JP4038113B2 - Active matrix display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an active matrix display device, and more particularly to an active matrix display device having a light emitting element made of an organic semiconductor film or the like and a transistor for controlling the light emitting operation of the light emitting element.
[0002]
[Prior art]
In recent years, thin displays typified by liquid crystal displays (hereinafter referred to as LCDs) have been incorporated into various electric products, and demand has been expanding. Among these thin displays, organic EL elements (hereinafter referred to as OELDs), which are self-luminous displays, have a wide viewing angle, and have high brightness and contrast, are attracting attention as next-generation displays that replace liquid crystals.
[0003]
Generally, there are an active matrix driving type and a simple matrix driving type as an OELD driving method. Many OELDs employ an active matrix drive system like LCDs in order to increase power efficiency.
[0004]
In an active matrix display device, in general, n data lines to which image signals are supplied and m scanning lines (gate lines) to which scanning signals are supplied are arranged in a pixel display region, and the data lines and scanning lines are arranged. Each pixel has a structure in which pixels are arranged in the vicinity of each intersection and two TFTs and one storage capacitor are connected to one pixel.
[0005]
A scanning signal is periodically applied to the plurality of scanning lines sequentially.
[0006]
FIG. 1 shows a circuit in a typical OELD pixel using an active matrix driving method. Pixels are arranged near the intersection of the scan line 6 and the data line 5. The scan line 6 is connected to the gate of a switching transistor 1 made of a TFT (Thin Film Transistor), and the switching transistor 1 is switched on and off by a scanning signal sent through the scanning line 6.
[0007]
When the switching transistor 1 is on, an image signal sent through the data line 5 is applied to the gate of the driving transistor 2 through the switching transistor 1 and is stored as a charge in the storage capacitor 3. When an image signal is applied to the gate of the drive transistor 2, the drive transistor 2 is turned on, a current flows through the OELD element 4, and the OELD element 4 emits light. Even if the scanning signal sent to the scanning line 6 becomes low level and the switching transistor 1 is turned off, the gate voltage of the driving transistor 2 made of TFT is held by the charge stored in the storage capacitor 3. Therefore, current continues to flow through the OELD element 4 until the next frame, and emits light.
[0008]
When the scanning lines 6 finish scanning in the vertical direction in this way and scanning signals are sequentially sent to all the scanning lines 6, all the pixels emit light in accordance with the respective image signals, and an image of one frame is displayed. . Then, scanning is started again from the first scan line 6 in order to display the next frame.
[0009]
Generally, 60 frames are displayed per second, and 1 frame is assigned 1/60 seconds. In the selected pixel, since the charge is held even when the switching transistor 1 is switched off, the OLED element emits light continuously in 1/60 second frame as shown in FIG. . Such a display method is called a hold type.
[0010]
Edge blur is a problem in the hold-type display method. Edge blur is a phenomenon in which the edge of an animal body appears blurry, and occurs because humans add up and perceive continuous images. In order to solve this problem, in Patent Document 1, after applying a scanning signal to each scanning line, an extinction period is provided in the OELD of each pixel, so that there is no integration of the white background when the line of sight moves during the extinction period. A structure that prevents blurring is used.
[0011]
[Patent Document 1]
JP2002-91376
[0012]
[Problems to be solved by the invention]
However, when the extinction period is provided to prevent edge blur as described above, the light emission time is shortened and the display luminance is weakened. Therefore, for example, Patent Document 1 describes that the emission intensity is increased in order to compensate the display luminance. In Patent Document 1, as shown in FIG. 2 (b), in an apparatus that provides an extinction period, the current value flowing through the OELD is made higher than in the prior art to prevent the image from becoming dark.
[0013]
However, since a large current always flows through the OELD when the OELD emits light, the OELD deteriorates quickly due to an increase in the amount of heat generated in the pixel, and the life of the display device is shortened.
[0014]
An object of the present invention is to provide an active matrix display device capable of minimizing deterioration of a light emitting element and eliminating an edge blur phenomenon that occurs in moving image display.
[0015]
[Means for Solving the Problems]
The problem described above is that a display panel having a light emitting element that is disposed in an intersection region of a plurality of scan lines and a plurality of data lines and has a pixel electrode, and an active element that turns on and off a signal to the light emitting element, A data driving circuit for applying a data signal to the data line, a scanning driving circuit for applying a scanning signal to the scan line, and comparing image signal data of different frames to determine whether it is a still image or a moving image. A signal discriminating circuit for outputting either a still image or a moving image discriminating signal; and when the discriminating signal from the signal discriminating circuit is the still image, the light emission intensity of the light emitting element in one frame is set. When the determination signal is the moving image, the light emission of the light emitting element is stopped and extinguished in the middle of one frame, and the light emission intensity of the light emitting element is set to the first value. 1 It is solved by an active matrix display device characterized by a control circuit for sending a signal for setting the second higher value than the value in the scan driving circuit.
[0016]
According to the present invention, a moving image and a still image are identified, and when displaying a moving image, a light extinction time is provided and the emission intensity of the light emitting element is increased. When a still image is displayed, light emission is performed without providing a light extinction time. A control circuit for reducing the light emission intensity of the element is provided.
[0017]
Therefore, by providing a time for suppressing the magnitude of the current or voltage to the display panel, it is possible to suppress the deterioration of the light emitting element and to eliminate the phenomenon of edge blur in both moving images and still images.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0019]
FIG. 3 is a block diagram of the active matrix display device of the present invention.
[0020]
In FIG. 3, the display device 10 includes a display unit A and a control unit B.
[0021]
In the display portion A, M data lines 20 are formed on the display panel 12 at intervals, and the data drive circuit 16 is connected to the data lines 20 to supply an image signal. In the display panel 12, N write scan lines 21 and N current supply lines 22 that are insulated from and intersect each data line 20 are alternately formed at intervals.
[0022]
The write scan line 21 is connected to a write scan drive circuit 17 disposed on one side of the display panel 12 and supplied with a write scan signal. The current supply line 22 is connected to a current scanning drive circuit 18 disposed on the other side of the display panel 12 and supplied with current.
[0023]
In the display panel 12, a plurality of areas defined by the write scan lines 21, the current supply lines 22, and the data lines 20 are respectively pixel areas 23, and the number of pixel areas 23 is the number of data lines 20. M × N corresponding to the number of scanning lines 21 for insertion.
[0024]
As shown in FIG. 4, a switching transistor 51, a driving transistor 52, a storage capacitor 53, and an OELD element 54 are formed in the pixel region 23. TFTs are applied as the switching transistor 51 and the drive transistor 52, respectively. The OELD element 54 has a structure (not shown) in which an organic light emitting layer is sandwiched between a pixel electrode and a common electrode, and is shown as a light emitting diode as an equivalent circuit.
[0025]
Of the switching transistor 51, the gate is connected to the write scan line 21, one of the source / drain is connected to the data line 20, and the other of the source / drain is connected to the gate of the drive transistor 52. One of the source / drain of the driving transistor 52 is connected to the cathode of the OELD element 54, and the other is connected to the common potential line 57. The anode of the OELD element 54 is connected to the current supply line 22. The storage capacitor 53 is connected between the gate of the drive transistor 52 and the common electrode line 57, and stores the image signal sent from the data drive circuit 16 as electric charge. The common potential line 57 is formed in the display panel 12 and is connected to a fixed potential source (not shown) having a voltage lower than that of the current supply line 22 when the OELD element 54 emits light. The current flowing from the current scanning drive circuit 18 to the current supply line 22 is changed by the current or voltage control by the display control circuit 15 so as to be larger in the case of moving image display than in the case of still image display. The cathode of the OELD element 54 is a pixel electrode, and the anode is a common electrode.
[0026]
The control unit B described above includes an image memory 13, a signal determination circuit 14, and a display control circuit 15.
[0027]
The image memory 13 is configured to store image signal data and send the image data to the data driving circuit 16 through the display control circuit 15 and also to the signal determination circuit 14.
[0028]
As shown in FIG. 5, the signal determination circuit 14 includes first and second memories 31 and 32 that store image signal data output from the image memory 13, and first and second memories 31 and 32. Each has a comparison circuit 33 that compares the stored data, and a moving image / still image determination circuit 34 that determines either a still image or a moving image based on the output of the comparison circuit 33.
[0029]
The first memory 31 stores all of the nth frame (n is an integer) of the image signal data, and the second memory 32 is the (n + x) th frame of the image signal data (n and x are integers). The data stored in the first memory 31 and the second memory 32 are output to the signal determination circuit 14 in synchronization. The number of frames is counted based on a vertical clock input from the outside.
[0030]
Further, the comparison circuit 33 compares the image signal data from the first memory 31 and the image signal data from the second memory 32 to obtain a ratio in which the image signal data matches, and the data of the ratio is obtained. The moving image / still image determination circuit 34 is configured to output.
[0031]
Further, the moving image / still image determination circuit 34 determines that the data of the ratio from the comparison circuit 33 is a still image when the data is a predetermined value, for example, 20% or more, and determines that the data is a moving image when the data is lower than that. For example, a signal “1” is sent to the display control circuit 15 when it is determined as a moving image, and a signal “0” is sent to the display control circuit 15 when it is determined as a still image.
[0032]
The display control circuit 15 synchronizes the image signal from the image memory 13 with the horizontal clock, sends one frame of data to the M data lines 20 through the data driving circuit 16, and further writes it in synchronization with the vertical clock. A write scan signal is sent to the write scan line 21 via the scanning scan drive circuit 17, and flows to the current supply line 22 via the current scan drive circuit 18 based on the output data of the signal determination circuit 14. By adjusting the current value, a current adjustment signal for changing the light emission intensity of the OELD element 54 or quenching the OELD element 54 is sent.
[0033]
Note that the pulse width of the signal sent from the writing scan driving circuit 17 to one writing scan line 21 is 1 / N time (T / N time) of the writing time T of one frame.
[0034]
Further, when a still image discrimination signal “0” indicating a still image is sent from the signal discrimination circuit 14, the display control circuit 15 is extinguished during the period T in one frame as shown on the left side of FIG. 6. The OELD element 54 is caused to emit light without any change, and the amount of current flowing to the OELD element 54 through the current scanning drive circuit 18 and the current supply line 58 is set to a low-level first value, while a moving image is displayed from the signal determination circuit 14. When the moving image discrimination signal “1” is sent, the amount of current flowing through the current supply line 58 is set to a second value that is higher than the first value, as shown on the right side of FIG. In addition, an extinction time for stopping the light emission of the OELD element 54 is provided by adjusting the current value of the current supply line 22 from the middle to the end of the period of one frame.
[0035]
That is, when the moving image determination signal “1” is input to the display control circuit 15, the amount of current flowing through the OELD element 54 is displayed by the light emission time / light emission intensity changing circuit 15a provided in the display control circuit 15 when a still image is displayed. OELD element by adjusting the current or voltage from the current scan driving circuit 18 after the lapse of T / s time (T <s <0) from the start of input of the scanning signal to the writing scan line 21. 54 is extinguished in the middle of one frame.
[0036]
In the display device 10 having the above-described configuration, when the switching transistor 51 is turned on by the writing scanning signal applied from the writing scanning drive circuit 17 to the writing scanning line 21, the switching transistor 51 is applied to the data line 20. The image signal is stored as a charge in the storage capacitor 53 through the switching transistor 51. With this electric charge, a voltage corresponding to the image signal is applied to the gate of the drive transistor 52 in a period of one frame.
[0037]
After T / N time has elapsed from the start of application of the write scan signal to the gate of the switch transistor 51, the write scan signal goes low and the switch transistor 51 is turned off. The charge transfer path is disconnected, and the charge of the storage capacitor 53 is held. In other words, the voltage applied to the gate of the drive transistor 52 is kept substantially the same from the start of application to the lapse of T time. Even in this case, the light emission of the OELD element 54 is stopped when the signal applied from the current scanning drive circuit 18 to the current supply line 22 reaches the extinction level.
[0038]
In this manner, the OELD element 54 in each pixel region 23 is controlled to emit and extinguish light by the display control circuit 15, and an image is displayed on the image display unit 12.
[0039]
By the way, the image signal taken into the image memory 13 is sent to two circuits of the signal discrimination circuit 14 and the display control circuit 15.
[0040]
The image signal is a signal to which frame data is continuously transmitted. In the signal determination circuit 14, if the signal taken in by the first memory 31 is the nth frame signal, the second memory 32 stores the (n + x) th frame. Capture the signal. When x = 1, it means that the first memory 31 and the second memory 32 capture the image signal data of the frames before and after. The data of one frame of image signal is data input to the data driving circuit 16 in order to control light emission of each OELD element 54 in one frame, for example. The frame signal data stored in each of the first memory 31 and the second memory 32 is input to the comparison circuit 33. One frame signal has pixel signal data assigned to M × N pixels, and the comparison circuit 33 uses the pixel signal as the nth frame signal data and the (n + x) th frame signal data. And outputs the result to the moving image / still image determination circuit 34.
[0041]
The moving image / still image determination circuit 34 determines whether the image signal is a moving image or a still image based on the result output from the comparison circuit 33. In this embodiment, when the comparison circuit 33 is equal to or more than 20% for the data of the image signals output from the first memory 31 and the second memory 32, the moving image / still image determining circuit 34 If it is smaller than that, it is determined to be a moving image, but if it is 50% or more identical, it is determined to be a character image, or assigned to a pixel at a specific location such as a peripheral area of the image display unit 19. If the signal matches as a comparison target, it is determined as a still image, or when a video signal is Fourier-transformed and the discrete signal component is 30% or more, it is determined as a still image, and the other is determined as a moving image. May be.
[0042]
The determination result by the moving image / still image determination circuit 34 is input to the display control circuit 15. In addition to the image signal and the determination result, a horizontal synchronization signal and a vertical synchronization signal are input to the display control circuit 15, and are respectively input to the data drive circuit 16, the write scan drive circuit 17, and the current scan drive circuit 18. An image signal, a writing scanning signal, and an extinction scanning signal are sent.
[0043]
Here, when the identification result of the moving image / still image determination circuit 34 is a still image, the image signal and the scanning signal for writing are each data bus line in T seconds assigned to one frame, for example, 1/60 seconds. 20. An image signal and a writing scan signal are sequentially sent to the writing scan line 21. A scan signal having a signal voltage value V ₁ is applied to each of the write scan lines 21 from the scan drive circuit 17 in (1/60) × (1 / N) seconds.
[0044]
In the case of a still image, the extinction scanning signal is not sent from the current scanning driving circuit 18 within 1/60 hours allocated to one frame to each of the writing scanning lines 21, and the left side of FIG. As shown, the OELD element 54 continues to emit light during one frame. In this case, the maximum light emission intensity of the OELD element 54 is L ₁ .
[0045]
On the other hand, when the identification result of the moving image / still image discrimination circuit 34 is a moving image, the image signal and the scanning signal for writing are the first half of 1/60 second in one frame after the application to the pixel region 13 is started. After the elapse of 1/120 seconds, the value of the current flowing from the current scanning drive circuit 18 to the current supply line 22 is reduced, and the OELD element 54 is extinguished.
[0046]
When displaying moving images, the integrated value of the emission intensity in one frame of the OELD element 54 in the case of moving image display is substantially the same as the integrated value of the emission intensity in one frame of the OELD element 54 in the case of still image display. Determine the peak value of the data signal. For example, in order to prevent the substantial light emission intensity of the OELD element 54 from decreasing, when the half of one frame at the time of moving image display is used for the extinction time, the light emission intensity of the OELD element 54 is The current value or voltage value from the data driving circuit 16 to the OELD element 54 is corrected so as to be twice that when displaying a still image.
[0047]
In this case, the light emission time of each OELD element 54 during one frame display time T is T _ON , the extinction time is T _OFF (T _OFF = T−T _ON ), and the light emission intensity of the OELD element 54 at the time of still image display. when the the L _1, the voltage value or current value luminous intensity L ₂ of OELD device 54 when the display of the moving image is applied to the _{L 2 = L 1 × (T} oN + T OFF) / T OELD device 54 so that the _oN May be changed. In this case, the light intensity of the OELD element 54 is changed by changing the current value or voltage value between the current supply line 58 and the common potential line 57.
[0048]
When the emission intensity of the OELD element 54 is switched, in addition to this, the γ value of the image signal may be corrected to a value suitable for moving image display. The γ value is a value indicating the relationship between the signal intensity and the luminance, and the luminance that is visually perceived differs between the moving image and the still image, and thus correction correction may be required.
[0049]
Accordingly, in the display device 10, when displaying a still image, the current supply line 22 is held at a low level in one frame to cause the OELD element 54 to emit light, while when displaying a moving image, the current supply line 22 is connected to the current supply line 22 in the middle of one frame. Since the OELD element 54 is forcibly extinguished by applying an erasing scan signal and the current value flowing through the OELD element 54 is increased to increase the luminance, the apparent brightness of the display image is reduced. In addition, the blur of the image is improved by always applying the edge of the image regardless of whether it is a still image or a moving image. In the case of moving image display, since the light emission intensity increases and the light is extinguished in the middle of one frame, the light emission integral amount is almost the same as that in the still image display, and an edge can be applied. On the other hand, in the case of a still image, no extinction time is provided, but even if an afterimage of the previous frame remains visually, there is no adverse effect, and in this case as well, there will be an edge. As a result, deterioration of the OELD element 54 in the display device is suppressed, and the life of the display device is extended.
[0050]
When the determination by the signal discrimination circuit 14 is changed from a moving image to a still image, or when a still image is changed to a moving image, the voltage value or current value of the data signal is changed from the (n + x + 1) th frame, and the erasing scan is performed at the same time. The signal will be changed. The above-described configuration may be applied to a liquid crystal display device and other flat display devices. In the case of a liquid crystal display device, a pixel electrode, a liquid crystal, and a common electrode are used instead of the OELD element.
(Supplementary Note 1) A display panel having a light emitting element that is disposed in an intersection region of a plurality of scan lines and a plurality of data lines and has a pixel electrode, and an active element that turns on and off a signal to the light emitting element;
A data driving circuit for applying a data signal to the data line;
A scan driving circuit for applying a scan signal to the scan line;
A signal discriminating circuit that compares data of image signals of different frames and discriminates either a still image or a moving image and outputs either a still image or a moving image;
When the discrimination signal from the signal discrimination circuit is the still image, the light emission intensity of the light emitting element in one frame is set to a first value, and when the discrimination signal is the moving image, 1 is set. The scanning drive circuit generates a signal for stopping the light emission of the light emitting element in the middle of the frame and extinguishing the light and setting the light emission intensity of the light emitting element to a second value higher than the first value. An active matrix display device comprising:
(Supplementary note 2) The active matrix display device according to supplementary note 1, wherein the light emitting element is an organic light emitting element.
(Supplementary Note 3) When the determination signal is the moving image, the second value of the light emission is obtained by dividing the sum of the light emission time until the middle of the one frame and the time of the subsequent quenching by the light emission time. The active matrix display device according to appendix 2, which is a size obtained by multiplying the first value by the first value.
(Supplementary note 4) The active matrix display device according to any one of supplementary notes 1 to 3, wherein a capacitor for storing image data is connected to the light emitting element.
(Supplementary Note 5) A light emission intensity changing circuit for controlling the light emission amount of the light emitting element by changing a voltage or a current applied to the light emitting element based on a signal from the signal determination circuit includes the control circuit. The active matrix display device according to any one of appendix 1 to appendix 4, wherein the active matrix display device is provided.
(Supplementary note 6) The active matrix display device according to any one of supplementary notes 1 to 5, wherein the control circuit also changes a γ value of the image signal during the extinction.
(Supplementary note 7) The active matrix display device according to any one of supplementary notes 1 to 6, wherein a current supply line is connected to an electrode of the light emitting element to which the active element is not connected.
(Supplementary note 8) The active matrix display device according to supplementary note 1, wherein the light emitting element has a structure having a liquid crystal.
[0051]
【The invention's effect】
As described above, according to the present invention, a moving image and a still image are identified, and when displaying a moving image, a quenching time is provided and the light emitting element has a high emission intensity, and when displaying a still image, the quenching time is set. Since a control circuit that reduces the light emission intensity of the light emitting element without providing it is provided, it is possible to suppress the deterioration of the light emitting element by securing a time for suppressing the magnitude of the current or voltage to the display panel. The phenomenon of edge blurring when displaying images and still images can be eliminated.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a pixel region of a conventional display device.
FIG. 2 (a) is a waveform diagram showing the emission intensity of the OELD before improvement of one frame of the conventional display device, and FIG. 2 (b) is the OELD after improvement of one frame of the conventional display device. It is a wave form diagram which shows the emitted light intensity.
FIG. 3 is a configuration diagram illustrating an active matrix display device according to an embodiment of the present invention.
FIG. 4 is a block diagram showing a configuration in a signal discrimination circuit provided in the active matrix display device according to the embodiment of the present invention.
FIG. 5 is a circuit diagram of a pixel region of an active matrix display device according to an embodiment of the present invention.
FIG. 6 is a graph showing the emission intensity of one frame of OELD when displaying a still image and the emission intensity of one frame of OELD when displaying a moving image in an active matrix display device according to an embodiment of the present invention. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Display apparatus, 12 ... Display panel, 13 ... Image memory, 14 ... Signal discrimination circuit, 15 ... Display control circuit, 16 ... Data drive circuit, 17 ... Scanning drive circuit for writing, 18 ... Scanning drive circuit for quenching, 20 ... data line, 21 ... write scan line, 22 ... quenching scan line.

Claims (6)

A display panel having a light-emitting element that is arranged in an intersection region of a plurality of scan lines and a plurality of data lines and has a pixel electrode, and an active element that turns on and off a signal to the light-emitting element;
A data driving circuit for applying a data signal to the data line;
A scan driving circuit for applying a scan signal to the scan line;
A signal discriminating circuit that compares data of image signals of different frames and discriminates either a still image or a moving image and outputs either a still image or a moving image;
When the discrimination signal from the signal discrimination circuit is the still image, the light emission intensity of the light emitting element in one frame is set to a first value, and when the discrimination signal is the moving image, 1 is set. The scanning drive circuit generates a signal for stopping the light emission of the light emitting element in the middle of the frame and extinguishing the light and setting the light emission intensity of the light emitting element to a second value higher than the first value. And an active matrix display device characterized by comprising: The control circuit integrates the integrated value of the light emission intensity of the light emitting element in one frame when the determination signal is a still image and the light of the light emitting element in one frame when the determination signal is a moving image. 2. The active matrix display device according to claim 1, wherein the first value and the second value are set so that an integrated value of the emission intensity is the same. The active matrix display device according to claim 1, wherein the light emitting element is an organic light emitting element. The second value of the light emission when the determination signal is the moving image is the value obtained by dividing the sum of the light emission time until the middle in the one frame and the time of the subsequent quenching by the light emission time. 4. The active matrix display device according to claim 3, wherein the active matrix display device has a size multiplied by the first value. A light emission intensity changing circuit for controlling the light emission amount of the light emitting element by changing a voltage or a current applied to the light emitting element based on a signal from the signal determination circuit is provided in the control circuit. The active matrix display device according to claim 1, wherein the active matrix display device is a display device. 6. The active matrix display device according to claim 1, wherein the control circuit also changes a γ characteristic of the image signal during the extinction.

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