JPS6015279B2 - Maintenance drive circuit for thin film EL element with memory - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for sustaining and driving a thin film EL element with a memory, and in particular, the sustaining drive circuit is constituted by a thyristor.

The structure and characteristics of the thin film EL matrix element with memory have been explained in Japanese Patent Application No. 50-183767 filed by the present applicant entitled "Drive Circuit for Large Capacitance Display Element" and others, but will be briefly explained again.

In a thin film EL display device, transparent electrodes are arranged in a cotton-like manner on a glass substrate, and on this, for example, Y203, Si3N4, Ti0
2. Add a dielectric material such as Kawa 203, and then add, for example, Mn on top of this.
A dielectric layer such as ZnS (yellow light emitting) doped with ZnS (yellow light emitting) is formed on top of the dielectric layer, such as Y203, Si3N4, Ti02, AI203, etc., using a thin film technique such as vapor deposition or sputtering.
It is deposited to a thickness of 0.00 to 10,000 A to form a double-insulated three-layer structure, and a cotton-like electrode is arranged thereon in a direction perpendicular to the transparent electrode to form a matrix electrode.

In the three-layer thin film EL display device having such a structure, the first
When one of the electrode groups and one of the second electrode group are selected and an appropriate alternating current voltage is applied, a small area sandwiched between the south electrodes will emit light. This corresponds to one picture element on the screen. By combining these, characters, symbol patterns, etc. are displayed. EL with this structure has superior characteristics in terms of brightness, lifespan, and stability compared to conventional distributed EL elements, but this EL has a new hysteresis between applied voltage and luminance. Show characteristics.

When first applying a pulse of voltage amplitude V, the brightness is at a low level of brightness B,. Here, the sustaining voltage V, is V,>Vm, where the light emission function voltage Vth is assumed. When the sustaining voltage V, is continuously applied, the brightness B, is maintained. Next, write voltage V2
When V is applied, the brightness increases all at once to a high level of brightness &, and even if the voltage is returned to the maintenance voltage V again within a certain period of time, the brightness settles to the previous brightness B, which is higher brightness &. Maintaining voltage V. When continuously applied, the brightness B2 is maintained. In this state, when the erase voltage V3 is applied next, the brightness level decreases rapidly, and when it is returned to the sustaining voltage V, it settles down to the previous low level of brightness B. This hysteresis phenomenon can take any 4>rape depending on the amplitude, pulse width (not shown), and pulse frequency of the written lightning pressure. That is, it is also possible to display intermediate steel. A major feature of this EL display device, which other display devices do not have, is that once a write voltage or erase voltage is applied, each picture element continues to emit light without losing the gradation given to it by the sustain pulse. It is. The above voltages vary greatly depending on the composition, intensive physical conditions, manufacturing conditions, and applied waveform, but in a prototype example, Vth = 200V, Vth
,=210V, V2; 210~280V, V3=190
It is V. The present invention relates to a sustain drive circuit for the above-mentioned three-layer structure thin film EL display device, and a circuit according to an embodiment of the present invention is provided in a first embodiment of the present invention.
This will be explained below as shown in the figure. 10 is the thin film EL
element, here a row (X) consisting of transparent electrodes 1 1
A row consisting of electrodes X, ~Xm and aluminum electrode 12 (
Y) Only electrodes Y, ~Yn· are shown.

20' is a circuit that supplies a positive sustaining voltage Vs to the Y electrode from power supply line A, and includes a thyristor 21 and a pulse transformer 2.
2, and each electrode Y, ~Yn is a diode 23, .
Connect via... Reference numeral 30 denotes a switching circuit that leads the x electrode to ground, and transistors 31, . . . are connected to each electrode X, to Xm and the ground.

A readout signal, a write signal, an erase signal, and a sustain signal are applied to the base of this transistor. These transistors 31, . . . act as switching elements that select the X electrode during writing, erasing, and displaying. A diode 32, . . . is connected between the collector emitters of the transistors 31, .
... are connected in parallel. This diode 32...
... is useful when performing maintenance drive. Reference numeral 40 designates a circuit for grounding all the X electrodes, which is composed of a thyristor 41 operated by a sustaining signal T applied to line B, and connected to each electrode X, ~Xm via a diode 42, . . . be done.

50 is a circuit that supplies a negative sustaining voltage -Vs from all Y electrodes H to Yn line C, and each electrode is connected to a diode 5.
1, . . . are connected to a thyristor 52 operated by a sustaining signal L given from a pulse transformer 53.

60 is a switching circuit that selects the Y electrodes Y, to Yn, and high voltage switching transistors 61, . . . and diodes 62, . . . are connected between each electrode and the voltage Vwer of the power line D. and the transistor 61
is controlled by vertical binary address signals.

A power supply 70 selectively outputs a write voltage, an erase voltage, and a read voltage to the power supply line D according to the operation mode of the thin film EL element, and outputs a write voltage, an erase voltage, and a read voltage to one of the selected Y electrodes through one of the transistors 61. Apply the above voltage to . A power transformer that supplies maintenance voltage to lines A and C for 800 mA.
It is also possible to use a HZ or 60 HZ single-phase AC power supply, or it is also possible to use a power supply whose frequency is converted from a single-phase AC power supply.

When performing frequency conversion, it is necessary to use a power source that generates a sine wave with low output impedance and high conversion efficiency. For this purpose, ACIOOV6 is used as shown in Figure 2.
A voltage of 0 HZ (282 Vpp) is rectified by a rectifier circuit 101, and a sine wave output of a desired frequency is obtained as an output via a switching circuit 102 and a filter 103. The circuit according to the present invention is constructed as described above, and applies a sinusoidal AC voltage having a maintenance voltage shown in FIG. 3a to the power transformer 8 lines A and C.

Here, when the sinusoidal AC voltage is 0, a sustain signal T shown in FIG. 3B is generated and applied to the thyristors 21 and 41 at the same time, turning them on. For this reason, from the thyristor 21 to the diodes 23, 23,..., Y
Current flows through the electrode, the X electrode, the diodes 42, 42, . . . , and the thyristor 41 in this order. When the positive half cycle of the sine wave passes and the current flowing through the thin film EL element becomes 0, the thyristors 21 and 41 are automatically turned off due to their characteristics. At this time, the sustain signal T2 shown in FIG. 3c is applied to the thyristor 52 via the transformer 53,
Turn on. Since a negative sine wave maintaining pressure is applied to line C, the diodes 51, 51, . . .
and a diode 32 connected between the × electrode and the ground.
A voltage in the opposite direction to the above is applied to the thin film EL element via . When the negative half period of the sine wave has passed in the thin film EL element, the value becomes 0 again, so the thyristor 52 is turned off. The above operation is performed every few cycles of the sinusoidal AC voltage, and a sustaining voltage consisting of one cycle of the sinusoidal voltage is applied to the thin film EL element at predetermined intervals as shown in FIG. 2d. In addition, if the transistors 31, .
The transistor 31 is replaced by a thyristor 41, a diode 42,
. . . can be used instead, and the thyristor 41 and diode 32 can be omitted. In the circuit shown in FIG. 1, when writing, erasing, or reading a selected picture element, a commit voltage, an erase voltage, and a read voltage are applied from the power supply 70 to the line D, and at the same time, the transistors 31, . . .
..., 61, . . . are selectively turned on to apply a required voltage to the selected picture element.

As described above, in the present invention, a sine wave voltage is used as a power source for sustaining drive, and the application is controlled by a thyristor. Therefore, the thyristor is more suitable for switching large currents than other switching elements, and the thyristor is turned on when the thyristor is turned on. It is only necessary to apply a pulse to start the thyristor, and when a reverse voltage is applied to the thyristor, it will automatically turn off due to its own characteristics, so the pulse applied to the thyristor can be a very narrow pulse; The pulse generation circuit can be simplified.

In the above-mentioned embodiment of the present invention, the sustain drive applies one period of sine wave voltage, so the reason why the power consumption is reduced according to this embodiment is explained below as proposed by the applicant to date. This will be explained in comparison with the case where sustain driving is performed by applying a pulse sustaining voltage that has been previously applied.

In the equivalent circuit of a thin film EL element, all electrodes are driven simultaneously during sustain drive, so the total resistance of the transparent electrode is R, the insulating layer sandwiched between the electrode and the Y electrode, and the total capacitance of all pixels due to the EL layer. When C is denoted by C, it can be represented by a two-terminal circuit network as shown in FIG.

When a pulse voltage of equal positive and negative amplitudes is applied as a maintenance voltage to the circuit shown in Fig. 4, the power consumption Pp per cycle is P
p=2 CV cost C: total capacity of all picture elements Vo: voltage of sustain pulse.

Next, when a one-cycle sinusoidal voltage is applied to the thin film EL element, the following equation holds true, assuming that the current flowing through the equivalent circuit in FIG. 4 is i(t).

R-i(t)+Ji(t)dt:V is in, t: When solving the above equation under the angular frequency of the applied sine wave j(0)=0, we get 0 ni n-, 1 '' CR The first term in the above equation is the current that flows in a steady state, and the second term is the transient current that occurs when the applied voltage is applied for only one period.

The power consumption Ps per cycle when applying a sine wave is as follows.

Since a transient term is added to the steady term, power consumption may be higher than in the case of applying a pulse voltage depending on the values of C and R. The ratio of power consumption during sine wave application and pulse application, and when driving a 6 inch thin film E screw, the 6 inch thin film EL element used by the present inventors has a C: 0.3.
2 peaks F, R = 5.20, and maintenance frequency 4ooHZ
When calculated as follows, it becomes 8-7-3, and the power consumption is extremely smaller when a sine wave is applied.

When applying a sine wave, a large current does not flow instantaneously like when applying a pulse, so a low on-resistance switching element such as a thyristor can be used, and the on-resistance of this thyristor is at most about IQ, which is quite small. .

If we estimate the resistance generated in parts other than this thyristor to be as large as possible and set it as 10oQ, the above power ratio will be equal to 10oQ.・
It becomes 7. By the way, when a sine wave voltage is applied, the luminance of light emission is slightly lower than when a pulse voltage is applied.

In order to make the luminance equal to that when a pulse voltage is applied, it is necessary to increase the sinusoidal applied voltage. For example, if the sine wave voltage is made 50% higher peak-to-peak than the pulse voltage (in reality, it is not necessary to make it this high), the power source,
The vine = o-38, and the power consumption when applying a sine wave voltage is:
Even in the worst case, it will be about 40% of the time when pulse voltage is applied.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of Kazumi implementing the sustain drive method of the present invention, FIG. 2 is a block diagram of a sine wave sustain power supply in another embodiment, and FIG. 3 is a sustain drive in the circuit of FIG. 1. FIG. 4 is a time chart showing an equivalent circuit diagram of a thin film EL element. 10: Thin film EL panel, 20, 40, 50: Maintenance voltage supply circuit, 21, 41, 52: Siris evening, 80: Power transformer. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In a maintenance drive circuit for a thin film EL element with a memory, which applies a voltage with a sufficiently large difference in luminance between voltage rise and voltage fall as a maintenance voltage to a thin film EL element that exhibits a hysteresis phenomenon in its luminance characteristics with respect to applied voltage. , is connected between a power supply that generates a sine wave of the maintenance voltage and the thin film EL element, and is turned on in synchronization with each positive and negative half period of the sine wave, and is connected to the thin film EL element in the positive direction. 1. A sustain drive circuit for a thin film EL element with memory, comprising: a thyristor that applies a sustain voltage of 1, and a thyristor that applies a sustain voltage in a negative direction.