US2218989A - Detector - Google Patents

Description

OCL 22, 1940. w. KLEEN 2,218,989

DETECTOR Filed Aug. 11, 1938 0 1 (w) wfzxzg zw v BY MIT-14.}

ATTORN EY Patented Oct. 22, 1940 UNITED A STATES Werner Kleen, Berlin, Germany, assignor to Telefunken Gesellschaft fiir- Drahtlose Telegraphic m/b. H., Berlin, Germany, a corporation of Germany.

Application August 11, 1938, Serial No. 224,297 In Germany September 1, 1937 4 Claims. (01.250-27) The invention is concerned with a rectifier adapted for the detection of signal currents, demodulation of modulated carrier waves, etc., which distinguishes itself by a particularly satis- '5 factory rectifying effect. 7

What is utilizeed in-the so-called plate-current detection to insure a rectifier effect-is the fact that the characteristic, upon, both sides of the operating point, in the neighborhood of the lower bend of the grid voltage-plate current curve, presents a different slope. The slope, in the ideal case, is of zero value upon one side, that is, in the direction of negative grid biasing voltages, while, upon the other side, it is equal to the slope of the 5 straight portion of the characteristic. However, the situation would be most favorable if the slope upon one side of the operating point were not merely zero, but rather negative, that is, as negative as it is positive in the other direction. To

20 realize such a characteristic for rectifier work is the object of this invention.

What is used according to this invention is an electron tube in which a virtual cathode is built up between the electrode controlled by the oscilla- 25 tions to be rectified or detected and the anode or plate to which the consuming device or load is connected, the result and action of the said virtual cathode being that the plate current, as a function of the voltage of the input electrode,

30 assumes a crest value which preferably is located inside the range of negative potentials of the input electrode.

In the drawing, Fig. 1 shows an exemplified embodiment of the invention, and Fig. 2 shows 35 characteristic curves which'will serve to explain the invention.

In the circuit of Fig. 1, the tube R acting as the detector or demodulator comprises a cathode K indirectly heated by the heater H, four grid elec- 40 trodes denoted by GI to G4, and an anode or plate A. The heating potential is applied .across the terminals l and 2. Impressed upon the grid GI adjacent the cathode are a negative biasing potential as well as the oscillations to be rectified, the latter being fed in by way of terminals 3, 4. The other grids are impressed with constant potentials; that is to say, the second and the fourth grid receive a positive potential which is 50 less than the plate D. C. voltage, and the third grid is impressed with a low negative biasing voltage. Under certain circumstances, this lastnamed grid could be impressed with zero potential or even a small positive potential. The recti- 55 fied potential or modulation frequency with which the input potentials are modulated is delivered from the anodecircuit by way of terminals 5, 6;

The characteristics shown in Fig. 2 we're-ob tained with an indirectly heated four-grid'type of tube, the electrodes of which were spaced apart, 5 as follows:

-'1V[illimeters Cathode to first grid (GI) 'L 0.4 First grid to second grid (G2) 1.0 Second grid to third grid (G3) 4 to 6 10 Third grid to fourth grid (G4) 2.0 Fourthgrid to plate (A) 2.0

The potentials that were applied were as follows: 200 volts to the plate (A) and 80 volts to the second and fourth grids (G2 and G4).

In the space between the second (G2, and the third grid (G3) there is set up a virtual cathode KV. The action of the latter is such that, from a definite density of the current, the electrons flowing through the second grid do not continue traveling towards the anode or plate, but are arrested or reverse their sense of flow. In order to promote the said virtual cathode it is, on the one hand, expedient to make the distance between the grids where the virtual cathode is to be built up, appreciably greater than the other inter-electrode spacings; moreover, it is expedient to work l with a comparatively great current density. For

instance, with the tube here used, the electronic current escaping from the cathode, at a potential of the input grid of zero value, amounted to 25 milliamps, and of this only a fraction reaching the anode or the fourth grid, while the balance of electrons was caused to-reverse anteriorly of the third grid.

The operating point for rectification is placed in the crest of the plate-current curve, and this may be accomplished by variation of the biasing voltages at the first or at the third grid. As can be seen from the characteristics, the slope, in both 40 directions from the crest of the graphs, is approximately of like value, though of opposite signs. In other words, the presuppositions and conditions for particularly efiicient rectification are here fulfilled, contradistinct from what is true in the conventional type of discharge tubes of a simila nature. I

What I claim is:

1. A circuit arrangement for the detection of hig-hfrequency currents comprising a discharge device having a cathode, an anode, and a plurality of grids interposed in the space between said cathode and anode, means for impressing signal potentials upon the first grid adjacent the cathode, means for impressing upon the remainand means for impressing upon the signal grid a negative potential for locating the operating point at the crest of the converging portions of the characteristic curve.

2. A circuit arrangement for the detection of high frequency currents comprising a discharge,

device having a cathode, an anode, and a plurality of grids interposed in the space between said cathode and anode, an input circuit for impressing signal potentials upon the first grid adjacent the cathode, means for impressing upon the remaining grids and the anode potentials of such values and the spacings of the several electrodes being such that a. virtual cathode is built up between two of said remaining grids, the curve of the anode current-input grid voltage characteristic being comprised of two converging portions having positive and negative slopes in the region of negative voltage, and means for impressing upon the signal grid a negative potentialof such value that the operating point is located at the crest of the converging portions of. the characteristic curve.

3. A circuit arrangement for the detection of high frequency currents comprising a discharge device having a cathode, an anode, and a plurality of grids interposed in the space between said cathode and anode, means for impressing a positive potential upon the anode, means for impressing signal potentials upon the first grid, means for impressing upon an intermediate grid a positive potential which is less than that impressed upon the anode, and means for maintaining a third grid at a relatively low constant potential with respect to the cathode, the spacing between the intermediate and third grids being such that a virtual cathode is formed in the space between said grids.

4. A circuit arrangement for the detection of high frequency currents comprising a discharge device having a cathode, an anode, and first, second, third and fourth grids interposed in the space between said cathode and anode, means for impressing a positive potential upon the anode, means for impressing sign-a1 potentials upon the first grid, means for impressing upon the second and fourth grids a positive potential which is less than that impressed upon the anode, and means for maintaining the third grid at a relatively low constant potential with respect to the cathode, the spacing between the second and third grids being such that -a virtual cathode is formed in the space between said second and third grids.

WERNER KLEEN.

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