KR0141540B1 - Color picture tube with reduced primary and secondary moire - Google Patents

Abstract

The improved color receiver, operable in a multi-standard television receiver, has a viewing screen 22, a shadow mask 24 and an electron gun 26 which generates three electron beams and projects them on the screen through the shadow mask. The screen includes a phosphor line extending in the first direction. The electron beam is likely to be deflected in the first direction and the second direction and the first direction which are substantially perpendicular to the phosphor lines. The shadow mask includes an elongated slit-shaped opening 36 that is aligned in the form of vertical lines that are nearly parallel to the phosphor lines. Adjacent openings in each column are separated from each other by a tie bar 38 in the mask, and the tie bars in one column are offset in the first direction from the tie bar in the adjacent vertical row. The present invention is characterized by an alternating vertical bar-shaped tie bar that forms approximately two degrees (θ) with respect to the second direction.

Description

Collar water tube with reduced first and second moire

1 is a side longitudinal cross-sectional view cut along the axial direction of the collar receiving tube embodying the present invention.

FIG. 2 is a rear plan view of the faceplate panel of FIG. 1. FIG.

3 is a partially enlarged view of the shadow mask of the water pipe of FIG.

4 is a partial view of the screen of the water pipe of FIG. 1 showing various angular relationships.

5 is a graph showing the dependence of the first moire 'pitch on the row inclination to visible scanning lines.

6 is a graph showing the dependence of the second moire pitch on the transverse plane to the visible scan line.

7 is a graph showing the relationship between the first moire pitch versus the visible scan line of the improved mask implementing the present invention.

8 is a graph showing the relationship between the second moire pitch versus the visible scan line of the improved mask embodying the present invention.

Explanation of symbols on the main parts of the drawings

10: color water pipe 22: viewing screen

24: shadow mask 26: electron gun

28: electron beam 36: slit opening

38: Thai Cat Ba

FIELD OF THE INVENTION The present invention relates to color water tubes with shadow masks in which the slit-shaped openings are arranged in a vertical row, separated by tiebars in the shadow mask, in particular the first and second on the entire screen of the water tube. A color picture tube having a shadow mask with a tie bar arrangement to reduce moire 'and operable in a multi-standard TV set.

Most of the color water tubes used today have shadow masks with line screens and slit openings. These openings are arranged in rows and the adjacent openings in each row are separated from each other by a web or tie bar in the mask. This tie-bar is an essential element in the shadow mask to maintain its integrity when the shadow mask is formed in a dome shape that is almost parallel to the inner shape of the viewing faceplate of the water pipe. The tie bars in the column are offset from the tie bars in the adjacent column directly in the longitudinal direction (vertical direction) of the column. When the electron beam hits the shadow mask, the tie bar blocks some of the beam, causing shadows to appear on the screen directly behind the tie bar.

When electron beams are repeatedly scanned in a direction perpendicular to the opening (horizontal direction), these electron beams form a series of bright and dark horizontal lines on the screen. These light and dark horizontal lines interact with the shadows formed by the tie-bar, which is the generating factor of lighter and darker areas on the screen that generate wave patterns called moire'patterns. Such patterns greatly damage the quality of the visible image displayed on the screen. Moire analysis in shadow mask tubes using Fourier analysis and geometry The visibility of moire depends mainly on the amplitude and pitch of the moire pattern. The moire amplitude depends on the handwriting spot size and the taava width, and the moire pitch is dependent on the periodic repeatability of the tie bar aligns and the interference between the periods of the scan lines. It is highly desirable to select shadow mask tie-bar spacing and size that will minimize the moire pattern for any scanning conditions used in TV receivers. The complexity of the choice due to the change from one mode to a multistandard TV receiver is necessary to reach some compromise to achieve acceptable moire for all multistandard modes. The two injection conditions currently in use are interlaced scans and non-interlaced scans. The following table shows the standards (interlaced and interlaced) that were considered in implementing the present invention.

TABLE 1

In the table, 4/3 and 16/9 represent the horizontal to vertical aspect ratio of the screen. Overscan in the second column shows the amount of vertical overscan of the 4/3 standard transmission and the amount of vertical underscan of the 16/9 standard transmission. In the 16/9 standard there is a corresponding overscan amount in the horizontal direction to achieve 16/9. The third column shows the number of visible lines in the standard PAL / SECAM transmission, and the fourth column shows the number of visible lines in the NTSC transmission. For example, in a PAL transmission with 625 lines and 107% overscan, there will be 537 visible lines on the screen. The standard 4/3 and 4/3 are related to two zoom modes, magnified 119% and 137% respectively. This magnification reduces the number of viewing lines on the screen. Similarly, 16/9 is an enlargement mode of the 16/9 standard. The numbers in parentheses indicate interlaced mode. In the case of an actual TV receiver, the modes to be considered in teletext transmission are 268 lines for PAL and 227 lines for NTSC. However, it is also useful to consider interlacing modes to account for the possibility of inadequate interlacing in a moiré-generating receiver for moiré calculations.

There are several techniques proposed to eliminate the moire problem. Most of these techniques adjust the vertical size of the electron beam spot on the screen, such as modifying the electron gun and yoke, or adjust the position of the mask's tie bar to reduce the possibility of electron beam scanning lines interacting or beating with tiebar shadows. Includes reordering techniques. U.S. Patent No. 4,751,425, filed to Barten on June 14, 1988, shows a mask with a tie bar arranged on a straight line that forms a 3-8 degree angle with the horizontal deflection direction. Although techniques such as those shown in the Barten patent have been used successfully in the past to reduce moire to some extent, now these techniques are used intensively to correct the first moire pitch and the second caused when the tie bar line is inclined. It doesn't take into account moire pitch. Thus, there is a need for an improved moire reduction technique that takes into account the second moire pitch. This improved technology is particularly needed in the case of newer, higher quality color picture tubes required for high definition televisions. For example, the improved electron gun produces smaller electron beam spots on the screen as the quality of the electron gun is improved to meet the need for high resolution television. This reduction in the electron beam spot size creates visually sharper scan lines on the screen that interact with the tie-wrap shadow and increase the moire 'pattern visibility problem.

The improved color receiver has a viewing screen, a shadow mask, and an electron gun that generates three electron beams and projects them onto the screen through the shadow mask. The screen includes a phosphor line extending in the first direction. The electron beam is likely to be deflected in the first direction and the second direction and the first direction which are almost perpendicular to the phosphor lines. The shadow mask includes a slit-shaped opening that is elongated and aligned in vertical lines substantially parallel to the phosphor lines. Adjacent openings in each column are separated from each other by a tie bar in the mask and the tie bars in one column are offset in a first direction from the tie bar in the adjacent column. A feature of the invention resides in an alternating vertical tie bar that lies on a straight line forming an angle of about 2 degrees with respect to the second direction.

FIG. 1 illustrates a longitudinal collar water tube 10 having a glass envelope 11 comprising a rectangular faceplate panel 12 and a tubular neck 14 connected by a rectangular funnel 15. The funnel 15 has an internal conductive coating (not shown) that extends from the anode bottom 16 to the neck 14. The panel 12 includes a peripheral flange or side wall 20 and a viewing faceplate 18 sealed to the funnel 15 by a glass frit 17. The tricolor fluorescent screen 22 is supported by the inner surface of the face plate 18. The screen 22 is a line screen with fluorescent lines arranged in a triad form each containing three fluorescent lines of three colors. The multiple aperture opening color selection electrode or shadow mask 24 is removably mounted by conventional means in a predetermined spaced relationship with respect to the screen 22. In this regard, it is detachably mounted by conventional means. The electron gun 26, denoted dashed line in FIG. 1, generates an electron beam and mounts in the center of the neck 14 to direct three electron beams 28 along the convergence path through the mask 24 to the screen 22. do.

The water tube of FIG. 1 is designed for use with an internal magnetic deflection yoke, such as yoke 30 shown near the Funnelchenek coupling. In operation, the yoke 30 exposes three beams 28 to a magnetic field so that the beams are scanned horizontally and vertically in a rectangular raster on the screen 22. An initial deflection plane (zero deflection) is present around the center of the yoke 30. Due to the fringe field, the deflection zone of the water tube extends axially from the yoke 30 into the region of the electron gun 26. For simplicity of illustration, the actual curve of the deflection beam path is not shown in FIG.

The shadow mask 24 is part of the mask frame assembly 32 that includes the peripheral frame 34. Mask frame assembly 32 is located within faceplate panel 12 in FIG. The shadow mask 24 includes a curved opening 25, a void-free boundary 27 surrounding the opening 25, and a skirt extending away from the screen 22 while bent backward from the boundary 27. Part 29 is included. The mask 24 is stacked in or on the frame 34 (as shown), and the skirt portion 29 is welded to the frame 34.

The shadow mask 24 shown in detail in FIGS. 2 and 3 has a rectangular perimeter having two long sides and two short sides. The mask 24 has a major axis X passing through the center of the mask and parallel to the long side, and a minor axis Y passing through the center of the mask and parallel to the short side. Mask 24 includes a slit-shaped opening that is elongated and aligned in the form of a vertical row substantially parallel to axis Y. Adjacent openings 36 in each column are separated by tie bars 38 in the mask, with the spacing between the tie bars 38 in the vertical lines being limited to the tie bar pitch at a particular position on the mask.

In US Pat. No. 4,751,425 cited above, the reduction of moire can be achieved by placing the mask tie bar on a straight line angled 3 to 8 degrees with respect to the horizontal direction of the electron beam scanning. Due to this angle formation of the tie bar, the first moire pitch is reduced. Such first moire pitch Rm ₁ can be calculated from the following equation.

(One)

Where P _V is the vertical mask pitch,

S is the scanning line spacing,

θ is the angle of inclination of the tie bar

n is the harmonic of the scan line spectrum (e.g., first, second, third, etc.),

m is the harmonic of the mask vertical pitch spectrum (eg, first or second).

The negative tie-bar bar inclination angle θ is shown in FIG. 3 and the positive tie-bar bar inclination angle θ is shown in FIG. 4. 4 is a small portion of the screen 22 of the water tube 10 showing a reddish green-blue fluorescent line triad excited by an electron beam passing through the mask opening 36. The short horizontal line in FIG. 4 is the shadow caused by the tie bar 38 of the mask 24.

5 is a graph of a first moire-pitch large scan line showing two harmonics that cause moire for a mask with a vertical mask pitch Pv of 0.68 mm on the screen. This graph has a set of seven curves, labeled 0 to 6 degrees. These curves are described in U.S. An angle formed between the horizontal direction of beam deflection as described in patent 4,751,425 and a straight line along a tie bar. As can be seen in the graph, the first moiré pitch decreases as the slope of the Tischenba line increases at two harmonics. However, another form of second moire occurs due to the inclination of the tie-kamba line. The cause of this second moire is the interference between the scanline and the diagonal structure of the aligned tie bar. The second moire is characterized by an angle that can be determined from the mask horizontal and vertical pitch using the following relational formula.

Is the second tie bar tilt resulting from the tie bar tilt angle θ (counterclockwise and clockwise, respectively), P _V is the vertical mask pitch, and PH is the horizontal mask pitch. Second tie bar inclinations + Φ and Φ and tie bar inclination angle θ are shown in FIG.

If the two inclination angles are smaller, a second moire lasting on the side of the screen where the spot size is reduced by the focusing operation is determined. The second moire pitch Pm ₂ can be calculated by the following equation.

(3)

6 is a graph of the second moire pitch versus the visible scan line showing the two harmonics causing the second moire. This graph has seven curves representing the angle of inclination of the tie bar in the horizontal deflection direction. As can be seen in the graph of FIG. 6, the second moire pitch increases as the inclination angle increases, which is the opposite effect of the first moire pitch. It was confirmed that the second moire pitch was seen better than the first moire pitch. This occurs because there is no alternating shift of the tie bar along the diagonal line (at each Φ) as it exists along the horizontal scan line. Thus, to achieve the same visual effect, a smaller reduction in the second moire pitch is required than in the first moire pitch. Unlike the prior art which proposes a 3 to 8 degree tie bar, the present inventors have found that an improved visual effect can be achieved with a tilt bar of about 2 degree. At 2 degrees, although the first moire pitch was higher at 3 degrees, the first moire pitch is less pronounced than the second moire pitch of these angles. Moreover, at 2 degrees, the second moire is near the eye resolution limit.

7 is a graph showing the number of first moire pitch large-scan lines in the case of a mask constructed according to the present invention. In this graph, the vertical mask pitch P _v is 0.635 mm and the inclination angle θ of the tie bar is 2 degrees. The first harmonic number does not exist in this graph because the vertical spacing of the tie bars of the masks in the adjacent vertical rows is actually alternated by P _v / 2. Thus, the mask spectrum moves as if the vertical pitch giving the harmonic peak is Pv / 2 if S = P _V / 2 allowing 1200 visible lines.

8 is a graph showing the second moire pitch versus the number of visible scan lines for a mask constructed in accordance with the present invention. In this graph, the vertical mask pitch PV is 0.635 mm and the tie bar inclination angle θ is 2 degrees. The thick solid line in FIG. 8 is the first harmonic number, and the other harmonics are shown in various dotted lines.

The method of the present invention involves calculating a desired tie bar frequency for a flat mask that takes into account several factors. Firstly, for a given scan line pitch, the desired tie-wrap shadow position is calculated at various separations as can be seen from the distance of the viewing screen square. Such desired tie-wamba shadow positions are those that provide a nearly optimized compromise for the moire of each separation area. The corresponding tie-wrap shadow on the screen is then determined taking into account the beam deflection angle of the separation area. Then the corresponding tie-bar pitch is determined on the shadow mask of the shape formed taking into account the mask-to-screen spacing in each separation area. The tie bar pitch on the unformed flat mask is then calculated by subtracting the stretch caused by the mask forming step. Such stretch is determined by actually measuring the vertical pitch in the isolation region on the aperture forming mask and comparing this measurement with the measurements made on the flat mask prior to formation. Such a decision may involve several cycles. Once the stretch measurements are obtained, the results are processed by least squares. Finally, the least square method is done on a flat mask tie bar. The evaluation of the least squares method provides the pratt mask tie bar position for any X and Y position.

Claims (1)

Viewing screen 22 comprising a phosphor line extending in a first direction, adjacent openings in each of the vertical rows are separated from each other by tie bars 38 of the mask and tie bars in one vertical row from the tie bars of adjacent vertical rows. A shadow mask 24 comprising an elongated slit-shaped opening 36 which is offset in one direction and aligned substantially in parallel with the phosphor lines and in the form of a longitudinal line, the second direction and the second direction substantially perpendicular to the first direction and the phosphor lines; In the color receiving tube (10) having an electron gun (26) for generating three electron beams (28) which are easily deflected in one direction and projecting them onto the screen through the shadow mask, Said tie bar in the form of alternating vertical lines is placed on a straight line forming an angle [theta] about 2 degrees with respect to said second direction.