JP2003150118A - El display device and its driving method, and information display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve excellent moving picture displaying performance and high contrast display in a display panel using organic EL (electroluminescent) elements. SOLUTION: In this EL (electroluminescent) display device, a current is programmed from a source driver IC 18 to a pixel so that an EL element 16 emits light with luminance being n times as large as a prescribed luminance. The programmed current is held in a capacitor 14. A TFT (thin film transistor) 17d is controlled so that the EL element 16 is lighted for a period being one n-th as long as one frame. As a result, an average luminance becomes the prescribed luminance. The vale of (n) is made to be 2 to 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to an EL display device which displays an image by self-luminous display, an information display device such as a mobile phone using the same.

[0002]

2. Description of the Related Art A conventional EL display device includes a power source line for supplying electric power to an EL element, a driving thin film transistor, a storage capacitor for holding electric charges for driving the driving transistor,
It has a switching element for storing a voltage in the storage capacitor and a gate signal line for operating the element. By switching the switching element, the voltage flowing in the source signal line is stored in the storage capacitor of an arbitrary pixel, and the voltage of the power source line is changed to a current by the driving thin film transistor EL.
The device was emitting light.

However, this display device has a problem that variations in the characteristics of the thin film transistor elements for driving are displayed on the screen and the uniformity of the screen is extremely poor. FIG. 1 shows a circuit for eliminating the variation in the characteristics of the transistor.
2 shows.

The circuit of FIG. 12 has an EL element 121 in each pixel, a power supply line 122 for supplying power to the EL element, a switching element 123b for turning on / off the power supply line, and a gate signal line 124a for operating the element. . EL element 1
A driving thin film transistor 123a is connected to the driving circuit 21, and the driving thin film transistor 123a controls a current flowing through the EL element 121. The driving thin film transistor 123a includes a storage capacitor 12 for holding a driving voltage.
5 and the current flowing in the source signal line 126 are stored in the storage capacitor 125.
Switching elements 123c and 123d for writing in
And a gate signal line 12 for controlling the switching element
4b.

The driving method of the circuit of FIG.
A desired current is caused to flow through the switching element 123 to turn off the switching element 123b and turn on the switching elements 123c and 123d so that electric charge is stored in the storage capacitor 125 so that a current equivalent to that of the source signal line 126 flows through the driving thin film transistor 123a. After the electric charge is stored, the switching elements 123c and 123d are turned off and the switching element 123b is turned on, so that a current flows from the power supply line 122 to the EL element 121 in accordance with the electric charge stored in the storage capacitor.

In this driving method, the variation in the characteristics of the driving thin film transistor can be corrected by directly writing the current to be supplied to the EL element 121.

However, in this driving method as well, the power consumption is increased by driving with a current, and the time for writing to the storage capacitor is long because the current is stored in the storage capacitor, resulting in insufficient writing. There's a problem.

[0008]

[Problems to be Solved by the Invention] As described above,
The driving method in which the current is stored in the storage capacitor has problems of power consumption and writing time to the storage capacitor.

[0009]

EL element 1 with a predetermined N-fold brightness
The pixels are current programmed so that 21 emits light. EL
The element controls the switching element 123b so that it lights up for 1 / N of one frame. Therefore, the average luminance and the average applied current are predetermined, but the current programmed in the pixel is N times, so that the writing time to the storage capacitor 125 is shortened and the insufficient writing is eliminated.

Further, when N is 2 or more and 6 or less, the average brightness with respect to the average applied current increases, and the power consumption for producing a predetermined brightness can be reduced.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present specification, each drawing has a portion omitted or / and enlarged or reduced in order to facilitate understanding and / or drawing. For example, in the circuit block shown in FIG. 1, only the parts necessary for the description are shown. Further, the parts having the same numbers or symbols have the same or similar forms or materials or functions or operations.

As a display panel which has low power consumption and high display quality and which can be further thinned, an organic EL display panel constructed by arranging a plurality of organic electroluminescence (EL) elements in a matrix has attracted attention. ing.

In the organic EL display panel, at least one organic functional layer composed of an electron transport layer, a light emitting layer, a hole transport layer, etc. is formed on a glass plate (array substrate) on which a transparent electrode as a pixel electrode is formed. EL layer), and metal electrode (reflection film)
Are laminated. By applying a positive voltage to the transparent electrode (pixel electrode) anode (anode) and a negative voltage to the metal electrode (reflective electrode) cathode (cathode), that is, by applying a direct current between the transparent electrode and the metal electrode, the organic functional layer The (EL layer) emits light. By using an organic compound, which can be expected to have good light emitting characteristics, in the organic functional layer, the EL display panel can be put to practical use.

A circuit diagram of an image display panel using organic EL elements is shown in FIG. The image display panel includes a source driver 18 unit for inputting a video signal and a gate driver 19 unit for displaying the input video signal.
In the source driver 18, the video signal for one line converted into grayscale data in accordance with the horizontal synchronizing signal HD is passed to each source signal line 11.

The gate driver 19 section has two types of gates, a gate signal line 12 for writing a video signal into a pixel and a gate signal line 12 for holding the input video signal and keeping the organic EL element 16 lit. By operating the signal line 12, the video signal flowing in the source signal line 11 is written in the pixel, and the organic EL element 16 is caused to emit light.

FIG. 2 shows a detailed structure of the pixel. This pixel includes drive transistors (hereinafter referred to as TFTs) 17a and 3
TFTs 17b and 17c as two switching elements,
17d and a gate signal line 12 for operating the TFT, an organic EL element 16a, a capacitor 14a, a power supply line 15a and a source signal supply line 11. The TFT 17 changes depending on the type of element, but here the gate signal line 12 connected to the element is H
i is non-conductive, and Low is conductive.

Next, the mechanism of lighting of this pixel will be described. The size of each pixel of the display part such as a mobile phone and a monitor is about 100 μm in width and 250 μm in length,
The current value required for the source signal line 11 to obtain a brightness of 100 candela / square meter is about 1 μA although it depends on the display color and the external quantum efficiency. In order to flow 1 μA to the organic EL element 16, the source driver 18 side causes a current value of 1 μA to flow from the current source 10.

In the selected row, a signal for turning on the TFT 17 is applied to the gate signal line 1 and a signal for non-conducting is applied to the gate signal line 2, and in the non-selected row, on the contrary, the non-conducting signal is applied to the gate signal line 12a and the gate signal line 12b. A conduction signal is applied to.

As a result, in the selected row (first row in this example), the current of the source signal line 11 is the TFT1.
7b and the TFT 17c to flow into the pixel. Since the current path in the pixel is only connected to the EL power supply line 15a through the TFT 17a, the TFT
The current of A flows, and the capacitor 14a accumulates the charge corresponding to the gate voltage at this time. In the non-selection period, 17
Since d is conductive and 17b and 17c are non-conductive, 1 is set based on the charge accumulated in the capacitor 14a during the selection period.
The current flowing through 7a is regulated and 1 μA is applied to the EL element 16a.
Current flows. This allows the organic EL element to emit light.

That is, by activating the gate signal line 12a (applying an ON voltage), the EL element 16 is connected to the TFT 17a through the TFT 17b and the TFT 17c.
Apply the current value that should be applied to. The TFT 17b is turned on so that the gate and drain of the TFT 17a are short-circuited, and the gate voltage (or drain voltage) of the TFT 17a is stored so that the current value flows through the capacitor 14.

The capacitor 14 preferably has a capacitance of 0.2 pF or more. As another configuration, a configuration using the channel capacitance of the TFT is also exemplified. That is, the TFT 1 is not provided separately from the capacitor 14.
The channel width W of 7a is set to a certain size or more.

From the viewpoint of preventing a decrease in brightness due to leakage of the TFT 17c and stabilizing the display operation, it is preferable to separately form a capacitor as described above.
The size of the capacitor 14 is 0.
It is preferable to set it to 2 pF or more and 2 pF or less, and above all, it is preferable to set the size of the capacitor (capacitor) 14 to 0.4 pF or more and 1.2 pF or less.

It is preferable that the capacitor 14 is generally formed in a non-display area between adjacent pixels. Generally, when forming a full-color organic EL, since the organic EL layer is formed by mask vapor deposition using a metal mask, the formation position of the EL layer occurs due to the mask position shift. When the position shift occurs, there is a risk that the organic EL layers of the respective colors overlap.
Therefore, the non-display area between adjacent pixels of each color is 10μ.
You have to leave This portion does not contribute to light emission. Therefore, forming the capacitor 14 in this region is an effective means for improving the aperture ratio.

Next, the gate signal line 12a is made inactive (OFF voltage is applied) and the gate signal line 12b is made active, and the current flow path is set to the first TFT 17a.
Also, the TFT 17d connected to the EL element 16 and the path including the EL element 16 are switched to operate so that the stored current flows through the EL element 16.

In FIG. 1, all TFTs are composed of P channels. P channel is a little N channel TF
The mobility is lower than that of T, but it is preferable because the withstand voltage is large and deterioration is less likely to occur. However, the present invention is EL
The configuration of the element 16 is not limited to the P-channel configuration. You may comprise only N channels. Further, both N channel and P channel may be used.

It is preferable that the TFTs 17b and 17c have the same polarity and have N channels, and the TFTs 17a and 1d have P channels. Generally, P-channel TFT is N-channel TFT
Compared to the above, it has advantages such as high reliability and a small kink current. For an EL element that obtains a desired light emission intensity by controlling the current, the effect of using the TFT 17a as a P channel is great.

The structure of the EL element 16 of the present invention is controlled by two timings. The first timing is a timing for storing a necessary current value. T at this timing
A predetermined current I1 is written from the source signal line 11 by turning on the FT 17b and the TFT 17c. As a result, the gate and drain of the TFT 17a are connected to each other, and the current I1 flows through the TFT 17a and the TFT 17c. Therefore, the gate-source voltage of the TFT 17a becomes the voltage V1 at which I1 flows.

The second timing is TFT 17a and TFT.
It is the timing when 17c is closed and the TFT 17d is opened.
The voltage V1 between the source and gate of the TFT 17a remains held. In this case, since the TFT 17a always operates in the saturation region, the current I1 is constant.

The gate of the TFT 17a and the TFT 17
The gate of c is connected to the same gate signal line 12a. However, the gate of the TFT 17a and the gate of the TFT 17c may be connected to different gate signal lines 12 (T
The FT 17b and the TFT 17c can be individually controlled). That is, the number of gate signal lines for one pixel is three (the configuration of FIG. 1 is two). ON / OFF timing of the gate of the TFT 17a and ON of the gate of the TFT 17c
By controlling the ON / OFF timing individually, TF
It is possible to further reduce the variation in the current value of the EL element 16 due to the variation in T17.

If the first gate signal line 12a and the second gate signal line 12b are made common and the third and fourth TFTs have different conductivity types (N channel and P channel), the drive circuit is simplified. , And the aperture ratio of the pixel can be improved.

FIG. 3 shows this operation as an actual waveform. The gate control signal 32a of the gate 12a falls in response to the horizontal synchronizing signal HD. At this time, the charge corresponding to the video signal is accumulated in the capacitor 14. Then, before the next horizontal synchronizing signal, the input period of this selected row ends and the gate control signal 32a rises. Corresponding to that, organic E
The gate control signal 33a of the gate 13a falls to make the TFT 17 connected to the L element 16 pass through. As a result, a current corresponding to the capacitor 14 flows from the power supply line 15 to the organic EL element 16 to emit light. The gate waveform 33a is Lo until the signal input period of this row comes next.
It keeps w and keeps the lighting state of the organic EL element.

However, the actual source signal line 11 has stray capacitance 20 due to wiring capacitance or the like. When the stray capacitance 20 exists on the source signal line 11, a rounding of the waveform determined by the wiring resistance of the source signal line 11 and the time constant of the stray capacitance 20 is observed. When gradation display is performed by the current value, this waveform rounding also varies depending on the current value flowing in the source signal line, and the smaller the current value, the longer it takes to rise and fall. For example, wiring capacitance is 100 pF, wiring resistance is 5
At 00 ohms, the time required to change the current value of the source signal line 11 and the current value of the contact 1001 from 0.24 μA to 40 nA when the current value of the current source 10 is changed is 300 μsec, from 40 nA. The time required to change to 0.24 μA was 250 μsec.

This is because it is difficult to charge and discharge the charge accumulated in the stray capacitance 20 because the amount of charge movement per unit time is small in the low current region. As a result, when the current value flowing through the source signal line 11 is low, the time required to write the video signal becomes long. Therefore, in the conventional gradation display method using current, the minimum time for one horizontal scanning period is 300 μsec. With this, the number of scanning lines is 2 as in a mobile phone.
In the case of 20 lines, one frame needs to be driven at about 10 Hz, and the flicker occurs due to a change in the amount of charge in the capacitor 14 and a change in the current flowing through the EL element 16 depending on the OFF characteristics of the TFT 17.

In order to solve this problem, therefore, an n-fold pulse drive for applying a normal n-fold current to the source signal line 11 as shown in FIG. 4 for a normal 1 / n time is used. By this driving method, it is possible to write a higher current than usual, thereby shortening the writing time to the capacitor. When an n-fold current flows through the source signal line, an n-fold current also flows through the organic EL element. Therefore, by outputting the gate control signal to 53a and setting the conduction time of the TFT 17d to 1 / n, the organic EL element A current is applied to the element 16 for a period of 1 / n so that the average applied current does not change.

The time t required to change the current value of the source signal line 11 is t = C · V, where C is the size of the stray capacitance 20, V is the voltage of the source signal line 11, and I is the current flowing through the source signal line 11. Since / I, the current value can be increased ten times, and the time required to change the current value can be shortened to nearly one tenth. Alternatively, it shows that the source current can be changed to a predetermined current value even if the source capacitance 20 becomes 10 times. Therefore, it is effective to increase the current value in order to write a predetermined current value within a short horizontal scanning period.

If the input current is multiplied by 10, the output current is also increased by 10.
1 times the brightness of the EL, so that the conduction period of the TFT 17d in FIG.
By setting the luminance to 1/0 and the light emitting period to 1/10, the predetermined luminance is displayed.

That is, the parasitic capacitance 20 of the source signal line 11
Fully charged and discharged, and a predetermined current value is applied to the pixel TFT1.
To program 7a, source driver 18
It is necessary to output a relatively large current from the. But,
When such a large current is passed through the source signal line 11, this current value is programmed in the pixel, and a large current flows through the EL element 16 with respect to a predetermined current. For example, 1
If programming is performed with a current of 0 times, naturally, a current of 10 times flows through the EL element 16, and the EL element 16 emits light with a brightness of 10 times. In order to obtain a predetermined emission brightness, the EL element 16
It suffices to reduce the time for flowing to 1/10. By driving in this way, the parasitic capacitance of the source signal line 11 can be sufficiently charged and discharged, and a predetermined light emission luminance can be obtained.

A 10 times larger current value is applied to the pixel TFT 17.
It is assumed that the data is written in a (correctly, the terminal voltage of the capacitor 14 is set) and the ON time of the EL element 16 is set to 1/10, but this is an example. In some cases, 10
A double current value may be written in the TFT 17a of the pixel, and the ON time of the EL element 16 may be reduced to 1/5. On the contrary, there may be a case where a 10-fold current value is written in the TFT 17a of the pixel to double the ON time of the EL element 16. The present invention is
It is characterized in that the write current to the pixel is set to a value other than a predetermined value and the current flowing through the EL element 16 is driven in an intermittent state. In this specification, for ease of explanation, it is assumed that an N-fold current value is written in the TFT 17 of the pixel and the ON time of the EL element 16 is made 1 / N-fold. However, the present invention is not limited to this, and the N1 times the current value is applied to the pixel TF.
Write to T17 and set ON time of EL element 16 to 1 / N2
It goes without saying that it may be doubled (different from N1 and N2). The intermittent intervals are not limited to equal intervals.

Also, for ease of explanation, 1 / N is 1
It is assumed that 1F is set to 1 / N based on F (1 field or 1 frame). However, when one pixel row is selected and the current value is programmed (typically 1
There is a horizontal scanning period (1H), and an error occurs depending on the scanning state. Therefore, the above explanation is only a matter of convenience for facilitating the explanation,
It is not limited to this.

Another problem is that the organic (inorganic) EL display device is basically different in display method from a display such as a CRT which displays an image as a set of line displays by an electron gun. That is, the EL display device holds the current (voltage) written in the pixel for a period of 1F (one field or one frame). Therefore, when a moving image is displayed, the problem occurs that the outline of the displayed image is blurred.

According to the present invention, E only during the period of 1 F / N
Apply a current to the L element 16 for another period (1F (N-1)
/ N) does not pass an electric current. Consider the case where this driving method is implemented and one point on the screen is observed. In this display state, image data display and black display (non-lighting) are repeatedly displayed for each 1F. That is, the image data display state becomes a temporally intermittent display (intermittent display) state. When the moving image data display is viewed in this intermittent display state, the outline of the image is not blurred and a good display state can be realized. That is, it is possible to realize moving image display close to that of a CRT. Although the intermittent display is realized, the main clock of the circuit is the same as the conventional one. Therefore, the power consumption of the circuit does not increase.

In the case of a liquid crystal display panel, image data (voltage) for light modulation is held in the liquid crystal layer. Therefore,
In order to perform black insertion display, it is necessary to rewrite the data applied to the liquid crystal layer. Therefore, it is necessary to raise the operation clock of the source driver IC 18 and alternately apply the image data and the black display data to the source signal line 11. Therefore, black insertion (intermittent display such as black display)
In order to realize, it is necessary to raise the main clock of the circuit. Also, an image memory for performing the time axis expansion is required.

In the pixel structure of the EL display panel of the present invention shown in FIG. 1 etc., the image data is held in the capacitor 14. A current corresponding to the terminal voltage of the capacitor 14 is passed through the EL element 16. Therefore, the image data is not held in the light modulation layer like the liquid crystal display panel.

The present invention controls the current flowing through the EL element 16 only by turning on and off the switching TFT 17d and the like.

That is, even if the current Iw flowing through the EL element 16 is turned off, the image data is still held in the capacitor 14. Therefore, at the next timing, TFT1
If 7d or the like is turned on and a current is passed through the EL element 16, the flowing current is the same as the current value that was flowing before. In the present invention, when black insertion (intermittent display such as black display) is to be realized, it is not necessary to raise the main clock of the circuit. Also, an image memory is unnecessary because it is not necessary to perform time-axis expansion. Further, the organic EL element 16 has a short response time from application of current to light emission, and has a high-speed response. Therefore, it is suitable for displaying moving images, and by implementing intermittent display, it is possible to solve the problem of displaying moving images, which is a problem of conventional data-holding type display panels (liquid crystal display panels, EL panels, etc.).

For example, the gate signal line 12b has a conventional conduction period of 1F (when the current program time is 0, the normal program time is 1H, and the number of pixel rows of the EL display device is at least 100 rows or more, so 1F is used). However, if N = 10, it is possible to change from gradation 0 to gradation 1, which takes the longest time to change, to gradation 1 in about 75 μsec if the source capacitance is about 20 pF. This indicates that an EL display device of about 2 type can be driven at a frame frequency of 60 Hz.

When the source capacitance 20 is large in a larger display device, the source current may be increased 10 times or more. Generally, when the source current value is increased N times, the conduction period of the gate signal line 12b (TFT 17d) may be set to 1 F / N. As a result, it can be applied to display devices for televisions and monitors.

As described above, if the TFT 17d is turned on for a period of 1 / N of the time (about 1F) that is originally turned on and is turned off for the other period (N-1) / N periods, the average brightness of the entire 1F. Has a predetermined brightness. This display state is similar to that of a CRT scanning the screen with an electron gun. The difference is that
The range where the image is displayed is the point where 1 / N of the entire screen is illuminated (the entire screen is 1) (In the CRT, the illuminated range is 1 pixel row (strictly 1 pixel is is there).

In the present invention, the 1 / N image display area 7
1 moves from the top to the bottom of the screen 21 as shown in FIG.
In the present invention, the current flows through the EL element 16 only during the period of 1F / N, and the current does not flow during the other period (1F · (N−1) / N). Therefore, the image is displayed intermittently. However, since the image is held by the afterimage in human eyes, the entire screen appears to be displayed uniformly.

In this display state, the image data display 71 and the black display (non-lighting) 72 are repeatedly displayed for each 1F.
That is, the image data display state becomes a temporally intermittent display (intermittent display) state. In the liquid crystal display panel (EL display panel other than the present invention), data is held in the pixel for the period of 1F, and therefore, in the case of moving image display, even if the image data changes, the change cannot be followed, The image was blurred (outlined image). However, in the present invention, since the image is displayed intermittently, the outline of the image is not blurred and a good display state can be realized. That is, it is possible to realize moving image display close to that of a CRT.

Further, in the EL display device, the black display is completely non-lighted, so that the contrast is not lowered unlike the case where the liquid crystal display panel is intermittently displayed. Further, as shown in FIG. 1, the intermittent display can be realized only by turning on / off the TFT 17d. This is because the image data is stored in the condenser 14. That is, the image data is held in each pixel 16 during the period of 1F. The electric current corresponding to the held image data is E
Whether or not to flow to the L element 16 is realized by controlling the TFT 17d.

Therefore, the number of TFTs 17 forming one pixel does not change between the case where the intermittent display is realized and the case where it is not realized. In other words, the effect of the parasitic capacitance 20 of the source signal line 11 is eliminated and the current programming is realized without changing the pixel configuration. In addition, a moving image display similar to a CRT is realized.

Since the operating clock of the gate driver circuit is sufficiently slower than the operating clock of the source driver circuit 18, the main clock of the circuit does not become high. Moreover, the value of N can be easily changed.

The image display direction (image writing direction) is 1
In the field, from the top of the screen downwards,
In the field, the direction may be from the bottom of the screen to the top. Further, in the first field, the screen is changed from the top to the bottom, and once the entire screen is displayed in black (non-display) 72, the second
In the field, the direction may be from the bottom of the screen to the top. As shown in FIG. 2, an ON voltage (Vgl) is applied to the gate signal line 12a (1) to select a pixel. At this time, the off voltage (Vgh) is applied to the gate signal line 12b (1).
Is applied. Therefore, the switching TFT 17b
And 17c are turned on, and the TFT 17d is off.

The program current Iw is applied to the source signal line 11.
Flows. This program current Iw is supplied by the TFT 17a. (Current Idd = Iw). This current Id
When d flows, the potential of the source signal line 11 becomes a predetermined voltage, and the gate terminal voltage Vg of the TFT 17a is current-programmed. Current Programmed current is Iw
It is an electric current. That is, the TFT 17a has the program current I
The Vg voltage is set so that w flows. In other words, it can be said that the potential of the source signal line 11 is programmed in the pixel. In other words, it can be said that the operating state of the pixel is that the voltage is programmed.

After 1H (one horizontal scanning period), the off voltage (Vgh) is applied to the gate signal line 12a (1), and TF is applied.
The T17b and the TFT 17c are turned off, and the voltage required to flow the program current Iw in the capacitor 14a is held. Further, the gate signal line 12b (1) has an on-voltage (Vg
l) is applied and the TFT 17d is turned on. Therefore, an Ie (= Iw) current flows through the EL element 16, and the EL element 16 is lit with the programmed current (Ie).

The above is the operation of the current program method described above. However, the operation is actually different. E
This is because the current Ie flowing through the L element 16 is smaller than Iw.

First, the operation of the P channel of the TFT will be described. P-channel TFT has gate terminal voltage V
A larger on-current flows as g is on the negative side. 0
In (V), it is completely off. ON current is W / L of TFT
And mobility and S value. TFT W /
When L is 6/12, the channel current (Idd) is very small up to about −3 (V). -4 (V) ~-
A current of 1 to 5 μA flows at 4.5 (V).

Another important matter is that there is a capacitance problem between the potential of each element and the terminals of the element. Gate of TFT 17b-
There is a capacitance between the source terminals. This capacity is
When the W / L of b is 6/6 μm double gate, 0.0
It is about 1 to 0.03 pF. The capacity of this capacitor is called the penetration capacity.

When a pixel is selected, the gate signal line 12a
Changes from Vgh to Vgl, the potential of the gate signal line 12a penetrates due to the penetration capacitance. This penetration causes the Vg voltage to shift in the + direction.

Next, the TFT 17a passes a current equal to the current Iw absorbed by the source driver circuit 18. But,
In the case of black display, the value of the current passed through the TFT 17a is small.
As an example, it is 30 nA or less. With such a current,
The parasitic capacitance of the source signal line 18 cannot be sufficiently charged / discharged within 1H period. Therefore, the source signal line 18
It is not possible to set the potential of 1 to a predetermined voltage within 1H period.
That is, the Vg voltage is also low and cannot be set to a voltage required for black display.

Therefore, the TFT 17a corresponds to the EL element 16
In addition, a larger current than the original black display is passed. for that reason,
The EL element 16 emits light brighter than a desired value. Therefore, in the EL display panel, black floating occurs and high contrast display cannot be realized.

However, since the gate signal line 12a changes from the on-voltage (vgl) to the off-voltage (Vgh), the punch-through voltage is generated again due to the punch-through capacitance. Due to this punch-through voltage, the Vg voltage shifts to the required black display voltage. Therefore, the TFT 17a is programmed so as not to allow a current to flow at all, or programmed so as to allow a desired value of black current to flow. That is, EL
The element 16 is programmed so that only a small current flows. Therefore, the EL display panel of the present invention is free from blackening, and high contrast display can be realized. This Vg voltage is held for one field (one frame), that is, until the pixel is next selected and rewritten.

In the method of applying n times as many pulses as shown in FIG. 4, the current applied to the EL element 16 is large, and therefore the terminal voltage generated in the EL element 16 is also high.
Therefore, the EL element 16 cannot be driven unless the amplitude value of the gate signal line 12 is increased. As the amplitude value of the gate signal line 12 increases, the punch-through voltage generated through the punch-through capacitance also increases. Therefore, in the present invention, excellent black display can be realized. This effect is n = 2
The above becomes remarkable. Therefore, in the invention, n is preferably 2 or more.

Also in the circuit of FIG. 12, the current flowing in the source signal line 126 can be written in the storage capacitor 125 by turning off the switching element 123b and turning on the switching elements 123c and 123d. When the switching elements 123c and 123d are turned off and the switching element 123b is turned on, a current flows from the power supply line 122 to the EL element 121 according to the electric charge stored in the storage capacitor 125.

Therefore, the current flowing through the source signal line is set to N
Doubling doubles the current written in the storage capacitor N times. Further, by setting the conduction time of one frame of the switching element 123b to 1 / N, the time flowing to the EL element becomes 1 / N of one frame. Therefore, the same driving method can be used for the circuit of FIG. It is possible.

The present invention takes advantage of the punch-through voltage to
A good black display is realized. When the corresponding pixel row is selected and the ON voltage is applied to the gate signal line 12a, the voltage of the gate signal line penetrates and the Vg voltage is further shifted toward white display. However, this penetrating voltage is charged in a short time by the voltage from the source signal line 18. In particular, since the gate terminal voltage of the TFT 17a tends to decrease, the TFT 17a tends to flow more current and is charged in a short time. Therefore, when the on-voltage is applied to the gate signal line 12a, the punch-through does not pose any problem.

After the period of 1H, when the corresponding pixel row is unselected and the off voltage is applied to the gate signal line 12a, the Vgh voltage is applied to the gate signal line 12a and the punch-through voltage is generated. Due to this penetration voltage, the TFT1
The gate terminal voltage of 7a reaches the target black display voltage.

As described above, according to the present invention, the gate signal line 12
The voltage fluctuation of “a” is supplied to the TFT 17a through the through capacitor to control the current flowing through the EL element 16. This control is particularly effective for realizing black display.

Now, let us consider a case where a current for displaying white is applied to the EL element 16. When a pixel is selected,
The gate terminal of the TFT 17a is programmed so that the white display current flows. This programmed current is EL
It flows to the element 16.

In the method of applying n times as many pulses as shown in FIG. 4, the current applied to the EL element 16 is large. In order to pass a large current through the EL element 16, it is necessary to lower the gate terminal voltage Vg of the TFT 17a. Of course, the potential of the source signal line 11 also becomes low.

Therefore, in white display, Vg is programmed at a low potential. However, the punch-through voltage generated through the punch-through capacitance is the same as in the case of black display. On the other hand, in the case of n = 1 or more, the potential of the source signal line 11 is lower than that in the case of n = 1, and thus the white display brightness increases. Therefore, as shown in FIG. 6, n =
A brightness of 2 increases.

FIG. 6 shows a change in luminance when n is changed when n-fold pulse driving is used. The brightness in this figure is n
Is a value obtained by dividing the brightness when the value is changed by the value of the current flowing across the organic EL element 16 (that is, the average brightness),
The graph shows the luminance ratio of each pulse drive when the luminance of normal drive is 1.

From FIG. 6, it can be seen that when n is 1 or more and 6 or less, the brightness is higher than normal (n = 1). However, when n is 6 or more, the brightness decreases. this is,
As shown in FIG. 7, the relationship between the current applied to the organic EL element and the brightness of emitted light is not a perfect proportional relationship, and it is known that the graph draws a curve from a certain current value (that is, the luminous efficiency per unit current). Will decrease). For this reason, if n is increased and the current applied to the organic EL element becomes too large, the luminous efficiency of the organic EL element itself deteriorates, and the brightness decreases even if the average applied current is the same.

Therefore, in the driving method of the organic EL element, n is 1
When the pulse drive of 6 or more is used, the brightness with respect to the average applied current increases. Further, as shown in FIG. 4, when an image is displayed by n-fold pulse driving, black display becomes good when n = 2 or more, and the display contrast is improved. In addition, the moving image display performance is also dramatically improved.

By turning on / off the TFT 17d, the current flowing through the EL element 16 is turned on / off. Therefore, the image display area 71 is in a state of being scanned in the vertical direction of the screen as shown in FIG. At this time, the black display portion is the area where the EL element 16 is turned off.

When the ratio of the black display portion 16 to the entire area of the screen is 20% or more, the moving image display performance is remarkably improved.
Especially, when it is 50%, the improvement effect is high. When the black display area 16 is 20%, N = 1.2. Therefore, in order to improve the moving image display performance, N is 1.
It may be 2 or more and 6 or less. Furthermore, N is preferably 1.5 or more and 6 or less.

If N = 5 is exceeded, flicker may be noticeable from the viewpoint of the frequency of the frame rate. Therefore, N is preferably 1.2 or more and 5 or less. Further, N is preferably 1.5 or more and 5 or less.

In addition, holding capacitor C1 (14a) and T
The ratio of the gate-source capacitance (C2) of FT11b is C
It is preferable that the range is 1: C2 = 200: 1 or more and C1: C2 = 20: 1 or less. By setting this range, the current flowing through the TFT 11a during black display is optimized.

FIG. 9 shows at least one of the forms of the present invention.
Display device 92 using one of the two forms, a demodulation device, an antenna 9
1, a button 94 is attached, and a casing 93 is used as a portable information terminal.

When the display panel 92 is used in an information display device such as a mobile phone, it is preferable to mount the driver IC on one side of the display panel (note that the driver IC is mounted on one side in this way is free from three sides). In the past, the gate driver IC was mounted on the X side of the display area and the source driver IC was mounted on the Y side of the display area). This is because it is easy to design so that the center line of the screen becomes the center of the display device, and the mounting of the driver IC becomes easy. It should be noted that the gate driver circuit may be formed in a three-side free configuration by using high temperature polysilicon or low temperature polysilicon technology (that is, at least one of the gate driver and the source driver in FIG. 1 is formed on the substrate by polysilicon technology). Form directly).

Generally, in an information display device such as a mobile phone, low power consumption is prioritized over the number of display colors. The power consumption increases because the operating frequency of the circuit that increases the number of display colors increases or the voltage (current) waveform applied to the EL element 16 changes more often. Therefore,
The number of display colors cannot be increased so much. To solve this problem, the present invention displays the image by performing error diffusion processing or dither processing on the image data.

Although not shown in the mobile phone of the present invention described with reference to FIG. 9, a CCD camera is provided on the back side of the housing. Images taken with a CCD camera can be immediately displayed on the display screen of the display panel. Data captured by the CCD camera can be displayed on the display screen 92. Image data of CCD camera is 24-bit (16.7 million colors), 18-bit (260,000 colors), 16-bit (650,000 colors), 12-bit (4096 colors), 8-bit (256 colors) by key input 94 You can switch.

When the display data is 12 bits or more, the error diffusion process is performed to display. That is, when the image data from the CCD camera exceeds the capacity of the built-in memory, error diffusion processing or the like is performed, and the image processing is performed so that the number of display colors falls below the capacity of the built-in memory.

Further, as shown in FIG. 11, when the current is multiplied by N1 and the application time is set to 1 / N2, if the relationship of N1> N2 is satisfied, the average applied current flowing through the EL element is increased and the average brightness is increased. . For example, when N2 = 2N1, the time for emitting light with the same luminance is doubled, and therefore the average luminance for emitting light from the EL element is doubled. Therefore, the average luminance of the EL element can be changed by changing the relationship between the amount of current applied and the application time. Utilizing this fact,
It is also possible to use it as a lighting device by making the display panel 92 emit light on one surface in a portable information device as shown in FIG.

This illumination device can be switched between a display screen as a portable information device and a display screen as an illumination device by key input 94.

However, when it is intended to be used as an illuminating device, the brightness of the display screen of the portable information device is insufficient to illuminate the front for more than 1 meter. When the driving method of the present invention is used to display a portable information device, a current higher than a predetermined current is applied and a cutoff time is provided to control the average current applied to the EL element. Therefore, when the time for interrupting the current is changed by the key input 94, the average current applied to the EL increases and the brightness of the display panel 92 increases. As a result, it can be used as a lighting device that can illuminate a distance of 1 meter or more and can arbitrarily change the brightness.

FIG. 10 shows a video signal input 10 to a display device 101 using at least one of the modes of the present invention.
6 and the video signal processing circuit 104 are attached, and a television is provided by the housing 107.

In the television shown in FIG. 10, the surface of the screen is covered with a protective film (may be a protective plate). This is for one purpose to prevent the surface of the display panel 92 from being hit and damaged. An AIR coat is formed on the surface of the protective film, and the surface is embossed to prevent external conditions (external light) from being reflected on the display panel 92.

A certain space is arranged by dispersing beads or the like between the protective film and the display panel 92. Further, a fine convex portion is formed on the back surface of the protective film, and the convex portion holds a space between the display panel 92 and the protective film. By holding the space in this way, it is possible to prevent the impact from the protective film from being transmitted to the display panel 92.

It is also effective to dispose or inject an optical coupling agent such as a liquid acrylic resin such as alcohol or ethylene glycol or a solid resin such as epoxy between the protective film and the display panel 92. This is because interface reflection can be prevented and the optical coupling agent functions as a buffer material.

As a protective film, a polycarbonate film (board), a polypropylene film (board), an acrylic film (board), a polyester film (board), P
An example is a VA film (plate). It goes without saying that other engineering resin films (ABS, etc.) can be used. It may also be made of an inorganic material such as tempered glass. The same effect can be obtained by coating the surface of the display panel 92 with an epoxy resin, a phenol resin, or an acrylic resin in a thickness of 0.5 mm or more and 2.0 mm or less, instead of disposing the protective film.
It is also effective to emboss the surface of these resins.

It is also effective to coat the surface of the protective film or the coating material with fluorine. This is because stains on the surface can be easily wiped off with a detergent or the like. In addition, the protective film may be formed thick to serve also as the front light.

The screen is not limited to 4: 3,
A wide display may be used. Resolution is 1280x
It is preferably 768 dots or more. With the wide type, you can enjoy full-screen titles and programs in landscape display such as DVD movies and TV broadcasts. The brightness of the display panel is preferably 300 cd / m ² (candela / square meter). More preferably, the brightness of the display panel is preferably 500 cd / m ² (candela / square meter). Also, the brightness (20
The changeover switch is installed so that it can be displayed at 0 cd / m ² ).

Therefore, the user can set the brightness of the screen to the optimum depending on the display content or the usage method. Furthermore, only the window displaying the video is 500
in the cd / m ^2, the other parts are also available settings to 200cd / m ^2. It is flexible enough to display TV programs in the corner of the display and check mail. The speaker has a tower shape and is designed to spread the sound not only in the front direction but also in the entire space.

The technical idea described in the embodiments of the present invention can be applied to a video camera, a projector, a stereoscopic television, a projection television and the like. Further, it is also applicable to a viewfinder, a mobile phone monitor, a PHS, a personal digital assistant and its monitor, a digital camera and its monitor.

Further, it can be applied to an electrophotographic system, a head mounted display, a direct view monitor display, a notebook personal computer, a video camera and an electronic still camera. Also, monitors of cash drawers, payphones, videophones, personal computers,
It can also be applied to a wristwatch and its display device.

Further, it goes without saying that the present invention can be applied or expanded to a display monitor of a household electric appliance, a pocket game machine and its monitor, a backlight for a display panel or a lighting device for home or business use. It is preferable that the lighting device is configured so that the color temperature can be changed. In this, the color temperature can be changed by forming RGB pixels in a stripe shape or a dot matrix shape and adjusting the current flowing through these. Further, the present invention can be applied to display devices for advertisements or posters, RGB traffic lights, alarm indicators, etc.

The organic EL panel is also effective as the light source of the scanner. The object is irradiated with light using the RGB dot matrix as a light source to read an image. Of course, it is needless to say that it may be a single color. Further, the matrix is not limited to the active matrix, and a simple matrix may be used. If the color temperature can be adjusted, the image reading accuracy will be improved.

The organic EL display device is also effective for the backlight of the liquid crystal display device. It is possible to change the color temperature and easily adjust the brightness by forming the RGB pixels of the EL display device (backlight) in a stripe shape or a dot matrix shape and adjusting the current flowing through them. In addition, since it is a surface light source, a Gaussian distribution that brightens the central part of the screen and darkens the peripheral part can be easily configured. It is also effective as a backlight for a field-sequential liquid crystal display panel that alternately scans R, G, and B lights. Further, even if the backlight blinks, by inserting black, it can be used as a backlight for a liquid crystal display panel for displaying moving images.

[0101]

The display panel, display device and the like of the present invention can realize high image quality, good moving image display performance, and uniform display in the screen plane.

By using the present invention, an information display device with low power consumption can be constructed, so that no power is consumed.
In addition, since the size and weight can be reduced, resources are not consumed. Further, even a high-definition display panel can be sufficiently dealt with.
Therefore, it is friendly to the global environment and space environment.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a display device of the present invention.

FIG. 2 is a diagram showing a pixel, a source signal line, and a power supply according to an embodiment of the present invention.

FIG. 3 is a diagram showing a timing of a gate control signal in a horizontal scanning period.

FIG. 4 is a diagram showing a relationship between an applied current value and an application time in N times pulse driving.

FIG. 5 is a diagram showing a timing of a gate control signal in a horizontal scanning period when using N times pulse driving.

FIG. 6 is a diagram showing the relationship between the change in N and the luminance with respect to the average applied current when N-fold pulse driving is used.

FIG. 7 is a diagram showing the relationship between applied current and brightness of an organic EL element.

FIG. 8 is a diagram showing a display state of the display panel of the present invention.

FIG. 9 is a diagram of a personal digital assistant incorporating a display device according to an embodiment of the present invention.

FIG. 10 is a diagram showing a television incorporating a display device according to an embodiment of the present invention.

FIG. 11 is a diagram for explaining the operation of the embodiment of the present invention.

FIG. 12 is a diagram showing a drive circuit for a conventional organic EL element.

[Explanation of symbols]

10 current source 11 Source signal line 12, 13 Gate signal line 14 Capacitor 15 EL power line 16 Organic EL device 17 TFT 18 Source driver 19 Gate driver 31,51 Horizontal sync signal HD 32, 33, 52, 53 Gate control signal

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09G 3/20 642 G09G 3/20 642A 680 680T H05B 33/14 H05B 33/14 A F term (reference) 3K007 AB02 AB05 AB17 BA06 BB07 DB03 GA04 5C080 AA06 BB05 DD05 DD26 EE28 FF11 JJ01 JJ02 JJ03 JJ04 JJ05 JJ06 KK07 KK47

Claims (9)

[Claims] 1. A driving method of an EL display device, wherein pixels are arranged in a matrix, and a source signal line for applying image data to be written to the pixel is provided, wherein the source signal line has substantially N times the luminance of the pixel. A first operation of writing image data, a second operation of applying a current corresponding to the image data written to the pixel to an EL element of the pixel, and a third operation of cutting off the current for a predetermined period. And a value of N is 1.2 or more and 6 or less, the method for driving an EL display device. 2. The driving method of an EL display device according to claim 1, wherein the predetermined period is a time shorter than 1 / N of one frame or one field. 3. The method for driving an EL display device according to claim 1, wherein N is 1.2 or more and 6 or less. 4. An organic EL display device in which pixels are arranged in a matrix, wherein an EL element formed in each pixel, a driving transistor for supplying a current applied to the EL element, and the driving transistor. A first switching element that applies a voltage to the capacitor, a second switching element that turns on and off a current flowing through the EL element, and a gate driver circuit that selects the switching element. A source driver circuit for setting a voltage to be written to the capacitor, wherein the source driver circuit sets a voltage to be written to the capacitor so that a current flowing through the EL element is N times a predetermined value, A voltage is applied to the pixel of the first switching element selected by the gate driver circuit, Second switching element for a predetermined period of one frame, cut off the current flowing in the EL device, EL display device wherein the value of said N is 1.2 or more and 6 or less. 5. An organic EL display device in which pixels are arranged in a matrix, wherein an EL element formed in each pixel, a driving transistor for supplying a current applied to the EL element, and the driving transistor. A first transistor element for applying a voltage to the capacitor, a second transistor element for turning on / off a current flowing through the EL element, and a gate driver circuit for selecting the transistor element. A source driver circuit for setting a voltage to be written to the capacitor, wherein the source driver circuit sets a voltage to be written to the capacitor so that a current flowing through the EL element is N times a predetermined value, The voltage is applied to the pixel of the first transistor element selected by the gate driver circuit, The second transistor element interrupts the current flowing through the EL element for a predetermined period of one frame, and the ratio of the capacitor capacitance C1 to the gate-source capacitance C2 of the first transistor element is: C1: C2 = 2
An EL display device, characterized in that it is 00: 1 or more and C1: C2 = 20: 1 or less. 6. An EL element formed in each pixel, and the E element
A driving transistor that supplies a current to be applied to the L element, a capacitor that is connected to the gate terminal of the driving transistor, a first transistor element that applies a voltage to the capacitor, and a current that flows to the EL element are turned on and off. A second transistor element, a gate driver circuit for selecting the transistor element, a source driver circuit for setting a voltage to be written to the capacitor, an antenna, an audio demodulation circuit, and a key input circuit. Mobile information terminal equipped. 7. An information display device, comprising: the EL display device according to claim 4; a video signal processing circuit; and an applied voltage adjusting means. 8. An EL display device in which pixels are arranged in a matrix and has a source signal line for applying image data to be written in the pixels, the EL display device comprising: a current applied to an EL element of each pixel; The display brightness is adjusted by controlling the size and the application and interruption of the current flowing through the EL element, and the brightness is changed by changing the current application time and the interruption time for the EL element. EL display device. 9. The EL display device according to claim 8, further comprising a voice demodulation function.