Patent Publication Number: US-9892690-B2

Title: Control circuit for backlight, a control method and a liquid crystal display device

Description:
TECHNICAL FIELD 
     The disclosure to relates a liquid crystal display field, particularly a control circuit for backlight, a control method and a liquid crystal display device. 
     BACKGROUND 
     Content Adaptive Backlight Control (CABC) is a method for analyzing contents of displaying and adjusting backlight of display panel based on contents of gray level and Gamma correction technology. 
     In present panel display control system, all of the modulation functions of CABC transmit Pulse Width Modulation (PWM) waves from display driving chip to PWM pin of backlight driving chip in order to implement brightness modulation of backlight, and then modulate brightness of a liquid crystal display device. 
     When video frame data enable signal of liquid crystal display panel during a frame data disable period, brightness of the liquid crystal display device should be constant because PWM wave doesn&#39;t change. However, video frame data on liquid crystal pixels are not updated state, meaning that liquid crystal pixels is in charge sustained state, but leakage characteristic of thin film transistor itself causes the decline of pixel voltage of liquid crystal pixels to reduce brightness of the liquid crystal display device. 
     SUMMARY 
     The disclosure mainly solve a technical problem that a control circuit for backlight, a control method and a liquid crystal display device, and increase brightness of the liquid crystal display device when a video frame data enable signal is during a frame data disable compensate for decreasing of brightness of the liquid crystal display device caused by leakage characteristic of thin film transistor itself. 
     To solve the aforementioned technical problem, the disclosure uses a technical solution is providing a control circuit for backlight, and the control circuit includes: a display driving chip used to generate a video frame data enable signal and a first PWM signal; a pulse width modulation control circuit for receiving the video frame data enable signal and the first PWM signal, and modulating a duty ratio of the first PWM signal under the video frame data enable signal control to get a second PWM signal; a backlight driving chip for receiving the second PWM signal, and controlling brightness of the backlight based on the second PWM signal to increase brightness of the backlight during a frame data disable period of the video frame data enable signal. 
     Wherein, a duty ratio of the second PWM signal is larger than the duty ratio of the first PWM signal during the frame data disable period of the video frame data enable signal. 
     Wherein, a duty cycle of the second PWM signal is the same as a duty cycle of the first PWM signal during the frame data disable period of the video frame data enable signal; wherein, the duration of the frame data disable period of the video frame data enable signal is integer times of duty cycle of the first PWM signal or duty cycle of the second PWM signal. 
     Wherein, the duty ratio of the second PWM signal is the same as the duty ratio of the first PWM signal during a frame data enable period of the video frame data enable signal. 
     Wherein, the control circuit further comprises a signal generator, and the signal generator is used to generate a video frame signal; wherein, the display driving chip connects to the signal generator for generating the video frame data enable signal and the first PWM signal under the video frame signal control. 
     To solve the aforementioned technical problem, the disclosure uses another technical solution is: providing a liquid crystal display device including aforementioned backlight of the control circuit. 
     To solve the aforementioned technical problem, the disclosure also uses another technical solution is providing a control method for backlight, and the control method includes: receiving a video frame data enable signal and a first PWM signal, and modulating a duty ratio of the first PWM signal under the video frame data enable signal control to obtain a second PWM signal; controlling brightness of the backlight based on the second PWM signal to increase brightness of the backlight during a frame data disable period of the video frame data enable signal. 
     Wherein, steps of modulating the duty ratio of the first PWM signal to obtain the second PWM signal under the video frame data enable signal control is specifically: starting to modulate the duty ratio of the first PWM signal to obtain the second PWM signal in order that a duty ratio of the second PWM signal is larger than the duty ratio of the first PWM signal when the video data enable signal get into the frame data disable period; stopping modulating the operation of the duty ratio of the first PWM signal to make the first PWM signal and the second PWM signal joint when the video data enable signal get into a frame data enable period from the frame data disable period. 
     Wherein, steps of controlling brightness of the backlight based on the second PWM signal to increase brightness of the backlight located in a frame data disable period of the video frame data enable signal is specifically: providing an output current for the backlight based on the duty ratio of the second PWM signal to increase the output current for the backlight during the frame data disable period of the video frame data enable signal. 
     Wherein, before obtaining the video frame data enable signal and the first PWM signal, the method further comprises steps: receiving the video frame signal; generating the video frame data enable signal and the first PWM signal under the video frame signal control. 
     The benefit of the disclosure is the control circuit for backlight, the control method and the liquid crystal display device of the disclosure modulate the duty ratio of the first PWM signal to obtain the second PWM signal under the video frame data enable signal control, thereby control brightness of the backlight based on the second PWM signal to increase brightness of the backlight during a frame data disable period of the video frame data enable signal, then compensate for decreasing of brightness of the liquid crystal display device within the frame data disable period caused by leakage characteristic of thin film transistor itself and achieve that brightness of the liquid crystal display device is consistent. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural schematic diagram of a control circuit for backlight according to an embodiment of the present disclosure; 
         FIG. 2  is a control sequential diagram of the control circuit for backlight according to  FIG. 1 ; 
         FIG. 3  is a control sequential diagram of the control circuit for backlight according to the present technology; 
         FIG. 4  is a control sequential diagram of a controlling method of the control circuit for backlight according to  FIG. 1 ; and 
         FIG. 5  is a structural schematic diagram of a liquid crystal display device according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. The present disclosure will hereinafter be described in detail with reference to the accompanying drawings and embodiments. 
     Referring to  FIG. 1  and  FIG. 2 ,  FIG. 1  is a structural schematic diagram of a control circuit for backlight according to an embodiment of the present disclosure, and  FIG. 2  is a control sequential diagram of the control circuit for backlight according to  FIG. 1 . As shown in  FIG. 1 , the control circuit  100  comprises a signal generator  10 , a display driving chip  11 , a pulse width modulation control circuit  12 , a backlight driving chip  13  and a backlight  14 . 
     The signal generator  10  is used to generate a video frame signal Vout. 
     The display driving chip  11  connects to the signal generator  10  for generating the video frame data enable signal DE and the first PWM signal PWM 1  under the video frame signal Vout control. 
     The pulse width modulation control circuit  12  connects to the display driving chip  11  for receiving the video frame data enable signal DE and the first PWM signal PWM 1 , and modulating a duty ratio of the first PWM signal under the video frame data enable signal control DE to get a second PWM signal PWM 2 . 
     Specifically, the video frame data enable signal DE includes a frame data disable period T 1  and a frame data enable period T 2 ; wherein, when the video frame data enable signal DE is at low potential, the video frame data enable signal DE is within the frame data disable period T 1  and when the video frame data enable signal DE is at high potential, the video frame data enable signal DE is within the frame data disable period T 2 . Certainly, one skilled in the art could understand, and in other embodiments, it also could be that when the video frame data enable signal DE is at high potential, the video frame data enable signal DE is within the frame data disable period T 1  and when the video frame data enable signal DE is at low potential, the video frame data enable signal DE is within the frame data disable period T 2  and the disclosure is not limited thereof. 
     When the video frame data enable signal DE get into the frame data disable period T 1 , that is, the video frame data enable signal DE turns into low potential from high potential, the pulse width modulation control circuit  12  starts to modulate the duty ratio of the first PWM signal PWM 1  to obtain the second PWM signal PWM 2  in order that a duty ratio of the second PWM signal PWM 2  is larger than the duty ratio of the first PWM signal PWM 1 ; Preferably, a duty cycle of the second PWM signal PWM  2  is the same as a duty cycle of the first PWM signal PWM 1  during the frame data disable period T 1  of the video frame data enable signal DE; wherein, the duration of the frame data disable period T 1  of the video frame data enable signal DE is twice of duty cycle of the first PWM signal PWM 1  or duty cycle of the second PWM signal PWM 2 , for example twice illustrated in  FIG. 2 . 
     When the video frame data enable signal DE get into the frame data enable period T 2  from the frame data disable period T 1 , that is, the video frame data enable signal DE turns into high potential from low potential, the pulse width modulation control circuit  12  stops modulating the operation of the duty ratio of the first PWM signal PWM 1  to make the first PWM signal PWM 1  and the second PWM signal PWM 2  joint. That is, when the video frame data enable signal DE is within the frame data disable period T 2 , the duty ratio of the second PWM signal PWM 2  is the same as the duty ratio of the first PWM signal PWM 1 , and the duty cycle of the second PWM signal PWM  2  is the same as the duty cycle of the first PWM signal PWM 1 . 
     The backlight driving chip  13  connects to the pulse width modulation control circuit  12  for receiving the second PWM signal PWM 2 , and controlling brightness of the backlight  14  based on the second PWM signal PWM 2  to increase brightness of the backlight  14  during a frame data disable period T 1  of the video frame data enable signal DE. 
     Specifically, the backlight driving chip  13  provides an output current I for the backlight  14  based on the duty ratio of the second PWM signal PWM 2 . Wherein, the output current I for the backlight  14  and the duty ratio of the second PWM signal PWM 2  are in direct proportion, that is, the larger the duty ratio of the second PWM signal PWM 2  is, the more the output current I for the backlight  14  is. the duty ratio of the second PWM signal PWM 2  during the frame data disable period T 1  of the video frame data enable signal DE is larger than during the frame data enable period T 2 ; therefore, the backlight driving chip  13  provides the output current I for the backlight  14  within the frame data disable period T 1  larger than provides the output current I within the frame data enable period T 2  so that brightness of the backlight  14  during a frame data disable period T 1  is increased, and then brightness of the liquid crystal display device is also increased. 
     Wherein, during a frame data disable period T 1  of the video frame data enable signal DE, the output current provided the backlight  14  is larger than 20 mA, and during a frame data enable period T 2  of the video frame data enable signal DE, the output current provided the backlight  14  is the same as 20 mA. 
     Please also refer to  FIG. 3 , and  FIG. 3  is a control sequential diagram of the control circuit for backlight according to the present technology. Comparing  FIG. 1  and  FIG. 2  can be understood: 
     the duty ratio of the second PWM signal PWM 2  of the control circuit for backlight in the disclosure during the frame data disable period T 1  of the video frame data enable signal DE is larger than during the frame data enable period T 2  so that the backlight driving chip  13  provides the output current I for the backlight  14  within the frame data disable period T 1  larger than provides the output current I for the backlight  14  within the frame data enable period T 2 , thereby brightness of the backlight  14  during a frame data disable period T 1  is increased, and then brightness of the liquid crystal display device is also increased to counteract leakage characteristic of thin film transistor itself that causes the decline of pixel voltage within the frame data disable period T 1  to reduce brightness of the liquid crystal display device. 
     Still, no matter during a frame data disable period T 1 A of the video frame data enable signal DEA or during a frame data enable period T 2 A, a duty ratio of a LEDPWM signal LEDPWM of the present control circuit for backlight is constant so that no matter during the frame data disable period T 1 A or during the frame data enable period T 2 A, an output current IA should be constant, thereby leakage characteristic of thin film transistor itself that causes the decline of pixel voltage within the frame data disable period T 1 A to reduce brightness of the liquid crystal display device. 
       FIG. 4  is a control sequential diagram of a controlling method of the control circuit for backlight according to  FIG. 1 . As shown in  FIG. 4 , the method comprises steps: 
     Step S 101 : receiving the video frame signal. 
     In step S 101 , the display driving chip  11  receives the video frame signal Vout generated by the signal generator  10 . 
     Step S 102 : generating the video frame data enable signal and the first PWM signal under the video frame signal Vout control. 
     In step S 102 , the display driving chip  11  generates the video frame data enable signal DE and the first PWM signal PWM 1  under the video frame signal Vout control. Wherein, the video frame data enable signal DE includes a frame data disable period T 1  and a frame data enable period T 2 ; wherein, when the video frame data enable signal DE is at low potential, the video frame data enable signal DE is within the frame data disable period T 1  and when the video frame data enable signal DE is at high potential, the video frame data enable signal DE is within the frame data disable period T 2 . Wherein, the first PWM signal PWM 1  is a PWM signal with an unchanged duty ratio and an unchanged cycle. 
     Step S 103 : receiving a video frame data enable signal and a first PWM signal, and modulating a duty ratio of the first PWM signal under the video frame data enable signal control to obtain a second PWM signal; 
     In step S 103 , the pulse width modulation control circuit  12  receives the video frame data enable signal DE and the first PWM signal PWM 1  generated by the display driving chip  11 , and modulates a duty ratio of the first PWM signal under the video frame data enable signal control DE to get a second PWM signal PWM 2 ; 
     Specifically, when the video frame data enable signal DE get into the frame data disable period T 1 , that is, the video frame data enable signal DE turns into low potential from high potential, the pulse width modulation control circuit  12  starts to modulate the duty ratio of the first PWM signal PWM 1  to obtain the second PWM signal PWM 2  in order that a duty ratio of the second PWM signal PWM 2  is larger than the duty ratio of the first PWM signal PWM 1 . Preferably, a duty cycle of the second PWM signal PWM  2  is the same as a duty cycle of the first PWM signal PWM 1  during the frame data disable period T 1  of the video frame data enable signal DE; wherein, the duration of the frame data disable period T 1  of the video frame data enable signal DE is twice of duty cycle of the first PWM signal PWM 1  or duty cycle of the second PWM signal PWM 2 , for example twice illustrated in  FIG. 2 . 
     When the video frame data enable signal DE get into the frame data enable period T 2  from the frame data disable period T 1 , that is, the video frame data enable signal DE turns into high potential from low potential, the pulse width modulation control circuit  12  stops modulating the operation of the duty ratio of the first PWM signal PWM 1  to make the first PWM signal PWM 1  and the second PWM signal PWM 2  joint. That is, when the video frame data enable signal DE is within the frame data disable period T 2 , the duty ratio of the second PWM signal PWM 2  is the same as the duty ratio of the first PWM signal PWM 1 , and the duty cycle of the second PWM signal PWM  2  is the same as the duty cycle of the first PWM signal PWM 1 . 
     Step S 104 : controlling brightness of the backlight based on the second PWM signal to increase brightness of the backlight during a frame data disable period of the video frame data enable signal. 
     In step S 104 , the backlight driving chip  13  receives the second PWM signal PWM 2  generated by the display driving chip  11 , and controls brightness of the backlight  14  based on the second PWM signal PWM 2  to increase brightness of the backlight  14  during a frame data disable period T 1  of the video frame data enable signal DE. 
     Specifically, the backlight driving chip  13  provides an output current I for the backlight  14  based on the duty ratio of the second PWM signal PWM 2 . Wherein, the output current I for the backlight  14  and the duty ratio of the second PWM signal PWM 2  are in direct proportion, that is, the larger the duty ratio of the second PWM signal PWM 2  is, the more the output current I for the backlight  14  is. The duty ratio of the second PWM signal PWM 2  during the frame data disable period T 1  of the video frame data enable signal DE is larger than during the frame data enable period T 2 ; therefore, the backlight driving chip  13  provides the output current I for the backlight  14  within the frame data disable period T 1  larger than provides the output current I within the frame data enable period T 2  so that brightness of the backlight  14  during a frame data disable period T 1  is increased, and then brightness of the liquid crystal display device within the frame data disable period T 1  is also increased to counteract leakage characteristic of thin film transistor itself that causes the decline of pixel voltage within the frame data disable period T 1  to reduce brightness of the liquid crystal display device. 
       FIG. 5  is a structural schematic diagram of a liquid crystal display device according to an embodiment of the present disclosure. As shown in  FIG. 5 , the liquid crystal display device  1  includes the control circuit  100  for backlight. 
     The benefit of the disclosure is the control circuit for backlight, the control method and the liquid crystal display device of the disclosure modulate the duty ratio of the first PWM signal to obtain the second PWM signal under the video frame data enable signal control, thereby control brightness of the backlight based on the second PWM signal to increase brightness of the backlight during a frame data disable period of the video frame data enable signal, then compensate for decreasing of brightness of the liquid crystal display device caused by leakage characteristic of thin film transistor itself and achieve that brightness of the liquid crystal display device is consistent within the frame data disable period. 
     Above are only embodiments of the present disclosure is not patented and therefore limit the scope of the present disclosure, any use of the contents of the present specification and drawings made equivalent or equivalent structural transformation process, either directly or indirectly related technologies used in other areas are included in the patent empathy scope of the disclosure.