JP2003031358A - Driving circuit for organic electroluminescent element display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driving circuit capable of efficiently charging junction capacitance in an equivalent circuit of an organic EL element and suppressing a manufacturing cost regarding the driving circuit for a display device using the organic EL element. SOLUTION: This driving circuit for the organic EL element display device comprises at least a current source for supplying a driving current to the organic EL element; a voltage source for charging the function capacitance of the organic EL element; and a control means. The current source and voltage source are connected to the positive electrode side of the organic EL element. The voltage of the voltage source is lower than the positive electrode voltage of the organic EL element when driving the organic EL element by the current source. The control means controls so that the ON periods of the current source and voltage source are the same.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit of a display device using an organic electroluminescence element as a light emitting element.

[0002]

2. Description of the Related Art Organic electroluminescent elements (hereinafter referred to as organic EL elements) have voltage-current characteristics similar to those of light-emitting diodes, and luminance is proportional to current. A driving method using a constant current is used.

The organic EL element has a structure in which a thin organic layer is sandwiched between electrodes, and a junction capacitance exists between the electrodes. FIG. 5 is an equivalent circuit diagram for explaining the characteristics of the organic electroluminescence element. The organic EL element 1 can be equivalently approximated by a circuit of a light emitting diode 1c, a capacitor 1b that is a junction capacitance that enters in parallel, and a resistor 1a that enters in series.

Immediately after the constant current output is applied to the organic EL element 1, the junction capacitance 1b in the organic EL element 1 is not charged at all, so that all the current flows to the junction capacitance 1b, and the light emission in the organic EL element occurs. No current flows to the diode 1c, and the organic EL element does not emit light at all. Junction capacity 1b
As the voltage is charged, the voltage across the organic EL element begins to rise, but since the voltage-current characteristics of the organic EL element are similar to those of the light emitting diode as described above, the voltage across the organic EL element becomes the light emission threshold value. Light emitting diode 1c until it exceeds
Almost no current flows to the and does not emit light. When the light emission threshold value is started to be exceeded, the current to the light emitting diode 1c increases and the organic EL
The device gradually starts emitting light.

When the organic EL element is driven with a constant current as described above, there is a problem that sufficient luminance cannot be obtained due to delay of light emission due to charging of the junction capacitance. In order to avoid this, as a driving method of the organic EL element display device, a method provided with a charging means for quickly charging the junction capacitance of the organic EL element immediately after the start of the constant current output is proposed.

Further, when the organic EL element is stopped from emitting light, since the charged charge remains in the junction capacitance in the organic EL element, the charged charge gradually starts to discharge immediately after the driving pulse is turned off. Even if the voltage applied to the light emitting diode 1c in the organic EL element holds the voltage equal to or higher than the light emission threshold, light emission does not stop, and the light emission period becomes longer than the desired light emission period. There is also. Further, when the scan is ended and the next scan electrode is selected, the residual charge in the previous scan moves to the organic EL element connected to the next scan electrode, and the non-light emitting element is erroneously turned on, and the image quality is reduced. There is also the problem of deterioration. From such a problem, there has been proposed a method provided with a discharge means for quickly removing the electric charge of the junction capacitance in the organic EL element immediately after the light emission is stopped.

Japanese Patent No. 3102411 proposes a method of charging the junction capacitance of an organic EL element by pulse charging. Further, in JP-A-10-222127, an organic EL
A method of discharging the junction capacitance of the device has been proposed. FIG. 6 shows a drive circuit using a charging method similar to that of the first embodiment in Japanese Patent No. 31024411 and a discharging method similar to that of the embodiment in Japanese Patent Laid-Open No. 10-222127. In FIG. 6, the number of scanning electrodes in the scanning circuit is one row and the number of data electrodes in the data circuit is four columns in order to simplify the description, but the same embodiment is used regardless of the number of driving elements. Is possible. 1 is an organic EL element, 2 is a switch for turning on the current source 3, 3 is a current source, 4
Is a drive pulse for driving the current source 3, 6 is a voltage source, 11 is a charge pulse generation circuit, 12 is a switch for turning on the voltage source 6 during charging, and 7 and 8 are switches in the scanning side circuit. Reference numeral 21 is a switch for discharging the junction capacitance of the organic EL element, and 22 is a discharge pulse. FIG. 7 shows FIG.
3 is an example of a timing chart when driving the conventional organic EL element display device of FIG.

Next, the driving sequence of this conventional example will be described. When a drive pulse is input by a controller (not shown), a charge pulse synchronized with the drive pulse is output from the charge pulse generation circuit 11, the switch 12 is turned on by the charge pulse, and the switch 2 is turned on by the drive pulse, and the scanning side is turned on. In the circuit, the switch 7 turns from on to off and the switch 8 turns from off to on. The rising edge of the charging pulse is synchronized with the rising edge of the driving pulse, and the pulse width t of the charging pulse is set to be sufficiently shorter than the pulse width T of the driving pulse. As a result, both the voltage source VCC1 and the current source 3 are simultaneously connected to the organic EL element 1 at the moment when the driving pulse and the charging pulse are input. Immediately after turning on, since the accumulated charge in the junction capacitance of the organic EL element 1 is zero, the voltage source VC connected by the charging pulse is connected.
A charging current flows from C1 to the junction capacitance in the organic EL element. The junction current in the organic EL element is rapidly charged by this charging current. Subsequently, when the time t elapses and the charging pulse is turned off, only the current source is connected to the organic EL element 1. Since the junction capacitance of the organic EL element has already been charged, the organic EL element immediately starts emitting light by constant current driving.

After a lapse of time T, the drive pulse is turned off and the switch 2 is turned off. In the scanning side circuit, the switch 7 is turned on and the switch 8 is turned on. Immediately after the drive pulse is turned off, the discharge pulse is subsequently turned on. When the discharge pulse is turned on, the switch 21 is turned on, and the electric charge accumulated in the junction capacitance of the organic EL element is discharged to GND. The pulse width of the discharge pulse is set to such a time that the junction capacitance of the organic EL element can be sufficiently discharged. When the discharge pulse is turned off, the switch 21 is turned off.

FIG. 7 shows the relationship between the anode voltage waveform of the organic EL element 1 and the driving pulse, the charging pulse and the discharging pulse in the case of having a charging pulse and the case of not having the charging pulse in the conventional example. . When there is no charging pulse, light emission delay is caused for the above reason, and therefore the anode voltage in the organic EL element has a waveform of aie.
The organic EL element does not emit light until the time t2, which is the emission threshold level of the organic EL element, is reached, and the emission gradually starts from the moment when the time is exceeded. On the other hand, Japanese Patent No. 31024
In the conventional example which is the embodiment of No. 11, since the charging pulse is applied, the anode voltage in the organic EL element is ab-
The waveform becomes cd-e. In this conventional example, since charging is performed by the voltage source VCC1 having a higher potential than the anode voltage of the organic EL element being driven by the current source 3, the organic EL element is charged for a period up to t when the charging pulse is applied. Anode voltage is VC
It is fixed at the potential of C1. Next, after the time t has passed and the charging pulse is turned off, the junction capacitance of the organic EL element has already been charged, so that the waveform becomes cde from the point c. In this way, by driving the constant voltage for a period t by the charging pulse, the junction capacitance of the organic EL element can be instantly charged, and the anode voltage of the organic EL element can be instantly raised to start light emission quickly. Therefore, it is possible to obtain sufficient brightness.

According to the conventional example, a charging pulse is applied and a constant voltage source is connected to the organic EL element during the charging period to rapidly charge the junction capacitance of the organic EL element, thereby increasing the anode voltage of the organic EL element. It is possible to accelerate the rise and improve the emission brightness.

The pulse width of the charging pulse in the conventional example is the organic E
Junction capacitance 1b of L element, forward resistance 1 of organic EL element
It is determined based on a time constant obtained from parameters such as a, the switch 12 which is a transistor, the ON resistance of the switch 8 and the wiring resistance of electrodes.

[0013]

[Problems to be Solved by the Invention] However, organic E
The current flowing through the switch 8 in the scanning circuit of the L-element display device varies depending on the number of light emitting pixels per scanning row. Therefore, the voltage drop, which is the product of the ON resistance of the switch 8 and the charging current flowing through the switch 8, changes depending on the light emission pattern, and the cathode potential in the organic EL element increases as the number of light emitting pixels increases. However, since the charging voltage is a constant voltage, if the number of light emitting pixels per scanning row increases, the charging current will decrease.

Further, the organic EL element deteriorates in luminous efficiency and decreases in luminance due to continuous light emission, but at this time, the internal impedance of the organic EL element, that is, the forward resistance 1a, increases with the deterioration in luminous efficiency. I'm holding. On the other hand, since the charging voltage is still a constant voltage, the deterioration of the organic EL element will reduce the charging current.

In such a situation, the following problems occur. Organic EL when the organic EL element is driven by the current source 3
In the method of charging with a voltage higher than the anode voltage of the element, if the organic EL element is driven with a longer charging time so as not to cause a shortage of the charging current due to the above-mentioned reasons, etc. Since current driving cannot be performed and voltage driving is performed, image quality is adversely affected by voltage driving. Specifically, as described above, the organic EL element has a proportional relationship between the luminance and the current. Therefore, when the organic EL element display device is driven by voltage, uneven light emission is caused due to nonuniform current, and the image quality is deteriorated.

The cause of the uneven light emission is due to uneven light emitting efficiency due to the difference in the film thickness distribution of the organic layer and the difference in the wiring resistance due to the difference in the pixel position. In the case of current driving, these factors are eliminated. Although it is possible to achieve uniform brightness,
In voltage driving, current unevenness, that is, brightness unevenness is caused by these causes. Particularly in an organic EL element display device having a large number of scanning lines, the time of one scanning period T becomes short, but the charging period t does not depend on the number of scanning lines, so the ratio of the charging time t to the scanning period T increases. Will end up. When the ratio of voltage driving increases with respect to the ratio of current driving, luminance unevenness becomes particularly remarkable.

On the other hand, when the charging time t is set to be short, it is conceivable that the charging may be insufficient due to the reasons described above. There is also a method of compensating for insufficient charging by increasing the charging voltage instead of the charging time, but as the charging voltage increases, it becomes necessary to increase the breakdown voltage of the driver, which also causes an increase in the price of the drive circuit.

The details of the operation in the case of insufficient charging will be described. FIG. 7 also shows a waveform of the anode voltage of the organic EL element when insufficient charging occurs in the conventional example. As described above, in the state where the charging is completed at the charging time t, the anode voltage waveform is a-b-c-d-e.
Becomes However, it cannot be fully charged at the charging time t,
When the state of insufficient charging is reached, the anode voltage waveform is ab-c-
The waveform becomes f-g-e. With such a waveform, the voltage is held by the voltage source VCC1 during the charging period, but the charging of the junction capacitance of the organic EL element is not completed during the charging period.
At the moment when the charging pulse is turned off, the anode potential of the organic EL element suddenly drops to f. Since the voltage source has already been turned off, the junction capacitance is gradually recharged by the current source 3 after that. However, if only the current source is driven, the charging current will be limited, and the rise of the anode voltage will be delayed. In particular, when the forward resistance 1a in the organic EL element increases over time to cause insufficient charging, the panel brightness deteriorates due to the life of the element and a factor of the anode voltage rise delay in the organic EL element due to insufficient charging is rapidly added. It lowers the brightness. As a result, the product life is shortened.

As described above, the conventional example has a problem that if charging is not completed while the charging pulse is being applied, the brightness is lowered due to insufficient charging. Further, if the charging time is too long, although sufficient light emission brightness can be secured, there is a problem that the voltage driving period increases and the image quality deteriorates. Furthermore, the conventional charging method requires a charge pulse generation circuit for generating a charge pulse, which complicates the driver circuit and causes a cost increase in the drive circuit.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a drive circuit for an organic electroluminescence element display device having a configuration effective for solving these problems.

[0021]

A first aspect of the present invention for solving the above problems is an organic device for passively driving a display device in which a plurality of pixels having at least an organic electroluminescence element are arranged in a matrix. In a drive circuit for an electroluminescent element display device, a current source for supplying a drive current to the organic electroluminescent element, a voltage source for charging the junction capacitance of the organic electroluminescent element, and a control means. The current source and the voltage source are connected to the anode side of the organic electroluminescent element, and the voltage of the voltage source is the anode of the organic electroluminescent element when the organic electroluminescent element is driven by the current source. A voltage lower than the voltage, the control means is ON period of current sources and the voltage source is characterized in that control to be the same.

A second aspect of the present invention is a drive circuit for an organic electroluminescence element display device for passively driving a display device in which a plurality of pixels having at least an organic electroluminescence element are arranged in a matrix, wherein the organic electroluminescence element is used. A current source for supplying a drive current to the luminescence element, a voltage source for charging the junction capacitance of the organic electroluminescence element, and a control means are included at least, and the current source and the voltage source are the organic electroluminescent element. Connected to the cathode side of the luminescence element, the voltage of the voltage source is a voltage higher than the cathode voltage of the organic electroluminescence element when driving the organic electroluminescence element with the current source, the control means, The on period of the current source and the voltage source are the same. It is characterized in that controlled.

A third aspect of the present invention is a drive circuit for an organic electroluminescence element display device for passively driving a display device in which a plurality of pixels, each of which has at least an organic electroluminescence element, are arranged in a matrix. A current source for supplying a driving current to the luminescence element, a voltage source for charging the junction capacitance of the organic electroluminescence element, and at least a control means, further measuring the anode voltage of the organic electroluminescence element. For measuring, the current source and the voltage source are connected to the anode side of the organic electroluminescence element, the control means, the ON period of the current source and the voltage source is controlled to be the same. And with the current source, the organic electroluminescence Based on the output of the result of measuring the anode voltage of the organic electroluminescence element when the element is driven, the voltage of the voltage source is controlled to a voltage lower than the anode voltage. .

A fourth aspect of the present invention is a drive circuit for an organic electroluminescence element display device for passively driving a display device in which a plurality of pixels having at least an organic electroluminescence element are arranged in a matrix. A current source for supplying a driving current to the luminescence element, a voltage source for charging the junction capacitance of the organic electroluminescence element, and at least a control means, and further measures the cathode voltage of the organic electroluminescence element. For measuring, the current source and the voltage source are connected to the cathode side of the organic electroluminescent element, the control means, the ON period of the current source and the voltage source is controlled to be the same. And with the current source, the organic electroluminescence Based on the output of the result of measuring the cathode voltage of the organic electroluminescence element when the element is driven, the voltage of the voltage source is controlled to a voltage higher than the cathode voltage. .

Further, in the present invention according to the third aspect of the present invention, "the control means is based on a result of measurement by the measuring means of an anode voltage when all the organic electroluminescent elements are driven by the current sources. , Controlling the voltage of the voltage source with the minimum value of the anode voltage "," excludes from the measurement result of the measuring means an anode voltage that significantly deviates from the distribution with a specific threshold value, and "Controlling the voltage of the voltage source with the minimum value of the anode voltage within the frame" is included as a preferable embodiment.

Further, in the present invention according to the fourth aspect of the present invention, "the control means is based on a result obtained by measuring the cathode voltage when the organic electroluminescent elements are driven by the current sources by the measuring means. , Controlling the voltage of the voltage source with the maximum value of the cathode voltage "," excludes a cathode voltage significantly deviating from the measurement result from the measurement means with a specific threshold value, and "Controlling the voltage of the voltage source with the maximum value of the cathode voltage within the frame" is included as a preferable mode.

Further, in the first to fourth aspects of the present invention, it is preferable that the current source and the voltage source are connected to the organic electroluminescence element through a common switch.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, specific embodiments of the present invention will be described, but the present invention is not limited to these specific embodiments. In particular, in the following, a mode in which the current source and the voltage source are connected to the anode side will be described, and when connected to the cathode side, description thereof is omitted because it can be easily estimated from these.

(Embodiment 1) FIG. 1 shows an organic EL device of the present invention.
It is a conceptual diagram showing 1st Embodiment of the drive circuit of an element display apparatus. Here, only the part directly related to the present invention will be described. In the present invention, 2 is a switch that connects both the voltage source 6 and the current source 3 to the organic EL element 1. Reference numeral 5 is a diode, and 6 is a voltage source. FIG. 4 is a schematic timing chart when the drive circuit of the organic EL element display device of the present invention is driven, and shows the relationship between the anode voltage waveform of the organic EL element 1 and the drive pulse. In this embodiment, the switch 2
A driver (not shown) that generates a drive pulse corresponds to the control means.

In the form shown in FIG. 1, the switch 2 is a single switch that connects both the voltage source 6 and the current source 3 to the organic EL element 1, which is a preferable form. The switches may be provided separately. However, in this case, it is necessary to turn them on and off at the same time by the driver included in the control means. However, the period is not completely the same, and may be shifted by a time smaller than the drive pulse period.

When the organic EL element 1 is driven by the current source 3, the anode voltage of the organic EL element varies depending on the luminous efficiency of the element, wiring resistance, etc., but the voltage of the voltage source 6 is the above-mentioned organic EL element. In consideration of all the factors of variation in the anode voltage due to variations in the anode voltage and other factors such as deterioration over time, etc., the voltage is preset to a voltage lower than the lowest expected value of the anode voltage in consideration of the factors of variation.

The reason for setting in this way is that in the present invention, the voltage source 6 of the charging voltage and the current source 3 of the driving source are turned on for the same period, and the anode voltage becomes higher than the voltage source 6 when the charging is completed. This is because it is a method of switching the voltage drive to the current drive by interrupting the current supply from the voltage source 6.
Needs to be lower than the lowest anode voltage at the time of current driving by the current source 3. Therefore, when the element with the lowest anode voltage is driven, if the current drive is switched to the current source after the charging of the junction capacitance is completed, the minimum difference of the anode voltage of this organic EL element and the potential difference of the voltage source 6 are sufficiently small. It doesn't matter.

The operation will be described below with reference to FIGS.

When a drive pulse is input from the control means (not shown), the switch 2 selected by the drive pulse is turned on, and the voltage source 6 via the diode 5 and the current source 3 are simultaneously applied to the organic EL element 1. Connected. In synchronization with this, in the scanning side circuit, the switch 7 changes from on to off and the switch 8
Turns from off to on. Immediately after the drive pulse is turned on, since the junction capacitance in the organic EL element has no accumulated charge, a charging current flows from the voltage source to the junction capacitance of the organic EL element via the diode 5, and the anode voltage of the organic EL element is The voltage source instantly charges up to VCC2 and the anode voltage rises. Since the anode voltage when the organic EL element is driven by the current source 3 is higher than VCC2, when the charging from the voltage source is completed, the current supply from the current source 3 to the organic EL element starts and the junction capacitance in the organic EL element is further increased. To charge. Organic E
When the anode voltage of the L element rises and becomes higher than VCC2, the diode 5 cuts off the current from the voltage source 6, and the organic EL element 1 immediately shifts from voltage driving to current driving.

After the lapse of time T, the drive pulse is turned off and the switch 2 is turned off. In the scanning side circuit, the switch 7 is turned on and the switch 8 is turned on. Immediately after the drive pulse is turned off, the discharge pulse is subsequently turned on. When the discharge pulse is turned on, the switch 21 is turned on, and the electric charge accumulated in the junction capacitance of the organic EL element is discharged to GND. When the discharge pulse is turned off, the switch 21 is turned off.

Next, the case of performing gradation control will be described. Generally, when gradation control is performed in an organic EL element display device, a method of controlling a drive pulse width by pulse width modulation (PWM) and a method of controlling a drive current or a charging voltage can be considered. In the method of controlling the drive pulse width by PWM, which is a preferable method for applying the present invention, the drive pulse width becomes the shortest when the minimum gray level is output.

In the conventional example, even if the charging pulse is applied and the charging is completed before the charging pulse time t, the current drive is not switched until the time t, but in the embodiment of the present invention, the voltage source is changed to the current source. As the switching of, the diode 5 cuts off the current supply from the voltage source immediately after the charging of the junction capacitance by the voltage source is completed, and the drive from the voltage source is switched to the drive by the current source immediately. It has become possible to minimize the period of voltage drive. As a result, it is possible to extend the ratio of current drive during the scanning period, and it is possible to prevent uneven brightness and improve the image quality even when the drive pulse width is short. Especially when it is necessary to consider the case where the drive pulse width is short, it is preferable to separately provide a switch for the current source and a switch for the voltage source, turn off the voltage source after turning off the current source, and secure the charging time as much as possible. By doing so, it becomes possible to perform correction by voltage drive even if the brightness becomes insufficient especially when the drive pulse width is short.

Further, in the embodiment of the present invention, since the charging voltage is not turned off during the light emission period, the voltage source is turned off and the charging is not insufficient when the time t is exceeded as in the conventional example. Further, since the charging pulse generating circuit is not required, it is possible to provide a low-priced drive circuit having a simple circuit configuration as compared with the conventional one.

(Embodiment 2) FIG. 2 shows an organic EL device of the present invention.
It is a conceptual diagram showing Embodiment 2 of the drive circuit of an element display device. This embodiment is the same as the first embodiment except for the points described here. In order to simplify the explanation, the number of scan electrodes is 1
Although the number of rows and the number of data electrodes are three columns, the same configuration is possible regardless of the number of pixels.

Reference numeral 9 controls the scanning side circuit and the data side circuit, and when the organic EL element is driven by the current source, the anode voltage of the organic EL element in an arbitrary column is measured and the voltage source 6 is set to an optimum value. It is a microcomputer for controlling. 10 is a voltage source 6
, 19 and 20 are resistors.

The difference from the first embodiment is that in the present embodiment, an organic EL element display device for one arbitrary column in the organic EL element display device.
It consists in measuring the anode voltage of the device and controlling the charging voltage. In the case of the organic EL element display device in which the rows and columns are reversed,
Either the anode voltage for the rows is measured, but either one is acceptable.
In this embodiment, the switch 2 and the microcomputer 9
The transistor 10 and the resistors 19 and 20 are included in the control means. Further, the microcomputer 9 is also used as a measuring means and also serves as these means.

In the first embodiment, the variation of the anode voltage of the organic EL elements in the same organic EL element display device, variation factors due to deterioration over time, difference in the number of lighting pixels, and the like are all taken into consideration, and the lowest anode voltage is the minimum. Although the value is assumed in advance and set to a voltage lower than that, in the second embodiment of the present invention, the anode voltage for one row in the organic EL element is actually measured at the first scan when the power is turned on. Then, the minimum value of the anode voltage is detected, and the charging voltage is controlled at a voltage lower than the minimum value. The reason why the voltage lower than the minimum value is the charging voltage is the same as the reason described in the first embodiment of the present invention. Therefore, it is not necessary to consider a variation factor due to variations in manufacturing of the anode voltage due to the pixels of the organic EL element, changes over time, and the like. Therefore, in the second embodiment of the present invention, the charging voltage VCC2 is set as the embodiment It is possible to control to a potential higher than 1. If VCC2 can be set high, it is possible to further suppress the rise delay in the organic EL element immediately after the driving by the current source 3 starts after charging the junction capacitance in the organic EL element. Therefore, although the circuit configuration is slightly more complicated than that of the first embodiment of the present invention, there is an effect that the emission brightness can be further improved.

The timing chart in the second embodiment of the present invention is the same as that in FIG. 4, except that the VCC2 is higher in the second embodiment than in the first embodiment and closer to the vicinity of the anode voltage of the organic EL element. This is because the voltage is set, and the rise delay of the anode voltage of the organic EL element after the completion of charging is improved.

Next, the operation will be described. A drive pulse for driving a current source is input to the data circuit from the microcomputer 9, and the scan electrodes are sequentially selected to start selecting the scan electrodes, and the switch 7 is turned on and the switch 8 is turned on. The data side circuit outputs the charging voltage by the voltage source 6 and the current by the current source 3 to the organic EL element based on the drive pulse. Since the microcomputer 9 does not recognize the anode voltage of the organic EL element in the first scanning period after the power supply is turned on until the scan electrode completes one-cycle driving, the voltage source 6 uses the anode voltage when current-driving the organic EL element. Any initial value lower than the voltage is set. This initial value determines the charging voltage until the one-cycle driving of the scan electrodes is completed.

D / of the microcomputer 9 based on the above initial value
A charging voltage is output from the voltage source 6 from the A port via the transistor 10. Anode voltage V of the organic EL element in an arbitrary data row during the period in which the scan electrode is first driven once.
1 is taken in from the A / D port of the microcomputer 9. Immediately after the completion of the one-cycle driving, the microcomputer 9 detects the minimum value of the read voltage V1, but the anode voltage in the non-emission pixel is 0V.
Therefore, only the anode voltage of the organic EL element in the light emitting pixel is detected and the minimum value thereof is detected. FIG. 8 shows the waveform of V1 captured by this microcomputer. In this example, the anode voltage of the organic EL element in the fifth row is the lowest, and it is obtained as the minimum value of the anode voltage of the organic EL element. Preferably, the average value of the anode voltage values at the time of saturation during driving is taken as this minimum value, but a peak value may be taken if saturation is not reached.

Then, when the scan electrode enters the second driving cycle, the D / A port of the microcomputer 9 replaces the initial value with a voltage lower than the minimum value of the voltage V1 by the resistance 1
9. The voltage is output via the transistor 10, and thereafter, this voltage is held until the power supply to the drive circuit of the organic EL element display device is turned off.

In this way, when the scan electrode is driven for one cycle and enters the second cycle for driving, a voltage based on the minimum value of the anode voltage V1 for one column is output from the voltage source 6 via the transistor 10. The voltage source 6 outputs the same voltage until the power source of the drive circuit is turned off. Similar to the first embodiment of the present invention, the junction capacitance of the organic EL element is charged by this voltage source, and current driving is started after the end of charging. Although the circuit is slightly more complicated than that of the first embodiment, the voltage source 6 is controlled based on the actually measured anode voltage V1. Therefore, the voltage of the voltage source 6 is higher than that of the first embodiment of the present invention, that is, charging is performed. The voltage can be controlled high, and the anode voltage rise of the organic EL element can be accelerated,
The brightness in the display device can be improved.

(Third Embodiment) FIG. 3 shows an organic EL device of the present invention.
It is a conceptual diagram showing 3rd Embodiment of the drive circuit of an element display device. This embodiment is the same as the first and second embodiments except for the points described here.

In the third embodiment, as in the second embodiment, the anode voltage in the organic EL element is measured and the voltage source 3 is controlled, but in the second embodiment, one row of organic EL elements is used.
While only the anode voltage of the element is measured, the third embodiment is different in that all the anode voltages in the organic EL element display device are measured. In the second embodiment, it is possible to estimate the variation of the anode voltage in the organic EL element display device to some extent by measuring the anode voltage for one column, but it is necessary to measure all the anode voltages in the organic EL element display device. Therefore, it is necessary to consider the variation margin in the measurement result of the anode voltage V1, and the voltage of the voltage source 6 has to be set low accordingly. On the other hand, in the third embodiment, although the drive circuit is slightly more complicated than in the second embodiment, the anode voltage in all the organic EL elements is measured and the voltage source 6 is controlled at a voltage lower than the minimum value. In practice, the voltage of the voltage source 6 can be set to the upper limit value of the charging voltage that is the limit for automatically switching from voltage driving to current driving. This minimizes the delay in rising the anode voltage,
It is possible to maximize the emission brightness.

Next, the operation will be described. A driving pulse is output from the microcomputer 9 to sequentially start selecting scanning electrodes to the scanning circuit, and the data circuit outputs a charging voltage by the voltage source 6 and a current by the current source 3 to the data electrode based on the driving pulse. At this time, for the same reason as in the second embodiment, an arbitrary initial value lower than the anode voltage in the organic EL element is set until the circuit is driven once, and the transistor 10 is set from the D / A port of the microcomputer according to the initial value. Is output via. When the organic EL element is started to be driven, the switches 16 to 18 are sequentially turned on one by one during the scanning period. As a result, the anode voltages V1, V2, and V3 pass through the buffers of the operational amplifiers 13 to 15 and have a waveform V as shown in FIG.
It is input to the A / D port of the microcomputer 9 as a. Here, the microcomputer 9 calculates the minimum value of the organic EL element in the waveform Va.

As in the second embodiment, since the anode voltage of the non-light emitting element is 0V, the minimum value of the anode voltage in the light emitting pixel is calculated. In the second embodiment, the A / D port of the microcomputer 9 takes in the anode voltage of the organic EL elements for one column, but in the third embodiment, the organic EL elements for all the pixels are taken in.
The anode voltage in the device can be taken in. After the scan electrode has been driven for one round and has entered the second round of driving, the voltage based on the minimum value for the entire screen is output from the voltage source 6 via the transistor 10 and driven as in the second embodiment. The voltage source 6 outputs the same voltage until the power of the circuit is turned off. As described above, in the third embodiment, the charging voltage by the voltage source 3 is controlled based on the measurement result of the anode voltage at the time of current driving of all the organic EL elements in the display device. The voltage is further optimized,
The brightness of the organic EL display device can be improved.

Incidentally, the second and third embodiments of the present invention.
In the above description, the configuration in which the anode voltage of the organic EL element is read by the microcomputer 9 only immediately after the power is turned on is described. However, by further reading the anode voltage periodically and reflecting it in the charging voltage control, it is possible to further control the charging voltage. Further, in the second and third embodiments of the present invention, the anode voltage in the organic EL element is actually measured at the time of the first scanning, but the number of obtained anode voltage data decreases when the number of lighting pixels is small. At the time of scanning, all pixels may be turned on once to measure all anode voltages, and then a desired image may be output from the next scanning. In this case, higher precision voltage control can be realized.

In the second and third embodiments of the present invention, when the anode voltage of an organic EL element is measured, and when there is an element having a significantly low anode voltage due to a pixel defect or the like, a pixel defect of one pixel is detected. In order to prevent the overall charging voltage from being lowered due to, it is determined whether the minimum value of the detected anode voltage of the organic EL element deviates from a certain threshold value, and the value is distributed to a certain threshold value. It is preferable to set the minimum value only when it is considered. Specifically, for example, a method of controlling by ignoring the anode voltage value of 30 to 50% or less of the maximum value of the anode voltage measured values can be mentioned.

[0054]

As described above, according to the present invention, the luminance deterioration due to insufficient charging is suppressed, the image quality is improved by shortening the constant voltage drive period, and the charge pulse generation circuit is not required, so that the drive circuit can be provided. The cost reduction can be realized.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a first embodiment of a drive circuit of an organic EL element display device of the present invention.

FIG. 2 is a conceptual diagram showing a second embodiment of a drive circuit of an organic EL element display device of the present invention.

FIG. 3 is a conceptual diagram showing a third embodiment of the drive circuit of the organic EL element display device of the present invention.

FIG. 4 is a schematic timing chart at the time of driving a drive circuit of the organic EL element display device of the present invention.

FIG. 5 is an equivalent circuit diagram for explaining characteristics of an organic EL element.

FIG. 6 is a conceptual diagram showing an example of a drive circuit of a conventional organic EL element display device.

FIG. 7 is an example of a timing chart when driving a drive circuit of a conventional organic EL element display device.

FIG. 8 is an explanatory diagram illustrating an example of data captured by a control unit according to the second embodiment of the present invention.

FIG. 9 is an explanatory diagram illustrating an example of data captured by a control unit according to the third embodiment of the present invention.

[Explanation of symbols]

1 Organic EL element 1a resistance 1b capacitor 1c light emitting diode 2 switches 3 current source 4 drive pulse 5 diode 6 voltage source 7 switch 8 switches 9 Microcomputer 10 transistors 11 Charging pulse generation circuit 12 switches 13 Op-amp 14 Operational amplifier 15 operational amplifier 16 switch 17 switch 18 switch 19 resistance 20 resistance 21 switch 22 discharge pulse

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuhiro Aizawa             1248, Shimokagemori, Chichibu-shi, Saitama             N Electronics Co., Ltd. (72) Inventor Masatoshi Yamada             1248, Shimokagemori, Chichibu-shi, Saitama             N Electronics Co., Ltd. F-term (reference) 3K007 AB02 AB17 AB18 BA06 DA01                       DB03 EB00 GA02 GA04                 5C080 AA06 BB05 DD05 EE28 FF09                       JJ03 JJ04 JJ05

Claims (9)

[Claims] 1. In a drive circuit of an organic electroluminescence element display device for passively driving a display device in which a plurality of pixels each including at least an organic electroluminescence element are arranged in a matrix, a driving current is supplied to the organic electroluminescence element. For supplying a current source, a voltage source for charging the junction capacitance of the organic electroluminescent element, and at least a control means, the current source and the voltage source are the anode side of the organic electroluminescent element. The voltage of the voltage source is lower than the anode voltage of the organic electroluminescent element when the organic electroluminescent element is driven by the current source, and the control means is the current source and the voltage. Control so that the on-time with the source is the same. And a drive circuit for an organic electroluminescence element display device. 2. In a drive circuit of an organic electroluminescence element display device for passively driving a display device in which a plurality of pixels having at least an organic electroluminescence element are arranged in a matrix, a driving current is applied to the organic electroluminescence element. A current source for supplying, at least a voltage source for charging the junction capacitance of the organic electroluminescent element, and a control means, the current source and the voltage source are the cathode side of the organic electroluminescent element. The voltage of the voltage source is higher than the cathode voltage of the organic electroluminescent element when the organic electroluminescent element is driven by the current source, and the control means is the current source and the voltage. The on-time with the power source can be controlled to be the same. And a drive circuit for an organic electroluminescence element display device. 3. In a drive circuit of an organic electroluminescence element display device for passively driving a display device in which a plurality of pixels each including at least an organic electroluminescence element are arranged in a matrix, a driving current is applied to the organic electroluminescence element. A current source for supplying, a voltage source for charging the junction capacitance of the organic electroluminescent element, and at least a control means, further measuring means for measuring the anode voltage of the organic electroluminescent element. Prepare,
The current source and the voltage source are connected to the anode side of the organic electroluminescence element, the control means controls so that the ON period of the current source and the voltage source are the same, and in the current source Based on the output of the result of measuring the anode voltage of the organic electroluminescence element when the organic electroluminescence element is driven by the measuring means, the voltage of the voltage source is controlled to a voltage lower than the anode voltage. A driving circuit for an organic electroluminescence element display device. 4. The control means, based on the result of measuring the anode voltage when driven by the current sources of all of the organic electroluminescent elements, by the minimum value of the anode voltage, the control means The drive circuit for an organic electroluminescence element display device according to claim 3, wherein the source voltage is controlled. 5. The voltage of the voltage source is controlled with a minimum value of the anode voltage falling within the frame of the specific threshold value, from the measurement result of the measuring means, an anode voltage that deviates significantly from the distribution is excluded with a specific threshold value. The drive circuit for an organic electroluminescence element display device according to claim 3 or 4, wherein 6. In a drive circuit of an organic electroluminescence element display device for passively driving a display device in which a plurality of pixels having at least an organic electroluminescence element are arranged in a matrix, a driving current is applied to the organic electroluminescence element. A current source for supplying, a voltage source for charging the junction capacitance of the organic electroluminescent element, and at least a control means, further measuring means for measuring the cathode voltage of the organic electroluminescent element. Prepare,
The current source and the voltage source are connected to the cathode side of the organic electroluminescence element, the control means controls so that the ON period of the current source and the voltage source are the same, and in the current source. Based on the output of the result of measuring the cathode voltage of the organic electroluminescence element when the organic electroluminescence element is driven by the measuring means, the voltage of the voltage source is controlled to a voltage higher than the cathode voltage. A driving circuit for an organic electroluminescence element display device. 7. The control means, based on the result of measuring the cathode voltage when driven by the current sources of all the organic electroluminescence elements, by the maximum value of the cathode voltage, The drive circuit for an organic electroluminescence element display device according to claim 6, wherein the source voltage is controlled. 8. The voltage of the voltage source is controlled with a maximum value of the cathode voltage falling within the frame of the specific threshold value, by eliminating from the measurement result of the measuring means, the cathode voltage significantly deviating from the distribution. The drive circuit for an organic electroluminescence element display device according to claim 6 or 7. 9. The method according to claim 1, wherein the current source and the voltage source are connected to the organic electroluminescence element via a common switch. A drive circuit for an organic electroluminescence element display device.