JPS6010636B2 - 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 storage 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 storage device for a thin film EL display device having a matrix electrode. This invention relates to a lifting device with improved N.

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 Y203, Si3N4, Ti02A, etc., and on top of this a Z doped with, for example, Mn.
A luminescent layer 4 such as nS (yellow light emitting) is further applied on top of it.
, Sjbu4, Ti02Aso203, etc. by thin film technology such as vapor deposition or sputtering.
It is deposited to a thickness of A to form a double-insulated three-layer structure, and a cotton-like 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 L 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 sandwiched between the two emits light. This corresponds to a - picture element on the screen. By combining these, characters, symbol patterns, etc. are displayed. EL with such a structure has superior characteristics in terms of brightness, lifespan, and stability compared to conventional dispersion type EL elements, but this EL
newly exhibits a hysteresis characteristic between the applied voltage and the luminance as 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. 2a, the brightness is at the level of brightness B as shown in FIG. 2b and c. Here, the maintenance voltage V
, is the luminous threshold voltage Vth, then V,>Vth.
The brightness B is maintained by continuously applying the sustaining voltage V. Next, when the write voltage V2 is applied, the brightness rises all at once to &, and even if the voltage returns to the sustaining voltage V, within a certain period of time thereafter, the brightness remains the same as the previous brightness B. The brightness settles to a larger brightness B. 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
, settled on. These temporal relationships are shown by making the symbols t, t2, . . . , t2 attached to FIG. 2a correspond to the same symbols in FIG. 2c. 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 gray level given to it by the sustain pulse, which is a major feature of this EL display device that is not found in other display devices. It is a characteristic. Each of the above voltages varies greatly depending on the physical conditions such as composition and film thickness, and manufacturing conditions.
By the way, in the prototype example, Vthi200V, V, = 210
V, V2=210 to Z280y, and V3=190y. 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 determine the memory state.

Since a two-thin film EL element has a crab light layer sandwiched between two insulating layers, it can be thought of as a capacitive element, and a displacement current flows when a sustaining voltage is applied, but this element remembers the light emitting state. Sometimes, when a sustaining voltage is applied, two currents corresponding to the magnitude of the luminance are superimposed on the displacement current and flow. This current is called a polarization current, and in reality there is some background rise even in the erased state.
A correspondingly small polarizing current flows. For example, the third
When a sustaining voltage pulse as shown in Figure 3a is applied to the EL element, the current flowing through the element shows a displacement current waveform as shown by the solid line 11 in Figure 3B when it is in the erased state. In the light emitting state, a broken line 12 shows a waveform obtained by multiplying this by a polarization current. In order to determine the presence or absence of a polarized current, the third inventor of the present invention and others used a method J for detecting memory contents of a light-emitting element in Tokusekiseki Sho 51-28446. We have proposed a method and a circuit for detecting whether the entire light emitting state is the erased state based on whether the displacement current exceeds a certain predetermined level, which is the sum of the displacement current and the noise margin, at the time when the displacement current reaches its peak.

However, since this method separates the displacement current and polarization current at a specific level, careful consideration is not only required when setting the above-mentioned specific level, but also the level at which the polarization current exceeds the specific level. The magnitude of is equal to the amount obtained by subtracting the noise margin, and the absolute value of this signal becomes very small.

Therefore, the S/N is poor. It is also possible to remove the current during erasing by constructing an equivalent circuit for erasing using analog elements such as capacitors and resistors, or by storing the waveform itself during erasing in a ROM etc. .

For example, the above method is described in Japanese Patent Application Laid-Open No. 52-30191 entitled "Representation Apparatus for rEL Display Element". 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 Tomoe L element to the outside, at least the electrode on the display side is made of a transparent electrode, but when the resistance of this electrode is high, such as in a matrix display, where the display density needs to be high. Since the electrode line width is narrow and the resistance is high, a large difference in resistance value appears between 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 will change greatly depending on the position of the argument, and it will complicate the device to have a corresponding number of equal value circuits at the time of erasure, and to prepare the waveform at the time of erasure. This makes it large and uneconomical. In view of the above points, the present invention has a novel configuration to solve the above problems, easily and reliably extracts only the polarization current, and is suitable for the matrix type.

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, -E are prepared, and three switches SW, SW2, SW3 are operated in sequence to supply the three voltages E, ○, -E2 to the EL display device 50'. .

The transformer T forms a series resonant circuit together with the capacitive component of the EL display device 50, and supplies voltage with high efficiency. The second block is a write/read switch circuit 20, in which a write voltage Vw and a power supply E are applied to the line X to be written in the write phase.
This circuit applies voltage from w via switch Wsk (k=1 to m). It is also a switch circuit that applies a reading voltage Vr from the reading drive circuit 70 to the line x which is reading out at the time of reading & phase. Read drive circuit 7M
This is a circuit for applying a voltage equal to the sustaining voltage Vs. In the third block, all three switch groups provided on the transparent electrodes of the EL display element are short-circuited during maintenance drive, and only the desired Y line is turned on during write/erase and output drive.
Others are turned off.

The fourth block is a write initiation separation and maintenance amplitude holding 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 EL display device, and only the electrodes are shown in this figure.

The electrode at the far end of the panel on the transparent electrode side is prepared as a reference electrode r. The sixth block is a readout circuit 60 which is a feature of the present invention, in which a common mode signal removal amplifier 61 cancels out the voltages appearing in a resistor R commonly connected to each electrode 1 to n and a resistor R2 connected to a reference electrode r. extracts and outputs only the polarized current.

The specifications of the 8-inch EL panel prototyped by the inventor are as follows.

Line pitch: 2 lines/side 320 X lines (transparent electrodes) 240 Y lines (mountain electrodes) Display characters: 5 x 7 dot composition, 64 lotus Roman letters, Arabic numerals, symbols Number of characters displayed: × direction 5Z character Y Direction 24 lines Maximum number of display characters 1248 characters Number of effective display lines; × direction 260 lines (character spacing 1 line) Y direction 168 lines (line spacing 2 lines) When the first holding switch SW is opened, the third holding potential VH and the first holding switch SW are opened.
The difference between the voltage and the power supply potential E is a capacitive element (in this figure, the entire EL panel is considered to be a capacitive element Ct with approximately constant capacitance).

), and the first holding potential is maintained at VSI = EI + BI - V) (1).

Similarly, when the second holding switch SW2 is closed (at the second timing), the second holding potential is -VS2=-E2 (V
I+E2) ......[2), and then when the third holding switch SW3 is closed at the third timing J3, the third holding potential becomes VH=Katana V2
..."""...{31.Thus, three-phase sustain drive is realized.Three-phase sustain drive is performed by writing at the intermediate hold potential (in this embodiment, the third hold potential VH), so that the switch The withstand voltage requirements of Ds, to n can be reduced.

For writing, during the intermediate holding voltage (VH period), the X and Y sides of the write picture element M (i, i) are selected by the write and output switch circuits 20 and 30, respectively, and the write voltage Vw is released. I will do it.

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.

When driving, it corresponds to the selection point M(i, i)
The side switch DSj and the Y side switch WSi are selected and closed, and the sustain pulse voltage Vs is applied. This pulse current appears in the resistor K and is supplied to the terminal of the amplifier 61. At the same time, a reference current at the reference point P(i, r) of the reference electrode r appears at the resistor R2. Since the reference line r is never written to, it always outputs only an erase current, that is, a displacement current. This is supplied to one terminal of the amplifier 61. However, in the amplifier 61, only the displacement current at the starting picture element point is the resistance R.
2, a differential voltage is derived, and when the read pixel point is in the write state, only the polarization current is output. When the proposed picture point is in the erased state, all the points are canceled out, so the output becomes 0. In this way, the motion for proposing a proposal is performed.

Since the present invention prepares one transparent electrode in a thin film EL display device as a reference electrode, the output from this reference electrode is always equal to the output pixel point, including the influence of electrode resistance and the amount of written picture element points. It is possible to obtain a displacement current that is equal to the displacement current, and it is possible to obtain a signal with a large S/N ratio close to the ideal. Note that in other embodiments of the present invention, a differential transformer can be used to detect the polarization current, but when using an amplifier as in the above embodiment, it is possible to not only remove the common mode component (displacement current) but also to detect the required level. It is more advantageous because it can amplify up to

In addition, the reference electrode is not an electrode at the end of the thin film EL display device, but
Electrodes at the center or other locations may be used as reference electrodes.

[Brief explanation of the drawing]

Figure 1 is a 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, and Fig. 3 is a current waveform diagram during the start-up operation of the device. An example circuit diagram is shown. 2 channels are write logic output switch circuits, WS. to WSm are switches, 30' are switch circuits, 50 is a matrix type thin film EL display device, 6 channels are read circuits, 70 is a write logic output voltage. source, R,, R2 are resistors, r is a reference electrode, and 61 is an amplifier.

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 the applied voltage and luminance characteristics. A single reference electrode that is not written on is provided in the thin film EL display device, crossing the electrode group to which a voltage of 1. A readout device for a matrix type thin film EL display device, comprising circuit means for deriving a difference between the two.