US2512400A

US2512400A - Television horizontal deflection

Info

Publication number: US2512400A
Application number: US50302A
Authority: US
Inventors: Karl R Wendt
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1948-09-21
Filing date: 1948-09-21
Publication date: 1950-06-20
Anticipated expiration: 1967-06-20
Also published as: GB664216A; BE491135A; NL148552C; FR994278A

Description

June 20, 1950 DT 2,512,400

TELEVISION HORIZONTAL DEFLECTION Filed Sept. 21, 1948 IENTOR j f l s Patentecl June 20, 1950 ATENT OF C TELEVISION HORIZONTAL DEFLECTION Karl E. Wendt, Hightstown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application September 21, 1948, SerialNo. 50,302

This invention relates to wave forming systems and more particularly to television horizontal or line deflection systems.

Television horizontal magnetic deflection circuits normally employ high vacuum type tubes to generate the sawtooth wave currents required for deflection of the cathode ray beam used in the image scanning operation; Because of the possible gain in efficiency in such magnetic generators employed in television systems, attempts have often been made to use gas discharge tubes, such as those known in the art as thyr-atrons. However, the de-ionization time of thyratrons makes such tubes practically inoperative when used in conventional television horizontal deflection circuits.

In my co-pending United States application entitled D. C. Transfer Systems, Serial No. 730,852, filed February 25, 1947, there is shown and described a method and means whereby the grid controlled thyratron may be made to conduct during the short or retrace interval when an arbitrary conduction wave may be used, and the energy then stored may be utilized during the entire long or traced interval to produce the desired wave shape. In my co-pending application referred to immediately above, there is also provided current and voltage wave shapes during the retrace or short interval such that properconditions are established for the de-ionization of the thyratron immediately following the conduction interval, thus taking advantage of the large short-time currents available from the thyratron and allowing the de-ionization to take place during the longer trace interval when it will not interfere with the desired circuit operations.

According to this invention there is provided a circuit arrangement utilizing an auto-transformer to obtain voltage gain and there is provided an arrangement whereby the grid controlled thyratron may be made to conduct during the short or retrace interval when an arbitrary conduction wave shape can be tolerated.

The primary object of this invention is to provide for improved and more efficient television horizontal or line magnetic deflection.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing which illustrates schematically one form of this invention.

The operation of this invention may perhaps best be explained by referring briefly to sawtooth wave forming theory. v v

9 Claims. (01.315-27) If a D. C. potential is connected across an inductance, the current in the conductor builds up to a final value which is determined by the D. C. input voltage and the D. C. resistance value of the inductance. The build-up of current is gradual because of the counter-E. M. F. generated by the inductance. Immediately upon the starting of the flow of current through the inductance, magnetic lines of force move out, cutting the turns of wire in the inductance, building up a counter-E; M. F. which is opposed to the E. M. F. of the D. C. source. This opposition causes a delay in the time it takes the current through the inductance to build up to a maximum and uniform value. When the source of power is disconnected, the lines of force about the inductance collapse again cutting the turns of the inductance and building up an E. M. F. which tends to prolong the current flow to the inductance. This action causes the sawtooth wave which is utilized in the scanning operation.

It is upon this basic theory that the present invention operates.

Turning now in detail to the drawing there is shown acathode ray tube l which may, for example; take the form of the well-known kinescope with magnetic type deflection accomplished through vertical deflecting coils 3 and horizontal deflecting coils 5.

Details of construction and operation of tube l are not given here in view of the fact that the employment of this invention is not particularly limited to any specific form thereof. Typical kinescopes are well shown and described in the television art.

The switching or keying which is necessary to provide sawtooth waves is accomplished in driver tube 1 which, as illustrated, takes the form of a gas discharge device such as a thyratron which includes a control electrode 9 and an auxiliary electrode I l. Inthev operation of a thyratron the control electrode 9 is adapted to receive synchronizing pulses.

An auto-transformer l3 includes a terminal l5 which is'common to both the primary and secondary of theauto-transformer 13. There is also included an uncommon terminal H which is connected to the anode of tube 1. A second uncommon terminal [9 is connected through a condenser 2| to a diode 23. p

A parallel connected circuit including resistance 25 and capacity 21 is connected to terminal [5 of the auto-transformer l3 and the cathode of diode 23.

c Thyratron tube 1 is supplied with an operating anode potential through the primary of autotransformer I3 and through the resistance capacity circuit from terminal 29 to which there is applied a positive potential of the order, for example, of 300 volts.

A circuit output terminal is also provided at the junction of condenser 2| and the anode of diode 23. connected'as illustrated to the horizontal deflection coils of kinescope l. The other terminal of deflection coils 5 is connected to a point of fixed potential such as ground, through acondenser-3h The choke coil 33 having a high inductance value as compared to the inductanceof the de fiection coils 5 is connected between the sourceof positive potential at terminal 29 and the junction between condenser 2! and tli'ezanode of;diode 23'i.v

Among its other functions choke coil 33 permits centering of the scanning beam without resorting to auxiliary circuit arrangements to compensate for thedirect current componentflovving in the circuit from power supply terminal 29 The operation of the circuit shown in the-drawing may best be explained by considering the driver tube 7 and the diode'23 as switches; For the purpose of the description of the operation ofthe circuit let it be assumed that no power has been supplied to the circuit and'that for the initial part of this explanation none of the condensers of the circuit contain a charge.

Assume now that a supply voltage' of 300 volts is applied to terminal 29 and positivesnychronizing pulses are applied to control electrode 9 of the thyratron or driver tube 1.

Upon application of a positive synchronizing pulse to control electrode 9 of driver tube 1, tube 7 becomes conducting, driving point I! of transformer l3 to the ionization potential of tube 1 which is very close to ground potential. This drop in potential at point IT causes terminal IQ of auto-transformer I3 to go to a negative potential and extinguish tube 1. In view of the fact that diode 23 will be non-conducting when its anode is negative with respect to its associated cathode, a surge of current will be'formed" in the choke coil 33 and the deflecting coils-5. By reason of this surge of current in the induc tances of coils 33 and 5, energy will be stored therein which, in accordance with the well known fundamental theory of inductances, will'oscillate to cause on the other half of its cycle a-highly positive voltage on anode of diode 23. This'positive voltage on the anode of diode 23 will cause diode 23 to become conductive and a rectified this is not the case because of the actiontaking It is; of course, true" that the driver tube T does tend to draw current 70 place as described above.

from the circuit involving condensed; 21; The quantity of current drawn fromthis circuit in this. manner is, however, small as compared'to;

the current drawn through the circuitincludin'g' the, inductance 33. I

Now that condenser 21 has receivedits-charge This circuit output terminal may: be.

as illustrated, the normal operation of the circuit will be explained.

Upon the application of a positive synchronizing pulse to control electrode 9 of driver tube 1, terminal H, as has been explained above, will be dropped in potential to substantially ground potential. It follows then that the anode of diode 23 -wi1l be drivennegative to open thediode 23 thus causing the magnetic field in choke coil 33 and deflection coils 5 to collapse. This collapsing corrresponds to the short retrace time in the scanning cycle. The flywheel effect in the inductance of transformer l3 will cause point I1 tocontinue passground potential in a negative direction" to' extinguish the driver tube 1. Terminal I9willthen in its oscillation return to a positive potential and cause diode 23 to conduct by reason of the fact that the anode of diode 23" exceeds in a positive direction the potential of its associated cathode.

During the time that-diode 23 isconducting a substantially constant direct current potential which is stored in the condenser 21' will be impressed across the choke coil 33 and the deflection coils '5', to cause a linear deflection of the cathode ray beamv in accordance with well known sawtooth wave forming characteristics of an inductance. 1

Atthe arrival of the next positive synchronizing pulse, the driver tube 1 is againmade conducting and'the cycle repeats.

The difficulty in extinguishinggas tube 1 may beovercome by increasing the time duringwhich its anodeis negative with respect to its cathode. In the circuit shown this may beaccomplished by constructing auto-transformer I3- in such amanner that it has leakage inductance-or adding a small inductance between terminal I! and the anode of the driver tube.

It will be seen that the source of positive voltagemay'be applied to common terminal [5 of auto-transformer l3, but-by including the circuit consisting of condenser: 2'! and resistor 25' in the anode supply circuit of tube 1, an invision systems, its operation in that regard-pro-- vides for improvedand more efficient deflection.

What isclaimed is: 1. A sawtoothwave generator comprising, in combination, a transformer havin an input and output circuit, said transformer also having a terminal connected common to said input and output circuits, an uncommon terminal for said input circuit and an uncommon terminal for said'output circuit, a switching device connected between said uncommon input-terminal and a point. of

cuit; a condensernconnected to the uncommon output terminal of said transformer, a diode tube havinga cathode, said diode connected between said common terminal 'of said transformer andsaid condenser terminal opposite to the-termifixed potential, saidswitching device consisting nal connected to said uncommon output terminal, the cathode of said diode being connected to said common terminal, a choke coil connected between said source of positive potential and the junction of said condenser and diode tube, a circuit output terminal at the junction of said condenser and diode tube, and means for closing said switching device periodically for relatively small time intervals.

2. A sawtooth wave generator comprising, in combination, an auto-transformer having an input and output circuit, said auto-transformer also having a terminal common to said input and output circuits, an uncommon terminal for said input circuit, and an uncommon terminal for said output circuit, a thermionic switching device connected between said uncommon input terminal and a point of fixed potential, a, parallel connected resistance and capacity circuit, a source of potential positive with respect to said fixed potential connected to said common terminal through said parallel connected resistance and capacity circuit, a condenser connected to the uncommon output terminal of said transformer, a diode tube having a cathode, said diode connected between said common terminal of said auto-transformer and the terminal of said condenser opposite to the terminal connected to said uncommon output terminal, said diode cathode connected to said common terminal, a choke coil connected between said source of positive potential and the junction of said condenser and diode tube and a cathode ray tube deflection coil, said cathode ray tube deflection coil connected serially with a second condenser, said serially connected deflection coil and second condenser connected between a point of fixed potential and the junction of said condenser and diode tube, and means for closing said switching device during the snap-back time of the sawtooth wave.

3. A sawtooth wave generator comprising, in combination, an auto-transformer having an input and output circuit, said auto-transformer also having a terminal common to said input and output circuits, an uncommon terminal for said input circuit, and an uncommon terminal for said output circuit, said auto-transformer having a step-up turn ratio between its primary and secondary circuits, a gaseous discharge tube switching device connected between said uncommon input terminal and a point of fixed potential, a parallel connected resistance and capacity circuit, a source of potential positive with respect to said fixed potential connected to said common terminal through said parallel connected resistance and capacity circuit, a diode having a cathode and an anode, a condenser connecting said diode and said common terminal of said auto-transformer, said diode cathode connected to said common terminal, a choke coil connected between said source of positive potential and the junction of said condenser and diode and a cathode ray tube deflection coil, said cathode ray tube deflection coil connected serially with a second condenser, said serially connected deflection coil and second condenser connected between a point of fixed potential and the junction of said condenser and diode, and means for closing said switching device periodically for relatively small time intervals.

4. A sawtooth wave generator comprising, in combination, an auto-transformer having an input and output circuit, said auto-transformer also having a terminal common to said input and output circuits, an uncommon terminal for said input circuit, and an uncommon terminal for said i output circuit, said auto-transformer having a step-up turn ratio between its primary and secondary circuits, a switching device connected between said uncommon input terminal and a point of fixed potential, said switching device consisting of a gaseous discharge tube, a parallel connected resistance and capacity circuit, a source of positive potential connected to said common terminal through said parallel connected resistance and capacity circuit, one terminal of a condenser connected to the uncommon output terminal of said transformer, a diode connected between said common terminal of said auto-transformer and the other terminal of said condenser, a choke coil connected between said source of positive potential and the junction of said con denser and diode, a cathode ray tube deflection coil, said cathode ray tube deflection coil connected serially with a second condenser, said serially connected deflection coil and second condenser connected between a point of fixed potential, and the junction of said condenser and diode, and a source of synchronizing pulses for initiating the conduction of said gaseous discharge tube at the end of the long trace of the sawtooth wave.

5. A sawtooth wave generator comprising, in combination, an auto-transformer having an input and output circuit, said auto-transformer also having a terminal common to said input and output circuits, an uncommon terminal for said input circuit and an uncommon terminal for said output circuit, said auto-transformer having a step-up turn ratio between its primary and secondary circuits, a discharge switching device connected between said uncommon input terminal and a point of fixed potential, said switching device consisting of a gaseous discharge tube,

means for periodically firing said gaseous discharge tube, a parallel connected resistance and capacity circuit, a source of potential positive with respect to said fixed potential connected to said common terminal through said parallel connected resistance and capacity circuit, a diode having an anode, a condenser connected between said uncommon output terminal of said autotransformer and said diode anode, a choke coil connected between said source of positive potential and the junction of said condenser and diode, and a cathode ray tube deflection coil, said cathode ray tube deflection coil connected serially with a second condenser, said serially connected deflection coil and second condenser connected between a point of fixed potential and the junction of said condenser and diode.

6. A sawtooth wave generator comprising, in combination, an auto-transformer having an input and output circuit, said auto-transformer also having a terminal common to said input and output circuits, an uncommon terminal for said input circuit, and an uncommon terminal for said output circuit, said auto-transformer having a step-up turn ratio between its primary and secondary circuits, a thyratron switching device connected between said uncommon input terminal and a point of fixed potential, said switching device consisting of a gaseous discharge tube, a control electrode in said gaseous discharge tube for firing said gaseous discharge tube periodically, a parallel connected resistance and capacity circuit, a source of potential positive with respect to said fixed potential connected to said common terminal through said parallel' connected resistance and capacity: circuit;. 5;; condenser connected:- to: the uncommon. output: terminal @of: said"v transformer; a: diodezconnected. between: said common terminal. ofi said auto-- transformer: and! said i condenser terminal oppo-c site: that connected. to the-uncommon output: terminal :of the auto-transformer; thecathode of said diode. connected to said transformer come monflterminal, a choke coil connected: between. said source of positive: potential? and; the-ijunce tion' of: said condenser and: diode and a cathode: ray. tube"- deflection. coil, said cathode: ray' tube deflection coil connected. serially with; a second condenser; said serially. connected deflection coil; andsecond condenser connected between :a point. of fixed'potential:and:.the'junction ofwsaid con-'- denser and diode.

'7.- A? sawtooth Wave. generator comprising, in combination, anzauto-transformer having; an input and: output circuit, said? auto-transformeralso having aterminalcommon to said-input andoutput; circuits; arr-uncommon terminalfor said input circuit,. and. an: uncommon terminal for; said output: circuit, c said auto-transformer have ingia step up. turn. ratio ibetweenits primary and: secondary circuits, an electron discharge sWitch ing device connected between said; uncommon input terminal and a point of fixed potential, said switchingdevice consisting of .a gaseous discharge tube, means for firing said gaseousdischargetube periodically and at the beginning oi the snap backtimeinterval of the sawtooth. wave, a-parallel connected resistance and capacity circuit, a-source of potential positive-with re! spect to'said. fixedpotentialconnected to said. common'terminal through saidparallel connected resistance andcapacity circuit, acondenser connectedxto the'uncommon output. terminal of. said transformcr, a diode having a cathode, said diode connected between said common terminal of said auto-transformer and said". condenser and havingits anode connected to .the condenser terminalopposite that connected to the uncommon output terminal of-.tlie auto-transformer, the cathode of said .diode connected to said" transformer common terminal, a choke coil con; nected betweensaid source of positive potential" and the junctionof said' condenser'and" diode, anda cathode ray tube deflection coilpsaidcathode ray. tube defiec'tioncoil' connected serially with a secondf'con'denser, s'aidiserially connect: ed deflection ,coilland second condenser connected between a point of fi'xedpotential andthe junction of said condenser and diode.

8.-A.sawtooth wave generator comprising; in combination, an auto-transformer having a-n' in put and output circuit, said aut'o transformer also having a terminal common to said input and output circuits, an uncommon terminal for "said" input circuit, and an uncommon terminal forsaid output circuit; said auto-transformer having a step-up turn ratio between itsprimary and secondary circuits, a thyratron'switching-device'- connected'between said uncommon input'termi--- nal and a point of'fixedpotential, said'switching device consisting ofagaseous discharge tube, means for firing said' gaseous discharge tube: periodically and" at the "beginning of the snapback time interval of the sawtooth-wave," and'lian Numb er 8i inductance; connected in series with: said gas eous discharge'tubewfor making ;said:gaseous? dis.- charge: tube-conductive only during; aportion of: the sawtoothzwave, arsource of potential positive: with respect-to. said fixed. potential 'conn'ect edto said common terminal through said :rparal- Isl-connected:resistance andcapacity circuit, a1

condenser; connected 1 tothe uncommon output" terminal of said transformer, a: diode having a cathode. and an anode saiddiode "connected between said commonvterminal of said auto-trans--- former and said: condenser terminalopposite that: connected to (the.- uncommon output termi nal of a the auto-transformer, thecathode of said diode connected; t0 said transformer common: terminal, a; choke coil: connected between said source of :positivewpotential and the junction ofsaid: condenser and diode, and a cathode raytube deflection? coil; said cathode-ray tube defiec-- tion coil; connected serially with a secondcon-- denser, .said serially connected defiectioncoil and: second condenser: connected between e a point r of fixed potential and therjunction of saidzcondenser and diode. V

9: A sawtooth: wavegenerator comprising, incombination; arr auto-transformer. having aninput? and: output circuit, said auto-transformer-- alsov havingy-aiterminal :common to said input and output circuits, an uncommon :terminalfor said inputcircuit, and: an --uncommon--terminal for. said output circuit, said:auto-transformer havingya step-upturn ratio between its primary and. secondary; circuits-,..agaseous tube switching device? connected between said uncommon input.

terminal and a point of: fixed potential, said coil: connected between: said source of positive potentialiand the junction-of said condenser and diode, and a cathode ray tube deflection coiLsaid. c-athode-rayrtube: deflection coil connected seria'llyzwithra-secon-d condenser, said serially connected': deflection :coil and-second condenser connectedxbettveen a poi-nt offixed potential andthe junction-of said condenser anddiode.

L 'KARL .R. WEND'I'.

REFERENCE S. CITED The following references: are of record in th nleof this patent:

UNITED STNIESTATEN IS A Name Date 2,139,432, Andrieu 'D6C. .6, 1938 2,227,480: Andrieu Jan. 7, 1941 2,440,418; l ourshou Apr. 27,1948