JPS6010632B2 - Drive device for thin film EL display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive device for a double insulation type thin film EL display device.

The present invention is a double insulated thin film EL device having matrix electrodes.
To provide a circuit in which a circuit for applying a display voltage to the matrix electrode can be configured with one type of switching element such as an N-channel M○ or an NPN transistor when displaying characters, symbols, film shapes, etc. on a display device. It is something.

The present invention makes it possible to configure a drive circuit for a thin film EL display device using an integrated circuit. Further, the present invention provides a drive circuit for a thin film BL display device that can be constructed with a small number of switching elements.
Further, the present invention provides a field refresh type driving device.

Next, before explaining the drive device of the present invention, we will explain the double insulation type thin film E.
The L display device will be explained.

As shown in FIG. 1, a band-shaped transparent electrode 2 consisting of one peak 03 is provided in parallel on a glass substrate 1, and on this, for example, Y2
03, dielectric material layer 3 such as Si3N4, EL layer 4 made of S doped with an activator such as Mh, Y20 as above
3. A dielectric material layer 5 such as Si3N4 is formed using a thin film technique such as evaporation or sputtering.
A three-layer structure is obtained by sequentially laminating them to a thickness of , and a strip-shaped back electrode 6 made of A-line or the like is provided in parallel thereon in a direction perpendicular to the transparent electrode 2.

In the double insulation type thin film EL display device having this configuration, the first
When an appropriate AC voltage is applied to one of the electrode groups 2 and one of the second electrode groups 6, the EL layer 4 in a small area sandwiched between the two electrodes emits light. This minute area corresponds to one picture element when displaying characters, symbols, and pus-like objects. Therefore, characters, symbols, etc. are displayed by selectively scanning this picture* one by one, or by simultaneously driving all the selected picture elements. This thin film EL display device emits light with high brightness, has a long lifespan, and is stable. It also has superior characteristics compared to conventional distributed EL elements in that it is possible to manufacture devices with hysteresis type memory. The thin film EL element does not emit light unless a relatively high voltage of about 150V to 300V is applied. A high voltage switching element is required to be connected to the high voltage power supply circuit, and a high voltage switching element is required to be connected to the ground potential on the other electrode.

As mentioned above, two high voltage switching elements cannot be used with the same electrode on the ground side, and therefore two types of switching elements are required. For example, they are an NPN transistor and a PNP transistor, or an N-channel type MOS transistor and a P-channel type MOS transistor. These switching elements are made of thin film.
The same number of electrodes as the display device is required. However, it is currently extremely difficult to integrate high-voltage monolithic PNP and NPN (or P-channel and N-channel MOS) transistors, and research is currently underway. In view of the above points, the present invention provides an N-channel type M
This is a circuit that can be integrated into an IC using an OS or a high-voltage monolithic NPN transistor.

FIG. 2 shows a circuit diagram of the driving device of the present invention, and FIG. 3 shows its driving timing chart.

In FIG. 2, reference numeral 10 indicates the thin film EL display device, and in this figure, only the electrodes are shown, with the x-direction electrodes Xo to Xm being data-side electrodes and the Y-direction electrodes Y, to Yn being scanning-side electrodes. 1 1 is 1/2 write voltage (1'2
This is a drive circuit that applies VW).

12 indicates a diode array on the data side, which separates the data side disturbance line and protects against reverse bias between the source and drain (or emitter and collector in the case of an NPN transistor) of an N-channel high-voltage transistor. .

Reference numeral 13 denotes a switching element circuit on the data side, which is composed of an N-channel high-voltage MOS transistor with a common source, and forms a circuit for discharging charges stored in non-selected lines for writing.

Reference numeral 14 denotes a switching element circuit on the scanning side, which is composed of an N-channel MOS transistor with a common source, and forms a circuit for applying a write voltage to a selected supply point on a selected scan line for writing.

Reference numeral 15 denotes a diode array on the scanning side for providing reverse bias protection between the scanning side drive line and the source and drain (or emitter-collector in the case of an NPN transistor) of the switching element made of the N-channel MOS transistor.

A drive circuit 16 supplies a field refresh pulse to the drive line B in order to apply a field refresh pulse to the entire surface of the thin film EL display device at the end of one field scan.

Next, the operation of the above drive device will be explained.

First, as the first step, the switching element circuit 1 on the scanning side
All N-channel MOS transistors S constituting 4
A high level signal is supplied to the gates of S, -SSn to turn them on.

At this time, all transistors SD, -SDm of the switching element circuit 14 on the data one side are in an off state, that is, all gate inputs are set to O-level. Then, a level signal is supplied to the input terminal S, of the drive circuit 12 of the common line A, and the switching transistors T, , T2 are turned on, and a write voltage of 1'2 (1/2 Vw) is applied to the common line A. be done. Therefore, from all data lines (X, ~Xm), the thin film E
1/2 Vw is charged to all picture element points constituting the L display device. That is, in the thin film EL display device shown in FIG. 1, the dielectric layers 3 and 5 are formed on both sides of the EL layer 4, and the electrodes 2 and 6 are provided on both sides, so the thin film EL display device can be viewed as a capacitive element. The above voltage is charged to the capacitive component of each picture element.

Next, the transistor SDj connected to the data side selection line Xi including write picture elements i and i in the data side switching element circuit 13 is maintained in an off state, and the non-selection line Xk
Transistor SDk with ≠i is turned on by setting the input gate level of i to high level.

At this time, all transistors SS, ~n of the scanning side switching circuit 14 are kept in the on state. Therefore, since the data line Xi including the write picture elements i and j is separated from the Xk main i by the diode array 12, the charging voltage 1/2Vw is maintained, but the unselected data line Xk
The charge of the picture element contained in the sheep i is electrically charged through the transistor SDk main i.

Preliminary charging to the data side selection line Xi is completed in the above two steps. Thereafter, in the third step, all transistors SD, -SDm of the data-side switching circuit 13 are turned off.

On the other hand, in the scanning side switching circuit 14, writing picture elements i, i
A transistor SS connected to a scanning line Yj containing
Only transistor SS j is kept on, and the other transistors SS and j are turned off. In this state, the voltage 1/2 is applied to the common line A again.
In order to apply Vw, a high level signal is applied to the input terminal S to turn on the transistors T, , T2. When this voltage is applied, the selection data line Xi first becomes the voltage 1'2.
Vw is precharged, and this voltage is raised to Vw by combining with the voltage 1/2 Vw applied in the third stage. At this time, since the non-selected data line
Furthermore, the unselected scan line Y〆key i follows the raised voltage 1/2Vw' in three stages due to capacitive coupling. In the end, the writing voltage Vw is applied to the writing picture element i, i and it emits light, but the half-selected picture element i, i at the intersection of the selected data line Xi and the non-selected scanning line Y, and the non-selected data A voltage 1/2 Vw is applied to the half-selected picture elements k and j at the intersection of the line Xk i and the selected scanning line, but this voltage is below the threshold voltage of the thin film EL display device, so no writing or erasing operation is performed. . Furthermore, the same applies to the unselected picture element k located at the intersection of the unselected data line and the unselected scanning line. Finally, in the fourth step, the data-side switching transistors SD, -SDm and the scanning-side switching transistors SS, -SSn are turned off to return to the initial state.

In Fig. 3, SDi, SDk main i, SSj, SS evening≠j, S,, S2 indicate input signal waveforms, Xi, Xk≠
i, Yi, Y〆I shows the drive waveform of the electrode, selected pixel i, i, half-selected pixel k, i, j, unselected pixel k, its total pixel application waveform, and the picture The Qin applied waveform is the X electrode waveform seen from the Y electrode side.

Here, the voltage applied to the thin film EL display device will be devised using an equivalent circuit.

FIG. 4 shows before the third stage operation is started, that is, the transistor SSi of the selected scan line Yi is turned on;
The equivalent circuit is shown just before the other transistor SSZ i is turned off and the voltage 1/2 Vw is applied to the common line A.

In this diagram, each symbol has the following meaning. Number of matrix element lines, data side: m, scanning side: n, m, n》1 1 pixel capacity: Ce, selected scanning line: i, number of selected write data lines:
P Stray capacitance of scanning side wiring: Cs Stray capacitance of data side wiring: Cd All diodes connected to data lines including write pixels: ○s (reverse bias) Connected to data lines that do not include write pixels All diodes: Dn (forward bias) C. : Sum of all capacitances of non-selected picture elements (picture elements not selected from either the data side or the scanning side) (k, so), C
,=(n-1)(m-P)CeC2: Half-selected sum of capacitances (picture elements selected only from the data line side) (i, so) C2=P(n-1)Ce C3: Selection Sum of capacitances of picture elements (i, i) C3 = PCe C4: Half-selected picture elements (picture elements selected only from the scanning line side) Sum of capacitances of (k, i) C4 = (m - P) Ce C5: Scanning In the side line, the sum of stray capacitances of the scanning side wiring that does not include the write picture element (i, i) C5 ni (n - ・)CS C6: In the data side line, the data side that includes the write picture element (i, i) Total stray capacitance of wiring C6=PCd The capacitances C and C6 are at the following potential.

C,,C4,C5 are OV,C2,C3,C6 are 1'2V
It is w. In the next third step, the transistor SSi of the selected scan line Yj is turned on, the other transistors SS i are turned off, all the transistors SD, ~SDm on the data side are turned off, and 1/2Vw is applied to the common line A. is applied, the voltage Vs at point S in FIG. 4 is VS=-L;

Also, the voltage Vd at point D is determined by the law of conservation of energy.
2=Kyou (C20C20C6) (Vd-VS)2...(1)
from.・・・－・． (2) becomes.

Here (m-P)Ce》Cs...
...[3'(n-1)Ce]Cd
...[Assuming 41, C,》C5,C2》C3,C
6, '1', from equation (2), vS = science, vd = VW
．． ...{51.

In this way, as long as conditions [3} and '4' are satisfied,
The write voltage Vw is applied to all the selected write picture elements C3, and the half-selected picture elements C2 and C4 are applied with a half-axis key.

- Since voltage is not applied to all non-selected picture elements, writing can be performed only to selected picture elements. Through the above operations, one scanning line is written, and thereafter, writing to the next scanning line is performed sequentially.

When writing to the next scanning line, the previously written data line holds the write voltage, so no charging current flows through that data line. Preliminary charging current flows only to data lines that have not been written to. When the sequential scanning is completed and the field writing is completed, a field refresh pulse is applied via the drive circuit 16 and the diode array 15.

At this time, all transistors SS, .about.SSn on the scanning side 14 are turned off, and all transistors SD, .about.SDm on the data side switching circuit 13 are turned on. The voltage value of the field refresh pulse is equal to the write voltage Vw applied to each scanning line, and is applied with opposite polarity to the thin film EL display device. Therefore, the thin film EL display device has a write voltage of Vw.
and field refresh pulses. When the field refresh pulse is applied, the entire field to which the write voltage is applied is polarized, so the electric field due to this polarization and the field refresh pulse combine to cause write light to be emitted. Furthermore, this field refresh pulse eliminates polarization bias, allowing the writing picture element to emit light when the writing voltage Vw is applied in the next field. By the way, when the above-mentioned double insulation type thin film EL display device is driven with positive and negative symmetrical alternating current driving, voltage-luminance characteristics as shown in FIG. 5 can be obtained.

In Figure 5, the repetition frequency is 25 Z and the pulse width is 100 r.
In the case of symmetrical driving in which the positive and negative voltages are 200 V at sec, the characteristics are shown by the solid curve. Also, the frequency and pulse width should be the same, and the voltage of one polarity should be set to 200
If the polarity is fixed at V and the voltage of the other polarity is varied within 20 degrees for asymmetrical AC driving, the characteristics shown by the dotted line are obtained. In asymmetrical driving, by setting one polarity pulse to a fixed voltage and the other magnetic pulse to a variable voltage, and making the variable voltage below or above the emission threshold, it is possible to select between non-writing and writing emission. .

Therefore, the fixed voltage pulse of one polarity is used as a refresh pulse, the pulse of the other polarity that is higher than the luminous threshold voltage is used as a writing pulse, and the voltage pulse that is lower than the luminous threshold value is used as a non-writing (or half-selection in matrix drive) pulse. It becomes possible to write to any selected picture element during driving. Utilizing the voltage-brightness characteristic of asymmetrical driving, unidirectional writing and non-writing driving is performed during the field, and after the field ends, an inverted refresh pulse causes light to be emitted twice in one field by a writing pulse and an IJ fresh pulse. The brightness can be doubled compared to the previous method. This method is called a field refresh method because selective writing is performed sequentially during the field and after the completion of the field, an inverted refresh pulse of a fixed voltage is applied to all picture elements. Since the driving device of the present invention is configured and operates as described above, each transistor SD, to SDm of the data side switching circuit 13 and the scanning side switching circuit 14
, SS, -SSn are all directions in which current flows from the X or Y electrode of the thin film EL element to the ground point, so all transistors can be constructed by N-channel MOS transistors with their drains connected to ground.

As described above, according to the present invention, it can be manufactured using one type of conductivity type transistor, and it can be integrated into an IC. Furthermore, since the present invention uses a field refresh method of driving, there is no bias in polarization, and since light is emitted twice in one field, the average luminance is effectively doubled.

In the above embodiments, the thin film EL display device has been described as having no hysteresis characteristic in applied voltage and luminance. However, even in a thin film EL display device having hysteresis characteristic, the supply voltage from the drive circuit 11 is changed to the maintenance voltage. ,
If you change the write voltage, erase voltage, halftone write voltage, optical write voltage, or 1/2 of the start voltage, you can select sustain drive mode, write drive mode, erase drive mode, halftone write drive mode, optical write drive mode. , or can be in read drive mode.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a double-insulated thin film EL display device, FIG. 2 is a circuit diagram of a drive circuit according to an embodiment of the present invention, and FIG.
FIG. 4 shows an equivalent circuit diagram explaining the device of the present invention, and FIG. 5 shows a voltage-luminance characteristic diagram. 1 is a thin film EL display device, 11 is a drive circuit, 13 is a data side switching circuit, and 14 is a scanning side switching circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. In a drive circuit for a thin film EL display device in which dielectric layers are provided on both sides of an EL layer, and electrodes are formed in a matrix in directions perpendicular to each other on both surfaces of both dielectric layers, one of the electrodes is used as a scanning line. , the other is connected to the scanning line and the data line, and each of the above lines is selectively turned on and off, and when on, the above lines are connected to a common ground point, and when off, the above ground is connected to the above ground point. It has a switching element of the same conductivity type that opens the connection to the data line, and by supplying voltage to the line and controlling the on/off of each switching element, the potential on the data line side is raised and an arbitrary selected value is reached. A switching circuit is provided to apply a write voltage equal to or higher than a light emission threshold to a line intersection, and the switching circuit is shared, and after one field of sequential scanning is completed, power is supplied to the scanning line side and each switching element of both switching circuits is connected. 1. A driving device for a thin film EL display device, comprising a circuit that applies a refresh pulse voltage having a polarity opposite to the write voltage to all intersection points by on/off control of the EL display device.