JP4467900B2 - Driving method of light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technology of a light emitting device, and more particularly to a driving method of the light emitting device.
[0002]
[Prior art]
In recent years, development of display devices that display images has been promoted. As a display device, a liquid crystal display device that displays an image using a liquid crystal element is widely used as a display device for a mobile phone or a personal computer, taking advantage of high image quality, thinness, and light weight.
[0003]
On the other hand, development of a light-emitting device using a light-emitting element has been advanced in recent years. Since the light-emitting device does not require a light source such as a backlight, it has the advantages of low power consumption, small size, light weight, fast response speed, excellent video display, and wide viewing characteristics. It is attracting attention as a next-generation small mobile flat panel display that can use video content.
[0004]
A light-emitting element includes a wide variety of materials such as an organic material, an inorganic material, a thin film material, a bulk material, and a dispersion material. Among them, organic light emitting diodes (OLEDs) mainly composed of organic materials are listed as typical light emitting elements. The light emitting element has an anode and a cathode, and a structure in which a light emitting layer is sandwiched between the anode and the cathode. The light emitting layer is made of one or more materials selected from the above materials.
[0005]
The amount of current flowing through the light emitting element and the luminance of the light emitting element are in a directly proportional relationship, and the light emitting element emits light with luminance according to the amount of current flowing through the light emitting layer.
[0006]
By the way, as a driving method when displaying a multi-gradation image on the light emitting device, there are an analog gradation method and a digital gradation method. The former analog gradation method is a method in which a current corresponding to a desired gradation is supplied to the light emitting element, and the gradation is expressed by the magnitude of the current. The latter digital gradation method is a method in which the light emitting element is driven only in two states: an on state (a state where the luminance is approximately 100%) and an off state (a state where the luminance is approximately 0%). .
[0007]
As a driving method when displaying a multi-tone image on the light emitting device, a voltage input method and a current input method can be given. The former voltage input method is a method in which a video signal (voltage) input to a pixel is input to a gate electrode of a driving element, and the luminance of the light emitting element is controlled using the driving element. In the latter current input method, the luminance of the light emitting element is controlled by flowing a set signal current to the light emitting element. Note that both the analog gradation method and the digital gradation method described above are applied to the voltage input method and the current input method.
[0008]
In order to provide a display device capable of improving the operational reliability of a light-emitting element and a driving method thereof, there is one that shortens a light emission time of a pixel (see Patent Document 1).
[0009]
[Patent Document 1]
JP 2000-347622 A
[0010]
[Problems to be solved by the invention]
An operation when the analog gray scale method is applied to a light-emitting device will be described with reference to a timing chart of FIG. In the timing chart of FIG. 7, the horizontal axis indicates time, and the vertical axis indicates a row of scanning lines.
[0011]
As shown in FIG. 7, in the analog gray scale method, one frame period (F) is an address period (Ta) in which a video signal is written to the pixel, and a sustain period (Ts) in which the pixel emits light in accordance with the video signal. ). As the time elapses, the address period (Ta) and the sustain period (Ts) appear alternately. At this time, the light emission period of each pixel occupies most of one frame period. Therefore, each pixel emits light almost always unless a “black” video signal is input.
[0012]
Then, the light emitting element included in each pixel is deteriorated with time. When the light emitting element is deteriorated, even when the same amount of current is supplied to each pixel, the luminance generated by the light emitting element varies and the display pattern is burned. If it does so, it will become difficult to display the image expressed with the exact gradation in the light-emitting device.
[0013]
[Means for Solving the Problems]
In view of the above-described circumstances, the present invention provides a driving method of a light-emitting device in which a period in which a pixel does not emit light (off-time period) is provided in each frame period.
[0014]
By providing an off-time period in each frame period, a period in which the light-emitting element included in each pixel does not emit light can be provided. As a result, deterioration over time of the light emitting element can be reduced. Furthermore, the reliability of the light emitting element can be improved.
[0015]
The present invention includes a light emitting means provided with first and second electrodes, a driving means for supplying a current corresponding to an analog video signal to the light emitting means, and a sustain period and an off time period within a unit frame period. This is a driving method of a light emitting device provided with a plurality of pixels each having setting means for setting. In the sustain period, a current corresponding to the analog video signal is supplied to the light emitting means, and in the off time period, the light emitting means is turned off by turning off the driving means, or the first and The light emitting means is made to emit no light by setting the potential of the second electrode to the same potential.
[0016]
The light-emitting means corresponds to a light-emitting element, and specifically corresponds to a light-emitting element composed of any one of a wide range of materials such as an organic material, an inorganic material, a thin film material, a bulk material, and a dispersion material. The light emitting element has a structure in which a light emitting layer is sandwiched between an anode and a cathode, and the anode and the cathode, and the light emitting layer is made of one or more materials selected from the above materials. .
[0017]
The driving means corresponds to an element connected to the light emitting means, and specifically corresponds to a transistor connected to the light emitting means. In a pixel to which the voltage input method is applied, an analog video signal is input to the gate electrode of the transistor, whereby a source-drain current of the transistor is determined, and the source-drain current is converted into the light-emitting element. To be supplied. On the other hand, in a pixel to which the current input method is applied, a predetermined signal current is supplied between the source and drain of the transistor, and the source-drain current is supplied to the light emitting element.
[0018]
The setting means corresponds to an element arranged in the pixel, and specifically corresponds to a switching transistor that is an element having a function of controlling input of a signal to the pixel. Further, it corresponds to a scanning line driver circuit, a signal line driver circuit, a control circuit, and the like arranged around the pixel.
[0019]
The present invention relates to a light emitting means having first and second electrodes, a driving means for supplying a current corresponding to an analog video signal to the light emitting means, and n sustain periods (n Is a driving method of a light emitting device having first setting means for setting a natural number of 1 or more and second setting means for setting an off-time period. In the n sustain periods, a current corresponding to the analog video signal is supplied to the light emitting means, and in the off time period, the first or second electrode is floated to change the light emitting means. The light-emitting means is made non-light-emitting by making it non-light-emitting or making the potentials of the first and second electrodes the same.
[0020]
The first setting means corresponds to an element arranged in a pixel, and specifically corresponds to an element having a function of controlling input of a signal to the pixel. Further, it corresponds to a scanning line driver circuit, a signal line driver circuit, a control circuit, and the like arranged around the pixel.
[0021]
The second setting means corresponds to a wiring for supplying current to the light emitting means, a power source connected to the wiring, a switch disposed between the wiring and the power source, a control circuit for controlling the switch, and the like. To do.
[0022]
Further, the pixel of the light emitting device to which the present invention is applied is provided with a capacitor means.
[0023]
The capacitor means corresponds to any of a capacitor provided in the pixel, a gate capacitor and a channel capacitor of the driving means, and a parasitic capacitor such as a wiring. Note that when the gate capacitance and the channel capacitance of the driving means are used as the capacitive means, it is not necessary to explicitly arrange a capacitive element in the pixel. The capacitor means has a role of holding an analog video signal, in other words, has a role of holding a gate-source voltage of the driving means.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
In this embodiment, an example of a structure of a light-emitting device to which the present invention is applied will be described with reference to FIGS. Next, a driving method of the light-emitting device of the present invention will be described with reference to FIGS.
[0025]
FIG. 4A shows an outline of a light emitting device. The light-emitting device includes a pixel portion 302, a signal line driver circuit 303, a scanning line driver circuit 304, and a power source 305 which are arranged around the pixel portion 302.
[0026]
The pixel unit 302 includes x signal lines S arranged in the column direction. ₁ ~ S _x And x power lines V ₁ ~ V _x And y scanning lines G arranged in the row direction ₁ ~ G _y And y power lines C ₁ ~ C _y (X and y are natural numbers). And the signal line S ₁ ~ S _x And power line V ₁ ~ V _x , And scan line G ₁ ~ G _y And power line C ₁ ~ C _y A region surrounded by each one wiring corresponds to the pixel 301. In the pixel portion 302, a plurality of pixels 301 are arranged in a matrix.
[0027]
The signal line driver circuit 303, the scan line driver circuit 304, and the like may be formed integrally with the pixel portion 302 over the same substrate. Alternatively, the pixel portion 302 may be arranged outside the substrate. Further, the number of signal line driver circuits 303 and scan line driver circuits 304 is not particularly limited. The number of the signal line driver circuits 303 and the scan line driver circuits 304 can be arbitrarily set depending on the configuration of the pixel 301. Note that signals are supplied to the signal line driver circuit 303, the scan line driver circuit 304, and the like from the outside via an FPC (not shown) or the like.
[0028]
A detailed configuration of the pixel 301 arranged in the i-th column and the j-th row of the pixel portion 302 will be described with reference to FIG. The pixel 301 includes a switching transistor 323, a driving transistor 324, a capacitor 325, and a light emitting element 326.
[0029]
The gate electrode of the switching transistor 323 is the scanning line G _j The first electrode is connected to the signal line S _i The second electrode is connected to the gate electrode of the driving transistor 324. The first electrode of the driving transistor 324 is the power line V _i The second electrode is connected to one electrode of the light emitting element 326. The other electrode of the light emitting element 326 is a power line C. _j It is connected to the. The capacitor 325 is connected between the gate electrode and the first electrode of the driving transistor 324 and holds the gate-source voltage of the driving transistor 324.
[0030]
Here, one electrode of the light-emitting element 326 connected to the second electrode of the driving transistor 324 is referred to as a pixel electrode, and the other electrode connected to the power supply line Cj is referred to as a counter electrode.
[0031]
The switching transistor 323 has a function of controlling input of a signal to the pixel 301. Since the switching transistor 323 only needs to have a function as a switch, its conductivity type is not particularly limited. A transistor having either an n-channel or p-channel conductivity type may be used.
[0032]
The driving transistor 324 has a function of controlling light emission of the light-emitting element 326. The conductivity type of the driving transistor 324 is not particularly limited, but when the driving transistor 324 is a p-channel type, the pixel electrode is an anode and the counter electrode is a cathode. When the driving transistor 324 is an n-channel type, the pixel electrode is a cathode and the counter electrode is an anode.
[0033]
The switching transistor 323 and the driving transistor 324 have not only a single gate structure with one gate electrode but also a multi-gate structure such as a double gate structure with two gate electrodes and a triple gate structure with three gate electrodes. You may do it. Further, it may have either a top gate structure in which the gate electrode is disposed on the upper portion of the semiconductor or a bottom gate structure in which the gate electrode is disposed on the lower portion of the semiconductor.
[0034]
Although the capacitor 301 is provided in the pixel 301, the present invention is not limited to this. The gate element or the channel capacity of the driving transistor 324 may be used without providing the capacitor 325. Further, parasitic capacitance generated by wiring or the like may be used. The capacitor 325 plays a role of holding an analog video signal.
[0035]
The timing charts shown in FIGS. 1A and 1B and FIGS. 1C and 1D are based on different driving methods. In this embodiment mode, a method for driving a light-emitting device of the present invention will be described with reference to FIGS.
[0036]
Note that the voltage input method and the current input method described above can be applied to the light-emitting device of the present invention. In this embodiment, the case where the voltage input method is applied will be described below.
[0037]
In the timing chart illustrated in FIG. 1A, the horizontal axis indicates time, and the vertical axis indicates a scanning line. In FIG. 1A, the first address period T _a Sustain period T _s , Second address period T _b And off-time period T _e The timing chart of is shown. FIG. 1B shows a timing chart of a certain scanning line.
[0038]
First frame F ₁ First address period T _a1 , The scanning line drive circuit 304 to the scanning line G ₁ The scanning line G ₁ Is selected. Then, the scanning line G ₁ The switching transistors 323 of all the pixels 301 (pixels 301 in the first row) connected to are turned on.
[0039]
Then, the signal line driver circuit 303 to the signal line S ₁ ~ S _x The pixels in the first row are subjected to dot-sequential scanning, and the analog video signal is sequentially input from the pixel 301 in the first column arranged in the first row to the pixel 301 in the x-th column (final column). The pixel 301 emits light in response to the analog video signal. More specifically, an analog video signal is input to the gate electrode of the driving transistor 324 through the switching transistor 323 of the pixel 301. The gate-source voltage of the driving transistor 324 is determined according to the potential of the input analog video signal, and the current flowing between the source and drain of the driving transistor 324 is determined. This current is supplied to the light emitting element 326, and the light emitting element 326 emits light.
[0040]
Note that here, input of an analog video signal to the gate electrode of the driving transistor 324 is referred to as input of a video signal to the pixel 301.
[0041]
In this way, the analog video signal is input to the pixels 301 in the first row, and at the same time, the light emitting element 326 emits light, and the sustain period T in the pixels 301 in the first row. _s1 Is started.
[0042]
And scan line G ₁ When the selection of the scanning line G is completed, the scanning line G ₂ Is selected and the above operation is repeated. Thus, in order, all the scanning lines G ₁ ~ G _y Is selected and the input of the analog video signal to all the pixels 301 is completed, the first address period T _a1 Ends. In each pixel 301, the first address period T _a1 At the same time the sustain period T _s1 Has been started.
[0043]
Next, the sustain period T _s1 Is completed, the second address period T _b1 Is started. Second address period T _b1 , The scanning line drive circuit 304 to the scanning line G ₁ The scanning line G ₁ Is selected. Then, the scanning line G ₁ The switching transistors 323 of all the pixels 301 (pixels 301 in the first row) connected to are turned on.
[0044]
Then, the signal line S from the signal line driving circuit 303. ₁ ~ S _x Then, the pixels in the first row are dot-sequentially scanned, and the driving transistor 324 is sequentially turned off from the pixel 301 in the first column arranged in the first row to the pixel 301 in the x-th column (final column). Is input to the gate electrode of the driving transistor 324. More specifically, since the driving transistor 324 is a p-channel type in this embodiment, an H level signal is input to the gate electrode of the driving transistor 324. Note that if the driving transistor 324 is an n-channel transistor, an L level signal is input. Then, the driving transistor 324 to which the H level signal is input is turned off, so that no current flows through the light emitting element 326. Then, the light emitting element 326 enters a non-light emitting state.
[0045]
In this manner, an H level signal is input to the pixels 301 in the first row, and at the same time, the light emitting element 326 is in a non-light emitting state, and the pixels 301 in the first row have an off time period T. _e1 Is started.
[0046]
And scan line G ₁ When the selection of the scanning line G is completed, the scanning line G ₂ Is selected and the above operation is repeated. Thus, in order, all the scanning lines G ₁ ~ G _y Is selected and the input of the H level signal to all the pixels is completed, the second address period T _b1 Ends. Second address period T _b1 At the same time, each pixel 301 has an off-time period T _e1 Has been started.
[0047]
Subsequently, the off-time period T _e1 Is completed, the first frame F ₁ Ends. 1st frame F ₁ At the same time as the second frame F ₂ Is started. In this way, the frames are repeated in order.
[0048]
Here, the first address period T _a Sustain period T _s , Second address period T _b And off-time period T _e The scanning line G in each period of _m , Signal line S ₁ , S _n And S _x The operation in each period will be described in more detail with reference to FIG.
[0049]
2A to 2G, the horizontal axis indicates time, and the vertical axis indicates voltage. FIG. 2A shows the m-th scanning line G. _m (M is a natural number, 1 ≦ m ≦ y). 2B and 2E show the signal line S in the first column. ₁ FIG. 2C and FIG. 2F show the signal line S of the nth column. _n (N is a natural number, n ≦ x), and FIGS. 2D and 2G show the signal line S in the x-th column (final column). _x The relationship between voltage and time is shown.
[0050]
In FIG. 2A, a period indicated by 101 corresponds to one frame. The period indicated by 102 is the first address period T _a The period indicated by 104 is the second address period T _b Both periods correspond to one horizontal scanning period. The period indicated by 103 is the sustain period T _s The period indicated by 105 is the off-time period T _e It corresponds to.
[0051]
Here, the signal line S in the first column to the x column in the period 102 is displayed. ₁ ~ S _x Will be described with reference to FIGS.
[0052]
In the period 102, the scanning line G in the m-th row from the scanning line driving circuit 304. _m The scanning line G _m Is selected. Then, the scanning line G _m The switching transistors 323 of all the pixels 301 (pixels 301 in the m-th row) connected to are turned on.
[0053]
In this state, as shown in FIGS. 2B to 2D, dot-sequential scanning is performed on the pixels in the m-th row, and the signal line S is supplied from the signal line driver circuit 303. ₁ ~ S _x Then, analog video signals are sequentially input to the pixels 301 from the first column to the x-th column arranged in the m-th row.
[0054]
Next, the signal line S in the first column to the x column in the period 104 ₁ ~ S _x Will be described with reference to FIGS.
[0055]
In the period 104, the scanning line G in the m-th row from the scanning line driver circuit 304. _m The scanning line G _m Is selected. Then, the scanning line G _m The switching transistors 323 of all the pixels 301 (pixels 301 in the m-th row) connected to are turned on.
[0056]
In this state, as shown in FIGS. 2E to 2G, the signal line S is sent from the signal line driver circuit 303. ₁ ~ S _x Then, an H-level signal is sequentially input to the pixels 301 from the first column to the x-th column arranged in the m-th row.
[0057]
In FIG. 2, the horizontal blanking period is not shown.
[0058]
As described above, in the driving method of the light emitting device of this embodiment, the first address period T is included in one frame. _a And the second address period T _b This is characterized by providing a total of two address periods. First address period T _a Then, the analog video signal is written to the pixel 301 and the second address period T _b Then, a signal for turning off the driving transistor 324 is written into the pixel 301. The second address period T _b And the off-time period T in which the pixel 301 is in a non-light-emitting state at the same time _e Is started. As described above, the driving method of the light emitting device of the present embodiment is based on the off-time period T in one frame. _e There is a feature in providing. Off-time period T _e By providing, a period in which the light-emitting element included in each pixel does not emit light can be provided. As a result, deterioration of the light emitting element over time can be reduced. Furthermore, the reliability of the light emitting element can be improved.
[0059]
In the driving method of the light emitting device of this embodiment, the off time period T _e This is characterized in that the timing at which the “” starts varies depending on each pixel 301. That is, each pixel 301 has an off time period T _e Starts at different times.
[0060]
In the present embodiment, one off time period T per frame. _e However, the present invention is not limited to this. One off-time period T every few frames _e May be provided. Also, multiple off-time periods T per frame _e May be provided. However, the first address period T _a And the second address period T _b Must be set so that they do not overlap each other. This is because the first address period T _a And the second address period T _b This is because the two scanning lines are selected at the same timing and signals are not accurately input from the signal line driver circuit 303 to the pixels 301.
[0061]
(Embodiment 2)
In this embodiment, a method for driving a light-emitting device, which is different from that in Embodiment 1, will be described with reference to FIGS.
[0062]
Note that the voltage input method and the current input method described above can be applied to the light-emitting device of the present invention. In this embodiment, the case where the voltage input method is applied will be described below.
[0063]
In the timing chart illustrated in FIG. 1C, the horizontal axis indicates time, and the vertical axis indicates scanning lines. In FIG. 1C, the address period T _a , First sustain period T _sa , Second sustain period T _sb And off-time period T _e The timing chart of is shown. FIG. 1D shows a timing chart in a certain scanning line.
[0064]
First frame F ₁ Address period T _a1 , The scanning line drive circuit 304 to the scanning line G ₁ The scanning line G ₁ Is selected. Then, the scanning line G ₁ The switching transistors 323 of all the pixels 301 (pixels 301 in the first row) connected to are turned on.
[0065]
Then, the signal line driver circuit 303 to the signal line S ₁ ~ S _x The pixels in the first row are dot-sequentially scanned, and the analog video signal is sequentially input from the pixel 301 in the first column to the pixel 301 in the x-th column (final column), and according to the analog video signal Thus, the pixel 301 emits light. More specifically, an analog video signal is input to the gate electrode of the driving transistor 324 through the switching transistor 323 of the pixel 301. The gate-source voltage of the driving transistor 324 is determined according to the voltage of the input analog video signal, and the current flowing between the source and drain of the driving transistor 324 is determined. This current is supplied to the light emitting element 326, and the light emitting element 326 emits light.
[0066]
In this way, the analog video signal is input to all the pixels 301 in the first row, and at the same time, the light emitting element 326 emits light, and the first sustain period T in all the pixels 301 in the first row. _sa1 Is started.
[0067]
And scan line G ₁ When the selection of the scanning line G is completed, the scanning line G ₂ Is selected and the above operation is repeated. Thus, in order, all the scanning lines G ₁ ~ G _y Is selected and the input of the analog video signal to all the pixels 301 is completed, the address period T _a1 Ends. In each pixel 301, an address period T _a1 At the same time as the first sustain period T _sa1 Has been started.
[0068]
Subsequently, the first sustain period T _sa1 Is completed, all the pixels 301 simultaneously have an off-time period T _e1 Is started. This off-time period T _e1 Then, power line C ₁ ~ C _y By turning off a switch (see FIG. 4A) arranged between the power source 305 and the power source 305, power is not supplied from the power source 305 to the light-emitting element 326. Then, the counter electrode of the light-emitting element 326 is in a floating state, and no current flows through the light-emitting element 326 so that it does not emit light.
[0069]
The off-time period T _e1 Then, power line C ₁ ~ C _y In this state, the pixel electrode and the counter electrode of the light emitting element 326 are set to the same potential in a state where the switch arranged between the power source 305 and the power source 305 is kept on, so that no current is supplied to the light emitting element 326. Good. When there is no potential difference between both electrodes of the light emitting element 326, no current is supplied to the light emitting element 326, and the light emitting element 326 enters a non-light emitting state.
[0070]
Next, the off-time period T _e1 Is finished, the power line C ₁ ~ C _y And the power source 305 are turned on to turn on the second sustain period T _sb1 Is started. Power line C ₁ ~ C _y When the power source 305 and the power source 305 are electrically connected to each other, power is supplied to the light emitting element 326 and a current flows through the light emitting element 326.
[0071]
The address period T _a1 The analog video signal written to each pixel in the _e1 The inside is continuously held by the capacitor 325. Therefore, the second sustain period T _sb1 Is started and the power line C ₁ ~ C _y And the power source 305 are electrically connected, and at the same time, the first sustain period T _sa1 The same gradation display is performed.
[0072]
Thus, in the present invention, the off-time period T _e1 The analog video signal written in each pixel 301 is held in the capacitor 325. Therefore, the off-time period T _e1 After completion, there is no need to write the signal again, and there is no need to arrange a storage medium such as a memory.
[0073]
And the second sustain period T _sb1 Is completed, the first frame F ₁ Ends. 1st frame F ₁ At the same time as the second frame F ₂ Is started. In this way, the frames are repeated in order.
[0074]
Here, the address period T _a , First sustain period T _sa , Second sustain period T _sb And off-time period T _e The scanning line G in each period of _m , Signal line S ₁ , S _n And S _x Voltage and power line C _m The operation in each period will be described in more detail with reference to FIG.
[0075]
3A to 3E, the horizontal axis indicates time, and the vertical axis indicates voltage. FIG. 3A shows the m-th scanning line G. _m The relationship between voltage and time is shown. FIG. 3B shows the signal line S in the first column. ₁ FIG. 3C shows the relationship between the voltage and the time of the nth signal line S. _n FIG. 3D shows the relationship between the voltage and the time of the signal line S in the x-th column (final column). _x The relationship between voltage and time is shown. FIG. 3E shows the m-th power line C. _m The relationship between voltage and time is shown.
[0076]
In FIG. 3A, a period 201 is equivalent to one frame. A period indicated by 202 is an address period T _a This period corresponds to one horizontal scanning period. The period indicated by 203 is the first sustain period T _sa The period indicated by 204 is the off-time period T _e The period indicated by 205 is the second sustain period T _sb It corresponds to.
[0077]
Here, the signal lines S in the first column to the x column in the period 202 are displayed. ₁ ~ S _x Will be described with reference to FIGS.
[0078]
In the period 202, the scanning line G in the m-th row from the scanning line driving circuit 304. _m The scanning line G _m Is selected. Then, the scanning line G _m The switching transistors 323 of all the pixels 301 (pixels 301 in the m-th row) connected to are turned on.
[0079]
In this state, as shown in FIGS. 3B to 3D, the signal line S is sent from the signal line driver circuit 303. ₁ ~ S _x Then, analog video signals are sequentially input to the pixels 301 from the first column to the x-th column arranged in the m-th row.
[0080]
Next, the m-th power line C in the period 201 _m Will be described with reference to FIG.
[0081]
Power line C _m Of the address period T indicated by 202 is determined by the voltage supplied from the power source 305. _a , 203, the first sustain period T _sa And a second sustain period T indicated by 205. _sb Is kept constant. However, the off-time period T shown at 204 _e In, the power line C _m And the power source 305 are not electrically connected. Therefore, the off-time period T _e Power line C at _m The voltage of is indicated by a dotted line.
[0082]
As described above, in the driving method of the light-emitting device of this embodiment, the off-time period T is included in one frame. _e It has the feature in providing. Off-time period T _e Then, the power supply line C connected to the counter electrode of the light emitting element 326. ₁ ~ C _y And the power source 305 are turned off. Thus, the counter electrode of the light emitting element 326 is in a floating state, and no current is supplied to the light emitting element 326.
[0083]
The off-time period T _e1 Then, power line C ₁ ~ C _y In this state, the pixel electrode and the counter electrode of the light emitting element 326 are set to the same potential in a state where the switch arranged between the power source 305 and the power source 305 is kept on, so that no current is supplied to the light emitting element 326. Good. When there is no potential difference between both electrodes of the light emitting element 326, no current is supplied to the light emitting element 326, and the light emitting element 326 enters a non-light emitting state.
[0084]
In FIG. 3, the horizontal blanking period is not shown.
[0085]
By providing the off-time period as described above, a period in which the light-emitting element 326 included in each pixel 301 does not emit light can be provided, so that deterioration over time of the light-emitting element 326 can be reduced. Further, the reliability of the light emitting element 326 can be improved.
[0086]
In the driving method of the light emitting device of this embodiment, the off time period T _e This is characterized in that the timing at which “1” starts is the same in all the pixels 301.
[0087]
In the present embodiment, one off time period T per frame. _e However, the present invention is not limited to this. Off-time period T every few frames _e May be provided. Also, multiple off-time periods T per frame _e May be provided.
[0088]
In this embodiment mode, all the pixels 301 have an off-time period T _e However, the present invention is not limited to this. For example, each row has an off-time period T _e The start timing may be different. However, for that purpose, the power line C ₁ ~ C _y It is necessary to provide a switch between each one of them and the power supply 305. And by controlling the switch, the off-time period T in each row _e Can be controlled.
[0089]
(Embodiment 3)
In this embodiment mode, a relationship between a driving method and a lifetime will be described with reference to FIG.
[0090]
In FIG. 5A, reference numeral 501 denotes an analog driving voltage waveform having an off-time period, and reference numeral 502 denotes an analog driving voltage waveform having no off-time period. Note that the voltage during light emission is V ₅₀₁ And V ₅₀₂ Then the voltage V ₅₀₁ And voltage V ₅₀₂ Is V ₅₀₁ > V ₅₀₂ Satisfy the relationship.
[0091]
In FIG. 5B, the horizontal axis is time, and the vertical axis is luminance. In FIG. 5B, a broken line 503 indicated by circles and squares indicates the relationship between the luminance and time of the light-emitting element driven by the voltage indicated by 501. A broken line 504 indicated by a triangle mark and a square mark indicates the relationship between the luminance and time of the light emitting element driven by the voltage indicated by 502.
[0092]
As shown in FIG. 5B, the light emitting element driven by the voltage indicated by 501 has a longer lifetime than the light emitting element driven by the voltage indicated by 502. This shows that the former has a longer life in two cases, where there is a period in which no voltage is applied to the light emitting element and in which a voltage is always applied to the light emitting element. In other words, it can be seen that the former has a longer life in two cases, where the light emitting element has a non-light emitting period and when the light emitting element always emits light.
[0093]
In addition, the voltage V ₅₀₁ And voltage V ₅₀₂ Is V ₅₀₁ > V ₅₀₂ Despite satisfying this relationship, the light-emitting element driven by the voltage indicated by 501 has a longer lifetime. Thus, it can be seen that even when the voltage applied to the light emitting element is high, the light emitting element is provided with a non-light emitting period and has a longer lifetime.
[0094]
From the above results, it can be seen that the driving method of the light-emitting device of the present invention in which a time during which the pixel does not emit light (off-time period) is provided in each frame period is very effective. By using the driving method of the light emitting device of the present invention, the lifetime of the light emitting element can be improved and the deterioration of the light emitting element over time can be reduced. Further, the reliability of the light emitting element can be improved.
[0095]
(Embodiment 4)
In this embodiment, structures and operations of the signal line driver circuit 303 and the scan line driver circuit 304 are described with reference to FIGS.
[0096]
4C, the signal line driver circuit 303 includes a shift register 309, a buffer 310, and a sampling circuit 311. In brief, the shift register 309 sequentially outputs sampling pulses in accordance with a clock signal (S-CLK), a start pulse (S-SP), and a clock inversion signal (S-CLKb). Thereafter, the sampling pulse amplified by the buffer 310 is input to the sampling circuit 311. An analog video signal is input to the sampling circuit 311, and the signal line S is in accordance with the timing at which the sampling pulse is input. ₁ ~ S _x The video signal is input to.
[0097]
Next, the scan line driver circuit 304 includes a shift register 307 and a buffer 308. In brief, the shift register 307 sequentially outputs sampling pulses in accordance with a clock signal (G-CLK), a start pulse (G-SP), and a clock inversion signal (G-CLKb). Thereafter, the sampling pulse amplified by the buffer 308 is converted into the scanning line G. ₁ ~ G _y Are selected one line at a time. And the selected scanning line G _n In order to the pixels controlled by the signal line S, ₁ ~ S _x The analog video signal is written from.
[0098]
Note that a level shifter circuit may be arranged between the shift register 307 and the buffer 308. By arranging the level shifter circuit, the voltage amplitude of the logic circuit portion and the buffer portion can be changed.
[0099]
This embodiment can be arbitrarily combined with Embodiments 1 and 2.
[0100]
(Embodiment 5)
Electronic devices to which the driving method of the light emitting device of the present invention is applied include a video camera, a digital camera, a goggle type display (head mounted display), a navigation system, an audio playback device (car audio, audio component, etc.), and a notebook type personal computer. , Game devices, portable information terminals (mobile computers, mobile phones, portable game machines, electronic books, etc.), image playback devices equipped with recording media (specifically, digital Versatile Disc (DVD) and other recording media) And a device provided with a display capable of displaying the image). Specific examples of these electronic devices are shown in FIGS.
[0101]
FIG. 6A illustrates a light emitting device, which includes a housing 2001, a support base 2002, a display portion 2003, a speaker portion 2004, a video input terminal 2005, and the like. The present invention can be applied to the display portion 2003. Further, according to the present invention, the light emitting device shown in FIG. 6A is completed. Since the light-emitting device is a self-luminous type, a backlight is not necessary and a display portion thinner than a liquid crystal display can be obtained. Note that the light emitting device includes all display devices for displaying information such as for personal computers, for receiving TV broadcasts, and for displaying advertisements.
[0102]
FIG. 6B shows a digital still camera, which includes a main body 2101, a display portion 2102, an image receiving portion 2103, operation keys 2104, an external connection port 2105, a shutter 2106, and the like. The present invention can be applied to the display portion 2102. Further, according to the present invention, the digital still camera shown in FIG. 6B is completed.
[0103]
FIG. 6C illustrates a laptop personal computer, which includes a main body 2201, a housing 2202, a display portion 2203, a keyboard 2204, an external connection port 2205, a pointing mouse 2206, and the like. The present invention can be applied to the display portion 2203. Further, according to the present invention, the light-emitting device shown in FIG. 6C is completed.
[0104]
FIG. 6D illustrates a mobile computer, which includes a main body 2301, a display portion 2302, a switch 2303, operation keys 2304, an infrared port 2305, and the like. The present invention can be applied to the display portion 2302. Further, according to the present invention, the mobile computer shown in FIG. 6D is completed.
[0105]
FIG. 6E illustrates a portable image reproducing device (specifically, a DVD reproducing device) provided with a recording medium, which includes a main body 2401, a housing 2402, a display portion A2403, a display portion B2404, and a recording medium (DVD or the like). A reading unit 2405, operation keys 2406, a speaker unit 2407, and the like are included. Although the display portion A 2403 mainly displays image information and the display portion B 2404 mainly displays character information, the present invention can be applied to the display portions A, B 2403, and 2404. Note that an image reproducing device provided with a recording medium includes a home game machine and the like. Further, the image display device shown in FIG. 6E is completed by the present invention.
[0106]
FIG. 6F illustrates a goggle type display (head mounted display), which includes a main body 2501, a display portion 2502, and an arm portion 2503. The present invention can be applied to the display portion 2502. Further, according to the present invention, the goggle type display shown in FIG. 6F is completed.
[0107]
FIG. 6G illustrates a video camera, which includes a main body 2601, a display portion 2602, a housing 2603, an external connection port 2604, a remote control receiving portion 2605, an image receiving portion 2606, a battery 2607, an audio input portion 2608, operation keys 2609, and the like. . The present invention can be applied to the display portion 2602. Further, according to the present invention, the video camera shown in FIG. 6G is completed.
[0108]
FIG. 6H illustrates a mobile phone, which includes a main body 2701, a housing 2702, a display portion 2703, an audio input portion 2704, an audio output portion 2705, operation keys 2706, an external connection port 2707, an antenna 2708, and the like. The present invention can be applied to the display portion 2703. Note that the display portion 2703 can suppress current consumption of the mobile phone by displaying white characters on a black background. In addition, the mobile phone shown in FIG. 6H is completed by the present invention.
[0109]
If the emission luminance of the luminescent material is increased in the future, the light including the output image information can be enlarged and projected by a lens or the like to be used for a front type or rear type projector.
[0110]
In addition, the electronic devices often display information distributed through electronic communication lines such as the Internet and CATV (cable television), and in particular, opportunities to display moving image information are increasing. Since the response speed of the light emitting material is very high, the light emitting device is preferable for displaying moving images.
[0111]
In addition, since the light emitting device consumes power in the light emitting portion, it is desirable to display information so that the light emitting portion is minimized. Therefore, when a light emitting device is used for a display unit mainly including character information, such as a portable information terminal, particularly a mobile phone or a sound reproduction device, it is driven so that character information is formed by the light emitting part with the non-light emitting part as the background. It is desirable to do.
[0112]
As described above, the applicable range of the present invention is so wide that it can be used for electronic devices in various fields. In addition, the electronic device of this embodiment may use any of the light-emitting devices shown in any of Embodiments 1 to 4.
[0113]
【The invention's effect】
The driving method of the light emitting device of the present invention includes the first address period T in one frame. _a And the second address period T _b This is characterized by providing a total of two address periods. First address period T _a Then, the analog video signal is written to the pixel, and the second address period T _b Then, a signal for turning off the driving transistor of the pixel is written. The second address period T _b Simultaneously with the end of the off-time period T in which the pixel is in a non-light-emitting state _e Is started. In the driving method of the light emitting device according to the present embodiment, the off-time period T in one frame is thus obtained. _e There is a feature in providing. Off-time period T _e By providing, a period in which the light-emitting element included in each pixel does not emit light can be provided. As a result, deterioration over time of the light emitting element can be reduced. Further, the reliability of the light emitting element can be improved.
[0114]
Further, in the present invention in which a non-display period is provided by inputting a signal, it is not necessary to arrange a dedicated circuit for providing the non-display period. If a dedicated circuit is to be arranged, it is necessary to adopt either a method in which the circuit is formed integrally with the pixel portion or an IC or the like externally. In the present invention, both of them are necessary. Absent. With this configuration, a thin and lightweight device can be realized, which is particularly effective for portable terminals that have been actively developed in recent years.
[0115]
In the driving method of the light emitting device of the present invention, the off time period T _e The present invention is characterized in that a current is not supplied to the light emitting element by bringing the counter electrode of the light emitting element into a floating state. Further, the driving method of the light-emitting device of the present invention is characterized in that current is not supplied to the light-emitting element by setting the pixel electrode and the counter electrode of the light-emitting element to the same potential. Accordingly, a period in which the light-emitting element included in each pixel does not emit light can be provided, so that deterioration over time of the light-emitting element can be reduced. Furthermore, the reliability of the light emitting element can be improved.
[0116]
Further, according to the present invention in which dot sequential scanning is performed, the burden on the source side driving circuit is reduced as compared with the case of performing line sequential scanning. This is because, when performing line sequential scanning, it is necessary to dispose a holding circuit that temporarily holds a signal, but when performing dot sequential scanning, it is not necessary to dispose such a holding circuit. . Therefore, according to the present invention that performs dot sequential scanning, when the pixel portion and the driving circuit are integrally formed on the substrate, the area occupied by the source side driving circuit can be reduced, and the number of elements on the substrate can be reduced. In addition, the yield and the reliability can be improved.
[Brief description of the drawings]
1A and 1B illustrate a driving method of a light-emitting device of the present invention.
FIGS. 2A and 2B illustrate a method for driving a light-emitting device of the present invention. FIGS.
3A and 3B illustrate a method for driving a light-emitting device of the present invention.
FIG. 4 illustrates a light-emitting device to which the present invention is applied.
FIG. 5 is a graph showing a relationship between a driving method and a lifetime.
FIG. 6 is a diagram of an electronic device to which the driving method of the light-emitting device of the present invention is applied.
FIG. 7 illustrates a driving method of a light-emitting device.

Claims (5)

A plurality of pixels, switches and power supply circuits;
Each of the plurality of pixels has a first transistor, a second transistor, a capacitor and a light emitting element,
The gate of the first transistor is electrically connected to a scan line, one of the source or drain of the first transistor is electrically connected to a signal line, and the other of the source or drain of the first transistor is is electrically connected to a first electrode of the gate and the capacitance element of said second transistor, said source or of the second transistor one of the drain to the second electrode of the capacitor element and the first power supply line The other of the source and the drain of the second transistor is electrically connected to the first electrode of the light emitting element, and the second electrode of the light emitting element is electrically connected to the second power supply line. A terminal of the switch is electrically connected to the second power supply line, and the other terminal of the switch is electrically connected to the power supply circuit.
One frame period is a period in which the first period , the second period , the third period, and the fourth period appear in order ,
In the first period, Ri by that dot sequential scanning is performed for the plurality of pixels, in each of the plurality of pixels through said first transistor, a gate of said second transistor analog video signal is inputted Rutotomoni the analog video signal is retained in the capacitor element,
In the second period, the switch is on, and a current corresponding to the analog video signal held in the capacitor flows in the second transistor and the light-emitting element in each of the plurality of pixels. ,
In the third period, the switch is off , and all the light-emitting elements included in the plurality of pixels are not emitting light,
Oite the fourth period, the switch is turned on, the in each of the plurality of pixels, current corresponding to the analog video signal held in the capacitor element and the second transistor and the light emitting element the driving method of a light emitting device according to claim flows Rukoto to. In claim 1 ,
The driving method of the light-emitting device, wherein the second electrode of the light-emitting element is in a floating state in the third period. In claim 1 or claim 2 ,
A driving method of a light-emitting device, comprising a signal line driving circuit connected to the signal line. In claim 1 or claim 2 ,
A signal line driving circuit connected to the signal line;
The signal line driver circuit includes a shift register, a buffer, and a sampling circuit. In any one of claims 1 to 4,
A driving method of a light emitting device, comprising: a scanning line driving circuit connected to the scanning line.

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