US2195864A - Electro-optical image producing system - Google Patents

Description

April 2, 1940. KNQOP 2,195,864

ELECTRO-OPTICAL IMAGE PRODUCING SYSTEM Filed NOV. 20, 1935 2 Sheets-Sheet 1 April 2,. 1940. w KNQQP ELECTED-OPTICAL IMAGE PRODUCING SYSTEM Filed Nov. 20. 19:55

2 Sheets-Sheet 2 INVENTOR M. A. K/VO 0P Patented Apr. 2, i

ergo-omen. macs raonuomo SYSTM whom a. Knoop, West Hempstead, 51s., assignor to Bell Telephone Laboratories, Incorporated, New York, York N. Y a corporation or New Application November-2o, 1935, Serial No. saess 22 Claims.

10 a current of sine wave form into current impulses of rectangular wave form, the duration of each impulse being small compared to the period of the sine wave.

In accordance with a specific embodiment of the invention herein shown and described for the purpose of illustration, there is provided at a transmitting station apparatus for repeatedly scanning the elemental areas in succession of 2. held of view along successive parallel lines to 20 produce a television image current, each complete scanning of the field of view taldng place within the period of persistence of vision. At the receiving station there is provided a bank or light mltting'elements arranged in rows corresponding to the parallel scanning paths at the transmitter, there being one lamp corresponding to each elemental area of the field of' view. For example. there may be one hundred lamps in each horizontal row and one hundred 3O lamps in each vertical column, making ten thousand lamps in all. One set of terminals of the lamps of each row is connected together to a contact of a mechanical distributor, while the other lamp terminals of each column are connected together to the anode of a three-electrode thermionic tube, thus making a coordinate system. A mechanical commutator selects the rows of lamps in synchronism with the scanning of successlvelincs of the field of view at the transmitting station. The source of image current is impressed upon the horizontal rows of lamps in succession through the mechanical distributor.

The vertical column of lamps must be selected in sequence at a rapid rate and-this is done by a non-mechanical commutating arrangement; Ii a lamp bank of ten thousand lamps is tdbe commutated in one-twentieth of a second, for example, there is employed atransmission path dred sections, each having inductive and eaor relay network having characteristics such that pacitive elements. The control electrodes of th thermionic devices are connected to different network sections; respectively. The electrodes are normallynegatively biased to such a degree that the lamps emit no light or only a control very small amount of light. A high amplitudeimpulse of a duration preferably equal to the time required for seaming a single elemental area, .000005 second in the above example, is periodically impressed upon the delay network at a rate equal to the line -scanning frequency andthis impulse increases the grid potential of the thermionic tubes in succession to zero, for example, thus causing the lamps in succession to emit light of an intensity determined by the amplitude of the image current.

The periodic starting impulses impressed upon the delay circuit are derived from a source oi alternating current, the frequency of which is equal to the line scanning frequency. Each alternating current cycle lsconverted into a squaretopped unidirectional current having a duration apprommately equal to one-half cycle of the alternating current and each square-topped current impulse is converted into .an impulse of electromotive force of logarithmic wave form having a high amplitude and the top of this wave is cut oil, thus forming an approximately rectangular wave having a duration less than the time required for scanning a single elemental area.

Any suitable arrangement may be employed for maintaining synchronism between the scannings at the transmitting and receiving stations and for maintaining the correct relationship between the rate at which the logarithmic impulses are generated and the speed of themechanical commutator at the receiving station. For example, a constant frequency vacuum tube oscillator may be employed for generating the alternating current from which the logarithmic impuises are derived and current from this oscillator may also be supplied to a circuit for controlling the' speed of a. motor which drives the mechanical commutator at the receiver and to a circuit for controlling the speed of a motor which drives a scanning disc or other apparatus for scanning the field of view at the transmitting station.

InFlgs. 1 andlA of the drawings there is disclosed, for the .purpose of illustration, 9. complete television system embodying the features of the invention.

Fig. 2 shows a modification of the system shown in Fig. 1.

Referring to Figs. 1 and 1A or the drawings,

' areas of the field of view are thus illuminated in at the television transmitting station A the scanning disc I8 is driven by the motor 85 at a speed of 16 or more revolutions per second to cause light from source I I directed through th spirally arranged apertures I2 of the scannin disc to illuminate the elemental areas in succession of a field of view defined by the opening in screen l3 and including the subject l4. Elemental succession along successive parallel lines. Light reflected from the subject l4 impinges upon one or more light sensitive cells i 5 and the varying current produced by the action of the light sens sitive cells, after being amplified by the vacuum tube amplifier I6, is transmitted to the distant station B through a transformer I! and a transmission channel l8.

A source of alternating current of constant frequency produced by an oscillator 88 may be connected to a winding of transformer 42 by means of a switch 48. Current from this constant requency source, after being amplified by the vacuum tube amplifier 43 is impressed upon the speed control apparatus 31 for maintaining the motor 35 at a constant speed under control of the constant frequency current from source 38. This speed controlling arrangement is disclosed more in detail in Patent No. 1,999,376, granted to H. M. Stoller, April 30, 1935. Current from the constant frequency source 38 is also transmitted to the image producing station B over the line 41 to maintain the image production at station B in synchronism with the scanning of the field of view at station A.

At the receiving station B television images of the field of view scanned at station A are produced upon the image producing lamp bank comprising a plurality of lamps or lamp elements 50, one for each elemental area of the field of view.

. These lamps may be glow discharge lamps, for

example. Each transverse row of lamps corresponds to a scanning line of the field of view and if the field of view is square, the number of rows of lamps are equal to the number of vertical 'columns, as shown. While only six rows and columns of lamps are shown, any desired number may be employed. If, for example, the field of view at the transmitter is scanned along 100 parallel scanning lines, a lamp bank having 100 "mechanical distributor 54.

rows of 100 lamps each may be employed.

The television image current received from station A over line i8 is transmitted through transformer i9 and amplified by vacuum tube amplifiers 20 and 5!. The output circuit of vacuum tube amplifier 5! comprises a battery 52 the negative terminal of which is grounded and a resistive element 58. The anode of amplifier 5! is connected to the anodes of the rows of glow discharge'lamps 50 in succession by means of the This distributor has a number of contacts equal to the number of rows of lamps 50 and is driven by a motor 55 in synchronism with the scanning disc 10 at the transmitting station. Current from the constant frequency current source 38 received over line 41. after being transmitted through transformer 44. amplified by amplifier 45. and transmitted through the phase shiftin transformer 56 is impressed upon the speed control apparatus 51 like apparatus 81 for controlling the speed of motor 58.

The constant frequency current received over line 41 after being amplified by the amplifier 45 and transmitted through the phase shifter 56 is also impressed upon the primary winding of transformer 58 for controlling the circuit comprising the similar vacuum tubes 58 and 88 to produce a square-topped unidirectional voltage having a fundamental frequency equal to the frequency'of the constant frequency current source 38. The grids of each of the tubes 59 and 88 are negatively biased by the battery 8|. The grid of tube 58 is also biased due to the potential drop across resistive elements 88, 81, 88 in response to anode current from source 89 and the grid of tube is biased due to the potential drop across resistive elements 62, 83, 84 in response to the flow of anode current from source 85. The cathode-anode circuit of tube 88 comprises resistive elements 62, 83 and 84 and battery 85, while the cathode-anode circuit of tube 88 comprises resistive elements 86, 81 and 88, like resistive elements 82, 88 and 84, respectively and battery 69, like battery 85. An adjustable contact on resistive element 84 is connected to the control electrode of vacuum tube 88 while an adjustable contact of resistive element 88 is connected to the control electrode of vacuum tube 58. One terminal of the secondary winding of transformer 58 is connected to a common treminal of resistive elements 62 and 88 and the other terminal is connected to a common terminal of resistive elements 88 and 81. The circuit elements are so chosen, that when current fiows in the anode circuit of vacuum tube 88, the grid of vacuum tube 88 is negatively biased to such a potential that no current can fiow in the anode circuit of vacuum tube 60 and that when current fiows in the anode circuit of vacuum tube 6|! the grid of vacuum tube 59 is negatively biased to such a potential that no current can flow in the anode circuit of vacuum tube 58. There is thus generated between the negative terminal of battery and ground a unidirectional electromotive force of square-topped wave form, one such square-topped impulse being produced for each cycle of the current impressed upon the transformer 58.

During the periods that current is flowing in the anode circuit of vacuum tube 59, a portion of the anode current from battery 65 flows through the potentiometer winding 10 and resistive element H to charge the condenser 72. When anode current is not flowing through tube 59, the condenser is discharged through a circuit including resistive elements 62, 68, 64, i0 and H, one terminal of resistive element 82 and one terminal of resistive element 70 being grounded. The circuit elements may obviously be so chosen that the condenser is charged at a rapid rate to a high potential less than the potential drop across resistive elements 62, 63 and 64 during one-half cycle of the current from source 88 and is rapidly discharged during the next half cycle of the current from source 38. The charging-discharging current of logarithmic wave formfiowing through the resistive elements 10 and II produces an electromotive force of corresponding wave form which is applied to the input circuit of three electrode vacuum tube I3. The grid of this vacuum tube is negatively biased by the battery 14 to such an extent that current flows in the anode circuit of vacuum tube 18 only when discharge current of considerable amplitude is flowing from condenser 12 through resistive elements 10 and H. Moreover, the anode current of vacuum tube 18 reaches saturation when the amplitude of the condenser discharge current is less than its maximum value. Therefore, during each cycle of the alternating current from source 18 vacuum tube it a current impulse of extremely short duration and of considerable amplitude. The, wave shape of this impulse is'substantially rectangular. The output circuit of vacuum tube 73 is connected to theinput circuit of vacuum tube it through a coupling condenser 80 and resistive element ?5.

In the output circuit of vacuum tube 55 there is connected a. battery 11 and a delay network 82 of a plurality of sections. The delay network is so designed that the diflerent sections, respec tively, introduce substantially the some delay and so that the phase distortion introduced by one section is compensated for by the phase distortion introduced by an adjacent section, thus making any pair of sections substantially free of phase distortion. If desired, each section may be so designed as to introduce the same delay for all frequencies over a wide range. As shown in the drawings, the T-type sections each comprise two equal inductive elements 5| and a capacitive element 92, while each of the bridged T-type sections comprise the two equal inductive elements .93, capacitive element 94 and capacitive element 55. Satisfactory results have been obtained by employing a network of this type in which the inductive elements 9|, comprising two windings on a single core tapped in the center, has a total inductance of .0232 henries, the capacitive elements 92 .00575 microfarads, the inductive elements 93 each .01162 hen'ries, the capacitive elements as .00576 microfarads, and the capacitive elements 95 .00144 microfarads. The .value of the terminating resistive element 8! was 2010 ohms. The input circuits of the vacuum tubes BI are connected to the terminals of different sections respectively of the delay network 82. There are as many vacuum tubes BI as there are columns of neon lamps E0, the cathodes of the lamps of' a column being connected to the'anode .of the vacuum tube 8| which controls the lamps of that column. Due to the potential of battery ii, the grids of vacuum tube II are normally negatively biased to such an extent that the current from battery 52 flowing through the lamps 5i! of a row connected in circuit by the commutator 54 and the anode circuits of vacuum tubes CI is of such amplitude that the lamps emit no light or only a small amount of light such as would be produced to represent black tone value. The negative bias is the same for all of the vacuum tubes, in the absence'of a starting impulse imsuitable value of capacity the impulse impressed upon the delay network ,82 may be made suiilciently brief so that the grid bias of only one of the tubes 8| at atime is-rendered less negative than the normal negative biasing potential with the result that only one lamp 5| at a time will emit light in accordance with-the tone value ofthe elemental area of the image to be produced under control of the image potentials impressed upon the input circuit of vacuum tube. II.

It is thus apparent that the lamps 5|. 0! the image producing lamp bank are energized one at a time in succession in synchronism with the of this type is disclosed in Patent 1,999,376,

granted to H. M. Stoller April 30, 1935.

Instead of employing a large number of individual lamps, one for each elemental. area, a plurality of multi-electrode lamps of the type disclosed in Patent 1,759,504, granted to F. Gray May 20, 1930, one for each line, may be employed as shown in Fig. 2. In this arrangement, instead of impressing a direct current having the image current variations upon the circuits of lamps through the distributor 54, as shown in Fig. 1, the received image current after being amplified by the amplifier I20 is impressed upon an oscillator-modulator I5I to produce in itsoutput circult a high frequency alternating current modumay be maintained constant.

The individual electrodes are preferably formed on the glass tubing forming the gas chamber by first covering all portions of the tube, except the portions at which the electrodes are to be formed. with a suitable material, such as adhesive tape. The exposed portions of the glass tubing are sand blasted to roughen the surface of the glass and these portions are then covered with a suitable metal by means of a Schoop gun. The adhesive tape is then removed and contact is made with each electrode I by tying a fine wire around the lass tube so as to make contact with the electrode. The electrodes I55 of each column are connected to the anode of one of the three-electrode vacuum tubes I8I. The cathodes of these vacuum tubes are connected to ground as is also one side of the source of modulated high frequency image current from oscillator-modulator I5I. As in the arrangement shown in Fig. 1, the control electrodes of the vacuum tubes IOI are connected to difierent sections, respectively, of a delay network I82. The anode of each vacuum tube I8I is also connected to a source of direct current I55 .through a choke coil I51 which prevents the high frequency modulated current from flowing to ground through the battery'l56. It is thus apparent that when the anode-cathode impedance of one of the vacuum tubes I8I is reduced, due to a positive impulse impressed upon its" grld, a circuit is completed from the grounded source of high frequency modulated image current at the output of oscillator-modulator I SI,

through a contact of distributor I54, one of the common electrodes I52, I53, one of the individual electrodes I55, the anode of one of the vacuum tubes Ill, and thence to grounded cathode of the. vacuum tube I8I. As will be understood from a consideration of the above description in connection with Fig. 1, a glow discharge is thus produced at different positions in succession of the multi-electrode lamp bank to produce an image.

What is claimed is:

1. In combination, a plurality of electric discharge tubes, an input and an output circuit for each of said tubes, a plurality of signal responsive means each connected in the output circuit of one of said tubes, a source of electromotive force the amplitude of which varies in accordance with signals connected in said output circuits, a delay network having a plurality oi! delay sections connected in series, the input circuits of said electric discharge tubes being connected to diilerent sections respectively of said delay network, and means for impressing an electric impulse upon said delay network to cause said signal responsive means to be energized in succession in accordance with the amplitude of said signaling electromotive force.

2. In combination, a source of alternating current, means for converting said alternating current into a unidirectional current having a square-topped wave form and a fundamental frequency corresponding to that of said alternat ing current, means for converting said current of square-topped wave form into current impulses of logarithmic wave form, and means for converting said current impulses of logarithmic wave form into current impulses of high amplitude and of brief duration compared with the duration of said square-topped wave impulses.

3. In combination, a transmission network having a plurality of sections directly connected in series, each comprising inductive and capacitive elements, means comprising an electric discharge device for generating periodic impulses,

means for impressing said periodic impulses uponsaid network, and a plurality of devices responsive tosaid impulses associated with diflerent sections of said network respectively, each impulse having a duration less than the time required for transmitting it through one of said sections, thus causing said devices to be operated in succession.

4. In combination, a tron network having a plurality 01' sections directly connected 1 .0 in series, each section comprising inductive and capacitive elements, a plurality of electronic devices each having a control electrode connected to dlii'erent sections respectively oi. said network, a source of electromotive force connected to said network for simultaneously similarly biasing said control electrodes, and means for periodically changing said electromotive force to periodically change the biasing of said, control electrodes in succession.

6. A bank of light emitting elements for producing television images each within the period of persistence of vision, there being one element for each elemental area of the field of view an image of which is to be produced, a source of image current, a plurality of said light emitting elements being simultaneously directly associated with said source of image current, electronic means directly associated with said light emitting elements for causing them to emit light in succession in accordance with the variations of said image current, and means for controlling said electronic means comprising a delay network, and means for causing recurrent impulses tobe propagated along said network.

7. In combination, a plurality of signal producing devices each having two terminals, a source of signaling current connected to a common terminal of said devices, a plurality of electronic devices each having an anode-cathode circuit connected to the other terminals 01' said devices respectively, each signal producing device being directly connected in series with one of said anode-cathode circuits and said source of signaling current, and means for controlling said electronic devices to cause current from said source to energize said signaling devices in succession.

' 8. In combination, a delay network comprising a plurality of similar sections directly connected in series, each section comprising inductive and capacitive elements, a plurality of electron disto diflerent sections respectively of said delay netfor controlling said driving motor and said elec-.

tronic means for maintaining a desired time relationship between the selection of the rows and the selection of the light producing'elernents of each row, and means for simultaneously similarly changing the frequency or phase or the current from said source supplied to said motor and said electronic means.

11'. In combination, two electric discharge devices each having a control electrode, an anode and a cathode, a source of direct current connected in each anode circuit, a source of alternating current connected to corresponding portions of said anode circuits, means for connecting the control electrodes of each device to the anode circuit 'of the other device so that current flowing in the anode circuit of one of said devices will prevent the flow of current in the other of said devices, a circuit including a variable condenser and a resistive element in shunt with a portion of the anode circuit of one of said devices to cause current to flow-alternately in opposite directions in said condenser circuit, a third electric discharge device the input circuit of which is connected to said condenser charging and discharging circuit, a source of biasing potenreaching saturation before the current in said condenser circuit reaches a maximum amplitude.

12. In combination an electric discharge device, an input and an output circuit for said device, a source of varying current, means to be energized by current from said source connected to said output circuit,- commutator means for connecting saidsource-of varying current to said output circuit at intervals, a delay network connected to said input circuit, means for impressing an electric impulse upon said delay network to cause said first-mentioned means to 7 pulse upon said delay network.

13. In combination an electric discharge device, an input and an output circuit for said device, a series circuit comprising a source of signaling current, signal producing means to be energized by current from said source, said output circuit and commutating means for connecting'said source to said output circuit at intervals, a delay network connected'to said input circuit, means for impressing an electric impulse upon said delay network at substantially the same time that said source of signaling current is connected to said output circuit to cause said signal producing means to be energized by current from said source of signaling current at a predetermined interval after said electric impulse is impressed upon said delay network.

I I4. In combination a delay network comprising a plurality of sections directly connected and having a delay characteristic which is substantially the same for all frequencies over a wide frequency range, means for impressing electric wave energy upon said network, and a plurality of means responsive to said electric'wave energy connected to different sections, respectively, of said network.

15. In combination a delay network comprising a plurality of sections, alternate sections of which have different phase characteristics, respectively, such that the phase distortion introduced by one type of section is compensated for by the phase distortion introduced by the other type of section to obtain a substantially zero phase. distortion characteristic for any pair of connected sections, means .for impressing'electric wave energy upon said network and a plurality of means responsive to said electric wave energy connected to diiferent sections, respec-- tively, of said network, each of said sections comprising an inductive element and a capacitive element, said inductive elements being directly connected in series.

- 16. In combination a delay network comprising a plurality of sections directly connected.

5 one section of which has a delay characteristic different from that of another section to give an over-all desired delay characteristic, means for impressing electric wave energy upon said network, and a plurality of means responsive to d said electric wave energy connected to difierent sections, respectively, of said network.

17. In combination, an electrical transmission circuit comprising a plurality of delay network sections directly connected in series each having inductive and capacitive elements, means for generating and impressing upon said transmission circuit an electric impulse having a duration less than 01 second, a plurality of devices responsive to said electric impulse electrically is connected to said transmission circuit at positions following different delay sections respectively along the direction of transmission oi said impulse. I

18. In an apparatus for producing images of so a field of view, an electrical transmission circuit comprising a plurality ofdelay network sections directly connected each having inductive and capacitive elements, means for generating and impressing upon said transmission circuit an electric impulse having .a duration of the order of the product of the reciprocal of the number of elemental areas in the field of view and the period of persistence of vision, and a plurality of devices responsive to said electric impulse electrically connected to said nsmission circuit at positions following diner nt delay sections. respectively along the direction of transmission of said impulse.

18. In apparatus for producing images of a 35 field of view, a combination in accordance with claim 18 in which the delay period of each delay section of the transmission circuit is of the order or the duration of said electric impulse.

20. In combination, an electrical transmission circuit comprising a plurality of delay network sections directly connected in series each-having inductive. and capacitive elements and a plu- 'rality of electric discharge devices having control electrodes connected to difierent delay sections, respectively, means for normally negatively biasing said control electrodes to reduce the currents flowing in the anode circuits of said electric discharge devices, and means for similarly changing the potential of said control electrodes in succession to permit current of increased amplitude to flow in said anode circuits, said means comprising means for impressing an electric impulse upon said transmission circuit.

21. In combination, a bank of light-emitting elements for producing television images, there being one light emitting element-for each elemental area of the field of view, an image of which is to be produced, and means for causing Q0 said light emitting elements to be energized periodically in succession, all within the period of persistence of vision, each in accordance with cuits or said electric discharge devices in succession to cause current from said source of television image current to energize said light producing devices in succession said last-mentioned means comprising a continuous delay network along which electric impulses may be propagated, means for connecting said input circuits to diiierent portions 01' said network respectlvely along the line of propagation, and means for impressing upon said network impulses the duration of which is less than the propagation time along said network ifroni one input circuit to the following input circuit along the line of propagation. and the interval between successive impulses being substantially equal to the time of propagation from the first input circuit to the last input circuit along the line of propagation.

WILLIAM A. KNOOP.

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