JP2006038967A - Display device and driving method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prolong the lifetime of a self-luminescent type display device by a circuit like means. <P>SOLUTION: A pixel array 12 emits light with luminance corresponding to a level of an image signal to display an image on a screen per frame and continues luminescence of the screen within each frame for only a luminescence time prescribed by a duty ratio. An information detection part 16A detects information showing whether an image is a moving image or a still image, from the image signal per frame. A lifetime control part 16B simultaneously adjusts a maximum signal allowable level of the image signal and the duty ratio on the basis of detected information so as to prolong the lifetime of a light emitting element. A signal output part 14A outputs the image signal to the pixel array 12 within the adjusted maximum signal allowable level to drive the screen for display. A duty ratio transmission part 13D transmits the adjusted duty ratio to the pixel array 12 to make the screen luminescent for only the luminescent time prescribed by this duty ratio. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a flat display device having a screen configured by a set of light emitting elements such as organic EL. More specifically, the present invention relates to a technique for improving a light emission lifetime by suppressing a temporal deterioration of a light emitting element in a circuit.

  For example, organic EL displays have been actively developed as flat panel display devices using light emitting elements as pixels. The organic EL display can realize high image quality such as wide viewing angle characteristics, high response speed, wide color reproducibility, and high contrast. Further, the organic EL display has an advantage that the panel form is thin. From these characteristics, the organic EL display is regarded as the most promising flat panel display of the next generation of liquid crystal displays and plasma displays.

  It is generally known that a light emitting element used for a pixel of an organic EL display has a characteristic of deteriorating according to its accumulated light emission amount. In other words, the luminance tends to decrease in proportion to the light emission time. Improvement of the lifetime of this light emitting element is now a major development issue for organic EL displays.

  In such a situation, when the organic EL display is used as a monitor of a television set, for example, it is necessary to further improve the light emission life characteristics of the light emitting element. However, development of the organic EL material that constitutes the organic EL light emitting element takes a lot of time and cost, and has not yet improved dramatically. From this, in order to put organic EL displays into practical use at an early stage, rather than relying solely on material development to improve the lifetime of light-emitting elements, the light-emitting elements can be improved to a practical level by improving the driving method of the light-emitting elements. Improvement is desired.

For example, Patent Documents 1 to 8 listed below describe techniques for improving the lifetime of an organic EL display.
Japanese Patent Application Laid-Open No. 07-036410 JP 2003-150110 A JP 2002-169509 A Japanese Patent Laid-Open No. 08-248934 JP 2000-356981 A JP 2003-195816 A JP 2003-122305 A JP 2003-255895 A

  The organic EL display can control the screen brightness and contrast in the same manner as the cathode ray tube display. Specifically, the screen brightness can be controlled by variably adjusting the duty ratio. The duty ratio is an amount that defines the ratio of the light emission time of the light emitting element to one frame period. Patent Documents 6 and 7 use this duty control to extend the life of the light emitting element. By controlling the duty ratio, when the image of one frame is bright, the lifetime is shortened by shortening the light emission time of the light emitting element, and when the image of one frame is dark, the light emission time of the light emitting element is lengthened to increase the contrast. I am trying. This conventional method can only extend the life of the light emitting material by controlling the light emission time of the light emitting element only by controlling the duty ratio, and can improve the life of the light emitting element to a practical level. There wasn't.

  Patent Document 1 detects a change amount of a drive voltage of a light emitting element and controls a constant current drive signal according to the change amount. In Patent Document 2, reverse bias is applied so that the element does not deteriorate while the EL element does not emit light. In Patent Document 8, the lifetime is extended by applying a reverse bias to the EL element in synchronization with driving of the EL element such as writing, light emission, and erasing of a video signal. Patent Document 3 uses a pixel circuit capable of positively discharging a storage capacitor of a pixel to reduce unnecessary light emission time and prevent deterioration of the light emitting element. In Patent Document 4, the image display position is slightly shifted for each frame so that the same portion is not lit for a long time, and a burn-in phenomenon, which is a kind of life deterioration, is prevented. Patent Document 5 measures the time during which an image is displayed on a display, performs deterioration calculation based on this measurement information, and decreases the luminance of the light emitting element to reduce the deterioration speed.

  However, the lifetime improvement techniques described in Patent Documents 1 to 8 described above have not yet reached the practical level, and further improvement is necessary. SUMMARY OF THE INVENTION In view of such a problem of the prior art, an object of the present invention is to improve the lifetime of a flat type display device having a light emitting element as a pixel by means of circuit technology. In order to achieve this purpose, the following measures were taken. That is, the present invention is a display device having a pixel array, an information detection unit, a life control unit, a duty ratio transmission unit, and a signal output unit, and the pixel array constitutes a screen by a set of pixels composed of light emitting elements. The information detecting unit emits light at a luminance corresponding to the level of the image signal and displays an image on the screen for each frame, and continues to emit light on the screen within each frame for the light emission time specified by the duty ratio. , Detecting information indicating whether the image is a moving image or a still image in frame units from an image signal input from the outside, and based on the detected information, the lifetime control unit extends the lifetime of the light emitting element, Simultaneously adjusting the maximum signal allowable level and the duty ratio of the image signal, the signal output unit outputs the image signal to the pixel array within the adjusted maximum signal allowable level to display and drive the screen, Serial duty ratio transmission unit may be a light emitting operation only said screen defined emission time by which to transmit the adjusted duty ratio to the pixel array.

  Specifically, when the detected information indicates a moving image, the lifetime control unit decreases the duty ratio that defines the light emission time per frame while increasing the maximum signal allowable level, and the detected information is a still image. The duty ratio that defines the light emission time per frame is increased while the maximum signal allowable level is decreased, and the information detection unit further detects information indicating the average luminance of the image from the input image signal. The life control unit adjusts the duty ratio that defines the light emission time per frame to be smaller as the average luminance is higher, and at the same time lowers the maximum signal allowable level of the image signal.

  The present invention also includes a method for driving a display device. That is, a screen is composed of a set of pixels composed of light emitting elements, light is emitted with luminance according to the level of the image signal, and an image is displayed on the screen for each frame, and each frame is displayed for the light emission time specified by the duty ratio. A method for driving a display device that continues to emit light within a screen, and an information detection process for detecting information indicating whether an image is a moving image or a still image in frame units from an image signal input from the outside, and the detected Based on the information, a life control process of simultaneously adjusting the maximum signal allowable level and the duty ratio of the image signal so as to extend the life of the light emitting element, and the image signal within the adjusted maximum signal allowable level A signal output process for outputting and driving the screen to the pixel array, and transmitting the adjusted duty ratio to the pixel array, thereby causing the screen to emit light for a specified light emission time. That it is characterized in that it comprises a duty ratio transduction process.

  As described above, according to the present invention, it is possible to extend the lifetime of the light emitting element to a practical level by improving a relatively small circuit. Specifically, based on the information extracted from the input image signal, synergistically adjust the maximum signal allowable level (dynamic range) of the image signal as well as the duty ratio that defines the light emission time per frame. Thus, the lifetime of the light emitting element is dramatically improved. In particular, by simultaneously controlling the duty ratio and the maximum signal allowable level, it is possible to improve the reliability while maintaining the moving image response. In the present invention, it is possible to control the duty ratio and the maximum signal allowable level more effectively and optimally by determining whether the input image signal is a moving image or a still image. For example, in the case of a still image, the reliability of the light-emitting element can be greatly increased by increasing the duty ratio to nearly 100% while decreasing the maximum signal allowable level accordingly. The amount of light emission per frame is determined by the light emission time and the light emission intensity. The light emission time is defined by the duty ratio. The emission intensity corresponds to the maximum signal allowable level. In this case, it is a general tendency of the organic EL material that the lifetime is shortened when the light emission time is lengthened and the light emission intensity is kept lower than when the light emission time is shortened and the light emission strength is increased. In accordance with this tendency, when a still image is displayed, the light emission life can be extended by increasing the duty ratio and suppressing the maximum allowable signal level accordingly. However, if the duty ratio is increased when displaying a moving image, the response to the moving image becomes worse. Therefore, the duty ratio is kept relatively low to shorten the light emission time, while the maximum signal allowable level is increased to increase the amount of light emission in a short time. Is obtained.

  In a specific method, the determination of a moving image and a still image is binary-determined for each pixel in the previous and subsequent frames, and all pixels are added to obtain information. By using this information, more effective moving image / still image determination can be performed while considerably reducing the circuit scale. In particular, the simultaneous and synergistic control of the duty ratio and maximum signal tolerance level described above can dramatically improve the lifetime in the case of television set monitors and the like. When mounting such a long-life function on a board, adding a long-life function to a part of the IC, such as a timing generator, does not require a special peripheral system circuit and affects the mechanism of an existing display system. It is possible to achieve a long lifetime of the light emitting element without imparting.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a functional block diagram showing the overall configuration of a display device according to the present invention. As shown in the figure, the display device includes a pixel array 12, an information detection unit 16A, a life control unit 16B, a duty ratio transmission unit 13D, and a signal output unit 14A. The pixel array 12 constitutes a light emitting screen by a set of pixels composed of light emitting elements such as organic EL, emits light with luminance according to the level of the image signal, displays an image for each frame, and is defined by a duty ratio. The screen continues to emit light within each frame for the duration of the light emission. In other words, the pixel array 12 controls the brightness of the screen with the duty ratio. Since the light emission time is longer as the duty ratio is larger, the brightness of the entire screen is increased.

  The information detection unit 16A detects information about an image in units of frames from an image signal such as a video signal input from the outside. The lifetime control unit 16B simultaneously adjusts the maximum signal allowable level and the duty ratio of the image signal so as to extend the lifetime of the light emitting elements of the pixel array 12 based on the information detected by the information detection unit 16A. Here, the higher the maximum signal allowable level of the image signal, the higher the screen contrast. For example, when the minimum signal level corresponds to black display and the maximum signal allowable level corresponds to white display, the difference between the black display and white display increases as the maximum signal allowable level increases, so that the contrast is improved.

  The signal processing unit 14A outputs to the pixel array 12 an image signal that has been gradated within the maximum signal allowable level adjusted by the life control unit 16B, and displays and drives the screen. On the other hand, the duty ratio transmission unit 13D transmits the duty ratio adjusted by the life control unit 16B to the pixel array 12 and causes the screen to emit light for the light emission time defined thereby. In this way, a light emitting screen configured by the pixel array 12 by automatically and adaptively adjusting the duty ratio (brightness) and the maximum signal allowable level (contrast) based on the information obtained from the input image signal. The service life is extended.

  Specifically, the information detection unit 16A detects information related to the average luminance of the image (the average gradation of the screen constituting one frame) from the input image signal. In response to this, the life control unit 16B adjusts the duty ratio that defines the light emission time per frame to be smaller as the detected average luminance is higher, and at the same time lowers the maximum signal allowable level of the image signal. In order to extend the life, it is necessary to decrease the light emission amount of each light emitting element as the average luminance of the screen increases. As means for reducing the light emission amount, there are means for reducing the light emission time by reducing the duty ratio, and means for reducing the light emission intensity by reducing the maximum signal allowable level of the image signal. Conventionally, only the duty ratio is controlled according to the average luminance (average gradation) of the screen, but in the present invention, the life is further extended by simultaneously controlling the duty ratio and the maximum signal allowable level. In general, a light emitting element such as an organic EL deteriorates as the accumulated light emission amount increases. In this case, the light emission intensity has a greater influence on the life deterioration than the light emission time. Therefore, the lifetime of the light emitting element can be extended by suppressing the light emission intensity in addition to the light emission time.

  In addition to the above-described average gradation information, the information detection unit 16A also detects information indicating whether the image is a moving image or a still image from the image signal as a feature of the present invention. When the detected information indicates a moving image, the life control unit 16B increases the maximum signal allowable level while decreasing the duty ratio that defines the light emission time per frame, and conversely, when the detected information indicates a still image, While increasing the duty ratio that defines the light emission time, the maximum allowable signal level is lowered. In the case of moving images, reducing the duty ratio as much as possible to shorten the light emission time is closer to pulse light emission, and the moving image display characteristics are improved as in the case of CRT. In this case, the maximum signal allowable level is increased to compensate for the light emission amount. Conversely, in the case of a still image, even if the light emission time is increased, the display characteristics are not affected. Therefore, the life of the light emitting element is extended by taking a relatively large duty ratio and lowering the maximum allowable signal level. As described above, lowering the light emission intensity rather than the light emission time is more effective for the life. From this point of view, in the case of a still image, adaptive control is performed by lowering the maximum signal allowable level with priority over the duty ratio. .

  FIG. 2 is a block diagram showing a specific configuration of the information detection unit shown in FIG. As illustrated, the information detection unit 16A includes a first frame memory 161, a second frame memory 162, an average luminance calculation unit 163, and a still image determination unit 164. The first frame memory 161 stores the image signal of the current frame for all pixels. Pixel data has multiple gradations. The second frame memory 162 stores the input image signal of the previous frame for all pixels. The average luminance calculation unit 163 averages the multi-gradation data for all the pixels stored in the first frame memory 161, and calculates the average luminance of the screen of the frame. The calculated average luminance is output to the life control unit as control information. The still image determination unit 164 compares the pixel data stored in the first frame memory 161 and the pixel data stored in the second frame memory 162, and determines whether there is a change between them, thereby determining a still image / moving image. is doing. If there is no change in the pixel data between the current frame and the previous frame, it is determined as a still image, and if the change is large, it is determined as a moving image. This determination result is also output to the life control unit as control information.

  FIG. 3 is a block diagram schematically showing the still image determination operation of the information detection unit 16A shown in FIG. (1) represents the current frame data, and gradation data is stored for each pixel 11. (2) represents the previous frame data, and similarly, gradation data is stored for each pixel 11. (3) represents binary data of each pixel after still image determination. When there is no change in the gradation data of the corresponding pixel between the current frame data and the previous frame data, the binary data of each pixel after the still image determination is 1. Conversely, when there is a change in gradation between corresponding pixels between the current frame data and the previous frame data, the binary data after the still image determination is 0. Data obtained by adding the binary data of each pixel is used as still image / moving image determination information. This indicates that the higher the total value, the stronger the degree as a still image.

  FIG. 4 is a schematic diagram showing functions of the life control unit 16B shown in FIG. As illustrated, the life control unit 16B accepts still image determination data and average luminance data as control information from the information detection unit 16A described above. Based on the control information, a duty ratio calculation process and a maximum signal allowable level calculation process are performed with the main purpose of extending the life of the light emitting element. The life control unit 16B outputs the processing result as a duty signal to the subsequent duty ratio transmission unit 13D and supplies the maximum level control signal to the subsequent signal output unit 14A.

  Hereinafter, the calculation process performed by the life control unit 16B will be described in detail with reference to FIGS. FIG. 5 is a graph showing the basic principle of the life control process. In this graph, the lifetime of the light emitting element is plotted on the vertical axis and the amount of light emitted is plotted on the horizontal axis. The duty ratio is taken as a parameter in three stages. Here, the duty ratio of 75% means that light is emitted for 75% of the time in one frame, and the remaining time is in a non-light emitting state. Conversely, a duty ratio of 25% indicates that light is emitted for 25% of one frame period, and the remaining 75% is in a non-light emitting state. As is apparent from the graph, it is clear that the life of the light emitting element is shortened according to the amount of light emission at any duty ratio. Focusing on the light emission amount L1 here, it can be seen that the higher the duty ratio, the longer the life. If the duty ratio is increased, the light emission time becomes longer, and the light emission intensity can be lowered accordingly. Conversely, if the duty ratio is reduced, the light emission time is shortened. Therefore, in order to obtain the predetermined light emission amount L1, the light emission intensity must be increased. Similarly, even with a high light emission amount L2, the life is longer when the duty ratio is higher. As described above, the principle of extending the life of the light emitting element in the present invention is that the current flowing through the light emitting element is reduced to suppress the emission intensity, while the time for emitting light in one frame is lengthened, and the current flowing through the light emitting element is increased. Compared with the case where the emission intensity is increased while the time for emitting light in one frame is shortened, the smaller the amount of current that flows instantaneously in the light emitting element, the more the deterioration of the element can be suppressed. Focusing on this principle, the present invention performs adaptive control of the duty ratio and the maximum signal allowable level.

  FIG. 6 is a graph showing the relationship between the average screen brightness (average gradation) sent from the information detection unit and the duty ratio adjusted by the life control unit. For comparison, the duty characteristic line of the present invention and the conventional duty characteristic line are shown. In any case, as the screen average brightness increases, the duty ratio is adjusted downward to suppress the light emission amount, thereby extending the life of the light emitting element. If the screen is bright overall, reducing the duty ratio and reducing the brightness will not significantly affect the image quality. When the screen is bright, the brightness is reduced to reduce the amount of light emitted, thereby extending the life. However, as is apparent from the graph, the inclination of the downward adjustment of the duty ratio is gentler in the present invention than in the prior art. In this embodiment, the duty characteristic line is a straight line. However, the duty characteristic line is not necessarily limited to this, and an optimum duty characteristic line may be determined in accordance with the characteristics of the device.

  FIG. 7 is a graph showing the relationship between the average screen brightness (average gradation) sent from the information detection unit and the maximum output level (maximum signal allowable level) adjusted by the life control unit. For comparison, a conventional maximum output level characteristic line is shown in addition to the maximum output level characteristic line of the present invention. As is apparent from the graph, the maximum output level is conventionally fixed. In other words, conventionally, the contrast is constant regardless of the brightness of the screen. Therefore, conventionally, only the duty ratio is variably adjusted as a measure against the life. In contrast, the present invention adjusts the maximum output level downward as the screen average brightness increases. This suppresses the amount of emitted light and extends the life of the light emitting element. When the entire screen is bright, even if the contrast is slightly reduced, the image quality is not affected. This can contribute to longer life. Conventionally, when the screen is bright, the lifetime is extended by suppressing the light emission time and reducing the light emission amount. On the other hand, the present invention suppresses both the light emission time and the light emission intensity when the screen is bright to reduce the light emission amount, thereby extending the life. In the case of the same light emission amount, it is more effective for extending the life to reduce the light emission intensity than to reduce the light emission time. Although the present embodiment is also a straight line for the maximum output level characteristic line, it is not necessarily limited to this. The maximum output level characteristic curve is determined according to the characteristics of the display device.

  FIG. 8 shows the relationship between the duty signal, the output voltage, and the lifetime characteristics of the light emitting element material when the output luminance is varied from 200 nit to 600 nit by changing the signal gradation average value. In this graph, the output data maximum value information is used as the output voltage when the data write driving method of the display device is the voltage method. If the data writing driving method of the display device is a current method, it is replaced with a current value. Since it is the basis of this technique to vary the maximum current that flows through the organic EL material constituting the light emitting element, the difference in signal voltage and signal current in the pixel circuit does not affect this technique. The characteristic line shown in the graph is merely an example. In the case where the luminance is varied from 200 nit to 600 nit, in the conventional technique, the luminance is variably adjusted by using only the duty variable line. For this reason, the lifetime of the light emitting element could be improved only from level A to level B. On the other hand, in the present invention, the light emission element emits light with a duty signal longer than before, and the light emission intensity is lowered by suppressing the data output voltage by the amount of light emission. Thereby, the lifetime of the light emitting element is greatly improved from level A to level C. However, the duty variable line and the output voltage line in FIG. 8 are when the input image is determined to be a moving image.

  FIG. 9 shows changes in the duty signal and the output voltage when the output luminance is changed from 200 nit to 600 nit by changing the signal gradation average value. Basically, it has the same notation as the graph of FIG. However, the still image / moving image determination information sent from the information detection unit is taken as a parameter. The life control unit controls the duty ratio and the output voltage based on the still image / moving image determination information. As described above, the information detection unit supplies still image / moving image determination information as an integrated value obtained by adding binary data (binary data) for each pixel. If the integrated value is small, the image is a moving image, and if the integrated value is large, the image is a still image. The graph of FIG. 9 typically shows a comparison between a moving image and a still image. In actual operation, the duty and output voltage are continuously adjusted according to the integrated value supplied from the information detection unit. As the integrated value increases, the duty curve changes upward and the light emission time becomes longer. The data output voltage is shifted downward so as to be inversely proportional to this. That is, as the integrated value increases and becomes closer to a still image, long-term reliability of the light emitting element is required from the viewpoint of unnecessary moving image response and prevention of burn-in. Therefore, in the case of a still image, the life is effectively extended by relatively increasing the duty ratio while relatively decreasing the output voltage.

  With reference to FIG. 10, the operation of duty ratio transmission unit 13D shown in FIG. 1 will be described. As described above, the duty ratio transmission unit converts the duty signal input from the life control unit to the pixel array constituting the screen into a pulse for controlling the light emission time of the light emitting element and outputs the pulse. FIG. 10 shows the vertical synchronization signal and the duty signal. The duty ratio transmission unit includes a shift register, and outputs a pulse for controlling the light emission time for each line by sequentially transferring the duty signal in accordance with the vertical synchronization signal. A general organic EL display performs line sequential scanning. In this line-sequential scanning, data is displayed on a line-by-line basis, but the light emission time can be controlled for each line by turning on / off the pulse for driving the line in one frame period as shown in the figure. . By scanning this pulse for each line, the light emission time of the entire screen is controlled by one duty signal. That is, the duty ratio represents the proportion of the light emission time in one vertical period (one frame period). In the timing chart of FIG. 10, the light emitting element emits light when the duty signal is at a high level, and the light emitting element does not emit light when the duty signal is at a low level. The screen brightness can be adjusted by variably adjusting the time width of the pulse of the duty signal.

  Next, the operation of the signal output unit 14A shown in FIG. 1 will be described with reference to FIG. The signal output unit incorporates a D / A converter, and converts input grayscale data included in the input image signal into an output voltage. The graph of FIG. 11 represents the input / output conversion characteristics of this D / A converter. The signal output unit D / A converts the digital gradation data based on the maximum signal allowable level information sent from the life control unit, and outputs it to the light emitting element. The maximum signal permissible level information sent from the life control unit is a limit voltage that is output when the maximum gradation is input during D / A conversion. As described above, this information is variably adjusted in the life control unit for each frame. As described above, when the screen average brightness is high, the life control unit adjusts the maximum signal allowable level downward. As a result, the input / output characteristics of the data signal output unit according to the present invention are shifted downward compared to the conventional input / output characteristics.

  FIG. 12 is a hardware block diagram corresponding to the functional blocks of FIG. As is clear from comparison between FIG. 12 and FIG. 1, the information detection unit 16 </ b> A and the life control unit 16 </ b> B, which are the main parts of the present invention, are realized by the external system circuit 16. The duty ratio transmission unit 13D is realized by the gate driver 13. The signal output unit 14A is realized by the data driver 14. The system circuit 16 is constructed on an external circuit board, and includes a timing generator 19 and a power supply circuit 20. The timing generator 19 sends the variably adjusted duty signal to the gate driver 13. The power supply circuit 20 sends the variably adjusted limit voltage to the data driver 14. The gate driver 13 drives the scanning lines of the pixel array unit 12 by sequentially transferring the duty signal input from the system circuit 16. The data driver 14 converts the digital image signal input from the system circuit 16 into an analog data voltage and applies it to the signal line of the pixel array unit 12. The display device shown in FIG. 12 includes a normal system circuit 16, a gate driver 13, a data driver 14, and a pixel array unit 12. In some cases, the gate driver 13 and the data driver 14 are integrated with the pixel array unit 12 in a single panel. Alternatively, only the pixel array unit 12 may be configured by a single panel, and the gate driver 13 and the data driver 14 may be connected to the panel as external ICs. The present invention can be easily realized in hardware by incorporating an information detection function and a life control function in the system circuit 16 of a general display device. The life of the light emitting element can be improved by a relatively small circuit change. By mounting the information detection function and life control function of the present invention in a part of the external system circuit IC, the present invention can be implemented using an existing display system as it is without requiring a special peripheral circuit.

  FIG. 13 is a circuit diagram showing a specific configuration example of the display device shown in FIG. For example, an active matrix organic EL display device using an organic EL element which is a self-luminous element as a display element of each pixel. The active matrix organic EL display device according to this embodiment includes a pixel array unit 12 in which pixels 11 are arranged in a matrix, a gate driver 13 and a data driver 14 for driving the pixel array unit 12, and an organic EL panel. It is formed on a (substrate) 15 and has a system circuit 16 that drives the gate driver 13 and the data driver 14 outside the organic EL panel 15. In some cases, the gate driver 13 and the data driver 14 may be provided as driver ICs separately from the organic EL panel (substrate) 15, and the driver IC and the panel may be connected by TAB or FPC.

  The image display apparatus according to the present invention basically includes a pixel array unit 12, a data driver 14, a gate driver 13, and a system circuit 16. The pixel array unit 12 includes a row-like scanning line DSL, a column-like data DTL line, and matrix-like pixels 11 arranged at a portion where both intersect. The data driver 14 distributes the image signal supplied from the system circuit 16 to the data lines DTL-1 to DTL-m. The gate driver 13 operates in accordance with the control signal DS supplied from the system circuit 16 and sequentially outputs the drive pulses DS-1 to DS-n to the scanning lines DSL-1 to DSL-n so that the pixels 11 are lined up. The pixels 11 are sequentially selected, and the pixels 11 are driven by the time width of the driving pulse DS based on the distributed image signals, so that an image is displayed on the pixel array unit 12.

  The system circuit 16 supplies a start pulse VS (vertical line control signal), a clock signal VCK (vertical clock pulse), and correction data DS (duty control signal) to the gate driver 13. Further, the system circuit 16 supplies the horizontal scanning signal and the image signal to the data driver 14.

  Next, each component of the display device will be described individually with reference to FIG. In FIG. 13, the pixel 11 has a field effect transistor, for example, a polysilicon TFT (Thin Film Transistor) or an amorphous silicon TFT 18 as an active element for driving the organic EL element 17 to emit light, on the substrate on which these TFTs 18 are formed. In this configuration, the organic EL element 17 is formed. The organic EL element 17 forms a plurality of first electrodes made of a transparent conductive film provided on a substrate, and sequentially deposits a hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer on each first electrode. An organic layer is formed, and a second electrode made of metal is formed on the organic layer, and a direct-current voltage is applied between the first electrode and the second electrode, so that Light is emitted when electrons and holes recombine.

  In the pixel array unit 12, scanning lines DSL-1 to DSL-n are wired in each row for a pixel array of m columns and n rows. Data lines DTL-1 to DTL-m are wired in each column. One end of each of the scanning lines DSL-1 to DSL-n is connected to the output end of each row of the gate driver 13. The gate driver 13 is supplied with the vertical line control signal VS generated by the system circuit 16, the output time setting duty control signal DS, and the vertical control signal power supply, so that the vertical clock pulse similarly generated by the system circuit 16 is also provided. In synchronization with VCK, vertical control sequential scanning pulses DS-1 to DS-n are output to drive the scanning lines DSL-1 to DSL-n.

  One end of each of the data lines DTL-1 to DTL-m is connected to an output end of each column of the data driver 14. The data driver 14 has a current writing type or voltage writing type driving circuit configuration in which luminance information is written in the form of a current value or a voltage value to each of the pixels 11 through the data lines DTL-1 to DTL-m. .

  The system circuit 16 is formed on an external substrate disposed outside the organic EL panel 15. The system circuit 16 includes a timing generator 19 that controls the data driver 14 and the gate driver 13, and a power supply circuit 20 that sets a level of an image signal output from the data driver 14 to a desired voltage.

  The timing generator 19 receives an image signal and a synchronization signal supplied from the outside, and controls the vertical clock pulse VCK, the vertical control signal VS, the output time setting duty control signal DS for controlling the gate driver 13, and the data driver 14. The horizontal scanning control signal and the image signal to be generated are generated based on the synchronization signal and supplied to the gate driver 13 and the data driver 14, respectively.

  FIG. 14 is a block diagram showing a configuration example of the organic EL panel shown in FIG. The display panel 15 includes a pixel array unit 12 in which pixel circuits (PXLC) 11 are arranged in an m × n matrix, a data driver 14, a gate driver 13, and an additional gate driver 13 a and a data driver 14 constituting a part thereof. The selected data lines DTL-1 to DTL-m to which signals corresponding to the luminance information are supplied, the scanning lines WSL-1 to WSL-n that are selectively driven by the additional gate driver 13a, and the gate driver 13 are selectively driven. Scanning lines DSL-1 to DSL-n. Here, the gate driver 13 performs duty driving, and the gate driver 13a performs data writing driving to each pixel prior to duty driving.

  FIG. 15 is a circuit diagram showing a circuit configuration of the organic EL panel shown in FIG. As shown in the figure, the pixel circuit 11 is basically composed of a p-channel thin film field effect transistor (hereinafter referred to as TFT). That is, the pixel circuit 11 includes a drive TFT 111, a switching TFT 112, a sampling TFT 115, an organic EL element 17, and a storage capacitor C111. The pixel circuit 11 having such a configuration is arranged at the intersection of the data line DTL-1 and the scanning lines WSL-1 and DSL-1. The data line DTL-1 is connected to the drain of the sampling TFT 115, the scanning line WSL-1 is connected to the gate of the sampling TFT 115, and the other scanning line DSL-1 is connected to the gate of the switching TFT 112.

  The drive TFT 111, the switching TFT 112, and the organic EL element 17 are connected in series between the power supply potential Vcc and the ground potential GND. That is, the source of the drive transistor 111 is connected to the power supply potential Vcc, while the cathode of the organic EL element (light emitting element) 17 is connected to the ground potential GND. In general, the organic EL element 17 is represented by a diode symbol because of its rectifying property. On the other hand, the sampling TFT 115 and the storage capacitor C111 are connected to the gate of the drive TFT111. The gate-source voltage of the drive TFT 111 is represented by Vgs.

  The operation of the pixel circuit 11 is as follows. First, when the scanning line WSL-1 is in a selected state (low level here) and a signal is applied to the data line DTL-1, the sampling TFT 115 is turned on and the signal is written to the holding capacitor C111. It is. The signal potential written in the storage capacitor C111 becomes the gate potential of the drive transistor 111. Subsequently, when the scanning line WSL-1 is in a non-selected state (here, high level), the data line DTL-1 and the drive TFT 111 are electrically disconnected, but the gate potential Vgs of the drive TFT 111 is stabilized by the storage capacitor C111. Retained. Subsequently, when another scanning line DSL-1 is selected (here, at a low level), the switching TFT 112 becomes conductive, and a drive current flows through the TFT 111, TFT 112, and the light emitting element 17 from the power supply potential Vcc toward the ground potential GND. When DSL-1 is in a non-selected state, the switching transistor 112 is turned off and the driving current does not flow. The switching TFT 112 is inserted in order to control the light emission time of the light emitting element 17.

  The current flowing through the TFT 111 and the light emitting element 17 has a value corresponding to the gate-source voltage Vgs of the TFT 111, and the light emitting element 17 continues to emit light with a luminance corresponding to the current value. As described above, the operation of selecting the scanning line WSL-1 and transmitting the signal applied to the data line DTL-1 to the inside of the pixel circuit 11 is referred to as “writing”. As described above, once a signal is written, the light emitting element 17 continues to emit light at a constant luminance while the drive transistor 112 is on until it is rewritten next time.

It is a functional block diagram of the display apparatus which concerns on this invention. FIG. 2 is a configuration block diagram of an information detection unit illustrated in FIG. 1. It is a schematic diagram with which it uses for operation | movement description of an information detection part. It is a functional diagram of a lifetime control part. It is a graph with which it uses for operation | movement description of a lifetime control part. It is a graph with which it uses for operation | movement description of a lifetime control part. It is a graph with which it uses for operation | movement description of a lifetime control part. It is a graph with which it uses for operation | movement description of a lifetime control part. It is a graph with which it uses for operation | movement description of a lifetime control part. 3 is a timing chart for explaining the operation of the duty ratio transmission unit shown in FIG. 1. It is a graph with which it uses for operation | movement description of the signal output part shown in FIG. It is a hardware block diagram of the display apparatus shown in FIG. It is a circuit diagram which shows the specific structural example of the display apparatus shown in FIG. It is a block diagram which shows the structural example of the panel contained in FIG. It is a circuit diagram which shows the circuit structure of the panel contained in FIG.

Explanation of symbols

12 ... Pixel array, 13D ... Duty ratio transmission unit, 14A ... Signal output unit, 16A ... Information detection unit, 16B ... Life control unit

Claims (4)

A display device having a pixel array, an information detection unit, a life control unit, a duty ratio transmission unit, and a signal output unit,
The pixel array constitutes a screen by a set of pixels composed of light emitting elements, emits light at a luminance corresponding to the level of an image signal, displays an image on the screen for each frame, and emits light at a time specified by a duty ratio Only keep the screen glowing within each frame,
The information detection unit detects information indicating whether an image is a moving image or a still image in frame units from an image signal input from the outside,
The lifetime control unit simultaneously adjusts the maximum signal allowable level of the image signal and the duty ratio so as to extend the lifetime of the light emitting element based on the detected information,
The signal output unit outputs the image signal to the pixel array within the adjusted maximum signal allowable level to display and drive the screen,
The duty ratio transmission unit transmits the adjusted duty ratio to the pixel array and causes the screen to emit light for a light emission time defined thereby.   When the detected information indicates a moving image, the lifetime control unit decreases the duty ratio that defines the light emission time per frame while increasing the maximum signal allowable level, and when the detected information indicates a still image, the per-frame The display device according to claim 1, wherein the maximum signal allowable level is lowered while increasing the duty ratio that defines the light emission time. The information detection unit further detects information indicating the average luminance of the image from the input image signal,
2. The display according to claim 1, wherein the life control unit adjusts a duty ratio that defines a light emission time per frame as the average luminance increases, and simultaneously reduces a maximum signal allowable level of the image signal. apparatus. The screen is composed of a set of pixels composed of light emitting elements, emits light at a luminance according to the level of the image signal, displays an image on the screen for each frame, and within each frame for the light emission time specified by the duty ratio. A method of driving a display device that continues to emit light on a screen,
An information detection process for detecting information indicating whether the image is a moving image or a still image in frame units from an image signal input from the outside;
Based on the detected information, a lifetime control process for simultaneously adjusting the maximum signal allowable level of the image signal and the duty ratio so as to extend the lifetime of the light emitting element;
A signal output process for driving the display by outputting the image signal to the pixel array within the adjusted maximum signal allowable level; and
And a duty ratio transmission process for transmitting the adjusted duty ratio to the pixel array and causing the screen to emit light for a light emission time defined thereby.

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