Cross-Reference to Related Application

This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application Serial No. 60/640,912, entitled "Panel Mask Assembly for a CRT Having Transposed Scanning," filed December 31, 2004, which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention is related to a panel mask assembly for a cathode ray tube (CRT) operating in a fast vertical scan mode.

BACKGROUND OF THE INVENTION

Recently, the demand for large aspect ratio CRTs has led to the development of CRTs having a vertical electron gun orientation such that the plane in which the undeflected beams are located is parallel to the short axis (i.e. the vertical axis of the display screen). In such a CRT, the phosphor lines are horizontal with the triads being spaced vertically from one another. Further, in such a system, the mask apertures are horizontally oriented. Such a system is referred to as a digital orthogonal scan system (DOS). In a DOS system, the yoke is effectively rotated such that the line scan (fast scan) is also in the direction of the short axis (vertical) and the slow scan is in the direction of the long axis (horizontal).

The motivation for DOS has been the ever increasing demand and popularity for high definition television (HDTV). As such, the need for displays capable of receiving and displaying HDTV images continues to increase. DOS technology is now considered the preferred technology for CRTs in the HDTV regime. The reason is the surprising improvement in spot performance, which is that spot size and shape are uniform across

the entire screen and, as such, DOS provides a means for improving visual resolution performance.

Coincidently with the development of DOS technology has been the suggestion to reduce the depth of CRTs and increase the aspect ratio to 16:9. The decrease in depth and increase in aspect ratio requires a dramatic increase in deflection angle for the electron beams. CRTs having reduced depth have been otherwise referred as "SLIM" CRTs. Increasing the deflection angle in these displays presents the problem of greater obliquity of the electron beam spots. Although obliquity is problematic in DOS/SLIM CRTs, this problem is especially more apparent in CRTs having a standard gun orientation, that is, guns being aligned horizontally along the major axis of the screen. Obliquity is the effect of a beam intercepting a screen at an oblique angle causing elongation of the spot in the radial direction. As obliquity is increased, a spot which is generally circular in shape at the center of the screen becomes radially oblong or elongated as it moves toward edges of the screen. Based on this geometrical relationship, in a large aspect ratio screen, e.g. 16 x 9, the spot is most elongated at the edges of the major axis and in the corners. These obliquity effects cause the spot to grow radially. The radial spot size SS _rad i _a i is defined by the following equation:

SSradia! = SS _normal /cθS(A) where A is the deflection angle measured from Dc to De as shown in Figure 1 and nominal spot size SS _nor mai is the spot size without the effects of obliquity. In addition to the obliquity effects described in Figure 1, spot shape is further compromised by yoke deflection effects in self converging CRTs having horizontal gun orientation. To achieve self convergence, the horizontal yoke field having a pincushion

shaped field is provided while the vertical yoke field is barrel shaped field. These yoke fields cause the spot shape to be elongated. This elongation adds to obliquity effects further increasing spot distortion at the 3/9 and corner positions on the screen. The yokes for DOS have a first set of coils for generating a substantially pincushion shaped deflection field for deflecting the beams in the direction of the short axis of the display screen and a second set of coils for generating a substantially barrel shaped deflection field for deflecting the beams of the direction in the long axis of the display screen. This system's yoke deflection effects generally distort spots by elongating them vertically. This vertical elongation compensates for obliquity effects, thereby reducing spot distortion at the 3/9 and corner positions on the screen.

Furthermore, the yoke fields for yokes for DOS CRTs have different S-ratios. This is due to different yoke deflection geometries needed for DOS CRTs versus that for non-DOS CRTs. An S-value is the apparent separation between either outer beam and the center beam, in the deflection plane. An S-value is shown in Figure 2. S-ratio's are formed when the S-values are normalized at all locations by using the center S-value as the normalization divisor. The pattern has larger S-ratios near the end of the horizontal axis compared to non-DOS systems, which impacts the selection of mask contour for the shadow mask 10 and the interior panel contour for the panel 11. hi DOS CRTs described above the color selection system consists of a mask that has elongated apertures perpendicular to the short axis. The mask can be of either a formed or tensioned structure. The problem, however, in transitioning from a non-DOS to DOS system is that the mask and panel contour requirements have turned out to be dramatically different from each other and, as such, those skilled in the art recognize or

believe that many parameters must be changed to create a commercial DOS CRT. This is especially believed to be the case for DOS CRTs with SLIM configurations. SLIM CRTs are CRTs having higher deflection angles such as 118 degrees or greater. Some other SLIM deflection angles under exploration and consideration are as high as 125 and 140 degrees.

Therefore, with the dramatic differences between DOS CRT technology and the conventional non-DOS CRT technology and that fact that no commercial quality DOS CRTs having SLIM characteristics and 16x9 aspect ratio exist, there is a need for a front end design for a DOS/SLIM system to obtain a commercial quality DOS/SLIM CRT.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference to the accompanying figures of which:

FIGURE 1 is a diagram depicting the basic geometrical relationship between the throw distance and deflection angle in a CRT;

FIGURE 2 is a representation of the electron beam path from the deflection plane through the shadow mask and onto the screen;

FIGURE 3 is a drawing of the cathode ray tube according to the invention; and

FIGURE 4 is a drawing of the interior contour of the panel according to the invention.

SUMMARY OF THE INVENTION

Provided is a cathode ray tube designed for use in an electron beam scan system having a fast vertical scan rate and a slow horizontal scan rate. The CRT includes an interior panel surface contour fitting an eight order polynomial Z = C(I)X ² + C(2)X ⁴ + C(3) X ⁶ + C(4)X ⁸ + C(5)Y ² + C(6) X ² Y ² + C(7)X ⁴ Y ² + C(8)X ⁶ Y ² + C(9)X ⁸ Y ² .

DESCRIPTION OF THE INVENTION

The invention relates to a cathode ray tube (CRT) 1 as shown in Figure 3, wherein the CRT 1 is designed to operate in DOS mode. Figure 3 shows the cathode ray tube (CRT) 1 having a glass envelope 15 comprising a faceplate panel 11 and a tubular neck 14 connected by a-funnel 17. The funnel 17 has an internal conductive coating (not shown) that extends from an anode button 16 toward the faceplate panel 11 and to the neck 14. The A three-color phosphor screen 12 having a plurality of alternating phosphor stripes is carried by the inner surface of the faceplate panel 11. The screen 12 is a line screen with the phosphor lines arranged in triads, each of the triads including a phosphor line of each of the three colors. A mask assembly 10 is removably mounted in predetermined spaced relation to the screen 12. An electron gun assembly 26, shown schematically by dashed lines in Figure 3, is centrally mounted within the neck 14 to generate and direct three inline electron beams, a center beam and two adjacent or outer beams, along convergent paths through the mask 10 to the screen 12. The electron gun assembly 26 consists of three guns being vertically oriented, which direct an electron beam 28 to the screen 12.

Table 1 will be discussed with reference to various CRTs of significance to the application. The table provides some of the keys design features which must be considered in designing a DOS CRT. Table 1 focuses on the ends of the major axis of the CRT which have surprisingly turned out to be the most vulnerable region in the development of a commercial quality DOS/SLIM tubes. SLIM 1 design is the design for a 118 degree deflection angle W76 16x9 CRT having the conventional non-DOS configuration. The panel contour is described in terms of Z drop which simply is the

sagittal drop from the interior center location (X = 0 mm, Y = O mm) of the panel 11. The yoke S-ratio, the desired grouping errors, the desired screen pitch and the mask contour requirements are all shown in Table 1.

The design process starts with predicted or measured S values over some region of a non-DOS CRT. The S values are then mathematically converted into the DOS orientation by appropriate truncation and extension of the long and short axes, respectively. Next, these S values are converted into S-ratios to allow use with any desired screen pitch requirements. The panel contour is then derived from the geometric relationship between the desired screen pitch, the S-ratio, the deflection plane geometry and the desired grouping errors. The L value is the dimension between the deflection plane 22 and the panel 11 as shown in Figure 2. The Q value is the dimension between the mask and the screen location to which the transmitted electrons are to land. The screen pitch is the dimension between the centers of the center phosphor stripes in two adjacent phosphor triads on the screen 12.

As noted previously, an S-value is the apparent separation between either outer beam and the center beam, in the deflection plane (see Fig. 2a). S-ratio 's are formed when the S-values are normalized at all locations by using the center S-value as the normalization divisor.

The mask pitch, a, is determined from the desired screen pitch, D, and the mask-to- screen separation, Q (see Fig. 2b). Using the geometry from Figs. 2a and 2b, and the relation of 3d = D, the resulting relation, Q = La /3s is formed at the center of the screen. This relation can then be used to determine the panel and mask contours at all screen locations by using suitable geometric adjustments at the other locations.

Since the mask and panel contours are continuous functions, the desired Q may not be able to be achieved at all screen locations simultaneously, resulting in grouping errors. The grouping errors are a measure of how much the ratio 3d/D deviates from 1.

TABLE l

SLIM 1:

SLIM 1, as mentioned earlier, is a CRT having a reduced depth by design. The increase deflection to 118 degrees permits the reduction. The yoke is a conventional type yoke used to scan the electron beams rapidly in a horizontal direction and slowly in the vertical direction. The parameters are selected such that the CRT is commensurate with HDTV signal. Note that the grouping error is 1.8 % with the screen pitch being 0.80 mm and the S-ratio for the standard yoke being 1.12. The problem with this SLIM 1 CRT is that the beam profile suffers obliquity as the beams scan away from the center. The interior contour of the SLIM panel is described by the polynomial Z = C(I)X ² + C(2)X ⁴ + C(3) X ⁶ + C(4)Y ² + C(5) X ² Y ² + C(O)X ⁴ Y ² + C(T)Y ⁴ + C(8)X¥. The coefficients are shown in Table 2, wherein the coefficients have units which yield Z values in millimeters when the X and Y values are in millimeter also.

TABLE 2

DOS/SLIM 1:

DOS/SLIM 1 is CRT having a reduced depth by design, with the reduction being the same for the SLIM 1 sample. The major difference, however, from the SLIM 1 CRT is that the yoke has a dramatically different S-ratio. Here the S-ratio is now 1.36. The difference was surprising given that fact that the deflection plane for this CRT is the same as that for SLIM 1 and that the overall deflection angle between the two are the same. (Some difference would have been expected, but not such a large difference, because prior to actually employing a DOS yoke, to a first approximation the differences in the yokes is that the DOS yoke is simply rotated with respect to the SLIM 1 yoke.) The DOS yoke now scans the electron beams rapidly in a vertical direction and slowly in the horizontal direction. The parameters selected were intended to be the same as that for the SLIM 1 CRT, which included that mask contour and the interior panel contour. However, grouping error is -21.4 % with the screen pitch being 0.80 mm at the ends of the major axis and the S-ratio for the DOS yoke being 1.36. (The ends of the major axis are specifically discussed because surprisingly these locations turned out to be the most sensitive and worst location on the screen: one skilled in the art would have expected the . corner location to be the most problematic location.) The problem with this DOS/SLIM 1 CRT was many parameters changed by rotating the yoke and the direction of the phosphor stripes and the apertures of the mask. For example, the S-ratio changed from 1.12 to 1.36, the grouping error changed, and the image resolution dramatically changed (i.e., pixel-to-pixel scan pitch increased). It turns out that although the DOS/SLIM 1 CRTs can be made and can operate well for certain applications where HDTV signal is not used, the grouping error and the image resolution are unacceptable for HDTV applications. Grouping errors for CRTs to be acceptable must be less than 5%, otherwise screen printing variability, mask contour variability, panel contour variability, and ambient magnetic fields differences associated with the orientation of the CRT will cause clipping and/or leaving of the electron beams on the screen.

DOS/SLIM 2:

In an attempt to at least improve the image resolution observed in the DOS/SLIM 1, the mask pitch was reduce from 0.80 mm to 0.67 mm. This change was expected to improve the image quality. However, it turned out that although the resolution of the image increased, the grouping error increased to -45.0%, which made it more than 20 larger than that for SLIM 1 and twice that for the DOS/SLIM 1 CRT.

DOS/SLIM 3:

In an effort to develop a commercial DOS/SLIM CRT, DOS/SLIM 3 was invented in which the only differences with respect to the DOS/SLIM 2 CRT was that now the interior panel contour and mask contour were found to be the solution in that the grouping error at the ends of the major axis reduced to 0.2 %, without having to change many CRT design parameters with respect to DOS/SLIM 2.

In inventing the new DOS/SLIM 3, the designer had to ensure that inside panel contour must be contoured to avoid inflection points. Further the panel and mask contours must be designed and shaped to avoid unacceptable yoke "PIN and Gullwing" artifacts appearing on the screen. The DOS/SLIM 3 CRT turns out to not suffer from any of these potential deficiencies.

The CRTs described above in Table 1 are W76 True Flat CRTs. In the SLIM/DOS 3 CRT, the interior panel contour can be described by the following polynomial: Z _p = Cp(I)X ² + C _P (2)X ⁴ + Cp (3) X ⁶ + Cp (4)X ⁸ + C _p (5)Y ² + C _p (6) X ² Y ² + Cp (7)X ⁴ Y ² + Cp (8)X ⁶ Y ² + Cp (9)X ⁸ Y ² . The preferred embodiment of the coefficients are provided in Table 2 for a W76. The coefficients can be scaled up or down depending on the desired size of the CRT. Deviations in magnitude of the individual coefficients provided in Table 3 can vary by as much as +/- 10% and still meet the objectives of the invention which include minimizing pincushion and gullwing effects of the yoke raster on the screen and providing acceptable grouping error. Other adjustments to the coefficients can be made to target excellent image qualities for displays with different screen and mask pitch or different types of yokes and remain within the scope of the . invention, i.e., meaning that the general polynomial above can be used.

TABLE 3

The inside surface characteristics for the designed panel contour is shown in FIG. 4. Shown in FIG. 4 is the inside panel radial Z drop for the short axis, long axis, diagonal, mid way between the short axis and the diagonal and mid way between the diagonal and the long axis. RD, R _S , R _L , RX and Ry represent the surface contours along the diagonal, the short side, the long side, the major axis, and the minor axis, respectively.

In another embodiment of the invention the exterior panel contour is described by the following polynomial: Z _e = C _e (l)X ² + C _e (2)Y ² . The coefficients for this embodiment are provided in Table 4. The outside panel is generally flat in all directions. The coefficients can be scaled up or down depending on the desired size of the CRT. Other adjustments to the coefficients can be made to target excellent image qualities for displays with different screen and mask pitch or different types of yokes and remain within the scope of the invention, i.e., meaning that the general equation for the exterior contour can be used

TABLE 4

According to another embodiment of this invention, a tension mask is incorporated wherein the tension mask is tensioned and flat in the long axis direction.

It should be noted that while any grouping errors, yoke S-ratios and screen pitches can be specified, in the preferred embodiment, it is required that the grouping errors be less than +/- 0.5 % for the yoke S-ratios and screen pitches shown in Table 1 for commercial quality SLIM/DOS CRTs. hi another embodiment of the invention, the mask contour can be described by the following polynomial: Z _n , = C _m (I)Y ² + C _1n (2) Y ⁴ . The coefficients for this embodiment are provided in Table 5. Again, the coefficients can be scaled up or down depending on the desired size of the CRT. Other adjustments to the coefficients can be made to target excellent image qualities for displays with different screen and mask pitch or different types of yokes and remain within the scope of the invention, i.e., meaning that the general mask contour equation can be used.

TABLE 5

As with all of the Tables 2-5, the origin (i.e., X=O, Y=O) is along the z- axis, which is the line that is perpendicular to the center face of the panel. The coefficients shown in the tables have units which yield Z values in millimeters when the X and Y values are in millimeter also.

With reference to Fig. 2, the general formula for the screen according the invention is that the Q be equal to the product of the mask vertical pitch (a) and L divided by the 3 times the electron beam spacing at the deflection plane (s). Thus, Q = a*L/3s. A further relationship applicable to this invention is D/a = IV(L-Q ).

It should further be noted that mask contours as described above can be obtained with either tension masks or formed masks and provide adequate structural stability (i.e. resists flexing or "oil canning"). Further, the deviations in magnitude of the individual coefficients provided above can vary by as much as +/- 10% and still meet the objectives of satisfying the requirements for minimizing pincushion and gullwing effects of the yoke raster on the screen. Such a deviation can also be incorporated for the exterior panel

contour and the mask contour. Such deviation can be employed and still provide structural stability to a formed mask.

Regarding the exterior contour of the panel, the preferred embodiments are near true flat contours; however, the invention can include exterior contours at 2R or greater. (R is 1.767 times the diagonal dimension of the screen.)

Further, the invention is not limited to W76 tubes having screen pitches at or around 0.67 mm. The invention is applicable to all aspect ratio CRTs and CRTs with common screen pitches (e.g. the invention is applicable to CRTs with 0.15 mm screen pitches and those with 2.0 mm screen pitches).

Further, as mentioned earlier, the invention not only includes the use of the polynomials for the mask and interior panel provided above, but also includes the use of similar contours, which includes scaled coefficients to match different CRT sizes. For example, one wanting to design a larger size tube can use the polynomials provided to design the contours for the larger tube. Essentially, the designer can linearly scale the coefficients to get less curvature for the mask and interior panel contour for larger tubes or more curvature for smaller tubes.

Further, another embodiment involves the use the invention in a system with high deflection angles (i.e. 120 degrees or greater); however, the invention can be used in systems with lower deflection angles too.