US2229556A - Cathode-ray tube control device for television scanning apparatus - Google Patents

Description

1941- Q A. B. DU MONT EIAL 2,229,556

CATHODE-RAY TUBE CONTROL DEVICE FOR TELEVISION SCANNING APPARATUS Filed July 10, 1939 Patenteil Jan. 21, 1941 UNITED STATES CATHODE-RAY TUBE CONTROL DEVICESFOR TELEVISION SCANNING APPABATU Allen B. Du Mont,

T. Goldsmith, Jr.,

U per Montclair, and Thomas Montclair, N. J., assignors to Allen 13. Du Mont Laboratories, Inc., Passaic, N. J., a corporation of Delaware Application July 10, 1939, SerialNo. 283,548

1 Claim.

Our invention relates to a cathode-ray tube control device for televisionscanning apparatus.

The necessity, in television communication, of keeping the respective scanning devices at the transmitter and receivers in synchronism, has given rise to many problems. For this purpose, it has been proposed to generate at the trans mitter the required line, field or frame, and blanking pulses, and to transmit these on the same carrier with the video signals; The different pulses are selected out at the receiver and used to serve their respective purposes. A typical system belonging to this general class is disclosed in Patent No. 2,132,655, issued October 11, 1938, to John P. Smith.

Another proposed system or method of keeping in step the cathode-ray tube scanning devices at the transmitter and receivers resides in transmission to the receivers of the actual sweeps" for horizontal and vertical deflection respectively of the scanning electron rays. Such a system and method is disclosed in Patent No. 2,186,634, issued January 9, 1940, to Allen B. Du Mont, and Patents Nos. 2,164,176 and 2,201,309, issued June 27, 1939, and May 21, 1940, respectively, to Thomas T. Goldsmith, Jr.

While the various systems and methods above referred to have been effective to produce satisfactory results, there still is the disadvantage in each that the control or synchronizing signals or wave forms must be transmitted to and separated out at the receivers. This not only requires use of a greater band width than would be the case if it were not necessary for these signals or wave forms to be transmitted with the video signals, but also gives cause for distortion and interference generally, due to undesirable and 8X; traneous surges or signals which occur and which must be reckoned with.

With the foregoing in mind, it is one of the objects of our invention to provide an improved control device for television scanning apparatus which is simple in construction and reliable in operation, and by which the various disadvantages of the synchronizing means and methods proposed heretofore can be avoided.

Other objects and advantages will hereinafter appear.

The basic principle involved in our invention resides in the fact that certain substances or materials yield a greater number ofelectrons of secondary emission when bombarded *by primary electrons, than certain other substances. For example, there is a difference between the respective degrees of secondary emission from aluminum and carbon. or from silver and glass. when screens of these materials are bombarded or scanned by a ray or beam of electrons under the" same operating conditions.

In accordance with our invention, where it is required that there be produced line, field, frame and blanking pulses or signals for synchronization in television communication, or that any combination of such pulses or signals be produced, a screen is prepared comprising a supporting base of a given material having deposited over a surface thereof one or more substances in a certain configuration. The deposited substances have different secondary-emission properties, and each have a different secondary-emission property than that of the base material. The composite screen is embodied in a cathoderay tube of a conventional construction, and the treated surface serves as a target for the electron ray or beam which may have a sharp, spotfocus on the target. The beam or beams orig.- inate from a source of primary electrons in the form of a conventional electron gun. By means of plates or coils, the electron ray or beam is deflected electrostatically or electromagnetically to cause it to scan the target or screen. Thus, electrical control or synchronizing signals are generated at the screen, or on other electrodes of the cathode-ray tube, and they vary in accordance with the particular materials being bom-' barded by the electrons.

For the purpose of illustrating our invention,

an embodiment thereof is shown in the drawing, in which Figure 1 is a simplified, elevational view, part ly in section, of a cathode-ray tube constructed and operating in accordance with our invention; Fig. 2 is a simplified, detail, elevational view looking toward the right in Fig. 1, and is illustrative of the screen construction in Fig. 1; and Fig. 2a is a graphical representation illustra tive of the operating action obtained by our,

improved control device as shown in Figs. 1 and 2.

The cathode-ray tube shown in Fig. 1 comprises an evacuated tube I having in the neck portion thereof an electron gun of a conventional construction for developing a ray or beam II of electrons directed at and focused on a screen or target I 2 at the other end of the tube.

The screen l2 comprises a base plate 26 of aluminum foil to which a supporting contact I5 is electrically connected. The aluminum plate 28 may be backed by a suitable plate to impart suflicient rigidity, as will be well understood.

Instead of taking the control signals directly from the target or screen I! by the output line I 8. the tube It may be provided with a collector ring l9 adjacent the screen, and from which the synchronizing impulses or other control signals are taken by the output connection 20.

The signals taken from the collector ring l9 will be .of polarity opposite to that of the signals taken directly from the target itself. Having either polarity available is an advantage.

By the application of bias voltages between the target I! and the collector ring I! of the tube l0, it is possible to increase materially the amount of output signal from either of the output lines l8 and 20. For example, by making the potential of electrode I! one hundred volts positive with respect to the target l2, the amount of output signal is materially increased.

If the target l2 consists of more than two materials having different secondary-emission properties and each havingadiiferent secondary-emission property than that of the base plate such as the aluminum foil 26 in Fig. 2, the respective output signals can be made to have different amplitudes. This would be useful for special applications, as for example in producing blanking pulses at the ends of television lines and fields of scanning.

Blanking and; synchronizing pulse wave forms for television apparatus embodying cathode-ray tubes, may be actually produced by a suitably prepared target, as shown in Fig. 2. The aluminum surface 26 is provided with a silver coating 21. The central, rectangular picture region or area 28 is a coating of carbon ink or the aluminum surface. Scanning is with a spot focus,

and the electron beam or ray II is deflected horizontally and vertically in the usual manner by applying saw-tooth sweeps to the deflecting plates l6 and II. In scanning the line AA, for example, there will be produced a blanking pulse as represented at 29 in Fig. 2a when the spot traverses the aluminum surface 26, and a line pulse as represented at 30 when the spot traverses the silver surface 21. The frame or field pulse will be produced when the spot scans the horizontal band of the silver surface at the bottom, and this pulse will be on a blanking pulse on account of the scanning of the relatively wide horizontal bands of the aluminum surface at top and bottom.

We claim as our invention:

Apparatus for generating electrical control signals comprising a tube provided with a target and with means for developing a ray of electrons directed at and focused on a surface of said target, said surface being provided with a pattern the material of which has a different secondary-emission property than that of the intervening surface, said pattern being in the form of bands disposed substantially at ninety degrees with respect to each other and bounding adjacent sides of a central substantially rectangular picture area of said target, means for deflecting said ray to cause the same to scan said area and said bands whereby there are produced blanking pulses for the ends of television lines and flelds of scanning, and a contact for taking such impulses from said tube.

ALLEN B. DU MONT. THOMAS T. GOLDSMITH, JR.

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