WO2004040540A1

WO2004040540A1 - Apparatus for driving light emitting device of display having matrix structure

Info

Publication number: WO2004040540A1
Application number: PCT/KR2003/002292
Authority: WO
Inventors: Jae-Hoon Shim; Sung-Min Kim; Bong-Ok Kim; No-Gill Park; Mi-Young Kwak; Jong-Wook Seo; Young-Kwan Kim
Original assignee: Gracel Co., Ltd.
Priority date: 2002-10-30
Filing date: 2003-10-29
Publication date: 2004-05-13
Also published as: KR20040039021A; AU2003274773A1; KR100473153B1

Abstract

An apparatus for driving a light emitting device includes a diode, a capacitor, and the light emitting device. When the diode is turned on, the light emitting device emits light based on the amount of current corresponding to a potential difference between a received data signal and a received control signal. When the diode is turned off, the light emitting device emits light based on current discharged from the capacitor. Another apparatus for driving a light emitting device includes a transistor, a capacitor, and the light emitting device. When the transistor is turned on, the light emitting device emits light based on the amount of current corresponding to the voltage level of a received data signal. When the transistor is turned off, the light emitting device emits light based on current discharged from the capacitor. Thus, the rate of occurrence of cross talk of each of the pixels is minimized.

Description

03 002292

APPARATUS FOR DRIVING LIGHT EMITTING DEVICE OF DISPLAY HAVING MATRIX STRUCTURE

Technical Field The present invention relates to an apparatus for driving a light emitting device of a matrix type display, and more particularly, to an apparatus for driving a light emitting device of a matrix type display, the apparatus designed so as to drive a light emitting device located within each of a plurality of pixels by using a small number of electrical elements.

Background Art

With the recent advent of advanced information society, personal computers, portable terminals, information communications apparatuses, or multifunction devices that combine the above apparatuses are increasingly in demand. These products require thin, light displays, such as, liquid crystal displays or organic light emitting device (OLED) displays using self-luminescent organic electroluminescence (EL) devices and organic LEDs. An OLED is the general term for self-luminescent organic EL devices and organic LEDs.

OLEDs have excellent properties, such as a wide viewing angle, fast responsivity, and the like, and are accordingly suitable for moving picture display. Hence, displays using such OLEDs are anticipated to be more widely used. In practice, as a rapid improvement of the emission efficiency of OLEDs whose emission layer is formed of an organic material is realized together with a progress in the network technology enabling video communications, anticipation for OLED displays is continuously increasing.

Existing OLED displays have a plurality of pixels that are arranged in a matrix. Such OLED displays are classified into active matrix type displays or passive matrix type displays according to a way to drive OLEDs each located in each of the pixels.

FIG. 1A is a circuit diagram of an example of a general passive matrix type display. Referring to FIG. 1A, the general passive matrix type display is comprised of M X N pixels in which OLEDs Dn, ..., and D_nm are installed at intersections of rows N₂_ι, ... , and N_{2 n} and columns M-_M, ... . and Mι__m. In the existing passive matrix type display, in order to drive an OLED (e.g., D22) located in a pixel of a second row (e.g., N₂_2) and a second column (e.g., M-ι_₂), a voltage must be applied to the row (e.g., N₂_₂). Thus, the OLED (e.g., D₂₂) can emit light.

FIG. 1 B is a circuit diagram of pixels included in the area A of FIG. 1A. As shown in FIG. 1B, for example, the OLED D₂₂ among OLEDs D₁1, Di2, D21, and D2₂ can emit light by receiving a voltage through a first electrode (i.e., an anode) of the OLED D₂2- Referring to FIG. 1 B, the OLEDs D₂ι, which is located in the second row and the first column (i.e., N₂ 2 X M1 1), is circuit-coupled to the OLED Dn, which is located in the first row and the first column (i.e., N₂ x Mι_j). As a result, a leakage current flows in the OLEDs D₂1 and D₁1, such that the OLEDs D₂1, Dn, and Dι₂, respectively located in the second row and the first column (i.e., N_{2 2} X Mι_ι), in the first row and the first column (i.e., N_2j M-M), and in the first row and the second column (i.e., N₂ x M1 ₂), can emit light with a predetermined brightness. When the number of pixels emitting light increases, light emitted from the increased number of pixels appears in the shape of a cross. As described above, such a passive matrix type display has a structure in which all pixels are circuit coupled to one another by coupling the electrodes of each of the OLEDs to the row and column of each of the pixels. Hence, cross-talk occurs due to light emission by pixels other than the pixel desired to be driven. FIG. 2 is a circuit diagram of a general active matrix type display. Referring to FIG. 2, the general active matrix type display includes a display unit 10 made up of M X N pixels, a scan driving circuit 20 located on the left side of the display unit 10, and a data driving circuit 30 located on the upper side of the display unit 10. Each of the pixels of the display unit 10 includes two transistors, a capacitor, and an OLED.

Driving of the active matrix type display will now be described by exemplifying driving of the OLED D₂n, which is located in the pixel of row N1_{2 2} and column Mn .

When a control signal from the scan driving circuit 20 is applied to a gate of a first transistor T₂n (which is also called a switching transistor) located in the pixel Ni₂_₂X Mnj, the first transistor T₂n is turned on. When the first transistor T211 is turned on, a second transistor T₂₁₂ (which is also called a driver transistor) receives a data signal from the data driving circuit 30 through a gate and is accordingly turned on to make the OLED D₂1₁ emit light.

When the first transistor T₂n is turned off, the second transistor T₂-i₂ keeps its turn-on state on virtue of an electric potential difference with which a capacitor C-₂11 is charged when the first transistor T₂11 is turned on, thereby making the OLED D₂n emit light. As described above, such an active matrix type display must use at least two transistors in order to drive an OLED located in each pixel, which complicates a process for manufacturing the active matrix type display. Also, because at least four lines are needed to form each pixel, the manufacturing costs for the active matrix type display increase.

Disclosure of the Invention

The present invention provides an apparatus for driving a light emitting device of a matrix display, by which the rate of occurrence of cross talk of each pixel is minimized, and an organic light emitting device (OLED) of each pixel is driven using a small number of electrical elements so that a process of manufacturing the matrix display is simplified.

According to a first embodiment of the invention, there is provided an apparatus for driving a light emitting device located in each of a plurality of pixels of a matrix type display in which the plurality of pixels are arranged in a form of matrix, the apparatus comprising: a diode which receives a data signal through an anode of the diode, receives a control signal through a cathode of the diode in synchronization with the data signal, and operates based on a potential difference between the data signal and the control signal; a capacitor which, when the diode is turned on, receives the data signal from the diode through a first port coupled to the cathode of the diode, receives the control signal from the diode through a second port of the capacitor, is charged with charges corresponding to the potential difference between the data signal and the control signal, and, when the diode is turned off, discharges current corresponding to the charges; and a light emitting device which has an anode coupled to both the cathode of the diode and the first port of the capacitor and a cathode coupled to the second port of the capacitor, and when the diode is turned on, emits light with brightness corresponding to current corresponding to a potential difference between a data signal and a control signal that are received through the anode and cathode, respectively, and when the diode is turned off, receives the current discharged from the capacitor and emits light with brightness corresponding to the amount of the received current According to a second embodiment of the invention, there is provided an apparatus for driving a light emitting device located in each of a plurality of pixels of a matrix type display in which the plurality of pixels are arranged in a form of matrix, the apparatus comprising: a transistor which is turned on or off according to the level of a control signal received through a gate of the transistor and receives a data signal through a drain of the transistor in synchronization with the control signal and switches the received data signal; a capacitor which has a first port coupled to a source of the transistor and a second port coupled to a common electrode and, when the transistor is turned on, is charged with charges corresponding to the voltage level of a data signal received through the first port, and when the transistor is turned off, discharges current corresponding to the charges; and a light emitting device which has an anode coupled to both the source of the transistor and the first port of the capacitor and a cathode coupled to both the second port of the capacitor and the common electrode, and when the transistor is turned on, emits light with brightness corresponding to the amount of current corresponding to the voltage level of a data signal received through the anode and when the transistor is turned off, receives the current discharged from the capacitor and emits light with brightness corresponding to the amount of the received current.

Brief Description of the Drawings

FIG. 1A is a circuit diagram of an example of a general passive matrix type display; FIG. 1 B is a circuit diagram of pixels included in the area A of FIG.

1A;

FIG. 2 is a circuit diagram of a general active matrix type display; FIG. 3 is a circuit diagram of a matrix type display according to a first embodiment of the present invention; FIG. 4 is a circuit diagram of an apparatus for driving a light emitting device of the matrix type display of FIG. 3;

FIGS. 5A and 5B illustrate a control signal and a data signal, respectively, which are applied to a row and a column, respectively, of a certain pixel of FIG. 4; FIG. 6 is a timing diagram illustrating a current flowing into a diode and a light emitting device that constitute a pixel of FIG. 4;

FIG. 7 is a circuit diagram of a matrix type display according to a second embodiment of the present invention;

FIG. 8 is a circuit diagram of an apparatus for driving a light emitting device of the matrix type display of FIG. 7; and

FIGS. 9A and 9B illustrate a control signal and a data signal, respectively, which are applied to a row and a column, respectively, of a certain pixel of FIG. 7.

Best mode for carrying out the Invention

An apparatus for driving a light emitting device of a matrix type display according to the present invention will now be described with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. FIG. 3 is a circuit diagram of a matrix type display according to a first embodiment of the present invention. Referring to FIG. 3, the matrix type display according to the first embodiment of the present invention includes a display unit 100 made up of M X pixels, a scan driving circuit 200 located on the left side of the display unit 100, and a data driving circuit 300 located on the upper side of the display unit 100. Each of the pixels of the display unit 100 is made up of a diode, a capacitor, an organic light emitting device (OLED) (hereinafter, referred to as a light emitting device).

In the matrix type display according to the first embodiment of the present invention, the pixels receive control signals of the scan driving circuit 200 through light emitting devices D₁12, ... , and D_nm2 and capacitors Cm, ... , and C_nmι, which are coupled to the rows of the pixels, and data signals of the data driving circuit 300 in synchronization with the control signals through diodes Dm, ... , and D_nmi. which are coupled to the columns of the pixels. The pixels are driven based on potential differences between the received control signals and the received data signals to each emit light with predetermined brightness.

Light emission by the light emitting device Dι₁₂ within the pixel Nιo2 X M_{101 1} among the M X N pixels of FIG. 3 will now be described in detail with reference to FIG. 4.

FIG. 4 is a circuit diagram of an apparatus for driving a light emitting device of the matrix type display of FIG. 3. Referring to FIG. 4, the pixel N-ιo2_ι Mιoι is made up of a diode Dm, a capacitor Cm, and the light emitting device Dn2. The pixel N₁₀2_ι X Mιoι corresponds to an apparatus for driving the light emitting device Dn₂- FIGS. 5A and 5B illustrate a control signal and a data signal, respectively, which are applied to a row and a column, respectively, of a certain pixel of FIG. 4.

Referring to FIG. 4, the diode Dm receives a data signal from the data driving circuit 300 of FIG. 3 through an anode of the diode Dm and a control signal from the scan driving circuit 200 of FIG. 3 through a cathode of the diode D and is then driven based on a potential difference between the data signal and the control signal.

More specifically, when the diode D receives a control signal with a low voltage of a charging period A of FIG. 5A through its cathode and a data signal with a high voltage of a charging period A of FIG. 5B through its anode in synchronization with the received control signal, the diode Dm is turned on because a potential difference between the data signal and the control signal is equal to or greater than a turn-on voltage of about 0.7V. The turned-on diode Dm applies the data signal with the high voltage to the capacitor Cm, and the light emitting device D_i12.

When the diode D is turned on, the capacitor C receives the data signal with the high voltage of the charging period A of FIG. 5B through one port (a first port), which coupled to the cathode of the diode Dm, and the control signal with the low voltage of the charging period A of FIG. 5A through the other port (a second port) from the turned-on diode Dm. Then, the capacitor Cm is charged with charges corresponding to the potential difference between the data signal and the control signal.

When the diode Dm is turned on, the light emitting device Dn₂ receives the data signal with the high voltage of the charging period A of FIG. 5B through its anode, which is coupled to both the cathode of the diode Dm and the first port of the capacitor Cm, and the control signal with the low voltage of the charging period A of FIG. 5A through its cathode, which is coupled to the second port of the capacitor Cm, from the turned-on diode D . Then, the light emitting device D₁₁₂ emits light with brightness corresponding to the amount of current corresponding to the potential difference between the data signal and the control signal.

The light emitting device Dn₂ emits light with the greatest brightness based on the greatest potential difference between the data signal and the control signal obtained in the light emitting device D₁₁₂.

FIG. 6 is a timing diagram illustrating a current flowing into a diode and a light emitting device that constitute a pixel of FIG. 4. Referring to FIG. 6, currents l_Dm and IDH2 flow in the diode D and the light emitting device Dn₂, respectively, during the charging period A. At this time, the light emitting device Dn₂ emits light with brightness corresponding to the level of the current IDH2 with a constant level.

Referring back to FIG. 4, when the diode Dm receives the control signal with the low voltage of the charging period A of FIG. 5A through its cathode and the data signal with a low voltage of the charging period A of FIG. 5B through its anode, the diode Dm is turned off because the voltage level of the received data signal is less than the turn-on voltage of about 0.7 V. At this time, the light emitting device D₁₁₂ is also turned off because it receives a voltage less than the turn-on voltage, about 2 to 3 V of the light emitting device Dn₂. In this case, the light emitting device Dn₂ enters into the darkest state. When the diode Dm receives a control signal with a high voltage of a discharging period B of FIG. 5A through its cathode and a data signal with a high voltage of a discharging period B of FIG. 5B through its anode in synchronization with the received control signal, the diode Dm is turned off because a potential difference between the data signal and the control signal is equal to or less than the turn-on voltage of about 0.7V.

When the diode Dm is turned off, the capacitor Cm discharges current corresponding to the charges with which the capacitor Cm is charged during the charging period A.

When the diode Dm is turned off, the light emitting device D₁₁₂ is turned on because of a voltage corresponding to the charges with which the capacitor Cm is charged. The turned-on light emitting device D-ι₁₂ emits light with brightness corresponding to the level of current discharged from the capacitor Cm.

When the diode Dm receives a control signal with the high voltage of the discharging period B of FIG. 5A through its cathode and a data signal with a low voltage of the discharging period B of FIG. 5B through its anode, the diode Dm is turned off. At this time, the above-described operations of the capacitor Cm and the light emitting device Dn₂ during the discharging period B repeat.

Referring to FIG. 6, no current flows in the turned-off diode Dm during the discharging period B (i.e., IDIH = 0A), and current l_Dn₂ discharged from the capacitor Cm flows in the light emitting device Dn₂. At this time, the light emitting device Dn₂ emits light with brightness corresponding to the level of the current IDH2-

As shown in FIG. 6, as the current I_DH2 flowing in the light emitting device D^₂ during the discharging period B decreases to a slope (i.e., aV — , where Vo denotes an initial voltage and a denotes a

Rs C proportional constant) inversely proportional to a time constant T (which is Rs X C, where C and Rs denote the capacitance of the capacitor Cm and the internal resistance of the light emitting device Dn₂, respectively), the light emitting device Dι₁₂ becomes gradually darker and darker. However, since a human eye slowly responds, it cannot sense that the pixel including the light emitting device Dn₂ becomes gradually darker and darker during the discharging period B but only senses a time-averaged brightness of the pixel including the light emitting device D ₂. Hence, the human eye recognizes that the pixel including the light emitting device D₁12 has a constant brightness.

During the discharging period B, the current n₂ flowing in the light emitting device Dn₂ varies with the slope. If the time constant T corresponding to a product of the capacitance C of the capacitor Cm and the internal resistance Rs of the light emitting device D₁₁₂ exceeds aV_n the time constant T corresponding to the slop (i.e., -^■ — ) of the

Rsx C current IDH2, the absolute value of the slope of the current l_D112 is reduced. Hence, current n2' flows in the light emitting device Dn₂. on the other hand, if the time constant T corresponding to a product of the capacitance C of the capacitor Cm and the internal resistance Rs of the light emitting device D₁₁₂ becomes less than the time constant T aV corresponding to the slop (i.e., — ) of the current IDH₂, the

Rs C absolute value of the slope of the current n₂ increases. Hence, current IDH2" flows in the light emitting device D-ι₁₂.

As described above, the apparatus for driving a light emitting device of the matrix type display of FIG. 4 drives the light emitting device

Dιι₂₎ ... , or D_nm₂ to emit light with brightness corresponding to the amount of current corresponding to a potential difference between a data signal and a control signal that are applied when the diode Dm, ... , or D_nmi is turned on, during the charging period A, and to emit light with brightness corresponding to the amount of current discharged from the capacitor Cm, ... , or C_nmi, during the discharging period B.

FIG. 7 is a circuit diagram of a matrix type display according to a second embodiment of the present invention. Referring to FIG. 7, the matrix type display according to the second embodiment of the present invention includes a display unit 400 made up of M x N pixels, a scan driving circuit 500 located on the left side of the display unit 400, and a data driving circuit 600 located on the upper side of the display unit 400. Each of the pixels of the display unit 400 is made up of a transistor, a capacitor, and a light emitting device.

In each of the pixels of the matrix type display according to the second embodiment of the present invention, when each of transistors Tin, ... , and T_nrnι receives a control signal of the scan driving circuit 500 through each of their corresponding gates, which are coupled to the rows of the pixels, and is accordingly turned on, each of the transistors T , ... , and Tnmi switches a data signal of the data driving circuit 600 received through each of their corresponding drains, which are coupled to the columns of the pixels, to each of light emitting devices Dm, ... , and D_nmi. Hence, each of the light emitting devices Dm, ... , and D_nmi is driven to emit light with predetermined brightness.

Light emission by the light emitting device Dm within pixel N ₀₂_ι X M₄₀ι_ι among the M X N pixels of FIG. 7 will now be described in detail with reference to FIG. 8. FIG. 8 is a circuit diagram of an apparatus for driving a light emitting device of the matrix type display of FIG. 7. Referring to FIG. 8, the pixel N ₀₂ x M₄₀ι is made up of a transistor Tm, a capacitor Cm, and the light emitting device Dm. The pixel N ₀₂ x M₄₀ι corresponds to an apparatus for driving the light emitting device Dm. FIGS. 9A and 9B illustrate a control signal and a data signal, respectively, which are applied to a row and a column, respectively, of a certain pixel of FIG. 7.

Referring to FIG. 8, the transistor Tm is turned on or off depending on the level of a control signal of the scan driving circuit 500 of FIG. 7 received through an gate of the transistor Tm and switches a data signal received from the data driving circuit 600 of FIG. 7 through a drain of the transistor Tm to the capacitor C and the light emitting device Dm.

More specifically, when the transistor Tm receives a control signal with a high voltage of a charging period A1 of FIG. 9A through its gate and is accordingly turned on, it switches a data signal received through its drain in synchronization with the received control signal to the capacitor Cm and the light emitting device Dm, which are coupled to a source of the transistor Tm such as to be parallel to each other.

The capacitor Cm receives the data signal from the transistor Tm through one port (a first port), which is coupled to the source of the transistor Tm, and is then charged with charges corresponding to the voltage level of the data signal.

The light emitting device Dm receives the data signal from the transistor Tm through an anode, which is coupled to both the source of the transistor Tm and the first port of the capacitor Cm, and emits light based on current corresponding to the voltage level of the received data signal. A cathode of the light emitting device Dm and the other port (a second port) of the capacitor Cm are coupled to an identical electrode, to which a reference voltage (e.g., 0V) is preferably applied. On the other hand, when the transistor Tm receives a control signal with a low voltage of a discharging period B1 of FIG. 9A through its gate, it is turned off so as not to switch a data signal received through its drain to the capacitor Cm and the light emitting device Dm.

When the transistor Tm is turned off, the capacitor Cm discharges current corresponding to the charges with which the capacitor Cm is charged during the charging period A1.

Also, when the transistor Tm is turned off, the light emitting device Dm is turned on because of a voltage corresponding to the charges with which the capacitor Cm is charged. The turned-on light emitting device Dm receives the current discharged from the capacitor Cm and emits light with brightness corresponding to the level of the received current.

During the discharging period B1 , the light emitted from the light emitting device Dm becomes gradually darker and darker. This phenomenon was already described above with reference to FIG. 6.

As described above, the apparatus for driving a light emitting device of the matrix type display of FIG. 7 drives the light emitting device Dm, ... , or Dnmi to emit light with brightness corresponding to the amount of current corresponding to the voltage level of a data signal that is applied when the transistor Tm, ... , or T_nmi is turned on, during the charging period A1 , and to emit light with brightness corresponding to the amount of current discharged from the capacitor Cm, ... , or C_nmi, during the discharging period B1.

Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

In contrast with existing passive matrix type displays, an apparatus for driving a light emitting device of a matrix type display according to the present invention couples M light emitting devices to columns of M X N pixels and N diodes to rows thereof so as to prevent light emitting devices of the M x N pixels from being circuit-coupled to one another. Thus, the rate of occurrence of cross-talk of the M X N pixels can be minimized, and accordingly, the matrix display according to the present invention can have results similar to those of active matrix type displays.

Also, each of the pixels of the matrix type display according to the present invention uses a group of one diode and one capacitor or a group of one transistor and one capacitor in order to drive each light emitting device. Thus, a process of manufacturing the matrix type display according to the present invention can be simplified, which leads to a reduction of the cost of production.

Industrial Applicability

A light emitting device driving apparatus according to the present invention is applied to image display apparatuses that include a matrix type display, thereby improving the power efficiency, the quality, and the reliability of image display and simplifying a process for manufacturing the matrix display. The simple manufacturing process leads to a reduction of the cost of production.

Claims

What is claimed is:

1 . An apparatus for driving a light emitting device located in each of a plurality of pixels of a matrix type display in which the plurality of pixels are arranged in a form of matrix, the apparatus comprising: a diode which receives a data signal through an anode of the diode, receives a control signal through a cathode of the diode in synchronization with the data signal, and operates based on a potential difference between the data signal and the control signal; a capacitor which, when the diode is turned on, receives the data signal from the diode through a first port coupled to the cathode of the diode, receives the control signal from the diode through a second port of the capacitor, is charged with charges corresponding to the potential difference between the data signal and the control signal, and, when the diode is turned off, discharges current corresponding to the charges; and a light emitting device which has an anode coupled to both the cathode of the diode and the first port of the capacitor and a cathode coupled to the second port of the capacitor, and when the diode is turned on, emits light with brightness corresponding to current corresponding to a potential difference between a data signal and a control signal that are received through the anode and cathode, respectively, and when the diode is turned off, receives the current discharged from the capacitor and emits light with brightness corresponding to the amount of the received current.

2. The apparatus of claim 1 , wherein a cycle of the control signal is comprised of a first signal that has a constant low voltage during a predetermined period and a second signal that follows the first signal and has a constant high voltage during a period corresponding to a multiple of the period for the low voltage, and during one cycle of the control signal, the data signal is comprised of a third signal that repeats a constant high voltage and/or a constant low voltage at intervals of the period for the low voltage of the control signal and a fourth signal that has a phase difference from the third signal and represents a constant high voltage or a constant low voltage in synchronization the third signal.

3. The apparatus of claim 2, wherein when the diode receives a data signal with the high voltage through the anode in synchronization with a control signal with the low voltage received through the cathode, the diode is turned on based on a potential difference between the data signal with the high voltage and the control signal with the low voltage, and when the diode receives a data signal with the low voltage through the anode in synchronization with the control signal with the low voltage, the diode is turned off based on a potential difference between the data signal with the low voltage and the control signal with the low voltage, and on the other hand, when the diode receives the data signal with the high voltage through the anode in synchronization with a control signal with the high voltage received through the cathode, the diode is turned off based on a potential difference between the data signal with the high voltage and the control signal with the high voltage, and when the diode receives a data signal with the low voltage through the anode in synchronization with the control signal with the high voltage, the diode is turned on based on a potential difference between the data signal with the low voltage and the control signal with the high voltage.

4. The apparatus of claim 3, wherein when the diode is turned on, the light emitting device receives the data signal with the high voltage from the diode through the anode of the light emitting device and the control signal of the low voltage from the diode through the cathode of the light emitting device and emits light with brightness corresponding to the amount of current corresponding to the potential difference between 2292

the data signal and the control signal.

5. An apparatus for driving a light emitting device located in each of a plurality of pixels of a matrix type display in which the plurality of pixels are arranged in a form of matrix, the apparatus comprising: a transistor which is turned on or off according to the level of a control signal received through a gate of the transistor and receives a data signal through a drain of the transistor in synchronization with the control signal and switches the received data signal; a capacitor which has a first port coupled to a source of the transistor and a second port coupled to a common electrode and, when the transistor is turned on, is charged with charges corresponding to the voltage level of a data signal received through the first port, and when the transistor is turned off, discharges current corresponding to the charges; and a light emitting device which has an anode coupled to both the source of the transistor and the first port of the capacitor and a cathode coupled to both the second port of the capacitor and the common electrode, and when the transistor is turned on, emits light with brightness corresponding to the amount of current corresponding to the voltage level of a data signal received through the anode and when the transistor is turned off, receives the current discharged from the capacitor and emits light with brightness corresponding to the amount of the received current.

6. The apparatus of claim 5, wherein a cycle of the control signal is comprised of a first signal that has a constant high voltage during a predetermined period and a second signal that follows the first signal and has a constant low voltage during a period corresponding to a multiple of the period for the high voltage, and during one cycle of the control signal, the data signal is comprised of a third signal that repeats a constant high voltage and/or a constant low voltage at intervals of the period for the high voltage of the control signal and a fourth signal that has a phase difference from the third signal and represents a constant high voltage or a constant low voltage in synchronization the third signal.