JP2007233109A - Display device and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a stripe-like luminance variation due to a crystallizing process cannot be corrected when the entire screen is uniformly subjected to the correction of variation in light emission characteristics. <P>SOLUTION: In an active-matrix organic EL display device using a reference voltage selection type D/A conversion circuit, the luminance level for each pixel row of a display panel 20 is evaluated into three levels of a standard luminance level, a level brighter than the standard, and a level darker than the standard, and the evaluation result for each pixel row is stored in a memory device 55. When performing normal display driving, a reference voltage switching circuit 54 is switched and controlled by a control circuit 53 so that some of reference voltages VA0 to VAn-1, VB0 to VBn-1, VC0 to VCn-1 are selected for each pixel row, as a plurality of reference voltages V0 to Vn-1 to be supplied to a D/A conversion circuit 52 on the basis of the evaluation result of the luminance level stored in the memory device 55. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display device and a display device driving method, and more particularly, to a display device using a reference voltage selection type D / A conversion circuit as a D / A (digital / analog) conversion circuit for converting a digital video signal into an analog video signal. The present invention also relates to a method for driving the display device.

  In a circuit for driving a display device, for example, an active matrix display device such as a liquid crystal display or an organic EL (electroluminescence) display, a thin film transistor (TFT) made of low-temperature polysilicon is generally used. This is because a thin film transistor using low-temperature polysilicon has a large effect such as high mobility.

  On the other hand, in a display panel in which display pixels are two-dimensionally arranged in a matrix form on a substrate, a phenomenon in which luminance is uneven in a stripe shape due to energy variations in a crystallization process using laser annealing technology. Appears. The luminance variation that appears to be streaks, that is, the variation in the light emission characteristics, becomes the non-uniformity of the display characteristics as it is, and lowers the display quality. Therefore, it is necessary to correct variations in light emission characteristics.

  Conventionally, various techniques for incorporating a plurality of transistors for each pixel and correcting variations in light emission characteristics by the action of these transistors have been reported (see, for example, Patent Documents 1, 2, and 3). However, when a plurality of transistors are incorporated for each pixel, the pixel size increases, which hinders high definition by increasing the number of pixels.

  On the other hand, in an active matrix display device using a reference voltage selection type D / A conversion circuit, the reference voltage of the D / A conversion circuit is adjusted based on information on light emission adjustment of the light emitting element, and R (red ) A technique is known in which variations in light emission characteristics are corrected by changing the levels of RGB signals before being divided into drive signals for G (green) and B (blue) colors (for example, patents). Reference 4).

  Furthermore, a technique is also known in which variation in light emission characteristics is corrected by generating an original reference voltage used for generating a reference voltage for D / A conversion in accordance with original reference voltage setting data ( For example, see Patent Document 5).

JP 2003-022050 A JP 2003-216100 A JP-A-2005-157090 JP 2004-151501 A JP 2005-284037 A

  However, since all of the prior arts described in Patent Documents 4 and 5 perform correction uniformly for the entire screen, that is, for all pixels, a crystal using laser annealing technology is used. It is not possible to correct the luminance variation that appears as streaks due to the energy variation in the conversion process.

  In view of the above, an object of the present invention is to provide a display device and a display device driving method capable of reducing luminance variations that appear streaks due to characteristic variations in the crystallization process.

  In order to achieve the above object, the present invention adopts the following configuration. That is, a pixel array unit in which light-emitting pixels are two-dimensionally arranged in a matrix and a plurality of reference voltages corresponding to the number of bits of the digital video signal are generated, and the digital video signal is supported from the plurality of reference voltages And a D / A converter that selects an analog video signal for driving the light emitting pixels of the pixel array unit by selecting the one reference voltage, according to the light emission intensity for each pixel row of the pixel array unit Thus, the voltage values of the plurality of reference voltages are controlled for each pixel row.

  In a display device that converts a digital video signal into an analog video signal by using a reference voltage selection type D / A conversion circuit and drives a light emitting pixel to emit light, streaky luminance variations, particularly horizontal streaky luminance variations, It can also be said that this is a variation in emission intensity. Therefore, the voltage values of the plurality of reference voltages in the reference voltage selection type D / A conversion circuit are controlled for each pixel row in accordance with the emission intensity for each pixel row, specifically, in the direction of correcting variations in the emission intensity. By controlling, it is possible to correct the stripe-like luminance variation in units of pixel rows.

  According to the present invention, stripe-like luminance variations in units of pixel rows can be corrected. Therefore, luminance variations that look like stripes due to characteristic variations in the crystallization process can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  Hereinafter, an organic EL element that is a self-light-emitting element is used as an electro-optical element of a light-emitting pixel, and a thin film transistor (hereinafter referred to as “TFT”) that uses low-temperature polysilicon silicon as an active layer as an active element that drives the organic EL element. A case where the present invention is applied to an active matrix organic EL display using the above will be described as an example.

  However, the present invention is not limited to application to an organic EL display, but can be applied to all display devices using TFTs made of low-temperature polysilicon such as a liquid crystal display.

  FIG. 1 is a block diagram showing an outline of the configuration of an active matrix organic EL display according to this application example. As shown in FIG. 1, in an organic EL display according to this application example, light emitting pixels 10 including organic EL elements are two-dimensionally arranged in a matrix, scanning lines 11 for each row, and data lines 12 for each column. Of the light emitting pixels 10 via the data lines 12, a display panel (pixel array unit) 20, each of which is wired, a row scanning circuit 30 for scanning and selecting each of the light emitting pixels 10 in units of rows via the scanning lines 11. The driving circuit 40 supplies an analog video signal to each.

  The row scanning circuit 30 includes a shift register, an address decoder, and the like, and sequentially outputs a signal for selecting each light emitting pixel 10 of the display panel (pixel array unit) 20 in units of rows to the scanning line 11. The drive circuit 40 includes a D / A conversion circuit, converts an input digital video signal into an analog video signal by the D / A conversion circuit, and each of the light emitting pixels 10 in the row selected by the row scanning circuit 30. Is supplied via the data line 12.

  In the row scanning circuit 30, as the D / A conversion circuit, a plurality of reference voltages corresponding to the number of bits of the digital video signal are generated, and one reference voltage corresponding to the digital video signal is selected from the plurality of reference voltages. A so-called reference voltage selection type D / A conversion circuit that selects an analog video signal is used.

(Circuit configuration of light emitting pixel)
FIG. 2 is a circuit diagram illustrating an example of a circuit configuration of the light emitting pixel 10. As shown in FIG. 2, the light emitting pixel 10 has an organic EL element 21 whose anode is connected to, for example, the ground (GND), a drain connected to the cathode of the organic EL element 21, and a source connected to, for example, the negative power source Vss. The TFT 22, the capacitor 23 connected between the gate of the TFT 22 and the negative power source Vss, the gate to the scanning line 27 (corresponding to the scanning line 11 in FIG. 1), and the drain to the data line 28 (data line in FIG. 1) TFT 24 connected to the TFT 24, the drain connected to the source of the TFT 24, the source connected to the negative power source Vss, the gate connected to the gate of the TFT 22, the drain connected to the drain of the TFT 25, and the gate connected to the control line 29 includes a TFT 26 whose source is connected to the gate of the TFT 22.

  Here, the organic EL element 21 is often called an OLED (Organic Light Emitting Diode) because it often has a rectifying property. Therefore, in FIG. 2, a diode symbol is used as the OLED. However, the OLED is not necessarily required to have a rectifying property.

  The light emitting pixel 10 having the above configuration has a current writing type pixel circuit configuration in which luminance information is written in the form of current. That is, luminance information is written as a current through each data line 28 in each pixel 10 in a state where the scanning line 27 is selected. This current luminance information is taken into the pixel circuit by the TFT 24, converted into voltage luminance information by the TFT 25, and held in the capacitor 23.

  The TFT 22 converts the voltage luminance information held in the capacitor 23 into a current and causes the current to flow through the organic EL element 21 as a drive current, thereby driving the organic EL element 21 to emit light. As a result, the organic EL element 21 emits light with luminance according to the written current luminance information. The written luminance information is held in the capacitor 23 even after the scanning line 27 is not selected. Therefore, the organic EL element 21 continues to emit light at a luminance corresponding to the held voltage luminance information.

  In this light emission state, when a light emission time control signal is given to the gate of the TFT 26 through the control line 29, the TFT 26 is turned on in response thereto. As a result, the voltage luminance information (charge) held in the capacitor 23 is discharged through the TFT 26. When the gate-source potential of the TFT 22 falls below the threshold value, the TFT 22 is turned off and supply of the drive current to the organic EL element 21 is stopped. As a result, the organic EL element 21 in the light emitting state shifts to the non-light emitting state. That is, the TFT 26 controls the light emission time of the organic EL element 21 by turning on / off according to the light emission time control signal given through the control line 29.

  Note that FIG. 2 only shows an example of the circuit configuration of the light emitting pixel 10, and the present invention is not limited to this. That is, the light emitting pixel 10 may be a current writing type pixel circuit having another circuit configuration, and is not limited to the current writing type, and adopts a voltage writing type circuit configuration in which luminance information is written in the form of voltage. Is also possible.

(Structure of organic EL element)
FIG. 3 is a cross-sectional view showing an example of the structure of the organic EL element 10. As shown in FIG. 3, in the organic EL element 10, a first electrode (for example, an anode) 32 made of a transparent conductive film is formed on a substrate 31 made of transparent glass or the like, and a hole transport layer is further formed thereon. 33, a light emitting layer 34, an electron transport layer 35, and an electron injection layer 36 are sequentially deposited to form an organic layer 37, and then a second electrode (for example, cathode) 38 made of metal is formed on the organic layer 37. It has become the composition. In the organic EL element 10 having such a configuration, by applying a DC voltage E between the first electrode 32 and the second electrode 38, light is emitted when electrons and holes are recombined in the light emitting layer 34. It has become.

[First Embodiment]
FIG. 4 is a block diagram showing a system configuration example of the active matrix organic EL display according to the first embodiment of the present invention. The present embodiment is characterized by a specific configuration of the drive circuit 40A incorporating the reference voltage selection type D / A conversion circuit. Therefore, FIG. 4 shows the configuration of the drive circuit 40A, particularly the D / A conversion circuit portion.

  First, the basic configuration of the reference voltage selection type D / A conversion circuit will be described with reference to FIG. As shown in FIG. 5, the reference voltage selection type D / A converter circuit includes a reference voltage generation circuit 51 that generates n reference voltages V0 to Vn-1 corresponding to the number of bits of a digital video signal, and the reference voltage. A D / A conversion circuit 52 that selects a reference voltage having a voltage value corresponding to the data value of the digital video signal from n reference voltages V0 to Vn-1 generated by the generation circuit 51 and outputs the selected reference voltage as an analog video signal. It consists of and.

  The reference voltage generation circuit 51 has, for example, a resistance voltage dividing circuit configuration including n-1 resistors R1 to Rn-1 connected in series between the first power supply Vdd and the second power supply Vss. The voltage of the first power supply Vdd is the maximum voltage V0, the voltage of the second power supply voltage is the minimum voltage, and the divided voltages V1 to Vn-2 obtained at the connection points of the resistors R1 to Rn-1 are n in total. The reference voltages V0 to Vn-1 are generated.

  In the D / A conversion circuit 52, a switch element group corresponding to each bit of the digital video signal is connected in series for each of n reference voltages V0 to Vn-1, and the logical state (data value) of each bit of the digital video signal is determined. ) Are turned on, the reference voltage corresponding to the switch group is selected and output as an analog video signal having a voltage value corresponding to the data value of the digital video signal.

  In contrast to the reference voltage selection type D / A conversion circuit having the above basic configuration, the drive circuit 40A according to the present embodiment includes a plurality of reference voltage generation circuits 51 corresponding to the assumed luminance variation of the display panel 20, For example, there are three (reference voltage generation circuits 51A, 51B, 51C), and three systems of reference voltages VA0-VAn-1, VB0-VBn-1, VC0 generated by these reference voltage generation circuits 51A, 51B, 51C. ˜VCn−1 are appropriately switched by the reference voltage switching circuit 54 under the control of the control circuit 53 and supplied to the D / A conversion circuit 52.

  The reference voltage generation circuits 51A, 51B, 51C have, for example, a resistance voltage dividing circuit configuration shown in FIG. Then, the reference voltage generation circuit 51A generates reference voltages VA0 to VAn-1 having a non-linear characteristic (A) with respect to the gradation level, as shown in FIG. The power supply voltage Vdd at this time is set to VddA (the power supply voltage Vss is, for example, ground). The reference voltage characteristic (A) of the reference voltage generation circuit 51A is set as a standard reference voltage characteristic of the present D / A conversion circuit.

  The reference voltage generation circuit 51B generates reference voltages VB0 to VBn−1 having characteristics (B) that are shifted to a higher voltage value as a whole with respect to the standard reference voltage characteristics (A) of the reference voltage generation circuit 51A. appear. This characteristic (B) can be easily realized by using a power supply voltage VddB higher than the power supply voltage VddA as the power supply voltage Vdd, for example.

  The reference voltage generation circuit 51C has a reference voltage VC0 to VCn having a characteristic (C) that is shifted to a lower voltage value particularly at an intermediate gradation with respect to the standard reference voltage characteristic (A) of the reference voltage generation circuit 51A. -1. This characteristic (C) can be easily realized, for example, by using a power supply voltage VddC lower than the power supply voltage VddA as the power supply voltage Vdd.

  The reference voltage switching circuit 54 has, for example, a three-input one-output switch configuration, and is controlled by the control circuit 53 so that three systems of reference voltages VA0 to VAn-1, VB0 to VBn-1, VC0 to VCn- 1 is selected and supplied to the D / A conversion circuit 52.

  The control circuit 43 is configured by a microcomputer or the like, and is a reference voltage switching circuit according to the light emission intensity for each pixel row of the display panel (pixel array unit) 20 stored in the memory device 55 in advance, specifically, the luminance level. By switching and controlling 54, the voltage values of the n reference voltages V0 to Vn-1 supplied to the D / A conversion circuit 52 are controlled for each pixel row.

  In the memory device 55, in the stage before the final inspection in the manufacturing process of the display panel 20, the brightness level of each pixel row (line) of the display panel 20 is most easily observed by an inspector. In some cases, the evaluation is performed in three stages, specifically, the standard luminance level, three stages of brighter and darker than the standard, and the evaluation result is stored for each pixel row.

  Here, it is assumed that the luminance level for each pixel row is visually evaluated, but in addition, the display image of the display panel 20 is captured by an image capturing device such as a CCD (Charge Coupled Device) camera, and the captured image is captured. Based on the above, it is also possible to take a method of electrically evaluating the luminance level for each pixel row in, for example, three stages and storing the evaluation result for each pixel row.

  Next, the operation of the active matrix organic EL display according to the first embodiment having the above configuration will be described.

  Here, as an example, an 8-bit digital video signal for each of R (red), G (green), and B (blue) is input to the drive circuit 40A. The drive circuit 40A converts the input digital video signal into an analog video signal and supplies the analog video signal to the display panel 20.

  In the drive circuit 40A, the control circuit 53 synchronizes with the scanning timing of the row scanning circuit 30 in FIG. 1 based on the evaluation result of the luminance level stored for each pixel row in the memory device 55, and the reference voltage switching circuit. 54 switching control is performed.

  Specifically, the control circuit 53 selects the reference voltages VA0 to VAn-1 generated by the reference voltage generation circuit 51A for the image row whose luminance level evaluation result stored in the memory device 55 is the standard luminance level. Thus, the switching control of the reference voltage switching circuit 54 is performed. Thus, the D / A conversion circuit 52 performs D / A conversion based on the reference voltages VA0 to VAn-1. As a result, the light emitting pixels 10 in the pixel row driven by the analog video signal after the D / A conversion perform light emission display at the standard luminance level.

  On the other hand, for an image row in which the evaluation results stored in the memory device 55 are darker than the standard luminance level in all gradations, the control circuit 53 uses the reference voltages VB0 to VBn−1 generated by the reference voltage generation circuit 51B. Switching control of the reference voltage switching circuit 54 is performed so as to select. Thereby, the D / A conversion circuit 52 performs D / A conversion based on the reference voltages VB0 to VBn-1. As a result, in the light emitting pixels 10 in the pixel row driven by the analog video signal after the D / A conversion, the luminance level is corrected to the bright side, and the light emission display is performed at almost the standard luminance level.

  For an image row whose evaluation result stored in the memory device 55 is brighter than the standard luminance level only in the intermediate gradation, the control circuit 53 uses the reference voltages VC0 to VCn−1 generated by the reference voltage generation circuit 51C. Switching control of the reference voltage switching circuit 54 is performed so as to select. Thus, the D / A conversion circuit 52 performs D / A conversion based on the reference voltages VC0 to VCn-1. As a result, in the light emitting pixels 10 in the pixel row driven by the analog video signal after the D / A conversion, the luminance level is corrected to the dark side, and the light emission display is performed at the substantially standard luminance level.

  As described above, in a display device using a reference voltage selection type D / A conversion circuit as a D / A conversion circuit for converting a digital video signal into an analog video signal, for example, an active matrix organic EL display device, a plurality of reference voltages By controlling the voltage values of V0 to Vn−1 for each pixel row in accordance with the emission intensity for each pixel row, specifically, in the direction of correcting the variation in emission intensity, Luminance variations, particularly horizontal streak-like characteristic variations (brightness variations) can be corrected, so that the luminance variations (display variations) that appear to be streaks due to the characteristic variations in the crystallization process can be reduced.

  In particular, by correcting the luminance variation by switching the voltage values of the plurality of reference voltages V0 to Vn-1, it is possible to realize the optimum correction according to the characteristic variation in all gradation representations from black to white. Correction of only halftone (gray portion) can also be realized. Moreover, a wide correction range can be set in order to switch the voltage values of the plurality of reference voltages V0 to Vn-1 according to the degree of characteristic variation.

  Here, when a reference voltage corresponding to each of the RGB light emitting pixels is required for the purpose of adjusting the white balance, correction data corresponding to each reference voltage is stored in the memory device 55 and the correction is performed. This can be dealt with by the control circuit 53 correcting the reference voltage according to the data.

  In the present embodiment, three reference voltage generation circuits 51A, 51B, and 51C are used as the reference voltage generation circuit 51, and the power supply voltages VddA, VddB, and VddC are made different from each other (VddB> VddA> VddC). Therefore, the three reference voltages VA0 to VAn-1, VB0 to VBn-1, and VC0 to VCn-1 are generated, but the voltage value of the power supply voltage Vdd is shared by sharing the single reference voltage generation circuit 51. It is also possible to adopt a configuration in which three systems of reference voltages VA0 to VAn-1, VB0 to VBn-1, and VC0 to VCn-1 are generated by switching between VddA, VddB, and VddC.

  In the present embodiment, in order to facilitate understanding, any one of the three systems of reference voltages VA0 to VAn-1, VB0 to VBn-1, and VC0 to VCn-1 is selected and a plurality of reference voltages V0 to V0 are selected. Although it is assumed that the voltage value is Vn−1, it is clear that the luminance variation that appears streaks can be more reliably reduced when the number of reference voltage systems is larger.

[Second Embodiment]
FIG. 7 is a block diagram showing a system configuration example of an active matrix organic EL display according to the second embodiment of the present invention. In FIG. 7, the same parts as those in FIG. 4 are denoted by the same reference numerals. This embodiment is also characterized by a specific configuration of the drive circuit 40B incorporating the reference voltage selection type D / A conversion circuit. Accordingly, FIG. 7 shows the configuration of the drive circuit 40B, particularly the D / A conversion circuit portion.

  In the drive circuit 40A according to the first embodiment, for example, a configuration using three reference voltage generation circuits 51A, 51B, 51C as the reference voltage generation circuit 51 is adopted, whereas the drive circuit according to the present embodiment is used. 40B uses a single reference voltage generation circuit 51D as the reference voltage generation circuit 51, and has a configuration including a D / A conversion circuit 52, a control circuit 53, and a memory device 55 in addition to the reference voltage generation circuit 51D. Yes.

  The reference voltage generation circuit 51D has, for example, a circuit configuration that selects and outputs a reference voltage according to data given from the outside while adopting a resistance voltage dividing type similar to that of the reference voltage generation circuit 51. The reference voltage generation circuit 51D has an operation speed capable of selecting and outputting voltage values of a plurality of reference voltages V0 to Vn-1 at the resolution speed for each pixel row, that is, the scanning speed of the row scanning circuit 30 in FIG. Will be required.

  In the memory device 55, in the stage before the final inspection in the manufacturing process of the display panel 20, most simply, the luminance level for each pixel row (line) of the display panel 20 is evaluated visually by the inspector. Data indicating a reference voltage corresponding to the luminance level is stored for each pixel row.

  Here, it is assumed that the luminance level for each pixel row is visually evaluated. However, in addition to this, a display image of the display panel 20 is captured by an image capture device such as a CCD camera, and the electrical level is based on the captured image. Alternatively, it is possible to detect a luminance level for each pixel row and store data indicating a reference voltage corresponding to the luminance level for each pixel row.

  The control circuit 53 is configured by a microcomputer or the like, and controls the generation of the reference voltage in the reference voltage generation circuit 51D by the scanning speed of the row scanning circuit 30, for example, by bus control. Specifically, the control circuit 53 reads data indicating the reference voltage stored for each pixel row in the memory device 55 in synchronization with the scanning timing of the row scanning circuit 30 in FIG. This is applied to the reference voltage generation circuit 51D.

  When the reference voltage generation circuit 51D receives data indicating the reference voltage from the control circuit 53, the reference voltage generation circuit 51D decodes the data and selects the corresponding reference voltage V0 to Vn-1 at the scanning speed of the row scanning circuit 30. To the D / A conversion circuit 52.

  As described above, by adopting a configuration using a single reference voltage generation circuit 51D as the reference voltage generation circuit 51, as in the case of the first embodiment, stripe-like luminance variations, particularly horizontal Since the streak-like characteristic variation can be corrected, the luminance variation (display variation) that appears as a streak due to the characteristic variation in the crystallization process can be reduced. Compared to the case where a reference voltage generation circuit is used, the circuit scale can be reduced, so that there is an advantage that it is particularly easy to deal with small products.

  Also in the case of this embodiment, when a reference voltage corresponding to each of the RGB light emitting pixels is required for the purpose of adjusting the white balance, correction data corresponding to each reference voltage is stored in the memory device 55. This can be dealt with by the control circuit 53 correcting the reference voltage according to the correction data.

[Third Embodiment]
FIG. 8 is a block diagram showing a system configuration example of an active matrix organic EL display according to the third embodiment of the present invention. In FIG. 8, the same parts as those in FIG. This embodiment is also characterized by a specific configuration of the drive circuit 40C incorporating the reference voltage selection type D / A conversion circuit. Therefore, FIG. 8 shows the configuration of the drive circuit 40C, particularly the D / A conversion circuit portion.

  In the active matrix organic EL displays according to the first and second embodiments, the light emission intensity for each pixel row of the display panel 20 is evaluated and evaluated before the final inspection in the manufacturing process of the display panel 20. Is stored in advance in the memory device 55, and the voltage values of the reference voltages V0 to Vn-1 are determined according to the emission intensity for each pixel row based on the stored information in the memory device 55 during actual display driving. The structure which controls for every line was taken.

  On the other hand, the active matrix organic EL display according to the present embodiment includes detection means for detecting the emission intensity for each pixel row of the display panel 20, and for each pixel row based on the detection output of the detection means. The voltage values of the reference voltages V0 to Vn-1 are controlled for each pixel row in accordance with the light emission intensity, that is, the display variation (light emission variation) correction control is performed.

  Specifically, in the present embodiment, as detection means for detecting the light emission intensity for each pixel row of the display panel 20, for example, on both sides (left and right ends) of the display panel 20, light emitting pixels at both left and right ends of each pixel row. The light receiving elements 61A and 61B arranged adjacent to each other are used. At this time, the light emitting pixels at the left and right ends of each pixel row are light emitting pixels that actually do not contribute to display (light emitting pixels outside the effective pixel area). Then, in a correction mode set when the display device is turned on, the left and right light emitting pixels of each pixel row are caused to emit light in synchronization with other light emitting pixels in the same pixel row.

  When the light emitting pixels at the left and right ends of each pixel row emit light, the light receiving elements 61A and 61B can detect the light emitted by these light emitting pixels and detect the light emission intensity for each pixel row. In particular, with respect to the light emitting pixels at the left and right ends of each pixel row, the light receiving elements 61A and 61B can detect variations in luminance level for each pixel row by emitting the same color light (for example, white light). Become. Note that it is desirable to take a method such as masking the light emitting pixels at the left and right ends of each pixel row in order to prevent detection light emission from these light emitting pixels from leaking from the screen to the table. The light reception outputs of the light receiving elements 61A and 61B are supplied to the drive circuit 40C.

  In FIG. 8, the drive circuit 40C has an A / D conversion circuit 56 and a parallel-serial conversion circuit 57 in addition to the reference voltage generation circuit 51D, the D / A conversion circuit 52, the control circuit 53, and the memory device 55. It has become.

  The A / D conversion circuit 56 performs A / D conversion on the light reception outputs of the light receiving elements 61A and 61B corresponding to the light emission intensity for detection by the light emitting pixels at the left and right ends of each pixel row, and outputs the light emission intensity data. Since the emission intensity data output from the A / D conversion circuit 56 is a number of lines (number of rows) × 2 (left and right), the parallel-serial conversion circuit 57 converts the emission intensity data into parallel- The data is serially converted and sent to the control circuit 53.

  The control circuit 53 is constituted by a microcomputer or the like, and based on the light emission intensity data given from the parallel-serial conversion circuit 57, the control circuit 53 calculates which luminance level for each line (pixel row) with respect to the deviation of the entire screen. Is calculated how much the luminance level needs to be corrected, and data indicating the reference voltage is stored in the memory device 55 for each pixel row. Further, the control circuit 53 reads out the data indicating the reference voltage stored in the memory device 55 for each pixel row in synchronization with the scanning timing of the row scanning circuit 30 in FIG. The obtained data is applied to the reference voltage generation circuit 51D.

  When the reference voltage generation circuit 51D receives data indicating the reference voltage from the control circuit 53, the reference voltage generation circuit 51D decodes the data and selects the corresponding reference voltage V0 to Vn-1 at the scanning speed of the row scanning circuit 30. To the D / A conversion circuit 52.

  Next, drive control when correcting display variations (luminance variations) in the active matrix organic EL device having the above-described configuration will be described.

  In the correction mode set when the power is turned on, the light emitting pixels at the left and right ends of each pixel row are driven to emit light with, for example, white light in synchronization with other light emitting pixels in the same pixel row. When light emitting pixels at the left and right ends of each pixel row emit light, the light receiving elements 61A and 61B detect the light emission intensity, A / D conversion is performed on the detection output by the A / D conversion circuit 56, and parallel-serial The conversion circuit 57 converts the parallel data into serial data and supplies it to the control circuit 53 as emission intensity data.

  The control circuit 53 calculates the luminance level for each line (pixel row) with respect to the deviation of the entire screen based on the emission intensity data, and the memory device 55 for each pixel row as data indicating a reference voltage that allows for the correction amount of the luminance level. To remember.

  On the other hand, during normal display driving, the control circuit 53 reads out data indicating the reference voltage corresponding to the pixel row to be driven from the memory device 55 in synchronization with the scanning timing of the row scanning circuit 30 in FIG. Supply to the circuit 51D. Then, the reference voltage generation circuit 51D decodes the data indicating the reference voltage supplied from the control circuit 53, selects the voltage values of the corresponding reference voltages V0 to Vn-1, and outputs them to the D / A conversion circuit 52. To do.

  Note that the light emitting pixels to be detected by the light receiving elements 61A and 61B do not necessarily have to be light emitting pixels (light emitting pixels outside the effective pixel area) that do not actually contribute to display, and each pixel row in the effective pixel area. The left and right light emitting pixels can also be used. In this case, since it is necessary to make the light emitting pixels at both right and left ends emit light in the same color for all lines, correction control in real time is impossible, and a correction mode is set when the display device is turned on. In the correction mode, based on the detection results of the light receiving elements 61A and 61B, data indicating a reference voltage that allows for the correction amount of the luminance level is obtained and stored in the memory device 55, and the actual display drive is performed. Based on the data stored in the memory device 55, the voltage values of the corresponding reference voltages V0 to Vn-1 are selected.

  Also, the light receiving elements 61A and 61B need not be provided adjacent to the left and right light emitting pixels of each pixel row. If the light emission intensity of each pixel row can be sufficiently detected, the light receiving elements 61A and 61B can It is also possible to adopt a configuration in which the light receiving elements 61A and 61B are arranged adjacent to each other only on one side of the light emitting pixel.

  As described above, the detection means for detecting the light emission intensity for each pixel row of the display panel 20 is provided, and the reference voltages V0 to Vn−1 are determined according to the light emission intensity for each pixel row based on the detection output of the detection means. By controlling the voltage value for each pixel row, that is, by correcting the display variation (light emission variation), it is possible to correct the stripe-like luminance variation, particularly the horizontal stripe-like characteristic variation, in units of pixel rows. In addition to display variations that appear streaky due to characteristic variations in the crystallization process, display variations due to characteristic changes over time can be handled.

  Here, the light receiving elements 61A and 61B, which are detection means for detecting the light emission intensity for each pixel row of the display panel 20, will be described.

  As the light receiving elements 61A and 61B, well-known elements such as phototransistors can be used, but in the present embodiment, organic EL elements are used. In the case of an organic EL display device, the use of organic EL elements as the light receiving elements 61A and 61B has an advantage that the organic EL elements of the light emitting pixels 10 and the light receiving elements 61A and 61B can be simultaneously formed in the same process. The organic EL element is known to have a faster response speed than other light receiving elements. By using the organic EL element having a higher response speed as the light receiving elements 61A and 61B, the light emission luminance for each pixel row can be reduced. It can be quickly detected and reflected in display variation correction control.

  FIG. 9 shows an example of a circuit configuration when organic EL elements are used as the light receiving elements 61A and 61B. Here, the case of the light receiving pixel 60 arranged adjacent to the light emitting pixel 10 at the right end of the pixel row is shown.

  In FIG. 9, the circuit configuration of the light emitting pixel 10 is shown in a simplified manner, and in FIG. 9, the same parts as those in FIG. In FIG. 2, the positive power supply is shown as ground and the negative power supply is shown as Vss, whereas in FIG. 9, the positive power supply is shown as Vdd and the negative power supply is shown as Vcatode. There is no difference in operation.

  As shown in FIG. 9, the light receiving element 61 </ b> B is disposed adjacent to the organic EL element 21 of the light emitting pixel 10. The light receiving element 61B is connected in series with the light receiving level detection resistor 62 between the positive power supply Vdd and the negative power supply Vcathode. A light receiving line selection transistor 63 is connected between a common connection node N of the light receiving element 61B and the light receiving level detection resistor 62 and the detection line 64. The light receiving line selection transistor 63 has a gate connected to the scanning line 27 (scanning line 27 in FIG. 2) and is selectively driven at the same timing as the light emitting timing of the light emitting pixels 10 in the same pixel row (line). The detection signal (luminance level signal) of the element (organic EL element) 61B is output to the A / D conversion circuit 56 (see FIG. 8) through the detection line 64.

  In the present embodiment, the organic EL elements are arranged as the light receiving elements 61A and 61B separately from the organic EL elements 21 of the light emitting pixels 10. However, the organic EL elements 21 themselves of the light emitting pixels 10 are replaced with the pixels of the display panel 20. It can also be used as a detection means (light receiving element) for detecting the light emission intensity for each row. Specifically, the organic EL elements of the image row that is not driven to emit light are used for detection of the emission intensity of the adjacent image row that is driven to emit light.

  In this case, the single organic EL element 21 is shared, and the circuit configuration of the light receiving pixel 60 shown in FIG. 9 is basically changed to the circuit configuration of the light emitting pixel 10 shown in FIG. An integrated pixel circuit is assumed. In addition, two scanning lines 27 for light emission and light reception are prepared, and two lines for light emission and light reception are also prepared for the row scanning circuit 30 shown in FIG. In the mode, when the entire screen is uniformly emitted with white light, for example, the two row scanning circuits are driven to scan by shifting the timing by one line, so that the organic EL elements 21 of the light emitting pixels 10 It can also be used as a light receiving element for detecting the emission intensity of each.

  In each of the embodiments described above, the present invention is applied to a display device having a configuration in which the peripheral drive circuit that drives each light emitting pixel 10 in the pixel array unit, that is, the row scanning circuit 30 and the drive circuit 40 are arranged outside the display panel 20. As an example, for a so-called drive circuit-integrated display device in which both or one of the row scanning circuit 30 and the drive circuit 40 are arranged on the same substrate as the pixel array unit, that is, the display panel 20. However, the same applies.

It is a block diagram which shows the outline of a structure of the active matrix type organic electroluminescent display which concerns on this application example. It is a circuit diagram which shows an example of the circuit structure of a light emission pixel. It is sectional drawing which shows an example of the structure of an organic EL element. 1 is a block diagram illustrating a system configuration example of an active matrix organic EL display according to a first embodiment of the present invention. It is a basic block diagram of a reference voltage selection type D / A conversion circuit. It is a figure which shows the reference voltage characteristics (A), (B), (C) of 3 systems. It is a block diagram which shows the system structural example of the active matrix type organic electroluminescent display which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the system structural example of the active matrix type organic electroluminescent display which concerns on 3rd Embodiment of this invention. It is a circuit diagram which shows an example of a circuit structure at the time of using an organic EL element as a light receiving element.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Light emitting pixel, 11 ... Scanning line, 12 ... Data line, 20 ... Display panel, 21 ... Organic EL element, 22, 24-26 ... TFT (Thin film transistor), 23 ... Capacitor, 30 ... Row scanning circuit, 31 ... Substrate 32 ... 1st electrode, 33 ... Hole transport layer, 34 ... Light emitting layer, 35 ... Electron transport layer, 36 ... Electron injection layer, 37 ... Organic layer, 38 ... 2nd electrode, 40, 40A, 40B, 40C: drive circuit 51, 51A, 51B, 51C, 51D ... reference voltage generation circuit, D / A conversion circuit, 53 ... control circuit, 54 ... reference voltage switching circuit, 55 ... memory device, 56 ... A / D conversion circuit , 57... Parallel-serial conversion circuit, 60... Light receiving pixel, 61 A and 61 B... Light receiving element, 62.

Claims (8)

A pixel array unit in which light-emitting pixels are two-dimensionally arranged in a matrix;
A plurality of reference voltages corresponding to the number of bits of the digital video signal are generated, and one reference voltage corresponding to the digital video signal is selected from the plurality of reference voltages to drive the light emitting pixels of the pixel array unit. Digital / analog conversion means for converting an analog video signal;
And a control means for controlling the voltage values of the plurality of reference voltages for each pixel row in accordance with the light emission intensity for each pixel row of the pixel array section. The control means includes
Storage means for storing information on emission intensity for each pixel row of the pixel array section for each pixel row;
A plurality of reference voltage generating means for generating a plurality of reference voltages having different voltage values as the plurality of reference voltages;
The display device according to claim 1, further comprising: a reference voltage switching unit that selects one of the plurality of reference voltages based on the storage information of the storage unit and supplies the selected voltage to the digital / analog conversion unit. The control means includes
Storage means for storing information on emission intensity for each pixel row of the pixel array section for each pixel row;
A single reference voltage generating means for supplying a reference voltage having a voltage value corresponding to the stored information to the digital / analog converting means as the plurality of reference voltages based on the storage information of the storage means. The display device according to claim 1. A pixel array unit in which light-emitting pixels are two-dimensionally arranged in a matrix;
A plurality of reference voltages corresponding to the number of bits of the digital video signal are generated, and one reference voltage corresponding to the digital video signal is selected from the plurality of reference voltages to drive the light emitting pixels of the pixel array unit. Digital / analog conversion means for converting an analog video signal;
Detecting means for detecting the light emission intensity of each light emitting pixel of the pixel array section for each pixel row;
And a control means for controlling the voltage values of the plurality of reference voltages for each pixel row in accordance with the detection output of the detection means. The control means includes
Storage means for storing information of emission intensity for each pixel row detected by the detection means for each pixel row;
The reference voltage generating means for supplying a reference voltage having a voltage value corresponding to the storage information to the digital / analog conversion means as the plurality of reference voltages based on the storage information of the storage means. 4. The display device according to 4. The light emitting element of the light emitting pixel is an organic EL element,
The display device according to claim 4, wherein the detection unit is an organic EL element arranged adjacent to the light emitting pixel for each pixel row. A pixel array unit in which light-emitting pixels are two-dimensionally arranged in a matrix;
A plurality of reference voltages corresponding to the number of bits of the digital video signal are generated, and one reference voltage corresponding to the digital video signal is selected from the plurality of reference voltages to drive the light emitting pixels of the pixel array unit. A method of driving a display device comprising digital / analog conversion means for converting an analog video signal,
A method for driving a display device, comprising: controlling voltage values of the plurality of reference voltages for each pixel row in accordance with light emission intensity for each pixel row of the pixel array unit. A pixel array unit in which light-emitting pixels are two-dimensionally arranged in a matrix;
A plurality of reference voltages corresponding to the number of bits of the digital video signal are generated, and one reference voltage corresponding to the digital video signal is selected from the plurality of reference voltages to drive the light emitting pixels of the pixel array unit. A method of driving a display device comprising digital / analog conversion means for converting an analog video signal,
Detecting the emission intensity of each light emitting pixel of the pixel array section for each pixel row;
A method for driving a display device, wherein the voltage values of the plurality of reference voltages are controlled for each pixel row in accordance with the detected emission intensity for each pixel row.

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