Abstract:
A liquid crystal display (LCD) system for displaying three-dimensional video includes a backlight module for providing light, a liquid crystal panel for modifying brightness of the light, a backlight driver for controlling the backlight module according to a backlight module control signal, a temperature sensor for detecting temperature to generate a temperature signal, a television processor for increasing duty cycle of the backlight module control signal from a predetermined duty cycle to an increased duty cycle equaling sum of the predetermined duty cycle and an additional duty, and a shutter glasses control module coupled to the television processor for outputting a shutter glasses control signal according to the additional duty. The additional duty is based on the temperature signal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to liquid crystal display (LCD) devices for displaying three-dimensional (3D) video, and more particularly to a method for reducing left-eye/right-eye crosstalk in a 3D LCD device and related display system. 
         [0003]    2. Description of the Prior Art 
         [0004]    LCD displays utilize twisting of liquid crystal molecules to control transmission of light from a backlight module of the LCD display through red, green, and blue subpixel filters to display color images. Typical LCD displays include millions of pixels, each of which must be refreshed each time a displayed image changes. Speed with which the LCD display is able to refresh all of the pixels is referred to as “frame rate.” As LCD display technology has developed, frame rates have increased from 60 Hertz to 120 Hertz, and even 240 Hertz. 
         [0005]    Frame rates have quadrupled from 60 Hertz to 240 Hertz, which allows 3D video to be displayed at 120 Hertz by alternating left eye images and right eye images. However, because LCD devices adopt progressive scan for updating the pixels of the LCD device, some pixel rows are updated later than other pixel rows. If pixel rows updated relatively later are still updating while pixel rows updated relatively earlier start being updated again, crosstalk occurs between right eye and left eye images, causing degradation of 3D video quality for the viewer. One factor that affects crosstalk is operating temperature of the LCD device. If the LCD device is part of an end product that has an operating temperature range of 0-40° C., crosstalk level differs depending on the environment in which the LCD device is operated. 
       SUMMARY OF THE INVENTION 
       [0006]    According to an embodiment, a liquid crystal display (LCD) system for displaying three-dimensional video comprises a backlight module for providing light, a liquid crystal panel for modifying brightness of the light, a backlight driver for controlling the backlight module according to a backlight module control signal, a temperature sensor for detecting temperature to generate a temperature signal, a television processor for increasing duty cycle of the backlight module control signal from a predetermined duty cycle to an increased duty cycle equaling sum of the predetermined duty cycle and an additional duty, and a shutter glasses control module coupled to the television processor for outputting a shutter glasses control signal according to the additional duty. The additional duty is based on the temperature signal. 
         [0007]    According to an embodiment, a method of operating a liquid crystal display (LCD) system comprising an LCD panel, a backlight module, a television processor, a temperature sensor and a shutter glasses control module comprises the temperature sensor detecting temperature to generate a temperature signal, the television processor controlling the backlight module to output light at an increased duty cycle equaling sum of a predetermined duty cycle and an additional duty, and the shutter glasses control module outputting a shutter glasses control signal according to the additional duty. The additional duty is based on the temperature signal. 
         [0008]    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 
         [0009]      FIG. 1  is a diagram of a 3D LCD system according to an embodiment. 
           [0010]      FIG. 2  is a timing diagram illustrating operation of the 3D LCD system according to an embodiment. 
           [0011]      FIG. 3  and  FIG. 4  are timing diagrams of the backlight ON signal according to other embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Please refer to  FIG. 1 , which is a diagram of a 3D LCD system  10  according to an embodiment. The 3D LCD system  10  comprises a panel  100 , a backlight module  110 , and a television processor  120 . The backlight module  110  may be a cold cathode fluorescent lamp (CCFL) or light-emitting diode (LED) backlight module. The television processor  120  comprises a microprocessor  121 , a pulse width modulator (PWM)  122 , a low voltage differential signal (LVDS) transmitter  123 , a High Definition Multimedia Interface (HDMI) module  124 , an audio-video (AV) interface and tuner module  125 , a Universal Serial Bus (USB) and Ethernet controller  126 , and an analog-to-digital converter (ADC)  127 . A backlight driver  130  is electrically connected to the backlight module  110 , the microprocessor  121 , and the PWM  122 . The processor outputs two-dimensional (2D) and/or three-dimensional (3D) image control signals to the backlight driver  130 , and the PWM  122  outputs a pulse width modulated control signal to the backlight driver  130 . The backlight driver  130  drives the backlight module  110  according to the pulse width modulated control signal and the 2D/3D image control signal. The panel  100  is electrically connected to a panel timing controller  160 . The panel timing controller  160  is electrically connected to a frame rate conversion (FRC) and pattern formatting module  140 . The FRC and pattern formatting module  140  is electrically connected to the microprocessor  121  and the LVDS transmitter  123 . The LVDS transmitter  123  sends an LVDS signal at a first frequency, e.g. 60 Hz, to the FRC and pattern formatting module  140 . The FRC and pattern formatting module  140  sends an LVDS signal at a second frequency, e.g. 120 Hz or 240 Hz, to the panel timing controller  160 , and the panel timing controller sends a mini-LVDS signal at the second frequency to the panel  100  for controlling the panel  100 . The FRC and pattern formatting module  140  is further electrically connected to a first memory module  145 . An infrared emitter controller  142  is electrically connected to the FRC and pattern formatting module  140  for receiving a left/right synchronization signal. The infrared emitter controller  142  controls an infrared emitter  144  according to the left/right synchronization signal to emit a shutter glasses control signal as pulses of infrared light. The infrared emitter controller  142  and the infrared emitter  144  form a shutter glasses control module. Shutter glasses  150  receive the shutter glasses control signal for alternately turning on/shutting off left and right filters of the shutter glasses  150  in sync with display of the left and right images of the 3D video. The microprocessor  121  is further electrically connected to a second memory module  170  and a keypad/infrared input module  180 . 
         [0013]    The 3D LCD system  10  further comprises a temperature sensor  190  electrically connected to the ADC  127  for detecting operating temperature and/or ambient temperature of the 3D LCD system  10 , and generating a corresponding temperature signal to send to the ADC  127 . The ADC  127  converts the temperature signal to a digital temperature signal, and sends the digital temperature signal to the microprocessor  121 . The microprocessor  121  controls the PWM  122  according to the temperature signal to increase or decrease duty cycle of the backlight module  110  through the backlight driver  130 , so as to increase/decrease the operating temperature and/or ambient temperature. Thus, the temperature sensor  190 , the ADC  127 , the microprocessor  121 , the PWM  122 , the backlight driver  130 , and the backlight module  110  form a feedback loop for optimizing operating temperature/ambient temperature of the 3D LCD system  10  to reduce left-eye/right-eye crosstalk. 
         [0014]    Please refer to  FIG. 2 , which is a timing diagram illustrating operation of the 3D LCD system  10  according to an embodiment. In  FIG. 2 , operation of the 3D LCD system  10  is shown in comparison with operation of a 3D LCD system according to a traditional operation method. From time t 0  to time t 2 , a first left image is displayed; from time t 2  to time t 4 , a first right image is displayed; and from time t 4  to time t 6 , a second left image is displayed. In the traditional method, a backlight ON signal is asserted before the end of new image frame, e.g. before time t 2 , time t 4 , and time t 6  corresponding to display of the first left image, the first right image, and the second left image, and unasserted shortly thereafter. Shutter glasses switch from right filter to left filter (or vice versa) before the backlight ON signal switches from asserted to unasserted. Delay is generated between update of a last row of a panel and update of a first row of the panel. Thus, the asserted period of the backlight ON signal cannot entirely match saturated data for all rows, so the perceived image may include ingredients of the left-eye image and the right-eye image, and the viewer may continue to receive previous image frame information simultaneously with new image frame information (crosstalk). 
         [0015]    In the operation of the 3D LCD system  10  shown in  FIG. 2  (“temp. adjusted”), duty of a backlight ON signal is adjusted based on temperature measured by the temperature sensor  190 . For example, additional duty immediately precedes pulses of the backlight ON signal ending at time t 2 , time t 4 , and time t 6  (indicated by hashing). By increasing duty of the backlight ON signal, operating temperature of the backlight module  110  increases, which speeds up display of the first left image to time t 1 , as well as display of the first right image and the second left image to time t 3  and time t 5 , respectively. Brightness of the backlight module  110  is increased by increasing the duty of the backlight ON signal. Thus, duty of the shutter glasses control signal received by the shutter glasses  150  may decreased relative to increase of the duty of the backlight ON signal, as shown in  FIG. 2 . During display of the first left image, the left filter of the shutter glasses  150  is turned on in a period when the first row and the last row of the panel  100  are both fully updated. The period may correspond to an asserted period of the backlight ON signal minus the additional duty. During display of the first right image, the right filter of the shutter glasses  150  is turned on in a period when the first row and the last row of the panel  100  are both fully updated. Thus, crosstalk is reduced while maintaining the same brightness. 
         [0016]    Please refer to  FIG. 3  and  FIG. 4 , which are timing diagrams of the backlight ON signal according to other embodiments. As shown in  FIG. 3 , the additional duty may be added immediately following the pulses of the backlight ON signal ending at time t 1  and time t 4 . The additional duty may run from time t 1  to time t 2 , and from time t 4  to time t 5 . As shown in  FIG. 4 , the additional duty may be added at a time t 2  following a trailing edge of a first pulse of the backlight ON signal, and preceding a leading edge of a second pulse of the backlight ON signal. The first pulse may run from time t 0  to time t 1 , and the second pulse may run from time t 4  to time t 5 . 
         [0017]    In the 3D LCD system  10  shown in  FIG. 2 , 3D image left-eye/right-eye crosstalk is reduced by actively adjusting LCD operating temperature. Temperature adjustment is achieved through use of control mechanisms common to current generation liquid-type display devices (TV, monitor, public display, etc.). 
         [0018]    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.