US2081705A - Detector circuit - Google Patents

Description

May. 25, 1937. JOBST ET AL 2,081,705

DETECTOR CIRCUI T Filed July 1, 1932 l l I I I I l I l INVENTOR GUNTHER JOBST WALDEMA W HNERT ATTORNEY Patented May 25, 1937 UNITED STATES PATENT OFFICE DETECTOR CIRCUIT Application July 1, 1932, Serial No. 620,524 In Germany August 13, 1931 13 Claims.

The present invention relates to circuit arrangements for the operation of thermionic tubes, especially for amplification work.

The optimum operating point of an electron tube from the viewpoint of grid potential, is a function of the use of the tube. In the case of tubes having the purpose of insuring amplification in accordance with a linear law the working point must be so situated upon the characteristic curve that the grid alternating current potential varying about the working point will lie outside the range of grid current, i. e. the region where grid current flows.

Tubes which are used as detectors (in which the curvature, or knee, of the grid-current characteristic is used for rectification work) must work at a point where the applied grid alternating current potential is such that the flow of grid current is beginning. The optimum condition for the operation of a tube is to adjust the working point on the tube characteristic in each particular case, though this requires considerable outlay where low priced apparatus are concerned. Fixed grid potentials involve the drawback that the inherent fluctuations in the point where grid current starts to flow, are disregarded so that it is not possible to determine or choose the optimum point.

The use of polarized cells offers the advantage that the optimum operating point is automatically adjusted. Now, according to the invention, a polarized cell is inserted in the circuit of the control grid of a thermionic tube. If, then, an alternating current potential is impressed upon the control grid of the tube grid current will flow since the tube operates initially without any biasing potential on the grid, however, the grid current will flow only across the polarizing cell. As a result the counter-electromotive force becomes active with the consequence that the grid current'is no longer able to flow.

In the drawing,

Fig. 1a shows a linear amplifier employing the invention,

Fig. lb is a graphic explanation of Fig. 1a,

Figs. 2a and 2b show rectifier circuits employing the invention,

Fig. 2c is a graphic explanation of Figs. 2a and 2b.

Referring now to the drawing: In the case of linear amplification (radio frequency amplification, resistance-coupled amplification), the invention operates in such a way that first, because of the peak (crests) of grid alternating potential externally applied, the potential of the polarizing cell l becomes adjusted to the crest (peak) value of the grid alternating current by charging of the cell. This potential is preserved during the subsequent operating interval. In that instance the entire grid alternating potential is located outside the grid current range. There is produced neither a damping due to the grid current, nor rectification due to the incipient curvature of the grid current characteristic. Where two or more tubes are concerned, this action may in the main be initiated only by a single tube, and this tube would then produce also the grid biasing potential for the other grid circuits.

Cells moreover offer the advantage that their charging beyond two volts is out of the question so that in the presence of excessive potentials occasioned by abrupt disturbances, no blocking of the tubes is liable to arise, though this would be feasible alone for reasons of the large capacity of polarizing cells only where the disturbances are of long duration.

The polarizing cell l consists of two electrodes, for instance, made of platinum, which are confined inside a vessel filled with feebly acidulated water. This cell preferably is then enclosed completely in paraffin or in a similar insulating substance in order to preclude evaporation of the liquid and in order to make it possible to build the cell in any desired position within an apparatus. The operation of the cell is as follows: If direct current is passed through a polarizing cell a concentration drop occurs between cathode and anode of this cell within the liquid, and this in turn occasions an electromotive force which acts in opposition to the flow of the current; (as in charging of a storage battery). The limiting value of this potential is a constant which is a function of the material of the electrodes and the liquid.

Now, while the formation of the counter-electromotive force in the cell takes place almost instantaneously, the disappearance of the electromotive force, when there is no longer an alternating current potential acting upon the grid, 45 requires a certain length of time which is considerable compared with the audio frequency actions or phenomena. In other words the counter-electromotive force (the self-generated negative grid biasing potential) is maintained for an interval of sufficient duration so that it may be regarded as perfectly constant for audio frequency and radio frequency control of the thermionic tube. The size of the electromotive force, and thus of the negative grid biasing potential, may be varied by suitable selection of the cell material (electrodes and liquid) and by a corresponding choice of the number of cells used.

In the case of alternating'current the polarizing cell acts like an electrolytic condenser whose capacity is high for audio frequencies as well as for higher frequencies. In the light of what precedes Fig. 1b of the drawing will be intelligible. The grid alternating-potential initially will cause grid current to flow with the result that the operating point on the characteristic will be shifted correspondingly in accordance with such value as the counter-electromotive force may assume, towards the negative end of grid bias potential. After the counter-electromotive force as conditioned by the size of maximum alternating grid potential, has assumed a steady value the tube will operate as if a fixed negative grid potential were inserted in the grid'circuit.

In the case of grid rectification as in Figs. 2a and 2b where a suitable resistance is connected in parallel with reference to the cell, charging and simultaneously discharging of the cell is produced. The operation of this arrangement is very similar to that of an audion, except for this difference that by suitable dimensioning, as a result of the automatic adjustment of the optimum point Where grid current begins to flow independence of this position is obtainable, so that operation of the tube would also be independent of fluctuations in the said point.

If the thermionic tube whose grid circuit contains a polarizing cell is to be used as a detector care evidently must be taken so as to cause a speedy destruction of such counter-electromotive forces as may have been established in the cell for audio frequency actions. This is attained in that an ohmic resistance suitably chosen in value is connected in parallel relation to the cell. If, then, a radio frequency potential comes to act upon the grid of the tube a grid biasing potential will first be established by the electromotive force of the cell. Interrupting this radio frequency, the cell will become discharged by way of the said parallel resistance, the negative biasing potential will fall again to zero, i. e.., the effect of the polarizing cell as then present is the same as with a standard audion. This operation is illustrated in Fig. 2c. The field of application of polarizing cells is generally the whole field of radio frequency oscillations as the cell is usable both as a negative bias as well as for audion purposes. 'Figs. 1b and. 20 show only by way of example the effect for 100% modulation of the radio frequency.

While we have indicated and described several systems for carrying our invention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organizations shown and. described, but that many modifications may be made without departing from the scope of our invention as set forth in the appended claims.

What we claim is: 1. A high frequency transmission circuit in cluding an electron discharge tube, a resonant input circuit connected between the controlgrid and cathode of the tube, the output electrodes being adapted for connection to a suitable load circuit, a cell connected in the grid circuit of said tube, said cell including platinum electrodes and a feebly acidulated water electrolyte, and being normally polarized in such a manner that flow of rid current in the grid circuit produces a cell potential in opposition, and the impedance of the cell being sufficient to enable the said opposing: potential to bias said grid negatively after the flow of said grid current ceases.

2. A wave repeating system comprising a space discharge device, input and output circuits for the device, means for applying signal frequency energy to the input circuit, means comprising an electrolytic cell connected to be energized by the flow of current in one of said circuits for applying a biasing potential to said space discharge device fora period of time materially longer than the time said cell is energized.

3. A wave repeating system including a space discharge device, input and output circuits for the device, means for applying a signal to the input circuit, means characterized by having a limiting E. M. F. which is reached by the potential built'up therein due to the flow of grid current in said input circuit and which is not exmeans for applying a signal to the input circuit, n

a resistance-capacity circuit combination in said system, means for applying a biasing potential to said input circuit for a period of time materially longer than the time constant of the resistancecapacity combination, and connections for energizing said last mentioned means by the flow of current in one of said tube circuits.

5. A wave repeating system including a wave repeating device, input and output circuits for said device, means for applying a signal to the input circuit, a condenser, connections for passing current flowing in one of said circuits through said condenser, means for maintaining a potential diiference between two points thereof for a period of time materially longer than the discharge period of said condenser, connections for applying a potential from the last mentioned means to an input electrode of said device, and connections for energizing said last mentioned means to set up and maintain said potential difference from the current flow in one of said circuits.

6. A wave repeating system including a wave repeating device, input and output electrodes for said device, circuits connected to said electrodes, means for applying a signal to one of said circuits, a. capacitive reactor, connections for passing current flowing in one of said circuits through said reactor, means for maintaining a potential difference for a period oftime materially longer than the discharge period of said reactor, connections for applying a potential from the last mentioned means to an input electrode of said device, and connections for energizing said last mentioned means from the current flow in one of said circuits.

7. A wave repeating system comprising a thermionic device, input and output electrodes in said device, input and output circuits connected to said electrodes, means for applying a modulated radio frequency signal to an input circuit of said device, means including a polarization cell for maintaining for an interval materially longer than a cycle of the frequency of the modulation of said modulated radio frequency signal a potential set up therein, connections for energizing the last mentioned means from the radio frequency peaks of said modulated radio frequency signal, said last mentioned means having a limiting value for the potential built up therein by said radio frequency peaks, and connections for applying said potential to an input electrode of said device.

8. A wave repeating system comprising at least one vacuum tube, input and output circuits for each tube in said system, means for applying a wave train to said system, means including a polarization cell for maintaining a potential difference for a period of time materially longer than the cycle of the waves being repeated in said system, and connections for energizing said last mentioned means by the flow of current in one of said circuits to establish said potential difference, and connections for utilizing the potential difference established in said means for controlling the action of said system.

9. A wave repeating system comprising a vacuum tube, input and output circuits for said vacuum tube, a grid bias producing electrolytic cell, connections for applying a potential from said cell to said input circuit, connections for energizing said cell by the flow of current in one of said circuits, and means in said cell for maintaining the potential set up therein by the flow of energizing current therethrough for a period of time materially longer than the period during which said energizing current flows through said cell.

10. A wave repeating system comprising a space discharge device, input and output electrodes in said device, an input circuit connected between said input electrodes, a tuned circuit in said input circuit, an electrolytic cell connected in said input circuit between said tuned circuit and one of said input electrodes, and a resistor and a condenser each connected in parallel with said electrolytic cell.

11. A wave repeating system comprising a space discharge device, input and output electrodes in said device, a circuit connected between certain of said electrodes, a tuned circuit in said circuit, an electrolytic cell connected in said circuit between said tuned circuit and one of said electrodes, and a resistor connected in parallel with said electrolytic cell.

12. A wave repeating system comprising a space discharge device, input and output electrodes in said device, an input circuit connected between said input electrodes, a tuned circuit in said input circuit, an electrolytic cell connected in said input circuit between said tuned circuit and one of said input electrodes, a capacitor connected in parallel with said electrolytic cell and a resistor connected directly across the cell.

13. A radio frequency wave repeating system comprising a space discharge device, input and output electrodes in said device, a tuned input circuit connected between said input electrodes, an impedance connected across said tuned input circuit, and an electrolytic cell connected across at least a portion of said impedance.

GUN'IHER JOBST. WALDEMAR WEHNERT.

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