Abstract:
The present invention relates to a flat display panel device for compensating a threshold voltage of a panel. Because of an ability of compensating the panel threshold voltage, it is possible to simplify a circuit and a driving method, enhance particularly an image quality of a display unit and increase an opening ration of the panel.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a flat panel display device for compensating a threshold voltage of a panel; and, more particularly, to a flat panel display device capable of simplifying a circuit and a driving method, improving an opening ratio of a panel and enhancing an image quality of a display unit by compensating a panel threshold voltage through a driving circuit of the flat panel display device. 
     DESCRIPTION OF RELATED ARTS 
     Generally, electroluminescence (hereinafter referred as to EL) is a phenomenon that a fluorescent substance luminesces as a current passes through it. An EL panel is typically used for illuminating light at the back of a liquid crystal display (hereinafter referred as to LCD) of a portable computer such as a notebook computer. However, since the EL panel is recently enabled with a function of self-luminescence, an additional backlight is not required compared to a conventional LCD. Based on this advantage and studies on such methods for acquiring a high definition image and a longer lifetime of the EL, the EL panel, in today, is employed for a high definition display unit including a LCD for a mobile telecommunication terminal. Furthermore, the EL panel will have broad applications in a near future. The EL panel includes an organic or inorganic self-luminescent body being placed in between two thin electrodes. Indeed, one of the two thin electrodes is transparent. This luminescence is caused by the energy released when excited electrons of a particular impurity at a central luminescence of a luminescent substance return to their ground states. Herein, free electrons accelerated by the EL excite the electrons of the particular impurity, which is also called an activator. Intensity of the luminescence increases in proportion to exp(−c/{square root over (ν)}), and frequency also increases proportionally up to a certain point. 
     The luminescence phenomenon due to an organic substance is discovered by Anthracene in 1960s. Thereafter, Eastman Kodak Company developed an ultra thin film double layer stacking type organic EL device in 1987, and Pioneer Corporation commercialized a single color organic EL display device by the end of 1997. A 5.5 inched natural color organic EL display device developed by Sanyo-Kodak is further demonstrated at the Society for Information Display(SID) in 2000. 
     The organic EL device has about 10 V of a driving voltage, which is lower than driving voltages of other display devices such as a thin film transistor-liquid crystal display (TFT-LCD), a plasma display panel (PDP), a field emission display (FED) and so forth. Also, the organic EL device has an advanced perceptibility due to self-luminescence. Furthermore, it is possible to make a thickness of the organic EL device thinner because it does not need a backlight unlike the TFT-LCD. Compared to currently used LCD, the organic EL device also has a rapid responsiveness and a wide angular field, and thus, it is expected to be a next generation display device. 
     FIG. 1 is a circuit diagram showing an organic EL display unit according to a prior art. The conventional organic EL display unit  100  includes a first TFT  101  having a first (source) terminal that receives a data signal from a source line and a second (gate) terminal that receives a gate enable signal from a gate enable line (GE), a second TFT  102  having a first (source) terminal supplied with power from a power line and a second (gate) terminal connected to a third (drain) terminal of the first TFT  101 , a power maintenance capacitor  103  that charges a driving voltage of the second TFT  102  through which a first terminal is connected to the first terminal of the second TFT  102  and a second terminal to the third terminal of the first TFT  101 , and an organic EL device  104  having a first terminal connected to a third (drain) terminal of the second TFT  102  and a second terminal is coupled to a ground terminal luminesces in case that currents are flowing. 
     The following will describe operations of the organic EL display unit  100  in accordance with the prior art. 
     Firstly, a gate enable signal provided from the gate enable line (GE) is activated, and the first TFT  101  is turned on. At this time, display data are transmitted to the second terminal of the second TFT  102  through the source line and the first TFT  101 . This voltage is transmitted to the second TFT  102 , which is a driving transistor, and the power maintenance capacitor  103  of the power line. Once the power maintenance capacitor  103  is charged with the driving voltage, the organic EL device  104  luminesces since currents can flow from the power line to the organic EL device  104 . Even if the gate enable signal from the gate enable line (GE) is inactivated, the power maintenance capacitor  103  is still able to luminesce because the driving voltage for making the organic EL device  104  luminesce is still remained causes currents to flow from the power line to the organic EL device  104 . 
     However, in case of driving the organic EL device  104  based on the above scheme, the second TFT  102  of each display unit cell has a different threshold voltage (V th ), and thus, an amount of currents supplied to the organic EL device  104  in each cell is different. Herein, the second TFT  102  is a driving transistor for the organic EL device  104 . That is, there occur problems of a non-uniform screen and a decreased image quality because intensity of luminescent light of the organic EL device  104  changes inconsistently. 
     FIG. 2 is a circuit diagram showing a typical organic EL display unit  200  for coping with the inconsistent V th  according to another prior art. The typical organic EL display unit includes a first TFT  201  having a first (source) terminal that receives a data signal from a source line and a second (gate) terminal that receives a gate enable signal from a gate enable line (GE), a first capacitor  202  that charges a driving voltage of a second TFT  203  by being connected to a third (drain) terminal of the first TFT  201 , the second TFT  203  having a first (source) terminal supplied with power from a power line and a second (gate) terminal connected to a second terminal of the first capacitor  202 , a second capacitor  204  that charges a threshold voltage of the second TFT  203  through which a first terminal is connected to the first terminal of the second TFT  203  and a second terminal to the second terminal of the first capacitor  202 , a third TET  205  having a first (source) terminal connected to the second terminal of the second TFT  203 , a second (gate) terminal receiving a first switch control signal AZ and a third (drain) terminal connected to a third (drain) terminal of the second TFT  203 , a fourth TFT  206  having a first (source) terminal connected to the third terminal of the third TFT  205  and a second (gate) terminal receiving a second switch control signal AZB and an organic EL device  207  that luminesces when currents are flowing through which a first terminal is connected to a third (drain) terminal of the fourth TFT  206  and a second terminal coupled to a ground terminal. 
     FIG. 3 is a diagram showing procedural timing for operating the organic EL display unit  200  according to still another prior art. With reference to the operational timing, the following will describe operations of the organic EL display unit  200  in accordance with the prior art. 
     Firstly, once a gate enable signal from the gate enable line GE is activated in a state that a second switch control signal AZB is precedently activated, the first switch control signal AZ is activated to primarily turn the second TFT  203  on, thereby charging a threshold voltage of the second TFT  203  connected to the second capacitor  204 . Afterwards, the first switch control signal AZ is inactivated, and a driving voltage, i.e., DATA, of the second TFT  203  is transmitted from the source line to the first capacitor  202 . Herein, the second TFT  203  is a driving transistor. Once the first capacitor  202  is charged with the driving voltage, the first capacitor  202  is supplied with the driving voltage that allows the organic EL device  207  to luminesce. At this time, the threshold voltage and the driving voltage of the second capacitor  204  drive the second TFT  203 . Also, currents are set to flow from the power line to the organic EL device  207 , which in turn, luminesces. 
     However, in the organic EL display unit  200  in accordance with the prior art, the number of periphery circuits for driving the cell also increases. Thus, an area for pure luminescence decreases, resulting in problems of decreasing an opening ratio and complicating the driving circuit since it is required to have more than 4 signal lines accompanying to an increase of control signals. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a flat display panel device capable of simplifying a circuit and a driving method, enhancing particularly an image quality and increasing an opening ratio of a panel by compensating a panel threshold voltage when driving the flat panel display device. 
     In accordance with an aspect of the present invention, there is provided a flat display panel device for compensating a panel threshold voltage, including: a driving unit receiving a panel threshold voltage and outputting a driving signal, wherein the driving unit samples and charges the panel threshold voltage supplied from a source line and generates the driving signal from the panel threshold voltage charged therein when a displaying data are inputted thereto; and a displaying unit, wherein the displaying unit displays by driving a luminescent device therein with a gate enable signal from a gate enable line, a power from a power line and the driving signal from the driving unit, and supplies the panel threshold voltage to the driving unit by receiving a first switch control signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S) 
     The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a circuit diagram showing an organic electroluminescence (EL) display device according to a prior art; 
     FIG. 2 is a circuit diagram showing an organic EL display device according to another prior art; 
     FIG. 3 is a timing diagram showing operation of the organic EL display device according to still another prior art; 
     FIG. 4 is a circuit diagram showing a flat display panel device for compensating a threshold voltage of a panel in accordance with a preferred embodiment of the present invention; 
     FIG. 5 is a circuit diagram showing a flat display panel device for compensating a threshold voltage of a panel in accordance with another preferred embodiment of the present invention; 
     FIG. 6 is a circuit diagram showing a flat display panel device for compensating a threshold voltage of a panel in accordance with still another preferred embodiment of the present invention; 
     FIG. 7 is a circuit diagram showing a flat display panel device for compensating a threshold voltage of a panel in accordance with another preferred embodiment of the present invention; and 
     FIG. 8 is a timing diagram showing operation of a flat panel display device for compensating a threshold voltage of a panel in accordance with further preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 4 is a circuit diagram showing a flat display panel device for compensating a threshold voltage of a panel in accordance with a preferred embodiment of the present invention. The flat display panel device includes a driving unit  410 A and a display unit  420 A. 
     The driving unit  410 A including a source line samples and charges internally a threshold voltage of a panel supplied from the source line. The driving unit  410 A generates a driving signal through externally inputted data and the charged threshold voltage of the panel and outputs the driving signal through the source line. Herein, the driving unit  410 A has a first analog-to-digital converter (ADC)  411 , a first switch  412 , a first capacitor  413 , a first amplifier  414 , a second switch  415 , a third switch  416  and a second capacitor  417 . 
     The first ADC  411  included in the driving unit  410 A receives analog data from an external source and coverts the analog data to digital data, which is, in turn, outputted to the first switch  412 . 
     Also, the first switch  412  included in the driving unit  410 A has a first terminal connected to the first ADC  411 , and performs a switching operation for passing or blocking the outputted digital data. 
     Meanwhile, the first capacitor  413  included in the driving unit  410 A has a first terminal connected to a second terminal of the first switch  412 , and functions to store electric charges after being supplied with a voltage corresponding to the digital data from the first switch  412 . 
     In addition, the first amplifier  414  included in the driving unit  410 A has a positive terminal connected to a second terminal of the first capacitor  413  and a negative terminal connected to an output terminal in a feedback. The first amplifier  414  amplifies the inputted voltage. 
     In the meantime, the second switch  415  included in the driving unit  410 A has a first terminal connected to the output terminal of the first amplifier  414  and a second terminal connected to the source line, and performs a switching operation for passing the amplified voltage outputted from the first amplifier  414  to the display unit  420 A or blocking the amplified voltage from entering to the display unit  420 A. The display unit  420 A will be further described in the following section. 
     Also, the third switch  416  included in the driving unit  410 A has a first terminal connected to the source line, and performs also a switching operation for passing or blocking a panel threshold voltage sampled from the display unit  420 A. 
     The second capacitor  417  included in the driving unit  410 A has a first terminal connected to the third switch  416  and a second terminal connected to a terminal for reference voltage V ref , and functions to store charges as being supplied with the panel threshold voltage provided from the third switch  416 . Herein, the reference voltage V ref  is a voltage for storing the panel threshold voltage in an appropriate level. A compensation voltage for a threshold value or a pre-charge of a luminescent device  424  is used as the reference voltage, since the panel luminescent device  424  of the display unit  420 A has characteristics of a diode. 
     Furthermore, the display unit  420 A includes a control signal AZ input line, a gate enable line GE, a power line and the source line connected to the driving unit  410 A. The display unit  420 A receives a first switch control signal AZ and supplies a panel threshold voltage to the driving unit  410 A. Also, the display unit  420 A performs a display operation by driving the panel luminescent device  424  through inputs of a gate enable signal from the gate enable line GE, power from the power line and a driving signal from the driving unit  410 A. Herein, the display unit  420 A also includes a fourth switch  421 , a first thin film transistor (hereinafter referred as to TFT)  422 , a third capacitor  423 , the panel luminescent device  424  and a fifth switch  425 . 
     The fourth switch  421  receives a driving signal from the source line. A switching operation of the fourth switch  421 , for passing or blocking the driving signal, is controlled by a gate enable signal from the gate enable line GE. Also, the first TFT  422  included in the display unit  420 A has a first (source) terminal supplied with power from the power line and a second (gate) terminal connected to a second terminal of the fourth switch  421 . 
     The third capacitor  423  having a first terminal connected to the first terminal of the first TFT  422  and a second terminal connected to the second terminal of the fourth switch  421  functions to charge a driving voltage of the first TFT  422 . 
     Additionally, the panel luminescent device  424  having a first terminal connected to a third (drain) terminal of the first TFT  422  and a second terminal coupled to a ground terminal luminesces when currents are flowing and displays an image that a user can perceive. 
     Meanwhile, the fifth switch  425  has a terminal connected to the third terminal of the first TFT  422  and a second terminal connected to the gate of the first TFT  422 . A switching operation of the fifth switch, for passing or blocking the panel threshold voltage, is controlled by the first switch control signal AZ. 
     The following will provides detailed descriptions on procedural operations of the flat display panel device for compensating a threshold voltage of a panel in accordance with the present invention. 
     First of all, a gate enable signal is inputted to the fourth switch  421  included in the display unit  420 A through the gate enable line GE. A first switch control signal AZ is inputted to the fifth switch  425  through the control signal AZ input line. This input of the first switch control signal AZ turns the forth switch  421  and the fifth switch  425  on so to sample a panel threshold voltage of the first TFT  422 , which is a driving transistor of the panel luminescent device  424 , through the source line. Then, the sampled panel threshold voltage is charged to the second capacitor  417  included in the driving unit  410 A by turning on the third switch  416  included in the driving unit  410 A. 
     The third switch  416  is then turned off, and the first switch  412  and the second switch  415  both included in the driving unit  410 A are turned on to provide digital data outputted from the first ADC  411 . The positive terminal of the first amplifier  414  has a voltage as the following equation. 
     
       
           V +(voltage of the positive terminal)= V (driving voltage for data)+ V   th (panel threshold voltage)  Eq. 1  
       
     
     That is, a voltage compensating the panel threshold voltage of the first TFT  422 , which is a driving transistor, is supplied as a driving voltage to the display unit  420 A. 
     FIG. 5 is a circuit diagram showing a display unit  420 B included in a flat display panel device for compensating a threshold voltage of a panel in accordance with another preferred embodiment of the present invention. The display unit  420 B includes a second TFT  521 , a third TFT  522 , a fourth  523 , a panel luminescent device  524  and a fourth TFT  525 . 
     The second TFT  521  has a first (source) terminal that receives a driving signal from a source line and a second (gate) terminal that receives a gate enable signal from a gate enable line GE, and performs a switching operation for passing or blocking the driving signal in accordance with control of the gate enable signal. 
     The third TFT  522  has a first (source) terminal that is supplied with power from a power line and a second (gate) terminal connected to a third (drain) terminal of the second TFT  521 . 
     Meanwhile, the fourth capacitor  523  included in the display unit  420 B having a first terminal connected to the first terminal of the third TFT  522  and a second terminal connected to the third terminal of the second TFT  521  charges a driving voltage of the third TFT  522 . 
     The panel luminescent device  524  having a first terminal connected to a third (drain) terminal of the third TFT  522  and a second terminal coupled to a ground terminal luminesces when currents are flowing so as to display an image that a user can perceive. 
     The fourth TFT  525  included in the display unit  420 B has a first (drain) terminal connected to the third terminal of the third TFT  522 , a second (gate) terminal that receives a first switch control signal AZ from the control signal AZ input line and a third (source) terminal connected to the gate terminal of the third TFT  522 . Also, the fourth TFT  525  performs a switching operation for passing or blocking the panel threshold voltage in accordance with control of the first switch control signal AZ. 
     FIG. 6 is a circuit diagram showing a display unit  420 C included in a flat display panel device for compensating a threshold voltage of a panel in accordance with still another preferred embodiment of the present invention. The display unit  420 C includes a fifth TFT  621 , a sixth TFT  622 , a fifth capacitor  623 , a seventh TFT  624 , a panel luminescent device  625  and an eighth TFT  626 . 
     The fifth TFT  621  included in the display unit  420 C having a first (source) terminal that receives a driving signal form a source line and a second (gate) terminal that receives a gate enable signal from a gate enable signal line GE performs a switching operation for passing or blocking the driving signal in accordance with control of the gate enable signal. 
     The sixth TFT  622  included in the display unit  420 C has a first (source) terminal provided with power from a power line and a second (gate) terminal connected to a third (drain) terminal of the fifth TFT  621 . 
     Meanwhile, the fifth capacitor  623  included in the display unit  420 C having a first terminal connected to the first terminal of the sixth TFT  622  and a second terminal connected to the third terminal of the fifth TFT  621  charges a driving voltage. 
     Also, the seventh TFT  624  included in the display unit  420 C having a first (source) terminal connected to a third (drain) terminal of the sixth TFT  622  and a second (gate) terminal that receives a second switch control signal AZB performs a switching operation for passing or blocking the driving voltage in accordance with control of the second switch control, signal AZB. 
     The panel luminescent device  625  having a first terminal connected to a third (drain) terminal of the seventh TFT  624  and a second terminal coupled to a ground terminal luminesces when currents are flowing and displays an image that a user can perceive. 
     In the mean time, the eighth TFT  626  has a first (drain) terminal connected to the third terminal of the sixth TFT  622 , a second (gate) terminal that receives a first switch control signal AZ from the control signal AZ input line and a third (source) terminal connected to the second terminal of the sixth TFT  622 , and performs a switching operation for passing or blocking a panel threshold voltage in accordance with control of the first switch control signal AZ. 
     FIG. 7 is a circuit diagram showing a driving unit  410 B included in a flat display panel device for compensating a threshold voltage of a panel in accordance with another preferred embodiment of the present invention. The driving unit  410 B includes a second analog-to-digital converter (hereinafter referred as to ADC)  711 , a sixth switch  712 , a sixth capacitor  713 , a second amplifier  714 , a seventh switch  715 , an eighth switch  716  and a ninth switch  717 . 
     The second ADC  711  converts analog data inputted from an outer source into digital data, which is, in turn, outputted to the sixth switch  712 . 
     Also, the sixth switch  712  having a first terminal connected to the second ADC  711  performs a switching operation for passing or blocking the digital data outputted from the second ADC  711 . 
     Meanwhile, the sixth capacitor  713  included in the driving unit  410 B having a first terminal connected to a second terminal of the sixth switch  712  stores charges as being supplied with a voltage corresponding to the digital data from the sixth switch  712 . 
     Also, the second amplifier  714  included in the driving unit  410 B has a positive terminal connected to a second terminal of the sixth capacitor  713  and a negative terminal connected to a feedback of an output terminal amplifies an inputted voltage. 
     In the mean time, the seventh switch  715  included in the driving unit  410 B has a first terminal connected to the output terminal of the second amplifier  714  and a second terminal connected to a source line. The seventh switch  715  passes or blocks the amplified voltage outputted from the second amplifier  714  to the display unit  420 A. 
     Also, the eighth switch  716  included in the driving unit  410 B having a first terminal connected to the source line and a second terminal connected to the positive terminal of the second amplifier  714  performs a switching operation for passing or blocking a panel threshold voltage sampled from the display unit  420 A. 
     The ninth switch  717  included in the driving unit  410 B having a first terminal connected to a reference voltage V ref  and a second terminal connected to the first terminal of the sixth capacitor  713  performs also a switching operation for passing or blocking the V ref . Herein, the V ref  can be used as a reference voltage for storing the panel threshold voltage in an appropriate level and can be also used by supplying a compensation voltage for a threshold value of the panel luminescent device  424  or precharge since the panel luminescent device  424  has a characteristic of a diode. 
     FIG. 8 is a timing diagram showing operation of the flat display panel device for compensating a threshold voltage of a panel in accordance with preferred embodiments of the present invention. It is seen from FIG. 8 that providing the second switch control signal AZB can also control operations of the overall panel simultaneously. 
     In accordance with the present invention, the panel of the flat display panel device is constructed more simply so to increase an opening ratio of an organic electroluminescence (OEL) device. As a result of this increase, it is possible to prevent an increase in unnecessary currents for increasing levels of brightness and contrast and to compensate characteristics of the diode of the panel luminescent device. 
     While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.