JPS5828595B2 - Readout drive device for EL display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In a thin film EL display device having a hysteresis memory, writing or erasing is performed by instantaneously applying a voltage equal to or less than the maintenance AC amplitude under maintenance AC driving, and the subsequent maintenance AC voltage is Accordingly, the technology for maintaining the light-emitting state or the light-off state, and the technology for reading the light-emission or light-off state have already been filed by the present applicant as prior inventions.

The present invention relates to a circuit for reading out the light emitting state or non-lighting state of each picture element of a thin film EL matrix panel having an AC hysteresis phenomenon, that is, a memo IJ-function.

First, the technology of the prior invention, which is the basis of the present invention, will be briefly explained.

First, the configuration of a thin film EL display device will be explained.

As shown in FIG. 1, transparent electrodes 2 are arranged in stripes on a glass substrate 1.

A dielectric material 3 such as Y2O3 is deposited on top of this, a fluorescent layer 4 such as ZnS doped with Mn is further applied thereon, and a dielectric material 31 such as Y2O3 is further deposited on top of this by vapor deposition, sputtering, etc. The layer is deposited to a thickness of ~10,000 to form a double-insulated three-layer structure, and electrodes 5 perpendicular to the transparent electrode 2 are arranged in a striped pattern on top of the layer.

With such a structure, one of the first electrode group 2 and
When a suitable alternating current voltage is applied to one of the second electrode group 5, only a small area sandwiched between the two electrodes will emit light, which corresponds to one pixel on the screen. .

An EL display device can be constructed by sandwiching the phosphor layer 4 that emits light between the dielectrics 3 and 31 and further forming the electrodes 2 and 5 thereon, but as described above, the formation of the electrodes 2. By making it into a shape, a matrix display panel can be formed.

EL with this structure has superior characteristics in terms of brightness, lifespan, and stability compared to conventional distributed EL elements, but each pixel has a new characteristic between brightness and applied voltage. second to
The historical phenomenon shown in the figure is shown.

This characteristic will be explained with reference to FIG. 2. First, when a pulse of voltage amplitude v1 is applied as shown in FIG. 2a, the luminance is at the B1 level as shown in FIG. 2c.

Here, when the sustaining voltage (1) is the light emission threshold voltage vth, vl>vth.

When a write voltage V2 is applied to this, the brightness changes all at once to B.
After that, even if the voltage value is returned to the maintenance voltage ■1, the brightness settles to B2, which is larger than B1. When the erase voltage ■3 is applied to this, the brightness level decreases rapidly, and the brightness level decreases again to the maintenance voltage ■1. When the brightness is returned to B1, the brightness settles down to B1.

These temporal relationships are indicated by the symbol t1 in FIG. 2a. t
3......t2□ is shown by corresponding to the positions of the same symbols in C of the same figure.

As shown by the thin line in FIG. 2, this hysteresis phenomenon can take any small loop depending on the amplitude and pulse width (not shown) of the write voltage.

That is, it is also possible to display halftones. A major feature of the ELP, which is not found in other display elements, is that once a write voltage is applied, each picture element continues to emit light without losing the gradation given to it by the sustain pulse.

The above voltages vary greatly depending on the composition, film thickness, and applied waveform, but in a prototype example, vth=200V, V
=210V, V2=210~280V, ■3 =19
It is 0 ■.

The present invention is directed to a "driving device for an EL display device" (patent application filed July 18, 1975, Patent Application No. 5O-885), which was previously invented by the inventors.
10), and its purpose is to provide a readout circuit.

The present invention will be described in detail below using Examples.

FIG. 3 shows an embodiment of the present invention.

This diagram consists of five blocks.

The first block is a sustain drive circuit 10.

Although FIG. 3 shows a three-phase resonance maintaining drive circuit, a multi-phase circuit having four or more phases may also be used.

The second block is a write and read switch circuit 20,
Write voltage V to the X line to be written in the write phase
This is a switch circuit for applying W.

Also, if you want to read out, read out during the readout phase.
This is a switch circuit that applies a read voltage Vr from the read drive circuit 60 to the line.

In the circuit description to be described later, the X line will be treated as a scanning line.

The third block is a data switch circuit 30 consisting of switches DS1 to DSn and a detection resistor R.

All switches are shorted (grounded) during sustain drive and read drive.

In the write phase, only the Y line to be written continues to be short-circuited, and the non-write Y line is opened.

The fourth block is a write and read line isolation and sustain amplitude hold circuit 40.

This is a circuit for separating the scanning write lines in the X direction and a diode circuit for maintaining the resonance drive amplitude at the same time.

The fifth block is a matrix panel 50 as shown in FIG.

Further, FIG. 4 shows the switching pulse a, the charging/discharging current waveform, and the driving voltage waveform C applied to the X line.

The specifications of the 8-inch EL panel prototyped by the inventors are line pitch:
2 lines/mm, 320 X lines (transparent electrode side), 240 Y lines (back aluminum electrode side) Display characters: 64 types of Roman letters, Arabic numerals, and symbols of 5 x 7 dot configuration Number of characters displayed: X direction (scanning) side) 52 characters Y direction (data side) 24 lines Maximum number of display characters 1248 characters Effective display line number: X direction 260 lines (character spacing 194
7 minutes) 168 lines in the Y direction (line spacing of 2 lines).

In order to maintain and drive the above EL panel, the circuit shown in FIG. 5 was prototyped.

In this figure, U: oven collector TTL transistor switching transistor T1: interstage coupling transformer Dl: protection diode D: holding diode T: resonant transformer, and other symbols have the same meanings as in the previously explained drawings. It is used for.

In this circuit, circuit constants, inductance of resonant transformer: L = 29mH Panel capacitance when connecting the number of effective display lines: CT = 0.377μF φ1. φ2. φ3, pulse width: 200μec, repetition of each pulse: 330H2, resulting in resonance 1 drive +V1 = 215 volts held voltage 2 -V2 = -230 volts vH
The power supply voltage at this time is 70 volts, +0"-],]80d""'
1-E2-=135 volts Existing frequency: 4 to 5 KHz.

Now, in FIGS. 4 and 5, when the first holding switch SW1 is closed at the first timing φ1, the difference between the third holding potential ■□ and the first power supply potential E is (In this figure, the entire EL display panel is approximately considered to be a capacitive element cT having a constant capacity) and is held at the first holding potential.

Similarly, when the second maintaining switch SW2 is closed at the second timing φ2, the potential is set to the second holding potential, and then when the third maintaining switch SW3 is closed at the third timing φ3, the potential is set to the third holding potential. Become.

In this way, three-phase drive was realized. In this way, multi-phase sustaining drive with three or more phases is performed at an intermediate holding potential (
In this embodiment, data switching elements DSI, DS2 . ...
This is to reduce the pressure resistance requirements of .

As shown in FIG. 4, writing is performed by switching the X and Y sides of the writing picture element M(ji) by the writing and reading switch circuit 20 and the data switching circuit 30, respectively, during the intermediate holding period (■H period). Choose and do it.

Next, regarding the read drive which is the gist of the present invention, FIGS.
This will be explained using FIGS. 7 and 8.

It is provided with a read drive circuit 60 for read drive and detection resistors R connected to each data line.

The read drive circuit 60 has a read phase φ4 as shown in FIG.
Linear wave generation pulse φ that becomes bi-level only during the first half of
4 is applied to the pace terminal 61 of transistor Q1.

Therefore, transistor Q1 is turned on and PNP)
Transistor Q2 operates as a constant current source, and capacitor C
to charge.

The constant current at this time is i The voltage appearing at point B as teeth However, C is the capacitance value of capacitor C. becomes.

The time width of φ4 is T, and the maximum value of voltage b is the maintenance voltage v
Adjust so that it is equal to S.

That is, Adjust within the range.

In this way, a straight wave is generated at point B.

This straight wave is transmitted to the write/read switch circuit 20 via the driver transistor Q3 connected in a darling manner.
is added to line A of

Transistor Q3 is also inserted for the purpose of preventing the capacitance component of the read line from affecting the linear wave generation.

Diode D61 applies write voltage V to line A during write drive.
This is a diode for protecting transistor Q3 when w is applied.

Only during the latter half of the read phase φ4...the holding potential return pulse φl that goes to the high level is applied to the input terminal 62 of the transistor Q4.
added to.

Transistor Q4 only during the period when the pulse φl is at the no-low level.
turns on and supplies voltage VH to line A.

This is to return the read line Xi charged to the read voltage vS to the holding potential VH, and to return the potential of the capacitor C to the held potential VH.

The diode D3□ is a diode for protecting the transistor Q4 when the line A becomes lower than the holding potential VH.

The details of the data switch circuit 30 are as shown in FIG.
Data lines Y1-Yn are connected to the collectors of NPN transistors DS1-DSn, respectively, and their emitters are grounded via a detection resistor R.

The connection point between the emitter and the resistor R is connected to the + side terminals of the comparators C1 to Cn.

One side terminal is a power supply for polarization current separation■.

connected to. Each output of the comparators C1 to Cn is connected to a gate 1-G to which a pulse φ4' is applied so as to open only during the read period.
It is output via Gn.

During the read drive, the read mode switch R8 is closed and during the intermediate holding period (VH), the line switch WS of the X line Xi containing the picture element M(i-j) to be read out at the phase φ4
i closes.

At this time, the switches DS1 to D of the data lines Y1 to Yn
Sn is closed.

When pulse φ4' is applied, a straight wave signal is applied to line Xi via line A and switch WSi.

When this straight wave signal is applied to the line Xi to drive the read 1, the state of the picture elements on the line Xi (written and non-written states) is not affected in any way, and the picture elements on the data lines Y1 to Yn are A displacement current (current according to the pixel capacitance) flows together with a polarization current caused by the write state.

By separating this polarization current and displacement current and detecting the polarization current, the state of the picture element on the line Xi can be read out non-destructively.

Now, only the picture element M (i - j) on the line Xi is written and is in a light emitting state, and all other picture elements M (i, 1'<
When j) is in a non-written state and turned off, the current in the data side line Yj due to the read drive is a current in which the displacement current id caused by the pixel capacitance and the polarization current i based on the written state are superimposed. .

Only the displacement current id flows through the other data lines Yk=j.

The slope of the linear wave in this readout drive If the slope is - and the capacitance of one picture element is Ce, then t The displacement current id is It is expressed as The voltage Ud appearing between the terminals of the resistor R teeth becomes.

When the linear wave voltage exceeds the light emission threshold, the polarization current i, in other words, since an internal polarization electric field is formed in the writing picture element, the maintenance voltage S
Above the lower external emission threshold, there is a rapid flow.

FIG. 9a shows an enlarged voltage waveform when there is a polarizing current, and FIG. 9 shows an enlarged voltage waveform when there is no polarizing current.

Since the displacement current id is a current based on the pixel capacitance, a voltage equal to or higher than the voltage drop (id-R) due to this current id is set as the separation voltage Vf of the displacement current and the comparators C1 to Cn
If the comparison input is given to the comparison input of the polarization current i,
It is possible to separate and detect only the components based on

Therefore, a read signal is obtained from the comparator Cj connected to the written data line Yj, and the other comparators C1'
No output is obtained for =j.

Thereafter, a read signal is detected by ANDing the output of the comparator with pulse φ4'.

After reading is completed as described above, the read drive circuit 6
0 applies the intermediate holding voltage VH to the line A of the write/read switch circuit 20, and returns the voltage S applied to the picture element during reading to the intermediate holding voltage VH.

In the description of the above embodiment, the case where the number of written picture elements is ■ is described and only the l line is read out, but reading is possible in the same way when there are two or more written picture elements.

Furthermore, if the state of each picture element unit is not required, two or more lines can be read out simultaneously.

As described above, in the present invention, the read drive voltage is supplied from the scanning side of the matrix electrode, and the write state is read from the detection resistor connected to the data side, without affecting the maintenance and write 1 drive devices. In addition, since the switch circuit and the like used during maintenance and write driving can be used in common, the configuration of the reading device is simple and reliable and accurate reading can be expected.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of a thin film EL display device, FIG. 2 is a characteristic curve diagram of applied voltage and luminance to explain the operation of the device, and FIG. 3 is an embodiment of the present invention. FIG. 4 is an operational waveform diagram of sustain and write drive in this embodiment. FIG. 5 is a circuit diagram of the sustain drive block. FIG. 6 is a circuit diagram of the read drive circuit. 8 is a circuit diagram of a data switch circuit and a detection circuit, FIG. 8 is an operational waveform diagram during read drive, and FIG. 9 is a partially enlarged diagram of the waveforms shown in FIG. 8. 10 is a sustain drive block, 20 is a write and read switch circuit, 30 is a data switch circuit, 50 is an EL matrix panel, 60 is a read drive circuit, and R is a detection resistor.

Claims (1)

[Scope of Claims] 1. An EL display device having electrodes arranged in a matrix, comprising: a switch circuit that applies a read voltage to one of the electrodes during read drive; a detection resistor connected to the other electrode; E characterized by comprising means for separating the voltage appearing between the terminals of the detection resistor into a component due to displacement current and a component due to polarization current and detecting the presence or absence of the component due to polarization current.
Readout drive device for L display device.