US2050628A - Cathode ray television system - Google Patents

Description

Allg- 1936- D. PRINZ 2,050,528

CATHODE RAY TELEVISION SYSTEM Filed Feb. 29, 1932 '0 recewer and dezeviar INVENTOR DIETRKZH lNZ :ATTORNEY Patented Aug. 11, 1936 UNITED STATES PATENT OFFEQE Dietrich Prinz, Berlin,

Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application February 29, 1932, Serial No. 595,817 In Germany March 2, 1931 12 Claims.

The present invention relates to an improvement in television systems and covers an improvement in the general type of system disclosed by my patent application Serial No. 581,217, filed December 15, 1931, now Patent No. 2,011,260,

granted Aug. 13, 1935.

The aforementioned patent application relates to a circuit scheme adapted to insure variations of brightness of the luminous spots produced on the fluorescent end viewing wall of a Braun tube, and is particularly adapted for use in television work.

As shown by my above identified patent, a cathode ray tube is used as the medium by which electro-optical images may be reconstructed at various viewing points. In such type of tubes it is customary to provide a cathode as the electron emitting element and the electron stream emitted is arranged to pass through a tubular shaped anode element, and then between the two auxiliary deflector plates used as intensity controlling elements, after which the ray passes through a suitable diaphragm. The diaphragm controls the electron stream passing toward the fluorescent end wall of the tube. The electron stream which passes through the diaphragm is then caused to pass through the space between two deflector plate pairs which are positioned at right angles to each other to control the path of projection of the cathode ray in a manner known in the art. It is customary to connect one plate of each of the said pairs of deflecting plates with the grounded anode. It is only when the potentials prevailing at the auxiliary'intensity control plate is of zero value or nearly zero value that the cathode ray pencil will be able to pass through the screening diaphragm.

As, has been shown by my above identified patent, an undulating unidirectional potential is applied to the auxiliary intensity control plate so that the cathode ray pencil will find a chance to pass through the diaphragm only during the extremely brief periods of time when the pulsating D. C. waves supplied as controlling impulses pass through zero. Thus, by altering the pulsating D. C. potential it is possible to vary also the times during which the electron stream can pass beyond the diaphragm to reach the luminous or fluorescent screen with a resultant alteration also of the brightness of the impinging light spot produced by the applied pulsating D. C. potentials.

A scheme of this general arrangement involves the drawback that the brightness of the light spot is inversely proportional to the supplied potential on the control plate, and for the purposes of television work a special modulation of the transmitter is required.

The object of the present invention is, therefore, to provide a linear or approximately linear relationship between the brightness of the spot 5 and a potential fed to the tube. With this end in view the control plate of the tube is supplied with apulsating D. C. potential the value of which is zero not only for a brief instant, but rather for an appreciably long fraction of the period thereof.

Other objects and advantages of the invention will, of course, become apparent and at once suggest themselves to those skilled in the art to which the invention relates by reading the following specification and claims in connection with the accompanying drawing, wherein Figure l illustrates a cathode ray tube used for the production of an electro-optical image in accordance with the present invention; Figure 2 illustrates diagrammatically the form of the pulsating D. C. wave supplied; by this figure portion A indicates a pulsating D. C. wave produced by rectifying asymmetrically a sinusoidal wave, and portion 1) shows diagrammatically a pulsating D. C. produced by asymmetrically rectifying a triangular wave shape. Fig. 3 shows diagrammatically the underlying principles of the means used for producing the pulsating D. C. wave. Fig. 4 represents an embodiment of the scheme used to produce the pulsating D. C.

To refer to the drawing, the cathode ray tube I is provided with an electron emitting cathode, generally designated as 2, which emits a stream of electrons which are projected through a tubular anode 3 and then through a set of deflecting plates 4 and 4, after which they are caused topass through a diaphragm or screening member 5 provided with a central aperture 6 of predetermined size. In order to control the position at which the projected electron stream, conventionally shown by the dotted line within the tube, strikes the fluorescent end wall I of the tube, deflecting plates 8, 8 and 9, 9 have been provided. These pairs of plates 8, 8' and 9,

9' are positioned at right angles to each other in a manner well known in the art. It is of course, understood that the two sets of deflecting plates are supplied with suitable voltages for producing the scanning action as is well known in the art. It is, of course, to be understood that electromagnetic fields might be substituted for the electrostatic fields produced by the deflecting plates in order to control the position of the electron stream or beam in a manner well known in the art without departing from the 5 spirit and scope of this invention. As was taught in my above identified patent referred to, the controlling potentials for controlling that portion of the cathode ray stream which strikes the fluorescent end wall I are supplied across the deflecting plates 4 and 4. The deflecting plates 4 and 4' are fed pulsating D. C. which is dependent upon the amplitude of the rectified output of the radia receiver 25 which receives radiant energy by means of the antenna 24. Converting means 26 which supply the pulsating D. C. to the plates 4 and 4' are discussed below in further detail in connection with Figs. 3 and 4.

Fig. 3 shows schematically the principle of producing the pulsating D. C. in accordance with the rectified voltage received from the radio receiver. In this figure, I0 represents a local oscillator producing alternating currents. 'II is a rectifier, I2 is a variable voltage which represents the rectified output of the radio receiver 25, and I3 shows the load resistor across which potentials are taken off to feed the plates 4 and 4. It will be observed in connection with Fig. 3 that if the voltage shown as a variable battery I2 is made zero, for example, true half-wave rectification takes place so that there will appear across the resistance I3 a voltage whose wave shape will consist of the positive half-cycles of a sinusoidal wave. If, however, the battery voltage is made equal to the peaked voltage of the alternating current supplied by the generator I0, then the wave shape across the resistor I 3 will be pulsating D. C. whose wave shape will be a true sinusoidal wave and whose negative peaks will now coincide with the zero axis. If the variable voltage I2 is now made negative and equal to the peaked voltage, then the resultant output across the resistor I3 will be zero since the superimposed D. C. leaves no voltage available for forcing current through the rectifier I I. It will thus be apparent that dependent upon the amplitude of the D. C., the spacing period,

as well as the amplitude, of the resulting voltage appearing across the resistor I3, will be determined. Thus we have, in efiect, a system which will produce interruptions of the cathode ray beam which are of constant frequency but of variable duration. This feature provides an improvement over my invention described in Patent No. 2,011,260, issued August 13, 1935, inasmuch as the individual marking period is not broken up into a number of discrete marking and individual periods occuring at the rate of the modulated radio frequency wave.

The variable D. C. potential has the purpose of varying the length of the periods during which the pulsating D. C. potential is of zero value. If the said pulsating D. C. potential, for instance, is equal to zero then the valve II will be permeable just during a half-period. If the potential is equal to the crest value of the A. C. potential supplied by the generator II], the valve, according to the polarity of the said D. C. becomes permeable either for the full period or else impermeable for the full period, while intermediately all values are between zero and the full period.

a It will be readily understood that even in the presenceof a pulsating D. C. potential, such as is illustrated by Figure 2a, of the generator II] the dependence of the blocking time upon the auxiliary potential becomes almost linear. A

strictly linear function is insured if the potential of the generator is not sinuous, but of triangular wave shape as is illustrated y F g e 20. The production of A. C. potential of any desired frequency having a triangular curve shape is fundamentally known in the prior art (see, for instance, Archiv fuer Elektrotechnik, vol. 21, Heft 5, page 471, 1929) If an arrangement as described is to be used for picture telegraphy work or for television then the variable potential I2 is derived from the long-distance line or the rectifier of the television receiver apparatus.

Referring now to Fig. 4, it will be readily appreciated that the bridge circuit shown is an actual embodiment of the schematic sketch of Fig. 3 in which the battery I5 represents the rectified output of the detected radio signal. The circuit arrangement shown in Fig. 4 is the converter 26 of Fig. l, and it will be appreciated that the lead 22 is connected to the plate 4 to produce the deflecting voltage for producing the picture on the screen I. The generator I4 is the local source of alternating current and maybe either sinusoidal or triangular, as explained above, and the resultant output between the grounded point of the bridge and the lead 22 will then have a wave shape shown in Fig. 2a or 2b, depending on whether the oscillator I4 produces a sinusoidal wave or a triangular wave.

Where high frequencies are being dealt with, it may become necessary to compensate the capacity of the valve II by means of a convenient circuit arrangement in order that the capacitive wattless current may not occasion an undesired potential during the blocking period. A scheme of this sort is shown in Figure 4 wherein numeral I4 denotes the A. C. generator, I5 the, variable auxiliary potential or the potential derived from the receiver, I6 the rectifier, such as a thermionic valve, and I! designates a condenser whose capacity is equal to the valve capacity; I8 and I9 are two equal, resistances, and 2B is a resistance which at one end is grounded by way of the potential source I5, while at the other end 22 there is produced a potential which is to be fed to the auxiliary deflector plate 4 of the tube shown by Figure 1. This arrangement constitutes for the capacitive wattless currents a Wheatstone bridge so that these currents will not contribute to the potential prevailing at point 22.

In lieu of a condenser I I it would also be feasible to use another valve having similar dimensions and characteristics to the valve I6. The scheme then represents a. rectifier arrangement in which both halves of the wave are used.

While the invention has been illustrated in only its preferred forms, it is, of course, to be understood that many changes and modifications will become apparent and suggest themselves to those skilled in the art to which the invention relates and I therefore believe myself to be entitled to make and use all modifications of the invention which fall fairly within the spirit and scope of the invention as defined by the hereinafter appended claims.

Having now disclosed my invention, what I claim and desire to secure by Letters Patent is the following:

1. The combination of a cathode ray device having deflecting electrodes and means for applying rectified deflecting potentials thereto comprising electrical network comprising the series combination of an alternating current source, a halfwave rectifier and a resistance element, and means for applying to the network a variable direct current voltage to control the zero period leg thereofand a capacity element for compensating forthe watt-less current flowing forming the fourth leg thereof, means forapplying'across one diagonal of the bridge structure an alternating current voltage of predetermined frequency,- and a series combination of a resistor and a variable direct current signaling voltage source forming the opposite diagonal, whereby the potential drop across the last named resistor due to the flowof current through the rectifier occurs for time periods variable in accordance with the strength of the direct current supplied from the direct current source serially connected therewith serving to modify the output energy from the rectifier.

3. The method of controlling the brilliance of electro-optical images produced upon the fluorescent end wall of a cathode ray tube which com- .prises generating a cathode ray, projecting the generated ray toward the fluorescent end wall of the tube, and deflecting the projected ray by rectified current potentials of zero value for a portion of the time of control proportional to the intensity of fluorescence to be represented to vary the intensity of the projected cathode ray stream reaching the said screen.

4. The method of controlling the brilliance of electro-optical images produced upon the fluorescent end wall of a cathode ray tube which comprises generating a cathode ray, projecting the generated ray toward the fluorescent end wall of the tube, and deflecting the projected ray by unidirectional potentials of a variable period of zero value control to vary the intensity of the projected cathode ray stream reaching the said screen.

5. The method of controlling the brilliance of electro-optical images produced upon the fluorescent end wall of a cathode ray tube which comprises generating a cathode ray, projecting the generated ray toward the fluorescent end wall of the tube, and deflecting the projected ray by unidirectional potentials of other than sinusoidal wave formation and having a zero value for variable time periods to vary the intensity of the projected cathode ray stream reaching the said screen.

6. In a television receiver device a cathode ray image reconstructing tube provided with a fluorescent screen, means for developing a cathode ray to produce the fluorescent efiects upon the screen and means to cause the fluorescent eflects to traverse the screen according to predetermined pattern, an apertured electrode within the tube through which the electrons are adapted to pass to the fluorescent screen, means for producing within the tube an electron beam deflecting electrostatic field changing in intensity from zero intensity toward a maximum to regulate the time period during which the cathode ray pencil passes through the aperture in accordance with the zero value of the deflecting electrostatic field, and rectifier means responsive to received signals to vary the zero period of the field to produce in accordance with the time period during which the deflecting field is of zero value varying degree of brilliance of the fluorescent efiects due to the impact of the cathode ray upon the screen.

7. In a cathode ray television system, a cathode-ray tube ccmprisinga source of cathode rays,

a fluorescent screen, an anode from which the generated electrons are projected toward the screen, an apertured electrode in the path of the projected electrons, a pair of deflecting plates intermediate the anode and the apertured electrode, rectifier means for supplying to the defleeting plates unilateral pulsating voltages of variable zero amplitude duration for varying in accordance with the field intensity produced thereby upon the deflecting electrodes the proportionate time period of each cycle of the alternating current during; which the cathode ray pencil passes through the aperture of the apertured electrode toward the fluorescent screen to vary thereby in accordance with the time of impact percycle of the deflecting-voltage the brilliance of the resulting fluorescent efiect, and a plurality of angularly disposed ray deflecting fields for causing the point of impact of the controlled cathode ray pencil to traverse according to a predetermined pattern substantially the entire area of the flucrescent screeen.

8. A system for producing control voltages for use in connection with a cathode ray tube having deflecting electrodes for controlling the cathode ray developed within the tube, which comprises a local source of alternating current energy of substantially constant frequency, a rectifying device connected with said source adapted normally to pass to its output circuit alternate half cycles of the generated alternating current, means controlled in accordance with received Signaling energy for applying to the rectifying device direct current voltages so as to vary in accordance with the amplitude thereof the time period per cycle of the alternating current energy during which the rectifier output remains at zero and electrical connections to supply the rectifier output energy to the deflecting electrodes to control the electron beam in accordance with said output energy.

9. The method of controlling the brilliance of electro-optical images produced upon the fluorescent end wall of a cathode ray tube which comprises generating a cathode ray, projecting the generated ray toward the fluorescent end wall of the tube, and deflecting the projected ray by undulating current potentials of zero value for a portion of the time of control proportional to the intensity of fluorescence to be represented to vary the intensity of the projected cathode ray stream reaching the said screen.

10. The method of controlling the brilliance of electro-optical images produced upon the fluorescent end wall of a cathode ray tube which comprises generating a cathode ray, projecting the generated ray toward the fluorescent end wall of the tube, and deflecting the projected ray by undulating current potentials of a variable zero value period of control to vary the intensity of the projected cathode ray stream reaching the said screen.

11. In a television receiver device a cathode ray image reconstructing tube provided with a fluorescent screen, means for developing a cathode ray to produce the fluorescent effects upon the screen and means to cause the fluorescent eflfects to traverse the screen according to predetermined pattern, an apertured electrode within the tube through which the electrons are adapted to pass to the fluorescent screen, means for producing within the tube an electron beam deflecting electrostatic field changing in intensity from zero intensity toward a maximum to regulate the time period during which the cathode ray pencil passes through the aperture in accordance with the zero value of the deflecting electrostatic field, and means responsive to received signals to vary the zero period of the field to produce in accordance withthetime period during which the deflecting field is of zero value varying degrees of brilliance of the fluorescent effects due to the impact of the cathode rayupon the screen.

- l 12. In a cathode ray television system, a cathode ray tube comprising a source of cathode rays,

a fluorescent screen, an anode from which the generated electrons are projected toward the screen, an apertured electrode in the path of the projected electrons, a pair of deflecting plates intermediate the anode and the apertured electrode, means for supplying to the deflecting plates voltagesof variable-amplitude and of varying time period of zero magnitude duration for vary- -ing in accordancewith the field intensity proto a predetermined pattern substantially the entire area of the fluorescent screen. DIETRICH PRINZ.

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