JPS6118904B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a multi-gradation display device using a thin film electroluminescent panel (hereinafter referred to as thin film ELP). As shown in Fig. 1, the thin film ELP has a glass substrate 1.
A transparent electrode 2 in the form of a draft is disposed in parallel thereon, and on top of this, a dielectric material 3 such as _Y2O3 , a fluorescent material layer 4 such as Mn-doped ZnS, and the same dielectric as above _. A material layer 3' is formed into a three-layer structure using a thin film production technique such as evaporation spasotering, and a transparent electrode 5 in the form of a draft perpendicular to the transparent electrode 2 is arranged in parallel thereon. In this structure, when an appropriate AC voltage is applied to one of the first electrode group 2 and one of the second electrode group 5. Only the tiny area where the two electrodes intersect will emit light, which corresponds to one picture element on the screen. Thin film EL devices with such a structure have superior properties compared to conventional distributed EL devices in terms of brightness, lifespan, and stability. Also, depending on the manufacturing conditions, individual pixels may be of a memory type, which exhibits a hysteresis phenomenon between applied voltage and luminance, as shown in Figure 2a, or non-memory type, which does not exhibit a hysteresis phenomenon, as shown in Figure 2b. However, the present invention can be applied to both types. FIG. 3 shows an example of the brightness characteristics of the thin film ELP according to the present invention with respect to the applied pulse width t _W . As can be seen from this characteristic curve, depending on the amplitude of the applied voltage, there are linear regions and nonlinear regions with respect to the pulse width. Enough brightness or high. In many cases, nonlinear regions must be used to obtain contrast ratios. The present invention was made based on the discovery of the various properties of thin film ELP described above. The present invention aims to provide a thin-film ELP display panel that can display multiple gradations, and to realize such a display device with a simple circuit configuration. We decided to perform brightness modulation, and in more detail, we installed a pulse generator that outputs 2 ⁿ pulses with different time widths in parallel, converted the input signal into an n-bit digital signal, and then responded to the digital signal. The present invention is characterized in that pulse width modulation is performed by selecting one of the above-mentioned pulses to create a display signal pulse. Hereinafter, an embodiment of the present invention will be described in detail in which 8-gradation modulation of a TV image is performed using a thin film ELP having a memory function based on hysteresis characteristics. FIG. 4 is a circuit block diagram of an embodiment of the present invention. The composite video signal introduced into the video signal input terminal 6 is separated into a video signal and a synchronization signal by a signal separation circuit 7, and each is guided to a signal processing circuit 8 and a timing control circuit 9. The signal processing circuit 8 is composed of a sample and hold circuit and an A-D converter, and sequentially samples the video signal based on the clock signal and converts the video signal into eight gradations of brightness levels B ₀ ,
B ₁ , B ₂ ..., B ₇ are converted into 3-bit digital signals A, B, and C. Table 1 shows an example of conversion.

[Table] The signal holding circuit 10 is a shift register that holds the above-mentioned 3-bit luminance signal corresponding to each of the X column electrode groups X ₁ to Xm of the matrix display panel 18, and has a capacity of (3×m) bits. have. The display signal pulse generating circuit 11 is a circuit that generates a display signal pulse whose pulse width is modulated in accordance with a 3-pit digital luminance signal, and will be described later as it forms the main part of the characteristic part of the present invention. The X-column electrode drive circuit 12 is a circuit that generates a high voltage applied to the electrodes while maintaining the amplitude of the pulse-width-modulated display signal pulse, and its output is applied to the X-column electrode group of the panel 18.
Connected to X ₁ , X ₂ , ..., Xm. On the other hand, the sustain pulse generator 14, the erase pulse generator 15, and the row selection pulse generator 16 generate sustain pulses, erase pulses, and row selection pulses, respectively, and drive the Y row electrodes as appropriate according to instructions from the timing control circuit 9. It is supplied to the circuit 17. The drive circuit 17 generates a high-voltage output based on this input pulse to drive the Y row electrode groups Y ₁ , Y ₂ , . . . , Yn of the matrix type display panel 18 . The flow of these series of signals is controlled by a timing control circuit 9 which synthesizes the clock from the clock generation circuit 13 and the TV synchronization signal to generate timing pulses. Configuring the display panel 18 in FIG.
FIG. 5 shows the relationship between the applied voltage waveform and the light emission waveform for the picture element (i.times.m) that intersects the i-th column electrode Xi and the j-th row electrode Yj. In the figure, A is a write pulse, B is a sustain pulse, C is an erase pulse, D is a display signal pulse, and E is a row selection pulse. The voltage V (i, j) applied to the picture element (i, j) is the difference between the voltage Vxi, which is applied to the electrode Xi, and the voltage Vyj, which is applied to the electrode Yj, and when the display signal pulse N and the row selection pulse H are superimposed. When the write pulse I is applied, the picture elements (i and j) emit light, and after that, the light emitting state is maintained by the sustain pulse L, but when the erase pulse I comes next, the light emission is erased, and after that, the sustain pulse L is applied. The erased state is maintained. Furthermore, although the pulse width of the display signal pulse d changes as will be described later, the pulse width of the row selection pulse d is determined so as to always cover this. The scanning method for the entire surface of the display panel 18 is such that a row selection pulse and an erase pulse sequentially select the Y electrodes one row at a time, and in synchronization with this, display signal pulses are simultaneously applied to all the X electrodes X ₁ to Xm. A line scanning method is used. Next, the features of the present invention will be explained. 1st
In the table, 3-bit digital signals A, B, C
Eight types _{of pulse widths to, t 1 ,} . Now, if a linear relationship is established between the applied pulse width and the brightness, then there are 8 types of pulse widths.
t ₀ , t ₁ , ..., t ₇ may increase in an arithmetic progression. However, as shown in Figure 3, in order to obtain sufficient brightness and contrast ratio, there are cases where it is necessary to use ELP in a range where the brightness is non-linear with respect to the applied pulse width. The mutual relationship among the eight types of pulse widths t ₀ , t ₁ , . . . , t ₇ described above must be adjusted. FIG. 6 shows a specific circuit example of one of the m circuits forming the display signal pulse generation circuit 11 that realizes this. In the figure, reference numeral 19 denotes a pulse width generation circuit, which generates modulation pulse width signals t ₀ , t ₁ , . . . , t ₇ and a strobe signal t _S in parallel based on a trigger input from the timing control circuit 9. A specific example of this circuit is shown in FIG.
That is, 9 monostable multivibrators 2
1, 22, ..., 29, and each multivibrator has variable resistors VRS, VRO, ..., VR.
7 and capacitance CS, C0, ..., C1,
... C7 is provided and the output pulse width t _S ,
t ₀ , t ₁ , ... t ₇ can be adjusted independently. 20 is a logic element called a multiplexer, and its truth table is shown in Table 2.

[Table] In FIG. 6, Ai, Bi, and Ci are the output signals of the 3-bit memory element related to the electrode Xi of the signal holding circuit 10, and 12i is the output signal of the 3-bit memory element related to the electrode Xi of the X column electrode drive circuit 12. It is something. Figure 8 shows a time chart of the display signal pulse generation system shown in Figures 6 and 7.
The case of B ₅ , that is, Ai=1, Bi=0, and Ci=1 will be shown. According to the present invention, only one pulse generator is provided that outputs ²ⁿ pulses with different time widths in parallel, and an input signal representing the brightness level of a display pattern is sequentially converted into an n-bit digital signal. Since pulse width modulation is performed by creating a display signal pulse by selecting one of the outputs of the pulse generator that corresponds to the bit with the true value of the converted digital signal, the circuit configuration is greatly simplified. can do. In addition, by configuring the above 2 ⁿ pulse widths to be independently adjustable, it is possible to easily correct not only variations in ELP characteristics but also pulse width vs. brightness characteristics that vary depending on the voltage amplitude and frequency of the applied pulse. This makes it possible to achieve optimal multi-gradation display, and also to obtain good display even when the ELP brightness is expanded to the non-linear characteristic range. By the way, each pulse width in the experimental example is t _S = 120 μS, t ₁ = 20 μS, t ₂ = 40 μS.
S, t ₃ = 60 μS, t ₄ = 80 μS, t ₅ = 90 μS, t ₆ =
The width of the row selection pulse applied to the _row electrodes was 120 μS. In addition, light emission threshold voltage Vth = 200V, sustain pulse voltage V ₁ = 210V, write pulse voltage V ₂ = 210~
The voltage was 280V, and the erase pulse voltage V ₃ was 190V.

[Brief explanation of the drawing]

Figures 1 a and b are partially cutaway perspective views and cross-sectional views of thin film ELP, Figures 2 a and b are characteristic diagrams showing the relationship between applied voltage and luminance of thin film ELP, and Figure 3 is a thin film ELP.
A characteristic diagram showing the relationship between ELP applied pulse width and luminance, FIG. 4 is a circuit block diagram of an embodiment of the present invention, FIG. 5 is an explanatory diagram of the effect of light emission in the above embodiment, and FIG. 6 is a diagram of the above embodiment. FIG. 7 is a circuit example of the pulse width generation circuit 19 of FIG. 6, and FIG. 8 is an explanatory diagram of the operation regarding display signal pulse width modulation in the above embodiment. 7... Signal separation circuit, 8... Signal processing circuit, 1
1...Display signal pulse generator, 12...X column electrode drive circuit, 13...Clock generation circuit, 14...
Sustain pulse generator, 15... Erase pulse generator,
16... Row selection pulse generator, 17... Y row electrode drive circuit, 18... Matrix panel, 19...
...Pulse width generation circuit, 21-29... Monostable multivibrator.

Claims (1)

[Claims] 1 A pulse generator that outputs 2 ⁿ (n is a natural number) pulses with different pulse widths in parallel; and after converting an input signal representing a brightness level into an n-bit digital signal, The logic circuit section that selectively outputs the
1. A multi-gradation modulation device for an EL display panel, which is connected to an electrode drive circuit of the EL panel, and applies a ²ⁿ multi-gradation display signal to the thin film EL panel.