JPS6194091A - Thin film electroluminescence driving circuit and method therefor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film electroluminescent drive circuit for a thin film electroluminescent display device and a method for driving the same.

[Prior art and its problems]

Thin film electroluminescent display device (hereinafter referred to as "thin film electroluminescent display device")

It is called a thin film EL display device. ), the AC type with double insulation structure has characteristics such as high reliability and stable operation, and is considered to be a promising device with high potential for commercialization.
Some have already been commercialized.

As a driver for driving such a thin film EL,
A push-pull type drive circuit as shown in FIG. 6 is being studied because it can take advantage of features such as low power consumption and high speed operation. A driving power supply circuit 20 (already proposed in Japanese Patent Application No. 59-156125) that takes advantage of these features and can simplify the driving system and reduce costs is also shown in the same figure.

In the configuration shown in FIG. 6, CIIL corresponds to the light emitting cell of EL. This cell is scanned 1flj y s-
ya.

It is formed at the intersection of the data lines X1 to x3 with an insulating film such as Y2O3 interposed therebetween. These scan lines.

In order to drive the data line, a set meal side drive circuit 21 and a data side drive circuit 22 are provided. On the front side, there is a p-channel high voltage MOSFET (hereinafter referred to as p-MO8'F).

)l'l, P2. P3 and n-channel high voltage MO
SFET (hereinafter referred to as -1;', n-MO8T) N1°N2. N3, respectively scanning line)'t, yz+3
By charging and discharging 'a, a scanning pulse is applied to each cell of the EL. On'/off control of these MO8Ts is performed by a control circuit (not shown).

On the other data side, a circuit for selectively charging and discharging each data line according to the data signal, that is, p-MO8T
P11. PI3. PI3 and n-MO8TNI 1.
N12. N13 and each data line Xl.

N2. Drive N3. These MO8Ts are controlled by a control circuit not shown. Also, these p
, n is obtained from a switching drive power supply circuit 20. This power supply circuit includes a switching n-MO8TN21 connected in cascade to a power supply VD (the power supply voltage is VD), and a power supply VD.
a (Assuming the power supply voltage is Va, VB > VD.)
The switching p-MO8TP21 is connected in cascade to the switching p-MO8TP21.

FIG. 7 shows an operation timing diagram of a conventional EL drive circuit having such a configuration. The operating pulses are shown as a pulse train for performing line-sequential forward movement using gray left driving. During the period (period excluding TR') in which each data line is selectively driven, n-MO8TN21 is set to the on state, and the voltage of VD is supplied to the power supply line A. At this time, p
-MO8'l'P21 is controlled to be in the OFF state, so the power supply VB system is separated from the power supply line A. These controls are performed using n-MO8TN21. p-MO8TP21
The control pulse φ8. applied to the gate of φ8. φ8′(TT
L or MO8 level signal) is carried out.

During this data line drive period, a write operation is performed on each EL cell in a primary manner. First, in period T1, p
- MO8TP1 is turned on, and the amplitude voltage v is applied to the scanning line yl.
Apply 8 write pulses.

- As an example, each p-MO8TpH of the data side drive circuit 22
, P12. P13 is turned on and a non-selection pulse of amplitude V, a is applied to each data line X1. X2. Supply to XB. In this case, each cell of EL ()'1. XI)l Dt+x2
)ICYs+Xa) is not applied with a voltage V[1-VoL which is lower than the threshold voltage for light emission 6-Vt, so these cells do not emit light. Of course, the scanning line)'2
The cell corresponding to 1 ya also has a voltage of VD (Va (Vf<
Since Vli)L is not applied, no light is emitted.

Next, in the period T2, a scan pulse yzK is applied to the scan line yzK in the same manner, and for example, the data line Xl.

A non-selection pulse is applied to x3. In the data line X2,
Since n-MO8TN12 is turned on, no non-selection pulse is applied. At this time, the write pulse ``8'' is applied only to the cell [y2° x2] only emits light at the rising edge of the pulse. Furthermore, in the period TB, as in the period TI, a pulse train is supplied such that only a voltage lower than Vt is applied to any cell, and none of the nine cells emit light. In this case, in the scanning side drive circuit 21, only p-MO8TP3 is turned on. In the other data side drive circuit 22, p-M
O8TP11. PI3. All PI3s are turned on. In this way, writing is performed in a desired cell, and all scanning lines (dotma) (in the case of IJ socks, usually several lines to a sample) are line-sequentially scanned.

Next, the p-MO8TP21 is turned on by the control pulse φ8', and a refresh drive period (Ta') in which the voltage of the power supply line AKVa is supplied begins. In this period, n-
MO8TN21 is set to the off state by control pulse φB. Therefore, the power supply line A will be charged to Va. During a period TR of part of this TB', a refresh pulse is applied to all cells to cause written cells to emit light again. At this time, the electric field due to polarization and the Va Since the sum of the electric fields due to the voltage (>V+) is applied, only the selected cells emit light again.

By doing this, not only can the selected cell be caused to emit light twice within the refresh scan period, but also sufficient light emission can be obtained even if rewriting is performed in the fifth refresh scan period, and the EL cell can be made to emit light continuously. It is possible.

Next, the n-MO8TN21 is turned on again by the control pulse φB, and a period begins in which the data lines are selectively driven. In this case, the following problem arises. In other words, the power line A that was charged to the voltage of ■R during the period of Ta'
The moment the n-MO8TN21 is turned on, the charges are discharged while flowing as a reverse current through the power supply VD. Eventually, the potential of power supply line A becomes Va (200
Discharge is performed until the voltage drops from VD (approximately 50 to 60 V). At this time, 1. Normally, the capacitance loaded on the power supply line A can be suppressed to 0.01μF or less, but since the potential difference is large (140 to 150V), a large current (several hundred mA to I8) is applied to the power supply Vn. Power supplies that can flow such a large reverse current cannot handle large voltages (usually around 30 to 35 V), so
If an attempt is made to construct a power supply VD system having a withstand voltage of about V, the cost will be considerably high. Moreover, since a plurality of power supplies are connected in series, the size of the power supply system becomes large.

In order to eliminate such problems, the AIJ shown in Figure 8
Like the power supply section of the membrane EL drive circuit, another switching 1-M08TN22 is provided from the power line A through the resistor R, and after discharging the electric charge charged in the power line A, the control pulse φ8 is applied. Another possible method is to turn on the power supply VD system by raising the control pulse later than the control pulse φR' (the dotted line portion of the φ8 waveform in FIG. 7).

However, in this case, during this discharge period, from the power supply Vn to n-
Since current flows to the ground potential level via the diode (indicated by a dotted line in the figure) and the resistor in MO8TN21, power loss increases.

In addition, an extra period is required for such a discharging operation, and the circuit configuration becomes complicated.

As described above, the conventional thin film EL drive circuit has the disadvantage that an expensive power source must be used and its size is also large. This is a disadvantageous condition for competing with CRTs, and it impairs the inherent potential for miniaturization and cost reduction.

[Purpose of the invention]

An object of the present invention is to provide a thin film electroluminescence drive circuit and a method for driving the same, which are smaller in size, lower in cost, and lower in power consumption by eliminating such conventional drawbacks.

[Structure of the invention]

The thin film electroluminescence driving circuit of the present invention is a push-pull type thin film electroluminescence driving circuit that has a scanning side driving circuit and a data side driving circuit and sequentially drives scanning lines and data lines of a thin film electroluminescent display device. In the circuit, the drive power supply circuit of the data side drive circuit supplies the first power supply for refresh pulses by turning on a first transistor of one conductivity type connected in cascade to the first power supply. a second power supply having a lower power supply voltage than the first power supply voltage;
By turning on a second transistor of an opposite conductivity type connected to a parallel connection circuit of a power supply and a Zener diode array having a Zener voltage higher than the second power supply voltage, the second transistor is connected to the data side drive circuit. It consists of an OfL connection circuit with a second power supply means that supplies power.

Another aspect of the present invention is a method for driving a thin film electroluminescent drive circuit according to the present invention, wherein the refresh pulse is supplied to all the data lines. During a period in which the first transistor is kept on for a period slightly wider than the width of the sea pulse and the data lines are selectively driven line-sequentially, at the same time as or immediately before the first transistor is turned off. The method includes turning on the second transistor.

[Operation φ principle of the present invention J As described in the above configuration, the thin film EL drive circuit of the present invention uses a conventional power supply for driving the drive power supply circuit of the data side drive circuit for simultaneous KIJ Freche driving of all data lines. A supply means (for example, consisting of a p-MO8T connected in series with the power supply Va) and a conventional power supply means provided for selectively driving the data line (for example, consisting of a p-MO8T connected in series with the power supply VD). In addition to the power supply circuit which is OR-connected with the power supply voltage (V-Vn), a Zener diode array is provided in parallel with the power supply VD to discharge the charge corresponding to the potential of VR-Vn charged in the power supply line, and a large This prevents reverse current from flowing. and.

This discharge constitutes the first power supply means for performing refresh drive, and the second power supply means for selectively driving the data line at the same time or immediately before the p-MO8T is switched from on to off, for example. n- constituting the power supply means of
It is driven to turn on MO8T. The drive power supply circuit constructed in this way is connected to the power supply terminal of the data side drive circuit. In this way, it is possible to realize a thin film EL drive circuit consisting of a data side drive circuit that is inexpensive and has a simple configuration, and a method for driving the thin film EL drive circuit.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of a thin film EL drive circuit and an EL cell showing a first embodiment of the present invention. In this figure, the same numbers or symbols as those in FIG. 6 of the conventional example represent the same components. Further, in the present invention, an example is shown in which a high voltage MO8FET is used as a switching transistor for convenience, but other elements such as a bipolar transistor may be used as long as the functions and operations are the same.

In this embodiment, a push-pull type data side drive circuit 22
a (p-MO8TPI 1. PI 2. PI
3 and n-MO8TN11. N12. Each pair consists of N13. ), which supplies the output of an externally provided switching power supply type driving power supply circuit 20a. In this drive power supply circuit 20a, n-MO8TN2 is used as a second power supply means for selectively supplying a drive pulse (amplitude Vn) corresponding to non-selected data to the data line.
1 and the power supply Vn and power supply VD connected in series to the source part.
Zener diodes ZDI, ZD2. Z
A drive circuit consisting of a Zener diode array having cascade-connected Zener diodes is provided. As this Zener diode string,
Although a configuration in which three devices are connected in cascade is illustrated, the number is not limited to this number. The point is that it is sufficient if the Zener voltage VZ can be set so that the total Zener voltage VZ is slightly higher than the voltage of VD. Normally, Vo is 50 to 60V, so 24V,
It can be constructed by using two or three diodes having a Zener voltage such as 16V. In addition to this second power supply means, a power supply V
p-MOS for switching in series with n (LR>VD, corresponding to the amplitude of the IJ fresh pulse)
TP21 is provided. In this case, the source of p-MO8TP21 and the (G) terminal of power supply VB are connected. The output terminals of these two power supply means, namely n-MO
Connect each drain terminal of 8TN21 and p-MO8TP21 to O.
It is connected to R and is supplied to the power supply line A of the push-pull driver of the data side drive circuit 22a.

Next, the driving method of this embodiment will be explained using the operation timing chart shown in FIG. Line sequential driving in direct drive mode is performed as follows. That is, in the period T1 to T3, the p-MO8TPI of the scanning side drive circuit 21
, P2. While turning on P3 sequentially, the scanning lines Yt,
A scanning pulse is supplied to Y21 ya, p-MO8'l'pH, PI3. PI3 is turned on only when not selected, and data lines X1. X2. X3
Supply driving pulses to.

In the example shown in FIG. 2, since the data line X2 is selected during the period T2, the p-MO8TP12 is not turned on only during this period, and the n-MO8TN12 is set to the on state. In the period (period excluding Ta') in which writing to the selected line system by line sequential driving is performed over all scanning lines, the control pulse φ8 is set at the level of If I If (n-MO8T
Based on the source potential V m n of N21, VDD (
(approximately 5 to 10 V) level), and set the switching voltage to
- MO8TN21 is turned on and power supply VD is connected to power line A.
A voltage of Vo is supplied from At this time, the control pulse φa' of one switching p-MQSTP21 is applied with a pulse having the same potential as the source potential vgp, so this p-MO8TP21 is turned off. Therefore, the power supply line A is supplied with a low voltage power #VD. In addition.

Selection period TI, T2. Ta only n-MO8TN2
A method of driving by turning on 1 is also conceivable.

In period TB' after such line sequential driving ends,
p-MO8TP21 turns on, switch n-M
O8TN21 turns off. This is n-MO8TN
This is because the control pulse φ1 of the p-MO8TP21 is set to the level V an of the source potential, and the control pulse φB' of the p-MO8TP21 is set to a potential level lower than the source potential VIP by VDD. In this case, the power supply line A is supplied with the voltage Va from the power supply Va.

Therefore, within this period of T, /, p-MO8TP11~
If you turn on P13 and turn off all n-MO8TN11 to Nl3, the data lines Xl, x2゜x3
can be supplied with a refresh pulse of amplitude VB. At this time, the period T for turning on p-MO8TP21
From the viewpoint of operational stability, it is preferable to set R' to be slightly longer than the period TR during which refresh pulses are supplied. This is because charging and discharging occurs with the amplitude of the high voltage applied to the power supply line A, so it is necessary to take into account the time margin during switching.

In this way, it becomes fresh - when the driving period ends.

The period for selectively driving the data lines again begins. In other words, the amplitude VDD between the gate and source of n-MO8TN21
When the control pulse φa is applied, n-MO8TN21 is turned on. At this time, VB (~200V) is instantaneously applied to both ends of the Zener diode strings ZI)l~ZD3, which are set to a Zener voltage ■z (■z=VD tens of V) that is slightly larger than VD (50~60V). Since a voltage of V) is applied, the Zener diode string instantaneously causes Zener breakdown, and a current of 1 flows from the cand to the anode. As this Zener diode,
It is sufficient to select an element with a current capacity corresponding to the charge to be discharged. Therefore, the electric charge (
The charge corresponding to the potential of Va) is discharged, and the potential of power supply line A decreases to VZK. In this case, VZ −Vo
o A charge corresponding to the potential difference (several volts) is still charged in the power supply line A, but since the charge storage is small, a slight reverse current flows to the power supply VD and is quickly discharged to the level of VD. . This reverse current flowing through the power supply Vn is so small that it hardly affects the characteristics of the power supply. In order to cause discharge in this manner, if the current capacity is insufficient, a plurality of Zener diode arrays may be arranged in parallel. Furthermore, the discharge current corresponding to the aforementioned potential change from VB to Vz does not flow through the power supply VD, but always flows when the Zener diode causes Zener breakdown. This is because the impedance of the power supply is greater than the impedance of the diode when Zener breakdown occurs.

Due to this operation, the power supply #A is turned on again during the period excluding Ta'.
The potential of is set to the level of VD, and a state is reached where line sequential driving can be performed.

In the above driving method, the refresh driving period T R
When / ends and the data line is selectively driven again, the control pulse φ is raised at the same time as the control pulse φa or just before that (the part shown by the dotted line in the φR waveform in Figure 2). . In this way, most of the charges accumulated in the power supply line A are surely discharged through the Zener diode array.

In addition, when the control pulse is started immediately before the Bk control pulse φn', the Zener current of the Zener diode string also flows through the p-MO8TP21, so the time is extremely short so that the p-MO8TP21 is not destroyed due to the Zener current. It is necessary to set the time, for example, several tens to several hundred n5ec.

According to this embodiment, the switching type driving power supply circuit can be easily configured, so that the EL driving device can be realized compactly and at low cost. This is because Zener diodes can be obtained at low cost, and even if two or three are used, the occupied area hardly increases. Furthermore, unlike the conventional example in which a discharge circuit is added, extra time is not required.

FIG. 3 shows a partial configuration of a thin film EL drive circuit according to a second embodiment of the present invention. In this figure, the same numbers or symbols as in FIG. 1 represent the same components, and other drive systems and EL nacelles have the same configuration as in FIG. 1, so they are omitted. In this embodiment as well, a method of driving the ELs line-sequentially is applied. The driving operation timing chart is exactly the same as that shown in FIG.

In this embodiment, in order to supply the power supply Vm for refresh driving the entire data line, the power supply for supplying refresh pulses is divided into VB-VD and VD, and the power supply of Va-VD is connected in series with the power supply VD. The other configurations are the same as in FIG. 4. In this case, when p-MO8TP21 is turned on, power supply voltage VB is supplied to power supply line A. In this state, p-MO8TP11. PI3. Just like turning on PI3, the refresh pulse is connected to the data line x.
s +X2. Supplied to XB. Conversely, % n-MO8T
If N21 is turned on, the charge corresponding to the potential of Va-Vn will be 2
D1. It is discharged through the Zener diode string Zba in the same manner as the circuit shown in FIG. 1, and the potential of the power supply line A is set to VD. In this embodiment as well, the power source Vo
Since a large reverse current does not flow through the circuit, an ordinary inexpensive power supply can be used. That is, the effect obtained is the same as in the first embodiment.

FIG. 4 shows a partial configuration of a thin film EL drive circuit according to a third embodiment of the present invention. In the drawings, the same numbers or symbols as in FIG. 1 represent the same components. In this embodiment, data f! The second power supply means for selectively driving the switching n-MO
The configuration was such that the power supply VD and the Zener diode arrays ZD1 to ZD3 were connected in series to the drain of the 8T N 21. Furthermore, the configuration was such that the power supply line A can be driven by connecting the (2) terminal of the power supply VD and the cand of the Zener diode ZDI to the drain of the p-MO8TP21 constituting the first power supply means for supplying refresh pulses. In this case as well, the same operation as in the first embodiment is performed.

You can get the same effect.

FIG. 5 shows a partial configuration of a thin film EL drive circuit according to a fourth embodiment of the present invention. In this figure, the same numbers or symbols as in FIG. 1 represent the same components. In this embodiment, the first power supply means for supplying refresh pulses is implemented by connecting the drain of p-MO8TP21 and the ◯ terminal of the power supply VR. and,
The second power supply means for selectively driving the data lines was configured exactly the same as in the third embodiment. Further, these two power supply means are OR-connected to drive the power supply line A. In this case as well, the same operation as in the first embodiment can be performed and the same effects can be obtained.

〔Effect of the invention〕

As described in detail above, according to the present invention, the above configuration eliminates the need to use several expensive power supplies, so the data side drive power supply circuit can be configured compactly, compared to the conventional one. Compared to other devices, this method significantly reduces costs and contributes to making the thin film EL device more compact, including the drive circuit system.Furthermore, by providing a Zener diode array,
A thin-film EL drive circuit and its driving method that enables instantaneous entry into a write operation period that selectively drives data lines, enables higher-speed operation, and is fully compatible with larger EL panels. is obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. FIG. 2 is an operation timing chart, and FIGS. 3 and 4. FIG. 5 shows the second embodiment of the present invention. Third. A partial circuit diagram showing the fourth embodiment, FIG. 6 is a circuit diagram showing an example of a conventional thin film EL drive circuit, FIG. 7 is an operation timing diagram thereof, and FIG.
The figure is a partial circuit diagram of another example of a conventional thin film BL drive circuit. 20.20a... Drive power supply circuit, 21...
...Scanning side drive circuit, 22, 22a...Data side drive circuit, A...Power supply line, Cl8t,...
...Cell, Nl-N3°Nl 1-Nl 3. N
21. N22-...n channel MO8)
P1-P3. pH, PI3゜P21... p channel MO8) transistor ThV"1Va... power supply, Xl-X3... data line, yl~y3...
...Boss line, ZDI~ZD3... Zener diode, φ8. φB′...Control pulse, 几...Resistance. 4 pa 1゛・ , °1. ..., Agent Patent Attorney Susumu Uchihara', ,', Ippa / Figure 3, Figure 4, Figure 5, Figure 7, Figure 7, Figure a.

Claims (2)

[Claims] (1) In a push-pull type thin film electroluminescent drive circuit that has a scanning side drive circuit and a data side drive circuit and sequentially drives scanning lines and data lines of a thin film electroluminescent display device, the data side drive circuit a first power supply means for supplying the first power supply for a refresh pulse by turning on a transistor of one conductivity type connected in cascade to the first power supply; By turning on a transistor of an opposite conductivity type connected to a parallel connection circuit of a second power supply having a power supply voltage lower than the power supply voltage and a Zener diode string having a Zener voltage higher than the second power supply voltage. a second power supply supplying the second power supply to the data side drive circuit;
A thin film electroluminescence drive circuit comprising an OR connection circuit with a power supply means. (2) In a push-pull type thin film electroluminescent drive circuit that has a scanning side drive circuit and a data side drive circuit and sequentially drives scanning lines and data lines of a thin film electroluminescent display device, the data side drive circuit a first power supply means for supplying the first power source for a refresh pulse by turning on a first transistor of one conductivity type connected in cascade to the first power source; a second transistor of an opposite conductivity type connected to a parallel connection circuit of a second power supply having a power supply voltage lower than the first power supply voltage and a Zener diode string having a Zener voltage higher than the second power supply voltage; A driving method for a thin film electroluminescence driving circuit comprising an OR connection circuit with a second power supply means for supplying the second power to the data side driving circuit by turning on the data side driving circuit, the method comprising: During the period for supplying data to the data lines, the first transistor is kept on for a period slightly wider than the width of the refresh pulse, and during the period for selectively driving the data lines line-sequentially, the first transistor remains on. A method for driving a thin film electroluminescence driving circuit, comprising: turning on the second transistor at the same time as or immediately before turning off the second transistor.