KR20080046055A - Light emitting diode and driving method of the same - Google Patents

Abstract

The present invention provides a display device comprising: a display panel unit including subpixels arranged in a matrix; A monitoring pixel unit positioned at one side of the display panel unit; A sample converter configured to detect a state of the display panel unit through the monitoring pixel unit and convert the sample into a digital state value through a sampling process; A controller for finding a lookup table value corresponding to the state value received from the sample converter and adjusting a gain value of a data signal to be currently supplied; And a driving unit supplying a scan signal to a display panel unit and supplying the data signal received through a control unit to the display panel unit.

Description

EL display and driving method thereof {Light Emitting Diode and Driving Method of the same}

1 is an exemplary view schematically showing an area where a monitoring pixel unit is located.

2 is a structural diagram of subpixels.

3 is a schematic block diagram of an electroluminescent display device according to an embodiment of the present invention.

Figure 4 is an exemplary view showing a graph of brightness changes with temperature changes.

5 is an exemplary diagram for a lookup table.

6 is a flowchart of a driving method according to an embodiment of the present invention.

<Explanation of symbols on main parts of the drawings>

110: sample / hold circuit unit 120: AD conversion unit

130: gamma part 140: gain conversion part

150: halftone part 160: drive part

P: display panel portion Active Area: light emitting area

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

The electroluminescent device used in the electroluminescent display device was a self-light emitting device having a light emitting layer formed between two electrodes. Electroluminescent devices could be divided into inorganic electroluminescent devices and organic electroluminescent devices according to the material of the light emitting layer.

In the organic light emitting device, electrons and holes are injected into the light emitting layer from an electron injection electrode and a hole injection electrode, respectively, and an exciton in which the injected electrons and holes combine is excited. The device emits light when it falls from the ground state to the ground state.

The organic light emitting diode is classified into a passive matrix organic emitting diode (PMOELD) and an active matrix organic emitting diode (AMOELD) according to a driving method.

Among them, the active matrix method is suitable for a large screen display or a high resolution display because it has the advantages of low power consumption and low crosstalk between pixels as compared with the passive matrix type.

In general, an active matrix type organic light emitting display device has one subpixel formed in an area where N × M scan and data lines cross each other on a substrate, and the subpixel includes one or more thin film transistors, capacitors, and organic light emitting diodes. do.

The thin film transistor includes a source, a drain, and a gate electrode, and the organic light emitting diode is electrically connected to the source or drain electrode terminal of the thin film transistor.

The thin film transistor is classified into a switching thin film transistor and a driving thin film transistor, and a compensation circuit for compensating their characteristics (eg, Vth) may be further provided.

In general driving of the organic light emitting diode, when the switching thin film transistor is turned on by the scan signal supplied through the scan wiring, the data signal supplied through the data wiring is stored in the capacitor in the form of data voltage. The data voltage stored in the capacitor turns on the gate of the driving thin film transistor to emit light of the organic light emitting diode.

On the other hand, the characteristics of the organic light emitting device have changed due to changes in temperature and time with respect to devices such as thin film transistors, capacitors, and organic light emitting diodes. Accordingly, for example, when the ambient temperature changes, the driving current flowing through the organic light emitting diode does not flow at the expected current value, and thus a problem of failing to emit light with luminance based on the supplied data signal has occurred.

SUMMARY OF THE INVENTION An object of the present invention for solving the above problems is to provide an electroluminescent display device and a driving method thereof capable of stabilizing display quality.

The present invention for solving the above problems, the display panel unit including a sub-pixel arranged in a matrix form; A monitoring pixel unit positioned at one side of the display panel unit; A sample converter configured to detect a state of the display panel unit through the monitoring pixel unit and convert the sample into a digital state value through a sampling process; A controller for finding a lookup table value corresponding to the state value received from the sample converter and adjusting a gain value of a data signal to be currently supplied; And a driving unit supplying a scan signal to a display panel unit and supplying the data signal received through a control unit to the display panel unit.

The state value may be a gradient of luminance change according to the temperature of the organic light emitting diode included in the subpixel.

The state value is obtained by the state value = (Ln-1-Ln) / (Tn-Tn-1), where Ln-1 is the previous luminance conversion value, Ln is the current luminance conversion value, Tn is the current temperature change value, Tn-1 may be a previous temperature change value.

The control unit may include a gamma unit for receiving a data signal from an external source, and a gain converter unit for adjusting a gain value by finding a lookup table value corresponding to the data signal and the state value supplied through the gamma unit and multiplying the gamma value of the data signal to be supplied. Can be.

The controller may further include a halftone unit halftoning the data signal adjusted through the gain converter.

The gain converter may store the adjusted gain value in the internal memory and periodically call it up every sync.

The subpixels may include one or more thin film transistors and capacitors, and power lines of the subpixels may be connected in common.

It includes a power supply for supplying power to the power line, the power supply can receive the status value from the monitoring pixel unit to adjust the output power voltage value.

On the other hand, the present invention, the sampling step of detecting the state of the display panel unit through a monitoring pixel unit located on one side of the display panel unit including the sub-pixels arranged in a matrix form and converts to a digital state value through a sampling process; A gain adjusting step of adjusting a gain value of a data signal to be supplied currently by finding a look-up table value corresponding to a state value sampled as a digital state value; And a signal supply step of supplying a data signal and a scan signal whose gain value is adjusted to the display panel unit.

The state value may be a gradient of luminance change according to the temperature of the organic light emitting diode included in the subpixel.

The state value is obtained by the state value = (Ln-1-Ln) / (Tn-Tn-1), where Ln-1 is the previous luminance conversion value, Ln is the current luminance conversion value, Tn is the current temperature change value, Tn-1 may be a previous temperature change value.

In the gain adjustment step, the gain value may be adjusted by finding a lookup table value corresponding to the state value and multiplying by the gamma value of the data signal to be supplied.

The gain adjusting step may further include a halftone step of half-toning the data signal whose gain is adjusted.

The gain value may be stored in the internal memory and periodically retrieved every sync to apply to the data signal to be supplied.

The subpixels include one or more thin film transistors and capacitors, and power lines of the subpixels can be connected in common.

It includes a power supply for supplying power to the power line, the power supply can receive the status value from the monitoring pixel unit to adjust the output power voltage value.

<Example 1>

The present invention adjusts the gain of the data signal or the power voltage supplied to the subpixels so that the brightness of the organic light emitting diode is not lowered due to temperature change by sensing the state of the display panel through a monitoring pixel unit positioned in the display panel. do.

1 is an exemplary view schematically showing an area where a monitoring pixel unit is located.

Referring to FIG. 1, the monitoring pixel unit is positioned in one of the light emitting regions (non-light emitting regions) of the display panel unit P, and includes a thin film transistor TFT and an organic light emitting diode OLED. ). The monitoring pixel unit receives the gate signal MGB and the power supply voltage Mon_B from the driver to the gate of the thin film transistor TFT and a source or a drain.

Although not shown in the drawings, the monitoring pixel unit may have the same configuration as that of the subpixels positioned in the active area of the display panel unit P. Referring to FIG.

2 is a structural diagram of subpixels.

Referring to FIG. 2, an electroluminescent display device according to an exemplary embodiment of the present invention shows a structure diagram of subpixels RED, GREEN, and BLUE positioned in an active area of a display panel unit P. Referring to FIG.

As illustrated, the sub-pixels RED, GREEN, and BLUE of the electroluminescent display according to the present invention are connected to the power line VDD in common. The sensor detects the state of the display panel unit P using the monitoring pixel unit, and when the luminance of the organic light emitting diode is changed due to the temperature change, the output of the power supply is adjusted to adjust the subpixels (RED, GREEN, This is to control the power voltage supplied to BLUE).

For reference, the power supplied to the power line VDD may be effectively adjusted to the most efficient subpixels RED, GREEN, and BLUE corresponding to red, green, and blue.

Each of the subpixels RED, GREEN, and BLUE, although not shown in detail, includes one or more capacitors and thin film transistors electrically connected to data lines and scan lines. Meanwhile, a transparent electrode (ITO) is used as the pixel electrode electrically connected to the source or drain electrode of the thin film transistor, but an opaque electrode (eg, aluminum) may be used depending on the light emission method.

In addition, an organic light emitting diode including an organic light emitting layer EML is positioned between layers such as a hole injection layer HIL, a hole transport layer HTL, an electron transport layer ETL, an electron injection layer EIL, and the like on the pixel electrode.

Meanwhile, each of the subpixels RED, GREEN, and BLUE are electrically connected to correspond to each of the data lines R_data, G_data, and B_data. Although not shown, an upper portion of each of the subpixels RED, GREEN, and BLUE is not shown. The common electrode is located at.

3 is a schematic block diagram of an electroluminescent display device according to an embodiment of the present invention.

Referring to FIG. 3, the display panel unit P including subpixels arranged in a matrix form (active pixels) is positioned. As described above, only one monitoring pixel is positioned at one side of the active area of the display panel P, that is, the non-light emitting area.

The reference current source IREF may be supplied to the monitoring pixel unit through the second switching device S / W2 and the passive device R. Here, the second switching element S / W2 may be a thin film transistor capable of switching by receiving a signal from an external control device, and the passive element R may be an internal resistance.

The sample converters 110 and 120 detect the state of the temperature change of the display panel P through the first switching device S / W1 electrically connected to the monitoring pixel, and then perform a sampling process. Convert to status value.

Here, the state value may be a gradient of luminance change according to the temperature of the organic light emitting diode included in the subpixel.

4 is an exemplary diagram illustrating a graph of luminance change according to temperature change, and FIG. 5 is an exemplary diagram of a lookup table.

The state value described above may be obtained through the slope of the luminance change according to the temperature change as shown in FIG. 4.

Referring to Fig. 4, the state value is obtained by the state value = (Ln-1-Ln) / (Tn-Tn-1). Here, Ln-1 is a previous luminance conversion value, Ln is a current luminance conversion value, Tn is a current temperature change value, and Tn-1 is a previous temperature change value. Such a state value is applied to a lookup table as shown in FIG. 5 to be processed to set an appropriate gain value with reference to a gradient of luminance change according to temperature change.

The sample converters 110 and 120 are divided into a sample / hold circuit 110 for sampling after sensing the state of the display panel unit P and an AD converter 120 for converting the sampled data into digital state values. Here, it is noted that the higher the sampling frequency, the more sensitively the state of the display panel unit P can be detected.

In addition, the AD converter 120 provides a digital state value to the power supply device so as to adjust a power supply voltage according to the state of the display panel unit P to supply the sub pixels to the active pixels. In the drawing, the power supply is omitted, and the state value is reflected in the sub pixels.

The controller finds a lookup table value corresponding to the state value received from the sample converter and adjusts a gain value of a data signal to be supplied currently.

The controller finds a gamma part 130 that receives a data signal from an external source, a lookup table value corresponding to the data signal supplied through the gamma part 130, and a state value, and multiplies the gamma value of the data signal to be supplied by a current to obtain a gain value. It may include a gain converter 140 for adjusting the. The gain converter 140 may store the adjusted gain value in the internal memory and periodically retrieve it in every sync.

The controller may further include a halftone unit 150 that halftones the data signal adjusted through the gain converter 140. Here, the halftone unit 150 adjusts the expressive power of the gray value of the data signal whose gain is converted.

The half-toned data signal is transmitted to the driver 160.

The driver 160 supplies the scan signal and the previously adjusted data signal to the display panel unit P to express a desired image.

As described above, the present invention may detect the state of the display panel unit P through a monitoring pixel to adjust a gain value of the data signal, reflect it to the data signal, and correct the data signal. Incidentally, the power supply voltages supplied to the active pixels may also be adjusted with reference to the state values.

<Driving method>

6 is a flowchart of a driving method according to an embodiment of the present invention.

The driving method of the electroluminescent display device according to the present invention may be as follows.

In the sampling step S202, after sensing the state of the display panel unit P through a monitoring pixel unit located at one side of the display panel unit P including the subpixels arranged in a matrix form, sampling is performed. This is a step of converting the digital state value through a process.

Here, the state value may be a gradient of luminance change according to the temperature of the organic light emitting diode included in the subpixel.

The state value is obtained by the state value = (Ln-1-Ln) / (Tn-Tn-1). Here, Ln-1 is a previous luminance conversion value, Ln is a current luminance conversion value, Tn is a current temperature change value, and Tn-1 is a previous temperature change value. Such a state value is applied to a lookup table in the future and is processed to set an appropriate gain value with reference to a gradient of luminance change according to temperature change (see FIGS. 4 and 5).

The gain adjusting step (S204) is a step of adjusting a gain value of a data signal to be supplied currently by finding a lookup table value corresponding to the sampled digital state value. Here, the gain value is multiplied by the gamma value. In addition, the gain value may be stored in the internal memory and periodically retrieved every sync to apply to the data signal to be supplied.

On the other hand, the previously detected state value is sampled, converted into a digital state value, and transferred to the power supply device, and the power supply device adjusts the output power voltage value according to the state value to the common power line of the active pixels. See also supply.

The halftone step S206 is a step of halftoning a data signal whose gain is adjusted. Here, in the halftone step S206, the expression power of the gray level of the data signal whose gain is converted is adjusted.

The signal supply step S208 is a step of supplying a data signal and a scan signal whose gain is adjusted to the display panel unit P. FIG.

As described above, the present invention may detect the state of the display panel unit P through a monitoring pixel to adjust a gain value of the data signal, reflect it to the data signal, and correct the data signal. Incidentally, the power supply voltages supplied to the active pixels may also be adjusted with reference to the state values.

As described above, the present invention can secure a large bezel margin for the panel by using only one monitoring pixel unit, and reduces the line load effect by using the power lines of the sub pixels in common. can do.

In addition, the present invention stores the detected state value and the gain value in the look-up table so that the gain value of the control unit can be controlled to control the luminance of the RGB subpixels. In addition, the stored value uses the measured value and stores it in memory so that it can be modified as needed. In this case, it is possible to cope without changing the gamma value or the white balance by the gain value conversion.

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 shown by the claims below, rather than the above 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.

As described above, the present invention has the effect of providing an electroluminescent display device and a driving method thereof capable of stabilizing display quality.

Claims (16)

A display panel unit including subpixels arranged in a matrix; A monitoring pixel unit positioned at one side of the display panel unit; A sample converter configured to detect a state of the display panel unit through the monitoring pixel unit and convert the sample into a digital state value through a sampling process; A controller for finding a lookup table value corresponding to the state value received from the sample converter and adjusting a gain value of a data signal to be currently supplied; And And a driving unit supplying a scan signal to the display panel unit and supplying the data signal received through the control unit to the display panel unit. The method of claim 1, wherein the state value, And an inclination of a luminance change according to a temperature of the organic light emitting diode included in the sub-pixel. The method of claim 1, wherein the state value, Status value = (Ln-1-Ln) / (Tn-Tn-1) Ln-1 is a previous luminance conversion value, Ln is a current luminance conversion value, And wherein Tn is a current temperature change value and Tn-1 is a previous temperature change value. The method of claim 1, wherein the control unit, A gamma part receiving a data signal from the outside, And a gain converter which finds a lookup table value corresponding to the data signal supplied through the gamma part and multiplies the gamma value of a data signal to be supplied currently and adjusts the gain value. The method of claim 4, wherein the control unit, And a halftone unit for halftoning the data signal adjusted through the gain converter. The method of claim 4, wherein the gain converter, And storing the adjusted gain value in an internal memory to be periodically recalled at every sync. The method of claim 1, wherein the subpixels are: One or more thin film transistors and capacitors, And a power line of the subpixels is connected in common. The method of claim 7, wherein It includes a power supply for supplying power to the power line, And the power supply device receives the state value from the monitoring pixel unit and adjusts an output power voltage value. A sampling step of sensing a state of the display panel unit through a monitoring pixel unit located at one side of the display panel unit including sub pixels arranged in a matrix form, sampling the sample, and converting the sample into a digital state value; A gain adjustment step of adjusting a gain value of a data signal to be currently supplied by finding a lookup table value corresponding to the sampled digital state value; And And a signal supplying step of supplying the data signal and the scan signal of which the gain value is adjusted to the display panel unit. The method of claim 9, wherein the state value, And a slope of luminance change according to a temperature of an organic light emitting diode included in the subpixel. The method of claim 9, wherein the state value, Status value = (Ln-1-Ln) / (Tn-Tn-1) Ln-1 is a previous luminance conversion value, Ln is a current luminance conversion value, And wherein Tn is a present temperature change value and Tn-1 is a previous temperature change value. The method of claim 9, wherein in the gain adjusting step, And driving the gain value by finding a lookup table value corresponding to the state value and multiplying by a gamma value of a data signal to be supplied. The method of claim 9, wherein in the gain adjusting step, And a halftone step of halftoning the data signal whose gain is adjusted. The method of claim 9, The gain value is stored in an internal memory and periodically retrieved at every sync and applied to the data signal to be supplied currently. The method of claim 9, wherein the subpixels are: One or more thin film transistors and capacitors, And a power line of the subpixels is connected in common. The method of claim 15, It includes a power supply for supplying power to the power line, And the power supply device receives the state value from the monitoring pixel unit and adjusts an output power voltage value.

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