FI58232C - SJAELVKONVERGERANDE SYSTEM FOER FAERGTELEVISIONSAOTERGIVNING - Google Patents

Description

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Patent · och reglsterstyralsen AiwWtan utlagd och uti. $ Krift * n publtorad 29.08.80 - (32) (33) (31) Pyydetty «uolkwii — B« | lrd priority ll +. 01.72 USA (US) 2177® (71) RCA Corporation, 30 Rockefeller Plaza, New York, N.Y. 10022, USA (72) Albert Maxwell Morrell, Lancaster, Pennsylvania, William Henry Barkow,

This invention relates to color television display systems in which a plurality of electron beams are substantially converged at all points in the Pennsauken, New Jersey, Josef Gross, Princeton, New Jersey, USA (US) (7 * 0 Oy Kolster Ab (5¼) Self-Converging Color Television Display System that dynamic convergence hardware is used.

- Most color television receivers currently in use use a cathode ray tube with a plurality of electron beams generated by an electron gun assembly located at one end of the tube and directed toward an image surface containing a plurality of different colored phosphor elements located at the other end of the tube. A perforated plate or other color selection means such as a perforated grid or a focusing grid is interposed between the image surface and the electron gun assembly to shade the electron beams so that the beams of each beam hit only the associated color phosphor elements. The deflection coil unit located around the outer side of the cathode ray tube is energized to provide a magnetic field to deflect the beams horizontally and vertically to form a scanning raster on the image surface. Such a basic display system has been supplemented with accessories to provide dynamic convergence correction. One requirement in a display system is that the beams converge at all points on the scan grid. The effect of non-convergence is color fading, which occurs at the edges of objects in 2,58232 television images. Non-convergence can ideally be measured by the difference between the cross-shading formed by the overlapping reds, greens, and blues to the lines that appear on the raster when the relevant test signal is applied to the receiver.

It is common to statically converge the rays in the middle of the raster with, for example, permanent magnets placed around the neck of the picture tube in a predetermined ratio to the radii. The rays do not remain converged when they are deflected from the center of the raster because the image surface is relatively flat and the distance between the image surface and the center of the deflection coil unit increases when the rays are deflected from the center of the image surface. In addition, deflection aeration, such as image field deflection, astigmatism, and coma, cause additional convergence errors. It is common to use hardware to dynamically converge rays as they sweep across the raster. In picture tubes in which the electron gun assembly is of the delta type, in which three electron guns are placed at the vertices of an equilateral triangle, an electromagnetic convergence assembly is usually used in which electromagnets outside the tube activate magnetic pole pieces inside the tube neck to radiate radii. The electromagnets are activated by waveforms at horizontal and vertical sweep rates in order to provide time-varying convergence fields as the electron beams perform their sweeps. In addition, it is sometimes necessary to combine waveforms with horizontal and vertical scan rates such as horizontal-velocity waveforms modulated with vertical-speed waveforms and derive the resultant waveforms into convergence electromagnets or deflection coil windings to improve beam convergence at raster corners.

Color television receivers have been proposed in the past which include a color picture tube whose electron gun combination produces three planes of the same plane or in line, which are usually located on a horizontal line. To this end, it is known that the beams can be dynamically converged horizontally by feeding suitable horizontal or vertical sweep rate waveforms to electromagnetic or electrostatic convergence devices. A system in which the rays are converged by means of a deflection coil is described. However, when the coil is designed for this purpose, the effects on other deflection k-aherrations, such as coma, must be corrected. The device used for dynamic coma correction means the loss of cost savings achieved by eliminating horizontal dynamic convergence equipment.

It is known that the undesired effects of coma and non-convergence can be reduced by reducing the distances of the aligned rays in the deflection plane of the deflection coil unit. This can be accomplished by reducing the distances of the elements forming the rays adjacent to the electron-cannon assembly. The closer the aligned rays are in the deflection plane, the lower the transmission of the perforated plate must be for the electron beams in order to maintain the image surface tolerance between the fluorescence points and the phosphile elements placed on the image surface. When the transmission of the perforated plate is reduced, the light output of the picture tube becomes reduced. As a result, although proper convergence and an acceptable amount of coma can be produced by the system using in-line electron beams at relatively small intervals, the result is not satisfactory if the image is not bright enough for comfortable viewing under normal viewing conditions.

It is an object of the present invention to provide a color television display system that eliminates the need to use dynamic convergence and coma correction equipment and provides an image with commercially acceptable brightness.

The color television display system of the present invention includes a color television picture tube including a faceplate on which groups of phosphor elements of three different colors are arranged to form an image surface, an electron beam three electron beams , the electrode beam being selected to produce three generally radiating lines (Fig. 1) along said three beams directed toward the image surface, and a deflection coil unit including vertical and horizontal deflection coils disposed around the image tube on the perforated plate and the cannon to deflect the beams. The invention is characterized by the features mentioned in the characterizing part of claim 1.

In one embodiment of the invention, the image surface of the picture tube is formed by repeating groups of three adjacent phosphor strips of different colors. The perforated plate used with this image surface includes a number of slit apertures parallel to the phosphor strips and excite the respective phosphor strips to produce a brighter output.

The electron gun assembly includes at least one common beam-forming electrode having three apertures to form three in-line rays.

In another embodiment, the electron gun assembly includes magnetic shield members located around two outer paths of the three electron beams to protect these beams with respect to the deflection field.

A more detailed description of the invention is given below in connection with the accompanying drawings.

Figure 1 shows a longitudinal section of a top view of a color television display system according to the invention.

Fig. 2 shows a net magnetic deflection field generated by the deflection coil unit illustrated in Fig. 1.

Figure 3 illustrates the convergence of the electronic beams of the system of Figure 1 under the influence of the deflection field shown in Figure 2.

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Figure 4 illustrates the winding distribution of a toroidal deflection coil unit suitable for use in the system shown in Figure 1.

Figure 5 shows an electron gun assembly suitable for use in the system shown in Figure 1.

Figure 6 illustrates a perforated plate and a phosphor element image surface arrangement suitable for use in the image tube shown in Figure 1.

Figure 1 shows a longitudinal section of a top view of a color television display system according to the invention. The color television picture tube 10 comprises an evacuated glass shell 11. The front part of the shell 11 is an image surface and a front plate 12, on the inner side of which a number of red, green and blue phosphor elements 13, 13a and 13b are arranged. In the tube, next to the phosphor elements, there is a perforated plate 14 comprising a plurality of holes 15 · The holes 15 are aligned with the phosphor elements so as to shield the electron beams so that those parts of the electron beams passing through the apertures 15 only hit the phosphor elements. At the other end of the glass shell 11 there is an electron gun assembly 16 to form three electron beams in the same plane and in the same line. The electron gun assembly 16 is constructed such that the two outer electron beams are converted to a central beam at a location in the center of the picture tube. A more detailed description of the electron gun assembly 16 is provided below in connection with Figure 5.

Outside the glass envelope 11, along its propagating point, there is a deflection coil unit 17 * arranged to receive energy from suitable scanning current sources, not shown, to generate a magnetic field which deflects electron beams to form a scanning raster on the image surface. A more detailed description of the deflection coil unit 17 is given in connection with Figures 3 and 4.

Behind the deflection coil unit 17, a static convergence assembly 18 is placed on the neck of the glass shell 11. The static convergence assembly 18 includes magnets whose positions are adjustable to compensate for possible beam misalignment and cause beam convergence at the center of the image surface when the rays are not deviated A suitable static convergence combination for use with an in-line electron gun assembly is described in U.S. Patent No. 3,725,831 to Robert L. Barbin, entitled "Magnetic Beam Adjusting Arrangements". Behind the beam convergence combination is placed a beam purification device 19 of conventional construction, the purpose of which is to cause the rays to hit the relevant color phosphor elements.

As will be explained below, the deflection coil unit 17 and the electron gun assembly 16 together produce acceptable convergence for all three electron beams at all points on the scanning screen without the use of additional devices to dynamically converge the beams or correct for coma effects.

Figure 2 illustrates the prevailing magnetic deflection field produced by the deflection coil unit illustrated in Figure 1. Although the horizontal and vertical fields vary unevenly from point to point along the longitudinal axis of the tube, the net field effect is illustrated in Figure 2. The deflection field for deflection of radii in the horizontal direction produced by a pair of horizontal deflection coils is shown by solid lines 21 in the vertical direction. It should be noted that this magnetic field is of the pillow distortion type, the flux lines being convex when viewed from the center of the pattern. The horizontal deflection field produces a negative horizontal isotropic astigmatism of the electronic beams.

Figure 2 also shows flow lines 22 illustrating a magnetic deflection field for deflecting rays vertically, which field is formed by a pair of vertical deflection coils of the deflection coil unit 17. It should be noted that the vertical deflection field is usually barrel-shaped, the flow lines being concave when viewed from the center of the pattern. The vertical deflection field causes a positive vertical isotropic astigmatism of the rays. The purpose of the deviation fields of the described quality will be explained with reference to Fig. 3.

Figure 3 illustrates the convergence of the electronic beams of the system shown in Figure 1 under the influence of the deflection field of Figure 2. Fig. 3 & illustrates the relative positions of the green, red, and blue beams 20a, 20h, and 20c as they occur in the deflection coil deflection plane (plane C in Fig. 1) as viewed from the front plate side end of the picture tube. Figure 3¾ exaggerates the convergence conditions of the rays at the corner of the scan grid and along the vertical and horizontal deflection axes 25 and 26. It should be noted that each electron beam illuminates several phosphor elements of a given color at the same time. The forforement elements are, of course, separated from each other, but this is not shown in Figure 3t> », which illustrates the convergence of the entire rays in the different regions of the front panel.

In the center of the raster, the green, red, and blue rays are Converged.

This center convergence is achieved by directing the rays by means of an electron gun combination and the static convergence device 18 shown in Figure 1. Along the horizontal deflection axis 26, the green, red and blue beams are depicted as subconverged, i. the radii have a difference along the horizontal axis and their order is the same as that of the radii in the deflection plane shown in Fig. 3a. This space prevails at both ends of the raster along the horizontal axis. It is to be understood that the subconvergence of the rays at the ends of the horizontal axis decreases as a function of the distance from the center of the raster at which point the rays are Converged. The subconvergence of the rays on the horizontal axis is due to the nature of the horizontal deflection field shown in Fig. 2.

At the ends of the vertical axis 25 in Figure 3h, the red, green and blue radii are shown as overconverged, i. the blue and green rays have intersected at some point, so that on the front plate where the phosphor elements are located 6 58232 the blue and green rays are on opposite sides than in the deflection plane of the deflection coil. This superconvergence of the rays along the vertical axis decreases as a function of the distance from the center of the raster at which point the rays have converged. The superconvergence of the rays on the vertical axis is caused by the vertical deflection field described in Fig. 2. The beam convergence state is a consequence of the design of the deflection coil to cause some negative horizontal isotropic astigmatism and some positive vertical isotropic astigmatism. Although a state has been described in which the rays are overconverged along the vertical axis and underconverged along the horizontal axis, it is to be understood that these states of non-convergence along the axes can be used to produce acceptable convergence across the entire raster.

We have found that by proportioning the astigmatism in the deflection coils, the rays can be made substantially convergent at the corners of the raster as well as at all other points of the raster, as shown in Figure 3b. The convergence depicted in the upper right corner of the raster of Figure 3¾ indicates that the blue and green radii are slightly lateral to the red radius in the vertical direction. The upper left corner indicates that the blue and green rays are sideways from red in the opposite direction to what was described in the upper right corner. The effect of this on the raster is known as trapezoidal distortion (trap), under which conditions the shape of the raster is slightly trapezoidal instead of rectangular. In the past, attempts have been made to produce line-focus coils that ideally provide beam convergence along the deflection axes, but which generally cause an unacceptably large amount of trapezoidal distortion at the corners, with the corner convergence mode still characterized by horizontal beam separation as well as relatively large vertical separation.

The ideal line focusing deflection coil has a negative horizontal isotropic astigmatism and a positive vertical isotropic astigmatism. This type of astigmatism is necessary to maintain the convergence of three horizontally aligned beams along the horizontal and vertical deflection axes. This axis convergence should be applied to the corners of the raster and would ideally result in beam convergence at all points in the raster. In practice, it has been found that this ideal line focusing mode can only be realized in CRTs with a diagonal measurement of the image surface of about 36 cm or less. diagonal overlaps, the line focusing state cannot be realized and results in a trapezoidal split, as explained in connection with Fig. 3h.When a trapezoidal phenomenon occurs, positive and negative astigmatism must be properly proportioned between vertical and horizontal deflection coils. at all points in the raster.

As used herein, substantial convergence refers to a state that is commercially acceptable. It is common among television set manufacturers to set non-convergence limits for the design requirements of a particular television set. It is always desirable to keep the non-convergence as close to zero as possible, but in practice manufacturing variations make zero non-convergence virtually impossible to achieve. The design goal set by the manufacturer is that the non-convergence of the rays, measured at 13 mm from the corners of the scanning screen, should be less than 1.3 mm in CRTs with a diagonal (diagonal) of 38 cm. The design limit increases with the transition to larger image surface sizes and would be about 1.6 mm for an image tube with an image surface diagonal of 6k cm.

In practice, the above-mentioned manufacturing variations, variations in the color picture tube and the deflection coil unit, result in the distribution of convergence errors from one receiver to another. In many receivers, the error is less than the 1.3 mm design target. On the other side of the other receivers made from the same contribution to the parts of the same production line, is greater epäkonvergenssi. Non-convergence defects greater than 3.2 mm have been detected in commercially available receivers. In this specification, the term essential convergence means that the non-convergence does not exceed 3.2 mm. The non-convergence of the beams can be detected as the difference between the ideally overlapping red, blue, and green line shading patterns that appear on the picture tube when a suitable test signal is connected to the television receiver. It is possible that production variations in deflection coils and picture tubes connected as a non-optimum combination may result in convergence errors as large as 3.2 mm, but this condition is not often encountered and does not indicate that the invention has not been used advantageously.

The deflection coil unit described herein, which is described in more detail in U.S. Patent No. 3,721,930, entitled "Deflection Yoke For Use With In-Line Electron Guns" (deflection coil unit for use with in-line electron guns). As inventors, William H. Barkow et al., Produce a deflection field that results in substantial convergence of rays at all points in the "" raster by proportioning the astigmatism between horizontal and vertical deflection windings.

Figure k illustrates the distribution of the winding in a toroidal deflection coil suitable for producing the convergence properties described in Figure 3b. The deflection coil unit includes conductors 31 forming a pair of vertical deflection coils and conductors 32 forming a pair of horizontal deflection coils toroidally wound on the ferrite core 30. It is to be understood that the return conductors are located along the outer side of the ferrite core 30.

Figure 5 illustrates an electron gun assembly 16 suitable for use in the system shown in Figure 1. Three separate cathodes 35a, 35b and 35c have been used to generate three electron beams. The electrons emitted by the cathodes are accelerated, formed into beams and focused by other electrodes, including 8 58232 G1 electrode 36, G2 electrode 37 »G3 electrode 38 and G1 + electrode 39 · Although not shown, it must be understood that the cathodes and other electrodes are held in common positions. with suitable glass support strips attached to different electrodes. The electron gun assembly 16 produces three electron beams that converge in the center of the faceplate of Fig. 1 when there is no deflection field formed by the deflection coil unit. To achieve this converged state, the orientation and spacing of the different electrodes relative to each other are critical, especially for electrodes G3 and. It should be noted that all electrodes have three apertures and are common to the three radii. This monolithic type construction greatly facilitates the construction of a precise electron gun which produces the desired orientation (seam parallelism) of the rays, especially in the vertical direction. The spacing of the apertures relative to each other in the electrodes G3 and G1 allows the two outer rays to converge on the image surface. Minor differences in beam orientation (convergence at the center of the picture tube) are corrected by the arrangement of the above-mentioned static convergence combination.

For larger color picture tubes, such as those with a picture tube diagonal of 38 cm or more, it may be desirable to use a comic correction such that the scanning screens of the two outer beams are the same size as the scanning screen raster of the middle beam on the image surface. A coma can be caused by a deflection coil, and if it does occur, it tends to become more harmful to the viewer the larger the image surface size. To correct the effect of the coma, annular shields 10 and kl of a magnetically permeable material, such as nickel iron, are generally placed around the outlets of the electrode G1. These shields actually protect the two outer rays with respect to the magnetic deflection field and thus balance the effect of the magnetic deflection field on the three beams in such a way that three raster of the same size is formed. A suitable electron gun assembly of this type is described in more detail in U.S. Patent No. 3,725,500 to Richard Hughes, "In-Line Electron Gun."

We have found that in the self-converging color vision display system of the invention, the appropriate spacing of adjacent rays must be carefully selected. The minimum distance between adjacent rays is determined by the lowest acceptable brightness requirement in the picture tube. As the rays are generated at ever smaller intervals from each other, the transmission of the perforated plate must be reduced to maintain color purity. As a result, there is less light output from the picture tube. This lower limit between adjacent rays to provide satisfactory brightness with a particular picture tube can be calculated or empirically determined in a manner known to a person skilled in the art.

In another aspect of the invention in one aspect, there is a limit to the maximum of adjacent beams. This limit is approached when the deflection coil unit is no longer able to provide a beam sweep with satisfactory convergence at all points of the raster.

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It can be seen from Figure 1 that the distance between adjacent rays in the plane passing through point C is denoted by the letter S. The letter C indicates the deflection level of the deflection coil unit. S is measured away from the deflection plane away from the electron assembly, but it is to be understood that S is determined by the choice of electron gun that produces the desired gaps measured in a plane midway along the length of the deflection coil unit. The ratio of the gap S to the aperture intervals in the electrodes forming the beam of the cannon can be determined from trigonometric first by measuring the distance between the apertures and the distance at which the center of the deflection coil is from the apertures along the path to the image surface. The deflection plane C is generally in a plane midway along the longitudinal axis of the deflection coil unit perpendicular to this axis. The deflection coil unit is mounted outside the tube of the picture tube with a relatively small clearance between the inner surface of the coil and the glass shell. This clearance is usually of the order of 6.4 mm or less. We have found that a deflection coil unit of the type described can be moved in a direction perpendicular to the longitudinal axis of the picture tube to provide the best convergence of the beams. First, a static convergence combination is set to produce beam convergence at the center of the raster. The deflection coil unit is then moved transversely to the picture tube until the best general convergence is obtained for the raster. In this case, the deflection coil unit is fastened in place with suitable mounting means.

In the described system, a deflection coil unit in which the splitting of the deflection windings is selected to produce negative horizontal isotropic astigmatism and positive vertical isotropic astigmatism can help keep the convergence of the three electron beams satisfactory if the S distance does not exceed 5.1 mm. The color television display systems according to the invention have been successfully constructed using picture tubes with picture screen diameters of 38 and 43 cm and S spacing of 4.0 mm. Such a combination together with a slit hole plate results in a suitable light output from the picture tube. We have found that the effects of coma, i.e. different size of different colored rasters, increases with respect to the square of the S-distance. This is one reason that S should not be increased to a relatively large value just to get a higher light output from the picture tube. With an S-distance of up to 5.1 mm, it is unnecessary to correct the coma if there are no more than 36 cm from the image surface. When using picture tubes with larger image surfaces, the effect of coma becomes relatively larger and it is desirable to use the coma shields explained in connection with Figure 5. Although a toroidal deflection coil unit is described in the described embodiment, it is to be understood that suitable deflection coil units using saddle-type coils may be used as well. It is known that the coma properties of saddle-type coils can be controlled by dividing the saddle-type coils at the inlet and center of the boiling coils. Similarly, the astigmatism of the saddle coils can be controlled by dividing the windings in the middle and output portions of the deflection coils. In some cases, it may be possible to eliminate the coma guards illustrated in Figure 5 because the coma properties of the saddle-type deflection coil units can be monitored.

In some embodiments of the invention, it may be desirable to reduce the effects of coma by reducing the S-distance between adjacent rays to a point where the light output would be below a satisfactory level in an image tube using an image surface comprising fluorescent dots and a dot aperture plate. In this situation, the light output can be increased by using the phosphor elements and the perforated plate arrangement illustrated in Figure 6.

Fig. 6 illustrates a perforated plate and a line-type phosphor element arrangement suitable for use in the picture tube shown in Fig. 1. In Fig. 6, three electron beams 20a, 20b and 20c are directed through the elongate slit openings 15 in the perforated plate 14 to strike green, red and blue-stripe-type phosphor elements disposed on the image surface 12.

This type of combination, in which the slit apertures are parallel to the vertical phosphor element stripes, can be advantageously used in conjunction with the electron gun shown in Fig. 5, in which the rays are horizontally in line, because the vertical orientation of the rays is not critical. This is because the phosphor elements are continuous in the vertical direction on the image surface and there is no need to critically monitor the vertical tolerance of the rays because they always hit the desired color vertically. Thus, the elongate slit openings 15 in the perforated plate 14 allow a greater proportion of the radii to pass through than the corresponding dot openings in the case of image surfaces with point-like phosphor elements. As a result of the higher permeability of the perforated plate in the perforated plate with elongate slits in connection with the vertical phosphor elements of Figure 6, there is an increased light output of the picture tube, allowing a relatively small beam spacing S to be used to achieve substantial convergence for electron beams. In contrast to its delta cannon counterpart, the direct-beam electron gun assembly used in the present invention does not require dynamic convergence and, as a result, does not result in beam trion rearrangement, i. the increase in radius-trio spacing as the radii are deflected from the center of the raster. Thus, the optics for printing the phosphor elements becomes simpler.

An advantageous feature of the presented system is that no dynamic correction against non-convergence and coma effects is required. Since the effects of non-vergency and coma increase as the size of the image surface increases, the invention can be advantageously used in connection with color image tubes with direct electron beams having an image surface diagonal of 58-64 cm. However, under these conditions, it may be desirable for the 11,58232 self-converging feature to be supplemented with a simplified dynamic convergence device. In such a case, electrostatic or electromagnetic convergence means located in the neck area of the picture tube and powered by only one line and field scan rate can be used. For example, the use of only horizontal dynamic convergence correction in the electron gun combination with straight electron beams described above would result in a raster in which the beams are satisfactorily converged at all points.

Claims (3)

58232 Patent Requirements: A color television display system comprising a color television image tube (10) including a front plate (12) on which groups of phosphor elements (13 »13a, 13b) of three different colors are arranged to form an image surface, an electron beam (16) having three electron beams (20a, 20b, 20c) ) located horizontally substantially perpendicular to the image surface and the perforated plate (1U) including a plurality of holes (15) aligned with the phosphor element groups, the electrode beam being selected to produce three generally converging lines along said three beams (Fig. 1) towards the image surface, and a deflection coil unit (17)> comprising vertical and horizontal deflection coils (31 and 32, respectively), - arranged around the image tube between the perforated plate and the cannon to deflect the rays to form a raster on the image surface, characterized in that the deflection coils (31, 32 ) the winding distribution has been chosen to provide a positive _ vertical isotropic astigmatism and negative horizontal isotropic astigmatism, proportional to substantially balancing the beam convergence along the horizontal (26) and vertical (25) deflection axes against beam convergence at the corners of the grid, and that the electron beam is further selected to provide a gap of about 5 mm or less. s) between adjacent radii measured in a plane (c) located midway between the ends of the deflection coil unit. A color television display system according to claim 1, characterized in that the distribution of the windings of the deflection coils (31. 32) is such that overconvergence is achieved near the ends of the vertical axis and underconvergence near the ends of the horizontal axis. A color television display system according to claim 1, characterized in that the electron cannon assembly comprises shield means (Uo, Ui) located around two outer (20a, 20c) paths of said three radii (20a, 20b, 20c) to protect the two radii with respect to said deflection field. ! +. A color television display system according to claim 1, characterized in that the electron gun assembly is selected to produce a substantially 1+ mm gap between adjacent rays in the deflection plane.