Abstract:
An LCD includes a display panel, a plurality of fluorescent lamps, an electric field sensor, and an inverter. The electric field sensor senses electric fields of the plurality of fluorescent lamps to generate a voltage. The inverter is electrically connected the plurality of fluorescent lamps, and generates a driving voltage to drive the plurality of fluorescent lamps. The inverter adjusts an operating frequency of the driving voltage according to the voltage. Thus, the waving phenomenon of the LCD is improved effectively.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a Liquid Crystal Display (LCD), and more particularly, to an LCD improving a waving phenomenon. 
         [0003]    2. Description of the Prior Art 
         [0004]    The conventional backlight module of an LCD employs Cold Cathode Fluorescent Lamps (CCFL) as light source. When the CCFLs operate steadily, the CCFLs require sine wave without DC portion at the frequency around 30˜80 KHz as for power supplying, wherein the operating voltage during the CCFLs operate steadily is almost a constant. The brightness of the CCFLs is decided by the current flowing through the CCFLs. In actual applications, the CCFLs are driven with a fixed frequency and this manner is generally adopted because it is easier to control noises generated on the CCFLs. However, in the applications for LCDs of big sizes, because the number of the CCFLs is greatly increased, the high-frequency noises are greatly increased. Since the ends of the CCFLs are driven by high voltages (about 1000V), the Electro-Magnetic Interference (EMI) generated from the inverters and the CCFLs affect the display panel of the LCD. Furthermore, if the operating frequency of the inverter and the scanning frequency of the gate driver are not synchronized, the waving phenomenon is generated in the displayed frames of the display panel. Generally, waving stripes are horizontal stripes moving upwards and downwards, and the positions of the waving stripes relate to the operating frequency of the inverter. 
         [0005]    Please refer to  FIG. 1 .  FIG. 1  is a diagram illustrating the conventional LCD changing the polarities of the driving voltages of the CCFLs for improving the waving phenomenon. The LCD  10  comprises a display panel  12 , an inverter  14 , and a plurality of CCFLs  16 . Since the waving stripes relate to the operating frequency of the inverter, changing the electric field effect is able to improve the waving phenomenon, which is changing polarities of two adjacent CCFLs  16  for eliminating the two adjacent electric fields of inverse directions. The arrangements of the polarities of the CCFLs  16  comprise the following manners:
   1. “++++++”, which has the highest electric field effect;   2. “++−−++”, which has the normal electric field effect; and   3. “+−+−+−”, which has the lowest electric field effect.   
 
         [0009]    The arrangement of the CCFLs of  FIG. 1  is the manner  3  (the lowest one). Changing the arrangement of the polarities of the CCFLs and adjusting the operating frequency of the inverter for improving the waving phenomenon has to cooperate with human eyes in order to adjust the operating frequency of the inverter for generating lighter waving phenomenon. In this way, the electric fields eliminate each other and the waving phenomenon can be improved. However, different displayed frames come with waving phenomena of different degrees. Therefore, changing the arrangement of the polarities of the CCFLs and adjusting the operating frequency of the inverter do not effectively improve waving phenomena for all kinds of displayed frames. 
         [0010]    Please refer to  FIG. 2 .  FIG. 2  is a diagram illustrating a conventional LCD utilizing synchronous signals for improving the waving phenomenon. The LCD  20  comprises a display panel  22 , an inverter  24 , a plurality of CCFLs  26 , and a synchronization circuit  28 . By synchronizing the operating frequency of the CCFLs and the scanning frequency of the gate driver, the waving phenomenon is also improved, and such manner is not limited to particular displayed frames. The synchronization circuit  28  generates a synchronous frequency Sf according to the scanning frequency of the gate driver. In this way, the inverter  24  generates the operating frequency Lf synchronized to the scanning frequency of the gate driver according to the synchronous frequency Sf. However, the design of the synchronization circuit  28  is complicated, and the range of the synchronous frequency (the scanning frequency) is limited to the endurable range of the inverter  24 , which greatly reduces the applicability of the above-mentioned structure. 
       SUMMARY OF THE INVENTION  
       [0011]    The present invention provides an LCD improving waving phenomenon. The LCD comprises a display panel, a plurality of CCFLs installed under the display panel, a first electric field sensor for sensing an electric field generated by the plurality of the CCFLs for generating a first voltage, and an inverter electrically connected to the plurality of the CCFLs for generating a driving voltage to drive the plurality of the CCFLs, wherein the inverter adjusts operating frequency of the driving voltage according to the first voltage. 
         [0012]    The present invention further provides a method for improving waving phenomenon of an LCD. The method comprises sensing an electric field generated by CCFLs of a backlight module of the LCD, and adjusting operating frequency of a driving voltage of the CCFLs according to the sensed electric field. 
         [0013]    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  
         [0014]      FIG. 1  is a diagram illustrating the conventional LCD changing the polarities of the driving voltages of the CCFLs for improving the waving phenomenon. 
           [0015]      FIG. 2  is a diagram illustrating a conventional LCD utilizing synchronous signals for improving the waving phenomenon. 
           [0016]      FIG. 3  is a diagram illustrating a first embodiment of the LCD of the present invention. 
           [0017]      FIG. 4 ,  FIG. 5 , and  FIG. 6  are diagrams illustrating the positions of the installation for the first and the second electric field sensors according to the first embodiment of the present invention. 
           [0018]      FIG. 7  is a diagram illustrating a second embodiment of the LCD of the present invention. 
           [0019]      FIG. 8  is a diagram illustrating the installing position of the electric field sensor of the second embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0020]    Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, electronic equipment 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. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ” Also, the term “electrically connect” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
         [0021]    Please refer to  FIG. 3 .  FIG. 3  is a diagram illustrating a first embodiment of the LCD of the present invention. The LCD  30  comprises a display panel  32 , an inverter  34 , a plurality of CCFLs  36 , a first electric field sensor  381 , and a second electric field sensor  382 . The inverter  34  comprises a comparator  341 , and a micro-controller  342 . The comparator  341  compares the voltage S 1  sensed by the first electric field sensor  381  and the voltage S 2  sensed by the second electric field sensor  382 . The micro-controller  342  adjusts the operating frequency of the inverter  34  according to the output voltage Sout outputted from the comparator  341 . Because the waving phenomenon is generated from the EMI affecting the liquid crystal of the display panel and the un-synchronization between the operating frequency of the CCFLs and the scanning frequency of the gate driver, in the present embodiment, the LCD  30  utilizes two electric field sensors  381  and  382  for respectively sensing the highest and the lowest electric fields and decides if the operating frequency of the inverter  34  has to be adjusted according to the difference between the highest and the lowest electric fields, so as to improve the waving phenomenon. 
         [0022]    Please refer to  FIG. 4 ,  FIG. 5 , and  FIG. 6 .  FIG. 4 ,  FIG. 5 , and  FIG. 6  are diagrams illustrating the positions of the installation for the first electric field sensor  381  and the second electric field sensor  382  according to the first embodiment of the present invention. The arrangements of the polarities of the driving voltages of the CCFLs  36  comprise the following manners:
   1. “++++++” as shown in  FIG. 4 , which has the highest electric field effect;   2. “++−−++” as shown in  FIG. 5 , which has the normal electric field effect; and   3. “+−+−+−” as shown in  FIG. 6 , which has the lowest electric field effect.   
 
         [0026]    Since the arrangements of the polarities of the driving voltages of the CCFLs  36  affect the electric fields, the positions of the highest and the lowest electric fields of the above-mentioned arrangements are different. In  FIG. 4 , the highest electric field, generated from the arrangement “++++++”, is positioned at the top of the CCFLs  36 , which is the position that the first electric field sensor  381  is installed in, and the lowest electric field, generated from the arrangement “++++++”, is positioned at the middle of any two of the CCFLs  36 , which is the position that the second electric field sensor  382  is installed in. In  FIG. 5 , the highest electric field, generated from the arrangement “++−−++”, is positioned at the top of the CCFLs  36 , which is the position that the first electric field sensor  381  is installed in, and the lowest electric field, generated from the arrangement “++−−++”, is positioned at the middle of two adjacent CCFLs having the same polarity of the CCFLs  36 , which is the position that the second electric field sensor  382  is installed in. In  FIG. 6 , the highest electric field, generated from the arrangement “+−+−+−”, is positioned at the top of the CCFLs  36 , which is the position that the first electric field sensor  381  is installed in, and the lowest electric field, generated from the arrangement “++++++”, is positioned at the middle of two adjacent CCFLs having opposite polarities of the CCFLs  36 , which is the position that the second electric field sensor  382  is installed in. 
         [0027]    After the installing positions in the display panel  32  of the first electric field sensor  381  and the second electric sensor  382  are decided according to the arrangements of the polarities of the driving voltages of the CCFLs  36 , the first electric field sensor  381  and the second electric field sensor  382  sense the magnitudes of electric fields and convert the sensed magnitudes to digital values and transmit the digital values to the inverter  34 . The two digital values are compared and then transmitted to the micro-controller  342  for executing feedback determination. Assuming the range of the operating frequency of the inverter  34  is Δf=fmax−fmin, when the output voltage Sout is higher than a predetermined value A (Sout=|S 1 −S 2 |&gt;A), the micro-controller  342  adjusts the operating frequency of the inverter  34 . The adjustment of the micro-controller  342  for the inverter  34  comprises three phases: 
         [0028]    Phase 1: Within the operating frequency Δf, adjusting the operating frequency for the output voltage Sout being lower than the predetermined value A; 
         [0029]    Phase 2: Scanning the operating frequency Δf, and selecting the operating frequency corresponding to a smallest output voltage Sout among the operating frequencies corresponding to the output voltages Sout lower than the predetermined value A; and 
         [0030]    Phase 3: Selecting the operating frequency corresponding to a smallest output value if within the operating frequency Δf, the frequency corresponding to the output voltage Sout lower than the predetermined value A cannot be found. 
         [0031]    When the output voltage Sout is smaller or equal to the predetermined value A (Sout=|S 1 −S 21 |≦A), the micro-controller  342  adjusts the operating frequency of the inverter  34 . The adjustment of the micro-controller  342  for the inverter  34  comprises two phases: 
         [0032]    Phase 1: Keeping the current operating frequency; and 
         [0033]    Phase 2: Periodically scanning the operating frequency Δf, and selecting the operating frequency corresponding to a smallest output voltage Sout among the operating frequencies corresponding to the output voltages Sout lower than the predetermined value A. 
         [0034]    Because the magnitude of the predetermined value A is proportional to the degree of the waving phenomenon (when the predetermined value A equals to 0, it means no waving phenomenon occurs), it can be seemed as a standard if the predetermined value A is set to 0. The phases of the micro-controller  342  adjusting the operating frequency of the inverter  34  improve the waving phenomenon differently, but the predetermined value A is defined as the average electric field value within ±5%. 
         [0035]    Please refer to  FIG. 7 .  FIG. 7  is a diagram illustrating a second embodiment of the LCD of the present invention. The LCD  40  comprises a display panel  42 , an inverter  44 , a plurality of CCFLs  46 , and an electric field sensor  48 . The inverter  44  comprises a comparator  441  and a micro-controller  442 . The comparator  441  compares the voltage S sensed by the electric field sensor  48  with a reference voltage Sref. The micro-controller  442  adjusts the operating frequency of the inverter  44  according to the output voltage Sout outputted from the comparator  441 . In the present embodiment, the LCD  40  utilizes one single electric field sensor  48  for sensing the highest electric field of the LCD  40 . Generally, the position of the highest electric field is the position where the waving phenomenon occurs most obviously and seriously. The micro-controller  442  decides if the operating frequency of the inverter  44  has to be adjusted according to the highest electric field and accordingly improves the waving phenomenon. 
         [0036]    Please refer to  FIG. 8 .  FIG. 8  is a diagram illustrating the installing position of the electric field sensor  48  of the second embodiment of the present invention. In the present embodiment, the electric field sensor  48  is installed at the position where the highest electric field occurs, which is the top of the CCFL  46 . Assuming the range of the operating frequency of the inverter  44  is Δf=fmax−fmin, when the output voltage Sout is higher than a predetermined value B (Sout=|S 1 −Sref|&gt;B), the micro-controller  442  adjusts the operating frequency of the inverter  44 . The adjustment of the micro-controller  442  for the inverter  44  comprises three phases: 
         [0037]    Phase 1: Within the operating frequency Δf, adjusting the operating frequency for the output voltage Sout being lower than the predetermined value B; 
         [0038]    Phase 2: Scanning the operating frequency Δf, and selecting the operating frequency corresponding to a smallest output voltage Sout among the operating frequencies corresponding to the output voltages Sout lower than the predetermined value B; and 
         [0039]    Phase 3: Selecting the operating frequency corresponding to a smallest output value if within the operating frequency Δf, the frequency corresponding to the output voltage Sout lower than the predetermined value B cannot be found. 
         [0040]    When the output voltage Sout is smaller or equal to the predetermined value B (Sout=|S 1 −Sref|≦A), the micro-controller  442  adjusts the operating frequency of the inverter  44 . The adjustment of the micro-controller  442  for the inverter  44  comprises two phases: 
         [0041]    Phase 1: Keeping the current operating frequency; and 
         [0042]    Phase 2: Periodically scanning the operating frequency Δf, and selecting the operating frequency corresponding to a smallest output voltage Sout among the operating frequencies corresponding to the output voltages Sout lower than the predetermined value B. 
         [0043]    Because the magnitude of the predetermined value B is proportional to the degree of the waving phenomenon (when the predetermined value B equals to 0, it means no waving phenomenon occurs), it can be seemed as a standard if the predetermined value B is set to 0. The phases of the micro-controller  442  adjusting the operating frequency of the inverter  44  improve the waving phenomenon differently, but the predetermined value B is defined as the average electric field value within ±5%. 
         [0044]    From the description above, it can be understood that the present invention does not have to adjust the operating frequency of the inverter by human eyes for improving the waving phenomenon, and also does not adjust the operating frequency of the inverter when the displayed frames are different. Furthermore, the design of the present invention is much simpler but also improves the waving phenomenon. 
         [0045]    To sum up, the LCD of the present invention comprises a display panel, a plurality of CCFLs, an electric field sensor, and an inverter. The electric field sensor senses the electric field generated by the plurality of the CCFLs for generating a voltage. The inverter is electrically connected to the plurality of the CCFLs for generating a driving voltage to drive the plurality of the CCFLs. The inverter adjusts the operating frequency of the driving voltage according to the voltage generated from the electric field sensor. Therefore, the LCD of the present invention effectively improves the waving phenomenon. 
         [0046]    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.