US2981864A - Image display device - Google Patents

Description

April 1961 G. A. BURDICK ET AL 2,981,864

IMAGE DISPLAY DEVICE Filed June 26, 1958 INVENTORS 4241:? a smv: f

smv A. saw/ex ATTORNEY United States Patent IMAGE DISPLAY DEVICE Glen A. Burdick, Waterloo, and Elmer 0. Stone, Seneca Falls, N.Y., assignors, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Filed June 26, 1958, Ser. No. 744,797

2 Claims. (Cl. 315--16) This invention relates generally to electron discharge devices and more particularly to cathode ray tubes of the post deflection acceleration type.

Cathode ray tubes adapted for the reproduction of images may employ post deflection acceleration techniques. In such tubes, the beam is deflected in a relatively low potential region compared to the high potential region adjacent the screen. This type of structure requires less deflection power to scan a tube than the conventional unipotential type since the electrons are traveling at a relatively low rate through the low potential region and are more easily deflected. Adequate brightness is achieved by electron impingement on the screen of the tube through the utilization of a final high potential or high electron acceleration field. Although, theoretically, the deflection or scanning power required in tubes of such construction is reduced, the detrimental effects of the conventional bipotential electrostatic lens formed by the low and high potential electrodm causes bending of the beam inwardly toward the center line of the tube. Therefore, the theoretical reduction in power is offset to some extent by the necessary increase in power from the lower value to achieve the desired raster size. In addition, the theoretical reduction in power in this type of tube is less than desired and substantially less than an optimum reduction.

Accordingly, an object of the invention is to reduce the aforementioned disadvantages and to reduce the power needed to scan a picture tube.

A further object is to achieve adequate brightness in a cathode ray tube while using low deflection power and without appreciably bending the beam toward the tube axis.

A still further object is to enlarge the deflection raster of an electron beam in a cathode ray tube by an electrostatic beam deflection magnifier.

The foregoing objects are achieved in one aspect of the invention by the provision of a cathode ray tube employing in sequence a relatively low potential deflection region followed by a divergent electrostatic lens for magnifying the beam deflection. A high potential electrode is positioned in the screen area to provide final acceleration of the electrons. A convergent lens of determinable magnitude may be disposed adjacent the screen to provide final focusing for the beam.

For a better understanding of the invention, reference is made to the following description taken in conjunction with the accompanying drawings in which:

Fig. l is a sectional view of a portion of a cathode ray tube illustrating a plurality of spaced electrodes formed to provide an improved image display in accordance with one aspect of the invention;

Fig. 2 is a diagram illustrating the manner in which the electrostatic lens fields are formed to provide an enlarged beam raster for the tube;

And Fig. 3 illustrates an embodiment of the invention wherein a mesh is used to reduce the convergent effects of the beam amplifying lens field shown in Fig. 2.

Referring to Fig. 1, the cathode ray tube 11 is shown 2,981,864 Patented Apr. 25, 1961 comprising a glass envelope 13 having an image display face plate 15. A fluorescent screen 17 covered with an aluminum film 19 is attached to the inner surface of the face plate. Disposed within neck portion 21 of envelope 13 is an electron gun 23 formed to provide the source, modulation, focusing and acceleration of the electrons in electron beam 25. The conventional deflection yoke or coils 27 are positioned exterior to the neck portion 21 adjacent the cone 22 of the envelope to provide a magnetic field for deflecting the electron beam across screen 17 in a normal manner to produce the usual image display raster.

A plurality of electrodes are shown, for purposes of illustration, as conductive coatings disposed within the tube in a spaced relationship and in sequence toward screen 17 from electron gun 23. The first electrode 29 which is connected to voltage supply V is formed on the internal surface of neck portion 21 and extends into come 22 of the envelope. The second electrode 21 lies on the internal glass surface of the envelope cone and is connected to a voltage supply V The conductive coating forming the third electrode 33 is disposed adjacent screen 17 and is extended to contact aluminum film 19 to provide an electrical connection therewith. The lengths of electrodes 29 and 31 measured along the distance of electron travel is considerably more than the length of electrode 33. For instance, in a cathode ray or picture tube having a dimension of 8 inches between the interior surface of face plate 15 and the junction point between cone 22 and neck portion 21, electrodes 29 and 31 may have a length of 2% inches while electrode 33 may be 1 inch or less. The uncoated areas of the glass envelope or insulating strips 35 and 37 account for the remainder of the overall dimension. It has been found desirable to make spacing 37 slightly larger than spacing 35 since a larger potential difference exists between electrode 33 and electrode 31 during normal operation of the tube than between electrode 31 and electrode 29. The final electrode in gun 23 is connected to the first conductive coating 29 by means of straps 30.

Fig. 2 shows the effects of the electrostatic fields 39 and 41 formed by electrodes 29, 31 and 33 on beam 25. As the beam passes through the deflection region within coils 27, the beam is deflected in a prescribed conventional manner. While passing through the divergent electrostatic lens 39, the beam is bent outwardly as it proceeds toward the aluminum film 18 positioned behind screen 17. This bending magnifies the deflection of the beam normally provided by the yoke coils. The divergent effects of lens 39 may be increased, if desired, by connecting a wire mesh 28 to electrode 29 and extending it transversely across the end of this electrode positioned adjacent electrode 31 as shown in Fig. 3. Such a structure would flatten the convergent portion of lens 39. The bi-potential lens 41, which is convergent, bends the beam slightly back toward the axis of the tube. Since electrode 33 is in close proximity to the final impinging position of beam 25, the effects of convergent field 41 is minimized. However, field 41 does provide a final focusing action on the beam to compensate for any defocusing caused by the divergent field 39. This final focusing feature can be increased or decreased as desired by altering the voltages V and V relative to one another and by increasing or decreasing the axial length of electrode 33. Since beam 25 is focused as it leaves electron gun 23, convergent field 41 need only compensate for any beam defocusing of the divergent field 39 and the field of deflection coils 27.

For purposes of illustration, electrodes 29, 31 and 33 are shown as being connected to voltage supplies of 5 kv., l kv. and 10 kv. respectively. Since the electrons in beam 25 proceed from a high to low potential region when passing from electrode 29 to electrode 31, they are deflected outwardly due to the bi-potential electrostatic divergent lens 39. Since the electrons in beam 25 move from a low potential to a high potential region while passing from electrode 31 to electrode 33, they tend to become converged and bent back toward the axis of the tube. However, since the convergent field 49 is positioned very close to the screen, the deflection or bending of beam 25 is nominal.

The voltage supplies illustrated in Fig. 2 provide a cathode ray tube which requires relatively low scanning power for obtaining relatively wide deflection angles. However, these values may be altered to some extent. It has been found that satisfactory results may be obtained by making the V potential .5 times or less the potential on V and the V potential 1.5 times the potential on V or greater.

A tube constructed in accordance with the invention utilizes less scanning power than has been needed heretofore. Since the electrons in beam 25 are accelerated by a relatively low potential, e.g. 5 kv. on V through the yoke region, less deflection power is needed. In addition, the divergent or beam deflection magnifying lens 39 increases the deflection over that angle which is normally provided by coils 27. The convergent field 41 may then be used to help adjust raster shape, it needed, and to provide final beam forming, if desired.

Although several embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein Without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. An electron discharge device comprising an envelope, a screen, an electron gun spaced from the screen formed to provide a beam of electrons pre-defiected a given amount and directed to impinge upon said screen, and a plurality of spaced electordes formed as conductive coatings internally on the envelope disposed intermediate said gun and screen including in sequence a relatively long first electrode adapted for operation at a potential V a relatively long second electrode operated at a potential V less than .5 times V and a relatively short third electrode operated at a potential V greater than 1.5 times V said first and second electrodes forming a divergent electrostatic lens field for amplifying the beam deflection and said second and third electrodes forming a beam converging lens field for focusing said beam spaced from said divergent lens field, said converging lens field being positioned in close proximity to said screen.

2. An electron discharge device comprising a screen, an electron gun spaced from the screen formed to provide a beam of electrons directed to impinge upon said screen, and a plurality of electrodes disposed intermediate said gun and screen including in sequence a first electrode adapted for operation at a potential V a relatively long second electrode adapted for operation at a potential V of less than .5 times V a Wire mesh connected across said first electrode at the end thereof positioned adjacent said second electrode, and a relatively short third electrode adapted for operation at a potential V of more than 1.5 times V said first and second electrodes forming a divergent deflection amplifying electrostatic lens field and said second and thitrd electrodes forming a beam focusing lens field spaced from said divergent lens field, said focusing lens field being positioned in close proximity to the screen.

References Cited in the file of this patent UNITED STATES PATENTS 2,580,250 Smith Dec. 25, 1951 2,590,764 Forgue Mar. 25, 1952 2,734,147 Beckers Feb. 7, 1956 2,798,185 Hansen et al July 2, 1957 2,808,526 Davis Oct. 1, 1957 2,813,224 Francken Nov. 12, 1957 2,837,689 Dufour June 3, 1958 2,864,032 Amdursky et al Dec. 9, 1958 FOREIGN PATENTS 191,981 Switzerland Sept. 16, 1937 553,466 Great Britain May 24, 1943 109,216 Sweden Dec. 7, 1943

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