JPS6010635B2 - Drive device for thin film EL display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to reconfiguring the drive of a double-insulated thin film EL display device.

The present invention is based on a double insulated thin film L having a matrix electrode.
When displaying characters, symbols, patterns, etc. on a display device, the present invention provides a circuit in which a circuit for applying a display voltage to the matrix electrode can be composed of a single type of switching element such as an N-channel MOS or an NPN transistor. .

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 EL display device that can be configured with a small number of switching elements.
Furthermore, the present invention was developed by the inventor of the present invention in Tsubaki Gansho No. 51-92571 (
``Driving device for thin film L display device'' filed on July 30, 1975 (see Mochiseki 1703 Mountain Gazette) and Tokubuta 52-11363 filed on February 10, 1978.
No. 2 “Drive device for thin film EL display device” (Japanese Patent Application Laid-Open No. 53-9
9789), and provides a circuit that reduces the influence of the discharge time constant due to the wiring stray capacitance of the scanning line and the off-impedance of the switching element of the scanning line.

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

As shown in FIG. 1, a strip-shaped transparent electrode 2 made of Y2 is provided in parallel on a glass substrate 1.
EL layer 4 made of ZnS doped with an activator such as Mh, Y20 as above.
3. A mysterious electric material layer 5 of Si3N4 is sequentially laminated to a thickness of 500 to 10,000 A using a thin film technique such as vapor deposition or sputtering to form a three-layer structure, and a layer 5 of a mysterious electric material layer 5 of Si3N4 is layered on top of the layer in a direction perpendicular to the transparent electrode 2. A strip-shaped back electrode 6 made of A〆203 is provided in parallel.

In the double insulation type thin film EL display bag with 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 patterns. Therefore, characters, symbols, etc. are displayed by selectively scanning these picture elements one by one, or by simultaneously driving all the selected picture elements. This thin film EL display device has superior properties compared to conventional dispersion type EL devices in that it emits light with high brightness, has a long life, and is stable. The above thin film EL element is 150V
It does not emit light unless a relatively high voltage of about ~300V is applied, and in order to apply the high voltage to a specific point selected from the two orthogonal electrodes, one electrode is connected to a high voltage power supply circuit. The other electrode requires a high voltage switching element connected to the ground potential. 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, NPN transistor and PNP transistor,
Alternatively, they are an N-channel MOS transistor and a P-channel MOS transistor. The number of switching elements required is the same as the number of electrodes of the thin film EL display device. However, currently high voltage monolithic PNP and NPN (
It is extremely difficult to integrate P-channel and N-channel MOS transistors into ICs, and research is currently underway. In view of the above points, the present invention has relatively high feasibility,
The above-mentioned prior invention describes a circuit that uses a high-voltage monolithic N-channel MOS or NPN transistor and can be integrated into an IC.

FIG. 2 shows a circuit diagram of the drive device invented by Sendo, and FIG. 3 shows a time chart. In FIG. 2, IC indicates the above-mentioned EL display device, and in this figure, the electrodes X in the x direction,
~Xm is a data-side electrode, Y-direction main poles Y and ~Yn are scan-side electrodes, and only the electrodes are shown.

Reference numeral 11 denotes a drive circuit that applies 1/2 write voltage (1/2 Vw) to the common line A.

Reference numeral 12 denotes a diode array on the data side, which functions to isolate the data side drive line and protect reverse bias of a switching element made of a high voltage transistor, which will be described later.

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

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

Reference numeral 15 denotes a drive circuit that applies a write voltage of 1'2 (1/2 Vw) to the common line B.

Reference numeral 16 denotes a scanning-side diode array for separating scanning-side drive lines and protecting switching elements from reverse bias.

17 applies a field refresh pulse to the entire surface of the thin film EL display device at the end of one field scan;
This is a drive circuit that supplies a field refresh pulse to the drive line 8.

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

First, as a first step, the scanning side switching element circuit 14
A high level signal is supplied to the gates of all MOS transistors SS, -SSn constituting the MOS transistors to turn them on. At this time, all transistors SD, -SDm of the switching element circuit 14 on the data side are turned off.
Then, a signal is supplied to the input terminal S, of the write drive circuit 12, the switching transistors T, T2 are turned on, and 1/2 write voltage (1/2 Vw) is applied to the common line A. Therefore, from all the data lines (X, to Xm), a voltage of 1/2 Vw is charged to all Ema points constituting the thin film EL display device. That is, in a thin film EL display device, dielectric layers 3 and 5 are formed on both sides of an EL layer 4, and electrodes 2 and 6 are provided on both sides, so the thin film EL display device can be viewed as a capacitive element, and each The above voltage is charged to the capacitive component of the picture element. In the next second stage, the transistor SDi of the data side selection line Xi including the write picture elements i, i is turned off, and the transistor SDk i of the non-selection line Xk i is turned on.

Then, on the scanning side, all transistors SS, -n of all scanning lines Y, -n are turned off. At this time, a signal is applied to the terminal S, and 1/2 Vw is applied to the common line A. At the same time, a signal is applied to the terminal S2, and the half write voltage 1/2 Vw is applied to the common line B. Therefore, by this operation, the data line Xi including the write picture elements i and j becomes the voltage 1/
2Vw is maintained, but it is released through the charge transistor SDki of the unselected data line Xki. At this time, the voltage 1/2Vw is applied to the common line B, and all the transistors SSo~n of all the scanning lines Y,~n are off, so the drive wiring capacitance Cs of the non-scanning line Y and i is 1/2
Vw charging is performed. In the third stage, all the transistors SD, -m of the data side switching circuit 13 are turned off, and the transistor SSi of the selected scanning line of the scanning side switching circuit 14 is turned on. In this state, in order to apply the voltage 1'2Vw to the common line A again, the input terminal S
, and turns on the transistors T, , and L.
When this voltage is applied, the write picture elements i and j have been previously charged with a voltage 1/2 Vw, and this voltage is raised in parallel with the voltage 1/2 Vw applied in the third stage. At this time, the unselected data line
Follows the raised voltage 1/2Vw in stages. In the end, the writing voltage Vw is applied to the writing picture *i, j and they emit light, but the half-selected picture element i, y, located at the intersection of the selected data line Xi and the non-selected scanning line Y, and the non-selected data line X
Half-selected picture element k,j at the intersection of k principal i and selected scanning line
A voltage 1/2 Vw is applied to the thin film EL.
The voltage is below the display device's threshold voltage, and no writing or erasing operations are performed. Furthermore, the same applies to the unselected picture element k located between the unselected data line and the unselected scan line. During this operation, since the stray capacitance Cs is charged in advance, the stray capacitance Cs becomes the total capacitance of the non-written picture elements {(m
-P)Ce}, there is no restriction that it must be much smaller than 4. Therefore, even if the number of written picture elements becomes very large, a predetermined write voltage Vw is applied to all selected picture elements and they emit light with a predetermined brightness. do. Finally all transistors S
D, ~m, SS, ~n are turned off and return to their initial state.

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

FIG. 4 shows before the third stage write operation is started, that is, the transistor SSi of the selected scanning line Yj is turned on, the other transistors SS Somij are turned off, and the voltage 1/2 Vw is applied to the common line A. A simplified equivalent circuit immediately before is applied.

In this diagram, each magazine issue 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 the data line containing the writing picture element: Gourd (reverse bias) All diodes connected to the data line not containing the writing picture element: Dn (forward bias) C,: Non-selected picture element ( The sum of all capacitances (pixels that are not selected from either the data side or the scanning side) (k, so), C, = (n
-1) (m-p)CeC2: Capacitance sum of half-selected picture elements (picture elements selected only from the data line side) (i, so) C2=
p(n-1)Ce C3: Sum of capacitances of selected picture elements (i, i) C3=PCe C4: Sum of capacitances of half-selected picture elements (picture elements selected only from the scanning line side) (k, i) C4 = (m-p)Ce C5: Sum of stray capacitances of scanning line wiring C5 = (n-)CS C6: Sum of stray capacitances of data side wiring including write picture element (i, i) in data side line C6 =PCd R,: Total off-impedance R of all switching elements on the scanning side, =nR.

R.

is the off-impedance R2 of one switching element: the off-impedance R2 of the total switching elements of the selected data line = PR.

C,o: Total stray capacitance of the selected line among the data lines, C,.

=PCd At this time, the potential at point a is 1'2Vw, the potential at point b is Vw, and the potentials at points C and d are 1/2Vw.

In the next third step, the transistor SSj of the selected scan line Yj is turned on, and the other transistors SSj are turned off.
When all the transistors SD, -SDm on the data side are turned off and 1/2 Vw is applied to the common line A, the voltage Vs at point a in FIG. 4 is.

Also, the voltage Vd at point b is from the energy conservation side2 (science)
2,000 (C20C30C6) (Vd-VS)2[1}.

Here (m-1)Ce》Cs '3
}(n-1)Ce》Cd '4}, then C,》C5,C2》C3,C6,'
1', VS equation, Vd=VW '51.

In this way, as long as the condition '41' is satisfied, the write voltage Vw is applied to all the selected write picture elements C3.

, the half-select voltage of all the half-selected picture elements C2 and C is applied, and no voltage is applied to all the non-selected picture elements.
It is possible to write only to selected picture elements. Note that in the above circuit configuration and operation, the stray capacitance Cs of the scanning line is charged in advance before the third stage write voltage is applied.
There is no limit to one set, and therefore, even if the number of picture elements to be written is very large, a predetermined write voltage Vw is applied to all selected picture elements, and they emit light uniformly at a predetermined brightness.

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. Then, when the sequential scanning ends and the writing of the field ends, a field refresh pulse is applied via the drive circuit 15 and the diode array 16.

At this time, all transistors SS, ~SSn of the scanning side switching circuit 14 are turned off, and the data side switching circuit 13
All transistors SD, ~SDm of 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 is AC driven using the write voltage Vw and the field refresh pulse. When the field refresh pulse is applied, the picture element 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 only the write picture element to emit light. In addition, this field refresh pulse eliminates polarization bias, and the write voltage Vw is increased in the next field.
This allows the written pixels to emit light when added. By the way, the invention of the prior application charges the stray capacitance Cs of the scanning side drive wiring to a voltage of 1/2 Vw in the second step, and then charges the charging voltage of this stray capacitance Cs of 1/2 Vw to the writing picture element in the next third step. Although the write voltage Vw is applied, this charging voltage is discharged during the period of transition from the second stage to the third stage. The discharge circuit at this time is a circuit that passes through the off-chip pedance of the switching element of the scanning side switching circuit 14, and its time constant kemato=RoCs. Therefore, the time T for moving from the second stage to the third stage is sufficiently shorter than the time constant time to, otherwise there is no point in charging the stray capacitance. For example, T《2. Ball oCs (1
(discharge time constant of 0% to 90%) must be met. Normal, Ro three plates MQ, Cs Ni l OAF, T<1
Since the value is 0 Sec, the above condition is satisfied and no problem occurs.

However, in order to more completely eliminate the occurrence of the above problem, the present invention substantially increases the above stray capacitance Cs.

FIG. 5 shows a driving circuit according to an embodiment of the present invention, and this circuit is constructed by connecting external capacitors Ch to the electrodes or lead wires of all scanning lines Y, -Yn of a thin film EL display device.

Since the other parts are the same as those in FIG. 2, the same reference numerals are given and the explanation will be omitted. According to this circuit, when the stray capacitance Cs of the scanning lines Y to Yn is charged in the second stage, the external capacitor Ch is also charged at the same time. Therefore, the time constant bo, becomes t = Ro (Cs + CO.), and the time constant becomes large, making it easier to satisfy the problem of the present invention, which is the condition that the time T is sufficiently shorter than the time constant tm. . Other than that, the operation is the same as above.

FIG. 6 shows another embodiment of the present invention, in which capacitors Ce are inserted between the scanning lines Y, -Yn and the drive circuit 16 via a common line C, respectively.

This group of capacitors is represented by block 18. This capacitor Ce is not connected to an external capacitor, but is a capacitor formed at the end of the thin film EL display device by a part of the X-direction electrode and the Y-direction electrode. The common line C is grounded via a transistor circuit 19 whose on/off is controlled by a signal input to a terminal S4. Other configurations are the same as in FIG. 2. A time chart of this circuit is shown in FIG.
In FIG. 7, SSi-, is the previous scanning line, SS
i is the current scanning line, SSj is each signal waveform of the next scanning line, S, ~S4 is each signal waveform of terminal S, ~S4, (SD)s is the waveform of the selected data line, (S
D) n is the waveform of the unselected data line, Ds is the applied signal waveform of the selected data line when scanning the scanning line Yi, and Dn is the unselected data line when scanning the scanning line Yi. The applied signal waveform, Yi-, is the waveform of the previous scanning line, Yj is the waveform of the current scanning line, Yj+, is the waveform of the next scanning line, and Yj is the intersection of the selected data line Xi and the scanning line Yi. The voltage waveforms applied to the picture elements, Dn and Yi are the unselected data lines Xk main i
and the voltage waveform applied to the picture element at the intersection of scanning line Yi, Ds
, Y is the voltage waveform Dn applied to the picture element at the intersection of the selected data line Xi and the non-scanning line Y soj, and Y soj is the voltage waveform Dn of the voltage waveform Dn applied to the picture element at the intersection of the selected data line Xi and the non-scanning line Y soj. It shows the voltage waveform applied to the picture element at the point. FR indicates a field refresh pulse. The time chart in Fig. 7 is essentially the same as Fig. 3, and in this figure, the voltage waveform applied to the picture elements differs depending on the state of the previous scan line, and each written and non-written picture element in the next scan line is This indicates that the voltage waveform is different due to the influence on the state of

Since the driving device of the present invention is configured and operates as described above, each transistor SD, ~SDm, 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. Further, according to the present invention, a circuit that compensates for the influence of stray capacitance can be obtained, and more stable operation can be achieved.

Note that in the above embodiment, the thin film EL display device has been described as having no characteristics in applied voltage and luminance, but even in a thin film EL display device having hysteresis characteristics, the output voltage from the drive circuit 11 is changed to the sustaining voltage, If the write voltage, erase voltage, halftone write voltage, optical write voltage, or set voltage is changed to 1/2, the sustain drive mode, write drive mode, erase drive mode, halftone write drive mode,
An optical write drive mode or a write drive mode can be used.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a double insulation type thin film EL display device, Fig. 2 is a circuit diagram of a driving device of the prior invention, Fig. 3 is a time chart explaining the operation of the device of Fig. 2, and Fig. 4 5 is an equivalent circuit diagram for explaining the operation, FIG. 5 is a circuit diagram of a driving device according to an embodiment of the present invention, FIG. 6 is a circuit diagram of another embodiment of the device of the present invention, and FIG. 3 is a time chart of the circuit shown in the figure. 10 is a thin film EL display device, 11 is a drive circuit, 13 is a data side switching circuit, 14 is a scanning side switching circuit, 15 is a drive circuit, 16 is a scanning side diode array, C
h and Ce are capacitors. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

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. , and a capacitor connected to the scanning line, with the other being the data line, and a capacitor connected to the scanning line and the data line, which is selectively turned on and off for each line, and when turned on, connects the line to a common ground point. , has a switching element of the same conductivity type that opens the connection to the ground point when off, and by supplying voltage to the line and controlling on/off of each switching element, any selected line intersection point A switching circuit is provided to apply a write voltage equal to or higher than the light emission threshold to the data line, and the switching circuit pre-charges all the intersection points by supplying voltage to the data line and controlling on/off of each of the switching elements. and a charge discharging process of the non-selected data line, and when the charge of the non-selected data line is discharged, the scanning line is turned off by supplying voltage to the scanning line side and controlling off all switching elements of the scanning side switching circuit. A driving device for a thin film EL display device, comprising a circuit for pre-charging the stray capacitance and the capacitor to a voltage below a light emission threshold.