Abstract:
A thin cathode ray tube display system and associated components are disclosed. The system includes a thin cathode ray tube, a body having a substantially flat back element and a front element attached wherein a vacuum is maintained in the body, a neck element attached substantially perpendicular to the flat back element, wherein the neck element contains at least one electron gun for the emission of electrons, a transparent screen attached to the front element, the transparent screen having at least one phosphor layer operable to emit a photon of known wavelength and a substantially flat electron beam controller attached substantially perpendicular to the neck element operable to deflect an electron beam emitted by the at least one electron gun. The flat electron beam controller includes a plurality of coil sets oppositely positioned with regard to the neck to deflect the electron beam horizontally and vertically, wherein each of the coil sets further includes at least one coil arranged on at least one ferrite disk in a substantially trapezoidal shape.

Description:
PRIORITY FILING 
     This application claims the benefit of the earlier filing date of U.S. Provisional Patent Application Ser. No. 60/282,271, entitled “Flat Yoke of 145° Deflection Combined With a Thin CRT,” filed on Apr. 6, 2001, which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This application is related to the field of cathode ray tube (CRT) technology and more specifically to thin profile cathode ray tubes (CRTs) and thin electron beam controllers and their use in image display on televisions and computer monitors. 
     BACKGROUND OF THE INVENTION 
     Cathode Ray Tube technology has long dominated the television (TV) market and is also found in the computer market as computer monitors. Television picture tubes and computer CRT monitors use well known principles of electron beam deflection and scanning over phosphor covered CRT front screens to produce high quality visual images. Initially, using a single electron gun to generate an electron beam, television images were generated in only a black and white. Later, with the advent of the tri-color electron guns, and appropriate control logic, color images were produced. This has remained the standard for over 30 years. 
     Even with the advent of larger screen flat panel Liquid Crystal Displays (LCDs) and, recently, plasma displays, CRT technology continues to dominate the consumer television and computer market. While flat panel displays have certain advantages over CRTs, they also exhibit significant disadvantages. A comparison of the characteristics of flat panel displays compared to CRTs is discussed in “Flat-Panel Displays and CRTs” published by Van Nostrand Reinhold Company, New York, 1985. This comparison shows that CRTs continue to exhibit superior picture quality, durability and affordability over other display technologies. 
     Consumer demand has continually pushed television and CRT technology. First better quality images were demanded, then color images, and currently very large screen television with significant quality improvement, e.g. High Definition TV. However, CRT based televisions are generally limited to a typical size of 36 inches diagonally. Above this size, CRT technology experiences a number of significant problems. One problem is that as the diagonal dimension of the front screen of a CRT or picture tube increases, the weight of the tube increases, as the glass must be made thicker to maintain the necessary vacuum level within the picture tube. Another problem is that as the picture tube size increases, the size and weight of the electron beam controller, or yoke, used to direct the electron beam across the face of the picture tube increases. This increase in size is necessary to achieve a greater deflection of the electron beam to reach the outer edges of the larger picture tube face without undue image or color distortion. Still another problem is the current maximum deflection angle is limited to about one hundred twenty degrees (120°) as there is a need to maintain focus and color convergence of the three-color electron beams at the outer edges of the picture tube. Furthermore, as the size of the conventional cone-shaped magnetic yoke increases, both the mechanical structure and the magnetic field generated reach points of diminished return with regard to power consumption and beam defocusing. Hence, to achieve images greater than those displayed on a conventional 36-inch diagonal television, manufactures have developed front projection and back projection televisions. These systems optically enlarge an image produced by a much smaller CRT television and direct the enlarged image to a front panel. However, projection television does not have the image quality of a CRT of a comparable size. 
     Hence, there is a need in the industry for large screen CRTs and electron beam controllers that achieve much higher beam deflection and also do not exhibit significant increases in size or weight as the size of the CRT diagonal dimension increases. 
     SUMMARY OF THE INVENTION 
     A thin cathode ray tube display system and associated components are disclosed. The system comprises a thin cathode ray tube a body having a substantially flat back element and a front element attached wherein a vacuum is maintained in the body, a neck element attached substantially perpendicular to the flat back element, wherein the neck element contains at least one electron gun for the emission of electrons, a transparent screen attached to the front element, the transparent screen having at least one phosphor layer operable to emit a photon of known wavelength and a substantially flat electron beam controller attached substantially perpendicular to the neck element operable to deflect an electron beam emitted by the at least one electron gun. The flat electron beam controller comprises a plurality of coil sets oppositely positioned with regard to the neck to deflect the electron beam horizontally and vertically, wherein each of the coil sets further comprises at least one coil arranged on at least one ferrite disk in a substantially trapezoidal shape. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates cross-sectional view of a thin depth CRT in accordance with the principles of the invention; 
     FIG. 2 illustrates a cross-sectional of a thin depth CRT in accordance with a second aspect of the present invention; 
     FIG. 3 a  illustrates a cross-sectional view of a thin-depth CRT in accordance with another aspect of the present invention; 
     FIG. 3 b  illustrates a perspective view of a support grid in the thin-depth CRT shown in FIG. 3 a;    
     FIG. 3 c  illustrates a pixel control element in the thin-depth CRT shown in FIG. 3 a;    
     FIG. 4 a  illustrates a frontal view of a planar yoke element in accordance with the principles of the invention; 
     FIG. 4 b  illustrates a frontal view of a planar yoke element in accordance with a second aspect of the invention; 
     FIG. 5 a  illustrates a cross-sectional view, through section A—A, of the planar yoke element depicted in FIG. 4 a;    
     FIG. 5 b  illustrates a cross-sectional view of a planar yoke element in accordance with a second aspect of the invention; and 
     FIG. 6 illustrates a first application of a yoke module in accordance with the principles of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a cross-sectional view of a thin screen CRT  10  in accordance with the principles of the invention employing conventional TV technology. In this aspect of the invention, CRT  10  comprises a front element  14  and a back or rear element  12  which when attached together using known methods, e.g., Frit seal  16 , support a vacuum sufficient to enable electrons to traverse the distance between back element  12  and front element  14 . Front element  14  includes a conventional shadow mask  30  and, in color television, a tricolor, i.e., red, green, blue, phosphorous wall on front screen  32  over known region  34  corresponding to a front screen. Back element  12  includes a region  24  containing an inner graphite wall  26  that provides a black screen background. Attached to inner graphite wall  26  are vane elements  28  to shield the glass wall from the scanning electron beam. Protruding from back element  12 , substantially perpendicular, is neck  18  that includes electron gun  20 , which in the case of color CRT represents three electron beams corresponding to a red, green and blue phosphor on front screen  32 . As would be understood, an image is created on screen  32  by selectively illuminating corresponding pixel elements through the scanning of an electron beam emanating from electron gun  20 , as it passes through a magnetic field by yoke  22 . Surrounding neck  18  is a flat electron beam controller or yoke,  22 , as will be more fully described, that causes a deflection of an electron beam emitted from electron gun  20 . In one aspect of the invention, yoke  22  is operable to divert an electron beam emanating from electron gun  20  up to to 145 degrees. In one aspect of a thin depth CRT disclosed, back element  12  comprises a substantially flat surface that accommodates flat yoke  22 . A flat back element  12  is advantageous as it reduces the depth of CRT  10  and allows the magnetic field of yoke  22  to be brought closer to the front screen  32 . 
     In accordance with conventional TV technology, an electron beam is swept by yoke  22  horizontally, i.e., in rows, and then vertically, i.e., in lines, to create an image on screen  32 . 
     FIG. 2 illustrates a second aspect of a thin depth CRT  10 ′ in accordance with the principles of the invention. In this aspect, neck  18  is bent at a transition angle substantially ninety-degrees (90°) preferably. In this case, electrons emanating from electron gun  20  travel parallel to back element  12  and are then directed around the transition angle by bending magnet  40 . The transitioned electron beam then passes through yoke  22  substantially perpendicular to back element  12 , as previously discussed. This second aspect of the thin CRT is advantageous as it further reduces the depth of CRT  10 ′. 
     FIG. 3 a  illustrates cross-sectional view of a thin-depth CRT  50  in accordance with another aspect of the invention. In this aspect of the invention, back element  12  and front element  14  are joined together by Frit seal  16 , for example. Back element  12  comprises the same elements as previously described. However, front element  14  includes a metallic grid structure  52  fused in a thin transparent panel  32 ′. In this aspect of the invention metallic grid  52  provides structural support for transparent panel  32 ′, which includes phosphor layers and is essentially comparable to screen  32 . The use of metallic structure  52  is advantageous as this structure rather than a heavy glass panel provides structural support to withstand the vacuum stresses placed on CRT  50 . In this case, the weight of CRT  50  is significantly reduced over that of conventional CRT of a comparable size. 
     Further included in front element  14  is representative of an “Einzel” lens structure  54  aligned with pixel layer  55  which includes red, green, blue (RGB) pixel control lines, represented as  56   a ,  56   b ,  56   c , associated with each pixel element in layer  55 . Einzel lens  54  has a middle electrode that operates with a zero or negative potential and controls a video signal image arranged on pixel layer  55 . The use of a Einzel lens  54  to control the image presented on screen  32 ′ is advantageous as electron gun  58  may be a cold cathode device, e.g., field emission device rather than a hot cathode electron gun used in the current CRT technology. The use of cold cathode electron gun  58  is advantageous as less energy is required to create an electron beam and, consequently, less heat is generated. Furthermore, as the image control is on pixel layer  55  and Einzel lens  54 , only a single unmodulated electron bean is required to project an image onto screen  32 ′ rather than a tri-color electron beam modulated for each color. 
     Although not illustrated, it will be appreciated that metallic grid structure  52  may be used on the thin depth CRTs shown in FIGS. 1 and 2 whether conventional hot-cathode CRT technology or Einzel lens technology is incorporated. Thus, large screen CRTs may be fabricated using existing equipment and technology. 
     FIG. 3 b  illustrates a perspective view of exemplary metallic grid  52  in accordance with the principles of the invention. In this case, metallic grid  52  is represented as an interlocking grid of substantially horizontal rows  60  and vertical  62  columns that form substantially square-like elements  64 . As would be appreciated, grid  52  is formed as substantially rectangular-like elements that are matched to the Einzel lens structure  54 . 
     FIG. 3 c  illustrates control of individual pixel element using Einzel lens  54 . In this example, an image is applied to individual pixel element through to RGB controls,  56   a ,  56   b , and  56   c . Screen  32 ′ is maintained a typically high voltage, in the order of 10 kv, to attract electrons emitted by electron gun  58  (not shown). When a zero voltage is applied to Einzel lens  54 , emitted electrons are allowed to pass through Einzel lens  54  and a corresponding pixel element and bombard a corresponding phosphor strip on screen  32 ′. However, when sufficient negative voltage is applied to Einzel lens  54 , emitted electrons are blocked from passing through lens  54  and are no image is presented on screen  32 ′. Hence, Einzel lens  54  operates as a filter to allow or block an electron beam from bombarding a phosphor layer. Accordingly, an image may be formed on screen  32 ′ by the selective application of color control to individual pixel element controls, selective application of a voltage to Einzel lens  54  and using conventional yoke controlled horizontal and vertical scanning, as previously discussed, to direct electrons to each pixel element. 
     FIG. 4 a  illustrates an embodiment a planar yoke element  400  in accordance with the principles of the invention. In this embodiment, first coils  120 ,  120 ′, which are referred to as H 3  and H 3 ′, operate as a first cooperative set of coils to divert or deflect an electron beam passing through ring  115  in a horizontal direction and coils  220 ,  220 ′, which are referred to as V 3  and V 3 ′, operate as a first cooperative set of coils to divert or deflect an electron beam passing through ring  115  in a vertical direction. In the preferred embodiment illustrated, coils  120 ,  120 ′, and  220 ,  220 ′ are substantially trapezoidal shaped. Trapezoidal shaped coils are advantageous, and preferred, as they provide maximum, interaction of the magnetic field generated by each coil without overlapping the coil elements. The trapezoidal shape also assists in reducing a “pin-cushion” effect at the edge of the CRT screen. Pin-cushion-ing is a common problem in CRT technology that requires special circuitry to overcome. In one aspect, the length of a trapezoidal leg closest to the CRT neck is in the order of the neck radius. It will be appreciated that rectangular shaped coils may be used without altering the scope of the invention. 
     In the operation of the planar yoke element shown, when a potential is appropriately applied to a respective coil, the current flow in each coil generates a magnetic field that is used to divert the direction of an electron beam passing through circular ring  115 . Accordingly, an electron beam is swept horizontally when current  125  is applied to coil  120  and current  125 ′ is applied to coil  120 ′. As would be appreciated, currents  125  and  125 ′ operate to generate magnetic fields, as is well-known in the art, that extend outwardly from ferrite disk  110  and are returned through ferrite disk  110 . Coils  120 ,  120 ′ operate as a set or group to constructively add and produce a desired level of magnetic flux density across center hole or ring  115 . Although not shown, it will be appreciated that a similar application of current through coils  220 ,  220 ′ produces reinforcing magnetic fields that operate to direct an electron beam passing through circular ring  115  vertically. 
     In the illustrated embodiment, a material barrier  150  is inserted between adjacent coils  120 ,  220 ,  120 ′ and  220 ′, respectively, that is used to reduce the pincushion effect caused by undesirable component magnetic fields. Material barrier  150  is preferably a soft iron type material that shields undersirable magnetic flux. 
     Also arranged on disk  110 , are coils  320 ,  320 ′,  420 ,  420 ′, which are contained within and are associated with coils  120 ,  120 ′,  220 ,  220 ′, respectively. Coils  320 ,  320 ′, and  420 ,  420 ′, similar to coils  120 ,  120 ′, and  220 ,  220 ′, are operated as cooperative sets to produce constructively reinforced magnetic fields. These magnetic field further constructively reinforce the magnetic fields associated with their coils,  120 ,  120 ′ and  220 ,  220 ′, respectively. Hence, coils  320 ,  320 ′, which are referred to as H 2  and H 2 ′, operate to reinforce the magnetic field associated with coils  120 ,  120 ′ to direct an electron beam passing through ring  115  in a horizontal direction. Similarly, coils  420 ,  420 ′, which are referred to as V 2  and V 2 ′, operate to reinforce the magnetic field associated with coils  220 ,  220 ′, respectively, to direct an electron beam passing through ring  115  in a vertical direction. 
     Use of a second set of coils  320 ,  320 ′ and  420 ,  420 ′ is advantageous as it increases the magnetic flux density and deflection sensitivity of an electron beam horizontally and vertically, without incurring an increase in size, weight and power consumption that is necessary to achieve a substantially similar deflection sensitivity of an electron beam using only single coil  120 ,  120 ′ (or  220 ,  220 ′). In this aspect, deflection of an electron beam up to +/−75 degrees may be achieved. 
     Further arranged on disk  110  are third coil sets  520 ,  520 ′ and  620 , 620 ′, which are associated with and contained within coils  120 ,  320 ,  120 ′,  320 ′,  220 ,  420 ,  220 ′,  420 ′. In this case, third coil  520 , for example, is associated with and contained within coils  120  and  320 , while coil  520 ′ is associated with and contained within coils  120 ′ and  320 ′. Although, coils  520 ,  520 ′ are similar in shape to associated coils  120 ,  320  and  120 ′,  320 ′, they are wound in a reverse manner and operate to provide a negative or destructive interference on the deflection of electron beam passing through ring  115 . This negative interference on the deflection of an electron beam is advantageous as it provides more precise control of the beam convergence and allows for the incorporation of a planar yoke element in conventional television sets, as will be more fully explained. Hence, third coils  520 ,  520 ′, for example, may be used to alter electron beam  140  deflection from a nominal +/−75 degrees (i.e., total sweep of 150 degrees) to a conventional +/−60 degrees (total sweep of 120 degrees). Coils  620 ,  620 ′ similarly operate to provide a negative interference on the deflection of an electron beam in a vertical direction. 
     Although FIG. 4 a  illustrates a first aspect of the invention, it would be understood by those skilled in the art, that coils  120 ,  320 ,  520 , for example, may be fabricated as a single coil loop or may operate as independent coils that constructively or destructively interfere with associated magnetic fields. Furthermore, each coil, although operating in cooperative sets, may operate in combination or independent of any other associated coil. For example, coil  320  may be electrically connected in series (i.e., combination) or in parallel (i.e., independent) to associated coil  120 , which may be electrically connected in series or in parallel to associated coil  520 . Similarly, coil  320 ′ may be connected in series or parallel to associated coil  120 ′, which may be electrically connected in series or in parallel to associated coil  520 ′. The criteria for selecting electrically connecting of associated coils depends on by realizing a desired level of magnetic flux density across ring  115  to achieve a desired level of electron beam deflection. Determination of current flow to produce desired levels of magnetic flux density is well known in the art. 
     Furthermore, although associated coils are shown separated by a significant distance, it will be appreciated that the illustrated separation is merely to depict the coils and that the coils may in practice be electrically isolated but in physical contact. 
     FIG. 4 b  illustrates a second aspect of a planar yoke  450  in accordance with the principles of the invention. In this aspect, ferrite material  460  is placed on an insulating material, e.g., plastic,  470 . Horizontal and vertical beam deflection coils, e.g.,  120 ,  320 ,  530 , etc., are arranged on ferrite material  460 , as previously discussed. A separation or groove  480  is formed in ferrite material  460 . The use of groove  480  is advantageous as it provides a space to conductor wire  225  associated with each coil. Hence, groove  480  provides a means to maintain a substantially flat cross-section of planar yoke  450 . Although not illustrated, it will be appreciated that soft material  150  (not shown) may be laid in groove  480 . Furthermore, it will be appreciated that ferrite material  460  may be a single material containing grooves  480  or may be plurality of appropriately shaped similar materials separated by a distance, referred to as groove  480 . 
     FIG. 5 a  illustrates a cross-sectional view of the embodiment of planar yoke element  400  through section A—A. To more clearly illustrate the position of coils  120 ,  120 ′,  320 ,  320 ′,  520 ,  520 ′ on ferrite material disk  100 , the cross-section view of coils  220 ,  420 , and  620  is not shown. In this case, each of the illustrated coils comprises at least one wire conductor  225  mounted substantially in a plane perpendicular to ferrite material disk  100 . Wire conductor  225  typically is in the order of 0.15 to 0.4 mm. In a preferred embodiment wire conductor  225  associated with horizontal beam deflection coils  120 ,  320 ,  520 , for example, is in the order of 0.4 mm and conductor  225  associated with vertical beam deflection coils  220 ,  420 ,  620 , for example, is in the order of 0.15 mm. 
     FIG. 5 b  illustrates a planar yoke element  500  in accordance with a second aspect of the invention. In this aspect of the invention, coils are placed on both sides of ferrite disk  100  in a manner as previously discussed. In this configuration the magnetic field across center ring  115  is increased, reinforced or focused by the appropriate application of voltage, and current, to each coil loop to achieve a significant increase in magnetic field across ring  115  without significant increase in power. 
     FIG. 6 illustrates a cross-sectional view  600  of a planar yoke  605  comprised of a single planar yoke element  630 , as shown in FIG. 5 a  and a double planar yoke element  640 , as shown in FIG. 5 b . Yoke  605  is placed on a neck  610  of CRT  620 , in a conventional manner. Within neck  610  is placed electron gun  625  that emits electron beam  140 . Electron gun  625  conventionally outputs a modulated electron beam  140  that is directed toward the screen (not shown) of CRT  620 . Appropriate application, with regard to magnitude and polarity of voltage and current to each individual yoke element generates a corresponding level of magnetic field  650  that causes a relatively minor diversion in electron beam  140 . This configuration is advantageous as the magnetic flux generated is focused through each disk element and only relatively a low current is necessary in each planar yoke element. The cumulative effect of each minor electron beam deflection results in an overall deflection that may in one aspect achieve a sweep of up to 145°. 
     Although yoke  605  is shown having mixed planar yoke elements  630 ,  640 , it will be understood from the details disclosed herein that planar yoke  605  may comprise only single sided yoke elements such as shown in FIG. 5 a  or only double sided yoke elements as shown in FIG. 5 b . It will be appreciated that the outer coils, similar to the third coil in FIG. 4 b  on the outer disk elements of yoke  605  produce a magnetic field  660  not only necessary for limiting electron beam deflection from 145° to 120° but also to assist in the self convergence of the three (i.e., red, green, blue) electron beams of the mask-screen on a conventional color CRT. 
     As would be known, planar yoke  605  operates in conjunction with a means, such as a step-ferrite slab  670 , inside neck  610 , a processor or a line scanner controller (not shown) that applies an appropriate voltage to each yoke element to generate varying levels of magnetic field. The varying levels of magnetic field create a deflection in electron beam  140  as it traverses neck  610 . Hence, beam  140  enters CRT  620  at an angle that causes an excitement of an appropriate phosphor element on the screen of CRT  620 . As would be appreciated, in a color television system, electron gun  625  may comprise a single electron gun or a conventional tri-color electron gun. In this latter case, the level of deflection for associated color beams depends on the color level required at a corresponding pixel element on CRT  620  screen. 
     While there has been shown, described, and pointed out, fundamental novel features of the present invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the apparatus described, in the form and details of the devices disclosed, and in their operation, may be made by those skilled in the art without departing from the spirit of the present invention. For example, it is expressly intended that all combinations of those elements which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated.