JPS592911B2 - Writing drive method of thin film EL element - Google Patents

Description

[Detailed Description of the Invention] The present invention makes it possible to expand the variable range of the write pulse modulated according to the input signal applied between the sustain pulses by devising a way to apply the sustain pulses to the EL element. The present invention relates to a driving method.

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

In Figure 1, 1 is a glass plate, 2 is an electrode arranged in a striped pattern, and 3 is a glass plate.
is a dielectric material such as Y203, and 4 is Zn doped with Mn etc.
A fluorescent layer such as S, 3' is the same dielectric material as 3, and 5 is an electrode arranged perpendicular to 2. In an element having such a structure, when an appropriate alternating voltage is applied to one of the first electrode group 2 and one of the second electrode group 5, only the portion where the electrodes intersect will emit light. This corresponds to 10 picture elements of the display device. The second pixel of the matrix type EL element
When a bipolar pulse is applied as shown in FIG. 2B, the relationship between the emission brightness B and the applied pulse width is shown in FIG. 2A.

When a sustain pulse Ps of 15 pulse width ts is added, initially B
It emits light with a brightness of s.

Next, when a write pulse Pw with a pulse width tw is applied, light is instantaneously emitted with a brightness of BwM, and then with a subsequent sustain pulse PS2, light is emitted with a brightness of Bw. Next, when an erasing pulse 20 seconds Pe having a pulse width te is applied, the luminance of the light emission decreases instantaneously, and with the subsequent sustain pulse PS3, light is emitted again at a luminance of Bs. In this history characteristic, since the pulse width of the applied write voltage draws an arbitrary loop depending on the frequency or amplitude, it is also possible to display intermediate tones. 25 When applying the above-mentioned pulse width modulation method to an image display device, the range of pulse width that can be modulated may be restricted if the application time intervals of sustain pulses are equal.

First, this case will be explained by taking as an example a waveform applied to a picture element of a (3×3) matrix. In Figure 3 (1・
1) Shows the voltage waveform applied to the picture element. As shown in FIG. 3a, it is assumed that one frame P) of the video signal is composed of three horizontal scanning periods, and is sampled at three points in each horizontal scanning period. In the line sequential scanning method, the signal levels sampled at each time point during the horizontal scanning period 35 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. Figure 11-3B
4 is a sustain pulse, and θ is a signal whose pulse width is modulated according to the sampling point 5 of the video signal.

θ, 3 is a signal whose pulse width is modulated according to other sampling points. These signals are applied to the H1 electrode. Third
In the figure, @ is an erase pulse, and @ is a vertical line selection pulse. The applied waveform applied to picture element (1·1) is shown in FIG. 3d. 3 is a write pulse.

Here, the amplitudes of sustain pulse 4, erase pulse @, and write pulse 8 are set to different values (VE, VS, VS+V,
In the example shown in FIG. 2, the amplitude of Vs is commonly used), and amplitude and pulse width control are used together to ensure that sustaining, erasing, and writing operations can be performed more reliably. In other words, in the write pulse 4, the amplitude Vs+? at which the write signal 0 is superimposed on the vertical line selection pulse O? Only the period Ta is effective, and the luminance is controlled by the length of this period Ta. As described above, in the relationship shown in FIG. 3, the range in which pulse width modulation is possible is Tw. If the frequency of the sustain pulse is high, the value of Tw will become narrow. For this reason, the range that can be modulated is reduced, making it difficult to control the gradation level.

It is an object of the present invention to eliminate the above-mentioned conventional drawbacks and to widen the variable range of write pulses applied between sustain pulses.

The structure of the present invention is an EL element having a history characteristic between the pulse width, frequency, or amplitude of applied voltage and luminance.
In this sustain pulse application method, the application time intervals of the positive voltage pulse and the negative voltage pulse of the applied sustain pulse are unequal, and the amplitudes of the positive voltage pulse and the negative voltage pulse are different.

Next, a method according to an embodiment of the present invention that can widen the variable range of Tw will be explained with reference to the drawings.

FIG. 4 is a block diagram of the configuration of the image display device, and FIG. 5 is a timing chart. In FIG. 4, the composite video signal inputted from the input terminal 6 is passed through the signal separation circuit 7 to the video signal 8.
, a synchronization signal 9.

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, it is applied to the write drive circuit 21 and applied to the electrode groups Hl, H2, . . . Hm.
Reference numeral 13 denotes a clock pulse generating circuit, which is synthesized with a synchronizing signal in a timing pulse generating circuit 14.

An erase pulse is generated by the erase pulse generator circuit 16 in synchronization with the output from the timing pulse generator circuit, and a vertical line selection pulse 12 synchronized with the timing pulse is applied to the vertical line drive circuit 19. This output is a vertical electrode group,
Vl, v2, ...... are added to Vn. 17 is a sustain pulse generation circuit which adds a sustain pulse to the sustain pulse drive circuit 18.

20 is a high voltage power supply for the drive circuit.

FIG. 5 shows voltage waveforms and light emission waveforms applied to the (1.1) electrodes when a (3×3) matrix is assumed, for example.

It is assumed that one frame D of the input video signal is composed of three horizontal periods (self), and that it is sampled at three points in each horizontal scanning 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. FIG. 5b shows a voltage waveform applied to the H1 electrode, where 7 is a sustaining pulse in the positive voltage direction and 9 is a sustaining pulse in the negative voltage direction. The amplitude of the sustain pulse is +
It is possible to adjust VS1 and -VS2 separately. 8 is a write signal modulated according to the signal level of the sampling point [F], and 8 corresponds to the signal of 5.

FIG. 5c shows the voltage waveform applied to the V1 electrode. 7 is an erase pulse, and @ is a vertical line selection pulse.

FIG. 5d shows the voltage waveform applied to the picture element (1.1). [Stock] is the write pulse. 4 has an amplitude of VSl/
2, and does not contribute to the occurrence.

FIG. 5e shows the light emission waveform of picture element (1.1). As can be seen from FIG. 5, if the application time interval of sustain pulses 7 and 9 is widened at the point where write signal 8 is included, the range in which write pulse 7 can be varied becomes Tw, and the variable range in FIG. It is wider than Tw, making it easier to control by pulse width modulation. In the example of FIG. 5, sustain pulse 7,
The relationship between the amplitudes of the erase pulse 7 and the write pulse [share] is the same as in the example shown in FIG. Or, it becomes higher than VSl, but during the period when it effectively works as a write pulse, the write signal 8 is superimposed and the amplitude becomes VSl+? It is only while it becomes a book. This effective writing period (overlapping period) can be changed arbitrarily within the range of t''w. Modulation by the number of pulses can be considered in the same way as the pulse width modulation described above. Sustain pulse application time interval If the sustain pulse amplitude is made equal in the positive and negative voltage directions as shown in Figure 5, it is thought that more internal polarization charges will be accumulated in one side of the EL element. Voltage amplitude +V
By making it possible to vary Sl and -S2 separately, the internal polarization charges can be averaged. As described above, the present invention has the effect that when performing pulse width modulation and pulse number modulation, the range that can be modulated is increased and the gradation level can be easily controlled.

[Brief explanation of drawings]

Figures 1A and b are partially cutaway perspective views and cross-sectional views of a matrix-structured EL, Figures 2A, b, and c are EL B-V characteristic diagrams and voltage application waveform diagrams, Figures 3A, b, c, d, and e are diagrams of video input signals, applied voltage waveforms, and light emission waveforms of conventional examples. FIG. 4 is a block diagram showing the configuration of a display device according to an embodiment. 5A, b, c, and d are diagrams of video input signals, applied voltage waveforms, and light emission waveforms in one embodiment of the present invention. 7... Signal separation circuit, 10... Signal processing circuit, 11...
...Holding circuit, 13...Clock pulse generation circuit, 14...Timing pulse generation circuit, 16
... Erasing pulse generation circuit, 17 ... Sustain pulse generation circuit, 18, 19 ... Drive circuit,
20... High voltage power supply, 21... Write drive circuit, ({), 7, 6... Sustain pulse, 0,
8...Write signal, 8, [stock]...Write pulse.

Claims (1)

[Claims] 1 Electroluminescence (E
L) In the element, the periods from the positive voltage pulse to the negative voltage pulse of the applied sustain pulse are made different, and the amplitudes of the positive voltage pulse and the negative voltage pulse are made different,
A write drive method for a thin film EL element, characterized in that a write pulse corresponding to the longer period of the above periods is applied to perform a halftone display that is variable within the period.