US2258440A - Amplifying system - Google Patents

Description

Oct. 7., 1941.

H. BOUCKE AMPLIEYING- SYSTEM Fil ed Jan. 18, 1940 I NVENTOR Heinz Bouckc ATTORNEY Patented Oct. 7, 1941 AMPLIFYING SYSTEM Heinz Boucke, Berlin-Charlottenburg, Germany,

assignor to Radio Patents Corporation, a corporation of New York Application January 18, 1940, Serial No. 314,410 In Germany January 23, 1939 Claims.

The present invention relates to electric amplifiers for modulated signal energy known as ra dio frequency or intermediate frequency amplifiers in wireless systems such as broadcast receivers.

An Object of the invention is to provide a method of and system for controlling the acceptance band width or selectivity of an amplifier of the above character either manually or automatically in dependence upon variations of a condi tion or characteristic such as strength or amplitude of the received signal in a broadcast receiver or other wireless circuit.

A more specific object is to provide a method or system for band Width or selectivity control which is both simple in design by requiring a minimum of parts and circuit elements as well as eflicient in operation.

Another object is to obtain selectivity or fidelity control for both radio frequency and audio frequency signals in a single control or regulating stage.

A further object is to effect selectivity or band width control in an amplifier for composit signal energy comprising a band of component frequencies without affecting the signal strength or intensity of the signals being amplified.

The above and other objects of the invention will become more apparent from the following detailed description taken with reference to the accompanying drawing forming part of this specification and wherein:

Figure 1 is a diagram of a radio frequency amplifier embodying a band width or fidelity control arrangement according to the invention, and

Figure 2 shows a circuit diagram illustrating selectivity control for both radio frequency and audio frequency signals in a single amplifying or,

control stage.

Like reference numerals identify like elements in both views of the drawing.

With the above objects in View, the invention involves the use of an electron discharge amplifier having at least two output electrodes cooperating with the same electron discharge current and controlled simultaneously in inverse relation by a control potential in such a manner that with the current to one of the output electrodes increasing the current to the other output electrode decreases, and vice Versa as the control potential is varied in either a positive or negative direction from a normal valve. Both electrodes are connected to a common output circuit by Way of selective networks or circuits (oscillatory circuits, band-pass filters) having different band width or selectivity characteristics. In this manner varying relative portions of the total output current are passed through transmission circuits of different selectivity resulting in a corresponding variation of the total effective selectivity of the system.

Both selective circuits or networks may be coupled through a galvanic, inductive, capacitative, or a mixed coupling arrangement directly with the input or control grid of a succeeding amplifier. In this case provision should be made to effect a careful decoupling between the circuits and networks. If difiiculties should be encountered in this respect, the circuits and networks may be connected to the input of separate amplifying tubes having their outputs combined in a common circuit.

An especially eflicient regulation is obtained in an amplifying stage arranged as a reflex circuit for amplifying both radio frequency and audio frequency signals by proper design of the two output circuits both with regard to the high frequency and to the low frequency circuit elements in such a manner as to obtain simultaneously fidelity or selectivity control for both the radio frequency and audio frequency signals within the same control stage.

Referring to Figure 1 of the drawing, the circuit shown may represent a portion of the radio frequency or intermediate frequency section of a Wireless receiver or similar amplifying system. The high frequecny signals are impressed through input terminals a-b upon the grid-cathode path of an amplifier valve l2 of the hexode type through a suitable coupling device such as a band-pass filter of known design comprising primary and secondary resonantcircuits Iii and II.

prises a cathode 13 preferably of the indirect heated type followed in succession by a signal in-,

put or control grid M, a screen grid 15, an anode or output grid I6, a further control grid referred to as a current distribution grid I1, and a plate or anode [8. Proper biasing potential for the input grid is provided by means of a network IS the 200 volt point of a potentiometer or the like? The valve 12 in the example shown com-.

while the screen grid is connected to a lower positive potential such as 100 volt as shown in the drawing, these values being merely illustrative and by way of example. Resonant circuit is constructed to have low selectivity or a large band width such as by the provision of a resistance 22 shunted across the circuit, while the circuit 2| is designed to have narrow band width or high selectivity. The output potentials developed by the circuits 2!! and 2| are combined in series and impressed in the example shown upon the grid-cathode path of a succeeding amplifier 21 through the secondaries 23 and 24 arranged in inductive relation with the circuits20 and 2|, respectively. The amplifier 21 comprises a cathode 28, input or control grid 29, screen grid and plate 3|. The amplified output signals may be transmitted to a subsequent amplification stage or to a detector to be connected to terminals c-d through a tuned transformer having a primary 34 and a secondary 35.

In order to effect a selectivity or band width control, a variable bias or control potential Er supplied by way of terminals ef'is impressed upon the control or current distribution grid I! located between the positive grid l6 and plate 18. This potential may bemanually adjustable and supplied for this purpose by a battery in connectionwitha variable potentiometer. Alternatively, the control may be automatic in dependence .upon a condition or characteristic of .the received signal energy such as the signal intensity. In the latter case, a control potential generated .in the manner known in automatic volume control circuits (A. V. C..potential) after adequate filtering by means of resistance36 and condenser 31 is impressed upon the control grid II. If this control potential is applied in such a manner that normally the grid I! 'is kept at a negative potential relative to ground or cathode, it is seen that with increasing negative potential, thecurrent to the plate [8 will be reduced due to the blockingaction of the grid I! while the current to the anode grid [.6 will increase correspondingly. As a result, less potential will be'developed across the low selectivity circuit 20 and a corresponding greater potential will be developed by the high selectivity circuit'2l resulting in an increase of effective selectivity of the amplifier. The opposite effect will take place as the negative potential and grid ll decreases. In automatic operation, if the control (A. V. C.) potential 'is applied with proper polarity and grid l1 suitably initially biased, the operation may be such that with decreasing signal strength the selectivity will become greater while a decrease of selectivity or increased band width will be adjusted automatically when the signal strength increases.

Referring to Figure 2, there is shown a regulating stage for controlling both the radio :frequency and audio frequency selectivity known as tone control in a single valve and by means of a single control potential. The input and output circuits of the valves l2'and 21 are-similar to Figure 1. The output of valve 21 is impressed upon a diode rectifier having a cathode 3B and anode '31 through acoupling condenser 38. The diode is shunted by a pair of load resistances 4E! and 4| in series, the latter being shunted by a condenser 42 for by-passing the radio or intermediate frequency currents. There is thus developed across the resistance 4| demodulated or audio frequency potential which is impressed upon the input grid "M. of the valve 1 2 by way of a-coupling condenser 4 3and grid leak-resistance 45. Condenser 46 serves as a high frequency return path to cathode for the input circuit ll. Amplified low or audio frequency potentials are developed in the plate circuit by resistance 41 and in the circuit of the positive grid l6 by a resistance 5| arranged in series with the resonant circuits 20 and 2|, respectively. As is understood, choke coils may be substituted for the resistance 47 and 5| designed to have high impedance for audio frequency currents. The resistance 41 in the plate circuit is shunted by a series tuned or acceptor circuit comprising a condenser 49 and an inductance coil 50 designed to by-pass the high frequency currents. The audio frequency potential developed by the resistance 4! is transmitted to the grid 60 of audio frequency amplifier 58 through a high ohmic resistance 48 and similarly the audio frequency potential developed by the resistance 5i is transmitted to the grid of thesame amplifier through a high ohmic resistance 53. The purpose of the resistances 48 and 53 which maybe replacedby inductance coils is .to effect a decoupling between the output .circuits. Alternatively, the output potentials may be impressed upon the grids of separate valve amplifiers having their outputs combined to insure. a

complete and efficientdecoupling. Items 54 and.

55 represent acoupling condenser and grid leak resistance providing an input coupling element for the audio amplifier 58. comprises a cathode '59 and plate '6 I A grid biasing network 62 comprising .a resistance shunted by a condenser is insertedin the cathode lead in accordance with standard practice. The amplified audio frequency currentsimay be further amplified or applied as .in'the example shown to a.

translating device such as loud speaker 63. In order to provide different selectivity for the audio signals in the plate output circuit a'ndthe output circuitof grid 16, respectively, condenser 52 is shunted acrossthe coupling resistance'fil serving to by-pass components in the high audio frequency range thus preventing transmission of these frequencies to the amplifier 58.

frequency components efiicient-noise suppression is obtained in this manner.

In order to effect an automatic band width .or

selectivity control for both the radio frequency RF'and AF circuits in the-output circuit of'the grid l-B maybe rendered differentially efiective in .accordanceiwith the volume or signal strength to provide automatic selectivity andl'noise control in dep'endenceupon signal strength.

The operation of thesystem is as 'follows: For

normal signal strength a certain average current will fiow'through resistance '65 producing a certain negative potential on the grid I IT. AS the signaliincreases, the average current through '65- will decrease resulting. in alowering of the negativeipotentialonthe grid ll. This will result in an increaseof the current to the plate 18 and in The latter further.

Since noise is substantially composed of the higher audio turn in increased'RF and AF band width (high fidelity and increased noise level). Conversely, if the signal strength decreases, the average current through 65 will increase resulting in greater negativebias on grid H and increased output cur rent to the grid I6. This in turn will cause decreased RF and AF band width (high selectivity and decreased noise level).

An advantage of the invention over known systems of selectivity control is the fact that the band width or selectivity is variedwithout affecting the signal strength, the control being brought about byyarying the relative amounts of the output currents through the plate and positive grid electrode with the total output current remaining substantially constant as is understood from the above. I

It will be evident from the above that the invention is not limited to the specific details and steps shown and disclosed'herein for illustration, but that the invention is susceptible of numerous variations and modifications coming within its broader scope and spirit as defined in the appended claims. The specification and drawing are to be regarded accordingly in an illustrative rather than a limiting'sense.

I claim:

1. In an amplifier for modulated carrier signals, an electron valve comprising a cathode followed in succession by an input grid, a positively biased grid, a control grid and an anode, means for impressing signal potential to be amplified upon said input grid, an output circuit, coupling circuit connections from said output circuit to both said anode and said positively biased grid, resonant impedance means having relatively sharp selectivity characteristics inserted in one of said circuit connections and further resonant impedance means having relatively broad selectivity characteristics inserted in said other circuit connection, and biasing means for said control grid for controlling the ratio of discharge current conveyed to said anode and said positively biased grid, respectively.

2. In an amplifier for modulated carrier signals, an electron valve comprising a cathode followed in succession by an input grid, a positively biased grid, a control grid and an anode, means for impressing signal potential to be amplified upon said input grid, an output circuit, coupling circuit connections from said output circuit to both said positively biased grid and to said anode, parallel resonant circuits tuned to the carrier frequency inserted in each of said circuit connections, a high ohmic resistance shunted across one of said resonant circuits, and biasing means for said control grid for controlling the ratio of discharge current conveyed to said positively biased grid and said anode, respectively.

3. In an amplifier for modulated carrier signals, an electron valve comprising a cathode followed in succession by an input grid, a positively biased grid, a control grid and an anode, means for impressing signal potential to be amplified upon said input grid, an output circuit, coupling circuit connections from said output circuit to both said anode and said positively biased grid, resonant impedance means having relatively sharp selectivity characteristics inserted in one of said circuit connections and further resonant impedance means having relatively broad selectivity characteristics inserted in said other circuit connection, means for producing a potential varying in proportion to the average signal amplitude, and means for impressing said last potential upon said control grid.

4. In an amplifier as claimed in claim 1, a screen grid electrode arranged between said input grid and said positively biased grid.

5. In a receiving system for modulated carrier signals, an amplifying valve comprising a cathode followed'in succession by an input grid, a positively biased grid, a control grid and an anode, means for impressing carrier signals upon said input grid, an output circuit, resonant coupling means presenting high impedance to the carrier frequency between said output circuit and each of said anode and said positively biased grid, one of said coupling means having relatively sharp selectivity characteristics and the other coupling means having relatively broad selectivity characteristics, additional coupling means presenting high impedance to the modulating signal frequencies in series with each of said resonant coupling means, the additional coupling means in series With the sharp selectivity resonant coupling means being effective in blocking frequencies in the higher range of the modulating signals, demodulating means connected to said output circuit, further means for impressing demodulated signal potential upon said input grid, and means for impressing a varying bias potential upon said control grid to effect a control of the relative output current conveyed to said anode and to said positive grid, respectively.

6. In a system as claimed in claim 5, a screen grid arranged between said input grid and said positively biased grid.

7. In a system for receiving carrier signals modulated in accordance with a modulating signal wave comprising a band of component frequencies, an electron valve amplifier comprising a cathode followed in succession by an input control grid, a positively biased grid, a further control grid and an anode, means for impressing carrier signal potential upon said input grid, an output circuit, resonant coupling means offering high impedance to the carrier frequency arranged between said output circuit and each of said anode and said positively biased grid, one of said coupling means having relatively sharp selectivity characteristics and the other coupling means having relatively broad selectivity characteristics, additional coupling means offering high impedance to the modulating signal frequencies in series with each of said coupling means, the additional coupling means in series with the sharp selectivity resonant coupling means being effective in suppressing frequencies in the higher frequency range of said modulating signal band, demodulating means connected to said output circuit, further means for impressing demodulated signal potential upon said input grid, means for producing a control potential varying in proportion to the average signal amplitude, and means for impressing said control potential upon said further control grid to increase the selectivity for the carrier signals and to reduce the response to higher modulating frequencies in proportion to decreasing signal amplitude and vice versa.

8. In a system for receiving carrier signals modulated in accordance with a modulating signal wave comprising a band of component frequencies, an electron valve amplifier comprising a cathode followed in succession by an input control grid, a positively biased grid, a further control grid and an anode, means for impressing carrier signal potential upon said input grid, an out put circuit, resonant coupling means offering high impedance to the carrier frequency arranged between said output circuit and each of said anode and said positively biased grid, one of said coupling means having relatively sharp selectivity characteristics and the other coupling means having relatively broad selectivity characteristics, additional coupling means offering high impedance to the modulating signal frequencies in series with each of said coupling means, the additional coupling means in series with the sharp selectivity resonant'coupling means being effective in suppressing frequencies in the higher frequency range of said modulating signal band, demodulating means connected to said output circuit, further means for impressing demodulated signal potential upon said input grid, means for producing a control potential varying in proportion to the average carrier amplitude, and means for impressing said control potential upon said further control grid to increase the selectivity for the carrier signals and to reduce the response to the higher modulating frequencies in proportion to decreasing signal amplitude and vice versa.

9. In a receiving system for sound modulated carrier signals, an amplifying valve comprising a cathode followed in succession by an input grid, a screen grid, a positively biased grid, a control grid and an anode, means for impressing carrier signals upon said input grid, an output circuit, parallel tuned circuits resonant to the carrier frequency arranged to couple said output circuits with both said anode and said positively biased grid, one of said resonant circuits having a high ohmic resistance connected in shunt thereto to provide relatively broad selectivity compared with the other resonant circuit, a pair of coupling resistances each connected in series with one of said resonant circuits, the coupling resistance in series with the high selectivity resonant circuit being by-passed to suppress the higher frequencies in the audible range, demodulating means connected to said output circuit, further means for impressing demodulated potential upon said input grid, and means for impressing a varying bias potential upon said control grid to eifect control of the ratio of output current conveyed to said positively biased grid and anode, respectively.

10. In an amplifier for modulated carrier signals, an electron discharge tube provided with a cathode, a signal input grid, a positively biased anode grid, a selectivity control grid, and an anode arranged substantially in the order named, means for impressing a carrier signal potential to be amplified upon said input grid, an output circuit, coupling circuit connections from said output circuit to both said anode grid and said anode, first resonant impedance means having relatively sharp selectivity characteristics inserted in one of said circuit connections, further resonant impedance means having relatively broad selectivity characteristics inserted in the other of said circuit connections, and a source of biasing potential connected to said selectivity control grid and cathode.

HEINZ BOUCKE.

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