JPS583557B2 - Hakumaku Electroluminescence Sense Soshino Kudohoshiki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving electroluminescent elements of the type that emit light with high brightness by applying an alternating electric field.

Recently, J1500 has been developed in thin film electroluminescent devices (hereinafter referred to as thin film EL devices) based on Zns.
Elements have been developed that have high brightness exceeding ft-L (5 KHz operation) and long lifespan of 20,000 hours or more of continuous operation.

With the development of devices, various driving methods have been proposed, but all of them involve driving the device by applying a single pulse of large amplitude to the device.

In order to obtain sufficient brightness for display in the above device, it is necessary to apply a bipolar pulse of high voltage (for example, about 260 to 300 V).

As a practical matter, it is not easy to create such a high-voltage bipolar pulse, and it is also difficult to obtain a transistor with an appropriate current capacity, high breakdown voltage, and small size.

Furthermore, when used as a matrix panel display, a large number of drive circuits are required, and integration of the drive circuits becomes a problem, but even in that case, it is necessary to obtain high voltage integrated circuit elements. Difficult to integrate.

The present invention has been made in this regard, and proposes a method of driving the thin film EL element using a signal having a waveform structure in which a common large-amplitude pulse is superimposed with a small-amplitude pulse. Semiconductor elements can also be used as drive circuit components.

The present invention will be explained in detail below by giving examples.

FIG. 1 is a block diagram of a thin film EL element.

Now, to explain the configuration of this element according to the drawings, EL
Layer 1 is made of M as an element that forms a luminescent center in ZnS, for example.
The insulating layers 2 and 3 are transparent insulating thin films such as ¥203, the transparent electrode 4 is an oxide transparent conductive film such as Sn02In203, the back electrode 5 is a metal reflective film such as A7, and the substrate 6 is a vapor deposited material doped with n. It consists of a transparent insulating plate such as glass.

Each layer is formed on the substrate 6 by successive vapor deposition in the order shown.

What is shown in FIG. 2 is a matrix display panel in which the upper and lower electrodes of the element shown in FIG. 1 are made into parallel electrode groups 4' and 5' which are orthogonal to each other between the upper and lower sides.

This display panel is constructed by selecting one electrode from each of the upper and lower parallel electrode groups 4' and 5' and applying a voltage, thereby applying a voltage higher than the threshold for light emission of the EL element to the intersection of the selected upper and lower electrodes. , the point starts to emit light.

Figure 3 shows the emission brightness B characteristic (B-V characteristic) with respect to the applied voltage V of the element shown in Figure 1.As shown in the figure, this element has a fairly steep rise characteristic, with almost 200 ~ A change in brightness occurs between 250 cm and 250 cm.

In the present invention, this property of thin film EL elements is utilized, and a pulse having a large amplitude, which is below the threshold of light emission, is applied to the EL element in advance, and when driving the element, a pulse having a large amplitude is applied to the EL element. A small amplitude pulse that is superimposed and exceeds the light emission value is applied, and the element is made to emit light based on this pulse.

FIG. 4 shows a timing chart of a driving method according to an embodiment of the present invention, and in particular, each electrode X when displaying the letter E on the 5×5 matrix display panel 10 shown in FIG.

, X1, ... x4 and y. ,y1...
It is a time chart of the waveform applied to y4.

In addition, XQ, XI...X4 are the X electrodes driven by the X electrode drive circuit 8, and yo, y1...y4 are the Y electrodes driven by the Y electrode drive circuit 9. be.

The embodiment shown in FIG. 4 is for the case where each light emitting point is scanned line-sequentially, and a scanning pulse is applied to the Y electrode, and a pulse corresponding to data is applied to the X electrode.

This driving method will be explained below with reference to FIGS. 4 and 5.

First, the X electrode.

, X1...X4 are applied with a large amplitude pulse Px at a common timing.

A similar large-amplitude pulse py is applied to the Y electrodes yo, yt...y4, but the phase is 180 degrees with respect to the pulse Px.
° It's off.

The duty of this pulse PxsPY is 50%, and the amplitude V is suitably less than the light emission threshold of the thin film EL element, for example, about 170 cm for a device having the characteristics shown in FIG.

Further, the pulse width is selected to correspond to the scanning period T of one frame in the display device shown in FIG.

Therefore, the pulses Px and Py are of a type whose amplitudes are alternately changed every frame.

The time chart labeled X and Y in FIG. 4 is the time chart of this large amplitude pulse PxyPy.

The small amplitude pulses ax, by outputted in accordance with the data and scanning timing are superimposed on the large amplitude pulses Px, Py to the respective X electrodes and Y electrodes X.

,X1...X4tYotY1...y4
Each is output separately.

The small amplitude pulse by applied to the Y electrode is a scanning pulse in this example, and is applied to the electrode Y at time to.

The voltage is applied to the electrode y1 at time t1, to the electrode y2 at time t2, to the electrode y3 at time t3, and to the electrode y4 at time t4, thereby completing the scanning of one frame.

The small amplitude pulse ax applied to the X electrode is a data pulse, and when displaying the characters rEJ as shown in FIG.
1 (, electrode X at time.

, X4, X2, X3, X4, on electrode x1 at time t1 and on electrode X at time t2.

, XI, X2, x3, and electrode X at time t3.

Above, electrode X at time t4. ,X1,X2,X3,X4
Above, the data pulse ax is applied to complete one frame of rEJ display.

That is, the small amplitude pulse ax, by now has an amplitude △■
is a bipolar pulse that satisfies the relationship V+2Δv>vth (vth is the threshold of light emission of the thin film EL element),
When inputs are input to the X electrode and the Y electrode, and when the timings match and the two are superimposed, the thin film EL element receives 2△■
This means that a bipolar pulse with an amplitude of It begins to vibrate with an amplitude of △2V.

Therefore, the voltage actually applied to the element at this time is (■+2
ΔV), and the element emits light with high brightness.

In the device having the characteristics shown in FIG. 3, it is appropriate that the amplitudes of the pulses ax and by be about 40 volts for the pulses Px and Py of 170 volts.

When driving for one frame is completed as described above, driving for the second frame is performed in period t2.
In this case, the common potential is simply reversed from the previous frame, and the electrode y.

-V4, XO to X4, it is sufficient to output the same signals as in the case of the previous frame.

The same holds true for the third and subsequent frames. The embodiment shown here is related to a case where a bipolar small amplitude pulse is applied to a large amplitude pulse, but an embodiment in which a unidirectional small amplitude pulse is superimposed on a large amplitude pulse can also be easily applied. I can make suggestions.

FIG. 6 shows the X electrode X according to this embodiment.

, Xl...x4 and Y electrode y.

, y1...y4.

In this case as well, the basic operation is the same as in the embodiment in which bipolar small-amplitude pulses are applied, but it is necessary to apply small-amplitude pulses with different polarities for each frame.

This is because the thin film EL element is an AC driven element.

The embodiment shown in FIG. 6 also relates to the case where the letter "E" is displayed line-sequentially on the 5×5 matrix panel 10 shown in FIG. A scanning pulse is introduced.

FIG. 7 is a block diagram of a drive circuit for driving a thin film EL panel according to the scheme of the present invention.

The structure and operation will be explained according to the drawings. First, data D is set in the data register 11 from the outside in synchronization with the data input clock C.

Next, a scanning pulse is input to the shift register 15 from the clock and control circuit 19 driven by the scanning timing signal t, and at the same time, the output gate of the data register 11 is opened in synchronization with the scanning, and a corresponding small amplitude pulse is inputted to the shift register 15. ax is output from the X signal driver 12.

This signal is also applied to the output of the X signal driver 14 controlled by the scanning pulse from the clock and control circuit 19 (
X+xi) are superimposed in the signal generating circuit 13 and applied to the X-direction electrodes xo, X1, . . ., X4.

On the other hand, the output of the shift register 15 is also
6 and controlled by the scanning pulse from the clock and control circuit 19, the
Y+yj) The Y-direction scanning electrode y is superimposed in the signal generation circuit 17.

is applied to Repeat the above actions.

By repeating the process up to -y4, one frame of scanning is completed.

The next frame is displayed by changing the output polarity of the X and Y signal drivers 14 and 18 and continuing similar scanning.

FIG. 8 shows the (X+xi) signal generation circuit 13 of FIG.
The configuration of the (Y+yi) signal generation circuit 17 is shown.

What is shown with a field is a means for superimposing the X (or Y) signal and the output of the X (or y) signal driver 12 (or 10).

As is clear from FIG. 8, in the drive system of the present invention, the X electrode driver 14 and the Y signal driver 18 commonly supply large amplitude pulses to each X electrode and Y electrode, so only one each is required. do not have.

FIG. 9 is a diagram showing still another embodiment of the method of the present invention.
X signal, Y signal, xi (i=0 to n) signal, yj when scanning the light emitting point diagonally on the Xm matrix panel
(j=o to m) indicates the timing of the signal.

As explained above with reference to an example in which the method of the present invention is applied to a matrix panel, in the method of the present invention, a pulse with a relatively large amplitude, which is below the threshold for light emission, is applied to the element in advance, and display data is applied to this pulse. The thin-film EL element is driven by superimposing corresponding small-amplitude pulses, and only one set of large-amplitude pulse drive circuits are required for each of the X and Y electrodes, especially when driving a matrix panel with a large number of electrodes. In addition, the drive circuit that derives the signal corresponding to the display data can be driven with relatively small amplitude pulses, making the configuration of the drive circuit extremely simple, especially since it does not require many high-voltage transistors. , which has significant advantages over conventional methods.

Moreover, such an advantage is particularly effective when considering the use of an IC for the drive circuit.

The embodiments described above are all related to the case of driving a matrix panel, but the method of the present invention is not limited to these embodiments. Of course, it can also be applied to dot matrix displays such as those displayed in .

[Brief explanation of drawings]

Fig. 1 is a block diagram of a thin film EL element, Fig. 2 is a block diagram of a matrix panel formed with the elements shown in Fig. 1, Fig. 3 is a BV characteristic diagram of the element shown in Fig. 1, and Fig. 4 is a time chart of one embodiment of the present invention, FIG. 5 is a configuration diagram of a 5×5 matrix panel for explaining the time chart shown in FIG. 4, and FIG. 6 is a time chart of another embodiment of the present invention. , FIG. 7 is a block diagram of a drive circuit according to the method of the present invention, FIG. 8 is an enlarged view of the main part of the circuit shown in FIG. 9, and FIG. 9 is a time chart for yet another embodiment of the present invention. . Px, PY...Large amplitude pulse, ax, by...
. . . Small amplitude pulse, 8, 9 . . . X, Y electrode drive circuit, 10 . . . Matrix panel.

Claims (1)

[Scope of Claims] 1. A driving method for a thin film electroluminescent element that emits EL light by applying a voltage and is arranged as a light emitting element at the intersection of electrodes arranged in a matrix, the method comprising: one of the electrodes emitting light; A first voltage pulse signal having a relatively large amplitude in a range below a threshold of second phase
a voltage pulse signal corresponding to the display data is applied to each of the other electrodes, and a third voltage pulse signal having a relatively small amplitude Δ■ that is sequentially line-scanned is sequentially superimposed on each of the other electrodes. When the third and fourth voltage pulse signals are superimposed on the first and second voltage pulse signals, respectively, the amplitude (■+2Δ■) is obtained.
drive the thin film electroluminescent elements arranged in a matrix so as to form an amplitude greater than a threshold voltage value for light emission. .