JP3296263B2 - EL display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an EL (electroluminescence) display device which performs display by driving a light emitting element.

[0002]

2. Description of the Related Art An EL element has a structure in which an insulating layer and a light emitting layer are sandwiched between a pair of electrodes, and emits light by applying a positive and negative voltage pulse between the pair of electrodes. In this EL element, after a driving voltage is applied to emit light,
It is known that an internal polarization charge exists in a device. This will be described with reference to the QV characteristics of the EL element shown in FIG.

When no voltage is applied to the EL element and there is no internal polarization charge, the EL element is at the position. In the case where the EL element emits light, during a period in which a positive voltage is applied, E
The modulation voltage Vm is added to the light emission start voltage Vth to the L element (V
During the period in which a voltage pulse of (th + Vm) is applied and a negative voltage is applied, a voltage pulse of-(Vth + Vm) is applied to the EL element. In this case, when a positive voltage pulse is applied, the state changes from → to →. Therefore, even when the applied voltage becomes 0 V, the charge remains, and this becomes the internal polarization charge. Thereafter, when a negative voltage pulse is applied, the state changes from → to →.

When a positive voltage pulse and a negative voltage pulse are alternately applied, the voltage changes on a parallelogram. In this case, the EL element is
Flashes when In the case where the EL element that has emitted light is set to a non-emission state, during a period in which a positive voltage is applied,
During a period in which a voltage pulse of Vth is applied and a negative voltage is applied, a voltage pulse of -Vth is applied. In this case, by applying a voltage of -Vth when in the position of
When the voltage Vth is applied at the position of, the state changes from → to →, and returns to 戻 る in any case, so that the internal polarization charge does not remain.

[0005]

However, when the power supply to the EL element is cut off, the EL element that has emitted light has internal polarization charges, so that when the power supply is turned on the next time, the EL element is turned off. Even if a voltage is applied that causes the device to emit no light, light is emitted due to the internal polarization charge. For example, it is in the position at the time of power-off,
Applying a voltage of -Vth, which causes the L element to emit no light,
Changes from → to →, and the EL element emits light at →. Similarly, when a voltage of Vth, which is in the position at the time of power-off and makes the EL element non-emission state at the next power-on, is applied, the state changes from → to →, and the EL element emits light at →.

For this reason, when a dot matrix display or a segment display is performed by a plurality of EL elements, a display immediately before the power is turned off appears for a moment when the power is turned on. To be precise, the display is a mixture of the display immediately before the power is turned off and the first display after the power is turned on. For this reason, when the power is turned on, a strange feeling is generated in the display. The present invention has been made in view of the above problems,
An object of the present invention is to eliminate a sense of discomfort at the start of display.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, a power supply means (5) is provided.
When the timing to cut off the voltage supply to the driving means (2-4) from the device is reached, the driving means is configured to apply a voltage near the light emission start voltage at least once to all the EL elements that have been driven to emit light. A control means (8) for controlling and then interrupting the voltage supply from the power supply means to the drive means by the switch means (7).

Therefore, it is possible to reduce the internal polarization charge of all the EL elements by applying a voltage near the light emission start voltage at least once to all the EL elements that have been driven to emit light before the power is turned off. Therefore, it is possible to eliminate a sense of incongruity in the display such that a display immediately before the power is turned off appears at the start of the next display. In the invention described in claim 2, when the key switch of the vehicle is turned off, the driving means (2 to 2) is switched by the switch means (7) from the power supply means (5).
4) is maintained, and the driving means is controlled so as to apply a voltage near the light emission start voltage at least once to all the EL elements which have been driven to emit light.
Control means (8) for interrupting supply of voltage from the power supply means to the drive means by the switch means is provided.

Accordingly, even when the key switch of the vehicle is turned off, the voltage supply to the driving means is maintained, and a voltage near the light emission start voltage is applied at least once to all the EL elements which have been driven to emit light. Therefore, it is possible to reduce the internal polarization charges of all the EL elements, and to eliminate a sense of incongruity of display such that a display immediately before power-off is displayed at the start of the next display.

[0010] In this case, as the switch means, either one of the signal indicating that the key switch is on and the signal indicating that the voltage supply is maintained from the control means are used as the switch means. If the power supply means is configured to perform an operation of permitting the supply of voltage from the power supply means to the drive means when the power supply means is turned on, the power supply means performs the operation during a key switch ON period of the vehicle and a predetermined period after the key switch is turned OFF. A voltage can be supplied to the driving means.

According to a fourth aspect of the present invention, as the switch means, a switch for supplying a voltage from the vehicle-mounted battery to the power supply means when a signal indicating that the voltage supply is maintained is output from the control means. Element (73, 7
4), and a signal when the key switch is on between the switch element and the power supply means is a diode (7).
1), the voltage can be supplied after the key switch is turned off via the switch element, and the signal when the key switch is turned on is supplied via the diode during the normal operation. Thus, the voltage is supplied to the power supply means, so that the voltage can be supplied without receiving a voltage drop due to the switch element.

[0012] Further, according to the fifth aspect of the present invention, a voltage having a pulse width larger than the pulse width of the voltage for displaying the EL element as a voltage near the light emission start voltage as in the fifth aspect of the invention. Is applied, EL
The internal polarization charge of the device can be more effectively reduced. According to a sixth aspect of the present invention, in the EL display device performing the matrix display, the timing of shutting off the voltage supply from the power supply means (5) to the scan electrode drive circuits (2, 3) and the data electrode drive circuit (4). , The scanning voltage is sequentially applied to a plurality of scanning electrodes for one or more fields, and a data voltage for bringing the EL element into a non-light emitting state is applied to all data electrodes. Control means (8) for interrupting supply of voltage from the means to the scan electrode drive circuit and the data electrode drive circuit.

Therefore, by applying a scanning voltage and a data voltage for turning off the EL elements to all the EL elements before the power is cut off, the internal polarization charges of all the EL elements can be reduced. It is possible to eliminate a sense of incongruity of the display such that the display immediately before the power is turned off appears at the start of the next display. According to the seventh aspect of the present invention, when it is time to cut off the voltage supply from the power supply means (5) to the driving means (2-4), the voltage near the light emission start voltage is applied to the EL element at least once. Control means (8) for controlling the driving means so as to apply the voltage, and thereafter cutting off the voltage supply from the power supply means to the driving means by the switch means (7).

Therefore, before the power is cut off, one
By applying a voltage in the vicinity of the light emission start voltage more than once, the internal polarization charge of the EL element can be reduced, so that it is possible to eliminate a sense of incongruity in display such that a display immediately before power-off is displayed at the start of the next display.

[0015]

FIG. 1 shows an entire configuration of an EL display device according to an embodiment of the present invention. FIG. 2 shows a schematic cross-sectional configuration of the EL element. In FIG. 2, EL element 1
0 denotes a transparent electrode 1 laminated on a glass substrate 11.
2, a first insulating layer 13, a light emitting layer 14, a second insulating layer 15, and a back electrode 16; by applying positive and negative voltage pulses between the transparent electrode 12 and the back electrode 16,
The L element 10 emits light. In FIG. 2, the glass substrate 11
I try to extract more light. The back electrode 16
Is a transparent electrode, light can be extracted from both upper and lower directions in the figure.

The EL display panel 1 shown in FIG. 1 is different from the configuration shown in FIG. 2 in that a plurality of transparent electrodes 12 and rear electrodes 16 are arranged in rows and columns to form scanning electrodes and data electrodes, and EL elements are arranged in a matrix. It is configured to display. Specifically, the odd-numbered scan electrodes 201 and 20 are arranged in the row direction.
2,..., Even-numbered scanning electrodes 301, 302,.
Data electrodes 401, 402, 403,... Are formed in the column direction.

Scan electrodes 201, 301, 202, 30
.. And the data electrodes 401, 402, 403,.
.., 121,... Are formed. Since the EL element is a capacitive element, it is represented by a capacitor symbol in the figure. In order to drive the display of the EL display panel 1, scanning electrode driving circuits 2 and 3 and a data electrode driving circuit 4 are provided.

The scan electrode drive circuit 2 is a push-pull type drive circuit and has odd scan electrodes 201, 202,.
, And N-channel FETs 21b, 22b,... Connected to the odd-numbered scan electrodes 201, 20 according to the output from the logic circuit 20.
A scanning voltage is applied to 2,. In addition, FETs 21a, 2
Parasitic diodes 21c, 21d, 22c, 22d,... Are formed in each of 1b, 22a, 22b,.

The scan electrode driving circuit 3 has the same configuration, and has a logic circuit 30, P-channel FETs 31a, 32a,.
Have channel FETs 31b, 32b,... And apply a scan voltage to even-numbered scan electrodes 301, 302,. Similarly, the data electrode driving circuit 4 also has a logic circuit 40, P
Channel FETs 41a, 42a,... And N channel F
ET 41b, 42b,...
, 402, 403,...

A scan voltage and a data voltage are supplied from a power supply circuit 5 to the scan electrode drive circuits 2 and 3 and the data electrode drive circuit 4. The power supply circuit 5 outputs (Vth + V
m) or a voltage of 0 V (ground voltage) is supplied to the P-channel FET source-side common line L1, and the voltage of Vm or -Vth is supplied to the N-channel FET source-side common line L1.
Feed to 2.

The power supply circuit 5 outputs the data voltage
A voltage Vm is supplied to the P-channel FET source-side common line, and a ground voltage is supplied to the N-channel FET source-side common line. In the above-described configuration, in order to cause the EL element to emit light, it is necessary to apply a positive / negative voltage pulse between the scan electrode and the data electrode. And drive it.

The operation in the positive and negative fields will be described below with reference to the timing chart shown in FIG. In the timing chart shown in FIG.
In a, 21b, 31a, and 31b, the ON state is indicated by a high level, and the OFF state is indicated by a low level. The voltage waveforms are shown as having no rounding. (Operation in Positive Field) In the positive field, the power supply circuit 5 supplies the P-channel FET source side common line L1
(Vth + Vm) is supplied to the N channel FE
A voltage of Vm is supplied to the T source side common line L2.

At this time, the scanning electrodes 201, 301, 20
The reference voltages 2, 302,...
Are set to the voltage Vm by the operation of the parasitic diodes 21d, 22d,. Further, the FET 41a, 42a, 43a,... Side of the data electrode driving circuit 4 is turned on,
The voltage of the data electrode is set to Vm. In this state, the voltage applied to all the EL elements becomes 0 V, so that the EL elements do not emit light.

Thereafter, the light emission operation in the positive field is started. First, the P-channel FET 21a of the scan electrode drive circuit 2 connected to the scan electrodes 201 in the first row is turned on, and the voltage of the scan electrodes 201 is set to (Vth + Vm). Further, all the output stage FETs of the scan electrode driving circuits 2 and 3 connected to the other scan electrodes are turned off, and those scan electrodes are brought into a floating state.

The data electrodes 401, 402, 40
3, the P-channel FET of the data electrode driving circuit 4 connected to the data electrode of the EL element to emit light
Is turned off, the N-channel FET is turned on, and the P-channel FET of the data electrode drive circuit 4 connected to the data electrode of the EL element that does not want to emit light is turned on, and the N-channel FET is turned off.

As a result, the voltage of the data electrode of the EL element desired to emit light becomes the ground voltage, so that a voltage (Vth + Vm) higher than the threshold voltage is applied to the EL element, and the EL element emits light. Further, the voltage of the data electrode of the EL element that does not want to emit light remains at Vm, and the voltage of Vth is applied to the EL element, so that the EL element does not emit light. In the timing chart of FIG. 3, the P-channel FET 41a of the data electrode driving circuit 4 is turned off,
FIG. 3B shows a state in which b is turned on, a voltage of (Vth + Vm) is applied to the EL element 111, and the EL element 111 emits light.

Thereafter, the P-channel FET 21 of the scan electrode drive circuit 2 connected to the scan electrode 201 of the first row
By turning off a and turning on the N-channel FET 21b, the electric charge accumulated in the EL element on the scan electrode 201 is discharged. Next, the P-channel FET 31a of the scan electrode drive circuit 3 connected to the scan electrode 301 in the second row
Is turned on to set the voltage of the scanning electrode 301 to (Vth + Vm). Further, all the output stage FETs of the scan electrode driving circuits 2 and 3 connected to the other scan electrodes are turned off, and those scan electrodes are brought into a floating state.

The data electrodes 401, 402, 40
By setting the voltage levels of 3,... To the voltage levels corresponding to the EL elements to be caused to emit light and the EL elements not to be caused to emit light, light emission driving of the EL elements in the second row is performed in the same manner as described above. In the timing chart of FIG. 3, the P-channel FET 41a of the data electrode drive circuit 4 is turned on, the N-channel FET 41b is turned off, the voltage of the data electrode 401 is set to Vm, and a voltage of Vth is applied to the EL element 121, thereby turning the EL element 121 on. A non-light emitting state in which no light is emitted is shown.

Thereafter, the P-channel FET 31 of the scan electrode drive circuit 3 connected to the scan electrodes 301 in the second row
By turning off a and turning on the N-channel FET 31b, the electric charge accumulated in the EL element on the scan electrode 301 is discharged. Thereafter, line-sequential scanning is performed in the same manner until the last scanning line is reached. (Operation in Negative Field) In the negative field, the P-channel FET source-side common line L1
, And a voltage of −Vth is supplied to the N-channel FET source-side common line L2.

At this time, the scanning electrodes 201, 301, 20
The reference voltages 2, 302,...
Are set to the ground voltage by the operation of the parasitic diodes 21c, 22c,. Further, the FETs 41b, 42b, 43b... Of the data electrode drive circuit 4 are turned on, and the voltage of the data electrode is set to the ground voltage. In this state, all EL
Since the voltage applied to the element becomes 0 V, the EL element does not emit light.

Hereinafter, line scanning is performed on the negative field similarly to the positive field. In this case, a voltage of -Vth is applied to the scanning electrodes of the row for which display selection is performed. On the data electrode side, contrary to the positive field, the voltage of the data electrode to emit light is set to Vm, and the data electrode not to emit light is kept at the ground voltage. Therefore, the scan voltage to which the voltage of -Vth is applied, and the voltage V
When m is applied,-(Vth +
(Vm), the EL element emits light. When the voltage of the data electrode is the ground voltage, the EL element does not emit light because a voltage of -Vth is applied to the EL element.

By the driving of the positive and negative fields described above, one cycle of the display operation is completed, and this operation is repeated. Next, a specific configuration of the scan electrode driving circuit 4 will be described. FIG. 4 shows the configuration. In the present embodiment, the scan electrode drive circuit 4 is the μPD1630
2, a commercially available scan driver IC is used.

This scan driver IC has a shift register 211. The shift register 211 has a row selection pulse signal (input to the data input terminal A) when its R / L (the bar represents a negative logic signal as shown in the figure, the same applies hereinafter) terminal is at a high level. a signal) period corresponding to the vertical synchronization signal, and sequentially shifted by CLK signal, and outputs the order from S ₁ terminal S ₄₀ terminal.
Although one driver IC which outputs 40 outputs is shown in the figure, the output terminal B of this driver IC is shown.
Is connected to the data input terminal A of the subsequent driver IC, a desired number of outputs can be obtained by a plurality of driver ICs.

In this embodiment, the blanking (B
LK) signal and the OE bar signal serving as an output enable signal are always at a low level. The PC bar signal is P
Input as a signal for selecting a channel FET or an N-channel FET. In the configuration shown in FIG. 4, when a row selection pulse signal is input to the shift register 211, the row selection pulse signal is sequentially shifted and output. FIG. 5 shows a timing chart in the positive field. During the period when the row selection pulse signal is being output, the P-channel FET and the N-channel
The period during which the channel FET is turned on is switched, and a voltage corresponding thereto is output from the output terminal O. In addition, Z in the figure
Indicates a high impedance period, and P indicates a P channel F
ET is turned on to indicate a charging period, where N is N
This shows a period during which the channel FET is turned on to perform discharge. In the negative field, the H and L levels of the PC bar signal are opposite to those in the positive field.

Thus, the P-channel FET 21
a, 31a, 22a, 32a,... and N-channel FET
Are turned on and off as shown in the timing chart of FIG. 3 according to the positive and negative fields, and the scan electrodes 201, 301, 202, 302,.
.. Are sequentially applied. Next, the configuration of the drive circuit 40 in the data-side driver IC 4 will be described.

FIG. 6 shows the specific configuration. In this embodiment, a data driver IC commercially available as TD62C948 manufactured by Toshiba is used. This data driver IC includes a shift register circuit 411, a latch circuit 41
2, a counter 413, a comparator 414, an exclusive OR circuit 415, and an output circuit 416. This output circuit 416 is connected to the P-channel FET 4 shown in FIG.
1a, 42a,... And N-channel FETs 41b, 42
b,...

In the figure, a 4-bit column data signal (gradation data for performing gradation display) is input to A PORT IN and B PORT IN to the shift register circuit 411. The input column data signal is transferred to each shift register shown in the figure in synchronization with the rise of the dot clock signal CK1. . Shift register circuit 411
After all the column data signals have been transferred, the STB (strobe) bar signal forming the horizontal synchronizing signal goes low, the output of the shift register circuit 411 at that time is latched by the latch circuit 412, and the STB bar signal goes low. The data is retained for the duration of the level.

Next, when the CL (clear) bar signal changes from the L level to the H level, the counter 413 and the comparator 414 that determine the pulse width of the voltage applied to the light emitting layer become operable. At this time, from the comparator 414,
When the column data signal is other than 0 V (data not performing display), an H level signal is output. Counter 413
Counts up by the clock signal CK2,
The comparator 414 compares the count value of the counter 413 with the outputs Q ₁ ,..., Q ₁ latched by the latch circuit 412, and when they match, changes the output from H level to L level.
To level.

The output of the comparator 414 is input to an exclusive OR circuit 415. For negative fields,
When the P / C bar signal is at the L level and the comparator 414
Is output to the output circuit 416 as it is, and the voltage Vm is output to the data electrode. Also, in the case of the positive field, the P / C bar signal is at H level,
A signal obtained by inverting the output of 14 is output to the output circuit 416, and the ground voltage is output to the data electrode.

Accordingly, a voltage having a pulse width corresponding to the modulation data is applied to each data electrode, and a gray scale display is performed. Although FIG. 6 shows one data driver IC that outputs 40 data, the A PORT OUT and B PORT OUT of this driver IC are connected to the A PORT IN and B PORT IN of the subsequent driver IC. If you do
A desired number of outputs can be obtained with a plurality of data driver ICs.

Next, E applied to a meter display for an automobile
The overall configuration of the L display device will be described. FIG. 7 shows the overall configuration. The battery voltage (+ B voltage) is supplied from the vehicle-mounted battery 6 to the power supply circuit 5 via the switch circuit 7. From the power supply circuit 5, a scan voltage is supplied to the scan electrode drive circuits 2 and 3, a data voltage is supplied to the data electrode drive circuit 4, and an operation voltage of 5 V is supplied to the control circuit 8.

The control circuit 8 outputs various signals for displaying a meter for an automobile to the scan electrode drive circuits 2 and 3 and the data electrode drive circuit 4. Specifically, it creates and outputs various signals to be input to the above-described scanning driver IC and data driver IC. The switch circuit 7 includes diodes 71 and 72, transistors 73 and 74, and resistors 75 to 78.
When the key switch of the vehicle is at the ACC position and the ACC line is at the battery voltage, the transistors 73 and 74 are turned on to supply the battery voltage to the power supply circuit 5. Also, the key switch of the vehicle is turned off, and A
Even when the CC line becomes 0 V, the transistors 73 and 74 are turned on and the battery voltage is supplied to the power supply circuit 5 while the control circuit 8 outputs the high-level PWON signal. That is, the battery voltage is supplied to the power supply circuit 5 by the wired OR of the diodes 71 and 72 while the ACC line is at the battery voltage or while the high-level PWON signal is being output.

This high-level PWON signal is output only after the key switch of the vehicle is turned off (after the ACC line becomes 0 V), and only during a period in which one or more screens of the EL panel 1 can be completely erased. The control circuit 8 includes a circuit for outputting the PWON signal. FIG. 8 shows a specific configuration of the circuit. This circuit includes a counter 81, a flip-flop circuit 82, resistors 83 to 85, a transistor 86,
An inverter 87 and an AND gate 88 are provided.

When the ACC line is at the battery voltage, since the transistor 86 is on, the output of the inverter 87 goes high and the AND gate 8
8 outputs the above-described column data signal as it is. Further, the counter 81 is cleared, the flip-flop 82 is set, and the PWON signal is at a high level. In this case, an image is displayed on the EL panel 1 according to the normal operation.

When the key switch of the vehicle is turned off from this state, the ACC line becomes 0 V and the transistor 86 is turned off, so that the off of the key switch is detected. At this time, the high-level PWON is output from the flip-flop 82.
Since the output of the signal is continued and the transistor 86 is turned off, the output of the inverter 87 becomes low level, and the column data signal output from the AND gate 88 becomes 0V. In this case, a scanning voltage is output from the scanning driving circuits 2 and 3 and line-sequential scanning is continued. When the column data signal becomes 0 V, the screen is erased according to the line-sequential scanning. That is, all the EL elements enter a non-light emitting state.

The counter 81, when the row selection pulse signal input to the data input terminal A of the scan driver IC is counted twice, to reset the flip-flop 82 outputs a high level signal from its Q ₂ terminal, PWON signal To low level. When the PWON signal becomes low level, the transistors 73 and 74 in the switch circuit 7 are turned off, the battery voltage is not supplied to the power supply circuit 5, and the voltage supply to the EL display device is cut off.

In this case, since the cycle of the row selection pulse signal corresponds to the vertical synchronizing signal, even if the key switch of the vehicle is turned off during the screen scanning, the screen can be erased for one screen scanning period or more. it can. FIG. 9 shows a timing chart when the screen is erased in the negative field when the key switch is turned off. In this case, -V
The voltage of th is applied, and 0V is applied to the data electrode.
When the screen is deleted in the primary field,
A voltage of (Vth + Vm) is applied to the scan electrode, and a voltage of Vm is applied to the data electrode.

As described above, since the screen is erased for one screen scanning period or more after the key switch is turned off, the residual of the internal polarization charge of the EL element is eliminated, and the power is momentarily supplied when the power is supplied again.
The disadvantage of displaying the image immediately before the power is turned off can be eliminated. Note that the control circuit 8 described above
Although a control unit for generating image data and displaying the image on the EL panel 1 for displaying a meter for an automobile is included, the control unit may be separated and provided separately as a meter ECU. In this case, the meter ECU
The control of generating the PWON signal and the operation of erasing the screen may be performed by detecting the CC off. In the meter ECU, the control operation can be performed not only by hardware but also by software.

In the switch circuit 7, PWO
Since it is sufficient if the voltage can be supplied from the vehicle-mounted battery 6 to the power supply circuit 5 by OR logic of the N signal and the voltage of the ACC line, FIG.
0 can also be configured. In this case, since the voltage is normally supplied from the ACC and does not pass through the transistor 74, there is no voltage drop of V _CE and the normal wired O
It is more advantageous than R.

The switch circuit 7 is provided with a vehicle-mounted battery 6.
It is not limited to the one provided between the power supply circuit 5 and the power supply circuit 5, but may be provided on the output side of the power supply circuit 5 as shown in FIG. However, in this case, between the power supply circuit 5 and the scan electrode drive circuits 2 and 3 and between the power supply circuit 5 and the data electrode drive circuit 4
It is necessary to provide switch circuits 7 each having the same configuration between them.

The present invention can be similarly applied to a case where an EL display device is used for display on a personal computer, for example. In this case, when the power switch of the EL display device is turned off, as described above, until the screen erasure is completed,
The voltage supply from the power supply circuit 5 to the scan electrode drive circuits 2 and 3 and the data electrode drive circuit 4 may be maintained. In addition, the present invention is not limited to an EL display device that performs matrix display, and can be similarly applied to an EL display device that performs segment display. In the case of the segment display, as shown in FIG. 12, a segment electrode driving circuit and a common electrode driving circuit are provided. For example, the common electrode COM is set to the ground voltage, and the light emission start voltage Vth is applied to all the segment electrodes S1 to S5. , The screen can be erased.

In the case of erasing a screen, as shown in FIG. 13, if a voltage pulse having a pulse width larger than the voltage pulse in the normal operation is applied, the amount of charge transfer can be increased, and the internal polarization charge can be increased. The effect of reducing the residue can be increased. Furthermore, as shown by the QV characteristics in FIG. 14, if the number of voltage pulses applied during the screen erase period is increased, even if the amount of movement of the charge is small, the residual of the internal polarization charge should be reduced sequentially. Can be.

When erasing the screen, it is not necessary to apply the light emission start voltage to all the EL elements, and the light emission start voltage may be applied only to the EL element that has been driven to emit light. In each of the above-described embodiments, when the screen is erased, the voltage applied to the EL element is set to the light emission start voltage Vth. If,
Residual internal polarization charges of the EL element can be sufficiently reduced.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram illustrating a schematic configuration of an EL element.

FIG. 3 is a diagram showing a drive timing chart of the one shown in FIG. 1;

FIG. 4 is a diagram showing a specific configuration of a scan electrode drive circuit 4.

5 is a timing chart showing an operation in a positive field of the scan electrode driving circuit 4 shown in FIG.

FIG. 6 is a diagram showing a specific configuration of data electrode driving circuits 2 and 3;

FIG. 7 is a diagram illustrating a configuration of an EL display device applied to a meter display for an automobile.

8 is a diagram illustrating a configuration of a circuit unit that performs a screen erasing operation in the control circuit 8 illustrated in FIG. 7;

9 is a timing chart showing a screen erasing operation in the EL display device shown in FIG.

FIG. 10 is a view showing another embodiment of the EL display device shown in FIG. 7;

FIG. 11 is a view showing still another embodiment of the EL display device shown in FIG. 7;

FIG. 12 illustrates an EL according to an embodiment for performing segment display.
FIG. 3 is a diagram illustrating a configuration of a display device.

FIG. 13 is a timing chart showing an embodiment in which the pulse width of the voltage applied during the screen erase period is increased.

FIG. 14 is a QV characteristic diagram showing an embodiment in which the number of voltage pulses applied during a screen erase period is increased.

FIG. 15 is a diagram showing QV characteristics of an EL element.

[Explanation of symbols]

1 ... EL display panel, 2, 3 ... scan electrode drive circuit, 4 ...
Data electrode drive circuit, 5: power supply circuit, 6: onboard battery, 7: switch circuit, 8: control circuit.

Continuing from the front page (72) Inventor Hideki Saito 1-1-1, Showa-cho, Kariya-shi, Aichi Pref. Denso Co., Ltd. (72) Inventor Toshinori Ninoyu 1-1-1, Showa-cho, Kariya-shi, Aichi pref. References JP-A-8-328501 (JP, A) JP-A-7-129121 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G09G 3/00-3/38 H05B 33/08

Claims (7)

(57) [Claims] 1. A plurality of EL elements (111, 112,...)
An EL display panel (1), a driving unit (2-4) for selectively driving the plurality of EL elements to emit light, and a power supply unit (5) for supplying a voltage for driving light emission to the driving unit. Switch means (7) for permitting / cutting off the voltage supply from the power supply means to the drive means; and at least the light emission drive when the timing for cutting off the voltage supply from the power supply means to the drive means is reached. Control means for controlling the driving means so as to apply a voltage in the vicinity of the light emission start voltage to the EL element at least once, and thereafter interrupting the supply of voltage from the power supply means to the driving means by the switch means ( 8) An EL display device comprising: 2. A plurality of EL elements (111, 112,...)
An EL display panel (1), a driving unit (2-4) for selectively driving the plurality of EL elements to emit light, and a voltage supply from an on-vehicle battery (6) for causing the driving unit to emit light. Power supply means (5) for supplying a voltage to the drive means; switch means (7) for permitting and interrupting the supply of voltage from the power supply means to the drive means; and when the key switch of the vehicle is turned off, the switch means provides the power supply. Controlling the driving means to maintain a voltage supply from the means to the driving means and to apply a voltage near the light emission start voltage at least once to all the EL elements which have been driven to emit light, and thereafter, Control means (8) for interrupting the supply of voltage from said power supply means to said drive means by said switch means.
L display device. 3. The control means outputs a signal indicating that the voltage supply is maintained by the switch means when the voltage supply is maintained. The switch means turns on the key switch. When either the signal indicating that the voltage supply is being performed or the signal indicating that the voltage supply is maintained from the control unit is input, an operation of allowing the voltage supply from the power supply unit to the drive unit is performed. The EL display device according to claim 2, wherein the EL display device is configured as follows. 4. The switch element (73, 74) for supplying a voltage from the vehicle-mounted battery to the power supply means when a signal indicating that the voltage supply is maintained is output from the control means. Wherein a signal when the key switch is on is applied between the switch element and the power supply means via a diode (71). 4. The EL display device according to 3. 5. The apparatus according to claim 1, wherein the control unit applies a voltage having a pulse width larger than a pulse width of a voltage for displaying the EL element as a voltage near the light emission start voltage. An EL display device according to any one of the above. 6. A plurality of scanning electrodes (201, 301,...) Are formed on one side of the EL light emitting layer, and a plurality of data electrodes (401, 402,...) Are formed on the other side. At each position where the scanning electrode and the plurality of data electrodes intersect, a plurality of EL elements (111, 112,
..) Are formed, and a scan electrode drive circuit (2, 2) for sequentially applying a scan voltage to the plurality of scan electrodes with different polarities for each of the positive and negative fields.
3), a data electrode driving circuit (4) for applying a data voltage to the plurality of data electrodes, and a power supply for supplying the scanning voltage to the scanning electrode driving circuit and supplying the data voltage to the data electrode driving circuit. Means for selectively causing the plurality of EL elements to emit light by the scan voltage and the data voltage, wherein the power supply means supplies the scan electrode drive circuit and the data electrode drive circuit. Switch means (7) for permitting and interrupting the supply of voltage to the scan electrode; and when the timing for interrupting the supply of voltage from the power supply means to the scan electrode drive circuit and the data electrode drive circuit is reached, the scan voltage is applied for one or more fields. A data voltage for causing the EL element to emit no light is applied to all the data electrodes while sequentially applying the data to the plurality of scanning electrodes. Was, thereafter, EL display devices, characterized in that a control means (8) to shut off the supply of voltage to the scanning electrode driving circuit and the data electrode driving circuit from said power supply means by the switching means. 7. An EL display panel (1) having EL elements (111, 112,...), Driving means (2 to 4) for driving the EL elements to emit light, and applying a light emission driving voltage to the driving means. The power supply means (5) for supplying, the switch means (7) for permitting and cutting off the voltage supply from the power supply means to the driving means, and the timing for cutting off the voltage supply from the power supply means to the driving means. At this time, the driving means is controlled so as to apply a voltage in the vicinity of the light emission start voltage to the EL element at least once, and thereafter, the supply of the voltage from the power supply means to the driving means is cut off by the switching means. An EL display device comprising: means (8).