US3028521A

US3028521A - Image-reproducting device

Info

Publication number: US3028521A
Application number: US629825A
Authority: US
Inventors: Constantin S Szegho
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1956-12-21
Filing date: 1956-12-21
Publication date: 1962-04-03
Anticipated expiration: 1979-04-03
Also published as: GB862957A

Description

April 3, 1962 c. s. SZEGHO IMAGE-:REPRODUCING DEVICE 2 Sheets-Sheet 1 Filed Dec. 21. 1956 m e w n. r j m w a U W W & J g n 4% E m 0 mm m C Nw Nw W m Sm April 3, 1962 C. S. SZEGHO IMAGE-REPRODUCING DEVICE Filed' Dec. 21.- 1956 2 Sheets-Sheet 2 G 2 fiorzzqg United States Patent 3,028,521 IMAGE-REPRODUCING DEVICE Constantin S. Szegho, Chicago, Ill., assignor to Zenith Radio Corporation, a corporation of Delaware Filed Dec. 21, 1956, Ser. No. 629,825 6 Claims. (Cl. 315-13) This invention relates generally to color television image-reproducers and more particularly to a new and improved image-reproducer adaptable for post-deflectionacceleration operation.

It is well known to those skilled in the art of color television design that the brightness of present-day tricolor straight parallaxmask type image-reproducers is not quite adequate because an excessive proportion of the total electron beam current is intercepted by the masking or color-selection electrode. It has been suggested early in the development of such image-reproducers to enlarge the apertures of the color-selection electrode and to employ post-deflection-focusing by means of an accelerating field located between the colorselection electrode and the aluminized fluorescent screen. The apertures in the color-selection electrode, followed by the accelerating field, form an array of tiny electron lenses which reduce the cross-sectional area of each bundle of beam electrons emerging from each aperture of the higher transmission color-selection electrode into an area which is equal to or less than that of an individual sub-elemental color phosphor area at the screen.

In the fabrication of such post-deflection-acceleration image-reproducers, a plurality of groups of sub-elemental area color phosphor elements, which are preferably of equal size, are uniformly distributed in a predetermined pattern over the screen area by conventional photographic techniques utilizing straight optical projection from points corresponding to the respective electronic color-centers lying in the plane-of-deflection of the electron-beam components. The fluorescent pattern of each group of subelemental phosphor areas is a slightly enlarged image of the color-selection electrode used as the photographic master, with each group of sub-elemental areas possessing a different color-radiation response characteristic when bombarded by electrons.

In operation of such image-reproducers, in which an accelerating field is established between the color-selection electrode and the screen, the electron-beam components, arriving from their respective electronic colorcenters, are deflected by the accelerating field toward the normal to the screen and thus produce erection errors. For a given deflection angle, straight lines projected from the points of impingement of each beam component on the screen and back through the aperture of the color-selection electrode intersect the respective reference paths at points closer to the source of the electronbeam components and thus define new centers of optical projection. However, for different deflection angles, the landing point of each electron-beam component on the screen deviates from the projected point, with the deviation increasing rapidly with deflection angle. At very large deflection angles, the beams no longer impinge on phosphor elements of the proper color.

Another undesirable feature of po st-deflection-focusing, with a single accelerating field, is that the secondary electrons, which are released by electron bombardment of the color-selection electrode, start out at relatively low velocity from the vicinity of an aperture and do not follow the trajectory of the primary beam but, instead, are drawn to the screen at right angles thus giving rise to undesirable color desaturation or dilution.

The present application is a continuation-in-part of and is derived from copending application 510,186, filed May 3,028,521 Patented Apr. 3, 1962 23, 1955, by Mark E. Amdursky et all, for Method and Apparatus for Color Television, and assigned to the present assignee, now Patent 2,864,032, issued December 9, 1958, there is described and claimed apparatus and method for compensating erection effects, including associated errors, by providing a divergent electric field on the cathode side of the color-selection electrode to alter the trajectories of the electron-beam components so that they land on the same phosphor element as in the straight parallax image-reproducer. As described therein, satisfactory compensation for erection errors is obtained by operating the image-reproducer with the screen at a potential very much higher than that of the final anode and the color-selection electrode at a poten tial lower than that of the final anode. However, in order to realize full compensation, the apparatus preferably includes an auxiliary mesh electrode, which is operated at final anode potential, followed by the color-selection electrode which is operated at a lower potential and, in turn, is followed by the fluorescent target operated at a potential much higher than that of the final anode. Thus, in both instances, the electron-beam components are first subjected to a de-erection correction of an amount which varies as a function of the angle of deflection throughout substantially the entire area of the luminescent screen to compensate for the erection occurring between the color-selection electrode and screen.

However, when an auxiliary mesh electrode is utilized to improve the electron optics of focus-mask tubes, additional problems involving moir patterns, beam interception, and mechanical mounting arise, in addition to the practical difliculty encountered. in fabricating such an auxiliary mesh with large enough electron transmission characteristic but still firm enough to withstand handling and heating. In spherical-screen image-reproducers, satisfactory though incomplete erection compensation is obtainable with the screen, mesh and final anode operated at a common potential higher than that of the color-selection electrode; however, the erection compensation provided by two-potential operation of image reproducers with planar or cylindrical screens leaves much to be desired.

Therefore, it is an important object of this invention to provide a new and improved color-television imagereproducer which compensates for erection effects occurring during post-deflection-acceleration operation with out the necessity of an auxiliary mesh electrode.

It is another object of this invention to provide such a new and improved color-television image-reproducer which provides substantially complete erection compensation without requiring the application of more than one positive operating potential in addition to those normally employed in the operation of ordinary shadow-mask color-image reproducers.

A further object of the invention is to provide a new and improved color-image reproducer of the post-deflection-acceleration type in which substantially complete erection compensation may be achieved with the application of but a single positive operating potential in addition to those normally employed in the operation of ordinary shadow-mask reproducers, whether the screen is of planar, spherical or cylindrical configuration.

It is an additional object of this invention to provide a new and improved post-deflection-acceleration type colortelevision image-reproducer in which such compensation for erection effects is accompanied by a substantial improvement in color definition.

It is a specific object of this invention to provide a new and improved color-television image-reproducer which establishes an effective electronic center-of-deflection which is closely adjacent to or coincides with the position of a light source employed in manufacturing the luminescent screen of the image-reproducer.

It is a corollary object of this invention to provide a new and improved color television image reproducer which may be constructed by the most economical and expeditious techniques available.

A color television image-reproducer constructed in accordance with the invention comprises electron gun means for effectively projecting a plurality of electronbeam components through a deflection space along a corresponding plurality of reference paths. A multicolor mosaic luminescent target is disposed transversely of the reference paths in spaced relation to the electron gun means. A color-selection electrode is disposed transversely of the reference paths intermediate the target and the electron gun means. Means are employed for maintaining the color-selection electrode at a first predetermined potential positive wtih respect to the cathode and for maintaining the luminescent target at a second predetermined potential positive with respect to the cathode and higher than the first potential, whereby, during passage from the color-selection electrode to the target, electrons in the beams are accelerated and subjected to erection of an amount corresponding to a predetermined function of the distance between the point of intersection of the reference path with the plane of the color-selection electrode and central axis of the color-selection electrode. A velocity-determining electrode is provided and encompasses substantially all of the portions of the reference paths intermediate the color-selection electrode and the deflection space. Means are provided for maintaining the velocity-determining electrode at a potential positive with respect to the cathode and higher than the first potential, preferably at a potential equal to that of the luminescent target. Finally, means, including an auxiliary electrode, electrically connected to and circumferentially encompassing substantially the entire periphery of the color-selection electrode and extending toward the velocity-determining electrode, are provided for subjecting the electrons in the beams to de-erection of an amount substantially corresponding to the aforementioned predetermined function throughout substantially the entire area of the luminescent target to compensate for erection occurring between the color-selection electrode and target.

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

FIGURE 1 is a cross-sectional view, partly schematic, of one embodiment of a color television image-reproducer constructed in accordance with the invention, together with a block diagram of illustrative associated receiver circuitry;

FIGURE 2 is a cross-sectional and schematic view of a portion of the target structure of a conventional parallax mask color image-reproducer and is employed to illustrate certain operating characteristics of the device;

FIGURE 3 is a schematic view, partly in section, depicting the eifects of post-deflection-acceleration operation; and

FIGURE 4 is a cross-sectional view, partly schematic, illustrating the operational characteristics of an imagereproducer utilizing an auxiliary electrode in accordance with the invention.

The embodiment of the invention illustrated in FIG- URE 1 comprises an image reproducer including an envelope having a neck section 11 and an enlarged bulb or cone section 12. An electron gun assembly comprising three electron guns 13, 14 and 15 is mounted within neck section 11; the individual electron guns may be conventional in construction and each may include a cathode 16, a first control electrode 17, a second control electrode 18, and a focusing electrode or first anode 19. The three electron guns may be mounted in either collinear or delta alignment with respect to each other in the usual manner and may further include a common convergence electrode 20. Insofar as the present invention is concerned, the particular structure employed for the individual electron guns is not significant and any of the many known types of gun structures available in the art may be employed. The expression electron beam component is employed in this specification to designate the electronic energy which excites an individual group of phosphor areas; thus there are three electron-beam components in a tricolor image reproducer, whether produced by a single or a plurality of electron guns. This energy may be continuous or pulsating as desired without departing from the scope of the invention.

Image reproducer 10 further includes a mosaic multicolor luminescent target 21 disposed in spaced relationship to the electron gun means 13, 14 and 15 and preferably mounted closely adjacent to the face-plate of the image reproducer. In the illustrated embodiment, target 21 is preferably formed of a plurality of sub-elemental color dot target areas directly deposited on the inner surface of the face-plate; target 21 may also comprise a series of phosphor strips of sub-elemental width if so desired. If tri-color reproduction is desired, the dots may comprise phosphors which emit light corresponding to the conventional additive primary colors, red, blue and green and may be arranged in regularly repeating triad patterns as indicated by the target area designations r, b, and g, respectively. Although a spherical construction is shown for target 21, it should be understood that the target may be formed on a planar or cylindrical surface if desired. Luminescent target 21 is provided with a thin conductive backing layer 22 of aluminum or the like which may be deposited upon the phosphors of the target in conventional fashion. The term multi-color luminescent target, as employed throughout this specification and in the appended claims, refers to any luminescent target comprising discrete areas which respond to electron bombardment by emitting light of distinctively different colors and in which the phosphor areas of different colors are arranged in a regularly repeating pattern. For example, phosphor strips r, b and g may be made to extend in the vertical direction instead of the horizontal direction indicated in the drawing, or sub-elemental dot-type target areas of circular, hexagonal or other configuration may be employed; these alternative types of target construction are all well known in the art. Furthermore, it is not necessary that phosphors which emit light of a particular color be employed; for example, a uniform coating of a white phosphor may be utilized in conjunction with a multi-color filter interposed between the phosphor and the viewing surface or face-plate of the picture tube without departing in any way from the teaching of the invention.

A color-selection electrode comprising a parallax mask 23 is mounted within envelope 10 closely adjacent to target 21 and preferably in parallel relationship thereto. Electrode 23 includes a multiplicity of apertures 24 arranged in a pattern which corresponds to the distribution pattern of each individual phosphor on screen 21, so that mask 23 and target 21 constitute a direction-sensitive composite target structure 25 which effectively provides for color selection determined by the angle of incidence of an electron-beam component. Image reproducer 10 also includes a velocity-determining electrode which is most conveniently in the form of a conductive coating 26 applied to the internal surface of envelope 12 and extending from a point closely adjacent color-selection electrode 23 back into neck section 11 to a point closely adjacent the final electrode 20 of the electron gun assembly. Coating 26 may, for example, comprise a conventional colloidal graphite coating; alternatively, a metallic coating or a separate conductive member may be employed.

Conductive coating 26 is electrically connected to a first source of positive unidirectional operating potential B whereas parallax mask 23 and luminescent target 21 are individually connected to two additional sources of positive operating potential B and B respectively. Cathodes 16 are connected to a plane of reference potential, here indicated as ground. Control electrodes 17 are normally negatively biased with respect to cathodes 16; control electrodes 18 are maintained at a positive potential with respect to the cathodes. Focus electrodes 19 may be electrically connected to each other and to a source of positive potential B whereas the common convergence electrode 20 is connected to an additional operating potential source 13 Control electrodes 18 are respectively connected to variable taps on a potentiometer represented by a resistor 27 which may be connected in circuit with a source of operating potential, here represented by a battery 28.

A conventional electromagnetic deflection yoke 29 may be employed in conjunction with image reproducer and is preferably mounted at the junction of cone section 12 and neck section 11 of the envelope; the deflection system location establishes the plane-of-deflection which defines one boundary of the deflection space of the tube. An electrostatic deflection system may be employed instead of the electromagnetic deflection apparatus if desired, in which case suitable deflection plates may be mounted within the envelope.

FIGURE 1 also includes a simplified block diagram of receiver circuitry which may be employed to control the operation of image reproducer 10. This apparatus may comprise an antenna 30 coupled to a receiving circuit unit 31; receiving circuits 31 may, for example, include a tuner, a suitable radio-frequency amplifier of one or more stages, a first detector, an intermediate-frequency amplifying system of one or more stages, a second detector and a videofrequency amplification system of any desired number of stages. Receiving circuits 31 are coupled to a sweep signal generator 32 which, in turn, is connected to deflection yoke 29. The receiving circuits are also separately coupled to a color demodulating system 33 and to a color matrix 34; the color matrix is further coupled to the output stages of the color demodulating system. Color matrix 34 may have three individual output stages individually coupled to control electrodes 17 of electron guns 13, 14 and respectively.

In many respects, the apparatus illustrated in FIGURE 1 is conventional in form, so that a detailed description of its operation is unnecessary. In brief, a transmitted color television signal is intercepted at antenna 30 and applied to receiving circuits 31 wherein it is suitably amplified and demodulated in accordance with techniques known in the art. The sweep-synchronizing portions of the received signal are segregated and applied to sweep signal generator 32 wherein they are employed to generate conventional horizontal and vertical sweep signals which are in turn supplied to deflection yoke 29. The video information portions of the received signal are applied to color demodulating system 33, in which signals representative of the color content of the image to be reproduced are developed. These signals, commonly designated as color-difference signals, are supplied to color matrix 34, wherein they are combined with a signal supplied from receiving circuits 31 and representative of brightness and detail of the image to develop three primary color signals which may, for example, correspond to the red, blue and green color content of the image. These circuits may all be conventional in form and operation and may be considered to represent any suitable color television receiver system.

Each of electron guns 13, 14 and 15 develops a stream of electrons which is focused into a beam and projected along a reference path toward target 21. Thus, electron gun 13 projects an electron beam along the reference path indicated by dash line R, whereas guns 14 and 15 project electron beams along reference paths B and G respectively. In this particular embodiment, the three electron beams converge approximately in the plane of color-selection electrode 23, convergence being etfected by an electrostatic lens established between velocity-determining electrode 26 and the common convergence electrode 20 of the three guns. Alternatively, mechanically converged electron guns may be employed if desired, or convergence may be effected by electromagnetic means at the option of the designer. The operational characteristics of the individual electron guns may be conventional in all respects; for example, the bias potentials applied to control electrodes 18 may be adjusted to compensate for the different efficiencies of the particular phosphors employed for the red, green and blue target areas r, b and g in accordance with familiar techniques. The intensity of each of the electron beams is, of course, modulated in accordance with the primary color signals supplied to control electrodes from color matrix 34 so that the beam from electron gun 13 (for example) varies in intensity in accordance with the red content of the image to be reproduced and the electron beams from guns 14 and 15 are varied in intensity to control the blue and green content of the reproduced image respectively. Apertures 24 of colorselection electrode or barrier 23 restrict each of the electron beams according to its angle of incidence upon the barrier so that the beam following path R can impinge only upon target areas r, the beam following path G bombards only areas 3, and the beam proceeding along path B excites only target areas b. The three beams are simultaneously deflected across the composite target structure 25 by varying deflection fields produced within the space bounded by system 29 in the usual manner to form an image raster, the plane-of-deflection being generally indicated by dash line 35.

As thus far described, the apparatus of FIGURE 1 is in most respects entirely conventional, the principal difference being that target 21 is ordinarily electrically connected to coating 22 and to color-selection electrode 23, or, for post-deflection-acceleration operation, color-selection electrode 23 may be connected only to the velocitydetermining electrode comprising coating 26 with the target being maintained at a much higher potential than the color-selection electrode.

In order to appreciate the full significance of the invention, a brief discussion of the electron-optical characteristics of the conventional types of reproducer is desirable. FIGURE 2 illustrates, on a greatly expanded scale, a fragmentary portion of the luminescent target and color-selection electrode for a direction-sensitive color target similar to that of FIGURE 1 but not intended for post-deflection-acceleration operation. Consequently, in this figure the color-selection electrode, comprising parallax mask 23, is electrically connected to the conductive backing film 22 of luminescent target 21 so that a fieldfree space exists between the two electrodes. Conventionally, the color-selection electrode would also be connected to the velocity-determining electrode 26 (FIG- URE 1) of such a device. Beam electrons following path R pass through one of the apertures 24 of mask 23 and continue along a straight line to impinge upon one of the target areas r. Similarly, beam electrons following paths G and B proceed undisturbed through the space between the color-selection electrode and the target to excite target areas g and b respectively. Because there is no potential difference between the target and the parallax mask, the electron paths are not refracted and accurate color reproduction may be achieved. Furthermore, the manufacture of target 21 and/ or barrier 23 is relatively simple. Because the electron paths etfectively constitute uninterrupted straight lines, the luminescent target may be produced by exposing a photographically sensitive film through color-selection electrode 23 by means of a source of light sequentially located at positions corresponding to the respective color-centers located in the plane-of-deflection of the tube, the photographic surface being mounted in a position corresponding to that of the tube target. This simple technique is a familiar one in the art and represents an effective and economical method of manufacturing color television targets.

FIGURE 3 corresponds to FIGURE 2 except that it represents a portion of the target structure of a directionsensitive image-reproducer constructed for post-deflectionacceleration operation. In such a device, the colorselection electrode 23 is maintained at a first potential positive with respect to the cathode or cathodes of the tube, whereas the target 21 is maintained at an operating potential which is very much higher than that of the color-selection electrode. As a typical example, the operating potential of luminescent screen 21 may be maintained at approximately 20 kilovolts and the potential applied to color-selection electrode 23 may be of the order of 6 kilovolts so that an accelerating field is established between the color-selection electrode and the luminescent target. As a result, electrons traversing the space between parallax mask 23 and target 21 are subjected to a focusing action; consequently, the apertures 24 in mask 23 may be made substantially larger than the corresponding apertures in a tube which does not employ post-deflection acceleration (FIGURE 2). As a result, a substantially higher percentage of the beam electrons pass through color-selection electrode 23 to impinge upon target 21, so that a considerably brighter image may be reproduced.

Although the post-deflection acceleration structure illustrated in FIGURE 3 provides a substantially brighter image than may be obtained with corresponding voltages in a uniform-field device such as shown in FIGURE 2, it also introduces some extremely undesirable effects onto the operation of the picture tube. For example, secondary electrons emitted from color-selection electrode 23 may be attracted by the target electrode, which is at a much higher potential, and may result in considerable color dilution. Furthermore, the geometrical relationship between the target areas in the luminescent screen and the apertures in the color barrier is substantially changed in a manner which renders manufacture of the luminescent screen much more complex and expensive. The latter effect is graphically illustrated by the electron paths R B and G which individually correspond to paths R B and G of FIGURE 2.

In the usual post-deflection-acceleration tube, colorselection electrode 23 is connected to the velocitydetermining electrode 26, so that each electron-beam component approaches the color-selection electrode along a straight path. Taking path R as an example, it is seen that electrons following this path, if continued along a straight line, would impinge upon one of the red color target areas 1' as indicated by dotted line R' However, due to the accelerating field existing between colorselection electrode 23 and target 21, the electrons do not follow the linear path in the barrier-target-interelectrode space, but instead approach the target electrode along a path more nearly perpendicular thereto and thus describes a parabola which may, for example, terminate at one of the other types of color target areas. Thus, in the example shown, a beam following path R actually terminates at one of the blue color target areas 11.

If this effect were completely uniform throughout the target, it would be unimportant, since it would only require that a different one of the electron guns be employed to excite target areas of a given color. Unfortunately, this is not the case, since the degree of variation from the original straight-line path is entirely dependent upon the angle at which the electrons approach the target structure and is thus dependent upon the instantaneous amount of horizontal and vertical deflection of the beam from the axis of the tube. This is attributable to the fact that the accelerating field between the two electrodes has a uniform effect upon that component of beam velocity which is perpendicular to the target but has no effect upon the component of beam velocity parallel to the plane of the target. Consequently, the electrons attempt to approach the target from a direction more nearly perpendicular thereto than in the case of a conventional tube operated without the post-defiection-acceleration field, and this erection effect, along with its associated errors, increases with distance from the center of the target, which may be taken as the point at which the electron beam components impinge upon the target when undeflected. Consequently, it is no longer possible to make the luminescent target by direct photographic exposure through the color-selection barrier, and elaborate and difficult techniques must be employed to produce the requisite non-uniform target area distribution required for accurate color reproduction in this type of tube. Alternatively, the target area pattern may be maintained uniform and the aperture pattern of parallax mask 23 may be made non-uniform to compensate for the erection effect, but this expedient is just as complex and difficult as the production of non-uniform luminescent screens.

FIGURE 4 provides an enlarged view of a portion of image reproducer 10 of the present invention which cor responds to the portions of conventional image reproducers illustrated in FIGURES 2 and 3. As indicated in the foregoing description of tube 10, color-selection electrode 23 is maintained at a predetermined positive potential with respect to the cathodes of the tube by means of its connection to operating voltage source B In FIGURE 4, which depicts the preferred mode of operation, screen 21 is operated at a positive potential very much higher than that of color-selection electrode 23 by means of the connection to source B and the velocity-determining electrode, comprising coating 26, is directly connected to metal backing layer 22 for operation at a common potential with screen 21. By way of illustration only, velocitydetermining electrode 26 and luminescent target 21 may be maintained at approximately 20 kilovolts, while the colorselection electrode is maintained at approximately 6 kilovolts. Consequently, an accelerating field is established between the color-selection electrode and the target electrode, as in the apparatus in FIGURE 3. At the same time, however, a decelerating field is established between the velocity-determining electrode and the color-selection electrode.

In accordance with the present invention, an auxiliary electrode comprising a circular ring abutment 36 is electrically connected to and circumferentially encompasses substantially the entire periphery of color-selection electrode 23 and is disposed adjacent to and preferably extends into velocity-determining electrode 26 which is of slightly larger diameter. Auxiliary electrode 36 may be individually supported and electrically connected to colorselection electrode 23 or may be constructed as an integral part thereof without departing from. the spirit and scope of the invention.

With reference to FIGURE 1 of the drawings, with the addition of auxiliary electrode 36 in accordance with the present invention, a retarding field, indicated generally by the reference numeral 37, is produced on the cathode side of the color-selection electrode and is not limited to a narrow shell as in the aforementioned Amdursky et al. application but extends into the funnel which before was field-free. When the auxiliary mesh electrode of the aforementioned Amdursky et al. application is removed, and with the velocity determining electrode held at the potential of the screen, the equipotential lines or surfaces move from the space between the mask and the auxiliary mesh and into the entire space between the mask and the neck of the tube. The equipotential surfaces in the vicinity of the mask are then concave toward the approaching electron beam and the equipotential surfaces farther from the mask in the direction of the tube neck are convex. In between the concave and convex surfaces, the equipotential surface have an S shaped cross-section; that is, in the center region of the tube, these surfaces are convex and near the periphery they change to concave. As in a decelerating field, as the beam moves through equipotential surfaces at higher potential to surfaces at lower potential, the convex surfaces refract the beam away from the tube axis and the concave surfaces refract the beam towards the tube axis. If the mask is surrounded by a ring, of increasing depth and electrically connected to the mask, as shown in FIGURE 1 in accordance with the presentinvention, then two things happen. Firstly, the radius of curvature of the equipotential surfaces is aliected in such a manner that with increasing depth of the ring, the radius of curvature of the equipotential surfaces become shorter near the ring, thereby increasing the convergence of the electron trajectory in that region. Furthermore, a greater number of equipotential surfaces have an S shaped cross-section near the periphery and which contribute in the peripheral region to the convergence of the electron trajectory. Therefore, if the mask is not surrounded by a ring or if this ring is shallow, the electron beam lands at the mask at a distance farther from the tube axis, and, after refraction in the space between the mask and the screen, at a distance farther from the axis at the screen with resultant color error. This color error is corrected if the depth of the ring which surrounds the mask is increased as the electron trajectories in the peripheral region are moved inward. Specifically, as shown in FIGURE 1, the equipotential lines of field 37 are nearly spherical in the funnel; however, a gradual and continuous transition occurs that shifts the center of curvature of the equipotential lines as color-selection electrode 23 is approached. Near the rim or peripheral edge of auxiliary electrode 36, the curvatures of the equipotential lines increase and this curvature change is utilized 'for beamlanding correction near the edge. In the zone between color-selection electrode 23 and screen 21, the potential gradient is uniform along the radius of curvature and is of higher magnitude than in the funnel region because of the reduced electrode spacing.

To the left of color-selection electrode 23, a divergent electron-optical immersion lens is formed by aquadag coating 26 and auxiliary electrode 36. Thus, electrons projected along a path R bend away from projected axis 38 as they pass through the field 37 but as the beam approaches the mask near the rim, the divergence is reduced by the change in potential gradient. After passing through the color-selection electrode, the electron beam bends toward the axis of the tube because of the normalizing action of the accelerating field established between I color-selection electrode 23 and screen 21 as heretofore described. By adjusting the divergence of decelerating field 37 to complement the convergence of the accelerating field between mask 23 and screen 21, path R lands on phosphor areas of the appropriate group throughout the area of screen 31.

If the envelope of reproducer is conical-shaped, the preferred contour of the peripheral edge of auxiliary electrode 36, extending toward coating 26, can essentially be described as an intersection of a spherical surface with the envelope, the center of the sphere being located in the plane-of-deflection 35. In this instance, auxiliary electrode 36 is rotationally symmetrical about the central axis of reproducer 10 and is of substantially uniform width d whether the screen and/ or color-selection electrode be planar, spherical, cylindrical or any combination thereof. In addition, it is desirable to maintain a constant-width peripheral gap between electrode 36 and coating 26. The proper divergence of decelerating field 37 may empirically be determined by adjusting the ratio of the voltages on coating 26 and electrode 36, by adjusting the magnitude and/or contour of the gap therebetween, or by adjusting the amount of extension of electrode 36 into the space encompassed by coating 26 until optimum erection compensation is achieved. Obviously, auxiliary electrode 36 may be in the form of a conductive coating on the inner surface of the envelope, preferably uniformly spaced from conductive coating 26 to form a constant peripheral gap therebetween, and electrically connected to electrode 26.

Therefore, the foregoing electron optical system fulfills, in an extremely simple manner, the basic requirement that the electron-beam components passing through apertures 24 must be directed upon landing at the phosphor screen so as to appear to have originated at electronic color-centers identical in position to the respective optical color-centers of the light source, and this is accomplished without the necessity of an auxiliary mesh electrode and is capable of producing substantially complete compensation for planar-, sphericalor cylindrical-target reproducers with only two-potential operation. It has been found, however, that the retarding field produced with the use of auxiliary electrode 36 is not as strong as with the use of the aforementioned auxiliary mesh and, consequently, secondary emission collection is less eiiicient. However, secondary emission is still kept within acceptable limits by increasing the potential on the color-selection and auxiliary electrodes because the secondary emission ratio of metals drops with increasing voltage and because then the field which attracts the secondary electrons to the screen is reduced. Reducing the voltage ratio between

electrodes

23, 36 and accelerating electrode 26 increases the electron beam spot size and this, in turn, means that apertures 24 of color-selection electrode 23 cannot be enlarged to the full extent. However, a brightness increase by a factor of two over conventional shadow-mask tubes is nevertheless easily achieved. It may be desirable to utilize a non-metallic color-selection electrode coated on both sides with a. conductive coating and maintain the coating on the cathode side at a slightly higher positive potential for use as a secondary electron collector. The potential difference between the two sides need only be in the neighborhood of volts which leaves the potential distribution of retarding field 37 substantially unaltered while efficiently collecting secondary emission from the edges of the mask apertures.

The described system of electrode geometry establishes a spherical coordinate reference for conical-shaped, or the so-called round screen type image-reproducers. However, the invention is equally applicable to rectangularscreen tubes in order to achieve: trajectory control for proper beam landing because commercially available rectangular color tube bulbs have a feature that is important to the lens design. This feature is that the slope of the funnel wall is less at the diagonals than at the major and minor axes, and the transition is smooth and continuous. In rectangular-screen image-reproducers, auxiliary electrode 36 is no longer rotationally symmetrical about the central axis of reproducer 10, however, its width d is still essentially of constant dimension throughout its periphery. The peripheral edge of auxiliary electrode 36, extending toward coating 26, can be described as being essentially equidistantly spaced from the peripheral edge of colorselection electrode 23. In addition, it is desirable to form the contour of the peripheral edge of conductive coating 26 to be complementary to the contour of the peripheral edge of auxiliary electrode 36, so as to form a peripheral gap therebetween which may be empirically varied for vernier erection correction.

Thus, in accordance with the present invention, there has been provided a new and improved image-reproducer, capable of two-potential operation, which compensates for variations in refraction of the electron beam components due to post-deflection-acceleration operation in an extremely simple and economical manner without the necessity of an additional auxiliary mesh electrode, and these advantages may be achieved with luminescent screens of planar, spherical or cylindrical configuration.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

1 claim:

1. A color television image-reproducer comprising: electron gun means, including an electron-emissive cathode, for effectively projecting a plurality of electronbeam components through a deflection space along a corresponding plurality of reference paths; a multi-color mosaic luminescent target disposed transversely of said reference paths in spaced relation to said electron gun means; a color-selection electrode disposed transversely of said reference paths intermediate said target and said electron gun means; means for maintaining said colorselection electrode at a first predetermined potential positive with respect to said cathode; means for maintaining said luminescent target at a predetermined potential positive with respect to said cathode and higher than said first potential, whereby, during passage from said colorselection electrode to said target, electrons are accelerated and subjected to erection of an amount corresponding to a predetermined function of the distance between the point of intersection of said reference paths with the plane of said color-selection electrode and the central axis of said color-selection electrode; a velocity-determining electrode encompassing substantially all of the portions of said reference paths intermediate said color-selection electrode and said deflection space; means for maintaining said velocity-determining electrode at a potential positive with respect to said cathode and substantially higher than said first potential; and means, including an auxiliary electrode electrically connected to and circumferentially encompassing said color-selection electrode and extending toward said velocity-determining electrode a distance to establish with said velocity-determining electrode a non-uniform electric field, for subjecting said electrons to de-erection of an amount substantially corresponding to said predetermined function throughout substantially the entire area of said luminescent target to compensate for said erection occurring between said color-selection electrode and said target.

2. A color television image-reproducer comprising: electron gun means, including an electron-emissive cathode, for effectively projecting a plurality of electron-beam components through a deflection space along a corresponding plurality of reference paths; a multi-color mosaic luminescent target disposed transversely of said reference paths in spaced relation to said electron gun means; a color-selection electrode comprising an apertured parallax mask disposed transversely of said reference paths intermediate said target and said electron gun means to form with said luminescent target a directionsensitive composite target structure, said target including a plurality of groups of target areas interspersed with each other in distribution patterns corresponding to the aperture pattern of said parallax mask, each of said groups being established by direct optical projection through said mask apertures from a corresponding plurality of respective optical color-centers located in a common plane intermediate said electron gun means and said parallax mask; a velocity-determining electrode encompassing substantially all of the portions of said reference paths intermediate said parallax mask and said deflection space; an auxiliary electrode circumferentially encompassing said parallax mask and extending toward said velocity-determining electrode a predetermined distance; means for maintaining said parallax mask and said auxiliary electrode at a first predetermined potential positive with respect to said cathode; means for maintaining said luminescent target at a predetermined potential positive with respect to said cathode and higher than said first potential, whereby, during passage from said parallax mask to said target, electrons are accelerated and subjected to erection by an amount corresponding to a predetermined function of the distance between the point of intersection of said reference paths with the plane of said parallax mask and the central axis of said parallax mask; and means for maintaining said velocitydeterrnining electrode at a potential positive with respect to said cathode and substantially higher than said first potential and of a magnitude suflicient with respect to the other potentials and correlated with said predetermined distance to subject said electrons to de-erection of an amount corresponding to said predetermined function to establish an effective electronic color-center for said image-reproducer which substantially corresponds to its optical color-center.

3. A color television image-reproducer comprising: electron gun means, including an electron-emissive cathode, for effectively projecting a plurality of electronbeam components through a deflection space along a corresponding plurality of reference paths; a multi-color mosaic luminescent target disposed transversely of said reference paths in spaced relation to said electron gun means; a color-selection electrode disposed transversely of said reference paths intermediate said target and said electron gun means; means for maintaining said colorselection electrode at a first predetermined potential positive with respect to said cathode; means for maintaining said luminescent target at a predetermined potential positive with respect to said cathode and higher than said first potential, whereby, during passage from said colorselection electrode to said target, electrons are accelerated and subjected to erection of an amount corresponding to a predetermined function of the distance between the point of intersection of said reference paths with the plane of said color-selection electrode and the central axis of said color-selection electrode; a velocity-determining electrode encompassing substantially all of the portions of said reference paths intermediate said colorselection electrode and said deflection space; means for maintaining said velocity-determining electrode at a potential positive with respect to said cathode and substantially higher than said first potential; and an auxiliary electrode of constant peripheral width electrically connected to and circumferentially encompassing said colorselection electrode and extending toward said velocitydeterrnining electrode a distance correlated with the magnitudes of said potentials to subject said electrons to deerection of an amount substantially corresponding to said predetermined function throughout substantially the entire area of said luminescent target to compensate for said erection occurring between said color-selection electrode and said target.

4. A color television image-reproducer comprising: electron gun means, including an electron-emissive cathode, for effectively projecting a plurality of electron-beam components through a deflection space along a corresponding plurality of reference paths; 2. multi-color mosaic luminescent target disposed transversely of said reference paths in spaced relation to said electron gun means; a color-selection electrode disposed transversely of said reference paths intermediate said target and said electron gun means; means for maintaining said colorselection electrode at a first predetermined potential positive with respect to said cathode; means for maintaining s a1d luminescent target at a second predetermined potent al positive with respect to said cathode and substantially higher than said first potential, whereby, during passage from said color-selection electrode to said target, electrons are accelerated and subjected to erection of an amount corresponding to a predetermined function of the distance between the point of intersection of said reference paths with the plane of said color-selection electrode and the central axis of said color-selection electrode; a velocity-determining electrode encompassing substantially all of the portions of said reference paths intermediate said color-selection electrode and said deflection space; means for maintaining said velocity-determining electrode at a positive potential substantially equal to said second potential; and means, including an auxiliary electrode electrically connected to and circumferentially encompassing said color-selection electrode and extending toward said velocity-determining electrode a distance to establish with said velocity-determining electrode a nonuniform deceleratng electric field, for subjecting said electrons to de-erection of an amount substantially corresponding to said predetermined function throughout substantially the entire area of said luminescent target to compensate for said erection occurring between said color-selection electrode and said target.

5. A color television image-reproducer comprising: electron gun means, including an electron emissive cathode, for effectively projecting a plurality of electron-beam components through a deflection space along a corresponding plurality of reference paths; a multi-color mosaic luminescent target disposed transversely of said reference paths in spaced relation to said electron gun means; a color-selection electrode disposed transversely of said reference paths intermediate said target and said electron gun means; means for maintaining said color-selection electrode at a first predetermined potential positive with respect to said cathode; means for maintaining said luminescent target at a predetermined potential positive with respect to said cathode and higher than said first potential, whereby, during passage from said color-selection electrode to said target, electrons are accelerated and subjected to erection by an amount corresponding to a predetermined function of the distance between the point of intersection of said reference paths with the plane of said color-selection electrode and the central axis of said color-selection electrode; a velocity-determining electrode encompassing substantially all of the portions of said reference paths intermediate said color-selection electrode and said deflection space; means for maintaining said velocity-determining electrode at a potential positive with respect to said cathode and higher than said first potential; and means, including an auxiliary electron optical lens electrode integral with and circumferentially encompassing said color-selection electrode and disposed adjacent to and partially extending into the space encompassed by said velocity-determining electrode to establish with said velocity-determining electrode a non-uniform electric field defining a double convex magnetic lens, for subjecting said electrons to de-erection of an amount substantially corresponding to said predetermined function throughout substantially the entire area of said luminescent target to compensate for said erection occurring between said color-selection electrode and said target.

6. A color television image-reproducer comprising: electron gun means, including an electron emissive cathode, for effectively projecting a plurality of electron-beam components through a deflection space along a corresponding plurality of converging reference paths; a multicolor mosaic luminescent target disposed transversely of said reference paths in spaced relation to said electron gun means; a color-selection electrode disposed transversely of said reference paths intermediate said target and said electron gun means; means for maintaining said color-selection electrode at a first predetermined potential positive with respect to said cathode; means for maintaining said target at a predetermined potential positive with respect to said cathode and higher than said first potential, whereby, during passage from said color-selecticn electrode to said target, electrons are accelerated and subjected to erection by an amount corresponding to a predetermined function of the distance between the point of convergence of said reference paths and the central axis of said color-selection electrode; a velocity-determining electrode encompassing substantially all of the portions of said reference paths intermediate said color-selection electrode and said deflection space; means for maintaining said velocity-determining electrode at a potential positive with respect to said cathode and higher than said first potential; and means, including an auxiliary electrode electrically connected to and circumferentially encompassing said color-selection electrode and disposed with the peripheral edge thereof equidistantly spaced from said velocity-determining electrode to establish with said velocity-determining electrode a non-uniform electric field of generally decreasing concentration from said edge toward said central axis, for subjecting said electrons to tie-erection of an amount substantially corresponding to said predetermined function throughout substantially the entire area of said luminescent target to compensate for said erection occurring between said color-selection electrade and said target.

References Cited in the file of this patent UNITED STATES PATENTS 2,690,518 Fyler Sept. 28, 1954 2,727,172 Mark et a1. Dec. 13, 1955 2,728,024 Ramberg Dec. 20, 1955 2,793,319 Nunan May 21, 1957 2,795,720 Epstein June 11, 1957 2,798,185 Hansen July 2, 1957 2,813,224 Francken Nov. 12, 1957