KR102348762B1 - Organic Light Emitting Diode Display Device - Google Patents

Abstract

The present invention provides an organic light emitting diode display device including a protection circuit for protecting an EVSS supply unit that supplies a positive EVSS voltage or a ground voltage to a cathode of an organic light emitting diode, and the EVSS supply unit is stably controlled to prevent PMOS and NMOS burnt An object of the present invention is to provide an organic light emitting diode display having an EVSS control circuit capable of preventing a failure of the display device. The EVSS control circuit according to the present invention includes a first transistor for controlling the EVSS voltage so that the EVSS voltage becomes a positive polarity voltage, and a second transistor for controlling the EVSS voltage such that the EVSS voltage becomes a ground, and timing control and an EVSS protection circuit configured to receive a first control signal and a second control signal from and control operations of the first transistor and the second transistor.

Description

Organic Light Emitting Diode Display Device

The present invention relates to an organic light emitting diode display device, and more particularly, to an organic light emitting diode display device capable of preventing malfunction of the EVSS supply unit by improving the structure of an EVSS control circuit and simply controlling an EVSS swing from the outside.

Recently, as a flat panel display that is emerging, a liquid crystal display, a field emission display, a plasma display panel, and an organic light emitting diode display (Organic Light) Emitting Display), etc. Among them, the organic light emitting diode display device is a self-luminous device that emits light in the organic light emitting layer by recombination of electrons and holes. It has high luminance, low driving voltage, and is expected to be a next-generation display device because it can be made into an ultra-thin film.

Each of the plurality of unit pixels constituting the organic light emitting diode display includes an organic light emitting diode including an organic light emitting layer between an anode and a cathode, and a pixel circuit independently driving each organic light emitting diode.

The pixel circuit mainly includes a switching transistor, a capacitor, and a driving transistor. The switching transistor charges the capacitor with a data signal in response to the scan pulse, and the driving transistor adjusts the grayscale of each pixel by adjusting the amount of current supplied to each organic light emitting diode according to the magnitude of the data voltage charged in the capacitor.

The organic light emitting diode OLED has an anode connected to a source or drain electrode of the driving transistor and a cathode connected to a ground to receive a constant voltage EVDD through a channel of the driving transistor.

In recent years, in order to compensate for deterioration of the organic light emitting diode (OLED), a driving TFT that directly senses a threshold voltage of the organic light emitting diode (OLED) or controls a constant voltage (EVDD) supplied to the organic light emitting diode (OLED) A technique for luminance compensation by sensing the threshold voltage of Accordingly, there is a need for an EVSS supply unit that controls the organic light emitting diode (OLED) to emit light only during the light emission period without the organic light emitting diode (OLED) emitting light during the sensing period.

That is, the EVSS supply unit supplies a voltage EVSS having the same magnitude as the constant voltage EVDD to the cathode of the organic light emitting diode OLED to prevent the organic light emitting diode from emitting light during the sensing period, and During the period, a ground voltage (GND) is supplied to the cathode in order to emit light of the organic light emitting diode (OLED).

The conventional EVSS supply unit includes a PMOS first transistor and an NMOS second transistor having a drain electrode connected to each other, a voltage source Vsource is connected to a source electrode of the first transistor, and a source electrode of the NMOS. A ground is connected to , and a cathode of the organic light emitting diode (OLED) is connected to a node where the PMOS and the NMOS are connected to each other.

A timing controller supplies a control signal to the gate electrodes of the PMOS and the NMOS of the EVSS supply unit.

That is, during the light emission period, the timing controller supplies a high-level control signal to the first transistor and the second transistor to turn off the first transistor, and turns on the second transistor to control the second transistor. A ground voltage connected to a source electrode is supplied to the cathode of the organic light emitting diode (OLED), and during a sensing period, the timing controller supplies a low-level control signal to the first transistor and the second transistor to the first transistor is turned on and the second transistor is turned off so that the voltage of the voltage source Vsource connected to the source electrode of the first transistor is supplied to the cathode of the organic light emitting diode.

However, conventionally, the EVSS supply unit directly applies a control signal to the PMOS and NMOS of the EVSS supply unit from a timing controller. When the timing controller directly applies a control signal to the PMOS and the NMOS of the EVSS supply unit, a malfunction may occur and the PMOS and the NMOS may be simultaneously turned on for the following reasons.

The timing controller controls the first transistor and the second transistor to have a very short dead time during which neither the first transistor nor the second transistor is turned on, wherein the timing controller sends a high signal to the first transistor and A low signal must be transmitted to the second transistor. However, for example, when a malfunction of supplying a high signal to the second transistor while supplying a low signal of the first transistor occurs due to a malfunction of the timing controller, the first transistor and the second transistor may be turned on at the same time can

When the PMOS and the NMOS are simultaneously turned on, a short circuit occurs in the EVSS circuit, or the PMOS and the NMOS burn, resulting in a malfunction of the organic light emitting diode display.

In addition, in order to arbitrarily control the swing of the EVSS supply unit as described above from the outside, a separate control circuit must be provided in the timing controller, thereby complicating the process and increasing the cost.

The present invention is to solve the above problem, and by providing a protection circuit for protecting the EVSS supply unit in the conventional EVSS supply unit, the EVSS supply unit is stably controlled to prevent a short circuit or burnt of the PMOS and NMOS. An object of the present invention is to provide an organic light emitting diode display having an EVSS control circuit.

In addition, the present invention provides an organic light emitting diode display having an EVSS control circuit capable of facilitating inspection or repair of bad pixels by simply adjusting the swing of the output voltage simply by connecting the EVSS control circuit to an external power supply. Another object of the invention.

In order to achieve the above object, an EVSS control circuit according to the present invention includes a first transistor for supplying an EVSS voltage to a positive voltage level, a second transistor for turning the EVSS voltage to a ground level, and inputting a first control signal. The second transistor receives a third transistor for controlling on/off of the first transistor by receiving the input signal and discharging the second control signal input due to a malfunction to the ground by receiving the first control signal to maintain the turn-off state of the second transistor. It is characterized in that it is provided with a fourth transistor for controlling the.

In addition, in order to achieve another object of the present invention, an EVSS control circuit according to another embodiment of the present invention includes an external input pin connected to each of the source electrodes of the third and fourth transistors through a resistor, and the external By connecting an external power supply to an input pin and inputting a negative voltage in the direction of the source electrode of the third and fourth transistors, the EVSS voltage of the positive polarity is output to the cathode of the organic light emitting diode regardless of the first and second control signals It is characterized by making it possible.

By driving the EVSS control circuit according to the present invention, a protection circuit for protecting the EVSS supply unit is provided, so that the EVSS supply unit is stably controlled to prevent a short circuit or deterioration of the PMOS and NMOS.

In addition, the EVSS control circuit according to another embodiment of the present invention can easily control the EVSS swing from the outside without configuring a separate circuit inside the timing controller, and it is easy to check the defects of the panel, and in particular, the defects of the organic light emitting diode are reduced. It has the feature of being able to easily repair existing pixels.

1 is an exemplary diagram for explaining an EVSS control circuit according to the present invention.
2 is an exemplary diagram for explaining the EVSS protection circuit in detail according to the present invention.
3 is a waveform diagram for driving an EVSS control circuit having an EVSS protection circuit according to the present invention.
4 shows an EVSS control circuit with an EVSS protection circuit according to another embodiment of the present invention.
5 is a waveform diagram for driving an EVSS control circuit according to another embodiment of the present invention.

Hereinafter, an organic light emitting diode display device according to the present invention will be described in more detail with reference to the accompanying drawings.

1 shows an EVSS control circuit according to the present invention.

The EVSS control circuit 2 according to the present invention includes a first transistor TR_1 that is a PMOS and a second transistor TR_2 that is an NMOS as in the prior art, and has a ground or positive polarity at the cathode of an organic light emitting diode (OLED). In response to a signal from the EVSS supply unit 5 supplying the EVSS voltage swinging to the voltage, and the timing controller 3 , the signals supplied to the first and second transistors TR_1 and TR_2 of the EVSS supply unit 5 . and an EVSS protection circuit 4 that protects the EVSS supply unit 5 by controlling the timing controller and preventing the first transistor TR_1 and the second transistor TR2 from being turned on at the same time due to a malfunction of the timing controller.

2 is an exemplary diagram for explaining the EVSS protection circuit 4 in detail according to the first embodiment of the present invention.

The EVSS protection circuit 4 is connected to the gate electrode of the first transistor TR_1 of the EVSS supply unit 5 at the same time as the drain electrode is connected to the voltage source Vsource through the first resistor R1, and the source electrode A third transistor TR_3 connected to the ground GND through the second resistor R2 and a gate electrode connected to the timing controller 3 to receive a first control signal from the timing controller 3; , the drain electrode is connected to the timing controller 3 through the third resistor R3 to receive the second control signal, and is connected to the gate electrode of the second transistor TR_2 of the EVSS supply unit 5, and the source a fourth transistor TR_4 having an electrode connected to ground through a fourth resistor R4 and a gate electrode connected to a timing controller 3 receiving the first control signal from the timing controller 3 do.

Accordingly, the first transistor TR_1 of the EVSS supply unit 5 has a gate electrode connected between the drain electrode of the third transistor TR_3 and the first resistor R1, and the gate of the first transistor TR_1 The electrode is supplied with a voltage down by the first resistor R1 , the source electrode is directly connected to the voltage source Vsource, and the drain electrode is connected to the EVSS voltage output terminal 6 .

In the second transistor TR_2 , a gate electrode is connected between the third resistor R3 and a drain electrode of the fourth transistor TR_4 , a drain electrode is connected to the EVSS voltage output terminal 6 , and a source electrode It is connected to this ground (GND).

The ratio of the resistance of the third resistor R3 and the fourth resistor R4 is preferably about 10:1.

A cathode of an organic light emitting diode (OLED) is connected to the EVSS voltage output terminal 6 .

Hereinafter, a driving method of the EVSS control circuit including the EVSS protection circuit 4 according to the present invention will be described with reference to the drawings.

3 is a waveform diagram for driving an EVSS control circuit having an EVSS protection circuit according to the present invention.

As described above, in the EVSS control circuit according to the present invention, when the organic light emitting diode (OLED) positioned in each pixel of the organic light emitting diode display device emits light, the EVSS voltage must be in a ground state, and the When the driving transistor is turned on to sense the organic light emitting diode, a voltage EVSS equal to the constant voltage EVDD is applied to the cathode electrode of the organic light emitting diode to control the organic light emitting diode not to emit light.

In order to control the organic light emitting diode as described above, the EVSS control circuit 2 according to the present invention operates as follows.

In a sensing period in which the threshold voltage Vth of the organic light emitting diode OLED is sensed, the timing controller 3 outputs a first control signal in a high state and a second control signal in a low state. As the first control signal in the high state is supplied, all of the third and fourth transistors TR_3 and TR_4 are turned on.

When the third transistor TR_3 is turned on, the voltage source Vsource is dropped through the first resistor R1 and the third transistor TR3 to be supplied to the gate electrode of the first transistor TR_1, and Since the voltage supplied from the voltage source Vsource is applied to the source electrode of the first transistor TR_1 , a potential difference VGS between the gate and the source of the first transistor TR_1 is generated. Accordingly, since the potential difference VGS becomes higher than the threshold voltage, the first transistor TR_1 is turned on.

Also, when the fourth transistor is turned on, the third resistor R3 and the fourth resistor R4 have a magnitude ratio of 10:1, so that a malfunction of the second control signal output from the timing controller 3 occurs. Thus, even when a high signal is supplied, the second control signal is passed to the ground GND through the fourth transistor TR_4 and the fourth resistor R4.

Accordingly, the second transistor TR_2 maintains a turned-off state, and as a result, even if the first and second control signals in the high state are simultaneously applied due to a malfunction, the second transistor TR_2 maintains the turned-off state. Thus, the first transistor TR_1 and the second transistor TR_2 of the EVSS supply unit 5 are not turned on at the same time to protect the EVSS supply unit 5 .

Accordingly, the voltage EVSS is stably supplied to the cathode electrode of the organic light emitting diode OLED so that the organic light emitting diode OLED does not emit light.

During the emission period in which the organic light emitting diode (OLED) emits light, the timing controller 3 outputs the first control signal in a low state and the second control signal in a high state. Accordingly, at this time, since the fourth transistor TR_4 maintains a turned-off state, the second control signal is supplied to the second transistor TR_2 . In addition, since the third transistor TR_3 also maintains a turned-off state and a constant voltage Vsource is applied to the gate electrode of the first transistor TR_1 through the first resistor R1, the first transistor TR_1 is also turned off. Accordingly, since the ground voltage GND is applied to the cathode electrode of the organic light emitting diode OLED through the turned-on second transistor TR_2 , the organic light emitting diode OLED emits light normally.

In the EVSS control circuit 2 including the EVSS protection circuit 4 as described above, the third and fourth transistors TR_3 and TR_4 receive the first and second control signals from the timing controller 3 , and the first , since the on/off of the two transistors TR_1 and TR_2 is controlled, the EVSS voltage swing can be controlled more stably compared to when the timing controller 3 directly supplies the control signal to the first and second transistors.

In addition, in the EVSS control circuit according to the present invention, even if the EVSS control circuit 2 malfunctions during the sensing period, the second transistor is turned off and the organic light emitting diode (OLED) does not emit light, so that the organic light emitting diode ( It is possible to prevent a short or burnt phenomenon in the driving circuit including OLED).

The EVSS control circuit 2 including the EVSS protection circuit 4 according to the embodiment of the present invention as described above is designed to be controlled only by the input of the timing controller 3 . Therefore, in order to control the swing of the EVSS from the outside, a signal must be connected to the timing controller 3 , and a separate circuit for processing an external signal must be configured in the timing controller 3 .

Accordingly, when the EVSS protection circuit further includes an input pin capable of connecting an external signal, the swing of the EVSS can be easily controlled from the outside, which is advantageous for inspection or defect checking of the liquid crystal panel.

4 shows an EVSS control circuit 2 having an EVSS protection circuit according to a second embodiment of the present invention, and FIG. 5 is a waveform diagram for driving the EVSS control circuit of FIG.

The EVSS control circuit according to the second embodiment of the present invention is the same as the EVSS control circuit according to the first embodiment of the present invention described with reference to FIG. 2, but includes the ground, the second resistor R2 and the fourth resistor R4. It has a difference in which an input pin 7 to which a signal can be applied from the outside is further provided at one end of the .

The input pin 7 functions as a ground (GND) when there is no external connection, and drives the same as the EVSS control circuit 2 described in the previous embodiment.

When the input pin 7 is connected to an external swing control device, the external swing control device supplies a negative voltage to the EVSS control circuit 2 through the input pin 7 or the input pin ( 7) can be maintained in the ground (GND) state.

When the external swing control device supplies a negative voltage to the input pin 7 , a negative voltage is supplied to the source electrodes of the third and fourth transistors TR_3 and TR_4 . Then, since the VGS values of the third and fourth transistors TR_3 and TR_4 become greater than or equal to the threshold voltage, the third and fourth transistors TR_3 and TR_4 are turned on. Then, since the negative voltage is applied to the gate of the first transistor TR_1 through the channel of the third transistor TR_3, the first transistor TR_1, which is a PMOS, is turned on, and accordingly, the voltage EVDD This is output in the cathode direction of the organic light emitting diode (OLED).

At this time, when the second control signal is in a low state, the second transistor TR_2 maintains a turned-off state, and even when the second control signal is in a high state, the second control signal is applied to the fourth transistor TR_4. Since the negative polarity voltage is transferred to the external swing control device along the channel, the second transistor TR_2 maintains a turned-off state.

In other words, when a negative voltage is supplied to the EVSS control circuit 2 through an external swing control device, the EVSS swing control circuit 2 forcibly activates the EVSS swing control circuit 2 regardless of the state of the first and second control signals. The voltage EVSS may be output.

When the EVSS control circuit according to the present embodiment is used, the EVSS voltage may be applied to the cathode of the organic light emitting diode (OLED) even during the light emission period. In this case, if it is a normal organic light emitting diode (OLED), the It is only non-luminous without affecting the characteristics. However, when there is an abnormality in the organic light emitting diode (OLED), a short circuit occurs in the organic light emitting diode (OLED), thereby destroying and darkening the organic light emitting diode (OLED).

Therefore, the EVSS control circuit 2 according to the present invention can easily control the EVSS swing from the outside without configuring a separate circuit inside the timing controller 3 , and it is simple to check for defects in the panel, and in particular, the organic light emitting diode It has the feature of easily repairing defective pixels (OLED).

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is known in the art to which the present invention pertains that various substitutions, modifications and changes are possible within the scope without departing from the technical spirit of the present invention. It will be clear to those who have the knowledge of

2: EVSS control circuit 3: Timing controller
4: EVSS protection circuit 6: EVSS output stage
7: External input pins R1-R4: 1-4th resistor
TR_1, TR_2, TR_3. TR_4: 1-4th transistor

Claims (4)

a display panel including a plurality of pixels and an organic light emitting diode for each pixel;
In order to supply the EVSS voltage swinging to the ground or positive polarity voltage to the cathode of each organic light emitting diode, a first resistor having one end connected to a positive voltage source, and a source electrode connected to the positive voltage source, the first resistor A first transistor having a gate electrode connected to the other end and a drain electrode connected to an EVSS voltage output terminal, a third resistor having one end connected to a timing controller, a source electrode connected to the ground, and a drain electrode connected to the EVSS voltage output terminal and an EVSS supply unit including a second transistor having a gate electrode connected to the other end of the third resistor; and
A second resistor, a gate electrode of the first transistor, and a drain electrode are connected to the other end of the first resistor to control the operation of the EVSS supply unit by receiving the first control signal and the second control signal from the timing control a third transistor having a source electrode connected to one end of the second resistor and a gate electrode connected to the timing controller; a fourth resistor connected to the same line or pin as the other end of the second resistor; and An EVSS protection circuit including a gate electrode of a second transistor, a drain electrode connected to the other end of the third resistor, a source electrode connected to one end of the fourth resistor, and a fourth transistor connected to the timing controller with a gate electrode including,
The other end of the second resistor and the other end of the fourth resistor are connected to the ground or connected to an external swing control device through an input pin,
The external swing control device applies a negative voltage through the input pin so that the positive EVSS voltage is forcibly output to the cathode electrode of the organic light emitting diode to turn on the third and fourth transistors. . delete delete The method according to claim 1,
The first transistor is selected as a PMOS,
The second to fourth transistors are selected as NMOS.

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