US2714688A - Image-reproducing device - Google Patents

Description

Aug. 2, 1955 w. o. REED 2,714,688

IMAGE-REPRODUCING DEVICE Filed 061;. 51, 1952 2 Sheets-Sheet 1 F I G. 1

Phosphor- Cooted Mesh-screens Scanning System Video Amp.

Receiving Circuits Color Control Circuits I I I I I I I I Beam 8 WILLIAM O. REED INVENTOR.

HIS ATTORNEY Aug. 2, 1955 Filed Oct. 31, 1952 2 Sheets-Sheet 2 Phosphor-coated Mesh Screens Auxiliary Focus Electrode 48 Deflection Yoke 23 43 4| 44 45 P r M/\ '//I 'M/,i1 3 40 J'\ KIA V l 42 Video Signal F 5 G Color-Control Hollow Signal Cylindrical 48 Electron Beam c. c/f/ WILLIAM O. REED INVENTOR.

HIS ATTORNEY 2,714,688 Fatented Aug. 2, 1955 2,714,688 IMAGE-REPRODUCING nnvrcn William 0. Reed, Chicago, IlL, assignor to The Rauland Corporation, a corporation of Illinois Application October 31, 1952, Serial No. 317,867 6 Claims. (Cl. 31513) type of color reproducing tube employs a target area coat- L ed with interspersed groups of different phosphor materials luminescing in each of three primary colors, with a parallax mask preceding the target and a plurality of electron guns for directing respective beams at the several groups of target areas corresponding to each of the primary colors. Another known tube is generally similar except that a single electron beam is subjected to a cyclic radial deflection field to vary the approach angle of the beam to the parallax mask for providing color switching. In place of the parallax mask followed by a planar target, it has also been proposed to provide a target consisting of a myriad of elemental pyramids each bearing diiferent phosphor coatings on their respective surfaces. some tubes, the parallax mask is replaced by a fine grid or mesh supplied with deflection-control voltages to obtain color switching. Still other known devices comprise multilayer phosphor screens or successive mesh targets coated with different phosphors; such devices obtain color switching by velocity modulation of the electron beam or by selective energization of the phosphor-coated target meshes.

Each of the known image-reproducing devices for color television use has certain characteristic advantages and disadvantages. Some are inherently restricted to field sequential systems while others are best suited for use in dot sequential or simultaneous color television receivers. Nearly all known color tubes are mechanically complex and difiicult to assemble on a mass production basis. Some known tubes are particularly susceptible to scanning nonlinearities and some require the generation and application of high-frequency sampling signals to cut off one or more electron beams during color-switching intervals.

It is a primary object of the present invention to provide a novel image-reproducing device for use in a color television receiver.

It is a further object of the invention to provide a novel cathode-ray tube for the reproduction of images in color which avoids one or more of the disadvantages inherent in known color tubes.

It is a more specific object of the invention to provide a new color tube of the cathode-ray type which is relatively simple in construction yet adaptable to use in systems employing any type of color signal, whether field sequential, line sequential, or dot sequential.

Yet another object of the invention is to provide a novel color picture tube in which color-switching is achieved by merely varying the potential of a single electrode element.

In accordance with the present invention, a novel image-reproducing device for use in a color television system comprises an evacuated envelope having a predetermined longitudinal axis. A plurality of target areas are disposed in longitudinally spaced parallel planes transversely disposed with respect to the envelope axis, and the target areas are respectively coated with luminescent phosphors exhibiting dilferent color radiation characteristics in response to electron bombardment. Means are provided for producing a plurality of electron beams each initially transversely spaced from the tube axis; preferably, an infinite number of such beams are provided by producing a hollow cylindrical electron beam concentric with the tube axis. Focusing means are provided intermediate the electron-beam-producing means and the target areas for impressing a common focusing field on all of the electron beams to converge the beams at a common point and for varying the focal length of the focusing filed in response to an applied color control signal to shift the point of convergence of the beams in a longitudinal direction between the respective planes of the target areas. The device further comprises means for synchronously controlling the intensity of all of the beams in response to a single applied video signal.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood, however, by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals indicate like elements, and in which:

Figure l is a schematic cross-sectional view of an image-reproducing device constructed in accordance with the invention, together with a schematic diagram of apparatus for operating the device of the invention;

Figure 2 is a schematic diagram illustrating the operation of the device shown in Figure 1;

Figure 3 is a graphical representation of the waveform of a suitable color-control signal for application to the device shown in Figure 1;

Figure 4 is a fragmentary cross-sectional view, partly schematic, of an alternative embodiment of the invention, and

Figure 5 is a schematic view, similar to that of Figure 2, illustrating the operation of the device of Figure 4.

As shown in Figure 1, an image-reproducing device for use in a color television system comprises an evacuated envelope 10 having a predetermined longitudinal axis 11. in accordance with the invention, the device comprises a plurality of electron guns 12, of which only two are shown for simplicity, and a plurality of conductive mesh target electrodes 13, 14 and 15. The inner wall of the envelope is also provided with a conductive coating 16, of colloidal graphite or the like, which serves as a final anode. A focusing electrode 17 between electron guns 12 and final anode 16, which may convenientry be in the form of a second conductive wall coating spaced from final anode 16, is also provided. of the electron guns is transversely spaced from longitudinal axis 11 in symmetrical fashion so that electron guns 12 serve to produce a plurality of electron beams initially transversely spaced from the longitudinal axis. Preferably, the electron guns are arranged to project respective beams in a direction parallel to longitudinal guns may be of entirely conventional construction, and corresponding electrodes of each of the guns are preferably interconnected internally of the envelope to permit parallel electrical operation.

Target electrodes 13, 14 and 15, which may be constructed as conductive mesh screens or electron-pervious metallic films, are disposed in longitudinally spaced parallel planes transversely of axis 11, and each of the target electrodes is coated with an appropriate luminescent phosphor having a color radiation response to electron bombardment in one of three primary colors, for example red, blue or green. Although target electrodes 13 are illustrated as of a fiat or planar construction, they may be formed as spherical or cylindrical segments disposed in longitudinally spaced parallel curved planes. An additional electrode (not shown), in the form of a conductive ring or a transparent conductive coating for the face plate portion of the envelope, may be provided if desired for the purpose of collecting electrons which penetrate all three of the phosphor-coated target electrodes.

For the purpose of facilitating an understanding of the manner in which the image-reproducing device of the present invention operates, the receiver circuits are also schematically illustrated in Figure l. Incoming composite television signals are intercepted by a suitable antenna 20 and impressed on conventional receiving circuits 21 which may comprise a radio-frequency amplifier, an oscillator-converter, an intermediate-frequency amplifier, a video detector, and scanning-synchronizing signal and color-synchronizing signal separator circuits. The scanning-synchronization components from receiving circuits 21 are applied to a conventional scanning system 22 which supplies a deflection yoke 23 encompassing the neck of envelope with suitable scanning currents. The detected video components are amplified by video amplifier 24 and applied in parallel to the control electrodes of electron guns 12. The color-synchronizing components from receiving circuits 21 are impressed on suitable color-control circuits 25 which develop a colorcontrol or color-switching signal for application to focusing electrode 17. Final anode 16 and target electrodes 13, 14 and may be connected together and to a movable tap 26 on a potentiometer resistor 27 connected across a suitable source of positive unidirectional operating potential, and focusing electrode 17 may be returned to another movable tap 28 on potentiometer 27 through a dropping resistor 29 which also serves as a coupling resistor between color-control circuits and focusing electrode 17.

in operation, the electron beams originating at electron guns 12 are subjected to a common focusing field established between focusing electrode 17 and final anode 16. The focal length of the electron lens thus formed is determined by the potential difference between electrodes 17 and 16. Consequently, this focal length may be varied by merely varying the potential of electrode 17 while maintaining that of final anode 16 constant. If these variations are controlled in synchronism with the color-synchronizing components of the received composite television signal, and if the color-control signal is of appropriate amplitude, the focal length of the focusing field established between electrodes 17 and 16 may be varied to shift the point of convergence of the electron beams between the planes of target electrodes 13, 14 and 15.

This operation may perhaps more readily be tinderstood from a consideration of the schematic showing of Figure 2, in which the electron beams are designated beam A and beam B respectively. These beams are initially projected in a direction parallel to longitudinal axis 11, but upon encountering the focusing field between electrodes 17 and 16, the beams are caused to converge at a rate determined by the strength of the focusing field. Thus, for a condition in which the potential difference between electrodes 17 and 16 is a minimum, beams A and B may converge at a point in the plane of the most distant target electrode 15, as indicated by the dashed lines 39. If the potential difference between electrodes 17 and 16 is increased by a predetermined amount, the focal length of the electron lens is decreased, and beams A and B converge in the plane of the closest target electrode 13, as indicated by dotted lines 31. At an intermediate potential difference between electrodes A. 17 and 16, the focal length assumes an intermediate value, and the beams may be caused to converge in the plane of the intermediate target electrode 14.

Although each electron beam penetrates all three of the mesh target electrodes, the current density at the point of convergence of the several beams is higher than that of any single beam by a factor corresponding to the number of beams employed. Thus, at any instant of time, the primary luminescent response occurs at the point of convergence of the beams. The secondary or fringing luminescent responses causes by the penetration of elemental areas of the several target electrodes by individual beams are much less brilliant and may in fact be desirable for the purpose of color blending, producing a picture which is extremely pleasant to view.

In reproducing a received color television image, the several beams are caused to scan the target electrodes in bidirectional pattern; since the beams are all subjected to a common focusing field, the superposition of the required scanning fields has no effect upon the convergence plane. If the received signal is of the field-sequential type, with successive fields representing picture information corresponding to the respective primary colors, the potential of focusing electrode 17 may be varied in the manner indicated graphically in Figure 3, while the potential of final anode 16 is maintained constant. The color-control potential is in the form of a stepped rectangular wave, with the duration of each step corresponding to the scanning intervals for each of the respective color fields. In this manner, color-switching in synchronism with the received color field is obtained.

Although the fringe responses may actually produce a salutary effect in providing color blending, it is possible to reduce the magnitude of the fringe responses to such an extent as to render them substantially unnoticeable. This result may be accomplished by applying color-control voltages to the phosphor-coated target electrodes in synchronism with the color-switching signal applied to focusing electrode 17, in such a manner as to render the potentials of those target electrodes from which no response is desired materially lower than that of the target electrode from which the primary response is elicited. Gating of the phosphor-coated target areas in this manner, as a means of color switching in a sequential-type color tube, is well known in the art, as exemplified by Patent 2,46l,515-Bronwell. However, it is to be clearly understood that the application of gating voltages to the color targets is but an optional adjunct of the present invention, and no claim is made to this manner of color switching.

In the embodiment of Figure 1, a plurality of separate electron guns symmetrically positioned with respect to the longitudinal axis of the tube and each transversely spaced therefrom are employed to project a plurality of electron beams through a common focusing field whose focal length is varied to provide color switching between target areas disposed in longitudinally spaced parallel planes. As previously pointed out, the maximum contrast range of the reproduced image is limited in such a device to the ratio between the total area of the individual electron beams to the cross-sectional area of the image point at the plane of convergence. From this consideration, it is apparent that the most desirable construction would be one employing the largest practicable number of electron beams; however space limitations preclude the use of more than four electron guns in a single neck of an envelope of practical size. It is possible, however, to achieve a construction which effectively provides an infinite number of electron beams symmetrically disposed with respect to the longitudinal tube axis.

Such a construction is illustrated in Figure 4, in which a single electron gun is especially constructed in such a manner as to project a hollow cylindrical electron beam concentrically along the tube axis. In Figure 4, a cathode 40 is provided with an annular electron-emissive area 41, having a central nonemissive region 42. The intensity-control grid 43 is provided with an annular aperture 44 in registration with the annular emissive surface 41 of cathode in practice, it is necessary to provide some support for the central portion of grid 43 within the annular aperture, and this may be accomplished by the use of small connecting wires extending radially across the annular grid aperture. Following control grid 43 is a tubular anode 45 provided with a diaphragm 46 having a limiting aperture 57 of annular configuration corresponding to the annular aperture 44 of control grid 43. The tube is otherwise similar to the embodiment of Figure 1 except that the final target area 15 is formed as a phosphor-coated transparent plate 48, and an auxiliary focusing electrode, in the form of an electronpervious conductive mesh grid 49 in close proximity with the target electrodes, is also provided. Final target plate 43 may be provided with a transparent conductive coating (not shown) to permit all portions to be maintained at a common operating potential.

The operation of the device of Figure 4 is readily apparent from a consideration of the schematic view of Figure 5, in which a hollow cylindrical electron beam 50 is projected through a focusing field toward the target electrode assembly. The auxiliary focusing electrode 49 is designated F, while the other two mesh electrodes 13 and 14 and the final target electrode 48 are designated R, B and G respectively, signifying the primary response colors red, blue and green.

When the potential difference between focusing electrode 17 and final anode 16 is a minimum, the focal length of the focusing field is a maximum, and the cylindrical beam converges to a single image point in the plane of the final target electrode 48, to provide a primary green response. Conversely, when the potential difference between focusing electrode 17 and the final anode is a maximum, the cylindrical beam is focused to converge in the plane of the first target electrode 13, providing a primary red response. At an intermediate potential difference, the beam is focused to converge in the plane of target electrode 14- to provide a primary blue response. As in the case of the embodiment of Figure 1, gating voltages may be applied to the target electrodes 13, 14 and 48, in synchronism with the color-control signal applied to focusing electrode 49, to minimize the spurious or fringing responses caused by penetration or impingement of the unconverged or overconverged beam.

The construction of Figure 4 affords two distinct advantages in comparison to that of Figure 1. In the first place, the ratio between the total cross-sectional area of the electron beam as it enters the focusing field and the area of the image point to which the beam is converged is much greater than in the case of the construction employing physically separate electron guns; this permits the reproduction of color images with a considerably increased contrast range. In the second place, since focusing electrode 49 is disposed in close proximity to the target electrodes, and in a plane parallel to the target electrode planes, the depth of the focusing field is reduced to provide improved color fidelity, and the undesirable effect of distortion in the scanning waveforms are minimized. The provision of auxiliary focusing electrode 49, which may be operated at a constant potential different from those of the target electrodes but is preferably modulated in synchronism with focusing electrode 17 as by direct connection thereto, results in enhanced focusing of the individual rays constituting the cylindrical electron beam without substantially affecting the color-switching action effected by varying the focusing field between electrodes 17 and 16.

Thus the invention provides a novel image-reproducing device for use in color television systems. The device has the advantages of relative mechanical simplicity as compared with previously known color tubes, without being restricted to use in systems of any one particular type of color signal transmission. Color switching is obtained by merely varying the intensity of a focusing field, which is accomplished in turn by simple modulation of the voltage of a focusing electrode.

While particular embodiments of the present invention have been shown and described, it is apparent that various changes and modifications may be made, and it is therefore contemplated in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. An image-reproducing device for use in a color television system comprising: an evacuated envelope having a predetermined longitudinal axis; means for producing a plurality of electron beams each initially transversely spaced from said axis; a plurality of target areas disposed in longitudinally spaced parallel planes transversely disposed with respect to said axis and respectively coated with luminescent phosphors exhibiting different color radiation characteristics in response to electron bombardment; focusing means intermediate said electron-beamproducing means and said target areas for impressing a common focusing field on all of said electron beams to converge said beams at a common point and responsive to an applied color-control signal for varying the focal length of said focusing field and longitudinally shifting said point of convergence of said beams between the respective planes of said target areas; and means for synchronously controlling the intensity of said beams in response to a single applied video signal.

2. An image-reproducing device for use in a color television system comprising: an evacuated envelope having a predetermined longitudinal axis; means for producing a plurality of electron beams each initially transversely spaced from said axis; a plurality of target areas disposed in longitudinally spaced parallel planes transversely disposed with respect to said axis and respectively coated with luminescent phosphors exhibiting different color radiation characteristics in response to electron bombardment, at least all but the least distant of said target areas from said electron-beam-producing means being light-pervious and at least all but the most distant of said target areas from said electron-beam-producing means being electron-pervious; focusing means intermediate said electron-beam-producing means and said target areas for impressing a common focusing field on all of said electron beams to converge said beams at a common point and responsive to an applied color-control signal for varying the focal length of said focusing field and longitudinally shifting said point of convergence of said beams between the respective planes of said target areas; and means for synchronously controlling the intensity of said beams in response to a single applied video signal.

3. An image-reproducing device for use in a color television system comprising: an evacuated envelope having a predetermined longitudinal axis; means for producing a plurality of electron beams each initially transversely spaced from said axis; a plurality of target electrodes disposed in longitudinally spaced parallel planes transversely disposed with respect to said axis and respectively coated with luminescent phosphors exhibiting different color radiation characteristics in response to electron bombardment, at least all but the least distant of said target electrodes from said electron-beam-producing means being light-pervious and at least all but the most distant of said target electrodes from said electron-beam-producing means being electron-pervious; means including a focusing electrode intermediate said electron-beam-producing means and said target electrodes for impressing a common focusing field on all of said electron beams to converge said beams at a common point and responsive to an applied color-control signal for varying the focal length of said focusing field and longitudinally shifting said point of convergence of said beams between put the respective planes of said target electrodes; and means for synchronously controlling the intensity of said beams in response to a single applied video signal.

4. An image-reproducing device for use in a color television system comprising: an evacuated envelope having a predetermined longitudinal axis; means for producing a plurality of electron beams each initially transversely spaced from said axis; a plurality of target electrodes disposed in longitudinally spaced parallel planes transversely disposed with respect to said axis and respectively coated with luminescent phosphors exhibiting different color radiation characteristics in response to electron bombardment, at least all but the least distant of said target electrodes from said electron-beam-producing means being light-pervious and at least all but the most distant of said target electrodes from said electron-beam-producing means being electron-pervious; means for impressing a common focusing field on all of said electron beams to converge said beams at a common point and responsive to an applied color-control signal for varying the focal length of said focusing field and longitudinally shifting said point of convergence of said beams between the respective planes of said target electrodes; an auxiliary conductive mesh focusing electrode disposed in a plane intermediate said last mentioned means and said target electrodes and parallel to said target electrode planes; and means for synchronously controlling the intensity of said beams in response to a single applied video signal.

5. An image-reproducing device for use in a color television system comprising: an evacuated envelope having a predetermined longitudinal axis; means for producing a plurality of electron beams each initially transversely spaced from said axis; a plurality of conductive mesh target electrodes disposed in longitudinally spaced parallel planes transversely disposed with respect to said axis and respectively coated with luminescent phosphors exhibiting different color radiation characteristics in response to electron bombardment; focusing means intermediate said electron beam producing means and said target electrodes for impressing a common focusing field on all of said electron beams to converge said beams at a common point and responsive to an applied color-control signal for varying the focal length of said focusing field and longitudinally shifting said point of convergence of said beams between the respective planes of said target electrodes; and means for synchronously controlling the intensity of said beams in response to a single applied video signal.

6. An image-reproducing device for use in a color television system comprising: an evacuated envelope having a predetermined longitudinal axis; an electron gun including a cathode having an annular electron emissive surface for proiecting a hollow cylindrical electron beam along said axis; a plurality of target areas disposed in longitudinally spaced parallel planes transversely disposed with respect to said axis and respectively coated with luminescent phosphors exhibiting difierent color radiation characteristics in response to electron bombardment; focusing means intermediate said electron-beam-producing means and said target areas for impressing a common focusing field on all portions of said hollow cylindrical electron beam to converge said beam at a common point and responsive to an applied color-control signal for varying the focal length of said focusing field and longitudinally shifting said point of convergence of said beam between the respective planes of said target areas; and a control electrode included in said electron gun and including an annular aperture similar to said electron emissive surface for controlling the intensity of said beam in response to an applied video signal.

References Cited in the file of this patent UNITED STATES PATENTS 2,442,961 Ramberg June 8, 1948 2,461,515 Bronwell Feb. 15, 1949 2,580,073 Burton Dec. 25, 1951 2,619,603 Rajchman Nov. 25, 1952

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