JP2810458B2 - Driving method of thin film EL display device - Google Patents

Description

The present invention relates to a method for driving a thin film EL display device.

[Conventional technology]

In general, a thin-film EL element can achieve higher luminance and longer life by applying an AC voltage having a symmetric waveform to pixels.

Conventionally, as a driving method of a thin film EL display device, a driving voltage is applied to the thin film EL element from a scanning side and a signal side, and a bidirectional Push-Pull symmetric driving method using a bipolar element on the scanning side and the signal side (particularly, And a method of applying a drive voltage to the thin-film EL element from the scanning side and the signal side and providing a discharging process to reduce power consumption during driving (Japanese Patent Laid-Open No. 62-143096). Reference).

[Problems to be solved by the invention]

In the driving method of the thin-film EL display device, since a driving voltage is applied to the thin-film EL element from the scanning side and the signal side, the voltage is also applied to unselected pixels of the thin-film EL element. For this reason, it is necessary to adjust the driving voltage according to the luminance / voltage characteristics of the light emitting layer of the thin film EL element in order to avoid leakage light emission of unselected pixels in the thin film EL element. In addition, power is required on both the scanning side and the signal side. To reduce the cost, it is necessary to reduce the number of processes and the number of parts used, but this point is not taken into consideration.

The present invention solves the above-mentioned drawbacks and eliminates the need for a driving power supply on the signal side and does not apply a voltage to non-selected pixels of the thin-film EL element. It is an object to provide a driving method of an EL display device.

[Means for solving the problem]

In order to achieve the above object, the present invention drives a thin-film EL element provided with two sets of striped electrode groups orthogonal to each other on both sides of an EL light emitting layer as a scanning side electrode group and a signal side electrode group by a line sequential driving method. In the method of driving a thin-film EL display device that performs dot matrix display by using the thin-film EL, the driving voltage has the same absolute value and different polarity, and the absolute value is the thin-film EL.
Two types of voltages that are equal to or higher than the light emission start voltage of the element are used, and one of the two types of voltages is applied to only one scanning side electrode during scanning in the scanning side electrode group, and the other scanning side electrodes are in a floating state. The signal side electrode connected to the selected pixel of the thin film EL element in the signal side electrode group is connected to a ground potential point, and the signal side electrode connected to the non-selected pixel of the thin film EL element is set in a floating state. This turns on / off the drive voltage of each pixel in the thin film EL element.

〔Example〕

FIG. 1 shows an example of a driving circuit of a thin film EL device used in the embodiment of the present invention.

In this example, a driving voltage is applied to the thin film EL element only from the scanning side and no driving voltage is applied from the signal side. In FIG. 1, reference numeral 1 denotes an EL for displaying a dot matrix.
This is a thin-film EL element composed of a display panel. Two sets of stripe-shaped electrodes orthogonal to each other are provided on both sides of an EL light-emitting layer as a scanning-side electrode group and a signal-side electrode group. Reference numerals 2 and 3 denote power supplies that generate voltages (+ HV, −HV) whose absolute values are equal to each other, have different polarities, and whose absolute values are equal to or higher than the light emission start voltage of the pixels in the EL display panel 1. 4 and 5 connect ground potential to the signal-side electrodes of the EL display panel 1, a plurality of switching elements CP ₁ for performing _{non-connection, CP 2, ... CP N,} CN 1, CN 2, ... CN N
Is a switching element group. 6,7 These switching element group _{CP 1, CP 2, ... CP} N, CN 1, CN 2, a shift register that controls the ... CN _N, a logic circuit such as a latch. 8 is
ON + HV to each scanning electrode of the EL display panel 1, a plurality of switching elements RP ₁ for performing off, RP _2, ... switching element group consisting of RP _N, 9 are to each scanning electrode of the EL display panel 1 -Multiple switching elements RN for turning on and off HV
_1, RN _2, a switching element group composed of ... RN _N. 10,11
Is a logic circuit such as a shift register. Switching element _{RP 1, RP 2, ... RP} N has one end connected to each of the connected other end a common line to each scanning electrode of the EL display panel 1, the switching element _{RN 1, RN 2, ... RN} N also One end is EL display panel 1
And the other end is connected to a common line. 12 the switching element _{RP 1, RP 2, ... RP} N
Common line switch for switching and connecting to the power supply 2 and the ground potential point of 13 switching elements RN _1, RN _2, ... is a switch for switching connects the common line to a power source 3 and the ground potential point of the RN _N.

 Next, the operation of the driving circuit will be described.

This drive circuit basically includes two types of voltages + HV having an absolute value equal to or higher than a light emission start voltage of a pixel of the EL display panel 1 as a drive voltage for a scanning side electrode of the EL display panel 1 and having the same absolute value and different polarity. , -HV, EL display panel 1
The selection or non-selection of each pixel of the EL display panel 1 is controlled by switching the signal side electrode of the EL display panel 1 between the ground state and the floating state. The case where a positive voltage is applied to the scanning electrodes of the EL display panel 1 is mode I, and the case where a negative voltage is applied to the scanning electrodes of the EL display panel 1 is mode II.

Switching element RP ₁ In mode I, RP _2, ... RP _N
Common lines are connected by the switch 12 to the power supply 2 + H is applied, the switching element RN _1, RN _2, ... common line of RN _N is connected to a ground potential point by the switch 13. At this time,
Switching elements RN _1, RN _2, ... switching elements RN ₁ when the switching element group 8 is turned on to connect to the ground potential point common line of RN _N, RN _2, ... poles at both ends of the RN _N This is to prevent sex HV. In this state, the switching element RN of the scanning _1, RN _2, ... RN _N is any logic circuitry 11
RP ₁ , RP
_2, ... RP _N is turned off by the signal from the signal other switching elements are all logic circuit 10 is turned on by the switching element only a logic circuit 10 which is connected to the scanning electrode to be scanned of the EL display panel 1 Becomes Accordingly, the voltage + H is applied only to the scanning electrodes to be scanned in the scanning electrode group of the EL display panel 1. On the other hand, the switching element CP ₁ of the signal side, CP _2, ... CP _N are all turned off by the output signal of the logic circuit 6, switching element _{CN 1, CN 2, ... CN} N
Is turned on and off according to the display signal from the logic circuit 7, thereby selecting and deselecting each pixel of the EL display panel 1. Here, in order to simplify the description, one pixel will be described with reference to FIG. In FIG. 2, reference numeral 14 denotes a pixel connected to the first signal side electrode and the first scanning side electrode in the EL display panel 1, and includes a switching element CP.
₁ , CN ₁ , RP ₁ , RN ₁ . When the pixel 14 is the selected pixel, the switching element CN ₁ is turned on by a signal from the logic circuit 6, and the pixel 14 has + HV between both ends when + HV is applied from the power supply 2 to the first scanning electrode. To emit light. Off by a signal from the switching device CN ₁ logic circuit 6 when the pixel 14 is a non-selected pixel, the pixel 14 has one end does not emit light is applied voltage becomes open.

Oite mode II the switching element _{RN 1, RN 2, ... RN} N
Common line is connected to the power supply 3 by the switch 13, the switching element RP _1, RP _2, common line of ... RP _N is connected to the ground potential point by the switch 12. At this time, the switching element
RP _1, RP _2, ... switching element RP _1, RP ₂ when in mode I is similarly to switching element group 9 for connection is turned on to ground potential the common line of the RP _N, ... RP _This is to prevent bipolar HV from being applied to both ends of _N. In this state, the switching element RP ₁ of the scanning, RP _2, ... RP _N are all turned off by the output signal of the logic circuit 10, the switching element _{RN 1, RN 2, ... RN} N is to be scanned of the EL display panel 1 Only switching elements connected to the scanning electrode are logic circuits
The switching element is turned on by a signal from 11, and all other switching elements are turned off by a signal from the logic circuit 11. As a result, the scanning electrode group of the EL display panel 1 is applied with the voltage -H only to the scanning electrodes to be scanned. On the other hand, the switching element CN _1, CN ₂ of the signal side, ... CN _N are all turned off by the output signal of the logic circuit 7, the switching element CP _1,
CP ₂ , ..., CP _N are turned on in accordance with the display signal from the logic circuit 6,
By turning off, selection or non-selection of each pixel of the EL display panel 1 is performed. Next, a description will be given with reference to FIG. Across the switching element CP ₁ when the pixel 14 is selected pixels are turned on by a signal from logic circuit 6, the pixel 14 is -HV when scanning from the power supply 3 -HV is applied to the first scanning electrode Light is emitted when applied in between. Off by a signal from the switching element CP ₁ logic circuit 6 when the pixel 14 is a non-selected pixel, the pixel 14 has one end does not emit light is applied voltage becomes open.

4 and 5 show the operation of each element as described above in each mode.

By alternately performing mode I and mode II for each pixel, + HV and -HV are applied to the selected pixel from the scanning side electrode, and no voltage is applied to the non-selected pixels. That is, it is possible to prevent leakage light emission of non-selected pixels.

Note that the present invention does not limit how to switch the mode for compensating the polarity of each pixel. For example, a method for switching the mode for compensating the polarity of each pixel for each scanning line, For example, a method of switching the mode for compensating the polarity for each screen display can be used. The present invention does not impose any restrictions on the power supply voltages + HV and -HV used in the drive circuit, except that their absolute values are equal to or higher than the light emission start voltage. Further, the present invention does not impose any restrictions on the thin film EL display device. For example, the light emitting layer material of the thin film EL element is ZnS,
Using ZnSe, CaS, SrSe, CaSe and mixed crystals thereof, using Mn or a lanthanum-based rare earth as a light emitting center of a light emitting layer, and using a Y ₂ O ₃ , SiO ₂ , Al ₂ O ₃ , Ta Thin films using oxides such as ₂ O ₅ , nitrides such as Si ₃ N ₄ , BN, and AlN or ferroelectrics such as tungsten bronze and perovskite
As the transparent electrode material of the EL element, ITO, ZnO, or the like can be used. As the structure of the thin-film EL element, the so-called insulating structure in which the insulating layer is provided on one side or both sides of the light emitting layer,
Alternatively, a structure without an insulating layer may be employed.

In the embodiment of the present invention, a thin film EL display device having a display capacity of 32 × 32 dots using SrS: Ce for the light emitting layer is created and used,
The above driving circuit was created using NchMOSIC and PchMOSIC as driving elements.

The EL display panel 1 in the above thin film EL display device was formed in a structure as shown in FIG. 3 using SrS: Ce as a light emitting layer. That is, the EL display panel 1 includes two sets of striped electrode groups 21 and 24 orthogonal to each other on both sides of the EL light emitting layer 23.
It was created in a structure provided through 2. Striped electrode group 2
1 is Al ₂ O ₃ as target by RF magnetron sputtering
A film of 2000 mm was formed at a substrate temperature of 300 ° C. using ZnO doped with 2 wt%, followed by etching to 3 mm (electrode line width 200 μm).
m). The insulating layer 22 is made of Y _{2 by} EB evaporation.
Using O ₃ deposition source was prepared by 3000~5000Å formed at a substrate temperature of 70 ° C.. The light emitting layer 23 is 0.1 mol% of CeCl ₃ as an evaporation source.
A 1 μm film was formed at 450 ° C. substrate temperature using doped SrS. The striped electrode group 24 is formed by depositing Al by a resistance wire heating evaporation method, and then etching it to 3 mm (electrode line width).
(200 μm).

The above drive circuit has a 32-bit output number as a drive element, and each has a built-in shift register and latch.
It was created using OSIC and PchMOSIC. The control circuit for controlling the driving element uses TTL. In the above drive circuit, NchMOSIC and PchMOSIC are used as the switching elements, but the types of the switching elements are not limited.
A CMOS, a bipolar transistor, or the like can be used. The driving voltage HV is such that the luminance of the EL display panel 1 is 1 cd / cm ²
And a voltage (190 V) obtained by adding 60 V to the voltage. Also 2
As a method of switching the two modes, a method of alternately performing the mode I and the mode II for each scanning line and switching the mode for each frame was used.

As an evaluation of the thin film EL display device, when a still image and a moving image were reproduced by inputting data from the microcomputer to the thin film EL display device, as described above, the thin film EL display device was specially driven using two power supplies less than the conventional one. Good display quality without leakage light emission of non-selected pixels was obtained for both still images and moving images without adjusting the voltage.

〔The invention's effect〕

As described above, according to the present invention, a thin-film EL element provided with two sets of stripe-shaped electrode groups orthogonal to each other on both sides of an EL light-emitting layer as a scanning-side electrode group and a signal-side electrode group is driven by a line-sequential driving method. Thin-film EL for dot matrix display
In the method for driving the display device, two voltages having absolute values equal to each other, different polarities, and an absolute value equal to or higher than the light emission start voltage of the thin-film EL element are used as driving voltages during scanning by the scanning electrode group. One of the two types of voltages is applied only to one scanning-side electrode to bring the other scanning-side electrode into a floating state, and the thin film in the signal-side electrode group
The signal side electrode connected to the selected pixel of the EL element is connected to a ground potential point, and the signal side electrode connected to the non-selected pixel of the thin film EL element is brought into a floating state, thereby forming the thin film EL.
Since the drive voltage of each pixel in the element is turned on / off, only two power supplies that output positive and negative voltages as power supplies by applying the drive voltage to the thin-film EL element from the scanning electrode alone are used. This eliminates the need for a driving power supply on the signal side. In addition, since no voltage is applied to the non-selected pixels of the thin-film EL element, leakage of light from the thin-film EL element does not occur and good display quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an example of a driving circuit of a thin film EL display device used in the embodiment of the present invention, FIG. 2 is a circuit diagram showing a configuration of one pixel in a dynamic driving circuit, and FIG. FIG. 4 and FIG. 5 are perspective views showing the display device, and are diagrams showing the operation of each element in the drive circuit. 1. Thin-film EL element, 2,3 ... Power supply, 4,5,8,9 ... Switching element group, 12,13 ... Switch.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Yoshiyuki Kageyama 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Seiichi Oseto 1-3-6 Nakamagome, Ota-ku, Tokyo (56) References JP-A-2-32392 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G09G 3/00-3/38 H05B 33/00- 33/28

Claims (1)

(57) [Claims] 1. A dot matrix display by driving a thin-film EL element provided with two sets of stripe-shaped electrode groups orthogonal to each other on both sides of an EL light-emitting layer as a scanning side electrode group and a signal side electrode group by a line sequential driving method. In the method of driving a thin film EL display device to be performed, the scanning side electrode group uses two types of voltages having the same absolute value and different polarities as drive voltages, and the absolute value of which is equal to or higher than the light emission start voltage of the thin film EL element. Applying one of the two types of voltages to only one scanning-side electrode during scanning in the other to make the other scanning-side electrode in a floating state, and connecting a signal connected to a selected pixel of the thin-film EL element in the signal-side electrode group The driving voltage of each pixel in the thin film EL element is turned on / off by connecting the side electrode to the ground potential point and setting the signal side electrode connected to a non-selected pixel of the thin film EL element to a floating state. The driving method of a thin film EL display device, characterized in that to off.