Patent Publication Number: US-8542224-B2

Title: Display clip system and timing clip control method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Taiwan Patent Application No. 099137210, filed on Oct. 29, 2010, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a timing controller and a timing control method of a liquid crystal panel, and more particularly to a clip system and a timing clip control method, capable of providing a base working signal and a clip voltage of the same signal information before and after a frame rate of a system signal changes. 
     2. Related Art 
     Currently, requirements of energy saving of electronic devices have become one of major criteria in design performed by manufacturers, which is also true to active matrix displays, such as liquid crystal displays and Organic Light-Emitting Diode (OLED) displays. Therefore, manufacturers research and develop a method for decreasing power consumption of a display in various operating environments by adjusting a frame rate of a working signal. For example, during working, a frame rate of a base working signal provided by a timing controller of a display is 60 Hz, and during a standby period, the frame rate of the base working signal provided by the timing controller is 40 Hz, and a charging time length of each liquid crystal element is longer than that in the environment in which the frame rate is 60 Hz. 
     Additionally, during working, a base working signal is transmitted to each gate line one by one to open a semiconductor channel layer of a Thin Film Transistor (TFT) element that controls charging time of a liquid crystal unit connected to the gate line, so that a pixel data signal can be transmitted to a drain from a source after passing through the opened semiconductor layer, and charge the liquid crystal unit. When each of the arranged liquid crystal units is charged, the base working signal is affected by electric impedance caused by the liquid crystal units of a increasing number and through which the base working signal passes, such that a waveform of the base working signal deforms gradually, thus resulting in inconsistent charging charges of the liquid crystal units in the process. Therefore, the manufacturers dispose a clip module between the timing controller and the gate driver circuit, and the clip module is used to clip the base working signal so as to alleviate the influence from the electric impedance of the liquid crystal unit and maintain a voltage waveform of the base working signal provided to the liquid crystal unit, thus balancing the charging charges of the liquid crystal units. 
     However, after the frame rate is switched, the charging time lengths of the liquid crystal elements become inconsistent, which varies the imaging luminance of a liquid crystal panel, thus resulting in screen transient flickering. In addition, the change of the frame rate results in an inconsistent waveform of a clip voltage generated by a clip module, which leads to inconsistent charging power of charging charges, thus resulting in deteriorated screen transient flickering. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a clip system and a timing clip control method thereof, capable of providing a clip voltage and a working signal of the same signal information when a frame rate changes. 
     In order to solve the above problems, the present invention provides a display clip system, which is connected to a gate driver circuit of a display. The clip system comprises a timing controller and a clip module. 
     According to a system input signal, the timing controller is used to generate a first output enable signal, a first clip trigger signal, and a base working signal, whose frame rates are the same as a frame rate of the system input signal. When the frame rate of the system input signal changes, the timing controller adjusts the first output enable signal and the first clip trigger signal to a second output enable signal and a second clip trigger signal according to the change of the frame rate, and output the second output enable signal and the second clip trigger signal. The clip module is used for receiving the base working signal, the first output enable signal, and the first clip trigger signal, adjusting the base working signal by using the first output enable signal and the first clip trigger signal to form a first clip voltage and output the first clip voltage to the gate driver circuit, receiving the second output enable signal and the second clip trigger signal, and adjusting the base working signal by using the second output enable signal and the second clip trigger signal to form a second clip voltage equal to the first clip voltage and output the second clip voltage to the gate driver circuit. A trigger time length of the first clip trigger signal equals a trigger time length of the second clip trigger signal, a trigger time length of the first output enable signal equals a trigger time length of the second output enable signal, a time interval between a trigger point of the first clip trigger signal and a trigger point of the first output enable signal equals a time interval between a trigger point of the second clip trigger signal and a trigger point of the second output enable signal, so that a charging time length and charging charges of a liquid crystal element connected to the gate driver circuit remain the same before and after the frame rate changes. 
     In order to control the timing, the present invention provides a signal timing clip control method, which is applicable in a timing controller and a clip module of a display, and the clip module is connected to a gate driver circuit. The signal timing clip control method comprises: generating, by the timing controller, a first output enable signal, a first clip trigger signal, and a base working signal, whose frame rates are the same as a frame rate of a system input signal, according to the system input signal; adjusting, by the clip module, the base working signal according to the first output enable signal and the first clip trigger signal to form a first clip voltage, and outputting the base working signal carrying the first clip voltage to the gate driver circuit; and adjusting, by the timing controller, the first output enable signal and the first clip trigger signal to a second output enable signal and a second clip trigger signal according to change of the frame rate when the timing controller judges that the frame rate of the system input signal is changed. A trigger time length of the first clip trigger signal equals a trigger time length of the second clip trigger signal, a trigger time length of the first output enable signal equals a trigger time length of the second output enable signal, a time interval between a trigger point of the first clip trigger signal and a trigger point of the first output enable signal equals a time interval between a trigger point of the second clip trigger signal and a trigger point of the second output enable signal. The signal timing clip control method further comprises: adjusting, by the clip module, the base working signal by using the second output enable signal and the second clip trigger signal to form a second clip voltage equal to the first clip voltage, and outputting the base working signal carrying the second clip voltage to the gate driver circuit. 
     The characteristics of the present invention are as follows. In a clip system disclosed by the present invention, when system input signals of different frame rates are obtained, base working signals carrying the same clip voltage and having the same trigger time length are still provided, so that a charging time length and charging charges of a liquid crystal unit that receives the base working signal for charging remain the same before and after the frame rate switches, thus steadying imaging luminance and avoiding screen transient flickering. Moreover, the clip system disclosed by the present invention is applicable to existing active matrix display structures, and is applicable to existing active matrix display production lines, so that manufactures are not required to modify production line structures, no additional design and production cost is incurred, and the clip system can be applied to various active matrix displays, thus having a higher product practicability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a schematic architectural view of a first clip system according to an embodiment of the present invention; 
         FIG. 2A  and  FIG. 2B  are timing diagrams before and after a frame rate is switched according to an embodiment of the present invention; 
         FIG. 3A  is a flow chart of a signal timing clip control method of a liquid crystal panel according to an embodiment of the present invention; and 
         FIG. 3B  to  FIG. 3D  are detailed schematic flow charts of a process in  FIG. 3A  according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention are described below in detail with reference to the accompanying drawings. 
     Referring to  FIG. 1 , a schematic structural view of a clip system according to an embodiment of the present invention is shown. Referring to  FIG. 2A  and  FIG. 2B  together, it should be noted that, a liquid crystal panel is taken as an example in the following embodiments, but the techniques disclosed by the present invention are applicable to liquid crystals, OLEDs, and any other type of active matrix displays, and are not limited to the liquid crystal displays and liquid crystal panels. 
     The system includes a timing controller  10  and a clip module  20 . The timing controller  10  is electrically connected to the clip module  20 , and the clip module  20  is electrically connected to a gate driver circuit  30  of a liquid crystal panel  50 . The timing controller  10  is also connected to multiple source driver circuits  40  to provide a pixel data signal to the source driver circuits  40 , and controls the source driver circuits  40  and the gate driver circuit  30  to send the pixel data signal to each liquid crystal unit  51  of the liquid crystal panel  50 , so that a screen performs displaying and updating. 
     The timing controller  10  is a combination of a timing control circuit and a program (such as firmware) executed by the timing control circuit. The timing controller  10  is used to obtain a system input signal provided by an external device or the system, and generate a first output enable signal (1st OE signal)  71 , a first clip trigger signal  81 , and a base working signal V-gate-high (Vgh) which are of the same frame rate as that of the system input signal. All of the three signals, together with a second output enable signal (2nd OE signal)  72  and a second clip trigger signal  82  in the following, are sent to the clip module  20  through a clip trigger control line  12 , an output enable control line  11 , and a working signal control line  13 . It should be noted that, the clip module  20  transmits the base working signal and the first output enable signal  71  to the gate driver circuit  30 . According to a trigger point (in this example, the signal is from high to low), a trigger time length, and the number of trigger circles of the first output enable signal  71 , the gate driver circuit  30  determines a gate line  31  (Gn) to which the base working signal should be transmitted, so as to open a semiconductor channel layer of a TFT element that controls charging time of the liquid crystal unit  51  connected to the gate line  31  (Gn), so that a pixel data signal can be transmitted to a drain from a source after passing through the opened semiconductor layer, and charge the liquid crystal unit  51 . 
     Moreover, the clip module  20  determines a time period in which clip operation is performed according to the first clip trigger signal  81 , so as to adjust the base working signal, generate a first clip voltage  91  in the base working signal, and transmit the base working signal carrying the first clip voltage  91  to the gate driver circuit  30 . The first clip voltage  91  affects the gate line  31  that transmits the base working signal, so as to bring a clip effect to the base working signal. The base working signal transmitted by the gate line  31  forms a clip waveform. 
     When the frame rate of the system input signal changes, the timing controller  10  also makes changes according to the frame rate, so as to adjust the first output enable signal  71  and the first clip trigger signal  81  into a second output enable signal  72  and a second clip trigger signal  82 . The clip module  20  determines a time period in which the clip operation is performed according to the second clip trigger signal  82 , so as to adjust the base working signal, generate a second clip voltage  92  in the base working signal, and transmit the base working signal carrying the second clip voltage  92  to the gate driver circuit  30 . Trigger points and trigger time lengths of the second output enable signal  72  and the second clip trigger signal  82  are adjusted by the timing controller  10 , so that the trigger time length of the second clip trigger signal  82  is equal to the trigger time length of the first clip trigger signal  81 , the trigger time length of the second output enable signal  72  is equal to the trigger time length of the first output enable signal  71 , and a time interval between the trigger point of the second clip trigger signal  82  and the trigger point of the second output enable signal  72  is equal to a time interval between the trigger point of the first clip trigger signal  81  and the trigger point of the first output enable signal  71 . Therefore, the signal information (the clip time, the time period, and the waveform) of the first clip voltage  91  is the same as the signal information of the second clip voltage  92 . Therefore, the base working signal, in terms of both the signal waveform and the clip waveform, transmitted by each gate line  31  is consistent before and after the switch of the frame rate. Charging charges, the charging time length, and the clip waveform of the liquid crystal unit  51  that receives the base working signal are consistent before and after the switch of the frame rate. 
     Referring to  FIG. 2A  and  FIG. 2B , timing diagrams before and after the switch of the frame rate are shown, and  FIG. 1  is also referred to for better understanding. According to the change of the frame rate of the system input signal, the timing controller  10  calculates a charging time length difference between two different charging time lengths of the liquid crystal element connected to the gate driver circuit  30  when the base working signal carries the first clip voltage  91  and when the base working signal carries a clip voltage to be adjusted  92 ′ after the frame rate changes, so as to adjust trigger points and trigger time lengths of an output enable signal to be adjusted  72 ′ and a clip trigger signal to be adjusted  82 ′ that are provided after the frame rate changes; and calculate and form the second output enable signal  72  and the second clip trigger signal  82 , so that the base working signals transmitted by different gate lines  31  are consistent in terms of both the signal waveform and the clip waveform, and the charging charges of the liquid crystal element  51  that receives the base working signal remain the same before and after the change. A calculation example of the base working signal before and after the frame rate changes is described below. 
     As shown in  FIG. 2A , when the liquid crystal panel  50  is working, the timing controller  10  outputs the base working signal (Vgh) with the frame rate being 60 Hz, the liquid crystal element is charged during the period in which the first output enable signal (1st OE)  71  changes from high to low, and each trigger time length is the sum of T 1  and T 2 . 
     During a standby period of the liquid crystal panel  50 , the timing controller  10  outputs the base working signal (Vgh) with the frame rate being 40 Hz, the charging time length of each liquid crystal element is longer than that in the environment in which the frame rate is 60 Hz, and each trigger time length is the sum of T 3  and T 4 . Accordingly, the clip time of the clip operation is also longer than that in the environment in which the frame rate is 60 Hz, and the generated clip waveform does not satisfy requirements either. Here, the second output enable signal  72  and the second clip trigger signal  82  before the adjustment are referred to as the output enable signal to be adjusted  72 ′ and the clip trigger signal to be adjusted  82 ′ temporarily. The clip voltage carried by the base working signal is referred to as the clip voltage to be adjusted  92 ′ temporarily. 
     It is assumed that T 1  is the time interval between the trigger point of the first output enable signal  71  and the trigger point of the first clip trigger signal  81  in a circle when the frame rate is 60 Hz, and T 2  is the trigger time length of the first clip trigger signal  81  in the same circle. T 3  is the time interval between the trigger point of the second output enable signal  72  and the trigger point of the second clip trigger signal  82  in a circle when the frame rate is 40 Hz, and T 4  is the trigger time length of the second clip trigger signal  82  in the same circle. In view of the above, in order that the first clip voltage  91  equals the second clip voltage  92 , T 1  should be equal to T 3 , and T 2  should be equal to T 4 . It is assumed that T 3 ′ is a time interval between the trigger point of the output enable signal to be adjusted  72 ′ and the trigger point of the clip trigger signal to be adjusted  82 ′, and T 4 ′ is the trigger time length of the clip trigger signal to be adjusted  82 ′ in the same circle. In order that T 1 =T 3  and T 2 =T 4 , T 3 ′ is required to be adjusted to T 3 , and T 4 ′ is required to be adjusted to T 4 . 
     As shown in  FIG. 2B , in order that T 1 =T 3 , a first charging time length difference N 1  (clk) is calculated according to a formula (1), a formula (2), and a formula (3) in the following; and a second charging time length difference N 2  (clk) is calculated according to a formula (4), a formula (5), and a formula (6). When the frame rate is 40 Hz, the trigger point of the clip trigger signal to be adjusted  82 ′ in the whole clip trigger timing (KB) is adjusted, and is reduced by a time width of N 1  (clk), and an end point of the clip trigger signal to be adjusted  82 ′ is reduced by a time width of N 2  (clk), so that the trigger point and the trigger time length of the second clip trigger signal  82  are obtained, that is, T 4 ′ is adjusted to T 4 . Additionally, when the frame rate is 40 Hz, the timing controller  10  adjusts an end point of the output enable signal to be adjusted  72 ′ in the whole output enable timing at the same time, which is reduced by the time width of N 2  (clk), so that the trigger point and the trigger time length of the second output enable signal  72  are obtained (that is, T 3 ′+T 4 ′ is changed into T 3 +T 4 ), and T 3 ′ is adjusted to T 3 , thus meeting the above requirements. Therefore, after the output enable signal to be adjusted  72 ′ and the clip trigger signal to be adjusted  82 ′ are adjusted, the above second output enable signal  72  and second clip trigger signal  82  are formed. The clip voltage carried by the base working signal is also changed from the clip voltage to be adjusted  92 ′ to the second clip voltage  92 . The signal information of the second clip trigger signal  82 , the second output enable signal  72 , and the second clip voltage  92  is the same as the signal information of the first clip trigger signal  81 , the first output enable signal  71 , and the first clip voltage  91 . Therefore, before and after the frame rate changes, the charging time lengths of all liquid crystal units  51  are the same (T n =T n +1), and the charging charges obtained by all liquid crystal units  51  are the same (Q n =Q n +1), so that screen brightness remains the same, thus overcoming the problem of screen flickering. 
     
       
         
           
             
               
                 
                   
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     V total  is a total number of horizontal lines in one frame, Dotclk is a pixel rate, and R total  is a total number of all Dotclk in n horizontal lines. 
     Referring to  FIG. 1 , besides calculation by which the timing controller  10  adjusts and generates the second output enable signal  72  and the second clip trigger signal  82 , the timing controller  10  may also be electrically connected to a memory unit  60 . The memory unit  60  records signal information (trigger points and trigger time lengths) of the first clip trigger signal  81 , the second clip trigger signal  82 , the first output enable signal  71 , and the second output enable signal  72 , so that the timing controller  10  reads corresponding signal information according to the frame rate of the system input signal. Moreover, in this embodiment, the rate of the base working signal is 60 Hz, and the frame rate is changed to 40 Hz, but the present invention is not limited thereto. The frame rate of the base working signal may also be 75 Hz, and the frame rate may also be changed to 60 Hz, and alternatively, other available operation rates of the liquid crystal panel  50  may also be applicable. 
       FIG. 3A  illustrates a signal timing clip control method of the liquid crystal panel  50  according to an embodiment of the present invention, which is applicable to the timing controller  10  in  FIG. 1 . Refer to  FIG. 2A  and  FIG. 2B , and also refer to  FIG. 3B  to  FIG. 3D , which are detailed schematic flow charts of a process in  FIG. 3A , for better understanding. The following describes cases in which the method is specifically applied in two embodiments. 
     The timing controller  10  generates, according to a system input signal, a first output enable signal  71 , a first clip trigger signal  81 , and a base working signal, whose frame rates are the same as a frame rate of the system input signal (Step S 110 ). As stated above, when the timing controller  10  obtains the system input signal provided by an external device or a system, the timing controller  10  generates the first output enable signal  71 , the first clip trigger signal  81 , and the base working signal, whose frame rates are the same as the frame rate of the system input signal, and sends the signals to a clip module  20 . 
     As shown in  FIG. 3B , the step may be presented in another manner. As stated above, a memory unit  60  records signal information (including trigger points and trigger time lengths) of the first clip trigger signal  81 , a second clip trigger signal  82 , the first output enable signal  71 , and a second output enable signal  72 . The timing controller  10  first analyzes the frame rate of the system input signal (Step S 111 ), obtains pre-stored signal information from the memory unit  60 , and generates the first clip trigger signal  81  and the first output enable signal  71  (Step S 112 ). 
     The clip module  20  adjusts the base working signal according to the first output enable signal  71  and the first clip trigger signal  81  to form a first clip voltage  91 , and output the base working signal carrying the first clip voltage  91  to a gate driver circuit  30  (Step S 120 ). The clip module  20  adjusts the base working signal according to the first clip trigger signal  81 , so as to transmit the base working signal carrying the first clip voltage  91  to the gate driver circuit  30 . The first clip voltage  91  affects a gate line  31  that transmits the base working signal, so as to bring a clip effect to the base working signal. The base working signal transmitted by the gate line  31  forms a clip waveform. 
     It is judged whether the frame rate is changed (Step S 130 ). When the timing controller  10  judges that the frame rate of the system input signal is changed, the timing controller  10  adjusts the first output enable signal  71  and the first clip trigger signal  81  to a second output enable signal  72  and a second clip trigger signal  82  according to the change of the frame rate (Step S 140 ). As stated above, the timing controller  10  adjusts the first output enable signal  71  and the first clip trigger signal  81  to the second output enable signal  72  and the second clip trigger signal  82  according to the change of the frame rate. The clip module  20  determines a time period in which the clip operation is performed according to the second clip trigger signal  82 , adjusts the base working signal, and transmits the base working signal carrying the second clip voltage  92  to the gate driver circuit  30 . 
     A trigger time length of the first clip trigger signal  81  equals a trigger time length of the second clip trigger signal  82 . A trigger time length of the first output enable signal  71  equals a trigger time length of the second output enable signal  72 . A time interval between a trigger point of the first clip trigger signal  81  and a trigger point of the first output enable signal  71  equals a time interval between a trigger point of the second clip trigger signal  82  and a trigger point of the second output enable signal  72 . Therefore, the signal information (clip time, a time period, and a waveform) of the first clip voltage  91  is the same as the signal information of the second clip voltage  92 . 
     A manner in which the timing controller  10  adjusts the output enable signal and the clip trigger signal is shown in  FIG. 3C , and specifically, the timing controller  10  analyzes the change of the frame rate of the system input signal, and calculates a charging time length difference between two different charging time lengths of a liquid crystal element connected to the gate line  31  when the base working signal carries the first clip voltage  91  and when the base working signal carries a clip voltage to be adjusted  92 ′ after the frame rate changes (Step S 141 ). Equations used for the adjustment are as formula (1) to formula (6) and calculation descriptions stated above, and are not described herein again. 
     Then, the timing controller  10  adjusts trigger points and trigger time lengths of an output enable signal to be adjusted  72 ′ and a clip trigger signal to be adjusted  82 ′ provided after the frame rate changes, so as to form the second output enable signal  72  and the second clip trigger signal  82  (Step S 142 ). The timing controller  10  adjusts the trigger point of the clip trigger signal to be adjusted  82 ′ by reducing the trigger point of the clip trigger signal to be adjusted  82 ′ by a time width of N 1  (clk) and reducing an end point of the clip trigger signal to be adjusted  82 ′ by a time width of N 2  (clk), so that the trigger point and the trigger time length of the second clip trigger signal  82  are obtained, that is, T 4 ′ is adjusted to T 4 . The timing controller  10  adjusts an end point of the output enable signal to be adjusted  72 ′ at the same time, which is reduced by the time width of N 2  (clk), so that the trigger point and the trigger time length of the second output enable signal  72  are obtained (that is, T 3 ′+T 4 ′ is changed into T 3 +T 4 ), and T 3 ′ is adjusted to T 3 , thus meeting the above requirements. After the output enable signal to be adjusted  72 ′ and the clip trigger signal to be adjusted  82 ′ are adjusted, the above second output enable signal  72  and second clip trigger signal  82  are formed. 
     As shown in  FIG. 3D , Step S 140  may be presented in another manner. As stated above, the memory unit  60  records the signal information (including the trigger points and the trigger time lengths) of the first clip trigger signal  81 , the second clip trigger signal  82 , the first output enable signal  71 , and the second output enable signal  72 . 
     The timing controller  10  first analyzes the frame rate after the system input signal changes (Step S 143 ), obtains pre-stored signal information from the memory unit  60 , and generates the second clip trigger signal  82  and the second output enable signal  72  (Step S 144 ). 
     The clip module  20  uses the second output enable signal  72  and the second clip trigger signal  82  to adjust the base working signal to form the second clip voltage  92  equal to the first clip voltage  91 , and output the base working signal carrying the second clip voltage  92  to the gate driver circuit  30  (Step S 150 ). The signal information (the clip time, the time period, and the waveform) of the first clip voltage  91  is the same as the signal information of the second clip voltage  92 . Therefore, the base working signals transmitted by the gate lines  31  are consistent in terms of both the signal waveform and the clip waveform. Charging charges, a charging time length, and a clip waveform of a liquid crystal element  51  that receives the base working signal remain the same before and after the frame rate is switched. That is to say, a charge mode of each liquid crystal unit  51  remains the same before and after the frame rate is switched, so that imaging luminance of a liquid crystal panel  50  is steady, thus avoiding screen transient flickering. 
     When judging that the frame rate of the system input signal is not changed, the timing controller  10  continues to provide the current base working signal, output enable signal, and the clip trigger signal, and detects whether the frame rate is changed continuously. 
     In view of the above, implementation or embodiments of the technical solutions presented by the present invention to solve problems are described herein, which is not intended to limit the scope of implementation of the present invention. Equivalent modification and improvement in accordance with the claims of the present invention or made according to the claims of the present invention is covered by the claims of the present invention.