JP2003228324A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the variation in light emission luminance of optical elements in respective pixels in a matrix type display device. <P>SOLUTION: The display device 10 includes series in which optical elements 18, 20 or 22 are connected respectively to their driving elements Tr2, Tr4 or Tr6 and power source circuits 24, 26 of 28 which set variably voltages of both ends of the series. Then, voltages of the both ends of respective series are set in accordance with thresholds of the voltages required for light emission of respective optical elements 18, 20 or 22. Moreover, a variable power source circuit is provided individually for every color as to optical elements emitting rays of light having different colors. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device, and more particularly to a technique for improving the variation in luminance of pixels of an active matrix type display device.

[0002]

2. Description of the Related Art In recent years, organic ELs functioning as light emitting devices
(OLED: Organic Light Emitt
ing diode) is used for display devices such as CRT and L
It is drawing attention as a display device that replaces the CD. For example,
As an element for driving an OLED, a thin film transistor (Th
in Film Transistor: Hereinafter, simply T
Research and development of display devices including FT) have been actively promoted. The OLED includes a passive type and an active type. In the active type OLED, a switching TFT is arranged in each pixel of the display to hold luminance data and can be turned on even when the luminance data is not written.

Further, the development of a full-color display using OLED is being actively pursued. Full colorization of the OLED is realized by adding a dye-doped material to the light emitting material of the optical element.

FIG. 6 is a circuit diagram showing some pixels of an active type OLED display. This OLED display includes a plurality of pixels 11 each including optical elements OLED (R) 116, OLED (G) 118, and OLED (B) 120, which are OLEDs that emit different colors.
It is composed of 0, 112 and 114. The plurality of pixels 110, 112 and 114 are arranged in a matrix.

Each pixel 110, 112 and 114 has a T
FT transistor Tr10 and transistor T
Includes r20 and capacitor C. Transistor Tr
10 is for switching, and the transistor Tr20 is for driving to drive each optical element OLED.

First, the structure of the pixel 110 will be described. In the transistor Tr10, the gate electrode is the scanning line 130.
, The source electrode (or drain electrode) is connected to the data line 132, and the drain electrode (or source electrode) is connected to the gate electrode of the transistor Tr20 and one electrode of the capacitor C. The other electrode of the capacitor C is connected to the source electrode of the transistor Tr20. The data line 132 is connected to a constant voltage source (not shown),
It transmits the brightness data that determines the current flowing through the OLED (R) 116.

In the transistor Tr20, the source electrode is connected to the anode of the OLED (R) 116, and the drain electrode is connected to the power supply line 134. The power supply line 134 is connected to a power supply 140 provided outside the pixel region, and a voltage for actually causing the OLED (R) 116 to emit light is applied.

OLED (R) 116 includes a light emitting device layer sandwiched between an anode and a cathode. OLED
The anode of the (R) 116 is connected to the source electrode of the transistor Tr2, and the cathode is grounded.

The configuration of pixels 112 and 114 is pixel 1
An OL that emits a color different from that of the 10 OLED (R) 116
Pixel 11 is the same as pixel 110 except that it includes ED (G) 118 and OLED (B) 120.
The description of the configurations of 2 and 114 is omitted. OLED
(G) 118 and OLED (B) 120 are also OLED
Similar to (R) 116, it includes a light emitting element layer sandwiched between an anode and a cathode.

The operation of the OLED display having the above configuration will be described. First, the scanning line 130 is set to high to make the transistor Tr10 conductive, and then a data potential is applied to the data line 132. At this time, the potential of the electrode of the capacitor C rises. At the same time, the potential of the gate electrode of the transistor Tr20 changes to the same as the potential of the electrode of the capacitor C.

When the potential of the gate electrode of the transistor Tr20 exceeds a predetermined value, a current corresponding to the voltage is supplied from the power supply line 134 to the OLED (R) 116 and OLED (G) 11.
8 and OLED (B) 120, and each OLED emits light. Even if the scan line 130 is set to low, the transistor T
Since the gate potential of r20 is held by the capacitor C, the OLED (R) 116, the OLED (G) 118, and the OLED (B) 120 emit light with brightness according to the data potential applied to the gate electrode of the transistor Tr20. Continue.

[0012]

[Problems to be Solved by the Invention] However, color OLE
In the D display, red (R), green (G),
Since the light emitting element layers of the OLED that emits blue light and blue (B) are formed of different materials, variations in characteristics occur.

Therefore, when taking the white balance,
The data potential required to generate an appropriate luminance differs depending on the characteristics of the light emitting element layer of each color. Also, even if the same color,
The characteristics may change over time. Due to such a difference in characteristics, variations in luminance such as chromaticity deviation and white balance variation occur.

The present invention has been made in view of the above problems, and an object thereof is to provide a technique for improving a variation in brightness caused by a difference in characteristics of optical elements in a display device.

An object of the present invention is to facilitate white balance adjustment in a display device. Further, another object of the present invention is to easily absorb the influence of aging of the display device. Furthermore, another object of the present invention is to reduce the power consumption of the display device.

[0016]

One aspect of the present invention relates to a display device. This device comprises a current-driven optical element,
And a power supply circuit that variably sets the voltage across the optical element.

The power supply circuit may set the both-end voltage according to the threshold value of the voltage required for the light emission of the optical element.

The optical elements may be classified into a plurality of types according to the color of light emitted, and the power supply circuit may be provided individually for the plurality of types. The power supply circuit may set the voltage between both ends according to the light emission characteristics of the optical element for each color. Here, the light emission characteristic means that even if the same data potential is applied, it looks bright or dark depending on the color emitted by the optical element. That is, it means that the data potential required to emit light of a desired brightness differs depending on the color.

Another aspect of the present invention relates to a display device. This device includes a system to which an optical element and its driving element are connected, and a power supply circuit that variably sets a voltage across the system. Here, the power supply circuits may be provided at both ends of the system, but may be provided at only one end. Further, for example, a fixed power supply circuit that sets a fixed voltage may be provided at one end of the system, and a variable power supply circuit may be provided at the other end.

The power supply circuit may set the both-end voltage according to the threshold value of the voltage required for the light emission of the optical element. The power supply circuit may variably set the voltage across the optical element.

The optical elements may be classified into a plurality of types according to the color of light emitted, and the power supply circuit may be provided individually for the plurality of types. The power supply circuit may set the voltage between both ends according to the light emission characteristics of the optical element for each color.

Another aspect of the present invention also relates to a display device. This apparatus includes a first system to which a first optical element and its driving element are connected, a second system to which a second optical element and its driving element are connected, a first system and a first system. And a power supply circuit for setting a voltage between both ends of the second system, the power supply circuit taking into account a difference in voltage required for the first optical element and the second optical element to emit light of desired brightness. Then, the voltage between both ends of at least one of the first system and the second system is variably set.

The driving element may include a thin film transistor, and the power supply circuit may be provided on the drain electrode side of the transistor. If a power supply circuit that variably sets the voltage between both ends is provided on the drain electrode side, the voltage applied to the optical element can be made variable while keeping the source-drain voltage constant. As a result, the voltage applied to the optical element can be set to a desired value while keeping the source-gate voltage at a predetermined value, and it is not necessary to reset the data potential.

It is to be noted that any combination of the above constituent elements and the expression of the present invention converted between methods, devices, systems, etc. are also effective as an aspect of the present invention.

[0025]

FIG. 1 shows a circuit diagram of two pixels each including, for example, OLEDs (A) and OLEDs (B) that emit different colors. Each pixel further includes a transistor Tr1 for switching and a transistor Tr2 for driving the OLED.

FIG. 2 is a schematic diagram showing the characteristics of the OLED in the circuit having the configuration shown in FIG. In FIG. 2, the gate-source voltage of the transistor Tr2 is Vg on the right side.
The relationship between the source-drain voltage Vsd and the drain current Id at s ₂ is shown on the left side in OLED (A) and OLE.
Voltage Vel across D (B) and current Iel flowing through them
Shows the relationship.

[0027] Here, considering the case where the transistor Tr2 operates in the saturation region, as shown in FIG. 2, the drain current Id = Id ₂ of the transistor Tr2. At this time, since a current of Iel = Id ₂ also flows through the OLED (A) and the OLED (B), the OLED (A)
And the voltage Vel across the OLED (B) is V
el ₂ (A) and Vel ₂ (B).

Assuming that a voltage Vdd is applied to each pixel from the power supply, the source-drain voltage of the transistor Tr2 is Vdd to the voltage Vel across the OLED (A).
₂ (A) and OLED (B) both ends voltage Vel
₂ (B) is subtracted. OLED of FIG.
From the characteristics of (A) and OLED (B), OLED
Since the voltage Vel ₂ (A) at both ends of (A) is larger than the voltage Vel ₂ (B) at both ends of OLED (B),
The source-drain voltage Vsd (A) of the transistor Tr2 connected to (A) is the source-drain voltage Vsd of the transistor Tr2 connected to the OLED (B).
It is smaller than (B). That is, in the entire OLED display, in order to operate the transistor Tr2 in the saturation region, it is necessary to set the voltage Vdd applied from the power supply in accordance with the pixel including the OLED having the largest power consumption. Therefore, the OLED display as a whole consumes more power than necessary.

Further, depending on the material of the light emitting element layer, the OLED
Since the voltage Vel at both ends of the
The source-drain voltage Vsd also changes. Even when the transistor Tr2 is operating in the saturation region, a slight variation occurs in the drain current Id due to the variation in the source-drain voltage Vsd, resulting in variation in brightness.

Therefore, in the following embodiments, the above problem is solved by variably setting the power supply voltage applied to each pixel in consideration of the difference in the voltage Vel across the OLEDs of the optical elements having different characteristics. It is a thing.

In the following embodiments, an active type organic EL display will be described as a display device. This display is a matrix type including a plurality of pixels. Each pixel includes an optical element that is an OLED that functions as a light emitting element inside.

First Embodiment: FIG. 3 is a circuit diagram showing some pixels of the display device according to the first embodiment of the present invention. In the present embodiment, the display device 10 includes a first pixel 12, a second pixel 14 and a third pixel 16.

The first pixel 12 includes a first transistor T
r1, second transistor Tr2, first capacitor C
1, a first OLED (R) 18 and a first variable power supply (R) 24. Here, the first OLED (R) 18
Is a red (R) light emitting element. The second pixel 14 includes a third transistor Tr3, a fourth transistor Tr4,
It includes a second capacitor C2, a second OLED (G) 20 and a second variable power supply (G) 26. Where the second O
The LED (G) 20 is a green (G) light emitting element. Third
The pixel 16 includes a fifth transistor Tr5, a sixth transistor Tr6, a third capacitor C3, and a third OLE.
It includes a D (B) 22 and a third variable power source (B) 28.
Here, the third OLED (B) 22 is a blue (B) light emitting element.

The first transistor Tr1, the third transistor Tr3 and the fifth transistor Tr5 are TFTs.
And for switching. Second transistor T
r2, the fourth transistor Tr4, and the sixth transistor Tr6 are TFTs, and the first OLED (R) 1
8, second OLED (G) 20 and third OLED
(B) It is for driving to control the driving currents flowing in 22 respectively. Here, the first transistor Tr1, the third transistor Tr3, and the fifth transistor Tr5 are
The n-channel type second transistor Tr2, the fourth transistor Tr4, and the sixth transistor Tr6 are p-type.
It is a channel type. A predetermined voltage Vdd is applied from the power supply 40 to the source electrodes of the second transistor Tr2, the fourth transistor Tr4, and the sixth transistor Tr6 via the power supply line 38.

In the first transistor Tr1, the gate electrode is connected to the scanning line 30, the drain electrode (or source electrode) is connected to the data line 32, and the source electrode (or drain electrode) is the gate of the second transistor Tr2. It is connected to the electrode and one electrode of the first capacitor C1. The other electrode of the first capacitor C1 is connected to the source electrode of the second transistor Tr2. The data line 32 is connected to a constant voltage source and is connected to the first OLED (R) 18
Luminance data is sent that determines the current flowing through. In the second transistor Tr2, the source electrode is the power supply line 38.
And the drain electrode is connected to the first OLED (R) 18
Connected to the anode of. The cathode of the first OLED (R) 18 is connected to the first variable power supply (R) 24. The first variable power supply (R) 24 is connected to the first OLED (R) 18
Of the first OLED by changing the potential of the cathode of the
(R) 18 and a second transistor T which is a driving element thereof
The voltage between both ends of the system to which r2 is connected (hereinafter, "the voltage between both ends" is that of the system unless otherwise specified) is variably set.

In the third transistor Tr3, the gate electrode is connected to the scanning line 30, the drain electrode (or source electrode) is connected to the data line 34, and the source electrode (or drain electrode) is the gate of the fourth transistor Tr4. It is connected to the electrode and one electrode of the second capacitor C2. The other electrode of the second capacitor C2 is connected to the source electrode of the fourth transistor Tr4. The data line 34 is connected to the constant voltage source and is connected to the second OLED (G) 20.
Luminance data is sent that determines the current flowing through. In the fourth transistor Tr4, the source electrode is the power supply line 38.
And the drain electrode is connected to the second OLED (G) 20.
Connected to the anode of. The cathode of the second OLED (G) 20 is connected to the second variable power source (G) 26. The second variable power supply (G) 26 is connected to the second OLED (G) 20.
By changing the potential of the cathode of the second OL
The voltage across the system in which the ED (G) 20 and the fourth transistor Tr4 that is the driving element thereof are connected is variably set.

In the fifth transistor Tr5, the gate electrode is connected to the scanning line 30, the drain electrode (or source electrode) is connected to the data line 36, and the source electrode (or drain electrode) is the gate of the sixth transistor Tr6. It is connected to the electrode and one electrode of the third capacitor C3. The other electrode of the third capacitor C3 is connected to the source electrode of the sixth transistor Tr6. The data line 36 is connected to a constant voltage source and is connected to the third OLED (B) 22.
Luminance data is sent that determines the current flowing through. In the sixth transistor Tr6, the source electrode is the power supply line 38.
And the drain electrode is connected to the third OLED (B) 22.
Connected to the anode of. The cathode of the third OLED (B) 22 is connected to the third variable power source (B) 28. The third variable power source (B) 28 is connected to the third OLED (B) 22.
By changing the potential of the cathode of the third OL
The voltage across the system in which the ED (B) 22 and the sixth transistor Tr6 that is the driving element thereof are connected is variably set.

Next, a method of setting the voltage between both ends by the first variable power source (R) 24, the second variable power source (G) 26 and the third variable power source (B) 28 will be described. As described above with reference to FIGS. 1 and 2, the OLEDs that emit different colors have different characteristics such as the threshold value of the voltage required for the OLEDs to emit light. In the present embodiment, the first variable power source (R) 24, the second variable power source (G) 26, and the third variable power source (B) 28 are used to change the voltage across both ends according to the characteristics of each OLED. . Also, OLEDs that emit different colors
In the above, the data potential necessary for emitting light having a desired brightness may differ due to the difference in the light emission characteristics. In the present embodiment, the voltage between both ends is set by the first variable power source (R) 24, the second variable power source (G) 26, and the third variable power source (B) 28 in consideration of such a difference in the light emission characteristic. May be changed.

Next, the operation of the display device 10 having the above configuration will be described. In the first pixel 12, first, the scanning line 30 is set high and the first transistor Tr1 is turned on, and then the data potential is applied to the data line 32. As a result, the first capacitor C1 and the second transistor T1
Luminance data is set to the gate electrode of r2. When the writing of the brightness data is completed and the scanning line 30 is set to low, the first transistor Tr1 is turned off and the transistor Tr2 is turned on.
A current according to the voltage set on the gate electrode of the capacitor and the capacitor C1 flows through the OLED (R) 18. This causes the first OLED (R) 18 to emit light. Second pixel 14
Also in the third pixel 16, the second pixel is operated by the same operation.
OLED (G) 20 and third OLED (B) 22
Current flows through the second OLED (G) 20 and the third OLED (B) 22 to emit light.

First OLED (R) 18, second OLE
When an electric current flows through the D (G) 20 and the third OLED (B) 22, the first OLED is changed according to the characteristics of each OLED.
(R) 18, second OLED (G) 20, and third O
The voltage across the LED (B) 22 is different. In the present embodiment, since the voltage across the system is set in consideration of the influence of the voltage across each OLED, the second transistor T
The voltage between the source and drain of r2, the fourth transistor Tr4, and the sixth transistor Tr6 can be maintained at a predetermined value. At this time, it is possible to apply a voltage to each OLED so as to realize light having a desired brightness. Further, in the present embodiment, since the voltage across both ends is set in consideration of the light emission characteristics of each OLED, it is possible to suppress the variation in the brightness of the OLED and reduce the power consumption.

Further, in the present embodiment, the first variable power source (R) 24, the second variable power source (G) 26 and the third variable power source (B) 28 are connected to the second transistor Tr2.
Fourth transistor Tr4 and sixth transistor T
Since it is provided on the drain electrode side of r6, the source-gate voltage does not change even if the cathode potential of each OLED is changed by the variable power supply, so that the OLED drive current can be maintained at a preset value. .

The display device 10 includes a first variable power source (R) 2
4, a second variable power source (G) 26 and a third variable power source (B) 28 may be collectively provided with a power source control unit (not shown), and the power source control unit may have characteristics of each OELD. Even if the voltage between both ends is changed by changing the resistance values of the first variable power source (R) 24, the second variable power source (G) 26, and the third variable power source (B) 28 while considering Good.

In this embodiment, all pixels 1
A variable power source is provided for each of 2, 14, and 16,
For example, a variable power supply is not provided for a pixel including an optical element that consumes the least power, and the main power supply 40 supplies the minimum power consumption required for the pixel to adjust the variable power supply for the pixel including other optical elements. May be. This can simplify the configuration of the display device and reduce power consumption.

In the present embodiment, a common power source 40 is connected to the source electrode of each driving transistor, and each OL is connected.
Although the variable power source is connected to the cathode of the ED and the voltage between both ends is changed by the variable power source, the variable power source may be connected to the source electrode of the driving transistor without using the common power source 40. A variable power source may be connected to the source electrode of each driving transistor and the cathode of each OLED. Further, the variable power source may be provided for each pixel, but may be provided for each emission color of the OLED.

Second Embodiment: FIG. 4 is a circuit diagram showing a part of pixels of a display device according to a second embodiment of the present invention. In the present embodiment, the display device 50 includes the fourth pixel 52, the fifth pixel 54, and the sixth pixel 56. In the following description, the same components as those of the display device 10 according to the first embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

The fourth pixel 52 is connected to the first OLED (R).
18, a first transistor Tr1 for switching, a seventh transistor Tr7 for driving the first OLED (R) 18, and a first capacitor C1. The seventh transistor Tr7 is an n-channel type. The drain electrode of the seventh transistor Tr7 is the fourth variable power source (R) 58.
Connected to. The fourth variable power source (R) 58 has a first O
The voltage across the system in which the LED (R) 18 and the seventh transistor Tr7 that is the drive element thereof are connected is variably set. The source electrode of the seventh transistor Tr7 is connected to the first potential setting circuit 64. First potential setting circuit 64
Holds the potential of the source electrode of the seventh transistor Tr7 at a predetermined value during data writing.

The fifth pixel 54 has a second OLED (G).
20, a third transistor Tr3 for switching, an eighth transistor Tr8 for driving the second OLED (G) 20, and a second capacitor C2. The eighth transistor Tr8 is an n-channel type. The drain electrode of the eighth transistor Tr8 is the fifth variable power source (G) 60.
Connected to. The fifth variable power source (G) 60 has a second O
The voltage across the system in which the LED (G) 20 and the eighth transistor Tr8 that is the driving element thereof are connected is variably set. The source electrode of the eighth transistor Tr8 is connected to the second potential setting circuit 66. Second potential setting circuit 66
Holds the potential of the source electrode of the eighth transistor Tr8 at a predetermined value when writing data.

The sixth pixel 56 is the third OLED (B).
22, a fourth transistor Tr4 for switching, a ninth transistor Tr9 for driving the third OLED (B) 22, and a third capacitor C3. The ninth transistor Tr9 is an n-channel type. The drain electrode of the ninth transistor Tr9 is the sixth variable power source (B) 62.
Connected to. The sixth variable power source (B) 62 has a third O
The voltage across the system in which the LED (B) 22 and the ninth transistor Tr9 that is the driving element thereof are connected is variably set. The source electrode of the ninth transistor Tr9 is connected to the third potential setting circuit 68. Third potential setting circuit 68
Holds the potential of the source electrode of the ninth transistor Tr9 at a predetermined value during data writing.

As described above with reference to FIGS. 1 and 2, the OLEDs that emit different colors have different characteristics such as the threshold value of the voltage required for the OLEDs to emit light. In the present embodiment, the voltage across both ends is changed by the fourth variable power source (R) 58, the fifth variable power source (G) 60, and the sixth variable power source (B) 62 according to the characteristics of each OLED. . Further, in OLEDs that emit different colors, the data potential required to emit light of desired brightness may differ due to the difference in light emission characteristics. In the present embodiment, the voltage between both ends is set by the fourth variable power source (R) 58, the fifth variable power source (G) 60, and the sixth variable power source (B) 62 in consideration of such a difference in light emission characteristic. May be changed.
Further, in the present embodiment, the first potential setting circuit 64, the second potential setting circuit 66, and the third potential setting circuit 68 cause the seventh transistor Tr7 and the eighth transistor Tr7 to write data voltage. Since the potentials of the source electrodes of Tr8 and the ninth transistor Tr9 can be kept at a predetermined value, even if the drain potential and the source potential of each transistor are varied by the variable power source, the source-gate potential is a preset value. Can be kept at

Next, the operation of the display device 50 having the above structure will be described. In the fourth pixel 52, first, the scanning line 30 is set high and the first transistor Tr1 is turned on, and then the data potential is applied to the data line 32. Thereby, the brightness data is set to the gate electrodes of the first capacitor C1 and the seventh transistor Tr7. At this time, the first electrode is formed on the source electrode of the seventh transistor Tr7.
The potential setting circuit 64 sets the potential of a predetermined value. When the writing of the brightness data is completed and the scanning line 30 is made low, the first transistor Tr1 is turned off, and a current corresponding to the voltage set in the gate electrode of the transistor Tr2 and the capacitor C1 causes the first OLED (R) 18 to flow. Flow to. This causes the first OLED (R) 18 to emit light. In the fifth pixel 54 and the sixth pixel 56 as well, a current flows through the second OLED (G) 20 and the third OLED (B) 22 by the same operation, and the second OLED
(G) 20 and the third OLED (B) 22 emit light.

First OLED (R) 18, second OLE
When an electric current flows through the D (G) 20 and the third OLED (B) 22, the first OLED is changed according to the characteristics of each OLED.
(R) 18, second OLED (G) 20, and third O
The voltage across the LED (B) 22 is different. In the present embodiment, since the voltage across the system is set in consideration of the influence of the voltage across each OLED, the seventh transistor T
The voltage between the source and drain of r7, the eighth transistor Tr8, and the ninth transistor Tr9 can be maintained at a predetermined value. At this time, it is possible to apply a voltage to each OLED so as to realize light having a desired brightness. Further, in the present embodiment, since the voltage across both ends is set in consideration of the light emission characteristics of each OLED, it is possible to suppress the variation in the brightness of the OLED and reduce the power consumption.

Further, in the present embodiment, the seventh potential setting circuit 64, the second potential setting circuit 66, and the third potential setting circuit 68 make the seventh transistor Tr7, the eighth transistor Tr8, and the ninth transistor Tr8. Transistor Tr
While keeping the potential of the source electrode of No. 9 at a predetermined value,
Of the variable power source (R) 58, the fifth variable power source (G) 60, and the sixth variable power source (B) 62 of
7. Since the drain electrodes of the seventh, eighth, and ninth transistors Tr8 and Tr9 are provided, even if the drain potential and the source potential of each transistor are varied by the variable power source, the source-gate potential is a preset value. Can be kept at

The display device 50 includes a fourth variable power source (R) 5
8, a fifth variable power source (G) 60 and a sixth variable power source (B) 62 may be provided with a power source control unit (not shown), which is a characteristic of each OELD. Even if the voltage between both ends is changed by changing the resistance values of the fourth variable power source (R) 58, the fifth variable power source (G) 60, and the sixth variable power source (B) 62 while considering Good.

In this embodiment, all the pixels 5
A variable power source was provided for each of 2, 54 and 56,
For example, a fixed power supply is provided for a pixel that includes an optical element that consumes the least amount of power, and the fixed power supply supplies the minimum power consumption required for that pixel, and the variable power supply for the pixel that includes other optical elements is adjusted. May be. This can simplify the configuration of the display device and reduce power consumption.

In this embodiment, the variable power source is connected to the drain electrode of each driving transistor, and the voltage across the variable voltage source is changed. However, the drain electrode of each driving transistor and the cathode of each OLED are connected to each other. A variable power supply may be connected to each. Further, the variable power source may be provided for each pixel, but may be provided for each emission color of the OLED.

Third Embodiment: FIG. 5 is a circuit diagram showing a part of pixels of a display device according to a third embodiment of the present invention. In the present embodiment, the display device 70 includes a seventh pixel 72, an eighth pixel 74 and a ninth pixel 76. In the following description, the same components as those of the display device 10 according to the first embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

The seventh pixel 72 corresponds to the first OLED (R)
This is different from the first pixel 12 in the first embodiment in that it includes an n-channel type seventh transistor Tr7 as a driving TFT for 18. The eighth pixel 74 has a second O
This is different from the second pixel 14 in the first embodiment in that an n-channel type eighth transistor Tr8 is included as a TFT for driving the LED (G) 20. Ninth pixel 76
Includes an n-channel type ninth transistor Tr9 as a TFT for driving the third OLED (B) 22,
It is different from the third pixel 16 in the first embodiment.

As described above with reference to FIGS. 1 and 2, the OLEDs that emit different colors have different characteristics such as the threshold value of the voltage required for the OLEDs to emit light. In the present embodiment, the first variable power source (R) 24 and the second variable power source (G) are used according to the characteristics and the light emission characteristics of each OLED.
26 and the third variable power source (B) 28 are used to change the voltage across. Further, in OLEDs that emit different colors, the data potential required to emit light of desired brightness may differ due to the difference in light emission characteristics. In the present embodiment, the first variable power source (R) 24 and the second variable power source (G) 26 are considered in consideration of such a difference in the light emission characteristics.
The voltage across both ends may be changed by the third variable power source (B) 28.

Next, the operation of the display device 70 having the above structure will be described. In the seventh pixel 72, first, the scanning line 30 is set high and the first transistor Tr1 is turned on, and then the data potential is applied to the data line 32. As a result, the first capacitor C1 and the seventh transistor T1
Luminance data is set to the gate electrode of r7. When the writing of the brightness data is completed and the scanning line 30 is set to low, the first transistor Tr1 is turned off, and a current corresponding to the voltage set in the gate electrode of the seventh transistor Tr7 and the capacitor C1 is supplied to the OLED (R) 18. Flow to. This causes the first OLED (R) 18 to emit light. Also in the eighth pixel 74 and the ninth pixel 76, the second OLED (G) 20 and the third OLED are operated by the same operation.
A current flows through (B) 22, and the second OLED (G) 20 and the third OLED (B) 22 emit light.

First OLED (R) 18, second OLE
When an electric current flows through the D (G) 20 and the third OLED (B) 22, the first OLED is changed according to the characteristics of each OLED.
(R) 18, second OLED (G) 20, and third O
The voltage across the LED (B) 22 is different. Each OLE
The seventh transistor Tr is affected by the voltage across D.
The potentials of the source electrodes of the seventh, eighth transistor Tr8 and the ninth transistor Tr9 are also different. As a result, the gate-source voltage of the seventh transistor Tr7, the eighth transistor Tr8, and the ninth transistor Tr9 varies. In the present embodiment, the first variable power source (R) 24, the second variable power source (G) 26, and the third variable power source (B) 28 are used in consideration of variations in the gate-source voltage. Since the potential of the cathode of the OLED can be changed, the voltage between the gate and the source can be kept constant, and the variation in brightness can be reduced.

In this embodiment, all pixels 7
A variable power source was provided for each of 2, 74 and 76,
For example, a fixed power supply is provided for a pixel that includes an optical element that consumes the least amount of power, and the fixed power supply supplies the minimum power consumption required for that pixel, and the variable power supply for the pixel that includes other optical elements is adjusted. May be. This can simplify the configuration of the display device and reduce power consumption.

The present invention has been described above based on the embodiments. It is understood by those skilled in the art that these embodiments are mere examples, and that various modifications can be made to the combinations of the respective constituent elements and the respective processing processes, and such modifications are also within the scope of the present invention. By the way. Hereinafter, such an example will be described.

In the first and third embodiments, the end of the variable power supply on the side opposite to the OLED and the second embodiment are set to the ground potential at the cathode end of the OLED, respectively. These potentials may be set to a predetermined positive potential or negative potential.

Each pixel in the third embodiment may be provided with a potential setting circuit for setting the potential of the source electrode of the driving transistor, as in the second embodiment.

In the embodiments, the switching transistors are shown as n-channel type, but these transistors may be p-channel type, and the driving transistor and the switching transistor are n-channel type and p-channel type. It can be any combination with the mold. The circuit configuration in this case is set as appropriate.

Each of the switching transistors described in the embodiments may be composed of a combination of a plurality of transistors, or may be composed of any combination in terms of their capabilities. In this case, the plurality of transistors may be connected in series between the data line and the driving transistor.

[0067]

By suppressing the variation of the light emission luminance in each pixel, the quality of the entire display device can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing some pixels of an active OLED display.

FIG. 2 Voltage of OLED and driving transistor −
It is a figure which shows a current characteristic.

FIG. 3 is a circuit diagram showing some pixels of the display device according to the first embodiment of the present invention.

FIG. 4 is a circuit diagram showing some pixels of a display device according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing some pixels of a display device according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing some pixels of an active OLED display.

[Explanation of symbols]

10 ... Display device, 12 ... First pixel, 14 ... Second pixel
, 16th, 3rd pixel, 18th, 1st OLED
(R), 20 ... Second OLED (G), 22 ... Third
OLED (B), 24 ... First variable power source (R), 2
6 ... 2nd variable power source (G), 28 ... 3rd variable power source (B), 30 ... scanning line, 32 ... data line, 34 ...
Data line, 36 ... Data line, 38 ... Power line, 40 ...
・ Power source, 50, display device, 52, fourth pixel, 54
..Fifth pixel, 56..Sixth pixel, 58..Fourth variable power source (R), 60..Fifth variable power source (G), 62
..Sixth variable power source (B), 70 ... Display device, 72 ..
7th pixel, 74 8th pixel, 76 9th pixel, Tr 1 1st transistor, Tr 2 2nd transistor, Tr 3 3rd transistor, Tr 4
..Fourth transistor, Tr5..Fifth transistor, Tr6..Sixth transistor, Tr7..Seventh transistor, Tr8..Eighth transistor, Tr9
..Ninth transistor, C1 ... First capacitor,
C2 ... the second capacitor, C3 ... the third capacitor.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H05B 33/14 H05B 33/14 AF term (reference) 3K007 AB04 AB11 AB17 DB03 GA04 5C080 AA06 BB05 CC03 DD05 EE30 FF11 JJ03 JJ05

Claims (7)

[Claims] 1. A current-driven optical element, A power supply circuit for variably setting the voltage across the optical element, A display device comprising: 2. A display device comprising: a system to which an optical element and a driving element thereof are connected; and a power supply circuit for variably setting a voltage across the system. 3. The apparatus according to claim 1, wherein the power supply circuit sets the both-end voltage according to a threshold value of a voltage required for light emission of the optical element. 4. The optical element is classified into a plurality of types according to the color of light emitted, and the power supply circuit is provided individually for the plurality of types.
The device according to. 5. The apparatus according to claim 4, wherein the power supply circuit sets the both-end voltage according to the emission characteristics of the optical element for each color. 6. A first system in which a first optical element and its driving element are connected, a second system in which a second optical element and its driving element are connected, and said first system. And a power supply circuit for setting a voltage across the second system, the power supply circuit being necessary for the first optical element and the second optical element to emit light of desired brightness, respectively. A display device in which the voltage across at least one of the first system and the second system is variably set in consideration of the difference in voltage. 7. The display device according to claim 1, wherein the driving element includes a thin film transistor, and the power supply circuit is provided on a drain electrode side of the transistor.