US2163546A - Apparatus and method for television reception - Google Patents

Description

June 20, 1939. s. L. CLOTHIER ET AL 2,163,546

APPARATUS AND METHOD FOR TELEVISION RECEPTION Filed Oct. 8, 1937 Patented June 20, 1939 UNITED STATES PATENT OFFICE APPARATUS METHOD FOR TELEVISION RECEPTION Application October 8, 1937, Serial No. 167,912

7 Claims.

respective voltages for horizontal and vertical deflection of the ray be relatively high. In these tubes, the velocity of the electrons in travelling from the electron gun to the fluorescent screen is relatively high in order to produceon the screen an image of sumcient brllliancy for the projection and enlargement on the external screen. At the relatively high voltages it requires for this purpose, it becomes increasingly difiicult to obtain a sharp electron focus at the screen.

With the foregoing in mind, it is one of the objects of our invention to provide an improved apparatus and method for television reception whereby not only are the disadvantages of the prior constructions and methods referred to avoided, but with our improved apparatus it is possible to obtain much finer detail in the fluorescent image while still maintaining the necessary brilliance for optical projection onto a large, external screen.

In accordance with our invention, we employ a cathode-ray receiving tube comprising a. section in which the electrons travel ata relatively low velocity, and a section in which the electrons travel at a relatively high velocity. First, in the low-velocity section of the tube a ray of electrons of comparatively low density and very small scanning-spot size is deflected to scan a given plane in this section and is simultaneously modulated in accordance with the incoming picture or video signals to create in said plane a. rela tively small but complete and true electron image with relatively low velocity electrons and of fine texture or definition. The entire scanning operation and production of this electron image is accomplished at relatively low accelerating potentials. The true electron image so created is in effect a virtual cathode with respect to the highvelocity section of the tube and is employed as such. Without further scanning deflection or modulation. but purely by electron focusing and acceleration, a second electron image, which is a reproduction of the first, true electron image or virtual cathode, is produced at a fluorescent screen in the high-velocity section of the tube, with the electrons traveling at relatively high velocities to produce on the fluorescent screen a brilliant image for projection by an optical lens system onto a large, external screen.

For the purpose of illustrating our invention,

an embodiment thereof is shown in the drawing,

in which:

Figure 1 is a simplified, diagrammatic view of television receiving apparatus constructed and operating in accordance with our invention;

Fig. 2 is an enlarged, fragmentary, sectional view showing a modification, the section being taken on the line 2--2 in Fig. 3;

Fig. 3 is an elevational view, looking toward 'the left in Fig. 2;

Fig. 4 is a view similar to Fig. 1, showing a modification; and

Fig. 5 is an enlarged, detail, sectional view,the section being taken on the line 55 in Fig. 4.

With reference to Fig. 1, the reference numeral I designates a television receiving tube which is evacuated and comprises a section I I and a section l2 of larger cross-sectional dimension than the section II. Mounted in the section II is means in the form of an electron gun I 3 of a conventional construction for developing and modulating a ray I I of electrons directed at a fluorescent screen 15 at the far end of the tube section l2. The ray I4 is focused on a plane l6 between the fluorescent screen 15 and the gun l3, at about the junction of the adjacent ends oi the tube sections H and I2.

The ray I l-of electrons is deflected simultaneously in horizontal and vertical directions by deflecting plates l1 and I8 in any suitable, conventional manner, whereby the ray I4 is caused to scan the plane IS. The ray is also modulated in accordance with the incoming video signals by means of the conventional Wehnelt control electrode 25.

Disposed in the tube section I2 is an electronic lens system of any suitable, conventional construction for the purpose hereinafter described, and which in the presentinstance is shown as consisting of metal ring electrodes I9, 20 and II, and a metal disc electrode 22 having a central opening 23, these electrodes being disposed as shown and in this particular case at substantially the potentials designated in the drawing. The tube section I! may be provided on its inner surface, between the fluorescent screen l and the electrode 2 I, with a coating 24 of aquadag electrically connected to the electrode 2 l.

In the construction shown in Fig. 1, there is no material substance in the plane I6 on which the ray I4 is focused and which is scanned by the ray I4.

In the operation of our improved television receiving tube, aside from the facts that there is no fluorescent screen in the plane I6 to produce there a brilliant image forv projection and enlargement on a remote, external screen, and that the operating voltages are relatively low as designated in the drawing, the section II of our improved tube Ill operates in the same manner as a cathode-ray television receiving tube of wellknown construction. That is, the picture signals are applied to the control grid 25 to vary the ray intensity in accordance with occurring variations in the incoming picture signals, and with the ray I4 focused on the plane I6 and deflected to scan this plane, a true electron image of the' view being televised is produced in the plane I6. In other words, if there were a fluorescent screen in the plane I6, a visible image of good definition would appear on such a screen.

The effect of the electronic lens system in the tube section I2 is to cause the electrons, from the elemental areas in the plane I6, to travel to the corresponding and respective elemental areas of the fluorescent screen I5 and at a velocity substantially higher than the initial velocity of the electrons at the plane I6. In other words, it might be said that the electrons coming from the gun I3 are brought to a focus at a first focal plane such as the plane I6, to produce or develop in this plane a true electron image of the view being televised, and that by means of the electronic lens system operating in accordance with the well known principles of electron optics, the electrons passing on or emanating from the first focal plane I6 are greatly accelerated to a velocity substantially higher than the initial velocity of the electrons at the plane I6 and brought to a focus a second time at the fluorescent screen I5.

Further in the above connection, it might be said that the electron image in the first focal plane I6 is projected, by the electronic lens system, from the plane I 6 onto the fluorescent screen I5 remote from the plane I6. Also, in considering the principle, or manner of operation of our improved tube, it might be said that the electrons emanating from the plane I6 are refocused, but in an inverted relation as represented in Fig. 4, on a second remote plane, this in the'present instance being the plane in which the fluorescent surface of the screen I5 is disposed. In this manner the electron image developed in the plane I6 is transferred to the complementary surface of the remote fluorescent screen I5, but with the electrons bombarding the screen I5 at a velocity substantially higher than the initial velocity of the electrons at the plane I 6, and with the brilliant image appearing on the fluorescent screen I5 inverted with respect to the electron image developed in the plane I6. There is, therefore, produced on the screen I5 an inverted image of good definition and which is of grea brilliancy. This image is projected by a suitable lens system 26 onto a remote, external screen 21.

It will be understood that the relative positions of the various parts and the repsective potentials onthe latter may be varied considerably over the values designated.

In the modification shown in Figs. 2 and 3, a fine mesh, wire screen 28, which may be supported in a'mica frame 29, is mounted in the tube III, in the plane I6. It is proposed to first tre t the screen 28, such as by providing it with a cesium silver oxide coating, to give it a relatively high secondary-emissive characteristic. In the operation of this construction, there is also developed a true electron image of the view being televised at the plane of the screen 28. Some of the electrons of the ray I4 which pass through the screen 28, and electrons of secondary emission from the screen 28, come to a focus at the corresponding and respective elemental areas of the fluorescent screen I5 to produce on the latter a brilliant, inverted image of good definition for optical projection onto the external screen 21'. The construction and operating action of the embodiment shown in Figs. 2 and 3 are otherwise the same as in Fig. 1.

In lieu of using an electronic lens system con-' sisting of the rings I9, 20 and 2|, and the disc 22, a single, elemental anode 30, as shown in Figs. 4 and 5, may be used for the same purpose, this being to project or refocus the electron image in the plane IS on the fluorescent surface of the screen I5, and to greatly accelerate the electrons axis of the tube section I2 and at the proper 1 point along this axis to focus the electrons from the plane I6 on the fluorescent screen I5, in the same general manner and according to the same principle disclosed in our pending application, Serial No. 161,730, filed August 31, 1937. That is, with elemental anode 30 at the high potential designated, the electrons from any elemental area of the plane I6 are drawn to the anode and are greatly accelerated during this travel so that they reach the anode at a relatively high velocity. While some of the electrons pass to ground from the anode 30, many of them pass through the aperture 33 and pass on at the relatively high velocity and come to a focus on the corresponding and respective elemental area of the fluorescent screen I5. In this manner, the electron image in the plane I6 is projected or refocused, but'in an inverted relation as represented, on the fluorescent screen I5 to produce a brilliant, inverted image for optical projection and enlargement on the external screen 21.

Considering our invention from the broader aspect thereof, it will be seen that this resides in employment of a cathode-ray receiving tube comprising a section I I in which the electrons travel at a relatively low velocity and a section I2 in which the electrons travel at a relatively high velocity. Furthermore, the ray I4 in the low-velocity section II and which is of comparatively low density and very small scanning-spot size, is deflected and modulated to create in the plane I6 a relatively small but complete and true electron image with relatively low velocity electrons and of fine texture or definition. The entire scanning operation and production of this electron image is accomplished at relatively low accelerating potentials. It will be seen that the electron image so created is in effect a virtual cathode with respectto the high-velocity section I! of the tube and is employed as such. Beyond the plane [6, or in other words, in the high-velocity section l2 of the tube, there is no further scanning deflection or modulation, but purely by electron focusing and acceleration, a second electron image, which is an inverted reproduction of for projection onto the large, external screen 21.

By means of our novel construction and method of operation, it is possible to use very high accelerating potentials in the electron lens" section l2 of the tube, without the necessity for high deflection potentials and/ or high modulation potentials of the low-velocity section I l. Further than this, instead of attempting, as heretofore, to secure highest possible electron beam current and maximum electron density in a given size scanning spot at the fluorescent screen for securing the desired brightness, we employ electron beam current of comparatively low value and depend on the fact" that the effective mass ofthe electron increases tremendously at high velocities approaching the velocity of light. As a direct result of this high velocity and increased mass, the effect of theelectrons on the fluorescent screen is tremendously increased. Even if a saturation condition exists such that the beam current is limited to only a few microamperes, regardless of how much the final anode potential is increased, it is still possible to produce a greater surface brightness at the fluorescent screen, for a, given power expenditure, by employing extremely high velocities at this low beam current than by employing high values of beam current, for example, a few milli amperes, at correspondingly lower velocities.

It will be understood that various changesand modifications, within the conception of those skilled in the art, are possible without departing from the spirit of our invention or the scope of the claims.

We claim as our invention:

1. In a television receiving tube, 'a low voltage section and a high voltage section. the latter including a viewing screen of fluorescent materialat the inside end wall of the tube and optically unobstructed from the tube exterior, means including an electron gun within the low voltag section developing from received electrical impulses representing picture signals and at low velocity toward the low voltage section an electron image ofthe viewabeing televised, said electron image being in advance of the screen and apertured electrostatic electron lens electrode means between said electron image and the fluorescent screen for increasing the velocity of the electron beam and inverting and refocusing the electron image at substantially the same size on the fluorescent screen said apertured means passing only an electron beam of elemental size.

2. In a television receiving tube, a low voltage section and a high voltage section, the latter including a viewing screen of fluorescent material at the inside end wall of the tube and optically unobstructed from the tube exterior, means including an electron gun wthin the low voltage section developing from received electrical impulses representing picture signals and at low velocity toward the low voltage section an electron image of the view being televised, said electron image being in advance of the screen, and apertured electrostatic electron lens electrode means between said electron image and the fluorescent screen constricting the electron beam to elemental size and inverting and refocusing the image at substantially the same size at increased electron velocity on the fluorescent screen.

3. In a television receiving tube, a low voltage section and a high voltage section, the latter including a viewing screen of fluorescent material at the, inside'end wall of the tube and optically unobstructed from the tube exterior, means including an electron gun within the low voltage section developing from received electrical impulses representing picture signals and at low velocity toward the low voltage. section an electron image of the view being televised, said electron image being in advance of the screen, and apertured electrostatic electron lens electrode means between said' electron image and the fluorescent screen of minimum surface area and passing only an electron beam of elemental size for inverting and refocusing the image at substantially the same size at increased electron velocity on the fluorescent screen.

4. In a television receiving tube, a low voltage section and a high voltage section, the latter including a viewing screen of fluorescent material at the inside end wall of the tube and optically unobstructed from the tube exterior, means including an electron gun within the low voltage section developing from received electrical impulses representing picture signals and at low velocity toward the low voltage section an electron image of the view being televised, said electron image being in advance of the screen, and including secondaryer'nission means in the plane of said image, and apertured electrode means between-said electron image and the fluorescent screen for increasing the velocity of the electron beam and inverting and refocusing the electron image on the fluorescent screen.

5. In a television receiving tube, a low voltage section and a high voltage section, the latter including a viewing screen of fluorescent material at the inside end wall of the tube and optically unobstructed from the tube exterior, means including an electron gun within the low voltage section developing from received electrical impulses representing picture signal and at low velocity toward the low voltage section an electron image of the view being televised, said electron image being in advance of the screen, and including secondary emission means in the plane of said image, and apertured electrode means between said electron image and the fluorescent screen for increasing the velocity of the electron beam and inverting and refocusing the electron image on the fluorescent screen, said apertured means passing only an electron beam of elemental size.

6. In a television receiving tube, a low voltage section and a high voltage section, the latter including a viewing screen of fluorescent material at the inside end wall of the tube and optically unobstructed from the tube exterior, means including an electron gun within the low voltage section developing from received electrical impulses representing picture signals and at low velocity toward the low voltage section an electron image of the view being televised, said electron image being in advance of the screen, and including secondary emission means in the plane of said image, and apertured electrode means between said electron image and the fluorescent screen constricting the electron beam to elemental size for inverting and refocusing the image at increased electron velocity on the fluorescent screen.

7. In a television receiving tube, a low voltage section and a high-voltage section, the latter including a viewing screen of fluorescent material at the inside end wall of the tube and optically unobstructed from the tube exterior, means including an electron gun within the low voltage section developing from received electrical impulses representing picture signah and at low velocity toward the low voltage section an electron image of the view being televised, said ,electron' image being in advance of the screen, and including secondary emission means in the plane of said image, and apertured electrode means between said electron image and the fluorescent screen of minimum surface area and passing only an electron beam of elemental size for inverting and refocusing the image at increased electron velocity on the fluorescent screen.

STEWART L. CLOTHIER. HAROLD C. HOGENCAMP.

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