Abstract:
A field emission backlight unit comprises a substrate, first electrodes and second electrodes, a fluorescent lighting panel and an anode plate. The first electrodes are disposed on the substrate. The second electrodes are interlaced with the first electrodes and disposed on the substrate. The second electrodes receive a clock signal sequentially according to a first period. The fluorescent lighting panel is disposed at the opposite side of the substrate. The anode plate is disposed at the opposite side of the substrate. When there is a specific voltage between the first electrodes and the second electrodes to generate electrons, the anode plate pulls electrons to hit the fluorescent lighting panel to emit light.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a field emission backlight unit, and more particularly to a field emission backlight unit with a scanning driving method. 
         [0003]    2. Description of the Related Art 
         [0004]      FIG. 1  is a schematic diagram of conventional field emission backlight device  100 . Field emission backlight device  100  comprises anode plate  140 , gate G, cathode electrode Ca, carbon nanotubes CNT, fluorescent lighting plate  110  and substrate  150 . There are two driving methods for conventional field emission backlight devices  100 , a direct current (DC) driving method and an alternating current (AC) driving method. Anode plate  140  typically varies between 5000V and 10000V, and a DC voltage or an AC voltage is applied between gate G and cathode electrode Ca to generate electrons e′ by point discharge of carbon nanotubes CNT. Electrons e′ are pulled by anode plate  140  and gate G and hit fluorescent lighting plate  110  causing fluorescent lighting plate  110  to emit light. 
         [0005]      FIG. 2  shows a cross section of conventional field emission backlight device  100  with cathode electrode Ca and gate G. As shown in  FIG. 2 , gate G and cathode electrode Ca are interlaced and disposed on substrate  150 . In one example, cathode electrode Ca is connected to ground, and a DC voltage or an AC voltage is applied to gate G. Thus, there is a voltage drop between gate G and cathode electrode Ca to generate electrons e′. Electrons e′ are pulled by anode plate  140  and gate G and hit fluorescent lighting plate  110  causing fluorescent lighting plate  110  to emit light. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
         [0007]    A field emission backlight unit comprises a substrate, first electrodes of a first voltage level disposed on the substrate, second electrodes interlaced with the first electrodes on the substrate, a pulse signal inputted to the second electrodes sequentially according to a first period, a fluorescent lighting panel disposed at an opposite side of the substrate and an anode plate disposed at the opposite side of the substrate. If there is a specific voltage between the first electrodes and the second electrodes for generating a plurality of electrons, the electrons hitting the fluorescent lighting panel cause the anode to emit light. 
         [0008]    A scanning driving method for driving a field emission backlight unit is provided. The field emission backlight unit comprises a fluorescent lighting panel, an anode plate, a substrate, first electrodes and second electrodes. The first electrodes and the second electrodes are interlaced and disposed on the substrate. The fluorescent lighting panel and the anode plate are disposed at an opposite side of the substrate. The scanning driving method comprises applying a first voltage level on the first electrodes, and applying a pulse signal on the second electrodes sequentially according to a first period. If there is a specific voltage between the first electrodes and the second electrodes for generating a plurality of electrons, electrons hitting the anode cause the fluorescent lighting panel to emit light. 
         [0009]    A field emission backlight unit comprises a substrate, first electrodes, a fluorescent lighting panel and an anode. The first electrodes is disposed on the substrate and have a first voltage level The second electrode groups each comprises at least two second electrodes interlaced with the first electrodes on the substrate. A pulse signal is input to the second electrodes sequentially according to a first period. The fluorescent lighting panel is disposed at an opposite side of the substrate. The anode plate is disposed at the opposite side of the substrate. If there is a specific voltage between the first electrodes and the second electrodes for generating a plurality of electrons, electrons hitting the anode cause the fluorescent lighting panel to emit light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0011]      FIG. 1  is a schematic diagram of a conventional field emission backlight device; 
           [0012]      FIG. 2  shows a cross section of a conventional field emission backlight device; 
           [0013]      FIG. 3A  is a schematic diagram of a field emission backlight device according to an embodiment of the invention; 
           [0014]      FIG. 3B  is a schematic diagram of a field emission backlight device according to another embodiment of the invention; 
           [0015]      FIG. 4A  shows a cross section of a field emission backlight device according to an embodiment of the invention; 
           [0016]      FIG. 4B  shows a cross section of a field emission backlight device according to another embodiment of the invention; 
           [0017]      FIG. 5A  is a timing diagram of a field emission backlight device according to another embodiment of the invention; 
           [0018]      FIG. 5B  is a timing diagram of field emission backlight device according to another embodiment of the invention; and 
           [0019]      FIG. 6  is a schematic diagram of a field emission backlight device according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0021]      FIG. 3A  is a schematic diagram of field emission backlight device  300  according to an embodiment of the invention.  FIG. 4A  shows a cross section of field emission backlight device  300  with cathode electrodes Ca 1 , Ca 2  and Ca 3  and gate G according to an embodiment of the invention. As shown in  FIGS. 3A and 4A , field emission backlight device  300  comprises anode plate  340 , gate G, cathode electrodes Ca 1 , Ca 2  and Ca 3 , carbon nanotubes CNT, fluorescent lighting plate  310  and substrate  350 . As known in  FIG. 4A , gate G and cathode electrodes Ca 1 , Ca 2  and Ca 3  are interlaced and disposed on substrate  350 . If the voltage drop between gate G and cathode electrodes Ca 1 , Ca 2  and Ca 3 , is adequate, such as 300V, carbon nanotubes CNT are discharged from points thereof to generate electrons e′. Electrons e′ are pulled by anode plate  340  and gate G and hit fluorescent lighting plate  310  causing fluorescent lighting plate  310  to emit light. Anode plate  340  can be an ITO (Indium Tin Oxide) layer coated on a glass substrate or composed of a substrate and an anode electrode layer. The anode electrode layer can be formed by screen printing, spin coating, evaporation deposition, sputtering and similar. For brevity,  FIGS. 3A and 4A  only show three gates G interlaced with three cathode electrodes Ca 1 , Ca 2  and Ca 3  disposed on substrate  350  to represent that field emission backlight device  300  comprises a plurality of gates and a plurality of cathode electrode. Because each cathode of the field emission backlight device of the invention is driven by an independent driving element and each driving element consumes less power, the field emission backlight device of the invention can be used to light a larger area. 
         [0022]      FIG. 3B  is a schematic diagram of field emission backlight device  301  according to another embodiment of the invention.  FIG. 4B  shows a cross section of field emission backlight device  301  with cathode electrodes Ca and gates G 1 , G 2  and G 3  according to another embodiment of the invention. As shown in  FIGS. 3B and 4B , field emission backlight device  301  comprises anode plate  340 , gates G 1 , G 2  and G 3 , cathode electrode Ca, carbon nanotubes CNT, fluorescent lighting plate  310  and substrate  350 . As known in  FIG. 4B , gates G 1 , G 2  and G 3  and cathode electrode Ca are interlaced and disposed on substrate  350 . If the voltage drop between gates G 1 , G 2  and G 3  and cathode electrode Ca, is adequate, such as 300V, carbon nanotubes CNT are discharged from points thereof to generate electrons e′. Electrons e′ are pulled by anode plate  340  and gate G 1 , G 2  and G 3  and hit fluorescent lighting plate  310  causing fluorescent lighting plate  310  to emit light. 
         [0023]      FIG. 5A  is a timing diagram of field emission backlight device  300  according to another embodiment of the invention. Amplitude A 1 , frequency or pulse widths T 2  of each signal Vgc 1 , Vgc 2  and Vgc 3  are all the same and only the phases thereof are different. In one of embodiments, signal Vgc 2  is generated by delaying signal Vgc 1  by period T 1  and signal Vgc 3  is generated by delaying signal Vgc 2  by period T 1 . Using  FIGS. 4A and 4B  as examples, signal Vgc 1  is a voltage between gate G and cathode Ca 1 , signal Vgc 2  is a voltage between gate G and cathode Ca 2 , and signal Vgc 3  is a voltage between gate G and cathode Ca 3 . 
         [0024]    According to an embodiment of the invention, using  FIG. 4A  as an example, gate G receives 300V voltage and cathode electrodes Ca 1 , Ca 2  and Ca 3  receive a pulse signal with a specific frequency. The pulse signal has two voltage levels, 0V and 100V. The specific frequency is between 100 Hz and 50 KHz. According to the above conditions, amplitude A 1  of signals Vgc 1 , Vgc 2  and Vgc 3  in  FIG. 5A  is 100V. If the high voltage level of signal Vgc 1  is 300V, there is a 300V voltage drop between gate G and cathode Ca 1 , generating electrons e′. Electrons e′ are pulled by anode plate  340  and gate G, and hit fluorescent lighting plate  310  to cause fluorescent lighting plate  310  to emit light. If the low voltage level of signal Vgc 1  is 200V, there is a 200V voltage drop between gate G and cathode Ca 1  to generate few electrons e′. Similarly, if the voltage levels of signals Vgc 2  and Vgc 3  are 300V, electrons e′ cause the fluorescent lighting plate  310  to emit light. In another embodiment, using  FIG. 4B  as an example, cathode Ca is connected to ground, and gates G 1 , G 2  and G 3  receive a pulse signal with a specific frequency. The pulse signal has two voltage levels, 300V and 200V. The specific frequency is between 100 Hz and 50 KHz. The operation is similar to the previously described operation, thus, it is not described again here. 
         [0025]    Because the fluorescent powders of fluorescent lighting plate  310  have a characteristic decay time, the brightness of fluorescent lighting plate  310  decreases over time. Fluorescent lighting plate  310  must wait for the next period to receive electrons e′ before emitting light again. In addition, using  FIGS. 3A and 4A  as an example, because the voltage of signals Vgc 1 , Vgc 2  and Vgc 3  become 300v sequentially, and gate G and cathodes Ca 1 , Ca 2  and Ca 3  are interlaced and disposed on substrate  350 , cathodes Ca 1 , Ca 2  and Ca 3  sequentially generate electrons e′ for each part of fluorescent lighting plate  310  to emit light by turns. Thus, field emission backlight device  300  can uniformly emit light. In another embodiment, period T 1  of signals Vgc 1 , Vgc 2  and Vgc 3  is shorter than period T 2  of the pulse signals, as shown in  FIG. 5B . Thus, cathodes Ca 1 , Ca 2  and Ca 3  generate electrons e′ sequentially, and the periods of generating electrons of cathodes Ca 1 , Ca 2  and Ca 3  overlap each other for improving the brightness of light emitted by field emission backlight device  300 . In another embodiment, field emission backlight device  300  can be applied in the backlight of a liquid crystal display to improve the known motion blur problem. 
         [0026]      FIG. 6  is a schematic diagram of field emission backlight device  600  according to another embodiment of the invention. Field emission backlight device  600  comprises a plurality of cathode groups (such as Ca 1 , Ca 2  and Ca 3 ), and each cathode group comprises at least two independent cathodes. According to an embodiment of the invention, gate G receives 300V voltage, and cathode groups Ca 1 , Ca 2  and Ca 3  receive pulse signals with a specific frequency, such as signal Vgc 1 , Vgc 2  and Vgc 3  in  FIG. 5 . The anode plate, fluorescent light panel, carbon nanotubes and lighting method in  FIG. 6  are the same as those in  FIGS. 3A ,  3 B,  4 A and  4 B, thus, they are not described in detail here. Because electrodes of field emission backlight device  600  are separated into a plurality of groups, field emission backlight device  600  can use a single driver more efficiently and use fewer driving elements in a single driver to reduce costs. 
         [0027]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.