KR20170066771A - 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. It is checked whether or not the luminance condition of the OLED pixel is changed for dimming control of the OLED device including the panel including the plurality of OLED pixels and the driving circuit for controlling the driving of the plurality of OLED pixels. When there is a change in the luminance condition, a setting is made to change the level of each of the driving-related voltages in the direction of reducing the power consumption, within a range of margin voltage that can occur in the driving-related voltages related to the driving of the OLED pixel . This method can be implemented as a logic circuit in a driving IC.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a driving voltage setting method for reducing power consumption of an organic light emitting display device,

The present invention relates to a flat display device, and more particularly, to 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. The OLED device includes a plurality of pixels, each pixel having an OLED element, a pixel circuit for independently driving the OLED element, and a drive control circuit for driving each pixel circuit.

The OLED device uses various voltages for controlling the light emission of the OLED elements, for example, a voltage for generating the gradation voltage, a voltage for turning on and off the switching transistors of the pixel circuit, and a voltage for initialization. These voltages are set to a level suitable for each purpose. However, in the case of conventional OLED devices, the levels of the voltages are preset and used without considering the ambient brightness, for example, the ambient brightness in the indoor or outdoor environment. As a result, the set level of the voltages was set very loosely considering the worst case. That is, the level of each voltage is set to a sufficiently large value based on the case where the highest level voltage (maximum level voltage) should be used, for example, in the case where the maximum luminance should be exhibited. The maximum level voltage is always used even when the maximum level voltage is not used. If the level of the voltage is large, the swing width is large and the power consumption is large. Inefficiency occurs in power consumption.

In view of the above points, in the case of performing dimming control for lowering the brightness of a pixel, the present invention lowers the level of voltages necessary for driving the OLED pixel, thereby reducing power consumption by reducing unnecessary power consumption And a method thereof.

According to an aspect of the present invention, there is provided a method of setting a driving voltage of an OLED device. 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 the driving of the plurality of OLED pixels, it is checked whether or not the luminance condition of the OLED pixel is changed . A setting for changing the level of each of the driving-related voltages in a direction of decreasing power consumption within a range of a margin voltage that may occur in driving-related voltages related to driving of the OLED pixels when there is a change in the luminance condition can do.

According to an embodiment of the present invention, the setting may include setting a level of the driving-related voltages in association with a luminance condition of the OLED pixel, and adjusting the level of the driving-related voltages To the levels set in association with the changing brightness condition.

According to an embodiment of the present invention, the drive-related voltages set in advance can be set to voltage values of one level, respectively, irrespective of the degree of change of the brightness condition. According to another embodiment, the drive-related voltages that are set in advance may be set to voltage values of different levels according to degree of change of the brightness condition.

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

According to an exemplary embodiment of the present invention, the setting may include setting the gradation display voltage VREG1 of the OLED pixel in accordance with the luminance condition to be changed, when there is a change in the luminance condition. Further, the turn-off margin voltage of the transistor of the OLED pixel may be added to the set gray-scale voltage VREG1 to obtain the turn-off voltage VGH of the transistor.

According to an exemplary embodiment of the present invention, the setting may further comprise setting the first source voltage VLIN1 by adding a headroom margin voltage value to the turn-off voltage VGH of the transistor . Here, the first source voltage VLIN1 may be a source voltage for generating the gradation display voltage VREG1, the turn-off voltage VGH, and a turn-on voltage VGL for turning on the transistor of the OLED pixel. In addition, the headroom margin voltage value may be determined based on the gradation expression voltage VREG1, the turn-off voltage VGH, and the turn-on voltage VGL, which are direct current components in spite of the ripple component included in the first source voltage VLIN1 ) Can be stably extracted.

According to an exemplary embodiment of the present invention, the setting is performed by setting a low power supply voltage (ELVSS) of the OLED pixel corresponding to a brightness condition to be changed when the brightness condition is changed, And setting the voltage obtained by adding the conduction voltage (Vth_EL) of the OLED element to the voltage (ELVSS) to 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, the setting may be performed by setting a voltage value obtained by adding an OLED emission voltage (Vth_Margin) to a level sufficient to emit the OLED element (Do) To a turn-on voltage (VGL) level for turning on the transistor of the transistor.

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

According to an exemplary embodiment of the present invention, the conduction voltage Vth_EL of the OLED element may be set to voltage values of different levels depending on the degree of change of the brightness condition.

According to another aspect of the present invention, there is provided a driving voltage setting method for an OLED device. This driving voltage setting method is a method for setting a driving voltage in accordance with a luminance condition of an OLED pixel 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, The level of the voltages can be set in advance. It is possible to check whether or not the luminance condition of the OLED pixel is changed. As a result of the check, when there is a change in the luminance condition, within a range of margin voltages that can occur in driving-related voltages related to driving of the OLED pixels, the level of each of the driving- related voltages is changed to the changed luminance condition It is possible to reduce the power consumption by changing the levels to be associated with each other.

According to another exemplary embodiment of the present invention, the driving-related voltages include at least one of a gradation display voltage VREG1 of the OLED pixel, a turn-off voltage VGH for turning off the switching transistor of the OLED pixel, A turn-on voltage (VGH) for turning on the 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, the reduction of the power consumption includes setting the gradation display voltage VREG1 of the OLED pixel in accordance with the luminance condition to be changed when the luminance condition is changed, Off voltage (VGH) of the transistor by adding the turn-off margin voltage of the transistor of the OLED pixel to the gray-scale voltage (VREG1); determining a headroom margin ) Voltage value to set the first source voltage VLIN1. The first source voltage VLIN1 may be a source voltage for generating the gradation display 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 set to a value obtained by dividing the gradation expression voltage VREG1, the turn-off voltage VGH, and the turn-on voltage VGL, which are direct current components in spite of 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 includes setting a low power supply voltage (ELVSS) of the OLED pixel corresponding to a luminance condition to be changed when the brightness condition is changed, (Vth_Margin) at a level sufficient to cause the OLED element (Do) to emit light, setting a voltage obtained by adding the conduction voltage (Vth_EL) of the OLED element to the low power source voltage (ELVSS) 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.

According to another aspect of the present invention, there is provided a driving voltage setting method for an OLED device. This driving voltage setting method is a method for setting a driving voltage in accordance with a luminance condition of an OLED pixel 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 pre-setting the level of the voltages. It is also possible to check whether or not a change in the luminance condition of the OLED pixel occurs, and when there is a change in the luminance condition, a margin voltage And changing the level of each of the drive-related voltages to levels set in association with the changed brightness condition, thereby reducing power consumption. The driving-related voltages include at least one of a gray-level display voltage VREG1 of the OLED pixel, a turn-off voltage VGH for turning off the switching transistor of the OLED pixel, 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 consumption in OLED pixels is greatly increased as the swing width of the voltages involved in turning on and off the pixels is greater. In the conventional OLED device, the voltages (the gradation display voltage VREG1, the turn-off voltage VGH and the turn-on voltage VGL of the switching transistors of the pixel circuit, the initialization voltage (Vinit), and the source voltage (VLIN1) that produces these voltages) are set to be sufficiently large to cover all the driving (luminance) conditions of OLED pixels. Therefore, when the luminance is lowered through the dimming control, unnecessary power consumption is caused.

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

1 is a block diagram exemplarily showing a configuration of an OLED device to which the present invention is applied.
2 illustrates an exemplary circuit configuration of an OLED pixel to which the invention can be applied.
3 is an exemplary waveform diagram of signals involved in driving the OLED pixel circuit of FIG.
Fig. 4 exemplarily shows the waveforms of the gradation display voltage VREG1 provided to the driving transistor of the OLED pixel circuit of Fig. 2 and the turn-off voltage VGH and the turn-on voltage VGL provided to the switching transistor.
5 is a graph showing the relation between the gradation voltage VREG1, the turn-on voltage VGL, the initialization voltage Vinit, and the first source voltage VREG1 in the highest luminance condition (no dimming control application) (VLIN1).
FIG. 6 is a diagram for explaining a mechanism of reducing the turn-off voltage (VGH) of the switching transistor (decreasing the gradation expression voltage VREG1) in the dimming control of the OLED pixel circuit of FIG.
FIG. 7 is a diagram for explaining that the turn-off voltage VGH or the gray-scale display voltage VREG1 can be set to a large value when the OLED element needs to emit light at the maximum luminance in the circuit of FIG.
8 is a diagram for explaining that the level of the turn-off voltage VGH or the gray-scale display voltage VREG1 can be set lower when the OLED element needs to emit light with low brightness in the circuit of Fig.
FIG. 9 is a diagram for explaining a reduction mechanism of the turn-on voltage (VGL) and the initialization voltage (Vinit) of the switching transistor in the dimming control of the OLED pixel circuit of FIG.
FIG. 10 is a diagram for explaining that the level of the initialization voltage Vinit can be raised in accordance with the increase of the black margin voltage in the low luminance dimming control in FIG.
FIG. 11 is a diagram for explaining that the level of the initialization voltage Vinit can be raised by increasing the initialization voltage (Vinit) margin for data initialization in the low luminance dimming control in FIG.
12 is a flowchart briefly showing an overall flow of a method of adjusting the level of OLED pixel driving related voltages according to the present invention.
13 shows a first algorithm of the method according to the present invention, which shows an algorithm for applying the values of the OLED element driving related voltages to one, regardless of the luminance condition, when the dimming control is applied.
FIG. 14 shows a second algorithm of the method according to the present invention, and shows an algorithm for applying different OLED conduction voltages (Vth_EL) related to picture quality according to luminance conditions when dimming control is applied.
FIG. 15 is a graph showing the degree of expected power saving 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 illustrating an exemplary 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, the data driver 150, the scan driver 160 and the light emitting driver 170 may be implemented as one chip or a separate chip, and may be a chip on a flexible printed circuit (COF) A chip on glass (COG), or a flexible printed circuit (FPC).

The display panel 110 is connected to the scan driver 160 through a plurality of scan lines SL1 to SLn and n is a natural number of 2 or more and a plurality of data lines DL1 to DLm, And may be connected to the data driver 150 through the plurality of light emission control lines EL1 through ELn. The display panel 110 includes a plurality of subpixels positioned at intersections 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).

In addition, the display panel 110 is supplied with the high power supply voltage ELVDD and the low power supply voltage ELVSS from the power supply 180. The light emitting 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 drive control signal DCTL2.

The data driver 150 may provide the data voltage to each of the plurality of subpixels 11 through the plurality of data lines DL1 to DLm based on the first drive 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 that does not include black data in the normal mode, And can provide the data voltage to each of the plurality of pixels 200 based on the data DTA2.

The light emission driver 170 may provide the emission control signals to each of the plurality of subpixels 11 through the plurality of emission control lines EL1 to ELn based on the third drive control signal DCTL3. The brightness of the display panel 100 can be adjusted based on the light emission control signal.

The power supply 180 supplies the display panel 110 with the high power supply voltage ELVDD and the low power supply voltage ELVSS and the initialization voltage Vinit on the basis of the power supply control signal PCTL, The turn-on voltage (VGH) and the turn-on voltage (VGL) of the switching transistors involved in driving can be provided to the light emitting driver 170. The power supply 180 may also generate a first source voltage VLIN1 that produces the turn-off voltage VGH and the turn-on voltage VGL, 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 can detect the remaining amount of the rechargeable battery 181 and provide the battery detection signal BS. The power supply 180 may further include a DC-DC converter 185 that converts the DC voltage supplied from the battery 182 to a DC voltage of a different level using the DC voltage provided from the battery 182 and outputs the DC voltage. The DC-DC converter 185 can generate the above-mentioned various voltages ELVDD, ELVSS, Vinit, VGH, VGL, VLIN1, and the like.

The timing controller 130 receives the input image data RGB, the control signal CTL and the mode signal MS and outputs the first to third drive control signals < RTI ID = 0.0 > And supplies the first drive control signal DCTL1 to the data driver 150 and the second drive control signal DCTL2 to the scan driver 160 And the third control signal DCTL3 may be provided to the light emission driver 170. [ The third control signal DCTL3 may include a start line signal 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 the first display data DTA1 or the second display data DTA2 based on the mode signal MS. The timing controller 130 converts the input image data RGB into the first display data DTA1 when the mode signal MS indicates the normal mode and the input image data RGB when the mode signal MS indicates the normal mode, And converts the data RGB into second display data DTA2 and provides the second display data DTA2 to the data driver 150. [

The driving circuit 105 may further include a dimming control unit 140 for controlling the dimming control. The dimming control unit 140 may adjust the emission luminance of the pixel unit 200 by converting image data RGB or adjusting the duty ratio of the 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 independent module.

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

2 illustrates an exemplary 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 Tl for driving the same, a storage capacitor Cst, and switching transistors for controlling the operation of the OLED element Do and the driving transistor Tl. (T2 to T7).

The switching transistor T2 is connected to the data line DLn and includes a first electrode to which the data voltage DATA is applied, a gate electrode connected to the scan line SLn to receive the scan signal Scan [n] (PMOS) transistor having a second electrode connected to the node N1. The driving transistor Tl is 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 . The fifth and sixth switching transistors T5 and T6 may be connected to the first and second electrodes of the driving transistor T1, respectively. The first electrode of the fifth transistor T5 may be connected to the first node and the second electrode may be coupled to the high power source voltage ELVDD. The gate electrode of the fifth transistor T5 may be connected to the emission control line ELn, [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 thereof is connected to the second node N2, and the gate electrode thereof is connected to the emission control line ELn, The signal EM [n] may be applied. The storage capacitor Cst may have a first electrode terminal connected to the high power supply voltage ELVDD and a second electrode terminal connected to the third node. The first and second electrodes of the third transistor T3 may be coupled to the second and third nodes N2 and N3, respectively, and the gate electrode thereof may be coupled to the scan line SLn. The fourth transistor T4 may have 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. The cathode of the OLED element Do is connected to the low power supply voltage ELVSS.

The OLED pixel circuit 200 is a circuit that initializes a pixel circuit by applying signals as shown in FIG. 3, and then writes data to the OLED element Do and re-initializes the data, and then writes data to the OLED element Do again . 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, the second and third switching transistors are turned on, and the emission control signal EM [ n]) turn on the fifth and sixth switching transistors. Accordingly, a current corresponding to the data signal DATA flows through the driving transistor T 1 and also flows to the OLED element Do. Whereby the OLED element Do can emit light. Thereafter, 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 and initialized. Thereby stopping the emission of the OLED element Do.

OLED devices are configured to use multiple power sources. That is, the gradation display voltage VREG1 representing the gradation through the driving transistor Tl of the OLED pixel 200 and the turn-off voltage VGH for controlling on / off of each of the switching transistors T2 through T7, A turn-on voltage VGL, and an initialization voltage Vinit for controlling the initialization of the OLED pixel 200. [ 4 shows a mode in which the gradation display voltage VREG1 is provided to the driving transistor Tl and a turn-off voltage VGH and a turn-on voltage VGL are provided to the switching transistors T2 to T7.

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

power example function Setting condition VREG1 6.4V Vdata highest voltage
Black voltage expression Black luminance less than 0.005nit VGH 6.6V Switching transistor turn-off VREG1 + 0.2V Vinit -3.5V Gate initialization of the driving transistor T1, anode initialization of the OLED element T1 Gate, EL Anode
1 Frame initialization level VGL -8.0V Switching transistor turn-on Vinit - 4.5V

The turn-off voltage VGH, the initialization voltage Vinit, the turn-on voltage VGL, the gradation display voltage VREG1, and the like related to the driving of the OLED pixel 200 have a fixed level It is possible to ensure the stable operation of the OLED pixel 200 only by setting the voltage level at which any driving condition can be satisfied. Thus, in an OLED device, various power supplies can be set to a voltage level considering the worst case among various driving conditions that may occur.

Adopting such a voltage level in consideration of the worst case conditions has the advantage of ensuring stable operation of the OLED device. On the other hand, in order to ensure stable operation even under the worst conditions, the swing width of the voltage level must be increased so that the power consumption increases accordingly.

 However, the dimming control is to lower the luminance. The lowering of the brightness means that the swing width of the gradation expression voltage VREG1 level can be reduced. In order to turn off the switching transistor, the turn-off voltage VGH must be higher than the gradation display voltage VREG1 because of the characteristics of the transistor, so that VGH = VREG1 + DELTA V. Here,? V has a value of about 0.2 [V], for example. Therefore, the lower the luminance, the smaller the swing width of the turn-off voltage (VGH) level of the switching transistors can be.

Also, the lowering of the brightness means that the level of the initializing voltage Vinit of the switching transistors can be raised.

The turn-on voltage VGL of the switching transistors is set to a value that is a sum of a voltage of a level sufficient to cause the OLED element Do to emit light (referred to as OLED emission voltage Vth_Margin) to the initialization voltage Vinit. This expression is VGL = Vinit - Vth_Margin. The OLED emission voltage (Vth_Margin) may be, for example, about 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 also decreases.

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

The dynamic power consumption (P _c ) consumed by the transistors of the pixel circuit for driving each pixel of the OLED device can be expressed by the following equation.

P _c = C · ΔV ² · f

Here, C is the capacitance of the pixel circuit, which 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 the power supply voltages used to drive the transistors of the pixel circuit can be reduced. That is, the swing width of the gradation display voltage VREG1, the turn-on voltage VGL and the turn-off voltage VGH, the absolute value of the initialization voltage Vinit, and the level of the first source voltage VLIN1 can be reduced. This means a decrease in ΔV in the above power consumption equation. As a result, the reduction in the brightness means that the swing width and the level of the power supply voltages used for driving the pixel circuit can be lowered, thereby reducing the power consumption of the pixel circuit.

Fig. 5 schematically shows variations in the swing width and level of the power supply voltages as the luminance is lowered from, for example, 360 nits to 183 nits. In the figure, dim indicates a case in which luminance is reduced to 183 nits. For example, in the case of expressing the gradation of 255 steps, dimming is performed from 360 nits to 183 nits, so that the lowest level of the gradation display voltage VREG1 rises and the highest level decreases. As a result, the swing width h1 (dim) of the gradation expression voltage VREG1 at the time of dimming becomes smaller as compared with the swing width h1 of the gradation expression voltage VREG1 when dimming is not performed (A) and (b)). Depending on the relationship of VGH = VREG1 + DELTA V, the swing width of the turn-off voltage VGH may be reduced, though not shown.

When the level of the initialization voltage Vinit is not dimmed, for example, it is about 3.5 V, and when the dimming is performed for 183 nits, the level is raised to about -1.5 V, for example. The swing width h2 of the turn-on voltage VGL when the dimming is not performed is approximately 14.4 V (= 6.4 - (- 8)) and when the dimming is performed at 183 nits, the swing width h2 dim) is reduced to about 12V (= 6 - (- 6)) (see (a) and (c) of FIG.

The reason why the swing width of the turn-off voltage (VGH) and the turn-on voltage (VGL) of the switching transistor is reduced when the luminance is reduced is as follows.

First, a mechanism by which the swing width of the turn-off voltage VGH and the gray-scale display voltage VREG1 of the switching transistor can be reduced will be described with reference to FIGS. 6 to 8. FIG. The EM [n] signal repeats on-off. During the 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. In this case, theoretically, no current should flow through the driving transistor T1, but in reality, according to the voltage-current characteristic of the transistor, a leakage current may flow according to the magnitude of the voltage. The anode voltage of the OLED element Do rises and a current flows to the OLED element Do so that the OLED element Do approaches the conduction voltage Vth_EL capable of emitting light (see FIG. 7) . The fifth and sixth switching transistors T5 and T6 are off in a period in which the EM [n] signal is on, and the OLED element Do should not emit light in this period. In order 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 a leakage current flows.

When the OLED element Do needs to emit light with the maximum luminance (for example, 360 nits), the on period of the EM [n] signal must be maximized, so that the AMOLED Off Ratio (AOR) is small, . Therefore, by setting the turn-off voltage VGH sufficiently high so that the leakage current hardly flows, the anode voltage of the OLED element Do due to the leakage current can not be prevented from reaching the conduction voltage Vth_EL. If the level of the turn-off voltage VGH is high, the level of the gray-scale display voltage VREG1 is of course also high. As can be seen from the graph of FIG. 5A, when the OLED element Do emits light without dimming, for example, at a maximum luminance of 360 nits, the turn-off voltage VGH is set to, for example, 6.6 V, Accordingly, the gradation expression voltage VREG1 is set to, for example, 6.4V.

In contrast, when the OLED element Do emits light at a low luminance (for example, 183nit) due to dimming, the off-period of EM [n] increases, that is, the AOR increases, and accordingly, the amount of leakage current decreases . When the leakage current flows, the anode voltage (Vanode) rises. The amount of the anode voltage Vanode rising due to the leakage current does not reach the conduction voltage Vth_EL of the OLED element Do during the initialization period, that is, the black margin voltage increases as the AOR increases (See FIG. 8). For reference, the reason why the anode voltage (Vanode) of FIG. 8 is raised stepwise is that the section in which the leakage current flows and the section in which the leakage current does not flow are repeated as EM [n] is repeatedly turned on and off. This means that if the leakage current is not larger 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, allowing the flow of the leakage current less than the amount of current corresponding to the black margin voltage based on the current-voltage characteristic of the transistor means that the level of the turn-off voltage VGH of the switching transistor can be lowered so much . Naturally, the level of the gradation display voltage VREG1 can be lowered as well. As can be seen from the graph of FIG. 5A, when the OLED element Do is dimmed to 183 nits, for example, the turn-off voltage VGH may be set as low as, for example, 6.2 V, The gradation representation voltage VREG1 may also be set as low as 6.0 V, for example.

The magnitude of the black margin voltage may be different for each dimming luminance. Further, the characteristics of the transistor to be used, the manufacturing process, and the like may also be affected. Therefore, how to reduce the swing width of the turn-off voltage (VGH) at the time of dimming can be determined through simulation considering the target luminance value, the current-voltage characteristic of the transistor to be used, .

Next, referring to Figs. 9 to 11, a mechanism for reducing the swing width of the turn-on voltage VGL of the switching transistor at the time of dimming and raising the level of the initialization voltage Vinit will be described.

First, referring to FIG. 9 and FIG. 10, an initialization voltage Vinit for initializing data at the time of dimming is described as a level increasing mechanism of the initialization voltage Vinit as the margin increases. In order to drive the OLED element Do, the voltage of the capacitor Cst, that is, the gate voltage of the driving transistor Tl, can be periodically initialized. When the initialization voltage Vinit is set to -3 V and the fourth switching transistor T4 is turned on for initialization, the charge stored in the capacitor Cst is passed through the fourth switching transistor T4, The gate voltage of the driving transistor Tl decreases. However, since the fourth switching transistor T4 is turned off again, the turn-on time is not long, so that the gate voltage of the driving transistor T1 does not directly fall to -3V. For example, when the gate voltage of the driving transistor T1 is + 3V and the fourth switching transistor T4 is turned on for initialization, the gate voltage of the driving transistor T1 may drop to + 1V during that time. In this state, it is possible to use white again in the OLED element Do. In that case, if the luminance is lowered by the dimming, the voltage at which the gate voltage of the driving transistor Tl must necessarily reach a high level (for example, rising to +4 V). As described above, the level of the gate voltage of the driving transistor T1 may be lowered during the same initialization time if the level at which the gate voltage of the driving transistor T1 should rise (for example, by +1 V) is increased. That is, the level of the initialization voltage Vinit can be increased as much.

For example, consider the case where the OLED pixel Do is in a black state and then turned into a white state. In this case, when dimming is not performed, the gate voltage of the driving transistor Tl must be changed from a voltage of a black state (for example, 6.4 V) to a voltage of a white (high luminance) state (for example, 3.0 V). For such a state change, the initialization voltage should be set at -3.0 V, and the gate voltage of the driving transistor T 1 should be lowered by 3.4 V within a predetermined time. In the case of dimming, the voltage in the high luminance (white) state is higher than that in the case of not dimming (e.g., 4.0 V). That is, when dimming is applied, (High luminance) state, the gate voltage of the driving transistor Tl may be reduced to, for example, 4.0 V at 6.4 V within a predetermined time. That is, the gate voltage of the driving transistor Tl may be lowered by only 2.4 V, for example. Therefore, the level of the initialization voltage Vinit can be increased by, for example, 1.0V.

Figure 10 schematically illustrates this relationship. For example, 183 nits, the margin of the initialization voltage (Vinit) for data initialization increases and thus the level of the initialization voltage (Vinit) can be raised.

As shown in FIG. 8, for example, the black margin voltage can be increased in the case of dimming (for example, dimming in 183 nits) compared to the case of not dimming. Therefore, the initial level of the anode voltage (Vanode) of the OLED element Do can be raised within the range of the increased black margin voltage. Since the initial level of the anode voltage 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 described above, when the dimming control for lowering the brightness is performed, the initialization voltage (Vinit) can be lowered. The turn-on voltage VGL of the switching transistors is set to a sum of the OLED emission voltage Vth_Margin at a level sufficient to cause the OLED element Do to emit light at the initialization voltage Vinit. This expression is VGL = Vinit - Vth_Margin. Therefore, when the level of the initialization voltage Vinit rises, the swing width of the turn-on voltage VGL is reduced accordingly (see Fig. 5 (c)).

When the dimming control is performed as described above, the level adjustment of various voltages related to the driving of the OLED pixel Do, that is, the swing width of the gradation display voltage VREG1 and the turn-off voltage of the switching transistor VGH), the adjustment of the initialization voltage (Vinit) level, and the method of adjusting the swing width of the turn-on voltage (VGL) of the switching transistor.

The flowchart of FIG. 12 briefly shows an overall flow of a method of adjusting the level of OLED pixel driving related voltages according to the present invention. This method can be performed by a driving IC. The driving IC monitors whether or not the dimming control is started. When the dimming control start command is acquired (S400), the driving IC discriminates the brightness condition indicated by the dimming control command (S410). The turn-on voltage VGL of the switching transistor, the turn-on voltage VGH of the switching transistor, the turn-on voltage Vinit of the switching transistor, and the turn-on voltage VGL of the switching transistor are determined by applying various set values described below according to the applied brightness condition. (S420). The first source voltage VLIN1 may be obtained by applying a head room margin to the turn-off voltage VGH of the switching transistor at step S430. Here, the headroom margin voltage value is set such that the gradation expression voltage VREG1, which is a direct current component, the turn-off voltage VGH and the turn-on voltage VGL of the switching transistor, This is a margin voltage that can be reliably extracted.

In step S420, the voltages may be applied as one (regardless of which luminance condition is applied) (the first algorithm of FIG. 13 to be described later), or the voltages may be applied differently (The second algorithm of Fig. 14, which will be described later).

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

Figure 13 schematically shows the first algorithm. Specifically, the dimming control unit 140 in the driving IC of the OLED device can include the dimming resistor 300 designed according to the standard of 51h. A logic circuit implementing the algorithm according to the method of the present invention may be designed to operate in conjunction with the dimming register 300. [ The dimming register 300 may have information (300, 324) for setting the set values of the gradation representation voltage VREG1 and the low power supply voltage ELVSS during dimming control. The voltage margin required to turn off the transistor can be preset (312). The optimum value of the voltage margin is a value that can be determined according to the characteristics of the transistor to be used, the acceptable risk of malfunction, and the like (for example, 0.1V, 0.2V, ...). Then, the set value of the gray level representation voltage VREEG1 and the previously set transistor turn-off voltage margin set value are combined 314, and the turn-off voltage VGH of the switching transistor can be obtained (316).

In addition, the technique of determining the low power supply voltage (ELVSS) value according to the luminance value is a technology that has been used (324). When the value of the low power supply voltage ELVSS is determined according to the desired brightness value, the set value 326 of the conduction voltage Vth_EL for causing the OLED element Do to conduct by the set value of the low power supply voltage ELVSS (328) so that an initialization voltage (Vinit) value is obtained (330). The conduction voltage Vth_EL is a value that can be determined differently depending on the material and manufacturer of the transistor (for example, 1.0V, 1.5V, 2.0V, ...). When the initialization voltage Vinit is determined, the OLED emission voltage Vth_Margin 332 is added to the value 334 to obtain the turn-on voltage VGL of the transistor element (336). The value of the OLED emission voltage Vth_Margin can be set to a value that can be determined differently depending on the material, process characteristics, manufacturer, etc. of the transistor (for example, -3.5V, 4.0V,.

As described above, the setting value of the gradation display voltage VREG1 and the initialization voltage Vinit to be applied at the time of dimming is first obtained, and based on the algorithm, the turn-off voltage VGH and the turn-on voltage VGL of the switching transistor are determined These voltages can be obtained. When the dimming control needs to be performed in the driving IC, the method according to the present invention can be implemented by providing a driving circuit for performing this algorithm.

In addition, the logic circuit may be designed so that the gradation representation voltage VREG1, the turn-off voltage VGH of the switching transistor, and the first source voltage VLIN1 that makes the turn-on voltage VGL are obtained. That is, the first source voltage VLIN1 may be obtained (322) by adding the headroom margin voltage value 318 to the turn-off voltage VGH of the switching transistor 320. FIG. Since the swing width of the gradation display voltage VREG1, the turn-off voltage VGH of the switching transistor and the turn-on voltage VGL is reduced during dimming control, the level of the first source voltage VLIN1, which is the source voltage generating these voltages, Can be lowered.

The setting of the gray level representation voltage VREG1 310, the setting of the off margin of the transistor 312, the setting of the headroom margin 318, the setting of the conduction voltage Vth_EL of the OLED element 326, Vth_Margin) 332 can be set in consideration of the characteristics of the transistor used by the engineer of the present invention, the characteristics of the driving IC, the risk of malfunction that can be accommodated, the target power consumption reduction rate, There will be.

By implementing the algorithm according to the present invention as a logic circuit of the driving IC and operating it in conjunction with the dimming resistor 300, it is possible to control the gray scale expression voltage VREG1, the turn-off voltage VGH of the switching transistor, 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 can be caused by the problem of designing using the minimum number of logic gates.

13 shows a relationship between the gradation display voltage VREG1, the initialization voltage Vinit, the turn-off voltage VGH of the switching transistor, and the turn-on voltage VGL, irrespective of the dimming level, One way is to use the value. This method has a merit that the circuit configuration is simple for this method, but there is a disadvantage that the optimization for reducing power consumption may be insufficient depending on the degree of dimming control.

FIG. 14 shows an algorithm for applying the second algorithm, that is, the magnitude of the initialization voltage (Vinit) and the turn-on voltage (VGL) of the switching transistor differently according to the dimming level, that is, the luminance condition. The switching transistor OFF margin setting value 312 and the OLED light emitting voltage Vth_Margin value 332 are values related to the characteristics of the transistor to be used and the headroom margin value is a value related to the characteristics of the driving IC. ) Is a value related to the image quality characteristic of the OLED device. The change of the luminance value due to the dimming control is directly related to the image quality. When it is more important to obtain the best image quality than the reduction of the power consumption, the value of the conduction voltage Vth_EL of the OLED element Do depends on the luminance condition And may be set to an optimal value (340). When the conduction voltage Vth_EL of the OLED element Do is determined to be an optimum value according to the luminance level, the initial value voltage Vinit is obtained 344 by adding the value to the set value of the low power supply voltage ELVSS 342, The procedure of obtaining (336) the turn-on voltage VGL of the switching transistor by adding the initialization voltage Vinit to the OLED emission voltage (Vth_Margin) set value 332 is as described above. The setting of the turn-off voltage VGH from the setting of the gray-scale display voltage VREG1 310 to the setting of the turn-off voltage VGH 316 and the setting of the first source voltage VLIN1 322 can be set to one have.

This second algorithm can set various voltages (VREG1, VHG, Vinit, VGL, VLIN1, etc.) related to the driving of the OLED element (Lo) to a value optimized for the luminance condition as compared with the first algorithm, There is an advantage that the efficiency of power reduction can be further increased. On the other hand, there is a disadvantage that the configuration of the logic circuit for implementing this becomes more complicated.

The graph of FIG. 15 shows the power consumption when the various voltages are changed (after the change) and when the present invention is not applied (before the change) according to the present invention in the low luminance driving according to the dimming control for the four samples . As a result, it can be seen that the driving power consumption can be reduced by at least 3% as compared with the case where the method of the present invention is applied.

Although the present invention has been described above with reference to the OLED pixel 200 illustrated in FIG. 2, the present invention is not limited to the OLED pixel 200 shown in FIG. OLED pixels having transistors for on / off switching of the data lines can be widely applied. At least one of the third switching transistor T3, the fourth switching transistor T4 and the seventh switching transistor T7 is omitted in the OLED pixel circuit (for example, in the circuit of Fig. 2) in which the initializing circuit is simplified as compared with Fig. (For example, the fifth switching transistor T5 and the sixth switching transistor T6) which are implemented by only one transistor or all of which are omitted from the switching using the light emission control signal EM [n] A circuit in which at least one of them is omitted).

The method of the present invention can be implemented as a logic circuit, which logic circuit can be included as part of the driving circuit 105 of the OLED device. However, the method of the present invention does not preclude that at least some of its functions may be implemented in software. For example, a mixture of a logic circuit and a program.

The method of the present invention can be applied to a display device employing an OLED element without limitation of its kind. 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, navigation and the like.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the following claims. It can be understood that it is possible.

100: OLED device 105: driving circuit
110: display panel 130: timing controller
140: dimming control unit 150:
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 (20)

A method for controlling 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, comprising the steps of: checking whether a change in luminance condition of an OLED pixel occurs; And
A setting for changing the level of each of the driving-related voltages in a direction of decreasing power consumption within a range of a margin voltage that may occur in driving-related voltages related to driving of the OLED pixels when there is a change in the luminance condition Wherein the driving voltage is applied to the OLED device. The method of claim 1, wherein the setting comprises: pre-setting a level of the driving-related voltages in association with a luminance condition of an OLED pixel; And changing the levels of the drive-related voltages to the levels set in relation to the changed brightness condition when there is a change in the brightness condition. The method according to claim 2, wherein the predetermined drive-related voltages are each set to a voltage value of one level regardless of the degree of change of the brightness condition. 3. The method of claim 2, wherein the predetermined drive-related voltages are set to voltage values of different levels according to a degree of change of the brightness condition. 2. The method of claim 1, wherein the driving-related voltages include a gray-scale display voltage (VREG1) of the OLED pixel. 2. The method of claim 1, wherein the driving-related voltages comprise a turn-off voltage (VGH) for turning off the switching transistor of the OLED pixel. The method of claim 1, wherein the driving-related voltages include a turn-on voltage (VGH) for turning on the switching transistor of the OLED pixel. 2. The method of claim 1, wherein the driving-related voltages comprise a gate of a driving transistor of the OLED pixel and an initialization voltage (Vinit) for initializing the anode of the OLED element. The method according to claim 1, wherein the setting comprises: setting a gradation display voltage (VREG1) of the OLED pixel in accordance with a luminance condition to be changed, when the luminance condition is changed; And adding a turn-off margin voltage of the transistor of the OLED pixel to the set gradation voltage VREG1 to obtain a turn-off voltage VGH of the transistor. 10. The method of claim 9, wherein the setting further comprises setting a first source voltage (VLIN1) by adding a head room margin voltage value to a turn-off voltage (VGH) of the transistor , The first source voltage VLIN1 is a source voltage for generating the gradation display voltage VREG1, the turn-off voltage VGH, and a turn-on voltage VGL for turning on the transistor of the OLED pixel, The margin voltage value can be obtained by stably extracting the gradation expression voltage VREG1, the turn-off voltage VGH and the turn-on voltage VGL, which are direct current components, despite the ripple component contained in the first source voltage VLIN1 Wherein the driving voltage is a margin voltage that can be applied to the OLED display. The method of claim 1, wherein the setting comprises: setting a low power supply voltage (ELVSS) of the OLED pixel corresponding to a luminance condition to be changed, when the brightness condition is changed; And setting a voltage obtained by adding the conduction voltage (Vth_EL) of the OLED element to the set lower power supply voltage (ELVSS) to an initialization voltage (Vinit), wherein the initialization voltage (Vinit) And a voltage for initializing the gate and the anode of the OLED element. 12. The method of claim 11, wherein the setting comprises: applying a voltage value, which is a sum of an OLED emission voltage (Vth_Margin) at a level sufficient to emit light to the OLED element (Do) To a turn-on voltage (VGL) level for turn-on of the OLED device. 12. The method according to claim 11, wherein the algorithm according to the driving voltage setting method is implemented as a logic circuit in a driving IC of the OLED device. 12. The method according to claim 11, wherein the conduction voltage (Vth_EL) of the OLED element is set to a voltage value of one level regardless of the degree of change of the brightness condition. 12. The method of claim 11, wherein the conduction voltage (Vth_EL) of the OLED element is set to voltage values of different levels according to the degree of change of the brightness condition. 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, the level of the driving-related voltages is preset in association with the luminance condition of the OLED pixel step;
Checking whether a change in the luminance condition of the OLED pixel occurs; And
Within a range of margin voltages that can occur in driving related voltages associated with driving of the OLED pixels when the luminance condition is changed, the level of each of the driving related voltages is set in association with the changed luminance condition Level to reduce the power consumption of the OLED device. 17. The method of claim 16, wherein the driving related voltages are selected from the group consisting of: a gradation display voltage (VREG1) of the OLED pixel, a turn off voltage (VGH) for turning off the switching transistor of the OLED pixel, A turn-on voltage (VGH) for driving the OLED pixel, and an initialization voltage (Vinit) for initializing the gate of the OLED element and the anode of the OLED element. 17. The method of claim 16, wherein the step of reducing power consumption comprises: setting a gradation voltage (VREG1) of the OLED pixel corresponding to a luminance condition to be changed when the luminance condition is changed; Off voltage (VGH) of the transistor by adding a turn-off margin voltage of the transistor of the OLED pixel to the set gray-scale voltage (VREG1); And setting a first source voltage (VLIN1) by adding a head room margin voltage value to a turn-off voltage (VGH) of the transistor, wherein the first source voltage (VLIN1) And a turn-on voltage (VGL) for turning on the transistor of the OLED pixel, wherein the headroom margin voltage value is set to the first source voltage (VLIN1) Off voltage (VGH) and the turn-on voltage (VGL), which are direct current components, in spite of the ripple component included in the OLED device. Drive voltage setting method. 17. The method of claim 16, wherein the step of reducing power consumption comprises: setting a low power supply voltage (ELVSS) of the OLED pixel corresponding to a brightness condition to be changed when there is a change in the brightness condition; Setting a voltage obtained by adding the conduction voltage (Vth_EL) of the OLED element to the set low power supply voltage (ELVSS) to an initialization voltage (Vinit); And a turn-on voltage (VGL) level for turning on the transistor of the OLED pixel is set to a voltage value obtained by adding an OLED emission voltage (Vth_Margin) at a level sufficient to cause the OLED element (Do) to emit light to the initialization voltage Wherein the initialization voltage Vinit is a voltage for initializing the gate of the driving transistor of the OLED pixel and the anode of the OLED element. 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, the level of the driving-related voltages is preset in association with the luminance condition of the OLED pixel step;
Checking whether a change in the luminance condition of the OLED pixel occurs; And
Within a range of margin voltages that can occur in driving related voltages associated with driving of the OLED pixels when the luminance condition is changed, the level of each of the driving related voltages is set in association with the changed luminance condition Levels to reduce power consumption,
The driving-related voltages include at least one of a gray-level display voltage VREG1 of the OLED pixel, a turn-off voltage VGH for turning off the switching transistor of the OLED pixel, 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.

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