US2097902A - Detector circuit - Google Patents

Description

` Nov. 2, 1937. R, URTEL 2,097,902

DETECTOR C IRCUIT Filed June 1, 1953 Iig, z

INVENTOR eL/00u' UerEL Wwm/ ATTO R N EY Patented Nov. 2, 1937 PATENT OFFICE DETECTOR CIRCUIT Rudolf Urtel, Berlin, Germany, assignor to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin, Germany, a corporation of Germany Application June 1, 1933, Serial No. 673,877 In Germany June 2, 1932 4 Claims.

The present invention relates broadly to detector circuits and more particularly to detector circuits of the type utilizing grid rectification. It is one of the features of the present invention that screen grid type tubes are utilized in the detector circuits the screen element or which is used for the purpose of controlling certain characteristics of the tube.

The objects of the invention will be apparent from a reading of the following specication in connection with the accompanying drawing, wherein,

Figures 1 and 3 show Various curve sheets utilized in explaining the principles underlying the invention; and,

Figures 2 and 4 show various preferred embodiments of the invention.

The characteristic feature of grid rectification resides in the fact that with an increase of the amplitude of the carrier frequency the average voltage at the grid-condenser increases particularly in such manner that the grid potential moves into the negative region whereby the anode current decreases. The increase of the amplitude of the high frequency however is limited in that anode rectification begins when the negative bias is too highgso that an increase of the anode current occurs as indicated in Figure 1. The simultaneous occurrence of gridand anode-rectificaticn means distortion of the produced audio frequency. In View of the greater sensitivity of grid-rectification, it is in particular desirable to increase the range of control. This can obviously be accomplished by using higher voltages i. e. larger zero currents. However their choice is Very limited in view of the limitations in construction.

If for instance a screen grid tube is used as a demodulator, and if furthermore care is taken that at a higher negative bias the screen grid potential increases, (Figure 2), a compensation effect is obtained with the result that a considerably slower decrease of the anode current takes place than would be the case without compensating arrangement, in other words, at increasing negative bias the characteristic. again moves further towards the left, whereby the range of control increases. Thus it is possible in this manner to apply at the same operating currents as hitherto used, considerably greater amplitudes of the high frequency to the grid before additionalanode rectification occurs (Figure 3).

A special case of using a compensating circuit is presented by the so-called Wunderlich tube, see Electronics, April 1932 (Figure 4). Hereby (Cl. Z-27) it is however not intended to avoid occurrence of anode rectication, since this is from the beginning already avoided tc a very great extent due to the special construction of this tube and it is rather here the question of preventing ex- Vcess control at audio frequency. One could be inclined to consider to use a grid rectifier suited for great amplitudes, directly as end tube, however the fact is that by increasing the amplitude of the high frequency, the controllable anode current at audio frequency becomes smaller.

In using the above described compensating circuit it is possible to maintain the anode current nearly constant for any incident amplitudes of the high frequency and thus be able to control nearly the full anode current also for the highest carrier frequencies.

I claim:

1. In the operation of a screen-grid tube grid circuit detector, the method of maintaining the steady component of the plate current iiow substantially uniform despite variations in the strength of carrier energy applied to the input of the detector which comprises utilizing the variations in steady component of the plate current due to variations in the strength of the carrier energy to proportionately and in an opposite sense vary the screen grid voltage.

2. In the operation of a screen-grid detector circuit as a grid circuit detector, the method of preventing plate rectification within certain extended limits of operation of the detector which comprises producing in the plate circuit a voltage drop proportional to the ow of the steady component of the plate current therethrough and utilizing the produced potential drop to aifect the screen grid potential.

3. In a screen grid tube detector circuit arranged fcr grid-detection, a source of plate current and a circuit including said source and an impedance device in series connected from the cathode to the anode of said tube, a connection including a resistor element connected across said series source and impedance device sothat a series closed circuit is formed comprising the source, the impedance device and the resistance element, and a connection from the screen grid of the tube to a point intermediate the resistance element whereby the screen grid potential is caused to vary as the flow of plate current of the tube varies through the impedance element.

4. In a detecting circuit of the type including two signal grids connected so as to produce a radio frequency push-pull input circuit in connection with the cathode and an anode connected in connection With the cathode so as to produce a normal audio frequency output circuit, a shielding electrode for said tube, a source of plate cur- Y rent and a circuit including said source and an comprising the source, the impedance device and the resistance element, and a connection from the shielding electrode of the tube to a point intermediate the resistance element and arranged so that the screen grid potential is caused to vary 5 as the ow of plate current of the tube varies through the impedance element.

RUDOLF U'RTEL. l

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