JP2001042826A - Active matrix type light emitting panel and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make uniformly controllable the luminance over the surface of a light emitting panel by providing a conversion active element, which converts a data signal current into a data signal voltage, in each pixel or a data driver circuit. SOLUTION: In each pixel of a data driver circuit, a conversion active element is provided to convert a data signal current into a data signal voltage. In a light emitting panel, a current-voltage converting circuit 31 is provided between a source S of an address selecting electric field effect type transistor(FET) 11 and a gate G of a driving FET 12 and a data driver 26 is constituted of a constant current driver. The circuit 31 has a conversion FET 33, which is an active element to conduct a current-voltage conversion, and a buffer circuit 35 with a switch. The FET 33 has a same element structure of the FET 12. In other words, element structure parameters, which determine element characteristics such as a channel width and a carrier density profile, are formed in the same manner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type display device, and more particularly to an active matrix type display device using a light emitting element such as an organic electroluminescence element.

[0002]

2. Description of the Related Art An organic electroluminescent element (hereinafter, referred to as an organic EL element) can control the light emission luminance by a current flowing through a light emitting element, and is constituted by arranging such light emitting elements in a matrix. The development of a matrix type display using a light emitting panel has been widely promoted. As a light emitting panel using such an organic EL element, a simple matrix type light emitting panel in which organic EL elements are simply arranged in a matrix, and an active matrix type in which a driving element including a transistor is added to each of the organic EL elements arranged in a matrix are used. There is a light emitting panel. Active matrix light-emitting panels have advantages such as lower power consumption and less crosstalk between pixels than simple matrix light-emitting panels, and are particularly suitable for large-screen displays and high-definition displays.

FIG. 1 shows an example of a circuit configuration corresponding to one pixel 10 of a conventional active matrix light emitting panel. Such a circuit configuration is described in, for example,
It is disclosed in Japanese Patent Publication No. 41057. In FIG. 1, F
The gate G of the ET (Field Effect Transistor) 11 (address selection transistor) is connected to an address scan electrode line (address line) to which an address signal is supplied.
The source S of the FET 11 is connected to a data electrode line (data line) to which a data signal is supplied. FET11
Is connected to the gate G of the FET 12 (driving transistor), and is grounded through the capacitor 13. The source S of the FET 12 is grounded, the drain D is connected to the cathode of the organic EL element 15, and the organic EL element 15
Is connected to a power source through the anode. The light emission control operation of this circuit will be described first.
When the ON voltage is supplied to the gate G of the FET 11, the FET 11
Transmits the voltage of the data supplied to the source S to the drain D. When the gate G of the FET 11 is at the off voltage, FE
T11 is a so-called cutoff, and the drain D of the FET 11 is in an open state. Therefore, while the gate G of the FET 11 is in the ON voltage, the voltage of the source S is charged in the capacitor 13 and the voltage is supplied to the gate G of the FET 12, so that the FET 12 receives a current based on the gate voltage and the source voltage. The organic EL element 15 flows from the drain D to the source S through the organic EL element 15 to cause the organic EL element 15 to emit light. When the gate G of the FET 11 is turned off,
The FET 11 is opened, the voltage of the gate G is held by the electric charge accumulated in the capacitor 13, the driving current is maintained until the next scan, and the organic EL element 1 is turned off.
Light emission of No. 5 is also maintained.

However, for the following reasons, it has been difficult to control the brightness of each pixel uniformly over the surface of the light emitting panel. FIG. 2 shows the electrical characteristics (current-voltage characteristics) of the drive transistor when temperature is used as a parameter. As shown in FIG. 2, the electrical characteristics of the driving transistor have a remarkable temperature dependency.
That is, even if the gate-source voltage is kept constant, the drain-source current (drive current) greatly changes due to the temperature change, and the luminance of the organic EL element also largely changes. Therefore, the electrical characteristics of the driving transistor change depending on the temperature distribution in the light emitting panel surface, and the luminance varies in the light emitting panel surface. Note that the current-luminance characteristics of the light-emitting element have almost no temperature dependence. Furthermore, there is a case where manufacturing variations occur in the driving transistors provided in each pixel, and there is a problem that the brightness in the light emitting panel surface becomes non-uniform due to these causes.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an active matrix capable of uniformly controlling the luminance over the surface of a light emitting panel. It is to provide a type display device.

[0006]

A light-emitting panel according to the present invention comprises a light-emitting element arranged in a matrix, a holding circuit for accumulating and holding a data signal current, and a light-emitting element in accordance with the held voltage. An active matrix type light-emitting panel including a driving element for driving each of the driving elements, wherein a conversion active element for converting a data signal current to a data signal voltage is provided.

A display device according to the present invention is an active matrix type light emitting panel including light emitting elements arranged in a matrix and a driving element for driving each of the light emitting elements.
A signal voltage supply circuit that supplies a data signal voltage to the active matrix light-emitting panel, wherein the signal voltage supply circuit converts a data signal current into a data signal voltage. It is characterized by having.

As another feature of the present invention, the conversion active element has substantially the same element structure or substantially the same electrical characteristics as the driving element.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, substantially equivalent parts are denoted by the same reference numerals. FIG.
1 schematically shows a configuration of an organic EL display device 20 using an active matrix light emitting panel according to a first embodiment of the present invention.

In FIG. 3, analog / digital (A /
D) The converter 21 receives an analog video signal and converts it into digital video signal data. The digital video signal obtained by the conversion is sent from the A / D converter 21 to the frame memory 23.
And is written and accumulated under the control of the controller 24. The controller 24 controls each of the frame memory 23, the address scanning driver 25, the data driver 26, and the power supply circuit 28 in synchronization with the horizontal and vertical synchronization signals of the input video signal.

The digital video signal data stored in the frame memory 23 is read by the controller 24 and sent to the data driver 26. Further, the controller 24 sequentially controls the data driver 26 and the address scanning driver 25 connected to each row and each column of the active matrix type light emitting panel 30 so as to correspond to the video stored in the frame memory 23. The light emission of the organic EL element of each pixel of the light emitting panel 30 is controlled. In the light emitting panel 30, a plurality of organic ELs
The element 15 includes address lines A _{1 to} A _m , which are scanning electrode lines from the address scanning driver 25, and a data driver 2.
6 are arranged in a matrix at a plurality of intersections of data lines B _{1 to} B _n , which are data electrode lines. A desired image can be displayed on the light emitting panel 30 under the control of the controller 24 described above. The power supply circuit 28 also supplies power to all the organic EL elements of the light emitting panel 30.

FIG. 4 shows a circuit configuration corresponding to a unit pixel of an active matrix light emitting panel according to a first embodiment of the present invention. This embodiment differs from the prior art circuit configuration shown in FIG.
A current-to-voltage conversion circuit 31 is provided between the source S of the drive FET 11 and the gate G of the driving FET 12, and the data driver 26 is constituted by a constant current driver. The current-voltage conversion circuit 31 includes a conversion FET 33 which is an active element for performing current-voltage conversion, and a buffer circuit 35 with a switch. In this embodiment, the conversion FET 33 has the same element structure as the driving FET 12. That is, the device structure parameter values that determine the device characteristics such as the channel width and the carrier concentration profile are formed identically. Therefore, the conversion FET 33 has substantially the same electrical characteristics as the driving FET 12. The conversion FET 33 can be formed simultaneously with the driving FET 12 in the process of manufacturing the light emitting panel.

In FIG. 4, the source S of the conversion FET 33 is grounded to a common ground (GND) of the light emitting panel 30. The drain D and the gate G of the conversion FET 33 are connected and connected to the input terminal of the buffer circuit with switch 35. The output terminal of the buffer circuit with switch 35 is connected to the gate G of the driving FET 12 and the capacitor 13.
It is connected to the. An input terminal of a switch circuit (not shown) of the buffer circuit with switch 35 is connected to an address line, and the voltage obtained by current-voltage conversion by the conversion FET 33 is relayed to the gate G of the driving FET 12 and the capacitor 13 according to the address signal. I do.

Next, the conversion FET 33 is connected to the driving FET 1
The operation for canceling the temperature characteristic of No. 2 will be described. First,
The current-voltage characteristics of the driving FET 12 are described as follows.
can do. Current I flowing through FET 12_DSIs organic
Drive current I of EL element 15_{dr v}Equal to
Gate voltage to V_sigIs represented by the following equation.

[0015]

I _DS = I _drv = (１ ／ L) μ _n C _OX W (V _sig −V _T ) ² (1) where μ _n is the mobility of the channel, C _OX is the capacitance of the gate oxide film, W is the channel width of the transistor, L is the effective channel length of the transistor, V _T is the threshold voltage.

Of the above parameters, the light emitting panel 30
Of the light emitting panel 3
The parameters that vary due to the fabrication of 0 are μ _n ,
C _OX, it is all of W, L, and V _T. Meanwhile, the parameter that varies with temperature is mu _n, V _T. Therefore,
In the conventional driving circuit shown in FIG.
Even if a constant voltage (V _sig ) is applied to the gate of FET 12, the FET
12 and the variation due to the temperature distribution in the light emitting panel 30, the driving F
The drive current of the ET 12 greatly varies.

Next, the case where the conversion FET 33 is used will be described. The drive current I _drv of the organic EL element 15 is represented by the following equation, similarly to (1).

[0018]

I _drv = I _DS = (１ ／ L) μ _n C _OX W (V _GS −V _T ) ² = K (V _GS −V _T ) ² (2) where

[0019]

## EQU00003 ## K = (1 / 2L) .mu._nC_OXW (3) The current-voltage conversion formula of the conversion FET 33 is a constant current mode.
The current of the driver 26 is I _sigThen, it is expressed by the following equation.
In the following, the conversion FET 33 in the present embodiment will be described.
Are indicated with “′”.

[0020]

I _DS '= I _sig = (（L') μ _n 'C _OX ' W '(V _GS -V _T ') ² = K '(V _GS -V _T ') ² (4) Here so,

[0021]

K ′ = (１ ／ L ′) μ _n 'C _OX ' W '(5) Since V _GS = V _sig , from equation (4),

[0022]

V _sig = (I _sig / K ′) ^1/2 + V _T ′ (6) Accordingly, from equations (2) and (6), the drive current I _drv is expressed by the following equation.

[0023]

I _drv = K (V _sig −V _T ) ² = K ｛(I _sig / K ′) ^1/2 − (V _T −V _T ′)｝ ² (7) In the equation (7) representing the drive current I _drv obtained above, V _T ≫V _T − Since it is V _T ′, it can be seen that the temperature dependence of the drive current is offset as compared with the equation (2) representing the drive current I _{drv in the related} art.

Further, since it can be considered that V _T −V _T ′ ≒ 0, the drive current I _drv is given by the following equation.

[0025]

I _drv ≒ (K / K ′) I _sig (8) Further, in this embodiment, an FET 33 having the same element structure as that of the driving FET 12 and a parameter value conversion of the same element structure is formed for each pixel. Have been. That is, the driving FE
A conversion FET 33 having substantially the same element structure as the driving FET 12 is provided close to T12.
2 and the parameters of the FET 33 can be regarded as equal. Therefore, since K = K 'and V _T = V _T ', equation (8) is

[0026]

I _drv = I _sig (9), and the driving current I of the driving FET 12 of each pixel is obtained.
_drv is determined only by the signal current of the constant current data driver 26 regardless of the position in the light emitting panel surface. That is, the organic EL element 15 of each pixel can be driven at a desired luminance regardless of the temperature distribution in the light emitting panel surface and the variation of the driving transistor.

In this embodiment, the conversion FET 3
A buffer circuit 35 with a switch is provided between the driving FET 12 and the driving FET 12. This is because the gate voltage of the conversion FET 33 may be lower than the holding voltage of the capacitor 13 immediately after the address selection transistor 11 is turned on in response to the address signal, and the charge stored in the capacitor 13 at this time is converted. This is to prevent the current FET 33 from affecting the current-voltage conversion. As such a buffer circuit with a switch, for example, a source follower, a switch circuit, and the like can be configured by an FET.
In addition, a diode or the like may be used, but is not limited thereto. Further, a configuration in which a switch circuit is not provided by timing control of an address signal or another method may be employed.

FIG. 5 shows a circuit configuration corresponding to a unit pixel of an active matrix light emitting panel according to a second embodiment of the present invention. This embodiment is different from the first embodiment in that the current-voltage conversion circuit 31 is configured for each data line in the constant current data driver 26. The current-voltage conversion circuit 31 has an FET 33 as an active element for performing current-voltage conversion and a buffer circuit 36. In the present embodiment, the conversion FET 33 is the driving F
It has the same element structure as ET12, and each element structure parameter value is also formed identically.

In FIG. 5, the source of the conversion FET 33 is
S is grounded to a common ground (GND) with the light emitting panel 30
Have been. The drain D and the gate G of the FET 33 are connected.
Then, it is connected to the input terminal of the buffer circuit 36.
The output terminal of the buffer circuit 36 is generated as a data line Bj.
The light panel 30 is connected to each pixel in the column direction. conversion
FET 33 offsets the temperature characteristics of drive FET 12
The operation will be described in the same manner as in the first embodiment.
be able to. That is, in the above equations (2) and (4),
Then, V_GS≒ V_sigIs assumed, the organic EL element 15
Drive current I _drvIs represented by the following equation. In addition, the following smell
Thus, the parameters of the conversion FET 33 in this embodiment are
Is indicated with "".

[0030]

## EQU10 ## I_drv{K} (I_sig/ K '')^1/2− (V_T-V_T'')｝^Two (10) In the above equation (10), V_T≫V_T-V_T''
In the case where the conversion FET 33 shown in the equation (2) is not provided,
Temperature dependence of the drive current is greatly reduced
I understand. Also, V_T-V_T''
Drive current I_{dr v}Is given by the following equation.

[0031]

I _drv ≒ (K / K ″) I _sig (11) In the present embodiment, the conversion FET 33 provided in the constant current data driver 26 has the same element structure as the driving FET 12. Since the element structure parameter values are also formed identically, it can be regarded as K / K ″ Ｋ1 in equation (11). Therefore, the drive current I _drv of the organic EL element 15 is
Becomes substantially equal to the signal current of the constant current data driver 26, and the non-uniformity of the characteristics due to the temperature dependency of the driving FET 12 and the variation of the element characteristics is canceled.

In the above embodiment, the conversion FE is used.
As T33, an FET having the same element structure and the same element structure parameter value as the driving FET 12 was used, but the driving FET is constituted by an FET having a structure capable of obtaining substantially the same electrical characteristics as the driving FET 12. May be. Further, the driving FET is not necessarily limited to these.
FE for driving by FET having temperature characteristics similar to
T may be configured. Further, for example, the element structure parameter value may be changed for each row, for each column, or for each pixel according to the distance from the driver circuit.

The data driver 26 is connected to the light emitting panel 3.
0, the light emitting panel 3 is provided as an example.
A data driver circuit may be formed in 0. In the above-described first embodiment, the case where the active conversion element and the buffer circuit with the switch circuit are provided for each pixel has been described as an example. However, it is not always necessary to provide the active conversion element and the buffer circuit for every pixel. And can be appropriately selected and applied.

[0034]

As is apparent from the above description, according to the present invention, by providing a conversion active element for converting a data signal current into a data signal voltage in each pixel or data driver circuit, the light emitting panel surface is provided. Temperature distribution in the
In addition, it is possible to realize an active matrix type light emitting panel capable of canceling non-uniformity of characteristics due to variations in driving elements and controlling luminance uniformly over the light emitting panel surface.

[Brief description of the drawings]

FIG. 1 shows a conventional active matrix light emitting panel 1
FIG. 3 is a diagram illustrating an example of a circuit configuration corresponding to one pixel.

FIG. 2 shows current of a driving FET for driving an organic EL element.
FIG. 4 is a diagram illustrating voltage characteristics using temperature as a parameter.

FIG. 3 is a block diagram schematically illustrating a configuration of an organic EL display device using an active matrix light emitting panel according to a first embodiment of the present invention.

FIG. 4 is a diagram showing a circuit configuration corresponding to a unit pixel of the active matrix light emitting panel according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a circuit configuration corresponding to a unit pixel of an active matrix light emitting panel according to a second embodiment of the present invention.

[Explanation of Signs of Main Parts]

 DESCRIPTION OF SYMBOLS 10 Pixel 11 Address selection FET 12 Drive FET 13 Capacitor 15 Light emitting element 20 Display device 21 A / D converter 23 Frame memory 24 Controller 25 Address scanning driver 26 Data driver 28 Power supply circuit 30 Light emitting panel 31 Current-voltage conversion circuit 33 Conversion FET 35, 36 Buffer circuit

Claims (13)

[Claims] A light-emitting element arranged in a matrix;
An active matrix light-emitting panel including a holding circuit that accumulates and holds a data signal current, and a driving element that drives each of the light-emitting elements according to the held voltage, wherein the data signal current is A light-emitting panel comprising a conversion active element for converting a data signal voltage. 2. The device according to claim 1, wherein the conversion active element has substantially the same element structure as the driving element.
The light-emitting panel according to item 1. 3. The light-emitting panel according to claim 1, wherein the conversion active element is connected to the driving element via a buffer circuit for impedance conversion. 4. The light emitting panel according to claim 3, wherein the buffer circuit further includes a switch circuit that relays the converted signal voltage to the holding circuit according to an address signal. 5. The light emitting panel according to claim 1, wherein the conversion active element has substantially the same electrical characteristics as the driving element. 6. The light emitting panel according to claim 1, wherein the conversion active element is formed simultaneously with the driving element. 7. The light emitting panel according to claim 1, wherein the driving element and the conversion active element are field effect transistors (FETs). 8. An active matrix light emitting panel including light emitting elements arranged in a matrix and a driving element for driving each of the light emitting elements, and a signal voltage supply circuit for supplying a data signal voltage to the active matrix light emitting panel. And a signal voltage supply circuit having a conversion active element for converting a data signal current to the data signal voltage. 9. The display device according to claim 8, wherein the conversion active element has substantially the same element structure as the driving element. 10. The display device according to claim 9, wherein the conversion active element is connected to the active matrix light-emitting panel via a buffer circuit for impedance conversion. 11. The display device according to claim 10, wherein the buffer circuit further includes a switch circuit for outputting the converted signal voltage according to an address signal and outputting the data signal voltage. 12. The display device according to claim 8, wherein the conversion active element has substantially the same electrical characteristics as the driving element. 13. The display device according to claim 8, wherein the driving element and the conversion active element are field-effect transistors (FETs).