Abstract:
A beam-forming region (BFR) such as used in cathode ray tube (CRT) electron guns includes a cathode, a decelerating first electrode (G1), an accelerating secondelectrode (G2), an accelerating third electrode (G3) and an additional electrode (G2′) that introduces a pre-focusing lens. The decelerating first electrode (G1) and the accelerating second electrode include aperture arrays that introduce multiple emitting areas on the surface of the cathode. Electrons emitted from the cathode surface pass through their respective apertures and are then converged into a single high current beam by the pre-focusing lens. The high current electron beam passes through any one of many possible main-lens structures, which focuses the beam onto a phosphorescent display screen. The beam is swept across the display screen in a rater like manner while being modulated by a video source signal. In an alternate embodiment, a large diameter aperture is included on the display screen side of the first accelerating electrode (G2) in order to form the pre-focusing lens and converge the electrons into a single high current beam.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is entitled to the benefit of Provisional Patent Application Ser No. 60/261,046 filed Jan. 11, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to electron guns such as those used in cathode ray tubes (CRTs) and more specifically to a beam-forming region (BFR) of an electron gun having an array of cathode emitting areas.  
           [0004]    2. Description of the Related Art  
           [0005]    In recent years, due to technical advances in and general acceptance of flat panel displays, CRT design and development efforts have been directed toward more demanding applications such as high definition television (HDTV) displays, computer monitors, projection television receivers, wide-angle projectors, film recorders and diagnostic medical application.  
           [0006]    The most important operating characteristics of CRT displays are typically video image brightness, resolution and display size. Unfortunately, these properties are interrelated. In a typical CRT, increasing brightness reduces the resolution because the electron beam spot size degrades. Increasing the display size reduces the video image brightness because the emitted light must cover a larger display area. Increasing the video image resolution by increases the scan frequency, decreases “dwell time.” This effectively reduces the beam current density striking the display screen and thus degrades the video image brightness.  
           [0007]    One approach to providing acceptable video image brightness, at a given display size without appreciably diminishing image resolution, involves increasing the cathode emission current density. This approach greatly decreases the life of the cathode and thus the life of the CRT. So, the use of a dispenser cathode is sometime incorporated in the CRT. Dispenser cathodes can typically deliver five times the emission current density of a conventional oxide cathode and last over five times longer. While dispenser cathodes dramatically improving CRT life, the increased cathode emission current density does not appreciably improve the video image resolution or brightness. Also, dispenser cathodes are expensive costing approximately 50 times more than a convention oxide cathode.  
           [0008]    One technique for increasing video image resolution without affecting the cathode emission current density is to increase the size of the electron gun. This allows for a smaller beam spot size and improved resolution, but increases the size of the CRT neck size. The increased size is contrary to the current trends, which seek to reduce the non-display screen portions of the CRT.  
           [0009]    Another technique for achieving increased brightness and resolution involves the use of multi-beam electron guns. Conventional color CRTs employ three electron beams one for each of the primary colors (red, green and blue), while a monochrome CRT typically uses only one electron beam. In both cases the electron beams are swept across the CRT&#39;s display screen in a raster like manner. In multi-beam electron guns each of the standard electron beams are replaced with a group of electron beams.  
           [0010]    An approach disclosed in the prior art is the use of a multi-beam electron gun to form distinctly separate mini-rasters on the CRT display screen. For example, Keller U.S. Pat. No. 3,943,281 shows a multi-beam electron gun where the beams crossover each other at a steep angle and strike the display screen at widely separated location. When these electron beams are swept in a raster like manner a plurality of mini-rasters is formed on the display screen. Each beam is modulated with a distinct section of the video signal appropriate for their location on the screen. The low-resolution mini-rasters combine to form a single high-resolution video image. This approach effectively divides the horizontal frequency of the deflection yoke by the number of mini-rasters being swept.  
           [0011]    Another approach disclosed in prior art is the use of a multi-beam CRT to form alternating lines of video on the display screen. For example Chen U.S. Pat. Nos. 5,389,855; 5,350,978; 5,382,883 and Beck U.S. Pat. No. 4,338,541 both show designs that utilize multiple isolated electron beams that strike the display screen in close proximity to each other. The beams strike the display screen at separations equal to the line separation dictated by the display resolution. These separated beams are vertically aligned so that when they are swept across the display screen, in a raster like manner, each beam produces a line of video. Therefore the display can write a number of lines of video equal to the number of beams with each pass of the deflection yoke. This effectively divides the horizontal frequency of the deflection yoke by the number of beams being swept.  
           [0012]    By Simultaneously tracing two or more horizontal scan lines, electron beam horizontal scan frequency and deflection frequency rate may be reduced and deflection yoke power requirements may be relaxed. The reduction in beam scan frequency gives rise to a corresponding increase in “dwell time” of the electron beams on the display screen&#39;s phosphor elements. Increasing electron beam dwell time allows for a corresponding reduction in electron beam peak current giving rise to a corresponding improvement in electron beam spot size and video image resolution without sacrificing video imaging brightness.  
           [0013]    The problem with these types of multi-beam CRTs is that they require additional electronics in order to manipulate the video signal. These added components and design efforts could increase the manufacturing and selling cost of the display. CRT designers typically look for improvements that do not require extensive modification to the drive electronics.  
           [0014]    Another problem with multi-beam CRT displays is that the electron guns are complicated and difficult to manufacture. These multi-beam guns typically send electron beams through the main lens optics off axis. Because of this, the guns require complicated electron optics to correct for beam position and focus quality. The complicated optics can adversely affect the manufacturing yields and increase costs.  
           [0015]    Another approach disclosed in prior art utilizes multiple isolated electron beams, which are simultaneously swept across the display screen in order to form common lines of video on the display screen. For example Chen U.S. Pat. No. 5,389,855 describes an electron gun where separate beams are vertically aligned and superimposed on exactly the same location on the display screen. This effectively multiplies the video image brightness by the number of beams being swept without increasing the width of the lines of video on the display screen or increasing the required peak currents of the individual electron beams.  
           [0016]    The problem with this approach is that the electron beams must be superimposed on precisely the same location on the display screen. If the beams are not perfectly “converged” then the electron beam spot size and video image resolution will be reduced according to the degree of mis-convergence. They require an exceptionally high performance “self converging deflection yoke.” Standard self-converging yokes, such as those used in color CRT displays, are of unacceptable quality. As a result these types of CRT displays are difficult to manufacture, which can be costly and could affect the manufacturing and selling cost of the displays.  
           [0017]    Referring to FIG. 1, there is shown a simplified isometric view of a typical prior-art beam-forming region  112  of an electron gun such as that used in a CRT. A longitudinal sectional view of the beam-forming region  112  shown in FIG. 1 taken along site line  110 - 110  is shown in FIG. 2. Regardless of which of the preceding approaches is employed in the display, these CRTs all utilize electron guns that incorporate the standard prior-art beam-forming region (BFR)  112 . The BFR  112  is designed to provide a method for cutting off and modulating an electron beam  126 . The standard BFR  112  is comprised of four basic components a cathode  114 , a “Wehnelt” or decelerating first electrode (G1)  116 , an accelerating second electrode (G2)  118 , and an accelerating third electrode (G3)  120 . The electrodes  116 ,  118 ,  120  have apertures  116   a ,  118   a ,  120   a  that are linearly positioned.  
           [0018]    In the conventional BFR  112  electrons are emitted from the cathode  114  and are accelerated toward the display screen by the G2  118  and the G3  120  electrodes, which are always of higher potential than the cathode  114 . Along a path  122  toward the display screen the electrons pass through the G1 aperture  116   a . The G1 electrode  116  is always of lower potential than the cathode  114 . Thus the negatively charged G1 electrode  116  repels the electrons causing them to converge and “cross-over.” The electrons are now diverging and proceed to pass through the aperture in the G2 electrode  118   a . Since the G3 electrode  120  is always of higher potential than the G2 electrode  118 , the area between the G2  118  and G3  120  electrodes forms an accelerating lens  124 . When the electrons pass through the accelerating lens  124  they become less divergent. The beam  126  is now “formed” and is sent through one of many types of main lens systems.  
           [0019]    With this system the voltage on the G1 electrode  116  can be manipulated to allow more or fewer electrons to pass through the G1 aperture  116   a . If the voltage that is applied to the G1 electrode  116  is sufficiently less than the voltage applied to the cathode  114  then the beam  126  will be “cut-off.” As the beam  126  is swept across the display screen in a raster like manner, the voltage applied to the G1 electrode  116  is modulated. The modulated G1 voltage changes the beam current and causes the varied brightness of the video image to be written on the display screen. The problem with the conventional BFR  112  is that it cannot meet the increasing requirements of larger display size, higher video image brightness and high resolution.  
           [0020]    Referring to FIG. 3 there is shown a simplified isometric view of an alternate typical prior-art beam-forming region (BFR)  130  of an electron gun such as that used in a CRT, where an accelerating second electrode (G2)  136  is modified to introduce a pre-focusing lens  140 . A longitudinal sectional view of the beam-forming region shown in FIG. 3 taken along site line  128 - 128  is shown in FIG. 4. The alternate BFR  130  is comprised of four basic components a cathode  132 , a “Wehnelt” or decelerating first electrode (G1)  134 , the accelerating second electrode (G2)  136 , and an accelerating third electrode (G3)  138 . The electrodes  134 ,  136 ,  138  have apertures  134   a ,  136   a ,  138   a  that are linearly positioned. The electrons emitted from the cathode  132  travel along a path  142  to the display screen and form a beam  144 . In this BFR  130  the G2 aperture  136   a  diameter changes from one side of the G2 electrode  136  to the other. The G2 aperture  136   a  has a dimple which is a larger diameter on the display screen side  136   c  than on the cathode side  136   b . The only functional difference compared to the conventional BRF  112  is that the high potential electric field of the accelerating third electrode (G3)  138  penetrates into the dimple of the G2 aperture  136   c  and thus introduces the pre-focusing lens  140 . When the electrons pass through the pre-focusing lens  140  they are converged more so than in the conventional BFR  112 . This BFR  130  is beneficial because the strength of the pre-focusing lens  140  can be adjusted by changing the diameter and depth of the dimple in the G2 aperture  136   c . But, this adjustment is costly since the designer must re-tool the electrode each time an adjustment is made. Another drawback to this BFR  130  design is that it is more complicated and thus more difficult to manufacture than the conventional BFR  112 .  
           [0021]    Referring to FIG. 5 there is shown a simplified isometric view of an alternate typical prior-art beam-forming region  148  of an electron gun such as that used in a CRT, where an additional electrode (G2′)  156  is employed to introduce a pre-focusing lens  160 . A longitudinal sectional view of the beam-forming region  156  shown in FIG. 5 taken along site line  146 - 146  is shown in FIG. 6. The alternate BFR  148  is comprised of five basic components a cathode  150 , a “Wehnelt” or decelerating first electrode (G1)  52 , an accelerating second electrode (G2)  154 , the additional electrode (G2′)  156  and an accelerating third electrode (G3)  158 . The electrodes  152 ,  154 ,  156 ,  158  have apertures  152   a ,  154   a ,  156   a ,  158   a  that are linearly positioned. The electrons emitted from the cathode  150  travel along a path  162  to the display screen and form a beam  164 . This alternate BFR  148  uses the additional electrode (G2′)  156 , disposed between the accelerating second electrode (G2)  154  and the accelerating third electrode (G3)  158 , to introduce the pre-focusing lens  160 . The G2′  156  is always of lower potential than the G2  154 . The high potential electric field of the accelerating third electrode (G3)  158  penetrates into the G2′ aperture  156   a  and thus introduces the pre-focusing lens  140 . The only functional difference compared to a conventional BRF  112  is that when the electrons pass through the pre-focusing lens  160  they are converged more so than in the conventional BFR  112 . This type of BFR  148  is beneficial because the strength of the pre-focus lens  160  can be adjusted by applying an additional potential to the isolated extra electrode  156 . This method allows individual guns to be adjusted without the re-tooling of parts. Thus the optics of individual guns can be corrected for certain manufacturing errors. The draw back to the additional electrode  156  is that this BFR  148  is more difficult to manufacture than either of the previous BFRs  112 ,  130 .  
           [0022]    These methods of introducing the pre-focus lenses  140 ,  160  are used to control the electron beam diameter in the main lens system. The beam size must be optimized in order to achieve best video image resolution. The optimum beam size depends entirely on the main lens system and deflection system employed. If the beam is too large or too small for the main lens system or the deflection system then the video image resolution will be reduced.  
           [0023]    These standard beam-forming regions  112 ,  130 ,  148  can be combined with any of the standard prior-art “main lens” systems to form conventional monochrome electron guns. The function of the main lens is to convert the diverging beam from the BFR  112 ,  130 ,  148  into a converging beam and focus it onto the display screen. The accelerating third electrode (G3)  120 ,  138 ,  158  of the BFR  112 ,  130 ,  148  is typically shared as the first electrode of the main lens. The G3 electrode  120 ,  138 ,  158  typically includes a drift region that isolates the BFR from the main lens. Conventional monochrome guns are classified as standard-einzel, high-einzel, bi-potential, or quad-potential based upon the main lens system employed. The name of each main lens is derived from the number of high potential electrodes utilized in the system.  
           [0024]    Referring to FIG. 7 there is shown a simplified isometric view particularly in phantom of a typical prior-art electron gun  168  such as used in a conventional monochrome CRT with a conventional BFR  170  and a low uni-potential (standard-einzel) main lens  172 . A longitudinal sectional view of the electron gun  168  shown in FIG. 7 taken along site line  166 - 166  is shown in FIG. 8. The standard-einzel main lens  172  is comprised of three electrodes. A first electrode (G3)  174  and a third electrode (G5)  178  are electrically connected and held at a high potential, which is equal to the display screen anode potential. A second electrode (G4)  176  is held near ground potential. The presence of the lower potential G4 electrode  176  between the two high potential G3 and G5 electrodes  174 ,  178  forms a converging main lens  172  that focuses an electron beam  180  onto the display screen. By adjusting the potential of the G4 electrode  176  the beam&#39;s focus can be fine adjusted to match the beam&#39;s location on the display screen.  
           [0025]    Referring to FIG. 9 there is shown a simplified isometric view particularly in phantom of typical prior-art electron gun  184  such as used in a conventional monochrome CRT with a conventional BFR  186  and a high uni-potential (high-einzel) main lens  188 . A longitudinal sectional view of the electron gun  184  shown in FIG. 9 taken along site line  182 - 182  is shown in FIG. 10. The high-einzel main lens  188  is similar in construction to the standard-einzel main lens  172 . The high-einzel main lens  188  is comprised of three electrodes. A first electrode (G3)  190  and a third electrode (G5)  194  are electrically connected and held at anode potential. A second electrode (G4)  192  is held at a potential that is typically 20-40% of the anode potential. The potential of the G4 electrode  192  is used as the focusing adjustment for an electron beam  196 . The only functional difference between the standard-einzel  172  and high-einzel  188  main lenses is that the high-einzel G4  192  is held at a high potential.  
           [0026]    Referring to FIG. 11 there is shown a simplified isometric view particularly in phantom of typical prior-art electron gun  200  such as used in a conventional monochrome CRT with a conventional BFR  202  and a bi-potential main lens  204 . A longitudinal sectional view of the electron gun shown in FIG. 11 taken along site line  198 - 198  is shown in FIG. 12. The bi-potential main lens  204  is comprised of two electrodes. A first electrode (G3)  206  is held at a high potential, which is typically 20-40% of the anode potential. A second electrode (G4)  208  is held at a high potential equal to the display screen anode potential. In this lens system the potential of the G3 electrode  206  is used as the focusing adjustment for an electron beam  210 .  
           [0027]    Referring to FIG. 13 there is shown a simplified isometric view particularly in phantom of a typical prior-art electron gun  214  such as used in a conventional monochrome CRT with a conventional BFR  216  and a quad-potential main lens  218 . A longitudinal sectional view of the electron gun shown in FIG. 13 taken along site line  212 - 212  is shown in FIG. 14. The quad-potential main lens  218  is comprised of four electrodes. A first electrode (G3)  220  and a third electrode (G5)  224  are electrically connected and held at a high potential, typically 20-40% of the anode potential. A second (G4)  222  is held at low potential. A forth electrode (G6)  226  is held at anode potential. In this lens system the potential of the first (G3)  220  and third (G5)  224  electrodes are collectively used as the focusing adjustment for an electron beam  228 .  
           [0028]    The standard monochrome lens systems are used as the basis for the standard prior-art color electron gun configurations. Conventional color electron guns include three horizontally aligned electron beams, one for each of the primary phosphor colors, red, green and blue. Conventional color electron guns fall into one of two design schemes, “inline” and “Trinitron.” 
           [0029]    Referring to FIG. 15 there is shown a simplified isometric view particularly in phantom of a typical prior-art electron gun  232  such as used in a conventional inline-color CRT with conventional BFRs  234   a ,  234   b ,  234   c  and bi-potential main-lenses  236   a ,  236   b ,  236   c . A longitudinal sectional view of the electron gun  232  shown in FIG. 15 taken along site line  230 - 230  is shown in FIG. 16. In the inline color electron gun  232  three horizontally aligned beams  238   a ,  238   b ,  238   c  are sent through the distinctly isolated main-lenses  236   a ,  236   b ,  236   c . The inline color electron gun  232  is essentially three separate electron guns assembled from common parts.  
           [0030]    Referring to FIG. 17 there is shown a simplified isometric view particularly in phantom of a typical prior-art electron gun  242  such as is used in a conventional Trinitron-color CRT with conventional BFRs  244   a ,  244   b ,  244   c  and a high-einzel main-lens  246 . A longitudinal sectional view of the trinitron electron gun  242  shown in FIG. 17 taken along site line  240 - 240  is shown in FIG. 18. In the Trinitron electron gun  242  three horizontally aligned beams  248   a ,  248   b ,  248   c  are sent at through the center of the common shared main-lens  242 . The beams  248   a ,  248   b ,  248   c  are then redirected toward the display screen by a group of deflection plates  250   a ,  250   b ,  250   c ,  250   d . The Trinitron electron gun has a larger diameter main-lens  246  than the inline color electron gun  232 . For this reason the Trinitron electron gun  242  produces a higher resolution video image. But, the Trinitron electron gun  242  is more complicated and costly than the inline color electron gun  232 .  
         SUMMARY OF THE INVENTION  
         [0031]    In view of the above problems, the present invention provides a beam-forming region (BFR) such as used in cathode ray tube (CRT) electron guns, which has multiple emitting areas on the cathode. This solves the problem of simultaneously achieving a large display size, high video image brightness and high resolution.  
           [0032]    The present invention has the advantage of being a drop in replacement for any CRT electron gun&#39;s BFR. The present invention BFR can be substituted without changing the gun&#39;s main lens system therefore the present invention can be utilized in any type of monochrome or color CRT. The present invention has the further advantage of being a simple design and therefore easy and economical to manufacture. The present invention does not require modified or additional display electronics. The present invention does not requiring self-converging deflection yokes when used in monochrome CRT displays and does not requiring changes to the self-converging yoke when used in color CRT displays. The present invention has the advantage of being able to utilize any form of conventional CRT cathode, including field emitter array CRT cathodes.  
           [0033]    This is accomplished by having multiple apertures in the decelerating first electrode (G1) and the accelerating second electrode (G2). The accelerating third electrode (G3) and subsequent electrodes remain unmodified. This method introduces multiple emitting areas on the cathode. The emitted convergent electrons cross over and pass through their respective G1 and G2 apertures. The electrons are then redirected to form a single high current beam. This design can be compared to a macroscopic version of a field emitter array (FEA).  
           [0034]    The redirection of the electrons can be accomplished introducing a pre-focus lens. Any of the standard pre-focus methods can be employed for this purpose. The used of a dissimilar aperture diameters on either side of the accelerating second electrode (G2) provides a low cost version but allows for very little adjustability. The use of an additional electrode provides a higher cost version with the added advantage of adjustable pre-focus lens strength.  
           [0035]    These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of preferred embodiments, taken together with the accompanying drawings, in which: 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]    [0036]FIG. 1 is a simplified isometric view of a typical prior-art beam-forming region of an electron gun such as that used in a CRT.  
         [0037]    [0037]FIG. 2 is a longitudinal sectional view of the beam-forming region shown in FIG. 1 taken along site line  110 - 110 .  
         [0038]    [0038]FIG. 3 is a simplified isometric view of an alternate typical prior-art beam-forming region of an electron gun such as that used in a CRT, where a grid element is modified to introduce beam pre-focusing.  
         [0039]    [0039]FIG. 4 is a longitudinal sectional view of the beam-forming region shown in FIG. 3 taken along site line  128 - 128 .  
         [0040]    [0040]FIG. 5 is a simplified isometric view of an alternate typical prior-art beam-forming region of an electron gun such as that used in a CRT, where an extra grid element is employed to introduce beam pre-focusing.  
         [0041]    [0041]FIG. 6 is a longitudinal sectional view of the beam-forming region shown in FIG. 5 taken along site line  146 - 146 .  
         [0042]    [0042]FIG. 7 is a simplified isometric view shown particularly in phantom of typical prior-art electron gun such as used in a conventional monochrome CRT with a low uni-potential (standard einzel) electrode configuration.  
         [0043]    [0043]FIG. 8 is a longitudinal sectional view of the electron gun shown in FIG. 7 taken along site line  166 - 166 .  
         [0044]    [0044]FIG. 9 is a simplified isometric view shown particularly in phantom of typical prior-art electron gun such as used in a conventional monochrome CRT with a high uni-potential (high-einzel) electrode configuration.  
         [0045]    [0045]FIG. 10 is a longitudinal sectional view of the electron gun shown in FIG. 9 taken along site line  182 - 182 .  
         [0046]    [0046]FIG. 11 is a simplified isometric view shown particularly in phantom of typical prior-art electron gun such as used in a conventional monochrome CRT with a bi-potential electrode configuration.  
         [0047]    [0047]FIG. 12 is a longitudinal sectional view of the electron gun shown in FIG. 11 taken along site line  198 - 198 .  
         [0048]    [0048]FIG. 13 is a simplified isometric view shown particularly in phantom of typical prior-art electron gun such as used in a conventional monochrome CRT with a quad-potential electrode configuration.  
         [0049]    [0049]FIG. 14 is a longitudinal sectional view of the electron gun shown in FIG. 13 taken along site line  212 - 212 .  
         [0050]    [0050]FIG. 15 is a simplified isometric view shown particularly in phantom of a typical prior-art electron gun such as used in a conventional inline-color CRT.  
         [0051]    [0051]FIG. 16 is a longitudinal sectional view of the electron gun shown in FIG. 15 taken along site line  230 - 230 .  
         [0052]    [0052]FIG. 17 is a simplified isometric view shown particularly in phantom of a typical prior-art electron gun such as is used in a conventional Trinitron-color CRT.  
         [0053]    [0053]FIG. 18 is a longitudinal sectional view of the electron gun shown in FIG. 17 taken along site line  240 - 240 .  
         [0054]    [0054]FIG. 19 is a simplified isometric view of a beam-forming region  254  of an electron gun such as used in a CRT in accordance with one embodiment of the present invention.  
         [0055]    [0055]FIG. 20 is a longitudinal sectional view of the beam-forming region  254  shown in FIG. 19 taken along site line  252 - 252 .  
         [0056]    [0056]FIG. 21 is a simplified isometric view of a beam-forming region of an electron gun such as used in a CRT in accordance with an alternate embodiment of the present invention.  
         [0057]    [0057]FIG. 22 is a longitudinal sectional view of the beam-forming region shown in FIG. 21 taken along site line  270 - 270 .  
         [0058]    [0058]FIG. 23 is a simplified isometric view shown particularly in phantom of an electron gun such as used in a conventional monochrome CRT in accordance with one embodiment of the present invention with a low uni-potential (standard einzel) electrode configuration.  
         [0059]    [0059]FIG. 24 is a longitudinal sectional view of the electron gun shown in FIG. 23 taken along site line  290 - 290 .  
         [0060]    [0060]FIG. 25 is a simplified isometric view shown particularly in phantom of an electron gun such as used in a conventional monochrome CRT in accordance with one embodiment of the present invention with a high uni-potential (high-einsel) electrode configuration.  
         [0061]    [0061]FIG. 26 is a longitudinal sectional view of the electron gun shown in FIG. 25 taken along site line  306 - 306 .  
         [0062]    [0062]FIG. 27 is a simplified isometric view shown particularly in phantom of an electron gun such as used in a conventional monochrome CRT in accordance with one embodiment of the present invention with a bi-potential electrode configuration.  
         [0063]    [0063]FIG. 28 is a longitudinal sectional view of the electron gun shown in FIG. 27 taken along site line  322 - 322 .  
         [0064]    [0064]FIG. 29 is a simplified isometric view shown particularly in phantom of an electron gun such as used in a conventional monochrome CRT in accordance with one embodiment of the present invention with a quad-potential electrode configuration.  
         [0065]    [0065]FIG. 30 is a longitudinal sectional view of the electron gun shown in FIG. 29 taken along site line  336 - 336 .  
         [0066]    [0066]FIG. 31 is a simplified isometric view shown particularly in phantom of an electron gun such as used in a conventional inline-color CRT in accordance with one embodiment of the present invention.  
         [0067]    [0067]FIG. 32 is a longitudinal sectional view of the electron gun shown in FIG. 31 taken along site line  354 - 354 .  
         [0068]    [0068]FIG. 33 is a simplified isometric view shown particularly in phantom of an electron gun such as is used in a conventional Trinitron-color CRT in accordance with one embodiment of the present invention.  
         [0069]    [0069]FIG. 34 is a longitudinal sectional view of the electron gun shown in FIG. 33 taken along site line  364 - 364 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0070]    Referring to FIG. 19 there is shown a simplified isometric view of a beam-forming region  254  of an electron gun such as used in a CRT in accordance with one embodiment of the present invention. A longitudinal sectional view of the beam-forming region  254  shown in FIG. 19 taken along site line  252 - 252  is shown in FIG. 20. This BFR  254  is comprised of four components a cathode  256 , a “Wehnelt” or decelerating first electrode (G1)  258 , an accelerating second electrode (G2)  260 , and an accelerating third electrode (G3)  262 . The G1 and G2 electrodes  258 ,  260  have aperture arrays  258   a ,  260   a  that are linearly aligned with an aperture in the G3 electrode  262   a . Electrons emitted from the cathode  256  travel along a path  266  to the display screen and form a beam  268 . In this BFR  254  the G1 and G2 aperture arrays  258   a ,  260   a  are each comprised of seven smaller apertures  258   b ,  258   c ,  258   d ,  258   e ,  258   f ,  258   g ,  258   h ,  260   b ,  260   c ,  260   d ,  260   e ,  260   f ,  260   g ,  260   h.    
         [0071]    The aperture arrays  258   a ,  260   a  form multiple emitting areas on the surface of the cathode  254 . In this BFR  112  electrons are emitted from the cathode  256  and are accelerated toward the display screen by the G2  260  and the G3  262  electrodes, which are always of higher potential than the cathode  254 . Along the path  266  toward the display screen electrons pass through the G1 apertures  258   b ,  258   c ,  258   d ,  258   e ,  258   f ,  258   g ,  258   h . Since the G1 electrode  258  is typically of a lower potential than the cathode  256 , the negatively charged G1 electrode  258  repels the electrons causing them to converge and “cross-over.” The electron are now diverging and proceed to pass through their respective G2 apertures  260   b ,  260   c ,  260   d ,  260   e ,  260   f ,  260   g ,  260   h . This BFR  254  is equipped with a dimple or single large diameter screen side of the aperture  260   i . Since the G3 electrode  262  is typically of higher potential than the G2 electrode  260 , the high potential field of the G3 electrode  262  penetrates into the large diameter portion of the G2 aperture  260   i  and thus introduces a pre-focusing lens  264 . When electrons pass through the pre-focus lens  264  they are converged more so than in a conventional BFR  112 . By converging the electrons the single high current electron beam  268  is formed and sent through one of many main lens systems. This BFR  254  is beneficial because the strength of the pre-focusing lens  264  can be adjusted by changing the diameter and depth of the large diameter screen side of the G2 aperture  260   i.    
         [0072]    Referring to FIG. 21 there is shown a simplified isometric view of a beam-forming region of an electron gun such as used in a CRT in accordance with an alternate embodiment of the present invention, where an additional electrode (G2′)  280  is employed to introduce a pre-focusing lens  284 . A longitudinal sectional view of the beam-forming region shown in FIG. 21 taken along site line  270 - 270  is shown in FIG. 22. The alternate BFR  272  is comprised of five basic components a cathode  274 , a “Wehnelt” or decelerating first electrode (G1)  276 , an accelerating second electrode (G2)  278 , the additional electrode (G2′)  280  and an accelerating third electrode (G3)  282 . The G1 and G2 electrodes  276 ,  278 , have aperture arrays  276   a ,  278   a  that are linearly aligned with apertures in the G2′ and G3 electrodes  280   a ,  282   a . Electrons emitted from the cathode  274  travel along a path  286  to the display screen and form a beam  288 . In this BFR  272  the G1 and G2 aperture arrays  276   a ,  278   a  are each comprised of seven smaller apertures  276   b ,  276   c ,  276   d ,  276   e ,  276   f ,  276   g ,  276   h ,  278   b ,  278   c ,  278   d ,  278   e ,  278   f ,  278   g ,  278   h.    
         [0073]    This alternate BFR  272  uses the additional electrode (G2′)  280 , inserted between the accelerating second electrode (G2)  278  and the accelerating third electrode (G3)  282 , to introduce the pre-focusing lens  284 . The G2′  280  is always of lower potential than the G2  278 . The high potential electric field of the second accelerating electrode (G3)  282  penetrates into the G2′ aperture  280   a  and thus introduces the pre-focusing lens  284 . The predominant functional difference compared to the previous embodiment of the present inventive BRF  254  is that when the electrons pass through the pre-focusing lens  284  they are converged more or less depending on the potential of the G2′ electrode  280 . This inventive BFR  272  is beneficial because the strength of the pre-focus lens  284  can be adjusted. This method allows individual guns to be adjusted without the re-tooling of parts.  
         [0074]    Referring to FIG. 23 there is shown a simplified isometric view particularly in phantom of an electron gun  292  such as used in a conventional monochrome CRT with a BFR  294  that is in accordance with one embodiment of the present invention and with a low uni-potential (standard einzel) electrode configuration. A longitudinal sectional view of the electron gun  292  shown in FIG. 23 taken along site line  290 - 290  is shown in FIG. 24. The standard-einzel main lens  296  is comprised of three electrodes. A first electrode (G3)  298  and a third electrode (G5)  302  are electrically connected and held at a high potential, which is equal to the display screen anode potential. A second electrode (G4)  300  is held near ground potential. The presence of the lower potential G4 electrode  300  between the two high potential G3 and G5 electrodes  298 ,  302  forms a converging main lens  296  that focuses an electron beam  304  onto the display screen. By adjusting the potential of the G4 electrode  300  the beam&#39;s focus can be fine adjusted to match the beam&#39;s location on the display screen.  
         [0075]    Referring to FIG. 25 there is shown a simplified isometric view shown particularly in phantom of an electron gun  308  such as used in a conventional monochrome CRT with a BFR  310  that is in accordance with one embodiment of the present invention and with a high uni-potential (high-einsel) electrode configuration. A longitudinal sectional view of the electron gun  308  shown in FIG. 25 taken along site line  306 - 306  is shown in FIG. 26. The high-einzel main lens  312  is similar in construction to the standard-einzel main lens  296 . The high-einzel main lens  312  is comprised of three electrodes. A first electrode (G3)  314  and a third electrode (G5)  318  are electrically connected and held at anode potential. A second electrode (G4)  316  is held at a potential that is typically 20-40% of the anode potential. The potential of the G4 electrode  316  is used as the focusing adjustment for an electron beam  320 . The only functional difference between the standard-einzel  296  and high-einzel  312  main lenses is that the high-einzel G4  316  is held at a high potential.  
         [0076]    Referring to FIG. 27 there is shown a simplified isometric view shown particularly in phantom of an electron gun  324  such as used in a conventional monochrome CRT with a BFR  326  that is in accordance with one embodiment of the present invention and with a bi-potential electrode configuration. A longitudinal sectional view of the electron gun  324  shown in FIG. 27 taken along site line  322 - 322  is shown in FIG. 28. The bi-potential main lens  328  is comprised of two electrodes. A first electrode (G3)  330  is held at a high potential, which is typically 20-40% of the anode potential. A second electrode (G4)  232  is held at a high potential equal to the display screen anode potential. In this lens system the potential of the G3 electrode  330  is used as the focusing adjustment for an electron beam  334 .  
         [0077]    Referring to FIG. 29 there is shown a simplified isometric view shown particularly in phantom of an electron gun  338  such as used in a conventional monochrome CRT with a BFR  340  that is in accordance with one embodiment of the present invention with a quad-potential electrode configuration. A longitudinal sectional view of the electron gun  338  shown in FIG. 29 taken along site line  336 - 336  is shown in FIG. 30. The quad-potential main lens  342  is comprised of four electrodes. A first electrode (G3)  344  and a third electrode (G5)  348  are electrically connected and held at a high potential, typically 20-40% of the anode potential. A second (G4)  346  is held at low potential. A forth electrode (G6)  350  is held at anode potential. In this lens system the potential of the first (G3)  344  and third (G5)  348  electrodes are collectively used as the focusing adjustment for an electron beam  352 .  
         [0078]    Referring to FIG. 31 there is shown a simplified isometric view shown particularly in phantom of an electron gun  356  such as used in a conventional inline-color CRT with BFRs  358   a ,  358   b ,  358   c  that are in accordance with one embodiment of the present invention. A longitudinal sectional view of the electron gun  356  shown in FIG. 31 taken along site line  354 - 354  is shown in FIG. 32. In the inline color electron gun  356  three horizontally aligned beams  362   a ,  362   b ,  362   c  are sent through the distinctly isolated main-lenses  360   a ,  360   b ,  360   c . The inline color electron gun  356  is essentially three separate electron guns assembled from common parts.  
         [0079]    Referring to FIG. 33 there is shown a simplified isometric view shown particularly in phantom of an electron gun  366  such as is used in a conventional Trinitron-color CRT with BFRs  368   a ,  368   b ,  368   c  that are in accordance with one embodiment of the present invention. A longitudinal sectional view of the electron gun  366  shown in FIG. 33 taken along site line  364 - 364  is shown in FIG. 34. In the Trinitron electron gun  366  three horizontally aligned beams  372   a ,  372   b ,  372   c  are sent at through the center of the common shared main-lens  370 . The beams  372   a ,  372   b ,  372   c  are then redirected toward the display screen by a group of deflection plates  374   a ,  374   b ,  374   c ,  374   d.    
         [0080]    While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. Therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.