JPS6010637B2 - Readout device for matrix type thin film EL display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a memory readout device for a three-layer thin film EL display device having hysteresis memory characteristics in the relationship between applied voltage and luminance, and particularly to a memory readout device for a thin film EL display device having a matrix electrode. The same applies to the reading device mentioned above.

A three-layer thin film EL display device is constructed as shown in a partially cutaway perspective view in FIG.

Transparent electrodes 2 are arranged in stripes on a glass substrate 1, and on top of this a dielectric material 3 such as Y2Q, Si3N4, Ti02A and 2Q, and further on this, for example, Zn doped with Mn.
A light layer 4 such as S (yellow light emitting) is further formed on it, and Y2Q,
Dielectric material 3' such as Si3N4, Ti02A, etc. is deposited with a thickness of 500 to 10,000 using thin film techniques such as vapor deposition and sputtering.
It is deposited to a thickness of A to form a double-insulated three-layer structure, and a striped electrode 5 is arranged thereon in a direction perpendicular to the transparent electrode 2 to form a matrix electrode. In a three-layer thin film EL display device having such a structure, when one of the first electrode group 2 and one of the second electrode group is selected and an appropriate AC voltage is applied, the two electrodes intersect. The small area between them emits light. This corresponds to one picture element on the screen. By combining these, characters, symbols, patterns, etc. are displayed. ELs with this type of structure have superior characteristics in terms of brightness, lifespan, and stability compared to conventional distributed EL elements, but this EL has a new effect between applied voltage and luminance. The hysteresis IJ system characteristic is shown in FIG. 2b. To explain this according to FIG. 2, when a pulse of voltage amplitude V is first applied as shown in FIG.
is at the level of Here, the maintaining voltage V, is the luminescent voltage V
As a ratio, V,>Vm. The brightness B is maintained by continuously applying the sustaining voltage V. Next, when the write voltage V2 is applied, the brightness increases all at once to &, and even if the voltage returns to the sustaining voltage V again within a certain period of time, the brightness simply settles down to the previous brightness B, which is higher. The brightness B2 is maintained by continuously applying the sustaining voltage V. In this state, when the erase voltage V3 is applied next, the brightness level decreases rapidly, and when it returns to the sustaining voltage V, the brightness level B. I settled on. These temporal relationships are indicated by the symbols t,,t2,... in Figure 2a.
The illusion of t is shown by corresponding to the same symbol in c of the same figure. This hysteresis phenomenon can take any small loop depending on the amplitude, pulse width (not shown), and pulse frequency of the write voltage, as shown by the line in FIG. 2b. That is, it is also possible to display halftones. In this way, once a write voltage or an erase voltage is applied, each picture element continues to emit light without losing the gradation given by the sustain pulse.
This is a major feature of the display device that other display devices do not have. The above voltages vary greatly depending on the physical conditions of composition and film thickness, manufacturing conditions, and applied waveform, but in a prototype example, Vth = 2
00V, V, = 210V, V2 = 210~280V, V
3=190V. This three-layer structure thin film EL display device can not only perform writing, erasing, and memory by changing the applied voltage, pulse width, and pulse frequency as described above, but also can electrically output the memory state.

Thin-film EL elements can be thought of as capacitive elements because they sandwich the light layer between two insulating layers, and a displacement current flows when a sustaining voltage is applied, but when the element remembers the light-emitting state, , a current corresponding to the magnitude of the luminance is superimposed on the displacement current and flows due to the maintenance voltage.

This current is called a polarization current. In reality, even in the erased state, there is a slight rise in the background, and a correspondingly small amount of polarization current flows. For example, when a sustaining voltage pulse as shown in FIG. 3a is applied to an EL element, the current flowing through the element exhibits a displacement current waveform as shown by the solid line 11 in FIG. 3b in the erased state. However, in the light emitting state, as shown by a broken line 12, a waveform obtained by superimposing a polarization current is shown. In order to determine the presence or absence of a polarization current, the inventors of the present invention used Hakamaseki Sho 51-28446 ``Method for detecting memory contents of a light emitting element'' to detect a specific point in time when there is a current flowing through an EL element (for example, when there is a polarization current). We have proposed a method and a circuit for detecting whether the light emitting state or the erasing state is present based on whether the displacement current exceeds a certain predetermined level, which is the sum of the displacement current and the /is margin, at the time when the peak is given. but,
Since this method separates the displacement current and polarization current at a specific level, careful consideration is not only required in setting the specific level, but also the magnitude of the level at which the polarization current exceeds the specific level. After subtracting the noise margin, the absolute value of this signal becomes very small.

Therefore, the S/N is bad.
As disclosed in ``Reading Device for EL Elements'', an equivalent circuit at the time of erasing can be constructed using analog elements such as capacitors and resistors for a current similar to the above-mentioned displacement current, or the waveform itself at the time of erasing can be stored in a ROM or the like. It is possible to remove the erase current by

However, in this method, when the EL element is a single unit, there is only one waveform at the time of erasing, and the above idea can be applied, but in the case of a matrix element, there is the following problem. (2) In the case of matrix driving, as the number of matrices increases depending on the driving method, the magnitude of the displacement current changes significantly depending on the number of light emitting pixels and the number of erasing pixels due to causes such as interference.

Therefore, it is difficult to configure an equivalent circuit during erasing or create a waveform during erasing. ■ In order to efficiently guide the light emitted from the thin film EL element to the outside, at least the electrode on the display side is composed of a transparent electrode, but the resistance of this electrode is The electrode line width is narrow and the resistance is high, and there is a large difference in resistance value between near the lead wire extraction part and the display electrode tip part far from the lead wire extraction part, and the effective applied voltage changes greatly.

Therefore, even if the same pulse is applied from the outside, the current waveform changes greatly depending on the position of the output, and it is necessary to prepare a corresponding number of erase equivalent circuits. It is large in size and not economical.In view of the above points, the present invention has a novel configuration to solve the above problems, and easily and reliably extracts only the polarization current.
This is suitable for matrix type cases. The present invention provides a matrix-type thin film EL display device in which a reference electrode is prepared in a part of the display device, and the current flowing through the reference electrode is used as the above-mentioned erasing current, thereby canceling out the displacement current so that only the polarization current remains. It is an attempt to extract the

The present invention will be explained below using Examples. FIG. 4 shows a circuit diagram of an embodiment of the present invention.

This embodiment mainly consists of six blocks. The first block is a sustain drive circuit 10. Although FIG. 4 shows a three-phase resonance maintaining drive circuit, a multi-phase circuit having four or more phases may also be used.
Two sustaining voltage sources E and -E2 are prepared, and three switches SW, , SW2, and SW3 are sequentially operated to supply three voltages, ie, E, , 0, and -E2 to the EL display device 50.

The transformer T constitutes a series resonant circuit together with the capacitive component of the EL display device 50, and provides a highly efficient voltage distribution. The second block is a write and output switch circuit 20, which applies the write voltage Vw to the line to be written to the power source E in the write phase.
This circuit applies voltage from w via switch Vsk (k=1 to m). Further, when it is desired to issue a question, it is a switch circuit that applies a discussion voltage Vr from the read drive circuit 70 to the line x where the question is to be submitted during the submission phase. Hide drive circuit 70
is a power supply circuit for applying a voltage equal to the sustaining voltage Vs. The third block is a switch group 30 {11 and 30 {2} provided on the transparent electrode of the EL display element.

The switch groups 30'1} and 30' are all short-circuited during maintenance drive, and during write/erase and output drive, only the desired Y line is turned on, and the others are turned off. Fourth
The blocks are write and issue separation and maintenance amplitude hold circuit 40. This is a diode circuit for separating the write line and non-write line and at the same time for maintaining resonance drive amplitude. The fifth block is matrix type 3 shown in Figure 1.
This is a layered structure EL display device, and only the electrodes are shown in this figure.

One transparent electrode on the display side and one AZ electrode on the back side are alternately led out vertically and horizontally. In order to simplify the drawing, FIG. 4 shows that the transparent electrodes are led out alternately on the upper and lower sides, but the A electrode is shown as being led out only on the left side. In reality, the A electrodes are also alternately led out, one on each side. In the present invention, two reference electrodes r, . . . are prepared at the right end of the panel on the transparent electrode side, and terminals are led out from above and below. The sixth block is a readout circuit 60 which is a feature of the present invention, and a switch circuit 30[1' and 30].
[21] A logic output is obtained to a resistor R, which is commonly connected to each transparent electrode 0 to n+1.

On the other hand, the output of the odd-numbered reference electrode r is obtained by the resistor R3, the output of the even-numbered reference electrode r2 is obtained by the resistor R2, and this power is operated by the LSB signal of the decoder 62 of the binary address code and the readout electrode designation code. The signal is applied to the common-mode signal removal amplifier 61 via an analog switch 63 (that is, a switch that operates depending on whether the selection point is an odd number or an even number). A common mode signal rejection amplifier is a differential amplifier. In the amplifier 61, the output obtained from the resistor R is applied to the ten terminals. The specifications of the 8-inch EL pulse prototyped by the inventors are as follows.

Line pitch: 2 lines/fence Maximum number of display characters: 1248 characters Number of effective display lines: 260 lines in the X direction (character spacing of 1 line) 16 in the Y direction
8 lines (line spacing: 2 lines) Now, in Figure 4, the first timing? , when the first holding switch SW, is closed, the difference between the third holding potential VH and the first power supply potential E, Think of it as Ct.

), and the first holding power is VSI=EI+(BI
-VM) ...[Holded at 11].

During the second timing, the second maintenance switch SW2 is applied to the aircraft.
is closed, the second holding potential becomes 1 VS2 = 1 E2 1 Rik VI 0 E2) ... (21), and then when the third holding switch SW3 is closed at the third timing 3, the The holding potential is VH = V2
...{3} In this way, three-phase maintenance drive is realized. The three-phase sustain drive can reduce the withstand voltage requirements of the switches Ds, -n by performing writing at an intermediate hold potential (in this embodiment, the third hold potential VH).

Writing is performed by selecting the × and Y sides of the writing picture element M (i, i) by the writing and lowering switch circuit 20 and the switching circuit 30, respectively, during the intermediate holding potential (VH period), and applying the writing voltage V.
This is done by applying w.

Erasing is performed in the same manner as writing, except that the erase voltage (
(not shown) is supplied to the selected picture element.

Next, the issue drive, which is the gist of the present invention, will be explained.

X corresponding to the read selection point M(i, i) when driving
The side switch DSi and the Y side switch WSj are selected and opened, and the sustain pulse voltage Vs is applied. This pulse current appears in the resistor R, and is supplied to the ten terminal of the amplifier 61. At the same time, reference electrode r and r2's mare point P(r,,
Reference currents j) and (te2,j) appear across resistors R2 and R3. Since the reference lines r, , r2 are never written to, they always output only an erase current, that is, a displacement current. The outputs of the resistors R2 and R3 are applied to one terminal of the amplifier 61 by an analog switch 63 operated by the B signal of the decoder 62, depending on whether the electrode is an odd number or an even number. Therefore, in the amplifier 61, only the displacement current of the read picture element point is canceled by the output appearing on the resistor R2 or R3, that is, a difference voltage is derived, and when the read picture element point is in the write state, only the polarization current is output. do.
When the read pixel points are in the erased state, they are all canceled out, so the output becomes 0. In the present invention, in which the readout operation is performed in this way, two transparent electrodes in the thin film EL display device are prepared as reference electrodes, so the influence of electrode resistance and the amount of the output point are taken into account from this reference electrode. Depending on whether the electrode to which the pixel point belongs is an even number or an odd number, the output can always obtain a displacement current equal to the displacement current of that electrode, and a signal with a large S/N ratio that is almost ideal. It is possible to obtain

Note that in other embodiments of the present invention, a differential transformer can be used to detect the polarization current, but when an amplifier is used as in the above embodiment, it is possible to not only remove the common mode component (displacement current) but also to detect the polarization current. It is more advantageous because it can be amplified up to the level.

[Brief explanation of drawings]

Figure 1 is a partial perspective view of a three-layer thin film EL display device.
Fig. 2 is a characteristic curve diagram of applied voltage and luminance for explaining the operation of the device, Fig. 3 is a current waveform diagram during readout operation of the device, and Fig. 4 is an implementation of the device of the present invention. An example circuit diagram is shown. 20' write and output switch circuit, WS, ~WS
m is a switch, 30 is a switch circuit, 50 is a matrix type thin film EL display device, 60 is a logic circuit, 70 is a write and logic voltage source, R, R2, R3 are resistors r, ram reference electrodes, 61 is an amplifier. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In a thin film EL display device in which a phosphor layer sandwiched between dielectric layers is interposed between electrodes arranged in a matrix shape, at least one of which is a transparent electrode, and a hysteresis phenomenon appears in applied voltage and luminance characteristics, the transparent Electrodes are led out to one end and the other end of the panel, and at least one transparent electrode that is not written to and led out to the one end and the other end is used as a reference electrode, and a read current and the read current A readout device for a thin film EL display device, comprising circuit means for reading out and outputting the difference between the current obtained from the reference electrode on the side led out to the same end as the transparent electrode.