US1739005A - Circuit arrangement for the operation of photo-electric cells - Google Patents

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Dec. 10, 1929. "A, KAROLUS 1,739,005

CIRCUIT ARRANGEMENT FOR THE OPERATION OF PHOTO ELECTRIC CELLS Filed Oct. 10, 1927 INVENTOR AUGUST KAROLUS.

TORNEY Patented Dec. 10, 1929' UNITED. STATES PATENT OFFICE AUGUST KAROLUS, or 'LFJPSIG, GERMANY, ASSIGNOR r0 RADIO CORPORATION or AMERICA, OI NEW YORK, N. Y., A CORPORATION OF DELAWARE CIRCUIT ARRANGEMENT FORTHE OPERATION OF PHOTO-ELECTRIC CELLS Application filed October 10, 1927, Serial Ito. 225,065, and in Germany September 29, 1926.

An application for this invention filed in Germany September 29, 1926.

The invention relates to the use of photoelectric cells of all kinds, whether of the high vacuum or gas filled kind, for the conversion of light variations into electrical actions, for instance, for the purpose of picture transmis sion and related arts. According to former rent source and ohmic resistance, and, due to the fluctuations of the cell currents produced by varying intensities of light reaching the cell and causing varying Voltage drops across the resistance, varying potentials were applied on thegrid of an amplifier tube havingits input circuit connected across the resist ance member. Further above in the amplifier cascade arrangement there was generally introduced an alternating current potential of convenient frequency in the shape of a carrier wave, in order that the very wide frequencybandof the current variations resulting from the picture exploration may conveniently and undistortedly be further amplified. The picture-point frequencies appear in this scheme as modulations of the carrier wave introduced into the cascade arran ement.

ow, in an arrangement ofthis kind, there resulted difliculties of manipulation of the amplifiers, and these were due to the fact that the sensitivity of present-day photo-electric cells is not quite constant. As a result, the value of the direct current grid potential corresponding to a definite illumination of the photo-electric cell was found to undergo changes at the amplifier tube whose grid di rect current potential is superposed upon the carrier fre uenoy, and this in turn results in alterations 0th of the amplitude as well as of the degree of modulation of the carrier oscillations. When these were used for con-' trolling a radio transmitter, then similar fluctuations in both directions were caused also in the complete modulation of the transmitter, with the result that difiiculties usually arose in picture transmission. The present invention obviates this inconvenience, by using an alternating current potential whose frequency at the same time governs the carrier frequency to be further amplified is used as a suction or anode potential at the photo-electric cell for the electrons released by the light. A pure alternating current potential must be used, or else the alternating current potential is superposed upon a constant direct current potential. Also an intermittent direct current potential obtained by the rectification of alternating current may be employed. To insure the desired effect either one of the said schemes is practicable.

ing current potential is usedas the suction By virtue of the fact that an alternator anode potential of the electrons, the current of this carrier frequency in the absence of light will always be completely controlled, since the photo-electric cell is then impermeable. It is then also possible to apply a perfectly linear amplification even to the first amplifiertube, upon the grid of which the photo-electric cell currents are brought to act, and manipulation of the arrangement becomesfree from such diificulties as usually arise in connection with the use of a pure direct current potential to act as the suction or anode potential of the photo-electric cell. The value of the alternating current suction potential, or the sumtotal of direct current andalternating current potential, may be so chosen in practice thatin gas-filled cells the glow-discharge potential is nearly reached or even exceeded at the crest values of the alternating current potential. In this manner, a supplementary positive ionization is obtained, and thus alarger current effect in dependence upon the light. It is possible in to the maximum picture-point frequency which is to be transmitted, in other Words, it should be correspondingly higher than the latter. 4

In order that in a method as hereinbefore disclosed the harmful action of electrode capacity of the photo-electric cell may be precluded, any'alternating current as may flow across the cell by capacity action must be compensated. For this object any suitable sort of compensation scheme may be used, for instance, a bridge arrangement of the kind shown in the drawing which forms a part of this specification.

Referring to thedrawing, 1 is the photoelectric cell which conjointly with the variable compensating condenser 3 and the alternating current resistances 4 and 5 represents the arms of the bridge 2. At the terminals 6 the alternating current potential of convenient frequency and amplitude is introduced, while a suitable direct current potential may in addition be connected in series with the cell 1. When the alternating current resistances 4 and 5 are equal, then the adjustable capacity 3 must be made equal to the electrode capacity of cell 1. Hence, in this arrangement any flow of current due to capacity across the cell is completely neutralized, since the capacity 3 provides that no potential difference will result between grid and filament of amplifier tube 7. The alternating current potentials there arising are merely due to the electronic and ionic con duction current when cell 1 is illuminated, and

7 they fluctuate in their amplitude in proportion to irradiation. Further amplification may then be effected conveniently by way of a transformer coupling 8 through which the alternating current potentials are fed to additional tubes.

I claim as my invention:

1. An arrangement for modulating a carrier frequency in' accordance with variations in light intensity which includes, a bridge- I structure, a photo cell connected to form one leg of saidbridge structure, a capacity forming a leg of said bridge structure adjacent saldjphoto cell, said capacity being of the order of magnitude of the capacity of said cell electrodes for conditions of minimum illumination on said photo cell, and a plurality of resistors connected to form the other two legs of said bridge, means for applying a carrier frequency potential at opposite ends of the diagonal of said bridge structure between the point of connection of said cell and capacity at one end and the point of con-- nection of the said resistors at the other end, so .as to provide by said carrier frequency potential a source of anode potential for said cell, and means connected across the second diagonal of said bridge for amplifying said carrier fr uency when modulated by hght changes a ecting saidphoto cell.

2. An arrangement for modulating a carrier frequency in accordance with variations in light intensity which includes, a bridge structure, a photo cell connected to form one leg of said bridge structure, a variable ca-' pacity forming a leg of said bridge structure adjacent said photo cell, said variable capacity being adjusted to be of the order of magnitude of the capacity between said photo cell electrodes for conditions of minimum illumination on said photo cell and forming a balance for said bridge. means for applying a carrier frequency potential at opposite ends of the diagonal of said bridge structure between said cell and capacity so as to provide by said carrier frequency potential a source of anode potential for said cell, and means connected across the second diagonal of said bridge for amplifying said carrier frequency when modulated by light changes affecting said photo cell.

3. An arrangement for modulating carrier frequencies in accordance with varying fluctuations in light intensities which includes, a bridge structure, a photo cell forming one leg of said bridge structure, a variable capacity forming a leg of said bridge structure adjacent said photo cell, and resistances of equal value forming the other two legs of said bridge structure, said variable capacity being of such value that the capacity between the photo cell electrodes for minimum illumination on said photo cell is compensated and an unbalanced condition in said bridge structure is obtained only through variations in the conduction current through said photo cell produced by varying light falling thereon, means for impressing a carrier frequency potential upon said cell in a manner to utilize said carrier frequency as a source of anode potential for said cell by connecting the said carrier frequency potential across one diagonal of said bridge between'said cell and said capacity at one end and between said resistances at the other end, and an amplifying means connected across the opposite diagonal of said bridge for amplifying said carrier frequency when modulated by varying light values changing the conduction currents through said photo cell.

4. An arrangement for modulating a carrier frequency in accordance with varying intensities of light and shade, which includes, a bridge structure having a photo cell arranged to form one leg thereof, a capacity forming. an adjacent leg thereof, and a plurality of impedance members forming the other two legs of said bridge, said photo cell being subjected to varying intensities of light and shade for producing therein a varying members at the other end a carrier frequency potential of a Value such that the glow discharge potential of the cell is substantially reached when the carrier frequency alte1' hating current potential has its crest value across the said diagonal, and means connected across the second diagonal of said bridge for amplifying said carrier frequency po tential as modulated in accordance With variations produced in said photo cell, the variations in light and shade reaching the same.

AUGUST, KAROLUS.

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