Abstract:
A liquid crystal display device including: a signal converter which converts a selectively input analog image signal into a digital image signal according to a sampling clock; a scaler which samples the digital image signal output by the signal converter, to render the digital image signal suitable for a resolution, according to the sampling clock, and generates a horizontal synchronization signal of the input analog image signal; a controller which detects the horizontal synchronization signal and generates the sampling clock according to the detected horizontal synchronization signal; an inverter which is synchronized with the digital image signal and which generates a pulse signal used to drive the backlight; and a panel driver which receives the sampled image signal from the scaler and displays the received signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the priority of Korean Patent Application No. 2003-33342, filed on May 26, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device which controls operations of backlights by comparing a power source for driving the backlights to a power source for driving a video processing board, the power sources being supplied separately from each other.  
         [0004]     2. Description of Related Art  
         [0005]     As demands for display devices increase, lower power consumption which is directly related to usable time of the device is researched actively. Especially, in case of the display device used in portable devices with screens, liquid crystal displays (LCD) are mainly used as the displays. The LCD device, which was developed for substituting a cathode ray tube (CRT), has advantages such as small size, light weight, and low power consumption, thus the LCD is also used in a large scale information display apparatus as well as in a laptop computer and a desktop computer.  
         [0006]     Since the LCD device cannot illuminate itself, information is displayed by reflecting outer light passing through an LCD panel or by installing an additional light source, that is, a backlight assembly on a back surface of the LCD panel.  
         [0007]     The backlight assembly includes a lamp unit for radiating the light, a light guide panel for guiding the light radiated from the lamp unit toward the LCD panel, and optical sheets for diffusing and condensing the light guided by the light guide panel to improve an efficiency of the light.  
         [0008]     The lamp unit includes a lamp used as the light source of the LCD device, a reflecting panel for reflecting the light radiated from the lamp to improve the light efficiency, and an inverter connected to the lamp using a wire to apply a voltage to the lamp.  
         [0009]     Recently, as LCD devices have become larger, a direct type LCD device, in which the backlight is directly installed on the LCD, has been used.  
         [0010]     The number of backlights increases for forming higher brightness, thus power consumption of the backlights also increases. Therefore, since larger power consumption should be dealt with the low voltage of single power source, some problems such as power efficiency and heat generation are caused.  
         [0011]     When a power source of the inverter and the power source of an image board are supplied independently, status information of the inverter is not transmitted to the image board, thus causing a phenomenon that the displayed state is continued even when the backlight power source in the inverter is turned off. Especially, the backlight which consumes more electric power than the image board, is turned off earlier than the image board when the power source is turned on right after the power source is turned off due to an instant electric failure. In addition, when the power source is turned on before the image board is reset (the power source is turned on after the electric failure), the display is made in a state that the power source of the backlight is turned off.  
       BRIEF SUMMARY  
       [0012]     The present invention provides a liquid crystal display device, which controls turning-on and turning-off of backlights by comparing a power source for driving the backlight to a power source for driving a video processing board which are supplied separately.  
         [0013]     According to an aspect of the present invention, there is provided a liquid crystal display device including: a signal converter which converts a selectively input analog image signal into a digital image signal according to a sampling clock; a scaler which samples the digital image signal output by the signal converter, to render the digital image signal suitable for a resolution, according to the sampling clock, and generates a horizontal synchronization signal of the input analog image signal; a controller which detects the horizontal synchronization signal and generates the sampling clock according to the detected horizontal synchronization signal; an inverter which is synchronized with the digital image signal and which generates a pulse signal used to drive the backlight; and a panel driver which receives the sampled image signal from the scaler and displays the received signal.  
         [0014]     The inverter unit may include: a comparer which compares a first power source supplied to the panel driver with a second power source that is supplied separately from the first power source, and which outputs a comparing result signal; an inverter controlling pulse width modulator which generates a pulse width modulation signal synchronized with the horizontal synchronization signal, and is turned on or off according to the comparing result signal; a switching transformer which switches on or off the power source according to the pulse signal; and a backlight which radiates light when powered by the power source.  
         [0015]     According to another aspect of the present invention, there is provided a liquid crystal display device including: a signal converter which converts a selectively input analog image signal into a digital image signal according to a sampling clock; a scaler which samples the digital image signal output by the signal converter, to render the digital image signal suitable for a resolution, according to the sampling clock, and generates a horizontal synchronization signal of the input analog image signal; a comparer which compares a first power supplied to the panel driver with a second power that is supplied separately from the first power, and which outputs a comparing result signal; a controller which detects the horizontal synchronization signal and generates the sampling clock according to the detected horizontal synchronization signal; an inverter which is synchronized with the digital image signal and which generates a pulse signal used to drive a backlight; and a panel driver which receives the sampled image signal from the scaler and displays the received signal on a liquid crystal panel. The controller outputs inverter on/off signals which turn the inverter on and off, respectively, according to the comparing result signal.  
         [0016]     According to another aspect of the present invention, there is provided a method of improving an efficiency of an LCD illuminated by a backlight, including: comparing a first power for driving the backlight to a second power for driving a video processing board which controls a display of an image on the LCD; and turning-on/turning-off a backlight continuous in accordance with the comparing result, wherein the second power source is separate from the first power source.  
         [0017]     Additional and/or other aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     These and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following detailed description, taken in conjunction with the accompanying drawings of which:  
         [0019]      FIG. 1  is a block diagram of a configuration of a liquid crystal display device according to an embodiment of the present invention;  
         [0020]      FIG. 2  is a detailed view of an inverter unit in  FIG. 1 ;  
         [0021]      FIG. 3  is a detailed view of a comparing unit in  FIG. 2 ;  
         [0022]      FIG. 4  is a block diagram of a configuration of a liquid crystal display device according to another embodiment of the present invention;  
         [0023]      FIG. 5  is a detailed view of a comparing unit in  FIG. 4 ; and  
         [0024]      FIG. 6  is a detailed view of an inverter unit in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0025]     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
         [0026]      FIG. 1  is a block diagram of a configuration of a liquid crystal display (LCD) device according to a first embodiment of the present invention. The LCD device includes a switching mode power supply (SMPS)  100 , a video processing board  101 , and an LCD panel  102 . The video processing board  101  includes a power source unit  101 - 1 , a signal selection unit  101 - 2 , a radio frequency (RF) tuner  101 - 3 , a signal conversion unit  101 - 4 , a controlling unit  101 - 5 , a scaler  101 - 6 , and a digital transmission unit  101 - 7 . The LCD panel includes an inverter unit  102 - 1 , a panel driving unit  102 - 2 , and a backlight  102 - 3  (shown in  FIG. 2 ).  
         [0027]      FIG. 2  is a detailed view of the inverter unit  102 - 1  of  FIG. 1 . The inverter unit  102 - 1  includes an inverter controlling pulse width modulation (PWM) unit  102 - 11 , a comparing unit  102 - 12 , and a switching transformer  102 - 13 .  
         [0028]      FIG. 3  is a detailed view of the comparing unit  102 - 12  in  FIG. 2 .  
         [0029]     The present embodiment will be described with reference to  FIGS. 1 through 3 .  
         [0030]     The SMPS  100  generates a first power source (Vin) driving the video processing board  101  and a second power source (Vin(DC)) input into the switching transformer  102 - 13  for driving the backlight  102 - 3 . The video processing board  101  is operated with a low voltage of 5V˜12V, and the backlight  102 - 3  is operated with a high voltage of 120V. The SMPS  100  generates the first and second power sources separately in order to provide the two different voltages.  
         [0031]     The video processing board  101  processes an input video signal.  
         [0032]     The power source unit  101 - 1  generates a power source for driving the video processing board  101  with the first power source supplied from the SMPS  100 .  
         [0033]     The signal selection unit  101 - 2  selects a desired signal, for example, a PC signal, a DTV signal, or one of R/G/B image signals, an RF signal, or CVBS signals generated from the RF tuner  101 - 3  according to a selection signal of the controlling unit  101 - 5 .  
         [0034]     The signal conversion unit  101 - 4  converts the signal selected in the signal selection unit  101 - 2  into a digital image signal by sampling the signals according to a sampling clock supplied from the controlling unit  101 - 5 .  
         [0035]     The scaler  101 - 6  performs an up-sampling or a down-sampling operation of the digital image signal input from the signal conversion unit  1014  to correspond to a resolution of the panel using a clock pulse generated in the controlling unit  101 - 5 . Also, the scaler  101 - 6  generates a horizontal synchronization signal of the sampled image signal.  
         [0036]     The controlling unit  101 - 5  receives a user selected key signal and applies the selection signal to the signal selection unit  101 - 2 , and discriminates the display mode by detecting a horizontal or a vertical synchronization signal from the signal selected in the signal selection unit  101 - 2 . Also, the controlling unit  101 - 5  applies the sampling clock to the signal conversion unit  1014  and the scaler  101 - 6  so that the signal is processed according to the display mode, and receives the user selected key signal and applies the selection signal to the signal selection unit  101 - 2 . In addition, the controlling unit  101 - 5  generates inverter on/off signals for turning on/off the inverter operation according to an outer selection condition.  
         [0037]     The digital transmission unit  101 - 7  transmits the digital image signal converted in the scaler  101 - 6  in a low voltage differential signal (LVDS) format.  
         [0038]     The LCD panel  102  receives the signal from the video processing board  101  and displays it.  
         [0039]     The inverter unit  102 - 1  generates a PWM signal synchronized with the horizontal synchronization signal generated in the scaler  101 - 6 , and drives the backlight  102 - 3  using the PWM signal. The inverter unit  102 - 1  is turned on/off according to a result of comparing the first and second power sources output from the SMPS  100 .  
         [0040]     The panel driving unit  102 - 2  displays the digital signal, which is transmitted from the digital transmission unit  101 - 7  in the LVDS format, on the liquid crystal panel. That is, the panel driving unit  102 - 2  performs on/off switching operations to drive the LCD panel by inputting scaled image data or gain-controlled image data into the LCD panel or generates a driving signal corresponding to the brightness of the image data.  
         [0041]     Referring to  FIGS. 2 and 3 , the inverter controlling PWM unit  102 - 11  synchronizes with the horizontal synchronization signal output from the scaler  101 - 6  of the video processing board  101  to generate a PWM signal, and is turned on/off according to the inverter on/off signals generated in the controlling unit  101 - 5  of the video processing board  101 . For example, a falling edge or a rising edge of the horizontal synchronization signal is synchronized with a falling edge or a rising edge of the PWM signal. Also, the inverter controlling PWM unit  102 - 11  receives a brightness controlling signal to control the brightness of the backlight  102 - 3 . However, the operation of the inverter controlling PWM unit  102 - 11  is controlled by the comparing result signal of the comparing unit  102 - 12 .  
         [0042]     The comparing unit  102 - 12  compares the first power source transmitted from the video processing board  101  to the second power source input into the switching transformer  102 - 13  from the SMPS  100  for driving the backlight  102 - 3 . The comparing unit  102 - 12  uses the first power source as a reference value.  
         [0043]      FIG. 3  is a detailed view of the comparing unit  102 - 12 . A comparator compares the first power source (Vin) divided by resistances R 3  and R 4  to the second power source (Vin(DC)) divided by resistances R 1  and R 2 , and turns on/off the inverter controlling PWM unit  102 - 11  according to the compared result.  
         [0044]     When the first power source is smaller than the second power source, the comparator outputs a high signal to turn Q 1  on. When Q 1  is turned on, the first power source is input into the inverter controlling PWM unit  102 - 11 , and the inverter controlling PWM unit  102 - 11  is turned on. However, when the first power source is larger than the second power source, the comparator outputs a low signal to turn Q 1  off. When Q 1  is turned off, the first power source is not input into the inverter controlling PWM unit  102 - 11 , and the inverter controlling PWM unit  102 - 11  is in the turn-off status.  
         [0045]     When the inverter controlling PWM unit  102 - 11  is operated when the second power source is not set, the PWM duty which is generated in the inverter controlling PWM unit  102 - 11  for supplying more power to the backlight  102 - 3  is excessively generated and a shut-down phenomenon happens. For preventing the shut-down phenomenon, the power source (first power source) input into the inverter controlling PWM unit ( 102 - 11 ) is blocked until the second power source becomes larger than the first power source.  
         [0046]     Also, in an instant electric failure, the backlight power source (second power source) having larger power consumption is discharged rapidly. Therefore, when the second power source becomes smaller than the first power source, the operating power source of the inverter controlling PWM unit  102 - 11  is blocked by Q 1 , and when a stable second power source is applied, the inverter controlling PWM unit  102 - 11  is reset and reoperated to prevent the continued backlight  102 - 3  turning-off phenomenon.  
         [0047]     The switching transformer  102 - 13  is operated by the second power source, that is, the backlight power source (Vin(DC)) input from the SMPS  100 , and generates DC switching power source according to PWM signal input from the inverter controlling PWM unit  102 - 11 .  
         [0048]     The backlight  102 - 3  radiates the light using the switching power applied from the switching transformer  102 - 13 .  
         [0049]      FIG. 4  is a block diagram of a configuration of an LCD device according to a second embodiment of the present invention, and the LCD device includes an SMPS  400 , a video processing board  401 , and an LCD panel  402 . The video processing board  401  includes a power source unit  401 - 1 , a signal selection unit  401 - 2 , an RF tuner  401 - 3 , a signal conversion unit  401 - 4 , a controlling unit  401 - 5 , a scaler  401 - 6 , a comparing unit  401 - 7 , and a digital transmission unit  401 - 8 . The LCD panel of the present invention includes an inverter unit  402 - 1 , a panel driving unit  402 - 2 , and a backlight  402 - 3 .  
         [0050]      FIG. 5  is a detailed view of the comparing unit  401 - 7  in  FIG. 4 .  FIG. 6  is a detailed view of the inverter unit  402 - 1  in  FIG. 4 , and the inverter unit  402 - 1  includes an inverter controlling PWM unit  402 - 11 , and a switching transformer  402 - 12 .  
         [0051]     The present embodiment will be described with reference to  FIGS. 4 through 6 .  
         [0052]     The SMPS  400  generates first power source (Vin) driving the video processing board  401  and second power source (Vin(DC)) input into a switching transformer  402 - 12  for driving the backlight  402 - 3 . The video processing board  401  is operated by a low voltage of 5V˜12V, and the backlight  402 - 3  is operated by a high voltage of 120V. The SMPS  400  generates the first power source and the second power source separately to provide the two different voltage conditions.  
         [0053]     The video processing board  401  processes an input video signal. The power source unit  401 - 1  generates a power source for driving the video processing board  401  using the first power source input from the SMPS  400 .  
         [0054]     The signal selection unit  401 - 2  selects a desired signal, for example, one of a PC signal, DTV signal, R/G/B image signals or RF signal generated in RF tuner  401 - 3 , and CVBS signals according to a selection signal of the controlling unit  401 - 5 .  
         [0055]     The signal conversion unit  4014  converts the signal selected in the signal selection unit  401 - 2  into a digital image signal by sampling those signals according to a sampling clock supplied from the controlling unit  401 - 5 .  
         [0056]     The scaler  401 - 6  performs up-sampling or down-sampling operation of the digital RGB image signal input from the signal conversion unit  4014  using a clock pulse generated in the controlling unit  401 - 5  according to the controlling signal of the controlling unit  401 - 5  to make the signal suitable for the resolution of the panel, and generates a horizontal synchronization signal of the sampled image signal.  
         [0057]     The controlling unit  401 - 5  receives a user-selected key signal and applies the selection signal to the signal selection unit  401 - 2 , and discriminates the display mode by detecting horizontal or vertical synchronization signal from the signal selected in the signal selection unit  401 - 2 . Also, the controlling unit  401 - 5  applies the sampling clock to the signal conversion unit  401 - 4  and the scaler  401 - 6  so that the signal is processed according to the display mode, and receives the user selected key signal and applies the selection signal to the signal selection unit  401 - 2 .  
         [0058]     Also, the controlling unit  401 - 5  generates inverter on/off signals for turning on/off the inverter according to the result of comparison in the comparing unit  401 - 7 . The comparing unit  401 - 7  may be included is includable in the video processing board  401  as shown in  FIG. 4 , and may be disposable on an outer side of the video processing board  401 . The comparing unit  401 - 7  compares the first power source transmitted from the power source unit  401 - 1  to the second power source input into the switching transformer  402 - 13  from the SMPS  400  for driving the backlight  402 - 3 . The comparing unit  401 - 7  uses the first power source as a reference value.  
         [0059]      FIG. 5  is a detailed view of the comparing unit  401 - 7 . A comparator compares the first power source (Vin) divided by resistances R 3  and R 4  to the second power source (Vin(DC)) divided by resistances R 1  and R 2 , and turns on/off the inverter controlling PWM unit  102 - 11  according to the compared result. When the first power source is smaller than the second power source, the comparator outputs a high signal. When the comparator outputs the high signal, the controlling unit  401 - 5  receives the signal and turns the inverter unit  402 - 1  on. However, when the first power source is larger than the second power source, the comparator outputs a low signal. When the comparator outputs a low signal, the controlling unit  401 - 5  receives the signal and turns the inverter unit  402 - 1  off.  
         [0060]     The digital transmission unit  401 - 8  transmits the digital image signal converted in the scaler  401 - 6  in an LVDS format.  
         [0061]     The LCD panel  402  receives the signal from the video processing board  401  and displays it.  
         [0062]     The inverter unit  402 - 1  outputs a PWM signal as synchronizing with the horizontal synchronization signal generated in the scaler  401 - 6 , operates the backlight  402 - 3  using the PWM signal, and is turned on/off according to the control of the controlling unit  401 - 5 .  
         [0063]     The panel driving unit  402 - 2  displays the digital RGB signal, which is transmitted from the digital transmission unit  401 - 8  in the LVDS format, on the liquid crystal panel. That is, the panel driving unit  402 - 2  performs on/off switching operations so as to drive the liquid crystal panel by inputting scaled image data or gain-controlled image data into the liquid crystal panel, or generates a driving signal corresponding to the brightness of the image data.  
         [0064]     Referring to  FIG. 6 , an inverter controlling PWM unit  402 - 11  synchronizes with the horizontal synchronization signal output from the scaler  401 - 6  of the video processing board  401  to generate the PWM signal, and is turned on/off according to the inverter on/off signals generated in the controlling unit  401 - 5  of the video processing board  401 . For example, a falling edge or a rising edge of the horizontal synchronization signal is synchronized with a falling edge or a rising edge of the PWM signal. Also, the inverter controlling PWM unit  402 - 11  receives a brightness controlling signal and controls the brightness of the backlight  402 - 3 .  
         [0065]     If the inverter controlling PWM unit  402 - 11  is operated when the second power source is not set, PWM duty generated by the inverter controlling PWM unit  402 - 11  for supplying more power to the backlight  402 - 3  is excessively formed and a shut-down phenomenon happens. In order to prevent the shut-down phenomenon, the controlling unit  401 - 5  blocks the power source input into the inverter controlling PWM unit  402 - 11  (first power source) until the second power source becomes larger than the first power source, when the liquid crystal panel is initially operated.  
         [0066]     Also, in an instant electric failure, the power source (second power source) of the backlight  402 - 3  having larger power consumption is discharged rapidly. Therefore, when the second power source becomes smaller than the first power source, the controlling unit  401 - 5  turns the inverter unit  402 - 1  off to block the operating power source of the inverter controlling PWM unit  402 - 11 . When a stable second power source is applied, the inverter controlling PWM unit  402 - 11  is reset to prevent the backlight  402 - 3  turning-off phenomenon.  
         [0067]     The switching transformer  402 - 12  is operated by the second power source, that is, the backlight power source (Vin(DC)) input from the SMPS  400 , and generates DC switching electric power according to the PWM signal input from the inverter controlling PWM unit  402 - 11 .  
         [0068]     The backlight  402 - 3  radiates the light with the switching electric power applied from the switching transformer  402 - 11 .  
         [0069]     As described above, continuous turning-on/turning-off of the backlight is controlled by comparing the power source for driving the backlight to the power source for driving the video processing board which are supplied separately, thus improving the efficiency of the LCD.  
         [0070]     Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the described embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.