Abstract:
A monochromic, multi-color and full-color cold cathode fluorescent display (CFD), comprises of some shaped white or multi-color or red, green blue color cold cathode fluorescent lamps (CCFL), reflector, base plate, temperature control means, luminance and contrast enhancement face plate, shades and its driving electronics. CFD is a large screen display device which has high luminance, high efficiency, long lifetime, high contrast and excellent color. CFD can be used for both outdoor and indoor applications even at direct sunlight, to display a character, or graphic and video image.

Description:
This application is a continuation of Ser. No. 08/532,077 filed Sep. 22, 1995, U.S. Pat. No. 5,834,889. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to a cold cathode fluorescent display (CFD) and in particular, to a high luminance, high efficiency, long lifetime, monochrome or multi-color or full-color ultra-large screen display device, which can display character, graphic and video images for both indoor and outdoor applications. 
     2. Description of the Prior Art 
     The major prior technologies for ultra-large screen display are as follows: 
     A. Incandescent lamp display: 
     This display screen consists of a lot of incandescent lamps. The white lamps are always used for displaying a white and black character and graphic. The color incandescent lamps, which use red, green, and blue (R, G, B) color glass bubbles, are used for displaying multi-color or full-color character, graphic and image. An incandescent lamp display has been widely used for an outdoor character and graphic displays and possesses certain advantages such as high luminance, functionable at direct sunlight with shade and low cost of lamps. Nevertheless, this technology suffers from the following disadvantages: low luminous efficiency (i.e., white lamp about 10 lm/W; R, G, B&lt;⅓ of white); 
     high power consumption; poor reliability, unexpected lamp failure; short lifetime; expensive maintenance cost; long response time and is unsuitable for video-display. 
     B. LED: 
     LED has been widely used for indoor large screen and ultra-large screen displays, to display a multi-color and full-color character, graphic and video image. This display is able to generate high luminance for indoor applications and can maintain a long operation lifetime at indoor display luminance level. The disadvantages of LED, however, are as follows: low luminous efficiency and high power consumption especially for the ultra-large screen display; low luminance for outdoor applications especially when a wide viewing angle is required or at direct sunlight; is expensive, especially for an ultra-large screen display because of of the need of a lot of LEDs; and has a lower lifetime at a high luminance level. 
     C. CRT: 
     CRT includes Flood-Beam CRT (e.g., Japan Display &#39;92, p. 285, 1992), and matrix flat CRT (e.g., Sony&#39;s Jumbotron as disclosed in U.S. Pat. No. 5,191,259) and Mitsubishi&#39;s matrix flat CRT (e.g., SID &#39;89 Digest, p. 102, 1989). The CRT display is generally known for its ability to produce good color compatible with color CRT. The disadvantages of CRT are as follows: low luminance for outdoor applications; low contrast at high ambient illumination operating condition; short lifetime at high luminance operating condition; expensive display device due to complex structure and high anode voltage of about 10 kv. 
     D. Hot Cathode Fluorescent Display: 
     Hot cathode fluorescent technology has been used in a display system called “Skypix” (SID &#39;91 Digest. p. 577, 1991) which is able to generate a high luminance of about 5000 cd/m 2  and can be operated at direct sunlight. The disadvantages of this system are: low luminous efficiency due to hot cathode and short gas discharge arc length; very high power consumption and short lifetime because of the hot cathode and too many switching times for video display. 
     At present, the incandescent lamps are commonly used for an outdoor character and graphic display. 
     The matrix flat CRT, including food beam CRT and matrix CRT, is the most common display for an outdoor video display. Neither of these two technologies presents a display system which can be used in both indoor and outdoor applications possessing unique features overcoming all or substantially all of the disadvantages described above. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the foregoing disadvantages of the prior art. 
     Accordingly, it is an object of the present invention to provide a very high luminance large screen and ultra-large screen display using a shaped cold cathode fluorescent lamp (“CCFL”) with a special reflector and luminance enhancement face plate etc. It can be used for both indoor and outdoor applications even at direct sunlight. The dot luminance of the character and graphic display can be up to 15,000 cd/m 2  or more. The area average luminance of the full-color image can be up to 5000 cd/m 2  or more. 
     It is another object of the present invention to provide long lifetime large screen and ultra-large screen displays. The lifetime can be up to 20,000 hours or more at high luminance operating conditions. 
     It is one more object of the present invention to provide high luminous efficiency, low power consumption large screen and ultra-large screen displays. The luminance efficiency can be up to 30 lm/W or more. 
     It is a further object of the invention to provide a high contrast large screen and ultra-large screen display with the appropriate shades, black base plate and luminance and contrast enhancement face plate. 
     It is still a further object of the present invention to provide good temperature characteristics in large screen and ultra-large screen displays with a temperature control means. The CFD of the present invention can be used for both indoor and outdoor applications, and any ambient temperature condition. 
     In accordance with the present invention, a CFD is provided including some shaped R, G, B CCFLs, and R, G, B filters, reflectors, a base plate, a luminance and contrast enhancement face plate, a temperature control means, and its driving electronics to control the lighting period or lamp current or ON/OFF of CCFLs according to the image signal, and to control the luminance of CCFLs to display the character, graphic and image with monochrome, multi-color or full color. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
     FIGS.  1 ( a ) and  1 ( b ) show a mosaic CCFL assembly type CFD with FIG.  1 ( a ) being a partial top view of the mosaic CFD to illustrate the preferred embodiment of the invention and FIG.  1 ( b ) being a partial side cross-sectional view of the device in FIG.  1 ( a ). 
     FIG. 2 shows some shape examples of CCFL. 
     FIGS.  3 ( a ) and  3 ( b ) are partially cross-sectional views of two types of reflectors and the CCFLs. 
     FIG. 4 is an embodiment of the heating and temperature control means. 
     FIG. 5 is a cross-sectional view of an embodiment of the luminance and contrast enhancement face plate. 
     FIG. 6 shows the structure of a luminescent element of a CCFL lamp type CFD. 
     FIG. 7 is a schematic driving circuit diagram of CFD. 
     FIG.  8 ( a ) is another schematic driving circuit diagram of CFD. 
     FIG.  8 ( b ) is a timing diagram to illustrate the operation of the circuit of FIG.  8 ( a ). 
     FIG. 9 is a timing diagram to illustrate another operating method of the circuit of FIG.  8 ( a ). 
     FIG.  10 ( a ) is an alternative schematic driving circuit diagram of CFD. 
     FIG.  10 ( b ) is a timing diagram to illustrate the operation of the circuit of FIG.  10 ( a ). 
     FIG.  11 ( a ) is a different schematic driving circuit diagram of CFD. 
     FIG.  11 ( b ) is a timing diagram to illustrate the operation of the circuit of FIG.  11 ( a ). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, a CFD according to the present invention will be described with reference to the accompanying drawings. 
     The CFD of the present invention has two types: CCFL assembly type and CCFL lamp type. 
     The CFD of the present invention can be a single piece structure or a mosaic structure. For the ultra-large screen CFD, it is always made in a mosaic type, i.e., the display screen is assembled by some mosaic tiles. 
     FIGS.  1 ( a ) and  1 ( b ) show a mosaic CCFL assembly type CDF wherein FIG.  1 ( a ) shows a partial top view of a preferred embodiment of the mosaic CFD provided by the present invention and FIG.  1 ( b ) further shows a partial side-view of FIG.  1 ( a ).  101  is a partially sectional view of four (4) mosaic CFD tiles. The mosaic CFD tile includes shaped CCFLs  102 , which can emit white or R, G and B light. FIG.  1 ( a ) is an embodiment of R, G and B fill-color CFD.  103  is a pixel which comprises three shaped R, G and B color CCFLs. Generally, although not shown here, one or more pixels are combined together to form a module and one or more modules combined together to form a display screen to display full-color character, graphic and video image. The R, G and B color CCFLs may be respectively equipped with R, G and B filters whose functions are to absorb the variegated light emitted from gas discharge of the CCFLs to increase color purity, to improve the quality of the display images and to increase the contrast of the display image by absorbing the ambient incident light. Alternatively, the R, G and B CCFLs are made of R, G and B color glass tubes to absorb the variegated light emitted from gas discharge of CCFLs, to increase the color purity and to absorb the ambient incident light to increase the contrast of display image. 
     The shape of CCFL can be a “U” shape, serpentine shape, circular shape or other shapes. For the white or monochromic display, the pixels can be one shaped CCFL or two or more different color CCFLs.  104  is the base plate for the installation of the CCFLs  102 , its driver  105  and other parts are described below.  106  is a black non-reflective surface between CCFLs  102  and the base plate  104  to absorb the ambient incident light and to increase the contrast of the display image.  107  are the electrode terminals of CCFLs  102 , said electrode terminals  107  are bended towards the back of the base plate  104  and are connected to drivers  105 .  108  is a reflector.  109  is a luminance and contrast enhancement face plate.  110  is the black shade to absorb the ambient incident light, including sunlight, to increase the contrast of the display image.  111  is a heating and temperature control means seated between CCFL  102  and base plate  104 , and close to CCFL  102  to make the CCFL operating at an optimum temperature, e.g., 30° C. to 75° C., to guarantee the luminance and color uniformity of the display image and to get high luminance, high luminance efficiency, and to quickly start the display system at any ambient temperature. The heating and temperature control means  111  has a heat conductive plate  112 . One mosaic tile may have one or several pieces of the heat conductive plate  112  to ensure that all CCFLs are operated at the same optimum temperature. Between the heating and temperature control means  111  and base plate  104 , there is a heat preservation layer  113  to decrease the heat loss and to decrease the power consumption. 
     FIG. 2 shows some examples of the possible shapes of the shaped CCFL  102 . The shapes of  201 ,  202 , and  203  are for the white or monochromic display, and  204 ,  205 , and  206  are for multi-color and full-color displays. 
     FIGS.  3 ( a ) and ( b ) are the cross-sectional view of two kinds of reflectors and CCFL for the CCFL assembly type CFD as shown in FIG. 1. 301 is the CCFL.  302  is the base plate.  303  is the reflector which is made of high reflectance layer, e.g., Al or Ag or other alloy film,.or a high reflectance diffusing surface, e.g., white paint. The reflector  303  is used for reflecting the light emitted from the CCFL forward to viewers shown as  304 .  305  are a plurality of small shades seated between CCFLs to absorb the ambient incident light to increase the contrast of the display image. In FIG. 3 b,  the reflector  306  is made of a high reflectance film, e.g., Al, Ag or alloy film, deposited on the back surface of the CCFL. 
     FIG. 4 shows an embodiment of the heating and temperature control means.  401  is a CCFL.  402  is a reflector.  403  is the base plate.  404  is a heating means, e.g., it is made of an electric heating wire  405  or an electric heating film.  406  is a heat conductive plates and each mosaic tile has one or more heat conductive plate  106  to ensure that all CCFLs are operated at the same optimum temperature.  407  is a temperature sensor and  408  an automatic temperature control circuit.  409  is a heat insulating layer whose function is to decrease the heat loss and decrease the power consumption.  410  is a luminance and contrast enhancement face plate. The chamber between the face plate  410  and heat insulating layer  409  is a heat preservation chamber  411 . The temperature of the chamber is controlled at an optimum operating temperature of CCFL, e.g., 30° C. to 75° C. 
     The said heating means  404  can simply be a heated air flow. The heat air flows through the whole screen between the face plate and the base plate. Some temperature sensors and control circuits are used to detect and control the temperature of the CCFL chamber. 
     FIG. 5 is a cross-section view of an embodiment of the luminance and contrast enhancement face plate.  501  is the CCFL.  502  is the reflector.  503  is the luminance and contrast enhancement face plate, which consists of a cylinder lens or lens array  504  and the small shades  507 . The optical axis of the lens is directed towards the viewers. The light emitted from the CCFL can effectively go through the reflector  502  and becomes focused on the lens  504  to a viewer  505  and thus, increase the luminance of the display image and the effective luminous efficiency.  506  is the base plate.  507  is a small shade seated at the top of the CCFL to absorb ambient incident light, including sunlight, to increase the contrast of the display image. 
     FIG. 6 shows luminescent elements of a CCFL lamp type CFD.  601  is the CCFL. For monochrome or white/black displays,  601  is at least one shaped white or monochrome CCFL. For the multi-color display,  601  is at least one group multi-color CCFL. For the full-color display,  601  is at least one group of R, G, B three color CCFL as shown in FIG. 6. 602 is a glass tube.  603  is a lamp base which is sealed within the glass tube  602  to form a vacuum chamber  604 .  605  is a base plate on which the CCFLs are fixed. The base plate  605  is fixed on the lamp base  603  and its two ends are fixedly connected to the internal surface of the glass tube  602 . To obtain a good fixing effect, a vacuum adhesive  606  such as ceramic adhesive is applied between/among the base plate  605 , the lamp base  603  and the CCFLs. If the CCFL is more than one piece between the CCFLs, these CCFLs are also fixed to each other by an vacuum adhesive  607 .  608  is an exhaustion tube for exhausting the gas in the chamber  604 .  609  is a lamp head which is fixed to the lamp base by a fixing adhesive  610 .  611  are connectors of the lamp.  612  are electrodes of the CCFLs which are connected to the connector  611  and the lamp head  609  through leads  613 . The glass tube  602  can be a diffusing glass tube to obtain a diffusing light. Alternatively, the glass tube  602  as shown in FIG. 6, the glass tube  602  has a front face  614  and a backside  615 . The front face  614  is a transparent or a diffusing spherical surface and the backside  615  is a cone shape or a near cone shape tube. On the internal surface of the backside  615  of the glass tube, there is a reflective film  616 , e.g., an Al, Ag, or alloy thin film, to reflect the light and to increase the luminance of the lamp shown as  617 . The vacuum chamber  604  can reduce the heat loss of the CCFL and hence increase the efficiency of the CCFL. In addition, the vacuum chamber  604  can also eliminate any undesirable effects caused by the ambient temperature to the characteristics of the CCFL. The base plate  605  is a high reflective plate to reflect the light and to increase the luminance of the CFD. Some of the CCFL lamps shown in FIG. 6 can be used for making the monochromic, multi-color, full-color display system to display a character, graphic or video images. The CCFL lamps can also be used for the purposes of illumination. 
     Referring now to FIG. 7, the driving circuit of CFD is schematically diagramed.  701  are the CCFLs.  702  are DC/AC converters which change the DC input voltage to a high voltage and high frequency (e.g., tens kHz,) AC voltage to drive the CCFL. The symbols x 1 , x 2  . . . are scanning lines. The symbols y 1 , y 2  . . . are column data electrodes. One DC/AC converter  702  drive one CCFL  701 . To control the period of input voltage of the DC/AC converter  702  according to an image signal, the luminance of the CCFL can be controlled and the character, graphic and the image can be displayed. 
     The CFD as illustrated in FIG. 7 will need a lot of DC/AC converters to drive its CCFLs. In order to reduce the number of DC/AC converters and to reduce the cost of the display system, a method which uses one DC/AC converter driving one line of CCFL or one group of CCFL can be adopted as shown in FIG.  8 ( a ). FIG.  8 ( b ) is a timing diagram to further illustrate the operation of the circuit of FIG.  8 ( a ).  801  are the CCFLs.  802  are the DC/AC converters.  803  are coupled capacitors. The symbols x 1 , x 2  . . . are scanning lines. The symbols y 1 , y 2  . . . are column data electrodes. When one scanning line, e.g., x 1 , is addressed (FIG. 8 a , t ON ), the related DC/AC converter is turned ON to output a sustained AC voltage shown as  804 . This sustained voltage is lower than the starting voltage of the CCFL, and cannot start the CCFLs of this line, but can sustain lighting after CCFL started. Because the starting voltage of CCFL is much larger than the sustained voltage, when the column date electrode (y 1 , y 2 , . . ) is at 0 v, the related CCFL cannot be started and will stay at the OFF state. When the column date electrode supplies an anti-phase trigger voltage, the related CCFL will be started. The CCFL will light until the related DC/AC converter is turned OFF as shown in FIG.  8 ( b ) as t OFF . The lighting period t m  according to the image signal can be controlled to modulate the luminance of CCFL and to display character, graphic, and image with monochrome or multi-color or full-color. For example,  805  is for a high luminance  806 , the lighting period is t m1 , (=t OFF −t on1 ), and  807  is for a lower luminance  808 , the lighting period is t m2  (−t OFF −t on2 ) and so on. 
     FIG. 9 shows a different operating method than the circuit shown in FIG. 8 a.    901  is the same as  804  as shown in FIG.  8 ( b ) for line scanning.  902  and  904  are column data voltage, which have an anti-phase with the scanning voltage  901 . When a CCFL is applied to the scanning voltage  901  and the signal voltage  902  at the same time, the total voltage applied to the CCFL will be larger than the starting voltage of the CCFL which will light the CCFL in this period. The ON time t m1  and t m2 , i.e., lighting period, depend on image signals. Different t m  have different lighting periods shown as  903  and  905 , i.e., different luminance, to display a character, graphic and image. 
     FIG.  10 ( a ) is yet another schematic diagram for the driving circuit of CFD. The symbols x 1 , x 2  . . . are the scanning lines. The symbols y 1 , y 2  . . . are the column data electrodes.  1001  are the CCFLs.  1002  are the DC/AC converters.  1003  are AC voltage switches. One line of the CCFL or one group of CCFLs has one DC/AC converter  1002 . When the switch  1003  is turned ON according to the image signal, the related CCFL will be lighted, and the character, graphic and image can be displayed. In this case, because the starting voltage of CCFL is larger than the sustained voltage, all CCFLs in the same line or same group should start at the same time as shown in FIG.  10 ( b ) as t On . At this time, the related DC/AC converter will be turned ON to output a larger voltage  1004 , which can start the CCFL. Consequently, all the CCFLs connected with this DC/AC converter are started at this time if the related switch is turned ON. After the CCFL started, the DC/AC converter will output a lower sustained voltage  1005  to sustain the CCFL lighting. The turned OFF time t OFF , e.g., T off1 , and T off2 , can obtain a different lighting period, e.g.,  1006  and  1007 , different luminance  1008  and  1009  can be obtained to display the character, graphic and image. 
     FIG.  11 ( a ) shows a low AC voltage switch driving circuit. The symbols x 1 , x 2  . . . are scanning lines. The symbols y 1 , y 2  . . . are column data electrodes.  1101  are the CCFLs.  1102  are DC/AC converters, which outputs a low AC voltage, e.g., several to ten volts and tens kHz. One line of CCFL or one group of CCFLs has one DC/AC converter.  1103  are low AC voltage switches.  1104  are transformers from which the low AC voltage can be changed to a high AC voltage.  1105  are coupling capacitors. The driving timing diagram is shown in FIG.  11 ( b ).  1106  is the low AC voltage output from the DC/AC converter when the line is addressed.  1107  and  1110  are the AC switch control voltages, their widths are dependent on the image signals.  1108  and  1111  are the high AC voltage output transformers.  1109  and  1113  are the light waveforms emitted from the CCFLS. When an AC switch is turned ON, the related transformer will output a higher voltage  1114  to starting the related CCFL. After the CCFL is started, the transformer output a lower sustained voltage  1115  to sustain the CCFL lighting. When the DC/AC converter  1102  is turned OFF, shown as t OFF , all the addressed CCFLs are turned OFF. To control the ON time of the AC switch according to an image signal, the luminance of the CCFL can be modulated to display the character, graphic and image.