JPS6118900B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image display device using EL elements for display purposes.

Triple structure ZnS:Mn (or ZnSe:Mn) in which a semiconductor light emitting thin film doped with Mn such as ZnS or ZnSe is sandwiched with a dielectric thin film such as Y ₂ O ₃ , Si ₃ N ₄ or TiO ₂
Thin-film EL elements are characterized by emitting high-intensity light when an AC voltage of several kHz is applied and having a long life. Furthermore, the light emission of this thin film EL element has a hysteresis characteristic in which the luminance of the light emitted by the same applied voltage value differs in the process of increasing the applied voltage and in the process of decreasing it from the high voltage side. It was discovered that in the process of increasing the applied voltage to an EL element with this hysteresis characteristic, when light, electric field, heat, etc. are applied, the EL element is excited to a state of luminance corresponding to the intensity. ,
It is known that there is a memory phenomenon in which the luminance remains in a high state even after the light, electric field, heat, etc. are removed and the state is returned to its original state. EL element application technology that makes effective use of this memory phenomenon and uses EL elements as memory elements is currently being researched and developed in industry.

When an EL element with a memory function is applied to an image display device, a moving image being displayed can be stopped at any time and the moving image can be switched to a still image. In order to set the luminance brightness and contrast to the optimum state when displaying this switched still image, the present invention can set the sustain pulse conditions when displaying a still image independently of the sustain pulse conditions when displaying a moving image. This is an improved circuit system.

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 Y ₂ O ₃ , and 4 is a glass plate.
3 is a phosphor layer made of ZnS or the like doped with Mn or the like, 3' is the same dielectric material as 3, and 5 is a back electrode made of aluminum or the like arranged perpendicularly to the electrode 2. In an element having such a structure, one of the transparent electrode groups 2
Then, when a suitable alternating current voltage is applied to one of the back electrode group 5, only the portion where these electrodes intersect will emit light. This corresponds to one picture element on the screen.

Figures 2a, b, and c show the relationship between the applied voltage and luminance when a bipolar pulse is applied to one pixel of a matrix-type EL element. First, Figure 2a
As shown in Fig. 2b, the luminance when sustaining pulses of amplitude ±V _S are applied at timings t ₁ and t ₂ are as shown in Fig. 2b,
As shown in c, it is B _S. Next, when a write pulse of amplitude V _W is applied at timing t ₃ , B _W instantaneously
The light emission brightness becomes B _W with a sustain pulse of amplitude ±V _S applied at timings t ₄ to _{t 8} . Next, when an erasing pulse with an amplitude of ±V _E is applied at a timing from t ₉ to _{t 11} , the luminance becomes B _S again. There is a hysteresis characteristic between the emission brightness and the applied voltage as shown in FIG. 2b.

Figure 3 shows an animation using an EL element with the basic structure and basic characteristics shown in Figures 1 and 2.
1 shows a configuration block diagram of an image display device including a still image switching circuit. A composite video signal inputted from the input terminal 6 is separated into a video signal 8 and a horizontal and vertical synchronizing signal 9 by a signal separation circuit 7. The video signal 8 is further extracted by a signal processing circuit 10 using sampling pulses sequentially in time, and after converting the analog signal into a digital signal, this is sent to a holding circuit 11.
is held for a certain period of time, and then from the horizontal drive circuit 12.
It is applied to horizontal electrode groups H ₁ to _{H n} of the EL panel.
Reference numeral 13 denotes a clock pulse generation circuit, and a signal from this circuit is combined with horizontal and vertical synchronization signals 9 in a timing pulse generation circuit 14 to generate timing control signals for each circuit. The video/still image switching signal is generated by 14 circuits. Reference numeral 15 designates a selection pulse timing signal generation circuit, and reference numeral 16 designates an erasure pulse timing signal generation circuit.The selection and erasure pulses are synthesized by a synthesis circuit 18 and applied to a vertical drive circuit 19. Reference numeral 17 denotes a sustain pulse timing signal generation circuit related to the present invention, which generates sustain pulses having different pulse widths when displaying a moving image and when displaying a still image. The signal from 17 is applied to the vertical drive circuit at 19. Vertical drive circuit output is EL
It is applied to the vertical electrode groups V ₁ to _{V o} of the panel. By selectively applying voltages to the horizontal electrode groups H ₁ to _{H n} and the vertical electrode groups V ₁ to V _o , the EL panel displays an image as described above.

In Figure 3, when applying an EL panel to an image display device, as the display panel becomes larger and the number of electrodes increases, the period for applying write pulses increases and the period for applying sustain pulses becomes narrower when displaying moving images. Become. The reason for this will be explained using FIG. 4. Fourth
Figures a, b, c, d, and e show examples of timing waveforms when there are 160 vertical scanning electrodes. That is, FIG. 4 corresponds to the case where a write pulse is applied after sampling approximately every 3H (H is a horizontal scanning period). Fourth
PH in FIG. _4a is a horizontal synchronizing signal, P _S in FIG. 4b is a sampling period, and P _W in FIG. 4c is a write selection pulse signal. One field of a television signal has approximately 240 horizontal synchronization signals containing video signals. Therefore, we take out 80 out of 240 in the first field and another 80 in another field, and apply the selected scanning pulse to EL in an interlaced manner.
Applied to the vertical scanning electrode side of the panel. In this case, the write pulse application period is approximately 120 μsec at maximum, as shown in FIG. If a bipolar sustaining pulse is applied, the P _S period (approximately 63.5 μsec) is shown in Figure 4b, but if only one of the positive or negative voltage pulses of the bipolar sustaining pulse is applied to the P _S period, it may cause uneven luminance. This is not desirable because it causes To explain this in more detail, the write pulses are applied line-sequentially or dot-sequentially, and the sustain pulses are applied at the same timing to all electrode lines to simplify the circuit.
Therefore, the time from when a write pulse is applied to when a sustain pulse is applied differs for each picture element. Now, if a write pulse is applied between sustain pulses, the written picture elements will emit light one after another by application of the sustain pulse after the write pulse. At this time, if the sustain pulse immediately after the write pulse has the opposite polarity to the write pulse, the picture element will emit light from this sustain pulse, but if it has the same polarity, the picture element will hardly emit light from this sustain pulse. Light emission begins upon application of the next reverse polarity sustaining pulse.
Therefore, the luminance is higher in the former case. Although this is not much of a problem in a character display that displays information only by the presence or absence of light emission, it is an undesirable phenomenon when displaying halftones. For this reason, as many write selection pulses as possible are inserted between the sustain pulses shown in FIGS. 4d and 4e (it is not preferable to insert too many pulses because the sustain pulse frequency will drop and the memory width will become narrow). In the example shown in FIG. 4, 8
Write selection pulses are inserted. In this case P
In addition to _{the S} period, there is one extra horizontal scanning period, totaling about 120
A bipolar sustaining pulse is applied during μsec.

Hereinafter, the picture elements at the intersection of the horizontal electrode H _i and the vertical electrode V _j will be expressed as i and j, which are shown in FIG. That is, FIG. 5 is an explanatory diagram of the structure corresponding to the electrode arrangement of the matrix panel.

As an example, FIG. 6 shows the H ₁ ,
The voltage waveforms applied to the V ₂ and V ₄ electrodes are shown. When displaying a moving image, writing is performed by line-sequential interlaced scanning. That is, in the first field, 80 odd-numbered electrodes V ₁ , V ₃ , ...V ₁₅₉ are written, and in another field, 80 even-numbered electrodes V ₂ , V ₄ , ...V ₁₆₀ are written.
is being written. FIG. 6 shows a case where a still image is displayed after writing to even-numbered electrodes is completed. When displaying a moving image, an erasing pulse is applied before a writing pulse is applied, but the erasing pulse is not shown in FIG.

Figure 6a shows the horizontal synchronization signal, Si (i = 1 to 80)
The video signal is sampled at 220 points during the period. 6th
FIG. b shows a write pulse of amplitude V _W that is pulse width modulated in accordance with the intensity of the video signal at the sampling point. Figure 6c shows the waveform applied to the _V2 electrode, F is the bipolar sustaining pulse with amplitude ±V _S when displaying a moving image, and G is the bipolar sustaining pulse with amplitude ±V S.
It is a pulse of amplitude -V _E for selecting the V ₂ electrode. When switching from video to still image display,
No write pulse is applied to the horizontal electrode groups H ₁ , H ₂ , . . _. , H _n , and only sustain pulses are applied to the vertical electrode groups V ₁ , V ₂ , . , no selection pulse is given. At this time, as will be described later, in the method of the present invention, the width of the bipolar sustain pulse is made different from the width of the sustain pulse when displaying a moving image. FIG. 6d shows the _V4 electrode application waveform, and H shows the _V4 electrode selection pulse. FIG. 6e and f are applied waveforms of picture elements 1, 2, 1, and 4. Li is a composite waveform of Ni and G, and Nu is a composite of Ho and Chi. Figure 6 g and h are picture elements 1, 2, 1, 4
This is the emission waveform of In this way, when displaying a video, each picture element is written → maintained → erased → maintained repeatedly,
When switching to still image display, only sustain pulses are given. In the case of a moving image display, there is light emission B _W ′ due to a write pulse applied at a constant cycle and a sustain pulse immediately after that, but in the case of a still image display, there is no B _W ′, so the light emission is slightly lower than that of a moving image display. The brightness decreases (see Figure 6). In order to avoid the above-mentioned reduction in luminance when displaying a still image, the present invention sets the sustain pulse conditions (pulse width, amplitude, frequency) to different values when displaying a moving image and when displaying a still image. This method has been completed to increase the luminance of light emitted when displaying images.

Hereinafter, one embodiment of the present invention will be explained in detail with reference to the drawings.

As an example, a method of making the sustain pulse width variable will be described. As shown in FIGS. 7a and 7b, when a write pulse LO is applied with a sustain pulse I having a pulse width ts ₀ initially applied, light is instantaneously emitted at a brightness of B _W ' and then settles to the brightness of B _W. In the case of a moving image, the write pulse pulse is applied at a constant cycle, so the luminance is the average of B _W and B _W '. When a still image is displayed, the write pulse is applied only once, and thereafter the light is emitted at the brightness of _BW . If the brightness of B _W is low and difficult to see, change the pulse width of the sustain pulse to ts ₀
Therefore, if ts ₁ (ts ₁ >ts ₀ ) and a pulse of C is used, the brightness becomes B _W1 , and a decrease in brightness and contrast can be avoided, and a good image can be obtained.

FIG. 8 shows an example of a sustain pulse width switching circuit for switching between moving images and still images. FIG. 9 shows waveforms of various parts in the circuit of FIG. 8. In FIG. 9, DM indicates a moving image display period, and SM indicates a still image display period. Various timing pulses (sustain, write selection, erase pulses, etc.) are all generated with the horizontal synchronization signal as a reference. C ₁ , C ₂ , C ₃ are horizontal synchronization signal counters, G ₁ is P _WO , P _SMO , P
These are multiple gates that generate _SPO timing pulses. P _WO is a timing pulse for a write selection pulse, P _SMO is a timing pulse for a negative voltage sustain pulse, and P _SPO is a timing pulse for a positive voltage sustain pulse. M _DM and M _DP are monostable multivibrators that respectively generate a negative voltage sustain pulse P _DM and a positive voltage sustain pulse P _DP during moving image display. M _SM and M _SP are monostable multivibrators that generate timing pulses for a negative voltage sustaining pulse P _SM and a positive voltage sustaining pulse P _SP when displaying a still image. _G3 , _G4 , _G5
is a gate that switches the _PDM and _PSM signals for moving images and still images. G ₆ , G ₇ , G ₈ are P _DP , P _SD
This is a gate that switches the signal. Gate output P
_M and P _P are signals with different pulse widths for displaying moving images and still images, and are applied to the input terminals of the drive transistors for generating negative and positive voltages. M _W is a monostable multivibrator for generating write selection pulses, and G ₉ is a gate for passing write selection pulses during moving image display. SW is a switch for switching between video and still images;
F is a flip-flop for switching between moving images and still images. The P _D signal is logically on the high potential side (indicated by "H") when displaying a moving image, and is on the low potential side (indicated by "L") when displaying a still image.

The counters C ₁ , C ₂ , and C ₃ count the horizontal synchronizing signal _PH shown in FIG. 9b except during the period when the reset pulse P _RS shown in FIG. 9i is applied. The outputs from the counters are combined at gate _G1 to generate timing pulses P _SMO , P _SPO , P _WD , which are input to monostable multivibrators such as M _DM , M _MS , M _DP , M _SP , M _W etc. . When displaying moving images, the switch SW is on the contact A side.
The D terminal input signal P _DS of the flip-flop F shown in FIG. 8 is "H", and the Q terminal output signal P _D is "H" at the time the field switching signal P _F is input. If you want to stop any screen while displaying a video image and display a still image, press the switch.
Connect SW to contact B. At this time, the P _DS signal becomes "L", and when the field switching signal P _F shown in FIG. 9a is input, P _D becomes "L". Also, the signal P _S at the terminal of flip-flop F
is switched from "L" to "H". and gate
A P _DM signal and a P _D signal with a pulse width tdm are input to _G3 , and a P _SM signal and a P _S signal with a pulse width tsm are input to an AND gate _G4 . The outputs of G ₃ and G ₄ are combined by OR gate G ₅ to obtain the P _M signal shown in FIG. 9g. AND gate G ₆ has P _DP with pulse width tdp.
The P _SP signal and _the P _S signal with a pulse width tsp are input to the AND gate _G7 .
The outputs of G ₆ and G ₇ are combined by OR gate G ₈ to obtain the P _P signal shown in FIG. 9h. The P _M and P _P signals are negative and positive voltage sustaining pulse signals having different pulse widths for displaying moving images and still images. The write selection pulse signal is applied only during the moving image display period, as shown by _fPW in FIG. The sustaining pulse widths tsm and tsp when displaying a still image may be set to optimal conditions that make the displayed image most visible.

In the above description, an embodiment has been described in which the sustain pulse width is switched between displaying a moving image and displaying a still image in order to achieve optimal display, but the same effect can be obtained by changing the amplitude or frequency of the sustain pulse.

As described above, according to the present invention, when a moving image is switched to a still image, the luminance brightness and contrast for displaying the still image can be easily set to the optimum conditions.
A display device can be driven.

[Brief explanation of the drawing]

Figure 1 a, b is a partially cutaway perspective view and cross-sectional view of an EL element with a matrix structure, Figure 2 a, b, and c are
A diagram showing the voltage waveform applied to the EL element, the relationship between the emission brightness and the applied voltage, and the emission brightness of the EL element,
Fig. 3 is a block diagram of the configuration of an image display device using EL elements, Fig. 4 a, b, c, d, and e are diagrams showing examples of timing pulse waveforms, and Fig. 5 shows an EL panel with a matrix structure. Figure 6a,
b, c, d, e, f, g, h are matrix EL
A diagram of voltage waveforms applied to the electrodes and picture elements of the panel,
Figures 7a and b are diagrams showing changes in luminance when the maintenance panel width is changed; Figure 8 is a circuit diagram for switching between video and still images; and maintenance pulse width switching; Figure 9 is a diagram showing the switching from video to still image. It is a figure which shows the timing waveform of the time.

Claims (1)

[Claims] 1. In an image display device using an EL element having a hysteresis characteristic between applied voltage and luminance, a first drive circuit that generates an optimal sustain pulse when displaying a moving image to drive the image display device. and a second drive circuit that generates an optimal sustain pulse to drive the image display device when switching and displaying a moving image to a still image. 1. A circuit system for an image display device, characterized in that a circuit switching means for selecting the first drive circuit or the second drive circuit in accordance with the above is provided.