KR100843786B1 - circuit for compensating voltage of driving pixel in organic electro luminescence display - Google Patents

Abstract

The present invention relates to a pixel driving voltage compensation circuit for an organic light emitting display device that compensates for a threshold voltage of a driving transistor.

The present invention discloses an organic light emitting means that emits light by applying an electric field to an organic material by a supplied current, a driving transistor for supplying current to the organic light emitting means, and a data signal voltage at which a threshold voltage of the driving transistor is compensated for a gate of the driving transistor A first switching means for providing a path through which the threshold voltage is charged to the capacitor according to the first gate signal, and a data signal to which the threshold voltage is compensated by applying the data signal to the capacitor according to the second gate signal. And a second switching means for applying to the gate of.

Description

Pixel driving voltage compensation circuit for organic electroluminescent display {circuit for compensating voltage of driving pixel in organic electro luminescence display}

1 illustrates a basic pixel structure of a conventional organic light emitting display device;

2 illustrates a basic pixel structure of an organic light emitting display device according to an embodiment of the present invention;

3 is an operation timing diagram of a basic pixel of the organic light emitting display device of FIG. 2;

4A through 4C are circuit diagrams for describing an operation of a basic pixel of an organic light emitting display device in the timing section of FIG. 3.

The present invention relates to an organic light emitting display device, and more particularly, to a pixel driving voltage compensation circuit for an organic light emitting display device that compensates for a threshold voltage of a driving transistor.

In general, an organic electroluminescence display (OELD) refers to a flat panel display using a self-luminescence phenomenon in which an external electric field is applied to an organic light emitting material and electrons and holes are combined to emit light in an organic material.

Organic electroluminescent display devices have low power, high brightness, high response speed, and low weight and high quality, so most electronic applications such as mobile communication terminals, car navigation system (CNS), personal digital assistants (PDA), camcorders, palm PCs, etc. In addition, since the manufacturing process is simple, the production cost can be reduced more than conventional LCDs.

1 illustrates a basic pixel structure of a conventional organic light emitting display device. Referring to FIG. 1, when a gate signal SCAN N is applied to a gate of a switching transistor ST, a basic pixel of a conventional organic light emitting display device is turned on and a data signal transmitted from a data line. VDATA is applied to the gate of the capacitor C and the driving transistor DT.

When the data signal VDATA is applied to the gate of the driving transistor DT, the driving transistor DT is turned on to supply a current to the organic light emitting diode OLED. The organic light emitting diode (OLED) emits light in proportion to the amount of current supplied.

However, when the pixel is turned on by the gate signal SCAN N in the basic pixel of the conventional organic light emitting display, the driving transistor DT is always turned on for one frame by the data signal VDATA so that the organic light emitting diode OLED is turned on. It has a structure that continuously applies current.

As a result, the characteristics of the driving transistor DT are deteriorated, thereby changing the threshold voltage of the driving transistor DT. The change in the threshold voltage causes a change in the output current of the driving transistor DT, resulting in the organic light emitting diode OLED. There arises a problem that the uniformity and brightness of the light emitted by the light fall.

The present invention has been made to solve the above problems, and an object thereof is to compensate for a threshold voltage of a driving transistor provided in a pixel of an organic light emitting display device.

In order to achieve the above object, the present invention provides an organic light emitting means for emitting light by applying an electric field to the organic material by the current supplied, a drive transistor for supplying the current to the organic light emitting means, the drive to the gate of the drive transistor A capacitor for applying a data signal voltage compensated by a threshold voltage of a transistor, first switching means for providing a path for charging the threshold voltage to the capacitor according to a first gate signal, and the data to the capacitor according to a second gate signal And second switching means for applying a signal to the gate of the driving transistor to apply a data signal compensated for the threshold voltage.

The organic light emitting means is preferably an organic light emitting diode whose cathode is connected to a reference voltage source.

The first switching means may include a first NMOS transistor having a drain to which a data signal voltage is applied, a gate to which the first gate signal is applied, and a source connected to one end of the capacitor, a drain connected to the other end of the capacitor, And a second NMOS transistor having a gate to which the first gate signal is applied and a source connected to a source of the driving transistor.

Preferably, the capacitor has one end connected to a gate of the driving transistor, and the other end connected to a source of the first NMOS transistor and a drain of the second NMOS transistor.

The driving transistor may be a gate connected to the source of the first NMOS transistor and one end of the capacitor, a drain to which a power supply voltage is applied, and a third NMOS transistor connected to the drain of the second NMOS transistor.

Preferably, the second switching means is a fourth MOS transistor having a drain to which the data signal voltage is applied, a gate to which the second gate signal is applied, and a source connected to the other end of the capacitor.

The semiconductor device may further include a PMOS transistor having a drain connected to an anode of the organic light emitting diode, a gate to which the first gate signal is applied, and a source connected to a source of the driving transistor.

In addition, the driving transistor can supply a current proportional to the square of the voltage difference between the data signal voltage and the source voltage of the driving transistor.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 illustrates a basic pixel structure of an organic light emitting display device according to an exemplary embodiment of the present invention. As shown in FIG. 2, an organic light emitting diode OLED, a driving transistor T3, a capacitor CST, and a plurality of switching transistors T1, T2, T4, and T5 are included.

The organic light emitting diode (OLED) is an element that converts electrical energy into light by applying an electric field to an organic material by a current supplied from the driving transistor T3.

The organic light emitting diode OLED emits light in proportion to the amount of current supplied from the driving transistor T3. An anode of the organic light emitting diode OLED is preferably connected to the driving transistor T3 through the switching transistor T5 and a cathode of the organic light emitting diode OLED is connected to the reference voltage VSS. The reference voltage VSS is a voltage lower than the power supply voltage VDD and may be a ground voltage.

The driving transistor T3 transfers a current corresponding to the voltage difference between the gate and the source to the organic light emitting diode to drive the organic light emitting diode. When the driving transistor T3 drives the organic light emitting diode, a voltage VDATA + VTH in which the threshold voltage VTH of the driving transistor T3 is added to the data signal voltage VDATA is applied to the gate of the driving transistor T3. It is preferred to be applied.

The driving transistor T3 has a gate connected to the source of the switching transistor T1 and one end of the capacitor, a power supply voltage VDD is applied to the drain, and the source of the organic light emitting diode OLED is connected through the switching transistor T5. It is preferably an NMOS transistor connected to the anode.

The capacitor CST charges a charge corresponding to the threshold voltage of the driving transistor T3 to maintain a constant voltage difference between the gate and the source of the driving transistor T3, and then the threshold voltage is applied to the gate of the driving transistor. The driving transistor T3 is turned on by applying a compensated compensation voltage, that is, a voltage having a threshold voltage added to the data signal voltage.

One end of the capacitor is connected to the gate of the driving transistor T3, and the other end thereof is connected to a connection node of the source of the switching transistor T4 and the drain of the switching transistor T2.

The switching transistors T1, T2, T4, and T5 are switching transistors T1 and T2 and a gate signal SCAN N1 that provide a path to charge a capacitor voltage according to the gate signals SCAN N1 and SCAN N2. To regulate the current supplied from the driving transistor to the organic light emitting diode according to the gate signal SCAN N1 and the switching transistor T4 which provides a path for applying a compensation voltage to the gate of the driving transistor T3 according to the SCAN N2. Switching transistor T5.

The switching transistor T1 is preferably an NMOS transistor having a data signal voltage VDATA applied to a drain, a gate signal SCAN N1 applied to a gate, and a source connected to one end of the capacitor CST.

The switching transistor T2 is preferably an NMOS transistor having a drain connected to the other end of the capacitor CST, a gate signal SCAN N1 applied to a gate, and a source connected to a source of the driving transistor T3.

The switching transistor T4 is preferably an NMOS transistor having a data signal voltage VDATA applied to a drain, a gate signal SCAN N2 applied to a gate, and a source connected to the other end of the capacitor.

In the switching transistor T5, the drain is connected to the anode of the organic light emitting diode, the gate signal SCAN N1 is applied to the gate, and the source is preferably a PMOS transistor connected to the source of the driving transistor T3.

Hereinafter, an operation process of a basic pixel of an organic light emitting display device according to an exemplary embodiment of the present invention will be described in detail with reference to an operation timing diagram of FIG. 3 and a circuit state according to a timing section of FIGS. 4A to 4C.

First, in the period A of the operation timing diagram, the basic pixel of the organic light emitting display device of the present exemplary embodiment has the circuit state of FIG. 4A. In the operation timing diagram, section A is a section in which the gate signal SCAN N1 is 'HIGH' and the gate signal SCAN N2 is 'LOW'.

Since the gate signal SCAN N1 is 'HIGH', the NMOS switching transistors T1 and T2 to which the gate signal SCAN N1 is applied are turned on and the PMOS switching transistor T5 is turned off. The threshold voltage VTH of the driving transistor T3 is applied across the capacitor by the data signal voltage VDATA.

Since the gate signal SCAN N2 is 'low', the NMOS switching transistor T4 to which the gate signal SCAN N2 is applied to the gate is turned off. Since the PMOS switching transistor T5 is turned off, the driving transistor T3 does not supply current to the organic light emitting diode.

In the section B of the operation timing diagram, the basic pixel of the organic light emitting display device of the present exemplary embodiment has the circuit state of FIG. 4B. In the operation timing diagram, the section B is a section in which the gate signal SCAN N1 is 'LOW' and the gate signal SCAN N2 is 'HIGH'.

Since the gate signal SCAN N2 is 'HIGH', the NMOS switching transistor T4 to which the gate signal SCAN N2 is applied to the gate is turned on. The capacitor adds the threshold voltage VTH to the data signal voltage VDATA according to the data signal voltage VDATA applied through the NMOS switching transistor T4 to the charged threshold voltage VTH. Applied to the gate.

Since the gate signal SCAN N1 is 'low', the NMOS switching transistors T1 and T2 to which the gate signal SCAN N1 is applied are turned off and the PMOS switching transistor T5 is turned on. Since the PMOS switching transistor T5 is turned on, the driving transistor T3 supplies a current flowing from the drain to the source to the organic light emitting diode OLED by the power supply voltage VDD. That is, as shown in FIG. 4B, the gate voltage of the driving transistor T3 is constant to the organic light emitting diode in a state where the gate voltage of the driving transistor T3 is maintained at the voltage VDATA + VTH plus the threshold voltage VTH. Can supply current.

In the C section of the operation timing diagram, the basic pixel of the organic light emitting display device of the present exemplary embodiment has the circuit state of FIG. 4C. In the operation timing diagram, the section C is a section in which the gate signal SCAN N1 is 'low' and the gate signal SCAN N2 is 'low'.

Since the gate signal SCAN N1 is 'low', the NMOS switching transistors T1 and T2 to which the gate signal SCAN N1 is applied are turned off and the PMOS switching transistor T5 is turned on. Since the gate signal SCAN N2 is 'low', the NMOS switching transistor T4 to which the gate signal SCAN N2 is applied to the gate is turned off.

The capacitor applies a voltage (VDATA + VTH) of the data signal voltage (VDATA) plus the threshold voltage (VTH) to the gate of the driving transistor (T3). Since the PMOS switching transistor T5 is turned on, the driving transistor T3 supplies a current flowing from the drain to the source to the organic light emitting diode OLED by the power supply voltage VDD.

The current IOLED supplied from the driving transistor T3 to the organic light emitting diode OLED is a current corresponding to the gate-source voltage VGS of the driving transistor T3. The current supplied to the organic light emitting diode OLED may be represented by Equation 1 below.

Where u is the mobility of the driving transistor T3, C represents the gate capacitance per unit area of the driving transistor T3, and W / L represents the size of the driving transistor T3.

In Equation 1, since the gate-source voltage VGS of the driving transistor T3 is the difference between the gate voltage VG and the source voltage VS, the current supplied from the driving transistor T3 to the organic light emitting diode OLED ( IOLED) can be expressed as Equation 2 below.

According to Equation 2, the current IOLED supplied from the driving transistor T3 to the organic light emitting diode OLED is determined regardless of the threshold voltage. Therefore, the driving transistor T3 of the pixel driving voltage compensation circuit for the organic light emitting display device of the present exemplary embodiment can supply a stable current to the organic light emitting diode OLED even when the threshold voltage changes due to the deterioration of the characteristics of the driving transistor T3. .

As described above, the pixel driving voltage compensation circuit for the organic light emitting display device of the present invention compensates the threshold voltage of the driving transistor included in the pixel of the organic light emitting display device, thereby reducing the luminance nonuniformity according to the change of the threshold voltage. It is effective in eliminating the deterioration of image quality.

In addition, preferred embodiments of the present invention are disclosed for the purpose of illustration, those skilled in the art will be able to various modifications, changes, additions, etc. within the spirit and scope of the present invention, these modifications and changes should be seen as belonging to the following claims. something to do.

Claims (8)

Organic light emitting means comprising an organic light emitting diode whose cathode is connected to a reference voltage source so as to emit light by applying an electric field to the organic material by a supplied current; A driving transistor for supplying the current to the organic light emitting means; A capacitor applying a data signal voltage of which the threshold voltage of the driving transistor is compensated to a gate of the driving transistor; In order to provide a path through which the threshold voltage is charged to the capacitor according to a first gate signal, a drain to which a data signal voltage is applied, a gate to which the first gate signal is applied, and a source connected to one end of the capacitor are provided. First switching means including a second NMOS transistor having a first NMOS transistor and a drain connected to the other end of the capacitor, a gate to which the first gate signal is applied, and a source connected to a source of the driving transistor; And Second switching means for applying the data signal to the capacitor according to a second gate signal to apply a data signal compensated for the threshold voltage to a gate of the driving transistor; A pixel driving voltage compensation circuit for an organic light emitting display device comprising a. delete delete The method of claim 1, wherein the capacitor One end is connected to the gate of the driving transistor, and the other end is connected to the source of the first NMOS transistor and the drain of the second NMOS transistor. A pixel driving voltage compensation circuit for an organic light emitting display device. The method of claim 1, wherein the driving transistor A third NMOS transistor connected to a source of the first NMOS transistor and one end of the capacitor, a drain to which a power supply voltage is applied, and an anode of the organic light emitting diode; A pixel driving voltage compensation circuit for an organic light emitting display device. The method of claim 5, wherein the second switching means A fourth MOS transistor having a drain to which the data signal voltage is applied, a gate to which the second gate signal is applied, and a source connected to the other end of the capacitor; A pixel driving voltage compensation circuit for an organic light emitting display device. The method of claim 6, And a PMOS transistor having a drain connected to an anode of the organic light emitting diode, a gate to which the first gate signal is applied, and a source connected to a source of the driving transistor. A pixel driving voltage compensation circuit for an organic light emitting display device. 8. The driving transistor of claim 4, wherein the driving transistor comprises: Supplying current to the organic light emitting diode in proportion to a square of a voltage difference between the data signal voltage and a source voltage of the driving transistor; A pixel driving voltage compensation circuit for an organic light emitting display device.

Images