JP2015049399A - Display control unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display control unit capable of suppressing a temperature rise of a panel by controlling a value of current flowing through a pixel circuit and of reducing a change in image quality.SOLUTION: The display control unit supplies a gradation signal according to image data to a light emission panel in which a plurality of pixels each having a light-emitting element are two-dimensionally arrayed, and allows the light emission panel to display image information. The display control unit comprises: an operational circuit acquiring an average of the image data; an operational circuit acquiring, from the average of the image data, an estimated value of current flowing through a common electrode of the light emission panel; an operational circuit acquiring a measured value of current flowing through the common electrode when the light-emitting element emits light; an operational circuit comparing the estimated value to the measured value; and a correction circuit correcting the gradation signal according to the image data depending on a comparison result.

Description

  The present invention relates to a display control device, and more particularly, to a display control device that can suppress a temperature rise of a panel by controlling a value of a current flowing in a pixel circuit and suppress a change in image quality.

  2. Description of the Related Art In recent years, a light-emitting element type display device (light-emitting device) including a display panel (pixel array) in which light-emitting elements are arranged in a matrix is drawing attention as a next-generation display device following a liquid crystal display device. As such a light-emitting element, for example, a current-driven light-emitting element such as an organic electroluminescence element (organic EL element), an inorganic electroluminescence element (inorganic EL element), or a light-emitting diode (LED) is known.

  In particular, a light-emitting element type display device to which an active matrix drive method is applied has a higher display response speed and almost no viewing angle dependency compared to a known liquid crystal display device, and has high luminance and high brightness. It has excellent display characteristics such that contrast, high definition display quality, etc. are possible. Further, unlike a liquid crystal display device, a light emitting element type display device does not require a backlight or a light guide plate, and thus has an extremely advantageous feature that it can be further reduced in thickness and weight. Therefore, application to various electronic devices is expected in the future.

  As such a light emitting element type display device, for example, an organic EL display device as described in Patent Document 1 is known. This organic EL display device is an active matrix drive display device that is current-controlled by a voltage signal, and a current signal that causes a current to flow through an organic EL element as a light emitting element when a voltage signal corresponding to image data is applied to a gate. A circuit (for convenience, referred to as a “pixel circuit”) having a switching thin film transistor and a switching thin film transistor that performs switching for supplying a voltage signal corresponding to image data to the gate of the current control thin film transistor is provided for each pixel. Is provided. Further, the brightness is controlled by controlling the number of horizontal scanning lines (lighting rate) lit on one screen from the display video data and the power supply capacity.

JP 2005-189636 A

  However, in a light emitting element such as an organic EL display device, the panel temperature rises due to the environmental temperature and the heat generated by its own light emission, so that the current value flowing through the pixel circuit rises higher than the current value necessary for display. As a result, the emission luminance tends to increase. Therefore, there is a problem that the image quality changes depending on the temperature of the panel even with the same display video data. Moreover, the panel temperature rises due to the increase in the current value, and as a result, a vicious cycle occurs in which the current value further increases.

  The present invention has been made in the above-described problem, and an object of the present invention is to suppress a temperature rise of a panel by controlling a value of a current flowing in a pixel circuit and suppress a change in image quality.

  The display control apparatus according to the present invention includes an arithmetic circuit that calculates a predicted value of the cathode current flowing through the common electrode according to the characteristics of each pixel PIX arranged on the display panel, and an average of a plurality of frames from the measured value of the cathode current. An arithmetic circuit that calculates a current value, a circuit that compares the calculation results of the arithmetic circuit, and a correction circuit that emits light with data corrected based on the comparison result are provided.

  According to the display control apparatus of the present invention, it is possible to suppress light emission at a desired luminance or higher due to panel temperature increase due to light emission, and it is possible to prevent an excessive temperature increase due to light emission.

1 is a schematic configuration diagram showing an embodiment of a display device to which a display control device according to the present invention is applied. The circuit block diagram which shows an example of the pixel applied to the display panel which concerns on one Embodiment The graph which shows the example of measurement which observed the time transition of the organic EL current which light-emits the whole surface with the initial luminance of 100 cd / m < ² > in a display panel. The graph which shows the example of measurement which observed the temporal transition of the organic EL current which light-emits the whole surface with the initial luminance of 200 cd / m < ² > in a display panel. In the display panel, a graph showing measured example of observing a temporal transition of the center temperature of the initial luminance ^{100cd / m 2, 200cd / m} 2 at the panel surface to entire emission In the display panel according to the present invention, an approximate polynomial used in current value prediction is obtained from an actual measurement value of a cathode current value when light is emitted from the entire surface. Diagram showing controller circuit configuration Flow chart showing average predicted current value calculation processing Flow chart showing average cathode current value calculation processing Flow chart showing calculation processing of driver transfer data Verification results in the embodiment of the present invention (transition of panel surface temperature) Verification result (luminance transition) in the embodiment of the present invention Verification result in the embodiment of the present invention (current transition)

  Hereinafter, a display control apparatus for a display panel according to an embodiment of the present invention will be described in detail with reference to the embodiment.

  FIG. 1 is a schematic configuration diagram showing an embodiment of a display device to which a display control device according to the present invention is applied. As shown in FIG. 1, a display device (light emitting device) 100 according to the present embodiment schematically includes a display panel (light emitting panel) 101, a scan driver 102, a power driver 103, a data driver 104, and a controller 105. It is equipped with.

  As shown in FIG. 1, the display panel 101 has a plurality of two-dimensional arrays (for example, p rows × q columns; p and q are positive integers) in the scanning direction (up and down direction in the drawing) and the column direction (left and right direction in the drawing). Pixels PIX106, a plurality of scanning lines Ls and a plurality of power supply lines La arranged so as to be connected to the pixels PIX106 arranged in the scanning direction (row direction), and a common common to all the pixels PIX. The electrode Ec has a plurality of data lines Ld arranged so as to be connected to the pixels PIX arranged in the column direction. Here, the current flowing through the common electrode Ec is hereinafter referred to as a cathode current for convenience. The controller 105 has a function of performing current-voltage conversion on the common electrode Ec and converting the analog value into a digital value, and performs control using the cathode current in the present invention.

  Further, as will be described later, the pixels PIX 106 arranged on the display panel 101 include a current-driven light emitting element and a light emission driving circuit that generates a current for driving the light emitting element to emit light.

  The scanning driver 102 is connected to each scanning line Ls arranged in the scanning direction of the display panel 101 described above. The scanning driver 102 sequentially applies a scanning signal Ssel of a predetermined voltage level (scanning level or non-scanning level) to each scanning line Ls at a predetermined timing based on a scanning control signal supplied from the controller 105 described later. Thus, the pixels PIX106 of each scan are sequentially set to the scan state.

  As such a scan driver 102, for example, a configuration including a shift register and an output circuit is applied. The shift register sequentially outputs a shift signal corresponding to each scanning line Ls based on a scanning control signal (scanning clock signal, scanning start signal) supplied from the controller 105. The output circuit converts the shift signal from the shift register into a predetermined signal level (scanning level; for example, high level), and outputs to each scanning line Ls based on the scanning control signal (output enable signal) supplied from the controller 105. It outputs sequentially as scanning signal Ssel.

  Further, in the scan driver 102 applied to the present embodiment, the output order (shift direction) of the shift signals in the shift register is forward or reverse based on the scan control signal (shift switching signal) supplied from the controller 105. It is configured to be controlled to switch in the direction. Accordingly, the scan driver 102 sequentially outputs the scan signal Ssel from the first scan line Ls of the display panel 101 in the forward direction in the direction of the last scan line Ls, and the last scan line Ls. The scanning direction is switched to the state in which the output is sequentially performed in the direction opposite to the scanning line Ls direction of the first row. Specific output control of the scanning signal Ssel in the scanning driver 102 will be described later.

  The power driver 103 is connected to each power line La arranged in the scanning direction of the display panel 101. Based on a power control signal (for example, an output control signal) supplied from a controller 105 described later, the power driver 103 applies a predetermined voltage level (light emission level and non-light emission level) to the power line La for each scan at a predetermined timing. A power supply voltage Vsa is applied.

  The data driver 104 is connected to a plurality of data lines Ld arranged on the display panel 101, and each data driver 104 is driven based on a data driver control signal supplied from a controller 105 described later, and at least a display operation ( During the light emission operation, a gradation signal (gradation voltage Vdata) corresponding to the image data is generated and supplied to the pixels PIX 106 simultaneously through the data lines Ld.

  FIG. 2 is a configuration diagram illustrating an example of a pixel applied to the display panel according to the present embodiment. Here, a configuration of a pixel corresponding to an active matrix driving method is shown, and a case where an organic EL element is applied as a light emitting element will be described.

  As shown in FIG. 2, the pixel PIX 106 applied to the display panel 101 according to the present embodiment is near each intersection of the scanning line Ls connected to the scanning driver 102 and the data line Ld connected to the data driver 104. Has been placed. Each pixel PIX includes an organic EL element OEL, which is a current-driven light emitting element, and a light emission drive circuit DC that generates a current for driving the organic EL element OEL to emit light.

  The light emission drive circuit DC shown in FIG. 2 generally has a circuit configuration including transistors Tr11 to Tr13 and a capacitor Cs. The transistor Tr11 has a gate terminal connected to the scanning line Ls, a drain terminal connected to the power supply line La, and a source terminal connected to the contact N11. The transistor Tr12 has a gate terminal connected to the scanning line Ls, a source terminal connected to the data line Ld, and a drain terminal connected to the contact N12. The transistor (drive control element) Tr13 has a gate terminal connected to the contact N11, a drain terminal connected to the power supply line La, and a source terminal connected to the contact N12. The capacitor (capacitance element) Cs is connected between the gate terminal (contact N11) and the source terminal (contact N12) of the transistor Tr13. Here, the capacitor Cs may be a parasitic capacitance formed between the gate and the source terminal of the transistor Tr13. In addition to the parasitic capacitance, a separate capacitive element is connected in parallel between the contact N11 and the contact N12. It may be a thing.

  The organic EL element OEL has an anode (anode electrode) connected to the contact N12 of the light emission drive circuit DC and a cathode (cathode electrode) connected to the common electrode Ec. The common electrode Ec is connected to a constant voltage source (not shown), and a predetermined reference voltage Vsc (for example, ground potential GND) is applied.

  In the pixel PIX shown in FIG. 2, for example, thin film transistors (TFTs) having the same channel type can be applied to the transistors Tr11 to Tr13. The transistors Tr11 to Tr13 may be amorphous silicon thin film transistors or polysilicon thin film transistors.

  In particular, as shown in FIG. 2, when, for example, an n-channel thin film transistor is applied as the transistors Tr11 to Tr13 and an amorphous silicon thin film transistor is applied as the transistors Tr11 to Tr13, the already established amorphous silicon manufacturing technology. As a result, it is possible to realize a transistor with uniform and stable operating characteristics (such as electron mobility) by a simple manufacturing process as compared with a polycrystalline or single crystal silicon thin film transistor.

  When the transistors Tr11 to Tr13 are polysilicon thin film transistors, the transistors Tr11 to Tr13 may be p-channel thin film transistors. In this case, in the configuration of the light emission drive circuit DC, the source terminal and the drain terminal of each of the transistors Tr11 to Tr13 are reversed.

  Further, in the pixel PIX described above, the circuit configuration including the three transistors Tr11 to Tr13 as the light emission drive circuit DC is shown. The present invention is not limited to this embodiment, and the light emission drive circuit DC may have another circuit configuration including three or more transistors.

  Next, a display operation of a display device including the pixel PIX having such a circuit configuration will be briefly described. In the display operation of the display device including the pixel PIX illustrated in FIG. 2, first, in the scanning period, the scanning driver 102 applies a scanning voltage (for example, a high level) scanning voltage Vsel to the scanning line Ls of a specific row. The power supply driver 103 applies a power supply voltage Vsa of a non-light emission level (voltage level equal to or lower than the reference voltage Vsc; for example, a negative voltage) to the power supply line La of the scanning line. As a result, the transistors Tr11 and Tr12 of each pixel PIX are turned on, and the pixels PIX in the row are set in the scanning state. In synchronization with this timing, the gradation voltage Vdata having a negative voltage value corresponding to the image data is applied from the data driver 104 to the data line Ld of each column, whereby the potential corresponding to the gradation voltage Vdata is changed to each pixel. Applied to contact N12 of PIX.

  Thereby, the transistor Tr13 of each pixel PIX is turned on, and the write current corresponding to the potential difference generated between the gate and the source of the transistor Tr13 is transferred from the power supply line La through the transistor Tr13, the contact N12, and the transistor Tr12. It flows in the direction of the line Ld. At this time, charges corresponding to the potential difference generated between the contacts N11 and N12 are accumulated in the capacitor Cs of each pixel PIX.

  Here, the power supply line La is set so that the power supply voltage Vsa equal to or lower than the reference voltage Vsc is applied, and the write current is drawn from the pixel PIX in the direction of the data line Ld. As a result, the potential applied to the anode (contact N12) of the organic EL element OEL is lower than the cathode potential (reference voltage Vsc). Therefore, no current flows through the organic EL element OEL, and the organic EL element OEL Does not emit light (non-emission operation). Then, such a writing operation is sequentially performed on the pixels PIX of all the scanning lines that are two-dimensionally arranged on the display panel 110.

  Next, in a non-scanning period, by applying a scanning voltage Vsel of a non-scanning level (for example, low level) from the scanning driver 102 to the scanning line Ls, the transistors Tr11 and Tr12 of each pixel PIX are turned off, Pixel PIX is set to a non-scanning state. As a result, the charge accumulated in the scanning period is held in the capacitor Cs of each pixel PIX, so that the transistor Tr13 is kept on. Then, by applying a power supply voltage Vsa having a light emission level (a voltage level higher than the reference voltage Vsc) from the power supply driver 103 to the organic EL element OEL from the power supply line La via the transistor Tr13 and the contact N12. A predetermined light emission drive current flows.

  At this time, the electric charge (voltage component) accumulated in the capacitor Cs of each pixel PIX corresponds to a potential difference when a write current corresponding to the gradation voltage Vdata is caused to flow in the transistor Tr13, and thus light emission flowing through the organic EL element OEL. The drive current has a current value substantially equal to the write current. As a result, the organic EL element OEL of each pixel PIX emits light with a luminance gradation corresponding to the image data (gradation voltage Vdata) written during the writing operation, and desired image information is displayed on the display panel 101. .

FIGS. 3 and 4, in the display panel having a pixel PIX106 described above, each initial luminance ^{100cd / m 2, 200cd / m} 2 in the common electrode Ec time of the current and luminance during continuous light emission on the pixel data to fully emission It is a graph which shows the example of actual measurement which observed the target transition. FIG. 5 is a graph showing the center temperature of the display panel surface at that time. In a continuous light emission state, all shift to an equilibrium state over time, but the organic EL element has a tendency that the light emission luminance increases as the temperature rises. When viewed as a display, it does not appear as a desired display from the input image data. At an initial luminance of 200 cd / m ² , the temperature rise is close to 100 degrees, causing the organic EL element itself to deteriorate, and shortening the life of the organic EL element.

  Therefore, in the present invention, for the current flowing through the common electrode Ec, the average current value of all pixels predicted to be necessary for the original display is obtained from the image data input for a plurality of screens, and the image is actually displayed. The average current value for the same screen is obtained from the measured current value at the time when the current is being performed, and the two are compared, thereby controlling the brightness of the display image and preventing an excessive temperature rise.

  FIG. 6 shows a case where the display panel used in the above-described FIGS. 3, 4 and 5 emits light entirely for input data of gradation values (pixel values) 100 to 255 (2 to the 8th power) at an environmental temperature of 25 ° C. It is a figure which calculates | requires and shows the approximate polynomial used by the current value prediction mentioned later from the measured value of the cathode current at the time of making it. When calculating the approximate polynomial, a heat sink with a large heat capacity is placed in contact with both sides of the panel so that the temperature rise due to light emission is not affected, and the cathode current is measured after confirming that the center temperature of the display section does not rise. The reason why the input data (gradation value) is set to 100 or more in 256 gradations is that a certain amount of light emission is expected due to a large stress on the panel, and the present invention is not limited to this. . Then, the digital value of the cathode current obtained by this approximate polynomial is used as the predicted current value. In this example, the approximate polynomial is calculated from the measured value of the cathode current. However, it may be obtained from the transistor characteristics, the light emission efficiency of the organic EL element, and the panel pixel size.

  FIG. 7 is a diagram showing a circuit configuration of the controller 105 according to the present invention. FIG. 8 is a flowchart for calculating the average of image data of all pixels from input image data (tone values indicating shading) for a plurality of screens. FIG. 9 shows a flowchart for calculating an average current value for the plurality of screens actually displayed. FIG. 10 shows a flowchart for controlling the brightness by calculating the emission image data transferred from the controller 105 to the data driver 104 by comparing the results calculated by the flowcharts shown in FIGS.

Next, a control method using the circuit configuration shown in FIG. 7 will be described with reference to FIGS.
First, in S801, although not shown in FIG. 7, input to the data addition module 701 is started based on the input of the vertical synchronization signal.

  In step S <b> 802, the input image data (gradation value) is added in the column direction by the data addition module 701.

  Next, in step S803, it is determined whether or not all the data in the column direction pixels for one scan of the display panel, that is, all the data in the column direction pixels have been added.

  In step S804, the division module 702 divides the total addition data in the column direction for one scan by the number of pixels in the column direction.

  In step S <b> 805, the data addition module 703 adds the results calculated in step S <b> 804 in the scanning direction.

  Next, in S806, it is determined whether or not addition is performed by the data addition module 703 for the number of pixels in the scanning direction of the display panel. If not reached, the process returns to S802. If it has reached, the pixel average value in the column direction of one scan of the display panel is added by the data addition module 703 for all scans.

  In step S <b> 807, the division module 702 divides the result of the data addition module 703 by the number of pixels in the scanning direction. That is, the division result is an average of all pixels of input data for one screen.

  Next, in S808, the result calculated in S807 is added by the data addition module 704, and it is determined whether data for any n screens has been added. If not reached, the process returns to S801 to wait for the vertical synchronization signal. If it has reached, the result obtained by adding all the pixel averages of the input data for one screen for n screens is stored in the data addition module 704.

  In step S809, the division module 705 divides the data stored in the data addition module 704 by n. That is, this result is a pixel average of input data for n screens.

  Next, in S810, the current prediction module 706 performs an operation according to the approximate polynomial (see FIG. 6) based on the result calculated by the division module 705, and is necessary for the original display from the all pixel average data. The current value to be calculated is calculated (predicting the required current value). This necessary current value is digitally converted.

Next, description will be made according to the flowchart shown in FIG.
First, the cathode current flowing through the common electrode Ec is converted into a voltage value according to the cathode current by a current-voltage converter 707 in the controller 105 and is converted into digital data by an ADC (Analog Digital Converter) 708.

  In S901, processing is started based on the input of the vertical synchronization signal.

  In step S902, the cathode current value digitally converted by the data addition module 709 is added for each screen.

  In step S903, it is determined whether the cathode current values added by the data addition module 709 have been added for n screens. If not reached, the process returns to step S901. If it has reached, the result obtained by adding the cathode current values for n screens is stored in the data addition module 709.

In step S904, the division module 710 divides the cathode current value by n.
That is, this result is the actual cathode current average value for n screens.

  Next, description will be made with reference to FIG. In S101, the current value to be required for the original display calculated in the process of S810 from the average data of all the pixels for n screens, and the cathode current average value for the n screens calculated in the process of S904, Are compared by the comparison operation module 711. When the cathode current average value for n screens is larger than the current value that should be required for the original display calculated from the average data for all pixels for n screens, the process proceeds to S102. Proceed to the process.

  Next, in the processing of S102, since the average value of the cathode current actually flowing (average of the actual measurement values) is larger than the current value predicted to be necessary for the original display, the driver transfer data calculation module 712 The input data for n screens stored in the frame memory 713 for n screens is input, and arithmetic processing is performed on the data. More specifically, the driver transfer data calculation module 712 corrects the gradation value of the input data so that the brightness of the organic EL element OEL is lower than when the controller 105 transfers the input data to the data driver 104 as it is. Forward (decrease).

  Since the average value of the cathode current that is actually flowing is smaller than the current value that is predicted to be necessary for the original display, the driver transfer data calculation module 712 is n Input data for n screens stored in the screen frame memory 713 is input, and arithmetic processing is performed on the data. Specifically, the driver transfer data calculation module 712 corrects the gradation value of the input data so that the luminance of the organic EL element OEL is higher than when the controller 105 transfers the input data to the data driver 104 as it is. Forward (increase).

The result of having verified by the controller which implement | achieved a present Example with the panel used by the test of FIG.3, FIG.4, FIG.5 is shown. 11 shows the center temperature of the display unit, FIG. 12 shows the luminance, and FIG. 13 shows the temporal transition of the cathode current. The environmental temperature is 28 degrees, the panel does not take heat measures such as a heat sink, and only radiates heat by natural convection. The input data was the same data for all pixels, and the initial luminance was 170 cd / m ² , 370 cd / m ² , and 775 cd / m ² . All the results suppress excessive increase, and have a remarkable effect on the target temperature increase suppression.

  The present invention can be used for a display control device or the like that can suppress a temperature rise of a panel by controlling a value of a current flowing in a pixel circuit and suppress a change in image quality.

DESCRIPTION OF SYMBOLS 100 Display apparatus 101 Display panel 103 Power supply driver 104 Data driver 105 Controller 106 Pixel PIX
120 selection driver PIX pixel DC light emission drive circuit Tr11, Tr12, Tr13 transistor Cs capacitor OEL organic EL elements 701, 703, 704, 709 data addition module 702, 705, 710 division module 706 current prediction module 707 current voltage converter 708 ADC
711 Comparison operation module 712 Driver transfer data operation module 713 Frame memory

Claims (3)

In a display control device for supplying a gradation signal corresponding to image data to a light emitting panel in which a plurality of pixels each having a light emitting element are two-dimensionally arranged and displaying image information on the light emitting panel,
An arithmetic circuit for obtaining an average of the image data;
An arithmetic circuit for obtaining a predicted value of the current flowing through the common electrode of the light emitting panel from the average of the image data;
An arithmetic circuit for obtaining an actual measurement value of a current flowing through the common electrode when the light emitting element emits light;
An arithmetic circuit for comparing the predicted value and the measured value;
A display control apparatus comprising: a correction circuit that corrects a gradation signal corresponding to the image data in accordance with a comparison result between the predicted value and the actually measured value.   The arithmetic circuit for calculating the predicted value calculates an average of image data of all pixels from image data constituting a plurality of continuous frames, and calculates an average of current flowing in the common electrode of the light-emitting panel from the average of image data of all pixels. The display control apparatus according to claim 1, wherein a predicted value is obtained.   The display control apparatus according to claim 1, wherein the arithmetic circuit for obtaining the actual measurement value measures the current flowing through the common electrode in a plurality of consecutive frames, and obtains an average current value thereof.

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