KR100820056B1 - Distributed Pulse Amplitude Modulation Driving Method of OLED - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving an organic light emitting display, and in particular, by setting an output reference time of a drive current within one horizontal period differently according to a column and outputting a driving pulse, a time for which current is concentrated and output within one horizontal period. The present invention relates to a method of driving an organic light emitting display using a pulse amplitude modulation method capable of minimizing an increase in display characteristics.

The constituent means of the organic light emitting display driving method using the pulse amplitude modulation method of the present invention is an organic light emitting display driving method using the pulse amplitude modulation method, wherein the output reference time of the driving current within one horizontal period is determined. The driving pulse is output by dividing into two viewpoints for each column, and for the half of the pixels, a start mode for outputting the driving pulse at the start of one horizontal period is applied, and to the other half of the pixels. In this case, an end mode (E mode) for outputting a driving pulse when a predetermined time has elapsed based on the start time of the one horizontal cycle is applied, wherein an end time point of the driving pulse coincides with the end time point of the one horizontal cycle. It is done.

OLED, organic light emitting diode, organic light emitting display, pulse amplitude modulation

Description

Distributed Pulse Amplitude Modulation Driving Method of OLED

1 is a schematic diagram illustrating a structure of a general organic light emitting display.

2 is a schematic diagram for describing an operation of an organic light emitting display device.

3 is a pulse waveform diagram of a pulse width modulation method used in a conventional organic light emitting display driving method.

4 is a pulse diagram of a pulse width modulation method used in another conventional organic light emitting display driving method.

5 is a driving pulse waveform diagram of a pulse amplitude modulation method used in a conventional organic light emitting display driving method.

6 is a driving pulse waveform diagram of the pulse amplitude modulation method used in the organic light emitting display driving method according to an embodiment of the present invention.

7 and 8 are driving pulse waveform diagrams of a pulse amplitude modulation method for explaining the precharge method according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving an organic light emitting display, and in particular, by setting an output reference time of a drive current within one horizontal period differently according to a column and outputting a driving pulse, a time for which current is concentrated and output within one horizontal period. The present invention relates to a method of driving an organic light emitting display using a pulse amplitude modulation method capable of minimizing an increase in display characteristics.

First, a schematic description of an organic light emitting display and a conventional driving method will be described.

1 is a perspective view showing a schematic configuration of an organic light emitting display constituting each pixel of a general organic EL display.

As shown in Fig. 1, an organic light emitting display of an organic EL display has a transparent glass substrate 1, on which a plurality of anode layers 2 are transparent, such as ITO. Each conductive material is provided in a stripe shape at predetermined intervals. On each of the anode layers 2, electrons are supplied by applying a direct current voltage to the organic light emitting layer 4 including a hole transport layer 3 for supplying holes and a small amount of organic dye as a dopant, and a direct current voltage. The electron transport layer 5 is sequentially stacked on the glass substrate 1.

On the electron transport layer 5 corresponding to the uppermost layer in the laminated layer, a plurality of cathode layers 6 made of a conductive material are orthogonal to the direction in which the respective anode layers 2 extend at predetermined intervals. It is installed in a stripe shape. On the other hand, each anode layer 2 on the glass substrate 1 is connected to the anode of the DC power supply 7, respectively, and each cathode layer 6 corresponding to the uppermost layer is the cathode of the DC power supply 7, respectively. Is connected to.

In the organic light emitting display of the organic EL display having the above configuration, when a DC voltage is applied by the DC power supply 7 between each anode layer 2 and the cathode layer 6, the anode to which the DC voltage is applied. From the hole transport layer 3 stacked on the layer 2, holes are injected into the organic light emitting layer 4 and electrons are emitted from the electron transport layer 5 below the cathode layer 6 to which a direct current voltage is applied. ) Is injected into.

In the organic light emitting layer 4 in which the holes from the hole transport layer 3 and the electrons from the electron transport layer 5 are respectively injected, energy is generated while the holes and the electrons recombine. Then, the energy is absorbed by the organic dye contained in the organic light emitting layer 4, the light is emitted. The light generated from the organic light emitting layer 4 is sequentially transmitted through the hole transport layer 3, the anode layer 2, and the glass substrate 1, and is emitted to the lower side of the glass substrate 1.

The hole transport layer 3, the organic light emitting layer 4, and the electron transport layer 5 among the several layers constituting the organic EL display performing the above operation are organic thin films made of organic compounds.

Next, the structure and operation of the organic light emitting element will be described.

In general, as shown in FIG. 2, an anode and a cathode are arranged in a matrix shape of columns and rows, and organic materials are formed at intersections of columns and rows, as shown in FIG. 2. As a device that emits light from organic materials as it is deposited and flows from row to row, and emits light by itself, it does not need a backlight device such as a liquid crystal display, so it is optimal for thinning and has no limitation on viewing angle. It has been largely used as a display device.

The conventional organic light emitting display driving method is a method of supplying a pulse width modulation (PWM) driving pulse to each drive circuit, and supplying a scan signal to the cathode through a row drive circuit as shown in FIG. The column drive circuit supplies a pulse width modulated signal having a pulse width corresponding to the gray level to the anode as a drive signal, wherein the drive signal supplied to the column drive circuit is shown in the pulse waveform diagram of FIG. 3. The driving pulses for all columns (column1 to m) are output based on the start time t1 of one horizontal period (1H).

However, in this driving method, the pulse width modulation (PWM) type driving pulse concentrates the output of driving current for all columns at the start of one horizontal period. Therefore, the density of current shows a high density of 7 at the beginning of one horizontal period. While it is formed, it can be seen that only 1 flows at the end of one horizontal period. As such, the amount of current flowing out to the corresponding scan line increases in the initial stage of driving, and thus, a voltage drop largely occurs at the start of one horizontal line. As a result, such a voltage drop causes a drop in the operating voltage of the driving IC used in the drive circuit, which causes the driving IC to operate in a region having a large voltage dependence of current rather than a normal operating range.

Therefore, the current fluctuates even with a small voltage fluctuation, which causes a change in luminance, which causes a decrease in display characteristics such as luminance loading of the light emitting device.

On the other hand, Japanese Patent Application Laid-Open No. 2000-221943 (see the pulse waveform diagram of FIG. 4) is disclosed as one of the conventional technologies developed to solve the problem caused by the current concentration phenomenon.

According to the prior art, a first driver circuit for supplying a scan signal to a cathode and a second driver circuit for supplying a pulse width modulated signal having a pulse width according to a gray level to the anode as a drive signal, wherein the second driver circuit is provided. The start timing of the output of the drive signal supplied by the driver circuit is set to be different for each column, that is, dividing one horizontal period into predetermined sections and outputting driving pulses for each column sequentially at the start of each section. It is a driving method.

According to the conventional driving method, when the driving start time point is not the start time point of one horizontal line, a case where the driving pulse does not end until the end point of one horizontal period may occur. For example, as shown in the pulse waveform diagram of FIG. 4, the driving pulses for the fourth column (column 4) and the sixth column (column 6) of one horizontal period are driven until the end point of the one horizontal period. In this case, the driving pulse should be composed of distributed pulses so that the remaining current can be output from the beginning of one horizontal line.

However, such a prior art has a problem in that the configuration of the driving circuit is not only complicated, but also a difference in luminance occurs during distributed pulse driving and continuous pulse driving. That is, even if the current is output for the same time to express the same gray level, the driving pulses (constant pulses) for the third column (column 3) and the driving pulses (column 4) for the fourth column (column 4) of FIG. Pulse), the luminance is unlikely to be the same.

In addition, there is a problem in that the luminance difference due to the difference in the start time of the driving pulse occurs. That is, even if the current is output for the same time (the first and second column driving pulses of FIG. 4) to express the same gray scale, the pulse (first column of FIG. 4) which starts outputting at the first section (time t1) and If the start point of the driving pulse is different, such as the pulse (second column of FIG. 4) which starts output in the second section (time point t2), the luminance is not likely to be the same.

Meanwhile, even when the organic light emitting display is driven by using a conventional pulse amplitude modulation (PAM) method, as shown in FIG. 5, since all current outputs are concentrated during one horizontal line time, the corresponding scan line (scan) The amount of current flowing to the line increases, resulting in a large voltage drop.

This voltage drop causes the operating voltage of the driver IC to drop, which causes the driver IC to operate in a linear region, which is a region where the voltage dependence of the current is large, rather than a saturation region. As a result, even a small voltage fluctuation causes a large fluctuation in current, which causes a change in luminance. This causes degradation of display characteristics such as luminance loding. This phenomenon is commonly referred to as cross-talk and is one of the biggest causes of deterioration of the characteristics of an organic light emitting display.

That is, as shown in FIG. 5, the driving voltage is simultaneously applied to all pixels of one horizontal line (row 1) at the same time as the start of one horizontal period or after the discharge and precharge time. (Current) is output. In this case, looking at the concentration of the current, it can be seen that the current is concentrated from the beginning to the end of one horizontal period.

In this case, when the voltage drop increases due to the output current of the driver IC and the wiring resistance of the panel, when the driver IC operates in the linear region at 9 points of current amount, the driver IC is operated for the entire time of 1H. It operates in the linear region. Therefore, the above problems arise.

The present invention was devised to solve the problems of the prior art as described above, and the pulsed amplitude modulation (PAM) driving pulses outputted in one horizontal period are output at intervals without outputting the pulses at the same time. For some pixels, the temporal reference of the driving pulse is a time after a predetermined time with respect to the start of one horizontal period, and the end point of the driving pulse is coincident with the end of one horizontal period. By alternately using, the pulse amplitude modulation method can improve luminance while preventing display performance deterioration due to the luminance difference that could be caused by the distributed driving pulse or the output start point of the driving pulse instead of the continuous driving pulse. An object of the present invention is to provide a method of driving an organic light emitting display.

In order to solve the above technical problem, the constituent means of the organic light emitting display driving method using the pulse amplitude modulation method of the present invention, which is proposed in the organic light emitting display driving method using the pulse amplitude modulation (Pulse Amplitude Modulation) method, 1 Start mode (S mode) for dividing the output reference time of the drive current in the horizontal period into two time points for each column and outputting the driving pulse at the start of one horizontal period for half of the pixels. For the other half of the pixels, the end mode (E mode) for outputting a driving pulse after a predetermined time has elapsed based on the start point of the first horizontal period is applied, but the end point of the driving pulse is It is characterized by coinciding with the end of the horizontal period.

The driving pulse may be divided and output based on a start time and an end time of the one horizontal period.

The start mode and the end mode may be alternately applied to adjacent pixels or adjacent unit pixels.

The start mode and the end mode are alternately applied to adjacent pixels or adjacent unit pixels, and alternately applied to adjacent rows.

In addition, the start mode and the end mode are alternately applied to adjacent pixels or adjacent unit pixels, and are alternately applied to each adjacent pixel or each adjacent unit pixel whenever the frame is changed.

In addition, when precharge is performed in the start mode and the end mode, when the scan voltage is on, the precharge is performed in the start mode and the end mode. It features.

In addition, when precharge is performed in the start mode and the end mode, when the scan voltage is on, precharge is performed in the end mode and scan is performed. ) When the voltage is off, the precharge is performed in the start mode.

Hereinafter, with reference to the accompanying drawings will be described in detail the operation and embodiment of the organic light emitting display driving method using a pulse amplitude modulation method of the present invention consisting of the above configuration means.

Hereinafter, a method of driving an organic light emitting display will be described as an example. However, the main concept of the present invention can be applied to other display devices using a pulse amplitude modulation (PAM) type driving pulse. The idea is not limited to this and may be variously modified and modified by those skilled in the art.

6 is a driving pulse waveform diagram of the pulse amplitude modulation method used in the organic light emitting display driving method using the pulse amplitude modulation method according to an embodiment of the present invention, the organic light emitting display driving method according to an embodiment of the present invention. The output reference time of the drive current within 1 horizontal period, i.e., is set differently according to columns 1-7, and the driving pulse is output, and the concentration of the current distributed within one horizontal period is illustrated. In this case, the concentration of the current shows that the current is concentrated only for a part of one horizontal period, and thus, the section in which the current is concentrated becomes relatively small as compared with the conventional art.

In this example, the driving currents of the first, second, fourth, and seventh columns are one gradation L1, and the driving currents of the third and fifth columns are two gradation L2 and the sixth row, respectively. Exemplifies a case of three gray scales L3, and in particular, an arrow indicates a reference time point and direction of gray scale calculation.

In the driving method of the organic light emitting display using the pulse amplitude modulation (Pulse Amplitude Modulation) method of the present invention illustrated in FIG. 6, the driving reference pulse by dividing the output reference time of the drive current in one horizontal period into two time points for each column. In particular, a start mode (S mode) for outputting a driving pulse is applied to one half of the pixels at a start point of one horizontal period, and a start point of the one horizontal period is applied to the other half of the pixels. An end mode (E mode) for outputting a driving pulse at a time elapsed by a predetermined time is applied, but the end point of the driving pulse coincides with the end point of the one horizontal period.

That is, in the driving method according to the present invention illustrated in FIG. 6, some pixels, that is, the first column (column 1), the third column (column 3), the fifth column (column 5), and the seventh column (column) The reference point of time of output of the driving current for 7) is set at the start of one horizontal period, and some other pixels, namely, the second column (column 2), the fourth column (column 4), and the sixth column (column 6) The reference point of time for outputting the driving current is set at a point in time after which a predetermined time has elapsed (at point t2 in FIG. 6) from the start point of the first horizontal period.

The driving pulse may be divided and output based on a start time and an end time of the one horizontal period. Therefore, when a time elapsed after a predetermined time with respect to the start time of the first horizontal period is the output reference time point of the driving current, it is preferable that the end time point of the driving pulse coincides with the end of the first horizontal period. . However, the present invention is not limited thereto, and depending on the application example, the ends of the horizontal period may not coincide.

In this case, the pulse in which the output reference time point of the driving current is set to the start time point of one horizontal period is called a pulse of the start mode (S mode), and the output reference time point of the drive current is based on the start time point of the one horizontal period. Therefore, the pulse set to the point where a predetermined time has elapsed is called pulse of the end mode (E mode). In this case, the end mode (E mode) may be implemented to coincide with the end of one horizontal period. Alternatively, the end mode (E mode) may be implemented so as not to coincide with the end of one horizontal period.

In the driving method according to the embodiment of the present invention, a method of outputting driving pulses in the start mode to the number of pixels corresponding to half in one horizontal period and outputting the driving pulses of the end mode to the other half of the pixels is applied. .

On the other hand, the driving method according to the embodiment of the present invention may be applied to the start mode and the end mode alternately for each adjacent pixel or adjacent unit pixel.

Table 1 below is an example in which the start mode and the end mode are alternately applied to adjacent pixels or adjacent unit pixels, and the adjacent unit pixels change from the E mode to the E ?? S ?? E mode, that is, Regardless of the row, the driving pulse of the start mode (S mode) is output to the odd columns (1, 3, ..., m-1), and then the even columns (2, 4, ..., m) This is a method of outputting the driving pulse in the end mode (E mode).

1 row 2 rows 3 row 4 rows ..... m-1 rows m column 1 row S E S E ... S E 2 row S E S E ... S E 3 rows S E S E ... S E 4 rows S E S E ... S E .... ... .... ... ... ... ... ... n-1 rows S E S E ... S E n rows S E S E ... S E

Table 1

Table 2 below is an example in which the start mode and the end mode are alternately applied to adjacent pixels or adjacent unit pixels, and starting from the E mode, the adjacent unit pixels change to the S ?? E ?? S mode. Regardless of the row, the output pulse of the end mode (E mode) is output to the odd columns (1,3, ..., m-1), and then the even columns (2,4, ..., m) This is a method of outputting a driving pulse in start mode (S mode).

1 row 2 rows 3 row 4 rows ... m-1 rows m column 1 row E S E S ... E S 2 row E S E S ... E S 3 rows E S E S ... E S 4 rows E S E S ... E S ... ... ... ... ... ... ... ... n-1 rows E S E S ... E S n rows E S E S ... E S

Table 2

As shown in Table 1 and Table 2, the start mode and the end mode may be alternately applied to adjacent pixels or adjacent unit pixels. The above scheme may be alternately applied according to frame units or other time units. That is, for the first frame, the pattern shown in Table 1 is applied as a driving method, for the next frame, the pattern shown in Table 2 is applied as a driving method, and for the next frame, the patterns shown in Tables 1 and 2 The driving method can be applied alternately.

Meanwhile, the driving method according to the embodiment of the present invention is a method of alternately driving the operation mode of the driving pulse for each adjacent row while changing the operation mode of the driving pulse for each adjacent pixel or adjacent unit pixel. Other embodiments may be configured.

Table 3 below shows the driving pulse of the start mode (S mode) in the odd columns (1, 3, ..., m-1) in the first row (row 1), and then the even columns (2, 4, ..., m) outputs the driving pulse of the end mode (E mode), and in the second row (row 2), the end mode (E mode) to the odd columns (1, 3, ..., m-1) This method alternates the method of outputting the driving pulse of and outputting the driving pulse of the start mode (S mode) to the next even columns (2, 4, ..., m).

1 row 2 rows 3 row 4 rows ... m-1 rows m column 1 row S E S E ... S E 2 row E S E S ... E S 3 rows S E S E ... S E 4 rows E S E S ... E S ... ... ... ... ... ... ... ... n-1 rows S E S E ... S E n rows E S E S ... E S

Table 3

Table 4 shows output pulses of the end mode (E mode) in odd columns (1, 3, ..., m-1) in the first row (row 1), and then the even columns (2, 4, ..., m) outputs driving pulses in the start mode (S mode), and in the second row (row 2), the odd mode columns (1, 3, ..., m-1) are used in the start mode (S mode). It outputs the driving pulse of and outputs the driving pulse of the end mode (E mode) to the next even columns (2, 4, ..., m).

1 row 2 rows 3 row 4 rows ... m-1 rows m column 1 row E S E S ... E S 2 row S E S E ... S E 3 rows E S E S ... E S 4 rows S E S E ... S E ... ... ... ... ... ... ... ... n-1 rows E S E S ... E S n rows S E S E ... S E

Table 4

As shown in Tables 3 and 4, the start mode and the end mode may be alternately applied to adjacent pixels or adjacent unit pixels, and may be alternately applied to adjacent rows. The above scheme may be alternately applied according to frame units or other time units. That is, for the first frame, the pattern shown in Table 3 is applied as a driving method, for the next frame, the pattern shown in Table 4 is applied as the driving method, and for the next frame, the patterns of Tables 3 and 4 The driving method can be applied alternately.

In addition, the driving method according to the embodiments of the present invention alternates with respect to adjacent frames in such a manner that, in driving a single pixel, a driving pulse in the start mode is output in one frame and an end mode driving pulse is output in the next frame. Change the operation mode of the driving pulse, change the operation mode of the driving pulse for each unit pixel of each of the red (R) / green (G) / blue (B), or drive the red (R) / green ( Another embodiment can be configured by a method in which the operation mode of the driving pulse is changed for each pixel forming three display pixels in which G) / blue (B) units form one display unit.

Meanwhile, in the method of driving the organic light emitting display according to the present invention, precharge may be performed by applying a voltage to a scan line. In FIG. 7 and FIG. 8, the precharge is performed in the start mode and the end mode. A precharge section is shown.

First, as shown in FIG. 7, when the voltage of the scan line is in an on state, a method of performing precharge in the start mode and the end mode may be applied. have.

Second, as shown in FIG. 8, when the voltage of the scan line is in an on state, precharge is performed in the end mode, and the voltage of the scan line is increased. When in the off state, a method in which precharge is performed in the start mode may be applied.

In the precharge method illustrated in FIG. 8, the difference in luminance may occur because the precharge method is different between the start mode and the end mode, but for the same pixel or the same unit pixel, the start mode and the end mode are the same. By being applied alternately in time, the luminance difference can be canceled out.

According to the organic light emitting display driving method using the pulse amplitude modulation method of the present invention having the above-described configuration, operation and preferred embodiment, the drive pulse by setting the output reference time of the drive current in one horizontal period differently according to the column (column) Since the output time is minimized, the time for which the current is concentrated and output within one horizontal period is minimized, so that the cross-talk phenomenon is reduced, thereby improving display characteristics.

Claims (9)

In the organic light emitting display driving method using a pulse amplitude modulation (Pulse Amplitude Modulation) method, 1 Output the drive pulse by dividing the output reference time of the drive current in the horizontal period into two time points for each column. For the half of the pixels, a start mode (S mode) for outputting a driving pulse at the start of one horizontal period is applied. For the other half of the pixels, a start time starts when a predetermined time elapses from the start of the first horizontal period, and an end mode (E mode) in which the end time coincides with the end of the first horizontal period is applied. An organic light emitting display driving method using a pulse amplitude modulation method. delete The method of claim 1, And the start mode does not coincide with the end of the one horizontal period. The method of claim 1, wherein the driving pulse, The organic light emitting display driving method using a pulse amplitude modulation method characterized in that the divided output based on the start time and the end time of the one horizontal period. The method of claim 1, The start mode and the end mode are alternately applied to adjacent pixels or adjacent unit pixels, and the organic light emitting display driving method using a pulse amplitude modulation method. The method of claim 1, The start mode and the end mode are alternately applied to adjacent pixels or adjacent unit pixels, and are alternately applied to adjacent rows, and the organic light emitting display driving method using the pulse amplitude modulation method. The method of claim 1, The start mode and the end mode are alternately applied to adjacent pixels or adjacent unit pixels, and are alternately applied to each adjacent pixel or each adjacent unit pixel every time the frame is changed. Display driving method. The method of claim 1, When precharge is performed in the start mode and the end mode, when the scan voltage is on, precharge is performed in the start mode and the end mode. An organic light emitting display driving method using a pulse amplitude modulation method. The method of claim 1, When precharge is performed in the start mode and the end mode, when the scan voltage is on, precharge is performed in the end mode, and the scan voltage is performed. And when it is off, precharge is performed in the start mode.

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