Patent Publication Number: US-2011050554-A1

Title: Display device and backlight control method thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a display device and, more particularly, to a device and method thereof for controlling backlight timing of a display device. 
     2. Description of the Prior Art 
     A liquid crystal display (LCD) using light emitting diodes as a backlight module is usually applied to a notebook. Referring to  FIG. 1 ,  FIG. 1  is a functional block diagram illustrating a conventional LCD  1 . As shown in  FIG. 1 , a panel power  20  and a data signal  22  are transmitted from external devices to a timing control module  12  via a receiving interface  10 . After process and transformation, the timing control module  12  outputs a data/control signal  24  to a source/gate driver  140  of a panel  14 . Furthermore, an LED backlight power  26  and an LED backlight control signal  28  are also transmitted from external devices to an LED backlight driving unit  16  via the receiving interface  10 , so as to control a voltage  30  and a feedback current  32  for an LED backlight module  18 . In general, the LED backlight control signal  28  comprises a pulse width modulation (PWM) signal  280  and an enable signal  282 . The PWM signal  280  is used for controlling brightness of the LED backlight module  18  and the enable signal  282  is used for controlling on/off of the LED backlight module  18 . In the past, the LED backlight driving unit  16  is controlled by the LED backlight control signal  28  directly. If the LED backlight control signal  28  has noise or does not be outputted based on correct timing when power is on, some undesired images, such as white image or power-on noise, will be displayed on the panel  14 . 
     Referring to  FIG. 2 ,  FIG. 2  is a timing diagram illustrating the backlight powered on under normal and abnormal conditions. As shown in  FIG. 2 , the normal condition shows a desired on/off timing for common panels. After supplying the panel power  20  to the panel  14 , the timing control module  12  will reach steady state after time t 0 -t 2  and the data signal  22  is then inputted. After time t 2 -t 3 , the data signal  22  will reach steady state and the voltage  30  is then inputted, so as to prevent the panel  14  from displaying undesired images while the LED backlight module  18  is powered on. On the other hand, the LED backlight module  18  should be powered off before time t 4 , so as to avoid generating power-off noise. 
     However, if the LED backlight control signal  28  from external devices is abnormal, the panel will display images with noise while power is on or off. As shown in  FIG. 2 , the enable signal  282  is used for controlling on/off of the LED backlight driving unit  16 . For example, the LED backlight driving unit  16  is on while the enable signal  282  is high and the LED backlight driving unit  16  is off while the enable signal  282  is low. The PWM signal  280  is used for controlling output current of the LED backlight driving unit  16 , so as to adjust brightness of the LED backlight module  18 . As shown in  FIG. 2 , the sum of time t_on and time t_off is constant, and there is positive correlation between the time t_on and the output current of the LED backlight driving unit  16  (i.e. the brightness of the backlight module  18 ). Moreover, as shown in  FIG. 2 , the voltage  30 ′ will be transmitted from the LED backlight driving unit  16  to the LED backlight module  18  while the abnormal condition occurs. For example, the LED is on while the voltage  30 ′ is high and the LED is off while the voltage  30 ′ is low. 
     When power is on and provided that the power of the LED backlight driving unit  16  has reached steady state, a transient voltage occurs in the enable signal  282  during time t 0 -t 1  and the PWM signal  280  is high. At this time, the LED backlight driving unit  16  will output voltage to power on the LED backlight module  18  at time interval a. After the time interval a, the enable signal  282  is pulled low and then the LED backlight driving unit  16  stops to output voltage, such that the LED backlight module  18  is powered off. At time t 1 -t 2  within time interval b, the enable signal  282  is pulled high again, so that the LED backlight module  18  is powered on again. It should be noted that, at time t 2 -t 3  within the time interval b, the data signal  22  may not reach steady state yet, such that the panel  14  may display an image with noise. At this time, since the LED backlight module  18  has been powered on, the panel  14  will display the image with noise clearly. After time t 3 , the enable signal  282  is pulled low again, so that the LED backlight module  18  is powered off again. 
     When power is off (i.e. after time t 4 ), the LED backlight module  18  should be powered off at the same time under normal condition. However, since the enable signal  282  and the PWM signal  280  are still pulled high, the LED backlight driving unit  16  will be on. Accordingly, the panel may display images with noise due to unstable data signal  22  during time t 4 -t 5  and display white image during time t 5 -t 6  (provided that the panel  14  will display white image while there is no data signal). 
     SUMMARY OF THE INVENTION 
     Therefore, one objective of the invention is to provide a display device and backlight control method thereof for controlling timing of the backlight control signal, such as enable signal and/or PWM signal, so as to solve the aforesaid problems. 
     According to one embodiment, a display device of the invention comprises a panel, a receiving interface, a timing control module, a backlight module and a backlight driving unit. The timing control module is electrically connected to the receiving interface and the panel. The backlight driving unit is electrically connected to the receiving interface, the timing control module and the backlight module. The receiving interface receives a first data signal and a first backlight control signal with a first timing. The timing control module converts the first data signal into a second data signal and then outputs the second data signal to the panel. Furthermore, based on the second data signal, the timing control module converts the first backlight control signal into a second backlight control signal with a second timing different from the first timing and then outputs the second backlight control signal. After receiving the second backlight control signal from the timing control module, the backlight driving unit is controlled by the second backlight control signal to output an output voltage signal to the backlight module. 
     According to another embodiment, a backlight control method of the invention comprises steps of: receiving a first data signal and a first backlight control signal with a first timing; converting the first data signal into a second data signal and then outputting the second data signal to a panel; based on the second data signal, converting the first backlight control signal into a second backlight control signal with a second timing different from the first timing and then outputting the second backlight control signal; and based on the second backlight control signal, outputting an output voltage signal to a backlight module. 
     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 
         FIG. 1  is a functional block diagram illustrating a conventional LCD. 
         FIG. 2  is a timing diagram illustrating the backlight powered on under normal and abnormal conditions. 
         FIG. 3  is a functional block diagram illustrating a display device according to one embodiment of the invention. 
         FIG. 4  is a functional block diagram illustrating the timing control module shown in  FIG. 3 . 
         FIG. 5  is a timing diagram illustrating backlight control of the invention. 
         FIG. 6  is a flowchart showing a backlight control method according to one embodiment of the invention. 
         FIG. 7  is a flowchart showing a backlight control method according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 3 ,  FIG. 3  is a functional block diagram illustrating a display device  4  according to one embodiment of the invention. As shown in  FIG. 3 , the display device  4  comprises a panel  40 , a receiving interface  42 , a timing control module  44 , a backlight module  46  and a backlight driving unit  48 . The timing control module  44  is electrically connected to the receiving interface  42  and the panel  40 . The backlight driving unit  48  is electrically connected to the receiving interface  42 , the timing control module  44  and the backlight module  46 . In practical applications, the display device  4  can be, but not limited to, a liquid crystal display, the panel  40  can be, but not limited to, a liquid crystal panel, and the backlight module  46  can be, but not limited to, an LED backlight module. 
     The receiving interface  42  receives a first input voltage signal  50  and a second input voltage signal  52  from external devices. Afterward, the receiving interface  42  supplies the first input voltage signal  50  to the backlight driving unit  48  and supplies the second input voltage signal  52  to the timing control module  44 . Furthermore, the receiving interface  42  also receives a first data signal  54  and a first backlight control signal  56  with a first timing from external devices. In this embodiment, the first backlight control signal  56  comprises a PWM signal  560  and an enable signal  562 . The PWM signal  560  is used for controlling brightness of the backlight module  46  and the enable signal  562  is used for controlling on/off of the backlight module  46 . The PWM signal  560  and the enable signal  562  both have the first timing. 
     The timing control module  44  is driven by the second input voltage signal  52  to convert the first data signal  54  into a second data signal  58  and output the second data signal  58  to the panel  40 . Furthermore, based on the second data signal  58 , the timing control module  44  converts the first backlight signal  56  into a second backlight control signal  60  with a second timing different from the aforesaid first timing and then outputs the second backlight control signal  60  to the backlight driving unit  48 . As mentioned in the above, since the first backlight control signal  56  comprises the PWM signal  560  and the enable signal  562 , the second backlight control signal  60  also comprises a PWM signal  600  and an enable signal  602  and the PWM signal  600  and the enable signal  602  both have the second timing. 
     After receiving the second backlight control signal  60  from the timing control module  44 , the backlight driving unit  48  is controlled by the second backlight control signal  60  to output an output voltage signal  62  to the backlight module  46 , so as to power on the backlight module  46 . Moreover, the backlight module  46  will output a feedback current  64  to the backlight driving unit  48 . The backlight driving unit  48  can unify brightness of the backlight module  46  based on the feedback current  64 . 
     Referring to  FIG. 4 ,  FIG. 4  is a functional block diagram illustrating the timing control module  44  shown in  FIG. 3 . As shown in  FIG. 4 , the timing control module comprises a first receiving unit  440 , a processing unit  442 , a transmitting unit  444 , a control unit  446 , a second receiving unit  448 , a logic unit  450  and a signal regenerating unit  452 . The first receiving unit  440  is electrically connected to the receiving interface  42 , the processing unit  442  is electrically connected to the first receiving unit  440 , the transmitting unit  444  is electrically connected to the processing unit  442  and the panel  40 , the control unit  446  is electrically connected to the processing unit  442  and the panel  40 , the second receiving unit  448  is electrically connected to the receiving interface  42 , the logic unit  450  is electrically connected to the control unit  446  and the second receiving unit  448 , and the signal regenerating unit  452  is electrically connected to the logic unit  450  and the backlight driving unit  48 . 
     The first receiving unit  440  receives the first data signal  54  from the receiving interface  42  and transmits the first data signal  54  to the processing unit  442 . The processing unit  442  converts the first data signal  54  into the second data signal  58  in a specific format in compliance with the panel  40  and then transmits the second data signal  58  to the transmitting unit  444  and the control unit  446 . The transmitting unit  444  outputs the second data signal  58  to the panel  40 . Furthermore, based on the second data signal  58 , the control unit  446  outputs control signals  66 , such as start pulse (STH) signal, latch pulse (LP) signal, point of load (POL) signal, see through vision (STV) signal, output enable (OE) signal and so on, to the panel  40 . 
     Moreover, after receiving the first backlight control signal  56  from the receiving interface  42 , the second receiving unit  448  transmits the first backlight control signal  56  to the logic unit  450 . At this time, the logic unit  450  determines whether the second data signal  58  has been transmitted to the panel  40  or terminated first. Once the second data signal  58  has been transmitted to the panel  40  or terminated, the signal regenerating unit  452  converts the first backlight control signal  56  into the second backlight control signal  60  and then outputs the second backlight control signal  60  to the backlight driving unit  48 . 
     Referring to  FIG. 5  along with  FIGS. 3 and 4 ,  FIG. 5  is a timing diagram illustrating backlight control of the invention. As shown in  FIG. 5 , the PWM signal  560  and the enable signal  562  both have an abnormal timing before adjustment. When power is on at time t 0  and provided that the power of the backlight driving unit  48  has reached steady state, a transient voltage occurs in the enable signal  562  during time t 0 -t 1  and the PWM signal  560  is high. At this time, the backlight driving unit  48  will output the output voltage signal  62  to power on the backlight module  46  at time interval a. After the time interval a, the enable signal  562  is pulled low and then the backlight driving unit  48  stops to output voltage, such that the backlight module  46  is powered off. At time t 1 -t 2  within time interval b, the enable signal  562  is pulled high again, so that the backlight module  46  is powered on again. It should be noted that, at time t 2 -t 3  within the time interval b, the data signal  58  may not reach steady state yet, such that the panel  40  may display an image with noise. At this time, since the backlight module  46  has been powered on, the panel  40  will display the image with noise clearly. 
     In general, after supplying the second input voltage signal  52  to the panel  40 , the timing control module  44  will reach steady state after time t 0 -t 2  and the data signal  58  is then inputted. To avoid the aforesaid situation, the backlight driving unit  48  should output voltage to the backlight module  46  after time t 2 -t 3  when the data signal  58  has reached steady state, so as to prevent the panel  40  from displaying undesired images while the backlight module  46  is powered on. 
     In one embodiment, after the transmitting unit  444  transmits the second data signal  58  to the panel  40 , the logic unit  450  of the invention may determine that the second data signal  58  has been transmitted to the panel  40  after a first predetermined time. Then, the logic unit  450  outputs a control signal to control the signal regenerating unit  452  to adjust the timing of the PWM signal  560  and the enable signal  562  to be the timing after adjustment shown in  FIG. 5 . In this embodiment, the aforesaid first predetermined time represents time t 2 -t 3  shown in  FIG. 5 . Therefore, the backlight driving unit  48  will be controlled by the adjusted PWM signal  560  and enable signal  562  to output the output voltage signal  62  to the backlight module  46 , so as to power on the backlight module  46  at time t 3 . Since the data signal  58  has reached steady state at time t 3 , the panel  40  will display images without noise. 
     In another embodiment, after the timing control module  44  receives the second input voltage signal  52 , the logic unit  450  of the invention may determine that the second data signal  58  has been transmitted to the panel  40  after a second predetermined time. Then, the logic unit  450  outputs a control signal to control the signal regenerating unit  452  to adjust the timing of the PWM signal  560  and the enable signal  562  to be the timing after adjustment shown in  FIG. 5 . In this embodiment, the aforesaid second predetermined time represents time t 0 -t 3  shown in  FIG. 5 . 
     In another embodiment, after the timing control module  44  receives the second input voltage signal  52  and reaches steady state, the logic unit  450  of the invention may determine that the second data signal  58  has been transmitted to the panel  40  after a third predetermined time. Then, the logic unit  450  outputs a control signal to control the signal regenerating unit  452  to adjust the timing of the PWM signal  560  and the enable signal  562  to be the timing after adjustment shown in  FIG. 5 . In this embodiment, the aforesaid third predetermined time represents time t 1 -t 3  shown in  FIG. 5 . 
     On the other hand, the backlight module  46  should be powered off before time t 4 , so as to avoid generating power-off noise. Since time t 4 -t 5  when the second data signal  58  will be terminated cannot be obtained, the timing control module  44  of the invention may pull low the PWM signal  560  and the enable signal  562  at time t 5  when the second data signal is terminated, so as to power off the backlight module  46 . Accordingly, the power-off noise can be avoided. 
     Referring to  FIG. 6  along with  FIGS. 3 and 4 ,  FIG. 6  is a flowchart showing a backlight control method according to one embodiment of the invention. When the display device  4  is powered on, the backlight control method of the invention comprises the following steps. In the beginning, step S 100  is performed to power on the display device  4 . Afterward, step S 102  is performed to receive the first data signal  54  and the first backlight control signal  56 . Step S 104  is then performed to convert the first data signal  54  into the second data signal  58  and then output the second data signal  58  to the panel  40 . Step S 106  is then performed to determine whether the second data signal  58  has been transmitted to the panel  40 , wherein if it is YES, step S 108  will be performed, otherwise step S 102  is performed again to receive the first data signal  54  and the first backlight control signal  56  continuously. Step S 108  is performed to convert the first backlight control signal  56  into the second backlight control signal  60  and then output the second backlight control signal  60 . Step S 110  is then performed to output the output voltage signal  62  to the backlight module  46  based on the second backlight control signal  60 . Finally, step S 112  is performed to power on the backlight module  46 . 
     Referring to  FIG. 7  along with  FIGS. 3 and 4 ,  FIG. 7  is a flowchart showing a backlight control method according to another embodiment of the invention. When the display device  4  is going to be powered off, the backlight control method of the invention comprises the following steps. In the beginning, step S 200  is performed to power off the display device  4 . Afterward, step S 202  is performed to receive the first data signal  54  and the first backlight control signal  56 . Step S 204  is then performed to convert the first data signal  54  into the second data signal  58  and then output the second data signal  58  to the panel  40 . Step S 206  is then performed to determine whether the second data signal  58  has been terminated, wherein if it is YES, step S 208  will be performed, otherwise step S 202  is performed again to receive the first data signal  54  and the first backlight control signal  56  continuously. Step S 208  is performed to convert the first backlight control signal  56  into the second backlight control signal  60  and then output the second backlight control signal  60 . Step S 210  is then performed to stop outputting the output voltage signal  62  to the backlight module  46  based on the second backlight control signal  60 . Finally, step S 212  is performed to power off the backlight module  46 . 
     Still further, when the timing control module  44  converts the first backlight control signal  56  into the second backlight control signal  60 , the invention may change the output mode of the backlight control signal, such as frequency, amplitude and so on, at the same time. 
     It should be noted that the invention can adjust the timing of the PWM signal and the enable signal at the same time or just adjust one of the both signals, so as to avoid generating power-on or power-off noise. In other words, the power-on or power-off noise can be avoided as long as one of the PWM signal and the enable signal is pulled high at time t 3  and pulled low at time t 5 . If we cannot know which of the PWM signal and the enable signal will be inputted to the timing control module  44  first, the timing control module  44  has to perform the aforesaid adjustment for the PWM signal and the enable signal at the same time. 
     Compared to the prior art, the invention utilizes the timing control module to adjust the PWM signal and/or the enable signal in advance rather than inputting both of them to the backlight driving unit directly. The logic unit of the timing control module determines an optimal time for powering on/off the backlight module and determines a duty ratio and frequency for the PWM signal. Furthermore, the signal regenerating unit regenerates the PWM signal and the enable signal and then outputs both of them to the backlight driving unit. Accordingly, the backlight module will be powered on after the data signal reaches steady state, so as to avoid generating power-on noise. Moreover, the backlight module will be powered off after the data signal has been terminated and the power-off process is going to be performed, so as to avoid generating power-off noise. 
     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.