JPS5857191A - Driving of thin film el display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention uses EL (Electr) by applying an alternating electric field.

It relates to a method of driving a thin film EL display device that emits light (luminescence), and is particularly applicable to high-voltage MOS type ICs.
This has established a drive method with low power consumption that is effective when using

Conventionally, regarding thin film EL elements used as display bodies of display devices, a high alternating current electric field (106V1) is regularly applied to the light emitting layer.
0.1 to 2.0 wt% Mn
(or Cu, AI, Br, etc.) doped Z
Semiconductor light emitting layer such as nS and Zn5e is made of Y208 +TiO
Three-layer structure ZnS sandwiched with dielectric thin films of grade 2:
Mn (or Zn5e:Mn) EL devices have been developed, and improvements in light emitting properties have been confirmed. This thin film EL element emits light with high brightness in response to an alternating current electric field of several KHz, and is characterized by long life.

FIG. 1 shows the basic structure of a ZnS:Mn thin film EL device as an example of a thin film EL device.

The structure of the thin film EL element will be explained in detail based on FIG.
A first dielectric layer 3 made of iO2, Al2O3, 5iBN4.5i02, etc. is formed in an overlapping manner by sputtering, electron beam evaporation, or the like. A ZnS light emitting layer 4 is formed on the first dielectric layer 3 by electron beam evaporation of ZnS:Mn sintered pellets. At this time, the ZnS:Mn sintered pellets used for vapor deposition are pellets in which Mn, which is an active substance, is set at a concentration depending on the purpose. A second dielectric layer 5 made of the same material as the first dielectric layer 8 is laminated on the ZnS light emitting layer 4, and a back electrode 6 made of A/ or the like is further deposited thereon. The transparent electrode 2 and the back electrode 6 are connected to an AC power source 7, and the thin film E
The L element is driven.

When an AC voltage is applied between the electrodes 2 and 6, the ZnS light emitting layer 4
The above AC voltage is induced between the dielectric layers 3 and 5 on both sides of the ZnS light emitting layer 4. Therefore, the electric field generated in the ZnS light emitting layer 4 excites electrons into the conduction band and accelerates them to obtain sufficient energy. The free electrons become free electrons and are attracted to the luminescent layer interface, and the free electrons moving at this interface directly excite the Mn luminescent center, and when the excited Mn luminescent center returns to the ground state, it emits yellow-orange light. That is, in the process of free electrons accelerated by a high alternating current electric field moving from one interface of the luminescent layer to the other interface, they excite the electrons of the Mn atoms that have entered the Zn site, which is the luminescence center, in the ZnS luminescent layer 4, returning them to the ground state. When falling, strong EL light is emitted in a wide wavelength range with a peak of approximately 5850λ.

When a rare earth fluoride other than Mn is used as the active substance, green and other luminescent colors characteristic of this rare earth element can be obtained.

The thin film EL element having the above structure can be used as a flat thin display device that takes advantage of the space factor, and can be used to display characters, symbols, still images, moving images, etc. on computer output display terminal equipment and various other display devices that contain characters and figures. It can be used as a means of displaying images, etc. Moreover, the specific driving method is disclosed in Japanese Patent Application No. 51-925.
No. 71.

Japanese Patent Application No. 52-18680, Japanese Patent Application No. 18631-1983, Japanese Patent Application No. 121218-1982, Japanese Patent Application No. 1987-1212
No. 14, Japanese Patent Application No. 1983-10098, Japanese Patent Application No. 1984-11
The details are explained in No. 0794 and the like.

The conventional thin film EL element described above can be viewed as a capacitive element that operates like a capacitor. By the way, this thin film EL element has a very high driving voltage of about 200 V and a large capacitance of about 6 nF/a#. Therefore, when calculating the power consumption in driving a light emitting display, even if the power involved in light emission is omitted and the power used to simply charge and discharge a capacitor is regarded as the amount of power consumed, there is not much difference from the power actually consumed. Therefore, considering the thin film EL element as a simple capacitor C, the amount of power required to charge and discharge the voltage Vo once is determined. First, the charging and discharging operations in the conventional drive method are simplified and the second
As shown in the figure. Turn off switch S2, turn on switch S1
When the capacitor C is charged with the voltage vo through the resistor R, the following equation holds true.

“f Ri+te 1dt=E song... Sichuan...
1) (If you rewrite the equation with charge q, R-!!L + engineering q=E...
......(2) t C .

The general solution to this equation is well known. (However, consider that q=0 at t=o.) That is, the electric energy wR1wc in the resistance R and the capacitance C is calculated from the following equations.

At t-(1), equations (5) and (6) show the following values.

1 2 ・・・・・・・・・・・・・・・(7
)WR=Wc=2CV.

Equation (7) shows that 1 of the energy supplied from the power supply is connected to the resistance R
2 shows that the remaining amount is stored in the capacity C. Further, the energy stored in the capacitor C is completely consumed by the resistor R when it is discharged by turning off the switch S1 and turning on the switch S2. Therefore, it is clear that the total power consumption required to charge and discharge the voltage Vo to the capacitor C in the conventional method is WR+WC=CVo.

FIG. 8 is a circuit diagram showing the configuration of a drive circuit in a conventional thin film EL display device. 4 is a diagram of voltage waveforms input to each terminal of the drive circuit and the thin film EL element 8 shown in FIG. 3.

Each terminal IN1 of the circuit to which the power supply voltage Vo is supplied,
IN2. IN8. By applying a pulse voltage to IN4 at the timing shown in FIG. 4, the base potential of the transistor Tr is changed, switching is performed, and the thin film EL is
An alternating pulse electric field is applied to the element 8 and it is driven in a seesaw manner, thereby obtaining EL light emission. That is, the terminal IN
When a pulse is applied to I and IN4, the transistor Tr
1 and Tr4 become conductive, becoming thinner than the transistor Trl, and the thin film EL element 8 enters a charged state. When a pulse is applied only to the terminal IN2 in the next period, the transistor Tr
2 becomes conductive, and the charges in the thin film EL element 8 are discharged. Next, when a pulse is applied to the terminals IN2 and IN8, the transistors Tr2 and TrB become conductive, and a current flows from the transistor Tr'B to the transistor Tr2 via the thin film EL element 8, and the thin film EL element 8 is The battery becomes charged with reverse polarity. When a pulse is applied only to the terminal IN4 in the next period, the transistor Tr4 becomes conductive, and the charge in the thin film EL element 8 is discharged.

The thin film EL element 8 is driven with alternating current by applying the above-mentioned pulse voltage, and an EL light emission pattern is obtained.

An object of the present invention is to provide a new and useful method for driving a thin film EL display device that can reduce the power consumption for display driving by making full use of technical means.

FIG. 5 is a simplified circuit configuration diagram illustrating a basic driving method of a thin film EL display device using a step driving method.

Switches S1 and S2 are turned OFF, switch S3 is turned ON, and the power supply KVo (0
<K<1), the capacitor C (thin film EL element) is charged via the resistor R. Next, turn off switch S2+58, switch S
, and charge the capacitor C with the power source Vo. This charging method is called a step drive method. At the time of discharging, only the switch S2 is ONL discharged as in the conventional method. Next, the amount of power required for charging and discharging using this step drive method is determined as follows.

The amount of electric power in the resistor R and capacitor C due to charging from the power source KVQ can be determined from equation (7) as follows.

12 WR=Wc=-C(KVo)...
・・・・・・・・・・・・(8) Next, the amount of electricity when charging the capacitor C from the power source Vo is q when using equation (2) and 1=0.
Since o=cKV1), it becomes (101).

At t-ω, equation (9) and equation (io) show the following values.

wR"=Leaving C(1-K)"Vo2 ・・・・・・・・・・・・・・・0D WR'=C(I K ) Vo" 2 C(I
K)2Vo''...O'JTherefore, the total amount of power WR5+ wcs at each of the resistors R1 and capacitance C during charging by the step drive method is calculated using equation (8) (111 equation (1
The following value is shown from equation '4.

WR5 = Engineering CK2V2 + Engineering C (l-K) 2vo'...In the song...o lecture 2 02 Wcs = Jin CV,” ・,,・ Song,
, , , (+4+θ) The energy stored in the capacitor C expressed by the formula is completely consumed by the resistor R during discharge.

Therefore, the power consumption Ws required to charge and discharge the voltage vo to the capacitor C in the step drive method takes the following value from the Oat equation 041.

W5'' WR5+WC5 Figure 6 shows the relationship between the power consumption Ws and the parameters of the WR5+WC5 type.

The dashed line P1 in the figure corresponds to the conventional driving method, and the curve P2 corresponds to the step driving method shown in FIG. As is clear from FIG. 6, when =, the power consumption Ws takes a minimum value, and compared to the conventional method, the power consumption becomes τ.

Furthermore, when a thin film EL display device is driven by the step driving method, experimental results that are in good agreement with the above principle have been obtained.

FIG. 7 is a circuit configuration diagram showing a schematic configuration of a drive circuit for realizing the step drive method described above. FIG. 8 is a voltage waveform diagram of pulse voltages input to each terminal of the drive circuit and the thin film EL element 8 shown in FIG.

Terminals INI, IN2. A pulse voltage is applied to INB and IN4 as in FIG. 4. The step drive method uses terminal I
This is done by a pulse applied to the terminal N5, and the rise of the drive pulse applied to the thin film EL element 8 rises in two steps in synchronization with the rise of the pulse applied to the terminal IN5. Further, the electric charge charged in the thin film EL element 8 is transferred to the terminal IN2.
．． By selecting IN4 and applying a pulse voltage, it is discharged as in the conventional case. Transistor January and Tr4
By alternately conducting Tr2 and TrB, the thin film EL element 8 is driven with alternating current, and by making the transistor Tr5 conductive during the rise of the forward and reverse pulses applied to the thin film EL element 8, a step drive method can be applied to the seesaw drive method. A superimposed driving scheme is established.

The present invention is to drive a thin film EL display device based on the above-mentioned step driving method, and hereinafter, a high voltage N-channel M
A driving method using an O5 type IC will be described in detail with reference to the drawings according to an embodiment.

FIG. 9 is a configuration diagram of a drive circuit for a thin film EL display device, explaining one embodiment of the present invention. FIG. 10 is a pulse waveform diagram of each part in the drive circuit of FIG. 9.

In FIG. 9, the thin film EL display device 10 has an X-direction electrode Xl.
-Xm is the data-side electrode, and the Y-direction electrodes Y1 to Yn are the scanning-side electrodes. A thin film EL element is interposed between the matrix electrodes, and the display picture element E(i, j) is configured. A drive circuit 20 that applies a preliminary charging voltage by transistors 21 and 22 operated by a signal Sl and a diode array 30 on the data side are connected to the X electrode via a common line A, and the diode array 30 is connected to each of the X electrodes. Corresponding diodes 81a, 81b, . . . 81m are connected and arranged. This is connected to the data side drive line and the N-channel MO5) transistors SD, , SD2 .・Acts to protect against 5Dm reverse bias. Between the diode array 30 and the X electrode, a switching element circuit 40 on the data side is an N-channel MO
5) Ransistor SD.

The N-channel MO8) transistor is composed of Sn2, . . . SDm, and is connected between the X electrode and the ground line. This forms a discharge circuit for the electric charge charged at the non-selected pixel point for writing, and also forms a charging circuit when a field refresh pulse is applied. On the Y electrode, a switching element circuit 50 on the scanning side is connected to an N-channel MO3I-
Ranjistor SS.

ss2. ...SSn, and an N-channel MO5) transistor is similarly connected between the Y electrode and the ground line. This forms a circuit that applies a write voltage to the selected pixel point for writing. Further, a diode array 60 whose cathode is connected to the odd-numbered line of the Y electrode and whose anode is connected to the common line B is arranged. Furthermore, a diode array 70 whose cathode is connected to the even-numbered line of the Y electrodes and whose anode is connected to the common line C is arranged. These diode doors □Reiro 0°70 are for separating the scanning side drive lines and protecting the reverse bias of the switching elements. Connected to the common lines B and C is a drive circuit 80 that applies a boosted charging voltage through transistors 81 and 82 operated by a signal S2. Further, a drive circuit 90 that applies write and field refresh pulse voltages to the common line C is connected to the common line C by a transistor 91 operated by a signal S8, and a drive circuit 90 is connected to the common line B by a transistor 101 operated by a signal S4. Drive circuit 10 applying write and field refresh pulse voltages to line B
0 is connected. Drive circuit 110 for applying preliminary charging voltage and boosting charging voltage by step driving method
is connected to the drive circuit 20 and the drive circuit 80 via a power supply line, and is pulled up by a transistor 111 operated by a signal S5. Further, transistor 112 charges capacitor 118 by signal 956 when transistor 111 is off. Drive circuit 90 and drive circuit 1
00 is connected to a drive circuit 120 for applying a write voltage pulse and a field refresh pulse by a step drive method via a power supply line E, and is raised to Vw (=VR) from a transistor 121 operated by a signal S7. Further, a signal S8 is applied to the transistor 123 to charge the capacitor 123 when the transistor 121 is OFF.

Next, the operation of this circuit will be explained with reference to the time chart of FIG. 10 (AlO2). In the above embodiment, the write drive voltage Vw is equal to the light emission start voltage vth and has the highest brightness, and the field refresh drive voltage vR is equal to the write drive voltage Vw.
uses the same voltage value to reduce the number of power supplies.

O First stage T1: Pre-charging period A high level signal is supplied to the gates of all scanning side switching elements SS1 to SSn of the switching element circuit 50 to turn them all on, and the potential of the Y electrode is set to the ground potential. At this time, the picture element whose Y electrode potential is higher than the X electrode potential is the diode 23. Accumulated charges are discharged via the diode array 30 and the switching element circuit 50. Also, at this time, the MOS of the switching element circuit 40 on the data side
) All of the transistors are set to the OFF state.

Next, the drive circuit 20 receives the signal S1 from the transistor 21.
22 is turned on and the diode array 30 is charged, the drive circuit 110 turns on the transistor 11 by the signal s5.
1 is ONL, capacitor 113 transistor 112 is O
It is held in FF.

Here, the voltage vM has a relationship of VM = VQ - Vth between the light emission start voltage vth and the highest brightness light emission voltage Vo.

O Second stage T2: Discharge modulation and scanning side pull-up period All MOS transistors ss1 to SSn of the scanning side switching element circuit 50 are turned off, and only the MOS transistors connected to non-light emitting pixels in the data side switching element array are turned on. , MOS) transistors connected to the light-emitting pixels are kept OFF.

After the discharge of the non-light-emitting picture element is completed, the transistor 81 of the drive circuit 80 that applies the scan-side boost charging voltage is turned on by the signal S2, and the common line B of the switching element circuit 50 and the diode array 60 is turned on.

Next, in the drive circuit 110, the transistor 111 is turned on by the signal S5, and the capacitor 113 is turned on.

0 Third stage T8: In the write drive period method, if the picture element E (i, j) shown in FIG. In B, when the transistor 101 of the drive circuit 100' receives the signal S4, only the scanning side MO5) transistor SSj of the picture element E(i, j) is ON, and all the other scanning side MO5) transistors are kept OFF. In a state where only this MOS) transistor SSj is turned on, the transistor 121 of the drive circuit 120 then receives the signal S
7, and the power line E and the common line C are pulled up to the voltage Vw. During this period, all data side MOS transistors are kept OFF.

By this writing drive, all the scan side electrodes except the selected scan electrode Yj are raised to the light emission start voltage Vth and the maximum brightness.

As a result of the above-mentioned first to third stages of driving, each picture element on the selected scanning electrode is When light emission is not desired, voltage Vw-TVM is applied and the modulation voltage becomes vM. Incidentally, -vM is applied to each wheel 1 element outside the selected scanning electrode, but the normal voltage 2VM is the voltage v
Since it is kept sufficiently lower than th, no light is emitted.

When sequential scanning for all scanning lines is completed, the next Tre
Field refresh driving is performed during period f.

0 4th stage: Field refresh drive period (Tre
f) Transistor 91 in drive circuit 90 and drive circuit 100
, 101, all MO5) transistors of the common scanning side switching element circuit 50 are turned OF by the signal S8+54.
F, all MO8) transistors of the data side switching element circuit 40 are turned on. When these MOS) transistors are in the same state, the transistor 121 in the drive circuit 120 is turned on by the signal S7, and the capacitor 128 is turned on.
The common lines B and C are pulled up to voltage vR, and voltage vR is applied to all picture elements.

By this field refresh drive, a field refresh pulse having a polarity opposite to that of the write drive is applied to the thin film EL display device 10, thereby closing the AC drive cycle of one field (one frame). Note that when the field refresh pulse is applied, since the picture elements that have already emitted light due to the application of the write voltage have been polarized, the electric field due to this polarization and the field refresh pulse are superimposed, and only the picture elements that have emitted light due to writing will emit light.

As described above, the power consumption reduction effect of the step drive method can be demonstrated using a high-voltage N-channel MO3IC (X-Y motor) IJ
A driving method applied to a sock thin film EL display device is established. In the above-described embodiment, the same voltage is used for the field refresh pulse voltage vR and the write voltage Vw, and the same voltage is used for the preliminary charging voltage Vpre and the boosting charging voltage vBs.

This is to simplify the drive circuit, and the present invention can be applied even when different voltages are used.

As explained in detail above, the present invention utilizes the fact that the thin film EL element is a capacitive element to reduce the driving power during display, and is a very effective technique as a method for driving a thin film EL display device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic structure of a thin film EL element. 2 is an explanatory diagram illustrating charging and discharging operations in a conventional driving method. FIG. 3 is a circuit diagram showing the configuration of a drive circuit in a conventional thin film EL display device. FIG. 4 is a timing waveform diagram showing the voltage waveform input to the drive circuit shown in FIG. 3. FIG. FIG. 5 is a simplified configuration diagram of a circuit explaining the basic operation of the step drive method. FIG. 6 is an explanatory diagram for comparing and explaining the power consumption in the conventional driving method and the step driving method. FIG. 7' is a configuration diagram of a drive circuit for a thin film EL display device that executes the step drive method shown in FIG. 5. FIG. 8 is a timing waveform diagram showing voltage waveforms input to the drive circuit shown in FIG. 7. FIG. 9 is a configuration diagram of a drive circuit for a thin film EL display device showing one embodiment of the present invention. FIG. 10 is a voltage waveform diagram of each part in the drive circuit shown in FIG. 9. lO...Thin film EL display device, 20...X electrode pre-charging drive circuit, 40...X electrode switching element circuit, 50...Y electrode switching element circuit, 110...
- Drive circuit for applying charging voltage, 120... Drive circuit for step drive. Figure l Figure 3 Patemometer K

Claims (1)

[Claims] 1. In a method for driving a thin-film EL display device in which a thin-film light-emitting layer that emits EL light in response to the application of an electric field is interposed between a pair of electrodes, the drive voltage value Vo for emitting EL light is doubled. (
By applying a voltage having a value of 0<K<1), the thin film EL
After charging the display device, a voltage having a value of Vo is continuously applied to selectively apply a write pulse to the thin film light emitting layer, and then a refresh pulse of opposite polarity is applied to the entire surface to reduce the write pulse. The write and refresh pulses that rise in a step manner cause EL light emission to occur from the portion of the thin film light emitting layer to which E is applied.
A method for driving a thin film EL display device, characterized in that it performs an L-light emission operation.