Abstract:
A pixel circuit, a pixel, and an AMOLED (Active Matrix Organic Light-Emitting Diode) display device comprising the pixel and a driving method thereof. The pixel circuit comprises a power supply circuit, a basic circuit and a compensation circuit, which are sequentially connected. The power supply circuit is connected to a first power supply to supply power to the basis circuit. The compensation circuit is connected to second and third power supplies, respectively, for providing difference values compensating for a voltage and current of an OLED (Organic Light-Emitting Diode). The pixel comprises an OLED and the pixel circuit. The AMOLED display device comprises the pixel circuit. By compensating for a difference between threshold and power supply voltages of a transistor, the response characteristics of the AMOLED may be improved to generate light of a same brightness, thereby meeting requirements on image uniformity and consistency of an AMOLED.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a flat panel display technology, and in particular relates to a pixel circuit, a pixel, and an active matrix organic light-emitting diode (AMOLED) comprising the pixel and a driving method thereof. 
       BACKGROUND 
       [0002]    In recent years, various flat panel display devices with a smaller weight and a smaller size when compared with cathode ray transistors have been developed. 
         [0003]    In various flat panel display devices, since active matrix organic light-emitting diode (AMOLED) display devices use a self-illuminating organic light-emitting diode (OLED) to display an image, they typically have properties such as short response time, low power consumption for driving, and a relatively better brightness and color purity. In view of this, organic light-emitting devices have become the focus of the display technology of the next generation. 
         [0004]    With regard to a large AMOLED display device, a plurality of pixels located in a cross region of a scan line and a data line is included. Each pixel includes an OELD and a pixel circuit used for driving the OELD. The pixel circuit typically includes switch transistors, driving transistors and storage capacitors. 
         [0005]    Since the pixel properties of AMOLEDs are influenced by the difference between driving transistors and the leakage current of the switch transistors, an image displayed by such a plurality of pixels has a relatively poor quality uniformity and consistency. 
         [0006]      FIG. 1  is a schematic view of a pixel of an active matrix organic light-emitting diode (AMOLED) display device in the prior art. As shown in  FIG. 1 , the transistor of the pixel circuit  112  thereof is a PMOS transistor (a MOS transistor which has an n-type substrate and a p-channel and transfers current through hole migration). 
         [0007]    The pixel  110  of the AMOLED display device includes: an OLED, and a pixel circuit  112  connected to a data line Dm and a scanning control line Sn 1  to control the OLED. 
         [0008]    An anode of the OLED is connected to the pixel circuit  112 , and a cathode of the OLED is connected to a second power supply ELVSS. The OLED emits light with a corresponding brightness to the current intensity provided by the pixel circuit  112 . 
         [0009]    When providing a scanning control signal to the scanning control line Sn 1 , the pixel circuit  112  controls the amount of current provided to the OLED correspondingly to the data signal provided to a data line Dm. To this end, the pixel circuit  112  includes a second transistor T 2  (i.e., a driving transistor) connected between a first power supply ELVDD and an anode of the OLED (Organic Light-Emitting Diode), a first transistor T 1  (i.e., a switch transistor) connected between a gate of the second transistor T 2  and the data line Dm, and a first capacitor C 1  connected between the gate of the second transistor T 2  and the first power supply ELVDD, wherein the gate of the first transistor T 1  is connected to the scanning control line Sn 1 . 
         [0010]    The gate of the first transistor T 1  is connected to the scanning control line Sn 1 , and the source (or the drain) of the first transistor T 1  is connected to the data line Dm. The drain (or the source) of the first transistor T 1  is connected to one terminal of the first capacitor C 1  (the other terminal thereof is connected to the first power supply ELVDD). When a scanning control signal is provided from the scanning control signal line Sn 1  to the first transistor T 1 , the first transistor T 1  is turned on, and a data signal provided from the data line Dm is provided to the first capacitor C 1 . At this time, a voltage corresponding to the data signal is stored in the first capacitor C 1 . 
         [0011]    The gate of the second transistor T 2  is connected to one terminal of the first capacitor C 1  (the other terminal thereof is connected to the first power supply ELVDD), and the source of the second transistor T 2  is connected to the first power supply ELVDD. The drain of the second transistor T 2  is connected to the anode of the OLED. The second transistor T 2  controls a current flowing to the second power supply ELVSS from the first power supply ELVDD via the OLED, and the current intensity corresponds to the voltage stored in the first capacitor C 1 . 
         [0012]    One terminal of the first capacitor C 1  is connected to the gate of the second transistor T 2 , and the other terminal of the first capacitor C 1  is connected to the first power supply ELVDD, and a voltage corresponding to the data signal is charged into the first capacitor C 1 . 
         [0013]    The pixel  110  controls the brightness of the OLED by adjusting the current supplied to the OLED correspondingly to the voltage discharged into the first capacitor C 1 , and an image with a predetermined brightness is displayed. However, in such a traditional AMOLED display device, due to the change in threshold voltage of the second transistor T 2  and the leakage current of the first transistor T 1 , it is difficult to display an image with a uniform brightness. For example, in different pixels, due to the difference in threshold voltage of the second transistor T 2  and the difference in first power supply ELVDD, the current flowing through the OLED is inconsistent when a same gate driving voltage is applied, leading to inconsistency in the brightness of the OLED. Each pixel generates light of different brightness in response to a same data signal, and as a result, the displayed image hardly has a uniform brightness. 
       SUMMARY 
     Technical problems 
       [0014]    With regard to this, a main objective of the present invention is to provide a pixel, an active matrix organic light-emitting diode (AMOLED) display device using the pixel and a driving method thereof. By compensating for a difference value between a threshold voltage and a power supply voltage of a transistor, the response characteristics of the AMOLED may be improved to generate light of a same brightness, thereby meeting requirements on image uniformity and consistency of an AMOLED display device. 
       Solution to the technical problems 
       [0015]    To achieve the aforementioned object, the technical solutions of the present invention are realized as follow. 
         [0016]    A pixel circuit  112  is provided, including a basic circuit  1122 . The pixel circuit  112  also includes a power supply circuit  1121  and a compensation circuit  1123 ; wherein the power supply circuit  1121 , the basic circuit  1122  and the compensation circuit  1123  are sequentially connected; and the power supply circuit  1121  is connected to a first power supply ELVDD to supply power to the basic circuit  1121 ; and the compensation circuit  1123  is connected to a second power supply ELVSS 1  and a third power supply ELVSS 2  respectively to compensate for a difference of a voltage and current of an OLED. 
         [0017]    The power supply circuit  1121  is a second transistor T 2 ; wherein the gate of the second transistor T 2  is connected to a scanning control signal line Scan 1 , the source thereof is connected to the first power supply ELVDD, and the drain thereof is connected to the basic circuit  1122 . 
         [0018]    The basic circuit  1122  is connected to the compensation circuit  1123  via an OLED and a parasitic capacitor Coled which are connected in parallel. 
         [0019]    The basic circuit  1122  includes a first transistor T 1 , a fifth transistor T 5  and a first capacitor C 1 ; wherein and a gate of the first transistor T 1  is connected to a second scanning control line Scan 2 , the source of the first transistor T 1  is connected to a data line Dm, and the drain of the first transistor T 1  is connected to the gate of the fifth transistor T 5 ; and the first capacitor C 1  is connected in parallel between the gate and the source of the fifth transistor T 5 . 
         [0020]    The compensation circuit  1123  includes a parasitic capacitor Coled connected in parallel to the OLED, a third transistor T 3  and a fourth transistor T 4 ; and the OLED is, after being connected in parallel to the parasitic capacitor Coled, connected in series between the drain of the fifth transistor T 5  of the basic circuit  1122  and the sources of the third transistor T 3  and the fourth transistor T 4  of the compensation circuit  1123 ; and the gates of the third transistor T 3  and the fourth transistor T 4  are connected to an emission control line Eml and an emission control line Em 2  respectively; and the drains of the third transistor T 3  and the fourth transistor T 4  are connected to the second power supply ELVSS 1  and the third power supply ELVSS 2  respectively. 
         [0021]    The present invention also provides a pixel in any aforementioned pixel circuit. 
         [0022]    The present invention further provides an AMOLED display device having the pixel. 
         [0023]    A pixel driving method is provided, including the following steps: 
         [0024]    A: connecting to a power supply circuit ( 1121 ) and a basic circuit ( 1122 ) via a first power supply ELVDD, and connecting the basic circuit ( 1122 ) to a compensation circuit ( 1123 ) via an OLED; wherein the compensation circuit ( 1123 ) is connected to a second power supply ELVSS 1  and a third power supply ELVSS 2 ; 
         [0025]    B: supplying power to the basic circuit ( 1122 ) by using a second transistor T 2  of the power supply circuit ( 1121 ), and supplying power to the compensation circuit ( 1123 ) by using the second power supply ELVSS 1  and the third power supply ELVSS 2  respectively; wherein the gate of the second transistor T 2  of the power supply circuit ( 1121 ) inputs a scanning control signal Scan 1 ; the gate of the first transistor T 1  of the basic circuit ( 1122 ) inputs a scanning control signal Scan 2 , and the source the first transistor T 1  inputs a data signal Dm; and the gates of the third transistor T 3  and the fourth transistor T 4  of the compensation circuit ( 1123 ) input an emission control signal Em 1  and an Emission control signal Em 2  respectively, and the sources the third transistor T 3  and the fourth transistor T 4  are connected to the cathode of the OLED; 
         [0026]    C: during a period t1 of a work cycle T of a pixel, providing a scanning control signal, and providing a first power supply voltage ELVDD by the second transistor T 2  to initialize a first capacitor C 1 ; 
         [0027]    D: during a period t2 in which a scanning control signal Scan 2  is provided to the first transistor T 1 , storing a voltage corresponding to the data signal Vdata provided by the first transistor T 1  in the first capacitor C 1 ; and meanwhile, turning on the first transistor T 1  in response to the scanning control signal Scan 2  of low level, and providing the data signal Vdata, which is provided to the data line Dm, to the gate of the fifth transistor T 5  via the first transistor T 1 ; and providing a voltage corresponding to the drain of the second transistor T 2  to the anode of the OLED, and charging, by the second power supply voltage ELVSS 1 , which supplies power to the cathode of the OLED, the first capacitor C 1  through the parasitic capacitor Coled of the OLED and the drain of the fifth transistor T 5 ; 
         [0028]    E: during a threshold voltage compensation period t3, causing the scanning control signal Em 2  to transition to a low level, such that the fourth transistor T 4  is turned on in response to the emission control signal Em 2 ; and causing charges at the drain of the second transistor T 2  to flow to the third power supply ELVSS 2  along a path of the fifth transistor T 5  and the anode of the OLED; when the voltage at the drain of the second transistor T 2  is a threshold voltage higher than the voltage at the gate of the fifth transistor T 5 , turning off the fifth transistor T 5 , and causing charges at the drain of the second transistor T 2  to stop flowing; 
         [0029]    F: during a light-emitting period t4 of the OLED, causing the scanning control signal Scan 1  to transition to a low level; and turning on the second transistor T 2  in response to the scanning control signal Scan 1 , and causing the driving current to flow to the third power supply ELVSS 2  along the first power supply via a path of the second transistor T 2 , the fifth transistor T 5 , the OLED and the fourth transistor T 4 . 
         [0030]    During the period t1, the voltage of the second power supply ELVSS 1  is further provided to the source of the third transistor T 3  as a reset voltage by using the third transistor T 3 , such that the source of the third transistor T 3  is constantly reset in each frame. 
         [0031]    During a light-emitting period t4 of the OLED, the current holed flowing through the OLED is: 
         [0000]        Ioled =½ Cox (μ W/L )(Vdata)̂2;
 
         [0032]    where the Cox, μ, W and L represent the channel capacitance per unit area, the channel mobility, the channel width and the channel length of the fifth transistor T 5  respectively, and Vdata represents a data voltage. 
         [0033]    The current holed flowing through the OLED is approximately expressed as: 
         [0000]        Ioled= ½ *K* [Vdata]̂2
 
         [0034]    where k represents a constant, and Vdata represents a data voltage. 
         [0035]    Beneficial effects of the present invention 
         [0036]    The present invention provides a pixel circuit, a pixel, and an AMOLED (Active Matrix Organic Light-Emitting Diode) display device and a driving method thereof. The present invention has advantages as follows. 
         [0037]    With the pixel of the present invention and the AMOLED display device including the pixel, by compensating for a difference between a threshold voltage and a power supply voltage of a transistor, the response characteristics of the AMOLED may be improved to generate light of a same brightness, thereby meeting requirements on image uniformity and consistency of an AMOLED display device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]      FIG. 1  is a schematic view of a pixel circuit of an active matrix organic light-emitting diode (AMOLED) in the prior art; 
           [0039]      FIG. 2  is a functional block diagram of an active matrix organic light-emitting diode (AMOLED) including a pixel according to the present invention; 
           [0040]      FIG. 3  is a schematic architecture diagram of the pixel of  FIG. 2 ; and 
           [0041]      FIG. 4  is a waveform diagram of a driving signal for driving the pixel of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    The pixel circuit, the pixel, and the active matrix organic light-emitting diode (AMOLED) including the pixel and the driving method thereof of the present invention will be described in detail with reference to the accompanying drawings and the embodiments of the present invention. 
         [0043]    Herein, when a first element is described to be connected to a second element, the first element can be directly connected to the second element, or can be indirectly connected to the second element via one or more additional elements. Further, for the purpose of clarity, some elements that are not necessary for fully understanding the present invention are omitted. 
         [0044]      FIG. 2  is a functional block diagram of an active matrix organic light-emitting diode (AMOLED) including a pixel according to the present invention. As shown in  FIG. 2 , the AMOLED display device mainly includes a display unit  100 , a scanning driver  200  and a data driver  300 . 
         [0045]    The display unit  100  includes a plurality of pixels  110  (as shown in  FIG. 3 ), wherein the plurality of pixels  110  are arranged in a matrix in cross regions of a scanning control line Scan 1   n , a scanning control line Scan 2   n , an emission control line Em 1   n , an emission control line Em 2   n , and a data line D 1  to a data line Dm, where n is the number of a row in which a pixel is located. Each pixel  110  is connected to a scanning control line (for example, Scan 1   n , Scan 2   n ), and an emission control line (for example, Em 1   n , Em 2   n ) and a data line respectively. The data line is connected on a column basis to the pixel  110  in each column of pixels respectively. For example, a pixel  110  in the i th  row and the j th  column is connected to scanning control lines Scan 1   i  and Scan 2   i  in the i th  row, emission control lines Em 1   i  and Em 2   i  in the i th  row and a data line Dj in the j th  column. 
         [0046]    The display unit  100  is supplied with power by an external power supply, for example, a first power supply ELVDD, a second power supply ELVSS 1  and a third power supply ELVSS 2 . The first power supply ELVDD and the third power supply ELVSS 2  are used as a voltage source of high level and a voltage source of low level respectively. The first power supply ELVDD and the third power supply ELVSS 2  are used as driving power supplies for the pixel  110 . The second power supply ELVSS 1  is configured to compensate for the change in driving current of an organic light-emitting diode caused by fluctuation in threshold voltage of the fifth transistor T 5  (referring to  FIG. 3 ) 
         [0047]    The scanning driver  200  generates a scanning control signal and an emission control signal, which are both used for the pixel  110 . The scanning control signal generated by the scanning controller  200  is provided to the pixel  110  sequentially from the scanning control line Scan 1   i  to the scanning control line Scan 1   n  respectively; and the emission control signal generated by the scanning controller  200  is provided to the pixel  110  sequentially from the emission control line Em 1   i  to the emission control line Em 1   n  respectively. 
         [0048]    The data driver  300  generates data for the pixel  110  and a data signal corresponding to the data control signal. The data signal generated by the data driver  300  and the scanning signal are synchronously provided to the pixel  110  via the data line D 1  to the data line Dm. 
         [0049]      FIG. 3  is a schematic architecture diagram of the pixel of  FIG. 2 . The pixel as shown in  FIG. 3  can be applied to the AMOLED display device as shown in  FIG. 2 . For ease of description, in  FIG. 3 , the pixel  110  in the n th  row and the m th  column is exemplified for description, and a data line Dm is included. 
         [0050]    As shown in  FIG. 3 , the pixel  110  includes a pixel circuit  112  and an OLED. The pixel circuit  112  is connected between a first power supply ELVDD and a third power supply ELVSS 2  for providing a driving current to the OLED (Organic Light-Emitting Diode). 
         [0051]    The pixel circuit  112  mainly includes a power supply circuit  1121 , a basic circuit  1122  and a compensation circuit  1123 , which are sequentially connected. 
         [0052]    The power supply circuit  1121  includes a second transistor T 2 . The gate of the second transistor T 2  is connected to a first scanning control line Scan 1 , the source (or the drain) thereof is connected to the first power supply ELVDD, and the drain (or the source) thereof is connected to the source (or the drain) of the fifth transistor T 5  in the basic circuit  1122 . 
         [0053]    The basic circuit  1122 , i.e., a 2T1C circuit, is an existing common pixel circuit. The basic circuit  1122  includes a first transistor T 1 , a fifth transistor T 5 , a first capacitor C 1 .The gate of the first transistor T 1  is connected to a second scanning control line Scan 2 , and the source (or the drain) of the first transistor T 1  is connected the data line Dm, and the drain (or the source) thereof is connected to the gate of the fifth transistor T 5 . The first capacitor C 1  is connected in parallel between the gate of the fifth transistor T 5  and the source (or the drain) of the power supply circuit  1121 . In other words, the basic circuit  1122  is connected to the drain (or the gate) of the second transistor T 2  of the power supply circuit  1121  through the source (or the drain) of the fifth transistor T 5 . 
         [0054]    The basic circuit  1122  is connected to the anode of the OLED in the pixel  110  through the drain (or the source) of the fifth transistor T 5 , and the cathode of the OLED is connected to the sources (or the drains) of the third transistor T 3  and the fourth transistor T 4  of the compensation circuit  1123 . A parasitic capacitor Coled is connected in parallel between the anode and the cathode of the OLED, to form the compensation circuit  1123  with the third transistor T 3  and the fourth transistor T 4 . 
         [0055]    In the compensation circuit  1123 . the drains (or the sources) of the third transistor T 3  and the fourth transistor T 4  are connected to the second power supply ELVS S 1  and the third power supply ELVSS 2  respectively. The gate of the third transistor T 3  is connected to the emission control line Em 1 , and the gate of the fourth transistor T 4  is connected to the emission control line Em 2 . The sources (or the drains) of the third transistor T 3  and the fourth transistor T 4  are of a same potential. 
         [0056]    The first transistor, the second transistor, the third transistor, the fourth transistor and the fifth transistor as described above are all field effect transistors, and the sources and the drains thereof are the same. 
         [0057]    When the pixel circuit  112  of the present invention works: 
         [0058]    with regard to the first transistor T 1 , during a period t2 in which a scanning control signal is provided to the scanning control line Scan 2 , the first transistor T 1  provides a data voltage Vdata to the gate of the fifth transistor. 
         [0059]    The second transistor T 2  is connected between the first power supply ELVDD and the source (or the drain) of the fifth transistor T 5 , and the gate of the second transistor T 2  provides, by being connected to the scanning control line Scan 1 , the scanning control signal to the scanning control line Scan 1  during the period t2, and at this time, the second transistor T 2  in the power supply circuit  1121  is turned on, such that the first power supply ELVDD and the pixel  110  are turned on. 
         [0060]    The third transistor T 3  is connected between the cathode of the OLED and the second power supply ELVSS 1 , and the gate of the third transistor T 3  is connected to the emission control line Em 1 . During a period T3 in which the scanning control signal is provided to the emission control lien Eml, the third transistor T 3  is turned on, such that the OLED and the second power supply voltage ELVSS 1  are turned on. In this way, the pixel  110  is controlled such that the amplitude of the cathode driving voltage of the OLED is a voltage of the second power supply ELVSS 1  during the initialization period t1 and the data voltage write period t2. 
         [0061]    The fourth transistor T 4  is connected between the cathode of the OLED and the third power supply ELVSS 2 , and the gate of the fourth transistor T 4  is connected to the emission control line Em 2 . During a period t4 in which the scanning control signal is provided to the emission control line Em 2 , the fourth transistor T 4  is turned on, such that the OLED and the third power supply voltage ELVSS 2  are turned on. In this way, the pixel  110  is controlled such that the amplitude of the cathode driving voltage of the OLED is a voltage of the third power supply ELVSS 2  during the threshold voltage compensation period t3 and the light-emitting period t4. 
         [0062]    The fifth transistor T 5  is serially connected between the second transistor T 2  and the anode of the OLED, and the gate of the fifth transistor T 5  is connected to the drain (or the source) of the first transistor T 1 . When the scanning control signal Scan 2  provided from the scanning control line transitions to a low level, the first transistor T 1  is turned on, and the data signal is sent to the gate of the fifth transistor T 5  through the first transistor T 1 . 
         [0063]    The first transistor C 1  is connected between the drain (or the source) of the second transistor T 2  and the gate of the fifth transistor T 5 . During the period t1 in which the scanning control signal is provided to the scanning control line Scan 1 , a first power supply voltage ELVDD is provided through the second transistor T 2  to initialize the first capacitor C 1 . Then, during the period t2 in which the scanning control signal is provided to the scanning control line Scan 2 , a voltage corresponding to the data signal provided through the first transistor T 1  is stored in the first transistor C 1 . 
         [0064]    The OLED is serially connected between the drain (or the source) of the fifth transistor T 5  and the source (or the drain) of the third transistor T 3 . During the light-emitting period t4 of the OLED, the OLED will emit light with a corresponding intensity to the intensity of the driving current provided through the first power supply ELVDD, the fifth transistor T 5 , the second transistor T 2  and the fourth transistor T 4 . 
         [0065]    In pixel  110 , due to inconsistency of the threshold voltage of a driving transistor (for example, the fifth transistor T 5 ), the current flowing through the OLED is also inconsistent. As a result, the consistency of brightness of the pixel  110  becomes poor, and the image non-uniformity is finally caused. However, by the addition of the fourth transistor T 4  and the third transistor T 3 , the change in threshold voltage of a driving transistor (for example, the fifth transistor T 5 ) is compensated for during the initialization period t1 of each frame, so that the product defect of image non-uniformity resulted from the aforementioned poor uniformity of brightness of the pixel  110  may be avoided. 
         [0066]      FIG. 4  is a waveform diagram of a driving signal for driving the pixel of  FIG. 3 . For ease of description,  FIG. 4  shows a waveform of a driving signal provided by the pixel of  FIG. 3  during a frame signal period 4. The driving process of the pixel will be described with reference to  FIG. 3 . 
         [0067]    The scanning control signal Scan 1  configured to control the second transistor T 2  to control the ON-connection between the second transistor T 2  and the first power supply ELVDD. 
         [0068]    The scanning control signal is configured to control the first transistor T 1  to write a data level. 
         [0069]    The emission control line Em 1  is configured to control the third transistor T 3  to control the ON-connection between the third transistor T 3  and the second power supply ELVSS 1 . 
         [0070]    The emission control line Em 2  is configured to control the fourth transistor T 4  to control the ON-connection between the fourth transistor T 4  and the third power supply ELVSS 2 . 
         [0071]    As shown in  FIG. 4 , during a period set to perform initialization, i.e., period t1, first, a scanning control signal Scan 1  of low level is provided to the pixel  110 . Thus, the second transistor T 2  is turned on through the scanning control signal Scan 1  of low level, such that the voltage of the first power supply ELVDD is provided to the source (or the drain) of the fifth transistor T 5 . An emission control signal Em 1  of low level is provided to the pixel  110 . Thus, the third transistor T 3  is turned on through the emission control signal Em 1  of low level, such that the voltage of the second power supply ELVSS 1  is provided to the source (or the drain) of the third transistor T 3 . 
         [0072]    With reference to  FIG. 3 , during the period t1, the voltage of the second power supply ELVSS 1  may be also provided to the source (or the drain) of the third transistor T 3  as a reset voltage by the third transistor T 3 , so as to constantly reset the source (or the drain) of the third transistor T 3  in each frame. 
         [0073]    Then, during the period t2 set to perform data voltage writing (i.e., a stage for writing a data voltage), a scanning control signal Scan 2  of low level is provided to the pixel  110 . Then, the first transistor T 1  is turned on in response to the scanning control signal Scan 2  of low level. Thus, a data signal Vdata provided to the data line Dm is provided to the gate of the fifth transistor T 5  via the first transistor T 1 . At this time, since the fifth transistor T 5  is in an ON state, a voltage corresponding to the drain (or the source) of the second transistor T 2  is provided to the anode of the OLED. However, the second power supply voltage ELVSS 1  provided to the cathode of the OLED supplies power to the first capacitor C 1  through the parasitic capacitor Coled of the OLED and the drain (or the source) of the fifth transistor T 5 . 
         [0074]    Then, during the period t3 set to perform threshold voltage compensation (i.e., threshold compensation), the emission control signal Em 2  transitions to a low level. Then, the fourth transistor T 4  is turned on in response to the emission control signal Em 2 ,and charges at the drain (or the source)of the second transistor T 2  flow to the third power supply ELVSS 2  along a path of the fifth transistor T 5  and the anode of the OLED; when the voltage at the drain (or the source) of the second transistor T 2  is one threshold voltage higher than the voltage at the gate of the fifth transistor T 5  (i.e., threshold voltage of the fifth transistor T 5 ), the fifth transistor T 5  is turned off, and charges at the drain (or the source) of the second transistor T 2  stop flowing. 
         [0075]    Herein, a voltage of the fifth transistor T 5  corresponding to the threshold voltage provided to the fifth transistor T 5  is stored in the first capacitor C 1 , such that the threshold voltage of the fifth transistor T 5  is compensated for during the period T3. 
         [0076]    At last, during the period t4 set to emit light (i.e., the light-emitting stage), the scanning control signal Scan 1  transitions to a low level. Then, the second transistor T 2  is turned on in response to the scanning control signal Scan 1 . Thus, the driving current flows to the third power supply ELVSS 2  along the first power supply ELVDD via a path of the second transistor T 2 , the fifth transistor T 5 , the OLED and the fourth transistor T 4 . The current bled flowing through the organic light-emitting diode (OLED) is: 
         [0000]        Ioled= ½ Cox (μ W/L )(Vdata)̂2;
 
         [0077]    where Cox, μ, W and L represent the channel capacitance per unit area, the channel mobility, the channel width and the channel length of the fifth transistor T 5  respectively, and Vdata represent a data voltage. 
         [0078]    The current flowing through the OLED can be approximately expressed as: 
         [0000]    
       
         
           
             
               
                 
                   
                       
                     
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                         ^ 
                         2 
                       
                     
                   
                 
               
               
                 
                   
                     = 
                     
                       
                         1 
                         / 
                         2 
                       
                       * 
                       K 
                       * 
                       
                         
                           [ 
                           Vdata 
                           ] 
                         
                         ^ 
                         2 
                       
                     
                   
                 
               
             
             , 
           
         
       
     
         [0079]    where k is Cox* μ *W*L, which is a constant; and Vsg is the voltage difference between a source and a gate; Vth represents a threshold voltage; Vdd represents the first power supply voltage ELVDD; Vc 1  represents a voltage stored in the first capacitor C 1 ; Vdata represents a data voltage; and N is a natural number greater than 1. 
         [0080]    Described above are merely preferred embodiments of the present invention, but are not intended to limit the protection scope of the present invention. This listing of claims replaces all prior versions and listings of claims in the application: