JP2009098433A - Display and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving method and device of a display which uses an organic electroluminescent device without causing burning, by appropriately correcting luminance by correctly detecting luminance degradation of the organic electroluminescent device. <P>SOLUTION: The driving method of a display using the organic electroluminescent device is for a display including the plurality of organic electroluminescent devices, a voltage for a predetermined current value is measured for each of the plurality of the organic electroluminescent device after an initial period and a predetermined period, and a driving current value is corrected according to change of the voltage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a display device using an organic electroluminescent element (organic EL element) provided with an organic compound layer having at least an organic light emitting layer on a transparent electrode and a reflective electrode, and a driving method thereof, and particularly to durability when driven for a long time. The present invention relates to a driving method of an organic electroluminescent element in consideration. The present invention also relates to a method for driving a display device including at least one organic electroluminescent element that is formed between electrodes and emits light when a current is applied.

  The organic electroluminescent element is a spontaneous light emitting element that injects electrons and holes from a cathode and an anode, recombines carriers in the organic light emitting layer, causes light emission, and extracts light to the outside. Organic electroluminescence devices have excellent characteristics such as high-speed response due to self-emission and a wide viewing angle, and application development for full-color displays and the like has been activated. However, the durability of the organic electroluminescent device when it is driven for a long time is still insufficient.

  In particular, since the organic electroluminescent element display is a self-luminous element, if it continues to display a fixed image, only the pixel of the part deteriorates in luminance due to deterioration, and the color reproducibility differs from the surroundings depending on the degree, So-called “burn-in” occurs. Therefore, it is necessary to take measures for preventing the burn-in.

  Patent Document 1 discloses a method of performing current driving in order to avoid a driving current change resulting from an impedance change due to deterioration of an organic electroluminescent element. However, since the deterioration of the organic electroluminescent element also causes a decrease in the luminance current efficiency, a constant luminance cannot be maintained even if the driving current is constant.

  Further, Patent Document 2 discloses a method of correcting the luminance in accordance with a known life characteristic curve according to the lighting time, assuming that the life characteristic can be roughly estimated by the current density to be input. However, since the life characteristic curve changes depending on the input current density, a decrease in luminance cannot be accurately estimated from the life characteristic curve, which is a time-luminance relationship, when the driving current value varies.

  Further, Patent Document 3 discloses a method of directly monitoring the light emission of the light emitting unit and feeding back to the light emission luminance for correction. However, if correction is to be made for each pixel, a photosensor must be provided for every pixel, which is a disadvantageous configuration for practical use.

  In order to solve these problems, focusing on the fact that the drive voltage increases with the deterioration of the luminance of the organic electroluminescent element, it is possible to correct the luminance deterioration of each pixel by increasing the drive current by the increase of the drive voltage. A method is disclosed in US Pat.

  Further, Patent Document 5 includes a detection unit that detects at least one drive voltage of the organic electroluminescence element, and the control unit drives drive power to the plurality of organic electroluminescence elements according to the magnitude of the detection voltage of the detection unit. What controls is disclosed.

Further, according to Patent Document 6, the analog value of the voltage value, current value, and temperature applied to the organic electroluminescent element, the time-dependent change of the voltage-current characteristic and the current-luminance characteristic obtained in advance for the organic electroluminescent element of the same configuration. The change with time and the temperature at the time of characteristic measurement are compared. And what analogizes the electric current-luminance characteristic of an organic electroluminescent element is disclosed. For this purpose, the current flowing by applying a predetermined voltage to the organic electroluminescent element is measured in advance, and the temperature of the organic electroluminescent element is estimated by a temperature measuring circuit.
JP-A-10-319910 JP-A-11-109918 JP 2002-278506 A JP 2004-287046 A JP 2001-236040 A JP 2002-278514 A

  As mentioned above, display burn-in of organic electroluminescence displays is caused by differences in the input current and lighting time of each pixel, so it can be prevented unless an appropriate correction amount is set for each pixel. Can not. In other words, seizure cannot be prevented unless the following problems can be satisfied at the same time.

(Decrease in current efficiency)
Deterioration of the organic electroluminescent element not only increases the impedance of the element but also decreases the luminance for a constant current value, that is, the current efficiency itself. For this reason, burn-in cannot be prevented by so-called simple current control in which the drive voltage is increased so that a constant current flows. Unless the light amount of the element is directly detected as in the method of Patent Document 3, it is necessary to detect the amount of decrease in current efficiency by some method.

(Correction for each pixel)
Further, since correction for each pixel is necessary, the feedback operation for correcting the deterioration needs to be easily performed for each pixel. In this way, when correcting for all pixels, it is much easier to monitor the current value and voltage value as in Patent Documents 1, 2, and 4, rather than detecting the amount of light that requires a photosensor. .

(High correction accuracy)
In addition, as described in Patent Document 4, it is possible to make the half time as long as possible by correction such that the drive current is increased in the direction in which the approximate brightness increases by the increase in drive voltage. However, in the case of preventing burn-in, the luminance variation of the pixels can be visually recognized even at a few percent, so that an accurate correction is necessary. For this reason, burn-in cannot be prevented by a control method of roughly increasing the drive current.

  As described above, even though the conventional technique can delay the decrease in luminance due to deterioration, it cannot satisfy all of the above conditions at the same time, so that it is insufficient in terms of preventing burn-in.

(Deterioration due to driving)
Further, in an organic electroluminescent element whose electrical characteristics change by driving, the electrical characteristics of each organic electroluminescent element vary depending on the emission intensity and the history of the emission time.

  For example, when an arbitrary current is applied to each organic electroluminescent element for an arbitrary period, the rate of change in emission luminance may be different. Similarly, when each organic electroluminescent element is driven at an arbitrary voltage value, the rate of change in the emission luminance may be different. In many cases, the light emission luminance of the organic electroluminescent element tends to decrease with continued driving. For this reason, the brightness of the display device provided with the organic electroluminescent element may decrease at a different rate depending on the usage time. In other words, in a display device having a plurality of organic electroluminescent elements, organic electroluminescent elements having different luminances depending on the driving history of the individual organic electroluminescent elements and partially different in luminance are generated or displayed. Spots or burn-in may occur.

  The present invention has been made in view of the above-mentioned problems, and its object is to accurately detect luminance deterioration of an organic electroluminescent device, perform appropriate luminance correction, and prevent the occurrence of burn-in. And providing a driving device.

  In order to achieve the above object, a driving method of a display device according to the present invention is a driving method of a display device including a plurality of organic electroluminescent elements. Each step includes measuring each voltage with respect to a predetermined current value and correcting each drive current value according to the change in the voltage.

  In the present invention, the step of correcting the driving current value calculates a luminance current efficiency from the measured change in voltage according to a predetermined calculation formula, and corrects the driving current value using the calculated luminance current efficiency. The amount may be determined. Further, the step of correcting the driving current value selects a luminance current efficiency from the measured change in the voltage according to correspondence information measured in advance, and uses the selected luminance current efficiency to calculate the driving current value. The correction amount may be determined.

  The display device according to the present invention includes a plurality of organic electroluminescent elements and a driving device that drives the plurality of organic electroluminescent elements, and the driving device includes the plurality of organic electric fields. Each of the light emitting elements includes a measuring unit that measures a voltage with respect to a predetermined current value, and a correcting unit that corrects the driving current value according to the measured change in the voltage.

  In the present invention, the correction means calculates a luminance current efficiency from a measured change in the voltage according to a predetermined calculation formula, and determines a correction amount of the drive current value using the calculated luminance current efficiency. Also good. The correction unit may select a luminance current efficiency from the measured change in voltage according to correspondence information measured in advance, and determine the correction amount of the drive current value using the selected luminance current efficiency. Good.

  The second display device driving method according to the present invention includes an organic electroluminescent element that emits light by applying a current, a power supply circuit that supplies power to the organic electroluminescent element, and a drive circuit that instructs the power supply circuit to supply power. And a display device driving method for controlling by changing a power supply amount to the organic electroluminescent element based on a change in an electrical characteristic value of the organic electroluminescent element, the electrical characteristic value And obtaining the electrical resistance of the organic electroluminescent element and controlling the amount of power supply based on the obtained electrical resistance.

  In the present invention, the organic electroluminescent element is composed of a plurality of organic electroluminescent elements, and the display device includes an electric resistance value acquisition unit that acquires electric resistance values of the plurality of organic electroluminescent elements, The step of controlling the power supply amount may control the power supply amount to the organic electroluminescent element based on the output of the electrical resistance value acquisition unit. The step of controlling the amount of power supply may be controlled to achieve the maximum light emission luminance of the organic electroluminescent element by drive control that maintains the electric resistance value of the organic electroluminescent element at a predetermined value. The step of controlling the amount of power supply is a control for setting the maximum light emission luminance of the organic electroluminescent element by drive control for reducing the electric resistance value of the organic electroluminescent element in accordance with a change in electrical characteristics of the organic electroluminescent element. May be performed.

  A second display device according to the present invention includes an organic electroluminescent element that emits light by applying a current, a power supply circuit that supplies power to the organic electroluminescent element, and a drive circuit unit that instructs the power supply circuit to supply power. A display device that controls the amount of electric power supplied to the organic electroluminescent element by changing the electric characteristic value of the organic electroluminescent element, the electric characteristic value of the organic electroluminescent element being It has a control means which acquires an electrical resistance and controls the amount of power supply based on the acquired electrical resistance.

  In the present invention, the organic electroluminescent element is composed of a plurality of organic electroluminescent elements, and the control means includes an electrical resistance value acquisition unit that acquires electrical resistance values of the plurality of organic electroluminescent elements, You may control the electric power feeding amount to the said organic electroluminescent element based on the output of the said electrical resistance value acquisition part. The control means may perform control to achieve the maximum light emission luminance of the organic electroluminescent element by drive control that maintains the electric resistance value of the organic electroluminescent element at a predetermined value. The control unit may perform control to obtain a maximum light emission luminance of the organic electroluminescent element by driving control to reduce an electric resistance value of the organic electroluminescent element in accordance with a change in electrical characteristics of the organic electroluminescent element. Good.

  According to the present invention, it is possible to correct luminance deterioration for each pixel easily and at low cost. Furthermore, since the luminance deterioration can be corrected with high accuracy, burn-in can be prevented.

  Hereinafter, embodiments of a display device using an organic electroluminescent element and a driving method thereof according to the present invention will be described in detail with reference to the drawings.

(First embodiment)
First, a first embodiment of the present invention will be described with reference to FIG.

  In the driving method of the display device according to the present embodiment, a predetermined current is supplied at certain intervals during which the organic electroluminescence element is lit, and a necessary voltage value (driving voltage) at this time is measured. The predetermined current value to be passed at this time is not particularly limited, but for example, a current value necessary for standard luminance that is lit for the longest time may be used.

  FIG. 1 shows temporal variations in voltage V and luminance L of an organic electroluminescent element when driven at a constant current value. As shown in FIG. 1, when driven at a constant current value, the organic electroluminescent element has a reduced luminance L (luminance current efficiency η = luminance L / current I) as the drive time t increases, and the impedance of the element increases. Therefore, the necessary drive voltage V increases. When the current is changed, the way of variation changes from FIG. 1, but the relationship between the voltage V and the luminance L does not change greatly depending on the current. When the current is doubled, the fluctuations in the voltage V and the luminance L are also accelerated. In this case, it can be considered that the time progress in FIG. 1 is equivalent.

  Even when current histories differ from pixel to pixel, the degree of deterioration can be uniquely determined from the voltage change. In the present embodiment, by utilizing this fact, the amount of change in voltage with respect to a constant current is obtained for each pixel to estimate the degree of deterioration, that is, the decrease in luminance.

  Specifically, first, an increased drive voltage value that is the difference between the required drive voltage value that has increased after a predetermined time has elapsed and the initial required drive voltage value is obtained. Next, the luminance current efficiency (= luminance / current) is obtained from the increased drive voltage value according to a predetermined relationship. Further, a current value necessary for a desired luminance is obtained from the luminance current efficiency, and a current having this current value as a driving current value is passed through the organic electroluminescent element.

  As described above, in the present embodiment, the luminance current efficiency of each organic electroluminescent element arranged in the pixel is obtained and the drive current is corrected, so that the luminance deterioration can be compensated accurately. Further, since the measurement necessary for the correction is a voltage, the correction can be easily made individually for each element only by providing a voltage detection part in a part of the circuit.

  In the present embodiment, the luminance current efficiency can be determined from the increased drive voltage value by using a calculation device such as a microcomputer using the following equation 1 as a predetermined calculation equation.

Here, V represents the rising drive voltage value, and η represents the luminance current efficiency (η = luminance L / current I). Further, ε and d are the dielectric constant and the layer thickness of the organic layer of the organic electroluminescent element, respectively, and q represents the elementary charge. n ₀ is the initial density of the light emitter in the light emitting layer of the organic electroluminescent device, and this equation is based on the phenomenon that the light emitting element decomposes as it deteriorates to become a quencher, and the rising drive voltage is determined by the quencher density. Yes. This n ₀ is obtained in advance by fitting from a luminance degradation curve and a voltage rise curve, and this records luminance and voltage data during lighting in an aging process which is a process of eliminating initial degradation. Can also be calculated.

  The calculation formula used here is not limited to Formula 1 as long as the correction accuracy is guaranteed. An empirical formula derived from an empirical rule may be used as a theoretical formula applicable to the element.

  In order to estimate the luminance after deterioration, the following may be performed.

As an example, the dependency of the drive voltage V on the deterioration progress t (for example, lighting time) is V (t), and the dependency on the luminance deterioration progress t (for example, lighting time) is L (t). Then, the luminance L ₁ when the drive voltage at the deterioration progress t ₁ is V ₁ may be L ₁ = L (V ⁻¹ (V ₁ )).

  As another example, the correspondence relationship between the rising drive voltage V and the luminance current efficiency η is measured in advance, and the measured correspondence information is stored in a storage device as a database. Then, the luminance current efficiency η corresponding to the increased drive voltage value V may be selected according to the database, and the correction amount of the drive current value may be determined from the selected luminance current efficiency η.

  The interval for performing the correction is not particularly limited, but the drive deterioration of the organic electroluminescent element does not proceed extremely quickly, and therefore, it may be performed every time the device equipped with the light emitting element is started.

  In order to realize the above driving method, the display device according to the present embodiment may have the following configuration. That is, the driving device measures the voltage with respect to the predetermined current value for each of the plurality of organic electroluminescent elements after the initial period and the predetermined time has elapsed, and the correcting unit corrects the driving current value according to the change in the measured voltage. As long as it has. The correcting means may calculate the luminance current efficiency η from the measured voltage change according to a predetermined calculation formula (for example, the above formula 1), and determine the correction amount of the drive current value from the luminance current efficiency η. Alternatively, the correction unit may select the luminance current efficiency η according to the correspondence information measured in advance from the measured voltage change, and determine the correction amount of the drive current value from the luminance current efficiency η.

  Therefore, according to the display device and the driving method thereof according to the present embodiment, it is possible to correct luminance deterioration for each pixel easily and at low cost. Furthermore, since the luminance deterioration can be corrected with high accuracy, burn-in can be prevented.

(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIGS.

  The present embodiment includes at least one organic electroluminescent element that emits light by applying current, a power supply circuit that supplies power to the organic electroluminescent element, and a drive circuit unit that instructs the power supply circuit to supply desired power. It is a drive method of a display apparatus. In this configuration, the electrical resistance is acquired as the electrical characteristic value of the organic electroluminescent element, and the power supply amount is controlled based on the acquired electrical resistance. Moreover, an electrical resistance value acquisition unit is provided as means for acquiring the electrical resistance of the organic electroluminescence element, and the amount of power supplied to the organic electroluminescence element is controlled based on the output of the electrical resistance value acquisition unit. Further, the power supply amount is controlled so as to keep the electric resistance of the organic electroluminescent element at a predetermined value.

  The display device according to the present embodiment shown in FIG. 3 includes a drive circuit unit 21 that instructs the power supply circuit 22 to supply a drive signal, a power supply circuit 22 that supplies power to the organic electroluminescent element 23 based on the drive signal, It comprises an organic electroluminescent element 23 and an electrical resistance acquisition unit 24 that acquires the electrical resistance. The drive circuit unit 21, the power feeding circuit 22, the organic electroluminescent element 23, and the electrical resistance acquisition unit 24 are electrically connected by signal lines, respectively. Among these, the electrical resistance acquisition unit 24 corresponds to the control means of the present invention.

  The drive circuit unit 21 is not particularly limited as long as the power supply circuit 22 outputs a signal for applying predetermined power to the organic electroluminescent element 23. The signal for the feeder circuit 22 to apply a predetermined power to the organic electroluminescent element 23 may be a signal that regulates the gradation of the luminance of the organic electroluminescent element 23, or a predetermined current applied to the organic electroluminescent element 23. A value or a voltage value may be specified.

  The configuration of the power feeding circuit 22 is not particularly limited as long as it has a function of applying power to the organic electroluminescent element 23 based on a control signal output from the drive circuit unit 21. A circuit that defines a current value applied to the organic electroluminescent element 23 or a circuit that defines a voltage value may be used.

  If the organic electroluminescent element 23 is an organic electroluminescent element 23 including at least one organic light emitting layer that emits light by applying current between two electrodes, at least one of which is transparent, the configuration, material, and manufacturing method thereof are particularly Not limited. Known materials, element configurations, and manufacturing methods may be used. The substrate on which the organic electroluminescent element 23 is formed is preferably transparent when the electrode disposed on the substrate side among the two electrodes constituting the organic electroluminescent element 23 is a transparent electrode. The physical properties such as mechanical strength of the substrate are not particularly limited as long as the organic electroluminescent element 23 can be produced.

  The configuration of the electrical resistance acquisition unit 24 is not particularly limited as long as the electrical resistance value of the organic electroluminescence element 23 can be acquired and the signal can be output to the drive circuit unit 21 or the power feeding circuit 22. A method for obtaining the electric resistance of the organic electroluminescent element 23 is not particularly limited. There is no particular limitation as long as the resistance value of the organic electroluminescent element 23 can be acquired and the signal can be output to the drive circuit unit 21 or the power feeding circuit 22.

  As a method for obtaining the electrical resistance of the organic electroluminescent element 23, a voltage applied to the organic electroluminescent element 23 and a voltage applied to a resistor having a known resistance value arranged in series with the organic electroluminescent element 23 are measured. You may obtain | require from one voltage value and the resistance value of a resistor. Alternatively, the resistance value may be obtained from the current value applied to the organic electroluminescent element 23 by the power feeding circuit 22 and the voltage applied to the organic electroluminescent element 23. Alternatively, the voltage value applied to the organic electroluminescent element 23 by the power feeding circuit 22 and the voltage applied to the resistor having a known resistance value arranged in series with the organic electroluminescent element 23 are measured, and the two voltage values and the resistance are measured. You may obtain | require from the resistance value of a vessel.

  The present display device is an example of a display device including one organic electroluminescent element 23, but the number of organic electroluminescent elements 23 is not particularly limited. One or a display device including a plurality of organic electroluminescent elements 23 may be used. The numbers of the drive circuit unit 21, the power feeding circuit 22, and the electrical resistance acquisition unit 24 are not particularly limited. You may provide the drive circuit part 21, the electric power feeding circuit 22, and the electrical resistance acquisition part 24 of the same number as the organic electroluminescent element 23 corresponding to each one of the some organic electroluminescent element 23. FIG. Alternatively, one drive circuit unit 21 and one electrical resistance acquisition unit 24 are provided for a plurality of organic electroluminescent elements 23, and a power feeding circuit 22 including a switch circuit and similarly an organic electroluminescent element 23 including a switch circuit. And a circuit for connecting the electrical resistance acquisition unit 24 may be provided.

  Next, the principle of the driving method of the organic electroluminescent element by the display device of this embodiment will be described.

  A driving method for controlling the applied power based on the electric resistance of the organic electroluminescent element 23 is a useful driving method. The reason is that the resistance-luminance characteristic (see FIG. 4B) of the organic electroluminescent element 23 has a characteristic that the luminance decreases as the electric resistance increases, and the luminance gradually approaches 0 in the high electric resistance region. It is.

  In FIG. 4B, the horizontal axis represents electric resistance, the vertical axis represents luminance, and the resistance-luminance characteristic line of the organic electroluminescent element 23 is indicated by a thick solid line.

  The organic electroluminescent element 23 can be driven at a desired luminance corresponding to the resistance value by a driving method that maintains a specific resistance value. That is, the organic electroluminescent element 23 can be driven with a desired electric resistance value due to the characteristics of the voltage-current characteristics of the organic electroluminescent element 23 described below. The voltage-current characteristic of the organic electroluminescent element 23 has a characteristic that current rapidly rises above a specific threshold voltage (see FIG. 4A).

  In FIG. 4A, the horizontal axis represents voltage, the vertical axis represents current, and the voltage-current characteristics of the organic electroluminescent element 23 are indicated by a thick solid line and the constant electric resistance line is indicated by a broken line. The electric resistance value of the organic electroluminescent element 23 changes depending on the value of the current flowing through the organic electroluminescent element 23 and the voltage value at that time, and the electric resistance decreases as the current and voltage increase. The electric resistance increases as the voltage decreases. Therefore, the voltage or current may be decreased when the resistance value of the organic electroluminescent element 23 is increased, and the voltage or current may be increased when the resistance value of the organic electroluminescent element 23 is decreased.

Resistance of the organic electroluminescent element 23 - luminance characteristics, the continuation of the drive, the resistance shown in FIG. 4 (b) - resistance from the luminance characteristic RL ₁ - changes the direction of the luminance characteristics RL _2. That is, the electric resistance of the organic electroluminescent element 23 tends to decrease if the driving is continued under the condition where the luminance is constant, and the luminance tends to decrease if the driving is continued under the condition where the resistance is constant. It is in. Therefore, in order to continue driving with the luminance of the organic electroluminescent element 23 kept constant, a driving method that changes the electric resistance of the organic electroluminescent element 23 is a good driving method. For example, a driving method for reducing the electric resistance value of the organic electroluminescent element 23 according to time is a good driving method.

By the way, the voltage-current characteristic of the organic electroluminescent element 23 changes from the voltage-current characteristic VI ₁ shown in FIG. 4A toward the voltage-current characteristic VI ₂ as driving is continued. That is, if the predetermined current application is continued, the voltage increases and the electric resistance tends to increase, and if the specific voltage application is continued, the current decreases and the electric resistance tends to increase. Therefore, when the organic electroluminescent element 23 is driven with a predetermined current or a predetermined voltage, the luminance of the organic electroluminescent element 23 is changed simultaneously with the change of the resistance-luminance characteristic (see FIG. 4B). The luminance may decrease due to the increase in the electrical resistance of 23.

  As an example, let us consider a case where driving is continued with the voltage and current at point a in FIG. When driving is continued under the condition that the current is constant as the driving continuation condition, the driving voltage / current of the organic electroluminescent element 23 becomes point c in FIG. When driving is continued under a constant voltage condition, the driving voltage / current of the organic electroluminescent element 23 becomes point d in FIG. 4A along with the change in voltage-current characteristics. When driving is continued under the condition that the resistance is constant, the driving voltage / current of the organic electroluminescent element becomes point b in FIG. 4A along with the change of the voltage-current characteristics. Accordingly, the electrical resistance of the organic electroluminescence element increases under the constant voltage condition and the constant current condition.

  This change appears in the resistance-luminance characteristics of the organic electroluminescent element 23 as follows. Resistance / luminance when the organic electroluminescent element 23 is driven under the condition of point a in FIG. 4A is point a in FIG. 4B. When driving is continued under the condition that the resistance is constant from the point a in FIG. 4B, the resistance / luminance of the organic electroluminescent element 23 is changed in FIG. B point. Further, when the driving is continued under a constant current condition, the resistance / luminance of the organic electroluminescent element 23 becomes a point c in FIG. 4B with the change of the resistance-luminance characteristics. When driving is continued under a constant voltage condition, the resistance / luminance of the organic electroluminescent element 23 becomes point d in FIG. Therefore, the decrease in luminance when the organic electroluminescent element 23 is driven with a predetermined current or predetermined voltage is greater than the decrease in luminance when the organic electroluminescent element 23 is driven with a predetermined resistance.

  For this reason, a driving method in which the electric resistance of the organic electroluminescent element 23 is constant is a good driving method. Compared with the case where the voltage or current is driven at a predetermined value, a decrease in luminance due to an increase in the electrical resistance of the organic electroluminescent element 23 is prevented, and a variation in luminance tends to be suppressed.

When the driving method in which the electric resistance of the organic electroluminescent element 23 is made constant is adopted, the driving voltage and the driving current are determined by the intersection of the broken line in FIG. 4A and the current-voltage characteristic curve of the organic electroluminescent element 23. Become. As described above, the voltage of the organic electroluminescent device 23 - current characteristic, the continuation of the drive voltage - from current characteristic VI ₁ voltage - for changing the direction of current characteristics VI _2, by the driving method of the electric resistance is constant, The current and voltage for driving the organic electroluminescent element 23 tend to increase.

  As a method for maintaining the electric resistance value of the organic electroluminescent element 23 constant, the voltage or current applied to the organic electroluminescent element 23 is changed as needed based on the electric resistance value acquired by the electric resistance acquiring unit 24, and There is a method of applying to the electroluminescent element 23.

One example is the following method. Here, the electric resistance value to maintain the organic electroluminescent device 23 to a predetermined electric resistance value R _0, the organic light emitting current value applied to the organic light emitting element 23 in step n I _n, the current application of I _n the voltage applied to the element 23 and _{V n.} Further, the current value applied to the organic electroluminescent element 23 in step n + 1 is set to In _{+ 1} . The current value obtained by the following equation can be used as In _{+ 1} (n is an integer).

I _{n + 1} = I _n × R _n / R ₀ = I _n × V _n / (I _n × R ₀ )
By repeating this update of the applied current as needed, it is possible to drive the organic electroluminescent element 23 to keep the electric resistance value constant.

Other methods, from the difference between the resistance value R ₀ of the organic electroluminescent device 23 to maintain the electric resistance value R _n and predetermined resistance value in applying the current value I _n in step n, PID (proportional-integral-derivative There is a method of determining the current value I _{n + 1} at step n + 1 by control. Each parameter of PID control may be determined according to the electrical characteristics of the organic electroluminescent element 23.

The resistance value R ₀ of the organic electroluminescent element 23 maintained at a predetermined resistance value may be determined in advance as a predetermined electric resistance value. Also, R ₀ (= V ₀ / I ₀ ) is determined based on the voltage V ₀ applied to the organic electroluminescent element 23 when the current I ₀ applied in the initial stage is determined and I ₀ is applied. May be. Alternatively, R ₀ (= V ₀ / I ₀ ) is determined based on the current I ₀ applied to the organic electroluminescent element 23 when the voltage V ₀ applied at the initial stage is determined and V ₀ is applied. May be.

  The luminance of the organic electroluminescent element 23 may be controlled based on the resistance value of the organic electroluminescent element 23 in the entire luminance range, but a method of controlling only the maximum luminous luminance based on the resistance value is good. This is one of the driving methods. When control is performed based on the resistance value of the organic electroluminescent element 23 in the entire luminance range, driving may be performed with a resistance value corresponding to desired light emission luminance based on the resistance-luminance characteristics. On the other hand, when only the maximum light emission luminance is controlled based on the resistance value, the current value applied to the organic electroluminescent element 23 based on the current value or voltage value that realizes the maximum light emission luminance for the luminance less than the maximum light emission luminance or The voltage value may be controlled.

  As described above, the driving method of the display device according to the present embodiment is a driving method that compensates for the change in the current-luminance characteristics accompanying the driving of the organic electroluminescent element. The power supply amount is controlled based on this.

In particular, the applied electric power is controlled so that the electric resistance of the organic electroluminescent element becomes constant. In performing driving to keep the electric resistance of the organic electroluminescence device constant predetermined electrical resistance value R _0, the current value I _n in step _n, the voltage applied to the organic electroluminescent device by application of current I _n V _n , and the current value at step n + 1 is I _{n + 1} . Then, it can obtain | require by following Formula as In _{+ 1} .

I _{n + 1} = I _n × R _n / R ₀ = I _n × V _n / (I _n × R ₀ )
This operation can be repeated as necessary to keep the electric resistance value of the organic electroluminescent element constant and minimize the change in luminance over a long period of time.

  According to the above, the reference element and / or pre-determined temporal change data is used in response to the change in the electrical characteristics of the individual organic electroluminescent elements of the display device in which the plurality of organic electroluminescent elements are arranged. Without this, it is possible to drive the organic electroluminescence device with less variation in luminance.

  Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

  First, the first embodiment of the present invention will be described with reference to FIG. This example corresponds to the first embodiment described above.

  FIG. 2 is a block diagram of the display device according to the present embodiment. In the figure, reference numeral 11 denotes a plurality of organic electroluminescent elements (only one is illustrated in the figure), and 11 to 16 denote driving devices for driving the organic electroluminescent elements 11. The drive device includes a voltage detection means 12, a calculation device 13, a storage device 14, and a current supply device 15. Among these, the voltage detection means 12 corresponds to the measurement means of the present invention, and the calculation device 13, the storage device 14, and the current supply device 15 correspond to the correction means of the present invention. The current supply device 15 includes a correction unit 16. In this configuration, the current supply device 15 supplies a current (drive current value) corresponding to the luminance signal to each organic electroluminescent element 11 to control light emission.

  Next, a control procedure (control method) will be described as a method for driving the display device according to the present embodiment. Here, it is assumed that the organic electric field element 11 has an initial characteristic of luminance current efficiency = 2.0 cd / A.

(1) First, a monitor current of 10 mA / cm ² is supplied to the organic electroluminescent element 11 from the current supply device 15, and the drive voltage value v of the organic electroluminescent element 11 is measured by the voltage detection means 12. Then, the measured drive voltage value v is stored in the storage device 14 as data of the organic electroluminescent element 11 as the initial drive voltage value v ₀ .

(2) Next, as a step of degrading the organic electroluminescent element 11, a drive current of 5 mA / cm ² is passed through the organic electroluminescent element 11 in all the pixels and lighted for 1 hour (predetermined time).

(3) After lighting for 1 hour, in order to monitor the deterioration amount, a monitor current of 10 mA / cm ² is supplied to the organic electroluminescent element 11 as in (1), and the driving voltage of each organic electroluminescent element is detected by the voltage detecting means 12. The value v is measured.

(4) Next, transfer the measured drive voltage value v to the computing device 13 calculates a difference v ₀ -v the initial driving voltage value v _0, which is the storage device in the storage device 14, increase the driving voltage V.

  (5) Next, the luminance current efficiency η is calculated by the calculation device 13 using the above-described increased drive voltage value V according to the above-described equation 1.

  (6) Next, the luminance current efficiency η is sent to the correction unit 16 provided in the current supply device 15 and multiplied by 1 / η to correct the drive current value.

  (7) Then, the drive current value multiplied by 1 / η is supplied from the current supply device 15 to the organic electroluminescent element 21 to be lit. Thereafter, the lighting is continued while repeating the same steps.

  By performing such drive control, the organic electroluminescent element 11 can maintain the initial luminance because the drive current corresponding to the deterioration amount is supplied, and can prevent burn-in as a result.

  Next, a second embodiment of the present invention will be described. This example also corresponds to the first embodiment described above in the same manner as the first example.

  In the present embodiment, combination data of the rising drive voltage value V and the luminance current efficiency decrease rate η measured in advance is stored in the storage device 14 of the block diagram shown in the first embodiment. Then, similarly to the first embodiment, the increased drive voltage value V of the organic electroluminescent element 11 is obtained, and the calculation device 13 collates with the previous combination data to determine the luminance current efficiency decrease rate η. Thereafter, the drive with the drive current value corrected is performed as in the first embodiment.

  Also in this embodiment, by performing such drive control, the organic electroluminescent element can be supplied with a drive current commensurate with the amount of deterioration, so that the initial luminance can be maintained, and as a result, burn-in can be prevented.

  Next, a third embodiment of the present invention will be described. This example corresponds to the second embodiment described above.

  The display device using the organic electroluminescent element according to the present embodiment shown in FIG. 3 includes a drive circuit unit 21, a power feeding circuit 22, and an electrical resistance acquisition unit 24 in one organic electroluminescent element 23, and an electrical resistance acquisition unit. 24 is a display device that reflects the information acquired by 24 on the drive circuit unit 21.

The organic electroluminescent element 23 is manufactured on a substrate by a known material, element configuration, and manufacturing method. A glass substrate having a thickness of 1 mm is used as the substrate. As the electrode, a silver electrode is formed on the substrate side by vapor deposition, an organic layer including a layer that emits light by applying current is formed thereon by vapor deposition, an ITO electrode is formed thereon by sputtering, and a protective film is formed thereon. To form an organic electroluminescent element 23. The area of the organic electroluminescent element 23 is 1 mm ² .

  A computer having an interface capable of communicating with the power supply circuit 22 and the electrical resistance acquisition unit 24 is used as the drive circuit unit 21. A current source is used as the power feeding circuit 22 and a current is generated based on an instruction from the drive circuit unit 21. A voltmeter is used as the electrical resistance acquisition unit 24 to measure the voltage applied to the organic electroluminescent element 23. The voltage applied to the organic electroluminescent element 23 acquired by the electrical resistance acquisition unit 24 is transmitted to the drive circuit unit 21 through the interface with the drive circuit unit 21. The drive circuit unit 21 determines a current value to be applied to the organic electroluminescent element 23 based on information from the electrical resistance acquisition unit 24.

  The method of controlling the applied current amount is as follows.

Voltage across a predetermined value to maintain the electric resistance value of the organic electroluminescent element 23 in R _0, the organic electroluminescent device 23 by application of current I _n, I _n the current value applied to the organic light emitting element 23 in step n It is referred to as _{V n.} Further, the current value applied to the organic electroluminescent element 23 in step n + 1 is set to In _{+ 1} . Then, the current value obtained by the following equation is used as In _{+ 1} .

I _{n + 1} = I _n × R _n / R ₀ = I _n × V _n / (I _n × R ₀ )
This operation is repeated as needed to drive the organic electroluminescent element 23 so as to keep the electric resistance value constant.

When driving is performed with R ₀ = 5 kΩ in this embodiment, the light emission luminance of the organic electroluminescent element 23 is maintained for a long time.

  Next, a fourth embodiment of the present invention will be described with reference to FIG. This example also corresponds to the above-described second embodiment as in the third example.

  The display device using the organic electroluminescent element according to the present embodiment shown in FIG. 5 has organic electroluminescent elements 23 arranged in a matrix on the display device.

In this embodiment, a 3 × 3 organic electroluminescent element 23 is arranged on a substrate, and a drive circuit unit 21, a power feeding circuit 22, and an electric resistance acquisition unit 24 are further arranged and wired. As the substrate, glass having a thickness of 1 mm is used. The organic electroluminescent element 23 is produced by vapor deposition using a known material. As for the electrodes, the electrode on the substrate side is made of silver and the opposite electrode is made of ITO. The area of the organic electroluminescent element 23 is 1 mm ² .

  The drive circuit unit 21 is arranged on two opposite sides of the display device, wirings are arranged from the drive circuit unit 21 in the x-axis direction and the y-axis direction of the display device, and a switch circuit 25 is arranged at the intersection. As the switch circuit 25, a TFT is manufactured by a known method.

  Each switch circuit 25 is connected to a power supply circuit 22 connected to each organic electroluminescence element 23, and has a structure for transmitting a drive signal of the drive circuit unit 21 to the power supply circuit 22 through the switch circuit 25. The power feeding circuit 22 arranged for each organic electroluminescent element 23 applies power to the organic electroluminescent element 23 based on the drive signal. At the same time, the electric resistance acquisition unit 24 acquires the electric resistance of the organic electroluminescent element 23 while the power feeding circuit 22 applies power to the organic electroluminescent element 23.

  As a method for obtaining the electrical resistance, a resistor having a known electrical resistance value is arranged in series with the organic electroluminescent element 23, the voltage applied to the resistor and the organic electroluminescent element 23 is read, and the organic electroluminescent element 23 is read from the ratio. The electrical resistance value of is to be obtained. The resistance value of the resistor is 1 kΩ.

  The electrical resistance acquisition unit 24 is disposed for each organic electroluminescent element 23. Information on the electrical resistance value acquired by the electrical resistance acquisition unit 24 is transmitted to the power feeding circuit 22 connected to the same organic electroluminescent element 23.

  The power feeding circuit 22 is configured to control the amount of power applied to the organic electroluminescent element 23 based on the information on the electrical resistance value. The method for controlling the amount of applied power is as follows.

Voltage across a predetermined value to maintain the electric resistance value of the organic electroluminescent element 23 in R _0, the organic electroluminescent device 23 by application of current I _n, I _n the current value applied to the organic light emitting element 23 in step n It is referred to as _{V n.} Further, the current value applied to the organic electroluminescent element 23 in step n + 1 is set to In _{+ 1} . Then, the current value obtained by the following equation is used as In _{+ 1} .

I _{n + 1} = I _n × R _n / R ₀ = I _n × V _n / (I _n × R ₀ )
This operation is repeated as needed to drive the organic electroluminescent element 23 so as to keep the electric resistance value constant.

When driving is performed with R ₀ = 5 kΩ in this embodiment, the light emission luminance of the organic electroluminescent element 23 is maintained for a long time.

  The display device driving method and driving device using the organic electroluminescent element according to the present invention can prevent burn-in even when lit for a long time, and thus can be widely applied to flat panel displays, projection displays, and the like. . In addition, the display device using the organic electroluminescence device according to the present invention may be used for a television, a personal digital assistant, a mobile phone, a monitor of a digital camera / digital video camera, and the like.

5 is a graph showing changes in light emission luminance and drive voltage when the organic electroluminescent element is driven at a constant current in the method for driving a display device according to the first exemplary embodiment of the present invention. It is a block diagram explaining an example of the structure of the display apparatus which concerns on the 1st Example corresponding to the 1st Embodiment of this invention, and its organic electroluminescent element drive method. It is a block diagram which shows the structure of the display apparatus which concerns on the 3rd Example corresponding to the 2nd Embodiment of this invention. (A) is a graph which shows the example of the voltage-current characteristic of the organic electroluminescent element concerning this invention, (b) is a graph which shows the example of the resistance-luminance characteristic of the organic electroluminescent element concerning this invention. It is a block diagram which shows the structure of the display apparatus which concerns on the 4th Example corresponding to the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Organic electroluminescent element 12 Voltage detection means 13 Calculation apparatus 14 Memory | storage device 15 Current supply apparatus 16 Correction | amendment part 21 Drive circuit part 22 Feeding circuit 23 Organic electroluminescent element 24 Electrical resistance acquisition part 25 Switch circuit

Claims (14)

A driving method of a display device including a plurality of organic electroluminescent elements,
Driving a display device, characterized by comprising steps of measuring a voltage with respect to a predetermined current value for each of the plurality of organic electroluminescent elements and correcting a driving current value according to a change in the voltage after an initial period of time and a predetermined time elapse. Method.   The step of correcting the drive current value calculates a luminance current efficiency from the measured change in the voltage according to a predetermined calculation formula, and determines a correction amount of the drive current value using the calculated luminance current efficiency. The display device driving method according to claim 1.   The step of correcting the drive current value selects a luminance current efficiency in accordance with correspondence information measured in advance from the measured change in the voltage, and uses the selected luminance current efficiency to correct the drive current value The method of driving a display device according to claim 1, wherein: A display device having a plurality of organic electroluminescent elements and a driving device for driving the plurality of organic electroluminescent elements,
The driving device includes a measuring unit that measures a voltage with respect to a predetermined current value for each of the plurality of organic electroluminescent elements after an initial period and a predetermined time, and a correcting unit that corrects the driving current value according to the change in the measured voltage. And a display device.   The correction means calculates a luminance current efficiency from the measured change in voltage according to a predetermined calculation formula, and determines the correction amount of the drive current value using the calculated luminance current efficiency. The display device according to claim 4.   The correction means selects a luminance current efficiency from the measured change in the voltage according to correspondence information measured in advance, and determines a correction amount of the drive current value using the selected luminance current efficiency. The display device according to claim 4, characterized in that: An organic electroluminescent element that emits light when a current is applied;
A power feeding circuit for feeding power to the organic electroluminescent element;
A drive circuit unit that instructs the power supply circuit to supply power;
A driving method of a display device that controls by changing a power supply amount to the organic electroluminescent element based on a change in an electrical characteristic value of the organic electroluminescent element,
A method for driving a display device, comprising: obtaining an electrical resistance of the organic electroluminescent element as the electrical characteristic value, and controlling the power supply amount based on the obtained electrical resistance. The organic electroluminescent element is composed of a plurality of organic electroluminescent elements,
The display device includes an electrical resistance value acquisition unit that acquires electrical resistance values of the plurality of organic electroluminescent elements,
The method for driving a display device according to claim 7, wherein the step of controlling the amount of power supply controls the amount of power supplied to the organic electroluminescent element based on an output of the electrical resistance value acquisition unit.   The step of controlling the amount of power supply is controlled so as to obtain a maximum light emission luminance of the organic electroluminescent element by driving control for maintaining an electric resistance value of the organic electroluminescent element at a predetermined value. 8. A method for driving the display device according to 7.   The step of controlling the amount of power supply is a control for setting the maximum light emission luminance of the organic electroluminescent element by drive control for reducing the electric resistance value of the organic electroluminescent element in accordance with a change in electrical characteristics of the organic electroluminescent element. The method for driving a display device according to claim 7, wherein: An organic electroluminescent element that emits light when a current is applied;
A power feeding circuit for feeding power to the organic electroluminescent element;
A drive circuit unit that instructs the power supply circuit to supply power;
A display device that controls the amount of power supplied to the organic electroluminescent element by changing the electrical characteristic value of the organic electroluminescent element.
A display device comprising: a control unit that acquires an electrical resistance of the organic electroluminescent element as the electrical characteristic value and controls the amount of power supply based on the acquired electrical resistance. The organic electroluminescent element is composed of a plurality of organic electroluminescent elements,
The control means includes an electrical resistance value acquisition unit that acquires an electrical resistance value of each of the plurality of organic electroluminescence elements, and controls an amount of power supplied to the organic electroluminescence element based on an output of the electrical resistance value acquisition unit. The display device according to claim 11, wherein the display device is controlled.   The control unit according to claim 11, wherein the control unit performs control to obtain a maximum light emission luminance of the organic electroluminescent element by driving control that maintains an electric resistance value of the organic electroluminescent element at a predetermined value. Display device.   The control means performs control to achieve the maximum light emission luminance of the organic electroluminescent element by driving control to reduce the electric resistance value of the organic electroluminescent element in accordance with a change in electrical characteristics of the organic electroluminescent element. The display device according to claim 11, wherein the display device is characterized.

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