US2253355A - Television scanning system - Google Patents

Description

Aug. 19, 1941. M. K. TAYLOR I TELEVISION SGANNING SYSTEM Filed Sept. 25, 1939 ATTORNEY fiection is Patented Aug. 19, 1941 UNITED STATE s PATENT OFFICE 2,253,355 'rELEvrsroN scANNnvc sYs'rEM Maurice K. Taylor,

Application .September In Great Britain This invention relates to television scanning systems and more particularly to such systems comprising cumulative deflection of a cathoderay beam by means of an electromagnetic scanning'eld and an electrostatic scanning neld.

In conventional television receivers, it has been the practice to provide scanning o! thelcathoderay beam of the cathode-ray signal-reproducing device in one direction by means of either an electromagnetic scanning field or an electrostatic scanning held. Due to the tact that the lengths of the cathode-ray tubes heretofore in general use are great in comparison with their screen diameters, the cabinets oi television receivers in' which `such tubes are horizontally disposed therein have, of necessity, been quite'large. 'This diinculty has been overcome to some extent by -Hollinwoom England, assigner .to Hazeltine Corporation,

a corporation of Dela- 23, 1939, Serial N0. 296,220

September 24, 1938 8 Claims.l 5,(Cl. P18-7.5)

arranging the cathode-ray tube vertically, but I this has necessitated the use of a viewing mirror. To avoid these disadvantages, shorter cathoderay tubes have been produced with a view to reducing both the bulk andthe cost of-the cabinets required `'to accommodate them. lHowever.

vthese shortertubes have the disadvantage of Furthermore, the energy required to provide a given deiiection'by a neld oi one given type varies approximately as vthe square of the deflection. For this reason the energy requirements are considerably reduced if a part of the required deprovided by a neld of one type and the remainder of the-required deflection is provided by a field of the other type.

the dpresent invention, thereimproved television scanning It is an object o! fore, to provide an system which is not theA above-mentionedfdisadvantages o! the arrangements ci the prior art.

. It isa further object'oi` the presentinvention to provide an improved television scanning systern which provides simultaneously electromagnetlc and electrostatic scanning nelds which are cumulative iinv theirdefiecting action en the cathode-ray beam.

`such high ilux values when the time ratio is high.

In accordance with the invention, a television scanning system for denecting a cathode-ray beam comprises an oscillation generator, electromagnetic scanning windings, and means including the generator for producing a current oi substantially saw-tooth wave form in the electromagnetic scanning windings. There are also provided electrostatic scanning plates and .means including the same oscillation generator for supplying thereto, simultaneously with the application of said saw-tooth current to said electromagnetic scanning windings, a scanning voltage of substantially saw-tooth wave form and of periodicity the same as the abovementioned sawtooth current. The electromagnetic scanning windings and the electrostatic scanning plates are relatively positioned and excited to providel a cumulative deection of the cathode-ray beam.

For agbetter understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing alncilnilts scope will be pointed out in the appended c a s.

In the accompanying drawing, Fig. 1 is acomplete circuit diagram, partly schematic, o! a television receiving system including a scanning system in accordance with the present invention, whileFigs. 2, 3, and 4 are circuit diagrams oi' different embodiments of the scanning system of the invention.

Referring now more particularly to Fig. 1 of the drawing, the system there illustrated comprises a receiver oi the superheterodyne type including an antenna system i0, Il connected to a radio-frequency ampliner I2 to which is connected in cascade, in the order named, an oscil-v lator-modulator I3, an intermediate-frequency amplifier Il, a detector Il, a video-frequency ampliiler I8, and an image-reproducing device l1.

For developing saw-tooth waves for the scanning elements included in cathode-ray signal-reprosubject to oneor more oi plates 22 of ducing device i1, there are provided a line-frequency generator I9 and a held-frequency generator- 2li. The output circuit of detector l5 is coupled to a television scanning system for defiiecting a cathode-ray beam and including generators i9 and 20 for maintaining them in synchronism with the scanning system at the transmitter in a conventional manner. The output circuits of line-frequency generator I8 are connected to f the scanning elements including electromagnetic g scanning winding 2| and electrostatic scanning device i1. similarly, 'the dutput circuits or neidthe cathode-ray signal-reproducing' frequency generator 20 are connected to ileldfrequency electromagnetic scanning winding 23 and held-frequency electrostatic scanning plates 24. Line-frequency electromagnetic scanning winding 2| and line-frequency electrostatic scanning plates 22 are relatively positioned so that they provide a cumulative deflection of the cathode-ray beam in the line-frequency scanning direction.` Similarly, held-frequency electromagnetic scanning winding 23and eld-frequency electrostatic scanning plates 24 are positioned for a cumulative deiiection of the cathode-ray beam in the held-frequency scanning direction.

Line-frequency scanning generator I9 comprises an oscillation generator including a lowimpedance triode vacuum tube'25 and a. source of unidirectional operating potential +B therefor, to which the anode of tube 25 is connected through a self-saturating reactor 26 in Vseries with the anode winding of a feed-back coupling transformer 21. The grid winding of feed-back coupling transformer 21 is coupled to the grid of vacuum tube 25 and there is provided an additional winding on the transformer 21 through which synchronizing impulses are applied to vacuum tube 25 from theoutput circuit of detector I5. The line-frequency electromagnetic scanning winding 2| are included in the anode circuit oi' vacuum tube 25 by way of saturating reactor 2l and blocking condenser 3l. A suitable cathode-biasing-resistor 28, bypassed by condenser 29, is provided for vacuum tube 25. There is also included in line-frequency scanning generator I9 a pentode vacuum tube 30 having input electrodes connected by way of a cathode-biasing resistor 3|, shunted by by-pass condenser 32, and blocking condenser 33 to the output electrodes of triode 25 through a wave form changing means comprising a series-connected resistor 35 and condenser 31. The anode of pentode 36 is connected by" way oi.' a load resistor 35 to the source of unidirectional operating potential +B and is also connected by way oi' a blocking condenser 38 to one of the pair of line-frequency electrostatic scanning plates 22, the other of the scanning plates 22 being y grounded.

The details oi.' the held-frequency scanning generator 20 have not been shown and it will be understood that this generator may be constructed in a manner similar to that described for line-frequency generator I3.l

Coming now toan explanation of the operation of the system of Fig. i, it will be understood `that the elements I-I5, inclusive, `may all be of conventional well-known construction so that detailed illustrations and description thereof are deemed unnecessary herein. Briey described, however, signals intercepted by the antenna circuit iD, il are selected and amplied in radiofrequency amplifier I2. and supplied to the oscillator-modulator I3 wherein they are converted to intermediate-frequency signals which are, in turn, selectively ampliiled in the intermediatefrequency amplifier I l and delivered to the dev, The modulation components of the tector I5. signal are derived by detector I and the videofrequency components are supplied to the videotrequency amplier I6 wherein they are ampliiled and from which they are supplied to the brilliancy-control element of the signal-reproducing device I1. 'I'he intensity of the scanning beam of the image-reproducing device I1 is with the video-frequency voltages impressed on its input circuit.

The saw-tooth scanning waves developed by the line-frequency generator i9 and held-frequency generator 20 and applied to the scanning elements of cathode-ray reproducing device l1 cause the beam to be deflected so as to trace a rectilinear scanning pattern on the target ofthe reproducing device I1 .and thereby reconstruct the transmitted image. The generators I9 and 20 are synchronized with the corresponding scanning apparatus at the transmitter by synchronizing pulses appearing in output circuits of detector I5, it being understood that suitable synchronizing-signal separatingY circuits of a conventional form are included in the circuit of detector l5.

Referring now more particularly to the part of the system involving the present invention, the triode 25 generates oscillations at the linescanning frequency of the system due to the feed-back coupling existing between its grid and anode circuits through transformer 21, the frequency of these oscillations being maintained constant by the synchronizing pulses introduced into the input circuit of tube 25 from detector l5. The circuit constants of the relaxation osv cillator including tube 25 are so related that thereby modulated or controlled in accordance a voltage of rectangular wave form is produced at the anode of tube 25 which is effective to develop current of substantially saw-tooth wave form in the line-frequency electromagnetic scanning winding 2l,- the degree of linearity of this current during the trace interval oi' the system being increased by saturating reactor 26 in a manner fully described in applicant/s British Patent No. 493,142, accepted October 5, 1938. By suitably proportioning the circuit constants of the elementsassociated with tube 25, the current of saw-tooth wave form thro'igh the scanning winding 2l may readily be made to provide about half the required deilection of the cathoderay beam of image-reproducing device I1 in the line-frequency scanning direction.

Vacuum-'tube 30 is provided in order to supply to line-frequency electrostatic scanning plates 22 a scanning voltage of substantially saw-tooth Wave form simultaneously with the application of the current of saw-tooth wave form to scanping winding 2 l. Coupling network 36, 31 serves to derive from the voltage of rectangular wave form` at the anode of tube 25 a voltage of sawtooth wave form and of periodicity the same as the saw-tooth current supplied to windirgs 2| which voltage appears across condenser 31 and is applied to the input circuit of vacuum tube ,3o and which, after amplification thereby, is

Vapplied to the de ecting plates 22 of the cathoderay image-reproducing device I1. The windings 2| and the plates 22 are relatively positioned and energized to provide a cumulative deflection of the cathode-ray beam of reproducing device I1.

Since each of the electromagnetic and electrostatic scanning fields contributedl by generator I9 is of a magnitude usually provided in connection with conventional relatively long cathode-ray tubes, suiiicient deflection of the scanning beam of a relatively short cathode-ray tube can be obtained without resorting to high current values in the scanning winding or to high potentials on the scanning plates with the attendant higher power requirements.

Fig. 2, in which circuit elements similar to those of Fig. 1, have identical reference numerals, is a circuit diagram of a modied embodiment f of the invention wherein' two vpentode vacuum .nection 40 to potential divider 4l, 42 across the output terminals of pentode 30.

A further embodiment of the modification shown in Fig. 2 is illustrated in Fig. 3, in which 'similar circuit elements have identical reference numerals. The circuit of Fig. 3 differs from that of Fig. 2 only in that the input voltage for pentode 30' is derived by means of conductor Il directly from the input circuit of vacuum tube rather than from the output circuit of vacuum tube as inFig. 2.

In the above examples, it has been assumed that a substantially linear saw-tooth current lis applied to scanning winding 2l and that a substantially linear saw-tooth voltage is applied to electrostatic scanning plates 22. Due to the resistance ofthe scanning winding 2i and to the resistances of the coupling circuit between tubes 25 and 30, these ideal conditions will not actually obtain and there willresult some slight nonlinearity during the trace interval in each of the saw-tooth scanning wave forms these nonlinearities being oi' opposite sense. By properly proportioning the resistance ofthe scanning winding 2l and the resistance and capacitance of the coupling elements between tubes 25 and 30, the eiTect of these deviations from linearity during thetrace interval can be made substantially to compensate one another. In other words, an effective resultant scanning ileld which is linear during the trace interval is provided, even though neither the magnetic component nor the electrostatic component is linear during the trace interval.

In Fig. 4 there is shown a modification of the invention in which only a single triode vacuum tube is employed in the oscillator. Circuit elemnts which are similar to those of corresponding elements of the preceding ilgures have identical reference numerals; The saw-tooth An input voltage of opposite phase' current for electromagnetic scanning winding 2l is derived from the output of vacuum tube 25 in the manner described in detail above. However, in the modification of Fig. 4 the pentode amplifier i`s omitted and a voltage of saw-tooth wave form for electrostatic scanning plates 22 is derived directly from the output circuit of vacuum tube 25 by means of an integrating resistor-.condenser combination including a resistor 44 and a condenser 45, series-connected across the output circuit of vacuum tube 25. The embodiment of Fig. 4 requires a higher value of current in the scanning winding 2| than do the other embodiments described, but the saving of an amplifier stage effects a saving in manufacturing cost.

While there have been described what are at 'suchI changes 'and modiilcations as fall within the true spirit and scope of the invention.

What is claimed is: 1. A television scanning system for defiecting a cathode-ray beam' comprising, an oscillation generator, electromagnetic scanning windings,

means including said generator for producing a current of substantially saw-tooth wave form in said windings, electrostatic scanning plates,

and means including said generator for supplying to said plates simultaneously with said sawtooth current, a scanning voltage of substantially saw-tooth wave frm and of periodicity the same n as said saw-tooth current, said windings and said plates being relatively positioned to provide a cumulative deflection of the cathode-raybeam.

2. A'television scanning system for deecting a cathode-ray beam comprising, an oscillation generator including a synchronizing 4circuit adapted to be excited by input synchronizing pulses, electromagnetic scanning windings, means including said generator for producing a current oi' substantially saw-tooth wave form in said windings, electrostatic scanning plates, and means including said generator for supplying to said plates simultaneously with said 'saw-toothv current, a scanning voltage of substantially saw'- tooth wave form and oi periodicity the same as said saw-tooth current, said windings and said plates being relatively positioned to provide a cumulative deection of the scanned cathoderay beam. y

3. A television scanning system for deilecting a cathode-ray beam comprising. an oscillation generator including a low-impedance triode having inductively coupled input and output circuits, electromagnetic scanning windings, means including said generator for producing a current of substantially saw-tooth wave form in said windings, electrostatic scanning plates, and means including said generator for supplying to said plates simultaneously with said saw-tooth current, a scanning voltage of substantially s awtooth wave form and of periodicity the same as said saw-tooth current, said coils and said plates being relatively positioned to provide a cumulative deilection of the -scanned cathode-ray beam.

v 4. A television scanning system for deflecting a cathode-ray beam comprising, an oscillation generator for providing an output current of saw-tooth wave form and an output voltage of with the application of said current of sawtooth wave form to said scanning windings, said windings and said plates being relatively positioned to provide a cumulative deflection4 of the scanned cathode-ray beam. n

5. A television scanning systemA for deflecting a cathode-ray beam comprising, an oscillation generator, electromagnetic scanning windings, means including said generator for producing a current of substantially saw-tooth Wave form in said windings, electrostatic scanning plates, a vacuum-tube amplier, andl means including said generator and said vacuum-tube amplifier for supplying to said plates, simultaneously with said saw-tooth current, a scanning voltage of substantially saw-tooth wave form and .of pe'- riodicity the came as said saw-tooth current, said windings and said plates being relatively positioned 'to provide a cumulative deflection of the scanned cathode-ray beam. y

6. A television scanning system for deecting a cathode-ray beam comprising, an loscillation generator, electromagnetic scanning windings, means including said generator for producinga current of substantially saw-tooth wave form in said windings, electrostatic scanning plates, and means including said generator and two vacuum tubes having a balanced output circuit connection forsupplying to said plates, simultaneously with said saw-tooth current, a balanced scanning voltage of substantially sawtooth wave form and of periodicity the same as said saw-tooth current, said windings and said plates being relatively positioned to provide a cumulative deilection of the scanned cathode-ray beam.

7. A television scanning system for deflecting a cathode-ray beam comprising, an oscillation generator, electromagnetic scanning windings, means including said generator for producing a current in said windings of substantially sawtooth wave form, having relatively long trace intervals, and being subject to slight deviations from linearity during said trace intervals, electrostatic scanning plates, and means including said generator for supplying to said plates, simultaneously with said saw-tooth current, a voltage of substantially saw-tooth wave form and f periodicity the same as said saw-tooth current,

said voltage having relatively llong trace intervals and being subject to slight deviations from linearity during said trace intervals of -opposite sense to that of said saw-tooth current. said windings and said plates being relatively positioned to provide a cumulative deflection of the scanned cathode-ray beam, and the circuit constants oi' said generator being so proportioned that the eiect of said deviations from linearity during said trace intervals substantially compensates one another.

8. A television scanning system for deecting a cathode-ray beam comprising, an oscillation generator including a single vacuum tube, electromagnetic scanning windings, means including' said generator' for producing a current oi' substantially saw-tooth wave form in said windings, eelctrostatic scanning plates, and wave form changing means coupled to said generator for supplying to said plates, simultaneously with said saw-tooth current, a scanning voltage of substantially saw-tooth form and of periodicity the same as said saw-tooth current, said windings and said plates being relatively positioned to provide a cumulative deilection of the scanned cathode-ray beam.v

MAURICE K. TAYLOR.

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