFT is connected between the other end of the lighting switch 24 and a gate of the driver TFT 26. One end of a storage capacitor 30 is also connected to the gate of the driver TFT 26. The other end of the storage capacitor 30 is connected to the data signal line DAT. As illustrated in
In the pixel circuit 10 of
In manufacturing the display panel 2, the first step is a low temperature polycrystalline silicon (LTPS) step where, as illustrated in
The next step is an organic light emitting diode (OLED) step in which a detailed mask for separating R, G, and B from one another is used to form an organic EL layer, and a transparent cathode CD is formed from indium-zinc oxide (IZO) so as to cover the entire display area. The transparent cathode CD needs to be thinned into a thin film. For that reason, an auxiliary electrode AUX is further formed in order to reduce the resistance between adjacent pixels. Lastly, a sealing substrate SUB2 to which a drying agent has been applied to prevent the permeation of moisture is used to seal the display panel in an N2 environment, whereby the manufacture of the display panel is completed.
The description of the sectional structure given here assumes that the image display device 1 is a top emission organic EL display device. However, the image display device 1 is not limited thereto and may be a bottom emission organic EL display device.
Power for making light emitting elements of the respective pixels emit light is supplied to the partial areas A1, A2, and A3 independently of one another. Specifically, the power supply lines PWR in the partial area A1 are connected to a main power supply line Pm1, and power is supplied to pixels in the partial area A1 through the main power supply line Pm1. Power supply to pixels in the partial area A2 and power supply to pixels in the partial area A3 are executed through a main power supply line Pm2 and a main power supply line Pm3, respectively. The main power supply lines Pm1, Pm2, and Pm3 are power supply routes independent of one another. This way, the entire screen is fairly well protected against a luminance gradient within the screen.
Further, in this embodiment, power supplied from the main power supply lines Pm1, Pm2, and Pm3 to their associated partial areas is controlled independently of one another. The magnitude of power supplied to the partial areas A1 to A3 may therefore be set differently from one another.
The image data control unit 32 receives an input of an image data signal from the outside, and executes image processing for displaying the received image data on the display panel 2. The driver circuit control unit 34 receives, frame by frame, signals that are related to image data output from the image data control unit 32, and supplies luminance information of each pixel which reflects the image data to the data signal output circuit 12 in the display panel 2.
The area image information obtaining unit 36 and the power control unit 38 use information about image data output from the image data control unit 32 to control power supplied from the power output unit 40 to the display panel 2.
In the example of
Based on the index value calculated in the step S2, the power control unit 38 determines for each partial area a control parameter that corresponds to the value of a power supply voltage to be output (step S3). The control parameter is expressed by, for example, a 6-bit value from 0 to 63, each of which is associated with a power supply voltage value from 5.00 V to 10.0 V. To elaborate, each control parameter value is associated with one of power supply voltage values spaced at an interval of 0.08 V, so that control parameter values “0” and “1” are associated with 5.00 V and 5.08 V, respectively. The power control unit 38 outputs the control parameter determined in the step S3 to the power output unit 40 (step S4).
The power output unit 40 includes a power supply circuit and other components to output power supplied from a power source (a battery or the like) to the main power supply lines Pm1, Pm2, and Pm3 separately. The power output unit 40 controls power that is supplied to the main power supply lines Pm1, Pm2, and Pm3 separately based on the values of the control parameters, which are output from the power control unit 38 in the step S4 described above. Specifically, the power output unit 40 here varies the voltage to be applied to each main power supply line Pm to match one of the voltage values from 5.00 V to 10.0 V that is associated with the control parameter value calculated for each partial area. This way, power may be supplied to the partial areas A1 to A3 at different voltages from one another. Also, the voltage applied to each partial area is varied here depending on the index value which is related to an image to be displayed in the partial area, such as the number of pixels in the partial area that emit light or the light emission amount in the partial area. This way, power may be supplied at a high voltage to a partial area that is expected to be affected more by a drop in voltage, and the influence of a luminance gradient within the screen is thus lessened.
In the above description, power supplied to each partial area is controlled in accordance with input image data. However, the image display device 1 is not limited thereto and the magnitude of power supplied to each partial area may be controlled based on the location of the partial area in the display area SA. For example, the power control unit 38 may control the power output unit 40 such that a larger power is supplied to a partial area that is closer to the center of the display area SA whereas a smaller power is supplied to a partial area that is further from the center of the display area SA.
To give a concrete example, the power output unit 40 may output a higher voltage to the main power supply line Pm2, which is associated with the partial area A2, than voltages output to the other main power supply lines Pm1 and Pm3, and output lower voltages to the main power supply lines Pm1 and Pm3, which are associated with the partial areas A1 and A3, respectively, than the one output to the main power supply line Pm2.
An image display device according to a second embodiment of this invention is described next. The following description focuses on differences from the first embodiment while omitting a description on the structure and functions of the image display device according to this embodiment that are similar to those of the image display device according to the first embodiment. Components similar to those in the first embodiment are referred to by the same reference symbols.
This embodiment differs from the first embodiment in the arrangement of the partial areas within the display area SA and the arrangement of the main power supply lines Pm which corresponds to the arrangement of the partial areas.
Also, each partial area in this embodiment receives power supply from a plurality of main power supply lines Pm. Specifically, power to pixels in the partial area A4 is supplied from two main power supply lines Pm4, power to pixels in the partial area A5 is supplied from two main power supply lines Pm5, and power to pixels in the partial area A6 is supplied from two main power supply lines Pm6.
The magnitude of power supplied through these main power supply lines Pm may be controlled based on what image is to be displayed in the associated partial area as in the example described in the first embodiment. Alternatively, the magnitude of power supplied to each partial area may be controlled based on the location of the partial area in the display area SA.
An image display device according to a third embodiment of this invention is described next. The image display device according to this embodiment has the same structure as that of the image display devices according to the other embodiments, except for the arrangement of the partial areas within the display area SA and the arrangement of the main power supply lines Pm which corresponds to the arrangement of the partial areas.
The magnitude of power supplied through these main power supply lines Pm may be controlled based on what image is to be displayed in the associated partial area as in the examples described in the first and second embodiments. Alternatively, the magnitude of power supplied to each partial area may be controlled based on the location of the partial area in the display area SA.
To give a concrete example, the image display device according to this embodiment may output a relatively high voltage to the main power supply line Pm11, which is associated with the partial area All containing the center of the display area SA, in relation to voltages output to the other main power supply lines Pm. Voltages output to the main power supply lines Pm7, Pm9, Pm13, and Pm15, which are respectively associated with the partial areas A7, A9, A13, and A15 whose median points are apart from the center of the display area SA, may be set lower than voltages output to the main power supply lines Pm8, Pm10, Pm12, and Pm14, which are respectively associated with the partial areas A8, A10, A12, and A14 relatively close to the center of the display area SA. Pixel luminance distribution that is observed in this case along the lines A-A′ and B-B′ of
Unlike the other embodiments described above, one of the partial areas in this embodiment (specifically, the partial area A11) are not in contact with the perimeter of the display area SA. This makes it impossible to supply power to every partial area solely with the main power supply lines Pm arranged along the perimeter of the display area SA, and the main power supply line Pm11 for supplying power to the partial area A11 needs to be arranged so as to run through other partial areas. In this case, too, the main power supply lines Pm may be arranged within the display area SA in a manner that avoids interference with the pixel circuits 10 in the other partial areas by forming the main power supply lines Pm in a layer between the layer where the pixel circuits 10 are formed and the glass substrate SUB1, for example, immediately above the glass substrate SUB1 in the sectional view of
The image display devices according to the embodiments of this invention described above may control power supplied to each pixel to make a light emitting element emit light based on the location of the pixel in the display area. Thus, a luminance gradient within the screen in which the luminance is varied depending on the location in the screen may be reduced, and power necessary to make light emitting elements in the respective pixels emit light may be kept low without lowering the apparent luminance sensed by a viewer.
The image display devices according to the embodiments of this invention may be employed as display devices for displaying various types of information, such as displays for personal computers, displays for receiving TV broadcasting, and displays for displaying advertisements. The image display devices according to the embodiments of this invention may also be used as display parts of various electronic devices such as digital still cameras, video cameras, car navigation systems, car audio systems, game machines, and portable information terminals.
A few modification examples of the image display devices according to the embodiments of this invention are described below.
First, in the image display devices according to the embodiments of this invention, one partial area to which power is supplied independently of other partial areas may be constituted of a plurality of small areas which are apart from one another. To give a concrete example, the display area SA may be divided into a plurality of small areas along the x axis direction or the y axis direction, so that power to a first partial area constituted of two or more small areas that are picked alternately out of the plurality of small areas is supplied from a first main power supply line Pm, whereas power to a second partial area constituted of the rest of the small areas is supplied from a second main power supply line Pm. In this case, too, power may be supplied to each of a plurality of partial areas of the display area SA independently of one another, and the influence of a luminance gradient within the screen which is caused when pixels in the display area SA are lit at once may thus be reduced. In addition, with each partial area constituted of small areas that are dispersed throughout the screen in this manner, when pixels that are to emit light concentrate in a specific region of the display area SA, for example, this region is highly likely to stretch over a plurality of partial areas, and reducing the influence of a luminance gradient within the screen is accordingly facilitated.
At least some of the partial areas may be arranged so as to contain an area where the partial area overlaps with other adjacent partial areas. In this case, the area overlapping with other partial areas has a mixture of pixels that receive power supply from different main power supply lines Pm from one another, such as pixels of staggered pixel rows Prow or pixel columns Pcol that receive power supply from the main power supply lines Pm independent of one another. This way, a phenomenon in which pixels that are intended to emit light at the same luminance emit light at different luminance near the border between adjacent partial areas is reduced, and the border between partial areas is made inconspicuous.
The power control unit 38, which controls the magnitude of power supplied to each main power supply line Pm, may control power supply based on other conditions than the location of the associated partial area and information about an image to be displayed in the associated partial area. For instance, the power control unit 38 may vary the magnitude of power supplied to each main power supply line Pm depending on the external environment of the image display device 1 (e.g., the brightness of ambient light). To give a concrete example, the power control unit 38 regularly obtains information about the brightness of ambient light from an output of a photo sensor or the like and chooses one out of a plurality of display modes in accordance with the obtained information. The power control unit 38 then changes the magnitude of power supplied to each main power supply line Pm such that the overall brightness of the display screen suits the chosen display mode. In changing the supplied power, the power control unit 38 may uniformly change power supplied to all the main power supply lines Pm, or may individually change power supplied to each main power supply line Pm, in accordance with the obtained information. For example, power may be supplied to a plurality of partial areas at different voltage values from one another based on the respective outputs of a plurality of photo sensors, which are placed in different directions from one another in relation to the display screen.
The power control unit 38 may also vary power supplied to each main power supply line Pm depending on what application contents are to be displayed. Specifically, power supplied when a menu window is to be displayed and power supplied when a photographic image is to be displayed may be set differently from each other. The power control unit 38 in this case obtains, for example, information about the type of the image to be displayed from the image data control unit 32, and controls supplied power in accordance with the obtained information.
The power control unit 38 may also vary power supplied to each main power supply line Pm depending on the continuous operation time or what image has been displayed in the past. To give a concrete example, when a partial area undergoes little change for a given period of time in terms of what image is displayed, the power control unit 38 performs control that reduces power supplied to this partial area. The power control unit 38 accomplishes this control by, for example, calculating, for each partial area, for every given period of time, statistics information about what image is displayed. When the statistics information indicates a change equal to or larger than a given threshold from the last time the calculation is made, the power control unit 38 determines that the image has changed and writes information that indicates the timing of the change (e.g., time information) in a given area of a memory. The information indicating the timing is regularly referred to in order to determine whether or not a given period of time has elapsed since the specifics of the image displayed in each partial area have changed last. When the same image is kept displayed in a given partial area within the display screen, for example, when a menu is displayed, controlling power supply in this manner is effective in preventing burn-in in the partial area without lowering the luminance of other areas by reducing only power that is supplied to this partial area.
The various conditions described above as conditions used by the power control unit 38 to determine how much power is to be supplied to each main power supply line Pm may be used in combination. For instance, the power control unit 38 may vary the voltage applied to each main power supply line Pm based on a control parameter that is calculated by adding evaluation values determined by different conditions. The power control unit 38 may also execute power control based on the location of each partial area in the display area SA (e.g., control that enhances the luminance in a partial area around the center of the screen) when the brightness of ambient light is equal to or more than a given threshold, while setting the entire screen to a uniform light emission luminance instead of executing this control when the brightness of ambient light is less than the given threshold.
In the above description, an organic EL element is used as a light emitting element. However, the image display devices according to the embodiments of this invention are not limited thereto and may use various light emitting elements whose luminance is varied depending on the input current or voltage, for example, inorganic EL elements and field emission devices (FEDs). Also, the structure of the pixel circuits and the light emission control method of the pixels are not limited to those described above, and other structures and methods may be employed.
While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-004590 | Jan 2009 | JP | national |
