JPS6011356B2 - Driving method of image display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When performing halftone display using an EL element, the transient characteristics of the EL element, which did not pose a problem in binary image display such as character or graph display, are related to luminance.

For this reason, if the time between cutting off the write pulse and applying the sustain pulse is different, the luminance of light emission becomes unstable. The present invention relates to an image display device capable of displaying halftones using a driving method that reduces such variations in luminance. Generally, when an EL element is used as a display element, a matrix type electrode arrangement is adopted as shown in FIGS. 1a and 1b.

In Fig. 1, 1 is a glass plate, 2 is a transparent electrode arranged in a grid pattern, 3 is a dielectric material such as Y203, 4 is a light emitting layer such as ZnS doped with Mn, etc., 3' is the same dielectric material as 3, Reference numeral 5 denotes a back electrode made of aluminum or the like and arranged perpendicular to the electrode 2. When an appropriate AC voltage is applied to one of the transparent electrode group 2 and one of the back electrode group 5 in an element having such a structure, only the portion where these two electrodes intersect emits light. This corresponds to one picture element on the screen. FIGS. 2a, b, and c show the relationship between the applied voltage and the luminance when a bipolar pulse is applied to one picture element of the matrix type EL element.

First, as shown in Figure 2a, when the sustaining pulse of the amplitude modulator Vs is applied at the timing t2, the luminance is the second
As shown in Figures b and c, it was a loss. Next, when a write pulse of amplitude Vw is applied at timing t3, light is emitted momentarily with a brightness of Bw', and the amplitude value V applied at timing t3 is instantaneous.
In the sustain pulse of s, the emission brightness becomes Bw. Next t9~
t,. When the erasing pulse of amplitude modulator V8 is applied at the timing of t, the emission brightness decreases, and the emission brightness becomes Bs again with the sustain pulse applied at t, 3. There is a history characteristic between the luminance of light emission and the applied voltage as shown in FIG. 2b. As is well known, when a write pulse is applied to an EL element having the above characteristics, polarized charges are generated and a voltage (hereinafter referred to as a holding voltage) is generated across the light emitting layer (ZnS layer).

Thereafter, when a sustain pulse is applied, the sustain pulse voltage and the hold voltage are applied synergistically to the light emitting layer (ZnS layer), and light emission is sustained. The problem here is the holding voltage. The holding voltage decreases over time as shown in FIG. 3 when the write pulse is turned off. For this reason, when the time interval t between the write pulse and the sustain pulse changes, the voltage applied to the light emitting layer changes, resulting in a slight difference in luminance. The change in this holding voltage is particularly large up to T, (this value varies depending on the EL element, but is approximately several tens of seconds) immediately after the write pulse is turned off. By devising the way to apply the sustain pulse, it is possible to increase the distance between the write pulse and the sustain pulse by more than T, thereby reducing the variation in luminance due to changes in the holding voltage, but this is not possible when using a matrix panel. In the moving image display layer, since the write pulse is applied and released by scanning the electrode lines at a constant period, the interval between the write pulse and the sustain pulse cannot be greater than a constant period. SUMMARY OF THE INVENTION An object of the present invention is to provide a new and useful method for driving an image display device in which the width of a selection pulse applied to a vertical electrode line is varied to reduce variations in luminance caused by a holding voltage. Hereinafter, the present invention will be described in detail according to one embodiment with reference to the drawings.

FIG. 4 shows the scanning lines of a matrix type panel used in the present invention. One embodiment of the present invention is shown in FIG. 4, taking as an example the waveforms applied to two picture elements of the matrix type panel. explain.

FIG. 5a represents a pulse P applied to a horizontal electrode with an amplitude Vw modulated in accordance with the video signal. When the sustain pulse voltage is Vs, Vw is 1/2Vs or less. Fifth
Figure b shows the waveform applied to the vertical electrode V. P2 is a sustaining pulse with an amplitude of ±Vs, and P3 is a selection pulse for selecting the electrode V, with an amplitude of 1VE. Fifth
Figure c shows a waveform applied to the vertical electrode V8, P2 is a sustain pulse, and P4 is a selection pulse for selecting the electrode V8. FIG. 5d is a voltage waveform applied to picture elements 1 and 1, which is a composite of the waveforms a and b in FIG. P5
is a write pulse, and the time until the next sustaining pulse related to light emission is applied is Tb (in the prototype device, this value is approximately 1.3 seconds). Tb corresponds to that in FIG. FIG. 5e shows a voltage waveform applied to the picture elements 8 and 1, which is a composite of the waveforms a and c in FIG. P6 is a write pulse and is related to light emission. The time until the next sustaining pulse is applied is Ta (this value is approximately 100 msec in the prototype device). Ta corresponds to that in FIG. In this case, picture elements 1, 1, 8, and 1 are synergistically applied to the light-emitting layer of the EL element by the holding voltages at times Th and Ta in Fig. 3 and the sustaining pulse voltage at P'2 in Figs. When applied, it emits light. However, at this time, if the write pulse width is the same, the holding voltages are slightly different, so the picture elements 8 and 1 emit light a little brighter, which is not preferable when performing halftone display. Therefore, as shown in Figure 5e, if the width of the write pulse near the sustain pulse is slightly narrowed to W', the write intensity will drop slightly and the effect of changes in the holding voltage can be canceled out. . The write pulse width can be changed by changing the width of the write pulse P4 shown in FIG. 5c. Similarly, if the pulse widths of the selection pulses other than picture elements 1, 1, 8, and 1 are set according to the distance from the sustain pulse, variations in luminance can be improved. FIG. 6 shows a block diagram of the configuration of an image display device using the pulse application method described above.

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 8G video signal is extracted from the signal processing circuit 1 using sampling pulses sequentially in time, and after converting the analog signal into a digital signal, this is sent to the holding circuit 1.
1 for a certain period of time, and then the horizontal drive circuit 12 outputs EL.
It is applied to the horizontal electrode of the panel, ~Hm. 13 is a clock pulse generation circuit, and the signal from this circuit is 1.
A timing pulse generating circuit 4 synthesizes the signal with horizontal and vertical synchronizing signals 9 to generate timing control signals for each circuit.

Reference numeral 15 indicates a selection pulse timing signal generation circuit, and reference numeral 16 indicates an erase pulse timing signal generation circuit.The selection and erase pulses are synthesized by the matrix circuit 18 and applied to the vertical drive circuit 19.

17 is a sustain pulse timing signal generation circuit; 19
is applied to the vertical drive circuit.

The output of the vertical drive circuit No. 19 is the vertical electrode group V of the EL panel.
, ~Vn.

FIG. 7 shows a selection pulse generation circuit (circuit 15 in FIG. 6) and a matrix circuit (circuit 18 in FIG. 6) that can vary the selection pulse width depending on the time up to the sustain pulse.

In the image display device, a matrix type panel was used in which the number of horizontal electrodes m=22 and the number of vertical electrodes n=160. Since the interlace method is adopted, about 240 horizontal synchronizing signals are counted down in the first field and 8 fixed horizontal synchronizing signals are extracted. A selection pulse is generated based on this signal. Eight additional hard selection pulses are generated in another field. In Figure 7, Hp is a horizontal synchronization signal, CH is a counter that takes out an 8q fixed horizontal synchronization signal, CH2 is an octal counter, and CH3 is a 1G
On the ship's counter, count 8 solid horizontal synchronization signals on CH2 and CH3. M, to M8 are eight monostable multivibrators for variable selection pulse width. M, ~M
The signal No. 8 is applied to the field gates Go and G8. OEp and EEp are signals for switching between the first field and another field. First G. The signals from are applied to the matrix circuit driving transistors TYo, -TYo8 through the buffer. The collector side of this transistor obtains outputs as shown in FIGS. 8a and 8a. The signal from the C ratio is applied to the matrix circuit driving transistors Tx, ˜Tx, o through an inverter. Figure 8 shows b and output. The signals at the 8 fixed intersections of the matrix are applied between the base and emitter of the selection pulse application drive transistor. (Since interlaced scanning is performed, in this case it is applied to the transistors that drive the odd lines 1, 3, to 159 of the matrix panel.) On the base side of the transistor that drives the first electrode 1, the waveform q in Figure 8 is applied. The waveform shown in FIG. 8a is applied to the emitter side. In another field, the signal from M.about. is applied to gate G8 and applied to matrix circuit driving transistors TYE, .about.TYB8 through a buffer. The signal from counter CH3 is applied to transistors Tx, ˜Tx,o through an inverter.
The signals at the 80 intersections of the matrix are applied between the base and emitter of the transistors driving the even lines 2, 4, through 160 of the matrix panel. The sustain pulse is applied every 8 selection pulses, so if a matrix circuit as shown in Figure 7 is adopted, all the 8 selection pulses, M, to M8, can be adjusted by simply attaching monostable multivibrators for varying the selection pulses. Pulse width can be adjusted. EL in Figure 9
The waveform applied to the element is shown.

For example, if we consider 23 blocks of horizontal synchronization signals as shown in Figure 9a, the periods during which the video signal is sampled are S, ~S8. 220 points are sampled in each scanning period of S, ~S8. 9b shows the write voltage applied to the electrodes of the matrix panel, and pulses P7 to P,4 are pulse width modulated according to the intensity of the video signal at the first sampling point of S, to S8. Figure 9c shows the voltage applied to the electrodes V and P.
．． 6, P', and 6 are sustain pulses whose period is about 1.6 skin seconds. P,7 is V, electrode selection pulse. FIG. 9d shows the waveform applied to the V3 electrode. P,8 is a selection pulse for the V3 electrode. Similarly, Figures 9e to 9i
is the waveform applied to the V5~V,5 electrode, and P,9~P
Pine is the selective pulse of each electrode. Since interlaced scanning is performed, a selection pulse is applied to the odd numbered electrodes at this time. Picture elements 1, 1, 3, 1, 5, 1, ...... 15, 1 of the matrix panel shown in Figure 10
The write pulses applied to P7 and P in FIG.
7, P8 and P, 6, P9 and P, 9, ......P, 4 and P2
It is a combination of 4. What is the relationship between sustain pulse P',6 and selection pulse P,? The selection pulse of is the farthest away,
Since the selection pulse of P is the closest, if the selection pulse width from P,7 to P is set as tw,>t ground>...>W7>W8, the write pulses will be in the same order. Since it becomes narrower, it is possible to correct variations in light emission brightness due to the transient characteristics of EL. As explained in detail above, the present invention provides an extremely industrially significant drive that eliminates the instability of luminance by setting the selection pulse width to different values in an image display device using an EL element having hysteresis characteristics. It's a method.

[Brief explanation of drawings]

Figure 1 a, b is a partially cutaway perspective view and cross-sectional view of an HL element with a matrix structure, and Figure 2 a, b, c shows the relationship between the waveform applied to the EL element and the luminance of the EL element and the applied voltage. Figure 3 is a diagram showing the change in holding voltage of the EL element after write pulse interruption, Figure 4 is a diagram showing a matrix type panel, Figure 5 is a diagram showing a matrix panel. 6 is a configuration block diagram of an image display device using the selection pulse application method according to the present invention. FIG. 7 shows a selection pulse generation circuit and matrix circuit using the circuit method of the present invention. The figure shows the transistor output waveform of the matrix circuit, FIG. 9 shows the pulse waveform applied to the electrodes of the matrix panel, and FIG. 10 shows the matrix panel. Figure 1 Figure 2 Figure 10 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] 1 EL with history characteristics between applied voltage and luminance
In a matrix electrode type image display device using a matrix electrode element, when a sustain pulse is applied and a selection pulse for write drive is sequentially scanned and applied to each electrode line at a constant period, the sustain pulse and each selection pulse are applied. 1. A method for driving an image display device, comprising: setting a selection pulse width according to a time difference between the two, and correcting an error in light emission brightness due to transient characteristics of an EL element during scanning for the writing drive.