Abstract:
A charge recycle system implemented in a liquid crystal display includes a common voltage source, a control unit, and a source driving circuit. Before the common voltage source switches its common voltage level, the control unit controls the common voltage source to let a voltage driving circuit of the common voltage source not coupled to the output end of the common voltage source, and sends a charge recycle enable signal to the source driving circuit to adjust the source voltage level. By boosting or pulling down the source voltage level, the charges stored in liquid crystal units of the liquid crystal display can be recycled to the common voltage source, therefore raising charge utilization efficiency and lowering power consumed by the liquid crystal display.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a power supplying mechanism, and more particularly, to a charge recycling system applying a common voltage source of a liquid crystal display (LCD). 
         [0003]      2 . Description of the Prior Art 
         [0004]    Generally, a conventional LCD comprises a plurality of LCD cells arranged in a matrix.  FIG. 1  shows a connection relationship between an LCD cell  10 , a gate driving circuit  12 , a common voltage source  14  and a source driving circuit  16  of the conventional LCD. When the common voltage source  14  switches the common voltage level V COM  or when the source driving circuit  16  switches the source voltage level V SOURCE , a storage capacitor C S , a parasitic capacitor C P  and a parallel-plate capacitor C LCD  in the LCD cell  10  are charged or discharged, respectively. Then, when conducted by a gate driving signal outputted from the gate driving circuit  12 , the LCD cell  10  displays luminance according to the voltage level of the storage capacitor C S , the parasitic capacitor C P  and the parallel-plate capacitor C LCD ; therefore, pictures having different colors can be shown on the LCD after the LCD cells are filtered by RGB filters. 
         [0005]      FIG. 2  is a diagram of a conventional common voltage source structure. As shown in  FIG. 2 , the common voltage source  14  comprises a high common voltage source  142  for providing a high common voltage level V COMH , and a low common voltage source  144  for providing a low common voltage level V COML . A high common voltage driving circuit  146  of the high common voltage source  142  stores positive charges in a capacitor  148  and keeps the cross voltage of the capacitor  148  at the high common voltage level V COMH . Likewise, a low common voltage driving circuit  152  of the low common voltage source  144  stores negative charges in a capacitor  154  and keeps the cross voltage of the capacitor  154  at the low common voltage level V COML . When switching the common voltage level V COM , the common voltage source  14  controls the close and open states of switches  150  and  156 . In this way, charges stored in the capacitor  148  or the capacitor  154  will transfer into the capacitors C S , C P , C LCD  of the VCD cell  10 , and charge or discharge (respectively) the capacitors C S , C P , C LCD  to the switched common voltage level. Meanwhile, the high common voltage driving circuit  146  or the low common voltage driving circuit  152  continues to provide charges to the capacitor  148  or  154  to maintain the cross voltage of the capacitor  148  or  154  at the high common voltage level V COMH  or the low common voltage level V COML , respectively. 
         [0006]    Charges stored in the capacitors C S , C P , C LCD  vanish through discharging routes naturally after the display of the LCD cell  10  is complete, however, and these insufficiently utilized charges give rise to a charge utilization efficiency and power consumption problem for LCDs. 
       SUMMARY OF THE INVENTION 
       [0007]    One objective of the present invention is therefore to provide a common voltage source and a charge recycling system applied to the common voltage source, to allow the common voltage source to reuse charges stored in the LCD. The charge utilization efficiency of the LCD is thereby raised and power consumption is significantly reduced. 
         [0008]    According to an exemplary embodiment of the present invention, a common voltage source applied in an LCD is disclosed. The common voltage source comprises a charge-storing unit, a voltage driving circuit, a first controlling circuit and a second controlling circuit. The voltage driving circuit is for providing a common voltage level. The first controlling circuit selectively couples an output end of the voltage driving circuit to the charge-storing unit according to a first controlling signal, and the second controlling circuit selectively couples the charge-storing unit to an output end of the common voltage source according to a second controlling signal. 
         [0009]    According to another exemplary embodiment of the present invention, a charge recycling system is disclosed. The charge recycling system comprises a common voltage source, a controlling unit and a source driving circuit, wherein the common voltage source comprises a first voltage source for outputting a first common voltage level. The first voltage source comprises a charge-storing unit for regulating and storing the first common voltage level, a voltage driving circuit for providing a voltage, a first controlling circuit and a second controlling circuit. The first controlling circuit selectively couples an output end of the voltage driving circuit to the charge-storing unit according to a first controlling signal, and the second controlling circuit selectively couples the charge-storing unit to an output end of the common voltage source according to a second controlling signal. The controlling unit is coupled to the common voltage source, and generates the first and second controlling signals and a charge recycling enabling signal, wherein the charge recycling enabling signal is outputted when the first controlling circuit is not coupled to the voltage driving circuit and the charge-storing unit, and the second controlling circuit is coupled to the charge-storing unit and the output end of the common voltage source. The source driving circuit is coupled to the controlling unit, and is for adjusting a source voltage level when receiving the charge recycling enabling signal. 
         [0010]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a connection relationship between an LCD cell, a gate driving circuit, a common voltage source and a source driving circuit of a conventional LCD. 
           [0012]      FIG. 2  is a diagram of a conventional common voltage source structure. 
           [0013]      FIG. 3  is a diagram of a charge recycling system implemented in an LCD according to an exemplary embodiment of the present invention. 
           [0014]      FIG. 4  is a diagram showing a relationship between a source voltage level V SOURCE , a common voltage level V COM  and controlling signals utilized by the charge recycling system shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Please refer to  FIG. 3 , which is a diagram of a charge recycling system  300  implemented in an LCD according to an exemplary embodiment of the present invention. The charge recycling system  300  includes a common voltage source  310 , a controlling unit  350  and a source driving circuit  360 . The common voltage source  310  and the source driving circuit  360  are respectively coupled to each end of the parasitic capacitor C P  of an LCD cell  370 , and are controlled by the controlling unit  350  to recycle charges from the parasitic capacitor C P . Please note that, for clarity,  FIG. 3  only shows a single LCD cell  370 , though the common voltage source  310  and the source driving circuit  360  actually are coupled to a plurality of LCD cells. Compared to the conventional common voltage source  14  shown in  FIG. 2 , first controlling circuits  318  and  326  are further included in a high common voltage source  312  and a low common voltage source  314 , respectively, in the common voltage source  310  in this embodiment. The first controlling circuits  318  and  326  are utilized to selectively couple the output ends of the high common voltage driving circuit  316  and the low common voltage driving circuit  324  to the capacitors  320  and  328 , respectively. In this embodiment, the first controlling circuits  318  and  326  and second controlling circuits  322  and  330  for selectively coupling the capacitors  320  and  328  to the output end V A  of the common voltage source  310  are all implemented by switches. That said, any circuit or element able to achieve coupling and opening functions (such as a switching circuit composed of transistors) or able to form high impedance at output ends of the high common voltage driving circuit  316  and the low common voltage driving circuit  324  can be utilized to implement the first controlling circuits  318  and  326  and the second controlling circuits  322  and  330 . 
         [0016]      FIG. 4  shows a diagram of a relationship between controlling signals utilized by the charge recycling system  300  shown in  FIG. 3  and source voltage level V SOURCE  and common voltage level V COM . Referring to  FIG. 3  in conjunction with  FIG. 4 , when the output voltage level of the common voltage source  310  is the high common voltage level V COMH  and the charge recycling system starts to act, the first controlling circuits  318  and  326  are both open while the second controlling circuit  322  is closed and the second controlling circuit  330  is open. Therefore, the output end of the high common voltage driving circuit  316  is not coupled to the capacitor  320 , the output end of the low common voltage driving circuit  324  is not coupled to the capacitor  328 , and the output end V A  of the common voltage source  312  is coupled to the capacitor  320 . When the LCD cell  370  switches its polarity (i.e. the common voltage level V COM  is switching from the high common voltage level V COMH  to the low common voltage level V COML ), the controlling unit  350  outputs the charge recycling enabling signal CR_EN to the source driving circuit  360 , boosting the source voltage level V SOURCE  for ΔV 1 . (Note that when the LCD cell  370  is about to switch its polarity, the driving signals of both the gate line and source line corresponding to the LCD cell  370  are disabled, and the LCD cell  370  is therefore not conducting, whereas the source driving voltage for the next conduction has not yet been inputted to the LCD cell  370 .) Since the voltage across the capacitor C P  does not change immediately, the common voltage level V COM  raises ΔV 1  correspondingly. Charges stored in the parasitic capacitor C P  therefore charge the capacitor  320  through the second controlling circuit  322  conducted by the second controlling signal S 2 , achieving the objective of recycling the charge. Because the capacitor  320  has already stored part of the charges recycled from the parasitic capacitor C P , next time when the common voltage source  310  provides the high common voltage level V COMH , the time required for the high common voltage driving circuit  316  to charge the capacitor  320  to the high common voltage level V COMH  is shortened and power consumption is further reduced. Because part of the charge is provided by the previous recycle charge from the parasitic capacitor C P . 
         [0017]    Next, when the charge recycling is complete and the LCD cell  370  switches its polarity, the controlling circuit  350  controls the first controlling signal S 1  and the second controlling signal S 2  to open the first controlling circuit  318  and the second controlling circuit  322 , and then controls the second controlling signal S 2 ′ to conduct the second controlling circuit  330  in order to reuse the charges recycled into the capacitor  328 . After that, the controlling circuit  350  controls the first controlling signal S 1 ′ to conduct the first controlling circuit  326 . The low common voltage driving circuit  324  keeps providing charge to the capacitor  328  to maintain the voltage across capacitor  328  at the low common voltage level V COML  until the output voltage level of the common voltage source  310  reaches the low common voltage level V COML . 
         [0018]    When the LCD cell  370  is going to switch its polarity another time, (i.e. when the common voltage level V COM  is to be switched from the low common voltage level V COML  to the high common voltage level V COMH ), the controlling unit  350  outputs the charge recycling enabling signal CR_EN to the source driving circuit  360  to pull down the source voltage level V SOURCE  for ΔV 2 . Similarly, since the voltage across the capacitor C P does not change immediately, the common voltage level V COM  drops ΔV 2  correspondingly. Hence, negative charges stored in the parasitic capacitor C P  are recycled to the capacitor  328  through the second controlling circuit  330  conducted by the second controlling signal S 2 ′; the capacitor  328  is charged by the parasitic capacitor C P . Because the capacitor  328  has already stored part of the negative charges recycled from the parasitic capacitor C P , next time when the common voltage source  310  provides the low common voltage level V COML , the time required for the low common voltage driving circuit  324  to discharge the capacitor  328  to the low common voltage level V COML  is shortened and power consumption is reduced. In the above embodiments, ΔV 1  and ΔV 2  are voltage adjusting values for the source voltage level V SOURCE  to enable the charge recycling mechanism during charge recycling. The values of ΔV 1  and ΔV 2  are adjustable according to different system requirements. 
         [0019]    When the charge recycling is complete and the common voltage level V COM  is switched from the low common voltage level V COML  to the high common voltage level V COMH , the controlling circuit  350  controls the first controlling signal S 1 ′ and the second controlling signal S 2 ′ to open the first controlling circuit  326  and the second controlling circuit  330 , respectively. The controlling circuit  350  also controls the second controlling signal S 2  to conduct the second controlling circuit  322  in order to reuse the charges recycled into the capacitor  320 . Then, controlling circuit  350  controls the first controlling signal S 1  to conduct the first controlling circuit  318 . The high common voltage driving circuit  316  keeps providing charge to the capacitor  320  to maintain the voltage across capacitor  320  at the high common voltage level V COMH  until the output voltage level of the common voltage source  310  reaches the high common voltage level V COMH . 
         [0020]    To further save power, the controlling unit  350  further outputs a third controlling signal S 3  to the high common voltage driving circuit  316  to turn off at least some circuit elements (such as operational amplifiers) of the high common voltage driving circuit  316  when outputting the first controlling signal S 1  to decouple the high common voltage driving circuit  316  from capacitor  320 . In another example, the controlling unit  350  further outputs a third controlling signal S 3 ′ to the low common voltage driving circuit  324  to turn off at least some of the circuit elements (such as operational amplifiers) of the low common voltage driving circuit  324  when outputting the first controlling signal S 1 ′ to decouple the low common voltage driving circuit  324  from the capacitor  328 . 
         [0021]    Please note that the charge recycling system  300  mentioned above is only an embodiment of the present invention. The charge recycling mechanism disclosed can also be implemented only in the high common voltage source  312  or the low common voltage source  314  to recycle charges in a specific time period. This also achieves the advantages of higher charge utilization efficiency and lower power consumption. Moreover, the capacitors  320  and  328  can be replaced by any charge-storing unit, and these modifications belong to the scope of the present invention. 
         [0022]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.