JP3883890B2 - Luminance control method and luminance control circuit for organic EL display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a luminance control method and a luminance control circuit for an organic electroluminescence (organic EL) display.
[0002]
[Prior art]
Organic EL displays include a passive type having a simple matrix structure and an active type using TFTs.
[0003]
FIG. 1 shows a basic pixel configuration of an active organic EL display.
[0004]
A circuit for one pixel of the active type organic EL display includes a switching TFT 101, a capacitor 102, a driving TFT 103, and an organic EL element 104.
[0005]
A display signal Data (Vin) is applied to the drain of the switching TFT 101 via the display signal line 111. A selection signal SCAN is applied to the base of the switching TFT 101 via a selection signal line 112. The source of the switching TFT 101 is connected to the base of the driving TFT 103 and grounded via the capacitor 102.
[0006]
A drive power supply voltage Vdd is applied to the drain of the drive TFT 103 via the power supply line 113. The source of the driving TFT 103 is connected to the anode of the organic EL element 104. The cathode of the organic EL element 104 is grounded.
[0007]
The switching TFT 101 is ON / OFF controlled by a selection signal SCAN. The capacitor 102 is charged by a display signal Data (Vin) supplied via the switching TFT 101 when the switching TFT 101 is on. When the switching TFT 101 is off, the charging voltage is held. The driving TFT 103 supplies a current corresponding to the holding voltage of the capacitor 102 applied to the base to the organic EL element 104.
[0008]
FIG. 2 shows the relationship between the display signal Data (Vin) and the light emission luminance (drive current) of the organic EL element 104 in the basic pixel configuration shown in FIG.
[0009]
In FIG. 2, RefW represents a white side reference voltage for defining the light emission luminance with respect to the white level of the input signal, and RefB represents a black side reference voltage for defining the light emission luminance with respect to the black level of the input signal. .
[0010]
[Problems to be solved by the invention]
By the way, in the active organic EL display as described above, a large current flows through the organic EL element 104 in an image with a bright entire screen. When a large current flows through the organic EL element 104, power consumption increases. Further, if a large current continues to flow through the organic EL element 104, the performance thereof is accelerated. Therefore, when an organic EL display is used over a long period of time, the organic EL element deteriorates and the light emission luminance decreases.
[0011]
In a color organic EL display, one pixel is composed of three types of organic EL elements (R light emitting element, G light emitting element, and B light emitting element) that respectively emit RGB light. In such a color organic EL display, due to the type of the light emitting element for each RGB used in the color organic EL display, the deterioration rate of light emission luminance over time between the light emitting elements for each RGB (for example, the light emitting element is continuously changed). In many cases, there is variation in the emission luminance reduction rate after elapse of a predetermined time.
[0012]
In the present invention, when there is a variation in the temporal deterioration rate of light emission luminance among the light emitting elements for each RGB due to the types of RGB light emitting elements used in the organic EL display, the organic EL display An object of the present invention is to provide a luminance control method and a luminance control circuit for an organic EL display capable of extending the lifetime of the display.
[0013]
[Means for Solving the Problems]
According to the first aspect of the present invention, in the luminance control method of the organic EL display, the RGB input signal integrated values for all pixels or pixels in a predetermined area are calculated for each screen based on the digital video input signal, A first step of calculating a value obtained by adding the RGB integrated values at a predetermined ratio or a value equal to the value as an RGB weighted addition value for each screen, and converting the digital video input signal into an analog video output signal For controlling the amplitude of the analog video output signal by controlling the reference voltage supplied to the DA converter for controlling based on the RGB weighted addition value for each screen calculated in the first step. A second step of supplying an analog video output signal to the organic EL display is provided.
[0014]
According to a second aspect of the present invention, in the first aspect of the invention, in the second step, the amplitude of the analog video output signal is small when the RGB weighted addition value of one screen unit calculated in the first step is large. As described above, the amplitude of the analog video output signal is controlled.
[0016]
According to a third aspect of the present invention, in the second aspect of the present invention, the reference voltage supplied to the DA converter includes a black-side reference voltage and an input signal for defining light emission luminance with respect to the black level of the input signal. And the white side reference voltage for defining the light emission luminance with respect to the white level of the white level. In the second step, the white side reference voltage is controlled based on the RGB weighted addition value of one screen unit calculated in the first step. It is characterized by that.
[0017]
According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the ratio used for calculating the RGB weighted addition value for one screen unit is an R light emitting element or G light emitting element included in the organic EL display. Of the elements and the B light emitting elements, the ratio corresponding to the emission color of the light emitting element, which is assumed to have a fast deterioration rate of the light emission luminance with time, is set to a larger value.
[0018]
The invention according to claim 5, the luminance control circuit of an organic EL display, based on the input-output characteristics defined by a given reference voltage, converts the digital image input signal to an analog Film image output signal, A DA converter to be supplied to the organic EL display and a reference voltage control circuit for controlling a reference voltage supplied to the DA converter based on a digital video input signal are provided. based on the signals, for each screen, calculates the input signal integrated value of RGB respectively with respect to pixels of all the pixels or the predetermined region, the equalization value to the value of the RGB integrated value obtained by adding a predetermined ratio or said value Calculated by an RGB weighted addition value calculation circuit and an RGB weighted addition value calculation circuit that are calculated as RGB weighted addition values per screen. Based on the RGB weighted sum of each screen was, characterized in that it comprises a voltage regulating circuit for controlling a reference voltage supplied to the DA converter.
[0019]
According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the reference voltage supplied to the DA converter includes a black-side reference voltage for defining the light emission luminance with respect to the black level of the input signal, and an input A white side reference voltage for defining the light emission luminance with respect to the white level of the signal, and the voltage adjustment circuit determines the white side reference voltage based on the RGB weighted addition value for each screen calculated by the RGB weighted addition value calculation circuit. It is characterized by controlling.
[0020]
According to a seventh aspect of the present invention, in the sixth aspect of the present invention, when the voltage adjustment circuit has a large RGB weighted addition value per screen calculated by the RGB weighted addition value calculation circuit, The white-side reference voltage is controlled so that the light emission luminance with respect to the level is lowered.
[0021]
According to an eighth aspect of the present invention, the voltage adjustment circuit according to any of the sixth to seventh aspects of the invention is based on the RGB weighted addition value for each screen calculated by the RGB weighted addition value calculation circuit. A gain calculation circuit that calculates a gain for controlling the voltage, and a control circuit that controls the white-side reference voltage based on the gain calculated by the gain calculation circuit are provided.
[0022]
The invention according to claim 9 is the invention according to claim 8 , wherein the gain calculation circuit sets the output gain to a constant value when the input RGB weighted addition value for each screen is equal to or less than a predetermined value. When the input RGB weighted addition value per screen exceeds a predetermined value, the input circuit has an input / output characteristic that decreases the output gain as the input RGB weighted addition value per screen increases. The white-side reference voltage is controlled so that the light emission luminance with respect to the white level of the input signal decreases as the gain decreases.
[0023]
According to a tenth aspect of the present invention, in the inventions according to the fifth to ninth aspects, the ratio used for calculating the RGB weighted addition value for one screen unit is an R light emitting element or G light emitting element included in the organic EL display. Of the elements and the B light emitting elements, the ratio corresponding to the emission color of the light emitting element, which is assumed to have a fast deterioration rate of the light emission luminance with time, is set to a larger value.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
[0025]
FIG. 3 shows the configuration of the luminance control circuit of the organic EL display.
[0026]
The luminance control circuit of the organic EL display includes a reference voltage control circuit 1 and a DAC 2. The digital video input signals R_in, G_in, and B_in are sent to the reference voltage control circuit 1 and to the DAC 2. The reference voltage control circuit 1 controls the reference voltage supplied to the DAC 2. The reference voltages supplied to the DAC 2 include black reference voltages R_RefB, G_RefB, B_RefB (referred to collectively as RefB) and white reference voltages R_RefW, R, G, B respectively. G_RefW, B_RefW (When referring to these, they are described as RefW).
[0027]
The black side reference voltage RefB is a reference voltage for defining the light emission luminance with respect to the black level of the input signal, and is fixed in this embodiment. The white side reference voltage RefW is a reference voltage for defining the light emission luminance with respect to the white level of the input signal, and is controlled by the reference voltage control circuit 1 in this embodiment.
[0028]
The DAC 2 analogizes the digital video input signals R_in, G_in, and B_in based on input / output characteristics defined by the black-side reference voltage RefB and the white-side reference voltage RefW ′ supplied from the reference voltage control circuit 1. Video output signals R_out, G_out, and B_out are converted. Analog video output signals R_out, G_out, and B_out obtained by the DAC 2 are supplied to the organic EL display 3. The analog video output signals R_out, G_out, and B_out correspond to the display signal Data (Vin) in FIG.
[0029]
The reference voltage control circuit 1 includes three multipliers 11, 12, 13, one adder 14, an integration circuit 15, a gain calculation circuit 16, a reference voltage adjustment circuit (Ref voltage adjustment circuit) 17, and a plurality of DACs 18 to 23. I have.
[0030]
The multiplier 11 multiplies the digital video input signal R_in by a weighted addition coefficient K _R for each pixel. The multiplier 12 multiplies the weighted-addition coefficient K _G for each pixel in the digital video input signal G _in. The multiplier 13 multiplies the weighted-addition coefficient K _B for each pixel in the digital image input signal B _in.
The adder 14 adds the output signals of the multipliers 11, 12, and 13 for each pixel. The integration circuit 15 calculates an integrated value of the output signal of the adder 14 (hereinafter referred to as an RGB weighted addition value for each frame) for each frame. The gain calculation circuit 16 calculates a gain Gain for controlling the white side reference voltage RefW according to the size of the RGB weighted addition value for each frame obtained from the integration circuit 15. 4A and 4B show examples of input / output characteristics of the gain calculation circuit 16, that is, gain characteristics with respect to RGB weighted addition values in units of one frame.
[0031]
In the characteristic of FIG. 4A, the gain is 1.00 until the RGB weighted addition value in units of one frame is 0 to a, and when the RGB weighted addition value in one frame unit exceeds a, the gain gradually decreases. Yes. In the characteristic of FIG. 4B, the gain is 1.00 when the RGB weighted addition value in units of one frame is 0 to b, and the gain gradually decreases until the RGB weighted addition value in units of one frame is b to c. When the RGB weighted addition value in units of one frame exceeds c, the gain decreases slightly abruptly.
[0032]
The reference voltage adjustment circuit 17 is set in advance for each of R, G, and B, a black reference voltage (hereinafter referred to as a reference black side reference voltage) R_RefB, G_RefB, B_RefB, and R, G, B. The adjusted white-side reference voltages (hereinafter referred to as reference white-side reference voltages) R_RefW, G_RefW, B_RefW and the gain Gain calculated by the gain calculation circuit 16 are adjusted for each of R, G, and B. White side reference voltages R_RefW ', G_RefW', B_RefW 'are generated.
[0033]
Each reference black side reference voltage R_RefB, G_RefB, B_RefB and each reference white side reference voltage R_RefW, G_RefW, B_RefW are given as digital signals.
[0034]
The reference voltage adjustment circuit 17 includes reference voltage adjustment circuits for R, G, and B. Since the respective configurations are the same, the reference voltage adjustment circuit for R 1 will be described here.
[0035]
FIG. 5 shows a reference voltage adjustment circuit for R 1.
[0036]
The reference voltage adjusting circuit includes a subtracter 31, a multiplier 32, and a subtracter 33.
[0037]
The subtractor 31 calculates the difference (R_RefB−R_RefW) between the reference black side reference voltage R_RefB for R 1 and the reference white side reference voltage R_RefW for R 1. The multiplier 32 multiplies the output (R_RefB−R_RefW) of the subtractor 31 by the gain Gain. The subtractor 33 calculates the adjusted white-side reference voltage R_RefW ′ by subtracting the output (Gain × (R_RefB−R_RefW)) of the multiplier 32 from the reference black-side reference voltage R_RefB.
[0038]
When the gain Gain is 1.00, the adjusted white-side reference voltage R_RefW ′ is equal to the reference white-side reference voltage R_RefW. Then, the smaller the gain Gain, that is, the larger the RGB weighted addition value in one frame unit, the larger the adjusted white side reference voltage R_RefW ′ and the closer to the reference black side reference voltage R_RefB side. That is, as the RGB weighted addition value for each frame increases, the light emission luminance (drive current) of the organic EL element with respect to the white level of the input signal decreases.
[0039]
The reference black side reference voltages R_RefB, G_RefB, and B_RefB are converted into analog signals by the DACs 18, 19, and 20 and supplied to the DAC2. The adjusted white-side reference voltages R_RefW ′, G_RefW ′, and B_RefW ′ are converted into analog signals by the DACs 21, 22, and 23 and supplied to the DAC 2.
[0040]
FIG. 6 shows the input / output characteristics of the DAC 2.
[0041]
In FIG. 6, RefW′1 represents the white side reference voltage (= reference white side reference voltage RefW) supplied to the DAC 2 when the RGB weighted addition value in units of one frame is small. RefW′3 indicates the white-side reference voltage supplied to the DAC 2 when the RGB weighted addition value per frame is large. RefW′2 represents the white-side reference voltage supplied to the DAC 2 when the RGB weighted addition value for each frame is an intermediate value.
[0042]
When the white-side reference voltage supplied to the DAC 2 is RefW′1, the input / output characteristics of the DAC 2 are characteristics indicated by the straight line L1. In this case, when an input signal that changes from the black level to the white level is periodically input to the DAC 2, an output waveform as shown by the curve S1 is obtained.
[0043]
When the white-side reference voltage supplied to the DAC 2 is RefW′3, the input / output characteristics of the DAC 2 are characteristics indicated by a straight line L3. In this case, when an input signal that changes from the black level to the white level is periodically input to the DAC 2, an output waveform as shown by the curve S3 is obtained.
[0044]
When the white-side reference voltage supplied to the DAC 2 is RefW′2, the input / output characteristics of the DAC 2 are characteristics indicated by the straight line L2. In this case, when an input signal that changes from the black level to the white level is periodically input to the DAC 2, an output waveform as shown by the curve S2 is obtained.
[0045]
That is, it can be seen that the amplitude of the output signal of the DAC 2 is controlled by controlling the white side reference voltage according to the RGB weighted addition value in units of one frame.
[0046]
By the way, in the organic EL display 3, one pixel is composed of three types of organic EL elements each emitting RGB. Such an organic EL display 3 includes organic EL elements (R light emitting element, G light emitting element, B light emitting element) for light emission of each color of RGB. In such an organic EL display 3, due to the type of light emitting element for each RGB used in the organic EL display 3, the deterioration rate of light emission luminance with time between the light emitting elements for each RGB (for example, the light emitting elements are continuously used). In many cases, there is variation in the emission luminance reduction rate after elapse of a predetermined time.
[0047]
In such a case, the weighted addition numbers K _R , K _G , and K _B given to the multipliers 11, 12, and 13 correspond to the colors of the light-emitting elements that have a fast deterioration rate with time (short lifetime). By setting a larger value, the life of the organic EL display 3 can be extended.
[0048]
For example, a case is assumed where the light emission luminance deterioration rates with time of each of the R light emitting element, the G light emitting element, and the B light emitting element are as shown in FIG.
[0049]
The time-dependent deterioration rate of the emission luminance of each of the R light emitting element, the G light emitting element, and the B light emitting element is, for example, in a state where each of the R light emitting element, the G light emitting element, and the B light emitting element is continuously lit at 100% white. The emission luminance deterioration ratio of each RGB light emitting element after 10,000 hours (emission luminance after 10,000 hours with respect to the initial emission luminance) ΔR (%), ΔG (%), ΔB (%) is obtained.
[0050]
In this example, ΔR>ΔG> ΔB, the light emission luminance degradation rate of the R light emitting element with time is the fastest, the light emission luminance deterioration time with time of the B light emitting element is the slowest, and the light emission luminance of the G light emitting element with time. The degradation rate is between them. The weighted addition numbers K _R , K _G , and K _B are determined by the following equation (1).
[0051]
K _R = ΔR / (ΔR + ΔG + ΔB)
K _G = ΔG / (ΔR + ΔG + ΔB)
K _B = ΔB / (ΔR + ΔG + ΔB) (1)
[0052]
When ΔR>ΔG> ΔB, K _R = 1 and K _G = K _B = 0.0 may be set. When the weighted addition numbers K _R , K _G , and K _B are set in this way, the RGB weighted addition value for each frame is larger when the input image is a red video image that causes the R light emitting element to emit light strongly. The gain Gain decreases, the adjusted white side reference voltage R_RefW ′ increases, and the light emission luminance (drive current) of the light emitting element with respect to the white level of the input signal of each color decreases. That is, the entire screen becomes dark. For this reason, it is possible to slow down the deterioration rate with time of the R light emitting element. As a result, the lifetime of the organic EL display can be extended.
[0053]
Even in this case, since the white side reference voltage is adjusted by the same gain Gain for the RGB signals, the hue does not change and only the brightness of the entire screen changes. Also, since the amplitude of the video input signal is controlled by controlling the reference voltage at the time of DA conversion, the gradation does not decrease. Furthermore, since the amplitude control of the video input signal (display signal) is performed by feedforward control, hunting does not occur.
[0054]
The output signals of the multipliers 11, 12, and 13 may be added for each frame, and the addition result may be added to calculate an RGB weighted addition value for each frame. Also, the input signals R_in, G_in, and B_in are integrated for each frame, and the obtained R integrated value, G integrated value, and B integrated value for each frame are respectively added to the corresponding weighted addition coefficients K _R , An RGB weighted addition value for each frame may be calculated by multiplying K _G and K _B and adding the multiplication results.
[0055]
【The invention's effect】
According to this invention, due to the type of RGB light emitting elements used in the organic EL display, when there is a variation in the temporal deterioration rate of the light emission luminance among the light emitting elements for each of the RGB, The lifetime of the organic EL display can be extended.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a basic pixel configuration of an active organic EL display.
FIG. 2 is a graph showing a relationship between a display signal Data (Vin) and light emission luminance (drive current) of an organic EL element in the basic pixel configuration shown in FIG.
FIG. 3 shows a configuration of a luminance control circuit of an organic EL display according to an embodiment of the present invention.
FIG. 4 is a graph showing an example of input / output characteristics of the gain calculation circuit 16;
FIG. 5 is a circuit diagram showing a reference voltage adjustment circuit for R;
FIG. 6 is a graph showing input / output characteristics of DAC2.
FIG. 7 is a graph showing an example of how to determine the rate of deterioration with time of the emission luminance of each of the R light emitting element, the G light emitting element, and the B light emitting element.
[Explanation of symbols]
1 Reference voltage control circuit 2 DAC
3 Organic EL Display 11, 12, 13 Multiplier 14 Adder 15 Integration Circuit 16 Gain Calculation Circuit 17 Reference Voltage Adjustment Circuit (Ref Voltage Adjustment Circuit)

Claims (10)

In the method of controlling the brightness of an organic EL display,
Based on the digital video input signal, 1 for each screen, it calculates the respective input signal integrated value RGB for a pixel for all the pixels or the predetermined region, equalizing the RGB integrated value value or said value added at a predetermined ratio A first step of calculating a correct value as an RGB weighted addition value for each screen, and
By controlling the reference voltage supplied to the DA converter for converting the digital video input signal into the analog video output signal based on the RGB weighted addition value calculated in the first step, A second step of controlling the amplitude of the output signal and supplying the analog video output signal after the amplitude control to the organic EL display;
A method for controlling the brightness of an organic EL display. The second step, as the amplitude of the analog video output signal when RGB weighted addition value of each screen calculated by the first step is large is small, and controlling the amplitude of the analog video output signal The brightness | luminance control method of the organic electroluminescent display of Claim 1. The reference voltage supplied to the DA converter includes a black side reference voltage for defining the light emission luminance with respect to the black level of the input signal and a white side reference voltage for defining the light emission luminance with respect to the white level of the input signal. 3. The luminance control method for an organic EL display according to claim 2 , wherein the second step controls the white-side reference voltage based on the RGB weighted addition value for each screen calculated in the first step. 4. . The ratio used to calculate the RGB weighted addition value for one screen unit is assumed to have a fast deterioration rate of the emission luminance with time among the R light emitting element, G light emitting element and B light emitting element included in the organic EL display. luminance control method for an organic EL display according to any one of claims 1, 2 or 3, characterized in that it is set to a larger value as the ratio corresponding to the emission colors of the light emitting element that. In the luminance control circuit of the organic EL display,
Based on the input-output characteristics defined by a given reference voltage, converts the digital image input signal to an analog Film image output signal, and a DA converter supplied to the organic EL display, based on the digital video input signal And a reference voltage control circuit for controlling a reference voltage supplied to the DA converter, and the reference voltage control circuit applies to all pixels or pixels in a predetermined area for each screen based on the digital video input signal. An RGB weighted addition value calculation circuit that calculates an input signal integration value for each of RGB and calculates a value obtained by adding the RGB integration values at a predetermined ratio or a value equal to the value as an RGB weighted addition value for each screen. Based on the RGB weighted addition value for each screen calculated by the RGB weighted addition value calculation circuit. Brightness control circuit of the organic EL display which is characterized by comprising a voltage regulating circuit for controlling the Arensu voltage. The reference voltage supplied to the DA converter includes a black side reference voltage for defining the light emission luminance with respect to the black level of the input signal and a white side reference voltage for defining the light emission luminance with respect to the white level of the input signal. 6. The organic EL display according to claim 5 , wherein the voltage adjustment circuit controls the white side reference voltage based on the RGB weighted addition value for each screen calculated by the RGB weighted addition value calculation circuit. Brightness control circuit. The voltage adjustment circuit controls the white-side reference voltage so that the emission luminance with respect to the white level of the input signal is low when the RGB weighted addition value for each screen calculated by the RGB weighted addition value calculation circuit is large. The luminance control circuit for an organic EL display according to claim 6 . The voltage adjustment circuit is calculated by a gain calculation circuit and a gain calculation circuit that calculate a gain for controlling the white side reference voltage based on the RGB weighted addition value of one screen unit calculated by the RGB weighted addition value calculation circuit. was based on the gain, the luminance control circuit of the organic EL display according to claim 6 or claim 7, characterized in that it comprises a control circuit for controlling the white-side reference voltage. The gain calculation circuit sets the output gain to a constant value when the input RGB weighted addition value for one screen unit is less than or equal to a predetermined value, and when the input RGB weighted addition value for one screen unit exceeds the predetermined value. Has an input / output characteristic in which the output gain is reduced as the RGB weighted addition value in one screen unit is increased, and the control circuit is configured such that the emission luminance with respect to the white level of the input signal decreases as the gain decreases. 9. The brightness control circuit for an organic EL display according to claim 8 , wherein the brightness control circuit controls a white side reference voltage. The ratio used to calculate the RGB weighted addition value for one screen unit is assumed to have a fast deterioration rate of the emission luminance with time among the R light emitting element, G light emitting element and B light emitting element included in the organic EL display. brightness control circuit of the organic EL display according to any one of claims 6, 7, 8 or 9, characterized in that it is set to a larger value as the ratio corresponding to the emission colors of the light emitting element that.

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