US2093395A

US2093395A - Television system

Info

Publication number: US2093395A
Application number: US584943A
Authority: US
Inventors: Randall C Ballard
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1932-01-06
Filing date: 1932-01-06
Publication date: 1937-09-14
Anticipated expiration: 1954-09-14
Also published as: GB394597A; DE620174C

Description

Sept. 14, 1937. R, BALLARD 2,093,395

TELEVISION SYSTEM Filed Jan. 6, 1932 mul JNVENTOR. Rand all C. E) cLLlcand= /S A TTORNE Patented Sept. 14, 193

TELEVISION SYSTEM Randall C. Ballard, Merchantville, N. J., assignor to-Radio Corporation of America, a corporation of Delaware Application January 6,

6 Claims.

sub-multiple of the frequency of horizontal deection of the ray.

In television systems of the character referred to, it is essential, for satisfactory operation, that vthe frequency of vertical deection of the cathode ray remain fixed at a definite sub-multiple of the frequency of horizontal deection of the ray. In the various systemsproposed heretofore for this purpose, and wherein the action has been such as to provide for about twenty frames a second, each having about 120 lines or, in other Words, wherein conditions have been such as to provide for about 2400 picture lines a second, diiiiculty has been experienced in the Way of maintaining the vertical deflection system in .synchronism with the horizontal defiection system. In these systems, frequentvadjustments are necessary to maintain this synchronism. With the advent of present developments tending to- 25 for which purpose the number of picture lines per second has been greatly increased, that is, to at least 4000 lines a second, the diiculty referred to above has been found to be still more troublesome. This is due to the fact that at these lvery high picture-line frequencies necessary, for example, to obtain 24 frames a second each of which has 180 picture lines, the various adjustments for synchronism in the systems proposed heretofore are relatively critical and, therefore, difficult to control.

With the foregoing in mind, it is one of the objects of my invention to provide an improved television system in which the picture-line frequency may be as high as desired, for example, 4000 cycles, the action being such that the frequency of vertical deflection of the cathode ray `is easily and positively maintained at a definite desired vsub-multiple of the frequency of horir zontal deflection of the ray.

Other objects and advantages will hereinafter appear.

In accordance with my invention, a cathode ray is deflected horizontally by electromagnetic U0 coils connected to a generator of a saw-tooth current wave at the horizontal-deflection fre quency, and the ray is deflected vertically by electromagnetic coils connected to a generator r of a current Wave at the framing frequency,

"" these two frequencies providing for at least 4000 ward better detail of picture reproduction, andA 1932, Serial No. 584,943V

picture lines. The two generators are maintained in synchronism'with respect to each other by means of a frequency divider constituted by a single electrical circuit having at its input end an oscillator operating at the horizontal-deflection frequency, and developing at its output end i synchronizing impulses which are supplied to and drive the generators. The connections and adjustments are such that the frequency of the synchronizing impulses supplied to the verticaldeection generator are always a definite, desired sub-multiple of the frequency of those supplied to the horizontal-deiection generator.

Further, in accordance with my invention, the condition of synchronism referred to is maintained by utilizing a suitable oscillator operat` ing at the desired picture-line /frequency and which is caused to drive a series of the so-called blocking oscillators, each of which develops impulses at a frequency which is a definite submultiple of the frequency of those developed by the preceding blocking oscillator.

My invention resides in the improved system and method of operation of the character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in thedrawing', wherein Figure 1 is a diagrammatic View of a television transmitting systeml embodying my invention; and

Figs. 2 and 3 are graphs illustrative of the principle of operation in Fig. 1.

With reference'to Fig. l, the numeral l0 designates a cathode ray transmitting tube of the general type described in the co-pending applications of Vladimir K. Zworykin, bearing Serial Nos. 468,610 and 574,772, and filed July 17', 1930 and November 13, 1931, respectively. A suitable generator or deecting circuit I2 operates to cause a saw-tooth current Wave, at a frequency of 4320 cycles, to pass through electromagnetic coils Ill for delecting the cathode stream or ray I6 horizontally at this frequency. A second suitable generator or deflecting circuit I8 operates to cause a saw-tooth current Wave at a frequency of 24 cycles to pass through electromagnetic coils 20 for deflecting the Aray vertically at this frequency. For the purpose of developing picture signals, the deecting coils i4 and 20 cause the ray to-scan a target in the form of a 'suitable photo-sensitive mosaic structure 22, onto which is projected an image of the object, such as a moving picture film 24 interposed between a light source 26 and the tube I0.

indicated by the line d3.

The picture signals or impulses are supplied by a connection 23 to a suitable radio transmitter 30.

The generators i2 and i8 may be of the general type described in detail in the co-pending application by Arthur W. Vance, Serial No. 544,959, filed June 17, 1931. Each of these generators, as is well known, is adjusted to have a normal frequency of operation substantially equal to the desired frequency, and are driven or caused to lock in step at the desired frequency by synchronizing impulses occurring at the latter frequency.

The means for developing these synchronizing impulses at the respective desired frequencies will now be described. Such means is constituted by the single electrical circuit designated generally by the referencey character A. This circuit has at its input end a suitable oscillator, suchA as a dynatron oscillator 32 adjusted to operate at a frequency of 4320 cycles to develop in its plate circuit a sine wave at this frequency.

Connected to the plate circuit of the oscillator 32 is a relaxation oscillator tube 34 having its grid and plate circuits inductively coupled by the transformer windings 36 and 38. The polarities of these windings are such that when the plate begins to draw current, the grid of the tube is made more positive and, likewise, as the plate current decreases, the grid potential becomes more negative. A condenser i and a resistance l2 are connected as shown in the grid circuit. In operation, when the negative potential on the grid decreases to the level indicated by the .broken line ill in Fig. 2, whereat the grid is biased to cut-off, the plate begins to draw current. By reason of the polarities of the transformer windings 36 and 38, the grid potential rises rapidly toI the point of saturation and then decreases to a. point Il@ below the cut-off level. This action is attributed to the storing up of an electrostatic charge in the condenser 40 during the time ti, t2, so that at the end of the impulse the negative potential on the grid is at the point d6 below cut-01T. The Value of the resistance i2 is suficiently high to permit only a relatively gradual leakage of the negative charge on the grid, as The capacity of the condenser 40 and the value of the resistance l2 are such that only a single impulse develops in the grid circuit, the time ti, t3 being equal to the period for one cycle of operation of the oscillator 32. These Values, furthermore, are such that. at the time t3 the charge in the condenser l0 will have leaked off by Way of the resistance i2 to a point 50 slightly removed from the point 52 whereat the plate will again begin to draw current. At the time t3 the next voscillation of the oscillator 32 is effective to decrease the negative grid potential from the point 50 to or slightly beyond the point 52. From the foregoing, it will be seen that single sharp impulses are developed in the grid circuit of the tube 34 at the frequency of oscillation of the oscillator 32.' There will, therefore, be developed in the plate circuit similar sharp impulses 5G, as indicated in Fig. 3, at this same frequency, that is, 4320 cycles. By adjusting the resistor 56, the level of the impulses supplied by the oscillator 32 may beladjusted to the point whereat each oscillation is,I effective at the time t3 to' decrease the negative potential on the grid of the tube 34 from the point to or slightly beyond the point 52. A.

tube connected and adjusted to operate in the manner just explained in connection with, the

aooset tube 3d is commonly referred to as a blocking oscillator, and Where this term is used in the specification and claims, it is intended to embrace a thermionic device which, while resembling a thermionic oscillator, is permitted to oscillate only once along a sharp wave during each operating cycle, this being due to the blocking action provided by the condenser l0 and the resistance d2. The theory of operation of a, blocking oscillator of this type is discussed in greater detail in the co-pending application by W. A. Tolson and J. R. Duncan, bearing Serial No. 595,484, and led Feb. 27, 1932.

A second relaxation oscillator tube 5l, which operates in the same manner as tube 34, has its grid circuit inductively coupled to the plate circuit of the latter by the transformer winding 59. The voltage impulses in a resistor 60, and which occur at the frequency of oscillation of the oscillator 32, are impressed on the grid circuit of tube 5l. The resistor 60 is adjusted to bring the level of these impulses to a point whereat only every sixth impulse is effective at the time t3 to start the tube 5l on a new cycle of operation. The impulses in the resistor 02 will, therefore, occur at a frequency one-sixth that of the frequency of the impulses in the resistor 90, that is, the impulses in the resistor 62 will occur at the rate of 720 a second.

A third relaxation oscillator tube 0G is also connected and adjusted to operate in the same manner as the tubes 34 and 5l. The resistor t2 is adjusted to bring the level of the impulses applied to the grid circuit of the tube tl to a point whereat every sixth impulse is effective at i" the time t3 to start the tube @il on a new cycle of operation. The impulses in the resistor B will, therefore, occur at the rate of a second, and these are applied to a fourth relaxation oscillator tube 63 which also operates in the same manner as the tubes 3d, 5l and Btl. The adjustment of the resistor 66 is such that every fifth impulse in this resistor is effective to drive the tube 69 at the time t3. There will, therefore, occur in a resistor 'l0 connected as shown across the condenser 'l2 and the resistance lli, impulses at 24 cycles. The impulses at 24 cycles are amplied by a suitable tube 'i6 and appear, in a resistor 'i8 connected in the plate circuit of tube llt, as amplied negative impulses at 24 cycles.

The impulses at 4320 cycles in the resistor 60 are supplied by a connection 8@ to a resistor 82 connected in the grid circuit of a suitable amplifier tube 84 connected in parallel to the tube i6. These impulses are amplified and appear in the resistor 718 as amplied negative impulses at 4320 cycles. By adjusting the resistors l0 and 82, the respective levels of the synchronizing impulses at the two frequencies may be adjusted as desired. These impulses are applied to the generators i2 and i8 by av connection 86. The adjustment of the resistor 32 is such that the synchronizing impulses at 4320 cycles are effective to drive the generator i2, but are not of sucient amplitude to drive the generator i8.

The supply voltages for the various tubes are taken from a supply line 88.

A suitable lter circuit, comprising a condenser 90 and a resistance 92, may be connected between the supply line 88 and the common ground connection 94.

It is proposed to transmit the synchronizing impulses at the two frequencies, for utilization at the receiving station, by impressing the same On the grid circuit of a suitable stage in the transmitter 30, for which purpose a connection 96 is shown.

From the foregoing, itwill be seen that I have provided an improved television system embodying a cathode ray tube wherein the frequency of vertical defiection of the ray is always a definite sub-multiple of the frequency of horizontal deflection of the ray, and that by reason of the connections. and arrangements, synchronization can be easily and positively maintained.

While but one embodiment;v of my invention has been disclosed, it will be understood that various modifications within the conception of those skilled in the art may be adopted without departing from the spirit of my invention or the scope of the claims.

I claim as my invention:

Y1. InY a te1evisiontr'ansmitter of the type including a cathode ray transmitter tube and horizontal and vertical deflecting means therefor, al

generator of synchronizing impulses comprising means for producing voltage impulsesy occurring at a rate at least equal to the frequency at which it is desired to produce the horizontal deflection of the cathode ray, a generator of sawtooth waves coupled to said horizontal deflecting means, means for applying said voltage impulses to said generator and thereby producing said horizontal deflection under the control of said voltage impulses, means'for deriving from said voltage impulses other voltage impulses occurring at a frequency at which it is desired to produce the vertical deflection, of the cathode ray and which is a sub-multiple of the frequency' at which said first voltage impulses occur, a generator of sawtooth Waves coupled to said vertical defiecting means, and means for applying said other voltage impulses to said second-named generator and thereby producing said vertical deflection under the control of said other voltage impulses.

y2. The invention according to claim l characterized in that the means for deriving said other voltage impulses comprises a plurality of relaxation oscillators of the blocking oscillator type connected in cascade.

3. The method of controlling the scanning action of an electron stream in a cathode ray tube having horizontal and vertical scanning means which are coupled to a generator of sawtooth Waves occurring at a comparatively high frequency and to a generator of saw-tooth Waves occurring at a comparatively low frequency, respectively, which comprises generating electrical impulses at a frequency corresponding to the desired horizontal scanning frequency, deriving other electrical impulses from said first impulses at a frequency which is a sub-multiple thereof to control the vertical scanning, applying said first impulses to said first saw-tooth wave generator and applying said other .impulses to said second saw-tooth wave generator whereby the horizontal defiection frequency always bears a definite relation to the vertical deflection frequency irrespective of changes in the potential supply sources associated with the system.

4. In combination, a sine wave oscillator adjusted to oscillate4 at a certain frequency, a blocking oscillator coupled to said sine wave oscillator and adjusted to produce sharp voltage impulses occurring at said frequency, means for supplying said voltage impulses to a utilization device, means for deriving from said voltage impulses other voltage impulses occurring at a frequency which is a sub-multiple ofsaid certain frequency, and means for supplying said other voltage irnpulses to a utilization device.

5. In combination,'a dynatron oscillator adjusted to oscillate at a certain frequency, a blocking oscillator coupled to said dynatron oscillator and adjusted to produce sharp voltage impulses occurring at said frequency, means. for supplying said voltage impulses to a utilization device, means for deriving from said voltage impulses other voltage impulses occurring at a frequency which is a sub-multiple of said certain frequency, and means for supplying said other voltage impulses t-o a utilization device.

6. In a television transmitter, the method of controlling the scanning action of an electron stream in a cathode ray transmitter tube having horizontal and vertical deiiecting means therefor which are coupled to a generator of saw-tooth waves occurring at a comparatively high frequency and to a generator of saw-tooth waves occurring at a comparatively low frequency, respectively, which comprises producing voltage impulses occurring at a rate at least as high as the frequency at which it is desired to produce the horizontal deflection of the cathode ray, deriving from said voltage impulses other voltage impulses occurring'at a' frequency at which it is desired to produce the horizontal deflection of the cathode ray, applying said derived impulses to the saw-tooth wave generator which is coupled to said horizontal deflecting means and thereby producing said horizontal deflection under the control of said derived impulses, deriving from said first voltage impulses other voltage impulses occurring at a frequency at which it is desired to produce the vertical deflections of the cathode ray and which is a sub-multiple of the frequency at which the first voltage impulses occur, applying the last mentioned derived impulses to the saw-tooth wave generator which is coupled to said vertical deflecting means and thereby producing said vertical deflection under the control of the last-mentioned derived impulses.

RANDALL C. BALLARD.