US2267251A - Television receiver - Google Patents

Description

Dec. 23, 1941. F. OKOLICSANYI TELEVISION RECEIVER 2 Sheets-Sheet 1 l4 fly? FQfQuQ (DKoHQSanJI I Filed Jan. 19, 1939 Dec. 23, 1941. F. OKOLICSANYI TELEVISION RECEIVER Filed Jan. 19, 1939 2 Sheets-Sheet 2 Patented Dec. 23, 1941 TELEVISION RECEIVER Ferene Okolicaanyi, Kensington, London, England Application January 19, 1939, Serial No. 251,844 In Great Britain January 21, 1938 9 Claims.

The present invention relates to television receiving apparatus using a supersonic light control device, that is a device in which modulated mechanical waves of supersonic frequency are generated in a body or on its surface and are used to modulate a light beam falling on the body in accordance with the modulations of the waves.

Such a device is described in British Patent specification No. 439,236. In one method of using such a device a train of waves is produced in the cell by a piezo-electric crystal set into oscillation by a high frequency electrical oscillation modulated in accordance with the received picture signals. The train of waves therefore represents in its amplitude the brightnesses of a number of successive picture points; an image of this train of waves, which modulate the light passing through them in accordance with their amplitude is formed on the screen and moved over it at such a speed that the movement of the waves themselves is immobilised on the screen, that is each picture point is reproduced on one spot on the screen so long as the corresponding modulations in the cell are present therein. In such a method the waves in the cell move in the line scanning direction.

It has been proposed to construct a television receiver by placing side by side a number of Kerr cells. and to cause these cells to operate one after the other by applying a Potential to their plates from a cathode ray beam of which moves over a number of contacts arranged within a cathode ray tube, each contact being connected to one of the Kerr cells. In this way there is produced a beam of light having a scanning motion along the line of cells and if the intensity of the cathode ray beam is modulated with received picture signals, the moving light beam will trace out on a screen on to which it is projected, a picture line having as many elemental areas in it as there are Kerr cells.

It is an object of the present invention to improve on a device of this kind so that the disadvantages inherent in the Kerr cell type of light modulator are removed.

It is a further object of the present invention to provide a television receiver in which the light is modulated by a number of wave trains of high frequency mechanical waves moving parallel to one another, the wave trains being produced by a number of vibrating bodies which are set into oscillation in turn by means of a cathode ray commutator.

As a further object-the present invention proposes to employ in place of a series of Kerr cells.

a cell employing high frequency mechanical waves for light modulation, and to construct the cell in such a manner that a series of wave trains moving at right angles to the line scanning direction of the apparatus, each wave train being modulated in accordance with the brightness of one element of the reproduced picture, are produced by a cathode ray beam modulated in accordance with the received picture signals.

Various embodiments of the inv ntion or parts thereof are shown in the accompan ng drawings of which Fig. 1 shows diagrammatically the optical system and the light modulating device of a receiver according to the invention,

Fig. 2 shows a cathode ray commutating device for use with the apparatus of Fig. 1,

Fig. 3 shows an alternative method of eifecting cooperation with the commutating device and the light modulating device,

Fig. 4 shows an alternative form of cathode ray tube,

Figs. 5 and 6 show in end view and plan view a part of Fig. 4.

Figs. '7 and 8 show in detail alternative constructions of the light modulating device. Referring to Fig. 1 of the drawings, a television receiver embodying the present invention comprises a lamp I, having a long incandescent filament 2. Light from the filament is collected by a lens 3 and projected on to one transparent wall of a composite light modulator cell 4. The upper wall of this cell 4 is composed of a steel plate adjacent the liquid and having fixed on its upper surface a number of piezo electric crystals arranged side by side along the length of the cell (that is in a direction parallel to the filament 2) and each being provided on its upper surface with a second electrode. These second electrodes are shown at 5. In the drawings fifteen of such electrodes are shown, but in practice the cell would be provided with as many crystals as elemental areas it is desired to reproduce in a line of the received picture. The transparent side walls of the cell 4 through which the light passes are provided with cylindrical lenses la. and lb having power in the plane of the wi ith of the cell 4. Beyond the cell 4 is an opaque bar 6 and a mirror oscillograph I of the Rochelle salt type and designed to provide the low speed scanning component, and to project light from the cell 4 on to a screen.

Between the oscillograph l and the screen 8 are provided two cylindrical lenses 9 and III, the lens 9 having power in the plane containing the length I of the cell l and the lens in having power in the plane of the width of the cell 4. The function of these lenses will be described hereinafter.

The crystals of the cell 4 are set into oscillation by means of a cathode ray communication shown in Fig. 2. In that figure, a cathode ray tube comprises a straight filamentary cathode H and an astigmatic electron lens system shownby way of example in the form of two slotted diaphragms l2 and I3 so positionedand in operation given such voltages that a line electron image of the cathode II is formed on a contact assembly I I4. Deflector plates l5 and [6 are provided for deflecting the beam over the contact'assembly |2.. The cathode II is surrounded by a wehnelt cylinder ll having a slit-shaped aperture Ila to act as a modulating electrode for the cathodev beam.

The contact assembly [4 comprises as many contacts l8 as there are crystals on the cell 4,

, line is being generated.

which extends the whole width of the received picture).

Any suitable form of low speed scanner-may be used, such as a mirror drum, in place of the oscillograph mirror I. The present invention however permits the use oi such small scanning elements owing to the fact that it is-not'necessary to focus an image of the cell in its longer dimension as in thecase oi the cell described in British Patent specification No. 439,236, thus giving freedom of focussing in this dimension.

It is possible to make the-width of the cell 4 (that is the dimension in the direction of movement of the waves) sufliciently large so that one train of waves is still moving through the cell while a second train corresponding to the next This can be done by 1 choosing a liquid medium in which the waves mounted on an insulating member lll which istravel slowly, for example ethyl iodide. In this case the slow speed scanner .1 can be arranged tomove at such a speed thatithe images of the waves formed on the screen 8 are always projected on the same spot thereon, that is to say th'emovement or the waves in the cell is immogenerating supersonic mechanical waves in the.

liquid of the cell 4 of Fig. 1 is modulated with the received picture signals and applied to the modulator electrode ll of the gun of the cathode ray tube of Fig. 2. The line synchronising impulses are used to generate a'saw tooth oscillation which is used to deflect the beam over the contact assembly M at line frequency. For this purpose the normal television receiving circuits may be employed, such are illustrated in Fig. 4 and described later in this specification.

As the beam moves over the contacts I 8, an oscillating potential will be applied across each of the crystals of the cell 4 in turn for a short time, and each crystal will set up in the liquid of the cell a short train of waves, which will travel from the crystal surface downwards as the cell is shown in Fig. 1. Each train of waves willdifiract part of the light passing through it, th'e amount of light difiracted being dependent upon the amplltude of the waves. The undififracted light is arrested by the opaque bar 6, and the diffracted light passes on to the low speed scanner 1, and thence to the receiving screen 8.

The optical system consists of a number of cylindrical lenses, each having power in oneof two mutually perpendicular planes, and therefore the focussing in each plane can be considered separately. In the plane parallel to the direction of movement of the supersonic waves the lenses 4a, 4b and Ill have power. The light from the filament light source 2 is rendered parallel by the lens 4a, and brought to a focus on the bar 6 by lens 42;. The lens Ill forms an image of a plane near the bar 6 on the screen 8. In the plane at right angles to this, the lens 3 acts as a condensing lens to throw light on to the cell 4: the

lens 9 forms an image of the cell 4 on the screen 5. The distances of the lenses 8 and in from the cell i and bar 6 are arranged to be such that the image on the screen is narrow (i. e. the lens W forms a reduced image of th'e light passing the bar, and the lens 9 forms an image of the cell thepicture may be projected bilised on the screen. Thus, two or more lines of on the screen simultaneously.

Instead of having the cathode ray beam commutator at a point remote from the cell as shown in Figs. 1 and 2, with wire'connections between the contacts of the commutator and the crystal electrodes, the cathode ray beam may be ar- 7 ranged to fall directly on the electrodes 5 of the crystals by constructing the end wall 01 the tube as the cell itself. A preferred construction is shown in Fig. 3. I

In this flgure, the end of a cathode ray tube, part'of the walls of which are shown at 24, has sealed into it a plate 25 or ceramic material, the centre part of which 26, is made very thin. On the side of the part 28 are fixed a number of contacts 21 on to which the cathode ray beam, indicated by the dotted line 28, falls. On the outer side of the plate 25 is attached the light modulating device 29. The end of this is closed by a thin steel plate 30, on to the outer side of which are attached a number of piezo-electric crystals 3i, each of which is provided with a second electrode 32, these second electrodes lying opposite the contacts 21 on the opposite side of the plate 25. Between the contacts 21 is a layer of resistive material connected to earth in such a manner that there is a resistive electrical path between each contact and earth. When the beam falls on a contact 21, the potential of the latter varies according to the modulation of the beam, and a corresponding voltage is set up across the crystal between the electrode 32 and the plate 30, due to the capacitive connection between the contact 21 and the electrode 31. The V vibration of the crystal sets up high frequency waves in the liquid of the cell 29, which waves are used to modulatea light beam and to reproduce th'e received picture in the manner described with reference to Fig. 1.

In the case where it is desired to produce a larger picture on the screen, the cell 4 of Fig. 1 must be made large in order that sufficient light may be present in the system to illuminate with a reasonable bright intensity a large screen. The crystals must then be also comparatively large, and in practice a simple cathode ray tube of the type shown in Fig. 2 may not give the power required to set the crystals into oscillation with suiiicient amplitude. In Fig. 4 is shown an electrode arrangement for a cathode ray commutator in which a larger power than that given by the arrangement of Fig. 2 can be obtained.

In Fig. 4, a cathode ray tube has a first cathode 35 which is in the form of a short filament running at right angles to the plane ofthe paper. This cathode is heated by current from a battery 36. Next to the cathode 35 Ba modulating grid 31 and then a magnetic focusing coil 38, which is designed to project a line image of the cathode on the grid 39, in close proximity to which is placed a collecting electrode 34. The arrangement and function of this part of the apparatus will be described more fully later. A pair of defleeting plates 40, 4i, are provided for deflecting the electron beam from the cathode 35 over the grid 39. A second cathode 42 is arranged on the side of the grid 39 nearest the cathode 35, and to one side of the path of the electrons from the first cathode 35, so that these electrons pass it, and fall on one side of the grid 39. The cathode 42 is heated by a battery 45. On the side of the grid 39 remote from the cathodes is placed a modulating grid 43, then a magnetic focusing coil 44, and finally a contact assembly 45, the contacts on which may be connected by wires to the electrodes of the cell, as described with reference to Figs. 1 and 2, or may be attached to the cell as described with reference to Fig. 3.

The construction of the grid 39 and the relative positions of this grid, the electrode 34,and the cathode 42 are shown in Figs. 5 and 6. The grid 39 comprises two supporting uprights 56 and 51, the upright 51 being made of, or being coated with a layer of resistive material. The connection to the outside of the tube is made by a metal conducting strip 58. The grid consists of a number of small grids 59 arranged side by side spaced apart from one another, and connected to the resistive element 51. The number of grids 59 is made equal to the number of elements it is desired to reproduce in a picture line, that is equal to the number of crystals of the modulating cell 4 of Fig. 1. The position of the cathode 42 relative to the grid 39 is shown in dotted lines in Fig. 5, and as a full line in Fig. 6, and the beam from the cathode 35 falls on the grids 59 on that part of them which is between the cathode 42 and the support 56. The electrode 34 consists of two plates (which are suitably connected together electrically) arranged one on each side of the beam from the cathode 35, and held at a high potential relative to the grid 39, which is biassed negatively relatively to the cathode 42. The connections of these electrodes to the battery 55 are shown in Fig. 4.- Preferably a shielding electrode 69 connected to the cathode 42 is provided between the latter and the collecting elecgrid 31, which is biassed negatively with respect to the cathode 35 by connecting it to the negative terminal of a source of voltage 55, and connecting the centre tapping of the battery 35 to a more positive tappin on the source 55. In this way the beam falling on the grid 39 will be modulated with the received picture signals.

Now when the beam falls on one of the grids 59, this grid emits secondary electrons, and it is arranged by suitably choosing the potential difference between the cathode 35 and grid 39, and by making that part of the grid 59 of suitable material (e. g. by coating it with a substance which readily emits secondary electrons) that the number of secondary electrons emitted exceeds the incident electrons. There will be produced on the grid 59 in question a positive charge proportional to the strength of the beam falling thereon, which is in turn proportional to the brightness of the corresponding picture element. The resulting decrease in negative. bias of the grid 59 will result in a fiow of electrons from the cathode 42 through the grid 59. This electron current passes through the grid 43 (Fig. 4) on which is impressed a high frequency oscillation of the frequency required for driving the crystals of the light modulating device. This frequency is generated by an oscillator 6! and fed to the grid 43 through a transformer 62. The focussing coil focusses an electron image of the grid 39 on to the contact assembly 45, the image of each grid 59 in the grid 39 being imaged on one contact. Thus each contact will have falling on it a beam of electrons which is modulated in amplitude by the picture signal corresponding to it and by the high frequency oscillation from the generator GI. and a corresponding train of waves will be set up in the cell and used as described with reference to Fig. 1. When the beam from the cathode 35 moves ofi one grid 59 on to the next one, the charge on the first grid will begin to leak away through the resistive support 51, the resistance being such that the charge received from the beam from the cathode 35 has substantially entirely leaked away within' one line period. It will be seen that'the above apparatus provides a certain storage effect, since a modulated oscillation continues to be applied to each contact after the beam has moved away from the corresponding grid, due to the time required for the charge to leak away. from the grid.

It has been observed that if a quartz piezoelectric crystal has only a part of its surface covered with the electrodes, and an oscillation is applied thereto, only the part of the crystal covered with the electrodes will vibrate, the retrode 34. The bias on the grid 39 is such that no emission from the cathode 42 passes it.

The operation of the cathode ray tube is as follows. Television signals received by the aerial 41 are amplified by an amplifier 49, and applied to a separating arrangement 49 which separates the picture signals, line synchronising signals and frame synchronising signals from each other. The frame synchronising signals appear at 59 and are used to control the slow speed scanner 1 of Fig. 1. The line synchronising signals appearing at 5| are fed to a time base circuit 52 to control the generation of saw tooth impulses at line frequency which are fed to the deflecting plates 40, 4|. The picture signals appear at 53 and are fed through a condenser 54 to the modulating mainder being unaffected.

The present invention therefore provides a modification of the arrangements previously described, in which the crystal assembly is replaced by a single crystal extending over the whole length of the cell. In one example, illustrated in Fig. 'l, the crystal 8B is covered on the side remote from the liquid by a number of separate electrodes 8|. These electrodes may be formed of fine wires, and the spaces between them may be filled with an insulating material. On the other side of the crystal is fixed a common electrode 92, for example a steel plate.

In an alternative arrangement using the above stated fact, the crystal surface is itself exposed to the cathode ray beam in place of the capacity connection shown in Fig. 3. In this case the focussing system of the tube, which may be a cylindrical focussing system, preferably causes the beam to fall on a narrow strip of the crystal taken at right angles to the longer dimension of the latter.

In any of the embodiments of the invention described above, the distance between the crystal or crystals and the opposite wall of the cell can be made such that the wave reflected from this wall produces standing waves with the waves from the crystal. By utilising the reflection of the waves to and fro across the cell, the effect of the waves may be made to persist for some time after the scanning cathode 'ray beam has passed on to another part of the crystal or crystal assembly, thereby giving an enhancement-of the light passing through to the screen.

The cell wall may be fitted with a special refiecting surface as shown in Fig. 8. The reflector can be made from, for example, a polished plane metal surface 83, which may be of stainless steel. The distance of the reflector from the crystals 84 is made very short to achieve a multiple reflection. In this way, the short excitation of the supersonic waves in the liquid is prolonged for the whole duration time of a line. It is also an advantage to apply only a low damping to the crystal to obtain in this way a persistance of the oscillations, for example by exciting it with a frequency which is a harmonic of the natural frequency of oscillation of the crystal itself. The width of the resonance band may be, for instance 100 kilocycles instead of the usual 2 megacycles.

It will be noticed that in any arrangement of the present invention the'waves are not travelling along the cell parallel to the direction of line scanning as in the case of the device according to British Patent specification No. 439,236. In that arrangement, owing to the necessity for the light beam to be parallel in the direction of movement of the waves, the major restriction of the size of the light source and its aperture is in the line scanning direction. In the present invention there is no restriction in this direction, with consequent increase in light. The only restriction is in the direction at right angles to this, Where in both cases there is a restriction owing to the necessity of forming a narrow image on the screen, and owing to the necessity for keeping the width of the low speed scanning member reasonably small. For example, the present invention makes it possible to use a cinema arc lamp with a large arc crater, and full use of the light available from which such a source can be made.

The piezo-electric crystal assembly may be made from a large number of small crystals stuck on a steel plate, acting as one electrode, and having on the other side the separate electrodes for the generation of the separate wave-trains. such an assembly acts in a similar way-to the arrangements previously described.

I claim:

l. A television receiver comprising, in combination, a cathode ray tube having an electron gun for producing a beam of electrons and an electrode system for modulating said beam with received picture signals and with a high frequency electrical oscillation, a light modulating device of the kind utilising the diffraction effeet on light of high frequency mechanical waves in a liquid medium, said light modulating device comprising a plurality of generators equal in number to the number of elemental areas in the picture line for generating a plurality of parallel trains of high frequency mechanical waves in said liquid medium, said light modulating device being arranged in the path of said beam of electrons so that said beam scans said generators at line frequency to cause them to produce said trains of waves in said liquid medium, and an optical system for forming an optical diffraction image 01' said trains of waves to reconstitute a picture line on a receiving screen, and frame scanning means for sweeping said image over said screen.

2. A television receiver according to claim 1 wherein said generators comprise a piezo-electric crystal assembly having a plurality of electrodes arranged on the side thereof remote from said liquid medium a plurality of contacts arranged within said cathode ray tube and in close proximity to said electrodes, whereby voltages induced on said contacts by said beam of electrons are transmitted to said electrodes by virtue of the capacity existing between said contacts and said electrodes.

3. In combination in a television receiver, means for producing a picture line comprising a supersonic wave light modulating device in which there are provided a plurality of generators of mechanical waves equal in number to the number of elements it is desired to reproduce in a line of the received picture, cathode ray tube commutating means for relegating to each generator a high frequency oscillation modulated with that part of the picture signal in each line apportionate thereto, and an optical system for producing from light diffracted by said trains of waves a picture line on a screen.

4. A television receiver comprising a light modulating device of the kind utilizing the diffraction effect on light of high frequency mechanical waves in a liquid medium and comprising a plurality of similar generators for generating a plurality of trains of high frequency mechanical waves in said liquid medium, each train corresponding to an elemental picture area of a picture line, electronic line-scanning means for exciting said generators one after the other with an electron stream modulated in intensity in accordance with received picture signals and interrupted at a high frequency suitable for exciting said generators, optical means for forming an optical diifraction image of said trains of waves on a receiving screen, and mechanical frame scanning means for sweeping said image in a direction at right angles to its length over said screen to produce the frame scanning component and thus reconstitute a received picture.

5. A television receiver comprising a light modulating device of the kind utilizing the diffraction effect on light of high frequency mechanical waves in a liquid medium and comprising a plurality of similar generators for generating a plurality of trains of high frequency mechanical waves in said liquid medium, each train corresponding to an elemental picture area of a picture line, a cathode ray tube having an electron gun for producing a beam of electrons. means for modulating said beam with received picture signals and also with high frequency suitable for exciting said generators, a plurality of contacts, each of said contacts being associated with one of the said generators through an alternating current path, and means for deflecting said modulated beam of electrons over said contacts at line frequency, optical means for forming an optical diffraction image of said trains of waves on a receiving screen, and me-- chanical frame scanning means for sweeping said image in a direction at right angles to its length over said screen to produce the frame mechanical waves in said liquid medium, each v train corresponding to an elemental picture area means for exciting said generators one after the other with an electron stream modulated in intensity in accordance with the received picture signals and interrupted at a high frequency and optical means for forming an optical diffraction image of said trains of waves on a receiving screen, said means for exciting said generators comprising a cathode ray tube having a first cathode for producing a first electron stream,

means for modulating said stream with the received picture signals and for deflecting it at line frequency over a plurality of modulating grids. a second cathode for producing a second electron stream which passes through said modulat' ing grids, a plurality of contacts, means for tocussing the electron stream passing through said grids on to said contacts, means for modulating said second stream with a high frequencyoscillation, and means for feeding the voltages produced on said contacts to said generators to produce the frame scanning component and thus reconstitute a received picture.

7. A television receiver according to claim tin which the plurality of generators of said light modulating device are comprised by a single piezo-electric crystal extending over the length of the light modulating device and provided with a plurality of electrodes arranged along its length.

8. A television receiver according to claim 4 wherein the dimension of said modulating device in the direction of movement of the waves which is the same as the frame scanning direction is such that, in operation, waves representative of more than one line of the received image are present therein at anyinstant, and wherein said optical means and said frame scanning means are adapted to image in the correct position on said screen more than one line of the picture simultaneously.

9. In a television receiver, means for reproducing a transmitted picture line comprising a cathode ray tube, means for modulating the beam of said tube with received picture signals, and with a high frequency oscillation, a supersonic wave light modulating device having a plurality of identical generators of mechanical waves, equal in number to the number of elements it is desired to reproduce in a line of the received picture, for producing a plurality of trains of waves in said device moving at right angles to the line direction, each train corresponding to an elemental picture area, a plurality of electrodes in said cathode ray tube each electrically associated with one of said generators, and means for scanning said electrodes under the influence of received line scanning oscillations, whereby each generator has relegated thereto a high frequency oscillation modulated with that part of the picture signal in each line apportionate thereto, and an optical system for forming on a screen an optical diifraction image of said trains of waves to produce the frame scanning component and thus reconstitute a received picture.

FERENC OKOLICSANYI.

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