WO2016027425A1 - 表示装置及びその駆動方法 - Google Patents
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- WO2016027425A1 WO2016027425A1 PCT/JP2015/003887 JP2015003887W WO2016027425A1 WO 2016027425 A1 WO2016027425 A1 WO 2016027425A1 JP 2015003887 W JP2015003887 W JP 2015003887W WO 2016027425 A1 WO2016027425 A1 WO 2016027425A1
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
- G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
- G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
- G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
- G09G3/3225—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix
- G09G3/3233—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix with pixel circuitry controlling the current through the light-emitting element
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/10—OLED displays
- H10K59/12—Active-matrix OLED [AMOLED] displays
- H10K59/121—Active-matrix OLED [AMOLED] displays characterised by the geometry or disposition of pixel elements
- H10K59/1213—Active-matrix OLED [AMOLED] displays characterised by the geometry or disposition of pixel elements the pixel elements being TFTs
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/10—OLED displays
- H10K59/12—Active-matrix OLED [AMOLED] displays
- H10K59/121—Active-matrix OLED [AMOLED] displays characterised by the geometry or disposition of pixel elements
- H10K59/1216—Active-matrix OLED [AMOLED] displays characterised by the geometry or disposition of pixel elements the pixel elements being capacitors
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/10—OLED displays
- H10K59/12—Active-matrix OLED [AMOLED] displays
- H10K59/131—Interconnections, e.g. wiring lines or terminals
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2300/00—Aspects of the constitution of display devices
- G09G2300/08—Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
- G09G2300/0809—Several active elements per pixel in active matrix panels
- G09G2300/0842—Several active elements per pixel in active matrix panels forming a memory circuit, e.g. a dynamic memory with one capacitor
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2300/00—Aspects of the constitution of display devices
- G09G2300/08—Active matrix structure, i.e. with use of active elements, inclusive of non-linear two terminal elements, in the pixels together with light emitting or modulating elements
- G09G2300/0809—Several active elements per pixel in active matrix panels
- G09G2300/0842—Several active elements per pixel in active matrix panels forming a memory circuit, e.g. a dynamic memory with one capacitor
- G09G2300/0861—Several active elements per pixel in active matrix panels forming a memory circuit, e.g. a dynamic memory with one capacitor with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
- G09G2300/0866—Several active elements per pixel in active matrix panels forming a memory circuit, e.g. a dynamic memory with one capacitor with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes by means of changes in the pixel supply voltage
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2310/00—Command of the display device
- G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
- G09G2310/0243—Details of the generation of driving signals
- G09G2310/0251—Precharge or discharge of pixel before applying new pixel voltage
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2310/00—Command of the display device
- G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
- G09G2310/0243—Details of the generation of driving signals
- G09G2310/0254—Control of polarity reversal in general, other than for liquid crystal displays
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2310/00—Command of the display device
- G09G2310/08—Details of timing specific for flat panels, other than clock recovery
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/02—Improving the quality of display appearance
- G09G2320/0271—Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/04—Maintaining the quality of display appearance
- G09G2320/043—Preventing or counteracting the effects of ageing
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/04—Maintaining the quality of display appearance
- G09G2320/043—Preventing or counteracting the effects of ageing
- G09G2320/045—Compensation of drifts in the characteristics of light emitting or modulating elements
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2320/00—Control of display operating conditions
- G09G2320/06—Adjustment of display parameters
- G09G2320/0626—Adjustment of display parameters for control of overall brightness
Definitions
- the present disclosure relates to a display device and a driving method thereof.
- a display device using an organic EL (Electro Luminescence) element As a display device using a current-driven light emitting element, a display device using an organic EL (Electro Luminescence) element is known.
- An organic EL display device using organic EL elements does not require a backlight necessary for a liquid crystal display device, and is optimal for thinning the device. Moreover, since there is no restriction
- an active matrix display device such as an organic EL display device
- a plurality of pixels are arranged in a matrix.
- the pixel includes an organic EL element and a driving transistor that supplies a driving current corresponding to the pixel signal to the organic EL element.
- a thin film transistor (TFT: Thin Film Transistor) is used as the driving transistor.
- TFT Thin Film Transistor
- the threshold voltage of the TFT shifts with time due to stress such as a gate-source voltage during energization.
- the shift of the threshold voltage over time causes fluctuations in the amount of current supplied to the organic EL element, and thus affects the brightness control of the display device, degrading the display quality.
- Patent Document 1 discloses a configuration that suppresses fluctuations in the threshold voltage of the drive transistor by applying a reverse bias voltage corresponding to a video signal during a non-light emitting period.
- Patent Document 1 has a problem in that an appropriate reverse bias voltage is not applied due to the influence of variations in the electrical characteristics of the organic EL element or the parasitic capacitance of the drive transistor. For this reason, for example, when the reverse bias voltage is too small, fluctuations in the threshold voltage of the drive transistor that occur during the light emission period cannot be sufficiently suppressed. On the other hand, when the reverse bias voltage is too large, the threshold voltage of the driving transistor is shifted in the reverse direction, and fluctuations in the threshold voltage cannot be suppressed.
- the present disclosure provides a display device and a driving method thereof that can suppress the variation with time of the threshold voltage of the transistor with higher accuracy.
- a display device driving method including a plurality of pixels arranged in a matrix, and each of the plurality of pixels includes a supplied current.
- a reverse bias application step of applying a reverse bias voltage between the sources, and the reset step is reverse to the light emission step. It is performed between the bias application step.
- FIG. 1 is a block diagram showing a schematic configuration of the organic EL display device according to the first embodiment.
- FIG. 2 is a circuit diagram illustrating a circuit configuration of a pixel in the organic EL display device according to the first embodiment.
- FIG. 3 is a timing chart illustrating the operation of the pixel in the organic EL display device according to the first embodiment at the time of low gradation light emission.
- FIG. 4A is a state transition diagram illustrating the operation of the pixel in the organic EL display device according to the first embodiment at the time of low gradation light emission.
- FIG. 4B is a state transition diagram illustrating the operation of the pixel in the organic EL display device according to Embodiment 1 when light is emitted at low gradation.
- FIG. 1 is a block diagram showing a schematic configuration of the organic EL display device according to the first embodiment.
- FIG. 2 is a circuit diagram illustrating a circuit configuration of a pixel in the organic EL display device according to the first embodiment.
- FIG. 5 is a timing chart illustrating the operation of the pixel in the organic EL display device according to the first embodiment at the time of high gradation light emission.
- FIG. 6A is a state transition diagram illustrating the operation of the pixel in the organic EL display device according to Embodiment 1 at the time of high gradation light emission.
- FIG. 6B is a state transition diagram illustrating the operation of the pixel in the organic EL display device according to Embodiment 1 at the time of high gradation light emission.
- FIG. 7 is a timing chart showing the operation of the pixel in the organic EL display device according to the second embodiment.
- FIG. 8A is a state transition diagram illustrating an operation of a pixel in the organic EL display device according to the second embodiment.
- FIG. 8B is a state transition diagram illustrating the operation of the pixel in the organic EL display device according to Embodiment 2.
- FIG. 9 is a timing chart showing the operation of the pixel in the organic EL display device according to the third embodiment.
- FIG. 10 is a timing chart showing the operation of the pixel in the organic EL display device according to the fourth embodiment.
- FIG. 11A is a state transition diagram illustrating an operation of a pixel in the organic EL display device according to the fourth embodiment.
- FIG. 11B is a state transition diagram illustrating the operation of the pixel in the organic EL display device according to Embodiment 4.
- FIG. 12 is a timing chart illustrating the operation of the pixel in the organic EL display device according to the fifth embodiment at the time of high gradation light emission.
- FIG. 13 is a timing chart illustrating the operation of the pixel in the organic EL display device according to the fifth embodiment at the time of low gradation light emission.
- FIG. 14 is an external view of a
- FIG. 1 is a block diagram showing a schematic configuration of an organic EL display device 1 according to the present embodiment.
- FIG. 2 is a circuit diagram showing a circuit configuration of the pixel 4 in the organic EL display device 1 according to the present embodiment.
- the organic EL display device 1 includes a display area 2 and a control unit 3.
- the display area 2 pixels 4 to be described later are arranged in a matrix.
- the control unit 3 performs various controls on the plurality of pixels 4 arranged in the display area 2.
- the control unit 3 includes a timing control circuit 5, a scanning line driving circuit 6, a data line driving circuit 7, and a voltage control circuit 8.
- the timing control circuit 5 performs, for example, synchronization of the scanning line driving circuit 6, the data line driving circuit 7, and the voltage control circuit 8, timing control of the operation of the organic EL display device 1 for each frame, and the like.
- the scanning line driving circuit 6 drives the scanning lines 60 in the display area 2 based on the control signal from the timing control circuit 5.
- the scanning line driving circuit 6 is a gate driver IC.
- the scanning line driving circuit 6 outputs a scanning signal to each pixel 4 for each row based on the vertical synchronizing signal and the horizontal synchronizing signal.
- the scan signal is a pulse signal that is output to the scan line 60 and is used to control conduction and non-conduction of the connection switching transistor 43 (see FIG. 2).
- the data line driving circuit 7 drives the data lines 70 in the display area 2 based on the control signal from the timing control circuit 5.
- the data line driving circuit 7 is a source driver IC (data driver IC).
- the data line driving circuit 7 outputs a pixel signal indicating the luminance of the pixel to each pixel 4 based on the horizontal synchronization signal.
- the pixel signal is output to the data line 70 and used to indicate the luminance of the connection destination pixel 4.
- the voltage control circuit 8 supplies various power supply voltages to the display area 2.
- the various power supply voltages are Vtft and Vel in the pixel example shown in FIG. 2, and are supplied to each pixel 4 via power supply lines 80 and 81 (not shown in FIG. 1), respectively.
- the voltage control circuit 8 may be incorporated in a gate driver IC or a data driver IC, for example.
- the organic EL display device 1 includes, for example, a CPU (Central Processing Unit), a storage medium such as a ROM (Read Only Memory) storing a control program, a working memory such as a RAM (Random Access Memory), although not illustrated.
- a communication circuit may be included.
- the pixel signal may be generated, for example, when the CPU executes a control program.
- the pixel 4 includes an organic EL element 40, a drive transistor 41, a storage capacitor 42, and a switching transistor 43.
- a scan line 60, a data line 70, a power supply line 80, and a power supply line 81 are connected to the pixel 4.
- the organic EL element 40 emits light with a luminance corresponding to a voltage (that is, a signal voltage) corresponding to the pixel signal supplied via the data line 70.
- the organic EL element 40 is an example of a light emitting element that emits light according to a supplied current. Specifically, the organic EL element 40 emits light with a luminance corresponding to the amount of current supplied from the drive transistor 41.
- the organic EL element 40 has a cathode connected to the power supply line 81 and an anode connected to the source of the drive transistor 41.
- the driving transistor 41 supplies current to the organic EL element 40.
- the drive transistor 41 is a voltage-driven drive element that controls the amount of current supplied to the organic EL element 40, and causes the organic EL element 40 to emit light by flowing a current through the organic EL element 40.
- the drain of the drive transistor 41 is connected to the power supply line 80, and the gate is connected to the data line 70 via the switching transistor 43.
- the gate of the drive transistor 41 is connected to the first electrode of the storage capacitor 42, and the source is connected to the second electrode of the storage capacitor 42 and the anode of the organic EL element 40.
- the source and drain of the drive transistor 41 are switched between a light emission period and a capacitance reset period described later. That is, in the light emission period, the terminal on the power supply line 80 side of the drive transistor 41 is the drain and the terminal on the power supply line 81 side is the source, whereas in the capacitance reset period, the terminal on the power supply line 81 side of the drive transistor 41. Is the drain, and the terminal on the power supply line 80 side is the source.
- the terminal on the power supply line 80 side of the drive transistor 41 is assumed to be the drain and the terminal on the power supply line 81 side is assumed to be the source. The same applies to other embodiments.
- the driving transistor 41 can pass a current through the organic EL element 40 with a current amount corresponding to the voltage held in the holding capacitor 42. That is, the organic EL display device 1 can cause the organic EL element 40 to emit light with a luminance corresponding to the voltage held in the holding capacitor 42 by the light emitting operation.
- the threshold voltage of the drive transistor 41 may vary from pixel 4 to pixel 4 due to an initial distribution at the time of forming a TFT substrate provided with the drive transistor 41 and a threshold voltage shift over time.
- the effect of this variation can be suppressed by applying a reverse bias voltage.
- a reverse bias voltage having a polarity different from that of the signal voltage is applied between the gate and the source of the driving transistor 41.
- the signal voltage is a positive bias voltage in the range of 0 to 10V
- the reverse bias voltage is a negative bias voltage (for example, ⁇ 10V).
- the holding capacitor 42 is connected between the gate and source of the driving transistor 41 (the holding capacitor 42 holds not only the threshold voltage but also the reverse bias voltage and the image signal voltage). Specifically, the second electrode of the storage capacitor 42 is connected to a node to which the source of the driving transistor 41 (on the power supply line 81 side) and the anode of the organic EL element 40 are connected. The first electrode of the storage capacitor 42 is connected to the gate of the drive transistor 41. The first electrode of the storage capacitor 42 is connected to the data line 70 through the switching transistor 43.
- the switching transistor 43 is an example of a switch connected between the gate of the driving transistor 41 and the data line 70.
- the switching transistor 43 switches between conduction and non-conduction between the data line 70 for supplying a pixel signal and the first electrode of the storage capacitor 42 (that is, the gate of the drive transistor 41).
- the switching transistor 43 has a function for writing a voltage (that is, a signal voltage) corresponding to the pixel signal supplied via the data line 70 into the storage capacitor 42.
- the scan line 60 is provided for each row of the plurality of pixels 4 in the display area 2.
- the scan line 60 is connected to the scan line driving circuit 6 and transmits a scan signal for switching between conduction and non-conduction of the switching transistor 43.
- the data line 70 is provided for each column of the plurality of pixels 4 in the display area 2. That is, the data line 70 is connected to the pixel 4 arranged in the column for each column of the plurality of pixels 4.
- the m-th column data line 70 is connected to the switching transistors 43 of the plurality of pixels 4 in the m-th column.
- the data line 70 is selectively set to a plurality of potentials including a signal potential corresponding to the pixel signal.
- the data line 70 is selectively set to a signal potential, a reset potential, and a reverse bias potential.
- the signal potential is a potential corresponding to the luminance of the pixel 4 and is a potential supplied to the first electrode of the storage capacitor 42 (that is, the gate of the driving transistor 41). Note that the luminance of the pixel 4 is determined according to the signal voltage written to the storage capacitor 42. Therefore, the signal potential is set to a value obtained by adding a signal voltage corresponding to the luminance of the pixel 4 to the reference potential.
- the reference potential is a second potential (described later) set on the power supply line 80.
- the reset potential is a potential for making the driving transistor 41 conductive.
- the reset potential is a predetermined potential independent of the signal potential.
- the reset potential is a value obtained by adding a voltage higher than the threshold voltage (for example, 2 V) of the drive transistor 41 to the reference potential.
- the reverse bias potential is a potential for applying a reverse bias voltage between the gate and source of the drive transistor 41.
- the reverse bias potential is lower than the reference potential.
- the reverse bias potential is lower than the lowest signal potential and is a negative potential.
- the power lines 80 and 81 are provided for each row of the plurality of pixels 4 in the display area 2, for example. That is, the power supply lines 80 and 81 are connected to the pixels 4 arranged in the row for each row of the plurality of pixels 4. For example, the power lines 80 and 81 in the nth row are connected to the drains of the drive transistors 41 of the pixels 4 in the nth row.
- the power supply line 80 may be arranged for each row, and the power supply line 81 may be arranged for each column.
- the power supply line 80 is connected to the drain of the drive transistor 41 and is a power supply line for supplying a current for causing the organic EL element 40 to emit light.
- the power supply line 80 is selectively set to a first potential and a second potential that is lower than the first potential.
- the first potential is a potential for causing a current to flow through the organic EL element 40, and is higher than, for example, a potential set in the power supply line 81.
- a current for causing the organic EL element 40 to emit light can be supplied.
- the first potential is 16V.
- the second potential is a potential that serves as a reference when resetting the charges of the storage capacitor 42 and the parasitic capacitance of the organic EL element 40.
- the second potential is a reference potential when writing the signal voltage to the storage capacitor 42.
- the second potential is a potential obtained by adding a voltage lower than the threshold voltage (for example, 2 V) of the organic EL element 40 to the potential set in the power supply line 81.
- the second potential is 1V.
- the second potential may be lower than the potential set for the power supply line 81. That is, when the second potential is set in the power supply line 80, the value of the second potential is determined so as not to supply a current for causing the organic EL element 40 to emit light.
- the power line 81 is a power line connected to the cathode of the organic EL element 40.
- the power supply line 81 is grounded. In other words, a potential of 0 V is set for the power supply line 81.
- the organic EL display device 1 can apply the reverse bias voltage to the driving transistor 41 with high accuracy, and can suppress the variation with time of the threshold voltage of the transistor with higher accuracy. . This mechanism will be described in detail in the following operation description.
- the several transistor which comprise the pixel 4 demonstrates below as an n-type TFT, it is not restricted to this.
- the plurality of transistors may be p-type TFTs. In a plurality of transistors, an n-type TFT and a p-type TFT may be mixedly used.
- FIG. 3 is a timing chart showing an operation at the time of low gradation light emission of the pixel 4 in the organic EL display device 1 according to the present embodiment.
- 4A and 4B are state transition diagrams showing the operation of the pixel 4 in the organic EL display device 1 according to the present embodiment at the time of low gradation light emission.
- FIG. 3 shows, in order from the top, the potential “Vtft” set on the power supply line 80, the potential “Vdata” set on the data line 70, the scan signal “Scan” supplied to the scan line 60, In addition, the gate potential (thick solid line) and the source potential (thin solid line) of the driving transistor 41 are shown.
- the first potential Vtft_H and the second potential Vtft_L are selectively set in the power supply line 80. Specifically, Vtft_H is set in the light emission period, and Vtft_L is set in the non-light emission period.
- the signal potential (“video” in FIG. 3) for each row of the plurality of pixels 4 is sequentially set in the data line 70 every horizontal period (1H). Specifically, in one horizontal period, a first period 101 in which a signal potential is set in the data line 70, a second period 102 in which a reset potential is set in the data line 70, and a reverse bias potential is set in the data line.
- the third period 103 is included.
- the data line 70 is set to three different potentials in one horizontal period. That is, in the present embodiment, the data line driving circuit 7 drives the data line 70 at a frequency that is three times the one horizontal frequency (that is, the reciprocal of one horizontal period: 1 / 1H).
- first period 101, the second period 102, and the third period 103 are periods having the same length, specifically, one third of one horizontal period, but are not limited thereto.
- the first period 101, the second period 102, and the third period 103 may be periods having different lengths.
- the signal potential needs to be set to an accurate voltage in the storage capacitor 42 of each pixel 4, it is preferable to set the first period 101 longer.
- the second period 102 may be shorter than the first period 101 as long as the driving transistor 41 can be made conductive and it is not necessary to set the voltage as accurately as the signal potential.
- the reverse bias potential does not need to be set as accurately as the signal potential, but has an accuracy equal to or higher than the reset potential (because an appropriate value must be set to suppress the temporal variation of the threshold voltage of the driving transistor). Therefore, it is preferable to set the voltage. That is, it is more preferable to set the first period 101 to be longer than the second period 102 and the third period 103.
- the signal voltage is written at time t4. That is, the signal potential illustrated in FIG. 3 indicates signal potentials corresponding to pixels in other rows, except for the signal potential at time t4.
- Scan signals 111 to 113 for making the switching transistor 43 conductive are supplied to the scan line 60 at a predetermined timing.
- the scan signals 111 to 113 are pulse signals, and each pulse width is shorter than each of the first period 101, the second period 102, and the third period 103.
- the pulse widths of the scan signals 111 to 113 may be common, or may be set individually according to the first period 101, the second period 102, and the third period 103.
- the switching transistor 43 conducts only for a period corresponding to the pulse width of the pulse signal.
- Vtft_H is set to the power supply line 80, as shown in FIG. 4A, the signal voltage (for example, 2.5 V) held in the holding capacitor 42 is set. ) Flows through the organic EL element 40 via the drive transistor 41.
- Vtft_H is, for example, 16V.
- the organic EL element 40 emits light with low luminance.
- the anode potential of the organic EL element 40 that is, the source potential of the drive transistor 41 is 4V, and the gate potential of the drive transistor 41 is 6.5V.
- Vtft_L is, for example, 1V.
- the driving transistor 41 is turned on, and the signal voltage held in the holding capacitor 42 is supplied to the power supply line via the driving transistor 41. Exit to 80. Due to the loss of charge, the potential at both ends of the storage capacitor 42 decreases, and the gate potential of the drive transistor 41 becomes 4 V and the source potential becomes 1.5 V, for example, as shown in FIG. 4A (b).
- the threshold voltage of the driving transistor 41 is 2V
- the charges of the parasitic capacitances of the storage capacitor 42 and the organic EL element 40 gradually escape to the power supply line 80.
- the parasitic capacitance is large, and the on-voltage of the drive transistor 41 is insufficient to remove charges from both the storage capacitor 42 and the parasitic capacitance of the organic EL element 40 within a specified time. For this reason, electric charge remains at the source of the driving transistor 41 and becomes an indefinite potential.
- the undefined potential varies according to the parasitic capacitance of the storage capacitor 42 and the organic EL element 40.
- the undefined potential is also affected by the potential of the power supply line 81.
- the potential of the power supply line 81 varies in the plane of the display region 2 due to a voltage drop due to wiring resistance. For this reason, the source potential differs for each pixel 4 and can only be said to be approximately 1.5 V, and strictly speaking, it becomes an indefinite potential.
- the source of the driving transistor 41 since the source of the driving transistor 41 has an indefinite potential, the magnitude of the reverse bias voltage varies depending on the source potential, and an appropriate reverse bias voltage cannot be applied. Therefore, in the present embodiment, the source potential of the drive transistor 41 is stabilized by resetting the charges of the parasitic capacitances of the storage capacitor 42 and the organic EL element 40 before applying the reverse bias voltage.
- ⁇ Time t2 to t3 Capacity reset period>
- a reset signal is supplied to the gate of the drive transistor 41 by supplying the scan signal 111 to the scan line 60 and making the switching transistor 43 conductive.
- the power supply line 80 is set to Vtft_L, and the data line 70 is set to the reset potential.
- the reset potential is a potential for applying a voltage equal to or higher than the threshold voltage between the gate and drain (power supply line 80) of the drive transistor 41.
- the reset potential is, for example, 8V.
- the source potential of the drive transistor 41 becomes 1 V, which is the same as that of the power supply line 80.
- the source potential of the drive transistor 41 can be made the same as the potential of the power supply line 80.
- the reset period (time t2 to t3) is approximately two horizontal periods, but is not limited thereto.
- the length of the reset period may be set to a time sufficient for discharge depending on the size of the parasitic capacitance of the storage capacitor 42 and the organic EL element 40.
- ⁇ Time t3 to t4 Reverse bias application period>
- a reverse bias potential is supplied to the gate of the drive transistor 41 by supplying the scan signal 112 to the scan line 60 and making the switching transistor 43 conductive.
- the power supply line 80 is set to Vtft_L, and the data line 70 is set to a reverse bias potential.
- the reverse bias potential is a potential for applying a reverse bias voltage between the gate and the source of the driving transistor 41.
- the reverse bias voltage is, for example, a voltage having a polarity different from that of the signal voltage held in the holding capacitor 42.
- the reverse bias voltage is a negative voltage applied between the gate and source of the drive transistor 41.
- the reverse bias voltage corresponds to the gate potential of the drive transistor 41, that is, the difference between the reverse bias potential and the source potential. Since the source potential is set to Vtft_L having the same potential as that of the power supply line 80 by the reset period, the reverse bias voltage is set to the difference between the reverse bias potential set to the data line 70 and Vtft_L set to the power supply line 80. Become. That is, a reverse bias voltage having an appropriate value can be applied between the gate and the source of the drive transistor 41 without being affected by variations in the organic EL element 40 and a voltage drop in the power supply line 81.
- the reverse bias potential is lower than Vtft_L set to the power supply line 80, for example, ⁇ 9V. Since the source potential of the drive transistor 41 is set to 1 V, a reverse bias voltage of ⁇ 10 V is applied between the gate and source of the drive transistor 41 as shown in FIG. 4B (f). Thereby, the temporal variation of the threshold voltage of the drive transistor 41 can be suppressed.
- the reverse bias potential is not necessarily a negative voltage. For example, it may be 0V. This is because, since the source potential of the drive transistor 41 is set to 1 V, a reverse bias voltage of ⁇ 1 V is applied between the gate and source of the drive transistor 41, and the same effect can be expected. As described above, the reverse bias potential may be set in consideration of the potential that can be output from the data line driving circuit 7 and the characteristics of the driving transistor 41, and is not necessarily a negative voltage.
- the reverse bias application period (time t3 to t4) is approximately 5 horizontal periods, but is not limited thereto.
- the length of the reverse bias application period may be set to a period sufficient to suppress the variation with time of the threshold voltage depending on the characteristics of the drive transistor 41 and the like.
- the signal potential at this time is a signal potential corresponding to the own pixel. That is, the signal potential is a signal potential corresponding to the luminance that the pixel should emit in the next light emission period.
- the signal potential corresponds to a value obtained by adding a low gradation (low luminance) signal voltage (for example, 2.5 V) to a reference potential (for example, 1 V). Is 3.5V.
- the source potential of the drive transistor 41 may become an indefinite potential before applying the reverse bias voltage. Therefore, by providing a capacitor reset period before applying the reverse bias voltage and setting the source potential of the drive transistor 41 to the second potential (Vtft_L) of the power supply line 80, an appropriate value of the reverse bias voltage is set. Can be applied.
- FIG. 5 is a timing chart showing an operation at the time of high gradation light emission of the pixel 4 in the organic EL display device 1 according to the present embodiment. Specifically, in the figure, in order from the top, the potential “Vtft” supplied to the power supply line 80, the potential “Vdata” supplied to the data line 70, the scan signal “Scan” supplied to the scan line 60, In addition, the gate potential (thick solid line) and the source potential (thin solid line) of the driving transistor 41 are shown.
- 6A and 6B are state transition diagrams showing the operation of the pixel 4 at the time of high gradation light emission in the organic EL display device 1 according to the present embodiment.
- the driving transistor 41 becomes conductive, and the signal voltage held in the holding capacitor 42 is supplied to the power supply line 80 via the driving transistor 41. Go through. Due to the loss of charge, the potential at both ends of the storage capacitor 42 decreases, and the gate potential of the drive transistor 41 becomes 6V and the source potential becomes 1V as shown in FIG. 6B.
- the source potential of the drive transistor 41 becomes the same as Vtft_L set in the power supply line 80 in a state where the drive transistor 41 is completely turned on. That is, since the storage capacitor 42 and the parasitic capacitance of the organic EL element 40 are reset, it is not necessary to provide a reset period.
- the source and drain of the drive transistor 41 become conductive.
- the charges held in the holding capacitor 42 and the parasitic capacitance of the organic EL element 40 are discharged to the power supply line 80 during the discharge period (time t1 to t2), in reality, the charge flow during the reset period.
- the source potential of the drive transistor 41 is maintained at Vtft_L.
- the source potential of the drive transistor 41 becomes 1 V, which is the same as that of the power supply line 80, as shown in FIG.
- ⁇ Time t3 to t4 Reverse bias application period>
- a reverse bias potential is supplied to the gate of the drive transistor 41 by supplying the scan signal 112 to the scan line 60 and turning on the switching transistor 43.
- the power supply line 80 is set to Vtft_L, and the data line 70 is set to a reverse bias potential.
- a reverse bias voltage of ⁇ 10 V is applied between the gate and source of the drive transistor 41. Thereby, the temporal variation of the threshold voltage of the drive transistor 41 can be suppressed.
- ⁇ Time t4 Signal voltage writing>
- the scan signal 113 is supplied to the scan line 60 and the switching transistor 43 is turned on, whereby the signal voltage is written into the storage capacitor 42.
- the power supply line 80 is set to Vtft_L
- the data line 70 is set to the signal potential.
- the signal potential corresponds to a value obtained by adding a high gradation (high luminance) signal voltage (for example, 5 V) to a reference potential (for example, 1 V). 6V.
- the source potential of the drive transistor 41 becomes the same as the potential set on the power supply line 80 before applying the reverse bias voltage. For this reason, it is not necessary to provide a capacitor reset period before applying a reverse bias voltage, but by providing a reset period in preparation for low gradation light emission, an appropriate value of reverse bias voltage can be applied. . Even when the reset period is provided, the operation at the time of high gradation light emission is not affected as described above.
- the driving method of the organic EL display device 1 is a driving method of the organic EL display device 1 including the plurality of pixels 4 arranged in a matrix. Each of them includes an organic EL element 40 that emits light according to the supplied current, a drive transistor 41 that supplies current to the organic EL element 40, and a storage capacitor connected between the gate and the source or drain of the drive transistor 41. 42, and the driving method of the organic EL display device 1 includes a light emission step for causing the organic EL element 40 to emit light by supplying a current to the organic EL element 40, and a parasitic capacitance of the storage capacitor 42 and the organic EL element 40. A reset step for resetting at least one of the charges, and a reverse bias application step for applying a reverse bias voltage between the gate and source of the drive transistor 41. , Reset step is performed between the light emitting step and a reverse bias application step.
- the charge of at least one of the storage capacitor 42 and the parasitic capacitance of the organic EL element 40 is reset, so that an appropriate value of the reverse bias voltage is applied between the gate and the source of the drive transistor 41.
- an appropriate reverse bias voltage can be applied between the gate and the source of the drive transistor 41 by setting an appropriate reverse bias potential on the data line 70. Therefore, it is possible to suppress the variation with time of the threshold voltage of the drive transistor 41 with higher accuracy.
- the organic EL display device 1 is further provided for each column of the plurality of pixels 4 and the power supply line 80 connected to the drains or sources of the drive transistors 41 of the plurality of pixels 4.
- Each of the plurality of pixels 4 further includes a switching transistor 43 connected between the gate of the driving transistor 41 and the data line 70, and in the reset step, the switching transistor 43 is made conductive.
- the reset potential is supplied from the data line 70 to the gate of the drive transistor 41, the drive transistor 41 is turned on, and the charge of at least one of the storage capacitor 42 and the parasitic capacitance is discharged to the power supply line 80.
- the drive transistor 41 can be used to make the source potential of the drive transistor 41 the same as the potential of the power supply line 80. That is, there is no need for a reset transistor or the like for resetting the source potential of the drive transistor 41, and the circuit configuration can be simplified.
- FIG. 2 it can be realized by a so-called 2Tr1C circuit configuration including two transistors and one capacitor.
- the power supply line 80 is selectively set to a first potential and a second potential lower than the first potential, and the data line 70 has a signal potential corresponding to the pixel signal.
- the power supply line 80 is set to the first potential so that a current is supplied to the organic EL element 40 from the power supply line 80 via the drive transistor 41, and the reset step.
- the switching transistor 43 is turned on to supply the reset potential to the gate of the drive transistor 41 and vice versa.
- the switching transistor 43 is turned on in a state where the power supply line 80 is set to the second potential and the data line 70 is set to the reverse bias potential. Thereby passed, by supplying a reverse bias voltage to the gate of the driving transistor 41, a reverse bias voltage is applied.
- the reset potential is a predetermined potential independent of the signal potential.
- the signal potential for each row of the plurality of pixels 4 is set in order for each horizontal period in the data line 70, and the signal potential is set for the data line 70 in one horizontal period. Includes a first period 101, a second period 102 in which a reset potential is set in the data line 70, and a third period 103 in which a reverse bias potential is set in the data line 70.
- the data line 70 is driven at a frequency three times the one horizontal frequency (1 / 1H). That is, the data line 70 is driven three times.
- the data line driving circuit 7 needs to be driven at a triple frequency (triple drive) so as to supply each of the signal potential, the reset potential, and the reverse bias potential within one horizontal period.
- the voltage control circuit 8 may drive the power supply line 80 with two values of the first potential and the second potential. That is, power consumption can be suppressed as compared with the case where the power supply line 80 is driven in three values, and an increase in cost can be suppressed because it can be realized with a simple configuration.
- the charge of the capacitor can be reset within the range used for the light emission of the organic EL element 40.
- the reverse bias potential may be ⁇ 9 V, and the breakdown voltage required for the data line driving circuit 7 may be small. For this reason, since the conventional voltage control circuit 8 can be utilized, the increase in cost can be suppressed.
- Embodiment 2 an organic EL display device and a driving method thereof according to Embodiment 2 will be described.
- the configuration of the organic EL display device and the configuration of the pixels are the same as those in the first embodiment, and the driving operation is different. Therefore, in the following, description of each component will be omitted, and description will be made focusing on driving operation.
- FIG. 7 is a timing chart showing the operation of the pixel 4 in the organic EL display device 1 according to the present embodiment.
- 8A and 8B are state transition diagrams showing the operation of the pixel 4 in the organic EL display device 1 according to the present embodiment.
- FIG. 7 shows, in order from the top, the potential “Vtft” set on the power supply line 80, the potential “Vdata” set on the data line 70, the scan signal “Scan” supplied to the scan line 60, In addition, the gate potential (thick solid line) and the source potential (thin solid line) of the driving transistor 41 are shown.
- the first potential Vtft_H, the second potential Vtft_L2, and the third potential Vtft_L1 are selectively set in the power supply line 80.
- Vtft_H is set in the light emission period
- Vtft_L1 or Vtft_L2 is set in the non-light emission period.
- Vtft_L1 is lower than Vtft_H and higher than Vftf_L2.
- Vtft_L1 is a potential serving as a reference when writing a signal voltage.
- Vtft_L2 is a potential that serves as a reference when resetting the charges of the storage capacitor 42 and the parasitic capacitance of the organic EL element 40.
- the signal potential (“video” in FIG. 7) for each row of the plurality of pixels 4 is sequentially set in the data line 70 every horizontal period (1H).
- One horizontal period includes a first period 201 in which a signal potential is set in the data line 70 and a third period 203 in which a reverse bias potential is set in the data line 70.
- the data line 70 is set to two different potentials in one horizontal period. That is, in the present embodiment, the data line driving circuit 7 drives the data line 70 at a frequency twice as high as one horizontal frequency (1 / 1H).
- the signal potentials of other rows are used as reset potentials used to reset the charges of the parasitic capacitances of the storage capacitor 42 and the organic EL element 40. That is, in this embodiment mode, the reset potential is a signal potential of another row.
- first period 201 and the third period 203 are periods having the same length as each other, specifically, a half period of one horizontal period, but are not limited thereto.
- the first period 201 and the third period 203 may be periods having different lengths.
- the first period 201 is preferably set to be longer.
- the third period 203 may be shorter than the first period 201.
- the signal voltage is written at time t16. That is, the signal potential illustrated in FIG. 7 indicates signal potentials corresponding to pixels in other rows, except for the signal potential at time t16. Note that in this embodiment, the signal potential is set using Vtft_L1 as a reference potential.
- Scan signals 211 to 214 for making the switching transistor 43 conductive are supplied to the scan line 60 at a predetermined timing.
- the scan signals 211 to 214 are pulse signals, and each pulse width is shorter than each of the first period 201 and the third period 203.
- the pulse widths of the scan signals 211 to 214 may be common, or may be set individually according to the first period 201 and the third period 203.
- the switching transistor 43 conducts only for a period corresponding to the pulse width of the pulse signal.
- the organic EL element 40 emits light with low luminance.
- the anode potential of the organic EL element 40 that is, the source potential of the drive transistor 41 is 4V, and the gate potential of the drive transistor 41 is 6.5V.
- Vtft_L2 is, for example, ⁇ 7V.
- the driving transistor 41 becomes conductive, and the signal voltage held in the holding capacitor 42 is supplied via the driving transistor 41 to the power source. Go through line 80. Due to the loss of charge, the potential at both ends of the storage capacitor 42 decreases, and the gate potential of the drive transistor 41 becomes ⁇ 4 V and the source potential becomes ⁇ 6.5 V as shown in FIG. 8A (b).
- the threshold voltage of the driving transistor 41 is 2V
- the charges of the parasitic capacitances of the storage capacitor 42 and the organic EL element 40 gradually escape to the power supply line 80.
- the parasitic capacitance is large, and the on-voltage of the drive transistor 41 is insufficient to remove charges from both the storage capacitor 42 and the parasitic capacitance of the organic EL element 40 within a specified time. For this reason, electric charge remains at the source of the driving transistor 41 and becomes an indefinite potential.
- the undefined potential varies according to the parasitic capacitance of the storage capacitor 42 and the organic EL element 40.
- the charges of the parasitic capacitances of the storage capacitor 42 and the organic EL element 40 are reset using the signal potential of another row.
- the signal potential of the other row is, for example, an indefinite potential of 0V to 10V. Therefore, by setting Vtft_L2 set to the power supply line 80 to ⁇ 7V, the drive transistor 41 can be made conductive regardless of the signal potential applied to the data line 70.
- the gate of the driving transistor 41 is set to a potential of 0V to 10V corresponding to the signal potential of the other row, and the drain is set to a potential of ⁇ 7V. Is set. Therefore, a voltage of at least 7 V or more is applied between the gate and drain of the drive transistor 41, and the source and drain of the drive transistor 41 are conducted. Therefore, the charge remaining in the storage capacitor 42 and the parasitic capacitance of the organic EL element 40 is released to the power supply line 80.
- the source potential of the drive transistor 41 becomes ⁇ 7 V, which is the same as that of the power supply line 80.
- the source potential of the drive transistor 41 can be made the same as the potential of the power supply line 80.
- ⁇ Time t13 to t14 Reverse bias application period>
- a reverse bias potential is supplied to the gate of the drive transistor 41 by supplying a scan signal 212 to the scan line 60 and turning on the switching transistor 43.
- the power supply line 80 is set to Vtft_L2, and the data line 70 is set to the reverse bias potential.
- the reverse bias voltage is set to the reverse bias potential set to the data line 70 and the power supply line 80. This is a difference from Vtft_L2. That is, a reverse bias voltage having an appropriate value can be applied between the gate and the source of the drive transistor 41 without being affected by variations in the organic EL element 40 and a voltage drop in the power supply line 81.
- the reverse bias potential is lower than Vtft_L2 set to the power supply line 80, for example, ⁇ 17V. Since the source potential of the drive transistor 41 is set to ⁇ 7V, a reverse bias voltage of ⁇ 10V is applied between the gate and source of the drive transistor 41 as shown in FIG. 8A (d). Thereby, the temporal variation of the threshold voltage of the drive transistor 41 can be suppressed.
- the source potential of the drive transistor 41 is ⁇ 7V, which is lower than that in the first embodiment (that is, 1V). For this reason, the potential required as the reverse bias potential is also ⁇ 17 V, which is lower than that in the first embodiment (ie, ⁇ 9 V).
- a value equal to or higher than the threshold voltage (2 V) (specifically a value equal to or higher than 7 V) is applied between the gate and source of the driving transistor 41, and therefore the conduction between the drain and source of the driving transistor 41 is established. .
- Vtft_L1 is set to the power supply line 80 as shown in (f) of FIG. 8B.
- Vtft_L1 is, for example, 1V. Since the drive transistor 41 is in a conductive state, electric charge is supplied from the power supply line 80 to the storage capacitor 42, and the source potential of the drive transistor 41 becomes 1 V, which is the same as that of the power supply line 80.
- the source potential is set to Vtft_L1 before the signal voltage is written, an appropriate value of the signal voltage can be written to the storage capacitor 42.
- the signal potential supplied to the data line 70 is determined based on Vtft_L1. Therefore, by providing the write preparation period (t14 to t16), the source potential is set to the reference potential Vtft_L1, and an appropriate signal voltage can be written to the storage capacitor 42.
- the signal potential at this time is a signal potential corresponding to the own pixel. That is, the signal potential is a signal potential corresponding to the luminance that the pixel should emit in the next light emission period.
- the signal potential corresponds to a value obtained by adding a low gradation (low luminance) signal voltage (for example, 2.5 V) to a reference potential (for example, 1 V). Is 3.5V.
- the source potential of the drive transistor 41 may become an indefinite potential before applying the reverse bias voltage. Therefore, by providing a capacitance reset period before applying the reverse bias voltage and setting the source potential of the drive transistor 41 to the second potential (Vtft_L2) of the power supply line 80, an appropriate value of the reverse bias voltage is set. Can be applied.
- the signal potential of an appropriate value can be written to the storage capacitor 42 by setting the source potential of the drive transistor 41 to the third potential (Vtft_L1) of the power supply line 80.
- the reset potential is a signal potential of another row.
- the data line 70 is driven at a frequency twice as high as one horizontal frequency (1 / 1H). That is, the data line 70 is driven twice.
- the signal potential of another row is used as the reset potential, so that the data line 70 is set at a double frequency so as to supply each of the signal potential (reset potential) and the reverse bias potential within one horizontal period. What is necessary is just to drive (double drive). Therefore, as compared with the first embodiment, the data line 70 can be driven at a low speed, so that the power consumption of the data line driving circuit 7 can be reduced.
- the power supply line 80 is further selectively set to a third potential that is lower than the first potential and higher than the second potential
- the driving method of the organic EL display device 1 further includes In a state where the power supply line 80 is set to the second potential and the data line 70 is set to the signal potential of the other row, the switching transistor 43 is turned on, and the signal of the other row is connected to the gate of the driving transistor 41.
- the drive transistor 41 is turned on, and the power supply line 80 is set to the third potential in a state where the drive transistor 41 is turned on, whereby the source and drain of the drive transistor 41 are set to the third potential.
- the power supply line 80 is set to the third potential, and the data line 70 is set to the signal potential corresponding to the pixel, It is to conduct static 43, and a write step of writing a signal voltage to the storage capacitor 42.
- the signal voltage can be appropriately written, and the organic EL element 40 can emit light with a desired luminance. Therefore, variations in display within the display area 2 can be suppressed.
- Embodiment 3 an organic EL display device and a driving method thereof according to Embodiment 3 will be described.
- the configuration of the organic EL display device and the configuration of the pixels are the same as those in the first embodiment, and the driving operation is different. Therefore, in the following, description of each component will be omitted, and description will be made focusing on driving operation.
- FIG. 9 is a timing chart showing the operation of the pixel 4 in the organic EL display device 1 according to the present embodiment.
- FIG. 9 shows, in order from the top, the potential “Vdata” supplied to the data line 70, the potentials “Vtft (n)” to “Vtft (n + 3)” set to the power supply line 80 for each row, Scan signals “Scan (n)” to “Scan (n + 3)” supplied to the scan line 60 for each row, and the gate potential (thick solid line) and source potential (thin solid line) of the drive transistor 41 are shown.
- Vtft (n) to Vtft (n + 3) indicate potentials set to the power supply lines 80 in the nth to n + 3th rows, respectively, and Scan (n) to Scan (n + 3) respectively represent the nth to n + 3th.
- 2 shows a scan signal supplied to the scan line 60 of the second row.
- the signal potential (“video” in FIG. 9) for each row of the plurality of pixels 4 is sequentially set in the data line 70 every horizontal period (1H). That is, one horizontal period includes a first period 301 in which a signal potential is set in the data line 70. One of the two consecutive horizontal periods includes a second period 302 in which a reset potential is set for the data line 70, and the other of the two consecutive horizontal periods is a third in which a reverse bias potential is set for the data line 70. A period 303 is included. That is, two horizontal periods are one repeating unit. That is, in the present embodiment, the data line driving circuit 7 drives the data line 70 at a frequency twice as high as one horizontal frequency (1 / 1H).
- the voltage control circuit 8 sets the potential of the power supply line 80 every two rows. Specifically, as indicated by Vtft (n) and Vtft (n + 1), the same potential is set to the power supply lines 80 in the nth and n + 1th rows at the same timing. The same applies to the (n + 2) th and n + 3th power supply lines 80.
- the scanning line driving circuit 6 supplies the scanning signal for writing for each row at different timing (specifically, by shifting by one horizontal period). For example, as shown in Scan (n) and Scan (n + 1), the scan signal 313 is supplied to the nth scan line 60, and after one horizontal period has passed, the scan line 60 of the (n + 1) th row is scanned. A signal 314 is provided.
- the scanning line driving circuit 6 generates a reset scan signal and a reverse bias application scan signal at different timings every two rows (specifically, for example, a reset scan signal and a reverse bias).
- the scanning signal for application is supplied (shifted by one horizontal period).
- the scan signal 311 for reset and the scan signal 312 for applying reverse bias are respectively the same in the scan lines 60 of the nth and n + 1th rows. Supplied at timing. The same applies to the (n + 2) th and n + 3th scan signals.
- Vtft_L is set in the power supply line 80, thereby terminating the light emission of the organic EL element 40.
- the charge is released from the storage capacitor 42 to the power supply line 80 through the source and drain of the drive transistor 41. Due to the loss of charge, the potential at both ends of the storage capacitor 42 decreases, and the gate potential of the driving transistor 41 becomes 4 V and the source potential becomes 1.5 V (see FIG. 4A (b)). Further, after the elapse of 2 horizontal periods from the end of the nth and n + 1th light emission periods (time t21), the n + 2th and n + 3th light emission periods are completed.
- ⁇ Time t22 to t23 Capacity reset period>
- a scan signal 311 is supplied to the scan line 60 to turn on the switching transistor 43, thereby supplying a reset potential (specifically, 8 V) to the gate of the drive transistor 41.
- the source and drain of the drive transistor 41 are made conductive, and the charge remaining in the storage capacitor 42 and the parasitic capacitance of the organic EL element 40 is discharged to the power supply line 80.
- the source potential of the drive transistor 41 can be made the same as the potential of the power supply line 80 (specifically, 1 V) (see (c) and (d) in FIG. 4A).
- the reset period (time t22 to t23) is substantially one horizontal period, the present invention is not limited to this.
- the length of the reset period may be set to a time sufficient for discharge depending on the size of the parasitic capacitance of the storage capacitor 42 and the organic EL element 40.
- ⁇ Time t23 to t24 Reverse bias application period>
- a scan signal 312 is supplied to the scan line 60 to turn on the switching transistor 43, whereby a reverse bias potential (specifically ⁇ 9V) is supplied to the gate of the drive transistor 41.
- a reverse bias voltage (specifically, ⁇ 10 V) is supplied between the gate and source of the drive transistor 41 (see (e) and (f) of FIG. 4B).
- the light emission periods of the (n + 2) th and (n + 3) th rows end during the reverse bias application period of the nth and (n + 1) th rows, but the present invention is not limited to this. Specifically, depending on the length of the reset period (time t22 to t23), the light emission periods of the (n + 2) th and (n + 3) th rows may end during the capacity reset period.
- the data line 70 is provided for each column, it is necessary to write the signal voltage for each row. In other words, since the signal voltages of a plurality of rows cannot be written to the storage capacitor 42 at the same time, the timing for writing the signal voltage is shifted between the nth row and the n + 1th row.
- the signal potential for each row of the plurality of pixels 4 is sequentially set in the data line 70 for each horizontal period, and each of the two consecutive horizontal periods is applied to the data line 70.
- One of the two horizontal periods includes a first period 301 in which the signal potential is set, and further includes a second period 302 in which the reset potential is set in the data line 70, and the other of the two horizontal periods further includes 70 data.
- a third period 303 in which a reverse bias potential is set for the line is included.
- the data line 70 is driven at a frequency twice as high as one horizontal frequency (1 / 1H). That is, the data line 70 is driven twice.
- the voltage control circuit 8 may drive the power supply line 80 with a binary value of the first potential and the second potential, and the data line drive circuit 7 may drive the data line 70 at twice the frequency. . Therefore, power consumption can be suppressed as compared with the case where the data line 70 is driven at a frequency three times as high.
- the voltage control circuit 8 can be realized with a simple configuration as compared with the case where the power supply line 80 is driven in three values, and an increase in cost can be suppressed.
- the voltage control circuit 8 sets the potential of the power supply line 80 every two rows. However, every three rows or every four rows, every m rows (m ⁇ 2 natural numbers). ) May be set to a potential. Specifically, as indicated by Vtft (n) to Vtft (n + m ⁇ 1), the same potential is set to the power supply lines 80 in the nth to n + m ⁇ 1th rows at the same timing. In this case, the nth to n + m ⁇ 1th rows are performed simultaneously in the discharge period, the capacity reset period, the reverse bias application period, and the light emission period, excluding the signal voltage writing period. That is, in the present embodiment, the light emission step, the reset step, and the reverse bias application step may be executed simultaneously in a plurality of rows.
- the voltage control circuit 8 can control a plurality of rows of the power supply lines 80, so that the circuit scale can be reduced, compared with the case where the power supply lines 80 are driven for each row.
- the voltage control circuit 8 can be realized with a simple configuration, and an increase in cost can be suppressed.
- Embodiment 4 an organic EL display device and a driving method thereof according to Embodiment 4 will be described.
- the configuration of the organic EL display device and the configuration of the pixels are the same as those in the first embodiment, and the driving operation is different. Therefore, in the following, description of each component will be omitted, and description will be made focusing on driving operation.
- This embodiment is different from the operation of the first embodiment in that the threshold voltage of the drive transistor 41 is detected.
- FIG. 10 is a timing chart showing the operation of the pixel 4 in the organic EL display device 1 according to the present embodiment.
- 11A and 11B are state transition diagrams illustrating the operation of the pixel 4 in the organic EL display device 1 according to the present embodiment.
- FIG. 10 shows, in order from the top, the potential “Vtft” set on the power supply line 80, the potential “Vdata” set on the data line 70, the scan signal “Scan” supplied to the scan line 60, In addition, the gate potential (thick solid line) and the source potential (thin solid line) of the driving transistor 41 are shown.
- the first potential Vtft_H and the second potential Vtft_L are selectively set in the power supply line 80. Specifically, Vtft_H is set for the light emission period and the threshold detection period, and Vtft_L is set for the non-light emission period excluding the threshold detection period.
- the drive timing of the data line 70 is the same as that of the first embodiment.
- Vtft_L is, for example, ⁇ 5V.
- the drive transistor 41 is turned on, and the signal voltage held in the holding capacitor 42 is applied to the power supply line 80 via the drive transistor 41. Go through. Due to the loss of charge, the potential at both ends of the storage capacitor 42 decreases, and the gate potential of the drive transistor 41 becomes 0V and the source potential becomes ⁇ 5V, as shown in FIG. 11A (b).
- ⁇ Time t32 to t33 Capacity reset period>
- a reset signal is supplied to the gate of the drive transistor 41 by supplying a scan signal 411 to the scan line 60 and turning on the switching transistor 43.
- the power supply line 80 is set to Vtft_L, and the data line 70 is set to a reset potential (specifically, 2V).
- the source and drain of the drive transistor 41 are conducted.
- the charges held in the holding capacitor 42 and the parasitic capacitance of the organic EL element 40 are discharged to the power supply line 80 during the discharge period (time t1 to t2), in reality, the charge flow during the reset period.
- the source potential of the drive transistor 41 is maintained at Vtft_L ( ⁇ 5 V).
- the parasitic capacitance of the storage capacitor 42 and the organic EL element 40 is reset, so that it is not necessary to provide a reset period, but what gradation of signal voltage is written to each pixel 4. Since it is unknown whether it is inserted, a reset period is necessary to reliably reset the parasitic capacitance of the storage capacitor 42 and the organic EL element 40.
- ⁇ Time t33 to t34 Reverse bias application period>
- a reverse bias potential is supplied to the gate of the drive transistor 41 by supplying a scan signal 412 to the scan line 60 and turning on the switching transistor 43.
- the power supply line 80 is set to Vtft_L, and the data line 70 is set to a reverse bias potential (specifically, ⁇ 15V).
- a reverse bias voltage of ⁇ 10 V is applied between the gate and source of the drive transistor 41. Thereby, the temporal variation of the threshold voltage of the drive transistor 41 can be suppressed.
- ⁇ Time t34 Preparation for detection of threshold voltage>
- the scan signal 413 is supplied to the scan line 60 to turn on the switching transistor 43, whereby the reset potential (specifically, 2V).
- the reset potential specifically, 2V
- a voltage equal to or higher than the threshold voltage is applied between the gate and source of the drive transistor 41, and the drive transistor 41 becomes conductive.
- the source potential of the drive transistor 41 is set to ⁇ 5 V, which is the same as that of the power supply line 80.
- the scan signals 414 to 416 are supplied a plurality of times, specifically, at times t35, t36 and t37 three times.
- the threshold voltage of the drive transistor 41 can be held in the storage capacitor 42.
- the number of times the scan signal is supplied is not limited to this, and may be one time, for example.
- a current corresponding to the signal voltage and the mobility of the drive transistor 41 flows from the power supply line 80 to the storage capacitor 42, and fluctuates according to the current into which the signal voltage written to the storage capacitor 42 flows. . That is, mobility correction can be performed.
- the driving method of the organic EL display device 1 further includes a threshold detection step of detecting the threshold voltage of the driving transistor 41 after the reverse bias application step.
- Embodiment 5 an organic EL display device and a driving method thereof according to Embodiment 5 will be described.
- the configuration of the organic EL display device and the configuration of the pixels are the same as those in the first embodiment, and the driving operation is different. Therefore, in the following, description of each component will be omitted, and description will be made focusing on driving operation.
- Embodiments 1 to 4 described above the example in which the reverse bias voltage is a constant value has been described.
- the threshold voltage is negatively shifted.
- the threshold voltage that has been positively shifted during the light emission period is negatively shifted, so that variation with time of the threshold voltage can be suppressed.
- the threshold voltage may shift too negative in some cases. For example, when a reverse bias voltage of ⁇ 10 V is continuously applied to a pixel that is almost black and has a positive bias close to 0 V, the threshold voltage of the drive transistor 41 may shift negatively. When the threshold voltage is negatively shifted, light is emitted brighter than surrounding pixels, which may cause reverse image sticking.
- the reverse bias voltage is determined to be a value corresponding to the signal voltage (that is, the positive bias voltage).
- the threshold fluctuation of the drive transistor 41 can be appropriately suppressed. In other words, it can be prevented from shifting too negatively.
- FIG. 12 is a timing chart showing an operation at the time of high gradation light emission of the pixel 4 in the organic EL display device 1 according to the present embodiment.
- FIG. 13 is a timing chart showing an operation at the time of low gradation light emission of the pixel 4 in the organic EL display device 1 according to the present embodiment.
- the gate potential is 12V and the source potential is 7V. Therefore, the organic EL element 40 emits light in a state where a signal voltage of 5V is written in the storage capacitor 42. is doing.
- the gate potential is ⁇ 4 V and the source potential is 1 V. Therefore, a ⁇ 5 V reverse bias voltage is applied between the gate and the source of the drive transistor 41. Applied.
- the organic EL element 40 emits light while a 3V signal voltage is written in the storage capacitor 42. is doing.
- the gate potential is ⁇ 2V and the source potential is 1V. Therefore, a reverse bias voltage of ⁇ 3V is applied between the gate and the source of the drive transistor 41. Applied.
- the reverse bias voltage is determined based on the signal voltage supplied to the corresponding pixel 4.
- the reverse bias voltage and the signal voltage supplied to the corresponding pixel have a positive correlation.
- a larger reverse bias voltage is applied as the signal voltage supplied to the corresponding pixel is larger.
- the signal voltage is, for example, the signal voltage of the frame immediately before applying the reverse bias voltage, as shown in FIGS.
- the organic EL display device 1 includes a memory for storing the signal voltage of the immediately previous frame.
- the signal voltage may be the signal voltage of the frame immediately after applying the reverse bias voltage.
- the organic EL display device 1 since the organic EL display device 1 does not have to include a memory for storing the signal voltage, the cost can be reduced.
- the reverse bias voltage may be set stepwise for each signal voltage range. That is, the reverse bias voltage may be set to a plurality of discrete values.
- the reverse bias voltage corresponding to a signal voltage of 0V to 10V, when the signal voltage is 0V to 3V, the reverse bias voltage is ⁇ 2V, when the signal voltage is 3V to 7V, the reverse bias voltage is ⁇ 5V, and the signal voltage is 7V to In the case of 10V, the reverse bias voltage may be set to -10V. Thereby, the number of bits of the data line driving circuit 7 can be reduced.
- the organic EL display device 1 including the organic EL element 40 as a light-emitting element has been described as the display device according to the present disclosure.
- the present disclosure is not limited thereto, and a current-driven light-emitting element is used. Any display device may be used.
- the circuit configuration of the pixel 4 in the display device according to the present disclosure is not limited to the circuit configuration described above, and may be a circuit configuration having another configuration.
- the operation of the pixel 4 is not limited to the operation shown in the timing chart described above, and may be another operation.
- Each transistor in the pixel 4 may be a P-channel transistor or an N-channel transistor.
- a device in which an element such as a transistor, a resistor element, or a capacitor element is connected in series or in parallel to a certain element within a range in which a function similar to the circuit configuration described above can be realized.
- the term “connected” in the above embodiment is not limited to the case where two terminals (nodes) are directly connected, and the two terminals ( Node) is connected through an element.
- a reset transistor for resetting the charge of the parasitic capacitance of the storage capacitor 42 and the organic EL element 40 may be provided.
- a program for causing the computer to function as a characteristic control unit included in the display device or as a program for causing the computer to execute characteristic steps included in the driving method.
- Such a program can be distributed via a computer-readable non-transitory recording medium such as a CD-ROM (Compact Disc-Read Only Memory) or a communication network such as the Internet. .
- the display device and the driving method thereof according to the present disclosure can be used for a display device such as a flat panel display such as a television as shown in FIG.
Abstract
Description
[1.有機EL表示装置]
まず、本実施の形態に係る有機EL表示装置の構成について、図1及び図2を用いて説明する。図1は、本実施の形態に係る有機EL表示装置1の概要構成を示すブロック図である。図2は、本実施の形態に係る有機EL表示装置1における画素4の回路構成を示す回路図である。
次に、画素4の回路構成について、図2を用いて説明する。
次に、有機EL表示装置1の動作について、図3~図6Bを用いて説明する。なお、以下で説明する各動作は、制御部3により実行される。なお、以下では、駆動トランジスタ41の閾値電圧が2Vである場合を例に説明する。
まず、画素4の低階調発光時の動作について、図3、図4A及び図4Bを用いて説明する。
図3に示す発光期間(~時刻t1)では、電源線80にVtft_Hが設定されているので、図4Aの(a)に示すように、保持容量42に保持された信号電圧(例えば2.5V)に応じた電流が駆動トランジスタ41を介して有機EL素子40に流れる。Vtft_Hは、例えば、16Vである。
次に、時刻t1で、電源線80にVtft_Lを設定することにより、有機EL素子40の発光を終了する。Vtft_Lは、例えば、1Vである。
時刻t2で、図4Aの(c)に示すように、スキャン線60にスキャン信号111を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートにリセット電位を供給する。このとき、電源線80はVtft_Lに設定され、かつ、データ線70はリセット電位に設定されている。
時刻t3で、図4Bの(e)に示すように、スキャン線60にスキャン信号112を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートに逆バイアス電位を供給する。このとき、電源線80はVtft_Lに設定され、かつ、データ線70は逆バイアス電位に設定されている。
時刻t4で、図4Bの(g)に示すように、スキャン線60にスキャン信号113を供給して、スイッチングトランジスタ43を導通させることで、保持容量42に信号電圧を書込む。このとき、電源線80はVtft_Lに設定され、かつ、データ線70は信号電位に設定されている。
時刻t5で、電源線80をVtft_Hに設定することで、有機EL素子40に電源線80から駆動トランジスタ41を介して電流を供給する。これにより、図4Bの(h)に示すように、保持容量42に保持された信号電圧(例えば2.5V)に応じた電流が流れて、有機EL素子40が発光する。
次に、画素4の低階調発光時の動作について、図5、図6A及び図6Bを用いて説明する。
図5に示す発光期間(~t1)では、電源線80にVtft_Hが設定されているので、図6Aの(a)に示すように、保持容量42に保持された信号電圧(例えば5V)に応じた電流が駆動トランジスタ41を介して有機EL素子40に流れる。これにより、有機EL素子40は高輝度で発光する。このとき、有機EL素子40のアノード電位、すなわち、駆動トランジスタ41のソース電位は7Vであり、駆動トランジスタ41のゲート電位は12Vである。
次に、時刻t1で、電源線80にVtft_Lを設定することにより、有機EL素子40の発光を終了する。
時刻t2で、図6Aの(c)に示すように、スキャン線60にスキャン信号111を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートにリセット電位を供給する。このとき、電源線80はVtft_Lに設定され、かつ、データ線70はリセット電位に設定されている。
時刻t3で、図6Bの(e)に示すように、スキャン線60にスキャン信号112を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートに逆バイアス電位を供給する。このとき、電源線80はVtft_Lに設定され、かつ、データ線70は逆バイアス電位に設定されている。
時刻t4で、図6Bの(g)に示すように、スキャン線60にスキャン信号113を供給して、スイッチングトランジスタ43を導通させることで、保持容量42に信号電圧を書込む。このとき、電源線80はVtft_Lに設定され、かつ、データ線70は信号電位に設定されている。例えば、図6Bの(g)に示す例では、信号電位は、基準電位(例えば1V)に高階調(高輝度)の信号電圧(例えば5V)を加えた値に相当し、具体的には、6Vである。
時刻t5で、電源線80をVtft_Hに設定することで、有機EL素子40に電源線80から駆動トランジスタ41を介して電流を供給する。これにより、図4Bの(h)に示すように、保持容量42に保持された信号電圧(例えば5V)に応じた電流が流れて、有機EL素子40が発光する。
以上のように、本実施の形態に係る有機EL表示装置1の駆動方法は、行列状に配置された複数の画素4を備える有機EL表示装置1の駆動方法であって、複数の画素4のそれぞれは、供給された電流に応じて発光する有機EL素子40と、有機EL素子40に電流を供給する駆動トランジスタ41と、駆動トランジスタ41のゲートとソース又はドレインとの間に接続された保持容量42とを備え、有機EL表示装置1の駆動方法は、有機EL素子40に電流を供給することで、有機EL素子40を発光させる発光ステップと、保持容量42と有機EL素子40の寄生容量との少なくとも一方の電荷をリセットするリセットステップと、駆動トランジスタ41のゲート-ソース間に逆バイアス電圧を印加する逆バイアス印加ステップとを含み、リセットステップは、発光ステップと逆バイアス印加ステップとの間で実行される。
以下では、実施の形態2に係る有機EL表示装置及びその駆動方法について説明する。
図7に示す発光期間(~時刻t11)では、電源線80にVtft_Hが設定されているので、図8Aの(a)に示すように、保持容量42に保持された信号電圧(例えば2.5V)に応じた電流が駆動トランジスタ41を介して有機EL素子40に流れる。
次に、時刻t11で、電源線80にVtft_L2を設定することにより、有機EL素子40の発光を終了する。Vtft_L2は、例えば、-7Vである。
時刻t12で、図8Aの(c)に示すように、スキャン線60にスキャン信号211を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートに、他の行の信号電位を供給する。このとき、電源線80はVtft_L2に設定され、かつ、データ線70は他の行の信号電位に設定されている。
時刻t13で、図8Aの(d)に示すように、スキャン線60にスキャン信号212を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートに逆バイアス電位を供給する。このとき、電源線80はVtft_L2に設定され、かつ、データ線70は逆バイアス電位に設定されている。
時刻t14で、図8Bの(e)に示すように、スキャン線60にスキャン信号213を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートに他の行の信号電位を供給する。このとき、電源線80はVtft_L2に設定され、かつ、データ線70は他の行の信号電位に設定されている。
時刻t16で、図8Bの(g)に示すように、スキャン線60にスキャン信号214を供給して、スイッチングトランジスタ43を導通させることで、保持容量42に信号電圧を書込む。このとき、電源線80はVtft_L1に設定され、かつ、データ線70は信号電位に設定されている。
時刻t17で、電源線80をVtft_Hに設定することで、有機EL素子40に電源線80から駆動トランジスタ41を介して電流を供給する。これにより、図8Bの(h)に示すように、保持容量42に保持された信号電圧(例えば2.5V)に応じた電流が流れて、有機EL素子40が発光する。
以下では、実施の形態3に係る有機EL表示装置及びその駆動方法について説明する。
図9に示す発光期間(~時刻t21)では、Vtft(n)及びVtft(n+1)に示すように、電源線80にVtft_Hが設定されているので、有機EL素子40は、保持容量42に保持された信号電圧に応じた電流が流れて発光する(図4Aの(a)参照)。このとき、n番目の行の画素4の有機EL素子40と、n+1番目の行の画素4の有機EL素子40とが発光している。
時刻t21で、Vtft(n)及びVtft(n+1)に示すように、電源線80にVtft_Lを設定することにより、有機EL素子40の発光を終了する。発光が終了すると同時に、駆動トランジスタ41のソース-ドレイン間を通って電源線80に、保持容量42から電荷が抜ける。電荷の抜けによって、保持容量42の両端の電位が下がり、駆動トランジスタ41のゲート電位が4V、ソース電位が1.5Vになる(図4Aの(b)参照)。また、n番目及びn+1番目の発光期間の終了時(時刻t21)から2水平期間経過後に、n+2番目及びn+3番目の発光期間が終了する。
時刻t22で、スキャン線60にスキャン信号311を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートにリセット電位(具体的には、8V)を供給する。これにより、駆動トランジスタ41のソース-ドレイン間を導通させて、保持容量42及び有機EL素子40の寄生容量に残っていた電荷を、電源線80に放出させる。これにより、駆動トランジスタ41のソース電位を電源線80の電位(具体的には、1V)と同じにすることができる(図4Aの(c)及び(d)参照)。なお、リセット期間(時刻t22~t23)を略1水平期間としたが、これに限らない。リセット期間の長さは、保持容量42及び有機EL素子40の寄生容量の大きさなどによって、放電に十分な時間が設定されればよい。
時刻t23で、スキャン線60にスキャン信号312を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートに逆バイアス電位(具体的には、-9V)を供給する。これにより、駆動トランジスタ41のゲート-ソース間に逆バイアス電圧(具体的には、-10V)を供給する(図4Bの(e)及び(f)参照)。
時刻t24で、図9のScan(n)に示すように、n番目の行のスキャン線60にスキャン信号313を供給して、n番目の行の保持容量42に信号電圧を書込む(図4Bの(g)参照)。そして、時刻t25で、n+1番目の行のスキャン線60にスキャン信号314を供給して、n+1番目の行の保持容量42に信号電圧を書込む。
時刻t26で、図9のVtft(n)及びVtft(n+1)に示すように、電源線80をVtft_Hに設定することで、有機EL素子40に電源線80から駆動トランジスタ41を介して電流を供給する(図4Bの(h)参照)。これにより、保持容量42に保持された信号電圧(例えば2.5V)に応じた電流が流れて、有機EL素子40が発光する。このとき、n番目の行の画素4の有機EL素子40と、n+1番目の行の画素4の有機EL素子40とが同時に発光する。
以下では、実施の形態4に係る有機EL表示装置及びその駆動方法について説明する。
図10に示す発光期間(~時刻t31)では、電源線80にVtft_Hが設定されているので、図11Aの(a)に示すように、保持容量42に保持された信号電圧(例えば5V)に応じた電流が駆動トランジスタ41を介して有機EL素子40に流れる。これにより、有機EL素子40は高輝度で発光する。このとき、有機EL素子40のアノード電位、すなわち、駆動トランジスタ41のソース電位は7Vであり、駆動トランジスタ41のゲート電位は12Vである。
次に、時刻t31で、電源線80にVtft_Lを設定することにより、有機EL素子40の発光を終了する。Vtft_Lは、例えば、-5Vである。
時刻t32で、図11Aの(c)に示すように、スキャン線60にスキャン信号411を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートにリセット電位を供給する。このとき、電源線80はVtft_Lに設定され、かつ、データ線70はリセット電位(具体的には、2V)に設定されている。
時刻t33で、図11Aの(d)に示すように、スキャン線60にスキャン信号412を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートに逆バイアス電位を供給する。このとき、電源線80はVtft_Lに設定され、かつ、データ線70は逆バイアス電位(具体的には、-15V)に設定されている。
時刻t34で、図11Bの(e)に示すように、スキャン線60にスキャン信号413を供給して、スイッチングトランジスタ43を導通させることで、駆動トランジスタ41のゲートにリセット電位(具体的には、2V)を供給する。これにより、駆動トランジスタ41のゲート-ソース間に閾値電圧以上の電圧が印加されて、駆動トランジスタ41が導通する。これにより、駆動トランジスタ41のソース電位が電源線80と同じ-5Vに設定される。
時刻t35で、図11Bの(f)に示すように、電源線80がVtft_Hに設定され、かつ、データ線70がリセット電位に設定された状態で、スキャン線60にスキャン信号414を供給して、スイッチングトランジスタ43を導通させる。これにより、駆動トランジスタ41のゲート-ソース間に閾値電圧以上の電圧が印加されて、駆動トランジスタ41が導通し、電源線80から保持容量42に電荷が供給される。
時刻t38で、図11Bの(g)に示すように、スキャン線60にスキャン信号417を供給して、スイッチングトランジスタ43を導通させることで、保持容量42に信号電圧を書込む。このとき、電源線80がVtft_Hに設定され、かつ、データ線70が信号電位に設定されている。
時刻t39で、スイッチングトランジスタ43が非導通になった後、図11Bの(h)に示すように、電源線80から駆動トランジスタ41を介して有機EL素子40に電流が供給される。これにより、保持容量42に保持された信号電圧(例えば5V)に応じた電流が流れて、有機EL素子40は発光する。
以下では、実施の形態5に係る有機EL表示装置及びその駆動方法について説明する。
以上のように、本出願において開示する技術の例示として、実施の形態を説明した。しかしながら、本開示における技術は、これに限定されず、適宜、変更、置き換え、付加、省略などを行った実施の形態にも適用可能である。また、上記実施の形態で説明した各構成要素を組み合わせて、新たな実施の形態とすることも可能である。
2 表示領域
3 制御部
4 画素
5 タイミング制御回路
6 走査線駆動回路
7 データ線駆動回路
8 電圧制御回路
40 有機EL素子
41 駆動トランジスタ
42 保持容量
43 スイッチングトランジスタ
60 スキャン線
70 データ線
80、81 電源線
101、201、301 第1期間
102、302 第2期間
103、203、303 第3期間
111、112、113、211、212、213、214、311、312、313、314、411、412、413、414、415、416、417 スキャン信号
Claims (14)
- 行列状に配置された複数の画素を備える表示装置の駆動方法であって、
前記複数の画素のそれぞれは、
供給された電流に応じて発光する発光素子と、
前記発光素子に電流を供給する駆動トランジスタと、
前記駆動トランジスタのゲートとソース又はドレインとの間に接続された保持容量とを備え、
前記表示装置の駆動方法は、
前記発光素子に電流を供給することで、前記発光素子を発光させる発光ステップと、
前記保持容量と前記発光素子の寄生容量との少なくとも一方の電荷をリセットするリセットステップと、
前記駆動トランジスタのゲート-ソース間に逆バイアス電圧を印加する逆バイアス印加ステップとを含み、
前記リセットステップは、前記発光ステップと前記逆バイアス印加ステップとの間で実行される
表示装置の駆動方法。 - 前記表示装置は、さらに、
前記複数の画素の前記駆動トランジスタのドレイン又はソースに接続される電源線と、
前記複数の画素の列毎に設けられたデータ線とを備え、
前記複数の画素のそれぞれは、さらに、
前記駆動トランジスタのゲートと前記データ線との間に接続されたスイッチングトランジスタを備え、
前記リセットステップでは、前記スイッチングトランジスタを導通させることで、前記データ線からリセット電位を前記駆動トランジスタのゲートに供給して、前記駆動トランジスタを導通させ、前記保持容量及び前記寄生容量の少なくとも一方の電荷を前記電源線に放出させる
請求項1に記載の表示装置の駆動方法。 - 前記電源線は、第1電位と、前記第1電位より低い第2電位とに選択的に設定され、
前記データ線は、画素信号に応じた信号電位を含む複数の電位に選択的に設定され、
前記発光ステップでは、前記電源線を前記第1電位に設定することで、前記発光素子に前記電源線から前記駆動トランジスタを介して前記電流を供給し、
前記リセットステップでは、前記電源線が前記第2電位に設定され、かつ、前記データ線が前記リセット電位に設定された状態で、前記スイッチングトランジスタを導通させることで、前記駆動トランジスタのゲートに前記リセット電位を供給し、
前記逆バイアス印加ステップでは、前記電源線が前記第2電位に設定され、かつ、前記データ線が逆バイアス電位に設定された状態で、前記スイッチングトランジスタを導通させて、前記駆動トランジスタのゲートに前記逆バイアス電位を供給して、前記逆バイアス電圧を印加する
請求項2に記載の表示装置の駆動方法。 - 前記リセット電位は、前記信号電位とは独立して予め定められた電位である
請求項3に記載の表示装置の駆動方法。 - 前記データ線には、前記複数の画素の行毎の前記信号電位が、1水平期間毎に順に設定され、
前記1水平期間は、
前記データ線に前記信号電位が設定される第1期間と、
前記データ線に前記リセット電位が設定される第2期間と、
前記データ線に前記逆バイアス電位が設定される第3期間とを含む
請求項4に記載の表示装置の駆動方法。 - 前記データ線は、1水平周波数の3倍の周波数で駆動される
請求項5に記載の表示装置の駆動方法。 - 前記データ線には、前記複数の画素の行毎の前記信号電位が、1水平期間毎に順に設定され、
連続する2水平期間はそれぞれ、前記データ線に前記信号電位が設定される第1期間を含み、
前記2水平期間の一方は、さらに、前記データ線に前記リセット電位が設定される第2期間を含み、
前記2水平期間の他方は、さらに、前記データ線に前記逆バイアス電位が設定される第3期間を含む
請求項4に記載の表示装置の駆動方法。 - 前記リセット電位は、他の行の前記信号電位である
請求項3に記載の表示装置の駆動方法。 - 前記電源線には、さらに、前記第1電位より低く、前記第2電位より高い第3電位が選択的に設定され、
前記表示装置の駆動方法は、さらに、
前記電源線が前記第2電位に設定され、かつ、前記データ線が他の行の前記信号電位に設定された状態で、前記スイッチングトランジスタを導通させて、前記駆動トランジスタのゲートに前記他の行の前記信号電位を供給することで、前記駆動トランジスタを導通させた後、前記駆動トランジスタを導通させた状態で、前記電源線を前記第3電位に設定することで、前記駆動トランジスタのソース及びドレインを前記第3電位に設定する書込み準備ステップと、
前記電源線が前記第3電位に設定され、かつ、前記データ線が当該画素に対応する前記信号電位に設定された状態で、前記スイッチングトランジスタを導通させることで、前記保持容量に信号電圧を書込む書込みステップとを含む
請求項8に記載の表示装置の駆動方法。 - 前記データ線は、1水平周波数の2倍の周波数で駆動される
請求項7~9のいずれか1項に記載の表示装置の駆動方法。 - 前記発光ステップと、前記リセットステップと、前記逆バイアス印加ステップとが、複数行において同時に実行される
請求項10に記載の表示装置の駆動方法。 - 前記表示装置の駆動方法は、さらに、前記逆バイアス印加ステップの後に前記駆動トランジスタの閾値電圧を検出する閾値検出ステップを含む
請求項1~11のいずれか1項に記載の表示装置の駆動方法。 - 前記逆バイアス電圧は、対応する画素に供給される信号電圧に基づいて決定される
請求項1~12のいずれか1項に記載の表示装置の駆動方法。 - 行列状に配置された複数の画素を備える表示装置であって、
前記複数の画素のそれぞれは、
供給された電流に応じて発光する発光素子と、
前記発光素子に電流を供給する駆動トランジスタと、
前記駆動トランジスタのゲートとソース又はドレインとの間に接続された保持容量とを備え、
前記表示装置は、
(i)発光期間に、前記発光素子に電流を供給することで、前記発光素子を発光させ、(ii)リセット期間に、前記保持容量と前記発光素子の寄生容量との少なくとも一方の電荷をリセットし、(iii)逆バイアス印加期間に、前記駆動トランジスタのゲート-ソース間に逆バイアス電圧を印加する制御部を備え、
前記リセット期間は、前記発光期間と前記逆バイアス印加期間との間である
表示装置。
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