WO2015063980A1 - 表示装置の電源断方法および表示装置 - Google Patents
表示装置の電源断方法および表示装置 Download PDFInfo
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- WO2015063980A1 WO2015063980A1 PCT/JP2014/003886 JP2014003886W WO2015063980A1 WO 2015063980 A1 WO2015063980 A1 WO 2015063980A1 JP 2014003886 W JP2014003886 W JP 2014003886W WO 2015063980 A1 WO2015063980 A1 WO 2015063980A1
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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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- 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
- G09G2300/0819—Several active elements per pixel in active matrix panels used for counteracting undesired variations, e.g. feedback or autozeroing
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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
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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
- G09G2310/0256—Control of polarity reversal in general, other than for liquid crystal displays with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
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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
- G09G2320/0257—Reduction of after-image effects
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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
- G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
- G09G2330/02—Details of power systems and of start or stop of display operation
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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
- G09G2330/00—Aspects of power supply; Aspects of display protection and defect management
- G09G2330/02—Details of power systems and of start or stop of display operation
- G09G2330/027—Arrangements or methods related to powering off a display
Definitions
- the present disclosure relates to a power-off method and a display device for a display device, and more particularly to a power-off method and a display device for a display device using a light-emitting element that emits light according to an electric current.
- a thin film transistor (TFT: Thin Film Transistor) is used as a drive transistor in an active matrix display device such as an organic EL display.
- Patent Document 1 discloses that a characteristic shift occurs with time.
- a threshold voltage a gate-source voltage at the time of off / on transition
- an electrical stress such as energization.
- the shift of the threshold voltage over time causes fluctuations in the amount of current supplied to the organic EL light emitting element, which affects the brightness control of the display device and deteriorates display quality.
- the present disclosure has been made in view of the above-described problems, and provides a power-off method for a display device and a display device that suppress a threshold voltage shift of a driving transistor.
- the power-off method for a display device is a power-off method for a display device including a display panel having a plurality of pixel circuits arranged in a matrix.
- each of the plurality of pixel circuits has a light emitting element that emits light with luminance corresponding to the amount of current supplied, a driving transistor that supplies current to the light emitting element, and a voltage that represents luminance that is connected to the gate of the driving transistor. And a capacitor element to be held.
- the above-described power-off method of the display device includes a step of detecting a power-off operation for the display device, and when a power-off operation is detected, an electric stress on the driving transistor is applied to the capacitive element in each of the plurality of pixel circuits.
- a step of setting a voltage to be suppressed, and a step of stopping power supply to the display panel immediately after the voltage is set, and in the step of setting the voltage, the capacitive element in each of the plurality of pixel circuits, A voltage corresponding to the threshold voltage of the driving transistor is set.
- the display device is a display device including a display panel having a plurality of pixel circuits arranged in a matrix, and each of the plurality of pixel circuits emits light according to the amount of current supplied.
- the display device has a plurality of elements, a driving transistor that supplies current to the light-emitting element, and a capacitive element that is connected to the gate of the driving transistor and holds a voltage that represents luminance.
- the capacitor element in each of the pixel circuits includes a control unit that sets a voltage that suppresses electrical stress on the drive transistor, and a power source unit that stops power supply to the display panel immediately after setting the voltage by the control unit, The control unit sets a voltage corresponding to a threshold voltage of the drive transistor as the voltage for suppressing electrical stress on the drive transistor.
- the display device power-off method and the display device according to the present disclosure it is possible to suppress the threshold voltage shift of the drive transistor during the power-off period of the display device.
- FIG. 1 is a block diagram illustrating a configuration example of a display device according to an embodiment.
- 2 is a circuit diagram illustrating a configuration example of a pixel circuit arranged two-dimensionally on the display panel in FIG. 1 according to the embodiment.
- FIG. 3 is a flowchart illustrating a power-off method of the display device according to the embodiment.
- FIG. 4 is a time chart illustrating a normal display operation of the display device according to the embodiment and an off sequence performed immediately before the power is turned off.
- FIG. 5 is a time chart showing a detailed timing example of the off sequence in FIG.
- FIG. 6A is an explanatory diagram showing the operation of the pixel circuit in the period T21 in FIGS.
- FIG. 6B is an explanatory diagram illustrating the operation of the pixel circuit in the period T22 of FIGS.
- FIG. 6C is an explanatory diagram illustrating the operation of the pixel circuit in the period T ⁇ b> 23 in FIGS. 5 and 7.
- FIG. 6D is an explanatory diagram illustrating the operation of the pixel circuit in the period T24 in FIGS.
- FIG. 7 is a time chart showing a detailed timing example of the normal display operation in FIG.
- FIG. 8 is a diagram illustrating a circuit example of a display pixel in a modification of the embodiment.
- FIG. 9 is a time chart showing a detailed timing example of the normal display operation in another embodiment.
- FIG. 10 is a time chart illustrating a detailed timing example of the off sequence according to another embodiment.
- a thin film transistor has a high electron mobility and is used as a driving transistor in a pixel of an active matrix display device.
- Each pixel of the display device includes a capacitor that holds a voltage representing luminance, and the capacitor is connected to the gate of the moving transistor.
- the driving transistor supplies a current corresponding to the luminance value to the organic EL element (light emitting element).
- the light emitting element emits light with a light emission amount corresponding to the current value by the supplied current.
- the oxide thin film transistor used as such a driving transistor has an advantage that the leakage current at the time of off is extremely small and the magnitude of the leakage current is on the order of pA.
- the inventors of the present application have found the following problems with respect to the extremely small leakage current.
- the leakage current is extremely small, even when the power of the display device is turned off, a voltage representing luminance immediately before the power is turned off is held for several days inside each pixel, and the voltage is applied to the driving transistor. Sometimes. As a result, even though the power supply of the display device is off, electrical stress is applied to the driving transistor for several days, causing a threshold voltage shift.
- the threshold voltage of the drive transistor shifts even when the power source of the organic EL display device is off.
- the threshold voltage shift differs depending on the type of oxide thin film transistor, for example, the threshold voltage shift appears larger on the positive side as the positive bias stress increases between the gate and the source.
- the power-off method for the display device sets a voltage for suppressing electrical stress on the drive transistor when a power-off operation is detected for the display device, and sets the voltage. Immediately after that, the power supply to the display panel is stopped.
- the voltage for suppressing electrical stress is specifically a voltage corresponding to the threshold voltage of the driving transistor. In a state where a voltage corresponding to the threshold voltage is applied to the gate of the driving transistor, the electric field of the driving transistor is in a stable equilibrium state, so that electrical stress can be substantially suppressed. In addition, variation in threshold voltage shift of the driving transistor between pixels can be suppressed.
- FIG. 1 is a block diagram illustrating a configuration example of a display device according to an embodiment.
- FIG. 2 is a circuit diagram showing a configuration example of a pixel circuit arranged two-dimensionally on the display panel in FIG.
- control unit 2 includes a control unit 2, a scanning line driving circuit 3, a power supply unit 4, a data line driving circuit 5, and a display panel 6.
- the display panel 6 is, for example, an organic EL panel.
- the display panel 6 includes a pixel circuit including a thin film transistor and an EL element at each intersection of the source signal line and the scanning line.
- the pixel circuits arranged corresponding to the same scanning line are appropriately referred to as “display lines”. That is, the display panel 6 has a configuration in which N display lines having M EL elements are arranged.
- the control unit 2 controls the operation for each frame in the normal display when the power of the display device is on, and the operation of the off sequence when the power-off operation is detected.
- the control unit 2 shifts the control from the normal display operation to the off-sequence operation.
- the control unit 2 sets a voltage that suppresses electrical stress to the drive transistor in each pixel circuit, and immediately after the voltage is set, the power supply unit 4 is turned off so as to stop the power supply to the display panel 6. Control.
- control unit 2 In normal display, the control unit 2 generates a first control signal for controlling the data line driving circuit 5 based on the display data signal, and outputs the generated first control signal to the data line driving circuit 5. .
- the control unit 2 generates a second control signal for controlling the scanning line driving circuit 3 based on the input synchronization signal, and outputs the generated second control signal to the scanning line driving circuit 3.
- the display data signal is a signal indicating display data including a video signal, a vertical synchronization signal, and a horizontal synchronization signal.
- the video signal is a signal that designates each pixel value that is gradation information for each frame.
- the vertical synchronization signal is a signal for synchronizing the processing timing in the vertical direction with respect to the screen, and is a signal serving as a reference for processing timing for each frame.
- the horizontal synchronization signal is a signal for synchronizing the processing timing in the horizontal direction with respect to the screen, and is a signal serving as a reference for processing timing for each display line here.
- the first control signal includes a video signal and a horizontal synchronization signal.
- the second control signal includes a vertical synchronization signal and a horizontal synchronization signal.
- the power supply unit 4 supplies power to each unit of the control unit 2, the scanning line driving circuit 3, and the display panel 6, and supplies various voltages to the display panel 6.
- the various voltages referred to here are V INI , V REF , V TFT , and V EL in the pixel circuit example shown in FIG. 2.
- the initialization power line 71, the reference voltage power line 68, the EL anode power line 69, and EL It is supplied to each pixel circuit via the cathode power line 70.
- the data line driving circuit 5 drives the source signal line (Data line 76 in FIG. 2) of the display panel 6 based on the first control signal generated by the control unit 2. More specifically, the data line driving circuit 5 outputs a source signal to each pixel circuit based on the video signal and the horizontal synchronization signal.
- the scanning line driving circuit 3 drives the scanning lines of the display panel 6 based on the second control signal generated by the control unit 2. More specifically, the scanning line driving circuit 3 outputs a scanning signal, a REF signal, an enable signal, and an init signal to each pixel circuit based on the vertical synchronizing signal and the horizontal synchronizing signal at least for each display line. These scanning signals, REF signals, enable signals, and init signals are output to the scan line 72, the ref line 73, the enable line 75, and the init line 74 in the pixel circuit example shown in FIG. Used to control off.
- the display device 1 is configured.
- the 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), and a communication, although not illustrated.
- a circuit may be included.
- the display data signal S1 is generated when the CPU executes a control program, for example.
- a pixel circuit 60 shown in FIG. 2 is one pixel included in the display panel 6 and has a function of emitting light with a light emission amount corresponding to a data signal (data signal voltage) supplied via a data line 76 (data line). .
- the pixel circuit 60 is an example of a display pixel (light emitting pixel) and is arranged in a matrix.
- the pixel circuit 60 includes a drive transistor 61, a switch 62, a switch 63, a switch 64, an enable switch 65, an EL element 66, and a capacitor element 67.
- the pixel circuit 60 includes a data line 76 (data line), a reference voltage power line 68 (V REF ), an EL anode power line 69 (V TFT ), an EL cathode power line 70 (V EL ), And an initialization power supply line 71 (V INI ).
- the Data line 76 is an example of a signal line (source signal line) for supplying a data signal voltage.
- the reference voltage power supply line 68 (V REF ) is a power supply line that supplies a reference voltage V REF that defines the voltage value of the first electrode of the capacitive element 67.
- the EL anode power line 69 (V TFT ) is a high voltage side power line for determining the potential of the drain electrode of the drive transistor 61.
- the EL cathode power supply line 70 (V EL ) is a low voltage side power supply line connected to the second electrode (cathode) of the EL element 66.
- the initialization power supply line 71 (V INI ) is a power supply line for initializing the voltage between the source and gate of the drive transistor 61, that is, the voltage of the capacitive element 67.
- the EL elements 66 are an example of light emitting elements and are arranged in a matrix.
- the EL element 66 has a light emission period in which light is emitted when a drive current is passed, and a non-light emission period in which light is not emitted without a drive current being passed. Specifically, the EL element 66 emits light with a light emission amount corresponding to the amount of current supplied from the drive transistor 61.
- the EL element 66 is, for example, an organic EL element.
- the EL element 66 has a cathode (second electrode) connected to the EL cathode power supply line 70 and an anode (first electrode) connected to the source (source electrode) of the drive transistor 61.
- the voltage supplied to the EL cathode power supply line 70 is VEL , for example, 0 (v).
- the drive transistor 61 is a voltage-driven drive element that controls the amount of current supplied to the EL element 66, and causes the EL element 66 to emit light by passing a current (drive current) through the EL element 66.
- the drive transistor 61 has a gate electrode connected to the first electrode of the capacitor 67 and a source electrode connected to the second electrode of the capacitor 67 and the anode of the EL element 66.
- the switch 63 is turned off (non-conductive state), the reference voltage power supply line 68 and the first electrode of the capacitor 67 are non-conductive, and the enable switch 65 is turned on (conductive state).
- the EL anode power supply line 69 and the drain electrode are made conductive, the EL element 66 is caused to emit light by causing the drive current, which is a current corresponding to the data signal voltage, to flow through the EL element 66.
- the voltage supplied to the EL anode power supply line 69 is V TFT, for example, 20V.
- the drive transistor 61 converts the data signal voltage (data signal) supplied to the gate electrode into a signal current corresponding to the data signal voltage (data signal), and the converted signal current is supplied to the EL element 66. Supply.
- the switch 63 is turned off (non-conducting state), the reference voltage power line 68 and the first electrode of the capacitor 67 are non-conducting, and the enable switch 65 is off (non-conducting).
- the EL anode power supply line 69 and the drain electrode are non-conductive, the EL element 66 is not caused to emit light by not causing the drive current to flow through the EL element 66.
- the threshold voltage of the drive transistor 61 may vary from pixel circuit to pixel circuit due to a threshold voltage shift over time. The influence of this variation can be suppressed by the threshold voltage compensation operation and the threshold setting operation.
- the threshold compensation operation and the threshold setting operation are simply described. This is an operation for setting a voltage corresponding to the threshold voltage of the corresponding drive transistor 61 to the capacitor 67 in each pixel circuit. Details of this operation will be described later.
- the capacitor element 67 is an example of a storage capacitor for holding a voltage, and holds a voltage that determines the amount of current that the drive transistor 61 flows.
- the second electrode (node B side electrode) of the capacitive element 67 is connected between the source of the drive transistor 61 (EL cathode power supply line 70 side) and the anode (first electrode) of the EL element 66.
- a first electrode (electrode on the node A side) of the capacitive element 67 is connected to the gate of the driving transistor 61.
- the first electrode of the capacitive element 67 is connected to the reference voltage power supply line 68 (V REF ) via the switch 63.
- the switch 62 switches between conduction and non-conduction between the Data line 76 (signal line) for supplying the data signal voltage and the first electrode of the capacitive element 67.
- the switch 62 one terminal of the drain and the source is connected to the Data line 76, the other terminal of the drain and the source is connected to the first electrode of the capacitor 67, and the scan is the scan line.
- a switching transistor connected to line 72.
- the switch 62 has a function of writing a data signal voltage (data signal) corresponding to the video signal voltage (video signal) supplied via the Data line 76 to the capacitor 67.
- the switch 63 switches between conduction and non-conduction between the reference voltage power supply line 68 that supplies the reference voltage V REF and the first electrode of the capacitive element 67.
- the switch 63 one terminal of the drain and the source is connected to the reference voltage power supply line 68 (V REF ), the other terminal of the drain and the source is connected to the first electrode of the capacitor 67, and the gate Is a switching transistor connected to the Ref line 73.
- the switch 63 has a function of applying the reference voltage (V REF ) to the first electrode of the capacitor 67 (the gate of the driving transistor 61).
- Switch 64 switches between conduction and non-conduction between the second electrode of capacitive element 67 and initialization power supply line 71.
- the switch 64 has one terminal of the drain and the source connected to the initialization power supply line 71 (V INI ), the other terminal of the drain and the source connected to the second electrode of the capacitor 67, and the gate Is a switching transistor connected to the Init line 74.
- the switch 64 has a function of applying an initialization voltage (V INI ) to the second electrode of the capacitor 67 (the source of the driving transistor 61).
- the enable switch 65 switches between conduction and non-conduction between the EL anode power supply line 69 and the drain electrode of the drive transistor 61.
- the enable switch 65 has one of drain and source terminals connected to the EL anode power supply line 69 (V TFT ), the other drain and source terminal connected to the drain electrode of the drive transistor 61, Is a switching transistor connected to the Enable line 75.
- the pixel circuit 60 is configured as described above.
- the switches 62 to 64 and the enable switch 65 constituting the pixel circuit 60 will be described below as n-type TFTs, but are not limited thereto.
- the switches 62 to 64 and the enable switch 65 may be p-type TFTs. Further, in the switches 62 to 64 and the enable switch 65, an n-type TFT and a p-type TFT may be used together. Note that the voltage level described below may be reversed for the signal line connected to the gate of the p-type TFT.
- the potential difference between the voltage V REF of the reference voltage power supply line 68 and the voltage V INI of the initialization power supply line 71 is set to a voltage larger than the maximum threshold voltage of the drive transistor 61.
- the voltage V REF of the reference voltage power supply line 68 and the voltage V INI of the initialization power supply line 71 are set as follows so that no current flows through the EL element 66.
- Voltage V INI ⁇ voltage V EL + (forward current threshold voltage of EL element 66), (Voltage V REF of reference voltage power supply line 68) ⁇ Voltage V EL + (Forward current threshold voltage of EL element 66) + (Threshold voltage of drive transistor 61)
- the voltage V EL is the voltage of the EL cathode power supply line 70 as described above.
- FIG. 3 is a flowchart showing a power-off method of the display device according to the embodiment.
- FIG. 4 is a time chart illustrating a normal display operation of the display device according to the embodiment and an off sequence performed immediately before the power is turned off.
- FIG. 5 is a time chart showing a detailed timing example of the off sequence in FIG.
- the off-sequence operation (power-off method) will be described before the normal display operation.
- the control unit 2 detects a power-off operation for the display device 1 (S20).
- the power-off operation here is, for example, a timer for measuring the time when the user presses the power button on the remote controller, the power button on the main body of the display device 1, the time when the user sets the off timer, and the time when the user is not operating. This includes the elapse of the set time due to, and the decrease in the AC power supply voltage during a power failure.
- the operation of the control unit 2 shifts from the normal display control to the off-sequence control by detecting the power-off operation.
- the control unit 2 When the power-off operation is detected, the control unit 2 performs a specific process, that is, sets a voltage that suppresses electrical stress to the drive transistor 61 in the capacitive element 67 in each of the plurality of pixel circuits 60. (S30).
- the voltage for suppressing electrical stress is specifically a voltage corresponding to the threshold voltage of the driving transistor. This is because, when a voltage corresponding to the threshold voltage is applied to the gate of the driving transistor, the electric field of the driving transistor is in a stable equilibrium state, so that electrical stress is substantially suppressed. .
- the power supply unit 4 stops supplying power to the display panel 6, the scanning line driving circuit 3, and the data line driving circuit 5 immediately after setting the voltage (S40). As a result, the display device 1 is turned off.
- the voltage setting in the above step S30 can be set as in steps S31 to S33, for example. That is, when a power-off operation is detected, first, the control unit 2 sets the initial voltage at which each of the capacitive elements 67 of the plurality of pixel circuits 60 is higher than the threshold voltage of the drive transistor 61 and does not cause the EL element 66 to emit light. Is held (S31). This operation is performed in the period from the rising edge of the REF signal (reference voltage power supply line 68) to the falling edge of the INI signal (Init line 74) in the off sequence of FIG. 4, and more specifically, in FIG. It is performed during a period T22 (initialization period).
- the control unit 2 turns on the enable switch 65.
- the drive transistor 61 to which the initial voltage higher than the threshold voltage and not causing the EL element 66 to emit light is applied to the gate is turned on (S32). This operation is conducted when the ENB signal (Enable line 75) in the off sequence in FIG. 4 rises to a high level, and more specifically, at time t3 (at the start of the power supply voltage setting period) in FIG. .
- the voltage of the capacitive element 67 is lowered by the conduction current flowing through the drive transistor 61.
- the drive transistor 61 is naturally turned off from the conduction state.
- the state is changed (S33).
- the capacitive element 67 holds a voltage corresponding to the threshold voltage of the drive transistor 61. More specifically, this operation is performed within a period T24 (power supply voltage setting period) in FIG.
- control unit 2 turns off the enable switch 65.
- the operation of turning off the enable switch 65 is based on the falling edge of the ENB signal (Enable line 75) in the off sequence of FIG.
- the pixel circuit 60 individually applies a voltage corresponding to the threshold voltage of the drive transistor 61 to the capacitive element. 67 can be set. That is, a voltage corresponding to the individual threshold voltage of the drive transistor 61 in which the threshold voltage shift occurs can be set in the corresponding capacitive element 67, and variation in threshold voltage shift in the power-off state of the display device 1 is suppressed. can do.
- 6A to 6E are explanatory diagrams showing the operation of the pixel circuit 60 in the periods T21 to T25 shown in FIG.
- the operation of the pixel circuit 60 in the periods T21 to T25 in the off sequence in FIG. 5 is the same as that in the periods T21 to T25 in one frame in FIG.
- a voltage corresponding to the threshold voltage of the driving transistor 61 is held in the capacitor 67 and applied to the gate.
- Period T21 In the period T21 from time t0 to time t1 shown in FIG. 5, only the switch 64 is turned on to stabilize the potential of the node B (set the potential of the node B to the voltage V INI of the initialization power supply line 71). It is a period.
- the scanning line driving circuit 3 sets the voltage levels of the Scan line 72, the Ref line 73, and the Enable line 75 to LOW. While maintaining, the voltage level of the Init line 74 is changed from LOW to HIGH. That is, at time t0, the switch 62, the switch 63, and the enable switch 65 remain in a non-conductive state (off state), and the switch 64 is in a conductive state (on state).
- the potential of the node B is set to the initializing power line 71.
- the voltage V INI can be set.
- the capacitance of the EL element 66 increases, and the wiring time constant of the initialization power supply line 71 increases. It takes time to set the voltage at the node B to the voltage V INI of the initialization power supply line 71. Therefore, by providing the period T21 in which the switch 64 is first turned on, the potential of the node B can be reliably set by the voltage V INI of the initialization power supply line 71.
- the target for charging and discharging the voltage V REF is the wiring time constant of the capacitive element 67 and the reference voltage power supply line 68. That is, the wiring time constants of the reference voltage power supply line 68 and the initialization power supply line 71 are substantially equal, but the capacitance of the EL element 66> capacitance element 67, and the capacitance ratio is (EL element 66) / (capacitance element). 67) is 1.3 to 9 times.
- charging the EL element 66 (writing the voltage V INI of the initialization power supply line 71 to the potential of the node B) charges the capacitive element 67 (the voltage V REF of the reference voltage power supply line 68 is set to the potential of the node A). Takes more time than writing).
- the load for writing the voltage V INI of the reference voltage power line 68 to the node A can be reduced by providing a period for writing the voltage V INI of the initialization power line 71 to the potential of the node B in the period T21. is there. That is, by providing the period T21, the voltage of the node A can be set to a low voltage, and the reference voltage power line 68 only needs to supply a current (voltage) for charging the pixel circuit 60. In other words, since the voltage V REF of the reference voltage power supply line 68 is not used as a voltage for charging the EL element 66, there is an advantage that the load on the reference voltage power supply line 68 is reduced.
- the switch 64 is switched to the conductive state (ON state), and the period T21 for determining the potential of the node B is provided.
- the total time of the period T22 after the period T21 can be shortened while reducing the power consumption of the display panel 6 and the influence of the luminance fluctuation of the display panel 6.
- Period T22 Initialization period
- the capacitor 67 holds the initial voltage necessary for flowing the drain current to compensate the threshold voltage of the driving transistor 61, and the source and gate of the driving transistor 61 It is the initialization period for applying to.
- the scanning line driving circuit 3 maintains the voltage levels of the Scan line 72 and the Enable line 75 at LOW and the Init line 74.
- the voltage level of the Ref line 73 is changed from LOW to HIGH while maintaining the voltage level of REF. That is, at time t1, the switch 62 and the enable switch 65 are in a non-conduction state (off state), and the switch 64 is in a conduction state (on state) while the switch 63 is in a conduction state (on state).
- the potential of the node A is set to the voltage V REF of the reference voltage power supply line 68.
- the switch 64 is conductive, the potential of the node B is set to the voltage V INI of the initialization power supply line 71. That is, the drive transistor 61 is applied with the voltage V REF of the reference voltage power line 68 and the voltage V INI of the initialization power line 71.
- the period T22 is set to a length (time) until the potential of the node A and the node B reaches a predetermined potential.
- the gate-source voltage of the drive transistor 61 needs to be set to an initial voltage that can secure an initial drain current necessary for performing the threshold compensation operation. That is, the initial voltage needs to be higher than the threshold voltage of the driving transistor 61 in each of the capacitor elements 67 of the plurality of pixel circuits 60 and not to cause the EL element 66 to emit light. Therefore, the potential difference between the voltage V REF of the reference voltage power supply line 68 and the voltage V INI of the initialization power supply line 71 is set to a voltage larger than the maximum threshold voltage of the drive transistor 61.
- the voltage V REF and the voltage V INI are such that the voltage V INI ⁇ the voltage V EL + the forward current threshold voltage of the EL element 66 and the voltage V REF ⁇ the voltage V EL + EL element 66 so that no current flows through the EL element 66.
- the forward current threshold voltage is set to the threshold voltage of the driving transistor 61.
- Period T23 A period T23 from time t2 to time t3 shown in FIG. 5 is a period for preventing the switch 64 and the enable switch 65 from being in the conductive state at the same time.
- the scanning line driving circuit 3 maintains the voltage levels of the Scan line 72 and the Enable line 75 at LOW, and the Ref line.
- the voltage level of the Init line 74 is changed from HIGH to LOW while maintaining the voltage level of 73 at HIGH. That is, at time t2, the switch 62 and the enable switch 65 are in a non-conductive state (off state), the switch 63 remains in a conductive state (on state), and the switch 64 is in a non-conductive state (off state).
- the switch 64 and the enable switch 65 are turned on at the same time without the period T23, and the enable switch 65, the drive transistor 61, Further, it is possible to prevent a through current from flowing between the EL anode power supply line 69 and the initialization power supply line 71 via the switch 64.
- a period T24 from time t3 to time t4 in FIG. 5 is a threshold setting period for compensating for variations in the threshold voltage of the drive transistor 61 in the plurality of pixel circuits 60.
- this is a period in which a voltage corresponding to the threshold voltage of each drive transistor 61 is set in the corresponding capacitor 67.
- the period T21 to T25 is the same in the off sequence in FIG. 5 and the normal display in FIG. 7, but the purpose is different between the off sequence and the normal display. Therefore, the period T25 is called a threshold setting period in FIG. 7 is referred to as a threshold compensation period.
- the purpose of the threshold setting period in FIG. 5 is to define the voltage of the capacitive element 67 after the power of the display device 1 is turned off, whereas in the normal display of FIG. 7, writing is performed in the capacitive element 67 after the period T25.
- the difference is that the purpose is to make the voltage representing the brightness to correspond to the variation of the threshold voltage.
- the scanning line driving circuit 3 sets the voltage level of the Scan line 72 and the Init line 74 to LOW and the voltage level of the Ref line 73 at time t3. Maintaining HIGH, the voltage level of the Enable line 75 is changed from LOW to HIGH. That is, at time t3, the switch 62 and the switch 64 are in a non-conductive state (off state), and the switch 63 is maintained in a conductive state (on state), while the enable switch 65 is in a conductive state (on state). .
- the driving transistor 61 is the drain current supplied by the voltage V TFT of the EL anode power supply line 69, the source potential of the driving transistor 61 is changed therewith. In other words, the driving transistor 61, the source potential of the driving transistor 61 to the drain current supplied by the voltage V TFT of the EL anode power supply line 69 becomes 0 is changed.
- the enable switch 65 when the enable switch 65 is turned on with the voltage VREF of the reference voltage power supply line 68 being input to the gate electrode of the drive transistor 61, the threshold compensation operation of the drive transistor 61 is started. Can do.
- the potential difference between the node A and the node B is a potential difference corresponding to the threshold value of the driving transistor 61. Is held in the capacitor 67.
- Period T25 A period T25 from time t4 to time t5 shown in FIG. 5 is a period for ending the threshold setting operation or threshold compensation operation.
- the scanning line driving circuit 3 sets the voltage level of the Scan line 72 and the Init line 74 to LOW, and sets the voltage level of the Ref line 73 to HIGH.
- the voltage level of the Enable line 75 is changed from HIGH to LOW. That is, at time t4, the switch 62 and the switch 64 are kept in a non-conducting state (off state), and the switch 63 is kept in a conducting state (on state), while the enable switch 65 is brought into a non-conducting state (off state).
- each capacitor element 67 in the plurality of pixel circuits 60 holds a voltage corresponding to the threshold voltage of the corresponding drive transistor 61.
- the power supply unit 4 controls the display panel 6 and the scanning line driving circuit 3 at any time in the period T90 after the time t5 in FIG.
- the power supply to the data line driving circuit 5 and the like is stopped. As a result, the display device 1 is turned off.
- the capacitor 67 holds a voltage corresponding to the threshold value of the driving transistor 61, that is, a voltage corresponding to the threshold value is applied to the gate of the driving transistor 61. Yes. In this state, the electric field of the driving transistor is in a stable equilibrium state, so that electrical stress is substantially suppressed.
- the pixel circuits 60 individually hold voltages corresponding to the threshold voltages of the corresponding drive transistors 61 in the capacitor elements 67. That is, the corresponding capacitive element 67 holds a voltage corresponding to the individual threshold voltage of the drive transistor 61 in which the threshold voltage shift occurs. Therefore, it is possible to obtain an effect of suppressing the threshold voltage shift in the power-off state of the display device 1 and suppressing the variation of the threshold voltages of the individual drive transistors 61.
- FIG. 7 is a time chart showing a detailed timing example of the normal display operation in FIG. 6A to 6H are explanatory diagrams showing the operation of the pixel circuit 60 in the periods T21 to T30 shown in FIG.
- the periods T21 to T25 shown in FIG. 7 are the same as the periods T21 to T25 shown in FIG. Here, the period T26 and after will be described.
- Period T26 In the period T26 from time t5 to time t6 shown in FIG. 7, the data signal voltage supplied via the data line 76 and the voltage V of the reference voltage power supply line 68 are set by turning off the switch 63. This is a period for preventing REF from being applied to the node A at the same time.
- the scanning line driving circuit 3 maintains the voltage levels of the scan line 72, the init line 74, and the enable line 75 at LOW.
- the voltage level of the Ref line 73 is changed from HIGH to LOW. That is, at time t5, the switch 62, the switch 64, and the enable switch 65 remain in a non-conduction state (off state), and the switch 63 is in a non-conduction state (off state).
- the switch 63 is further turned off by the operation of the Ref line 73, and the switch 62 and the switch 63 are supplied from the switch 62 through the Data line 76 by providing the period T26 in which the switch 62 and the switch 63 are turned off.
- the data signal voltage (video signal voltage) and the voltage V REF of the reference voltage power line 68 are prevented from being applied to the node A at the same time.
- the enable switch 65 connected to the Enable line 75 is connected to the drain side of the drive transistor 61 as shown in FIG. 6F (FIG. 2).
- the enable switch 65 is formed of an n-type transistor, the ON resistance of the enable switch 65 tends to be high, and the voltage drop due to the ON resistance affects the power consumption of the display panel 6. Therefore, the on-resistance of the enable switch 65 is lowered as much as possible.
- a method of decreasing the on-resistance by increasing the channel size of the enable switch 65 or increasing the on-control voltage of the enable line 75 is known. 75 will cause the fall time to be longer.
- the period T25 during which the Enable line 75 falls before the Ref line 73 the period during which the voltage at the node A becomes unstable can be shortened. Time can be shortened.
- Period T27 Write period
- a video signal voltage (data signal voltage) corresponding to the display gradation is captured from the Data line 76 to the pixel circuit 60 via the switch 62 and is stored in the capacitor 67. It is a writing period for writing.
- the scanning line driving circuit 3 maintains the voltage levels of the Init line 74, the Ref line 73, and the Enable line 75 at LOW at time t6. Meanwhile, the voltage level of the scan line 72 is changed from LOW to HIGH. That is, at time t6, the switch 63, the switch 64, and the enable switch 65 are maintained in the non-conductive state (off state), while the switch 62 is in the conductive state (on state).
- the voltage difference between the video signal voltage and the voltage V REF of the reference voltage power supply line 68 is set in the capacitive element 67 (EL element 66). Capacity) / (capacitance of EL element 66 + capacitance element 67) and stored (held). Since the enable switch 65 is in a non-conduction state, the drive transistor 61 does not pass a drain current. Therefore, the potential of the node B does not change greatly during the period T27.
- the period for writing video signals to the pixel circuits 60 (horizontal scanning period) is shortened.
- the scan line 72 wiring time constant also increases, so that it becomes difficult to write a predetermined gradation voltage in the pixel circuit 60 as the horizontal scanning period is shortened.
- the time for which the switch 62 is turned on (period T27) is increased.
- the scan line 72 completes rising before a predetermined video signal (data signal voltage) is input to the data line 76, and the switch 62 Is in a conductive state (on state). This is because the node B potential fluctuation does not occur greatly in the period T27.
- the voltage corresponding to the data signal voltage (video signal voltage) and the threshold voltage of the driving transistor 61 is stored (held) in the capacitor 67.
- Period T28 A period T28 from time t7 to time t8 shown in FIG. 7 is a period for surely turning off the switch 62.
- the scanning line driving circuit 3 maintains the voltage levels of the Ref line 73, the Init line 74, and the Enable line 75 at LOW at time t7.
- the voltage level of the scan line 72 is changed from HIGH to LOW. That is, at time t7, the switch 63, the switch 64, and the enable switch 65 remain in a non-conduction state (off state), and the switch 62 is in a non-conduction state (off state).
- the switch 62 can be surely turned off (off state) before the enable switch 65 is turned on (on state).
- the enable switch 65 and the switch 62 are simultaneously turned on (on state) without providing the period T ⁇ b> 28, the potential of the node B rises due to the drain current of the drive transistor 61, while the potential of the node A Since this becomes a data signal voltage, the voltage between the source and gate of the driving transistor 61 becomes small. In this case, there is a problem that light is emitted with a luminance lower than the desired luminance. In order to prevent this, in the present embodiment, after the period T28 is provided to ensure that the switch 62 is non-conductive, the enable switch 65 is turned on in the subsequent period T29.
- Period T29 Light emission period
- the scanning line driving circuit 3 changes the voltage level of the Enable line 75 from LOW to HIGH while maintaining the voltage levels of the Scan line 72, the Ref line 73, and the Init line 74 at LOW. . That is, at time t8, the switch 62, the switch 63, and the switch 64 are maintained in a non-conduction state (off state), while the enable switch 65 is in a conduction state (on state).
- Period T30 A period T30 from time t9 to time t0 shown in FIG. 7 is a period for setting all the switches in a non-conductive state and changing the potentials of the nodes A and B to a voltage close to the voltage required in the period T21.
- the scanning line driving circuit 3 changes the voltage level of the Enable line 75 from HIGH to LOW while maintaining the voltage levels of the Scan line 72, the Ref line 73, and the Init line 74 at LOW. Let That is, at time t9, the switch 62, the switch 63, and the switch 64 remain in a non-conduction state (off state), and the enable switch 65 is further in a non-conduction state (off state).
- the potentials of the node A and the node B are set to voltages necessary for the next period T21 without charging / discharging the current by the power supply line. It can be changed to a close voltage.
- the pixel circuit 60 performs normal display by the sequence as described above.
- the operation from period T21 to T25 in FIG. 7 (up to the threshold voltage compensation operation) in this normal display is the same as the operation from period T21 to T25 in FIG. 5 (up to the threshold voltage setting operation) in the off sequence.
- a voltage corresponding to the threshold voltage of the drive transistor 61 is set to 67.
- the EL element 66 is caused to emit light with a light emission amount corresponding to the data signal voltage (video signal voltage). be able to.
- the electrical stress of the drive transistor 61 after the power is turned off can be suppressed.
- the operations in the periods T21 to T25 in FIG. 7 are basically line-sequential operations performed sequentially for each display line of the display panel.
- the operations in the periods T21 to T25 in FIG. 5 may be line-sequential operations, or may be a batch setting operation in which all display lines of the display panel are collectively performed simultaneously. In this collective setting, a voltage corresponding to the threshold voltage of the drive transistor 61 is simultaneously set in the capacitive element 67 in each of the plurality of pixel circuits 60 of all display lines.
- the off-sequence period in FIG. 5 may be the same as or different from the one-frame period in FIG.
- the operation of collectively setting the off sequence in FIG. 5 is more affected by the delay due to the stray capacitance of the wiring than the line sequential operation, but the off sequence period is longer than the total time of all line sequential pixel lines. Can be shortened.
- one aspect of the method for terminating a display device is a method for powering off a display device including a display panel having a plurality of pixel circuits arranged in a matrix, and the plurality of pixel circuits Each includes a light emitting element that emits light with luminance according to the amount of current supplied, a driving transistor that supplies current to the light emitting element, and a capacitor element that is connected to the gate of the driving transistor and holds a voltage representing luminance.
- the method for powering off the display device includes a step of detecting a power-off operation for the display device, and when the power-off operation is detected, the capacitive element in each of the plurality of pixel circuits includes: A step of setting a voltage for suppressing electrical stress on the driving transistor, and a step of stopping the power supply to the display panel immediately after the setting of the voltage. Has the door, in the step of setting said voltage to said capacitive element in each of the plurality of pixel circuits, sets a voltage corresponding to the threshold voltage of the driving transistor.
- the threshold voltage shift of the drive transistor during the period when the power supply of the display device is off. That is, the threshold voltage shift can be suppressed by suppressing the electrical stress applied to the driving transistor while the power is off.
- each of the capacitor elements of the plurality of pixel circuits is allowed to hold an initial voltage that is higher than a threshold voltage of the driving transistor and does not cause the light emitting element to emit light, and
- the drive transistor is made conductive, the voltage of the capacitive element is lowered by a conduction current flowing through the conductive drive transistor, and the drive transistor is made non-conductive by a voltage drop of the capacitive element, and the voltage corresponding to the threshold voltage is The voltage when the driving transistor is turned off may be used.
- a voltage corresponding to a threshold voltage of the driving transistor may be simultaneously set in the capacitive element in each of the plurality of pixel circuits.
- the time until the power supply is stopped can be shortened because the capacitive elements of all the pixel circuits are collectively set.
- One embodiment of the display device is a display device including a display panel having a plurality of pixel circuits arranged in a matrix, and each of the plurality of pixel circuits is in accordance with a supplied amount of current.
- a light emitting element that emits light
- a driving transistor that supplies current to the light emitting element
- a capacitor element that is connected to a gate of the driving transistor and holds a voltage representing luminance.
- a control unit configured to set a voltage for suppressing electrical stress on the drive transistor in each of the plurality of pixel circuits when detected, and the display panel immediately after the setting of the voltage by the control unit
- a power supply unit that stops power supply to the drive transistor, and the control unit uses the drive transistor as the voltage to suppress electrical stress on the drive transistor. Setting a voltage corresponding to the threshold voltage of Njisuta.
- FIG. 8 is a diagram illustrating a circuit example of a display pixel in a modification of the embodiment.
- the pixel circuit in FIG. 8 includes a drive transistor 61, a switch 62, an EL element 66, and a capacitor element 67, and has a simpler configuration than the pixel circuit shown in FIG.
- the drive transistor 61 shown in the figure is not an n-type TFT but a p-type TFT, and its drain is connected to a power supply line having a voltage V1.
- One electrode of the capacitive element 67 is connected to the power supply line of the voltage V2.
- the voltage V1 may be the same as the voltage V2.
- One of the source and the drain of the switch 62 is connected to the Data line 76, and the other of the source and the drain is connected to the other electrode of the capacitor 67.
- the gate of the switch 62 is connected to the Scan line 72.
- the potential of the data line 76 is set to (voltage V2) ⁇ (threshold voltage of the driving transistor 61), and then the scan line 72 is set to high level (that is, the switch 62 is turned on). ).
- the capacitor 67 holds a voltage corresponding to the threshold voltage of the drive transistor 61.
- the held voltage is applied to the gate of the drive transistor 61.
- the power supply unit 4 stops the power supply to the display panel 6.
- the pixel circuit 60 is not limited to the circuit example of FIG. 2 but may be the circuit example of FIG.
- a circuit configuration in which a switch is added between the power supply line of the voltage V1 and the drive transistor 61 and the Enable line 75 is connected to the gate of the circuit example of FIG.
- a circuit configuration in which a switch is added between the power supply line of the voltage V2 and the driving transistor 61 and the Ref line 73 is connected to the gate of the circuit example of FIG.
- a circuit configuration in which the initialization power supply line 71 is connected to the anode of the EL element 66 via a switch and the Init line 74 is connected to the gate of the switch may be employed.
- the driving transistor 61 may be n-type or p-type.
- FIGS. 1 The configurations of the display device and the pixel circuit in this embodiment are the same as those in FIGS. Also, the power-off method and the time chart in this embodiment are the same at the levels of FIGS.
- the display device 1 is compatible with a so-called 4k television and has effective pixels of horizontal 3840 pixels ⁇ vertical 2160 pixels or more.
- FIG. 9 is a time chart showing a detailed timing example of the normal display operation in another embodiment.
- one frame period that is, the period 1V of the vertical synchronization signal
- a 2250 horizontal period that is, 2250 times the period of the horizontal synchronization signal.
- FIG. 9 is the same as FIG. 7 in that the initialization period, the threshold voltage compensation period, the writing period, and the light emission period are performed in this order, but the drive timing is partially different.
- different points will be mainly described.
- the Ref line 73 changes from the low level to the high level. This rise causes the EL element 66 to emit no light.
- the non-light emitting period of the EL element 66 can be adjusted by adjusting the width of the period T11.
- the Init line 74 changes from the low level to the high level. With this rise, the initialization period starts.
- Period T12 is an initialization period.
- the initialization period a period for sufficiently discharging the parasitic capacitance of the node B (capacitance of the EL element 66) to the Init line 74 is provided.
- the initialization period is also a period for discharging the parasitic capacitance at the node A to determine the potential. This period is determined by a trade-off between charging the parasitic capacitance and the current flowing through the driving transistor 61.
- the initial voltage necessary for flowing the drain current to compensate the threshold voltage of the driving transistor 61 is held in the capacitor 67.
- the Init line 74 transitions from the high level to the low level, and the threshold voltage compensation period starts.
- the period T14 is a threshold voltage compensation period similar to the period T24 in FIG.
- the switch 63 due to the fall of the Ref line 73 changes from the on state to the off state, and the threshold voltage compensation period ends.
- the potential difference between the node A and the node B (the gate-source voltage of the driving transistor 61) is a potential difference corresponding to the threshold value of the driving transistor 61, and this voltage is held in the capacitor 67.
- the period T15 is a period for determining the gate potential in the row because the gate potential of the driving transistor 61 fluctuates when the switch 63 changes from the on state to the off state at time t04. This period is called a REF transition period.
- the Enable line 75 changes from the high level to the low level, the enable switch 65 is turned off, and the current supply to the drive transistor 61 is stopped.
- the period T16 is a period for making the potential of the EL anode power supply line 69 (VTFT) the same in all the pixels in the row after the enable switch 65 is turned off.
- the period T17 is a writing period, and is different from FIG. 7 in that the falling edge of the scan line 72 is overdriven. That is, at time t07, the potential is lowered to a potential lower than the normal low level at the fall of the pulse. This is because the pulse of the scan line 72 is actually a waveform that is considerably reduced, so that the fall time is shortened and the writing to the capacitive element 67 is determined early.
- Period T18 is an overdrive period.
- the period T19 is a period for determining the gate potential in the row because the gate potential of the driving transistor 61 changes when the switch 62 changes from the on state to the off state at time t07. This period is called an SCN transition period.
- the Enable line 75 changes from the low level to the high level. This starts the light emission period.
- Period T20 is a light emission period. This period is about 95% of one frame period (2250H), for example. That is, light can be emitted during a period of about 95% of one frame period.
- the example of the normal display driving timing shown in FIG. 9 is suitable for a display device having a large number of pixels such as a 4k television, and can emit light for most (about 95%) of one frame period.
- FIG. 10 is a time chart showing a detailed timing example of the off sequence in another embodiment.
- FIG. 10 is the same as FIG. 5 in that the initialization period and the threshold voltage setting period are performed in this order, but part of the drive timing is different.
- the period T11 to the period T15 shown in FIG. 10 are the same as the period T11 to the period T15 shown in FIG. Here, a description will be given after the period T15.
- each capacitive element 67 in the plurality of pixel circuits 60 holds a voltage corresponding to the threshold voltage of the corresponding driving transistor 61. Therefore, the voltage corresponding to the threshold voltage held by the capacitive element 67 is maintained even after the off sequence is finished and the power supply of the display device 1 is turned off. That is, when the display device 1 is powered off, a voltage corresponding to the threshold is applied to the gate of the drive transistor 61. In this state, the electric field of the driving transistor is in a stable equilibrium state, so that electrical stress is substantially suppressed.
- the data line 76 may be don't care (that is, an arbitrary voltage) during the off sequence period.
- the data line driving circuit 5 may operate in the same manner in the normal operation even in the off sequence, and in this case, the displayed data is output if it is not the off sequence at time t06. Of course, this data is not reflected in the display in the off sequence and is ignored.
- the material of the semiconductor layer of the driving transistor and the switching transistor used in the light-emitting pixel of the present disclosure is not particularly limited, but an oxide semiconductor material such as IGZO (In—Ga—Zn—O) can be employed, for example.
- IGZO In—Ga—Zn—O
- a transistor including a semiconductor layer made of an oxide semiconductor such as IGZO has little leakage current.
- the threshold voltage can be positive, so that leakage current from the gate of the driving transistor can be suppressed.
- an organic EL element is used as the light emitting element.
- any light emitting element can be used as long as the light emitting element changes in light emission amount according to current.
- the above-described display device such as the organic EL display device can be used as a flat panel display, and can be applied to all electronic devices having a display device such as a television set, a personal computer, and a mobile phone.
- the present disclosure can be used for a display device, particularly for a display device such as a television set.
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Abstract
Description
以下、本開示の詳細を説明する前に、本開示の基礎となる知見について説明する。
以下、本開示における表示装置の電源断方法および表示装置について図面を参照しながら説明する。
本実施の形態において、本開示の一態様に係る表示装置の発光素子として有機EL素子を用いる場合について、図1および図2を用いて説明する。
(基準電圧電源線68の電圧VREF)<電圧VEL+(EL素子66の順方向電流閾値電圧)+(駆動トランジスタ61の閾値電圧)
次に、図1および図2に示した表示装置の構成例における動作について図3および図4を用いて説明する。
図5に示す時刻t0~時刻t1の期間T21は、スイッチ64のみを導通状態として、節点Bの電位を安定させる(節点Bの電位を初期化電源線71の電圧VINIに設定する)ための期間である。
図5に示す時刻t1~時刻t2の期間T22は、駆動トランジスタ61の閾値電圧補償を行うためにドレイン電流を流すのに必要な初期電圧を容量素子67に保持させ、駆動トランジスタ61のソースゲート間に印加するための初期化期間である。
図5に示す時刻t2~時刻t3の期間T23は、スイッチ64とイネーブルスイッチ65とが同時に導通状態とならないようにするための期間である。
次に、図5の時刻t3~時刻t4の期間T24は、複数の画素回路60における駆動トランジスタ61の閾値電圧のばらつきを補償する閾値設定期間である。つまり、複数の画素回路60における駆動トランジスタ61の閾値電圧にばらつきがあっても、個々の駆動トランジスタ61の閾値電圧に相当する電圧を対応する容量素子67に設定する期間である。
図5に示す時刻t4~時刻t5の期間T25は、閾値設定動作または閾値補償動作を終了させるための期間である。
最後の行に対する期間T21~T25の動作の完了後、図5の時刻t5以降の期間T90の任意の時点に、制御部2からの制御によって電源部4は、表示パネル6、走査線駆動回路3、データ線駆動回路5等への電力供給を止める。これにより表示装置1は電源オフの状態になる。
図7に示す時刻t5~時刻t6の期間T26は、スイッチ63を非導通状態(オフ状態)にすることで、Data線76を介して供給されたデータ信号電圧と基準電圧電源線68の電圧VREFとが同時に節点Aに印加されるのを防止する期間である。
次に、図7の時刻t6~時刻t7の期間T27は、Data線76から表示階調に応じた映像信号電圧(データ信号電圧)を画素回路60にスイッチ62を介して取り込み、容量素子67に書き込む書込期間である。
図7に示す時刻t7~時刻t8の期間T28は、スイッチ62を確実に非導通にさせるための期間である。
次に、図7に示す時刻t8~時刻t9の期間T29は、発光期間である。
図7に示す時刻t9~時刻t0の期間T30は、すべてのスイッチを非導通状態として、節点Aおよび節点Bの電位を、期間T21で必要な電圧に近い電圧まで変化させるための期間である。
以上説明してきたように本開示における表示装置の終了方法の一態様は、行列状に配置された複数の画素回路を有する表示パネルを備える表示装置の電源断方法であって、前記複数の画素回路のそれぞれは、供給される電流量に応じた輝度で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に接続され輝度を表す電圧を保持する容量素子とを有し、前記表示装置の電源断方法は、前記表示装置に対する電源オフ操作を検出するステップと、前記電源オフ操作が検出されたとき、前記複数の画素回路のそれぞれにおける前記容量素子に、前記駆動トランジスタへの電気的ストレスを抑制する電圧を設定するステップと、前記電圧の設定直後に前記表示パネルへの電力供給を止めるステップとを有し、前記電圧を設定するステップにおいて、前記複数の画素回路のそれぞれにおける前記容量素子に、前記駆動トランジスタの閾値電圧に相当する電圧を設定する。
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、前述した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、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。
次に、本開示における他の実施の形態について図9、図10を用いて説明する。この実施の形態における表示装置および画素回路の構成は、図1および図2と同じである。また、この実施の形態における電源断方法およびタイムチャートも、図3および図4のレベルでは同じである。ただし、表示装置1は、いわゆる4kテレビ対応であり、横3840画素×縦2160画素以上の有効画素を有するものとする。この実施の形態では、実施の形態における図7に示した通常表示動作、および、図5に示したオフシーケンスの駆動タイミングとは異なる駆動タイミングを有し、上記表示装置に適した動作例について説明する。
2 制御部
3 走査線駆動回路
4 電源部
5 データ線駆動回路
6 表示パネル
60 画素回路
61 駆動トランジスタ
62、63、64 スイッチ
65 イネーブルスイッチ
66 EL素子
67 容量素子
68 基準電圧電源線
69 ELアノード電源線
70 ELカソード電源線
71 初期化電源線
72 Scan線
73 Ref線
74 Init線
75 Enable線
76 Data線
Claims (4)
- 行列状に配置された複数の画素回路を有する表示パネルを備える表示装置の電源断方法であって、
前記複数の画素回路のそれぞれは、供給される電流量に応じた輝度で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に接続され輝度を表す電圧を保持する容量素子とを有し、
前記表示装置の電源断方法は、
前記表示装置に対する電源オフ操作を検出するステップと、
前記電源オフ操作が検出されたとき、前記複数の画素回路のそれぞれにおける前記容量素子に、前記駆動トランジスタへの電気的ストレスを抑制する電圧を設定するステップと、
前記電圧の設定直後に前記表示パネルへの電力供給を止めるステップとを有し、
前記電圧を設定するステップにおいて、前記複数の画素回路のそれぞれにおける前記容量素子に、前記駆動トランジスタの閾値電圧に相当する電圧を設定する
表示装置の電源断方法。 - 前記電圧を設定するステップにおいて、
前記複数の画素回路の前記容量素子のそれぞれに前記駆動トランジスタの閾値電圧よりも高く、かつ、前記発光素子を発光させない初期電圧を保持させ、
前記初期電圧によって前記駆動トランジスタを導通させ、
導通した前記駆動トランジスタに流れる導通電流によって前記容量素子の電圧を低下させ、
前記容量素子の電圧低下によって前記駆動トランジスタを非導通にさせ、
前記閾値電圧に相当する電圧は、前記駆動トランジスタが非導通になったときの電圧である
請求項1に記載の表示装置の電源断方法。 - 前記電圧を設定するステップにおいて、前記複数の画素回路のそれぞれにおける前記容量素子に前記駆動トランジスタの閾値電圧に相当する電圧を同時に設定する
請求項1に記載の表示装置の電源断方法。 - 行列状に配置された複数の画素回路を有する表示パネルを備える表示装置であって、
前記複数の画素回路のそれぞれは、
供給される電流量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に接続され輝度を表す電圧を保持する容量素子とを有し、
前記表示装置は、
電源オフ操作が検出されたとき、前記複数の画素回路のそれぞれにおける前記容量素子に、前記駆動トランジスタへの電気的ストレスを抑制する電圧を設定する制御部と、
前記制御部による前記電圧の設定直後に前記表示パネルへの電力供給を止める電源部とを備え、
前記制御部は、前記駆動トランジスタへの電気的ストレスを抑制する前記電圧として、前記駆動トランジスタの閾値電圧に相当する電圧を設定する
表示装置。
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