Abstract:
An active matrix organic light emitting diode (AMOLED) panel is disclosed. The AMOLED panel comprises a pixel array, a temperature sensor and a feedback control circuit. The temperature sensor measures the temperature of the AMOLED panel. The feedback control circuit decides the driving current of the AMOLED panel according to the temperature of the AMOLED panel. Since the driving current is inversely proportional to the measured temperature of the AMOLED panel in the present invention, the possibility of subjecting the AMOLED to too high in a temperature and a current is avoided and the lifetime of the AMOLED can be increased.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority benefit of Taiwan application serial no. 95137292, filed Oct. 11, 2006. All disclosure of the Taiwan application is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an active matrix organic light emitting diode (AMOLED) panel, and more particularly to a method of regulating the temperature of a AMOLED panel by adjusting a driving current. 
         [0004]    2. Description of Related Art 
         [0005]    Organic light emitting diode (OLED) panel has a faster response, lighter weight, lesser viewing angle restrictions and greater contrast compared with a liquid crystal display panel. Therefore, in recent years, OLED is one of the principle focuses of research for display panels. According to the driving method, the OLED panel can be classified as a passive matrix organic light emitting diode (PMOLED) panel or an active matrix organic light emitting diode (AMOLED) panel. In general, the AMOLED panel is particularly adapted to the production of high resolution and large size display panels. 
         [0006]    The brightness of a pixel in the AMOLED panel is proportional to the conducting current of the organic light emitting diode and the size of the conducting current is decided by the transistor. When the temperature of the AMOLED panel continuously increases, the threshold voltage of the transistor is gradually lowered so that the current at the drain terminal of the transistor will increase. Because the anode of the light emitting diode and the drain terminal of the transistor are coupled together, the current passing through the organic light emitting diode will also increase. Since the AMOLED panel includes a considerable amount of organic material, the aging of the AMOLED panel is accelerated by the conditions of a high temperature and a high current. As a result, the lifetime of the display panel will be shortened. 
         [0007]      FIG. 1  is a graph showing the variation of the driving current of a conventional display panel at different temperatures. As shown in  FIG. 1 , the driving current increases with the rise in temperature of the AMOLED panel. In other words, there is a direct proportion relationship of the driving current to the temperature of the AMOLED panel. This implies that the currents passing through the organic light emitting diodes are increased when the temperature of the AMOLED panel rises so that the aging of the AMOLED panel is accelerated and its lifetime is shortened. 
       SUMMARY OF THE INVENTION 
       [0008]    Accordingly, the present invention is to provide a flat panel display and its active matrix organic light emitting diode (AMOLED) panel is capable of regulating its driving current according to the variation of temperature in operation. 
         [0009]    In addition, the present invention is to provide a method of controlling an AMOLED panel such that the driving current of the AMOLED panel is inversely proportional to the temperature. 
         [0010]    To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an AMOLED panel comprising a pixel array, a temperature sensor and a feedback control circuit. The pixel array has a plurality of pixel units arranged to form an array and the temperature sensor is used for measuring the temperature of at least a portion of the pixel units. Thus, the feedback control circuit can adjust the driving current of the pixel array according to the temperature. In the present invention, the feedback control circuit is capable of controlling the driving current of the pixel array to be inversely proportional to the temperature measured by the temperature sensor. 
         [0011]    According to another aspect of the present invention, a flat panel display comprising an AMOLED panel, a temperature sensor and a feedback control circuit is provided. The AMOLED panel has a plurality of pixel units and the temperature sensor is used for measuring the temperature of the AMOLED panel. In addition, the feedback control circuit can adjust the driving current of the AMOLED panel according to the temperature. In the present invention, the feedback control circuit is capable of controlling the driving current of the pixel array to be inversely proportional to the temperature measured by the temperature sensor. 
         [0012]    According to another aspect of the present invention, a method of controlling an AMOLED panel is provided. First, a temperature sensor is used to measure the temperature of at least a portion of the area of the AMOLED panel and transmit the result of the measurement to a feedback control circuit. Then, the feedback control circuit adjusts the driving current of the AMOLED panel according to the temperature in such a way that the driving current of the AMOLED panel is inversely proportional to the temperature. 
         [0013]    The present invention uses a temperature sensor to measure the temperature of the AMOLED panel. Furthermore, a feedback control circuit is used to adjust the driving current of the AMOLED panel according to the temperature such that the driving current is inversely proportional to the temperature. Hence, any rise in the temperature of the AMOLED panel will lower the conducting current of the organic light emitting diodes and thereby increase in the lifetime of the panel. 
         [0014]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
           [0016]      FIG. 1  is a graph showing the variation of the driving current of a conventional display panel at different temperatures. 
           [0017]      FIG. 2  is a circuit diagram of an active matrix organic light emitting flat panel display according to one preferred embodiment of the present invention. 
           [0018]      FIG. 3  is a circuit diagram of a pixel unit according to one preferred embodiment of the present invention. 
           [0019]      FIG. 4  is a graph showing the variation of the driving current of a display panel at different temperatures according to the present invention. 
           [0020]      FIG. 5  is a circuit diagram of an active matrix organic light emitting flat panel display according to another preferred embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
         [0022]      FIG. 2  is a circuit diagram of an active matrix organic light emitting flat panel display according to one preferred embodiment of the present invention. As shown in  FIG. 2 , the present invention provides a flat panel display  200  comprising an AMOLED panel  210 , a temperature sensor  212  and a feedback control circuit  214 . The temperature sensor  212  is disposed on the AMOLED panel  210  for measuring the temperature when the AMOLED panel  210  is in operation and transmitting this information to the feedback control circuit  214 . In one embodiment, the temperature sensor  212  and the feedback control circuit  214  can be integrated into the AMOLED panel  210 . 
         [0023]    The AMOLED panel  210  includes a scan line driving circuit  220 , a data line driving circuit  222  and a pixel array  224 . The pixel array  224  has a plurality of pixel units  228  arranged in an array. The scan line driving circuit  220  is coupled to the pixel array  224  through a plurality of scan lines  230 . Similarly, the data line driving circuit  222  is coupled to the pixel array  224  through a plurality of data lines  234 . 
         [0024]      FIG. 3  is an explanatory circuit diagram of a pixel unit according to one preferred embodiment of the present invention. The explanatory circuit is suitable for the pixel unit  228  in  FIG. 2 . As shown in  FIG. 3 , the pixel unit  2281  comprises a transistor  310 , a transistor  312  and an organic light emitting diode  320 . In the present embodiment, the transistors  310  and  312  can be implemented using NMOS transistors or PMOS transistors. The transistor  310  has a gate terminal coupled to a scan line  230 , a source terminal coupled to a data line  234  and a drain terminal coupled to a gate terminal of the transistor  312 . On the other hand, the transistor  312  has a source terminal coupled to a working voltage V DD , and coupled to the gate terminal of the transistor  312  through a capacitor C 1 , a drain terminal coupled to the anode of the organic light emitting diode  320 . Furthermore, the organic light emitting diode  320  is coupled to a common voltage V SS  through the cathode. In the embodiment of the present invention, the common voltage V SS  can be a ground potential. 
         [0025]    As shown in  FIG. 2 , the scan line driving circuit  220  is used for generating scan signals and the data line driving circuit  222  is used for generating data voltages. To drive the pixel unit  2281  in  FIG. 3 , the scan line driving circuit  220  enables the scan signal on the scan line  230  so that the transistor  310  is conductive. At this moment, the data line driving circuit  222  outputs a data voltage signal. The data voltage signal is transmitted to the pixel unit  2281  through the data line  234  and then transmitted to the gate of the driving transistor  312  through the transistor  310 . Thus, the transistor  312  is activated and a driving current I D  is generated to drive the organic light emitting diode  320 . 
         [0026]    As shown in  FIG. 3 , the driving current I D , the data voltage, the working voltage and the common voltage are all related. This particular characteristic is utilized to adjust the driving current in the present invention. 
         [0027]    As shown in  FIG. 2 , the temperature of the AMOLED panel  210  will continue to gradually rise with longer period of operation. If the temperature sensor  212  measures a rise in temperature in a portion of the pixel units in the AMOLED panel  210 , the feedback control circuit  214  will lower the voltage through the data line driving circuit  222 . In the meantime, the voltage at the gate terminal of the transistor  312  is also reduced so that the operating voltage of the transistor  312  is lowered. With a lowering of the operating voltage of the transistor  312 , a smaller driving current I D  is generated by the transistor  312  so that the driving current I D  passing through the light emitting diode is reduced. 
         [0028]      FIG. 4  is a graph showing the variation of the driving current of a display panel at different temperatures according to the present invention. As shown in  FIGS. 2 and 4 , the feedback control circuit  214  in  FIG. 2  controls the driving current of the AMOLED panel according to the temperature of an area measured by the temperature sensor  212 . The driving current is adjusted so that it is inversely proportional to the temperature of the measured area. Therefore, when the temperature of the AMOLED panel rises, the driving current I D  is lowered to reduce the aging of the AMOLED panel  210 , thereby extending the lifetime of the AMOLED panel. 
         [0029]      FIG. 5  is a circuit diagram of an active matrix organic light emitting flat panel display according to another preferred embodiment of the present invention. As shown in  FIG. 5 , the present invention provides a flat panel display  200  comprising an AMOLED panel  210 , a temperature sensor  212  and a feedback control circuit  214 . The temperature sensor is disposed on the AMOLED panel  210  for measuring the temperature of the AMOLED panel  210  in operation and transmitting the information to the feedback control circuit  214 . 
         [0030]    As shown in  FIGS. 3 and 5 , the temperature will continuously rise when the AMOLED panel is being operated for a time period. If the temperature sensor  212  detects a rise in temperature of a portion of the pixel units in the AMOLED panel  210 , the feedback control circuit  214  will reduce the working voltage V DD  of the transistor  312 . With a reduction in the working voltage V DD  of the transistor  312 , the voltage difference between the working voltage V DD  and the common voltage VSS is reduced so that the driving current I D  generated by the transistor  312  is also reduced. As a result, the driving current I D  of the organic light emitting diode  320  is reduced to prevent a hastening of the aging of the AMOLED panel  210  and extend the lifetime of the panel. 
         [0031]    In addition, if the temperature sensor  212  detects a rise in temperature of a portion of the pixel units of the AMOLED panel  210  after the AMOLED panel  210  is being operated for a period of time, the feedback control circuit  214  in the present invention can be used to lower the driving current I D  by adjusting the common voltage V SS  of the pixel unit  2281 . As shown in  FIG. 3 , the voltage difference between the working voltage V DD  and the common voltage V SS  can be reduced by adjusting the potential of the common voltage V SS  under a fixed working voltage V DD  condition. Therefore, the driving current I D  generated by the transistor  312  will be reduced. With a reduction in the driving current I D  passing through the organic light emitting diode  320 , the aging of the AMOLED panel  210  may be reduced. 
         [0032]    In summary, the present invention uses a temperature sensor to measure the temperature of the AMOLED panel and a feedback control circuit to adjust the driving current of the AMOLED panel according to the temperature such that the driving current is inversely proportional to the temperature. Hence, any rise in the temperature of the AMOLED panel will lower the conducting current of the organic light emitting diodes so that the aging of the AMOLED panel may be reduced to increase its lifetime. 
         [0033]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.