US2305930A

US2305930A - Television system

Info

Publication number: US2305930A
Application number: US372466A
Authority: US
Inventors: Ciro C Martinelli
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1940-12-31
Filing date: 1940-12-31
Publication date: 1942-12-22
Anticipated expiration: 1959-12-22

Description

i W42 c. c. MARTuNELLl 30,930

TELEVISION SYS-TEM Filed Dec. 51, 1940 Brwentor @iro @Marznlli Bg l 0 "m '.llEMESlIUN SYSTEM om o. Martinelli, oarlyn, N. r., assioito adio ilorporation oil erica, a corporation ol )Delaware Application Ueceniber 3l, i940, Serial No. 372,466

(Cl. litt-7.5)

6 Gla.

invention relates to improvements in television systems and more particularly to an improved method and apparatus for synchronizing a receiving station with a transmitting station.

lin television receiving systems of the general type including a cathode ray tube with horizont and vertical ray deecting coils, a. horizontal dedection system is used for causing a saw-tooth current wave at a desired line scanning ire-v uuency to pass through the horizontal ray denecting coils and a vertical deflection system is used iol: causing a saw-tooth current wave at the desired framing frequency to pass through the vertical deecting coils. For the purpose of synchronization, an oscillator is used to generate sharp voltage peaks whose frequency is locked in step with the operating action at the transmitting station by the transmission of synchroninng impulses which are caused to control the frequency of the oscillation circuit. Heretofore it has been customary to use such an oscillator for producing saw-tooth wave current in the horizontal ray deecting coils and another similar oscillator for producing a saw-tooth Wave current to pass through the vertical deection coils.

lin the design of television receivers, it is desirable to incorporate both horizontal and vertical deection oscillators within one envelope in order to reduce the number of tubes required. Noally there is enough plate-to-plate coupl within closely adjacent discharge devices to aect adversely the interlacing of the scanning.

According to this invention a single tube provig two discharge paths is utilized tov generate both the horizontal and vertical deflection signal and furthermore a circuit is provided whereby coupling between the two discharge devices is prevented.

The primary object of this invention is to provide an improved cathode ray deiiection system.

Another object of this invention is to include both the horizontal and vertical oscillator control paths in one envelope.

Still another object of this invention is to reduce the inter-electrode coupling effect of two closely adjacent oscillator circuits. i

Other and incidental objects ofthe invention will be apparent to those skilled in the art from the follow specification considered in connection with the accompanying drawing, in which the single gure of'the drawingV is a combination block and circuit diagram showing a preicrrcd iorm ol this invention.

Referring more particularly to the drawing, block l represents a television receiver, amplifier and detector which is adapted to receive a television signal including a video signal and synchronizing pulses. A portion of the output signal from the receiver and the amplifier and detector l is applied to a video amplifier 3 which amplies the picture signals of the composite television signals and applies them to the control electrode t of the picture tube l.

The picture tube 'l includes an electron gun comprising a heater element 9, a cathode element ll, a first anode i3, and a second anode It for producing an electron beam which is adapted to scan a screen it at the opposite end of the picture vtube l from the electron gun.

A. portion of the signal from the receiver l is applied to a synchronizing signal clippercircuit shown by block Il of the type, for example, which is described in Toison U. S. PatentNo. 2,207,839, issued July 16, 1940, to Radio Corporation of America.

The output signal from the synchronizing signal clipper is passed through a vertical synchronizing pulse filter circuit and channel I9 to the control electrode 2l in the left section of the tube 23 through series resistor 25 and series condensers 2l and 29.

The left section of the tube 23 also includes a cathode 3l and an anode 33. The anode 33 is supplied with a iixed positive potential and is bypassed to ground by a bypass condenser 35.

An inductance 3l has a terminal intermediate its two ends connected to the cathode 3|. One end of the inductance is connected tothe junction between the series condensers 21 and 29 and the other end of the inductance is connected through a potentiometer 39 to ground. Potentiometer 39 and condenser 4| form the circuit across which appears a sawtooth wave of voltage. The potentiometer controls the amplitude of voltage applied to the grid of the vertical deiiection amplifier t2.

The right section of the tube 23 includes a cathode t3, a control electrode t5, and an anode ill. The coupling between the control electrode t5 and anode tl isprovided by a transformer its having a winding 5| connected to the control electrode t5 through coupling condenser 53, 'Ihe winding 5I is also connected to a horizontal synchronizing pulse filter and channel represented by block 55. The horizontal synchronlzing pulse lter circuit receives its signal from :311160 lyhronzing Signal clipper represented by y coils t2 are energized through the horizontal defiection signal amplier '53.

When the receiver l is tuned to ythe desired television signal radio frequency, the video amplifier 3 applies a picture modulated signal 'tol the controlelectrode ii of the picture tube'l to modulate in intensity the electron beam which is generated by the associated lelectron gun.

A portion of the signal from the receiver i is which passes only that portion of the composite television signal including the horizontal andvertical synchronizing pulses. The output from the synchronizing pulse clipper l 'I is applied to the vertical synchronizingpulse lter circuit I9 which passes those synchronizing pulses which `are adapted to synchronize the scanning of theV electron beam ina vertical direction. The vertical synchronizing pulses are applied to the con- Itrol electrode 2l of -the lft section of the tube 23 to control the frequency of the oscillation of the circuit including the left section of the tube 23. The lnductance 31 provides the oscillating circuit with the feedback necessary to sustain oscillations by the 180 out of phase potential built up on the cathode 3| with respect to the control electrode 2|.

It will be noticed that the anode 33 is supplied with a constant positive voltage so that it may be considered to have a zero alternating current voltage potential. It is therefore necessary to cause the cathode 3i to vary in potential in accordance with the Wave shape and frequency of the voltage which it is desi-red to produce. -The 'coupling provided by the inductance 31 and its natural frequency is adjusted so that the oscillating circuit would oscillate freely at a frequency slightly below thatA of the incoming synchronizing pulses and the synchronizing pulses provide a trip eilect on the oscillator circuit each time these pulses are allowed to disturb lthe oscillation circuit.

The resulting voltage produced in the inductance 31 is applied across the potentiometer 33 vapplied to the synchronizing signal clipper Il The frequency at which the vertical `deflection voltage generator will oscillate without any synchronizing signal may be adjusted by varying lthe resistance of the variable resistance 63. The frequencyat which the horizontal deflection voltage generator will operate may be adjusted by varying the resistor 35 connected between the control electrode 33 and the cathode i3 of the right section of the tube 23 or by changing the resistance of the variable resistance 53 in the anode supply voltage source of the right section ofthe tube 23.

The image size control may be controlled in a vertical direction by varying the variable tap on resistance 33 which in effect varies the amount of saw-tooth wave current applied to the vertical deiiecting coil 6|. A similar adjustment is provided for adjusting the image size control in the horizontal direction by the variation of the resistance 59 and the anode voltage supply circuit of the horizontal deilection voltage generator. Any change in the fundamental frequency of the whole horizontal deflection voltage generator caused by the change of the resistor 39 in the adjustment ofthe size control may be compensated for by causing a corresponding change in the resistance 35.

It will be noticed that the left-hand section of the-tube 23 is operated such that its anode is at ground potential and the anode` of the right-hand section of the tube 23 is operated with its anode at high alternating current potential. Each oscillator circuit also contains its own electron discharge path so that one tube such as the 6C8G is all that is required to produce both horizontal and vertical deflection voltages and satisfactory interlacing may be obtained because of the fact that the grounding of the anode 33 of the left sectionof the tube 23 with respect to the alternating current voltage the anode 33 acts as a shield between the left and the right-hand sections of the tube 23 whereby there is no coupling between the two oscillating circuits. The grounding of the anode 33 forms an eective shield between the anode M winch is varying at an alternating current potential and the control electrode 2l and cathode 3i of the vertical oscillator section of 4the tube 23. Furthermore, the cathode of the horizontal oscillator or right-hand section of the tube 23 is at ground potential while the cathode which containsfa variable tap connected and adapted to cause a current -to iiow through the vertical deflecting coils 6I in such a manner as to cause the electron beam to be deflected at the predetermined scanning frequency.

The horizontal synchronizing pulses from the synchronizing pulse clipper il are applied to an oscillator circuit including the right hand section of the tube 23. For .the purpose of illustration. the circuit described ltaires a slightly different form than the circuit for the vertical syn' chronizing voltage generator. In the case of the horizontal deflection voltage generator the necessary coupling between the control electrode i3 and the anode 41 produce sustained oscillations as provided by the transformer 49 having one of its windings 5i in series with the synchronizing puise source andthe control electrode i3 whereby the oscillator including the right-hand section of the tube 23 is tripped in accordancevwith the frequency of the incoming horizontal synchronizing pulses.

of the vertical oscillator or left-hand section of the tube 23 is at a high alternating current potential. 'I'his prevents vcoupling in the cathode leads between the two oscillating circuits. There would otherwise be considerable coupling between the cathode leads which come out of the same end of the tube' 23. Since the control electrodes of the 6C8-G2 come out at opposite ends oi the tube envelope, external coupling between the control electrodes 2| and 35 can easily be eliminated.

While a preferred system for carrying this invention into effect has been indicated and def scribed, it will be apparent to one skilled in the art that this invention is by no means limited to the particular organization shown and described but that many modications may be made without departing, from the scope of this invention as set forthin the appended claims.

I claim as my invention:

l. In a television system including. an electron ray scanning device, the combination of an envelope having means therein to develop a. plurality of separate electron discharge paths. each of g between said discharge paths is eliminated.

2. In a television system including an electron ray scanning device, the combination of an envelope having means therein to develop a plurality of separate electron discharge paths, each of said means containing a cathode, an anode and a control electrode, each of said means adapted to control the scanning of said electron ray in one of two directions, means for applying to one of said discharge paths a synchronizing signal representative of a predetermined rate of scanning in one direction, means l'or applying to the other of said discharge paths a synchronizing si representative of a predetermined rate ofscanning in another directionand wherein the potential of the anode associated with one of said discharge pathsand the cathode associated with the other of said discharge paths is maintained substantially constant. Y

3. In a television system including an electron ray scanning device, the combination of an en-` sc in another direction, and means for maintaining constant the difference in potential between the cathode associated with one of said discharge paths and the anode of another of the said discharge paths.

4. .An oscillation generator including an electron discharge device comprising an evacuated envelope containing a plurality of separate electron sources and a plurality of electrodes toward which said electrons from said separate sources are directed in separate paths, andv means for maintaining substantially constant the difference in potential between the electron source of one of said paths and the electrode toward which the electrons in another of said paths are directed whereby said separate electron paths are shielded one from another.

5. An` oscillationgenerator including an electron discharge device comprising an evacuated envelope containing a plurality of separate electron sources and a plurality of electrodes toward which said electrons from said separate sources are directed in separate paths, and means for maintaining the electrode associated with one of said electron paths, and the electron source of the other of said electron paths at fixed potentials."

6. In a television system including an electron ray scanning device, a. scanning signal generator comprising an envelope having means therein to develop a plurality of separate electron discharge paths, each of said means containing a cathode, and an anode and means for maintaining the potential of the anode associaiedllwith one of said discharge paths and the cathode associated with thenther of said discharge paths substantially constant.

' CIRO C;