An electron gun structure for a colour picture tube apparatus

Abstract: A color picture tube apparatus comprises an envelope including a funnel(11), a face plate(12) and a neck(17), a phosphor screen(15) on an inner surface of the face plate, an electron gun structure(16) in the neck of the envelope for generating at least one electron beam, resistor means(120) for supplying predetermined voltage to the electron gun structure, and deflection means(18) for generating non-uniform deflection magnetic field to deflect the electrom beam. The electron gun structure includes a focusing electrode(70) including first means(74) for generating an asymmetric converging electric field near the focusing electrode having a relative strong converging action in one direction compared with the converging action in another direction perpendicular to the one direction, an accelerating electrode(100) including second means(101) for generating an asymmetric diverging electric field near the accelerating electrode having a relative strong diverging action in the one direction compared with the diverging action in the other direction, and at laest one intermediate electrode(80), (90) between the focusing electrode and the accelerating electrode for separating the converging electric field from the diverging electric field.

Description: This invention relates to improvements in an electron gun structure for a colour picture tube apparatus. In general, colour picture tubes with three electron gun systems are currently used. Particularly, a colour picture tube with an in-line type electron gun is currently used, since self-convergence of three electron beams is easily achieved by using non-uniform deflection magnetic fields for deflecting three electron beams 1, 2 and 3. These fields consist of a pincushion type horizontal deflection magnetic field shown in Figure 1A and a barrel type vertical deflection magnetic field shown in Figure 1B. Further, it is possible to reduce the power consumption in a colour picture tube of the self-convergence type and it is also possible to improve quality and performance, because of its simple construction. On the other hand, the colour picture tube has the disadvantage that the resolution at the periphery of the screen is reduced due to such a non-uniform deflection magnetic field. Namely, the shape of the electron beam on the screen is distorted in accordance with the deflection angle of the electron beam. As shown in Figure 2, the beam spot 4 in the center of the screen is almost circular, but the beam spot 5 at the periphery of the screen is distorted, so that the electron beam consists of horizontally elongated elliptical shape core 6 with high brightness and a vertically elongated halo 7 with low brightness. Consequently, the resolution at the periphery of the screen is greatly reduced. Such beam distortion, because of the non-uniform deflection magnetic field shown in Figure 2, is caused by the mechanism that the focus of the electron beam in the deflection magnetic field is weakened in the horizontal direction, while the focus in the vertical direction is strengthened. Accordingly, the electron beam at the periphery of the screen is deformed. The reduction of the resolution due to such beam distortion can be reduced in some degree by supressing the diameter of the electron beam which passes through the main lens and the deflection region. For this purpose, generaly, the electron beam may be prefocused by a prefocus lens. However, in this design, there is the disadvantage that the beam spot size at the center of the screen is increased, since the crossover diameter increases. As another design for compensation of such beam distortion, it has been proposed to use an asymmetric lens ( astigmatic lens ) as the prefocus lens. For example, U. S. Patent No.4,443,736, issued to Chen on April 17, 1984, which describes an improved screen grid structure including a first portion having a circular aperture, a second portion having at least one elongated aperture and a third portion having a circular aperture. Since the electron beam is in the condition of under-focused in the vertical direction by the asymmetric lens, such deflection distortion can be reduced. In this design, however, the beam spot at the center of the screen becames elliptical with the long axis in the vertical direction, so that resolution at the center of the screen is reduced. As another design for compensation of the beam distortion, it has also been proposed to use a quadrupole lens. For example, Japanese Laid- Open Patent Application Nos. 61-39346 and 61-39347 describe first and second pairs of plate electrodes with non-circular openings, which are provided between a first and second focus electrodes. A first focusing voltage is applied to both of the first pair of plate electrodes and the first focusing electrode, and a second focusing voltage is applied to both of the second pair of plate electrodes and second focusing electrode. Thus, the quadrupole lens is formed at the plate electrodes. In addition, at least one of the focusing voltages is varied in accordance with the deflection angle to compensate for the beam distortion through the entire screen. European Patent Applications with Publication Nos. 231964 and 235975 also describe an electron gun structure having a quadrupole lens to compensate for the beam distortion. The former application discloses an electron gun structure for a colour picture tube including first and second quadrupole lens electrodes between a beam forming region and a main focusing lens region to provide a quadrupole lens. The first and second focusing voltages are applied to the quadrupole lens electrodes, respectively. The latter application discloses an electron gun structure for a colour picture tube having first and second focusing electrodes to provide a main focusinging lens between them. The first focusing electrode consists of a pair of cup-shaped electrodes with a plate-shaped supplemental electrode between them. The plate-shaped supplemental electrode has three non-circular openings where the electron beams pass. By applying a control voltage to the supplemental electrode, beam spots with an optimum size are obtained throughout the entire screen, since the quadrupole lens is constructed at the supplemental electrode. Such electron gun structure having a quadrupole lens separated from the main focusing lens may obtain improved resolution over screen center and screen periphery in some degree in comparison with the electron gun structure having an asymmetric lens as the prefocus lens. There are, however, some considerable disadvantages in these electron gun structures. That is, since the action of the quadrupole lens is weakened by the separately provided main focusing lens, the resolution at the periphery of the screen is not sufficently improved. The quadrupole lens has the action of making the distance of the virtual object point from the main focusing lens differ between the horizontal and vertical directions. At the same time, the spread of the electron beam incident upon the main focusing lens is also made to differ between the horizontal and vertical directions. The relationship between the position of the object point and spread of the electron beam incident on the main focusing lens weakens the action of the quadrupole lens. Consequently, when the focusing voltage is dynamically varied in accordance with the beam deflection, improvement of the resolution at the periphery of the screen ( hereafter called sensitivity) cannot be satisfactorily achieved. In particular, since it is necessary to achieve sufficient sensitivity in the case of large current performance and of large and wide deflection angle tubes, the resolution at the periphery of the screen cannot be sufficiently improved by an electron gun structure with the above mentioned design. Further, the electron gun structure requires a focussing voltage power source which may supply two values of focussing voltages consisting of a constant focussing voltage to establish the main focussing lens and a variable focussing voltage varying in synchronism with the beam deflection. In general, since the focussing voltage is as high as 7kV to 8kV, it is necessary for a conventional colour picture tube to supply the focussing voltage through a socket unit attached to pins mounted on the neck portion of the picture tube. Thus, a colour picture tube with this electron gun structure does not have interchangeability with a conventional picture tube. Moreover, a special construction is required to prevent arcing at the socket unit because of the high focussing voltage when two focussing voltages are supplied through the socket unit. Published European Patent Application 152933 describes a further example of an electron gun structure whose construction provides a long-focus lens equivalent to one which may be obtained by increasing the distance between the first and second electrodes, an auxiliary electrode having one opening being formed between the first and second electrodes. It is an object of the invention to provide a colour picture tube apparatus with an electron gun having a high resolution over both the center and periphery of the screen. The invention provides a colour picture tube apparatus responsive to a plurality of voltages including a focussing voltage, an accelerating voltage higher that the focussing voltage and at least one intermediate voltage between the focussing and accelerating voltages comprising an envelope including a funnel having a front and a rear sides, a face plate on the front side of the funnel having an inner surface, and a neck on the rear side of the funnel, a phosphor screen on the inner surface of the face plate including a plurality of phosphor stripes extending in a vertical direction and arranged in a horizontal direction, a shadow mask with a plurality of apertures therein disposed near the phosphor screen, an electron gun structure in the neck for generating three electron beams arranged in the direction parallel to the horizontal direction including cathode means for emitting the electron beams, a focussing electrode responsive to the focussing voltage, an accelerating electrode responsive to the accelerating voltage and at least one intermediate electrode between the focussing electrode and the accelerating electrode responsive to the intermediate voltage, resistor means inside the envelope for supplying the intermediate voltage to the electron gun structure, and deflection means for generating a non-uniform deflection magnetic field to deflect the electron beams onto the screen, characterised in that the focussing electrode includes first means for establishing common equipotential lines horizontally transversing a passing area of the electron beams so as to generate an asymmetric converging electric field near the focussing electrode which has a relatively strong converging action in one direction parallel to the vertical direction compared with the converging action in another direction perpendicular to the one direction, the accelerating electrode includes second means for establishing common equipotential lines horizontally traversing the passing area of the electron beams so as to generate an asymmetric diverging electric field near the accelerating electrode having a relative strong diverging action in the one direction compared with the diverging action in the other direction, and the converging electric field is separated from the diverging electric field by the at least one intermediate electrode which includes three holes where the electron pass therethrough. The above and other features of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figures 1A and 1B show sectional views of electron beams in horizontal and vertical deflection magnetic field, respectively. Figure 2 shows front view of the electron beam shapes at the center and periphery of the phosphor screen in accordance with the conventional colour picture tube. Figure 3 shows perspective view of colour picture tube apparatus in accordance with this invention. Figures 4A and 4B show a schematic cross-section view of the electron gun structure for the colour picture tube apparatus of the invention. Figures 5A and 5B show a cross-sectional view of part of the electron gun structure for the colour picture tube apparatus of the invention. Figures 6A and 6B show the optical model to illustrate the principle of the invention when the electron beam is projected on the center of the phosphor screen. Figures 7A and 7B show the optical model to illustrate the optical model to illusrate the principle of the invention when the electron beam is deflected to the periphery of the screen. Figures 8A and 8B show a cross-sectional view of part of the electron gun structure for the conventional colour picture tube apparatus. Figure 9A and 9B show the optical model of the main lens of the electron gun for the conventional colour picture tube when the electron beam is projected on the center of the screen. Figures 10A and 10B show the optical model of the main lens in the electron gun for the conventional colour picture tube when the electron beam is deflected to the periphery of the screen. Figure 11A and 11B show time chart of deflection current and dynamic focusing voltage superimposed on the focusing voltage for the invention. Figure 12 shows a front view of the electron beam shapes at the center and periphery of the phosphor screen according to the invention. Figure 13 shows a front view of the focusing and accelerating electrodes for another embodiment of this invention. Figure 14 shows a perspective view of the focusing and accelerating electrodes for another embodiment of the invention. Figure 15 shows a cross-sectional view of the part of the electron gun structure for another embodiment of the invention. Figure 16 shows a cross-sectional view of the part of the electron gun structure for another embodiment of the invention. In the colour picture tube apparatus, each electron beam is converged and diverged through the main focusing lens, and finally focused on the phosphor screen. The beam spot of the electron beam is distorted due to the non-uniform deflection magnetic field of the deflection apparatus. Such beam distortion caused by the non-uniform magnetic field is considered as " a quadrupole distortion ", since the electron beam is forced so as to spread in the vertical direction, but, in the horizontal direction, it is forced so as to be compressed. So, it is preferable to use the quadrupole lens as the main focusing lens for compensating such beam distortion due to the deflection magnetic field. The quadrupole lens is a lens which works on the electron beam in different direction between the vertical and horizontal directions. For example, the quadrupole lens compresses the electron beam in the vertical direction, it spreads the electron beam in the horizontal direction. However, since it is difficult to adjust the focusing voltage for the compensation of the beam distortion without changeing the convergence condition of three electron beams, the quadrupole lens has not been used as the main focusing lens. Namely, since the voltage difference between the focusing and accelerating electrodes changes when the focusing voltage is changed for adjusting the focusing condition of each electron beam on the screen, three electron beams fail to converge. Accordingly, in the conventional design of the electron gun for the colour picture tubes, such as the electron gun shown in Japanese Laid-Open Patent Application Nos. 61-3946 and 61-39347 and European Patent Application with Publication Nos. 231964 and 235975, the quadrupole lens should be separately provided from the main focusing lens. In the electron gun structure used for the colour picture tube apparatus of this invention, a main electric field of the main focusing lens is divided into a converging electric field on the focusing electrode side and a diverging electric field on the accelerating electrode side by an intermediate electrode disposed between the focusing and accelerating electrodes. Consequently, the main focusing lens itself can be made the quadrupole lens. European Patent Application with Publication No. 226,145 discloses an intermediate electrode interposed between the focusing and accelerating electrodes. However, the main focusing lens between the focusing and accelerating electrodes is not an asymmetric lens, such as the quadrupole lens, but a symmetric lens. With reference to the drawings, the preferred embodiment of this invention is explained. As seen from Figure 3, the colour picture tube apparatus according to the invention comprises a funnel 11, a face plate 12 formed on a front side of the funnel 11, an shadow mask 13 with slit apertures 14 which is disposed inside of the face plate 12 so as to closely face a phosphor screen 15 coated on an inner surface of the face plate 12, and an in-line electron gun structure 16 received in the neck 17 and having three linearly arranged electron guns 16a, 16b and 16c to emit three electron beams. A deflection coil 18 generating a pincushion type horizontal deflection magnetic field and a barrel type vertical deflection magnetic field shown in Figure 1 is mounted on the funnel 11. The phosphor screen 15 comprises red, green and blue phosphor stripes 19a, 19b and 19c, which emit red, green and blue light, respectively, and black stripes 20 interposed between the phosphor stripes 19a, 19b and 19c. A stem 21 insulatively supporting pins 22 is mounted at the end of the neck 17. The pins 22 penetrate the stem 21 so as to supply the predetermined voltages to electrodes of the electron gun structure 16. A socket unit ( not shown ) is attached to the pins 22. The electron gun structure 16, as shown in Figure 4A, includes three cathodes KR, KG and KB linearly arranged and housing heaters ( not shown ), respectively. The electron gun structure 16 also includes a first electrode 30, a second electrode 40, a third electrode 50, a fourth electrode 60, a fifth electrode 70, two intermediate electrodes 80 and 90, a sixth electrode 100 and a convergence cup 110. These electrodes are supported by a pair of insulating rods ( not shown ). As shown in Figure 4B, a resistor 120 is provided near the electron gun structure 16 to supply the predetermined constant voltages to the intermediate electrodes 80 and 90. One end terminal 121 of the resistor 120 is connected to the sixth electrode 100 and another end terminal 122 is connected to ground. Intermediate terminals 123 and 124 of the resistor 120 are connected to the intermediate electrodes 80 and 90, respectively. Also, the terminal 121 of the resistor 120 is connected to working voltage supply system 130. For example, the resistor shown in U. S. Patent No. 4,672,269 issued on January 9, 1987 may be used as the resistor 120 of the invention. The first electrode 30 is made of a thin plate electrode with three small holes linealy arranged in the horizontal direction for the path of the electron beam. The second electrode 40 is also made of a thin plate electrode with three small holes linearly arranged. The third electrode 50 consists of first and second cup-shaped electrodes 51 and 52 which are fixed together at their open ends. The first cup-shaped electrode 51 has three holes with slightly larger diameter than that of holes of the second electrode 40 on the side of the second electrode 40. The second cup-shaped electrode 52 has three holes with larger diameter than that of the holes of the first cup-shaped electrode 51 on the side of the fourth electrode 60. The fourth electrode 60 also consists of first and second cup-shaped electrodes 61 and 62 which are fixed together at their open ends. The first and second cup-shaped electrodes 61 and 62 have three holes with large diameter, respectively. The fifth electrode 70 consists of four cup-shaped electrodes 71, 72, 73 and 74, each of which has three large-diameter holes. The intermediate electrodes 80 and 90 are made of thick plate electrodes with three large-diameter holes. The sixth electrode 100 is composed of two cup-shaped electrodes 101 and 102, each of which has three large-diameter holes. The convergence cup 110 is secured to the bottom of the cup-shaped electrode 102. All of the electrodes from the first electrode 30 to the convergence cup 110 have circular holes. In order to operate the electron gun, the electrodes are applied the following voltages, respectively. On the cathodes KR, KG and KB are supplied, for example, direct current voltages of 150V and modulated image signals corresponding to the picture image, respectively. The first electrode 30 is connected to ground potential and a direct current voltage of about 600V is supplied on the second electrode 40. Thus, the cathodes KR, KG and KB, the first electrode 30 and the second electrode 40 construct a triode. The third and fifth electrodes 50 and 70 are connected in the inside of the envelope and about 7kV to 8kV is applied to them as focusing voltage. These electrodes 50 and 70 are also superimposed dynamic focusing voltage V D which varies in accordance with the deflection angle. The fourth electrode 60 is connected to the second electrode 40 in the inside of the envelope. Also, an accelerating voltage of about 25kV to 30kV is impressed on the sixth electrode 100. The second and third electrode 40 and 50 form a pre-focus lens which preliminarily focuses the electron beams passing through the triode. The third, fourth and fifth electrode 50, 60 and 70 form an auxiliary focusing lens and the electron beams are further focused at the auxiliary focusing lens. Voltages of 40% and 65% of the accelerating voltage are applied to the intermediate electrodes 80 and 90 through the resistor 120. The fifth electrode 70, intermediate electrodes 80 and 90 and the sixth electrode 100 form the main focusing lens which focuses respective electron beams and converges the three electron beams on the phosphor screen. Since, in this type of the main focusing lens, the area of the main focusing lens is expanded by the intermediate electrodes 80 and 90, the main focusing lens can be made a lens with a long focal length called an expanded electric field lens. Next, refering to Figures 5A and 5B, the equipotential distribution formed in the main lens of the electron gun according to the embodiment is shown. At first, in Figure 5A showing a horizontal cross-section of the electric field, converging electric field between the cup-shaped electrode 74 and one of the intermediate electrodes 80, which penetrates into the last cup-shaped electrode 74 of the fifth electrode 70, consists of the equipotential lines which are common to the center hole 74G and both side holes 74R and 74B. In addition, since the equipotential lines in the horizontal cross-section are common to these holes 74G, 74R and 74B, the curvature of the electric fields is small. On the contrary, as shown in Figure 5B showing a vertical cross-section of the electric field, the curvature of the electric field of the vertical cross-section is larger than that of the horizontal cross-section due to the influence of the side wall 75. Consequently, the converging action on the electron beam in the vertical direction is relatively stronger than in the horizontal direction. Due to the same reason, the diverging electric field between another intermediate electrode 90 and the sixth electrode 100, which penetrates into the sixth electrode 100 is also stronger in vertical direction than in the horizontal direction. As explained above, the main focusing lens of the electron gun 16 consists of the converging electric field near the fifth electrode 70 and the diverging electric field near the sixth electrode 100 which are independantly separated from each other by the intermediate electrodes 80 and 90. Further, since the curvature of the converging and diverging electric field in the vertical direction are relatively larger than in the horizontal direction, the main focusing lens has a converging action relatively stronger in the vertical direction and diverging action relatively stronger in the vertical direction. The action of the main focusing lens will be explained. When the electron beams are projected at the center of the screen, respective electron beams are focused into an almost circular shape by applying a predetermined focusing voltage to the fifth electrode 70 so that the asymmetric converging electric field and the asymmetric diverging electric field are balanced. Next, when the electron beams are deflected to the periphery of the screen, the focusing voltage is increased over the predetermined value in accordance with the deflection angle. At this time, since the focusing voltage approaches to the value of the voltage applied to the intermediate electrode 80, the converging electric field becomes weaker. On the other hand, as the potential difference between the intermediate electrode 90 and the sixth electrode 100 does not change, the diverging electric field between the intermediate electrode 90 and sixth electrode 100 does not vary. So, the diverging electric field becomes relatively stronger in the main focusing lens compared with the converging electric field. Accordingly, for the electron beam, an under-focused state occurs in the vertical direction, and thus, the over-focused state caused by the deflection magnetic field can be cancelled out. Referring to the optical model shown in Figures 6 and 7, the action of the main focusing lens is more explained in detail. As shown in Figure 6A, the main focusing lens of the horizontal direction can be represented by the combination of a relatively weak converging lens ( convex lens ) 200 and diverging lens ( concave lens ) 300 when no deflection is imparted. Also, as shown in Figure 6B, the main focusing lens of the vertical direction can be also represented by the combination of a relatively strong converging lens 210 and diverging lens 310. So, the electron beam is focused on the screen in both of the horizontal and vertical direction, and an circular beam spot is obtained. As shown in Figure 7A, when the electron beam is deflected, the converging lens 200 and the diverging lens 300 do not change compared with the lenses shown in Figure 6A. On the other hand, as shown in Figure 7B, since the potential difference between the fifth electrode 70 and the intermediate electrode 80 is reduced by increasing the focusing voltage in the vertical direction, the converging lens becomes weak as shown by a lens 220, but the diverging lens does not change as a strong lens 310. Consequently, an under-focused state ocurrs in the vertical direction of the electron beam. In order to clarify the difference between the electron gun structure of this invention with the intermediate electrodes and an electron gun without the intermediate electrode, action of the main focusing lens in the electron gun without the intermediate electrode is explained by referring to Figures 8 to 10. Figures 8A and 8B show horizontal and vertical cross-section of the equipotential distribution, respectively. As seen from Figure 8B, strong converging electric field is formed in the vertical direction of the main focusing lens near the focusing electrode 70 and a strong diverging electric field is also formed in the vertical direction as well as the electron gun of this embodiment. However, since the converging and the diverging electric field are not separated from each other, the diverging electric field becomes weaker when the focusing voltage is increased in order that the converging electric field is to be weaker. Therefore, the optimum beam focusing state on the screen is not obtained at the periphery of the screen. This phenomenum will be clealy understood by referring to Figures 9 and 10. Figures 9 and 10 show the optical models when the electron beam is projected on the center and periphery of the screen, respectively. As shown in Figure 10B, the converging lens and the diverging lens in the vertical direction both become weak due to the increased focusing voltage when the electron beam is projected on the periphery of the screen. So, it is impossible to achieve the under-focused state of the electron beam in the vertical direction alone. Consequently, the beam distortion due to the deflection magnetic field is not compensated. The fifth electrode 70 of this embodiment receives the dynamic voltage V D shown in Figure 11B which is superimposed on the focusing voltage and synchronised with the deflection of the electron beam. When the deflection current shown in Figure 11A is zero, namely, when the electron beam is projected at the center of the screen, the dynamic voltage is also zero. As the electron beam is deflected to the screen periphery, the dynamic voltage also rises in a parabolic curve. Since the focusing voltage rises in synchronism with the deflection to the screen periphery, as described above, it is possible to achieve the under-focused state of the electron beams in the vertical direction alone. As the dynamic voltage can be superimposed on the focusing voltage, the conventional socket unit with one terminal for supplying the focusing voltage can be used. The electron beam spot configuration of the embodiment is almost circular in the center of the screen, and, at the screen periphery, the halo in the vertical direction can be almost eliminated, as shown in Figure 12. Therefore, high resolution can be realized over the entire screen. Another embodiment of this invention will be explained referring to Figure 13. In general, the larger the size of the picture tube, the larger becomes the distortion of the electron beams due to the deflection magnetic field and the larger the haloes appearing in the vertical direction at the screen periphery become. In this case, when the focusing voltage is increased, it is necessary also to increase the under-focused state in the vertical direction. In other words, it is necessary to strengthen the asymmetry of the converging electric field and diverging electric field. In the embodiment shown in Figures 4A and 4B, although the fifth electrode and the sixth electrode have circular holes on the intermediate electrode sides, elliptically-shaped holes 74R', 74G' and 74B' having the long axis in the horizontal direction can be used, as shown in Figure 13. Due to the elongated hole, the converging electric field is further strengthened in the vertical direction and the diverging electric field is also further strengthened in the vertical direction. The ratio of the long axis to the short axis of the elliptical holes may be made the same in both the fifth and the sixth electrodes, or they may be made to differ. Also, the ratio of the center holes 74G'(101G') to the holes on both sides holes 74R'(101R') and 74B'(101B') may also differ. By combining these designs mentioned above, superimposing the dynamic focusing voltage on the focusing voltage may be eliminated. As a further embodiment of this invention, as shown in Figure 14, a pair of plate-shaped components 300 may be arranged with the condition of facing each other in the vertical direction in the inside of the last cup-shaped electrode 74 of the fifth electrode 70 and the cup-shaped electrode 101 of the sixth electrode 100. In this complex electrode, since the penetration of the electric field is constricted in the vertical direction alone, the converging electric field is further strengthened in the vertical direction and the diverging electric field is also further strengthened in the vertical direction. Also, if the length ℓ of the plate-shaped components 300 in the axial direction of the tube is made longer, the strength of the electric fields in the vertical direction can be increased. The length ℓ in the axial direction of the tube of the component 300 which are arranged in the inside of the fifth and sixth electrodes may be the same or different. Also, the elliptical hole shown in Figure 13 and the component shown in Figure 14 may be combined. In this complex electrode, the strengths of the asymmetric converging and diverging electric field will become even stronger than those in the embodiments shown in Figures 13 and 14. It is also possible to eleminate superimposing the dynamic focusing voltage by employing these complex electrodes. As another embodiment, as shown in Figure 15, cylindrical walls 76 and 103 which inwardly extend to the hole may be provided in one or both of the fifth and sixth electrodes. If the length k of cylindrical walls 76 and 103 is made longer, the asymmetry is weakened in the case of circular hole, but the asymmetry is strengthened in the case of elliptical hole. Also, as shown in Figure 16, thick plate-shaped component 77 and 104 may be added to one or both of the fifth and sixth electrodes. If thickness m of these thick plate-shaped component is increased, the asymmetry is weakened in the case of circular holes, but the asymmetry is strengthened in the case of elliptical hole. In the embodiments of this invention, although a complex type electron gun called the quadrupotential type is explained, this invention can be applied to other combined electron guns and can also be applied to the bi-potential type and unipotential type electron gun. Also, although the electron gun having two intermediate electrodes, this invention can be applied to the electron gun having one intermediate electrode and more than three intermediate electrodes. Moreover, this invention can also be applied to other multi-beam system and single beam system. Furthermore, this invention can be also applied to the delta type electron gun.

Claims: A colour picture tube apparatus responsive to a plurality of voltages including a focussing voltage, an accelerating voltage higher that the focussing voltage and at least one intermediate voltage between the focussing and accelerating voltages comprising an envelope including a funnel (11) having a front and a rear sides, a face plate (12) on the front side of the funnel having an inner surface, and a neck (17) on the rear side of the funnel, a phosphor screen (15) on the inner surface of the face plate including a plurality of phosphor stripes (19a, 19b, 19c) extending in a vertical direction and arranged in a horizontal direction, a shadow mask (13) with a plurality of apertures therein disposed near the phosphor screen, an electron gun structure (16) in the neck for generating three electron beams arranged in the direction parallel to the horizontal direction including cathode means for emitting the electron beams, a focussing electrode (70) responsive to the focussing voltage, an accelerating electrode (100) responsive to the accelerating voltage and at least one intermediate electrode (80, 90) between the focussing electrode and the accelerating electrode responsive to the intermediate voltage, resistor means (120) inside the envelope for supplying the intermediate voltage to the electron gun structure, and deflection means (18) for generating a non-uniform deflection magnetic field to deflect the electron beams onto the screen, characterised in that the focussing electrode includes first means (74) for establishing common equipotential lines horizontally transversing a passing area of the electron beams so as to generate an asymmetric converging electric field near the focussing electrode which has a relatively strong converging action in one direction parallel to the vertical direction compared with the converging action in another direction perpendicular to the one direction, the accelerating electrode includes second means (101) for establishing common equipotential lines horizontally traversing the passing area of the electron beams so as to generate an asymmetric diverging electric field near the accelerating electrode having a relative strong diverging action in the one direction compared with the diverging action in the other direction, and the converging electric field is separated from the diverging electric field by the at least one intermediate electrode which includes three holes where the electron beams pass therethrough. A colour picture tube apparatus according to Claim 1, characterised by means for varying the focussing voltage in accordance with the deflection of the electron beams. A colour picture tube apparatus as claimed in Claim 1, characterised in that the focussing electrode and/or accelerating electrode includes non-circular holes with a long axis parallel to the other direction facing the intermediate electrode. A colour picture tube apparatus as claimed in Claim 2, characterised in that the focussing electrode and/or accelerating electrode includes circular holes facing the intermediate electrode. A colour picture tube apparatus as claimed in Claim 3, characterised in that the focussing electrode and/or accelerating electrode further includes a pair of plate-shaped components defining a space therebetween and the holes being aligned with the space. A colour picture tube apparatus as claimed in Claim 1, characterised in that the focussing electrode and/or accelerating electrode includes circular holes facing the intermediate electrode and a pair of plate-shaped components defining a space therebetween and the holes being aligned with the space. A colour picture tube apparatus as claimed in Claim 3 or 4, characterised in that the focussing electrode and/or accelerating electrode further includes a cylindrical wall defining each hole and extending toward the appropriate electrode. A colour picture tube apparatus as claimed in Claim 1, characterised in that the focussing electrode and/or accelerating electrode further includes a thick plate component with a plurality of circular openings therein, each opening being aligned with one of the holes. A colour picture tube apparatus as claimed in Claim 1, characterised in that the focussing electrode and/or accelerating electrode further includes a thick plate component with a plurality of non-circular openings therein, each opening being aligned with one of the holes.

Inventors: HASEGAWA TAKAHIRO C O PATENT D, KOSHIGOE SHINPEI C O PATENT DI, SHIMOMA TAKETOSHI C O PATENT D, HASEGAWA, TAKAHIRO C/O PATENT DIVISION, KOSHIGOE, SHINPEI C/O PATENT DIVISION, SHIMOMA, TAKETOSHI C/O PATENT DIVISION
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1988
Main classification: H01J29
IPC codes: H01J29