JPS6334592A - Drive circuit for thin film el display device - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a drive circuit for an AC driven capacitive flat matrix display panel, that is, a thin film EL display device.

<Prior Art> For example, a double insulation type (or three-layer structure) thin film EL display device is configured as follows.

As shown in FIG.
A band-shaped transparent electrode 2 made of 3 is provided in parallel, and on top of this a dielectric material layer 3 such as Y2O3, Si3N4, TlO2, At203, etc., an EL layer 4 made of ZnS doped with an activator such as Mn, the same as above. Y203, Si3N4
, TiO2, Az2o3, etc., using a thin film technique such as vapor deposition or sputtering.
They are laminated to a thickness of 0 to +ooooX to form a three-layer structure, and a strip-shaped back electrode 5 made of At203 is provided in parallel thereon in a direction orthogonal to the transparent electrode 2.

The thin film EL element has a dielectric material 3,
Since the EL material 4 sandwiched between the ends 3' is interposed, it can be seen as a capacitive element in terms of an equivalent circuit. Further, as is clear from the voltage-luminance characteristics shown in FIG. 5, the thin film EL element is driven by applying a relatively high voltage of about 200V.

This thin film EL element emits high-intensity light when exposed to an alternating current electric field, and has a long lifespan.

Conventionally, for such a thin film EL display device, a diode for charging the modulation voltage VM and a switching circuit for discharging it to 0V are connected to each electrode on the data side, and an NchMOS driver and a Pch as a drive circuit for the scanning side electrode are connected.
A drive circuit that is equipped with a MOS driver, performs field inversion drive, and also inverts the polarity of the write waveform applied to the picture element for each scanning line.

Alternatively, in response to an increase in the number of scan-side electrodes, a Pch charging modulation voltage VM to the EL layer in each data-side electrode may be used.
A drive circuit has been proposed that connects a high voltage MOS driver and an Nch high voltage MOS driver that discharges to Ov, thereby charging and discharging a modulated voltage on the data side electrode at once according to display data during write driving.

<Problems to be solved by the invention> However, these proposals required two or more driver ICs (Nch high voltage MOS driver IC, Pch high voltage MOS driver IC, etc.) for one line of scanning electrodes. . In addition, in order to apply positive and negative high voltage pulses to the scanning side electrode, it is necessary to float each control signal of the Nch high voltage MOS driver and the Pch high voltage MOS driver. Therefore, isolators for each control signal and floating A power supply (interface circuit for driver control signals) was required. Therefore, it has been difficult to make the EL drive device thinner, more compact, and lower in cost.

Furthermore, since the entire display device is charged from the data side to the scanning side by changing the modulation voltage VM, approximately 7% of the total drive power is charged.
For an EL display device, which consumes a large amount of modulation power, the modulation power consumption becomes extremely large, making it unsuitable for increasing the display capacity due to an increase in the number of scanning lines and data lines.

The present invention has been made in view of these circumstances, and allows for thinner, more compact and lower costs.
An object of the present invention is to provide a drive circuit that can significantly reduce power consumption during modulation.

Means for Solving the Problems> The present invention provides a thin film EL structure in which EL layers are interposed between scanning side electrodes and data side electrodes arranged in directions crossing each other.
In the display device, the first and second switching circuits, which will be described later, have a push-pull function and include a high-voltage driver IC controlled by a logic circuit such as a single-potential shift register and a gate. A first switching circuit that applies a negative polarity voltage and a positive polarity voltage to the data side electrode is connected to each of the side electrodes, and a common line for pull-down of the high voltage driver IC in the first switching circuit is connected to the data side electrode. A third switching circuit that switches between the negative polarity write voltage, '/2 modulation voltage and Ov is connected, and the positive polarity write voltage and 1/2 are connected to the pull-up common line.
A fourth switching circuit for switching to a modulation voltage is connected, and a second switching circuit for charging and discharging a modulation voltage to the EL layer corresponding to the scanning side electrode is connected to each of the data side electrodes. A common line for pull-down of the high voltage driver IC in the second switching circuit is connected to 0V, and a fifth switching circuit for switching the common line to a floating level and a 1/2 modulation voltage is connected to the common line for the pull amplifier. Third. 4th. A driving circuit for a thin film EL display device, characterized in that a sixth switching circuit that divides a 1/2 modulated voltage and supplies it in stages is connected to a switching circuit that supplies a fifth false modulated voltage. .

As described above, since a high-voltage driver IC with a push-pull function is used, the interface circuit for the control signal input to the scanning side driver can be simplified, and the modulation power consumption can be significantly reduced.

<Examples> The present invention will be described in detail below based on examples shown in the drawings. Note that this invention is not limited to this.

FIG. 1 is a configuration diagram of a drive circuit showing an embodiment of the present invention.

10 is the emission threshold voltage Vth (Vw-'/2VM <
A thin film EL display device with Vth < Vw + '/2 VM) is shown, and in this figure, only the electrodes are shown, with the X-direction electrode being the data-side electrode and the Y-direction electrode being the scanning-side electrode.

Reference numerals 20 and 30 designate scan-side high-voltage push-pull type driver ICs (corresponding to the first switching circuit) corresponding to the odd lines and even lines of the Y-direction electrodes, respectively. 21
．． 31 is a logic circuit such as a shift register in each scanning side driver IC 20, 30, and 5 can data,
A state in which a pull-up or pull-down element is turned on in response to 5-can data in a shift register by a control signal such as PUP or PDW, and all pull-up or pull-down elements are turned on regardless of 5-can data.
o40, which creates a state of
1 is a logic circuit such as a shift register in the data side driver IC 40. An example of the configuration of the high voltage push-pull type driver shown in FIG. 2(,) is shown in FIG. 2(b). In FIG. 2(b), 501 is a Pc for pull-up.
h High voltage MO5FET, 502 is Nch for pull-down
High-voltage MO9FETs 503 and 504 are diodes that allow current to flow in the opposite direction to each FET. 5
01 and 502 are turned on and off by a circuit such as a level shifter according to input data. This high-voltage push-pull type driver can be used as long as it is composed of a switching element with a pull-up function and a switching element with a pull-down function.

100 is a circuit that switches the pull-down common line potential of the scanning side driver 20.30 (corresponds to the third switching circuit)
and control signals NVC, NGC.

Negative write voltage by NM8 -Vw + '/2
Switch S to switch between VM and modulation voltage 1/2vM and 0V
W.I.

SW2. It is composed of SW3.

200 is a circuit (corresponding to the fourth switching circuit) that switches the pull-up common line potential of the scanning side driver 20.30, and the positive polarity write voltage VW + 1/2 V M and Switch SW4 to change the modulation voltage to '/2 V M . SW
It is composed of 5.

300 is a circuit (corresponding to the fifth switching circuit) for switching the pull-up common line potential of the data side driver 40, and is composed of a switch SW6 that is switched to a modulation voltage '/2 V M and a floating state by a control signal M+.

400 is a switch 5W8iONL by control signal MDW
, by charging the capacitor CM with the modulation voltage '/4VM, and then turning switch SW8 to 0FFL and turning on the switch SWT with the control signal MUP, after applying the modulation voltage of '/4 VM, the modulation of '/2 VM is performed. This is a circuit that supplies voltage (corresponding to the sixth switching circuit), and is a circuit that supplies voltage
, NM2. Switch SW3. controlled by PM2. S
W5. Connected to SW6.

500 is a data inversion control circuit.

Next, the operation shown in FIG. 1 will be explained using the time chart shown in FIG. do.

In addition, this driving device is driven by reversing the polarity of the write voltage applied to the picture elements every l line, but the high voltage driver ICs 20 and 3 connected to the scanning side selection electrodes
The drive timing for one line in which the pull-down MO8FET of 0 is turned ON and a negative write pulse is applied to the picture elements on that electrode line is called the N drive timing. The drive timing for one line in which a positive write pulse is applied to the picture elements will be referred to as the P drive timing.

Also, a field (screen) in which N driving is performed for odd lines on the scanning side and P driving is performed for even lines is called an NP field, and the opposite field is called a PN field.

(A) All drivers SD on the NP field scanning side, Nch of 1 to 5Dri
By turning on the MOSFET and turning on the switch SW2 using the control signal NGC, all electrodes on the scanning side are maintained at 0V. At the same time, switch SW6 is turned on by control signal M1.
let At this time, the data side drivers DDrl~DD
, i is Pch MO when emitting light according to the display data signal
Turn on the SFET, and if it does not emit light, turn on the Nch MOSF
Turn on ET. If the display data signal is "H" to emit light and "L" to not emit light, the input display data signal (D
Since it is necessary to input the data (ATA) as is to the driver IC 40, the signal RVC in the data inversion control circuit 500 is set to "L". (However, Driver I
Pch MOSFET is ON at Ci″H”, Nch
MOSFET is OFF, Pch MOSFE is set to “L”
Assume that T is OFF and the Nch MOSFET is ON. Furthermore, since line sequential driving is performed, display data is transferred during the previous line driving and is held by a latch. ) Here, a modulation voltage of '/4 VM is applied to the light-emitting picture element, and the switch SW8 is set to 0NIC using the control signal MDWK to set the capacitor CM to '/4 V.
Charge the modulation voltage of M. Next, after the switch SW8 is turned off by the control signal MDWK:, the switch SW7 is turned on by the control signal MUP, and a modulation voltage of '/2VM is applied to the light emitting picture element. As a result, only the light-emitting picture elements are charged with the first modulation voltage '/2VM on the data side in stages, the non-light-emitting picture elements are not charged, and the data side electrode potential is maintained at 0V. When charging is completed, switch SW6. SW7 is O
Make it FF.

Only the driver connected to the selected scan electrode is NchMO8FE
Turn T ON, and other scanning side drivers are Pch MO
Turn on SFET. All scanning side driver ICs at the same time
Switch SW5 is turned on by control signal 2 and a modulation voltage of '/4VM is applied to the pull-up common line of 20 and 30, and then SW7 is turned on by control signal MUP.
By doing so, a modulation voltage of '/2VM is applied.

In addition, for pull-down common line cleaning, the switch SWI is turned on by the control signal NVC, and the negative polarity write voltage -Vw
+”/2 V pa. On the other hand, the data side driver 40 applies the first modulated voltage charging period (
TNI) continues to be driven.

As a result, since the light-emitting picture element is charged with a modulation voltage of '/2VM on the data side during the first modulation voltage charging period (TNI) in N drive, the data side electrode potential becomes VM, and the selected scanning side electrode is the negative polarity write voltage −VW +
Since 1/2 VM is applied, VM-
(-Vw+'/2VM)=VW+'/2VM is applied and light is emitted.

In addition, the data side electrode potential of the non-light-emitting picture element is 0■, and the negative polarity write voltage -vw+]72 is applied to the selected scanning side electrode.
Since 7M is applied, HaOV − is applied to the non-luminescent picture element.
(-Vw+'/2VM)=Vw-'/2VM is applied, but no light is emitted because it is below the light emission threshold voltage Vth.

Control signal NVC, PM! L, switch SW from MUPK
I, SW5. After turning off SW7, control signal NGC
The switch S W 2 is turned on, and at the same time, the Nch MOSFETs of all the scanning side drivers are turned on. As a result, the write voltage and the second modulation voltage are discharged,
All scan electrodes are at 0V.

All drivers on the scanning side 5Drl~SD, N of i
By turning on the ch MOSFET and turning on the switch SW2 by the control signal NGC, the potential of all scanning side electrodes is kept at 0V. At the same time, the control signal Ml turns on the switch SW6. At this time, the data side drivers DD rl-DD ri turn on the Nch MOSFET in the case of light emission and turn on the Pch MOSFET in the case of non-light emission according to the inverted signal of the display data signal.

Here, since it is necessary to input the inverted signal of the input display data signal (DATA) to the driver IC 40, the signal RVC in the data inversion control circuit 500 is 'H#
Keep it. In addition, a modulation voltage of '/LVM is applied to the non-light-emitting picture element, and the switch s is controlled by the control signal MDW.
Turn on ws and charge the capacitor CM with a modulation voltage of '/4VM. Next, the switch SW is controlled by the control signal MDW.
After turning off the switch S, the control signal MUP turns off the switch S.
Turn on W7 to apply a modulation voltage of '/2VM to the non-light-emitting picture element. At this time, the light emitting picture element is not charged and the data side electrode potential becomes 0V. As a result, only the non-light-emitting picture elements are charged with the modulation voltage '/2VM on the data side in stages. When charging is completed, switch SW6. Turn SW7 OFF.

Only the driver connected to the selected scan electrode is PchMO3FE
Turn on T, other scanning side drivers are Nch MOS
Turn on the FET. At the same time, all drivers IC2 on the scanning side
A positive write voltage V is applied to the pull-up common line of 0 and 30 by turning on the switch SW4 using the control signal PVC.
Apply W + 1/2 VM. In addition, a control signal NM♂ turns on the switch SW4 on the pull-down common line.
Then, a modulation voltage of 1/4 VM is applied, and then a modulation voltage of '/2 VM is applied stepwise by turning on the switch SW8 in accordance with the control signal MUP. On the other hand, the data side driver 40 continues driving during the first modulated voltage charging period (TP + ) in P drive.

As a result, the positive polarity write voltage Vw + '/2 VM is applied to the selected scan electrode of the light-emitting picture element, and since the data side electrode potential is OV, the light-emitting picture element has ("W" I
/2vM) OV = VW + l/2 VM is applied and light is emitted. In addition, the non-emissive picture element is on the data side during the first modulation voltage charging period (Tpl) in P drive.
Since the modulation voltage of is charged, the data side electrode potential becomes VM, and the positive polarity write voltage vw+1//2vM is applied to the selected scanning side electrode, so the non-light emitting pixel has (Vw + ' /2VM) -VM =VW-1/
Although 2VM is applied, no light is emitted because the voltage is below the light emission threshold voltage Vth.

Switch SW by control signals NM-&, PVC, MUP
3. SW4. After turning off SW7, the switch SW2 is turned on by the control signal NGC, and at the same time, the Nch MOSFETs of all the scanning side drivers are turned on. As a result, the write voltage and the second modulation voltage are discharged, and all scan electrodes become Ov.

(B) First modulated voltage charging period in PN field NP field P drive (
The same driving as Tp + ) is performed.

Driving similar to the second modulation voltage charging and writing period (TP2) in NP field P driving is performed.

Driving similar to the discharge period (Tpa) in NP field P driving is performed.

First modulation voltage charging period in NP field N drive (
TNI).

Driving similar to the second modulated voltage charging and writing period (TN2) in NP field N driving is performed.

Driving similar to the discharge period (TN3) in NP field N driving is performed.

As mentioned above, in this drive circuit, the NP field and PN field
Consists of field drive timing, NP
In the field, N for the odd numbered selection line on the scanning side.
Executing P driving for even-numbered selection lines;
In the PN field, driving is performed in the opposite direction to close off the alternating current pulses necessary for light emission to all picture elements of the thin film EL display device. FIG. 5 shows the voltage waveforms applied to the picture element B as a representative example.

By the way, in the case of a conventional drive circuit, in N drive, the light-emitting picture element is charged with VM, and the non-light-emitting picture element is not charged. In P drive, the light-emitting pixels are not charged, but the non-light-emitting pixels are charged with VM, so the modulation power consumption does not change for light-emitting and non-light-emitting pixels. The average modulation power consumption is (N
Power consumption in P drive (power consumption in P drive) total 2 = (CV
M”+O)+2=1/2CVM.

On the other hand, with this drive circuit, both light-emitting and non-light-emitting pixels are charged by '/2 VM in N drive, and '/2 VM is charged in both light-emitting and non-light-emitting pixels in P drive, so 1 in full light emitting state. The average modulation power consumption during line drive is (
Power consumption in N drive + Power consumption in P drive) Total 2 =
(C(”/2VM)2+C(/2VM)21+2=
'/4CVM.

In this way, this drive circuit reduces the modulation power consumption by l//2 compared to the conventional drive circuit. Furthermore, by applying l//2 modulation voltage in two stages, V4
reduced. Therefore, h is reduced as a whole.

In addition, the scanning side driver ICs 20 and 30 are (VW+'/2VM) -1/2VM=VW, P during N drive.
Even when driving '/2VM (VW+ 1/2VM) = V
W (7) A withstand voltage is required, but the voltage applied to the light-emitting picture element at this time is Vw +'/2 VM, so the voltage that can be applied to the light-emitting picture element is the scanning side driver IC breakdown voltage +'/ Since it is possible to apply up to 2 VM, it can be applied to ICs with low breakdown voltages or thin film EL display devices with high emission threshold voltages.

Furthermore, in this drive circuit, the pull-up and pull-down of the output stage driver is controlled by a single shift register and driver control signal, but in the conventional drive circuit, a shift register for pull-up control and a control signal, A shift register and a control signal for pull-down control are required, and both control signals must be floated in order to apply positive and negative high voltage pulses to the scan electrodes. However, with a push-pull type high-voltage driver, the floating control signal is halved compared to the conventional one, which reduces the number of driver control signal interface circuits and contributes to cost reduction.

Furthermore, while conventional drive circuits require two or more high-voltage drivers per line of scanning electrodes, push-pull type high-voltage drivers require only one, which significantly reduces costs and makes the device thinner and more compact.

<Effects of the Invention> As described above, according to the present invention, most of the drive power (approximately 7
Since the modulation power consumption, which accounts for 20% of the total power consumption, can be significantly reduced compared to conventional driving, the power consumption of the entire device can be significantly reduced. Furthermore, by using a high-voltage driver that has both pull-up and pull-down functions, the interface circuit for control signals input to the scanning side driver is simplified, and the driver cost per scanning electrode I line is reduced. Overall, it is possible to significantly reduce costs and provide a thin and compact drive circuit for a thin film EL display device.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention, FIGS. 2(a) and (b) are examples of a configuration of a push-pull type driver, and FIG. 3 is a time chart explaining the operation of FIG. 1. , FIG. 4 is a partially cutaway perspective view of a thin film EL display device,
FIG. 5 is a graph showing the brightness characteristics of a thin film EL display device with respect to applied voltage.

Claims (1)

[Claims] 1. In a thin film EL display device in which an EL layer is interposed between scan-side electrodes and data-side electrodes arranged in directions crossing each other, each of the scan-side electrodes has an EL layer interposed between the scan-side electrodes and the data-side electrodes. A first switching circuit that applies voltages of negative polarity and positive polarity to the data side electrodes via the electrodes is connected, and a modulation voltage is applied to each of the data side electrodes for the EL layer corresponding to the scanning side electrode. A second switching circuit for charging and discharging is connected, the first and second switching circuits each include a high-voltage driver IC having a push-pull function and controlled by a single-potential logic circuit; The pull-down common line of the high-voltage driver IC in the switching circuit is connected to a negative write voltage, a 1/2 modulation voltage, and a third switching circuit that switches to 0V, and the pull-up common line is connected to a positive write voltage and a 1/2 modulation voltage. A fourth switching circuit that switches to /2 modulation voltage is connected to the high voltage driver IC in the second switching circuit.
The pull-down common line is connected to 0V, and the pull-up common line is connected to a fifth switching circuit that switches the common line between a floating level and a 1/2 modulation voltage, and the third, fourth, and fifth 1. A drive circuit for a thin film EL display device, characterized in that the switching circuit that supplies the 1/2 modulated voltage is connected to a sixth switching circuit that divides the 1/2 modulated voltage and supplies the 1/2 modulated voltage in stages.