JP2000330517A - Display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily control the average luminance (apparent brightness) of a display element. SOLUTION: An organic EL(electroluminescence) 110 emits light in accordance with a charge amount to be injected by the application of a voltage. One side of the source and the drain of a driving Tr(transistor) 210 connected to the organic EL 110 and the other side of them is connected to a power source via a charge detecting circuit 220. The circuit 220 measures a charge amount to be injected to the EL 110 by measuring the magnitude of a current flowing through the circuit and measurs a total charge amount to be injected to the EL 110 in a prescribed time by accumulating the charge amount. A control circuit 230 controls the total charge amount to be injected to the EL 110 by applying a gate voltage to the Tr 210 according to the measured result by the circuit 220 to make the EL 110 emit light with a prescribed average luminance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a display device and a method of driving the same, and more particularly, to a display device capable of reducing power consumption and a method of driving the same.

[0002]

2. Description of the Related Art Organic EL (Electroluminescence)
Is composed of, for example, an electron transporting light emitting layer formed on the cathode electrode side, and a hole transporting layer formed on the anode electrode side. The organic EL emits light by injecting electrons from the cathode electrode side and holes from the anode electrode side by applying a voltage between the electrodes. The organic EL is shown in FIG.
It has characteristics as shown in FIG. 7 and FIG. FIG. 6 shows the time change of the voltage-current characteristics, FIG. 7 shows the voltage-current density characteristics at different temperatures, and FIG. 8 shows the current density-luminance characteristics at different temperatures.

In FIG. 6, when voltage application to the organic EL is started (initial time) and after a certain time or more (after a certain time), for example, 500 hours after the voltage application is started This shows the voltage-current characteristics later. As shown in FIG. 6, the characteristics of the organic EL change when voltage is applied and light continues to be emitted. Specifically, when a constant voltage is applied to the organic EL, the current flowing decreases with time. That is, the resistance value of the organic EL increases with time. As shown in FIG. 7, the organic EL has different voltage-current density characteristics depending on the temperature. In particular,
When a constant voltage is applied to the organic EL, the higher the temperature, the larger the current that flows. That is, the higher the temperature, the lower the resistance value of the organic EL. Further, as shown in FIG.
Has almost the same current density-luminance characteristics in the temperature range of 0 ° C. to 40 ° C. Specifically, even if the temperature changes,
If the density of the current flowing through the organic EL is constant, almost constant luminance is exhibited.

[0004] As described above, a driving method of a display device in which a plurality of organic ELs are arranged includes a constant voltage drive in which a constant voltage is applied to the organic EL to emit light, and a constant voltage drive in which a constant current flows in the organic EL to emit light. There are two types of current drive. In the constant voltage driving, there is a problem in that the current flowing in the organic EL decreases with time and the luminance decreases due to the characteristics of the organic EL shown in FIG. In the case of constant voltage driving, FIG.
Due to the characteristics of the organic EL shown in (1), there is a problem that the luminance changes due to a temperature change. Further, in the constant voltage drive, the pixel (organic E)
There is a problem that the luminance may be different for each L).

On the other hand, in the constant current driving, the magnitude of the current flowing through the organic EL is controlled based on the characteristics of the organic EL shown in FIG.
Brightness can be controlled with high accuracy. The display device driven by the constant current has, for example, a configuration as shown in FIG. As shown in FIG. 9A, the display device includes a display unit 500, a driving Tr (transistor) 600, and a control unit 700.

The display section 500 corresponds to each intersection (pixel) between data electrodes R1 to Rm formed vertically at predetermined intervals and selection electrodes L1 to Ln formed horizontally at predetermined intervals. An organic EL 510 is formed at the position. One end of each of the data electrodes R1 to Rm is
It is connected to the. On the other hand, one ends of the selection electrodes L1 to Ln are connected to the ground or the power supply Vdd by switching the switch 520. One drive Tr 600 is provided for each of the data electrodes R1 to Rm, one of its source and drain is connected to the data electrodes R1 to Rm, and the other is connected to the power supply Vdd. The gate of the driving Tr 600 is connected to the control unit 700.

The control unit 700 includes a driving Tr 600
The driving Tr 600 is turned on by applying a predetermined voltage to the gate of the driving Tr 600. Further, the control section 700 sequentially switches the switches 520 so as to synchronize with the application of the gate voltage.
The control unit 700 switches the switch 520 so that only one selection electrode is connected to the ground. In this way, the control section 700 causes the pixel (organic EL 510) to emit light for each selected electrode.

Hereinafter, the constant current driving in the display device having the above configuration will be described. As described above, since only one selection electrode is connected to the ground, FIG.
The circuit shown in FIG. 9B can be regarded as a circuit in which the circuits shown in FIG. As shown in FIG.
L510 and drive Tr600 are connected in series.
Therefore, the power supply voltage Vdd is equal to the driving voltage of the organic EL 510 and the driving Tr.
600, and a current of the same magnitude flows through the organic EL 510 and the driving Tr 600.

In the constant current driving, the following characteristics of the driving Tr 600 are used to keep the magnitude of the current flowing through the organic EL 510 and the driving Tr 600 constant. Drive Tr6
00 has normal transistor characteristics as shown in FIG. Specifically, the source-drain voltage Vsd
Below a certain value, the voltage Vsd is proportional to the drain current Id, and when the voltage Vsd exceeds a certain value, the current Id
d becomes saturated and constant. The magnitude of the saturation current Id increases as the gate voltage increases. Due to such characteristics, if a saturation current is allowed to flow through the driving Tr 600, a constant current can flow even if the magnitude of the voltage applied to the organic EL 510 and the driving Tr 600 changes.

FIG. 11 shows the organic EL 510 and the driving T
FIG. 9 is a diagram showing a change over time of a voltage-current characteristic of r600. In FIG. 11, the source-drain voltage Vsd of the driving Tr 600 is turned rightward and the organic EL 510 is turned leftward.
And the vertical axis represents currents Id and Iel.

In the above display device, for example, the power supply voltage Vdd
Is 21 (V), and the gate voltage of the driving Tr 600 is 10
Set to (V). By doing so, as shown in FIG. 11, the characteristics of the organic EL 510 change over time, and the voltage division ratio of the power supply voltage Vdd changes. However, due to the characteristics of the driving Tr 600, a constant current (see FIG.
In the case of 1, 40 (μA)) can flow. As described above, in the constant current driving, by setting the power supply voltage Vdd and the gate voltage Vg so that the saturation current flows through the driving Tr 600, the organic E drive can be performed regardless of the lapse of time or temperature change.
The luminance of L510 (pixel) can be kept constant.

[0012]

In the above constant current drive,
Even when the time elapses, the luminance can be kept constant by supplying a constant current to the organic EL 510. However, there is a problem that wasteful power consumption is large.

For simplification of description, for example, FIG.
It is assumed that the display device of FIG. 9A is configured by arranging a plurality of circuits of FIG. 9B, and a case where the duty ratio is ４ will be described. Note that the duty ratio of 1/4 is 1
A time t1 during which the selected electrodes are connected to the ground (one scanning time), and a time t during which all the selected electrodes L1 to Ln (one field) are scanned by switching the switch 520.
That is, the ratio (t1 / t2) to 2 is 1/4. Further, as shown in FIG. 11, the power supply voltage Vdd is 21
(V), the gate voltage of the driving Tr 600 is assumed to be 10 (V).

[0014] As shown in FIG.
The voltages applied between 10 and the source and drain of the driving Tr 600 are 12 (V) and 9 (V), respectively. After the elapse of the time T, the characteristics of the organic EL 510 change,
The voltages applied between the organic EL 510 and the source and drain of the driving Tr 600 are 15 (V) and 6 (V), respectively.
Becomes On the other hand, the current flowing through the organic EL 510 and the driving Tr 600 is constant as described above, and is 40 (μA) in the above setting. The time T is the cumulative driving time of the organic EL.

FIGS. 12 and 13 show waveforms of the voltage and current in one circuit shown in FIG. 9B. FIG. 12 is a waveform diagram when the characteristics of the organic EL 510 are in the initial state shown in FIG. 11, and FIG.
FIG. 12 shows a waveform chart when the characteristic of No. 10 is after the time T shown in FIG. 11 has elapsed. 12A and FIG. 13A, (a) shows the current (I = I) flowing through the organic EL 510 and the driving Tr 600.
(B) shows a waveform diagram of the source-drain voltage Vsd of the driving Tr 600, and (c) shows a waveform diagram of the voltage Vel applied to the organic EL 510.

While scanning one field, the driving Tr6
As shown in FIG. 12, the amount of power consumed by 00 and the organic EL 510 is 90 (μW) in the drive Tr 600 and 120 (μW) in the organic EL 510 at the initial stage. After the elapse of the time T, the driving Tr 600 sets 60
(ΜW) and 150 (μW) for the organic EL 510. The amount of power consumed by the drive Tr 600 and the organic EL 510 during one field scan is 210 (μW).

As described above, the amount of power consumed by the drive Tr 600 during one field scan is 90 (μW) at the initial stage and 60 (μW) after the lapse of the time T. These are respectively the total power consumption 210 (μ
W) accounts for about 43 (%) and about 29 (%). These power consumptions do not contribute to the emission of the organic EL 510 and are wastefully consumed. That is, the constant current drive has a problem that wasteful power consumption is large as described above. Therefore, an object of the present invention is to provide a display device capable of reducing power consumption and a driving method thereof.

[0018]

In order to achieve the above object, a display device according to a first aspect of the present invention comprises: a light emitting means for emitting light in accordance with a charge amount injected by applying a voltage; Charge measuring means for measuring a total charge injected into the means within a predetermined time; applying a voltage to the light emitting means in accordance with a measurement result of the charge measuring means; And control means for controlling According to the present invention, it is possible to control the total charge amount injected into the light emitting means within a predetermined time, and to easily control the average luminance (apparent brightness) of the light emitting means.

The charge amount measuring means measures the amount of electric charge injected into the light emitting means by measuring the magnitude of the current flowing through the light emitting means, accumulates the electric charge amount, and injects the electric charge into the light emitting means. Alternatively, the total charge amount may be measured. The resistance value of the light emitting means may change over time. The light emitting means may be connected to a power supply via a transistor, and the control means may supply a control signal to a control terminal of the transistor to apply a voltage to the light emitting means.

[0020] The control means may apply a control signal to a control terminal of the transistor so that a current flowing through the transistor is not saturated. Thus, power consumed by the transistor can be reduced as compared with the case where a saturation current flows through the transistor. The light emitting means may be formed from an organic electroluminescent material.

A driving method according to a second aspect of the present invention comprises:
A method for driving a display device, comprising: a light emitting unit that emits light in accordance with an amount of charge injected by applying a voltage, wherein a voltage application step of applying a voltage to the light emitting unit and a voltage application in the voltage applying step A charge measuring step of measuring a total amount of electric charge injected into the light emitting means within a predetermined time; and stopping a voltage application to the light emitting means according to a measurement result of the charge measuring step. And a voltage application stopping step of controlling the total amount of electric charge injected into the semiconductor device. According to the present invention as well, the total amount of electric charge injected into the light emitting means within a predetermined time can be controlled, and the average luminance of the light emitting means can be easily controlled.

The charge amount measuring step includes a step of measuring a magnitude of a current flowing through the light emitting unit to measure a charge amount injected into the light emitting unit, and a step of accumulating the charge amount and applying the accumulated charge amount to the light emitting unit. Measuring the total amount of injected charge. The light emitting means is connected to a power supply via a transistor, and its resistance value changes over time, and the voltage applying step applies a control signal to a control terminal of the transistor, and applies a control signal to the light emitting means. The method may include a step of applying a voltage. The voltage applying step,
The method may further include applying a control signal to the control terminal of the transistor so that the current flowing through the transistor is not saturated.

[0023]

Next, a display device using an organic EL (electroluminescence) according to an embodiment of the present invention will be described. The display device according to this embodiment uses a simple matrix driving method, and as shown in FIG.
0 and a control unit 300.
The display unit 100 includes m data electrodes R1 to Rm, n selection electrodes L1 to Ln, an organic EL 110, and a switch 120.

The data electrodes R1 to Rm and the selection electrodes L1 to L1
Ln are formed in parallel at predetermined intervals. The data electrodes R1 to Rm and the selection electrodes L1 to Ln are formed so as to be perpendicular to each other at a predetermined interval. One end of each of the data electrodes R1 to Rm is connected to a separate constant-charge driving circuit 200,
A voltage to be applied to 110 is supplied. On the other hand, the selection electrode L
One ends of 1 to Ln are connected to the ground or the power supply Vdd by the switch 120. The switch 120
Is switched so that only one selection electrode is connected to the ground and the other selection electrodes are connected to the power supply Vdd.

The organic EL 110 includes data electrodes R1 to Rm
It is formed at a position corresponding to each intersection (pixel) between and the selection electrodes L1 to Ln. The organic EL 110 includes, for example, a hole transport layer formed on the data electrode (anode) side and an electron transport light emitting layer formed on the select electrode (cathode) side. And the organic EL 110
When a voltage is applied between the electrodes, holes are injected from the data electrode side and electrons are injected from the selection electrode side to emit light. This voltage application is controlled for each of the selection electrodes L1 to Ln by supplying a voltage to the data electrodes R1 to Rm and switching the switch 120.

The constant charge driving circuit 200 is provided with an organic EL 110
This is a circuit for controlling the total amount of charges (holes or electrons) injected into the semiconductor device, and includes a drive Tr (transistor) 210, a charge detection circuit 220, and a control circuit 230, as shown in FIG. Have been. Further, one constant charge drive circuit 200 is provided for each of the data electrodes R1 to Rm.

The drive Tr 210 has one of a source and a drain connected to the data electrode, and the other has a charge detection circuit 2.
20, it is connected to the power supply Vdd. The gate of the driving Tr 210 is connected to the control circuit 230. When the drive Tr 210 is turned on, a current for causing the organic EL 110 to emit light is supplied to the data electrode. In the following, turning on the driving Tr 210 indicates supplying a current to the organic EL 110 via the data electrode. Also, the driving Tr 210
Turning off indicates that the current supply to the organic EL 110 is stopped.

The charge detection circuit 220 measures the magnitude and the supply time of the current supplied to the organic EL 110 via the data electrode, and measures the amount of charge injected into the organic EL 110. As described above, the organic EL 110 emits light by being injected with electric charges (holes and electrons) when a voltage is applied. Therefore, even if the magnitude of the current supplied to the organic EL 110 is not constant, the average brightness (apparent brightness) can be obtained by keeping the total amount of injected charge constant.
Can be kept constant. For example, when the magnitude of the current is small, the current is passed for a long time so that the total amount of electric charge injected into the organic EL 110 becomes a predetermined value. However,
The time during which the current flows is changed within a time that is sufficiently shorter than the resolution of the human eye.

The organic EL 110 has a current density-luminance characteristic as shown in the prior art (FIG. 8). Specifically, as shown in FIG. 8, 0 to 100 (mA / cm 2)
In a current density region of the order, the current density and the luminance are almost in a proportional relationship. That is, in this current density region, the organic EL 11
The quantum efficiency of 0 is almost constant. From this, organic E
When the current flowing through L110 is increased at a fixed rate, the amount of injected charge is also increased at a fixed rate, and the luminance is also increased at a fixed rate. Therefore, the charge detection circuit 220 can easily determine the amount of charge injected into the organic EL 110 by measuring the magnitude of the current.

Then, the charge detection circuit 220 can accumulate the charge amount by measuring the current supply time to determine the total charge amount injected into the organic EL 110. Note that a specific relational expression or the like showing the relation between the magnitude of the current and the amount of charge injected into the organic EL 110 is obtained from the characteristic diagram and theoretical calculation shown in FIG.
20 is set in advance.

The control circuit 230 includes a control unit 300
The drive Tr 210 is turned on according to the display data from
The operation of the charge detection circuit 220 is controlled. Further, the control circuit 230 turns off the drive Tr 210 according to the measurement result of the charge detection circuit 220. The display data is data indicating the total charge amount injected into the organic EL 110.

The control unit 300 generates the display data according to data provided in advance or data provided via a communication line or the like, and
To supply. The control unit 300 sequentially switches the switches 120 one by one in synchronization with the supply of the display data to the constant charge driving circuit 200, and switches the pixels (organic EL 110) to emit light for each selected electrode. As described above, the charge detection circuit 220 measures the total charge amount injected into the organic EL 110, and the control circuit 230 controls the average luminance of the organic EL 110 by turning on and off the drive Tr 210 according to the measurement result. can do.

Next, a method of driving the display device having the above-described configuration will be described. In this driving method, as described above, the average charge of the organic EL 110 is controlled by controlling the total charge amount injected into the organic EL 110. Further, in this driving method, the gate voltage and the power supply voltage Vdd of the driving Tr 210 are set so that the saturation current does not flow through the driving Tr 210.
Set the size of.

First, the control unit 300 controls the organic E
Display data indicating the total amount of charge injected into the organic EL 110 is generated according to the average luminance of L110, and is supplied to each constant charge drive circuit 200. Then, the control unit 300
Switches the switch 120 to connect the selection electrode L1 to the ground. The selection electrodes L other than the selection electrode L1
2 to Ln are connected to the power supply Vdd.

Control circuit 230 of each constant charge drive circuit 200
Is based on the display data from the control unit 300
The total amount of charge injected into the organic EL 110 is determined by the charge detection circuit 22
Set to 0. Then, the control circuit 230 controls the driving Tr
A predetermined voltage is applied to the gate of the driving
Turn on. As a result, a current flows from the power supply to the organic EL 110 connected to the selection electrode L1 via the driving Tr 210.

Each of the organic EL 110 and the driving Tr 210 has a voltage-current characteristic as shown in the prior art (FIGS. 6 and 10). Specifically, the organic EL 110 is
The resistance value increases with the passage of time, and the voltage-current characteristics at the start of voltage application (at the initial stage) and after a certain period of time (after a certain period of time) differ. The drive Tr 210 is provided with a source-drain voltage Vsd.
Below a certain value, the voltage Vsd is proportional to the drain current Id, and when the voltage Vsd exceeds a certain value, the current Id
d becomes saturated and constant.

FIG. 2 is a diagram similar to FIG. 11 shown in the prior art, and shows the above-mentioned voltage-current characteristics of the organic EL 110 and the driving Tr 210 together. In this driving method, as described above, the magnitudes of the gate voltage Vg and the power supply voltage Vdd of the driving Tr 210 are set so that the saturation current does not flow through the driving Tr 210. In such a setting, as shown in FIG. 2, the magnitude of the current flowing through the organic EL 110 and the driving Tr 210 changes due to a change in the characteristics of the organic EL 110. Specifically, the current flowing after the time T has elapsed is smaller than the current flowing at the initial time. The time T is the cumulative driving time of the organic EL 110.

As described above, the charge detection circuit 220
The magnitude of the current flowing according to the characteristics of the organic EL 110 is measured, and the amount of charge injected into the organic EL 110 is obtained from a predetermined relational expression or the like. Then, the charge detection circuit 22
A value of 0 measures the time during which current is flowing, and accumulates and accumulates the obtained charge amounts to determine the total charge amount injected into the organic EL 110. The charge detection circuit 220 determines that the total charge amount is
When the value set by 30 is reached, the control circuit 23
A charge supply stop signal is output to 0.

The control circuit 230 stops the application of the gate voltage to the drive Tr 210 and turns off the drive Tr 210 in response to the charge supply stop signal from the charge detection circuit 220. Subsequently, the control circuit 230 outputs a reset signal to the charge detection circuit 220, and resets the charge amount accumulated and integrated by the charge detection circuit 220. Thereafter, the selection electrodes L2 to L
By repeating the above operation in order for n, 1
Organic EL 110 of field (selection electrodes L1 to Ln)
Can be emitted at a predetermined average luminance for each selection electrode.

Since the magnitude of the current flowing through the organic EL 110 decreases with the lapse of time as described above, the time during which the drive Tr 210 is on (on time)
Increase over time. After a lapse of a predetermined time, one scanning time t3 during which one selection electrode L is connected to the ground during one field period is 0 <t3 ≦ t1 (1 according to the related art).
Scanning time), t3 = (the magnitude of the current I4 flowing at the initial stage) × (1 during one field period at the initial stage)
Scanning time t during which the selected electrodes L are connected to ground
4) / (the magnitude I3 of the current flowing after the lapse of a certain time). Here, at least the scanning time t4 is shorter than the conventional scanning time t1. Note that the fixed time is an arbitrary time from the initial time to the time T.

As described above, even if the magnitude of the flowing current changes, the average luminance of the organic EL 110 can be easily controlled by controlling the total charge amount injected into the organic EL 110. Further, by driving the display device as described above, wasteful power consumption can be reduced.

For the sake of simplicity, for example, the display device shown in FIG. 1 is assumed to be constituted by a plurality of circuits shown in FIG. 3 and a case where the duty ratio is substantially 1/4 will be described. I do. For example, as shown in FIG. 2, the power supply voltage Vdd is set to 18 (V), and the gate voltage V
g is set to 15 (V).

As shown in FIG. 2, the organic EL 11
The voltages applied between 0 and the source / drain of the driving Tr 210 are 12.5 (V) and 5.5 (V), respectively. After the elapse of the time T, the characteristics of the organic EL 110 change, and the voltage applied between the organic EL 110 and the source / drain of the driving Tr 210 is 15 (V), 3 (V).
(V). Further, the organic EL 110 and the driving Tr 21
The current flowing to 0 also changes with the passage of time, and is 65 (μA) at the initial stage, but is 40 (μA) after the passage of time T.
And gradually attenuated.

FIGS. 4 and 5 show waveforms of the voltage and current in one circuit shown in FIG. 3, respectively.
FIG. 4 is a waveform diagram when the characteristics of the organic EL 110 are in the initial state shown in FIG. 2, and FIG. 5 is a waveform diagram when the characteristics of the organic EL 110 are after the time T shown in FIG. ing. 4A and 4B, (a) is a waveform diagram of a current (I = Iel = Id) flowing through the organic EL 110 and the driving Tr 210, and (b) is a waveform diagram of a source-drain voltage Vsd of the driving Tr 210. (C) shows a waveform diagram of the voltage Vel applied to the organic EL 110.

As described above, as time passes, the organic E
The characteristics of L110 change, and the magnitude of the flowing current changes. Therefore, during the time t2 for scanning one field, 1
Time during which the drive Tr 210 is turned on to emit light from the organic EL 110 connected to the selection electrode L (on time)
t3 increases with time. As mentioned above,
Since t3 = t4 × I4 / I3, the ON time t3 after the elapse of the time T is t4 × 65/40 = 1.63 × t4.

Here, the drain current Id of the driving Tr 210 and the organic EL
If the scanning time t3 at which the current Iel flowing through the current 110 becomes 40 (μA) is set equal to the longest t1 (one conventional scanning time), the drive T
As shown in FIG. 5, the amount of power consumed by each of the driving Tr 210 and the organic EL 110 is 30 (μ).
W), and 150 (μW) for the organic EL 110. Here, since the electric charge flowing during one scanning time is always constant, one scanning time t4 is t4 = t1 × 40/65, and the driving Tr 210 and the organic EL1 are scanned during one field scanning at the initial stage.
As shown in FIG. 4, the amount of power consumed by the drive 10 is 55 (μW) for the drive Tr 210 and 125 (μW) for the organic EL 110. Note that the total amount of power consumed by the drive Tr 210 and the organic EL 110 during one field scan is 180 (μW).

As described above, the amount of power consumed by the drive Tr 210 without contributing to the light emission of the organic EL 110 can be made smaller than in the conventional constant power drive.
More specifically, at the initial stage, about 60% of the constant power drive and the time T
After the lapse of time, wasteful power consumption can be suppressed to about 50% of the constant power driving. The ratio of the power consumption of the driving Tr 210 to the total power consumption is about 26% at the initial stage and about 14% after the elapse of the time T, which is smaller than the conventional constant power driving.

As described above, in order to make the organic EL 110 emit light with a constant brightness irrespective of a change with time, (the amount of charge) ×
Organic EL generated when (charge supply time) is fixed
The current flowing through the driving Tr 210 in accordance with the temporal change of the partial pressure ratio between the driving Tr
Since the gate voltage Vg is set so as not to be saturated in the range of the highest current value per unit time or less at the time of initial light emission of the 110, the power consumption of the driving Tr 210 can be reduced and the conventional organic EL 110 consumes less. Almost same as electric power, that is, conventional organic EL
It can emit light with the same brightness as 110. And
Since the power supply voltage is reduced from 21 (V) to 18 (V), the voltage generation circuit can be reduced. In addition, organic EL11
By controlling the total amount of electric charge injected to 0, the average luminance of the organic EL 110 can be easily controlled.
In the above embodiment, the organic EL 110 and the driving Tr 21
Although only two points of the current flowing to 0 are described, 65 (μA) and 40 (μA), the total current is reduced from 65 (μA) to 40 (μA) as the organic EL 110 changes over time. It goes without saying that the charge amount is controlled.

In the above embodiment, one scanning time t
3. Turn on the drive Tr 210 only once in the organic EL 1
Charge is injected into the driving transistor 10 within one scanning time.
The organic EL 110 is repeatedly turned on and off a plurality of times.
May be set to a predetermined value. Even in this case, the organic EL 110 can be used within one scanning time.
The same effect as described above can be obtained because the total amount of electric charge injected into the substrate does not change.

In the above-described embodiment, the control unit 300 generates display data indicating the total charge amount injected into the organic EL 110 for each of the selection electrodes L1 to Ln.
Further, display data in which the total charge amount is changed for each of the data electrodes R1 to Rm may be generated. That is, the display data is data in which the data electrode is associated with the total charge amount, and indicates a different total charge amount for each pixel (organic EL 110). In this case, the control circuit 230 extracts, from the display data, the total charge amount associated with the data electrode to which the control circuit 230 is connected, and sets the total charge amount in the charge detection circuit 220.
As a result, the average luminance can be controlled for each pixel, not for each of the selection electrodes L1 to Ln. Further, one frame period required for forming one image can be divided into a plurality of fields to perform multi-gradation display.

Further, a bipolar transistor may be used as the driving Tr 210 instead of a unipolar transistor. In this case, the average luminance of the organic EL 110 can be controlled by controlling the supply of the base current (control signal) of the bipolar transistor and controlling the total charge injected into the organic EL 110 in the same manner as described above. .

[0052]

As is apparent from the above description, according to the present invention, the total amount of electric charge injected into the light emitting means can be controlled, and the average luminance of the light emitting means can be easily controlled. Further, in the present invention, since the current flowing through the transistor is not saturated, the magnitude of the current flowing varies depending on the magnitude of the voltage, and wasteful power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a display device according to an embodiment of the present invention.

FIG. 2 is a diagram showing together voltage-current characteristics of an organic EL (electroluminescence) and a driving Tr (transistor).

FIG. 3 is a diagram illustrating a circuit that can be regarded as a minimum unit constituting the display device of FIG. 1;

FIG. 4 shows a case where the organic EL has initial characteristics.
FIG. 4 is a waveform diagram of current and voltage supplied to the circuit of FIG.

5 is a waveform diagram of a current and a voltage supplied to the circuit of FIG. 3 when the organic EL has characteristics after a predetermined time has elapsed.

FIG. 6 is a diagram illustrating voltage-current characteristics of an organic EL.

FIG. 7 is a diagram showing voltage-current density characteristics of the organic EL at different temperatures.

FIG. 8 is a diagram showing current density-luminance characteristics of an organic EL at different temperatures.

FIG. 9A is a schematic diagram illustrating a configuration of a display device using a conventional constant current drive. FIG. 2B is a diagram illustrating a circuit that can be regarded as a minimum unit constituting the display device of FIG.

FIG. 10 is a diagram showing voltage-current characteristics of a driving Tr.

FIG. 11 is a diagram showing the voltage-current characteristics of the organic EL and the driving Tr together.

FIG. 12 is a waveform diagram of current and voltage supplied to the circuit of FIG. 9B when the organic EL has initial characteristics.

FIG. 13 is a waveform diagram of a current and a voltage supplied to the circuit of FIG. 9B when the organic EL has characteristics after a predetermined time has elapsed.

[Explanation of symbols]

100 display unit, 110 organic EL (electroluminescence), 120 switch, 200 constant charge drive circuit, 210 drive Tr (transistor), 220
..Charge detection circuit, 230 ... Control circuit, 300 ... Control unit, R1 to Rm ... Data electrode, L1 to Ln ... Selection electrode

Claims (10)

[Claims] A light emitting means for emitting light in accordance with an amount of charge injected by applying a voltage; a charge amount measuring means for measuring a total amount of charge injected into the light emitting means within a predetermined time; Control means for applying a voltage to the light emitting means in accordance with a measurement result of the means and controlling a total charge amount injected into the light emitting means. 2. The charge amount measuring means measures the amount of electric charge injected into the light emitting means by measuring the magnitude of a current flowing through the light emitting means, accumulates the electric charge, and supplies the electric charge to the light emitting means. The display device according to claim 1, wherein a total amount of injected charges is measured. 3. The display device according to claim 1, wherein the resistance value of the light emitting means changes with time. 4. The light emitting means is connected to a power supply via a transistor, and the control means supplies a control signal to a control terminal of the transistor to apply a voltage to the light emitting means. The display device according to claim 1, wherein the display device is a display device. 5. The display device according to claim 4, wherein said control means applies a control signal to a control terminal of said transistor so that a current flowing through said transistor is not saturated. 6. The display device according to claim 1, wherein said light emitting means is made of an organic electroluminescent material. 7. A method for driving a display device, comprising: a light emitting unit that emits light in accordance with an amount of charge injected by applying a voltage, wherein: a voltage applying step of applying a voltage to the light emitting unit; A charge measuring step of measuring a total charge injected into the light emitting means within a predetermined time by applying the voltage in the step, and stopping the voltage application to the light emitting means according to a measurement result of the charge measuring step. And a voltage application stopping step of controlling a total amount of electric charge injected into the light emitting means. 8. The charge measuring step includes measuring a current flowing through the light emitting means to measure a charge injected into the light emitting means, and accumulating the charge to produce the light emission. Measuring the total amount of electric charge injected into the means. 9. The light emitting means is connected to a power supply via a transistor, and its resistance value changes over time. In the voltage applying step, a control signal is applied to a control terminal of the transistor. The driving method according to claim 7, further comprising: applying a voltage to the light emitting unit. 10. The driving method according to claim 9, wherein said voltage applying step includes a step of applying a control signal to a control terminal of said transistor such that a current flowing through said transistor is not saturated. .