US3610993A

US3610993A - Electronic image device with mesh electrode for reducing moire patterns

Info

Publication number: US3610993A
Application number: US889550A
Authority: US
Inventors: Robert B Randels
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1969-12-31
Filing date: 1969-12-31
Publication date: 1971-10-05
Anticipated expiration: 1988-10-05

Abstract

An electronic image device in which an electron beam is generated within an envelope and caused to scan a target in a predetermined linear manner, and in which a mesh electrode is positioned between said electron gun and the target or between a photocathode and the target to cause a linear charge pattern. The mesh electrode is comprised of a first set of parallel equally spaced wires positioned at a positive angle of 50* to 70* to the linear scan of the beam and a second set of parallel equally spaced wires positioned at a positive angle of 110* to 130* to the linear scan.

Description

United States Patent ELECTRONIC IMAGE DEVICE WITH MESH ELECTRODE FOR REDUCING MOIRE PATTERNS 5 Claims, 3 Drawing Figs.

US. Cl 313 39, 313 293, 313/308, 313/348, 315 1 1 1m.c1 H01j1/46, H0lj29/36,H01j31/26 Field of Search 313/82 NC,

85 S, 106, 82 BF, T, 86, 89, 293, 294, 295

Primary Examiner-Roy Lake Assistant Examiner-V. Lafranchi AttorneysF. H. Henson and C. F. Renz ABSTRACT: An electronic image device in which an electron beam is generated within an envelope and caused to scan a target in a predetermined linear manner, and in which a mesh electrode is positioned between said electron gun and the target or between a photocathode and the target to cause a linear charge pattern. The mesh electrode is comprised of a first set of parallel equally spaced wires positioned at a positive angle of 50 to to the linear scan of the beam and a second set of parallel equally spaced wires positioned at a positive angle of to to the linear scan.

SSSSSSS ES PATENTEI] our Bi 3510.993

VY Yo 9a 2 iigw NNNNNN OR Robert B Ronde'g ELECTRONIC IMAGE DEVICE WITH MESH ELECTRODE FOR REDUCING MOIRE PATTERNS BACKGROUND OF THE INVENTION The present invention relates to electronic imaging devices which incorporate a mesh electrode and in which an electronic beam is scanned across the mesh electrode and outer charge pattern affected by a mesh electrode. In such devices, moire effects have been noted and have been a problem since the earliest days. The effect involves a mesh or the shadow of the mesh and the scanning lines forming the raster which is in essence a grating of equally spaced lines. Unless the angular relationships are carefully maintained and a mesh of small spacing employed, objectionable moire patterns are formed in the reconstructed picture. One partial solution to this problem has been to utilize very small mesh wire spacings of about 0.001 inch. This problem is increased as one goes to the smaller diameter type tubes and those tubes requiring high resolution. It is accordingly the general object of this invention to provide a mesh electrode of predetermined configuration and positioning with respect to the scanning raster to reduce the criticality of angular orientation and permit larger spacings between the mesh wire without the introduction of undesirable moire effects.

SUMMARY OF THE INVENTION This invention describes a particular configuration of a mesh electrode and positioning with respect to the scanning raster of an electron beam to reduce the moire effects. This is accomplished by providing a mesh or grid member comprised of a set of parallel equally spaced wires positioned at an angle from 50 to 70 with respect to the linear scan and a second set of parallel equally spaced wires positioned at an angle of 1 10 to 130 with respect to the linear scan. This structure provides in effect a diamond-shaped opening with one angle and the diametrically opposite angle being of a value from 40 to 80 and the other two angles of the diamond-shaped member varying from 100 to 140.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIG. I is an electronic tube incorporating the teachings of this invention;

FIG. 2 is an enlarged perspective view of the mesh control grid in FIG. 1, and

FIG. 3 is an enlarged perspective view of a modified mesh control grid that may be incorporated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, there is illustrated a secondary electron conduction camera tube which consists of an electrostatically focused diode image section 10, a target assembly 12 and an electrostatically focused and deflected reading section 14. The tube consists of an evacuated envelope 16. The image section 10 includes an input window 18 which may be of fiber optics having a photocathode 20 provided on the inner surface of the faceplate 18. The photocathode 20 may be ofiany suitable material responsive to input radiations directed through the transmissive faceplate 18. The photocathode 20generates photoelectrons from the illuminated areas of the image in direct proportion to the amount of incident radiation passing through the faceplate 18.

The photoelectrons generated by the photocathode 20 are accelerated toward the target assembly 12 where they are brought to focus by a suitable electrostatic lens formed between the photocathode surface 20 and an anode electrode 22. The electron image from the photocathode 20 is transferred to the target assembly 12 in a reduced size.

The target assembly 12 includes a target member 30. The target 30 is comprised of a supporting membrane or layer 32 of aluminum oxide which is supported on a Kovar ring 34. The

layer 32 has a thickness of about 500 Angstrom units. A conductive layer 36 of about 500 Angstrom units of aluminum forms the signal electrode of the target and is provided on the surface of the support layer 32 facing the reading section 14. A highly porous layer 38 of a suitable material exhibiting the property of secondary electron conduction such as potassium chloride is provided on the aluminum layer 36 and faces the reading section 14. The layer 38 is deposited to provide a density of less than 10 percent of the normal bulk density of potassium chloride and to a thickness of about 20 micron. An electrical lead-in 40 is provided from the exterior of the envelope to the signal electrode 36. I

An electron gun 42 is provided for generating an electron beam for scanning the raster over the target member 30. A positive potential of about 20 volts is applied by means of the lead-in 40 to the signal plate 36. The exposed surface of the porous layer 38 is stabilized to a potential of approximately ground by means of the low velocity scanning beam generated by the electron gun 42. In this manner, an electric field is established across the layer 38.

Positioned between the target 30 and the electron gun 42 is a suppressor mesh 46 which is of an electrical conductive material. The mesh electrode 46 shown in FIG. 2 consists of a first set of conductive members 50 which are positioned at an angle of 50 from the linear scan line 52 of the electron beam generated by the electron gun 42. A second set of conductive members 54 are positioned at an angle of l30 with respect to the linear scan line 52 and are secured to the first set of conductive members 50 to form a unitary control grid. The members 50 and 52 form nonrectangular parallelogram interstices 56 which includes two angles of and two angles of l00. The conductive elements 50 may be of a wire having a diameter of about 0.0005 inch and spaced apart by a distance of about 0.001 inch. The conductive members 54 may also be of a similar diameter and spaced of the same distance. The distance between the scanning lines 52 of the electron beam may be about 0.001 inch.

The mesh 46 is positioned at a distance of about 0.0l inch from the layer 38. The suppressor grid 46 is also provided with a lead-in 51 to the exterior of the envelope and is connected to a suitable potential of about 15 volts. The photoelectrons from the photocathode 20 penetrate the aluminum oxide layer 32 and the aluminum layer 36 and dissipate most of their energy within the layer 38 thereby generating secondary electrons. Under the influence of the internal electric field, the secondary electrons migrate through the voids of the porous structure of the layer 38 to the signal plate 36. The conduction takes place in the vacuum formed by the voids in the layer 38 and not in the solid-state conduction band of the layer 38. In this manner the undesirable persistence efiect found in camera tubes caused by trapping and subsequent release of charge carriers in solid materials is avoided. The movement of the electrons within the layer 38 creates a positive charge pattern on the exposed surface of the layer 38 corresponding to the input image. The charge pattern thus established on the layer 38 is periodically read out by the electron gun 42 which returns the exposed surface of the layer 38 to gun cathode potential by depositing electrons on the positively charged areas. This current pulse, constituting the video signal, is capacitively coupled to the signal plate 36. The current flowing in the signal plate 36 is used to develop a voltage across a load resistance connected to lead-in 40 which after amplification can be utilized to produce a video picture on a television monitor in the usual manner.

The alignment and deflection of the electron beam generated by the electron gun 42 is accomplished by either electrostatic or electromagnetic means. In the specific embodiment shown deflection plates 60 are provided for deflecting the beam in a vertical direction and plates 62 are provided for deflecting the beam in a horizontal direction. The voltage for the deflection may be provided by suitable voltage sources well known in the art. It is found that with a mesh electrode of the type described herein that the moire spacing reduction of up to 30 percent may be achieved by the mesh shown and described herein. This desirable effect is found regardless of the mesh opening size. For example, it is found with the mesh electrode described herein in which the mesh spacing, in units of scan lines separation is unity that the moire spacing is 1.0. In the prior art type of device in which rectangular openings were provided and in which the conductive members were positioned at 30 and 120 with respect to the scan, the moire spacing was l.3.

FIG. 3 illustrates a modified grid electrode 46 in which a first set of conductive members 70 is positioned at an angle of 70 to the scan line 52. A second set of conductive members 72 is positioned at an angle of 1 l to the scan line 1 The

members

70 and 72 form nonrectangular parallelograms interstices 76 having two angles of 40 and two angles of 140. The grid 46 may have its

conductive members

50 and 54 or 70 and 72 vary between the limits illustrated in FIGS. 2 and 3.

The conductive mesh electrode 46 may be formed in several ways. One particular method is to electroform by plating copper on a ruled glass master in which the rulings have been filled with sputtered palladium. [t is also possible to take a rectangular type configuration and stretch the structure so as to provide a substantially diamond-shaped interstices.

Since numerous changes, such as positioning the electrode 46 on the opposite side of the target 30 with respect to the electron gun 42, may be made in the above-described apparatus and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

lclaim:

1. An electronic tube comprising an evacuated envelope and having therein a target member, an electron gun for generating an electron beam and deflection means for scanning said electron beam over said target along a plurality of substantially spaced parallel lines, a grid electrode positioned adjacent said target, said grid comprised of a first set of parallel equally spaced members positioned at an angle different from with respect to a second set of parallel equally spaced members and forming diamond-shaped interstices.

2. The device set forth in claim 1 in which said interstices are nonrectangular parallelograms.

3. The device set forth in claim 2 in which two opposite equal angles of the parallelogram range from 40 80.

4. The device set forth in claim 1, in which said first set of parallel equally spaced members are positioned at an angle of from 50 to 70 with respect to the scanning lines of said electron beam and said second set of spaced members are posi tioned at an angle of from to with respect to the scanning line of said electron beam.

5. The device set forth in claim 1 in which said grid electrode is positioned between said target member and said electron gun.

Claims

1. An electronic tube comprising an evacuated envelope and having therein a target member, an electron gun for generating an electron beam and deflection means for scanning said electron beam over said target along a plurality of substantially spaced parallel lines, a grid electrode positioned adjacent said target, said grid comprised of a first set of parallel equally spaced members positioned at an angle different from 90* with respect to a second set of parallel equally spaced members and forming diamond-shaped interstices.

3. The device set forth in claim 2 in which two opposite equal angles of the parallelogram range from 40* 80*.

4. The device set forth in claim 1, in which said first set of parallel equally spaced members are positioned at an angle of from 50* to 70* with respect to the scanning lines of said electron beam and said second set of spaced members are positioned at an angle of from 110* to 130* with respect to the scanning line of said electron beam.