US2104107A - Automatic gain control - Google Patents

Description

4, 1938. A. J. H. VAN DERVEN 2,104,107

AUTOMATIC GAIN CONTROL I Filed Feb. 18, 1931 INVENTOR ADRIANUS 1. H. Van denVEN ATTORNEY Patented Jan. 4, 1938 UNITED STATES PATENT OFFECE 2,104,107 A 'roMATIo GAIN CONTROL Application February 18, 1931, Serial No. 516,539 In the Netherlands April 15, 1930 7 Claims.

This invention relates to wireless receiving cir' cuit arrangement with automatic volume con trol. Automatic volume controls are known, and are frequently used in present day radio receiving sets. In most cases a separate rectifier is used in the output circuit of which a resistance is connected, and Whose input circuit receives the high frequency oscillation which may be amplified, or not. According to the strength'of the signals being greater or smaller, a stronger or weaker'direct current is set up in the resistance connected intothe output circuit of the rectifier. This direct current causes a drop of potential in the resistance, and this drop is used for regulating the negative grid bias of one of the high frequency amplifying tubes. Furthermore, it has already been proposed to control the mega tive grid bias of one of the high frequency amplifying tubes by means of resistance connected in the plate circuit of the detector tube.

According to mypresent invention the negative bias in one of the high frequency amplifying tubes is obtained by connecting the'grid of the detector tube, preferably across a high resistance, to a point situated at the filament side of the grid circuit of one of the high frequency amplifying tubes. Between this point and the cathode of the high frequency amplifying tube in question a condenser is inserted, by which the production of undesired coupling effects is prevented, and,

in addition, the connection between the grid of the detector tube and the cathode of the high frequency amplifying tube is blocked for direct current.

The novel features which I believe to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically one circuit organization whereby my invention may be carried into effect.

The figure shows a receiving antenna I which, by means of a small condenser 3, is coupled with the tuned circuit 2, the latter being connected to The source of heating current is denoted by Instead of the battery shown on the diagram, another source of current, for example a transformer connected to a commercial power line, may naturally be used. Into the plate circuit of the detector 9 a telephone IE, or other load resistance is connected. The resistance !2, which may also be replaced by an impedance of a more general nature, is so chosen that the grid of the detector tube 9 is not unfavorably affected by the presence of this resistance, or impedance. The condenser I3 serves at the same time to prevent any undesired coupling between the grid circuit of the detector tube and that of the amplifying tube 4.

Furthermore, care should be taken, of course, that the grid bias of the tube 4 Which is regulated by the connection provided according to the invention, is independent of the low frequency voltage variations of the grid of the detector tube. This may be easily obtained by a proper choice of the magnitude 'of the resistance l2. The circuit arrangement, according to the invention, may be easily constructed, and requires only a small capacity of the condenser is, since there is no objection in giving the resistance I 2 a very high value (for example 1 to 2 bcgohms, or still more).

When applying the known device above referred 'to, in which the grid bias is obtained from a resistance placed in the plate circuit of the detector tube, then in order to prevent undesired coupling with the grid circuit of the amplifying tub-e 4, a much larger capacity'must be coupled in parallel to the resistance from which the grid bias is obtained.

Of course,'the invention may be also applied -to circuit arrangements comprising tubes having indirectly heated cathodes. The modifications required in this case in the diagram of connections may be easily provided by those skilled in the art. Again, while I have indicated and described one arrangement for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be amplifier tube to impress upon the amplifier grid a potential developed by grid current flowing through the detector gridleak.

2. In combination, in a radio receiver including a radio frequency amplifier stage provided with a tube having a tunable input circuit and a detector stage provided'with a tube having a tunable input circuit coupled to the output circuit of the amplifier tube, an electrically conductive path, including an impedance of a predetermined magnitude, connected between the grid of said detector tube and the grid of said amplifier tube, a condenser connected between the detector grid and the high potential side of the detector input 3 circuit, a grid leak resistor connected between the grid and cathode of the detector tube, said path being connected to the detector grid at a point intermediate the condenser and the grid terminal of said resistor.

3. In combination, in a radio receiver including a radio frequency amplifier stage provided with a tube having a tunable input circuit and adetector stage of the grid leak type provided with a tube having a tunable input circuit coupled to the output circuit of the amplifier tube, an electrically conductive path, including an impedance of a predetermined magnitude, connected between the grid of said detector tube and the grid of said amplifier tube to impress upon. the amplifier grid a potential developed 'by grid current flowing through the detector grid leak, saidimpedance consisting of a resistor having a magnitude such that the grid bias of the amplifier grid is independent of the low frequency voltage variations of the detector tube grid. 7 a

4. In a signalling system including an amplifier having a vacuum tube provided with a control grid, and operating to amplify signals at frequencies above audibility, and a grid-leak detector, the method of controlling the degree of amplification in said amplifier which comprises utilizing current flowing through said grid-leak to vary the bias on the control grid of said amplifier.

5. In a signalling system including an amp1ifier having a vacuum tube provided with a control grid and operating to amplify signals above audibility, and a grid-leak detector, the method of controlling the degree of amplification in said amplifier which comprises filtering current flowing through said grid-leak and utilizing the filtered current to control the bias on the control grid of said amplifier.

6. In a carrier wave receiving system, one or more carrier frequency amplifying tubes, a detector tube having a grid-cathode input circuit and a cathode-anode output circuit, means for deriving a uni-directional voltage from the grid rectification action of said detector tube, the value of said voltage depending on the carrier first voltage, and means for applying said first voltage to at least one of said carrier frequency amplifying tubes, whereby the efiiciency of said tubes is modified in accordance with the carrier 'wave amplitude. V

7. In a modulated carrier Wave receiving system, at least one modulated carrier wave transmission tube, a detector tube having at least a carrier wave input electrode, a cathode and an anode, a modulated carrier wave input circuit connected between the input electrode and cathode, and an output circuit connected between the anode and cathode, means for impressing carrier wave energy transmitted by said transmission tube upon said detector input circuit, means for deriving a uni-directional voltage from the grid rectification action of said detector tube, the

value of ,said voltage. depending on the carriervoltage, and means for applying said uni-directional voltage to said transmission tube whereby the efficiency of the tube is modified in accordance with the carrier wave amplitude.

ADRIANUS J OHANNES HEINS VAN DER VEN.

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