US1871994A - Light-sensitive device - Google Patents

Description

Aug. 16, 1932. H. A. [ms 1,871,994

' LIGHT SENSITIVE DEVICE- Filed Jan. 1s, 1929 I4 l5 INVENTOR= Harley/910075.

' ATTORNEY Patented Aug. 16, 1932 UNITED STATES PAT NT", OFFICE *IHABLEIY Arms, or WILKINSBURG, PENNSYLVANIA, AssIeNon 'ro WESTINGHQUSE ntnc'rnrc a MANUFACTURING COMPANY, A conroaA'rroN or rnNNsYLvANLA LIGHT-SENSITIVE DEVICE Application filed January 18, 1929. Serial No. 333,470;

My invention relates to light-sensitive devices, and it has particular relation to the 'utilization of such devices for modulating a carrier current 'by means of light variations.

b Substantially all television systems, as at output current from which is then utilized in the transmission. a

The relatively feeble photo-electric currents are more readily amplified if they are made to modulate a carrier wave. At the 7 present time, this carrier is most usually supplied by interrupting the beam of light before it reaches the photocell by means of a revolving wheel having numerous apertures.

The use of a fluctuating voltage on the photocell to achieve a result analogous to the interruption of the light beam has been impractical in the past by reason of the capacity etween connectingf wires between the electrodes in the cell,'the percentage of 'modulation being thereby rendered unsatisfactory. It is, accordingly, an object of my invention to provide a novel combination of a photo-electric cell with circuit networks and auxiliary apparatus whereby the cell may be more efliciently utilized in television and sound-reproduction systems. Another object of my invention is to pro" vide a novel combination of a photo-electric cell with circuit networks and auxiliary apparatus. whereby a modulated, high-frequency photoelectric current may be generated."

Another, and more specific, object of my 7 invention is to provide, in a novel combina- 'tion of thetype described, means for supf a pressing a carrier current during non-m0d11- .lating intervals.

.Inpracticing m invention, I interpose a photo-electric cell in one branch of a circuit network analogous to a Wheatstone bridge,

and associate an output transformer or resistor with that portion of the network which corresponds to the diagonal of the bridge.

A source of oscillations, of any desired frecharacter of the illumination.

By my invention, therefore, I am enabled to prevent overloading of an amplifier associated with the photo-electric cell during nonmodulation intervals, inasmuch as the carrier ing solely determined by the. intensity and frequency is impressed thereon only during such times as the conductivity of the cell is altered under the influence of light.

The novel features that I consider characterist'ic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, to-

gether with additional applications, objects and advantages thereof, will best be 'understood from the following description of certain specific embodiments, when read in connection with the accompanying drawing, in

which Fig. 1 is a diagrammatic view illustrating" a native form of my invention which is capable of use in either of the systems shown in Fig. 1andinFig.2.

The facsimile-transmitting system illus- 9 trated in Fig. 1 comprises a source l'of modulated carrier-frequency currents, a carrierand a radiating structure, or antenna Inasmuch as the specific manner in which the amplifiers and the harmonic generator are frequency amplifier 2, a harmonic producer or frequency changer 3, a power amplifier 4 I constructed constitutesno ipeaert n enyelope 8 in which are disposed a cathode 10 and an, anode 11, is. positioned within the cylinder. i Y Y The photo-electric cell is so included ina balanced-circuit network as to constitute one:

of the capacitative elementsthereof. The

network preferably comprises an input -in-. ductor 12, which mayor may not be shunted by a. tuning condenser 13, a resistor 14- and a balancing condenser 15 connected in the .bridge arm opposite thephotocell, and an output reactor 16 and biasing battery 17 connected between an intermed1ate.point on the input inductor and the cathode. The output inductor may be shunted by a condenser 18,

if desired.

-' A source 20 of carrier-frequency oscilla-- tions is coupled to the input inductor. The source maybe an oscillation generator of any desired type, or it may be constructed and ar- ."In the operation ranged as hereinafter described.

A fixed light source 21 is disposed adjacent to the rotatable cylinder, and a 1ense22 is provided to focus light therefrom to a point upon. the film.

scribed, the biasin battery is so adjusted that it is roughly equa to the peak voltage of the A. C. wave, permitting the voltage on the hotocell to swing from zero to approximatey twice the A. C; peak voltage. The balancing condenser 15 and balancing resistor 14 are next so adjusted that no potentials appear across the diagonal of the network, comprising the output reactor and the biasing battery, by reason of A. G. potentials impressed light from the source 21.

across the input inductor. from the oscillator, during such time as the photo-electric cell is in darkness, or is exposed to the normal amount of light incident thereon, exclusive of When the balance of the network is disturbed, however, by reason of, variations in resistance of the photoelectric cell occasioned by variations in the light falling thereon through the rotating film,'the carrier frequency will appear in the output reactor, modulatedproportionhlly to thelight variations.

It will, accordingly be apparent that, by my invention, I have provided a system whereby the carrier-frequency is preventedfrom causing overloading of the amplifier phocurrent modulated in accordance with a munity against the detrimental effect of strayof the system debalancing condenser 15 and the resistor 14,

cathode of thecell and e condenser 15.

on the amplifier stages is strictl propor- (0 'tional to the li ht falling upon t 'e photoelectric cell, an during non-modulating intervals, the carrier frequency is entirely absent from the coupling reactor and is not impressed at all upon the amplifier. 76

Theap lic'ation of my invention to systems for the electrical'reproduction of hotographiesound-records isillustrated in 2 of the drawing. Such system prefera 1y 1 comprises means 30'-for producing a carrier- 80 sound-record, a carrier-frequency amplifier 31, a detector and audio-frequency amplifier 32, and a'suitable loud-speaker v33.

The carrier-current producing and modulating portion of the system is substantially the same as the carrier-current source 1 shown in Fig. 1, conventional means for supporting and advancin a film 34, carrying a photographic soun record, being substitutedfor the rotating cylinder 6 of the facsimile transmitter.

' There are no essential differences in the operation of the two systems. An additional a vantage'accrues, however, from the use of '6 E my invention in the re roduction .of sounds photographically recor ed on motion-picture hns, inasmuch as it provides practical imelectrical potentials picked up by the am- 1 plifier wiring and by other connections. If the carrier frequenc employed is sufliciently high, the couplingevices in the carrier frequenc amplifier may be so constructed as tobe su stantially opaque to disturbances at audio-frequencies, with the result th'at the reproduced sound is singularly free from the back-ground noise inevitably present when all the amplification between the photo-elec tric cell and the loud-speaker is at audio-frequencies, asheretofore hasbeen' customary.-

In case it is considered desirable to coup the oscillator to the photo-electric cell direc 1y, instead of inductively, as shown in Figs. 1 and 2, this may readily be accomplished in many difierent wa s. One convenient cou pling network is i Iu'strate'd in Fig. 3 and comprises a thermionic tube 40, the grid and plate of which are so. connected to opposite terminals of the input inductor 12 as to constitute the. well known shunt-feed Hartly oscillation generator. The photo-electric cell and the alancing circuit, comprising the are connected to the inductor 12,: as herein.- before described,- and a connection, including the biasin -battery.17 and an out at resistor 35, exten between an ate point on the inductor and the 'un'ction between the that I have made a decided improvement in 1 the utilization of photo-electric cells in car- 'rier-current picture-transmission It will be apparent, from a consideration of the foregoing description of my invention,

s stems and in systems-for the electrical repro uction of photographic sound records. By reason of the fact that, when using my invention in systems of the types referred to, saturation and overloading of the amplifier stages are obviated, the amplifiers may be materially reduced in capacity, with a consequent saving in material cost and upkeep.

Many other advantages of my invention, as

well as modifications of the specific embodi-' ments thereof chosen for illustration, will at once be obvious to those skilledin the art to which it pertains. My invention, therefore,

is not to be restricted to theapparatus shown and described, butit is to be limited in scope only by the prior art and by the spirit of the ap ended claims;

jclalm as my invention: 1. 'In combination, a 11g 't-sensitive device having an anode and a cathode, a condenser, a resistor and an input inductor serially connected between said anode and said cathode, an output impedance device and a potentialsource extending between one of said electrodes and an intermediate point on said inut inductor, and means for impressing oscil- Y atory energy upon saidinput inductor. 2'. In combination, a light-sensitive device l 1 having an anode and a cathode, a condenser,

a resistor and an oscillatory input circuit serially connected between said anode and said cathode, an output impedance device and a potential source serially connected between one of said electrodes and a point on said Input circuit, and means for impressing oscillatory energy upon said input circuit.

'3. In combination, a light-sensitive device having an anode and a cathode, a condenser, a resistor and an oscillatory input circuit connected serially between said anode and said cathode, an oscillatory output circuit and a' potential source serially connected between one of said electrodes and a point on said input circuit, means .for impressing oscillatory energy upon said input circuit, and means for deriving light-modulated energy from said output circuit. a

In testimony whereof; I have hereunto subscriged my name'this 16th day oi January,

HARLEY A. IIAMS.

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