Organic light emitting display using a current sink driver to set the voltage of the driving transistor

A pixel including an organic light emitting diode for use in an organic light emitting display device and a method for driving the display device. First and second transistors are coupled with a current supply line and are turned-on by a scan signal supplied to a scan line to charge a first capacitor to a voltage corresponding to a current through the current supply line. A third transistor supplies a current corresponding to the voltage charged in the first capacitor to the diode. A fourth transistor coupled to a data line is turned-on by a select signal supplied to an address line to charge a second capacitor to a voltage corresponding to a current flowing in the data line. A fifth transistor is coupled between the third transistor and the diode, and is turned-on/off according to the voltage charged in the second capacitor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2006-0019353, filed on Feb. 28, 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 a pixel, an organic light emitting display device, and a method for driving an organic light emitting display device using the pixel, and more particularly to a method for driving an organic light emitting display device in a digital pattern, an organic light emitting display device being driven in the digital pattern, and a pixel included in the organic light emitting display device that is being driven in the digital pattern.

2. Discussion of Related Art

Organic light emitting display devices are a type of flat panel display device that make use of organic light emitting diodes that emit light by re-combination of electrons and holes. The organic light emitting display device has advantages of high response speed and small power consumption.

FIG. 1is a block diagram of a conventional organic light emitting display device. The conventional organic light emitting display device includes a display region30, a scan driver10, a data driver20, and a timing controller50. The display region30includes a plurality of pixels40formed at a crossing area of scan lines S1to Sn and data lines D1to Dm. The scan driver10drives the scan lines S1to Sn. The data driver20drives the data lines D1to Dm. The timing controller50controls the scan driver10and the data driver20.

The scan driver10generates a scan signal in response to a scan drive control signal SCS from the timing controller50, and sequentially provides the generated scan signal to the scan lines S1to Sn. The scan driver10also generates an emission control signal in response to the scan drive control signal SCS from the timing controller50, and sequentially provides the generated emission control signal to the emission control lines E1to En.

The data driver20receives the data drive control signal DCS from the timing controller50. Upon the receipt of the data drive control signal DCS, the data driver20generates data signals, and provides the generated data signals to the data lines D1to Dm. The data driver20provides the generated data signals to the data lines D1to Dm every 1 horizontal period.

The timing controller50generates the data drive control signal DCS and the scan drive control signal SCS according to externally supplied synchronous signals. The data drive control signal DCS is provided to the data driver20, and the scan drive control signal SCS is provided to the scan driver10. The timing controller50also provides externally supplied data Data to the data driver20.

The display region30receives power from a first power supply ELVDD and a second power supply ELVSS that are located outside the organic light emitting display device, and provides them to the pixels40. Upon receiving power from the first power supply ELVDD and the second power supply ELVSS, the pixels40control the amount of a current into the second power supply ELVSS from the first power supply ELVDD. The amount of the current is controlled to correspond to the data signal. The current is passed through a light emitting element in the pixel, thus generating light corresponding to the data signal. Furthermore, emission time of the pixels40is controlled by the emission control signal.

In the aforementioned conventional organic light emitting display device, the data signal generated by the data driver20is represented by a voltage corresponding to data provided to the data driver20. As a result, the pixel40is charged with the voltage corresponding to the supplied data signal to display an image. In other words, the conventional organic light emitting display device controls the voltage value of the data signal to be supplied to the pixel40, thereby controlling a luminance of light emitted in the pixel40. However, when the data signal is provided as a voltage, a desired image cannot be displayed in the pixel40.

Each of the pixels40includes a plurality of transistors. The threshold voltage and the electron mobility of transistors included in the pixels40may deviate from a desired value due to variations introduced during the fabrication process. Therefore, when a data signal having a certain voltage is provided to the pixels40, due to the deviation of the transistors included in the different pixels40from the ideal characteristics, an image of a desired luminance cannot be displayed.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to provide a pixel and an organic light emitting display device including the pixel which are driven in a digital pattern in order to display an image of a desired luminance, and a method for driving the organic light emitting display device, using the pixel, that employs the digital pattern.

One embodiment of the present invention provides a pixel including an organic light emitting diode, first and second transistors coupled with a current supply line, and being turned-on by a scan signal supplied to a scan line, a first capacitor being charged with a voltage corresponding to an electric current flowing into the current supply line when the first and second transistors are turned-on, a third transistor for supplying an electric current corresponding to the voltage charged in the first capacitor to the organic light emitting diode, a fourth transistor coupled with a data line, and being turned-on by a select signal supplied to an address line, a second capacitor being charged with a voltage corresponding to an electric current flowing into the data line when the fourth transistor is turned-on, and a fifth transistor coupled between the third transistor and the organic light emitting diode, and being turned-on/off according to the voltage charged in the second capacitor.

In one embodiment, an electric current to be supplied to the organic light emitting diode flows into the current supply line when the pixel emits light with maximum luminance. In one embodiment, the selection signal is supplied at predetermined intervals so that an image is displayed using a supply time of an electric current supplied to the organic light emitting diode.

Another aspect of the present invention provides an organic light emitting display device including a display region including a plurality of pixels coupled with scan lines, data lines, current supply lines, and address lines, a scan driver for supplying a scan signal to the scan lines to sequentially the pixels in horizontal lines, a current sink coupled with the current supply lines for sinking a current from pixels selected by the scan signal, an address driver for providing a select signal to the address lines at predetermined intervals, and a data driver for supplying a data signal to synchronize with the select signal in order to control emissions and non-emissions of the pixels.

In one embodiment, the current sink receives an electric current to be supplied to the organic light emitting diode from a pixel selected by the scan signal when the pixel emits light with maximum luminance. In one embodiment, the pixel is charged with a voltage corresponding to an electric current flowing into the current supply line, and the pixel receives the data signal, and emits or does not emit light according to the data signal when the select signal is supplied to the pixel. In one embodiment, the current sink includes sample/hold sections coupled with the current supply lines for sinking the current, a first switch for controlling coupling between the sample/hold sections and the current supply lines, a second switch for controlling a coupling to supply a reference current to at least one of the sample/hold sections, and a controller for controlling the sample/hold sections, the first switch, and the second switch.

According to another aspect of the present invention, there is provided a method for driving an organic light emitting display device including (i) selecting pixels by sequentially supplying a scan signal, (ii) sinking a current from the selected pixels to charge the pixel with a voltage corresponding to the current, and (iii) controlling emission or non-emission of the pixels charged with the voltage by supplying a data signal to the pixels at predetermined intervals.

In one embodiment, the current is set to be the same current as that to be supplied to an organic light emitting diode when the pixels emit light with maximum luminance in step (ii).

DETAILED DESCRIPTION

In the following description the term coupled is used to indicate a direct or indirect connection between two elements or an electrical connection between two elements of a circuit.

FIG. 2Ashows a block diagram of an organic light emitting display device according to a first embodiment of the present invention.FIG. 3shows waveforms of signals supplied from drivers shown inFIG. 2A.

As shown inFIG. 2A, the organic light emitting display device according to a first embodiment of the present invention includes a display region130, a scan driver110, a data driver120, and a current sink150. The display region130includes a plurality of pixels140formed at crossing areas of scan lines S1to Sn, address lines AD1to ADn, data lines D1to Dm, and current supply lines C1to Cm. The scan driver110drives the scan lines S1to Sn and the address lines AD1to ADn. The data driver120drives the data lines D1to Dm. The current sink150drives the current supply lines C1to Cm.

As shown inFIG. 3, the scan driver110sequentially provides a scan signal to the scan lines S1to Sn to sequentially select the pixels140located along consecutive scan lines. The scan driver110also provides a select signal to the address lines AD1to ADn. The scan driver110provides the select signal to the address line coupled with a pixel140selected by a scan signal at predetermined time intervals shown as T1, T2, T4, T8, etc. The predetermined time intervals may be, for example, intervals of 20, 21, 22, 23, . . . units of time such as 1, 2, 4, 8 . . . fractions of seconds.

In more detail, after the scan signal is supplied to a first scan line S1, the scan driver110provides the select signals to a first address line AD1. In one exemplary embodiment, the select signals are supplied at intervals of 20, 21, 22, 23, . . . units of time. When the select signal is supplied, a data signal is also provided to the pixels140. In the intervals between the select signals, when the select signal is not being supplied, the pixels140emit or do not emit light according to the data signal being provided to the pixel. Emission times of the pixels140overlap one another to express a gradation. The select signals supplied to the address lines AD1to ADn do not overlap so that desired data signals provided to the data lines D1to Dm may be provided to the pixels.

The data driver120provides a data signal to the data lines D1to Dm. The data signal may be set to have a voltage corresponding to a digital signal, namely, a logic value of “1” or “0.” Further, as shown inFIG. 3, the data signal is supplied in synchronization with the select signal. The data lines D1to Dm are shown as D inFIG. 3.

The current sink150sinks a current from pixels selected by a scan signal via the current supply lines C1to Cm. In practice, the current sink150receives an electric current Imax that flows through an organic light emitting diode included in the pixels selected by the scan signal when the pixels140emit light at their maximum luminance.

The display region130receives power from a first power supply ELVDD and a second power supply ELVSS that are located outside the organic light emitting display device, and provides the received power to the pixels40.

When the scan signal is supplied to the pixels140, the pixels140are charged with a voltage corresponding to the current Imax, and emit or do not emit light according to a data signal supplied in synchronization with the select signal. The pixels140emit light at predetermined intervals according to the data signal. For example, the pixels140emit or do not emit light at intervals of T1=20, T2=21, T4=22, T8=23, . . . to express an image of a predetermined gradation.

FIG. 2Ashows one scan driver110for driving both the scan lines S1. Sn and the address lines AD1to And. However, as shown inFIG. 2B, an address driver111for driving the address lines AD1to ADn can be installed in addition to a scan driver110′ for driving the scan lines. In other words, the address driver111can be included in the scan driver110as shown inFIG. 2A, or formed separately as shown inFIG. 2B.

FIG. 4shows an exemplary circuit for the pixel shown inFIG. 2AorFIG. 2B. For convenience of description,FIG. 4shows a pixel coupled with an n-th scan line Sn, an n-th address line ADn, an m-th current supply line Cm, and an m-th data line Dm.

The pixel according to an embodiment of the present invention includes an organic light emitting diode OLED and a pixel circuit142. The pixel circuit142supplies an electric current to the organic light emitting diode OLED.

The organic light emitting diode OLED generates light corresponding to the electric current supplied from the pixel circuit142. The generated light may be red, green, or blue depending on the type of the organic light emitting diode used in each pixel.

The pixel circuit142controls the supply time of an electric current flowing into the second power supply ELVSS from the first power supply ELVDD through the organic light emitting diode OLED corresponding to the scan signal, the data signal, and the select signal. So as to do this, the pixel circuit142includes first to fifth transistors M1to M5, and first and second capacitors CP1and CP2.

A first electrode of the first transistor M1is coupled with the current supply line Cm, and a second electrode thereof is coupled with a first node N1. A gate electrode of the first transistor M1is coupled with the scan line Sn. When the scan signal is supplied to the first transistor M1, the first transistor M1is turned-on to electrically connect the current supply line Cm and the first node N1to each other. Either of the first and second electrodes of the first transistor M1may be a source electrode or a drain electrode. For example, when the first electrode is set as the source electrode, the second electrode would be the drain electrode.

A first electrode of the second transistor M2is coupled with the current supply line Cm, and a second electrode thereof is coupled with a second electrode of the third transistor M3. Moreover, a gate electrode of the second transistor M2is coupled with the scan line Sn. When the scan signal is supplied to the second transistor M2, the second transistor M2is turned-on to electrically connect the current supply line Cm and the second electrode of the third transistor M3to each other.

A first electrode of the third transistor M3is coupled with the first power supply ELVDD, and the second electrode thereof is coupled with a first electrode of the fifth transistor M5. Furthermore, a gate electrode of the third transistor M3is coupled with the first node N1. The third transistor M3provides an electric current corresponding to the voltage charged in the first capacitor CP1to the first electrode of the fifth transistor M5.

A first electrode of the fourth transistor M4is coupled with the data line Dm, and a second electrode thereof is coupled with a second node N2. Moreover, a gate electrode of the fourth transistor M4is coupled with the address line ADn. When the select signal is supplied to the fourth transistor M4, the fourth transistor M4is turned-on to provide the data signal from the data line Dm to the second node N2.

The second electrode of the fifth transistor M5is coupled with the organic light emitting diode OLED. Further, a gate electrode of the fifth transistor M5is coupled with the second node N2. The fifth transistor M5is turned-on/off according to a voltage charged in the second capacitor CP2.

During a supply period of the scan signal, the first capacitor CP1is charged with a voltage corresponding to an electric current Imax flowing into the current supply line Cm.

When the fourth transistor M4is turned-on, the second capacitor CP2is charged with a voltage corresponding to a data signal supplied to the data line Dm. The fifth transistor M5is turned-on/off according to the voltage charged in the second capacitor CP2.

While, for convenience of description,FIG. 4shows transistors M1to M5as PMOS transistors, the present invention is not limited to transistors of one conductivity type.

FIG. 5is a waveform diagram showing a signal sequence for a method for driving the pixel shown inFIG. 4.

Operation of the pixel will be described referring toFIG. 4andFIG. 5. At first, an initialization signal510is supplied to the address line ADn. A first polarity signal520is supplied to the data line Dm in synchronization with the initialization signal such that the two signals510and520at least partially overlap. When the initialization signal510is provided to the address line ADn, the fourth transistor M4is turned-on. When the fourth transistor M4is turned-on, the first polarity signal520is supplied to the second node N2. The first polarity signal may be a high logic signal to initialize a charged voltage of the second capacitor CP2. For example, the first polarity signal may be set to the same voltage as the voltage of the first power supply ELVDD. Alternatively, the second capacitor CP2may be initialized without supplying the initialization signal to the address line ADn.

When the initialization signal510is supplied to the address line ADn, the scan signal530is supplied to partially overlap with the initialization signal510. When the scan signal is supplied to the scan line Sn, the first transistor M1and the second transistor M2are turned-on. When the first transistor M1is turned-on, the first node N1and the current supply line Cm are electrically connected with each other. When the second transistor M2is turned-on, the second electrode of the third transistor M3is electrically connected with the current supply line Cm.

As a result, a current path is formed between the first power supply ELVDD and the current supply line Cm through the third transistor M3and the second transistor M2. Accordingly, a current Imax from the first power supply ELVDD through the third transistor M3, the second transistor M2and the current supply line Cm is sunk to the current sink150. At the same time, the first capacitor CP1is charged with a voltage corresponding to the current Imax flowing through the third transistor M3.

The voltage charged in the first capacitor CP1is determined by the current Imax flowing through the third transistor M3. The voltage charged in the first capacitor CP1establishes a source to gate voltage between the source and the gate of the third transistor M3that is independent of the threshold voltage of the third transistor M3. As a result, any non-uniformity between the threshold voltages and electron mobilities of the transistors included in the various pixels will not impact the operation of the transistors that are located where M3is located in the pixel140.

After the first capacitor CP1is charged with the voltage corresponding to the current Imax, supply of the scan signal530stops and the first transistor M1and the second transistor M2are turned-off. In this case, the third transistor M3is turned-off in response to the change in the voltage charged in the first capacitor CP1. Next, a select signal540is supplied to the address line ADn to turn-on the fourth transistor M4. When the fourth transistor M4is turned-on, the data signal550supplied to the address line ADn is provided to the second node N2in synchronization with the select signal. The data signal may be set to a first polarity (high logic) or a second polarity (low logic).

When the data signal being applied is set to the first polarity, i.e. is high, the second capacitor CP2is not charged with a voltage. Accordingly, after the supply of the select signal has stopped, the fifth transistor M5is turned-off during the first period T1, with the result that the organic light emitting diode OLED does not emit light. In contrast, when the data signal being applied to the data line Dm has the second polarity or a low logic value, the second capacitor CP2is charged with a voltage. In this case, after the supply of the select signal has stopped, the fifth transistor M5is turned-on during the first period T1, with the result that the organic light emitting diode OLED emits light.

After the first period T1, another one of the select signals540is supplied to the address line ADn to turn-on the fourth transistor M4. In the exemplary embodiment shown, all select signals supplied to the address line ADn have the same width. When the fourth transistor M4is turned-on, the first polarity data signal or the second polarity data signal supplied to the data line Dm, is provided to the second node N2. Further, during the second period T2, the fifth transistor M5is turned-on/off according to the polarity of the data signal supplied to the second node N2before T2.

Accordingly, emission time intervals after the supply of the select signal are shown as T1, T2, T4, T8, etc. that may be respectively equal to 20, 21, 22, 23, etc. That is, in the embodiments of the present invention, the first capacitor CP1included in each of the pixels140is charged with the same voltage, and the desired gradation is expressed by controlling the emission times of the pixels140. As mentioned above, when the first capacitor CP1included in each of the pixels is charged with the same voltage and gradation is expressed using emission times of the pixels, the pixels can display an image of a desired luminance.

FIG. 6shows a first example of a current sink according to an embodiment of the present invention.

The current sink150includes a first switch array152, a plurality of sample/hold sections1581to158m+1, a second switch array154, and a controller156.

The sample/hold sections1581to158m+1 are electrically connected to the current supply lines C1to Cm to sink the current Imax. The first switch array152controls the electrical connection of the sample/hold sections to the current supply lines. In the exemplary embodiment shown, the number of the sample/hold sections1581to158m+1 is greater than the number of current supply lines C1to Cm by one.

The first switch array152connects m of the sample/hold sections among (m+1) sample/hold sections1581to158m+1 to the current supply line C1to Cm.

The second switch array154supplies the reference current Iref to one sample/hold section among (m+1) sample/hold sections1581to158m+1 which is not connected to the current supply lines C1to Cm. In the embodiment shown, the reference current Iref and the current Imax are associated with the same voltage.

The controller156controls operations of the first switch array152, the sample/hold sections1581to158m+1, and the second switch array154.

As shown inFIG. 7, during operation, the controller156controls the first switch array152to connect m of the sample/hold sections, including sample/hold sections1582to158m+1, to the m current supply lines C1to Cm. Accordingly, the m sample/hold sections1582to158m+1, which are selected by the scan signal and are coupled with the m current supply lines C1to Cm, sink a current Imax from the pixels.

On the other hand, the controller's156control of the second switch array154causes the second switch array154to supply the reference current Iref to the sample/hold section1581, which is not connected to the current supply lines C1to Cm. As a result, the sample/hold section1581having received the reference current Iref, is charged with a voltage corresponding to the reference current Iref. In other words, when the reference current Iref is supplied to the sample/hold section1581, the sample/hold section1581is charged with a voltage corresponding to the reference current Iref, and is capable of sinking a current Imax from the pixel140corresponding to the charged voltage.

Next, as shown inFIG. 8, the reference current Iref is supplied to another sample/hold section1582to again charge the sample/hold section1582with a voltage corresponding to the reference current Iref. In one embodiment of the present invention, the reference current Iref is sequentially sent to the sample/hold sections1581to158m+1. Accordingly, the sample/hold sections1581to158m+1 are sequentially charged with a voltage corresponding to the reference current Iref to stably sink the current from the pixels140.

FIG. 9is a circuit diagram of an example of a sample/hold section shown inFIG. 6. For convenience of description,FIG. 9shows the first sample/hold section1581.

The sample/hold section1581of the present invention includes first to sixth transistors M91to M96, a third capacitor CP3and a fourth transistor CP4.

The third transistor M93is installed between the first transistor M91and a current supply line C1(or the first switch array152). When a control signal CS of the second polarity is supplied to the third transistor M93, the third transistor M93is turned-on.

The fourth transistor M94is installed between the second switch array154and the first transistor M91. The fourth transistor M94has a conductivity type that is different from the third transistor M93. Therefore, when a control signal of a first polarity is supplied to the fourth transistor M94, it is turned-on. For example, the third transistor M93may be formed by a PMOS type transistor when the fourth transistor M94is configured by an NMOS type transistor. In the exemplary embodiment shown, the first, second, fourth, fifth, and sixth transistors M91, M92, M94, M95, and M96are configured by transistors of the same conductivity type that is different from the conductivity type of the third transistor M93. That is, except for M93, they are all NMOS transistors.

The first transistor M91and the second transistor M92are serially connected to each other between the third transistor M93and a ground voltage source GND. In the exemplary circuit shown, a first electrode of the first transistor M91is coupled with the third transistor M93, and a second electrode thereof is coupled with a first electrode of the second transistor M92. Further, a gate electrode of the first transistor M91is coupled with the third capacitor CP3.

A second electrode of the second transistor M92is coupled with a ground voltage source GND. A gate electrode of the second transistor M92is coupled with a fourth capacitor CP4.

The fifth transistor M95is coupled between the first electrode and the gate electrode of the first transistor M91. When a control signal CS of a first polarity is supplied to the fifth transistor M95, the fifth transistor M95is turned-on to diode-connect the first transistor M91.

The sixth transistor M96is coupled between the first electrode and the gate electrode of the second transistor M92. When a control signal CS of a first polarity is supplied to the sixth transistor M96, the sixth transistor M96is turned-on to diode-connect the second transistor M92.

The third capacitor CP3is coupled between a gate electrode of the first transistor M91and the ground voltage source GND. The third capacitor CP3is charged with a voltage corresponding to an electric current flowing through the first transistor M91.

The fourth capacitor CP4is coupled between a gate electrode of the second transistor M92and the ground voltage source GND. The fourth capacitor CP4is charged with a voltage corresponding to an electric current flowing through the second transistor M92.

In operation, when the control signal CS of a first polarity is supplied, the fourth transistor M94, the fifth transistor M95, and the sixth transistor M96are turned-on. When the fifth transistor M95is turned-on, the first transistor M91is diode-connected. When the sixth transistor M96is turned-on, the second transistor M92is diode-connected.

When the fourth transistor M94is turned-on, the reference current Iref is supplied to the ground voltage source GND through the fourth transistor M94, the first transistor M91, and the second transistor M92. As a result, the third capacitor CP3is charged with a voltage corresponding to the reference current Iref supplied through the first transistor M91. Moreover, the fourth capacitor CP4is charged with a voltage corresponding to the reference current Iref, which is supplied through the second transistor M92.

Thereafter, a control signal CS of a second polarity is supplied to the third transistor M93to turn this transistor on. When the third transistor M93is turned-on, the first transistor M91sinks a current Imax from the current supply line C1corresponding to the voltage charged in the third capacitor CP3. When the third transistor M93is turned-on, the second transistor M92sinks a current Imax from the current supply line C1corresponding to the voltage charged in the fourth capacitor CP4.

An organic light emitting display device includes a red pixel, a green pixel, and a blue pixel. The red pixel includes a red organic light emitting diode, the green pixel includes a green organic light emitting diode, and the blue pixel includes a blue organic light emitting diode. Emission efficiencies of the red, green, and blue organic light emitting diodes are different according to characteristics of materials. Accordingly, when each of the organic light emitting diodes emits light with maximum luminance, the current flowing through the diode would be different according to the color of the light being emitted. A current sink taking into account the different currents is shown inFIG. 10.

FIG. 10shows a second example of a current sink according to an embodiment of the present invention.

The current sink150′ includes a first switch array151, a plurality of sample/hold sections1571to157m+3, a second switch array153, and a controller155.

The sample/hold sections1571to157m+3 are coupled with the current supply lines C1to Cm through the first switch array151to sink a current Imax. The first switch array151controls the electrical connection between the sample/hold sections and the supply lines. In the exemplary embodiment shown, the sample/hold sections1571to157m+3 include red sample/hold sections1571,1574, . . . ,157m−2, and157m+1 coupled with the red pixels, green sample/hold sections1572,1575, . . . ,157m−1, and157m+2 coupled with the green pixels, and blue sample/hold sections1573,1576, . . . ,157m, and157m+3 coupled with the blue pixels.

The red sample/hold sections1571,1574, . . . ,157m−2, and157m+1 are coupled with the red pixels, and sink an electric current to be supplied to a red organic light emitting diode when a red pixel emits light with maximum luminance. The number of the red sample/hold sections1571,1574, . . . ,157m−2, and157m+1 is set to be greater than the number of the current supply lines C1, C4, . . . , Cm−2 by one.

The green sample/hold sections1572,1575, . . . ,157m−1, and157m+2 are coupled with the green pixels, and sink an electric current to be supplied to a green organic light emitting diode when a green pixel emits light with maximum luminance. The number of the green sample/hold sections1572,1575, . . . ,157m−1, and157m+2 is set to be greater than the number of the current supply lines C2, C5, . . . , Cm−1 by one.

The blue sample/hold sections1573,1576, . . . ,157m, and157m+3 are coupled with the blue pixels, and sink an electric current to be supplied to a blue organic light emitting diode when a blue pixel emits light with maximum luminance. The number of the blue sample/hold sections1573,1576, . . . ,157m, and157m+3 is set to be greater than the number of the current supply lines C3, C6, . . . , Cm by one. Consequently, the number of the sample/hold section1571to157m+3 is greater than the current supply lines C1to Cm by three.

The first switch array151connects m out of the (m+3) sample/hold sections1571to157m+3 to the current supply lines C1to Cm. One red sample/hold section, one green sample/hold section, and one blue sample/hold section remain that are not coupled with the current supply lines C1to Cm.

The second switch array153supplies reference currents Iref(R), Iref(G), and Iref(B) to the three sample/hold sections, which are not coupled with the current supply lines C1to Cm. A red reference current Iref(R) is supplied to a red sample/hold section, a green reference current Iref(G) is supplied to a green sample/hold section, and a blue reference current Iref(B) is supplied to a blue sample/hold section.

The red reference current Iref(R) is set as an electric current to be sent to a red organic light emitting diode when a red pixel is to emit light with maximum luminance. The green reference current Iref(G) is set as an electric current to be sent to a green organic light emitting diode when a green pixel is to emit light with maximum luminance. The blue reference current Iref(B) is set as an electric current to be sent to a blue organic light emitting diode when a blue pixel is to emit light with maximum luminance.

The controller155controls operations of the first switch array151, the sample/hold sections1571to157m+3, and the second switch array153.

During operation, as shown inFIG. 11, the controller155controls the first switch array151to electrically connect the m sample/hold sections1574to157m+3 with the m current supply lines C1to Cm, respectively. The red sample/hold sections1574, . . . ,157m−2, and157m+1 are coupled with the current supply lines C1, C4, . . . , Cm−2, which are coupled with the red pixels. The green sample/hold sections1575,157m−1, and157m+2 are coupled with the current supply lines C2, C5, . . . , Cm−1, which are coupled with the green pixels. The blue sample/hold sections1576,157m, and157m+3 are coupled with the current supply lines C3, C6, . . . , Cm, which are coupled with the blue pixels.

The m sample/hold sections1574to157m+3 that are electrically connected with the current supply lines C1to Cm by the first switch array151sink a current from pixels.

On the other hand, the controller155controls the second switch array153to supply reference currents Iref(R), Iref(G), and Iref(B) to sample/hold sections1571,1572, and1573, which are not coupled with the current supply lines C1to Cm. As a result, in the exemplary embodiment shown, the red reference current Iref(R) is supplied to the red sample/hold section1571, the green reference current Iref(G) is supplied to the green sample/hold section1572, and the blue reference current Iref(B) is supplied to the blue sample/hold section1573.

Thereafter, as shown inFIG. 12, the first switch array151changes the sample/hold sections coupled with the current supply lines C1to Cm. The controller155controls operations of the first and second switch arrays151and153so that the reference currents Iref(R), Iref(G), and Iref(B) are now sequentially provided to the sample/hold sections1571to157m+3. Accordingly, a voltage stored in each of the red, green, and blue sample/hold sections is recharged and they are stably driven.

As described above, according to a pixel, an organic light emitting display device, and a method for driving an organic light emitting display device using the pixel of the present invention, a pixel is charged with a voltage while sinking a current, and a luminance is expressed while controlling an emission time of the pixel charged with the voltage. Because each pixel is charged with a voltage using a current, the pixel can be charged with a desired voltage irrespective of threshold voltages and electron mobility of transistors included in the pixels. This causes an image of a desired luminance to be displayed.