In-Line SB Electron Gun With Large and Deep Main Lens Apertures

This invention relates generally to in-line electron guns for use in three beam cathode ray tubes and especially to a novel in-line electron gun of the SB (symmetrical outer beam) type that has a main lens that is configured to reduce spherical aberration.

In-line electron guns for cathode ray tubes are well known in the art. U.S. Pat. No. 5,170,101, assigned to Zenith Electronics Corporation, describes an in-line SB type electron gun for use in a high resolution tri-beam color cathode ray tube that has a self convergent yoke, as do most modern color cathode ray tubes. As is well known, such yokes undesirably introduce beam shape distortions which may be compensated by various electron lens configurations, one such being a dynamic lens, often referred to as a Dynamic Quadropole. Other types of distortion are also introduced to the electron beams by the electron lenses of the gun.

A major problem is spherical aberration that results when all portions of the electron beam do not focus at the same point because of the inherent increase in focussing power with radial distance from the optical center of the lens. The effect is that of halo about the electron spot, which detracts from resolution. This type of distortion may be compensated by making the lens appear large in comparison with the size of the electron beam.

The present invention reduces spherical aberration in the electron gun by enlarging and weakening the apparent aperture of the main lens. This is accomplished by enlarging the apertures in the G3 and G4 electrodes and by separating them by a greater than normal amount.

A principal object of the invention is to provide a novel in-line electron gun.

Another object of the invention is to provide an in-line electron gun that compensates for spherical aberration.

A further object of the invention is to provide a low cost, in-line electron gun.

These and other objects and advantages of the invention will be apparent upon reading the following description thereof in conjunction with the drawings, in which:

FIG. 1 is a simplified exploded view of an in-line SB type electron gun constructed in accordance with the invention; and

FIG. 2 depicts the various electrodes and apertures of the main lens in accordance with the present invention.

Referring to FIG. 1, an axes reference that identifies the X, Y and Z axes of the in-line electron gun of the invention is illustrated in the upper left hand corner of the drawing. It should be noted that the electrode representations are for illustrative and descriptive purposes only and should not be considered as depicting the actual construction of the electron gun nor of the precise location of its various components. Three cathodes (K) are positioned along the X axis and generate clouds of electrons in a well known manner. A G1 control electrode (shown in cut-away), having three apertures 12, 14 and 16 in respective alignment with the three cathodes K, is positioned in the X-Y plane adjacent to and in Z axis alignment with the cathodes. Positioned closely adjacent thereto in the X-Y plane and along the Z axis, is a G2 accelerating electrode that includes three apertures 18, 20 and 22 in alignment with the corresponding apertures in control grid G1. An elongated substantialy tubular G3 electrode is spaced along the Z axis from G2 and consists of: a G3L (lower) plate with apertures 24, 26 and 28 therein that are larger than the G2 apertures; a G3M (middle) insert electrode with apertures 30, 32 and 34, shaped in accordance with the invention, as will be seen; and a G3U (upper) electrode with open, chain link-shaped, apertures 36, 38 and 40 therein. An elongated, tubular G4 electrode (shorter than the G3 electrode) consists of a G4L (lower) plate with chain link-shaped apertures 42, 44 and 46 and a G4U (upper) plate with apertures 48, 50 and 52 shaped according to the invention, and is spaced from electrode G3 along the Z axis. The chain link or extended apertures derive their name from the fact that they resemble chain links when the connection portions between the apertures are removed.

In FIG. 2, diagram A represents a side view (in the Y-Z plane) of a portion of an actual in-line SB electron gun constructed in accordance with the invention. Diagram B represents (90 degrees rotated) frontal views (along the Z axis) of the G3M and G3U and the G4L and G4U electrodes of the gun of diagram A, which comprises the main lens of the gun. Diagram C represents respective end views of these electrodes. It should be noted that the outer apertures 30,34 and 48,52 of the G3M and G4U electrodes, respectively, are large and barrel-shaped and the center apertures 32 and 50, respectively are large, but elliptically shaped. The apertures are shaped to utilize as much of the area of the respective G3M and G4U electrodes as possible while still forming a proper electron optical lens. These large shaped apertures, in conjunction with the abnormally large distances between the G3M and the G3U electrodes (and the distances between G3M and--G3U and G4L and G4U), respectively, significantly enlarge and weaken the main lens apparent aperture size, thereby minimizing spherical aberration. The large chain link apertures of G3U and G4L introduce a minimal amount of comatic aberration because of the non symmetrical configurations of the electron lenses. Some of the electrodes and electrode structures, such as the heater/cathode structure, the G1 electrode (not shown in detail in FIG. 2, the G2 electrode and the G3U and G4L electrodes, include mounting tabs, 54,56, 55,57, 58,60, 62,64 and 68,70 that are imbedded in the glass pillars or multiforms 50 and 52 that secure the elements of the electron gun in position, in a manner well known in the art.

In a prior art SB type in-line electron gun, the spacings between G3M and G3U and between G4L and G4U are about 0.10", whereas in the invention, these spacings are substantially increased to about 0.15". Also, as mentioned, the G3M and G4U apertures are made very large, (as large as possible considering the areas of the inserts, the need for structural integrity and maintaining a proper electron lens), which together with the increased G3M-G3U and G4L-G4U spacings, enlarge and weaken the apparent aperture and significantly reduces the spherical aberration imparted thereby to the electron beams.

It should also be noted that the G3M and G4U aperture plate inserts are flat (FIG. 2, diagram C). In the prior art these inserts had a configuration that was created by extrusion of the insert. The extruded construction did not facilitate precision assembly of the electron gun. The flat G3M and G4U electrodes enable positioning tolerances (along the Z axis) to be tightly controlled in an inexpensive manner.

It is recognized that modifications and changes to the described embodiment of the invention will occur to those skilled in the art without departing from its true spirit and scope. The invention is to be limited only as defined in the claims.