JP7059862B2 - Display device - Google Patents

Description

The present invention relates to a display device including a display unit having a plurality of pixels made of a self-luminous element.

Conventionally, a display device having a plurality of pixels composed of spontaneous light emitting elements such as OLED (abbreviation of Organic Light Emitting Diode) and FED (abbreviation of Field Emis-sion Display) is known.

Here, the OLED has a characteristic that when continuously emitting light, the luminous efficiency decreases according to the emission time, and the emission brightness decreases even under the same driving conditions. Further, in the deterioration of the characteristics of the OLED, the degree of decrease in luminous efficiency is large in the initial stage, and the degree of decrease tends to be small when the predetermined light emission time is exceeded.

The term "light emission time" as used herein means the total time during which a certain pixel is made to emit light, that is, the cumulative light emission time, and is different for each pixel depending on the frequency of use.

By the way, in a display device, various images or the like are displayed on the display unit, and the drive history is usually different for each pixel constituting the display unit. Therefore, the degree of deterioration of the light emission characteristics varies depending on the pixels configured by the self-luminous element, and the pixels with high frequency of use are deteriorated more than the pixels with low frequency of use, and the brightness difference is different even under the same drive conditions. When it occurs, it looks like it is burnt, so-called burning occurs.

As a countermeasure against this seizure, a method of correcting the driving conditions of each pixel so that the luminance difference of each pixel becomes small has been proposed. Examples of the display device configured to correct the driving conditions of the self-luminous element include those described in Patent Document 1.

In the display device described in Patent Document 1, one correction data common to each pixel in which the correction coefficient is plotted with respect to the emission time of the pixel is stored in advance, and the emission time of each pixel is sequentially accumulated as an integrated value and integrated. Calculate the difference data of the integrated value based on the maximum value. Then, in this display device, based on the difference data of these integrated values and the above correction data, the driving conditions of each pixel are set so that the difference between the brightness of the frequently used pixel and the brightness of other pixels becomes small. Burning is suppressed by correcting.

Further, in Patent Document 1, the pixel with the highest frequency of use is used as a reference, and other pixels are made to emit light in a non-use state to be deteriorated to the same extent as the reference pixel, thereby equalizing the degree of deterioration between each pixel. A method to do so is also proposed.

Japanese Patent No. 3933485

However, in the former method described in Patent Document 1, the difference in brightness from the frequently used pixels is reduced by performing the correction to reduce the drive current of the infrequently used pixels, so that the seizure is suppressed. , The overall brightness is reduced. Further, in the former method, since the correction coefficient is determined by using the correction data common to each pixel, it cannot be said that the correction coefficient corresponds to the degree of deterioration of each pixel, and there is room for improvement.

Specifically, the OLED has the above-mentioned characteristic that the luminous efficiency is lowered, and the degree of deterioration thereof is large in the initial stage, but tends to be smaller in the long term than in the initial stage. However, in the former method, in the correction of the pixel whose deterioration is in the initial stage and the pixel whose deterioration is in the long-term stage, the correction coefficient is calculated based on the same correction data, so that the correction is made according to the actual degree of deterioration. This may not be the case, and excess or deficiency of correction may occur.

On the other hand, in the latter method, since the degree of deterioration of each pixel is equalized based on the degree of deterioration of the most frequently used pixel, the less frequently used pixel is also deteriorated according to the standard, and the frequency of use is low. The original life characteristics of pixels cannot be utilized.

The present invention has been made in view of the above points, and while the pixels configured by the self-luminous element emit light to the same extent as the initial brightness, the driving conditions are corrected according to the frequency of use of each pixel. The purpose is to provide a display device with higher reliability than before.

In order to achieve the above object, the display device according to claim 1 has a display unit (1) having a plurality of pixels configured by a self-luminous element and a storage unit (2) for storing the light emission time for each pixel. ), A determination unit (31) for determining whether or not the light emission time is equal to or less than a predetermined threshold value, a deterioration estimation unit (32) for estimating the degree of deterioration of the pixel based on the light emission time, and a determination result of the determination unit. A correction unit (33) that corrects the driving conditions of the pixels is provided based on the above. In such a configuration, the correction unit corrects the driving conditions based on the first correction formula for the pixels whose emission time is determined to be equal to or less than the threshold value by the determination unit among the plurality of pixels, and a plurality of pixels. For the pixels whose emission time is determined to exceed the threshold value by the determination unit, the driving conditions are corrected based on the second correction formula different from the first correction formula, and the threshold value is self-luminous. This is the initial part of the graph obtained by plotting the luminance at each emission time when the element is continuously emitted with a predetermined constant current, including the point where the emission time is zero, and the starting point is the zero point. It is the time when the brightness becomes zero in the linear formula obtained by linearly approximating the portion where the brightness decreases linearly .

As a result, when the pixel drive condition is corrected, the first correction formula is used when the light emission time is equal to or less than the threshold value, and the second correction is used when the light emission time exceeds the threshold value. It is a display device having a configuration using an expression. In other words, by switching the correction formula used for correcting the driving condition according to the driving condition of the pixel, it is possible to perform appropriate correction according to the deterioration condition of the pixel. Therefore, while the used pixels emit light to the same extent as the initial brightness, the driving conditions are corrected according to the frequency of use, and the display device is more reliable than the conventional one.

The reference numerals in parentheses attached to each component or the like indicate an example of the correspondence between the component or the like and the specific component or the like described in the embodiment described later.

It is a block diagram which shows the structure of the display device of 1st Embodiment. It shows an example of the time-dependent change of the relative luminance when the OLED whose emission color is green is driven by a constant current, and is a graph showing the time-dependent change after the aging treatment and the time-dependent change after that. It shows the calculation result of the relative luminance with respect to the light emission time of a pixel in the display device of FIG. 1, and is a graph which shows the difference in calculation before and after a predetermined threshold value. It is a figure which shows an example of the setting of the threshold value shown in FIG. It is a flowchart which shows the operation example of the display device of FIG. It is a graph which shows an example of the setting of the threshold value in the sub-pixel whose emission color is green in the modification of the display device of 1st Embodiment. It is a graph which shows an example of the setting of the threshold value in the sub-pixel whose emission color is blue in the modification of the display device of 1st Embodiment. It is a graph which shows an example of the time-dependent change of the relative luminance when the sub-pixel whose emission color is red and the sub-pixel which is green are driven by a constant current with a current value having the same predetermined initial luminance.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each of the following embodiments, the parts that are the same or equal to each other will be described with the same reference numerals.

(First Embodiment)
The display device of the first embodiment will be described with reference to FIG. The display device of the present embodiment is applied to, for example, a display device for in-vehicle use, but can also be applied to other uses.

As shown in FIG. 1, the display device of the present embodiment includes a display unit 1, a storage unit 2, a control unit 3 including a determination unit 31 and a correction unit 33, and a video input unit 4. It becomes. In this display device, an image based on a signal from the image input unit 4 is displayed on the display unit 1, and the correction unit 33 determines the usage status of each pixel based on the determination result by the determination unit 31. The drive conditions are corrected.

The display unit 1 has a plurality of pixels composed of self-luminous elements such as OLEDs and FEDs, and each of these pixels emits light based on the video signal of the video input unit 4 to display an image or the like. It is a thing. The display unit 1 has, for example, a thin film transistor (not shown) as a switching element for each pixel, and an active matrix method capable of controlling on / off for each selected pixel can be adopted. The display unit 1 is referred to as an "organic EL (abbreviation of Electro Luminescence) display" when an OLED is adopted as a self-luminous element.

In this embodiment, an example in which an OLED is adopted as a self-luminous element will be described, but since the configurations of an OLED (organic EL element) and an organic EL display are known, detailed description thereof will be omitted in the present specification. ..

The storage unit 2 stores various programs and table data used for driving history such as light emission time for each pixel, determination by the determination unit 31 described later, correction of driving conditions by the correction unit 33, and the like. For the storage unit 2, for example, a ROM, a RAM, a non-volatile RAM, or the like can be used.

The drive history can be obtained, for example, based on the history of the input signal by the video input unit 4 described later and the time by the time measurement unit (not shown).

As shown in FIG. 1, the control unit 3 includes a determination unit 31, a deterioration estimation unit 32, and a correction unit 33. For example, the control unit 3 reads and executes various programs and the like stored in the storage unit 2, so that the control unit 3 makes a determination by the determination unit 31 described later and corrects the pixel drive conditions by the correction unit 33. The control unit 3 may be configured as a control ECU (abbreviation of Electronic Control Unit) together with the storage unit 2, for example, but may have other embodiments.

The determination unit 31 determines whether or not each of the pixels constituting the display unit 1 emits light for a predetermined time or longer, that is, whether or not the light emission time of each pixel is equal to or less than a predetermined threshold value. The determination result by the determination unit 31 is reflected in the estimation of the degree of deterioration by the deterioration estimation unit 32 and the correction of the pixel driving conditions by the correction unit 33.

The deterioration estimation unit 32 estimates the degree of deterioration for each pixel. For example, the CPU executes a program for calculating the degree of deterioration stored in the ROM, and the light emission time of each pixel stored in the storage unit 2 is calculated. The degree of deterioration of each pixel is calculated using the data.

Here, the degree of deterioration of the pixel composed of the OLED can be estimated by, for example, the known life estimation method described in KONICA MINOLTA TECHNOLOGY REPORT VOL.9 (2012) "Product Development of All Phosphorescent OLED Lighting Panel". The estimated life curve to be used can be used. For example, as in the method described in the above-mentioned publicly known document, the deterioration of the pixel is separated into the deterioration in the initial stage and the deterioration in the subsequent long-term stage, and the acceleration coefficient is calculated from the measured value of the change with time of the brightness of the pixel. Creates an estimated lifetime curve showing the relationship between the emission time of a pixel and the change in brightness over time.

Specifically, for example, deterioration in the initial stage (hereinafter referred to as "initial deterioration") in which the degree of deterioration in brightness is large and deterioration after the deterioration in the initial stage, and the degree of deterioration in brightness is smaller than in the initial stage. The relative luminance L1 is calculated based on the deterioration in the long-term stage (hereinafter referred to as “long-term deterioration”). The calculation formula of the relative luminance L is expressed by the following formula (1).

L1 = a1 x exp (-t x b1) + a2 x exp (-t x b2) ... (1)
The first term on the right side of the equation (1) corresponds to the component of initial deterioration, and the coefficients a1 and b1 are coefficients related to initial deterioration. The second term on the right side of the equation (1) corresponds to the component of long-term deterioration, and the coefficients a2 and b2 are coefficients related to long-term deterioration. In the first term and the second term, t is the emission time of the pixel.

Further, the "relative brightness" refers to the ratio of the certain brightness to the initial brightness when the pixel reaches a certain brightness in a certain light emission time when the pixel is driven by a predetermined constant current. That is, in the undegraded state, that is, in the case of the initial luminance, the relative luminance becomes 1, and as the deterioration progresses, the relative luminance becomes close to 0.

For the sake of simplification of the following explanation, for convenience, the period during which the pixels show a tendency of initial deterioration in the emission time of the pixels composed of OLEDs is referred to as "initial", and the period after "initial". That is, the period during which the pixel shows a tendency of long-term deterioration is referred to as "long-term".

For example, the drive history such as the light emission time and the brightness of the pixels stored at predetermined intervals is applied to the storage unit 2 to the equation (1), and various coefficients a1, b1, a2, and b2 are calculated. By calculating the relative brightness with respect to the light emission time from the calculated various coefficients a1, b1, a2, b2 and the equation (1), the degree of deterioration of the pixel can be estimated.

In the present embodiment, a "threshold value" is set as a time that is a boundary between the initial and long-term emission times, that is, a time at which the tendency of the degree of deterioration of the pixels is switched, and the determination unit 31 determines the emission time of the pixels. It is determined whether or not it is equal to or less than the threshold value of. Then, based on this determination result, the deterioration estimation unit 32 appropriately selects the calculation formula of the relative luminance to be used according to the light emission time. The details of this threshold will be described later.

For example, the deterioration estimation unit 32 uses the data of the drive history of the pixel determined to be in the initial deterioration stage and the calculation formula of the first relative luminance L1 represented by the formula (1). The relative brightness is calculated and the degree of deterioration is estimated. Further, the deterioration estimation unit 32 uses the data of the drive history of the pixel in the long term and the calculation formula of the second relative luminance L2 in the long term for the pixel whose deterioration degree is determined to be in the stage of long-term deterioration. The relative brightness is calculated and the degree of deterioration is estimated. The calculation formula of the second relative luminance L2 is expressed by the following formula (2).

L2 = a3 x exp (-t x b3) + a4 x exp (-t x b4) ... (2)
The various coefficients a3, b3, a4, and b4 on the right side of the equation (2) are coefficients having different numerical values from the various coefficients a1, b1, a2, and b2 in the equation (1). Further, t is the light emission time of the pixel. Further, for the various coefficients a3, b3, a4, and b4 in the equation (2), the procedure is the same as the calculation of the various coefficients in the equation (1), but the pixel is driven in the emission time after the predetermined threshold value. It is calculated by applying the historical data to Eq. (2).

That is, the deterioration estimation unit 32 determines that the emission time exceeds the predetermined threshold value in the equation (1) for the pixel determined by the determination unit 31 to be equal to or less than the predetermined threshold value among the plurality of pixels. For the determined pixel, the degree of deterioration of each pixel is estimated using the equation (2). In this way, the deterioration estimation unit 32 estimates the degree of deterioration by switching the calculation formula according to the light emission time, which is an index of the degree of progress of deterioration of each pixel.

When each pixel is composed of a plurality of sub-pixels having different emission colors, for example, a red sub-pixel, a green sub-pixel, and a blue sub-pixel, the relative brightness of each of these sub-pixels is calculated by the above formula. By calculating L1 and L2, the degree of deterioration can be estimated for each sub-pixel. Further, in the following description, the sub-pixel having a red emission color, the blue sub-pixel, and the green sub-pixel are referred to as "R sub-pixel", "G sub-pixel", and "B sub-pixel", respectively.

The correction unit 33 is a pixel used for image display on the display unit 1 among a plurality of pixels (hereinafter, “pixels used”) based on the determination result by the determination unit 31 and the estimation of the degree of deterioration by the deterioration estimation unit 32. ”), The drive condition of the pixel is corrected.

Specifically, the correction unit 33 corrects the driving conditions of the used pixel so that the brightness thereof becomes the same as the predetermined initial brightness (hereinafter referred to as “initial equivalent brightness”). At this time, the correction unit 33 has a driving condition that reflects the degree of deterioration of the pixels used based on the calculation formula of the first relative luminance L1 or the calculation formula of the second relative luminance L2, depending on the determination result by the determination unit 31. Make corrections. That is, the correction unit 33 uses a first correction formula based on the first relative brightness L1 calculation formula or a second correction formula based on the second relative brightness L2 calculation formula, depending on the degree of pixel deterioration. The drive condition is corrected. The details of the correction of this driving condition will be described later.

The "initial equivalent brightness" here includes not only the same brightness as the predetermined initial brightness but also the brightness close to the predetermined initial brightness to the extent that no difference in brightness is visually perceived by humans. ..

The video input unit 4 inputs a predetermined video signal corresponding to the video displayed on the display unit 1 to the display unit 1, and various other electronic components (not shown) depending on the type of video to be displayed on the display unit 1. Connected to the component.

The above is the configuration of the display device of this embodiment.

Next, the details of the correction of the pixel drive conditions by the correction unit 33 in the display device of the present embodiment will be described, but first, the deterioration tendency of the pixels composed of the OLED will be described with reference to FIG. .. In FIG. 2, in order to make it easy to distinguish the deterioration tendency, the reference numerals of α and β are added for convenience.

When a pixel is fixed to a current value having a predetermined initial brightness and driven with a constant current, the pixel tends to have a large decrease in relative brightness in the initial stage and a smaller decrease in the relative brightness in the long term.

Specifically, the change with time of the relative luminance of α in FIG. 2 is the one in the initial stage, and the change with time of the relative luminance of β is the one in the long term. More specifically, before measuring the change with time indicated by α, the pixel having zero emission time is fixed at a current value of 1500 cd / m ² and driven for 24 hours in an environment of 85 ° C. Perform aging processing. After that, the deteriorated pixel is raised to a current value of 1500 cd / m ² and fixed, and the result of continuous driving in an environment of 85 ° C. is α in FIG. As shown by α in FIG. 2, the relative luminance at this time decreased from 1 to 0.9 after about 65 hours, and decreased to 0.8 after about 220 hours.

The change with time indicated by β is a result of the deteriorated pixel being continuously driven in an environment of 85 ° C. after being driven by a constant current indicated by α by raising the current value to a brightness of 1500 cd / m ² and fixing the pixel. As shown in β in FIG. 2, the relative luminance at this time decreased from 1 to 0.9 after about 160 hours, and decreased to 0.8 after about 510 hours. The current value at β is higher than the current value at α because the deterioration of the pixels progresses due to the influence of the drive at α and the luminous efficiency is lowered.

As shown in FIG. 2, the time required for the relative luminance to decrease from 1 to 0.8 is about 220 hours in α, whereas it is about 510 hours in β, which is about 2.3 times. The degree of decrease in relative brightness is smaller in the long term than in the initial stage. That is, the deterioration tendency of the pixel differs between the initial stage and the long-term stage, and the pixel life characteristics are divided into two components: initial deterioration in which the degree of decrease in relative brightness is large and long-term deterioration in which the degree of decrease in relative brightness is small. It can be said that it can be done.

Subsequently, the estimation of the degree of deterioration of the conventional pixels and the estimation of the degree of deterioration of the pixels in the display device of the present embodiment will be described with reference to FIG.

In FIG. 3, the initial change with time obtained by the calculation formula of the first relative luminance L1 and the long-term change with time obtained by the calculation formula of the second relative luminance L2 are shown by a solid line, and the first relative luminance L1 is shown. The conventional long-term change over time obtained by the calculation formula is shown by the broken line. Further, in FIG. 3, for convenience, the change with time of the relative luminance shown by the solid line is indicated by the reference numerals A1 and A2, and the change with time of the relative luminance indicated by the broken line is indicated by the reference numeral B. are doing.

In the conventional estimation of the degree of deterioration of a pixel, for example, the calculation formula of the first relative luminance L1 represented by the formula (1) is stored as the data of the reference life characteristic, and the data of the drive history of the pixel is stored in this formula. Apply to obtain various coefficients. Then, the initial time-dependent change A1 and the long-term time-dependent change B shown in FIG. 3 were collectively calculated. After estimating the degree of deterioration of each pixel based on the calculation formula of the relative brightness obtained by this (A1 and B in the example of FIG. 3), that is, the estimation formula of the degree of deterioration of the pixels, each pixel has the initial equivalent brightness. The driving conditions were corrected so as to be. That is, based on the data of the pixel drive history in the initial and long-term, the calculation formula of the relative brightness including the initial and long-term is obtained, and this calculation formula is used as the basis of the common correction formula for estimating the deterioration degree of each pixel. , The correction conditions were decided.

However, since the calculation formula of the relative brightness is obtained based on the data of the drive history of the initial and long-term pixels having different tendencies of the relative brightness decrease, even if the relative brightness in the initial and long-term is calculated, it is still the actual degree of deterioration. Misalignment may occur. Then, based on the degree of deterioration estimated in this way, the correction of the drive conditions of the pixels showing the initial deterioration tendency and the pixels showing the long-term deterioration tendency is determined by a common correction formula. Overs and shorts of correction can occur.

As a result of diligent studies, the present inventor estimates the degree of deterioration in each of the initial deterioration and the long-term deterioration by using different relative brightness calculation formulas, and corrects the driving conditions of the OLED based on the result to correct the actual degree of deterioration. It was found that more accurate correction can be made according to the above.

Specifically, as shown in FIG. 3, the time that is the boundary between the initial deterioration and the long-term deterioration is set as a threshold value for convenience, and the relative brightness calculation formula is used properly before and after this threshold value. That is, as shown in FIG. 3, the time-dependent change A1 of the relative brightness at the initial stage is calculated by the first calculation formula based only on the data of the drive history of the initial pixels. On the other hand, the change over time A2 of the relative brightness in the long term is calculated by the second calculation formula only based on the drive history of the pixels in the long term. As a result, the accuracy of estimating the degree of deterioration by the calculation formula of the relative brightness in each of the initial and long-term is improved, and the accuracy of the correction of the driving condition in each of the initial and long-term is improved. In other words, when correcting the pixel drive conditions, the pixels in the initial state are corrected based on the first correction formula, and the pixels in the long-term state are corrected based on the second correction formula. You can also say that.

For example, as shown in FIG. 3, when the emission time of a certain pixel is t1 equal to or less than a predetermined threshold value, and the relative brightness obtained by the calculation formula of the first relative brightness L1 is 0.84. To consider. At this time, the driving conditions such as increasing the current value of the one pixel to about 1.19 times so that the brightness of the one pixel becomes the initial equivalent brightness, that is, the relative brightness becomes 1.00. Perform the correction.

Further, as shown in FIG. 3, when the emission time of a certain other pixel is t2 exceeding a predetermined threshold value, the relative brightness obtained by the calculation formula of the second relative brightness L2 is 0.95. To consider. At this time, the driving conditions such as increasing the current value of the other pixel to about 1.05 times so that the brightness of the other pixel becomes the initial equivalent brightness, that is, the relative brightness becomes 1.00. Perform the correction.

The calculation formula of the second relative luminance L2 used for calculating the long-term change A2 with time in FIG. 3 is obtained as follows. When the light emission time reaches the threshold value, in order to return the relative brightness to 1, the drive current is increased to a predetermined current value, and the pixel is again referred to as the brightness corresponding to the initial brightness (hereinafter, referred to as "second initial brightness" for convenience). ) To emit light. At this time, constant current drive is performed at this predetermined current value, and the degree of decrease in relative brightness with respect to the light emission time is applied to, for example, Eq. (2) with reference to the second initial brightness, and various coefficients a3, b3, a4, Calculate b4. By using the formula (2) and the formulas obtained by the various coefficients a3, b3, a4, and b4 as the calculation formula for the second relative brightness L2, the degree of deterioration of the pixel over a long period of time in which the brightness gradually and linearly decreases. Can be estimated accurately.

In this way, for each pixel, the relative brightness calculation formula is divided according to the emission time (frequency of use) of the pixel, the degree of deterioration is estimated, and the driving conditions are corrected based on the result. It will be an appropriate correction according to the deterioration situation of.

Next, the setting of the threshold value used for the determination in the determination unit 31 will be described with reference to FIG.

The threshold is determined, for example, based on the initial change in relative luminance, as shown in FIG. Specifically, a linear approximation straight line is obtained by linearly approximating the relative luminance calculated by the calculation formula of the first relative luminance L1. As shown by the alternate long and short dash line in FIG. 4, this linear approximation straight line includes a portion of the initial relative brightness that decreases linearly, and is a linear type in which the relative brightness decreases in proportion to the emission time. In the linear equation of this linear approximation, the time when the relative brightness becomes zero can be set as a threshold value, and the initial and long-term can be separated.

Next, an operation example in the display device of this embodiment will be described with reference to FIG.

For example, when the display device of the present embodiment is turned on and the image is displayed on the display unit 1 due to the ignition power being turned on, the CPU advances the process to step S1. In step S1, the CPU reads the reference life characteristic data of the pixels stored in advance in the storage unit 2.

As the "reference life characteristic data" referred to here, for example, the first calculation formula for calculating the initial relative brightness shown in the formula (1) and the long-term relative brightness shown in the formula (2) are calculated. A second calculation formula for this is mentioned.

Next, the CPU advances the process to step S2. In step S2, the CPU reads and executes a predetermined program stored in advance in a ROM or the like, thereby determining whether or not the light emission time of the pixels is equal to or less than a predetermined threshold value. If it is determined in step S2 that the light emission time of the pixel is equal to or less than the threshold value, that is, if YES in step S2, the CPU advances the process to step S3.

In step S3, the CPU reads the first calculation formula for calculating the initial relative luminance, and proceeds to step S4. In step S4, first, the relative brightness of the pixels is calculated using the first calculation formula read by the deterioration estimation unit 32, and the degree of deterioration of the pixels is estimated. Subsequently, the correction unit 33 causes the pixels to emit light at a brightness comparable to a predetermined initial brightness (for example, 1500 cd / m ² ), that is, the relative brightness is approximately 1. Correct the driving conditions such as increasing the current value of the pixel. That is, the "first correction process" shown in FIG. 5 refers to correcting the driving conditions of the pixels in the initial state as described above.

On the other hand, if it is determined in step S2 that the light emission time of the pixel exceeds the threshold value, that is, if NO in step S2, the CPU advances the process to step S5. In step S5, the CPU reads a second calculation formula for calculating the relative luminance in a long period of time, and proceeds to step S6. In step S6, first, the relative brightness of the pixels is calculated using the second calculation formula read by the deterioration estimation unit 32, and the degree of deterioration of the pixels is estimated. Then, by the same procedure as in step S4, the correction unit 33 corrects the driving conditions of the pixel so that the pixel emits light with the initial equivalent brightness. That is, the "second correction process" shown in FIG. 5 refers to correcting the driving conditions of a pixel in a long-term state as described above.

When the steps S4 or S6 are completed, the CPU ends the process. The display device of the present embodiment operates as described above, for example. Note that FIG. 5 shows an example in which the process is terminated when the first correction process or the second correction process is completed, but the present invention is not limited to this, and the process shown in FIG. 5 may be repeated at predetermined intervals.

According to the present embodiment, a display device that switches the calculation formula of the relative brightness between the initial stage and the long term based on the threshold value, estimates the degree of deterioration according to the driving condition of the pixel, and corrects the driving condition. Become. Therefore, the accuracy of calculating various coefficients in the calculation formulas of the initial and long-term relative brightness is improved, the accuracy of estimating the degree of deterioration of the pixel is improved, and the accuracy of correcting the driving condition of the pixel is improved as compared with the conventional case. Further, by correcting the appropriate driving conditions for each pixel according to the frequency of use, excess or deficiency of the correction is suppressed, and it is not necessary to intentionally deteriorate the pixel that is used infrequently, and the life of each pixel is reduced. It will be a display device that can make the best use of its characteristics.

Further, the degree of deterioration of the pixels at the initial stage often varies depending on the production lot even if the pixels have the same element configuration. When such a variation occurs, the life characteristics of each pixel of the display device also vary, which causes a decrease in reliability. Therefore, in order to suppress the decrease in reliability due to such variation, it is known to perform a process of performing a predetermined constant current drive for a predetermined time (for example, several tens of hours) in advance, that is, an aging process. However, this aging process is not preferable because the cycle time until the display device is shipped becomes long and causes an increase in cost.

On the other hand, in the display device of the present embodiment, the calculation formula of the relative luminance is switched between the initial stage and the long-term stage, and the correction is performed according to the driving condition of the pixel. Since appropriate correction can be made even at the stage, aging processing becomes unnecessary. Therefore, normally, the time required for the aging process is added to the life characteristics, and the display device has improved pixel life characteristics by that amount. Further, since the aging process is not required, the cost reduction effect is expected.

(Variation example of the first embodiment)
A modification of the display device of the first embodiment will be described with reference to FIGS. 6A and 6B. In this modification, the setting of the threshold value is different from that of the first embodiment, and this difference will be mainly described.

In this modification, the threshold value is set as follows.

First, a predetermined initial brightness is set, the current value at this time is fixed, the pixel is driven with a constant current, and data on the change over time of the relative brightness with respect to the light emission time is acquired. This data is applied to the relative brightness calculation formula of Eq. (1), various coefficients are calculated, and the relative brightness calculation formula is obtained. The time required for the relative brightness to decrease from 1 to 0.8 at this time, that is, the time required for the brightness to decrease to 80% of the initial brightness (hereinafter referred to as "LT80") is defined as the "first life". And.

Next, a pixel having the same element configuration and having a light emission time of zero is fixed at a current value having a predetermined initial brightness, and is driven with a constant current for an arbitrary time X (X> 0, unit: hours). I do. After resetting the current value so that the pixel deteriorated by this drive has the above initial brightness, the LT80 when the pixel is driven with the constant current for the second time is calculated by the relative brightness calculation formula, and at this time. LT80 is referred to as "second life" for convenience.

Then, the ratio of the second life to the first life is set as the "life change rate" (unit:%), and X is changed at an arbitrary time to calculate the value of X that maximizes the life change rate. The value of X that maximizes the life change rate is set as the "threshold value". When the pixel is composed of a plurality of sub-pixels having different emission colors, this threshold value is set to be an appropriate value for each of the plurality of sub-pixels, in other words, for each element configuration. From another point of view, the threshold can be said to be the time when aging is completed.

For example, FIG. 6A shows the result of calculating the life change rate when an arbitrary time X is changed in increments of 24 hours in the G sub-pixel. As shown in FIG. 6A, when the arbitrary time X is 120 hours, the life change rate is 154% at the maximum, so 120 hours is set as the threshold value. Similarly, when the life change rate is calculated for the B sub-pixel, as shown in FIG. 6B, when the arbitrary time X is 168 hours, the life change rate is 109% at the maximum, so 109 hours is the threshold value. Set as.

In the above example, the first life and the second life are set as the time for reducing the initial brightness to 80% of the initial brightness, but the setting is not limited to this, and the setting of the reduction ratio to the initial brightness is appropriately changed. You may. Further, in the above example, the arbitrary time X is changed in increments of 24 hours, but the present invention is not limited to this, and the arbitrary time X may be changed as appropriate.

According to this modification, the threshold value can be set with higher accuracy than the threshold value setting in the first embodiment. Therefore, a display device having further improved reliability can be obtained as compared with the first embodiment.

(Other embodiments)
The display device shown in the first embodiment described above is an example of the display device of the present invention, and is not limited to each of the above embodiments, but is the scope described in the claims. It can be changed as appropriate within.

(1) For example, in the first embodiment described above, an example is described in which the initial and long-term values are separated by a threshold value, the calculation formula of the relative luminance is calculated at each of the initial and long-term stages, and the driving conditions of the pixels are corrected. However, it is not limited to the example of calculating and correcting the relative brightness in two stages of initial and long-term, and further subdividing the tendency of decrease in relative brightness in the initial stage, for example, the relative brightness in three stages of initial, medium-term, and long-term. Calculations and corrections may be made.

In this case, for example, the threshold value in the first embodiment and its modifications is set as the "first threshold value", and a "second threshold value" smaller than the first threshold value is set. Then, in each of the three cases where the light emission time is "below the first threshold value and below the second threshold value", "below the first threshold value and exceeding the second threshold value", and "exceeding the first threshold value", the relative brightness is achieved. Switch the calculation formula of.

Specifically, the determination unit 31 may be configured to execute a program for determining whether or not the light emission time is equal to or less than the second threshold value when it is determined to be equal to or less than the first threshold value. The deterioration estimation unit 32 uses the first calculation formula when the light emission time is equal to or less than the first threshold value and is equal to or less than the second threshold value, and the third deterioration estimation unit 32 is used when the light emission time is equal to or less than the first threshold value and exceeds the second threshold value. If the light emission time exceeds the first threshold value, the second calculation formula may be used. Then, the correction unit 33 corrects the driving conditions according to the frequency of use of the pixels based on the first, second, and third correction formulas based on the calculation formulas of each of the three stages. In this way, the display device may be configured to subdivide the stages prior to the long term and perform correction in two or more stages.

(2) In the first embodiment, when a pixel is composed of a plurality of sub-pixels having different emission colors, all the sub-pixels are determined by using a threshold value, the degree of deterioration is estimated, and the driving conditions thereof are corrected. An example was explained. However, when there is a large difference in the degree of decrease in relative brightness between the sub-pixels, the drive condition may be corrected based on the threshold value for at least the sub-pixels having a large degree of decrease in relative brightness.

Specifically, for example, as shown in FIG. 7, in a pixel having an R sub-pixel and a G sub-pixel, when the difference in the degree of decrease in relative luminance between the sub-pixels is large, at least the G sub-pixel is used. It suffices if the pixel is corrected based on the threshold value. In this case, the R sub-pixel may or may not be corrected based on the threshold value.

Note that FIG. 7 shows an example of the change over time in the relative brightness when the R sub-pixel and the G sub-pixel after the predetermined aging process are driven with a constant current value having the same predetermined initial brightness, respectively, and the R sub-pixel is shown. The R code is attached to the pixel data, and the G code is attached to the G sub-pixel data.

Further, in the example of FIG. 7, an example in which the driving condition is corrected for the G sub-pixel among the R sub-pixel and the G sub-pixel is shown, but the present invention is not limited to this, and the degree of decrease in the relative brightness of the B sub-pixel is other. If it is larger than the sub-pixel, the drive condition of the B sub-pixel may be corrected. For example, the degree of decrease in relative luminance may differ depending on the emission color of the sub-pixels depending on whether the light emitting material constituting the light emitting layer is a phosphorescent material or a fluorescent material, and whether or not it has high temperature resistance. The sub-pixels to be corrected may be appropriately determined according to the situation.

(3) In the first embodiment, an example in which the first correction process and the second correction process are executed by one deterioration estimation unit 32 and correction unit 33 has been described. However, the present invention is not limited to this, and the first correction process and the second correction process may be executed by separate deterioration estimation units 32 and correction units 33, respectively. As a result, the first correction process and the second correction process of the pixels are dispersed, and the drive conditions of each pixel can be smoothly corrected without slowing down the processing speed. Further, if necessary, the display device may have a plurality of storage units 2 and determination units 31. It can be said that it is preferable from the viewpoint of fail operation that the configuration is provided with a plurality of storage units 2 and control units 3.

1 Display unit 2 Storage unit 3 Control unit 31 Judgment unit 32 Deterioration estimation unit 33 Correction unit 4 Video input unit

Claims (4)

A display unit (1) having a plurality of pixels composed of self-luminous elements,
A storage unit (2) that stores the light emission time for each pixel, and
A determination unit (31) for determining whether or not the light emission time is equal to or less than a predetermined threshold value,
A deterioration estimation unit (32) that estimates the degree of deterioration of the pixel based on the light emission time,
A correction unit (33) that corrects the driving conditions of the pixels based on the determination result of the determination unit is provided.
The correction unit
Of the plurality of pixels, the pixel whose emission time is determined to be equal to or less than the threshold value is corrected for driving conditions based on the first correction formula.
Of the plurality of pixels, the pixel whose emission time is determined to exceed the threshold value by the determination unit is corrected for driving conditions based on a second correction formula different from the first correction formula. Do,
The threshold is the initial portion of the graph obtained by plotting the luminance at each emission time when the self-luminous element is continuously emitted with a predetermined constant current, and includes a point where the emission time is zero. A display device in which the time at which the brightness becomes zero in a linear formula obtained by linearly approximating the portion where the brightness decreases linearly starting from the zero point . A display unit (1) having a plurality of pixels composed of self-luminous elements,
A storage unit (2) that stores the light emission time for each pixel, and
A determination unit (31) for determining whether or not the light emission time is equal to or less than a predetermined threshold value,
A deterioration estimation unit (32) that estimates the degree of deterioration of the pixel based on the light emission time,
A correction unit (33) that corrects the driving conditions of the pixels based on the determination result of the determination unit is provided.
The correction unit
Of the plurality of pixels, the pixel whose emission time is determined to be equal to or less than the threshold value is corrected for driving conditions based on the first correction formula.
Of the plurality of pixels, the pixel whose emission time is determined to exceed the threshold value by the determination unit is corrected for driving conditions based on a second correction formula different from the first correction formula. Do,
When the self-luminous element in a state where the light emission time is zero is driven by a predetermined constant current having a predetermined initial brightness to continuously emit light, the brightness decreases from the initial brightness to a predetermined ratio to the initial brightness. The time required to do this is set as the first life.
The self-luminous element in a state where the light emission time is zero is continuously emitted for a predetermined time X (X> 0) with a predetermined constant current which is the initial brightness, and then the current value is increased to have the same brightness as the initial brightness. After returning to a certain second initial brightness , when the constant current drive is performed for the second time to continuously emit light, the brightness decreases from the second initial brightness to a predetermined ratio with respect to the second initial brightness. The time required to do this is set as the second life.
The threshold value is the predetermined time X, and is a display device having a value at which the life change rate, which is the ratio of the second life to the first life, is maximized. The pixel has at least a sub-pixel whose emission color is green.
The display device according to claim 1 or 2 , wherein the green sub-pixels have their driving conditions corrected by the correction unit based on the determination result by the determination unit. The storage unit stores the second threshold value smaller than the first threshold value in addition to the first threshold value with the threshold value as the first threshold value.
When the determination unit determines that the light emission time is equal to or less than the first threshold value, the determination unit further determines whether or not the light emission time is equal to or less than the second threshold value.
The correction unit
With respect to the pixel determined by the determination unit to be equal to or less than the second threshold value among the plurality of pixels, the driving conditions are corrected based on the first correction formula.
Of the plurality of pixels, the pixel determined to exceed the second threshold value is corrected for driving conditions based on a third correction formula different from the first correction formula and the second correction formula. The display device according to any one of claims 1 to 3 .

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