JP2007011205A - Organic led display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic LED display device capable of accurately controlling luminance. <P>SOLUTION: The organic LED display device includes a display means 11 constituted by arranging organic LEDs and voltage/current converting circuits in a matrix, a voltage/current conversion characteristic determining means 12 for determining voltage/current conversion characteristics of the voltage/current converting circuits, and a luminance voltage correcting means 13 for correcting a luminance voltage, based upon the voltage/current conversion characteristics determined by the voltage/current conversion characteristic determining means 12. A the voltage/current conversion characteristic measuring means 12 includes a reference voltage applying means 121 of applying a reference voltage to a voltage/current converting circuits, a current measuring mans 122 of measuring a current flowing to an organic LED through the voltage/current converting circuit when the reference voltage is applied from the reference voltage applying means 121, and a voltage/current conversion characteristic calculating means 123 of calculating voltage/current conversion characteristics, based upon the reference voltage and the current measured by the current measuring means 122. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic LED display device, and more particularly to an organic LED display device capable of accurately controlling luminance.

  In order to stably display high-brightness and high-contrast images over a long period of time on a display device in which organic LEDs are arranged in a matrix, the organic LEDs are activated by a voltage / current conversion circuit composed of TFTs (Thin Film Transistors). It is necessary to drive.

  Since an organic LED has a characteristic of emitting light with a luminance corresponding to a current flowing through the organic LED, a field effect transistor generally converts a luminance control voltage into a luminance control current and supplies it to the organic LED.

  However, the voltage-current conversion characteristics of the field effect transistor are affected by the threshold voltage and mobility of the field effect transistor, but the influence of the threshold voltage of the field effect transistor is particularly significant.

  For this reason, the light emission luminance of the organic LED is greatly influenced by the threshold voltage of the field effect transistor, and when the characteristics of the field effect transistor included in the organic LED display device vary, the same luminance voltage is used. There is a problem that the luminance becomes non-uniform even when the voltage is applied.

In order to solve the above problems, the following voltage / current conversion circuit has been proposed.
1. 1. A voltage program circuit in which a capacitor for storing a compensation voltage corresponding to a threshold voltage of a field effect transistor is installed in a voltage / current conversion circuit. A current program circuit that supplies a current corresponding to the display brightness from a constant current source and installs a capacitor in the voltage / current conversion circuit to store the gate voltage corresponding to the current corresponding to the display brightness, thereby suppressing variations in brightness. In the above voltage / current conversion circuit, since it is necessary to add a capacitor and a transistor in the circuit, the area occupied by the voltage / current conversion circuit in the display device is large, and the area occupied by the display element is small. This causes a new problem that the resolution of the display screen is lowered.

Therefore, in order to solve the uneven brightness of the organic LED display device, an organic LED display device that measures the current flowing through each organic LED and controls the current supply time to the organic LED according to the measured current value is also proposed. (For example, refer to Patent Document 1).
JP 10-254410 A ([0039] to [0041], FIG. 2)

  However, since the organic LED display device according to the above proposal controls the luminance by the pulse width, when performing multi-grayscale luminance control, the pulse becomes dull due to the stray capacitance of the voltage / current conversion circuit, and a predetermined value There was a problem that an image could not be displayed with luminance.

  The present invention has been made to solve the conventional problems, and an object of the present invention is to provide an organic LED display device capable of accurately controlling luminance even when performing multi-tone luminance control.

  According to a first aspect of the present invention, there is provided an organic LED display device comprising: a pixel circuit including an organic LED and a voltage / current conversion circuit that converts a luminance voltage for controlling luminance during light emission of the organic LED into a luminance current supplied to the organic LED. A plurality of display means arranged in a matrix, voltage / current conversion characteristic determining means for determining the respective voltage / current conversion characteristics of the voltage / current conversion circuit, and the voltage / current conversion circuit. Brightness voltage correction means for correcting the brightness voltage based on the voltage / current conversion characteristics determined by the voltage / current conversion characteristics determination means.

  With this configuration, the luminance voltage can be corrected based on the voltage / current conversion characteristics of the voltage / current conversion circuit to accurately control the luminance.

  In the organic LED display device according to the second invention, the voltage / current conversion characteristic determining means applies a reference voltage to each of the voltage / current conversion circuits, and the reference voltage applying means refers to the reference voltage applying means. When a voltage is applied, it is measured by a current measuring unit that measures a current flowing through the organic LED through the voltage / current conversion circuit, a reference voltage applied by the reference voltage applying unit, and the current measuring unit. Voltage / current conversion characteristic calculating means for calculating the voltage / current conversion characteristics of each of the voltage / current conversion circuits based on the measured current.

  With this configuration, the voltage / current conversion characteristics can be determined for each voltage / current conversion circuit.

In the organic LED display device according to a third aspect of the invention, the reference voltage applying unit applies at least two different reference voltages to each of the voltage / current conversion circuits, and the current measuring unit includes the When at least two reference voltages are applied, at least two currents flowing through the organic LED via the voltage / current conversion circuit are measured.
The voltage / current conversion characteristic calculation means is based on at least two reference voltages applied by the reference voltage application means and at least two currents measured by the current measurement means. The voltage-current conversion characteristic is calculated by calculating a proportionality constant and a threshold voltage that is a voltage axis intercept when the voltage-current conversion characteristic is expressed by a linear function with the voltage as an independent variable and the square root of the current as a dependent variable. Have.

  With this configuration, by measuring the current flowing through the organic LED when at least two different reference voltages are applied, the voltage / current conversion characteristics are determined as a linear function with the voltage as an independent variable and the current as a dependent variable. Will be.

  In the organic LED display device according to a fourth aspect of the present invention, the luminance voltage correction means converts the luminance voltage into a voltage / current conversion characteristic calculated by the voltage / current conversion characteristic calculation means and a reference voltage / current conversion characteristic. It has the structure which correct | amends based on.

  With this configuration, the luminance voltage can be corrected for each voltage / current conversion circuit.

  The organic LED display device according to a fifth aspect of the invention has a configuration in which the reference voltage / current conversion characteristic is determined based on the voltage / current conversion characteristic calculated by the voltage / current conversion characteristic calculation means. .

  With this configuration, the reference voltage / current conversion characteristics can be determined from the voltage / current conversion characteristics of each voltage / current conversion circuit.

  The present invention can provide an organic LED display device having an effect that brightness can be accurately controlled by providing voltage / current conversion characteristic determining means and brightness voltage correcting means.

Hereinafter, an embodiment of an organic LED display device according to the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 shows a block diagram of the organic LED display device according to the first embodiment of the present invention.

  That is, the organic LED display device according to the first embodiment is a display unit configured by arranging a plurality of pixel circuits each including an organic LED and a voltage / current conversion circuit that supplies a current for causing the organic LED to emit light in a matrix. 11, voltage / current conversion characteristic determining means 12 for determining the respective voltage / current conversion characteristics of the voltage / current conversion circuit, and luminance based on the voltage / current conversion characteristics determined by the voltage / current conversion characteristic determining means 12 Luminance voltage correction means 13 for correcting the voltage.

  The voltage / current conversion characteristic measurement unit 12 includes a reference voltage application unit 121 that applies a reference voltage to each of the voltage / current conversion circuits, and a voltage / current conversion circuit when the reference voltage is applied from the reference voltage application unit 121. Current measuring means 122 for measuring the current flowing through the organic LED via the reference voltage, the reference voltage applied by the reference voltage applying means 121 and the current measured by the current measuring means 122, the respective voltages of the voltage / current conversion circuit A voltage / current conversion characteristic calculation means 123 for calculating a current conversion characteristic;

  As shown in the hardware configuration diagram of FIG. 2, the organic LED display device according to the first embodiment includes a plurality of pixel circuits each including an organic LED and a voltage / current conversion circuit that supplies current for causing the organic LED to emit light. Display panel 21 arranged in a line, column selection unit 22 for supplying a reference voltage or luminance voltage to a specific column of display panel 21, and row selection unit 23 for activating a specific row of display panel 21 And a resistance element 24 for current measurement inserted into the common ground line of the organic LED, and a control unit 25 for controlling the organic LED display device.

  The control unit 25 is configured by, for example, a microprocessor, a CPU 251 that executes an organic LED display device control program, a memory 252 that stores the organic LED display device control program, and a luminance voltage V (i, j) and a power source from an external circuit. An external interface (I / F) 253 that inputs an on / off signal, a D / A converter 254 that outputs a reference voltage or a corrected luminance voltage, and a selection signal I that outputs a selection signal to the column selection unit 22 and the row selection unit 23 / F255, an A / D converter 256 that converts a voltage generated at both ends of the current measuring resistor element 24 into a digital value in order to measure a current flowing through the organic LED, a CPU 251, a memory 252, an external I / F 253, A bus 257 for connecting the D / A converter 254, the selection signal I / F 255 and the A / D converter 256 to each other; Including.

  FIG. 3 is a circuit diagram of one pixel circuit 3 arranged in a matrix in the display panel 21. In the pixel circuit 3, the source S1 is connected to one column selection line 221 extending from the column selection unit 22. The first FET 31 is connected to one row selection line 231 extending from the row selection unit 23, and the source S2 is connected to the positive line 26. The gate G2 is connected to the drain D1 of the first FET 31. Are connected to each other, a voltage-current conversion circuit 34 including a holding capacitor 33 connected to the source S2 and the gate G2 of the second FET 32, a drain D2 of the second FET 32, and a negative electrode line 27. And an organic LED 35 connected between the two. The negative electrode line 27 is grounded via the current measuring resistance element 24.

  The voltage / current conversion circuit 34 shown in FIG. 3 is an example, and the present invention can be applied to other voltage / current conversion circuits.

  Next, the operation of the organic LED display device according to the present invention will be described.

  FIG. 4 is a flowchart of an organic LED display device control program executed by the control unit 25. First, the CPU 251 determines whether the power of the organic LED display device is on or off via the external I / F 253. Is determined (step S4).

  The CPU 251 executes a voltage / current conversion characteristic determination routine when it is determined in step S4 that the power has transitioned from on to off (step S5), and when it is determined that the power is on in step S4, a normal display routine. Is executed (step S6).

  FIG. 5 is a flowchart of a voltage / current conversion characteristic determination routine executed by the control unit 25 in step S5 of the organic LED display device control program. The CPU 251 first selects a row selection index j for selecting a row of the display panel 21. Is initialized to "1" (step S50).

  Next, the CPU 251 initializes a column selection index i for selecting a column of the display panel 21 to “1” (step S51).

  Then, the CPU 251 executes a current measurement routine (step S52), and further executes a voltage / current conversion characteristic calculation routine (step S53).

  Next, the CPU 251 determines whether or not the column selection index i has reached the maximum value I (step S54). When it is determined that the column selection index i has not reached the maximum value I, the column selection index i i is incremented (step S55), and the process returns to step S52.

  On the other hand, when the CPU 251 determines that the column selection index i has reached the maximum value I, the CPU 251 determines whether or not the row selection index j has reached the maximum value J (step S56).

  When the CPU 251 determines that the row selection index j has not reached the maximum value J, the CPU 251 increments the row selection index j (step S57) and returns to the processing of step S51.

  On the other hand, when the CPU 251 determines that the row selection index j has reached the maximum value J, the routine is terminated.

  FIG. 6 is a flowchart of the current measurement routine executed by the control unit 25 in step S52 of the voltage / current conversion characteristic determination routine. First, the CPU 251 sets the number index m indicating the number of times of current measurement to “1”. Initialization is performed (step S520).

  Next, the CPU 251 outputs the column index i to the column selection unit 22 and the row index j to the row selection unit 23 via the selection signal I / F 255 (step S521).

  Next, the CPU 251 applies the mth reference voltage Vr (m) to the input terminal of the column selection unit 22 via the D / A converter 254 (step S522).

  Hereinafter, the operation of the pixel circuit 3 in this state will be described with reference to FIG.

  When the CPU 251 outputs the row index j to the row selection unit 23, the row selection line 231 is turned on, a voltage is applied to the gate G1 of the first FET 31, and the first FET 31 is turned on.

  When the CPU 251 outputs the column index i to the column selection unit 22, the reference voltage Vr (m) is applied to the gate G2 of the second FET 32 via the source S1 and the drain D1 of the first FET 31.

  Then, a current determined as a function of the reference voltage Vr (m) flows from the positive line 26 through the source S2 and the drain D2 of the second FET 32 to the organic LED 35 to cause the organic LED to emit light, and then the negative line 27 Then, it flows out to the ground line through the resistance element 24 for current measurement.

  Hereinafter, the description returns to the current measurement routine of FIG.

  The CPU 251 reads the voltage Vi generated at both ends of the current measuring resistance element 24 via the A / D converter 256 and stores it as the voltage Vi (i, j, m) (step S523).

  The CPU 251 determines whether or not the number index m has reached the maximum value M (step S524). When it is determined that the number index m has not reached the maximum value M, the CPU 251 increments the number index m (step S524). S525), the process returns to step S521.

  On the other hand, when the CPU 251 determines that the frequency index m has reached the maximum value M, this routine is terminated.

  FIG. 7 is a flowchart of a voltage / current conversion characteristic calculation routine executed by the control unit 25 in step S53 of the voltage / current conversion characteristic determination routine. The current measurement is performed twice, and the voltage / current conversion circuit (i, The case where the voltage-current conversion characteristic of j) is approximated by a linear function with the voltage as an independent variable and the square root of the current as a dependent variable as shown in [Formula 1] will be described.

When the CPU 251 applies the reference voltage Vr (1) by dividing the voltage Vi (i, j, 1) generated at both ends of the current measuring resistor 24 by the resistance value Rr of the current measuring resistor 24. A current I ₁ flowing through the organic LED 35 included in the pixel circuit 3 arranged in the i column and the j row is calculated (step S530).

Next, the CPU 251 applies the reference voltage Vr (2) by dividing the voltage Vi (i, j, 2) generated at both ends of the current measuring resistor element 24 by the resistance value Rr of the current measuring resistor element 24. Then, the current I ₂ flowing through the organic LED 35 included in the pixel circuit 3 arranged in the i column and the j row is calculated (step S531).

  The CPU 251 calculates the proportionality constant K (i, j) of the voltage / current conversion characteristics of the second FET 32 included in the pixel circuit 3 arranged in the i column and j row using [Equation 2] (step S532). ).

   Next, the CPU 251 calculates the threshold voltage Vth (i, j) of the voltage / current conversion characteristics of the second FET 32 included in the pixel circuit 3 arranged in i column and j row using [Equation 3]. (Step S533), and this routine is finished.

   This is the end of the description of the voltage / current conversion characteristic determination routine, and a correction method during normal display will be described.

FIG. 8 is a graph for explaining the correction method. The voltage V applied to the gate G2 of the second FET 32 of the voltage / current conversion circuit 34 in the right direction of the horizontal axis and the source of the second FET 32 in the left direction of the horizontal axis. The current I flowing from S2 toward the drain D2 is taken, and the source-drain voltage V _SD of the second FET 32 is taken on the vertical axis.

The first quadrant shows the gate voltage V vs. source-drain voltage V _SD characteristics, and the second quadrant shows the source-drain voltage V _SD vs. drain current I characteristics.

Of the gate voltage V versus source-drain voltage V _SD characteristics in the first quadrant, the solid line indicates the characteristics of the standard FET, and the alternate long and short dash line indicates the second FET 32 included in the pixel circuit 3 arranged in i columns and j rows. The characteristics of

The source-drain voltage V _SD vs. drain current I characteristic in the second quadrant is a curve in which the half power of the source-drain voltage V _SD becomes the drain current I, and there is no variation due to the second FET. Shall.

  Therefore, if the threshold voltage Vth (i, j) and the proportionality constant K (i, j) of the voltage / current conversion circuit 34 arranged in the i column and the j row are determined, the gate voltage V of the second FET 32 versus the drain current. The I characteristic is determined as [Equation 4].

The luminance voltage V vs. source-drain voltage V _SD characteristic of a standard FET is expressed by [Equation 5].

  Therefore, the current Id that flows from the source of the standard FET toward the drain when the voltage V (i, j) is applied to the gate of the standard FET is included in the pixel circuit 3 arranged in the i column and j row. The voltage Vc may be determined so that when the voltage Vc is applied to the gate of the second FET 32, the current flows from the source of the second FET 32 toward the drain.

  FIG. 9 is a flowchart of a normal display routine executed by the control unit 25 in step S6 of the organic LED display device control program. The CPU 251 first sets the row selection index j for selecting a row on the display panel 21 to “1”. (Step S60).

  Next, the CPU 251 initializes a column selection index i for selecting a column of the display panel 21 to “1” (step S61).

  The CPU 251 reads the luminance voltage V (i, j) of the pixel in i column and j row through the external I / F 253 (step S62).

  Then, the CPU 251 calculates the corrected luminance voltage Vc based on [Equation 6] (step S63).

  Next, the CPU 251 outputs the column index i to the column selection unit 22 and the row index j to the row selection unit 23 via the selection signal I / F 255 (step S64).

  Then, the CPU 251 outputs the corrected luminance voltage Vc (Step S65).

  Next, the CPU 251 determines whether or not the column selection index i has reached the maximum value I (step S66). When it is determined that the column selection index i has not reached the maximum value I, the column selection index i i is incremented (step S67), and the process returns to step S62.

  On the other hand, when it is determined that the column selection index i has reached the maximum value I, the CPU 251 determines whether or not the row selection index j has reached the maximum value J (step S68).

  When the CPU 251 determines that the row selection index j has not reached the maximum value J, the CPU 251 increments the row selection index j (step S69) and returns to the processing of step S61.

  On the other hand, when the CPU 251 determines that the row selection index j has reached the maximum value J, the routine is terminated.

As described above, according to the first embodiment, the voltage / current conversion characteristic of each pixel circuit arranged in the display panel is measured, and the luminance voltage is corrected according to the voltage / current conversion characteristic. Therefore, it is possible to correct luminance variations caused by variations in voltage / current conversion characteristics.
(Second Embodiment)
In the first embodiment, the luminance voltage V versus the source-drain voltage V _SD characteristic of the standard FET is predetermined, but since it is theoretically determined, the actual characteristic May not match.

The second embodiment solves this problem, and determines the luminance voltage V vs. source-drain voltage V _SD characteristics of a standard FET based on the current measurement result.

  FIG. 10 is a flowchart of a second voltage / current conversion characteristic determination routine used in the second embodiment, and a reference characteristic determination routine (step S7) is inserted between step S53 and step S54.

FIG. 11 is a flowchart of a reference voltage / current conversion characteristic determination routine, in which the average characteristic of the luminance voltage V vs. source-drain voltage V _SD characteristics of a plurality of pixel circuits constituting the display panel is expressed as a standard luminance voltage V vs. The source-drain voltage V _SD characteristics are shown.

First, the CPU 251 calculates the average value of the proportionality constants calculated in step S532 of the voltage / current conversion characteristic calculation routine shown in FIG. 7 by [Equation 7] as the proportionality between the standard luminance voltage V and the source-drain voltage _VSD characteristic. A constant is set (step S70).

Next, the CPU 251 calculates the average value of the threshold voltages calculated in step S533 of the voltage / current conversion characteristic calculation routine shown in FIG. 7 using [Equation 8] as the standard luminance voltage V vs. source / drain voltage V _SD characteristics. The threshold voltage is set (step S71).

As described above, according to the second embodiment, it is possible to determine the standard luminance voltage V vs. source-drain voltage V _SD characteristic based on the actual display panel.

Block diagram of an embodiment of an organic LED display device according to the present invention Block diagram of hardware configuration of organic LED display device according to the present invention The block diagram of the hardware constitutions of one pixel circuit in the organic LED display device which concerns on this invention Flowchart of organic LED display device control program executed by CPU of organic LED display device according to the present invention Flowchart of voltage / current conversion characteristic determination routine executed by CPU of organic LED display device according to the present invention Flowchart of current measurement routine executed by CPU of organic LED display device according to the present invention Flowchart of voltage / current conversion characteristic calculation routine executed by CPU of organic LED display device according to the present invention The graph explaining the correction method in the organic LED display device which concerns on this invention Flowchart of normal display routine executed by CPU of organic LED display device according to the present invention Flowchart of the second voltage / current conversion characteristic determination routine executed by the CPU of the organic LED display device according to the present invention. Flowchart of reference voltage / current conversion characteristic determination routine executed by CPU of organic LED display device according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Display means 12 Voltage / current conversion characteristic determination means 13 Luminance voltage correction means 121 Reference voltage application means 122 Current measurement means 123 Voltage / current conversion characteristic calculation means

Claims (5)

A display configured by arranging a plurality of pixel circuits in a matrix form, each of which includes an organic LED and a voltage / current conversion circuit that converts a luminance voltage for controlling the luminance when the organic LED emits light into a luminance current supplied to the organic LED Means,
Voltage / current conversion characteristic determining means for determining each voltage / current conversion characteristic of the voltage / current conversion circuit;
An organic LED display device comprising: a luminance voltage correction unit that corrects the luminance voltage supplied to the voltage / current conversion circuit based on the voltage / current conversion characteristic determined by the voltage / current conversion characteristic determination unit. The voltage / current conversion characteristic determining means includes:
Reference voltage application means for applying a reference voltage to each of the voltage / current conversion circuits;
Current measuring means for measuring a current flowing through the organic LED via the voltage / current conversion circuit when a reference voltage is applied from the reference voltage applying means;
Voltage / current conversion characteristic calculating means for calculating each voltage / current conversion characteristic of the voltage / current conversion circuit based on the reference voltage applied by the reference voltage applying means and the current measured by the current measuring means; The organic LED display device according to claim 1, comprising: The reference voltage applying means applies at least two different reference voltages to each of the voltage / current conversion circuits;
The current measuring means measures at least two currents flowing through the organic LED via the voltage / current conversion circuit when the at least two reference voltages are applied;
Based on at least two reference voltages applied by the reference voltage applying unit and at least two currents measured by the current measuring unit, the voltage / current conversion characteristic calculating unit calculates the voltage / current conversion characteristic, The organic LED display device according to claim 2, which calculates a proportionality constant and a threshold voltage which is a voltage axis intercept when the voltage is represented by a linear function having an independent variable and a square root value of a current as a dependent variable. The luminance voltage correcting means is
4. The organic LED display device according to claim 3, wherein the luminance voltage is corrected based on the voltage / current conversion characteristic calculated by the voltage / current conversion characteristic calculation means and a reference voltage / current conversion characteristic. The reference voltage / current conversion characteristic is
The organic LED display device according to claim 4, wherein the organic LED display device is determined based on the voltage / current conversion characteristics calculated by the voltage / current conversion characteristics calculation means.

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