Display device control method

Abstract

To provide a display device, etc., with which it is possible to suppress, by a simplified structure, the collapse of white balance that is dependent on temperature.SOLUTION: A display device 1 comprises a display unit 12 having a plurality of pixel circuits 10, and a control circuit 16. Each of the plurality of pixel circuits 10 includes a first and a second sub-pixel circuit, the first sub-pixel circuit including a first light emitting element, a first drive transistor, a first capacitor and a first write transistor, the second sub-pixel circuit including a second light emitting element, a second drive transistor for supplying a current to the second light emitting element, a second capacitor for holding a charge corresponding to a video signal, and a second write transistor connected to the second capacitor. The capacity of the first capacitor is larger than the capacity of the second capacitor, and the control circuit 16 controls the threshold compensation period of the first and second drive transistors of each of the plurality of pixel circuits 10 on the basis of the temperature pertaining to the display unit 12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a display device and a method for controlling the display device. [Background technology]

[0002] Conventionally, active matrix display devices (hereinafter referred to as display devices) using light emitting elements such as organic EL (Electro-Luminescence) elements have been put to practical use (see, for example, Patent Document 1, etc.). The display device includes a plurality of pixel circuits arranged in a matrix. Each of the plurality of pixel circuits is composed of, for example, three sub-pixel circuits equipped with organic EL elements emitting red (R), green (G), and blue (B), respectively. The sub-pixel circuit includes, for example, an initialization transistor, a reference transistor, a write transistor, and a capacitor. The initialization transistor, the reference transistor, and the write transistor each perform switching based on a control signal from a gate driver. The display device displays a color image by controlling the emission brightness of the organic EL element for each sub-pixel circuit based on signals from the gate driver and the source driver.

[0003] Among the organic EL elements of each subpixel circuit, the luminescence life of the organic EL material used in the blue organic EL element that emits blue light (i.e., the luminescence life of the organic EL material when a predetermined current density is continuously applied to the organic EL material) is shorter than the luminescence life of the organic EL material used in the red organic EL element that emits red light and the green organic EL element that emits green light. In other words, the blue organic EL element is more susceptible to deterioration than the red organic EL element and the green organic EL element. For this reason, in conventional display devices, the pixel area of ​​the blue organic EL element is made larger than the pixel areas of the red organic EL element and the green organic EL element to reduce the current density of the blue organic EL element. Accordingly, in the blue subpixel circuit having the blue organic EL element, the capacitance of the capacitor is designed to be larger than the capacitance of the capacitors of the other subpixel circuits, taking into consideration the balance with the characteristics of the blue organic EL element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-118952 A Summary of the Invention [Problem to be solved by the invention]

[0005] In each subpixel circuit, a small amount of current (hereinafter referred to as "off current") flows through the write transistor and the reference transistor even in the off state (non-conducting state or high resistance state). This off current causes charge to be discharged from the capacitor via the write transistor and the reference transistor after data is written (i.e., after the capacitor is charged with a charge corresponding to the luminance value). Here, the luminance value of each subpixel circuit corresponds to the gate-source voltage of the drive transistor, and this gate-source voltage depends on the charge charged in the capacitor. Here, as described above, the capacitance of the capacitor in the blue subpixel circuit is larger than that of the other subpixel circuits. Meanwhile, the amount of charge discharged from the capacitor by the off current is approximately the same in all subpixel circuits. Therefore, the ratio of the amount of charge discharged from the capacitor by the off current to the capacitance of the capacitor is smaller in the blue subpixel circuit than in the other subpixel circuits. Therefore, the rate of change of the gate-source voltage of the drive transistor due to the off current is smaller in the blue subpixel circuit than in the other subpixel circuits. In other words, the effect of the off-current on the luminance of the organic EL element of each subpixel circuit is smaller in the blue subpixel circuit than in the other subpixel circuits. This causes the white balance of the display unit to be lost. This loss of white balance can be suppressed, for example, by correcting the video signal.

[0006] However, because the magnitude of the off-current depends on the temperature of the writing transistor, when the temperature of the display unit fluctuates, the degree of white balance loss also fluctuates. Although it is possible to suppress such temperature-dependent white balance loss by dynamically correcting the video signal, the configuration of the control circuit becomes complicated.

[0007] The present disclosure has been made to solve the above problems, and aims to provide a display device and the like that can suppress temperature-dependent loss of white balance with a simplified configuration. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, a display device according to one embodiment of the present disclosure is a display device that displays an image based on a video signal, and includes a display unit having a plurality of pixel circuits arranged in a matrix, and a control circuit that controls the operation of the display unit, each of the plurality of pixel circuits has a first sub-pixel circuit and a second sub-pixel circuit, the first sub-pixel circuit has a first light-emitting element, a first drive transistor that supplies current to the first light-emitting element, a first capacitor that holds a charge corresponding to the video signal, and a first write transistor connected to the first capacitor, the second sub-pixel circuit has a second light-emitting element, a second drive transistor that supplies current to the second light-emitting element, a second capacitor that holds a charge corresponding to the video signal, and a second write transistor connected to the second capacitor, the capacitance of the first capacitor is larger than the capacitance of the second capacitor, and the control circuit controls the threshold compensation period of the first drive transistor and the second drive transistor of each of the plurality of pixel circuits based on a temperature related to the display unit.

[0009] Moreover, a control method of a display device according to one aspect of the present disclosure is a control method of a display device that displays an image based on a video signal, the display device having a display unit having a plurality of pixel circuits arranged in a matrix, each of the plurality of pixel circuits having a first sub-pixel circuit and a second sub-pixel circuit, the first sub-pixel circuit having a first light-emitting element, a first drive transistor that supplies a current to the first light-emitting element, a first capacitor that holds a charge corresponding to the video signal, and a first write transistor connected to the first capacitor, the second sub-pixel circuit having a second light-emitting element, a second drive transistor that supplies a current to the second light-emitting element, a second capacitor that holds a charge corresponding to the video signal, and a second write transistor connected to the second capacitor, the capacitance of the second capacitor being smaller than the capacitance of the first capacitor, and the control method of the display device includes a detection step of detecting a temperature associated with the display unit, and a control step of controlling a threshold compensation period of the first drive transistor and the second drive transistor of each of the plurality of pixel circuits based on the temperature. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a display device or the like that can suppress the loss of white balance that depends on temperature with a simplified configuration. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing an overall configuration of a display device according to an embodiment. [Diagram 2] FIG. 2 is a circuit diagram showing an example of a configuration of a pixel circuit according to an embodiment. [Diagram 3] FIG. 3 is a block diagram showing an overall configuration of a display device of a comparative example. [Figure 4] FIG. 4 is a schematic timing chart showing the relationship between each control signal in a sub-pixel circuit of a display device of a comparative example and the source potential and gate potential of a driving transistor. [Diagram 5]FIG. 5 is a graph showing the relationship between the luminance ratio and time in each sub-pixel circuit of the comparative example. [Figure 6] FIG. 6 is a graph showing the relationship between the average luminance ratio over one frame period and the magnitude of the off-current in each subpixel circuit of the comparative example. [Figure 7] FIG. 7 is a graph showing the relationship between the off current ratio and the temperature of the display unit in each sub-pixel circuit of the comparative example. [Figure 8] FIG. 8 is a graph showing the relationship between the gate-source voltage ratio (Vgs ratio) of the driving transistor in each sub-pixel circuit of the comparative example and the temperature of the display unit. [Figure 9] FIG. 9 is a graph showing an example of the relationship between the threshold compensation period and the temperature of the display unit in the display device according to the embodiment. [Figure 10] FIG. 10 is a schematic timing chart showing the relationship between each control signal in the subpixel circuit of the display device according to the embodiment and the source potential and gate potential of the drive transistor. [Figure 11] FIG. 11 is a graph showing the relationship between the gate-source voltage ratio (Vgs ratio) of the driving transistor in each sub-pixel circuit of the embodiment and the comparative example and the temperature of the display unit. [Figure 12] FIG. 12 is a graph showing the relationship between the length of the threshold compensation period and the luminance variation for each subpixel circuit according to the embodiment. [Figure 13] FIG. 13 is a flowchart showing the flow of a control method for the display device according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below shows a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, the arrangement and connection of the components, steps, and the order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Therefore, among the components in the following embodiments, components that are not described in the independent claims showing the highest concept in the present disclosure will be described as optional components.

[0013] In addition, each figure is a schematic diagram and is not necessarily precisely illustrated. Therefore, the scales and the like are not necessarily the same in each figure. In addition, in each figure, the same reference numerals are given to substantially the same configurations, and duplicated explanations are omitted or simplified.

[0014] (Embodiment) A display device and a driving method thereof according to an embodiment will be described.

[0015] [1. Overall configuration of the display device] First, the overall configuration of a display device according to the present embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing the overall configuration of a display device 1 according to the present embodiment.

[0016] The display device 1 according to this embodiment is a device that displays an image based on a video signal. As shown in Fig. 1, the display device 1 includes a display unit 12, a gate driver 13, a data driver 15, a control circuit 16, a power supply 17, and a temperature sensor 19. In this embodiment, the display device 1 is an active matrix type color display device.

[0017] The display unit 12 is an image display unit having a plurality of pixel circuits 10 arranged in a matrix. Each of the pixel circuits 10 has one or more first sub-pixel circuits and one or more second sub-pixel circuits. A detailed configuration of the pixel circuits 10 will be described later.

[0018] The display unit 12 has three control signal lines ini(i), ref(i), and ws(i) (i is an integer between 1 and N, and N is an integer greater than 1 that indicates the number of rows in the matrix) that are connected to a plurality of pixel circuits 10 arranged in each row of the matrix. The control signal lines ini(i), ref(i), and ws(i) each transmit a control signal supplied from the gate driver 13 to the pixel circuits 10. Note that the number of control signal lines and the control signals described above are merely an example, and are not limited to this example.

[0019] The display unit 12 has three data signal lines Ldr(j), Ldg(j), and Ldb(j) (j is an integer between 1 and M, and M is an integer greater than 1 that indicates the number of columns in the matrix) connected to a plurality of pixel circuits 10 arranged in each column of the matrix. The data signal lines Ldr(j), Ldg(j), and Ldb(j) transmit data signals related to the emission luminance of R, G, and B, respectively, supplied from a data driver 15 to the pixel circuits 10. The data signals input to each sub-pixel circuit are signals determined based on a video signal input to a control circuit 16.

[0020] The control circuit 16 is a circuit that controls the operation of the display unit 12. In the present embodiment, the control circuit 16 receives a video signal from the outside, and supplies a signal for displaying an image of each frame corresponding to the video signal on the display unit 12 to the gate driver 13 and the data driver 15. The detailed operation of the control circuit 16 will be described later.

[0021] The gate driver 13 is a circuit that outputs a control signal to the display unit 12 based on a signal from the control circuit 16. In this embodiment, the gate driver 13 outputs a drive pulse to each of the control signal lines ini(i), ref(i), and ws(i). The gate driver 13 is configured, for example, by a shift register circuit that sequentially shifts (transfers) a start pulse in synchronization with a clock pulse.

[0022] The data driver 15 is a circuit that outputs a data signal to the display unit 12 based on a signal from the control circuit 16 .

[0023] The power supply 17 supplies a reference potential, a power supply potential, and the like to the display unit 12, the gate driver 13, the data driver 15, and the control circuit 16. The power supply 17 supplies, for example, a reference potential VREF applied to a reference potential line Lref, an initialization potential VINI applied to an initialization potential line Lini, a positive power supply potential applied to a positive power supply line Lvcc, and a negative power supply potential applied to a negative power supply line Lcat to the display unit 12.

[0024] The temperature sensor 19 is a sensor that detects the temperature related to the display unit 12. The temperature sensor 19 may be capable of detecting a temperature corresponding to the temperature of the display unit 12. The temperature sensor 19 may be disposed on the rear surface of the display unit 12 (the surface behind the display surface), or may be provided in a driving circuit such as the gate driver 13 or the data driver 15. The configuration of the temperature sensor 19 is not particularly limited. The temperature sensor 19 may be of a contact type or a non-contact type. The display device 1 does not necessarily have to include the temperature sensor 19. For example, the display device 1 may detect the temperature related to the display unit 12 by acquiring information on the temperature related to the display unit 12 from the outside.

[0025] [2. Pixel circuit] Next, a circuit configuration example of the pixel circuit 10 will be described with reference to Fig. 2. Fig. 2 is a circuit diagram showing an example of the configuration of the pixel circuit 10 according to the present embodiment. Fig. 2 shows a pixel circuit 10 arranged in the i-th row and j-th column out of the multiple pixel circuits 10.

[0026] 2, in this embodiment, each of the pixel circuits 10 has sub-pixel circuits 11R, 11G, and 11B corresponding to the emitted light colors of R, G, and B, respectively. The sub-pixel circuit 11B is an example of a first sub-pixel circuit. Each of the sub-pixel circuits 11R and 11G is an example of a second sub-pixel circuit. The sub-pixel circuits 11R, 11G, and 11B included in the pixel circuit 10 according to this embodiment will be described below.

[0027] The sub-pixel circuit 11B includes an initialization transistor T1 B , reference transistor T2 B, write transistor T3 B , capacitor CS B , drive transistor TD B and the light-emitting element EL B The subpixel circuit 11B also has control signal lines ini(i), ref(i), and ws(i), an initialization potential line Lini, a reference potential line Lref, a data signal line Ldb(j), a positive power supply line Lvcc, and a negative power supply line Lcat. The control signal lines ini(i), ref(i), and ws(i) are also referred to as a first control signal line, a second control signal line, and a third control signal line, respectively.

[0028] Drive transistor TD B is a light-emitting element EL B TD is an example of a first drive transistor that supplies a current to B is the capacitor CS B In response to the voltage held on the B In other words, the capacitor CS B A current according to the voltage held in the drive transistor TD B Light emitting element EL B As a result, the light-emitting element EL B emits light with a luminance represented by a data signal input to the data signal line Ldb(j).

[0029] Write transistor T3 B is the capacitor CS B In this embodiment, the write transistor T3 B is the driving transistor TD B and a gate electrode of the light-emitting element EL B The write transistor T3 switches the conduction state between the data signal line Ldb(j) to which the data signal corresponding to the luminance of the pixel is input. B is turned on (i.e., conductive) in response to a signal input to the control signal line ws(i), and the voltage of the data signal input to the data signal line Ldb(j) is applied to the capacitor CS B is held in

[0030] Initialization transistor T1 B is a light-emitting element EL B The initialization transistor T1 is an example of a first initialization transistor that switches the conduction state between the initialization potential line Lini to which the initialization potential VINI is applied. B is turned on in response to the control signal applied to the control signal line ini(i), and the driving transistor TD B The source electrode of each of the transistors is set to the initialization potential VINI applied to the initialization potential line Lini.

[0031] Reference transistor T2 B is the driving transistor TD B The reference transistor T2 is an example of a first reference transistor that switches the conduction state between the gate electrode of the reference transistor T2 and the reference potential line Lref to which the reference potential VREF is applied. B is turned on in response to a control signal input to the control signal line ref(i), and the driving transistor TD B The gate electrode of the transistor is set to the reference potential VREF applied to the reference potential line Lref.

[0032] Capacitor CS B is an example of a first capacitor that holds a charge corresponding to a video signal. In other words, the capacitor CS B holds the charge and voltage corresponding to the data signal input to the sub-pixel circuit 11B.

[0033] Light-emitting element EL B is an example of a first light-emitting element that emits light in the sub-pixel circuit 11B. In the present embodiment, the light-emitting element EL B is a blue organic EL element that emits blue light.

[0034] The sub-pixel circuit 11R includes an initialization transistor T1 R , reference transistor T2 R , write transistor T3 R , capacitor CS R , drive transistor TD R and the light-emitting element EL RThe sub-pixel circuit 11G includes an initialization transistor T1 G , reference transistor T2 G , write transistor T3 G , capacitor CS G , drive transistor TD G and the light-emitting element EL G Each of the subpixel circuits 11R and 11G has a control signal line ini(i), ref(i), ws(i), an initialization potential line Lini, a reference potential line Lref, a positive power supply line Lvcc, and a negative power supply line Lcat, similar to the subpixel circuit 11B. In addition, the subpixel circuits 11R and 11G have data signal lines Ldr(j) ​​and Ldg(j), respectively.

[0035] Drive transistor TD R and T.D. G respectively represent the light-emitting element EL R and E.L. G TD is an example of a second driving transistor that supplies a current to R and T.D. G are the capacitors CS R and C.S. G In response to the voltage held on the R and E.L. G In other words, the capacitor CS R and C.S. G The current flows through the driving transistor TD according to the voltage held in the R and T.D. G Light emitting element EL R and E.L. G As a result, the light-emitting element EL R and E.L. G emit light at luminances represented by data signals input to data signal lines Ldr(j) ​​and Ldg(j), respectively.

[0036] Write transistor T3 R and T3 G are the capacitors CS R and C.S. GIn this embodiment, the write transistor T3 R and T3 G are the driving transistors TD R and T.D. G and a gate electrode of the light-emitting element EL R and E.L. G The write transistor T3 switches the conduction state between the data signal lines Ldr(j) ​​and Ldg(j) to which the data signal corresponding to the luminance of the pixel is input. R and T3 G are turned on in response to a signal input to the control signal line ws(i), and the voltage of the data signal input to the data signal lines Ldr(j) ​​and Ldg(j) is applied to the capacitor CS R and C.S. G is held in

[0037] Initialization transistor T1 R and T1 G respectively represent the light-emitting element EL R and E.L. G The initialization transistor T1 is an example of a second initialization transistor that switches the conduction state between the initialization potential line Lini to which the initialization potential VINI is applied. R and T1 G are turned on in response to a control signal applied to the control signal line ini(i), and the driving transistor TD R and T.D. G The source electrode of each of the transistors is set to the initialization potential VINI applied to the initialization potential line Lini.

[0038] Reference transistor T2 R and T2 G are the driving transistors TD R and T.D. G The reference transistor T2 is an example of a first reference transistor that switches the conduction state between the gate electrode of the reference transistor T2 and the reference potential line Lref to which the reference potential VREF is applied. R and T2 G are turned on in response to a control signal input to the control signal line ref(i), and the driving transistor TDR and T.D. G The gate electrode of the transistor is set to the reference potential VREF applied to the reference potential line Lref.

[0039] Capacitor CS R and C.S. G is an example of a second capacitor that holds a charge corresponding to a video signal. In other words, the capacitor CS R and C.S. G hold charges and voltages corresponding to data signals input to the sub-pixel circuits 11R and 11G, respectively.

[0040] Light-emitting element EL R and E.L. G are examples of second light-emitting elements that emit light in the sub-pixel circuits 11R and 11G, respectively. In this embodiment, the light-emitting element EL R and E.L. G are a red organic EL element emitting red light and a green organic EL element emitting green light, respectively.

[0041] Among the light-emitting elements of each subpixel circuit, the light-emitting element EL B The emission life of the organic EL material used in the red organic EL element is R and a light-emitting element EL that is a green organic EL element. G Therefore, in the present embodiment, the light-emitting element EL B The pixel area of ​​the light-emitting element EL R and E.L. G By making the pixel area larger than that of the light-emitting element EL B As a result, the current density of the light-emitting element EL B In the sub-pixel circuit 11B having the light-emitting element EL B Considering the balance with the characteristics of the first capacitor, capacitor CS B The capacitance of the second capacitor, capacitor CS R and C.S. G The capacity of each of the above is designed to be larger than that of the other.

[0042] The configuration of each of the transistors is not particularly limited, but each of the transistors is, for example, a Si-based semiconductor thin film transistor. Also, each of the transistors can be an N-channel MOSFET. It is also possible to configure each of the sub-pixel circuits using transistors other than N-channel MOSFETs. For example, it is also possible to configure each of the sub-pixel circuits using P-channel MOSFETs.

[0043] Since the pixel circuit 10 has the above-described configuration, the sub-pixel circuits 11R, 11G, and 11B each output the data signal Vdat at the same timing in accordance with the same control signal. R , Vdat G , and Vdat B The light emitting element EL is illuminated with a luminance according to the data signal. R , E.L. G , and E.L. B will emit light.

[0044] [3. Control mode and effect] Next, the control aspects and effects of the display device 1 will be described with reference to FIGS. 3 to 12 while comparing with comparative examples.

[0045] Fig. 3 is a block diagram showing the overall configuration of a comparative display device 1001. As shown in Fig. 3, the comparative display device 1001 includes a display unit 12, a gate driver 13, a data driver 15, a control circuit 1016, and a power supply 17. That is, the comparative display device 1001 differs from the display device 1 according to the present embodiment in that it does not include a temperature sensor 19 and in the configuration of the control circuit 1016, but is the same in other respects.

[0046] The control circuit 1016 is a circuit that controls the operation of the display unit 12. The control circuit 1016 receives a video signal from the outside, and supplies a signal to the gate driver 13 and the data driver 15 for displaying an image of each frame corresponding to the video signal on the display unit 12.

[0047] The control mode by the control circuit 1016 of the comparative example will be described below with reference to Figs. 2 to 4. Fig. 4 shows the control signals and the driving transistor TD B 10 is a schematic timing chart showing the relationship between the source potential Vs and the gate potential Vg of the sub-pixel circuit 11R. Note that, although only the sub-pixel circuit 11B among the sub-pixel circuits 11R, 11G, and 11G will be described here, the timing charts of the other sub-pixel circuits are similar to that of the sub-pixel circuit 11B.

[0048] As shown in FIG. 4, until time t1, all the control signals are at the L level, and the light-emitting element EL B are in an emission state corresponding to the data signal in the immediately preceding vertical period.

[0049] Subsequently, at time t1, a drive pulse is input to the control signal line ref(i). As a result, the control signal input to the control signal line ref(i) is at H level from time t1 to time t2. Accordingly, the reference transistor T2 B Since the source electrode and drain electrode of the driving transistor TD B The gate electrode of the driving transistor TD is connected to the reference potential line Lref. B The potential Vg of the gate electrode of the capacitor CS B The potential of one of the electrodes becomes equal to the reference potential VREF. Here, the reference potential VREF is, for example, about +1 V. As a result, the light-emitting element EL B That is, the drive pulse input to the control signal line ref(i) at time t1 is a light-off pulse. Since the light-off pulse is input to the control signal line ref(i), the drive transistor TD B The gate-source voltage Vgs (i.e., the difference Vg-Vs between the gate potential Vg and the source potential Vs) of the drive transistor TD B Therefore, the threshold voltage Vt of the driving transistor TD B Therefore, it is possible to suppress the voltage drop of the initialization potential line Lini caused by the flow of an on-current therethrough.

[0050] Subsequently, at time t2, the control signal input to the control signal line ref(i) becomes L level, and a drive pulse is input to the control signal line ini(i). As a result, the control signal input to the control signal line ini(i) becomes H level from time t2 to time t3. Accordingly, the initialization transistor T1 B Since the source electrode and the drain electrode of the light-emitting element EL B The anode electrode of the light-emitting element EL B The potential of the anode electrode and the driving transistor TD B The potential Vs of the source electrode of the light-emitting element EL becomes equal to the initialization potential VINI. Here, the initialization potential VINI is, for example, about −2 V. B The potential of the anode electrode and the driving transistor TD B The potential Vs of the source electrode of the driving transistor TD drops from a potential of about +1 V or more to a potential of about −2 V from time t2 to time t3. B The potential Vg of the gate electrode also decreases.

[0051] As described above, when the control signal input to the control signal line ini(i) is at the L level and the H level, the initialization transistor T1 R are in the off and on states, respectively. Here, the initialization transistor T1 B An initialization potential VINI is applied to the source electrode of the initialization transistor T1. R In order to turn off the initialization potential VINI, the L level of the control signal, i.e., the L level of the drive pulse, is set to a potential lower than the initialization potential VINI. In this comparative example, the L level and H level of the drive pulse are set to, for example, about −4 V and about 10 V, respectively.

[0052] In this embodiment, during the initialization period from time t2 to time t3, the driving transistor TD BA relatively large on-current flows through the initial potential line Lini, which may cause a voltage drop in the initial potential line Lini. Therefore, the potential applied to the initial potential line Lini may be increased by an amount equivalent to the voltage drop.

[0053] Subsequently, at time t3, the control signal input to the control signal line ini(i) becomes L level, and a drive pulse is input to the control signal line ref(i). As a result, the control signal input to the control signal line ref(i) becomes H level from time t3 to time t5. Accordingly, the reference transistor T2 B This causes the source electrode and drain electrode of the driving transistor TD B The potential of the gate electrode of the capacitor CS B The potential of one electrode of the driving transistor TD becomes equal to the reference potential VREF. Here, the reference potential VREF is, for example, about +1 V. B That is, the threshold compensation of the driving transistor TD B The difference Vg-Vs between the gate potential Vg and the source potential Vs of the sub-pixel circuit 100 becomes equal to the threshold voltage Vt. The period from time t3 to time t5 is the threshold compensation period. In this comparative example, the threshold compensation period is 2T. Here, the time T is a length of time determined based on the configuration of each sub-pixel circuit, etc.

[0054] Subsequently, at time t5, the control signal input to the control signal line ref(i) becomes L level, and a drive pulse is input to the control signal line ws(i). As a result, the control signal input to the control signal line ws(i) becomes H level from time t5 to time t6. Accordingly, the write transistor T3 B This causes the source electrode and drain electrode of the driving transistor TD B The potential of the gate electrode of the capacitor CS B The potential of one electrode of the capacitor CS becomes equal to the voltage of the data signal applied to the data signal line Ldb(j). In other words, the period from time t5 to time t6 is the data write period. BA voltage corresponding to the data signal is held in the drive transistor TD B A current corresponding to a data signal is applied to the light-emitting element EL B Therefore, the light emitting element EL B The other sub-pixel circuits 11R and 11G perform the same operation as the sub-pixel circuit 11B.

[0055] By using the above-described control mode, the display device 1001 can display an image corresponding to a video signal.

[0056] Here, the problem of the display device 1001 of the comparative example will be described with reference to Figs. 5 to 8. Fig. 5 is a graph showing the relationship between the luminance ratio and time in each subpixel circuit of the comparative example. The horizontal axis of Fig. 5 shows the time after the data writing end time (time t6 in Fig. 4). Fig. 6 is a graph showing the relationship between the luminance ratio of one frame period average in each subpixel circuit of the comparative example and the magnitude of the off current. Here, the luminance ratio means the ratio of the actual luminance of each subpixel circuit to the ideal luminance, which is the ideal luminance assumed when a predetermined data signal is supplied to each subpixel circuit. Fig. 7 is a graph showing the relationship between the off current ratio in each subpixel circuit of the comparative example and the temperature of the display unit 12. Here, the off current ratio (Ioff ratio) is the ratio of the amount of off current to the amount of off current at room temperature (RT). Fig. 8 is a graph showing the relationship between the gate-source voltage ratio (Vgs ratio) of the drive transistor in each subpixel circuit of the comparative example and the temperature of the display unit 12. Here, the gate-source voltage ratio (Vgs ratio) of the driving transistor is the ratio of the gate-source voltage to the gate-source voltage Vgs at room temperature. In Fig. 5 to Fig. 8, the graphs relating to the subpixel circuit 11B are shown by solid lines (see the symbol B in each graph), and the graphs relating to the subpixel circuits 11R and 11G are shown by dashed lines (see the symbols R and G in each graph). In Fig. 7, the solid line graph and the dashed line graph overlap each other.

[0057] In each subpixel circuit of the display device 1001, even when the write transistor and the reference transistor are in the off state, the off current Ioff flows as shown in the subpixel circuit 11B in FIG. 2. Note that although the off current Ioff is shown only in the subpixel circuit 11B in FIG. 2, the off current Ioff also flows in the other subpixel circuits 11R and 11G in the same manner. As a result, after data is written (i.e., the capacitor CS B After charging the charge corresponding to the brightness value, the capacitor CS B Write transistor T3 from B and reference transistor T2 B Here, the luminance value of the sub-pixel circuit 11B (that is, the light-emitting element EL B The brightness value of the driving transistor TD B The gate-source voltage Vgs corresponds to the gate-source voltage Vgs of the capacitor CS B As described above, the capacitance of the capacitor of the subpixel circuit 11B is larger than the capacitance of the other subpixel circuits. On the other hand, the capacitance of the capacitor CS R , C.S. G and C.S. B Therefore, the ratio of the amount of charge discharged from the capacitor by the off current Ioff to the capacitance of the capacitor is smaller in the sub-pixel circuit 11B than in the other sub-pixel circuits 11R and 11G.

[0058] Here, the capacitor CS R , C.S. G and C.S. B The capacitance of each R , C G and C B The charge discharged from each capacitor by the off-current Ioff is expressed as Qc. R , C.S. G and C.S. B The voltage applied to the drive transistor TD R , T.D. G and T.D. BThe amount of drop due to the off-state current is ΔVgs R , ΔVgs G , and ΔVgs B When expressed as:

[0059] ΔVgs R =Qc / C R (1) ΔVgs G =Qc / C G (2) ΔVgs B =Qc / C B (3) C B >C R =C G (4)

[0060] Therefore, the following equation holds:

[0061] ΔVgs B <ΔVgs R = ΔVgs G (5)

[0062] The gate-source voltage of each driving transistor corresponds to the luminance value of the light-emitting element to which current is supplied from the driving transistor. Therefore, the amount of reduction in the luminance value caused by the off-current Ioff is B The light-emitting element EL B and E.L. B 5, the luminance ratio of each subpixel circuit decreases as time passes after data is written, but the amount of decrease in the luminance ratio of the subpixel circuit 11B is smaller than the amount of decrease in the luminance ratio of the subpixel circuits 11R and 11G. Therefore, as shown in FIG. 6, the amount of decrease in the luminance ratio on average over one frame caused by the off current Ioff is also smaller in the subpixel circuit 11B than in the subpixel circuits 11R and 11G. In this way, the amount of decrease in the luminance ratio caused by the off current Ioff differs between the subpixel circuit 11B and the subpixel circuits 11R and 11G, and thus the white balance of the display unit 12 is lost. Such a loss of white balance can be suppressed, for example, by a method of correcting the video signal.

[0063] However, as shown in Fig. 7, the magnitude of the off-current Ioff depends on the temperature of each writing transistor and each reference transistor (that is, the temperature of the display unit 12). For this reason, as shown in Fig. 8, B and the gate-source voltage ratio of the driving transistors TD R and T.D. G The relationship between the gate-source voltage ratio and the gate-source voltage ratio changes according to temperature. Therefore, when the temperature of the display unit 12 fluctuates, the degree of white balance loss also fluctuates. Although it is possible to suppress such temperature-dependent white balance loss by, for example, dynamically correcting the video signal, the configuration of the control circuit 1016 becomes complicated.

[0064] In order to reduce such a loss of white balance, in the display device 1 according to the present embodiment, the control circuit 16 controls the threshold compensation period of each driving transistor of each of the plurality of pixel circuits 10 based on the temperature associated with the display unit 12. More specifically, the control circuit 16 shortens the threshold compensation period as the temperature associated with the display unit 12 increases. Here, the relationship between the threshold compensation period and the temperature of the display unit 12 in the display device 1 according to the present embodiment will be described with reference to FIG. 9. FIG. 9 is a graph showing an example of the relationship between the threshold compensation period and the temperature of the display unit 12 in the display device 1 according to the present embodiment.

[0065] 9, in this embodiment, the threshold compensation period is 2.0T at room temperature, as in the comparative example, but the threshold compensation period becomes shorter as the temperature of display unit 12 rises. Note that the control mode of control circuit 16 in this embodiment differs from control circuit 1016 in the comparative example in that it controls the threshold compensation period based on the temperature of display unit 12, but is the same in other control modes.

[0066] Here, the effect of controlling the threshold compensation period in the display device 1 according to the present embodiment will be described with reference to Fig. 10 and Fig. 11. Fig. 10 shows the control signals in the sub-pixel circuit 11B of the display device 1 according to the present embodiment and the driving transistor TD B 9 is a schematic timing chart showing the relationship between the source potential Vs and the gate potential Vg of the display unit 12. FIG 10 shows a timing chart in the case where the temperature of the display unit 12 shown in FIG 9 is a temperature RT+α which is higher than room temperature RT. FIG 11 is a graph showing the relationship between the gate-source voltage ratio (Vgs ratio) of the driving transistor in each sub-pixel circuit of the present embodiment and the comparative example and the temperature of the display unit 12. In FIG 11, the graphs showing the present embodiment and the comparative example are shown by solid lines and dotted lines, respectively.

[0067] As described above, the control circuit 16 according to the present embodiment controls the threshold compensation period of each driving transistor of each of the plurality of pixel circuits 10 based on the temperature of the display unit 12. When the temperature of the display unit 12 is a temperature RT+α, which is higher than room temperature RT, the control circuit 16 controls the gate driver 13 so that the threshold compensation period is T. As a result, the threshold compensation period ends with the gate-source voltage (Vgs=Vg-Vs) of each driving transistor being higher than the threshold Vt, as shown in FIG. The effect of such control will be described in more detail below.

[0068] For example, the capacitor CS B Capacity C B But the capacitor CS R Capacity C R and capacitor CS G Capacity C G is twice the capacitance of the capacitor CS during the threshold compensation period. R , C.S. G、 and C.S. B Here, the case where the discharge current amount is represented by Ic will be considered. Note that the off-state current Ioff will not be taken into consideration.

[0069] First, when the temperature of the display unit 12 is room temperature, the capacitor CS R , C.S.G、 and C.S. B The discharge capacity of the driving transistor TD is expressed as Ic×2T. R and T.D. G The change in the gate-source voltage during the threshold compensation period (2T) is Ic×2T / C R (=Ic×2T / C G ) Also, the driving transistor TD B The change in the gate-source voltage during the threshold compensation period (2T) is Ic×2T / C B where the capacitance C B is the capacity C R and C G Since it is twice as long as Ic×2T / C B is Ic × T / C R That is, the driving transistor TD B If the change in the gate-source voltage of the driving transistor TD during the threshold compensation period is expressed as ΔVx, R and T.D. G The amount of change in the gate-source voltage during the threshold compensation period (2T) can be expressed as 2ΔVx.

[0070] Therefore, when the temperature of the display unit 12 is room temperature, the driving transistor TD R and T.D. G The gate-source voltage Vgs_rg of the driving transistor TD B The gate-source voltage Vgs_b of the transistor is expressed as follows:

[0071] Vgs_rg=Vt+VREF-VINI-2ΔVx (6) Vgs_b=Vt+VREF-VINI-ΔVx (7)

[0072] On the other hand, when the temperature of the display unit 12 is a temperature RT+α, which is higher than the room temperature, the threshold compensation period is T, so that the capacitor CS R , C.S. G、 and C.S. B The discharge capacity of the driving transistor TD is expressed as Ic×T. R and T.D.G The change in the gate-source voltage during the threshold compensation period (T) is Ic×T / C R (=Ic×T / C G ) Also, the driving transistor TD B The change in the gate-source voltage during the threshold compensation period (T) is Ic×T / C B where the capacitance C B is the capacity C R and C G Since it is twice as long as Ic×2T / C B is Ic×T / (2C R ) In other words, when the above-mentioned change amount ΔVx is used, the driving transistor TD B The change in the gate-source voltage of the driving transistor TD during the threshold compensation period can be expressed as ΔVx / 2. R and T.D. G The amount of change in the gate-source voltage during the threshold compensation period (T) can be expressed as ΔVx.

[0073] Therefore, when the temperature of the display unit 12 is room temperature, the driving transistor TD R and T.D. G The gate-source voltage Vgs_rg of the driving transistor TD B The gate-source voltage Vgs_b of the transistor is expressed as follows:

[0074] Vgs_rg=Vt+VREF-VINI-ΔVx (8) Vgs_b=Vt+VREF-VINI-ΔVx / 2 (9)

[0075] As described above, when the off-current Ioff is not taken into consideration, the driving transistor TD B The gate-source voltage Vgs_b of the driving transistor TD is ΔVx / 2 higher at a temperature RT+α higher than room temperature than at room temperature. R and T.D. GThe gate-source voltage Vgs_rg of the driving transistor TD is higher by ΔVx at a temperature RT+α higher than room temperature than at room temperature. In other words, the increase in the gate-source voltage, i.e., the increase in the luminance of the subpixel circuit, caused by changing the threshold compensation period is B The driving transistor TD R and T.D. G Less than.

[0076] As described above, the amount of decrease in luminance due to the off-current Ioff increases as the temperature increases. Therefore, in the display device 1 according to the present embodiment, the control circuit 16 controls the threshold compensation period of each driving transistor based on the temperature of the display unit 12, so that at least a part of the decrease in luminance due to the off-current Ioff can be offset. More specifically, the control circuit 16 shortens the threshold compensation period as the temperature of the display unit 12 increases. As a result, as shown in FIG. 11, the decrease in the gate-source voltage Vgs ratio of each subpixel circuit due to the increase in temperature can be suppressed, so that the luminance fluctuation due to the off-current Ioff can be kept within the allowable luminance range. In other words, the collapse of the white balance depending on the temperature in the display device 1 can be suppressed. In addition, the above control by the control circuit 16 can be realized by varying the timing of the drive pulse output from the gate driver 13 based on the temperature detected by the temperature sensor 19, so that the control circuit 16 can be realized with a simplified configuration.

[0077] In the conventional display device, the threshold compensation period is sufficiently long so that the threshold compensation is sufficiently completed in all the subpixel circuits. On the other hand, in the display device 1 according to the present embodiment, when the temperature of the display unit 12 is high, the threshold compensation period is shortened, so that the degree of threshold compensation may vary for each subpixel circuit. The brightness variation for each subpixel circuit caused by the variation in the degree of threshold compensation will be described with reference to FIG. 12. FIG. 12 is a graph showing the relationship between the length of the threshold compensation period according to the present embodiment and the brightness variation for each subpixel circuit. In FIG. 12, the horizontal axis indicates the length of the threshold compensation period, and the vertical axis indicates the magnitude of the brightness variation. The length of the threshold compensation period on the horizontal axis becomes shorter from left to right.

[0078] As shown in Fig. 12, as the threshold compensation period becomes shorter, the brightness variation increases due to the variation in the degree of threshold compensation. Therefore, in this embodiment, in order to keep such brightness variation within an allowable range, the minimum value of the threshold compensation period (2T-TL in Fig. 12) may be obtained, and the threshold compensation period may be controlled to be equal to or greater than the minimum value. This allows the brightness variation to be kept within an allowable range.

[0079] [4. Control method] Next, a method for controlling the display device 1 according to the present embodiment will be described with reference to Fig. 13. Fig. 13 is a flowchart showing the flow of the method for controlling the display device 1 according to the present embodiment.

[0080] 13, first, the control circuit 16 detects the temperature associated with the display unit 12 (S10). In the present embodiment, the control circuit 16 detects the temperature associated with the display unit 12 based on a signal from the temperature sensor 19.

[0081] Next, the control circuit 16 controls the threshold compensation period of the first drive transistor and the second drive transistor of each of the plurality of pixel circuits 10 (S20). Specifically, the control circuit 16 adjusts the threshold compensation period of the drive transistor TD R , T.D.G and T.D. B The threshold compensation period is shortened.

[0082] According to the above-described control method, it is possible to suppress the loss of white balance that depends on temperature with a simplified configuration, as described above.

[0083] (Other embodiments) Although the display device and the like according to the present disclosure have been described above based on the embodiment, the display device and the like according to the present disclosure are not limited to the above embodiment. The present disclosure also includes other embodiments realized by combining any of the components in the embodiment, modified examples obtained by applying various modifications to the embodiment that a person skilled in the art can think of without departing from the gist of the present disclosure, and various devices incorporating the processing circuit and the like according to the present embodiment.

[0084] For example, in the above embodiment, organic EL elements are used as light-emitting elements, but the light-emitting elements are not limited to organic EL elements. For example, quantum-dot light-emitting diode (QLED) elements may be used as light-emitting elements.

[0085] In addition, the configuration of the pixel circuit in the display device according to the present disclosure is not limited to the configuration of the pixel circuit used in the above embodiment. For example, the pixel circuit may have only one or two sub-pixel circuits, or may have four or more sub-pixel circuits. In addition, the configuration of the sub-pixel circuit is not limited to the configuration of the pixel circuit used in the above embodiment. Other known sub-pixel circuits may be used as the sub-pixel circuits.

[0086] Furthermore, the arrangement of the sub-pixel circuits in the pixel circuit 10 is not limited to the stripe type arrangement as in the above embodiment. For example, the arrangement of the sub-pixel circuits may be an S-stripe type, a pentail type, or the like.

[0087] In the above embodiment, the gate driver 13 receives signals from only one side of the display unit 12. However, the gate driver 13 may receive signals from both sides of the display unit 12.

[0088] As a mounting form of the data driver 15, a COG (Chip On Glass) type mounting form or a COF (Chip On Flexible) type mounting form may be adopted. [Industrial Applicability]

[0089] INDUSTRIAL APPLICABILITY The present disclosure can be widely used as a display device capable of suppressing loss of white balance in various image display devices such as portable information terminals, personal computers, and television receivers. [Explanation of symbols]

[0090] 1, 1001 Display device 10 Pixel circuit 11R, 11G, 11B Sub-pixel circuit 12 Display section 13 Gate Driver 15 Data Driver 16, 1016 Control circuit 17 Power supply 19 Temperature Sensor CS B , C.S. G , C.S. R Capacitor EL B , E.L. G , E.L. R Light emitting element Lcat negative power line Lini initialization potential line Lref Reference potential line Lvcc positive power line T1 B , T1 G , T1 R Initialization Transistor T2 B , T2 G , T2 R Reference Transistor T3 B, T3 G , T3 R Write Transistor T.D. B , T.D. G , T.D. R Drive Transistor

Claims

1. A method for controlling a display device that displays an image based on a video signal, comprising the steps of: The display device includes: A display unit having a plurality of pixel circuits arranged in a matrix, each of the plurality of pixel circuits includes a first sub-pixel circuit and a second sub-pixel circuit; the first subpixel circuit includes a first light emitting element, a first drive transistor that supplies a current to the first light emitting element, a first capacitor that holds a charge corresponding to the video signal, and a first write transistor that is connected to the first capacitor; the second subpixel circuit includes a second light emitting element, a second driving transistor that supplies a current to the second light emitting element, a second capacitor that holds a charge corresponding to the video signal, and a second writing transistor that is connected to the second capacitor; The capacitance of the second capacitor is smaller than the capacitance of the first capacitor, The method for controlling the display device includes: a detection step of detecting a temperature associated with the display unit; and controlling a threshold compensation period of the first drive transistor and the second drive transistor of each of the plurality of pixel circuits based on the temperature. The display device control method further includes a step of determining a minimum value of the threshold compensation period based on an allowable range of luminance variation between the first light emitting element and the second light emitting element, In the control step, the threshold compensation period is controlled to be equal to or greater than the minimum value. A method for controlling a display device.

2. The control step shortens the threshold compensation period as the temperature increases. A method for controlling the display device according to claim 1.

3. the first light-emitting element is an organic EL element emitting blue light, The second light emitting element is an organic EL element that emits green or red light. A method for controlling the display device according to claim 1 or 2.

4. The first write transistor and the second write transistor are Si-based semiconductor thin film transistors. A method for controlling the display device according to any one of claims 1 to 3.

Images