Organic light emitting display device and driving method for the same

An organic light emitting display device and a driving method for the same is provided. The device includes a pixel portion adapted to receive a scan signal and a data signal and display an image. A scan driver generates and applies the scan signal to the pixel portion. A data driver generates and applies the data signal and a pixel voltage to the pixel portion. When the device is operating in the normal mode, the data driver also applies a drive voltage to a photo sensor also included in the display device. The photo sensor adjusts a luminance of the pixel portion according to a sensed brightness of ambient light. When the device is operating in the power saving or stand-by mode, the data driver controls the drive voltage off and thereby prevents power consumption by the photo sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2006-0028615, filed on Mar. 29, 2006, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to an organic light emitting display device and a driving method for the same. More particularly, the present invention relates to an organic light emitting display device and a driving method for the same that operates a photo sensor according to the brightness of ambient light and controls the photo sensor on and off.

2. Discussion of Related Art

A flat panel display device includes a display region defined by a plurality of pixels arranged on a substrate in a form of a matrix, and displays an image by selectively applying a data signal to the pixels to which a scan line and a data line are connected.

A flat panel display device is classified into an active matrix type and a passive matrix type according to its drive type. In a point of resolution, contrast, and operation speed, the active matrix type flat panel display device, which selectively lights every unit pixel has been widely used. An organic light emitting display device is one such example of a flat panel display device. In some organic light emitting display devices, when the organic light emitting display device operates in a power saving mode or in a stand-by mode, it does not display an image but a photo sensor continues to operate therein, which leads to continuous power consumption.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides an organic light emitting display device. The device includes a data driver, a photo sensor and a scan driver and a pixel portion. The device includes a data driver adapted to: receive an external voltage and generate a drive voltage. The data driver is also adapted to control on/off the drive voltage, wherein the drive voltage is controlled on when the organic light emitting display device is operating in normal mode and the drive voltage is controlled off when the organic light emitting display device is not operating in normal mode. The data driver is also adapted to generate and output a data signal. The photo sensor is adapted to: sense a brightness of an ambient light to determine a sensed brightness of the ambient light; receive the drive voltage output from the data driver; and output a brightness signal based on the sensed brightness of the ambient light. The scan driver is adapted to generate and transfer a scan signal. The pixel portion is adapted to: receive the data signal and the scan signal; receive the brightness signal; and display an image having a luminance indicative of the brightness signal.

In some embodiments, the data driver includes a control terminal for receiving the drive voltage. The drive voltage may also be a pixel voltage to drive the pixel portion.

In some embodiments, the photo sensor includes an optical sensing section adapted to output an analog sensing signal corresponding to the sensed brightness of the ambient light; an analog-to-digital converter adapted to convert the analog sensing signal from the optical sensing section into a digital sensing signal; and a counter adapted to count a predetermined number during one frame period and generate a corresponding counting signal. The photo sensor also includes a conversion processor adapted to output a control signal based on the digital sensing signal and the counting signal; a register generator adapted to divide the sensed brightness of the ambient light into a plurality of stages of brightness, and store a plurality of register set values corresponding to the plurality of stages of brightness. The photo sensor also includes a first selector adapted to select and output one of the plurality of register set values according to the control signal output from the conversion processor; and a gamma compensation circuit adapted to generate a gamma compensation signal according to the control signal output from the conversion processor.

In some embodiments, the photo sensor also includes a second selector adapted to provide an output for displaying an image after adjusting a luminance corresponding to the sensed brightness of the ambient light. The luminance of the image is adjusted according to the gamma compensation signal from the photo sensor. Further, the analog-to-digital converter compares a voltage of the analog sensing signal from the optical sensing section with a reference voltage to generate a compared result, and generates the digital sensing signal according to the compared result.

In another embodiment of the present invention, a method for driving an organic light emitting display device that adjusts a luminance according to an ambient light is provided. The method includes applying a first drive voltage to a photo sensor for outputting a signal corresponding to an ambient light. The method also includes adjusting a luminance according to the signal corresponding to the ambient light. The method also includes controlling off the drive voltage of the photo sensor when the organic light emitting display device operates in a power saving mode or in a stand-by mode.

In some embodiments, a data driver receives an external voltage and applies a pixel voltage to a pixel portion and also applies the pixel voltage of the pixel portion to the photo sensor.

DETAILED DESCRIPTION

With reference toFIG. 1, an embodiment of a conventional organic light emitting display device includes a pixel portion10, a data driver20, a scan driver30, a power supply40and a photo sensor50. The pixel portion10includes a plurality of pixels11, a plurality of scan lines S1, S2, . . . , Sn, and a plurality of data lines D1, D2, . . . , Dm. Each pixel11includes a pixel circuit (not shown) and a light emitting diode (not shown). The pixel circuit is connected to the scan lines S1, S2, . . . , Sn and the data lines D1, D2, . . . , Dm. The pixel circuit receives a scan signal and a data signal from the scan lines S1, S2, . . . , Sn and the data lines D1, D2, . . . , Dm, respectively, and applies them to the light emitting diode. When an electric current flows through the light emitting diode, the light emitting diode emits light according to a gradation value corresponding to the electric current.

The data driver20is connected to the plurality of data lines D1, D2, . . . , Dm, and applies a data signal to the pixel portion10. The data signal is applied to one row of the pixel portion10in parallel.

The scan driver30is connected to the plurality of scan lines S1, S2, . . . , Sn. The scan driver30applies a scan signal to the pixel portion10, thereby allowing a data signal to be applied to a row of the pixel portion selected by the scan signal.

The photo sensor50senses ambient light, and adjusts the luminance of the pixel portion10according to the sensed ambient light. Namely, when the ambient light is bright, the photo sensor50increases the luminance of the pixel portion10. In contrast to this, when the ambient light is dark, the photo sensor50reduces the luminance of the pixel portion10. This prevents a display of an image from becoming dark or bright due to the ambient light.

FIG. 2is a block diagram showing an organic light emitting display device according to an embodiment of the present invention.FIG. 3is a simplified block diagram showing a driving concept of a photo sensor.

With reference toFIG. 2andFIG. 3, the organic light emitting display device includes a pixel portion100, a photo sensor500, a data driver200, and a scan driver300. The pixel portion100includes a plurality of pixels101, a plurality of scan lines S1, S2, . . . , Sn, and a plurality of data lines D1, D2, . . . , Dm. The pixel101includes a pixel circuit (not shown) and a light emitting diode (not shown). The pixel circuit is connected to the scan lines S1, S2, . . . , Sn and the data lines D1, D2, . . . , Dm. The pixel circuit receives a scan signal and a data signal from the scan lines S1, S2, . . . , Sn and the data lines D1, D2, . . . , Dn, respectively, and applies them to the light emitting diode. When an electric current flows through the light emitting diode, the light emitting diode emits light according to a gradation value corresponding to the electric current.

The photo sensor500measures the brightness of ambient light. When the ambient light is bright, the photo sensor500elevates the luminance of the pixel portion100. When the ambient light is dark, the photo sensor500reduces the luminance of the pixel portion100. These prevent the occurrence of dazzling. The photo sensor500receives a drive voltage from the pixel portion100through the data driver200and is operated by the drive voltage.

The data driver200is connected to the plurality of data lines D1, D2, . . . , Dm, and applies a data signal to the pixel portion100. The data signal is applied to one row of the pixel portion100in parallel. Further, the data driver200applies a drive voltage to the photo sensor500, and may intercept an external voltage thereby controlling off the drive voltage to control an operation of the photo sensor500. That is, the data driver200intercepts the external voltage to prevent the drive voltage from being applied to the photo sensor500because it may unnecessarily adjust a luminance according to an ambient light when the organic light emitting display device operates in a power saving mode or in a stand-by mode. In contrast to this, when the organic light emitting display device operates in a normal mode, the data driver200applies the drive voltage to the photo sensor500to adjust the luminance according to the ambient light.

A pixel voltage (ELVdd) (not shown) applied to the pixel portion100may be used as the drive voltage that the data driver200applies to the photo sensor500. In one embodiment, the pixel voltage is output from a power supply400. The data driver200includes one of a plurality of terminals as a control terminal (not shown), and a power terminal (not shown) connected to pixel voltage (ELVdd). The data driver200may provide the pixel voltage to the pixel portion100through the data driver200. Further, the data driver200controls an external voltage received through its control terminal to control application of the drive voltage to the photo sensor500.

The reason why the data driver200receives and provides the pixel voltage applied to the pixel portion100to the photo sensor500is as follows. Since power consumption of the data driver200may be small, the voltage applied to the data driver200may be very small. Accordingly, the data driver200shares a drive voltage with the photo sensor500. The difference between the power consumption of the data driver200and that of the photo sensor500is not large, with the result that the data driver200is unstably operated.

However, when the pixel portion100uses the pixel voltage (ELVdd) applied thereto, since it consumes greater power than that of the data driver200or the photo sensor500, greater voltage should be supplied to the pixel portion100. Accordingly, although the photo sensor500shares the pixel voltage (ELVdd) applied to the pixel portion100with the pixel portion100, the power consumption of the photo sensor500is very small in comparison with that of the pixel portion100. Unlike in the data driver200, the pixel portion100is not influenced significantly to be unstably operated.

The scan driver300is connected to the plurality of scan lines S1, S2, . . . , Sn. The scan driver300applies a scan signal to the pixel portion100. The data driver200applies a data signal to a row of the pixel portion selected by the scan signal.

FIG. 4is a block diagram showing a photo sensor of the organic light emitting display device according to an embodiment of the present invention. The photo sensor500includes an optical sensing section511, an A/D converter512, a counter513, a conversion processor514, a register generator515, a first selector516, a second selector517, and a gamma compensation circuit600.

The optical sensing section511measures the brightness of ambient light, divides it into a plurality of stages, and outputs an analog sensing signal corresponding to the stages. The A/D converter512compares the analog sensing signal from the optical sensing section511with a reference voltage, and outputs a digital sensing signal corresponding to the compared result. For example, when the brightness of the ambient light is in the brightest stage, the A/D converter512outputs a sensing signal of ‘11’. When the brightness of the ambient light is in a bright stage, the A/D converter512outputs a sensing signal of ‘10’. When the brightness of the ambient light is in a dark stage, the A/D converter512outputs a sensing signal of ‘01’. When the brightness of the ambient light is in the darkest stage, the A/D converter512outputs a sensing signal of ‘00’.

The counter513counts a predetermined number for a predetermined time period in response to an externally supplied vertical synchronous signal Vsync and outputs a corresponding counting signal Cs. In one embodiment, where the counter513uses a binary value of 2 bits, when the vertical synchronous signal Vsync is input to the counter513, it is initialized as a value of ‘00’. Next, the counter513sequentially shifts a clock signal CLK and counts a number up to ‘11’. Then, the vertical synchronous signal Vsync is input to the counter513, the counter513is reset as an initialization state. Through the aforementioned operation, the counter513sequentially counts the number from ‘00’ to ‘11’ during one frame period, and outputs a counting signal Cs corresponding to the counted number to a conversion processor514.

The conversion processor514outputs a control signal to select a set value of each register based on the counting signal Cs from the counter513and the sensing signal from the A/D converter512. Namely, when the counter513outputs a predetermined signal, the conversion processor514outputs a control signal corresponding to a selected sensing signal, and maintains a control signal output during one frame period. Next, the conversion processor514resets an output control signal when a next frame period comes. Then, the conversion processor514outputs a control signal corresponding to a sensing signal output from the A/D converter512and maintains it during one frame period. In one embodiment, when the ambient light is in a brightest state, the conversion processor514outputs a control signal corresponding to a sensing signal of ‘11’, and maintains the control signal during one frame period when the counter513counts. When the ambient light is in a darkest state, the conversion processor514outputs a control signal corresponding to a sensing signal of ‘00’, and maintains the control signal during one frame period when the counter513counts. Further, when an ambient light is in a bright state and a dark state, the conversion processor514outputs a control signal corresponding to a sensing signal of ‘10’ and ‘01’, respectively, and maintains the control signal during one frame period when the counter513counts.

The register generator515divides the brightness of the ambient light into a plurality of stages, and stores a plurality of set values corresponding to the stages.

The first selector516selects a register set value among a plurality of register set values stored in the register generator515. The selected register set value corresponds to the control signal set by the conversion processor514.

The second selector517receives an external set value of 1 bit to adjust the second selector517on/off. When ‘1’ is selected, a brightness controller (not shown) starts an operation. When ‘0’ is selected, an emission controller (not shown) is turned-off to selectively control a brightness according to an ambient light.

The gamma compensation circuit600generates a plurality of gamma compensation signals corresponding to a register set value selected according to the control signal set by the conversion processor514. The control signal corresponds to the sensing signal output from the optical sensing section511. The gamma compensation signals have different values according to the brightness of the ambient light. The aforementioned operation is performed for R, G, and B. Although it is shown that the gamma compensation circuit600is included in the photo sensor500, in other embodiments, the gamma compensation circuit600may be configured to be separate from the photo sensor500.

Further, referring toFIGS. 2 and 3, the photo sensor500having the aforementioned construction receives the drive voltage from the external voltage at the control terminal (not shown) of the data driver200and is operated by the received drive voltage.

FIG. 5is a block diagram showing an embodiment of the gamma compensation circuit of the photo sensor shown inFIG. 4. The gamma compensation circuit600includes a ladder resistor61, an amplitude control register62, a curve control register63, a first selecting section64, a second selecting section65, a third selecting section66, a fourth selecting section67, a fifth selecting section68, a sixth selecting section69and a gradation voltage amplifier70.

The ladder resistor61generates a plurality of gradation voltages. The ladder resistor61includes a plurality of variable resistors between the lowest stage voltage VLO and a reference voltage to be serially connected to each other. The highest-stage voltage VHI is set as the reference voltage. Further, when a resistance value of the ladder resistor61is set to be small, a control range of an amplitude becomes less but a precision of the control amplitude is enhanced. In contrast to this, when a resistance value of the ladder resistor61is set to be great, a control range of an amplitude becomes greater but a precision of the control amplitude is deteriorated.

The amplitude control register62outputs a register set value of 3 bits to the first selecting section64, and outputs a register set value of 7 bits to the second selecting section65. An increase in the number of set bits may increase the number of gradation voltages that may be selected. A change in the register set value may select a different gradation voltage.

The curve control register63outputs a register set value of 4 bits to each of a first selecting section64, a second selecting section65, a third selecting section66, a fourth selecting section67, a fifth selecting section68and a sixth selecting section69. The register set value can be changed, and a gradation voltage to be selected can be adjusted according to the register set value. Referring toFIGS. 4 and 5upper 10 bits and lower 10 bits among register values generated by the register generator515are input to the amplitude control register62and the curve control register63, respectively, and are selected as register set values.

The first selecting section64selects a gradation voltage corresponding to a register set value of 3 bits set by the amplitude control register62among a plurality of gradation voltages divided by the ladder resistor61, and outputs it as the highest gradation voltage.

The second selecting section65selects a gradation voltage corresponding to a register set value of 7 bits set by the amplitude control register62among a plurality of gradation voltages divided by the ladder resistor61, and outputs it as the lowest gradation voltage.

The third selecting section66divides a voltage between the highest gradation voltage from the first selecting section64and the lowest gradation voltage from the second selecting section65into a plurality gradation voltages through a plurality of resistor rows, and selects and outputs a gradation voltage corresponding to a register set value of 4 bits.

The fourth selecting section67divides a voltage between the highest gradation voltage from the first selecting section64and the gradation voltage from the third selecting section66into a plurality of gradation voltages through a plurality of resistor rows, and selects and outputs a gradation voltage corresponding to a register set value of 4 bits.

The fifth selecting section68selects and outputs a gradation voltage corresponding to a register set value of 4 bits among the output gradation voltages of the first and fourth selecting sections64and67.

The sixth selecting section69selects and outputs a gradation voltage corresponding to a register set value of 4 bits among the output gradation voltages of the first and fifth selecting sections64and68. In the aforementioned operation, a curve of a middle gradation part can be controlled according to a register set value of the curve control register63that allows gamma characteristics to be adjusted suited to the characteristics of respective light emitting diodes. Moreover, in order to make a gamma curve characteristic convex downwardly, a resistance of the ladder resistor61is adjusted to increase a potential difference between respective gradations as a small gradation is expressed. In contrast to this, so as to make a gamma curve characteristic convex upwardly, a resistance of the ladder resistor61is adjusted to reduce a potential difference between respective gradations as a small gradation is expressed.

The gradation voltage amplifier70outputs a plurality of gradation voltages corresponding to a plurality of gradation voltages to be expressed.

In consideration of fluctuations in characteristics of R, G, and B light emitting diodes, so as to have almost the same luminance characteristics in R, G, and B light emitting diodes, gamma compensation circuits are installed at the R, G, and B light emitting diodes so that an amplitude and a curve through a curve control register63and an amplitude control register62can be differently set according to the R, G, and B light emitting diodes.

FIG. 6is a flow chart showing a driving method of the organic light emitting display device according to an embodiment of the present invention.

The organic light emitting display device displays (ST100) an image in one of a normal mode, a power saving mode or a stand-by mode. The normal mode is a mode for displaying an image. The power saving mode is a mode for reducing a power consumption using a limited amount of an electric current flowing through a pixel. During a process of expressing an image, when an external input does not occur for a predetermined time or more, it is determined that a user does not view a screen and the organic light emitting display device reduces a total luminance of a pixel portion to a value less than a predetermined value. This mode is referred to as “power saving mode.”

It is determined (ST110) whether the organic light emitting display device is selected as one of the normal mode, the power saving mode or the stand-by mode. The power saving mode and the stand-by mode are modes to reduce power consumption. In the power saving mode and the stand-by mode, a luminance of the pixel portion is not controlled corresponding to an ambient light.

When the organic light emitting display device operates in the stand-by mode or the power saving mode, a supply of the drive voltage to the photo sensor is controlled off (ST120) thereby substantially preventing power of the photo sensor from being consumed when the organic light emitting display device is in the stand-by mode or the power saving mode.

When the organic light emitting display device operates in the normal mode, the drive voltage is controlled on and thereby supplied (ST130) to the photo sensor so that the organic light emitting display device may adjust a luminance corresponding to the ambient light. The photo sensor provides a signal corresponding to the ambient light.

In accordance with the organic light emitting display device and a driving method for the same of the present invention, a photo sensor adjusts luminance according to ambient light. Accordingly a visible angle of the organic light emitting display device may be increased. Furthermore, the present invention can control a drive voltage such that when the organic light emitting display device operates in a power saving mode or a stand-by mode, external voltage is intercepted and therefore a drive voltage is not applied to the photo sensor. Accordingly, the power consumption of the photo sensor is reduced.