Abstract:
A deflection yoke is described for use in a cathode ray tube, which has an improved deflection sensitivity. The deflection yoke includes a ferrite core, a vertical coil to generate a vertically defecting magnetic field and a horizontal coil to generated a horizontally deflecting magnetic field. The core has a funnel-shaped body with an opening therethrough defining an inner surface. The horizontal coil includes a pair of saddle-type coils positioned in the core such that at least a portion of the horizontal coil is in contact with the inner surface of the core.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a deflection yoke for use in a cathode ray tube, and in particular, to a deflection yoke with improved deflection sensitivity. 
     2. Description of the Related Art 
     Cathode ray tubes (CRTs) are used in display devices to produce images. The basic elements of a CRT are a deflection yoke, one or more electron guns, and a phosphor screen. Color applications generally employ three electron guns, one for each primary color—red, green, and blue. Electron beams emitted by the electron guns are deflected by a deflection yoke. Typically, the deflection yoke consists of two pairs of coils in a CRT. One pair deflects the electron beam primarily in the horizontal direction and is called the horizontal coil. The other pair deflects the beam primarily in the vertical direction and is called the vertical coil. 
     FIG. 1 depicts a CRT  100  which is cylindrically symmetric. The CRT  100  includes a neck region  102 , a funnel region  104  and a phosphor screen  106 . FIG. 2 depicts a cross-section of a conventional deflection yoke  200  that has a separator  202  located between a vertical coil  204  and a horizontal coil  206 . Also included in the deflection yoke  200  is a ferrite core  210  that serves to enhance magnetic fields  212  produced by the coils  204 ,  206 . 
     One disadvantage associated with the conventional deflection yoke  200  is that the horizontal coil  206  is positioned a defined distance (D 1 ) away from the ferrite core  210  and therefore the amount of benefit the horizontal coil  206  receives from the ferrite core  210  is reduced. Specifically, the horizontal coil  206  is separated from the core  210  by the vertical coil  204  and the separator  202 . The separator  202  is usually a funnel-shaped plastic structure that serves to isolate the horizontal coil  206  in the deflection yoke from the vertical coil  204 . 
     Because the phosphor screen of a CRT is usually rectangular in shape, an electron beam from an electron gun going through the area  208  will never hit the phosphor screen, resulting in a poorer deflection sensitivity. One prior art solution solves this problem by introducing a rectangular deflection yoke  300 , as shown in FIG.  3 . The funnel region  104  of the CRT is still cylindrical but the rectangular deflection yoke  300  sits in the neck area  102  of the CRT. Since an unnecessary region  208  in FIG. 2 is eliminated, the deflection sensitivity (deflection per unit current) is increased and the amount of stored energy (E=½ LI 2 ) in the yoke  300  is decreased, where L is the horizontal coil inductance and I is the peak horizontal current. 
     It is well known in the art that when the stored energy of a deflection yoke is lowered or deflection sensitivity is improved, the cost of the deflection circuit is decreased. Also, certain countries (e.g., Japan) will soon require all televisions to satisfy overall power consumption limitations/requirements. It is also known in the art that by increasing the deflection sensitivity, the amount of power consumption required by the deflection circuit may be reduced. Thus, there is market pressure to find methods of lowering the stored energy and improving deflection sensitivity in a deflection yoke. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment of the present invention, a deflection yoke is provided for use in a cathode ray tube, which has an improved deflection sensitivity. The deflection yoke includes a ferrite core, a vertical coil to generate a vertically defecting magnetic field and a horizontal coil to generated a horizontally deflecting magnetic field. The core has a funnel-shaped body with an opening therethrough defining an inner surface. The horizontal coil includes a pair of saddle-type coils positioned in the core such that at least a portion of the horizontal coil is in contact with the inner surface of the core. 
     In one embodiment, channels are provided in the core that extend along the entire core length. The channels are configured to receive the vertical coil and is wider towards a large diameter end of the core and narrower towards a small diameter end of the core. By placing a vertical coil within each of the channels, the vertical coils can be supported by the core without significantly affecting the positioning relationship of the horizontal coil with respect the inner surface of the core. In one implementation, more than one half of the outer surface area of the horizontal coil is in contact with the inner surface of the core. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic side perspective view of a conventional cathode ray tube. 
     FIG. 2 is a cross-sectional elevational view of a conventional deflection yoke. 
     FIG. 3 is a cross-sectional elevational view of another conventional deflection yoke with a rectangular type core, illustrating a separation between a ferrite core and a horizontal coil. 
     FIG. 4A is a cross-sectional view of a deflection yoke according to one embodiment of the invention. 
     FIG. 4B is a cross-sectional view of a deflection yoke according to another embodiment of the invention. 
     FIG. 5 is a diagrammatic perspective view of a portion of a ferrite core according to one embodiment of the invention, illustrating a channel formed therein for accommodating winding of a vertical coil. 
     FIG. 6A is a cross-sectional view of a deflection yoke with a rectangular-type core according to one embodiment of the invention. 
     FIG. 6B is a cross-sectional view of a deflection yoke with a rectangular-type core according to another embodiment of the invention. 
     FIGS. 7A and 7B are a cross-sectional elevation view of a deflection yoke having no overlap between horizontal and vertical deflection coils according to an alternative embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 4A depicts a deflection yoke  400  constructed according to one embodiment of the present invention. The deflection yoke  400  generally comprises a ferrite core  402 , a vertical coil  404 , a liner  406  and a horizontal coil  408 . The core  402  is made of a ceramic material (i.e., ferrite material) and serves to enhance the magnetic field produced by the vertical and horizontal coils. The core  402  comprises a funnel-shaped body having a large diameter end and a small diameter end and an opening extending between the large and small diameter ends. 
     In accordance with one aspect of the invention, the deflection sensitivity of the deflection yoke  400  is improved by reducing or eliminating a separation between a ferrite core and a horizontal coil. The inventor has recognized that by placing the horizontal coil  408  closer to the core  402 , the deflection sensitivity of the horizontal coil will increase. Deflection sensitivity is more important for horizontal coils  408  than for vertical coils  404  because an electron beam in a CRT generally scans in the horizontal direction at a rate of 16 KHz and only 60 Hz in the vertical direction. In other words, deflection insensitivity in the vertical direction may not be as critical since the electron beam scans much fewer times per second than in the horizontal direction. 
     In one embodiment, the horizontal coil  408  comprises a pair of saddle-type coils which are installed against the inner surface of the core  402  such that at least a portion of the horizontal coil is in contact with the core. The location of the horizontal coil portion touching the core is preferably located (i.e., along a central horizontal axis  410 ) where the effect of the horizontal deflection is most important. In the illustrated embodiment, more than one half of the outer surface area of the horizontal coil  408  is in contact with the inner surface of the core  402 . 
     In accordance with another aspect of the invention, recess regions or channels  412  are provided in the core  402  to receive the vertical coil  404 . The channels  412  are located on opposite sides of the core  402  and extend along the entire core length. The channels  412  are arranged substantially symmetrical with respect to a central vertical axis  414  of the deflection yoke  400 . 
     In one embodiment shown in FIG. 4A, the vertical coil  404  comprises a pair of a saddle-type coil disposed within the recess regions  412  of the core. In another embodiment shown in FIG. 4B, the vertical coil  404  comprises a pair toroidal-type coil wound about the channels  412  of the core. A liner  406  is provided in each channel  412  over the vertical coil  404  to electrically separate the vertical and horizontal coils in overlapping regions  416 . In one implementation, the liner  406  is constructed of a rigid plastic material configured to provide support for the vertical coil  404 . If there are no overlap between vertical coil  404  and horizontal coil  408 , the liner  406  may not be needed except, possibly, to provide support. In the illustrated embodiment, the liner  406  only extends over the width of the recessed region  412  and does extend across the entire inner surface of the core. 
     FIG. 5 depicts a portion of a ferrite core  402  according to one embodiment of the invention. The channel  412  formed in the core  402  defines a recessed region  450  having a vertical coil bearing surface  452  that is recessed relative to horizontal coil bearing surfaces  454 . The recessed region  412  is shaped to receive a vertical coil. In the illustrated core, the recessed region  412  is wider towards the large diameter end  456  of the core and narrower towards the small diameter end  458  of the core. By placing a vertical coil within the channel  450 , the vertical coil windings can be supported by the core without significantly affecting the positioning relationship of a horizontal coil with respect to the horizontal coil bearing surface  454 . 
     As shown in FIGS. 4A and 4B, the liner  406  is placed between the vertical coil  404  and the horizontal coil  408  to electrically separate the coils in the overlapping regions  416 . In this regard, the depth of the recessed region  450  is selected to accommodate the thickness of the vertical coil winding in addition to the thickness of the liner. 
     FIG. 6A depicts a deflection yoke  600  according to one embodiment of the present invention. As discussed above, one way to increase the deflection sensitivity is to construct the neck of a CRT in a rectangular configuration to reduce the leakage of the magnetic field generated by a deflection yoke. The deflection sensitivity of a deflection yoke for such CRT can be further enhanced by incorporating the features of the present invention. In the illustrated embodiments shown in FIGS. 6A and 6B, the cross-section of the core  602  is substantially of a hollow rectangular shape and has channels  612  form in the core  602  to accommodate a vertical coil  604 . The deflection yoke  600  also includes a liner  616  to electrically separate the vertical coil  604  from a horizontal coil  608  arranged along the inner surface of the core. In one embodiment shown in FIG. 6A, the vertical coil  604  comprises a pair of a saddle-type coil disposed within the recess regions  612  of the core. In another embodiment shown in FIG. 6B, the vertical coil  604  comprises a pair of toroidal-type coil wound about the channels  612  of the core. 
     FIGS. 7A and 7B depict a deflection yoke  700  according to an alternative embodiment of the invention. In FIG. 7A, a deflection yoke  700  is shown which has a core  702 , a pair of toroidal-type vertical coils  704  wound on the core and a pair of saddle-type horizontal coils  708  arranged inside the core. In FIG. 7B, another deflection yoke  700  is shown which has a pair of saddle-type vertical coils  704  and a pair of saddle-type horizontal coils  708  arranged inside the core  702 . Because there is no overlap between the horizontal  708  and vertical  704  coils in the deflection yokes  700  shown in FIGS. 7A and 7B, a liner is not needed except, possibly, to provide support. 
     While most deflection yokes for color CRTs are configured such that there is usually an overlap between horizontal and vertical deflection coils, some deflection yokes may not require such overlap. For example, a deflection yoke adapted for use in a projection television may not require an overlap between horizontal coils  708  and vertical coils  704 . In a projection-type display system, there are generally three CRTs, one for each primary color; red, green and blue. The three tubes or beams converge mechanically or optically at the panel so the deflection yoke is monochrome. Here, because only one electron beam (one color phosphor) is needed, the yoke designer does not have to be concerned about convergence. For this reason, horizontal and vertical coils may be arranged in a deflection yoke without an overlap of horizontal and vertical coils that is usually present in a deflection yoke for a three-electron beam. 
     In a color display, convergence of the three beams is necessary. Since the horizontal and vertical coils have to be arranged in a particular fashion in order to achieve convergence, it is highly likely that the horizontal and vertical coils will overlap. Nevertheless, convergence of the three beams in a color display may be possible without an overlap of horizontal and vertical coils in certain instances. 
     According to the invention, by moving the horizontal coil closer to the ferrite core, a number of advantages may be achieved. By improving horizontal deflection sensitivity, the amount of stored energy in the yoke is decreased. As a result, the cost of manufacturing a deflection circuit for the deflection yoke of the present invention is reduced. Additionally, the amount of power consumed by the deflection circuit and the deflection yoke is also reduced. 
     While the foregoing embodiments of the invention have been described and shown, it is understood that variations and modifications, such as those suggested and others within the spirit and scope of the invention, may occur to those skilled in the art to which the invention pertains. The scope of the present invention accordingly is to be defined as set forth in the appended claims.