JP2016109913A - Display device, display method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of a pseudo contour and correct the amount of luminescence of a luminous element for each pixel according to a deterioration amount of the luminous element.SOLUTION: A display device comprises a pixel circuit arranged in a matrix form, the pixel circuit including a luminous element emitting light at brightness corresponding to a current amount, an optical sensor for detecting brightness of light emitted from the luminous element and a compensation control circuit for controlling a current amount supplied to the luminous element on the basis of an applied second voltage and the detection result of the optical sensor, in a light emission period of the luminous element, within a second period different from a first period of a predetermined length for always emitting light at brightness corresponding to a first voltage of controlling brightness of the luminous element.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a display device, a display method, and a program.

  In recent years, as a display device, a flat type display device in which pixels including self-luminous elements such as organic EL (Organic Electro-Luminescence) elements are arranged in a matrix is provided. ing.

JP 2001-524090 A JP 2006-506307 A

  On the other hand, it is known that a self-luminous element such as an organic EL element (hereinafter sometimes simply referred to as “light-emitting element”) has a characteristic that it deteriorates in proportion to its light emission luminance and light emission time. ing. The content of the image displayed on the display device is not uniform, and therefore, the deterioration of the light emitting element (organic EL element) also varies. For example, a light emitting element displaying a high brightness color such as white tends to easily deteriorate compared to a light emitting element displaying a low brightness color such as black.

  As the deterioration of the light-emitting element proceeds, the luminance of the light-emitting element tends to be relatively lowered as compared with other light-emitting elements whose progress of deterioration is slow. As a result, for example, when a uniform pattern is displayed after a certain pattern is displayed for a long time, a phenomenon may occur in which the pattern remains and is visually recognized. Such a phenomenon is generally known as “image sticking”.

  An example of a technique for reducing variation in luminance between pixels due to such deterioration of a light emitting element is disclosed in Patent Document 1. That is, in the technique disclosed in Patent Document 1, a part of light from the light emitting element is received by a photodiode provided in the pixel circuit, and the amount of current supplied to the light emitting element is controlled based on the light reception result. Thus, the luminance deterioration of the light emitting element is compensated. However, in the technique according to Patent Document 1, a transistor for controlling the amount of current supplied to the light emitting element is operated in a saturation region. Therefore, the operation is unstable due to the influence of the characteristic variation of the transistor. There is a case.

  As another example, in Patent Document 2, a part of light from a light emitting element is received by a photodiode provided in a pixel circuit, and a light emission time (duty ratio) of the light emitting element is controlled based on a light reception result. Thus, a technique for compensating for luminance deterioration of the light emitting element is disclosed. However, since the technique according to Patent Document 2 is a driving method that controls the light emission amount of the light emitting element by controlling the duty ratio at the time of light emission, a contour that is not originally displayed is observed when displaying a moving image. In other words, a so-called pseudo contour may occur.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to suppress the generation of pseudo contours and to perform the light emission according to the deterioration amount of the light emitting element for each pixel. An object of the present invention is to provide a display device, a display method, and a program capable of correcting the light emission amount of an element in a more preferable manner.

  In order to solve the above-described problem, according to an aspect of the present invention, there is provided a display device including pixel circuits arranged in a matrix, wherein the pixel circuit includes a light-emitting element that emits light with luminance according to a current amount; An optical sensor for detecting the brightness of light emitted from the light emitting element, and a first current for causing the light emitting element to emit light upon application of a first voltage for controlling the brightness of the light emitting element. A first control circuit that controls the amount; and a second voltage that is determined according to the first voltage; the second voltage based on the first current amount; and And a second control circuit that controls a second amount of current supplied to the light emitting element based on a detection result of the optical sensor.

  The second control circuit may control a light emission period of the light emitting element in one frame according to the second voltage.

  The second voltage corresponding to the first voltage may be set in advance based on a predetermined luminance deterioration rate as a reference.

  The second voltage corresponding to the first voltage is such that when the luminance deterioration rate of the light emitting element is the predetermined luminance deterioration rate, the light emission period of the light emitting element in one frame is a predetermined period. It may be set in advance so that

  The second voltage may be set in advance so that the light emitting element emits light at a predetermined duty ratio when the luminance deterioration rate of the light emitting element is the predetermined luminance deterioration rate.

  The second control circuit includes: a capacitor that holds the applied second voltage; a detection result of the photosensor in the second period; and the second voltage held in the capacitor. And a light emission control transistor that controls the amount of current flowing between the source and the drain based on the gate voltage determined accordingly.

  The discharge period of the second voltage held in the capacitor is controlled according to the detection result of the photosensor, and the length of the light emission period of the light emitting element in one frame is controlled based on the discharge period. May be.

  The first control circuit includes a drive transistor that controls an amount of current flowing between a source and a drain based on the first voltage applied to a gate terminal, and an amount of current supplied to the light emitting element is: Control may be performed based on the driving transistor and the second control circuit.

  The drive transistor is provided in a stage preceding the second control circuit, and the second control circuit is supplied to the light emitting element with reference to the first current amount supplied via the drive transistor. The second current amount may be controlled.

  In order to solve the above problems, according to another aspect of the present invention, a light emitting element that emits light with a luminance corresponding to an amount of current, and an optical sensor that detects the luminance of light emitted from the light emitting element are provided. A display method for displaying an image on a display device having a pixel circuit arranged in a matrix, wherein the light emitting element emits light based on a first voltage for controlling luminance of the light emitting element Controlling the first current amount to be controlled, based on the second voltage determined according to the first voltage with reference to the first current amount, and the detection result of the photosensor And a second current amount supplied to the light emitting element is provided. A display method is provided.

  In order to solve the above problems, according to another aspect of the present invention, a light emitting element that emits light with a luminance corresponding to an amount of current, and an optical sensor that detects the luminance of light emitted from the light emitting element are provided. A pixel circuit provided is a program for displaying an image on a display device arranged in a matrix, and causes the light emitting element to emit light based on a first voltage for controlling the luminance of the light emitting element. For controlling the first current amount for the first current amount based on the second voltage determined according to the first voltage with reference to the first current amount, and the detection result of the photosensor, A program is provided for causing the second current amount to be supplied to the light emitting element to be controlled.

  As described above, according to the present invention, it is possible to suppress the occurrence of pseudo contours and to correct the light emission amount of the light emitting element in a more preferable manner according to the deterioration amount of the light emitting element for each pixel. A display device, a display method, and a program are provided.

It is explanatory drawing for demonstrating an example of a structure of the display apparatus which concerns on one Embodiment of this invention. 4 is an explanatory diagram for describing an example of a configuration of a pixel circuit according to the embodiment. FIG. 3 is a schematic timing chart for explaining an example of drive timing of the pixel circuit according to the embodiment. 4 is a graph showing an example of a relationship between relative luminance and a sensor initial voltage corresponding to the relative luminance in the display device according to the embodiment. FIG. 4 is a graph showing an example of the relationship between the relative luminance and the luminance deterioration rate after the luminance deterioration is compensated when the sensor initial voltage according to the relative luminance is controlled. The example of the time change in the flame | frame time in the gate voltage of the light emission control transistor in a 1st model is shown. The example of the time change in the frame time of the gate voltage of the light emission control transistor in a 2nd model is shown. 3 is a schematic timing chart for explaining an example of drive timing of the pixel circuit according to the embodiment. 5 is a graph showing an example of a relationship between a luminance deterioration rate and a duty ratio in the display device according to the embodiment. 5 is a graph showing an example of a relationship between a luminance deterioration rate and a luminance deterioration rate after compensating for the luminance deterioration in the display device according to the embodiment. 5 is an explanatory diagram for describing an example of a method for setting a sensor initial voltage for each relative luminance in the display device according to the embodiment; FIG. 5 is an explanatory diagram for describing an example of a method for setting a sensor initial voltage for each relative luminance in the display device according to the embodiment; FIG.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Configuration of display device>
First, an example of a schematic configuration of a display device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is an explanatory diagram for explaining an example of the configuration of the display device according to the present embodiment. In FIG. 1, the horizontal direction in the drawing may be referred to as a row direction (X direction), and the vertical direction may be referred to as a column direction (Y direction). As illustrated in FIG. 1, the display device 10 according to the present embodiment includes a display unit 100, a scan driver 120, and a data driver 130.

  The display unit 100 includes a plurality of pixel circuits 110 and displays an image corresponding to the data signal on display pixels formed by the plurality of pixel circuits 110. In the display unit 100, each of a plurality of scanning lines 112 and compensation control signal lines 113 is provided so as to extend in the row direction (X direction). In the display unit 100, a plurality of columns of data lines 114 and compensation voltage signal lines 115 are provided so as to extend in the column direction (Y direction). In this description, as shown in FIG. 1, the display unit 100 includes M (M is an integer of 2 or more) rows of scanning lines 112 and compensation control signal lines 113, and N (N is an integer of 2 or more). In the following description, it is assumed that the column data line 114 and the compensation voltage signal line 115 are provided.

  Each of the plurality of pixel circuits 110 is arranged corresponding to each intersection of a plurality of scanning lines 112 extending in the row direction (X direction) and a plurality of data lines 114 extending in the column direction (Y direction). ing. The detailed configuration of the pixel circuit 110 will be described later.

  Further, the display unit 100 is supplied with a power supply voltage Vdd, a power supply voltage Vss, and a reference voltage GND from an upper control circuit (not shown). The power supply voltage Vdd and the power supply voltage Vss are signals for supplying a current for causing a light emitting element included in the pixel circuit 110 to emit light, for example.

  A plurality of scanning lines 112 and compensation control signal lines 113 arranged in the Y direction are connected to the scan driver 120. The scan driver 120 supplies a Scan signal to each pixel circuit 110 corresponding to the row via the scanning line 112 arranged for each row. The scan driver 120 supplies a SW signal to each pixel circuit 110 corresponding to the row via the compensation control signal line 113 arranged for each row. The details of the Scan signal and the SW signal will be described later separately.

  A plurality of data lines 114 and compensation voltage signal lines 115 arranged in the X direction are connected to the data driver 130. The data driver 130 supplies a DT signal corresponding to the emission luminance (in other words, gradation) to each pixel circuit 110 corresponding to the column via the data line 114 arranged for each column. Further, the data driver 130 applies the sensor initial voltage Vso corresponding to the light emission luminance (gradation) to each pixel circuit 110 corresponding to the column via the compensation voltage signal line 115 arranged for each column. . Details of the DT signal and the sensor initial voltage Vso will be described later.

<2. Configuration of pixel circuit>
Next, an example of the configuration of the pixel circuit according to the present embodiment will be described with reference to FIG. FIG. 2 is an explanatory diagram for explaining an example of the configuration of the pixel circuit according to the present embodiment.

  FIG. 2 shows an example of the pixel circuit 110 arranged corresponding to the intersection of i rows and j columns among the plurality of pixel circuits 110 constituting the display unit 100 shown in FIG. Further, the other pixel circuits 110 included in the display unit 100 can have the same configuration as that of the pixel circuit 110 illustrated in FIG. 2, and thus detailed description thereof is omitted.

  As shown in FIG. 2, the pixel circuit 110 includes an organic EL element OL, a holding capacitor C1, a switching transistor M1, a driving transistor M2, a photosensor Ps, a sensor capacitor Cs, a light emission control transistor M3, and a switching. A transistor M4.

  The drive transistor M2 and the light emission control transistor M3 can be configured by, for example, a P-channel MOSFET (metal-oxide-semiconductor field-effect transistor).

  As shown in FIG. 2, the drive transistor M2 has a drain terminal connected to the source terminal of the light emission control transistor M3, and a source terminal connected to a signal line for supplying the power supply voltage Vdd. The anode side of the organic EL element OL is connected to the drain terminal of the light emission control transistor M3. A power supply voltage Vss is connected to the cathode side of the organic EL element OL.

  The switching transistor M1 has a source terminal connected to the data line 114, a drain terminal connected to the gate terminal of the driving transistor M2, and is turned on or off in accordance with a Scan signal transmitted to the gate terminal via the scanning line 112. Turn off.

  The holding capacitor C1 has one terminal connected to the gate terminal of the driving transistor M2, and the other terminal connected to the reference voltage GND, and holds the potential of the gate terminal of the driving transistor M2.

  That is, when the switching transistor M1 is turned on, a DT signal corresponding to the light emission luminance (in other words, gradation) is transmitted from the data driver 130 to the gate terminal of the driving transistor M2 via the data line 114. . Next, when the switching transistor M1 is turned off, the DT signal transmitted via the data line 114 is held in the holding capacitor C1.

  The switching transistor M4 has a source terminal connected to the compensation voltage signal line 115, a drain terminal connected to the gate terminal of the light emission control transistor M3, and an SW signal transmitted to the gate terminal via the compensation control signal line 113. Turn on or off depending on the.

  The optical sensor Ps can be configured by, for example, a photodiode or a phototransistor. Examples of the material of the optical sensor Ps include polysilicon and amorphous silicon. The photosensor Ps has one terminal connected to the gate terminal of the light emission control transistor M3 and the other terminal connected to the reference voltage GND. The optical sensor Ps is provided so that a part of the light from the organic EL element OL is irradiated.

  One terminal of the sensor capacitor Cs is connected to the gate terminal of the light emission control transistor M3, and the other terminal is connected to the reference voltage GND. Based on such a configuration, the sensor capacitor Cs holds the potential Vg3 of the gate terminal of the light emission control transistor M3.

  When the switching transistor M4 is turned on, the sensor initial voltage Vso (Vso <0) is applied from the data driver 130 to the gate terminal of the light emission control transistor M3 via the compensation voltage signal line 115. The sensor initial voltage Vso corresponds to an example of a “second voltage”.

  As a result, the light emission control transistor M3 is turned on, and the drive transistor M2 is selectively turned on according to the DT signal transmitted from the data line 114 and held in the holding capacitor C1. Then, the drive current Ic corresponding to the DT signal held in the holding capacitor C1 is supplied to the organic EL element OL via the light emission control transistor M3, and the light emission state of the organic EL element OL is controlled. Hereinafter, when the current flowing between the drain and source of the light emission control transistor M3 is explicitly distinguished from the current Ic, it may be referred to as “current IL”.

  Next, when the switching transistor M4 is turned off, the gate terminal of the light emission control transistor M3 is in a floating state. As a result, the sensor initial voltage Vso applied via the compensation voltage signal line 115 is held in the sensor capacitor Cs. At this time, the light emission control transistor M3 is in the on state, and the current IL = Ic flowing between the drain and source of the light emission control transistor M3.

  Thereafter, the sensor initial voltage Vso held in the sensor capacitor Cs is discharged by the sensing current Is based on the detection result of the optical sensor Ps, and the gate voltage Vg3 of the light emission control transistor M3 rises from the potential Vso along with the discharge. . When the gate voltage Vg3 reaches the threshold voltage Vth3 of the light emission control transistor M3, the light emission control transistor M3 is turned off and the current IL = 0 (that is, the organic EL element OL is turned off).

  Note that the time from when the switching transistor M4 is controlled to the off state to when the light emission control transistor M3 is turned off is determined according to the relationship between the sensing current Is and the sensor capacitance Cs. Specifically, as the luminance of the organic EL element OL is higher, the current amount of the sensing current Is increases and the discharge time of the sensor capacitor Cs becomes shorter. In other words, the lower the luminance of the organic EL element OL, the smaller the amount of sensing current Is and the longer the discharge time of the sensor capacitor Cs.

  Therefore, for example, when the organic EL element OL deteriorates and the luminance decreases, the amount of the sensing current Is decreases and the discharge time of the sensor capacitor Cs becomes longer than before the deterioration. As a result, after the deterioration of the organic EL element OL, the period during which the light emission control transistor M3 is turned on becomes longer than before the deterioration, so that the effective luminance of the organic EL element OL increases, and as a result, the organic EL element The luminance degradation of the element OL is compensated.

  The example of the configuration of the pixel circuit according to the present embodiment has been described above with reference to FIG.

<3. Example of drive timing>
Next, with reference to FIG. 3, an example of drive timing of each element constituting the pixel circuit 110 according to the present embodiment shown in FIG. 2 will be described. FIG. 3 is a schematic timing chart for explaining an example of drive timing of the pixel circuit 110 according to the present embodiment. Note that in this description, the case of the pixel circuit 110 located in i row and j column will be described as an example, and the other pixel circuits 110 are the same and will not be described in detail.

In FIG. 3, reference symbol T ₀ schematically indicates a light emission period for displaying an image by causing the organic EL element OL to emit light during one frame period. In the timing chart shown in FIG. 3, for the sake of easy understanding, the light emission period T ₀ of the organic EL element OL is shown as one frame period, and the other control periods are not shown. Yes. Therefore, it goes without saying that, for example, a control period for compensating for variations in the threshold value of the drive transistor may be provided separately from the light emission period T ₀ in one frame period.

As shown in FIG. 3, the pixel circuit 110 according to the present embodiment is configured to be able to control the light emission period T ₀ by dividing the light emission period T ₀ into a constant light emission period T ₁ and a luminance deterioration compensation light emission period T ₂ . Always emission period T ₁ represents a period during which the organic EL element OL, thereby always based on the constant current Ic which is determined in accordance with the DT signal corresponding to the light emission luminance (gradation) light. The luminance deterioration compensation emission period T ₂ are, in accordance with the detection result of the optical sensor Ps, the current amount of the current IL supplied to the organic EL element OL, by controlling the period during which the current IL is supplied This is a period for compensating for the luminance deterioration of the organic EL element OL.

  Here, each timing shown in FIG. 3 will be described with reference to the circuit configuration of the pixel circuit 110 shown in FIG.

  As shown in FIG. 3, the switching transistor M <b> 1 in the pixel circuit 110 is turned on by an L-level Scan signal (that is, Scani) supplied via the i-th scanning line 112. Accordingly, a DT signal corresponding to the light emission luminance (in other words, gradation) is transmitted to the gate terminal of the driving transistor M2 in the pixel circuit 110 via the j-th data line 114. When the Scan signal becomes H level, the switching transistor M1 is turned off, and the DT signal (that is, DTj) transmitted through the data line 114 is held in the holding capacitor C1. The DT signal held in the holding capacitor C1 corresponds to an example of “first voltage”.

  In this manner, in synchronization with the Scan signal, the DT signal corresponding to the emission luminance is held in the holding capacitor C1 in the pixel circuit 110. Note that during the period in which the Scan signal is at the L level and the DT signal is held in the storage capacitor C1 (that is, data is written to the pixel circuit 110), the number of pixel circuits 110 that form the display unit 100 (that is, the pixel) Depending on the number, for example, it will be several tens of μs.

  In addition, in synchronization with the start of supply of the L-level Scan signal, supply of the L-level SW signal (ie, SWi) is started via the i-th compensation control signal line 113, and the pixel circuit 110 is started. The switching transistor M4 is turned on. Thus, the sensor initial voltage Vso (Vso <0) corresponding to the light emission luminance (gradation) is applied to the gate terminal of the light emission control transistor M3 in the pixel circuit 110 via the compensation voltage signal line 115 in the jth column. Is applied as the gate voltage Vg3. The details of setting the potential of the sensor initial voltage Vso will be described later.

  As a result, the light emission control transistor M3 is turned on, and the drive transistor M2 is selectively turned on according to the DT signal (that is, DTj) transmitted from the data line 114 and held in the holding capacitor C1. Then, the drive current Ic corresponding to the DT signal held in the holding capacitor C1 is supplied to the organic EL element OL via the light emission control transistor M3. Thereby, the organic EL element OL emits light with a luminance corresponding to the drive current Ic.

The period during which the organic EL element OL emits light with the luminance corresponding to the drive current Ic, that is, the supply of the L level SW signal turns on the switching transistor M4, and the light emission control transistor M3 is driven based on the sensor initial voltage Vso. period corresponds always emission period T _1.

  Next, when the SW signal becomes H level, the switching transistor M4 is turned off, and the sensor initial voltage Vso applied through the compensation voltage signal line 115 is held in the sensor capacitor Cs.

  Thereafter, the sensor initial voltage Vso held in the sensor capacitor Cs is discharged by the sensing current Is based on the detection result of the optical sensor Ps, and the gate voltage Vg3 of the light emission control transistor M3 rises from the potential Vso along with the discharge. . When the gate voltage Vg3 reaches the threshold voltage Vth3 of the light emission control transistor M3, the light emission control transistor M3 is turned off and the current IL = 0 (that is, the organic EL element OL is turned off).

In addition, the sensor initial voltage Vso held in the sensor capacitor Cs is discharged by the sensing current Is based on the detection result of the photosensor Ps, so that the luminance deterioration occurs during the period in which the gate voltage Vg3 of the light emission control transistor M3 is controlled. It corresponds to the compensation emission period _{T 2.} As described above, the length of the luminance deterioration compensation emission period T ₂ are corresponds to the discharge time of the sensor capacitance Cs, is determined in accordance with the relationship between the sensing current Is and the sensor capacitance Cs.

Thus, in the example shown in FIG. 3, the pixel circuit 110 is driven with a duty ratio of (T ₁ + T ₂ ) / T ₀ .

  The series of operations described above can be configured by a program for causing the CPU of the device that operates each component of the display device 10 to function. This program may be configured to be executed via an OS (Operating System) installed in the apparatus. In addition, the position of the program is not limited as long as the apparatus including the configuration for executing the above-described processing can be read. For example, the program may be stored in a recording medium connected from the outside of the apparatus. In this case, it is preferable to connect the recording medium storing the program to the apparatus so that the CPU of the apparatus executes the program.

  The example of the drive timing of each element constituting the pixel circuit 110 according to this embodiment shown in FIG. 2 has been described above with reference to FIG.

<4. Principle of compensation for luminance degradation>
Next, in the display device 10 according to the present embodiment described above, the principle of operation related to the compensation of the luminance deterioration of the organic EL element OL is referred to together with the circuit configuration of the pixel circuit 110 shown in FIG. This will be described based on a simple model formula.

First, when the resistance of the photosensor Ps in the pixel circuit 110 is Rs, a first model focusing on the characteristic that the resistance Rs is inversely proportional to the luminance of the organic EL element OL will be described. The luminance of the organic EL element OL is proportional to the current Ic when the drain-source current IL = Ic of the light emission control transistor M3, and becomes 0 when the current IL = 0. Further, when the luminance deterioration rate indicating the ratio of the luminance after deterioration to the luminance before deterioration is a, the resistance Rs of the optical sensor Ps in a state where the organic EL element OL emits light is inversely proportional to a · Ic. It is represented by (Formula 1) shown below. Note that K _rs in (Equation 1) shown below is a constant that determines the relationship between the resistance Rs and a · Ic.

  Further, the following relational expression is established between the gate voltage Vg3 of the light emission control transistor M3 and the resistance Rs of the optical sensor Ps.

When (Expression 2) shown above is integrated in each range of t from 0 to t and Vg3 from Vso to Vg3, the following relational expression expressed by (Expression 3) is derived.

Here, when (Equation 1) described above is substituted into (Equation 3) shown above, and Vg3 = Vth3 at t = T ₂ , the following relational expression is derived as (Equation 4). . In the following (Equation 4), K ₂ is a constant that determines the relationship between a · Ic and sensor capacitance Cs, and time T ₂ .

Next, a second model focusing on the characteristic that the current value of the sensing current Is flowing through the optical sensor Ps (hereinafter sometimes simply referred to as “current value Is”) is proportional to the luminance of the organic EL element OL. explain. The luminance of the organic EL element OL is proportional to the current Ic when the drain-source current IL = Ic of the light emission control transistor M3, and becomes 0 when the current IL = 0. Further, when the luminance degradation ratio was a is in a state in which the organic EL element OL is emitting light, the current value of the optical sensor Ps Is is proportional to a · Ic, using proportional coefficient K _IS, It is represented by (Formula 5) shown below.

  Further, a relational expression shown below as (Equation 6) holds between the gate voltage Vg3 of the light emission control transistor M3 and the current value Is of the optical sensor Ps.

  By integrating (Expression 6) shown above in each range of t to 0 to t and Vg3 to Vso to Vg3, a relational expression expressed by (Expression 7) below is derived.

Here, when (Equation 5) described above is substituted for (Equation 7) shown above and Vg3 = Vth3 at t = T ₂ , the following relational expression is derived as (Equation 8). .

As described above, as shown in (Expression 4) and (Expression 8), the definition of the constant K ₂ is different in both the first model and the second model, but the time T ₂ is expressed by the same expression. The As a result, the luminance L, by using the proportionality factor K ₁ showing the linear relationship between the brightness L and the current Ic, represented by the following (Equation 9).

Here, since the duty ratio (T ₁ + T ₂ ) / T ₀ described based on the timing chart shown in FIG. 3 does not exceed 100%, the following conditional expression is provided as (Expression 10).

  Based on the equation indicating the luminance L shown above as (Equation 9) and the conditional equation shown as (Equation 10), the luminance Li of the organic EL element OL before deterioration (hereinafter referred to as “initial luminance Li”). In some cases, the luminance deterioration rate is 1 (that is, there is no deterioration) and is expressed by the following (Formula 11).

  Further, the luminance Ld of the organic EL element OL after deterioration is expressed by the following (formula 12), where the luminance deterioration rate is a (a <1).

  Here, based on (Expression 11) and (Expression 12) shown above, the luminance deterioration rate Ld / Li after compensating for the luminance deterioration is expressed by (Expression 13) shown below.

Here, in (Expression 11), when T ₁ / T ₀ = 0 (that is, when the length of the constant light emission period T1 is set to 0), the initial luminance Li is expressed as follows (Expression 14) ).

Similarly, when T ₁ / T ₀ = 0 in (Expression 12), the luminance Ld of the organic EL element OL after deterioration is expressed by (Expression 15) shown below.

Here, since the duty ratio (T ₁ + T ₂ ) / T ₀ described based on the timing chart shown in FIG. 3 does not exceed 100%, conditional expressions shown as (Expression 16a) and (Expression 16b) below. Is provided.

As a result, under the condition that does not satisfy the expression on the left side of (Expression 16b), the luminance deterioration rate Ld / Li = 1 after the luminance deterioration is compensated, and 100% compensation is possible. However, as the current Ic increases, the duty ratio tends to decrease for both the initial luminance Li and the deteriorated luminance Ld. Therefore, in view of such a situation, in order to maintain the luminance deterioration rate Ld / Li = 1 after compensating for the luminance deterioration and to realize a relatively high duty ratio, the duty ratio is reduced after the luminance deterioration. You may adjust the constant _{K 2} to 100%. Incidentally, after the luminance degradation, for the duty ratio is 100%, the condition of the constant K ₂ is expressed by the following equation (17).

Therefore, when the current Ic changes at a certain luminance deterioration rate a, if it is possible to always satisfy the relational expression shown above as (Equation 17), 100% luminance deterioration compensation is performed in a wider luminance region. It can be realized. Therefore, in the display device 10 according to the present embodiment, even when the current Ic changes by controlling the sensor initial voltage Vso according to the change in the current Ic, the relational expression shown in (Expression 17) above is obtained. to achieve adjustment of the constants K ₂ as satisfied. The details of the control will be described below with specific examples.

For example, in the first model in which the resistance of the optical sensor Ps in the pixel circuit 110 is focused on the characteristic that Rs is inversely proportional to the luminance of the organic EL element OL, the relational expression of the constant K ₂ described above as (Expression 4a) is used. By substituting into (Expression 17), a conditional expression shown as (Expression 18) below is derived.

  Here, when the relative luminance is 100%, the sensor initial voltage Vso = −7 [V], the threshold voltage Vth3 = −2 [V] of the light emission control transistor M3, and the current Ic = Ico are shown above. (Expression 18) is expressed by (Expression 19) shown below. Note that in this description, the relative luminance indicates luminance that is standardized so that the total white luminance (that is, the maximum luminance value) is 100%.

  Further, assuming that the current Ic and the sensor initial voltage Vso when the relative luminance is L are Ic (L) and Vso (L), respectively, the conditions satisfying the relational expression shown above as (Equation 18) are as follows: (Equation 20) shown below is derived.

  When (Equation 19) shown above is substituted into (Equation 20), the following relational expression is derived as (Equation 21).

The current value of the optical sensor Ps Is is, in the second model which focuses on the characteristics proportional to the luminance of the organic EL element OL, the aforementioned constant K ₂ relational expression as (formula 8a) (Formula 17) By substituting, a conditional expression shown as (Expression 22) below is derived.

  Here, when the relative luminance is 100%, the sensor initial voltage Vso = −7 [V], the threshold voltage Vth3 = −2 [V] of the light emission control transistor M3, and the current Ic = Ico are shown above. (Expression 22) is expressed by (Expression 23) shown below.

  Further, assuming that the current Ic and the sensor initial voltage Vso when the relative luminance is L are Ic (L) and Vso (L), the following conditions are satisfied as the conditions satisfying the relational expression (Expression 22): (Equation 24) shown below is derived.

  Substituting (Equation 23) shown above into (Equation 24) leads to a relational expression shown as (Equation 25) below.

  Here, since the current Ic and the luminance are in a proportional relationship, Ic (L) / Ico corresponds to the relative luminance. For example, FIG. 4 is a graph showing an example of the relationship between the relative luminance and the sensor initial voltage Vso (L) corresponding to the relative luminance. In FIG. 4, the horizontal axis represents relative luminance. The vertical axis represents the sensor initial voltage Vso (L) [V] corresponding to the relative luminance. The example shown in FIG. 4 shows an example in which the sensor initial voltage Vso = −7 [V] and the threshold voltage Vth3 = −2 [V] of the light emission control transistor M3 described above are used. In FIG. 4, model 1 and model 2 correspond to (Expression 21) and (Expression 25), respectively.

  FIG. 5 shows the relationship between the relative luminance and the luminance deterioration rate Ld / Li after the luminance deterioration is compensated when the sensor initial voltage Vso (L) is controlled according to the relative luminance as shown in FIG. An example of the relationship between them is shown. In FIG. 5, the horizontal axis represents relative luminance. The vertical axis represents the luminance deterioration rate Ld / Li after the luminance deterioration is compensated.

  That is, as shown in FIG. 4, by controlling the sensor initial voltage Vso (L) according to the relative luminance, theoretically, the luminance after compensating for the luminance degradation in a wide range as shown in FIG. The deterioration rate Ld / Li = 100% (that is, 100% luminance deterioration compensation) can be realized.

Here, when the sensor initial voltage Vso = −7 [V] and the threshold voltage Vth3 of the light emission control transistor M3 = −2 [V], the time change within the frame time of the gate voltage Vg3 of the light emission control transistor M3. Pay attention. Note that the light emission period T ₀ in one frame does not necessarily coincide with the frame time (that is, the period of one frame). However, in this description, in order to make the control of the display device 10 according to the present embodiment easier to understand, the frame time and the light emission period T ₀ substantially coincide (that is, the frame time = the light emission period T ₀ ). Will be described.

For example, FIG. 6 shows the frame time of the gate voltage Vg3 of the light emission control transistor M3 in the first model focusing on the characteristic that the resistance Rs of the photosensor Ps in the pixel circuit 110 is inversely proportional to the luminance of the organic EL element OL. An example of the time change in the figure is shown. In FIG. 6, the horizontal axis indicates time t [ms]. The vertical axis represents the gate voltage Vg3 [V] of the light emission control transistor M3. In the example shown in FIG. 6, the change in threshold voltage Vth3 within the frame time is shown for each of the relative luminances of 10%, 50%, and 100%. The frame time T ₀ is T ₀ = 16.7 [ms].

  FIG. 7 shows the time change of the gate voltage Vg3 of the light emission control transistor M3 within the frame time in the second model focusing on the characteristic that the current value Is of the photosensor Ps is proportional to the luminance of the organic EL element OL. An example is shown. Note that the horizontal and vertical axes in FIG. 7 are the same as those in FIG. Further, in the example shown in FIG. 7, similarly to the example shown in FIG. 6, the change in threshold voltage Vth3 within the frame time is shown for each of the relative luminances of 10%, 50%, and 100%.

As shown in FIGS. 6 and 7, theoretically, by increasing the sensor initial voltage Vso (L) in accordance with the decrease in relative luminance, the frame time T ₀ = 16.7 for all the relative luminance conditions. In [ms], the gate voltage Vg3 can be adjusted to be −2 [V].

  Here, an example of drive timing of the pixel circuit 110 for realizing the control described with reference to FIGS. 4 to 7 will be described with reference to FIG. FIG. 8 is a schematic timing chart for explaining an example of the drive timing of the pixel circuit 110 according to the present embodiment. Note that in this description, the case of the pixel circuit 110 located in i row and j column will be described as an example, and the other pixel circuits 110 are the same and will not be described in detail.

  In the example illustrated in FIG. 8, the pixel circuit 110 is supplied to the pixel circuit 110 by supplying the L level SW signal in synchronization with the writing of data (that is, the DT signal) to the pixel circuit 110 accompanying the supply of the L level Scan signal. Thus, the sensor initial voltage Vso is written. In the example shown in FIG. 8, the time for writing the data and the sensor initial voltage Vso to the pixel circuit 110 is several tens [μs]. In the example illustrated in FIG. 8, when the Scan signal and the SW signal become the H level, the light emission control is performed based on the sensing current Is based on the detection result of the photosensor Ps in the pixel circuit 110 and the sensor initial voltage Vso. The gate voltage Vg3 of the transistor M3 increases along the time series from the potential Vso. When the gate voltage Vg3 reaches the threshold voltage Vth3 of the light emission control transistor M3, the light emission control transistor M3 is turned off, and the current IL = 0 supplied to the organic EL element OL is satisfied (that is, the organic EL element). OL goes off).

In the example shown in FIG. 8, except for the period during which the data and writing the sensor initial voltage Vso is performed to the pixel circuit 110, almost the entire emission period T ₀ in one frame and the luminance deterioration compensation emission period T ₂ Become. That is, in the example shown in FIG. 8, it can be seen that a duty ratio of almost 100% is realized.

  As described above, the organic EL element OL in the case where the luminance deterioration rate Ld / Li after the luminance deterioration is compensated at the predetermined luminance deterioration rate a (in other words, the luminance deterioration compensation rate Ld / Li) is maximized. Various characteristics relating to the emission of the light have been described.

In actual operation, the luminance degradation rate a _{0 as} the target value, the design parameters of the optical sensor Ps (for example, the size of the sensor, the amount of light irradiated to the sensor, the value of the sensor capacitance Cs, etc.), and the sensor initial voltage In accordance with each setting of Vso, the luminance deterioration rate a of the organic EL element OL sequentially changes. Here, the change of the luminance deterioration rate Ld / Li after compensating for the luminance deterioration in the actual operation will be specifically described. Note that the luminance deterioration rate a ₀ as the target value corresponds to an example of “a predetermined luminance deterioration rate as a reference”.

First, in (Expression 17) described above, the luminance deterioration rate a = a ₀ , and when (Expression 17) is substituted into (Expression 14), (Expression 15), and (Expression 16b) described above, the following ( The relational expressions shown as Expression 26), Expression 27, and Expression 28 are derived.

FIG. 9 shows an example of the change in the duty ratio accompanying the change in the luminance deterioration rate a in this case. FIG. 9 is a graph showing an example of the relationship between the luminance deterioration rate a and the duty ratio in the display device 10 according to the present embodiment. In FIG. 9, the horizontal axis represents the luminance deterioration rate a of the organic EL element OL. The vertical axis represents the duty ratio. In the example shown in FIG. 9, when the luminance degradation is not compensated, the luminance degradation rate a ₀ set as the target value is a ₀ = 0.95, and a ₀ = 0.9. For the case, the relationship between the luminance deterioration rate a and the duty ratio is shown.

As can be seen from the graphs of a ₀ = 0.95 and a ₀ = 0.9 shown in FIG. 9, in the display device 10 according to the present embodiment, the initial state (that is, the luminance) in deterioration rate a = 1), the duty ratio is substantially equal to the luminance degradation factor a ₀ that is set as the target value. As the luminance deterioration rate a decreases, the duty ratio increases, and reaches a maximum value of 1 when the luminance deterioration rate a ≦ a ₀ . Note that the luminance deterioration rate Ld / Li (that is, the luminance deterioration compensation rate Ld / Li) after the luminance deterioration is compensated based on (Equation 26), (Equation 27), and (Equation 28) described above is as follows. (Expression 29) and (Expression 30).

FIG. 10 shows an example of the relationship between the luminance deterioration rate a and the luminance deterioration rate Ld / Li () after compensating for the luminance deterioration in this case. FIG. 10 shows the display device 10 according to the present embodiment. 10 is a graph showing an example of the relationship between the luminance degradation rate a and the luminance degradation rate Ld / Li after compensating for the luminance degradation, where the horizontal axis represents the luminance degradation rate a of the organic EL element OL. The vertical axis represents the luminance deterioration rate Ld / Li after the luminance deterioration is compensated In the example shown in Fig. 10, the luminance deterioration compensation is not performed and the target value The relationship between the luminance deterioration rate a and the duty ratio is shown for the case where the luminance deterioration rate a ₀ set as is a ₀ = 0.95 and a ₀ = 0.9. Ld / Li is not present when luminance degradation is not compensated. It goes without saying that indicates the luminance degradation ratio a of the EL element OL.

As can be seen from the graphs of a ₀ = 0.95 and a ₀ = 0.9 shown in FIG. 9, in the display device 10 according to the present embodiment, the luminance of the organic EL element OL is shown. deterioration rate a is, the period from 1 to change to a ₀ is enabled 100% luminance deterioration compensation.

On the other hand, in a period in which the luminance deterioration rate a of the organic EL element OL is less than a ₀ (ie, a <a ₀ ), the luminance deterioration rate after compensating for the luminance deterioration as the luminance deterioration rate a decreases. Ld / Li will also decrease. However, even in the period in which the luminance degradation factor a is less than a _0, according to the display device 10 according to the present embodiment, as compared with the case without compensation of luminance degradation, brightness due to deterioration of the organic EL element OL It can be seen that the decrease in the is suppressed.

That is, as shown in FIG. 10, by setting the luminance deterioration rate a ₀ as the target value lower, the duty ratio becomes lower in the initial state (that is, the luminance deterioration rate a = 1), but over a wide range. Thus, the luminance degradation rate Ld / Li after compensating for the luminance degradation can be set to 1 (that is, 100% luminance degradation compensation is possible).

  As described above, the optical sensor Ps can be configured by, for example, a photodiode or a phototransistor. In general, photodiodes tend to exhibit characteristics close to the second model described above. Further, the phototransistor tends to exhibit characteristics intermediate between the first model and the second model described above.

  In the above description, a case where a P-channel transistor is applied as each transistor of the pixel circuit 110 illustrated in FIG. 2 is described as an example; however, the structure is not necessarily limited to this. As a specific example, each transistor of the pixel circuit 110 illustrated in FIG. 2 may be configured as an N-channel transistor. In this case, it goes without saying that the relationship between the potentials of the signals may be changed as appropriate in accordance with the characteristics of the transistors.

  As described above, the principle of the operation related to the compensation for the luminance deterioration of the organic EL element OL in the display device 10 according to the present embodiment has been described based on a simple model formula with reference to FIGS. 2 and 4 to 10.

<5. Setting method of sensor initial voltage Vso>
Next, an example of a method for setting the sensor initial voltage Vso will be described. In this section, an example of a method for setting the sensor initial voltage Vso for each relative luminance in accordance with the light emission characteristics of the organic EL element OL will be described with reference to FIGS. 11 and 12. 11 and 12 are explanatory diagrams for describing an example of a method for setting the sensor initial voltage Vso for each relative luminance in the display device 10 according to the present embodiment.

  In the method for setting the sensor initial voltage Vso for each relative luminance described in this section, the sensor initial voltage Vso is adjusted while measuring the luminance of the organic EL element OL at each relative luminance.

Specifically, as shown in FIG. 11, first, the light emission period T ₀ in one frame is controlled to always emit light (that is, T ₀ = T ₁ ) at each gradation (ie, each relative luminance). The luminance L of the organic EL element OL is measured. Note that, as shown in FIG. 11, the luminance L measured at this time is the luminance when the duty ratio is 100%.

Next, in the same gradation, the luminance L of the organic EL element OL is measured while the duty ratio is 100 while the sensor initial voltage Vso is changed with the constant light emission period T ₁ = 0 as shown in FIG. It adjusts so that it may become _a0 times the brightness in the case of%. That is, when the luminance deterioration rate a ₀ set as the target value is set to a ₀ = 0.95, the sensor initial voltage Vso is set so as to be 0.95 times the luminance when the duty ratio is 100%. adjust. In this case, as shown in FIG. 12, the luminance deterioration compensation period T ₂ and the light emission period T _{0 in} one frame satisfy the relationship of T ₂ = a ₀ · T ₀ , and the duty ratio is 95 %.

As described above with reference to FIG. 9, in the display device 10 according to the present embodiment, the duty ratio in the initial state (that is, the luminance deterioration rate a = 1 of the organic EL element OL) is set as a target value. substantially equal to the luminance degradation factor a _0. That is, as always emission period T _{1 =} 0, the luminance L of the organic EL element OL is measured previously, to adjust the sensor initial voltage Vso as the duty ratio becomes a _0-fold brightness when 100% in, so that the luminance degradation factor a ₀ as a target value is set. The sensor initial voltage Vso for each gradation may be specified by appropriately performing the adjustment described above for each gradation.

  Note that the adjustment described above is not necessarily performed for all gradations. As a specific example, the adjustment described above may be performed for some gradations, and the sensor initial voltage Vso may be derived by interpolation for other gradations. Of course, in order to correct the luminance deterioration of the organic EL element OL more accurately, it goes without saying that it is desirable to carry out the adjustment described above for all gradations (total relative luminance).

  The example of the method for setting the sensor initial voltage Vso has been described above with reference to FIGS. 11 and 12.

<6. Summary>
As described above, the display device 10 according to the present embodiment includes the control circuit for performing the luminance control of the organic EL element OL in response to the application of the DT signal according to the emission luminance (gradation), and the sensor initial voltage. And a control circuit for correcting the light emission amount of the organic EL element OL in response to the application of Vso. Based on such a configuration, the display device 10 according to the present embodiment controls the light emission period T ₀ in one frame by dividing it into a constant light emission period T ₁ and a luminance deterioration compensation light emission period T ₂ . That is, the display device 10 according to the present embodiment, the constant light emission period T _1, control the brightness of the organic EL element OL in accordance with the emission luminance (gradation). Further, the display device 10, by controlling the length of the continuously light-emitting period T ₁ to then in luminance deterioration compensation emission period T ₂ which is provided, in accordance with the luminance degradation of the organic EL element OL, the organic EL device The light emission amount of OL is corrected (that is, luminance deterioration is compensated).

  With such a configuration, the display device 10 according to the present embodiment independently controls the luminance control of the organic EL element OL according to the emission luminance (gradation) and the compensation for the luminance deterioration of the organic EL element OL. It becomes possible. That is, according to the display device 10 according to the present embodiment, the luminance setting of the organic EL element OL and the correction of the light emission amount according to the luminance deterioration amount of the organic EL element OL are realized in a more preferable aspect. It becomes possible.

In the display device 10 according to the present embodiment, the sensor initial voltage Vso is controlled in accordance with a change in the light emission luminance (in other words, the current Ic) of the organic EL element OL. With such a configuration, in the display device 10 according to the present embodiment, after the luminance degradation rate a of the organic EL element OL is equal to or lower than the luminance degradation rate a ₀ set as the target value, the luminance degradation is compensated. It is possible to control the luminance deterioration rate Ld / Li to 1 (that is, 100% luminance deterioration compensation is possible).

In the display device 10 according to the present embodiment, the luminance degradation factor a is less than a ₀ of the organic EL element OL (i.e., a <a ₀₎ in the composed period, with a decrease of the luminance degradation factor a, luminance The luminance deterioration rate Ld / Li after compensating for the deterioration also decreases. However, according to the display device 10 according to the present embodiment, even in a period during which the luminance degradation factor a is less than a _0, as compared with the case without compensation of luminance degradation, brightness due to deterioration of the organic EL element OL Can be suppressed.

In the display device 10 according to this embodiment, depending on the setting of the luminance degradation factor a ₀ as a target value, the initial state (i.e., the luminance degradation factor a = 1 in the state of the organic EL element OL) a duty ratio in It is possible to adjust appropriately. In the display device 10 according to the present embodiment, the duty ratio increases in accordance with the deterioration of the organic EL element OL, and the duty ratio becomes 1 when the luminance deterioration rate a <a ₀ is satisfied. That is, According to the display device 10 according to the present embodiment, the duty ratio is always controlled to be equal to or greater than the value determined on the basis of the luminance degradation factor a ₀ as a target value. Therefore, according to the display device 10 according to the present embodiment, the generation of the so-called pseudo contour is suppressed by appropriately setting the luminance deterioration rate a ₀ as the target value according to the operation mode of the display device 10. It becomes possible.

Further, in the display device 10 according to the present embodiment, it is possible to appropriately adjust the luminance deterioration rate a ₀ that is the target value by the simple procedure described as “5. Setting method of the sensor initial voltage Vso”. That is, according to the display device 10 according to the present embodiment, the control for luminance deterioration compensation according to the luminance deterioration rate a ₀ that is the target value is appropriately set according to the operation mode of the display device 10. Is possible.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Display apparatus 100 Display part 110 Pixel circuit 112 Scan line 113 Compensation control signal line 114 Data line 115 Compensation voltage signal line 120 Scan driver 130 Data driver

Claims (11)

A display device including pixel circuits arranged in a matrix,
The pixel circuit includes:
A light emitting element that emits light with a luminance according to the amount of current;
An optical sensor for detecting the luminance of light emitted from the light emitting element;
A first control circuit for controlling a first current amount for causing the light emitting element to emit light upon application of a first voltage for controlling the luminance of the light emitting element;
Receiving the second voltage determined in accordance with the first voltage, and based on the second voltage and the detection result of the photosensor with the first current amount as a reference, the light emission A second control circuit for controlling a second amount of current supplied to the element;
A display device comprising:   The display device according to claim 1, wherein the second control circuit controls a light emission period of the light emitting element in one frame in accordance with the second voltage.   The display device according to claim 1, wherein the second voltage corresponding to the first voltage is set in advance based on a predetermined luminance deterioration rate as a reference.   The second voltage corresponding to the first voltage is such that when the luminance deterioration rate of the light emitting element is the predetermined luminance deterioration rate, the light emission period of the light emitting element in one frame is a predetermined period. The display device according to claim 3, wherein the display device is preset so that   The second voltage is set in advance so that when the luminance deterioration rate of the light emitting element is the predetermined luminance deterioration rate, the light emitting element emits light at a predetermined duty ratio. The display device according to claim 3 or 4. The second control circuit includes:
A capacity for holding the applied second voltage;
A light emission control transistor for controlling the amount of current flowing between the source and the drain based on the gate voltage determined according to the detection result of the photosensor and the second voltage held in the capacitor;
The display device according to claim 1, comprising: The discharge period of the second voltage held in the capacitor is controlled according to the detection result of the photosensor,
The display device according to claim 6, wherein a length of a light emission period of the light emitting element in one frame is controlled based on the discharge period. The first control circuit includes:
A driving transistor for controlling an amount of current flowing between a source and a drain based on the first voltage applied to a gate terminal;
The display device according to claim 1, wherein an amount of current supplied to the light emitting element is controlled based on the driving transistor and the second control circuit. The driving transistor is provided in a stage preceding the second control circuit;
The said 2nd control circuit controls the said 2nd electric current amount supplied to the said light emitting element on the basis of the said 1st electric current amount supplied via the said drive transistor. Display device. A pixel circuit including a light emitting element that emits light with luminance according to the amount of current and a light sensor that detects the luminance of light emitted from the light emitting element displays an image on a display device arranged in a matrix. Display method for
Controlling a first current amount for causing the light emitting element to emit light based on a first voltage for controlling the luminance of the light emitting element;
Based on the second voltage determined according to the first voltage with the first current amount as a reference, and the detection result of the photosensor, a second current amount supplied to the light emitting element is obtained. Control and
The display method characterized by including. A pixel circuit including a light emitting element that emits light with luminance according to the amount of current and a light sensor that detects the luminance of light emitted from the light emitting element displays an image on a display device arranged in a matrix. A program for
Controlling a first current amount for causing the light emitting element to emit light based on a first voltage for controlling the luminance of the light emitting element;
Based on the second voltage determined according to the first voltage with the first current amount as a reference, and the detection result of the photosensor, a second current amount supplied to the light emitting element is obtained. Control and
A program characterized by having executed.

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