KR102469801B1 - Method of setting driving voltages to reduce power consumption in organic light emitting display device - Google Patents

Abstract

A driving voltage setting method for reducing power consumption of an organic light emitting display device is disclosed. For dimming control of an OLED device including a panel including a plurality of OLED pixels and a driving circuit for controlling driving of the plurality of OLED pixels, it is checked whether a luminance condition of an OLED pixel is changed. When there is a change in luminance conditions, settings are made to change the level of each of the driving-related voltages in the direction of reducing power consumption within the range of the margin voltage that can occur in the driving-related voltages related to driving the OLED pixel. . This method can be implemented with a logic circuit in a driving IC.

Description

Method of setting driving voltages to reduce power consumption in organic light emitting display device {Method of setting driving voltages to reduce power consumption in organic light emitting display device}

The present invention relates to a flat panel display device, and more particularly, to driving an organic light emitting display device and a display system including the same.

An organic light emitting display (OLED) device displays an image using an organic light emitting diode that generates light by recombination of electrons and holes. An OLED device includes a plurality of pixels, and each pixel has an OLED element, a pixel circuit that independently drives the OLED element, and a drive control circuit that drives each pixel circuit.

OLED devices use various voltages, for example, voltages for generating gradation voltages, voltages for turning on and off switching transistors of pixel circuits, and voltages for initialization to control light emission of OLED devices. These voltages are set to levels suitable for each purpose. However, in the case of existing OLED devices, the levels of the voltages were previously set and used without considering the surrounding environment, for example, the ambient brightness in the room or outdoors. As a result, the set levels of the voltages were set very generously in consideration of the worst case. That is, the level of each voltage is set to a sufficiently large value based on a case where the highest level voltage (maximum level voltage) is to be used, such as when maximum luminance is to be displayed. Even when it is not necessary to use all of the maximum level voltage, the maximum level voltage is always used. The higher the voltage level, the larger the swing width and the higher the power consumption. Inefficiency occurs in power consumption.

In consideration of the above points, the present invention, in the case of dimming control to lower the brightness of a pixel, lowers the level of voltages required to drive an OLED pixel accordingly, thereby reducing unnecessary power consumption and reducing power consumption. It aims to provide a method.

According to one embodiment of the present invention for achieving the above object, a method for setting a driving voltage of an OLED device is provided. According to this method, for dimming control of an OLED device including a panel including a plurality of OLED pixels and a driving circuit for controlling driving of the plurality of OLED pixels, it is checked whether a change occurs in the luminance condition of an OLED pixel. can Setting to change the level of each of the driving-related voltages in the direction of reducing power consumption within the range of the margin voltage that may occur in the driving-related voltages related to driving the OLED pixel when the luminance condition is changed. can do.

According to an embodiment of the present invention, the setting includes setting the level of the driving related voltages in advance in association with the luminance condition of the OLED pixel, and when the luminance condition is changed, the level of the driving related voltages. It may include changing the luminance to set levels associated with the changed luminance condition.

According to an embodiment of the present invention, the previously set driving-related voltages may be set to a voltage value of one level, regardless of the degree of change of the luminance condition. According to another embodiment, the preset driving-related voltages may be set to voltage values having different levels for each degree of change in the luminance condition.

According to an exemplary embodiment of the present invention, the driving related voltages may include the grayscale expression voltage VREG1 of the OLED pixel. According to another exemplary embodiment, the driving-related voltages may include a turn-off voltage (VGH) for turning off the switching transistor of the OLED pixel. According to another exemplary embodiment, the driving-related voltages may include a turn-on voltage (VGH) for turning on a switching transistor of the OLED pixel. According to another exemplary embodiment, the driving-related voltages may include an initialization voltage Vinit for initializing a gate of a driving transistor of the OLED pixel and an anode of the OLED element.

According to an exemplary embodiment of the present invention, the setting may include setting the grayscale expression voltage VREG1 of the OLED pixel in response to the changed luminance condition when there is a change in the luminance condition. Furthermore, the turn-off voltage VGH of the transistor may be obtained by adding the turn-off margin voltage of the transistor of the OLED pixel to the set grayscale expression voltage VREG1.

According to an exemplary embodiment of the present invention, the setting may further include setting the first source voltage VLIN1 by adding a head room margin voltage value to the turn-off voltage VGH of the transistor. can include Here, the first source voltage VLIN1 may be a source voltage that generates the gradation expression voltage VREG1, the turn-off voltage VGH, and the turn-on voltage VGL for turning on the transistor of the OLED pixel. In addition, the headroom margin voltage value is the gradation expression voltage VREG1, which is a direct current component, the turn-off voltage VGH and the turn-on voltage VGL despite the ripple component included in the first source voltage VLIN1. ) may be a margin voltage that can stably extract.

According to an exemplary embodiment of the present invention, the setting may include, when there is a change in the luminance condition, setting the low power supply voltage (ELVSS) of the OLED pixel in response to the luminance condition to be changed, and the set low power supply voltage ELVSS. A voltage obtained by adding the conduction voltage Vth_EL of the OLED device to the voltage ELVSS may be set as the initialization voltage Vinit. Here, the initialization voltage Vinit may be a voltage for initializing the gate of the driving transistor of the OLED pixel and the anode of the OLED element.

According to an exemplary embodiment of the present invention, setting the OLED pixel Do to a voltage value obtained by adding the OLED emission voltage Vth_Margin at a level sufficient to emit light to the initialization voltage Vinit. It may further include setting a turn-on voltage (VGL) level for turning on the transistor of .

According to an exemplary embodiment of the present invention, an algorithm according to the driving voltage setting method may be implemented as a logic circuit in a driving IC of the OLED device.

According to an exemplary embodiment of the present invention, the conduction voltage (Vth_EL) of the OLED device may be set to a voltage value of one level regardless of the degree of change of the luminance condition.

According to an exemplary embodiment of the present invention, the conduction voltage (Vth_EL) of the OLED device may be set to voltage values of different levels according to the degree of change of the luminance condition.

Meanwhile, a method for setting a driving voltage of an OLED device according to another exemplary embodiment of the present invention for achieving the above object is provided. This driving voltage setting method relates to the luminance condition of an OLED pixel to control the dimming of an OLED device including a panel including a plurality of OLED pixels and a driving circuit for controlling driving of the plurality of OLED pixels. The level of the voltages can be set in advance. And it can be checked whether there is a change in the luminance condition of the OLED pixel. As a result of the check, when there is a change in the luminance condition, within the range of the margin voltage that can occur in the driving-related voltages related to driving the OLED pixel, the level of each of the driving-related voltages corresponds to the changed luminance condition. It is possible to reduce power consumption by changing to relatedly set levels.

According to another exemplary embodiment of the present invention, the driving related voltages are a gray scale expression voltage (VREG1) of the OLED pixel, a turn-off voltage (VGH) for turning off a switching transistor of the OLED pixel, and It may include at least one of a turn-on voltage (VGH) for turning on a switching transistor and an initialization voltage (Vinit) for initializing the gate of the driving transistor of the OLED pixel and the anode of the OLED element.

According to another exemplary embodiment of the present invention, reducing the power consumption may include setting the gradation expression voltage VREG1 of the OLED pixel in response to the luminance condition to be changed when the luminance condition is changed, and The turn-off voltage VGH of the transistor is obtained by adding the turn-off margin voltage of the transistor of the OLED pixel to the gradation expression voltage VREG1, and the turn-off voltage VGH of the transistor is added to the head room margin. ) voltage value may be further included to set the first source voltage VLIN1. The first source voltage VLIN1 may be a source voltage that generates the gradation expression voltage VREG1, the turn-off voltage VGH, and the turn-on voltage VGL for turning on the transistor of the OLED pixel. The headroom margin voltage value is based on the gradation expression voltage VREG1, which is a DC component, the turn-off voltage VGH and the turn-on voltage VGL, despite the ripple component included in the first source voltage VLIN1. It may be a margin voltage that can be stably extracted.

According to another exemplary embodiment of the present invention, reducing the power consumption may include setting the low power supply voltage (ELVSS) of the OLED pixel in response to the luminance condition to be changed when there is a change in the luminance condition, and Setting the voltage obtained by adding the conduction voltage (Vth_EL) of the OLED element to the low power supply voltage (ELVSS) as the initialization voltage (Vinit), and setting the OLED emission voltage (Vth_Margin) at a level sufficient to emit light from the OLED element (Do). It may include setting a voltage value obtained by adding the initialization voltage (Vinit) to a turn-on voltage (VGL) level for turning on the transistor of the OLED pixel. Here, the initialization voltage Vinit may be a voltage for initializing the gate of the driving transistor of the OLED pixel and the anode of the OLED element.

Meanwhile, a method for setting a driving voltage of an OLED device according to another exemplary embodiment of the present invention for achieving the above object is provided. This driving voltage setting method relates to the luminance condition of an OLED pixel to control the dimming of an OLED device including a panel including a plurality of OLED pixels and a driving circuit for controlling driving of the plurality of OLED pixels. It may include setting the level of the voltages in advance. In addition, it is checked whether there is a change in the luminance condition of the OLED pixel, and as a result of the check, when there is a change in the luminance condition, the margin voltage that may occur in driving-related voltages related to driving the OLED pixel Within the range, it may include reducing power consumption by changing the level of each of the driving-related voltages to levels set in relation to the changed luminance condition. The driving-related voltages include a gradation expression voltage (VREG1) of the OLED pixel, a turn-off voltage (VGH) for turning off the switching transistor of the OLED pixel, and a turn-on voltage (VGH) for turning on the switching transistor of the OLED pixel. , and an initialization voltage Vinit for initializing the gate of the driving transistor of the OLED pixel and the anode of the OLED element.

The amount of power consumed in an OLED pixel greatly increases as the swing width of voltages involved in driving an operation of turning a pixel on and off increases. In an existing OLED device, voltages related to driving each OLED pixel (gray level expression voltage VREG1, turn-off voltage VGH and turn-on voltage VGL of switching transistors of the pixel circuit, initialization voltage of the pixel circuit (Vinit), and the source voltage (VLIN1) that generates these voltages, etc.) are set with enough margin to cover all driving (luminance) conditions of OLED pixels. Therefore, when the luminance is lowered through dimming control, unnecessary power consumption is caused.

In the case of dimming control with low luminance, a margin for reducing the swing width of voltages related to OLED driving may increase. In view of this point, the present invention can reduce power consumption by reducing the swing width of the driving-related voltages by reflecting the margin voltage thus generated to the OLED driving-related voltages. According to the present invention, according to simulation results for samples, an effect of reducing power consumption by at least 3% or more can be obtained.

1 is a block diagram exemplarily showing the configuration of an OLED device to which the present invention is applied.
2 exemplarily shows a circuit configuration of an OLED pixel to which the invention can be applied.
FIG. 3 is an exemplary waveform diagram of signals related to driving the OLED pixel circuit of FIG. 2 .
FIG. 4 exemplarily shows waveforms of the grayscale expression voltage VREG1 provided to the driving transistor of the OLED pixel circuit of FIG. 2 and the turn-off voltage VGH and turn-on voltage VGL provided to the switching transistor.
5 shows a gray level expression voltage (VREG1), a turn-on voltage (VGL) of a switching transistor, an initialization voltage (Vinit), and a first source voltage under a maximum luminance condition (dimming control is not applied) and a low luminance condition (dimming control is applied), respectively. This is a graph expressed by contrasting the levels of (VLIN1).
FIG. 6 is a diagram for explaining a mechanism of reducing the turn-off voltage VGH (reduction of the gray scale expression voltage VREG1) of the switching transistor during dimming control of the OLED pixel circuit of FIG. 2 .
FIG. 7 is a diagram for explaining that in the circuit of FIG. 6, when the OLED element needs to emit light with maximum luminance, the turn-off voltage VGH or the gray scale expression voltage VREG1 must be set high.
FIG. 8 is a diagram for explaining that in the circuit of FIG. 6, when the OLED element needs to emit light with low luminance, the level of the turn-off voltage VGH or the gray level expression voltage VREG1 can be set low.
FIG. 9 is a diagram for explaining a reduction mechanism of turn-on voltage VGL and initialization voltage Vinit of a switching transistor when controlling dimming of the OLED pixel circuit of FIG. 2 .
FIG. 10 is a diagram for explaining that the level of the initialization voltage Vinit can be increased according to the increase of the black margin voltage when controlling low luminance dimming in FIG. 9 .
FIG. 11 is a diagram for explaining that the level of the initialization voltage Vinit can be increased by increasing the margin of the initialization voltage Vinit for data initialization during the low luminance dimming control in FIG. 9 .
12 is a flowchart briefly showing the overall flow of a method for adjusting the level of voltages related to driving an OLED pixel according to the present invention.
FIG. 13 shows a first algorithm of the method according to the present invention, and shows an algorithm for applying a single value of voltages related to driving an OLED device regardless of a luminance condition when dimming control is applied.
14 shows a second algorithm of the method according to the present invention, and shows an algorithm that differently applies the OLED conduction voltage (Vth_EL) related to image quality according to luminance conditions when dimming control is applied.
15 is a graph showing the expected degree of power consumption reduction effect when the method of the present invention is applied.

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

First, FIG. 1 is a block diagram exemplarily showing the configuration of an OLED device to which the present invention is applied. Referring to FIG. 1 , an OLED device 100 may include a driving circuit 105 , a display panel 110 and a power supply 180 .

The driving circuit 105 may include a timing controller 130 , a data driver 150 , a scan driver 160 and a light emitting driver 170 . In an embodiment, the OLED device 100 may further include a mode signal generator 190. The timing controller 130, data driver 150, scan driver 160, and light emitting driver 170 may be implemented as one chip or separate chips, and may be implemented as a chip on flexible printed circuit (COF). , can be connected to the display panel 110 in the form of a chip on glass (COG) or flexible printed circuit (FPC).

The display panel 110 is connected to the scan driver 160 through a plurality of scan lines (SL1 to SLn, where n is a natural number greater than or equal to 2), and a plurality of data lines (DL1 to DLm, where m is a natural number greater than or equal to 2). It may be connected to the data driver 150 through a plurality of light emitting control lines EL1 to ELn and connected to the light emitting driver 170 through a plurality of light emitting control lines EL1 to ELn. The display panel 110 includes a plurality of subpixels positioned at each intersection of a plurality of scan lines SL1 to SLn, a plurality of data lines DL1 to DLm, and a plurality of emission control lines EL1 to ELn. (111) may be included.

Also, the display panel 110 receives a high power supply voltage ELVDD and a low power supply voltage ELVSS from the power supply 180 . Also, the light driver 170 may receive the first voltage VGH and the second voltage VGL from the power supply 180 . The scan driver 160 may provide a scan signal to each of the plurality of pixels 200 through the plurality of scan lines SL1 to SLn based on the second driving control signal DCTL2 .

The data driver 150 may provide a data voltage to each of the plurality of subpixels 11 through the plurality of data lines DL1 to DLm based on the first driving control signal DCTL1. The data driver 150 provides a data voltage to each of the plurality of pixels 200 based on the first display data DTA1 not including black data in the normal mode, and provides a data voltage to each of the plurality of pixels 200 in the dimming mode for the second display including black data. A data voltage may be provided to each of the plurality of pixels 200 based on the data DTA2 .

The emission driver 170 may provide an emission control signal to each of the plurality of subpixels 11 through the plurality of emission control lines EL1 to ELn based on the third driving control signal DCTL3. The luminance of the display panel 100 may be adjusted based on the emission control signal.

The power supply 180 provides a high power supply voltage ELVDD, a low power supply voltage ELVSS, and an initialization voltage Vinit to the display panel 110 based on the power control signal PCTL, and Turn-off voltages VGH and turn-on voltages VGL of switching transistors involved in driving may be provided to the light emitting driver 170 . Also, the power supply 180 may generate the first source voltage VLIN1 that generates the turn-off voltage VGH, the turn-on voltage VGL, and the initialization voltage Vinit. In an embodiment, the power supply 180 may include a rechargeable battery 181 and a battery detection module 183 . The battery detection module 183 may detect the remaining amount of the rechargeable battery 181 and provide a battery detection signal BS. In addition, the power supply 180 may further include a DC-DC converter 185 that converts the DC voltage provided from the battery 182 into a DC voltage of a different required level and outputs the converted DC voltage. This DC-DC converter 185 can produce various voltages (ELVDD, ELVSS, Vinit, VGH, VGL, VLIN1, etc.) mentioned above.

The timing controller 130 receives the input image data RGB, the control signal CTL, and the mode signal MS, and first to third driving control signals based on the control signal CTL and the mode signal MS. DCTL1 to DCTL3 and the power control signal PCTL are generated, the first drive control signal DCTL1 is provided to the data driver 150, and the second drive control signal DCTL2 is provided to the scan driver 160. and the third control signal DCTL3 may be provided to the light emitting driver 170 . The third control signal DCTL3 may include a frame line mark (FLM), a first clock signal CLK1 and a second clock signal CLK2. The timing controller 130 may also convert the input image data RGB to first display data DTA1 or second display data DTA2 based on the mode signal MS. The timing controller 130 converts the input image data RGB into first display data DTA1 when the mode signal MS indicates the normal mode, and converts the input image data RGB into first display data DTA1 when the mode signal MS indicates the dimming mode. The data RGB may be converted into second display data DTA2 and provided to the data driver 150 .

The driving circuit 105 may further include a dimming controller 140 in charge of dimming control. The dimming control unit 140 may control the light emission luminance of the pixel unit 200 by converting the image data RGB or adjusting the duty ratio of the light emission control signal according to a predetermined dimming mode. The dimming control unit 140 may be provided as a part of the timing control unit 130 or may be provided as a separate and independent module.

The mode signal generator 190 may generate a mode signal MS for determining the mode of the display panel 100 in response to a battery detection signal BS indicating a power state of a battery connected to the OLED device 100. .

2 exemplarily shows a circuit configuration of an OLED pixel 200 to which the present invention can be applied. The OLED pixel 200 basically includes an OLED element Do, a driving transistor T1 for driving it, a storage capacitor Cst, and switching transistors for controlling the operation of the OLED element Do and the driving transistor T1. (T2 to T7).

The switching transistor T2 includes a first electrode connected to the data line DLn to receive the data voltage DATA, a gate electrode connected to the scan line SLn to receive the scan signal Scan[n], and a first electrode connected to the scan line SLn to receive the scan signal Scan[n]. It may be implemented as a PMOS transistor having a second electrode connected to the node N1. The driving transistor T1 may be a PMOS transistor having a first electrode connected to the first node N1, a second electrode connected to the second node N2, and a gate electrode connected to the third node N3. can The fifth and sixth switching transistors T5 and T6 may be connected to the first electrode and the second electrode of the driving transistor T1, respectively. The first electrode of the fifth transistor T5 is connected to the first node, the second electrode is connected to the high power supply voltage ELVDD, and the gate electrode is connected to the light emission control line ELn to generate the light emission control signal EM. [n]) may be applied. The first electrode of the sixth transistor T6 is connected to the anode of the OLED element Do, the second electrode is connected to the second node N2, and the gate electrode is connected to the light emission control line ELn to control light emission. A signal EM[n] may be applied. The first electrode terminal of the storage capacitor Cst may be connected to the high power supply voltage ELVDD and the second electrode terminal may be connected to the third node. The first and second electrodes of the third transistor T3 may be connected to the second and third nodes N2 and N3, respectively, and the gate electrode may be connected to the scan line SLn. The fourth transistor T4 has a first electrode connected to the third node N3, a second electrode connected to the initialization voltage Vinit, and a gate electrode connected to the scan line SLn−1. The seventh transistor may have a first electrode connected to the anode of the OLED element Do, a second electrode connected to the initialization voltage Ninit, and a gate electrode connected to the scan line SLn+1. A cathode of the OLED element Do is connected to the low power supply voltage ELVSS.

The OLED pixel 200 circuit repeats an operation of initializing the pixel circuit by applying signals as shown in FIG. 3, writing data to the OLED element Do, initializing it again, and writing data to the OLED element Do again. works with That is, the charge stored in the storage capacitor Cst is discharged and initialized when the fourth switching transistor T4 is turned on. Then, when the Scan[n] signal is applied, the storage capacitor Cst is charged again to turn on the driving transistor T1, and at the same time, the second and third switching transistors are turned on, and the emission control signal EM[ n]), the fifth and sixth switching transistors are also turned on. Accordingly, a current corresponding to the data signal DATA flows through the driving transistor T1 and also flows through the OLED device Do. Accordingly, the OLED element Do may emit light. Then, when the scan signal SLn+1 is applied to the gate and the seventh switching transistor T7 is turned on, the anode of the OLED element Do is connected to the initialization voltage Vinit to be initialized. Accordingly, light emission of the OLED element Do is also stopped.

OLED devices are configured to use multiple power sources. That is, the gradation expression voltage VREG1 expressing the gradation through the driving transistor T1 of the OLED pixel 200 and the turn-off voltage VGH for controlling the on/off of the respective switching transistors T2 to T7 and turn-on voltage VGL, and initialization voltages Vinit controlling initialization of the OLED pixel 200. FIG. 4 shows how the gradation expression voltage VREG1 is provided to the driving transistor T1 and the turn-off voltage VGH and turn-on voltage VGL are provided to the switching transistors T2 to T7.

These power supply voltages are each set to a voltage level suitable for the purpose. The purpose and setting conditions for each power source may be as follows.

power example function setting conditions VREG1 6.4V Vdata top voltage Black voltage expression Black luminance less than 0.005 nit VGH 6.6V switching transistor turn off VREG1+0.2V Vinit -3.5V Gate initialization of driving transistor T1, anode initialization of OLED element Initialization level within T1 Gate, EL Anode 1 Frame VGL -8.0V switching transistor turn on Vinit - 4.5V

However, various voltages related to the driving of these OLED pixels 200, that is, the turn-off voltage (VGH), the initialization voltage (Vinit), the turn-on voltage (VGL), the gradation expression voltage (VREG1), etc., have their levels as fixed values. In the case of setting and using, stable operation of the OLED pixel 200 can be guaranteed only when the voltage level is set to a voltage level that can satisfy all driving conditions. Therefore, in the OLED device, various power sources may be set to voltage levels considering the worst case among various driving conditions that may occur.

If the voltage level considering the worst conditions is adopted, there is an advantage in guaranteeing stable operation of the OLED device. On the other hand, in order to guarantee stable operation even in the worst conditions, the swing width of the voltage level must be increased accordingly, and accordingly, power consumption is increased.

However, dimming control lowers the luminance. The lowering of the luminance means that the swing width of the level of the gray scale expression voltage VREG1 can be reduced. In order to turn off the switching transistor, the turn-off voltage VGH must be at a higher level than the gradation expression voltage VREG1 due to the nature of the transistor, and thus has a relationship of VGH = VREG1 + ΔV. Here, ΔV has a value of about 0.2 [V], for example. Therefore, when the luminance is lowered, it means that the swing width of the turn-off voltage (VGH) level of the switching transistors may also be reduced.

In addition, the decrease in luminance means that the level of the initialization voltage Vinit of the switching transistors may increase.

The turn-on voltage VGL of the switching transistors is determined as a sum of the initialization voltage Vinit and a voltage sufficient to emit light of the OLED element Do (this is referred to as OLED emission voltage Vth_Margin). Expressing this as an equation, VGL = Vinit - Vth_Margin. The OLED emission voltage (Vth_Margin) may be, for example, approximately 4.5V. Therefore, as the level of the initialization voltage Vinit increases, the turn-on voltage VGL of the switching transistors also increases, and the swing width of the turn-on voltage VGL level decreases.

The lowering of the luminance also means that the level of the first source voltage VLIN1 for generating these voltages VREG1, Vinit, VGH, and VGL may also be lowered.

Dynamic power (P _c ) consumed in transistors of a pixel circuit to drive each pixel of an OLED device can be expressed by the following equation.

P _c = C ΔV ² f

Here, C is the capacitance of the pixel circuit and is a fixed value automatically determined according to the design of the pixel circuit. f is the switching frequency of the pixel, and this value is also a fixed value determined according to the driving method. As mentioned above, as the luminance is lowered, the magnitude of power supply voltages used to drive the transistors of the pixel circuit can be reduced. That is, the swing width of the gradation expression voltage VREG1, the turn-on voltage VGL and the turn-off voltage VGH, the absolute value of the initialization voltage Vinit level, and the first source voltage VLIN1 level may be reduced. This means a decrease in ΔV in the above power consumption equation. As a result, the decrease in luminance means that the swing width and level of power supply voltages used to drive the pixel circuit can be lowered, and accordingly, the power consumption of the pixel circuit can be reduced.

FIG. 5 graphically illustrates variations in swing widths and levels of power supply voltages as the luminance decreases, for example, from 360 nits to 183 nits. In the figure, dim indicates a case where the luminance is reduced to 183 nits. For example, when 255 levels of gray are expressed, as dimming is performed from 360 nits to 183 nits, the lowest level of the gray level expression voltage VREG1 rises and the highest level goes down. As a result, compared to the swing width h1 of the gray scale expression voltage VREG1 when dimming is not performed, the swing width h1(dim) of the gray scale expression voltage VREG1 during dimming becomes smaller (FIG. 5). see (a) and (b) of). Depending on the relationship of VGH = VREG1 + ΔV, although not shown, the swing width of the turn-off voltage VGH will also decrease.

In addition, the level of the initialization voltage Vinit, which is, for example, about -3.5V when dimming is not performed, increases to, for example, about -1.5V when dimming is performed at 183 nits. Accordingly, the swing width h2 of the turn-on voltage VGL when dimming is not approximately 14.4V (= 6.4-(-8)), but when dimming to 183 nit, the swing width h2 ( dim) is reduced to approximately 12V (= 6-(-6)) (see (a) and (c) of FIG. 5).

When the luminance is reduced, the reason why the swing widths of the turn-off voltage VGH and the turn-on voltage VGL of the switching transistor are also reduced is as follows.

First, a mechanism by which the swing width of the turn-off voltage VGH and the grayscale expression voltage VREG1 of the switching transistor can be reduced will be described with reference to FIGS. 6 to 8 . The EM[n] signal repeats on-off. During a period in which the EM[n] signal is on, the fifth and sixth switching transistors T5 and T6 connected to both sides of the driving transistor T1 are turned off. At this time, theoretically, current should not flow through the driving transistor T1, but in practice, according to the voltage-current characteristics of the transistor, leakage current may flow depending on the magnitude of the voltage. Accordingly, the anode voltage (Vanode) of the OLED element (Do) rises and current flows through the OLED element (Do), thereby approaching the conduction voltage (Vth_EL) at which the OLED element (Do) can emit light (see FIG. 7). . In a period in which the EM[n] signal is on, the fifth and sixth switching transistors T5 and T6 are in an off state, and in this period, the OLED element Do should not emit light. To ensure this, it is necessary to prevent the anode voltage Vanode of the OLED element Do from reaching the conduction voltage Vth_EL even when leakage current flows.

When the OLED element (Do) needs to emit light with maximum luminance (e.g., 360 nit), the on-period of the EM[n] signal must be maximized, so the AMOLED Off Ratio (AOR) is small, and therefore the leakage current is large. . Therefore, by setting the turn-off voltage VGH high enough so that the leakage current almost does not flow, there is no choice but to prevent the anode voltage Vanode of the OLED element Do from reaching the conduction voltage Vth_EL due to the leakage current. When the level of the turn-off voltage VGH is high, the level of the grayscale expression voltage VREG1 is naturally high. As can be seen in the graph of (a) of FIG. 5 , when the OLED element Do emits light at, for example, maximum luminance of 360 nits without dimming, the turn-off voltage (VGH) is set to, for example, 6.6V, and accordingly Accordingly, the gradation expression voltage VREG1 is set to, for example, 6.4V.

In contrast, when the OLED element Do emits light with low luminance (eg, 183 nit) by dimming, the off period of EM[n] increases, that is, the AOR increases, and accordingly, the leakage current amount may decrease. . When leakage current flows, the anode voltage (Vanode) rises. During one initialization cycle, the degree to which the level of the anode voltage (Vanode) rising due to the leakage current does not reach the conduction voltage (Vth_EL) of the OLED element (Do), that is, the black margin voltage increases as the AOR increases. (See Fig. 8). For reference, the stepwise rise of the anode voltage Vanode in FIG. 8 is because a period in which leakage current flows and a period in which leakage current does not flow are repeated as EM[n] is turned on and off repeatedly. This means that, unless the leakage current is greater than the current corresponding to the magnitude of the black margin voltage, unwanted light emission of the OLED element Do does not occur. That is, based on the current-voltage characteristics of the transistor, allowing leakage current to flow less than the amount of current corresponding to the black margin voltage means that the level of the turn-off voltage VGH of the switching transistor can be reduced by that much. . Naturally, the level of the gradation expression voltage VREG1 may also be lowered correspondingly. As can be seen in the graph of FIG. 5 (a), when the OLED element Do is dimmed to, for example, 183 nit, the turn-off voltage (VGH) can be set as low as, for example, 6.2V, and accordingly The gradation expression voltage VREG1 may also be set as low as, for example, 6.0V.

The size of the black margin voltage may be different for each dimming luminance. In addition, it may be affected by the characteristics of the transistor used, the manufacturing process, and the like. Therefore, how much to reduce the swing width of the turn-off voltage (VGH) during dimming can be determined through simulation by comprehensively considering the target luminance value, the current-voltage characteristics of the transistor used, and the acceptable risk of false light emission. .

Next, a mechanism in which the swing width of the turn-on voltage VGL of the switching transistor decreases and the level of the initialization voltage Vinit increases during dimming will be described with reference to FIGS. 9 to 11 .

First, with reference to FIGS. 9 and 10 , a mechanism for increasing the level of the initialization voltage Vinit according to an increase in the margin of the initialization voltage Vinit for data initialization during dimming will be described. To drive the OLED device Do, the voltage of the capacitor Cst, that is, the gate voltage of the driving transistor T1 may be periodically initialized. When the fourth switching transistor T4 is turned on while applying the initialization voltage Vinit, for example, -3V for initialization, the charge stored in the capacitor Cst escapes through the fourth switching transistor T4, The gate voltage of the driving transistor T1 is reduced. However, since the fourth switching transistor T4 is turned off again, the gate voltage of the driving transistor T1 does not immediately drop to -3V because the turn-on time is not long. For example, when the fourth switching transistor T4 is turned on for initialization at a gate voltage of the driving transistor T1 of +3V, the gate voltage of the driving transistor T1 may drop to +1V during that time. In this state, white can be written to the OLED element Do again. In that case, if the luminance is lowered by dimming, the voltage that the gate voltage of the driving transistor T1 must necessarily reach becomes high (eg, rises to +4V). As such, if the level to which the gate voltage of the driving transistor T1 is to be reached rises (for example, by +1V), the level of the gate voltage of the driving transistor T1 may be lowered during the same initialization time. That is, the level of the initialization voltage Vinit can be increased by that much.

For example, consider a case where the OLED pixel Do needs to change from a black state to a white state. In this case, when dimming is not performed, the gate voltage of the driving transistor T1 must change from a black voltage (eg, 6.4V) to a white (high luminance) voltage (eg, 3.0V). For this state change, -3.0V is applied as an initialization voltage, and the gate voltage of the driving transistor T1 must be lowered by 3.4V within a predetermined time. In the case of dimming, the voltage in the high luminance (white) state is higher (for example, it can be 4.0V) than in the case of non-dimming. In order to change to the (high luminance) state, the gate voltage of the driving transistor T1 may be lowered from, for example, 6.4V to, for example, 4.0V within a predetermined time. That is, it is only necessary to lower the gate voltage of the driving transistor T1 by, for example, 2.4V. Accordingly, the level of the initialization voltage Vinit may be increased by, for example, 1.0V.

10 schematically shows this relationship. For example, when dimming to 183 nit, the margin of the initialization voltage Vinit for data initialization increases, and the level of the initialization voltage Vinit can rise accordingly.

In addition, as shown in FIG. 8 above, the black margin voltage can be increased in the case of dimming (eg, dimming to 183 nits) compared to the case of not dimming. Accordingly, the initial level of the anode voltage Vanode of the OLED element Do may be increased within the range of the increased black margin voltage. And since the initial level of the anode voltage Vanode of the OLED element Do corresponds to the initialization voltage Vinit, it means that the initialization voltage Vinit can be increased within the range of the black margin voltage.

As such, when the dimming control to lower the luminance is performed, the initialization voltage Vinit may be lowered. The turn-on voltage (VGL) of the switching transistors is determined by adding the initialization voltage (Vinit) and the OLED emission voltage (Vth_Margin) at a level sufficient to cause the OLED device (Do) to emit light. Expressing this as an equation, VGL = Vinit - Vth_Margin. Accordingly, when the level of the initialization voltage Vinit increases, the swing width of the turn-on voltage VGL also decreases by the same amount (see (c) of FIG. 5).

Meanwhile, in the case of dimming control as described above, level adjustment of various voltages related to driving of the OLED pixel Do, that is, the swing width of the gray scale expression voltage VREG1 and the turn-off voltage of the switching transistor ( Adjusting the swing width of VGH, adjusting the level of the initialization voltage Vinit, and adjusting the swing width of the turn-on voltage VGL of the switching transistor will be described.

The flowchart of FIG. 12 briefly illustrates the overall flow of a method for adjusting the level of voltages related to driving an OLED pixel according to the present invention. This method may be performed by a driving IC. The driving IC monitors whether the dimming control starts, and when the dimming control start command is captured (S400), it determines the luminance condition indicated by the dimming control command (S410). And, depending on the luminance condition to be applied, various setting values described below are applied to determine the gray level expression voltage (VREG1), the turn-off voltage (VGH) of the switching transistor, the initialization voltage (Vinit), and the turn-on voltage (VGL) of the switching transistor. etc. are determined (S420). Further, up to the first source voltage VLIN1 may be obtained by applying a head room margin to the turn-off voltage VGH of the switching transistor (S430). Here, the headroom margin voltage value is based on the gradation expression voltage VREG1, which is a DC component, and the turn-off voltage VGH and turn-on voltage VGL of the switching transistor, despite the ripple component included in the first source voltage VLIN1. It refers to the margin voltage that can be extracted stably.

In step S420, regardless of which luminance condition to apply, the voltages may be applied as one type (the first algorithm of FIG. 13 to be described later corresponds to this), or the voltages may be applied differently according to the luminance condition to be applied. (The second algorithm of FIG. 14 to be described later corresponds to this).

One way to implement these algorithms is to implement each algorithm as a logic circuit within the driver IC of the OLED device. For example, the above algorithm may be implemented using a standard dimming register called 51h and a logic circuit. A dimming resistor 51h may be embedded in the driver IC of the OLED device. The above voltage values can be obtained in conjunction with the setting value of the dimming register.

13 schematically shows the first algorithm. Specifically, the dimming controller 140 in the driving IC of the OLED device may include the dimming register 300 designed according to the 51h standard. A logic circuit implementing an algorithm according to the method of the present invention may be designed to operate in conjunction with the dimming register 300 . In the dimming register 300, information for determining the setting values of the gradation expression voltage VREG1 and the low power supply voltage ELVSS may be recorded (300, 324). A voltage margin required to turn off the transistor may be set in advance (312). The optimum value of this voltage margin is a value that can be determined according to the characteristics of the transistor used, the acceptable risk of malfunction, etc. (for example, it can be set to 0.1V, 0.2V, etc.). Then, the value of the turn-off voltage VGH of the switching transistor can be obtained by summing the set value of the gradation expression voltage VREEG1 and the preset set value of the transistor turn-off voltage margin (314).

In addition, determining the value of the low power supply voltage (ELVSS) according to the luminance value is a technique that has already been used (324). When the value of the low power supply voltage ELVSS is determined according to the desired luminance value, the set value 326 of the conduction voltage Vth_EL for emitting light by conducting the OLED element Do to the set value of the low power supply voltage ELVSS It is summed (328) so that the value of the initialization voltage (Vinit) can be obtained (330). The conduction voltage (Vth_EL) is a value that can be determined differently depending on the material or manufacturer of the transistor (for example, it can be set to 1.0V, 1.5V, 2.0V, etc.). When the initialization voltage Vinit is determined, the turn-on voltage VGL of the transistor device can be obtained by adding the OLED emission voltage Vth_Margin 332 to the value (334). The value of the OLED emission voltage (Vth_Margin) is a value that can be determined differently depending on the material and process characteristics of the transistor, manufacturer, etc. (eg, -3.5V, 4.0V, etc.).

As such, based on an algorithm that first obtains the setting values of the gradation expression voltage (VREG1) and the initialization voltage (Vinit) to be applied during dimming, and determines the turn-off voltage (VGH) and turn-on voltage (VGL) of the switching transistor based on those values to obtain these voltages. In the driving IC, the method according to the present invention can be implemented by providing a driving circuit that performs this algorithm when dimming control is required.

In addition to this, the logic circuit may be designed to further obtain the first source voltage VLIN1 that makes the gradation expression voltage VREG1 and the turn-off voltage VGH and turn-on voltage VGL of the switching transistor. That is, the first source voltage VLIN1 may be obtained by adding the headroom margin voltage value 318 to the turn-off voltage VGH of the switching transistor (320). During dimming control, since the swing width of the gradation expression voltage (VREG1), the turn-off voltage (VGH) and the turn-on voltage (VGL) of the switching transistor is reduced, even the level of the first source voltage (VLIN1), which is the source voltage that creates these voltages, is reduced. can be lowered

Setting of the gradation expression voltage (VREG1) (310), setting of the off margin of the transistor (312), setting of the headroom margin (318), setting of the conduction voltage (Vth_EL) of the OLED device (326), and OLED emission voltage ( Vth_Margin) setting 332 can be set by comprehensively considering the characteristics of the transistor used by the implementer (engineer) of the present invention, the characteristics of the driving IC, the acceptable risk of malfunction, and the target power consumption reduction rate. There will be.

As such, by implementing the algorithm according to the present invention in the logic circuit of the driving IC and operating it in conjunction with the dimming register 300, the gray scale expression voltage (VREG1), the turn-off voltage (VGH) of the switching transistor, and initialization during dimming control It can be obtained by linking the voltage (Vinit) and the turn-on voltage (VGL) of the switching transistor. How to configure the logic circuit of the driving IC for this purpose can result in a design problem using the minimum number of logic gates.

13 shows the gradation expression voltage VREG1, the initialization voltage Vinit, the turn-off voltage VGH and the turn-on voltage VGL of the switching transistor regardless of the dimming level, that is, regardless of which level the luminance is reduced. It is a way to set a value and use it. While this method has the advantage that the circuit configuration for this is simple, it has the disadvantage that optimization for reducing power consumption may be insufficient depending on the degree of dimming control.

14 illustrates the second algorithm, that is, an algorithm that differently applies the size of the initialization voltage Vinit and the turn-on voltage VGL of the switching transistor according to the dimming level, that is, according to the luminance condition. The switching transistor off margin set value 312 and the OLED emission voltage (Vth_Margin) value 332 are values related to the characteristics of the transistor used, and the headroom margin value is a value related to the characteristics of the driving IC. ) of the conduction voltage (Vth_EL) is a value related to the image quality characteristics of the OLED device. Since the change in luminance value according to dimming control is directly related to picture quality, when obtaining the best picture quality is more important than reducing power consumption, the value of the conduction voltage (Vth_EL) of the OLED element Do is determined according to the luminance condition. It can be set to an optimal value (340). When the conduction voltage (Vth_EL) of the OLED element (Do) is set to an optimal value according to the luminance level, the value is summed with the set value of the low power supply voltage (ELVSS) (342) to obtain the initialization voltage (Vinit) (344), The process of obtaining the turn-on voltage VGL of the switching transistor by adding the initialization voltage Vinit to the OLED emission voltage Vth_Margin setting value 332 (336) is the same as described above. In addition, setting the turn-off voltage (VGH) from setting 310 of the gradation expression voltage VREG1 (316) and setting up to the first source voltage (VLIN1) (322) can be set as one regardless of luminance conditions. have.

Compared to the first algorithm, this second algorithm can set various voltages (VREG1, VHG, Vinit, VGL, VLIN1, etc.) related to the driving of the OLED device Lo to values optimized for the luminance condition, so that consumption It has the advantage of further increasing the efficiency of power reduction. On the other hand, there is a disadvantage in that the configuration of a logic circuit for implementing this becomes more complicated.

The graph of FIG. 15 shows the power consumption when various voltages are changed according to the present invention (after change) and when the present invention is not applied (before change) when driving low luminance according to dimming control for four samples. . According to this, it can be seen that the effect of reducing driving power consumption by at least 3% or more can be obtained when the method of the present invention is applied compared to the case where it is not.

In the above, the present invention has been described by taking the OLED pixel 200 illustrated in FIG. 2 as an example, but the present invention is not limitedly applied only to the OLED pixel 200 shown in FIG. 2 . Any OLED pixel with a transistor for on/off switching of data lines can be widely applied. For example, an OLED pixel circuit in which an initialization circuit is simplified compared to FIG. 2 (eg, in the circuit of FIG. 2, at least one of the third switching transistor T3, the fourth switching transistor T4, and the seventh switching transistor T7 is omitted). circuit), OLED pixel circuit in which switching using the emission control signal EM[n] is implemented with only one transistor or all of them are omitted (for example, the fifth switching transistor T5 and the sixth switching transistor T6) Of course, it can also be applied to a circuit in which at least one of them is omitted) and the like.

The method of the present invention can be implemented in a logic circuit, which logic circuit can be included as part of the drive circuit 105 of the OLED device. However, the method of the present invention does not rule out that at least some functions thereof may be implemented in software. For example, it may be implemented in a mixed form of a logic circuit and a program.

The method of the present invention can be applied without being limited by the type of display device employing an OLED element. For example, the present invention can be applied to a notebook computer, a tablet computer, a mobile phone, a smart phone, a PDA, a PMP, a digital camera, a music player, a portable game console, a navigation device, and the like.

Although the above has been described with reference to the embodiments of the present invention, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention described in the claims below. You will understand that you can.

100: OLED device 105: driving circuit
110: display panel 130: timing controller
140: dimming control unit 150: data driving unit
160: scan driver 170: emission control line driver
180: power supply unit 200: OLED pixel
T1: driving transistor T2 to T7: switching transistor
Cst: storage capacitor

Claims (17)

Checking whether a luminance condition of an OLED pixel is changed for dimming control of an OLED device including a panel including a plurality of OLED pixels and a driving circuit for controlling driving of the plurality of OLED pixels; and
Setting to change the level of each of the driving-related voltages in the direction of reducing power consumption within the range of the margin voltage that may occur in the driving-related voltages related to driving the OLED pixel when the luminance condition is changed. Including the step of doing,
The driving-related voltages include a turn-on voltage (VGL) for turning on a switching transistor of the OLED pixel,
The driving-related voltages include an initialization voltage (Vinit) for initializing a gate of a driving transistor of the OLED pixel and an anode of the OLED device. The method of claim 1 , wherein the setting comprises: pre-setting the levels of the driving-related voltages in association with a luminance condition of an OLED pixel; and changing the levels of the driving-related voltages to levels set in relation to the changed luminance condition when the luminance condition is changed. 3. The method of claim 2, wherein the preset driving-related voltages are each set to one voltage level regardless of the degree of change in the luminance condition. 3. The method of claim 2, wherein the previously set driving-related voltages are set to voltage values having different levels for each degree of change in the luminance condition. The method of claim 1 , wherein the driving-related voltages include a gradation expression voltage (VREG1) of the OLED pixel. The method of claim 1 , wherein the driving-related voltages include a turn-off voltage (VGH) for turning off a switching transistor of the OLED pixel. The method of claim 1 , wherein the setting comprises: setting the gray scale expression voltage (VREG1) of the OLED pixel in response to the changed luminance condition when there is a change in the luminance condition; and obtaining a turn-off voltage (VGH) of the transistor by adding a turn-off margin voltage of the transistor of the OLED pixel to the set grayscale expression voltage (VREG1). 8. The method of claim 7, wherein the setting further comprises setting the first source voltage (VLIN1) by adding a head room margin voltage value to the turn-off voltage (VGH) of the transistor, , The first source voltage VLIN1 is a source voltage for generating the gradation expression voltage VREG1, the turn-off voltage VGH, and a turn-on voltage VGL for turning on the transistor of the OLED pixel, and the headroom The margin voltage value stably extracts the gradation expression voltage VREG1, the turn-off voltage VGH, and the turn-on voltage VGL, which are DC components, despite the ripple component included in the first source voltage VLIN1. Method for setting the driving voltage of an OLED device, characterized in that the margin voltage can be. The method of claim 1 , wherein the setting comprises: setting a low power source voltage (ELVSS) of the OLED pixel in response to the changed luminance condition when there is a change in the luminance condition; and setting a voltage obtained by adding the conduction voltage (Vth_EL) of the OLED element to the set low power supply voltage (ELVSS) as the initialization voltage (Vinit), wherein the initialization voltage (Vinit) is the voltage of the driving transistor of the OLED pixel. A method for setting a driving voltage of an OLED device, characterized in that the voltage for initializing the gate and the anode of the OLED device. 10 . The method of claim 9 , wherein the step of setting the transistor of the OLED pixel is a voltage obtained by adding the initialization voltage (Vinit) to the OLED emission voltage (Vth_Margin) having a sufficient level to emit light from the OLED element (Do). A method for setting a driving voltage of an OLED device, further comprising setting a turn-on voltage (VGL) level for turning on. 10. The method of claim 9, wherein an algorithm according to the driving voltage setting method is implemented in a logic circuit within a driving IC of the OLED device. 10. The method of claim 9, wherein the conduction voltage (Vth_EL) of the OLED device is set to one voltage level regardless of the degree of change in the luminance condition. 10. The method of claim 9, wherein the conduction voltage (Vth_EL) of the OLED device is set to voltage values of different levels according to the degree of change of the luminance condition. Checking whether a luminance condition of an OLED pixel is changed for dimming control of an OLED device including a panel including a plurality of OLED pixels and a driving circuit for controlling driving of the plurality of OLED pixels;
setting the levels of driving-related voltages in advance in relation to the luminance conditions of the OLED pixels; and
When there is a change in the luminance condition, within the range of the margin voltage that may occur in the driving-related voltages related to driving the OLED pixel, the level of each of the driving-related voltages is related to the changed luminance condition. Including reducing power consumption by changing to set levels,
The driving-related voltages include a turn-on voltage (VGL) for turning on a switching transistor of the OLED pixel,
The driving-related voltages include an initialization voltage (Vinit) for initializing a gate of a driving transistor of the OLED pixel and an anode of the OLED device. 15. The method of claim 14, wherein the step of reducing the power consumption comprises: setting a gray scale expression voltage (VREG1) of the OLED pixel in response to the luminance condition to be changed when the luminance condition is changed; obtaining a turn-off voltage (VGH) of the transistor by adding a turn-off margin voltage of the transistor of the OLED pixel to the set grayscale expression voltage (VREG1); and setting a first source voltage (VLIN1) by adding a headroom margin voltage value to the turn-off voltage (VGH) of the transistor, wherein the first source voltage (VLIN1) represents the gradation. A voltage VREG1, the turn-off voltage VGH, and a source voltage for generating a turn-on voltage VGL for turning on the transistor of the OLED pixel, and the headroom margin voltage value corresponds to the first source voltage VLIN1. The margin voltage capable of stably extracting the gradation expression voltage (VREG1), the turn-off voltage (VGH), and the turn-on voltage (VGL), which are DC components, despite the included ripple component of the OLED device, characterized in that How to set drive voltage. 15. The method of claim 14, wherein the reducing of the power consumption comprises: setting a low power supply voltage (ELVSS) of the OLED pixel in response to the changed luminance condition when there is a change in the luminance condition; setting a voltage obtained by adding a conduction voltage (Vth_EL) of an OLED device to the set low power supply voltage (ELVSS) as the initialization voltage (Vinit); and setting a voltage value obtained by adding the initialization voltage (Vinit) to the OLED emission voltage (Vth_Margin) sufficient to emit light of the OLED element (Do) as a turn-on voltage (VGL) level for turning on the transistor of the OLED pixel. and wherein the initialization voltage (Vinit) is a voltage for initializing a gate of a driving transistor of the OLED pixel and an anode of the OLED element. delete

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