Patent Publication Number: US-6670745-B2

Title: Cathode ray tube deflection yoke

Description:
This Application claims the benefit of U.S. Provisional Application Serial No. 60/279,006 filed Mar. 27, 2001, and U.S. Provisional Application Serial No. 60/279,573 filed Mar. 29, 2001. 
    
    
     The present invention relates to a deflection yoke for a cathode ray tube and, in particular, to a deflection yoke including a coil having a non-constant distribution of turns. 
     A deflection yoke for a cathode ray tube (CRT) includes a shaped horizontal coil for deflecting the beam or beams of electrons produced by an electron gun in a horizontal direction across the CRT faceplate (screen) and a shaped vertical coil for deflecting the beam(s) of electrons across the screen in a vertical direction. Typically, many horizontal scans are accomplished at a relatively high horizontal scan rate within each cycle of the relatively low frequency vertical scan rate. The horizontal and vertical deflection coils are usually shaped so as to lie in a generally conforming manner close to and generally surrounding the funnel-shaped glass envelope of the CRT proximate a tube neck that contains the electron gun. The deflection yoke usually has a shaped core of ferromagnetic material, such as a ferrite material, for more effectively concentrating the magnetic field produced by the horizontal and vertical coils in the interior of the tube envelope in a deflection region thereof for deflecting the electron beam(s) in the horizontal and vertical directions. 
     The inherent problem of deflection yokes is the significant inductance exhibited by the coils in combination with the ferrite core, particularly for the horizontal coil due to its operation at a higher horizontal scan rate or frequency. Such inductance dictates the amount of energy that must be stored in the magnetic field to produce a particular magnetic field strength in the deflection region of the CRT. A measure of the energy stored in the magnetic field produced by the horizontal coil is referred to as the “horizontal stored energy” or “HSE” and is a useful relative measure or parameter for comparing the relative efficiency of different deflection yokes. HSE is a value in milli-Joules (mJ) calculated by HSE=½ L(I p ) 2  where L is the inductance of the deflection coil in milli-Henries and I p  is the peak deflection current in amperes. 
     As certain desirable features of a CRT are pursued, e.g., a “short” or “slim” CRT having reduced depth between the CRT faceplate and the far end of the tube neck, greater deflection angles are desired which increases the strength of the magnetic deflection field required. Newer wider CRTs, such as the 16:9 aspect ratio CRTs employed in high-definition television (HDTV) displays, tend also to increase the required deflection angle and the strength of the deflection field required. The foregoing tends to increase the required coil size and/or number of turns and/or drive current magnitude, all of which tend to increase the HSE of the deflection yoke. 
     Practical considerations, such as heat generation, temperature rise, and the cost of the deflection yoke and of the circuitry employed to apply suitable drive currents thereto, serve to limit the maximum energy stored in the magnetic field to about 7-8 mJ. Conventional deflection yokes employ deflection coils having a “uniform” or “constant” turns distribution, i.e. the number of turns producing the magnetic deflection field is substantially the same over a majority of the entire Z-axis length of the yoke, except for relatively small regions at the yoke entrance and yoke exit where the number of turns changes rapidly from zero to the constant number of turns, and for small numbers of correction turns or correction coils for correcting coma, convergence, distortion and the like. Conventional deflection yokes tend to exhibit undesirably high HSE values for deflecting newer wide deflection angle CRTs. 
     While certain prior art deflection yokes have employed deflection coils wherein the coils have certain turns arranged for correcting convergence, pincushion distortion and/or other errors, all known prior art deflection yokes employ deflection coils wherein the magnetic field produced by essentially all of the turns thereof affect the electron beams over the entire deflection length of the yoke, although a few turns may be used for certain corrections. Examples include U.S. Pat. Nos. 5,121,028, 5,418,422, and 5,506,469 (e.g., gun-side end turns for correction of mis-convergence, coma errors, astigmatism, north-south raster errors), U.S. Patent 5,077,533 (e.g., screen end turns for modification of third and higher harmonics), and U.S. Pat. Nos. 5,077,533, 5,121,028, 5,418,422 (e.g., side turns for harmonic correction). 
     It would be desirable to provide greater deflection without increasing the deflection power (or HSE) or to reduce the deflection power (or HSE) required to produce a given deflection, or some combination thereof. 
     Accordingly, there is a need for an improved deflection yoke and CRT. 
     To this end, the deflection yoke of the present invention has an exit region between an entrance region and a yoke exit, wherein the exit region is substantially longer than the entrance region, and comprises first and second deflection coils, wherein at least one of the first and second deflection coils has a non-constant distribution of turns in the exit region between the entrance region and the yoke exit of the deflection yoke. A magnetic core is disposed for cooperating with the first and second deflection coils to form a deflection yoke. 
     According to another aspect, a cathode ray tube comprises a tube envelope, an electron gun providing an electron beam impinging on a screen, and a deflection yoke according to the previous paragraph positioned proximate the tube envelope for scanning deflection of the electron beam produced by the electron gun on the screen. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The detailed description of the preferred embodiments of the present invention will be more easily and better understood when read in conjunction with the FIGURES of the Drawing which include: 
     FIG. 1 is a cross-sectional schematic diagram of an example embodiment of a cathode ray tube; 
     FIG. 2 is a graphical representation of the potential in the cathode ray tube of FIG. 1; 
     FIG. 3 is a plan view schematic diagram of a Prior Art deflection coil. 
     FIG. 4 is a plan view schematic diagram of a deflection coil for a deflection yoke in accordance with the invention; 
     FIG. 5 is a graphical representation comparing a conventional deflection yoke having constant or uniform turns distribution with the example embodiment of FIG. 4 in accordance with the invention; 
     FIG. 6 is a plan view schematic diagram of an alternative deflection coil for a deflection yoke in accordance with the invention; 
     FIG. 7A is a graphical representation of parametric data comparing conventional deflection yokes to deflection yokes having a positive bias deflection coil and to deflection yokes having a negative bias deflection coil; 
     FIG. 7B is a graphical representation of parametric data for deflection yoke HSE in relation to deflection yoke turns distributions; 
     FIG. 8A is a plan view schematic diagram of an embodiment of a deflection coil in accordance with the invention having a negative biased non-constant turns distribution with negative and positive turns, and FIG. 8B is a plan view schematic diagram of a detail portion of FIG. 8A; 
     FIG. 9 is a graphical representation of parametric data comparing a conventional deflection yoke to a deflection yoke in accordance with FIG. 8; 
     FIGS. 10A,  10 B and  10 C are graphical representations illustrating certain cross-sections of three different deflection coil arrangements; 
     FIGS. 11A,  11 B and  11 C are graphical representations illustrating examples of turns distributions for a conventional deflection yoke and for example embodiments according to the invention having linear and nonlinear negative biased non-constant turns distributions; 
     FIG. 12 is a graphical representation of a sectional view of a deflection yoke and its position relative to a CRT for a deflection yoke including the invention; 
     FIGS. 13 and 14 are cross-sectional diagrams illustrating alternative example embodiments providing appropriately positioned electrodes within a cathode ray tube. 
     FIGS. 15A and 15B are computer-generated graphical representations of one quadrant of the horizontal and vertical deflection coils, respectively, of a deflection yoke according to the invention; 
     FIG. 16A shows a graphical representation of the cumulative number of turns of a horizontal deflection coil having a negative bias non-constant and non-linear turns distribution; 
     FIGS. 16B and 16C show graphical representations of parametric variation of HSE for the coil of FIG. 16A; and 
     FIGS. 17A,  17 B and  17 C are rear, bottom and side views, respectively, of an example deflection coil according to the invention, and FIG. 17D is a perspective view thereof. 
     In the Drawing, where an element or feature is shown in more than one drawing figure, the same alphanumeric designation may be used to designate such element or feature in each figure, and where a closely related or modified element is shown in a figure, the same alphanumerical designation primed may be used to designate the modified element or feature. Similarly, similar elements or features may be designated by like alphanumeric designations in different figures of the Drawing and with similar nomenclature in the specification, but in the Drawing are preceded by digits unique to the embodiment described. For example, a particular element may be designated as “xx” in one figure, by “1xx” in another figure, by “2xx” in another figure, and so on. According to common practice, the various features of the drawing are not to scale, and the dimensions of the various features are arbitrarily expanded or reduced for clarity. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     A cathode ray tube deflection yoke is provided wherein the deflection yoke includes a plurality of deflection coils. One or more of the deflection coils have a non-constant” or “non-uniform” distribution of turns, whereby an electron beam passing through the deflection yoke is deflected by a magnetic field that varies according to different numbers of turns in relation to position between the entrance and exit of the deflection yoke. 
     The end of the deflection yoke closest to the electron gun is generally referred to as the entrance or yoke entrance or entrance plane, because that is where the electron beam(s) enter the magnetic deflection field produced by the deflection yoke. The end of the deflection yoke closest to the CRT faceplate or screen is generally referred to as the exit or yoke exit or exit plane, because that is where the electron beam(s) leave the magnetic deflection field produced by the deflection yoke. Owing to the funnel-shape of the CRT glass envelope, the deflection yoke is also typically more or less funnel-shaped with the narrower central opening at its entrance and the larger central opening at its exit. 
     The central axis (usually referred to as the Z-axis) of the CRT is generally (due to symmetry) also the central axis of the electron gun, the deflection yoke and the glass funnel, and generally intersects the faceplate, which lies generally (ignoring curvature, if any) in the X-Y plane, at its center. The horizontal direction is usually considered as the X direction and the vertical direction as the Y direction. 
     In a cathode ray tube, the electrons of the electron beam(s) may be further deflected after leaving the influence of the magnetic deflection yoke, i.e. in what is referred to as the “drift region” or “field-free region” of a conventional CRT through which the electrons travel in substantially straight lines to the screen. In a conventional CRT, the electrons are at the screen or anode potential at the time they leave the gun and deflection regions and, not being under the influence of any electric or magnetic field, travel in straight lines to the screen or faceplate thereof. Such cathode ray tube may find application, for example, in television displays, computer displays, projection tubes and other applications where it is desired to provide a visual display. 
     FIG. 1 is a cross-sectional diagram of a cathode ray tube  10 . It is noted that unless otherwise specified, such cross-sectional diagrams may be considered to illustrate either the horizontal or the vertical deflection orientation because both appear similar in such diagrams. FIG. 1 illustrates a horizontal, i.e. X-Z plane, cross section. Electrons produced by electron gun  12  located in tube neck  14  are directed towards faceplate  20 , which includes a screen or anode electrode  22  biased at a relatively high positive potential, and are deflected by magnetic fields produced by deflection yoke  16  to scan across faceplate  20 . Electrodes  44 ,  46 ,  48  on tube envelope  40  are biased to predetermined potentials to establish electrostatic fields within tube envelope  40 , and may be biased to provide a field-free region or to deflect electron beams  30  either away from the tube  10  centerline further than they are deflected by the magnetic field produced by deflection yoke  16  or towards screen  22 , or both. Electrode  44  may be referred to as a neck electrode because it is proximate neck  14  and electrodes  46 ,  48  may be referred to as funnel electrodes because they are disposed along the funnel portions of tube envelope  40 . 
     A coating of phosphorescent material  23  is disposed on faceplate  20  for producing light in response to the beam of electrons  30  impinging thereon, thereby providing a monochromatic display, or a pattern of different phosphorescent materials  23  is disposed thereon for producing different colors of light in response to the plural beams of electron beam  30  impinging thereon through apertures in shadow mask  24 , thereby providing a color display. Usually, the three beams of electron beam  30  are referred to as the “red R beam,” the “green G beam,” and the “blue B beam” indicating the beams that are intended to illuminate the red phosphor, the green phosphor and the blue phosphor, respectively, of phosphor  23 . 
     Electrostatic fields may be established within tube  10  by a number of conductive electrodes located on or close to backplate  40  and biased at respective positive potentials, i.e. at potentials of like polarity to that of the screen or anode electrode  22 . The bias potentials on electrodes  44 ,  46 ,  48  of tube  10  provide an electrostatic field to control and/or affect the trajectories of the electrons of electron beam  30 , and may thereby reduce the required distance between the faceplate  20  and electron gun  12  of example tube  10 , and/or change the landing angle of electron beam  30  on screen  22 . 
     Electrode  44  surrounds the outlet of gun  12  in the vicinity of neck  14  and is biased at a positive potential that is preferably equal to or less than the potential at screen electrode  22 . The electrostatic field produced by electrode  44  being biased below screen potential may result in the electrons of electron beam  30  being slower moving proximate yoke  16 , and therefore more easily deflected. Such cooperation between electrode  44  and yoke  16  may be utilized to realize either a reduction of yoke power, and therefore a smaller, lighter, less expensive and likely more reliable deflection yoke  16 , or a greater deflection angle with the same yoke power and yoke. 
     Electrode  46  also surrounds the outlet of gun  12 , but is spaced away from neck  14  towards screen  22 , and is biased at a positive potential that is preferably equal to or greater than the potential at screen electrode  22 . Where electrode  46  is biased above screen  22  potential, the electrostatic field produced thereby may be utilized to cause the electrons of beam  30  to travel in a path that bends their trajectories away from faceplate  20 , thereby increasing the deflection angle from that produced by magnetic deflection yoke  16  alone, and also decreasing the “landing angle” of electron beam  30 . Electrode  46  is desirably positioned so that its electrostatic field does not act on electron beam  30  until after it has been substantially fully acted upon by deflection yoke  16 . 
     “Landing angle” is the angle with respect to the plane of the screen at which electron beam  30  impinges upon screen electrode  22 , and in a color CRT, the shadow mask  24  proximate thereto. As a result of the action of the field of electrode  46 , the landing angle may become smaller as the distance from the central or Z axis of tube  10  becomes greater and/or as the deflection angle of electron beam  30  increases. Because shadow mask  24  has a non-zero thickness, if the landing angle is too small, e.g., less than about 25°, too many of the electrons will hit the sides of the apertures in shadow mask  24  instead of passing therethrough, thereby reducing the intensity of the electron beam reaching phosphor  23  on the faceplate  20  and of the light produced thereby. 
     Advantageously, electrode  48  is located distal the central or Z axis of tube  10  and near the periphery of faceplate  20  where the landing angle is smallest. Electrode  48  surrounds the outlet of gun  12 , at least with respect to the horizontal deflection which is typically greater than the vertical deflection. Electrode  48  is substantially at the periphery of backplate  40 , and is biased at a positive potential that is preferably equal to or less than the potential at screen electrode  22 . When electrode  48  is biased at a potential below screen  22  potential, the field therefrom acts to direct electron beams  30  back towards faceplate  20  for increasing the landing angle thereof near the periphery of faceplate  20 . Electrode  48  may be biased to a potential less than the potential at neck electrode  44  where desired to provide greater reduction of landing angle. Thus, the electrostatic fields created by electrodes  46  and  48  may complement each other in that when electrode  46  increases the deflection angle (which decreases the landing angle at the periphery of faceplate  20 ), electrode  48 , which has its strongest effect near the periphery of faceplate  20 , may act to increase the landing angle in the region where it might otherwise be undesirably small. 
     The relationship and effects of the electrostatic fields described above cooperate in a tube  10  that may be shorter in depth than a conventional CRT and yet may operate at a comparable and/or reasonable deflection yoke power level. Two example potential distributions over the depth of tube  10  along its Z axis are illustrated in FIG.  2 . Potential characteristics  60   a ,  60   b  illustrate two different biasing potential characteristics and are plotted on a graph having distance from the exit of gun  12  along the ordinate and bias potential in kilovolts along the abscissa. Screen electrode  22  located at a distance L from gun  12  and represented by region Z 22  is biased at a relatively high positive potential V 22  represented at point  62 . In order from gun  12  at Z=0 are neck electrode  44  located proximate gun  12  and represented by electrode region Z 44  that is biased at a positive potential V 44 , electrode  46  located intermediate gun  12  and faceplate  20  and represented by electrode region Z 46  that is biased at a relatively high positive potential V 46  that is preferably equal to or higher than the screen potential V 22 , and electrode  48  located more proximate to faceplate  20  and represented by electrode region Z 48  that is biased at a positive potential V 48  that is preferably lower than screen potential V 22  (but could be equal thereto) and could preferably be lower than gun potential V 44 . 
     Electrodes  44 ,  46 ,  48 ,  22  and bias potentials V 44 , V 46 , V 48 , V 22  thereon produce potential characteristic  60   a  that has a portion  64   a  rising towards the screen potential V 22  thereby tending to slow the acceleration of electrons towards faceplate  20  to provide additional flight time during which the subsequent electrostatic fields act upon the electrons. Characteristic  60   a  has a portion  66   a  in which the potential peaks at a level relatively higher than the screen potential V 22  thereby to cause the electrons to move along trajectories that depart further from central axis Z of tube  10  to increase the deflection angle and a portion  68   a  in which the potential bottoms at a level lower than the screen potential V 22  and the gun potential V 44  thereby to cause the electrons to move along trajectories that turn toward faceplate  20  of tube  10  to increase the landing angle of electron beam  30  near the edges of screen  22 . 
     It is noted that the location of the gap between electrodes  44  and  46  may strongly affect the operation of tube  10 . If electrode  46  having a relatively very high positive potential bias extends too close to the exit of gun  12  (and/or neck electrode  44  does not extend sufficiently far therefrom), then the electrons emitted from gun  12  are accelerated and additional magnetic deflection effort is required of deflection yoke  16  (e.g., additional yoke power, field and/or size) to provide the desired magnetic deflection. On the other hand, if neck electrode  44  extends too far beyond the exit of gun  12 , then the electrons spend too much time in a region in which electrostatic forces act counter to the deflection sought to be produced by magnetic deflection yoke  16 , thereby increasing the power, field and /or size required of yoke  16  to deflect the electron to the corners of faceplate  20 , even with the beneficial effect of electrode  46 . 
     Alternatively, electrodes  44  and  46  may be biased to screen potential V 22  where deflection yoke  16  provides greater deflection, e.g., 135-140° deflection, as illustrated by segments  64   b ,  66   b  of graph  60   b  of FIG. 2, and electrode  48  may be biased to a potential substantially less than screen potential (segment  68  thereof) for increasing the landing angle of the electron beam  30 . 
     The particular values of bias potential are selected in accordance with a particular tube  10  to obtain, for example, a suitable balance of reduced tube depth and reasonable yoke power in consideration of the effects of each of the bias potentials. Examples of typical bias potentials and ranges thereof are set forth in the following table for an example CRT: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                 Electrode 
                 Symbol 
                 Example #1 
                 Example #2 
                 Example #3 
               
               
                   
               
             
            
               
                 Screen Electrode 22 
                 V 22  = 
                 30 kV 
                 30 kV 
                 30 kV 
               
               
                 Neck electrode 44 
                 V 44  = 
                  0-30 kV 
                 15 kV 
                 30 kV 
               
               
                 Back Electrode 46 
                 V 46  = 
                 30-35 kV 
                 35 kV 
                 30 kV 
               
               
                 Kick electrode 48 
                 V 48  = 
                  0-30 kV 
                 10 kV 
                 17-23 kV 
               
               
                   
               
            
           
         
       
     
     An example CRT may be an about 810-mm (about 32-inch) diagonal 16:9 aspect ratio format cathode ray tube having a viewable area of 660 mm (about 26 inch) width and 371 mm (about 14.6 inches) height. As a result of the reduced tube depth of the present invention, tube  10  has a depth D of about 280 mm (about 11 inches). Deflection yoke  16  may be a 110° or a 125° saddle-saddle type deflection yoke including a saddle-type horizontal coil, a saddle-type vertical coil, a ferrite core and a pair of permeable metal shunts for shaping vertical deflection for self convergence. With the 125° deflection-angle yoke, the diameter of tube neck  14  may be reduced to allow use of a smaller, lower power yoke  16 . Preferably, deflection yoke  16  is a non-converging (non-self-converging) deflection yoke providing a total deflection angle of about 135-140° wherein each of the horizontal and vertical deflection coils is of the saddle-type. Specifically, at least the horizontal deflection coil preferably has a non-constant distribution of turns so that the number of turns effective at the entrance of the yoke is substantially greater than the number of turns effective at the exit of the yoke. The distribution of turns typically decreases monotonically between the yoke entrance and exit, but not necessarily linearly, as is determined by the particular arrangement of the shape and electrode arrangement of the cathode ray tube  10 , the bias potentials to be applied thereto, and the desired characteristics. 
     Cathode ray tube  10  may employ a combination of electrodes including conductive coatings on tube enclosure  40  and metal electrodes supported within tube envelope  40 . In the illustrated arrangement, neck electrode  44  and deflection-enhancing electrode  46  are a conductive coating on the wall of tube envelope  40  and are biased at a potential applied via feedthrough  45  and/or  47  penetrating the wall of tube envelope  40 , or may be connected to screen electrode  22  to receive bias potential therefrom. Third electrode  48  is biased at a potential that is applied via feedthroughs  49  penetrating the wall of tube envelope  40 . Shadow mask  24 , supported by shadow mask frame  26 , receives screen electrode  22  bias potential via feedthrough  25  penetrating the wall of tube envelope  40 . Barium getter material  56  is placed at convenient locations, such as behind shadow mask frame  26  and electrodes  48   a ,  48   b.    
     Because faceplate  20  is much shorter in the vertical dimension than in the horizontal dimension (which is illustrated in FIG.  1 ), electrode  48  need not be rectangular so as to act on electrons directed toward the top and bottom edges of the viewable area of faceplate  20 , but may be two straight L-shaped formed metal electrodes  48   a ,  48   b  receiving bias potential via feedthroughs  49   a ,  49   b , respectively, to act only on those electrons directed towards the left and right vertical edges of tube  10 . Electrodes  48   a ,  48   b  are supported by feedthroughs  49   a ,  49   b , respectively, such as by a weld or a conductive glass frit to metal attachment. 
     A conductive coating electrode on the inside surface of tube  40 , such as on faceplate  20  or glass envelope  40 , is preferably a sprayed, sublimated, spin coated or other deposition or application of graphite, carbon or carbon-based materials, aluminum or aluminum oxide, or iron oxide, or other suitable conductive material. Where electrodes, such as electrodes  48   a ,  48   b , are spaced away from the wall of tube envelope  40 , such electrodes are preferably formed of a suitable metal such as a titanium, Invar alloy, steel, stainless steel, or other suitable metal, and are preferably stamped. If magnetic shielding is desired to shield electron beam  30  from unwanted deflection caused by the earth&#39;s magnetic field and other unwanted fields, a magnetic shielding metal, such as mu-metal, steel, or a nickel-steel alloy, may be employed. 
     In the FIGURES, arrows indicate an arbitrary reference direction of current flow in the various portions of the deflection coil, it being recognized that current in the coil is not static, but varies at the scanning rate (typically increasing and decreasing as a “sawtooth” shaped waveform), and may be positive and negative, during each scan cycle. Deflection coil “end turns” are the portions of the turns of the deflection coil transverse to the Z axis and intersecting the Y-Z plane, and are generally referred to as “gun end turns”or as “gun-side end turns” if transverse proximate the yoke entrance (the end nearer the electron gun) and as “screen end turns” or as “screen-side end turns” if transverse proximate the yoke exit (the end nearer the screen). End turns are distinguished from “side turns” which are the portions of the turns of the deflection coil disposed in a direction generally along the Z axis and on either side of the Y-Z plane, usually symmetrically. Also, “Le” represents the length of the yoke entrance region, “Lx” represents the length of the yoke exit region, and “Li” represents the length of the yoke region intermediate the entrance and exit regions wherein the cumulative turns count is substantially constant at or near the maximum number of turns, each of the foregoing lengths being defined in a direction parallel to the Z axis. 
     FIG. 3 is a plan view schematic diagram of a Prior Art saddle-type deflection coil. Conventional deflection yokes employ deflection coils having a “uniform” or “constant” turns distribution, i.e. the number of turns producing the magnetic deflection field is substantially the same over the entire Z-axis length of the yoke, except for relatively short (small) regions at the yoke entrance and exit where the number of turns changes sharply (i.e. over a short distance) from zero to the constant number of turns. Prior art deflection coils typically have all or almost all of their end turns grouped together in the relatively short entrance and exit regions, and have a relatively large central or intermediate region in which the cumulative turns count is relatively constant. 
     For example, conventional deflection yoke coil  300  of FIG. 3 represents a horizontal saddle-type coil that has 150 turns (150 T) arranged in a single loop. The 150 turns of coil  300  are bunched close together to define a single loop, e.g., as they cross transversely to the Z axis near the yoke entrance (gun-side end turns indicated by numeral  302 ) and near the yoke exit (screen end turns indicated by numeral  304 ), thereby with side turns  306 ,  308  to define a large central opening or window  310  surrounded by the coil  300 . Thus, the cumulative number of turns increases sharply in the relatively short distance of the entrance region between the entrance plane (line A) and coil window  310  )line B), is relatively uniform or constant over the relative long dimension of window  310  (intermediate region between lines B and D), and decreases sharply over a relatively short distance of the exit region between window  310  (line D) and the exit plane (line E), as is illustrated by graph G- 300  of FIG.  5 . Side turn portions  306   a - 306   c  and  308   a - 308   c  are identified for later reference. 
     As the electrons of an electron beam travel in the direction along the positive Z axis of the CRT from the electron gun towards the screen, they pass through the deflection region of the deflection yoke and are under the influence of the magnetic field produced by the deflection coils thereof. As the electrons of the electron beam pass the entrance of the conventional deflection yoke  300 , they quickly come under the influence of the magnetic field produced by all 150 turns  302  of deflection coil  300  disposed near the yoke entrance. As the electron beam passes through the deflection region of the deflection yoke, the electrons continue under the influence of the magnetic field produced by all 150 turns of deflection coil  300  (i.e. a region of constant or uniform cumulative turns count) over a relatively long distance until they reach the yoke exit. Then the electron beams leave the influence of the 150 turns of coil  300  relatively quickly as they pass the yoke exit and, having been deflected, continue to travel towards the screen. 
     As is known in the art, a small number of correction turns may be utilized in deflection coil  300  for correcting coma, pincushion distortion and other effects, and such correction turns are generally considered as being in the intermediate region. For example, a small number of the end turns in bundle  304  may be formed in a loop  304   p  extending towards the yoke entrance for correcting pincushion distortion 
     FIG. 4 is a plan view schematic diagram of a deflection coil  100  for a deflection yoke  16  in accordance with the invention. Deflection coil  100  has a negative-bias non-constant turns distribution. In a non-constant turns distribution or a non-constant turns biased deflection coil, the number of turns of the deflection coil producing magnetic field for deflecting electrons varies over the length of the coil (the deflection region of the deflection yoke) in relation to the location between the yoke entrance and yoke exit. In other words, there is a gradient of the number of turns effective at any given location between the yoke entrance and exit. The turns gradient may decrease in a monotonic and linear manner as illustrated by the example deflection coil  100  shown in FIG. 4, which is referred to as a negative-biased turns distribution, or may increase, and/or may be non-monotonic and/or non-linear. 
     As used herein, a deflection coil is referred to as having a “negative turns distribution” or a “negative bias” or a “negative turns bias” if the cumulative number of turns reaches a maximum near the end nearer the yoke entrance and decreases over the yoke length towards the yoke exit at which there are a lesser number of turns. A deflection coil is referred to as having a “positive turns distribution” or a “positive bias” or a “positive turns bias” if the cumulative number of turns is smaller near the yoke entrance and increases over the yoke length towards the yoke exit nearer which there are a greater number of turns. In any non-constant turns distribution, the decrease or increase may be monotonic or non-monotonic and/or may be linear or non-linear. Because each turn is a closed loop of wire, the cumulative number of turns along the Z-axis first increases from zero turns to a maximum value and ultimately returns to zero turns, and graphical representations may be utilized to describe the coil. Such graphical representations typically “smooth” the graphed data between discrete values, rather than illustrate discrete steps produced by each turn or group of turns. 
     Example deflection coil  100  has 275 turns (275 T) of which all 275 turns are bundled  110  at the gun-side end turn end, so that the cumulative number of turns increases sharply over a short distance near the yoke entrance, e.g., between lines A and B. Along the Z-axis direction of coil  100 , at least three additional bundles  120 ,  130 , . . .  160  of turns of varying number are disposed transversely at various locations along the Z axis so that the cumulative number of turns progressively decreases over the relatively long distance between lines B and E. For example, transverse bundle  120  of end turns with bundle  110  defines window  112  of a very small intermediate region, and additional bundles  120 ,  130 ,  140 ,  150 ,  160  of turns disposed progressively along the relatively long Z-axis length Lx of the exit region of coil  100  respectively define additional small windows  122 ,  132 ,  142 ,  152 . 
     As the electrons of the electron beam pass the entrance of the deflection yoke, they quickly come under the influence of the magnetic field produced by all of the 275 turns  110  of deflection coil  100  disposed near the yoke/coil entrance. As the electron beam passes through the relatively short intermediate deflection region of the deflection yoke, the electrons continue under the influence of the magnetic field produced by all 275 turns of deflection coil  100  (i.e. a region of constant or uniform cumulative turns count) over a relatively short distance. As the electron beam then passes through the relatively long exit region of the deflection yoke, the electrons continue under the influence of the gradually decreasing magnetic field produced by the cumulatively decreasing number of turns (i.e. less than all 275 turns) of deflection coil  100  over a relatively long distance. until they reach the yoke exit. Then the electron beams leave the influence of coil  100  and, having been deflected, continue to travel to the screen. 
     It is noted that the number of end turns comprising each of the bundles  120 ,  130 , . . .  160  may be same or may be different. In the 275 turn example of FIG. 4, bundles  120  and  130  combined include 125 turns, bundles  140  and  150  combined include 125 turns, and bundle  160  includes 25 turns. Alternatively, the end turns of the exit region may be evenly or unevenly spread over the exit region. Thus, the number of bundles or groups of turns in the exit region is at least three and may be as many as the total number of turns of deflection coil  100 . Typically, where the end turns are bundled, at least one bundle of end turns is disposed to the gun (entrance) side of the deflection center (not the physical midpoint) of the deflection yoke and at least two bundles of end turns are disposed to the screen (exit) side thereof. 
     Deflection coil side turns are disposed in two bundles  170   a ,  170   b  disposed symmetrically with respect to the Y-Z plane on opposite sides thereof and the turns therein may be relatively close together or may be relatively spread apart for imparting certain characteristics to the deflection yoke employing coil  100 . For example, the portions of turns in bundle  110  and in the portions  172   a ,  172   b  of side turn bundles  170   a ,  170   b  aside end-turn bundles  110  and  120  and window  112  may be spread to span a relatively wide angle for providing a winding turn distribution that is rich in “negative third harmonics” proximate the yoke entrance which is useful for the correction of coma. Also, the side turns of bundle portions  174   a ,  174   b  aside end-turn bundles  140  and  150  may be relatively close together to span a short distance to provide a winding distribution that is rich in “positive third harmonics” which is useful for self-convergence of the deflection yoke and for correcting astigmatism, and, more towards the exit plane, for the correction of top-bottom (north-south) pincushion distortion. 
     As is known to those of skill in the art, Fourier winding harmonics produced by the arrangement of side turns in a deflection coil refer to the magnetic field produced by the deflection coil. In a deflection coil for producing a uniform magnetic field, the side turns are arranged in a cosine distribution symmetrical with respect to the Y-Z plane. Side turns are referred to as providing “negative third harmonics” if the side turns are shifted towards the Y-Z plane relative to the uniform field cosine turns distribution (i.e. towards the center), and are referred to as producing “positive third harmonics” if the side turns are shifted away from the Y-Z plane relative to the uniform field cosine turns distribution (i.e. towards the side edges). 
     FIG. 5 is a graphical representation of cumulative turns count plotted against distance along the Z axis in the deflection region between the deflection yoke entrance and exit. FIG. 5 compares a conventional deflection yoke coil  300  having a constant or uniform turns distribution as in FIG. 3 (labeled Prior Art) with an example embodiment of a deflection yoke coil  100  having a non-constant turns distribution as in FIG.  4 . Lines A, B, C, D and E are provided to relate typical physical locations on the plan views of FIGS. 3 and 4 to the graphs of FIG.  5 . The respective intermediate region lengths Li and the exit region lengths Lx for each of coils  100  and  300  are also indicated thereon close to graphical representations G- 100  and G- 300 , respectively. 
     For the prior art coil represented by graph G- 300 , the cumulative turns count is constant at 150 turns over most of the length of the coil, with sharp changes over the very short entrance region (between lines A-B) and the very short exit region (between lines D-E). Typically, the length Li of the intermediate region of a conventional deflection coil is substantially greater than the length Le of the entrance region or the length Lx of the exit region thereof, and of the combined length Le+Lx. In addition, the cumulative number of turns in the intermediate region does not vary by more than about 5-10%, e.g., for correction turns, such as utilizing a small number of turns near the gun (entrance) end for coma correction and/or a small number of turns near the screen (exit end) for pincushion correction. Correction turns may be provided as part of the deflection coil or by an adjacent separate correction coil. 
     The deflection coil  100  embodiment represented in FIG. 5 by graph G- 100  has a negative-biased non-constant turns distribution in that the cumulative number of turns decreases between the yoke entrance region and the yoke exit, i.e. over a relatively long distance of the exit region. Typically, the length Le of the entrance region and the length Li of the intermediate region are very much smaller than is the length Lx of the exit region. One way to define the desirable non-constant turns distribution is in terms of the distance L P%  along the combined length (Li+Lx) of the deflection coils along the Z-axis direction at which the cumulative number of turns decreases to a given portion P of the maximum cumulative number of turns N T  of the deflection coil. Typically, the maximum cumulative number of turns N T  occurs at the boundary between the entrance region and the intermediate region, e.g., at the line B between the entrance and intermediate regions. 
     For example, where the portion P is 0.8 or 80%, the cumulative number of turns decreases to 80% of the maximum number of turns N T  no further than 0.68 (68%) of the distance from the beginning of the intermediate region to the exit end of the exit region, i.e. at a distance 0.68 (Li+Lx) or 68% of the combined length of the intermediate and exit regions. This condition may be represented by:                  L     80      %         Li   +   Lx       ≤   0.68           [     Equation                 1     ]                         
     for N/N T =0.8. In other words, the ratio N/N T  is 0.8 or less over 32% or more of the combined length of the intermediate and exit regions (Li+Lx). Typically, the length ratio of Equation 1 is less than 0.6 for most deflection coils and is less than 0.5 for a typical deflection coil. In other words, the ratio N/N T  is 0.8 or less over 40% or more and 50% or more, respectively, of the combined length (Li+Lx). 
     Further, the cumulative turns count decreases to 50% of the maximum number of turns N T  no further than 0.8 (80%) of the distance from the beginning of the intermediate region to the exit end of the exit region, i.e. at a distance 0.8 (Li+LX). This condition may be represented by:                  L     50      %         Li   +   Lx       ≤   0.8           [     Equation                 2     ]                         
     for N/N T =0.5. In other words, the ratio N/N T  is 0.5 or less over 20% or more of the combined length of the intermediate and exit regions (Li+Lx). Any one or more of the foregoing criteria may be utilized to define the invention. 
     Alternatively, the cumulative number of turns at the midpoint of the combined length of the intermediate and exit regions, i.e. at (Li+Lx)/2, is typically in the range of about 0.35-0.77 (35-77%) of the maximum cumulative number of turns N T  and is always less than 0.80 (80%) thereof. A typical deflection yoke according to the invention has negative bias and a cumulative turns count at the (Li+Lx)/2 midpoint of less than 80% of the maximum number of turns. Alternatively, the distribution of turns may be defined in terms of “slope” of the distribution of cumulative turns. For example, the cumulative turns distribution may be defined with respect to the (Li+Lx)/2 midpoint by the ratio:                  N       (     Li   +   Lx     )     /   2         N   T       ≤   0.8           [     Equation                 3     ]                         
     at (Li+Lx)/2, 
     where: 
     N represents the cumulative number of turns, and 
     N (Li+Lx)/2  represents the cumulative number of turns at the midpoint of the combined length of the intermediate and exit regions in the Z axis direction, and 
     N T  represents the maximum cumulative number of turns. 
     FIG. 6 is a plan view schematic diagram of an alternative deflection coil  100  for a deflection yoke in accordance with the invention in which certain turns of coil  100  are illustrated to show the approximate positions of certain turns thereof and to illustrate the winding of coil  100 . It is noted that the screen-side end turns in the exit region Lx are spread over the distance Lx+Li for providing a gradual progressively decreasing cumulative turns count over the exit region, and so the number of bundles or groups of turns may be as large as the number of turns. 
     In winding coil  100 , the first turn  101  is started at the beginning of the winding process to surround the small area that will become window  112  and the coil  100  is wound outward therefrom. As the wire is positioned to define the turns, the position is determined for providing the desired physical arrangement for increasing or decreasing the positive and negative third harmonics useful for certain corrections of the CRT deflection. Typically, the wire is placed onto a form that defines the shape of the coil and that has pins, pegs or other features against which or around which the wire is placed to form the desired turns and shape. The winding ends with the last or finish turn  161  which is at the extreme exit end of coil  100 . 
     In addition to the distribution of the end turns of coil  100  for reducing HSE, the distribution of the turns of coil  100  in the exit region in FIG. 6 illustrates that the turns may be physically spread over smaller or larger distances for defining a number of transverse end-turn bundles (between three and the number of turns) over the distance Lx. In addition, portions of side turns  170   a ,  170   b  may be spread or grouped for providing negative and/or positive third harmonics for correcting coma, and/or pincushion, and/or for providing self-convergence. For example, coil portions  172   a ,  172   b  may be used to provide negative third harmonics for correcting coma, and/or coil portions  174   a ,  174   b  may be used for providing positive third harmonics for correcting pincushion and/or for providing self-convergence. 
     It is noted that the arrangement of deflection coils  100  are negative bias coils wherein the cumulative turns count decreases gradually, and generally progressively, along the Z axis from the yoke entrance to the yoke exit. The lesser number of turns in the region of the deflection coil near the yoke exit tends to decrease the effective diameter of the deflection yoke. The arrangement tends to shift the deflection center of the deflection yoke towards the yoke entrance which tends to slightly reduce the angular deflection required to deflect the electron beam to the edges and corners of the screen. One or both of these aspects tend to increase the deflection sensitivity and/or reduce the HSE of the deflection yoke, whether the yoke cross section is circular or rectangular or something in between. Thus, a deflection yoke employing deflection coils having turns distributions as described may be non-converging or self-converging. 
     An example 140° deflection yoke having horizontal deflection coils as described herein reduced HSE from about 12 mJ (conventional yoke) to about 8.4 mJ with a 140° wide CRT (30 kV screen/anode potential) of the sort shown in FIG.  1 . An example 120° deflection yoke having horizontal deflection coils as described herein reduced HSE from about 7.1 mJ (conventional yoke) to about 5.4 mJ with a 120° CRT (30 kV anode potential). 
     FIG. 7A is a graphical representation illustrating parametric analysis data comparing conventional deflection yokes (square symbols PA) to deflection yokes having a positive turns bias coil (diamond symbols PB), and to deflection yokes (triangle and circular symbols) having negative turns bias coils. The positive turns bias deflection yokes (square symbols PB) have positive turns bias deflection coils with 75, 150 and 225 turns (cumulatively) at line positions B, C and D, respectively. The negative turns bias deflection yokes (triangle symbols NB) have negative turns bias deflection coils with 225, 150 and 75 turns (cumulatively) at line positions B, C and D, respectively, in FIG.  5 . Other negative turns bias deflection yokes (circular symbols GNB) have more highly negative turns bias deflection coils with 275, 150 and 25 turns (cumulatively) at line positions B, C and D, respectively, and provide the lowest HSE. In FIG. 7, plural symbols of like type represent different values for the deflection yoke length in the Z-axis direction. The parametric data appears to indicate that, at least within limited ranges, increasing the yoke exit diameter and/or increasing the yoke entrance position towards the electron gun each tend to reduce HSE. Dashed line MP represents an example of an upper practical level for HSE. 
     FIG. 7B is a graphical representation illustrating parametric data wherein the HSE of example deflection yokes is plotted against the relative turns count of the horizontal deflection coil. The relative turns count thereof is indicative of the cumulative number of turns at a location near the exit plane of the deflection yoke relative to the cumulative turns count at the mid-point of the Lx+Li length of the deflection coil. The horizontal axis is representative of the relative slope of the turns distribution over the Lx+Li length of the coil. N=0 corresponds to a constant turns distribution as in a prior art deflection coil, while N&gt;0 represents a positive turns bias and N&lt;0 represents a negative turns bias. FIG. 7B illustrates that a deflection yoke employing negative bias non-constant turns distribution horizontal deflection coils can provide an HSE reduction of about 25-35%. 
     FIG. 8A is a plan view schematic diagram of a deflection coil  200  having a negative biased non-constant turns distribution with reverse direction and forward direction turns, that may be employed as the horizontal coils for a self-converging deflection yoke. Forward and reverse direction turns carry current in opposite directions along the Z axis on the same side of the Y-Z plane, e.g., the current in one flows in a direction generally towards the coil exit and the current in the other flows in a direction generally away form the coil exit. Typically, the direction in which the principal current flows is referred to as the forward direction, e.g., that of side turns  270   a - 270   b.    
     Deflection coil  200  has coil turns arranged in bundles or groups  210 ,  220 ,  230 ,  240 ,  272  defining windows  212 ,  222 ,  232 , generally similar to groups  110 ,  120 ,  130 ,  140 ,  172 , and windows  112 ,  122 ,  132 , respectively, of deflection coil  100  of FIGS. 4 and 6, and may provide a winding distribution rich in negative third harmonics for coma correction. In coil  200  of FIG. 8, however, the side turns portions in side bundles  274   a ,  274   b  are spread over a relatively larger distance (e.g., at angles of about 0-30° with respect to the horizontal X-Z plane) and the turns in regions  254   a ,  254   b  of transverse end turn bundle  250  reverse direction (i.e. relative to the direction of current flow in regions  274   a ,  274   b ) and are also spread over a relatively larger distance (e.g., at angles of about 30-90° with respect to the horizontal X-Z plane), thereby to define a relatively wider angle of 0-90°. As a result, the winding distribution is very rich in positive third harmonic for self convergence and for top-bottom pincushion correction (where coil  200  is a horizontal coil). In turn bundle  250  of coil  200 , the turns  254   a ,  254   b  are formed in the region of the Z axis to extend back towards the coil entrance (e.g., in the reverse direction away from the coil exit opposite to the direction of the other turns of coil  200 ) to form an opening  252 . Such turns distribution arrangement provides correction turns that may be utilized for reducing pincushion distortion. 
     FIG. 8B illustrates an alternative arrangement for coil  200  in which turns bundle  250  is not shaped towards the coil entrance and a correction coil  255  is provided, e.g., for correcting distortion. The current in coil  255  flows in the opposite direction to the current in turns bundle  250 , thereby providing an effective net current of substantially zero where coil  255  overlies turns bundle  250  when both produce the same value of ampere-turns. If the current flow in side turns  274   a ,  274   b  is defined as the forward direction, then the current flow in coil  255  is in the reverse direction, as indicated by the respective arrows. Coil  255  defines a window  252 ′. 
     FIG. 9 is a graphical representation of parametric data comparing a conventional deflection yoke coil (dashed line G- 300  Prior Art) to deflection yoke coil  200  as in FIG.  8 . Along the Z axis direction from the yoke entrance to the yoke exit, the cumulative number of turns N of coil  200  increases sharply and then decreases gradually. Line G- 200 -ON represents the cumulative number of turns N of coil  200  “on axis,” i.e. taken where coil  200  intersects the Y-Z plane, and reaches zero at a certain distance before the yoke exit plane. Line G- 200 -OFF represents the cumulative number of turns N of coil  200  “off axis,” i.e. taken on either side of the Y-Z plane, and reaches zero at the yoke exit plane. Thus, coil  200  may be said to have a negative turns bias with all forward turns along the Z axis, but to have a negative turns bias with both forward and reverse turns on both sides of the Y-Z plane. As a result, the first harmonic tends to be reduced to zero at the yoke exit and the positive third harmonics are relatively high. 
     FIGS. 10A,  10 B and  10 C are graphical representations illustrating certain cross-sections of three different deflection coil arrangements. The first row of graphs (FIG. 10A) represents a conventional deflection yoke having coils with a constant or uniform turns distribution as in coil  300  of FIG. 3, the second row of graphs (FIG. 10B) represents a defection yoke having coils with a negative biased non-constant turns distribution with all forward direction turns as in coil  100  of FIGS. 4 and 6, and the third row of graphs (FIG. 10C) represents a deflection yoke having coils with a negative biased non-constant turns distribution with forward and reverse direction turns as in coil  200  of FIG.  8 . For each of FIGS. 10A to  10 C, each graph represents one quadrant of a spatial distribution of turns of a deflection coil, i.e. in cross-section cut in a plane parallel to the X-Y plane. For each of FIGS. 10A to  10 C, the first column depicts the cross-section of the side turns of the deflection yoke near the entrance region thereof, the center column depicts the cross-section of the side turns of the deflection yoke in the mid-region thereof, and the right column depicts the cross-section of the side turns of the deflection yoke near the exit thereof. Side turn regions of each of coils  100 ,  200 ,  300  are depicted in FIGS. 10A-10C using the same numerical identifiers as are used in FIGS. 4,  6  and  8 , respectively. 
     FIGS. 11A,  11 B and  11 C are graphical representations illustrating examples of turns distributions for a conventional deflection yoke G- 300 ′ and for example embodiments according to the invention having linear and nonlinear negative biased non-constant turns distributions. In FIG. 11A, characteristic G- 300 ′ of a prior art deflection coil similar to prior art coil  300  has a slight positive turns distribution near its entrance, perhaps reflecting turns spread for coma correction, and a slightly rising but substantially constant turns distribution through its mid-region. Characteristic G- 200  represents a linear negative bias turns distribution, as for deflection coil  200 , and has an intermediate region that is extemely small (not visible) and has a very long exit region Lx. Alternatively, characteristic G- 200  A illustrates a deflection coil  200 A wherein the negative turns bias is non-linear, and wherein the intermediate region Li is very small and the exit region Lx is very long. Specifically, more exit region end turns are disposed nearer to the portion of the exit region Lx that is proximate the entrance region, so that the characteristic G- 200  A over its exit region has a steeper negative slope near the entrance end of its exit region Lx than near the exit end thereof, thereby to have a concave or “sunken in” shape. For a 120° color CRT with a 30 kV screen potential, coil  200 A has an HSE of 5.14 mJ as compared to 5.5 mJ for coil  200 , as compared to 7.07 mJ for prior art coil  300 ′. 
     In FIG. 11B, a linear negative bias turns distribution characteristic G- 200  is shown for reference and characteristics G- 200 B and G- 200 C illustrate deflection coils  200 B and  200 C wherein the negative turns bias is non-linear, plotted against the left-hand vertical scale in turns. Illustrated against the right-hand vertical scale representing distance from the Z axis (in mm) are certain physical elements of a deflection yoke, specifically the deflection yoke core DYC of ferrite or other suitable magnetic material, and the horizontal deflection coil  200 ,  200 B,  200 C. The envelope of the CRT, which would be close to the horizontal coil (actually, the deflection yoke is assembled with the CRT so that the horizontal coil is closely adjacent the CRT envelope), is not shown. 
     Specifically, characteristic G- 200 B represents a deflection coil  200 B wherein more exit region end turns are disposed towards the portion of the exit region that is nearer to the entrance region, so that the characteristic G- 200 A over its exit region has a steeper negative slope near the entrance end of its exit region than near the exit end thereof, thereby to have a concave or “sunken in” shape. This arrangement decreases the number of turns near the yoke exit which may effectively reduce the average diameter of the deflection yoke coils and shift the deflection center towards the yoke entrance, thereby tending to reduce the deflection angle required to deflect the electron beam to the screen edges and corners. Alternatively, characteristic G- 200 C represents a deflection coil  200 C wherein more exit region end turns are disposed towards the portion of the exit region that is nearer to the yoke exit, so that the characteristic G- 200 C over its exit region has a shallower negative slope near the entrance end of its exit region than near the exit end thereof, thereby to have a convex or “bulged” shape. 
     In FIG. 11C, a linear negative bias turns distribution characteristic G- 200  is again shown for reference and characteristic G- 200 D illustrates deflection coil  200 D wherein the negative turns bias is non-linear and non-monotonic, plotted against the left-hand vertical scale in turns. Illustrated against the right-hand vertical scale representing distance from the Z axis (in mm) are deflection yoke core DYC and horizontal deflection coil  200 D. The CRT envelope is not shown. Specifically, characteristic G- 200 D represents a deflection coil  200 D wherein more end turns carrying current in the same direction as the entrance region end turns are disposed in the mid-portion of the exit region, so that the characteristic G- 200 A over its exit region has a negative slope near both the entrance end and the exit end of its exit region and has a positive slope over a middle (but not necessarily centered) portion of the exit region, thereby to have a “jagged” or “peaked” shape. 
     Deflection coils producing characteristics of shape like that of plots G- 200  through G- 200 C are sometimes referred to as “single bias” coils and those producing characteristics of shape like that of plot  200 D are sometimes referred to as “double bias” coils, because there are two regions of increasing cumulative turns count. Double bias coil arrangements as in deflection coil  200 D may provide a longer coil entrance length, which tends to reduce the deflection angle required to reach the screen corners and/or to reduce the average diameter of the deflection yoke, thereby tending to reduce the HSE of the deflection yoke. Example coil parameter values include: 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
               
               
                 Coil 
                 HSE 
                 Entrance Z 
                 Exit 
                 Exit Radius 
                 Coil Length 
                 Deflection 
               
               
                 Type 
                 (mJ) 
                 (mm) 
                 Z (mm) 
                 (mm) 
                 (mm) 
                 Angle 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 200 
                 10.12 
                 −69.2 
                 −4.43 
                 100 
                 65 
                 135° 
               
               
                 200B 
                 9.33 
                 −69.2 
                 −4.43 
                 100 
                 65 
                 133° 
               
               
                 200C 
                 10.08 
                 −69.2 
                 −4.43 
                  97 
                 65 
                 135° 
               
               
                 200D 
                 8.4 
                 −88.2 
                 −12.33 
                  97 
                 76 
                 132° 
               
               
                   
               
            
           
         
       
     
     FIG. 12 is a graphical representation of a sectional view of a deflection yoke and its position relative to a CRT (not shown) for a deflection yoke  20  including the invention. Yoke  20  has a ferrite core  20 C wherein the surface thereof adjacent the deflection coils and the CRT envelope is stepped to define a recess having a shoulder  22  between a thicker portion and a thinner portion, which may enhance correction of top-bottom (vertical) pincushion distortion. Vertical coil  20 V is turned up at its entrance and is shortened at the exit end so as to be under the core  20 C and to extend to shoulder  22 , thereby allowing core  20 C to be closer to the exit end of horizontal coil  200 H, which has a negative bias non-constant turns distribution. Horizontal coil  200 H extends beyond the end of core  20 C at its exit end and at its entrance end. For a 120° color CRT with a 30 kV electron beam, for example, a deflection yoke  20  of substantially similar size to a conventional yoke that has an HSE value of 7.07 mJ, exhibits an HSE of 5.41 mJ, i.e. a beneficial reduction of about 23%. 
     FIG. 13 is a cross-sectional diagram of an alternative example cathode ray tube  1210  showing an alternative arrangement for appropriately positioning a set of electrodes  1244 ,  1246 ,  1248  mounted within the interior of funnel-shaped glass bulb  1240  to deflect an electron beam (not shown) to land on screen electrode  1222  and phosphors  1223 , similarly to screen  22  and electrodes  44 ,  46 ,  48  described above. Electron gun  1212 , neck  1214 , faceplate  1220 , phosphors  1223 , shadow mask  1224 , mask frame  1226 , and funnel-shaped glass bulb  1240  are disposed symmetrically relative to centerline  1213 , and may include a getter material  1256  in a convenient location in the space between glass bulb  1240  and one or more of metal electrodes  1246 ,  1248 , mask frame  1226  and mask frame shield  1228 , all of the foregoing being substantially as described above. 
     Stamped metal mask shield  1228  and stamped metal electrodes  1246 ,  1248  are formed as a set of mirror-image plates and/or loops of ascending dimension and are positioned symmetrically with respect to tube central axis  1213  with the smallest proximate neck  1214  and the largest proximate mask frame  1226  and faceplate  1220 . Mask frame  1226  is a relatively rigid metal structure attached to the interior of faceplate  1220 , such as by metal clips or by embedment in glass support features such as glass beads or lips on the interior surface of faceplate  1220 , and provides support for mask shield  1228  and for electrodes  1246  and  1248  attached thereto Typically, two or more insulating supports  1252  (not visible) bridge the gap between mask shield  1228  and electrode  1248  for providing electrically insulating support therebetween to hold mask shield  1228  and electrode  1248  in a desired relative position. Similarly, two or more additional insulating supports  1252  (not visible) bridge the gap between electrode  1246  and electrode  1248  for providing electrically insulating support therebetween to hold electrode  1246  and  1248  in a desired relative position. Mask shield  1228  and electrodes  1246 ,  1248  are electrically isolated, unless it is desired that two or more of mask shield  1228  and electrodes  1246 ,  1248  be at the same bias potential. 
     In a typical tube  1210  having an about 81 cm (about 32-inch) diagonal faceplate  1220  in a 16:9 wide-format aspect ratio, depth D is about 28 cm (about 11 inches). Screen  1222 , mask  1224 , mask support  1226  and mask shield  1228  are biased to a potential of about 28-32 kV, and typically 30 kV, via high-voltage conductor  1225  (i.e. “button”  1225 ) penetrating glass bulb  1240 . Coated neck region electrode  1244  is biased in a range of about 18-24 kV, typically 22 kV, applied via button  1245 . High voltage electrode  1246  is biased to a potential higher than the screen bias potential in a range of about 30-35 kV, typically 35 kV, applied via button  1247 , for increasing the electron-beam deflection provided by deflection yoke  1216 . Electrode  1248  is biased to a potential less than the screen bias potential in a range of about 18-24 kV, typically 22 kV, applied via button  1249 , for directing the electron beam in the peripheral region near the edges of faceplate  1220  towards faceplate  1220 . Alternatively, bias potentials as described in relation to tube  10  may be utilized. 
     FIG. 14 is a cross-sectional diagram illustrating another alternative example arrangement of appropriately positioned electrodes  1244 ,  1248  within a cathode ray tube  1210 ′. Tube  1210 ′ is like tube  1210  of FIG. 13 except that stamped metal electrode  1246  is eliminated and coated neck electrode  1244 ′ extends to cover the portion of the interior surface of glass bulb  1240  that was behind and thus shielded by electrode  1246  in tube  1210 . Visible therein is support  1252  which is typically a ceramic support fused or otherwise attached to mask shield  1228  and electrode  1240  for supporting same in desired relative positions. 
     Neck electrode  1244 ′ is biased at the same potential as is screen electrode  1222  in tube  1210  and may extend to carry such bias potential applied via button  1245  to screen electrode  1222 , mask  1224 , mask frame  1226  and mask shield  1228 , e.g., such as via a metal clip thereon or other connection. Electrode  1248  is biased via button  1249  in like manner to tube  1210 . In any of the tubes  10 ,  1210 ,  1210 ′ and so on, high voltage feedthrough buttons  25 ,  45 ,  47 ,  49 ,  1225 ,  1245 ,  1247 ,  1249  may be positioned to penetrate glass tube envelope  40 ,  1240  at any convenient location. Alternatively, bias potentials as described in relation to tube  10  may be utilized. 
     FIGS. 15A and 15B are computer-generated graphical representations of one quadrant of example horizontal and vertical deflection coils, respectively, of a deflection yoke according to the invention. The contours include numbers that indicate the number of the turn, wherein the first turn wound would be numbered “1” (if shown), the fortieth turn wound would be numbered “40” and so forth. The contours are analogous to the number of turns and are suggestive of the physical layout of the wires of each coil. The horizontal coil represented in FIG. 15A has  220  turns in a negative bias non-constant turns distribution and the vertical coil represented in FIG. 15B has  122  turns in a conventional constant turns distribution. 
     FIG. 16A shows a graphical representation of the cumulative number of turns of a horizontal deflection coil having a negative bias non-constant turns distribution, wherein the turns distribution is non-linear to produce a characteristic having a convex shape. FIGS. 16B and 16C show graphical representations of parametric variation of HSE for the coil of FIG. 16A wherein the coil is employed in a deflection yoke with a CRT of the sort shown in FIG. 1 or in FIG.  13 . Specifically, FIG. 16B illustrates the parametric variation of HSE as a function of the location of the gap between electrodes  44  and  46  of CRT  10  or between electrodes  1244  and  1246  of CRT  1210  at a fixed bias potential (e.g., 22.5 kV) applied to electrode  44  or  1244 . FIG. 16C illustrates parametric variation of HSE as a function of the bias potential applied to electrode  44  or  1244  for a particular location of the gap between electrodes  44  and  46  of CRT  10  or between electrodes  1244  and  1246  of CRT  1210 . Because each parametric characteristic has a minimum point, it is generally desirable to select both the gap location and the bias potential for electrode  44 ,  1244  to reduce the value of HSE to a desired value. 
     FIGS. 17A,  17 B and  17 C are a rear view (from the tube/neck/electron gun end), a bottom view (side facing the CRT envelope) and a side view, respectively, of an example deflection coil  400  according to the invention, and FIG. 17D is a perspective view thereof. Example deflection coil  400  has 151 turns built up in entrance region  410  and reaching a maximum cumulative number at the boundary of the entrance (gun end) and intermediate regions. Coil  400  has six transverse annular bridges or bundles  420 - 470  of transverse turns of about 21-31 turns each, with the bundle  470  of turns nearest the coil exit having about 16 turns. Specifically, the turns counts of bundles  420 - 470  are about 29 turns, 21 turns, 25 turns, 29 turns, 31 turns and 16 turns, respectively. The bundles  420 - 470  of turns are approximately evenly spaced in the Z direction to provide a nearly linear negative turns bias between the screen end of the yoke entrance region and the yoke exit. 
     Bundles of turns  420 - 470  of example deflection yoke  400  are relatively evenly spaced apart as side turns between the center and the sides of deflection coil  400  to provide a desired near-uniform field for a non-converging deflection yoke, with some third harmonic near the exit end of coil  400  for correcting top/bottom pincushion distortion in the raster. In addition, the side turns of bundles  430 - 460  are further divided (e.g., divided into two sub-groups of side turns  462   a  &amp;  462   b , and  464   a  &amp;  464   b  for bundle  460 , and into six sub-groups for bundle  420 ) for distributing the side turns to provide the desired third harmonic content of coil  400 . The side turn bundles extend over angles of up to about 85-90° about the Z axis with respect to the Y-Z plane. 
     In general, a dimension, size, formulation, parameter, shape or other quantity or characteristic is “about” or “approximate”whether or not expressly stated to be such, and varies as by tolerances, conversion factors, rounding off, measurement error, and other factors known to those of skill in the art. The deflection coils described herein may be wound on a form having the shape of the CRT envelope (funnel) with which the coil is to conform, with pins positioned for defining the locations against and/or around which the wire is bent or positioned in placing the wire to form the desired coil. 
     While the present invention has been described in terms of the foregoing example embodiments, variations within the scope and spirit of the present invention as defined by the claims following will be apparent to those skilled in the art. For example, the horizontal deflection coils, the vertical deflection coils or both, may have non-constant turns distributions, and such non-constant turns distributions may be the same or may be different. In addition, the deflection yokes and deflection coils described are examples believed useful for reducing yoke HSE, may also have turns thereof physically arranged for providing correction for one or more of coma error, mis-convergence, pincushion and barrel distortion, astigmatism, north-south and/or east-west raster errors, harmonic correction, and the like. The deflection yoke herein may be used with CRTs for various applications including but not limited to black-and-white or color television (whether analog or digital or standard definition or high definition), video displays, monitors, graphic displays, computer displays, instruments and the like. Further, such CRTs may have tube necks and/or tube envelope funnels having a circular or elliptical or rectangular or other shape. 
     It is noted that while the central window or opening around which the maximum cumulative number of turns pass in the prior art deflection coils is generally large, the opening in a deflection coil according to the invention around which the maximum cumulative number of turns pass is generally small. The small opening may be decreased to leave essentially no window (i.e. the intermediate region length Li is essentially zero), although in a practical case the pin or pins or other portion of the winding form will leave some small opening. 
     Further, while the bias potential applied to the peripheral electrode  48  is preferably less than the screen potential when used in a CRT with a relatively wide screen and a wide angle deflection yoke according to the invention, it may be equal to screen potential, may be more or less than the bias potential of neck electrode  44  and may even be at zero or ground potential or may be negative. 
     Table I presents various benefits and features of various deflection yokes as described herein. Abbreviations indicate the type of yoke, i.e. “SC” for self-converged and “NC” for non-self-converged, and for each of the vertical and horizontal coils, whether the coil has a constant or uniform turns distribution or has a negative bias or non-constant (non-uniform) turns distribution. “Neg. Bias” indicated that the number of turns decreases from a relatively higher number at the end of the yoke entrance to a relatively lower number or zero at the yoke exit. Typically, self-converging type yokes are especially applicable and are typically utilized where the total yoke deflection angle is about  120 ° or less and non-self converging yoke are especially applicable and are typically utilized where the total deflection angle is greater than about 120°. 
     To use the Table I, select the deflection yoke type NC or SC of interest in the upper portion of the table and then select deflection coil types of interest using the column of the table in which are asterisks or other marks in the upper portion of the table. Then look down in the table in the column selected to determine which of the Benefits pertain to that deflection yoke arrangement as indicated by the asterisks or other marks in that column next to the Benefit. For example, information relating to a self-converging yoke having a negative turns bias horizontal coil and a constant turns bias vertical coil is given in the 6th column, whereas that for corresponding coil arrangements in a non-self-converging yoke is given in the 3rd column. 
     Table I lists various possible combinations of horizontal and vertical deflection coil types (constant turns or negative bias turns) that may provide certain benefits, e.g., reduced stored energy, reduced deflection angle, improved heat dissipation. Each of the yokes may be applied in a circular or rectangular CRT funnel shape. Any savings in stored energy attributable to the rectangular shape are typically additive to savings in stored energy attributable to coils with negative bias turns. The case where both the horizontal and vertical coils have constant turns is the prior art and is not presented. 
     
       
         
           
               
             
               
                 TABLE I 
               
             
            
               
                   
               
               
                 Matrix of Coil Combinations for Yokes with Negative Turns Bias 
               
            
           
           
               
               
               
               
               
            
               
                 Coil 
                 Turns 
                 NC 
                 SC 
                 Potential Benefits 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Horizontal 
                 Constant 
                   
                 * 
                   
                   
                 * 
                   
                   
               
               
                   
                 Neg. 
                 * 
                   
                 * 
                 * 
                   
                 * 
               
               
                   
                 Bias 
               
               
                 Vertical 
                 Constant 
                   
                   
                 * 
                   
                   
                 * 
               
               
                   
                 Neg. 
                 * 
                 * 
                   
                 * 
                 * 
               
               
                   
                 Bias 
               
               
                   
                   
                 * 
                   
                 * 
                 * 
                   
                 * 
                 1. Reduces HSE. 
               
               
                   
                   
                 * 
                 * 
                 * 
                 * 
                 * 
                 * 
                 2. Reduces deflection angle. 
               
               
                   
                   
                 * 
                 * 
                 * 
                 * 
                 * 
                 * 
                 3. Spreads out exit end-turns to improve heat 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 dissipation. 
               
               
                   
                   
                   
                 * 
                   
                   
                 * 
                   
                 4. Requires no change from conventional 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 horizontal coil. 
               
               
                   
                   
                   
                   
                 * 
                   
                   
                 * 
                 5. Requires no change from conventional 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 vertical coil. 
               
               
                   
                   
                 * 
                 * 
                   
                 * 
                 * 
                   
                 6. Reduces thickness of vertical coil enabling 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 smaller-diameter ferrite core for lower HSE. 
               
               
                   
                   
                   
                   
                   
                 * 
                   
                 * 
                 7. Particularly well-suited for achieving 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 winding harmonics for self-converging 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 horizontal coils. 
               
               
                   
                   
                 * 
                 * 
                   
                 * 
                 * 
                   
                 8. Increases separation of H and V deflection 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 centers for pincushion correction without 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 increasing gun seal length and tube depth. 
               
               
                   
                   
                 * 
                 * 
                   
                   
                   
                   
                 9. Particularly well-suited for non-self- 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 converging vertical coils. 
               
               
                   
                   
                 * 
                 * 
                   
                   
                   
                   
                 10. Amenable to auxiliary convergence 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 correction means, e.g., minor-axis shunts or 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 dynamic quadrupole coil for self-convergence.