Patent Publication Number: US-2012026139-A1

Title: Light feedback control system for a display device and method for feedback control

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a light feedback control system for a display device and a method for feedback control, and more particularly, to a light feedback control system and a method for feedback control which are used for monitoring light intensity or color signal of a light source. 
     2. Description of the Prior Art 
     Optical performance of a light emitting element in a liquid crystal display device decays due to various factors. For example, light emitting characteristic of a light emitting diode (LED) decays due to heat or long-time use. Accordingly, an optical sensor is usually added into a backlight unit (BLU) with light emitting diodes as its light source, so as to perform the feedback control for the backlight unit. Practically, optical sensors can further be categorized into light sensors and color sensors, which are utilized in feedback control on light intensity and color respectively. 
     Because transmittance rates of liquid crystal panels are gradually improved, TV panels may have transmittance rates up to 5 percent, and 20 percent for liquid crystal panels without color filters. In such conditions, when one of the aforesaid optical sensors detects alight signal of the backlight unit, the optical sensor also receives a signal of ambient light due to an external ambient light source. Accordingly, it will result in an error of the feedback control. 
     SUMMARY OF THE INVENTION 
     The present invention provides a light feedback control system capable of feeding precise optical characteristics of a backlight element and calibrating the optical performance of the backlight element. 
     The present invention also provides a method for feedback control capable of obtaining a correct feedback signal. 
     The present invention provides a light feedback control system. The light feedback control system includes a light source driver, an optical sensor, and a controller. The light source driver is connected to a backlight element for driving the backlight element. The controller is connected to the optical sensor and the light source driver, and the controller controls the optical sensor to sense a light source both when the backlight element is turned on and turned off so as to generate a plurality of signals correspondingly. The controller computes a feedback signal according to the plurality of signals, and the feedback signal is used for calibrating optical performance of the backlight element. 
     The present invention also provides a light feedback control system. The light feedback control system includes a light source driver, an optical sensor, and a controller. The light source driver is connected to a backlight element for driving the backlight element when an ambient illuminating device is turned off. The controller is connected to the optical sensor and the light source driver. The controller controls the optical sensor to synchronize with the light source driver and sense a light source so as to output a feedback signal. The feedback signal is used for calibrating optical performance of the backlight element. 
     The present invention also provides a light feedback control method including following steps: driving a back light element intermittently; sensing a light source and outputting a first signal correspondingly when the backlight element is turned on; sensing the light source and outputting a second signal correspondingly when the backlight element is turned off; computing a feedback signal according to the first signal and the second signal; calibrating optical performance of the backlight element according to the feedback signal. 
     The present invention also provides a light feedback control method including following steps: driving a backlight element and an ambient illuminating device intermittently and alternately; sensing a light source and outputting a feedback signal correspondingly when the backlight element is turned on; calibrating optical performance of the backlight element according to the feedback signal. 
     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 block diagram of a light feedback control system of a first embodiment of the present invention. 
         FIG. 2  is a schematic diagram showing an optical sensor sampling and outputting a feedback signal in the first embodiment of the present invention. 
         FIG. 3  is a block diagram of a light feedback control system of a second embodiment of the present invention. 
         FIG. 4  is a schematic diagram showing an optical sensor sampling and outputting a feedback signal in the second embodiment of the present invention. 
         FIG. 5  is a block diagram of a light feedback control system of a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     A light feedback control system of the present invention incorporates synchronizing control technology of an optical sensor into a display device (such as a flat display panel device or a flat TV that use light emitting diodes or cold cathode fluorescent lamps as a backlight light source), so as to obtain more precise feedback information for the backlight light source and to provide a correct feedback signal for the display device such that the lights emitted from the backlight light source of the display device can be optimized. 
     Please refer to  FIG. 1 .  FIG. 1  is a block diagram of a light feedback control system  100  of a first embodiment of the present invention. The light feedback control system  100  is implemented in a display device  10 , wherein the display device  10  includes a backlight unit  11  including a plurality of backlight elements  12  (only one backlight element is shown in  FIG. 1 ). In this embodiment, the backlight unit  11  can include backlight elements  12  such as cold cathode fluorescent lamps, white light emitting diodes, or light emitting elements  12  composed of red light LEDs, green light LEDs, and blue light LEDs. The backlight elements  12  are used for providing the display device  10  with a backlight and controlled to emit lights at a specific frequency by a light source driver  14 , which can be a pulse width modulation (PWM) circuit or an inverter. An optical sensor  13  is disposed in the backlight unit  11 . In practical application, the optical sensor  13  can be a color sensor capable of sensing light intensity and color signal of red, green, blue lights emitted from the emitting diodes, or a light sensor capable of sensing light intensity of the white light emitting diodes. 
     Since the optical sensor  13  in the backlight unit  11  senses not only a signal of the backlight elements  12  but also alight signal of an ambient light source  40  that penetrates a liquid crystal panel (not shown) and enters the backlight unit  11 , the ambient light source  40  affects the optical sensor  13  such that a sensing signal outputted from the optical sensor  13  is not only contributed by the backlight elements  12 . Accordingly, a controller  15  connected to the optical sensor  13  and the light source driver  14  is disposed in the light feedback control system  100 , and the controller  15  controls the optical sensor  13  to sense a light source both when the light source driver  14  drives the backlight elements  12  to be turned on and turned off so as to generate a plurality of signals correspondingly. When the light source driver  14  drives the backlight elements  12  in the backlight unit  11  to be turned on, the optical sensor  13  senses light intensity of a backlight light source of the backlight elements  12  adding a light source of the ambient light source  40 . When the light source driver  14  does not drive the backlight elements  12  of the backlight unit  11  to be turned on, the optical sensor  13  senses light intensity of the light source of the ambient light source  40 . The controller  15  then uses a subtractor  16  to subtract the ambient light source  40  according to the signals obtained from the optical sensor  13  in the aforesaid two situations so as to output a feedback signal simply generated by sensing the backlight elements  12 , and calibrates the optical performance of the backlight elements  12  of the display device  10 . 
     Please refer to  FIG. 2 .  FIG. 2  is a schematic diagram showing that the optical sensor  13  samples and outputs the feedback signal in the first embodiment. In order to control the optical sensor  13  to sense both when the backlight elements  12  is turned on and turned off, the light source driver  14  drives the backlight elements  12  at a specific frequency, and the controller  15  controls the optical sensor  13  to sense at a frequency doubling the specific frequency. Fox example, in  FIG. 2 , the backlight elements  12  generates a backlight signal  81  at a first frequency, the ambient light source  40  generates an ambient light signal  82 , and the optical sensor  13  outputs a sampling signal  83  at a frequency doubling the first frequency. In such a manner, the optical sensor  13  outputs a first signal  84  including the backlight signal  81  and the ambient light signal  82  and a second signal  85  including the ambient light signal  82  only. Then, a feedback control signal  86  simply contributed by the backlight elements  12  can be outputted by using the subtractor  16  to subtract the second signal  85  from the first signal  84 . Finally, the display device  10  calibrates the backlight light source generated by the backlight elements  12  according to the feedback signal  86 . 
     Furthermore, if the light emitting diode is used for illuminating the environment, the present invention can further combine the ambient light source and the output of the display device to make the display device have a better performance. Please refer to  FIG. 3 .  FIG. 3  is a block diagram of a light feedback control system  200  of a second embodiment of the present invention. The functions and the structures of a display device  20 , a backlight unit  21 , a backlight element  22 , an optical sensor  23 , and alight source driver  24  are similar to those in the first embodiment. In the second embodiment, the ambient light is provided by an ambient illuminating device  50 . Furthermore, in order to effectively implementing the system of the second embodiment of the present invention, the display device  20  for light feedback control is disposed in a space in which the ambient illuminating device  50  is the only ambient light source. Both of the ambient illuminating device  50  and the backlight element  22  are light emitting diodes or cold cathode fluorescent lamps driven by the light source drivers respectively. A communication interface  60  is further disposed between the ambient illuminating device  50  and the display device  20  and conveys signals between the ambient illuminating device  50  and the display device  20  in a wired (cable transmission interface) or a wireless (infrared ray interface or radio frequency) manner. The light illuminating device  50  is driven to emit lights by its light source driver, or it can also be driven by the light source driver  24  in the display device  20  via the communication interface  60 . The light source driver  24  in the display device  20  drives the backlight element  22  to emit light at a first frequency. The ambient illuminating device  50  conveys signals with the light source driver  24  via the communication interface  60  and generates an ambient light source at the first frequency. In this embodiment, the backlight element  22  and the ambient illuminating device  50  are driven to emit light alternately, that is, the light source driver  24  drives the backlight element  22  to emit light when the ambient illuminating device  50  is turned off. The controller  25  synchronizes with the light source driver  24  so as to drive the optical sensor  23 . Accordingly, the controller  25  can control the optical sensor  23  to sense only the backlight light source generated from the backlight element  22 . 
     Please refer to  FIG. 4 .  FIG. 4  is a schematic diagram showing that the optical sensor  23  samples and outputs the feedback signal in the second embodiment of the present invention. As shown in  FIG. 4 , the backlight element  22  is intermittently driven by the light source driver  24  for emitting a backlight signal  91 . The backlight signal  91  and an ambient light signal  92  emitted from the ambient illuminating device  50  are alternately generated, while a sampling signal  93  of the optical sensor  23  is generated synchronously with operation of the backlight element  22 . In such a manner, only the backlight signal  91  of the backlight element  22  in the backlight unit  21  can be sensed by the optical sensor  23  and is outputted as a feedback signal  94 , while the ambient illuminating device  50  is turned off and does not interfere with the optical sensor  23 . When the backlight element  22  is turned off and the optical sensor  23  stops sampling, the ambient illuminating device  50  is then driven to emit light. Accordingly, as the ambient light source is a light emitting diode that can be driven by the light source driver, the ambient light source and the backlight element of the backlight unit  21  can be easily driven in an alternate way. The optical sensor  23  of the display device  20  then can sense a more precise signal without being affected by the ambient light source. Furthermore, for the ambient illuminating device  50  that includes plural independent light emitting diode sources, the light emitting diode sources can be synchronized by conveying signals with the display device  20  via the communication interface  60  and to alternately emit lights in an aforesaid manner. 
     In the aforesaid light feedback control systems  100 , 200 , the optical sensors  13 , 23  for generating the feedback information are disposed in the backlight units  11 , 21  of the display devices  10 , 20 . According to a third embodiment of the present invention, the optical sensor may also be disposed outside the display device, such as on a remote control. In such a manner, the display device can control the light intensity and color of the liquid crystal panel more precisely. As a light feedback control system  300  shown in  FIG. 5 , the functions and the structures of a backlight unit  31 , a backlight element  32 , and a light source driver  34  in the display device  30  are similar to those in the aforesaid embodiments. In the third embodiment, the optical sensor  73  and the controller  75  are disposed on a remote control device  70  or on a wall outside the display device  30 . Both of the controller  75  and the ambient illuminating device  50  convey signals with the light source driver  34  in a wired or wireless manner via the communication interface  60 , and the light illumination device  50  is driven alternately with the optical sensor  73  and the backlight element  32 . In such a manner, the optical sensor  73  is controlled by the controller  75  to synchronously sense the backlight light source of the backlight element  32 , so as not to be interfered by the ambient light source of the ambient illuminating device  50 . Accordingly, the controller  75  transmits the feedback signal generated from the optical sensor  73  to the display device  30  via the communication device  60  for calibration of the display device  30 . 
     For the embodiment in  FIG. 5 , the first embodiment in  FIG. 1  may also be incorporated herein, i.e., the optical sensor  73  is controlled by the controller  75  to sense the backlight element  32  and the ambient light source at the double sampling frequency in a persisting ambient light source. Afterwards, a correct feedback signal can be obtained by using the subtractor to subtract the effect of the ambient light source. 
     In the light feedback control system of the present invention, the correct light feedback signal for the backlight source can be obtained by using the optical sensor disposed inside the backlight unit or outside the display device after subtracting the effect of ambient light sensed by the optical sensor when the backlight element is turned off. The optical sensor senses light intensity and the ambient light source at a double frequency of the frequency at which a backlight element emits light. The light feedback control system may further control the ambient light source and the backlight element and drive them to illuminate alternately, while the optical sensor synchronizes with the backlight element and senses light signals of the backlight element. Accordingly, exact information about the light intensity or color of the backlight element can be obtained for feedback control of the display device. 
     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.