JPS5852237B2 - display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image or character display device using electroluminescence (hereinafter referred to as EL), an electroluminescent device that has hysteresis characteristics in the relationship between applied voltage and luminance.

In an image or character display device using a matrix-type EL element with hysteresis characteristics, if various conditions such as the pulse width and frequency amplitude of the emission sustaining pulse can be varied, the influence of ambient light of the display device can be reduced. It is possible to set the display image to the optimum state that is most legible, taking into account the content of the display device (for example, an image that only displays text and has a high luminance ratio, or an image with a low gradation that is difficult to distinguish from the background). can.

Generally, when an EL is used as a display element, a matrix type electrode arrangement as shown in FIG. 1 is adopted.

In Figure 1, 1 is a glass plate, 2 is a transparent electrode arranged in a grid pattern, 3 is a dielectric material such as Y2O3, 4 is a fluorescent layer such as ZnS doped with Mn, etc., and 3' is the same dielectric material as 3. , 5 are electrodes made of aluminum or the like and arranged perpendicular to the electrode 2.

When an appropriate alternating current voltage is applied to one of the first electrode group 2 and one of the second electrode group 5 in an element having such a structure, only the portion where the electrodes intersect will emit light.

This corresponds to one picture element on the screen. When a bipolar pulse is applied to one pixel of a matrix type EL element as shown in Fig. 2a, the relationship between the average luminance B and the applied voltage ■, that is, the B-V characteristic, is determined by keeping the applied frequency f constant. , pulse width τ is τ1. τ2. As τ3 is gradually lowered, the B-V characteristic shifts to the right, resulting in a shape as shown in FIG. 2b.

In addition, the pulse width τ is constant, and the frequency f is fl, f2゜f
3, the BV characteristic becomes compressed from the upper side, as shown in FIG. 2c.

Now, a bipolar pulse as shown in FIG. 3b is applied to one pixel of the matrix type EL element having the hysteresis characteristic as described above.

At first, when a sustaining pulse Ps with an amplitude Vs and a pulse width τ1 is added, the emission brightness is Bs1, and then when a write pulse Pw with an appropriate time width and a sufficient amplitude Vw is added, as shown in Fig. 3a. As shown by the curve ■ in the figure, after emitting light at a brightness of Bmll, the subsequent sustain pulse P
It emits light with a brightness of Bwl at s.

The brightness ratio before and after writing is 3w1/Bs1.

Furthermore, by reducing the amplitude or pulse width of the write pulse Pw, it is possible to obtain an arbitrary light emission brightness between Bs1 and Bwl.

In other words, halftone writing is possible.

Next, when an erasing pulse Pr with an amplitude Vr is applied, the luminance of the emitted light becomes zero instantaneously, and thereafter, the sustain pulse Ps continues to emit light in the initial state.

As shown in FIG. 3c, when the pulse width of the sustain pulse Ps is changed to τ2 after adding the erase pulse Pr, the luminance before writing becomes Bs2.

Next, when a write pulse Pw with the amplitude Vw under the same conditions as before is applied, light is emitted instantaneously with a brightness of Bm2, and then the subsequent pulse width τ2
It emits light with a brightness of Bw2 with a sustain pulse Ps of .

The brightness ratio before and after writing is Bw 2 / B
s 2 .

After that, when an erasing pulse Pr of amplitude vR is added, the initial state is returned.

If we compare and consider when the pulse width of the sustain pulse Ps is τ1 and τ2, depending on the relative relationship, the luminance brightness Bw1
．． Bw2 and emission brightness ratio Bwt/Bst, 3
w2/Bs2 can be varied over a fairly wide range.

Next, considering the case of halftone writing, when the pulse width of the sustain pulse Ps is set to R1, the amplitudes Va, V
When write pulses b, Vc, and vd are applied, the fourth
As shown in the relationship diagram ``■'' in the figure, the luminances after writing by the sustain pulse are Ba1 t Bbl and 1, respectively.
It becomes 3c15 Bdt.

Furthermore, when the pulse width of the sustain pulse is τ2, the amplitude va
.

When write pulses of Vb, Vc, and Vd are applied, the luminance after writing by the sustain pulse is Ba2°Bb2. B
e2. Becomes Ba2.

Ba1. Bbl, Be1. Emission brightness ratio between Ba1 (gradation level when pulse width τ1) and Ba2. Bb2. Bc2
This is different from the luminance ratio between tBd2 (gradation level when the pulse width is τ2).

Therefore, it can be seen that the gradation level can be changed by changing the pulse width.

Above, we have explained the characteristics when the frequency and amplitude of the sustain pulse are constant and the pulse width is changed, but even if the frequency and amplitude are changed, the brightness after writing and the brightness ratio Bw/B
s (Bs and Bw are the brightness before and after writing, respectively) and the gradation level can be changed.

When a matrix EL element having the characteristics described above is used to display characters or images, the display image can be adjusted to a state that is easy to see by changing the conditions of the sustain pulse.

FIG. 5 shows a basic configuration block diagram of an image display device using matrix type EL elements having the above characteristics.

A composite video signal inputted from the input terminal 6 is separated into a video signal 8 and a synchronization signal 9 by a signal separation circuit 7.

The video signal 8 is further temporally extracted by a signal processing circuit 10 using sampling pulses, and is then extracted by a holding circuit 11.
After being held for a certain period of time, the gate circuit 18 controls the pulse generated by the timing pulse generator 14 which synthesizes the clock pulse 13 and the synchronization signal 9 together with the signals from the erase pulse generation circuit 16 and the sustain pulse generation circuit 17. , from the output drive circuit 12, the electrode group H1°R2...
Voltage is supplied to 1h.

In the game circuit 19, signals from the erase pulse generation circuit 16 and the sustain pulse generation circuit 17 are controlled by pulses generated from the timing pulse generator 14, and from the output drive circuit 15, the signals from the electrode groups 1. A voltage is supplied to v2...Vn.

A high voltage is supplied from the power supply circuit 20 to the output drive circuits 12 and 15.

Now, from the output drive circuit 12, electrode groups H1, H2...
・Writing pulse Pw0. applied to H stone. Pw2. Pw3
... is modulated according to the intensity of the input video signal, the brightness after writing can be adjusted by changing the pulse width of the sustain pulse.

Specifically, assuming that the sustaining pulse generating circuit 17 controlled by pulses generated by the timing pulse generator 14 is composed of a monostable multivibrator, the capacitor C and resistor R (Fig. (not shown)
What is necessary is to change the value of the time constant C-R determined by .

This can be realized by simple means such as making the resistor R a variable resistor.

To change the same wave number of sustain pulses, the timing pulse generator 14 can be adjusted. To change the amplitude of the sustain pulses, the power supply circuit 20 can be adjusted and the output drive circuit 12 can be changed.
It is only necessary to change the voltages supplied to and 15.

For ease of understanding, FIG. 6 shows the voltage waveform and light emission waveform applied to the (l·1) electrode when a (3×3) matrix is assumed.

Assume now that one frame F consists of three horizontal scanning periods H, and that sampling is performed at three points in each horizontal period.

In the line sequential scanning method, signal levels sampled at each point in time during a horizontal scanning period are held in a holding circuit, and at the end of the horizontal scanning period, they are simultaneously written to each picture element according to the signal level.

To explain the waveform applied to the (1-1) electrode in FIG. 5, ■ is a write pulse.

After this, the light emission continues at @no maintenance Hals with a pulse width τ1.

The light emission waveform at this time is shown by a solid line.

This light emission is erased by an erase pulse ◯ before writing the picture element signal of the next frame.

(2) is a vertical electrode selection pulse. Now, in order to set the display image to the most easily viewable state for a visual person, suppose we manually change the pulse width of the sustain pulse to τ2. If a write pulse ■ with the same amplitude as before is added, the emitted light waveform will be as shown by the dotted line. It changes like that.

The luminance of other picture elements in the (3×3) matrix also changes by changing the sustain pulse width, and the entire matrix panel is set to the most visible state.

As described above, even if the amplitude or the wave number of the sustain pulse is changed, it is possible to obtain an optimal display image that takes into account the contents of the display image, the influence of surrounding light, and the like.

In the figure, ■ is a signal related to the video signal, but (1・1
), and since there is no vertical electrode selection pulse corresponding to this signal (2), it does not become a write pulse.

This signal (2) has a much smaller amplitude than the erasing pulse O, so it does not have an erasing effect.

As described above, the present invention maintains a high-intensity light emitting display by applying a sustain pulse at °C based on the history characteristics after applying a write pulse, and since the drive is based on the history characteristics, the amplitude of the write pulse, Halftone writing can be performed by changing the pulse width and the same wave number, and the luminance obtained by the half tone writing drive can be changed as appropriate according to the history characteristic curve that changes by controlling the change in the pulse width (or the same wave number) of the sustain pulse. It can be changed to gradation.

That is, according to the present invention, it is possible to set the display screen to the most easily viewable brightness using the superimposed effect of the amplitude modulation of the write pulse and the pulse width (or frequency) modulation of the sustain pulse, and the gradation level can be set in a very wide range. Adjustments can also be made based on historical characteristics.

[Brief explanation of the drawing]

Figure 1 a, b is a partially cutaway perspective view and cross-sectional view of an EL with a matrix structure, and Figure 2 a, b, and c are voltage application waveforms and EL.
Figure 3 shows the voltage waveform with the pulse width of the applied voltage changed and the change in luminance brightness due to the change in pulse width. Figure 4 shows the write voltage amplitude and the luminance brightness due to the post-write sustain pulse. 5 is a block diagram of the configuration of a display device with adjustable brightness, and FIG. 6 is a time correlation diagram showing the relationship between the voltage application waveform and the luminance of light emission in the case of image display. 2 is an electrode, 3 and 31 are dielectric materials, 4 is a fluorescent layer, 5 is an electrode, Pw is a write pulse, Vw is a write voltage, Ps is a sustain pulse, and Vs is a sustain pulse voltage.

Claims (1)

[Scope of Claims] 1. History characteristic in which the change in light emission brightness in the process of decreasing the voltage from the high voltage side is maintained in a high brightness state with respect to the change in light emission brightness in the process of increasing the amplitude of the AC applied pulse voltage. In a display device having a voltage booster, a pulse voltage defined by an amplitude value that maintains a low luminance when the voltage is increased and a high luminance when the voltage decreases is applied as a sustaining pulse, and the pulse width or frequency of the sustaining pulse is changed. Emission brightness maintenance means having a control function; and writing means that applies a pulse voltage defined by an amplitude value higher than the sustaining pulse as a write pulse and has a function of amplitude modulating the write pulse, The light emission brightness obtained through the writing means is controlled in multiple gradations, and the light emission brightness is sustained by the light emission brightness maintaining means based on the history characteristics, and the pulse width or frequency of the sustain pulse is controlled to change the light emission brightness level. A display device characterized by adjusting the furniture.