JP2003150110A - Active matrix type display device using organic el element and its driving method, and portable information terminal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem wherein, when a long-time drive is performed, the reduction of the luminance and the rising of the inter-terminal voltage of the EL elements are generated in the display device in a display device in which E1 (electroluminescent) display elements and the like are used. SOLUTION: In the display device, a switching transistor 267d is provided between an EL element 266 and a driving transistor 267a controlling the current value of the element 266 in order to apply a reverse voltage to the EL element 266 and the EL element 266 is made to be in a non-conduction state in a reverse bias application period. Moreover, the value of a voltage to be applied to the transistor 267d is made to be lowered by enabling the value of a different voltage to be applied to a reverse bias signal line 269 for applying the reverse voltage to the EL element 266 in addition to the reverse bias voltage 268 and by making the conduction state or the non-conduction state of a transistor 267e which selects whether to apply the reverse voltage or not to be decided by the reverse bias signal line 269.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, such as an organic electroluminescence device, which performs gradation display by the amount of current.

[0002]

2. Description of the Related Art Organic light emitting elements are self-luminous elements, and therefore, do not require a backlight, which is required in liquid crystal display devices, and have a wide viewing angle. Therefore, they are expected as next-generation display devices. .

[0003]

In a current control type display element such as an organic light emitting element, the light emission intensity of the element and the electric field applied to the element are not in a proportional relationship, and the light emission intensity of the element and the current flowing through the element. Since the densities are in a proportional relationship, variations in light emission intensity can be reduced by performing gradation display by current control with respect to variations in element film thickness and variations in input signal value.

When used in a portable information terminal or the like, low power driving is required because the capacity of the power source is limited. Generally, the period during which there is no external input (standby period) is longer than the period during key input operation or telephone call, so it is effective to devise a method of lowering the power consumption during the standby period in order to extend the drive time. It can be said that there is.

As a method therefor, there is a mode called a partial display mode in which only a part of the screen is displayed in the liquid crystal display device, and as shown in FIG. 5, a part of the rows of the display section 52 is always in a non-illuminated state. (55b), and there is a method of displaying only the minimum necessary information at the time of standby as in 55a and 55c.

Further, even a folding terminal may be provided with a small display section for indicating reception of mails in a closed state. Therefore, as shown in FIG. 6, a hole 61 is provided in place of the small display section, and the display of the display section 60 is changed to the hole 6
There is also a way to see through 1. In this case, the display unit 60 may perform partial display of only the area 60b.

As described above, partial display in the portable information terminal is an essential condition for effectively using the limited power source.

Similarly, in a display device using an organic light emitting element, considering that the non-display portion 55b is provided to reduce the power consumption, the power consumption is almost zero in the non-display state by utilizing the characteristics of the organic light emitting element. Invent a system configuration with advantages.

[0009]

In order to solve the above problems, the active matrix display device of the present invention is characterized in that the power supply voltage or the current flowing through the pixel is reduced in both the display section and the non-display section during standby. .

In a display device using an organic light emitting element,
A structure in which a reverse bias is applied to the organic light emitting device to prevent the deterioration of luminance and the driving voltage increase due to the chemical reaction of redox of organic molecules due to the injection of carriers into the organic layer and the formation of space charge, and the increase of the driving voltage is suppressed. And

Further, there is a method of turning off the backlight to reduce the power consumption when a key operation is not performed for a certain period when a portable information terminal is made in a transmissive liquid crystal display device. Similarly in the device,
After a certain period of time, the brightness is reduced to reduce the power consumption.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment of the Invention) FIG. 1 is a block diagram of a display device according to a first embodiment of the present invention.

A display area storage means 12 is provided and a display section 16 is provided.
The size and position of the display area can be changed, and the partial switching unit 13 can select the full-screen display mode or the partial display mode.

The display area storage means 12 is a controller 11
The size of the display area and the start line designated by are stored.

The output of the partial switching unit 13 is input to the source driver 15 and the gate driver 17 so as to change the horizontal scanning period according to the number of display rows, and the information of the display area is transmitted.

Further, the gate driver 17 outputs different data for the non-display line and the display line.

The display section 16 has pixels arranged in a matrix as shown in FIG. 7, for example, and each pixel has one of the pixel configurations shown in FIGS. 2, 4, 8, 10, and 12, for example. Has been done.

By keeping the transistor connected to the EL element among the transistors of each pixel in the non-display row always in a non-conducting state, a current does not flow through the EL element and a non-light emitting state can be achieved. The operation will be described below by taking five pixel configurations as an example.

In FIG. 2, a signal indicating a conductive state is applied to the gate signal line 1 (22) in one horizontal scanning period of one frame so that the same current as the current flowing through the source signal line 21 is supplied to the drive transistor 27a. To do. In the remaining period, the gate signal line 1 (22) is made non-conductive, the gate signal line 2 (23) is made conductive, and the driving transistor 27
The current flowing in a is passed through the EL element 26. Gradation control is performed by changing the value of the current flowing through the source signal line.

As shown in FIG. 5, at the time of partial display in which only a part of the screen is displayed, a current representing black may be supplied to the non-display portion by the above scanning, but the non-display portion is easily formed. In order to achieve this, in the non-display area, the gate signal line 2 (23) is made non-conductive during the entire period of one frame, and the EL element 2
It suffices that no current be passed through 6. Gate signal line 1
Similarly, (22) is also made non-conductive.

As a result, the non-conduction signal always flows through the gate signal lines 1 and 2, so that the electric power due to the charging / discharging of the stray capacitance existing in the gate signal line is lost.

When black is written in the non-display portion, the current flowing in the source signal line 11 is small in the black writing, and the apparent resistance of the drive transistor 27a becomes large, which causes parasitic capacitance of the source signal line 21. It is possible to avoid the problem that the current indicating black is not sufficiently written due to the influence of the waveform rounding due to the product, and it is possible to perform display with low brightness during black display.

Even in the luminance change due to the off-leakage current of the transistor generated in the liquid crystal display device, the current flowing through the transistor 27d in the EL element 26 is at most about several nA, which is smaller than the current value emitted by the EL element 26. Therefore, there is an advantage that the luminance does not change due to the off leak current.

In order to perform such a display, the gate driver 17 of the present invention is characterized in that it can output as shown in FIG. 3 during partial display.

In this figure, the i + 1th to jth rows are non-display rows. During this period, a non-conduction signal is sent to the gate signal lines 1 and 2, and the other display rows are sequentially scanned.

In this example, all the rows are not selected while the j + 1th row, which is the display row next to the i-th row, is not selected. Alternatively, the j + 1th row may be selected immediately.

FIG. 22 shows an example of a circuit for generating such a gate signal line. 22A shows a latch unit 227 using a transfer gate, and FIG. 22B shows a block diagram for outputting each gate signal line.

The clock cycle is the same as the length of one horizontal scanning period, and the clock A 221a and the clock B 221b are the same.
Are outputs that are inverted from each other. The enable signal 222 is high active, and a high level is input to the non-display row and a low level is input to the display row.

The selection unit 228 selects whether the gate signal line output is the output of the latch unit or the enable signal, and selects the output of the latch unit in the display row and the output based on the enable signal in the non-display row. The output based on the enable signal outputs a level at which the gate signal line 1 and the gate signal line 2 become non-conductive. With the configuration of FIG. 22B, the waveform of FIG. 3 can be realized if the number of gate signal lines existing in one pixel is the same. In the waveform of FIG. 3, the enable signal 222 is input only to the selection unit 228, and the latch unit 22
No enable signal of 7 is required. On the other hand, when scanning the j + 1th row in the horizontal scanning period next to the i-th row, the enable signal 222 of the latch section 227 is used to transfer the data to the latch section 227 of the non-display section without latching. do it.

The circuit shown in FIG. 22 is an example.
The present invention can be implemented in any circuit that can output such a waveform.

In FIG. 4, a switching transistor 47e is arranged in parallel with a switching transistor 47d for controlling the connection of a current from the drive transistor 47a to the EL element 46, and the EL element 46 is supplied from the reverse bias power supply line 48 via 47e. A pixel configuration is shown that allows application of a voltage.

When the transistor 47d is a p-type transistor, by making 47e an n-type transistor, a current flowing through the drive transistor 47a is passed to the EL element 46 when the gate signal line 2 (43) is at a low level, and a high level is obtained. Sometimes a reverse bias voltage can be applied.

When a waveform similar to that shown in FIG. 3 is applied to the gate signal line, 47d becomes non-conductive and 47e becomes conductive in the non-display row, so that the reverse bias power supply line 48 has a voltage lower than the cathode potential of the EL element 46. The reverse voltage can be applied by applying, and the life can be extended.
It should be noted that the life is extended by applying a reverse voltage in the literature (Applied Physics Letters, Vol.69, No.15, P.2160).
~ 2162, 1996).

Therefore, the use of the configuration of FIG. 4 has an advantage that the life can be extended in addition to the reduction of power and the brightness of the non-display portion in the case of the configuration of FIG.

Similar to FIG. 2, FIG. 8 changes the brightness of the EL element 86 by controlling the charge of the storage capacitor 84 by the current flowing through the source signal line 81 and controlling the current flowing through the drive transistors 87a and 87c. , A circuit for performing gradation display.

In the display row, each gate signal line 82, 8
9 and 8 are as shown in FIG. 9A. In one horizontal scanning period, a signal indicating the conductive state is output to the gate signal lines 1 and 2, and a current is supplied from the source signal line 81 to the storage capacitor 84 (selection period). . Next, in the non-conductive state, the charge stored in the storage capacitor 84 is held, a signal indicating the conductive state is output to the gate signal line 3 (88), and the EL element 86 is supplied through the transistor 87e.
Apply current to.

On the other hand, in the non-display row, a signal indicating a non-conducting state is output to the three gate signal lines as shown in FIG. 9B, the current flowing through the EL element 86 is almost eliminated, and the non-display state is set. And

Also in this method, when the non-display portion outputs the gate signal line and the black display current flows through the source signal line similarly to the display portion, the apparent resistance of the drive transistor 87a is large, and this resistance and the source signal line are large. Since the rounding of the waveform due to the product of the stray capacitance and the white signal becomes larger than that of the white signal, an incorrect value of charge is accumulated in the storage capacitor 84 without changing to a predetermined current value within one horizontal scanning period, and There is a problem that will rise.

The addition of the gate signal line 3 and the transistor 87e according to the present invention to bring the transistor 87e into a non-conducting state during non-display eliminates the above-mentioned problems and enables blackened display. Also, as in FIG.
By connecting to the anode electrode of the L element 86, a reverse bias can always be applied in the non-display row, and the effect of extending the life can be obtained.

FIG. 12 shows a case where gray scale display is performed by storing the voltage of the source signal line 121 in the storage capacitor 124 and changing the luminance of the EL element 126 by changing the current flowing through the drive transistor 127a according to the stored charge amount. 2 shows the pixel configuration of FIG. The present invention is characterized in that the switching transistor 127c is provided.

In order to form a non-display row in the conventional structure, it is necessary to store a signal voltage for displaying black in the storage capacitor 124 at least every 10 frames. For example, even if the voltage indicating black is stored in the storage capacitor 124 once and the 127b is brought into the non-conducting state, a voltage applied to the storage capacitor 124 is caused because a leak current (off leak current) flows in the transistor 127b even when the transistor 127b is not conducting. (=
This is because the gate voltage of the driving transistor 127a) changes so as to become equal to the voltage of the source signal line 121. Therefore, when a voltage indicating white is applied to the source signal line 121, the gate current of the drive transistor 127a gradually changes to a voltage value indicating white due to the leakage current of 127b, and the EL element 126 receives a current of the same gradation as white. Is caused, there arises a problem that the brightness of the non-display portion changes in accordance with the video signal of the display portion.

In the present invention, the gate signal line 2 (12
3) and the switching transistor 127c is inserted in the current path of the drive transistor 127a and the EL element 126, and the transistor 127c is made non-conducting in the non-display row so that the current value of the drive transistor 127a due to the off-leakage current of the transistor 127b. There is an effect that black display is possible without being affected by the change. FIG.
FIG. 13A shows the gate signal line waveform in the display area row, and FIG. 13B shows the gate signal line waveform in the non-display area row.

Even if an off-leakage current occurs in the transistor 127c, its value is about several nA, so that black display is possible. By adding the transistor 127c in this way, it is possible to prevent the deterioration of display quality due to the off-leakage current.

Also in this pixel structure, the switching transistor 237 and the reverse bias power supply line 238 are arranged so that the reverse voltage can be applied to the EL element 126 when the 127c is not conducting, and the reverse voltage is applied to the EL element 126. Therefore, the life can be extended. In this configuration, the transistors 237 and 127c are easily n
Although it is configured as a p-type and a p-type, they may be reversed, or both may be n-type or p-type and the inverted signal of the other may be input to the gate input of one switching transistor.

FIG. 10 shows a configuration in which the capacitor 108 is provided so that the same drain current flows so as to be corrected even if the conduction threshold voltage of the drive transistor 107a varies between pixels. The gate signal waveform shown in FIG. 11A is applied to the display row. A current flows through the EL element 106 according to the charge stored in the storage capacitor 104.

In the non-display line, as shown in FIG.
The gate signal line 3 (108) allows the transistor 107d.
By making the EL element non-conductive so that no current flows through the EL element 106, black display can be performed in the non-display portion.

Also in this pixel configuration, the transistor that operates exclusively with the transistor 107d is the EL element 1.
By providing between 06 and the reverse bias power source, a reverse voltage can be applied to the EL element 106 in the non-display row, and the life can be extended.

(Second Embodiment of the Invention) FIG. 14 shows a circuit configuration for realizing low power consumption during partial display.

Whether the source driver 146 and the gate driver 147 are caused to perform full-screen display is displayed area storage means 14
The output of the partial switching unit 144 for selecting whether to display the row stored in 3 is output to the EL power supply unit 145,
The voltage value of the EL power supply is changed between full screen display and partial display. The EL power supply unit 145 is connected to the EL power supply line connected to each pixel, and the voltage applied to the EL element is supplied from the EL power supply unit 145 via the drive transistor. Excluding the voltage drop in the drive transistor, a voltage is applied to the EL element 152 as shown in FIG. 15B, and the power supply voltage Vdd (151) is changed by changing the output of the EL power supply unit 145.

FIG. 15A shows a typical EL element current-
The luminance (153 (a)) and the current-voltage (154) characteristics. Assuming that the required brightness is up to Lw, the current flowing through the EL element 152 at that time becomes Iw from the straight line 153 (a), and the voltage applied to the EL element 152 at that time becomes Vw. Therefore, the voltage required for the power supply voltage Vdd is at least Vw, and is approximately Vdd1 in view of the margin such as variations in EL elements.

Here, if the power supply voltage Vdd is lowered to Vdd2, no brightness is generated in which the voltage applied to the EL is Vdd2 or higher, and it does not increase even if the current value is increased above a certain brightness as shown in 153 (b). In other words, the gradation near white has almost the same brightness.

Since only the minimum necessary information is often displayed during partial display, the number of display gray scales is 2 to 8, which is less than the maximum displayable gray scale of 64 gray scales. The luminance change per adjustment is large, and even if the current-luminance characteristics such as 152 (b) are obtained by adjusting Vdd2, the display is not affected. In addition, Vdd2 that does not affect the display is adjusted by adjusting the way the gradation is required during partial display.
It is possible to increase the range of. Low power driving can be realized by reducing the power supply voltage.

(Third Embodiment of the Invention) When the number of display gradations is smaller in partial display than in full-screen display, the amount of change in luminance between gradations is large. This means that even when the power supply voltage Vdd is set to Vdd2 in FIG. 15A, the number of gray scales that take a current value with a constant luminance decreases. For example, if the number of display gradations is 1/4, only 1/4 gradation has the same brightness. Therefore, as the number of colors decreases, the display deterioration due to the characteristic of the alternate long and short dash line 153 (b) decreases, so that the power supply voltage can be lowered.

Generally, each power source of a display device generates a certain reference voltage value by boosting or lowering it by several times. E
If the value of the L power supply value is an integral multiple of the reference voltage value,
The power of the entire display device can be effectively used. Therefore, if the voltage value of the power supply voltage Vdd (151) is set to one of the integer multiples of the reference power supply and a voltage with a smaller magnification than that in full screen display is used during partial display, the power supply voltage is generated. The extra power required for the EL element 152 can be reduced, and the power consumed by the EL element 152 can also be reduced.

(Fourth Embodiment of the Invention) FIG. 20 is a block diagram showing a fourth embodiment of the present invention and one pixel circuit.

The source signal line 201 has a digital-analog converter 209 and an output buffer 20 according to input data.
Through 3, the voltage value according to the data is applied. At this time, the maximum voltage value applied to the source signal line is the voltage generator 20.
It is determined by the Vref output at 4.

The Vdd output from the voltage generator 204 is applied to the EL power supply line 208.

In the partial display, since the minimum necessary information needs to be displayed with as little power as possible, the brightness in the white display may be lower than that in the full screen display.

In order to reduce the luminance, if the voltage of the EL power source line 208 is the same, it is necessary to increase the source signal line voltage. On the other hand, even if the EL power supply line 208 and Vref are lowered by the same voltage value, the same brightness can be obtained. As the brightness decreases, the voltage applied to the EL element 206 also decreases. In order to reduce the voltage of all power supplies, the reference power supply V1 input to the voltage generation unit may be decreased. The partial switching unit 200 is used as a control signal input of the reference power source.
a. If the output of the data format detecting means 200b is used, the power supply voltage can be changed according to the size and the number of colors of the display area, and the reference voltage V1 is set to be the lowest when the number of colors is small in the partial display. You can As a result, it is possible to realize a display device capable of switching between image quality priority and power priority display.

The data format detecting means 200b detects control bits or packets in the input data,
For example, if data is sent as shown in FIG. 18,
The number of colors can be identified by determining the content of 183 containing the information of the number of colors.

(Fifth Embodiment of the Invention) FIG. 16 is a block diagram showing a sixth embodiment of the present invention. The present invention is characterized by having a plurality of oscillators 161, a switching circuit 162 for selecting one output of the plurality of oscillators 161, and a frequency dividing circuit 163.

The output of the switching circuit 162 and the frequency dividing circuit 163 is controlled by the partial switching unit 167, and the oscillation frequency can be changed during the full screen display and the partial display, and the frame frequency and the horizontal scanning period can be changed. You can

By lowering the frame frequency, the charge / discharge power of each signal line can be lowered.

Further, the horizontal scanning period can be lengthened in accordance with the change in the number of display rows with the same frame frequency.
This is because the apparent resistance of the drive transistor 27a is large and the capacitance of the source signal line 21 is large in the display device having the pixel configuration of FIG. 2, especially when performing gradation display of the EL element according to the current value of the source signal line. In contrast to the fact that the time constant due to the product becomes large and it is difficult to rise within the horizontal scanning period, it is effective to lengthen the horizontal scanning period by changing the oscillation frequency according to the present invention to facilitate display of a predetermined luminance. Is.

In the pixel configuration of FIG. 8 as well, the apparent resistance value of the drive transistor 87a is high, and the effect of the present invention can be similarly obtained.

Generally, the number of display colors is smaller in partial display than in full screen display.

In this case, when the frame rate control method (FRC) is used as the gradation display method, the minimum frame frequency at which flicker-free display is possible is different between full-screen display and partial display, and 15 Hz and 409 at partial display.
It is 80 Hz in 6-color full-screen display. (Increasing the display frequency in full screen display also increases the frame frequency) In the present invention, oscillator 1 (161a) is the oscillator for full screen display, and oscillator 2 (161b) is the oscillator for partial display, By setting the optimum oscillation frequency, it is possible to reduce the frame frequency during partial display.

(Sixth Embodiment of the Invention) When gradation control is performed by the current value of the source signal line, for example, a pixel configuration as shown in FIG. 4 can be considered. The operation of the gate signal line 1 causes the same current as the current flowing through the source signal line to flow through the drive transistor 27a during one horizontal scanning period, so that the node 28A
Change the potential of. At this time, the electric charge for changing the potential of the node 28A is supplied through the drive transistor 27a. When the current flowing through the source signal line is a few μA or less, the apparent resistance value obtained from the current-voltage characteristics of the drive transistor 27a is very large. Therefore, the product of the stray capacitance increases and the time required for the change is 250 μsec. That is all. Therefore, the frame frequency is 60 at 220 lines.
There was a problem that gray scale display was not possible for the input data at Hz.

As a method for solving this, a current of X times the predetermined gradation (where X is a natural number of 2 or more) is passed,
The apparent resistance value of the drive transistor 27a is lowered to speed up the change of the source signal line current. The adjustment to the predetermined brightness is performed by adjusting the pulse width applied to the gate signal line 2 and controlling the period during which the current flows through the EL element 26. Waveforms of the source signal line and the gate signal line at this time are shown in FIG.

In the fifth embodiment of the invention in which the horizontal scanning period can be lengthened during partial display, the time required for changing the current value of the source signal line may be delayed. When the frame frequency is fixed, if the display row is half, the horizontal scanning period is approximately doubled.

If the partial display line is approximately one third or less of the full screen, even if the frame frequency is 60 Hz,
Since one horizontal scanning period is 230 μs or more, it is possible to reduce the magnification of the write current as compared with the case of displaying the entire screen. If one horizontal scanning period is 250 μs or more, it is sufficient to write data according to a predetermined current. If this method is used, the current value required for writing will decrease, and
Since the voltage applied to the EL element decreases as the value of the current flowing through the element decreases, the voltage value applied to the EL power supply line 25 can also decrease and the power consumption can be reduced. For example, when writing was performed with a predetermined current instead of writing with 10 times the current, the EL power supply voltage was reduced by about 30%, which reduced the power consumption by 30%.

(Seventh Embodiment of the Invention) FIG. 17 shows an input data processing unit and a source signal line output unit for carrying out the seventh embodiment of the present invention.

The data RAM 174 is a feature of the present invention.
The conversion table 176 allows the setting of the current value to be sent to the source signal line for the data sent from the conversion table 176 to be changed.
Data format detection means 173, partial switching section 17
That is, it can be changed by the output of 2.

For example, in the timer 175, a signal is detected when a button operation is performed on the information terminal shown in FIGS. 5 and 6, and display is performed with a predetermined brightness after the button operation, but after a certain time, the conversion table 176 is displayed. By changing the value, it is possible to change the selection method of the current source 177 with respect to the display data value so as to reduce the brightness to 10% or more and 60% or less of the predetermined brightness. As a result, when an operation is performed by the user, gradation display is performed with display priority, after a certain period of time, the brightness is decreased, and the current value is decreased to enable low power driving, and the limited power supply is effectively used. Can be used.

This method is applicable to other than portable information equipment,
It can also be used as a monitor in a power-saving mode, and since it consumes less power, it is also useful for global environment conservation.

Further, the data format detecting means 173 detects the input display data and determines the number of colors, the moving image still image and the like. For example, if data is transmitted as shown in FIG. 18, a flag unit 181 indicating the start of each packet.
Detection, header section 182, color number 183, and control signal 1
The determination can be made by detecting the value of 84.

The result determined in this way is the data RAM
174 and the conversion table 176. Data RA
In M174, based on the output of the data format detection means 173, a method of storing in the RAM is selected according to the number of colors,
It is possible to effectively use the limited capacity.

On the other hand, in the conversion table 176, the gradation-luminance characteristic can be changed according to the number of display gradations detected by the data format detecting means 173. This makes it possible to obtain optimum gradation characteristics for each display gradation.

By combining the timer 175 and the data format detecting means 173, when the number of display gradations is small, when the user looks at the display screen such as during key operation,
It is possible to change the display brightness after a fixed time. For example, in a display device capable of displaying 16 gradations as shown in FIG.
Often takes gradation. The gradation is taken in this manner during the key operation or during a fixed period after the key operation, and four gradation display of gradations 0 to 3 is performed by the timer 175 after the fixed period. By performing this operation, the maximum current value flowing through the EL element can be reduced from I15 to I3, and thus low power driving is possible. Since there is a trade-off relationship between the brightness and the power, the method of taking four gradations may be changed according to the power and the required brightness.

In addition to the method for reducing the power consumption, the current source 177 is used.
It is also possible to reduce each current value of. A timer 175 and a data format detecting means 173 are used as a determining means for reducing the current value. In this case, the maximum brightness can be reduced regardless of the number of display gradations, and thus the power consumption can be reduced.

(Embodiment 8) In the configuration of FIG. 17, by sending the output of the partial switching unit 172 to the source driver and the gate driver as shown in FIG. 1 and also to the data RAM 174 and the conversion table 176, It is possible to effectively utilize the data RAM 174 area at the time of display. For example, assuming that the data RAM 174 can store data for one screen, data for a plurality of screens can be stored in partial display in accordance with the display ratio with respect to the entire screen. As a result, it is not necessary to transfer the display data to the data RAM 174 from the outside, and the power consumption can be reduced.

Also in the conversion table 176, since the number of display gray scales is the same in the full screen display and the partial display, the current source 177 to be selected can be changed for the same gray scale data. Image quality priority when displaying full screen,
It is possible to make a setting such that power is preferentially displayed during partial display.

Although not shown in FIG. 17, external adjusting means is provided to set the time of the timer 175 and the conversion table 176.
The setting of may be adjustable from the outside.

(Ninth Embodiment of the Invention) FIG. 26 is a diagram showing a ninth embodiment of the present invention.

The difference from FIG. 2 is that, as shown in FIG. 26A, a transistor 2 for applying a reverse bias voltage is applied between the switching transistor of the pixel structure of the current copier and the EL element.
67e is provided so that a reverse voltage can be applied to the EL element 266.

The operation of the circuit shown in FIG. 26A will be described.

In the row of the display area, the gate signal line 1 (261) is generated once per frame as shown in FIG.
Thus, the transistors 267b and 267c are turned on (first period).

At this time, the gate signal line 2 (262) makes the transistor 267d non-conductive, and the source signal line 2
The current flowing through 60 flows through the driving transistor 267a. The storage capacitor 264 is the drive transistor 267 at this time.
A charge corresponding to the gate potential of a is accumulated. The potential of the anode electrode of the EL element 266 is higher than the cathode potential. Therefore, whether the transistor 267e is on or off is determined by the potential of the reverse bias signal line 269.

The reverse bias power supply Va (268) has the purpose of extending the life of the EL element and preventing the terminal voltage from rising.
The voltage needs to be lower than the anode potential of the EL element 266 by a value of 5 V or more and 15 V or less. EL element 266
It is desirable to apply a reverse voltage equal to or higher than the driving voltage at the time of light emission. Therefore, in FIG. 26, approximately -15V or more and -5V
Take the following voltage values. Therefore, the reverse bias control line 259
Thus, when the reverse bias voltage Va is applied to the reverse bias signal line 269, the transistor 267e becomes conductive, and the reverse bias voltage is applied to the EL element 266.

On the other hand, a voltage above the gate signal line 263 of the transistor 267e is applied to the voltage value of the gate-off power supply Vb (258). The applied voltage value is the transistor 267.
Depending on the threshold voltage of e, a voltage of 0V or more and 3V or less may be applied. In particular, when 0V is applied, it is not necessary to newly create a power source, so that the circuit configuration can be simplified. As a result, the gate-off voltage Vb is applied to the reverse bias signal line 269.
Is applied, the transistor 267e becomes non-conductive.

Since the transistor 267d is in a non-conducting state during the first period, a current does not flow through the EL element 266 and no light is emitted. Therefore, as shown in FIG. The potential of 269 may be either Va or Vb. In order to prolong the life and prevent the terminal voltage from rising, it is desirable to apply the potential Va of the reverse bias power source 268 to the reverse bias signal line 269.

When a predetermined charge is accumulated in the storage capacitor 264 and the first period ends, the gate signal line 1 (261) and the gate signal line 2 (262) are set as shown in the second period of FIG. 26 (b). The potentials of the transistors 267b and 267c are turned off and the transistor 267d is turned on.

As a result, a current is supplied from the EL power source 265 according to the gate voltage of the driving transistor 267a, and E
The L element 266 lights up.

At this time, if the current flowing through the transistor 267a and the current flowing through the EL element 266 are not substantially equal to each other, the brightness is lowered. Therefore, the transistor 267e must be non-conductive. Since the anode potential of the EL element 266 is higher than the gate potential of the transistor 267e, if the potential of the reverse bias signal line 269 is made equal to the gate-off power source Vb (258), the transistor 267 will be generated.
It is possible to make e non-conductive. Therefore the second
The potential of the reverse bias signal line 269 in the period is Vb.

By setting one frame by the first period and the second period, the EL at the time of lighting and non-lighting with a predetermined brightness is obtained.
Reverse bias voltage application to the element 266 can be realized.

On the other hand, in the row of the non-lighted area, since the black display is performed, the gate signal line 2 (262) keeps the transistor 267d non-conductive at all times. As a result, since it is not necessary to store the charge corresponding to black display in the storage capacitor 264, it is not necessary to take in the black display current from the source signal line, and the gate signal line 1 (261) is always non-conductive. Reverse bias power supply Va (268) is applied to the reverse bias signal line 269.
Is applied, the transistor 267e becomes conductive, and the reverse bias voltage Va is applied to the EL element 266.

As a result, the predetermined current value flows only during the lighting period of the EL element 266 in the display area, and the reverse bias voltage is applied during the non-lighting period.

As an advantage of the pixel configuration shown in FIG. 26A, since the potential of the gate signal line 3 (263) is always constant, the source signal line or the like is not affected by noise due to coupling, and the gate is not affected. Since the potential of the signal line 3 (263) is the same as the cathode electrode of the EL element 266, the gate signal line 3 (263) and the cathode electrode of the EL element 266 are connected using a through hole or the like for each pixel. By eliminating the lead line to the outside of the pixel as shown by 32, the number of output terminals of the gate driver 328 is reduced,
The frame can be made smaller. Since the maximum voltage applied to each transistor 267 in the pixel is 10 V to 12 V, it is possible to use a transistor having a low breakdown voltage.

Further, when the reverse bias voltage is applied to a plurality of lines at the same time, the number of the reverse bias control lines 259 and the reverse bias signal lines 269 can be reduced by increasing the number of simultaneously selected lines. Can be reduced. When the reverse bias is applied simultaneously to all pixels within the blanking period within one frame, only one reverse bias control line 259 and reverse bias signal line 269 are required.

By controlling the conduction / non-conduction state of the transistor 267e not by changing the voltage of the gate signal line 3 (263) but by changing the potential of the source or drain electrode, the gate signal line 1 (26
1) and a voltage different from the gate voltage of the gate signal line 2 (262) was required. By changing the voltage value of the gate signal line 3 (263) from the on / off binary value to a constant one value, it is necessary for the gate driver 328. It was possible to reduce the number of voltage values. Further, by setting the potential of the gate signal line 3 (263) to a voltage value equal to the cathode potential, the number of voltage sources can be further reduced.

Of the four transistors 267a to 267d forming the current copier, if at least the transistor 267a controlling the current supplied from the EL power source 265 is an n-type transistor, a transistor 267 for determining whether to apply a reverse bias is selected. FIG. 27
A p-type transistor 267j may be used as shown in FIG.

This is because the direction of the current flowing in the pixel is changed by changing the driving transistor from the p-type to the n-type, and the current is passed through the EL element 266 and the EL element 266 to which the transistor for determining the reverse bias application is connected. This is because the light emitting potential of the EL element 266 and the non-light emitting potential of the EL element 266 are inverted at the contact point 257 between the transistors for determining whether or not to do so.

When the p-type driving transistor 267a is used, the potential of the contact 257 becomes (when light is emitted)> (when not emitting light), and when the n-type drive transistor 267i is used, the contact 257.
The potential of is (when not emitting light)> (when emitting light). The transistor that determines the application of the reverse bias needs to be conductive when not emitting light and non-conducting when emitting light. Gate signal line 3 (2
63), if the voltage value of 63) is kept constant and the source or drain voltage is changed, the p-type driving transistor 267a is in a non-conducting state when light emission (source or drain voltage)> (gate voltage) and a non-light emission state. Since (gate voltage)> (source or drain voltage) needs to be conductive, the n-type transistor 267e is used, and the n-type drive transistor 267f is non-conductive when emitting light (gate voltage)> (source or drain voltage). , (Source or drain voltage)> (gate voltage) at the time of non-light emission, the p-type transistor 267j is used.

The potential of the gate signal line 3 (263) of the transistor 267j is lower than that of the reverse bias power source Vc (268) (about 6V to 15V) and is equal to or higher than the voltage value lowered in the EL element 266 from the EL power source 265. Any value is acceptable, but use the gate signal line 3 (263) as the EL power source 2
Since it is possible to reduce the number of signal lines drawn to the outside of the pixel by connecting to 65, it is desirable to connect to the EL power supply line 265. At this time, the gate-off power supply Vd (25
8) may be equal to or lower than the same potential as the EL power source 265 and may be equal to or higher than the potential obtained by reducing the same potential by about 3V. The reverse bias power source Vc (268) may output a voltage higher than the EL power source 265 by 5 V or more and 15 V or less. Desirably, the voltage value applied in the opposite direction is larger than the voltage value applied to the EL element 266 during light emission.

FIG. 27 shows drive waveforms in rows of the display area.
FIG. 27 shows the drive waveform in the row of the non-display area in FIG.
It shows in (c).

By thus fixing the gate potential of the switching element for applying the reverse bias and controlling the reverse bias voltage, it is possible to control whether the switching element is turned on or off to apply the reverse bias to the EL element 266. The determination method is not limited to the current copier type pixel configuration shown in FIGS. 26 and 27, but also the current mirror type pixel configuration as shown in FIG. 30 (a) and the source signal as shown in FIG. 31 (a). Depending on the voltage value of the line 260, the transistor 26
It is also possible to implement a pixel configuration in which the current flowing through 7a is controlled to perform gradation display.

In the pixel configuration of FIG. 30A, in the row of the display area, the transistors 267d and 267b are turned on once per frame as shown in FIG. 30B, and the current of the source signal line 260 is set to the transistor 267a.
Shed on. The gate potential of the transistor 267a changes according to the drain current value, so that the same current as the source signal line current flows through the drain of the transistor 267c whose gate electrode is a common line.

At this time, the gate signal line G3 (303) may be at a high level or a low level, but it has a long life and E
In order to prevent the rise of the L terminal voltage, the transistor 267g is set to a high level to make it non-conductive, and the reverse bias power supply Va (268) lower than the cathode potential of the EL element 266 is applied to the reverse bias signal line 269, whereby the transistor 267e. Since the source or drain potential is sufficiently lower than the gate potential of 267e, 267e becomes conductive.
A reverse bias voltage is applied to L element 266.

When the row selection period ends, the gate signal line G1
(301) and the gate signal line G2 (302) are operated to make the transistors 267b and 267d non-conductive.
A current flows through the transistor 267c in accordance with the electric charge stored in the storage capacitor 264 during the row selection period. The current value at this time is approximately equal to the current value flowing through the source signal line 260 during the row selection period. A predetermined luminance is displayed by turning on the transistor 267g and passing a current through the EL element 266. At this time, in order to make the transistor 267e non-conductive, the gate signal line G4 (3
04) Apply the above potential. For this purpose, the reverse bias control line 259 is operated and the gate-off power source Vb
(258) is selected and the value of Vb is set to a value of 0V or more and 3V or less.

As a result, the current flowing through the transistor 267c leaks through the transistor 267e,
It is possible to avoid the problem that the brightness decreases due to the decrease in the current flowing through the EL element 266.

On the other hand, in the row of the non-display area, as shown in FIG. 30C, the transistor 267g is made non-conductive by the gate signal line G3 (303) to cut off the forward current of the EL element 266. At the same time, in order to apply the reverse bias, the reverse bias power supply Va (268) is output to the reverse bias signal line 269 to make the transistor 267e conductive, and the reverse bias voltage is applied to the EL element 266.

FIG. 31A shows a pixel configuration in which the drain current of the drive transistor 267a is controlled according to the voltage value of the source signal line to control the brightness of the EL element 266.

In the row of the display area, the voltage of the source signal line is taken into the pixel once per frame as shown in FIG. 31 (b). A signal for turning on the transistor 267d is applied to the gate signal line G2 (312), and a current flows through the EL element 266 to output a predetermined luminance. At this time, the reverse bias signal line 269 is connected to the gate-off power source Vb (2
58) is applied to turn off the transistor 267e.

In the row of the non-display area, as shown in FIG. 31C, by applying a signal for turning off the transistor to the gate signal line G1 (311) and the gate signal line G2 (312), the EL element Prevent forward current from flowing through 266. Further, in order to apply a reverse bias, the reverse bias power supply Va (268) is connected to the reverse bias signal line 269.
By applying, the transistor 267e becomes conductive and a reverse bias is applied to the EL element 266.

The voltage of the gate-off power supply Vb (258) is higher than the gate voltage value of the transistor 267e (0 V).
The voltage of the reverse bias power supply Va is E
Since the absolute value is preferably higher than the forward voltage applied to the L element 266, a voltage lower than the cathode potential of the EL element 266 in the range of 5 V to 15 V may be applied. This is common regardless of the pixel configuration when controlling the current value flowing in the EL element 266 by the p-type transistor.

Also in FIGS. 30 and 31, the transistors 267a and 267c can be realized as n-type transistors. At this time, similarly to FIG. 27, the transistor 267e that determines whether to apply the reverse bias voltage is a p-type transistor, and the connection direction of the EL element 266 and the power supply voltage are changed in accordance with the reverse current flow direction. Can be realized with. The inside of the dotted line in FIG. 27 may be changed to a current mirror type circuit and a circuit for performing gradation control according to the source voltage.

In the above invention, the switching transistors 267b, 267c, 267d, 267g, and 26 are provided.
7h and 267i can be p-type transistors or n-type transistors and reverse bias can be applied in either case. Inverting the polarity of the gate signal line,
This is because the change of the voltage value is only required to be adjusted, and since the potential of the node 257 and the values of the EL power source 265 and the reverse bias power source 268 do not change, the operation of 267e or 267j does not change. is there.

(Tenth Embodiment of the Invention) FIG. 28A shows a circuit configuration for realizing a tenth embodiment of the present invention. The difference from the ninth embodiment is that the reverse bias signal line 269 can be in a high impedance state, and the potential of the gate signal line G3 (263) changes between when the reverse bias is applied and when it is not applied.

In the row of the display area, as shown in FIG. 28B, the current flowing through the source signal line 260 is taken into the pixel in order to flow the current value corresponding to the display gradation to the EL element 266 once per frame. . At this time, the transistors 267b and 267c are turned on, the transistor 267d is turned off, and the same current as the current flowing through the source signal line 260 is passed through the driving transistor 267a. At this time, the EL element 266 is in a non-light emitting state, so that a reverse bias voltage is applied. The reverse bias power supply Va (268) is applied to the reverse bias signal line 269 to apply the gate signal line 3 (263).
Is set to a potential higher than Va to make the transistor 267e conductive and a reverse bias is applied. As with the case of FIG. 26, the value of the reverse bias power supply Va may be set to a value that is effective for extending the life and preventing the terminal voltage from rising depending on the EL element.

When the transistor 267d is turned on, E
The transistor 267e needs to be in a non-conducting state while the L element 266 is outputting a predetermined luminance. Therefore, the gate signal line G3 (263) is made lower than the source / drain voltage. Here, by operating the reverse bias control line 259 to disconnect the reverse bias signal line 269 from the reverse bias power source 268, the source / drain voltage rises, and the voltage value applied to the gate signal line G3 (263) can be increased. . The reverse bias power supply 26 is connected to the reverse bias signal line 269.
Compared with the case where 8 is applied (about -15V), the high impedance state can be set to 0V to about 3V. Therefore, the breakdown voltage of the transistor can be designed low.

In the row of the non-display area, as shown in FIG. 28C, the reverse bias voltage 268 is applied to the reverse bias signal line 269.
Then, a voltage higher than the reverse bias voltage is applied to the gate signal line 3 (263) to make 267e conductive and a reverse bias is applied to the EL element 266. At this time, the transistor 267d is provided to cut off the current from the EL power source 265.
Must be in a non-conducting state.

Note that this structure has a driving transistor 267a.
Can be realized in the same way even if is an n channel. Since the power supply voltage is changed and the direction of the current is changed, it is only necessary to reverse the connection direction of the EL element 266.

Further, as described above, the gate signal line G3 (26
The method of changing the potential of 3) is advantageous in that a transistor having the same carrier transport as that of the driving transistor can be used as a transistor for selecting whether to apply a reverse bias, which is advantageous because the film forming process can be simplified. is there. The circuit configuration at this time is shown in FIG.

The waveforms of the gate signal line G1 (261) and the gate signal line G2 (262) are similar to those of the pixel configuration of FIG. Since the transistor 267f connected to the reverse bias signal line 269 is a p-type transistor, the signal polarity of the gate signal line G3 (263) is only inverted. The potential of the gate signal line G3 (263) is higher than that of the source or drain electrode when the transistor 267f is non-conducting (the driving voltage of the EL element 266 or more, the driving voltage +
3 V or less), a potential lower than that of the source or drain electrode when the transistor 267f is conductive (value lower than the voltage value Va of the reverse bias power supply 268 by about 5 V to 15 V).
Is applied. It can be realized as in FIG. 28 except that the signal polarity and voltage value of the gate signal line G3 (263) are different. The same applies to FIG. 29C showing the waveform of the row in the non-display area.

Further, not only the pixel structure of the current copier, but also the method of performing the gradation display by the current mirror or the source signal line voltage can be similarly realized.

Not only the p-type driving transistor but also the n-type driving transistor can be realized.

In any of the embodiments of the present invention, the source driver 71 and the gate driver 70 shown in FIG. 7 may be formed on the glass substrate of the display device by using low temperature polysilicon. Alternatively, the source driver 71 and the gate driver may be formed as a semiconductor circuit and combined with the display panel. Alternatively, one driver may be formed of low-temperature polysilicon on a glass substrate of a display device, the other driver may be formed as a semiconductor circuit, and combined with a display panel.

The driver IC may be mounted in one direction as shown in FIG. Such mounting is advantageous in that the display section can be arranged symmetrically with respect to the device, as compared with placing in the two directions of XY in the portable information terminal shown in FIG. 5 or 6.

In this example, a P-channel switching element has been described as an example of the switching element.
The same can be realized by an N-channel switching element or a combination thereof. For example, in the case of the pixel configuration shown in FIG. 2, when the voltage value applied to the gate signal line 1 (22) and the gate signal line 2 (23) is an N-channel switching element, P-channel switching is considered at the logic level. It suffices to input an inverted signal of the signal of the element, the current flowing through the source signal line 21 is reversed in the flowing direction, and the voltage supplied from the EL power supply line 25 is set to the lowest potential in the pixel circuit. This is shown in FIG.
The waveform of the gate signal line in the non-display row is shown in FIG.
It shows in (b). In addition, FIG. 8, FIG. 10, and FIG. 1 other than FIG.
The configuration of 2 can also be realized by using an N-channel transistor.

Although the transistor used as the switching element in the present invention has been described by taking the thin film transistor as an example, it is not limited to the thin film transistor, and the varistor, the thyristor, the ring diode, the thin film diode (TFD,
The same effect can be obtained by using MIM).

Although the EL element has been described as the display element, an organic electroluminescent element, an inorganic electroluminescent element, a light emitting diode or the like may be used.

[0133]

As described above, according to the present invention, the current cutoff means is provided between the drive transistor for adjusting the current from the EL power source line and the EL element, and the luminance of the non-display portion is improved against the current change of the drive transistor. It is now possible to display black without writing black on non-displayed lines. As a result, crosstalk in the non-display part could be prevented.

Further, since the reverse voltage can be applied to the EL element while the current path between the drive transistor and the EL element is cut off, the life can be extended.

When the number of display colors is small, the gradation is changed or the power supply voltage is lowered to reduce the power consumption, and the brightness is lowered after a certain period by a timer, or a plurality of oscillators are mounted. The power consumption can be reduced by changing the driving frequency by using different oscillators depending on the display color and display area.

According to the present invention, it is possible to prevent an increase in black luminance of the non-display portion, to prolong the life and to reduce the power consumption.

[Brief description of drawings]

FIG. 1 is a diagram showing a control signal block necessary for switching a full screen or a partial display according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a pixel configuration applicable to the present invention.

FIG. 3 is a diagram showing waveforms of gate signal lines when partial display is performed using the pixel configuration shown in FIG. 2 and the embodiment of the present invention.

FIG. 4 is a diagram showing an example of a pixel configuration capable of applying a reverse bias to an EL element.

FIG. 5 is a diagram showing an example of applying partial display in a mobile information terminal.

FIG. 6 is a diagram showing an example of performing partial display on a foldable portable information terminal.

FIG. 7 is a diagram showing a configuration of a display device of the present invention.

FIG. 8 is a diagram showing a pixel configuration for implementing the present invention in a current mirror pixel configuration.

FIG. 9 is a diagram showing waveforms of gate signal lines in a display row and a non-display row in a current mirror pixel configuration.

FIG. 10 is a diagram showing an example of a pixel configuration in which a gradation control is performed by a source signal line voltage and a function of correcting variation in threshold voltage of a driving transistor is included.

11 is a diagram showing gate signal line waveforms of a display row and a non-display row according to the embodiment of the present invention in the circuit configuration of FIG.

FIG. 12 is a diagram showing an example in which a current disconnecting unit is provided between a drive transistor and an EL element in the case of a pixel configuration in which gradation control is performed by a source signal line voltage.

13 is a diagram showing a gate signal line waveform in the case of the pixel configuration of FIG. 12 using the embodiment of the present invention.

FIG. 14 is a block diagram for enabling the EL power supply voltage to be changed according to the size of the display area.

FIG. 15 is a diagram showing current-voltage-luminance characteristics of EL elements.

FIG. 16 is a block diagram in which the oscillation frequency is variable, which is one of the embodiments of the present invention.

FIG. 17 is a diagram in which different current outputs can be selected for the same input data depending on the number of gradations, the size of the display area, and the time.

FIG. 18 is a diagram showing an example of a display data input format.

FIG. 19 is a diagram showing the relationship between gradation and current value.

FIG. 20 is a diagram showing a relationship among a reference voltage, a voltage generator, a voltage output, a source signal line, and a pixel.

FIG. 21 is a diagram showing application patterns of source and gate signal lines during full-screen display and partial display in Embodiment 6.

FIG. 22 is a block diagram of an example for realizing the gate signal line generation unit according to the embodiment of the present invention.

FIG. 23 is a diagram showing a pixel configuration in which a reverse voltage can be applied to an EL element when gradation display is performed according to a voltage flowing in a source signal line.

FIG. 24 is a diagram in the case of being configured with an n-channel transistor.

FIG. 25 is a diagram showing an example in which a driving semiconductor circuit is arranged in a display device.

FIG. 26 is a diagram showing a pixel configuration and a drive waveform when a p-type drive transistor according to a ninth embodiment of the present invention is used.

FIG. 27 is a diagram showing a pixel configuration and a drive waveform when an n-type drive transistor according to a ninth embodiment of the present invention is used.

FIG. 28 is a diagram showing a reverse bias applying circuit using an n-type transistor and a driving waveform in the tenth embodiment of the invention.

FIG. 29 is a diagram showing a reverse bias applying circuit using a p-type transistor and a drive waveform in the tenth embodiment of the invention.

FIG. 30 is a diagram showing a current mirror type pixel configuration and drive waveforms according to a ninth embodiment of the present invention.

FIG. 31 is a diagram showing a circuit and a driving waveform when a pixel configuration in which a current is controlled according to a source signal line voltage value in a ninth embodiment of the invention is used.

FIG. 32 is a diagram showing a configuration of a display device according to a ninth embodiment of the present invention.

[Explanation of symbols]

11 Controller 12 display area storage means 13 Partial switching unit 14 Data RAM 15 Source driver 16 Display 17 Gate driver 21 Source signal line 22 Gate signal line 1 23 Gate signal line 2 24 storage capacity 25 EL power line 26 EL element 27 transistors 28 nodes 258 Gate-off power supply 259 reverse bias power supply 260 source signal line 261 Gate signal line 1 262 Gate signal line 2 263 Gate signal line 3 264 storage capacity 265 EL power line 266 EL element 267 thin film transistor 268 reverse bias power supply 269 Reverse bias signal line

Claims (4)

[Claims] 1. A display device using an organic EL element, comprising: a reverse bias transistor that forms a voltage path for applying a voltage in a direction opposite to the direction of light emission to the organic EL element; A reverse bias signal line connected through the reverse bias transistor, a plurality of voltage sources, and a voltage selection unit that selects one of the plurality of voltage sources and outputs the selected voltage source to the reverse bias signal line, A switching operation of the reverse bias transistor is performed by always applying a constant voltage value to the gate signal line of the reverse bias transistor and changing the voltage of the reverse bias signal line by operating the voltage selection unit. And a display device using an organic EL element. 2. A method of driving a display device using an organic EL element, wherein a reverse bias transistor forms a voltage path for applying a voltage in a direction opposite to a direction of light emission to the organic EL element, The reverse bias transistor is conductive when a voltage of a reverse bias power supply for applying a reverse voltage to the EL element is applied to the source or drain electrode of the reverse bias transistor on the gate signal line of the bias transistor. And a voltage value such that the reverse bias transistor becomes non-conductive when a voltage different from the voltage of the reverse bias power supply is applied to the source or drain electrode of the reverse bias transistor. A method for driving a display device using an organic EL element, comprising: 3. A display device using an organic EL element, comprising: a reverse bias transistor that forms a voltage path for applying a voltage in a direction opposite to the direction of light emission to the organic EL element; A reverse bias signal line connected via the reverse bias transistor; a voltage source for applying a reverse bias voltage; and a switch between the voltage source and the reverse bias signal line. The switch is conductive during the period when the transistor is conductive and the voltage source is applied to the organic EL element, and when the reverse bias transistor is non-conductive, the switch is non-conductive and the reverse bias signal is applied. A display device using an organic EL element, wherein the line is in a high impedance state. 4. A mobile information terminal comprising the display device according to claim 1 or 3, a demodulation section, an antenna, and a button.