US2363985A - Automatic volume control device - Google Patents

Description

NOV. 28, 1944. w MQsER 2,363,985

AUTOMATIC VOLUME coN noL DEVICE Filed May 15 1941 ENE W LMMJ [j llIl- I 12/ i,

(RECTIFIER HIE AMPLIFIE- RECTIFIER INVENTOR W/L/IELM MOSER ATTORNEY 4 Patented Nov. 2a, 1944 2,363,985 su'rom'rrc VOLUME cournonnavroa Wilhelm Moser, Berlin, Germany; vested in Alien Property Custodian I Application m 5, 1941,-$erial No. 393,526 In Germany February 24, 1940 o 4 Claims. (01. 179-171) I In some directional receivers, ior instance, re ceiver systems comprising a plurality of directional antennae for short wave transoceanic reception, an amplitude-controlled RF, IF, or AF amplifier is required in which the phase between the input potential and the output potential remains constant for the entire control range, that is, for all amplifications. 'This is difii'cult to achieve because of the fact that during the con trol action the internal resistances oithe amplifier tubes and possibly also their capacitances fluctuate with variations in the space charge.

' Referring firstto Fig.1, an amplifier tube I has its control grid 2 connected to a source of RF potential to be amplified, this potential being The effect of the control action, or regulation oi the grid biasing potential, alterssthe tube characteristics and thus'the phase, particularly if tuned grid and plate circuits" are employed, 'as is usually the case in 11'' and RF amplifiers. On the, other hand, the slighest phase variation between' the signal energies brought together from a number or receiving antennae and associated receives results in very unsatisfactorydistortion.

This is especially, noticeable in navigation systems and long distance short wave systems such asthe Musa system. 1

Conditions must thus be made so that even very small phase shifts do not occur in the receiver. It is, therefore, an object or my invention to provide means for preventing the occurrence oi.phase shiits as tar as possible, and throughout the entire control range.

It is another object of my invention to provide I means for avoiding large amplitude variations in the usual A. V. C. circuit. The control .bias isso chosen as to avoid variation in the total internal grids 2-and B.

resistance of the tubes connected in parallel. The

result is that a phase shift or the output potential with respect to the input potential is precluded.

My invention will now be described in more detail, reference being made to the accompanying drawing wherein.

Figure 1 shows one form of circuit organization; and

Pig. 3 shows a modification.

'fed through the tuned circuit 3. Y control potential is fed by way of resistance 4 The volume to the lower point of the oscillatory circuit, as is usual. 'The amplifier tube I has a plate-cathode path connected to the tuned circuit 5 which is coupled to the grid circuit of the following stage 6. I! desired, an input rectifier for an RF or IF stage may be connected with circuit 5, although this has not been shown in the drawing.

In parallel relationship .tothe plate-cathode path of tube I is connected another tube I which of itself acts like a variably controlled resistance. The control grid 8 is connected through resistor 9 to a potentiometerh the voltage drop across which depends upon the output potentials from the amplifier 8 after rectification in the device I0. This same device also supplies rectified potentials to the potentiometer d. The junction between potentiometers d and h is connected to the negative side of a direct current biasing source I I. A potentiometer I2 is connected across the terminals 01' the source II and has a grounded tap for adjusting the steady D. C. bias .on the two The A. V. C. action on grid 2 of tube I, as obtained through the tap on potentiometer d is exactly opposite to that which is applied to grid 8 or tube 1, since thegrid I derives its control bias from the tap on potentiometer it. What is thus obtained is that, for instance, with increasing internal resistance of tube I, the internal resistance of tube 1 decreases. The same holds true as far as a possible capacitance variation of the platecathode paths in the two tubes I and I is concerned. In other words, the capacitance variations of these two tubesare caused to vary in an opposite sense.

The circuit organization of the invention may be carried into practice, for instance, by choosing tubes I and 1 oi the same type. It .can then be easily understood that for small amplification variations the required symmetric variations or the internal resistances and capacitances of tubes I and l are actually fulfilled. But for large control ranges it is not always possible to obtain or even to expect symmetric variations of the tube characteristics. For this reason tube I is either chosen of such type in comof both tubes.

Referring now to Fig. 2, 'I show a modification in which the discharge tube 2| is provided with a novel input circuit arrangement designed to compensate for variations in its'grid-cathode capacitance. This input circuit leading to the grid 22 derives signal potentials across the transformer 23 the secondary of which may be tuned by means of the variable capacitor 24. The D. C. bias potential for the grid 22 is derived through resistor 25 and potentiometer d one end -of which is connected to the negative side of the D. C. source I I. This source has connected across its terminals a potentiometer I2 having an adjustable grounded 'tap, the same as shown in Fig. 1 and for the same purposes.

In parallel with the signal input circuit arrangement for the tube 2| I provide a space discharge path consisting of a discharge tube 26. This tube has a grounded cathode, a. grid 21, and an anode 28 fed with positive D. C. potential from the D. C. source 29 through the choke 30. The anode 28 is also coupled across capacitor 3| to the grid 22 of the tube 2|.

The tap on potentiometer d is connected to one end of resistor 32. Resistors 32 and 33 are interconnected and their junction is coupled across capacitor 35 to the grounded cathode of tube 26. The grid 21 is connected to the junction between resistor 33 and capacitor 34. The other side of this capacitor is connected to the anode 28. The plate to cathode impedance of tube 26 is caused to simulate a capacitance by employing the phase shifter 34-43. The condenser 3| 'applies signal potential to plate 28. The. phase shifter causes the signal potential across resistor 33 to be in 'phase quadrature with the plate potential. The A. V. C. biasv applied, throughre sistors 32 and 33, to grid 21 controls the amplifrom d.

TheA. V. C. lead, as will be noted, is preferably connected both to the grid 22 of tube 2|, across resistor 25, and to the grid 21 of tube 26, across resistors 32-33. The A. V. C. action may, however, be made the same or different with respect to the two tubes, the necessary adjustment being provided by the selection of values for the'two resistors 25 and 32 respectively. Hence the most favorable characteristics or working points of the two tubes may be obtained for insuring exact compensation. For example, when the negative volume control potential increases,

the grid-cathode capacitance of tube 2| tends toincrease as a result of the increased space charge,

7 while the capacitance acting between the plate,

and cathode of tube 26 decreases with a leveling off of the characteristic slope in this tube.

' I claim: I

1. In combination with a source of high frequency signal voltage, an amplifier tube having a tuned input circuit coupled to said source,

'for varying the gain of the second tube in a capacity change, said last varying means being i means responsive to signal amplitude variations for varying the gain of said amplifier tube; means for compensating for variations in tube input capacitance caused by said gain variation, said compensating means compvising an electron discharge device having at least a cathode, anode and control element, means connecting the oathode to anode impedance of said device in parallel to said amplifier inputcircuit, means for applying to said control element alternating potential which is in substantial phase quadrature with the anode alternating potential of said device thereby to cause said impedance to simulate a capacitance, and a connection from said control element to said ga'in varying means whereby the simulated capacitance and said input capacitance vary in inverse senses. I

2. In a wave amplifier of the type including a tube provided with at least a cathode, signal grid and anode, the method including applying signal voltage to said tube, adjusting the gain of the tube in response to signal amplitude variations, deriving from the applied signal voltage, a second signal voltage in phase quadrature therewith, establishing an electronic impedance, between said grid and cathode, utilizing saidquadrature voltage to cause said impedance to simulate a reactance, and varyingthe magnitude of said impedance in response to said signal variations in a sense to have the simulated reactance compensate for a shift of grid to cathode ca-. pacity shift arising during gain adjustment of said tube.

3. In combination with a source of alternating current voltage, a first tube having an input circuit coupled to said source, means for regulating the gain of said tube thereby causing an undesirable change in input capacity of said tube, means for compensating for said undesirable change comprising a second tube whose plate to cathodeimpedance is effectively in parallel with said input circuit, means for applying to a control element of the secondtube alternating current voltage derived from said source but in substantial phase quadrature with the alternating voltage at the plate of the second tube thereby to cause said impedance to simulate capacitance,

and means for varying the gain of the second tube in a sense such as to cause the simulated capacitance-magnitude to vary inversely to said undesirable capacity change.-

comprising a second tube whoseplate to cathode impedance is effectively in parallel with said input circuit, means for applying to a control element of the.second tube alternating current voltage derived from said source but in substantial phase quadrature with the alternating voltage at the plate of the second tube thereby to cause said' impedance-to simulate capacitance, and means sense such as to cause the simulated capacitancemagnitude to vary inversely to said undesirable common to said gain regulating means, andthe latter being responsive to intensity changes in

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