KR100811481B1 - Light emitting display and driving method for the same - Google Patents

Abstract

The invention provides a scan signal supplying step of supplying a scan signal to a scan line of a pixel circuit unit including at least one thin film transistor unit connected between the scan line and the data line and a light emitting unit emitting light by driving at least one capacitor; And a data signal supplying step of supplying a data signal to the data line, supplying a boost pulse to the pixel circuit part with a large width of the pulse in a first section and a small width of the pulse in a second section. The section provides a driving method of the electroluminescent display device, wherein the section is a start section to which a boost pulse is supplied, and the second section reaches a gray level to be expressed in the pixel circuit unit after the start section of the boost pulse.

EL display, driving method, data boost

Description

EL display and driving method thereof {LIGHT EMITTING DISPLAY AND DRIVING METHOD FOR THE SAME}

1 is a schematic circuit diagram of a pixel circuit portion and a data booster portion of a conventional electroluminescent display.

FIG. 2 is a conventional drive waveform diagram boosting FIG. 1. FIG.

3 is a diagram illustrating a configuration of a data booster unit and a pixel circuit unit according to the present invention.

4 is a boost driving waveform diagram according to the driving method of FIG.

5 is a driving waveform diagram of a D / A converter according to whether or not it is boosted.

6 is a view showing the output ratio by the boost method of the present invention.

<Explanation of symbols on main parts of the drawings>

210: pixel circuit unit 220: data booster unit

240: data line M1: thin film transistor portion

C: Capacitor OLED: Organic Light Emitting Part

The present invention relates to an electroluminescent display and a driving method thereof.

Recently, since high quality images are required in mobile phones and portable devices such as portable multimedia players (PMPs), still images and videos are represented on a screen by using a liquid crystal display (LCD) or an organic light emitting device (OLED). have.

For such a flat panel display, a desired image is represented by driving a panel using a driver IC.

Conventionally, the driver IC is divided into a current driving method and a voltage driving method according to the method of driving the panel. In the case of the current driving method, a relatively small current must be flowed to express a low gray level, and a relatively large current must flow a panel to express a high gray level.

1 is a schematic circuit diagram of a pixel circuit portion and a data booster portion of a conventional electroluminescent display, and FIG. 2 is a conventional driving waveform diagram for boosting FIG. 1.

As shown in FIG. 1, the conventional EL display device emits light by driving at least one thin film transistor unit M1 and at least one capacitor C connected to the scan line and the data line 140. A data booster unit 120 for boosting the data signal is provided to the pixel circuit unit 110 and the data line 140.

Here, the data booster 120 inputs a precharge signal during one scan signal Scan [n] period by using a driving waveform as shown in FIG. 2, and then boosts it to charge the internal load capacitance. , Data signal was input.

At this time, according to the input digital code value, a current corresponding to 2 ⁰ × I flows at the lowest gray level, and as the gray level increases, the output current value increases, and at the final highest gray level (2 ^N-1 + 2 ^N-2 +… + 2 ² + 2 ¹ + 2 ⁰ ) Outputs the current corresponding to I.

In this general structure, the output current ranges from tens [nA] to several hundreds [nA] when the low gray level is expressed in view of the large load capacitance corresponding to tens of [pF] and the resistance of several M [ohm] on the panel. If there is not enough driving time because of the current, then there is not enough time to charge the load capacitance. This is the greatest when expressing a low gray level, and this phenomenon occurs even when the level is raised, resulting in a problem that it is difficult to accurately express the color.

Although not shown, the current is not sufficiently charged by the parasitic capacitor and the resistor present in the data line 140 connected to the pixel circuit unit 110.

In addition, if the output is low compared to when the ideal at the overall level is not guaranteed enough driving time, there is a problem that it is difficult to accurately represent the color because there is not enough time to charge the load capacitance.

In addition, it is not possible to compensate for each case of every process, and the threshold voltage (Vth) and load conditions of the thin film transistor (TFT) are changed according to the case (worst, typical, best case). Therefore, if the boost time and the boost level are determined, the output value is changed for each TFT forming case, and an unwanted gray level is displayed.

An object of the present invention for solving the above problems is to supply a boost corresponding to the size of the load capacitance to improve low gray level charging failure and to improve the display quality of the electroluminescent device.

In order to solve the above problems, the present invention provides a scan for supplying a scan signal to a scan line of a pixel circuit unit including at least one thin film transistor unit connected between a scan line and a data line and a light emitting unit emitting light by driving at least one capacitor. A signal supplying step; And a data signal supplying step of supplying a data signal to the data line, supplying a boost pulse to the pixel circuit part with a large width of the pulse in a first section and a small width of the pulse in a second section. The section provides a driving method of the electroluminescent display device, wherein the section is a start section to which a boost pulse is supplied, and the second section reaches a gray level to be expressed in the pixel circuit unit after the start section of the boost pulse.

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Here, the data signal supply step includes a source comparison step for controlling the boost pulse, and in the source comparison step, load capacitances of parasitic capacitors applied to the internal load by monitoring current or voltage levels in the data line and the pixel circuit unit. The width of the boost pulse may be varied until the load capacitance is sufficiently satisfied.

In this case, the boost pulse may gradually become a negative slope at the beginning of the boosting output and approach a gradation level by using a variable delay latch, in which a delay component of an output signal varies according to a difference between two input signals. It may be controlled by the characteristic that the more gradually the (+) slope.

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Here, the boost pulse may gradually decrease in width when the boost pulse is adjacent to the gradation level, and may be fixed to a desired gray level by a data code of each boost channel.

Here, the boost pulse may be supplied by a boost level divided in several stages by current sources having different values.

Here, the boost pulse, the switching between the first section and the second section may be switched by the decision logic (Decision Logic).

The light emitting unit may be an organic light emitting diode.

On the other hand, the electroluminescent display device according to the present invention comprises: a pixel circuit portion including at least one thin film transistor portion connected to the scan line and the data line and a light emitting portion to emit light by driving at least one capacitor; A boost pulse for supplying a data signal to the data line and to the pixel circuit part includes a data booster for supplying a large width of the pulse in the first section and a small width of the pulse in the second section, wherein the first section is a boost. An electroluminescent display device is provided, wherein a pulse is supplied to a start section, and a second section reaches a gradation level to be expressed on the pixel circuit part after the start section of the boost pulse.

Here, the data booster unit includes a current type digital to analog (D / A) converter, two or more switches provided in the D / A converter, a comparator for comparing current or voltage levels required in the data line and the pixel circuit unit, Reference logic may include decision logic for selectively controlling two or more switches.

Here, the data booster unit further includes a variable delay latch (Variable Delay Latch) that the delay component of the output signal is changed according to the difference between the two input signals, the boost pulse is input by the variable delay latch (Variable Delay Latch) When the difference between the two signals becomes large, the width of the boost pulse is supplied large, and when the difference between the two input signals decreases, the width of the boost pulse may be reduced.

The light emitting unit may be an organic light emitting diode.

<Example 1>

3 is a diagram illustrating a configuration of a data booster unit and a pixel circuit unit according to the present invention, FIG. 4 is a boost driving waveform diagram according to the driving method of FIG. 3, and FIG. 6 is a view showing the output ratio by the boost method of the present invention.

As shown in FIG. 3, the electroluminescent display device according to the present invention emits light by driving at least one thin film transistor unit M1 and at least one capacitor C connected to the scan line and the data line 240. The pixel circuit unit 210 including the OLED is formed.

The data line 240 supplies a data signal, supplies a boost pulse to the pixel circuit 210 with a large width of the pulse in the first section, and a small width of the pulse in the second section. 220 is formed.

The data signal and the boost pulse may be supplied to the pixel circuit unit 210 at the same time, but in general, the boost pulse may be supplied first and then the data signal may be supplied.

The pixel circuit unit 210 may receive the boosting signal quickly by the boost pulse supplied to the first section, and may receive the detailed and accurate boosting signal by the boost pulse supplied to the second section.

The first section of the boost pulse may be a start section to which the boost pulse is supplied, and the second section may be a section reaching the gray level to be expressed in the pixel circuit unit 210 after the start section of the boost pulse. Interchange between the section and the second section is possible.

Although the illustrated pixel circuit unit 210 is illustrated around the data booster unit 220 for inputting a data signal to the thin film transistor unit M1, the pixel circuit unit 210 further includes a switching thin film transistor unit that is switched by a scan signal supplied from a scan line. can do.

Although not shown in detail, the pixel circuit unit 210 may further include a thin film transistor unit or the like to compensate for them, and the configuration of the pixel circuit unit 210 is not limited to the configuration shown in the drawings. See not.

The illustrated data booster unit 220 supplies a current corresponding to the final data to the pixel circuit unit 210 in a current driven driver IC (Integrated Circuit).

The data booster unit 220 may be formed inside the driver IC or outside the driver IC to receive an external input (external input). The data booster unit 220 includes two or more switches provided in the current type D / A converter and the D / A converter. And a comparator (comparator) for comparing current or voltage levels required in the data line 240 and the pixel circuit unit 210. The comparator may monitor the current or voltage level of the node Iout to determine whether the comparator is a value required by the data line 240 and the pixel circuit unit 210. In addition, it includes decision logic that selectively controls two or more switches with reference to a comparator. The apparatus may further include a variable delay latch for changing a delay component of an output signal according to a difference between two input signals.

As a result, when the difference between the two signals input to the variable delay latch becomes large, the width of the boost pulse is largely supplied, and when the difference between the two signals is smaller, the width of the boost pulse can be supplied small.

This uses the characteristic that the two differential signals input become the negative slope of the initial output of the Variable Delay Latch gradually and become the positive slope as the gradation level approaches.

The result is a precise boost operation, and the delay is increased when the desired gradation level is reached, which automatically stops the boost pulse supply, eliminating the need for additional logic to stop the boost pulse. .

Decision logic selectively boosts two or more boost switches by turning them on or off depending on the current or voltage level compared by the comparator. The decision logic can switch their supplied sections for the purpose of switching between the first and second sections of the boost pulse.

More than one switch can output a value corresponding to (2 ^N-1 + 2 ^N-2 +… + 2 ² + 2 ¹ + 2 ⁰ ) × I at the highest gray level, depending on the selective switching. have.

On the other hand, the current type D / A converter may be further provided with a current source as a means for additional charging to solve the phenomenon that the load capacitor is not fully charged when outputting a low current value. Here, the current source may be composed of one or more transistors, or may be one consisting of an operational amplifier, a resistor, or the like, or may include one or more transistors, an operational amplifier, a resistor, and the like.

The electroluminescent display as described above uses an analog type pulse width modulation (PWM) boost technique to represent an accurate gray level for a predetermined scan time as a current driving type.

Here, the data booster unit 220 monitors the node Iout current or voltage level in the data line 240 and the pixel circuit unit 210 to sufficiently load load capacitance of parasitic capacitors applied to the internal load. The boost pulse can be supplied variably until it is satisfied.

The width of the boost pulse is gradually reduced when adjacent to the gradation level, and is fixed to the desired gray level by the data code of each boost channel. Accordingly, even if the driving time is short, the load capacitance can be charged within the driving time to express the desired gray level.

The driving method of the electroluminescent display device as described above refers to the driving waveforms of FIGS. 3 and 4.

The scan signal supplying step may include a pixel circuit unit 210 including one or more thin film transistor units M1 connected between the scan line and the data line 240 and a light emitting unit OLED that emits light by driving one or more capacitors C. FIG. Is a step of supplying a scan signal to a scan line. The scan signal shown in the figure refers to one period t supplied by the scan signal supply step Scan [n].

In the data signal supplying step, a data signal is supplied to the data line 240, a boost pulse supplied to the pixel circuit unit 210 is supplied with a large width of the pulse in the first section, and a small width of the pulse in the second section. Supply step.

The data signal and the boost pulse may be supplied to the pixel circuit unit 210 at the same time, but in general, the boost pulse may be supplied first and then the data signal may be supplied.

The pixel circuit unit 210 may receive the boosting signal quickly by the boost pulse supplied to the first section, and may receive the detailed and accurate boosting signal by the boost pulse supplied to the second section.

The first section of the boost pulse may be a start section to which the boost pulse is supplied, and the second section may be a section reaching the gray level to be expressed in the pixel circuit unit 210 after the start section of the boost pulse. Interchange between the section and the second section is possible.

Referring to FIG. 4, while the boost clock Bst_clk is supplied, a "boost SW" signal for turning on a switch for boosting and a "sample" signal for sampling two signals input to a variable delay latch. Separated by. Here, it is referred to that a variable delay latch is enabled in a section in which a "sample" signal occurs.

By such a drive waveform, the boost pulse width is initially supplied to reach a desired gradation target level, and then the boost pulse width is supplied smaller as it approaches the desired gradation target level. It can be seen that the current or voltage gradually decreases.

The data signal supply step includes a source comparison step for controlling a boost pulse, and in the source comparison step, load capacitance of parasitic capacitors applied to the internal load by monitoring current or voltage levels in the data line and the pixel circuit unit. The boost pulse can be variably supplied until is sufficiently satisfied.

The boost pulse uses a variable delay latch in which a delay component of an output signal varies according to a difference between two input signals. Accordingly, the boost pulse may be controlled by a characteristic that gradually becomes a negative slope at the beginning of the boosting output and a characteristic that gradually becomes a positive slope as the gradation level approaches. In addition, the boost pulse can be supplied to last for 0 ms near the gradation level, providing precise and accurate boosting.

According to the above method, the boost pulse gradually decreases when the boost pulse is adjacent to the gradation level, and can be fixed to the desired gray level by the data code of each boost channel.

On the other hand, such a boost pulse can be divided into several stages, it is possible to generate a more accurate boost pulse by separating and supplying the boost pulse in stages.

This is because the boost pulse can be supplied by boost levels divided in stages by current sources having different values.

In addition, the boost pulse may be switched and input to switch the first section and the second section by decision logic. Accordingly, the pixel circuit unit 210 may receive a more precise and accurate boosting signal by the boost pulse supplied in the second section.

FIG. 5 shows the driving capability of the D / A converter according to whether or not it is boosted. When the output waveform slope of the D / A converter is urgent, a boost switch is turned on to boost and the output waveform slope is gentle. Note that the switch is off, allowing you to stop boosting and compare signals.

On the other hand, if there is no boost stage, the problem due to the charging failure of the load capacitance in the low gradation can be clearly revealed. However, as shown in FIG. 7, when boosting is performed using the driving method according to the present invention, an output of a D / A converter near an ideal precharge may be obtained.

The driving method as described above may variably supply the boost pulse until the node current or voltage level in the data line and pixel circuit unit is monitored to sufficiently satisfy the load capacitance of parasitic capacitors applied to the internal load.

The width of the boost pulse gradually decreases when adjacent to the gradation level, and is fixed to the desired gray level by the data code of each boost channel. Accordingly, even if the driving time is short, the load capacitance can be charged within the driving time to express the desired gray level.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the technical configuration of the present invention described above may be modified in other specific forms by those skilled in the art to which the present invention pertains without changing its technical spirit or essential features. It will be appreciated that it may be practiced. Therefore, the embodiments described above are to be understood as illustrative and not restrictive in all aspects. In addition, the scope of the present invention is represented by the claims to be described later rather than the detailed description. Also, it is to be construed that all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts are included in the scope of the present invention.

According to the above-described configuration of the present invention, by supplying a boost corresponding to the size of the load capacitance, there is an effect of improving low gray level charging failure and improving display quality of the electroluminescent device.

Claims (14)

A scan signal supplying step of supplying a scan signal to the scan line of the pixel circuit unit including at least one thin film transistor unit connected between the scan line and the data line and a light emitting unit emitting light by driving at least one capacitor; A data signal supplying step of supplying a data signal to the data line, supplying a boost pulse to the pixel circuit unit in a first section with a large width of the pulse, and in a second section with a small width of the pulse; And the first section is a start section to which the boost pulse is supplied, and the second section is a section reaching a gray level to be expressed in the pixel circuit part after the start section of the boost pulse. delete The method of claim 1, wherein the data signal supply step includes a source comparison step for controlling the boost pulse, In the source comparison step, the boost pulse is variably supplied until the current or voltage levels in the data line and the pixel circuit unit are monitored to sufficiently satisfy the load capacitance of parasitic capacitors applied to the internal load. A method of driving an electroluminescent display device. The method of claim 1, wherein the boost pulse, Variable delay latch (Variable Delay Latch) is a variable according to the difference between the two input signals (Variable Delay Latch) using a variable delay latch (Variable Delay Latch) at the beginning of the boosting output gradually becomes negative (-) slope gradually closer to the gradation level A method of driving an electroluminescent display device, characterized in that it is controlled by a property to be a slope. delete The method of claim 1, wherein the boost pulse, And a width of the boost pulse gradually decreases when adjacent to the gradation level, and is fixed to a desired gray level by a data code of each boosting channel. The method of claim 1, wherein the boost pulse, A method of driving an electroluminescent display device, characterized in that it is supplied by a boost level divided in several stages by a current source having a different value. The method of claim 1, wherein the boost pulse, And the switching between the first section and the second section is switched by decision logic. The method of claim 1, wherein the light emitting unit, A method of driving an electroluminescent display device, characterized in that the organic light emitting diode. A pixel circuit unit including at least one thin film transistor unit connected to the scan line and the data line and a light emitting unit emitting light by driving at least one capacitor; And a data booster unit for supplying a data signal to the data line and supplying a boost pulse to the pixel circuit unit in a first section with a large width of the pulse, and in a second section with a small width of a pulse. And the first section is a start section to which the boost pulse is supplied, and the second section is a section reaching a gray level to be expressed in the pixel circuit part after the start section of the boost pulse. delete The method of claim 10, wherein the data booster unit, Current type D / A (Digital to Analog) converter, At least two switches provided in the D / A converter, A comparator for comparing current or voltage levels required in the data line and the pixel circuit unit; And a decision logic for selectively controlling the two or more switches with reference to the comparator. The method of claim 12, wherein the data booster unit, It further includes a variable delay latch (Variable Delay Latch) that the delay component of the output signal is changed according to the difference between the two input signals, The boost pulse is configured to supply a large width of the boost pulse when the difference between the two signals input by the variable delay latch is increased, and decrease the width of the boost pulse when the difference between the two input signals is small. Electroluminescent display device, characterized in that. The method of claim 10, wherein the light emitting unit, Electroluminescent display device, characterized in that the organic light emitting diode.

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