US2273997A - Negative feedback amplifier - Google Patents

Negative feedback amplifier Download PDF

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Publication number
US2273997A
US2273997A US289408A US28940839A US2273997A US 2273997 A US2273997 A US 2273997A US 289408 A US289408 A US 289408A US 28940839 A US28940839 A US 28940839A US 2273997 A US2273997 A US 2273997A
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Prior art keywords
stage
cathode
grid
impedance
output
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Expired - Lifetime
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US289408A
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English (en)
Inventor
Rubin Leon
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INDUSTRIELLE DES PROCESE LOTH Ste
PROCESE LOTH SOC IND DES
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PROCESE LOTH SOC IND DES
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
    • H03F1/34—Negative-feedback-circuit arrangements with or without positive feedback
    • H03F1/36—Negative-feedback-circuit arrangements with or without positive feedback in discharge-tube amplifiers

Definitions

  • This invention relates to negative feed-back amplifiers, and has for its purpose to permit the application of negative feed-back coupling in' high-power amplifiers, for example in amplifiers of the B-class type, in which at least one of the stages, for example the final stage, is controlled by such a high alternating grid voltage that grid currents are produced.
  • control stage As is well known, in such an amplifying stage the unpleasant phenomenon occurs that the grid-cathode impedance depends on the amplitude of the alternating grid voltage to be amplified, and consequently constitutes a variable charging impedance for the preceding amplifying stage which will be called control stage hereinafter.
  • control stage is coupled to the following stage, which is controlled in grid currents and will be termed final stage" hereinafter, by means of a strong step-down transformerwhich steps up the impedance constituted by the gridcathode impedance of the final stage to a value which is great compared with the internal resistance of the control stage, the voltage across the primary, and consequently across the secondary winding, having a value which is independent of the grid-cathode impedance of the final stage.
  • This coupling has the property that the output impedance of the control stage measured between the terminals of the resistance in the cathode lead is low with regard to the variable grid-cathode impedance of the final stage, i. e. approximately equal to l/S, in which S is the slope of the amplifying tube of the control stage. Consequently, the variable control grid-cathode impedance of the final stage, which is in parallel to the resistance in the cathode lead, has a negligible influence on the amplification of the control stage so that the latter supplies to the grid of the final stage a voltage which is independent of the variable grid-cathode impedance of the final stage. Since, moreover, the phase displacement produced by this way of coupling is substantially independent of frequency, it is only with the use of such a coupling between the control stage and final stage that a strong negative feed-back coupling can be applied for suppressing non-linear distortions.
  • the amplifier in Fig. 1 has five amplifying stages i to 5, each of which comprises a pair of push-pull amplifying tubes.
  • the final stage 5 is coupled to the control stage 4 by means of resistances 6 which are interposed in the cathode lead of the amplifying tubes 1 and 8 of the control stage 4, and whose extremities are connected to the grid and cathode of the amplifying tubes 9 and ll) of the final stage 5.
  • This method of coupling as was mentioned above has the property that the alternating voltage set up across the resistances 6 is substantially independent of the variable grid-cathode impedance of the tubes 9 and I0 which is a result of grid currents being produced in these tubes.
  • the negative feed-back circuit extendends from the primary winding of the output transformer H to the secondary winding of the inputtransformer I! of the amplifier, and comprises two potentiometers constituted-respectively by the resistances l3 and I5, and I4 and IS.
  • the amplifying stages I and 2, 2 and 3, 3 and 4 are coupled to one another in known manner by means of resistance-condenser coupling.
  • a reducer constituted by a resistance 2
  • Fig. 1 has been explained by reference 'to an embodiment in which the control stage is coupled to the final stage of an amplifier by means of a resistance in the cathode lead of the control stage, the application of the invention is not limited thereto.
  • the said coupling can also be applied between two other stages of an amplifier, which are bridged by a negative feed-back circuit.
  • the improvement in Fig. 2 consists in that the resistance in the cathode conductor of the first of the two stages is replaced by a combination of resistances, inductances or capacities, preferably by a combination of resistances and inductances.
  • a resistance is included in the cathode conductor of the first of the said two amplifier stages, the anode direct current of this stage brings about a voltage drop across this resistance, it being necessary for this voltage drop to be compensated for by the source of grid bias of the following amplifier stage. This voltage drop is avoided if in the cathode conductor the resistance or at least a part of the resistance is replaced by a combination of resistances, inductances and capacities and preferably by an inductance.
  • the non-linear grid current of the final stage will pass both via the source of anode voltage of the control stage and via the source of grid voltage of the final stage.
  • the current which fiows via the source of anode voltage is inversely proportioned to the output impedance of the control stage, measured between the terminals of the resistance in the cathode conductor, said output impedance being about equal to 1/8, in which S designates the mutual conductance of the amplifier valve of the control stage.
  • the current which flows via the source of bias of the final stage is inversely proportioned to the said resistance in the cathode conductor with the addition of the internal resistance of the source of bias.
  • the cathode impedance is formed by the series combination of a resistance 30 and an inductance coil 3
  • an impedance in the cathode conductor formed by a combination of resistances, inductances or capacities, amplification independent of frequency is obtained over a wide frequency range if the said impedance is high relatively to output impedances of the control stage, measured between the terminals of this impedance.
  • a signal amplifying system comprising signal input and output circuits, a pair of electron discharge devices, each device having at least a control grid, a cathode and an output electrode, said input circuit being connected to said grids to apply signals thereto in phase opposition, a load impedance in the space current paths of both of said devices, said load impedance being connected between the cathodes of said first pair of devices, a second pair of electron discharge devices each including at least a control grid, a cathode and an output electrode, said signal output circuit connecting the output electrodes of said second pair of devices in push-pull relation, the control grids of said second pair of devices being connected to respectively different points of said load impedance which are of opposite phase, and a degenerative signal voltage feedback path from said output circuit to said input circuit.
  • a signal amplifying system comprising signal input and output circuits, a pair of electron discharge devices, each device having at least a control grid, a cathode and an output electrode, said input circuit being connected to said grids to apply signals thereto in phase opposition, a load impedance in the space current paths of both of said devices, a second pair of electron discharge devices each including at least a control grid, a cathode and an output electrode, said signal output circuit connecting the output electrodes of said second pair of devices in push-pull relation, the control grids of said second pair of devices being connected to respectively different points of said load impedance which are of opposite phase, and a degenerative signal voltage feedback path from said output circuit to said input circuit, said load impedance consisting of a resistor connected between the cathodes of said first pair of devices, said different points being the cathode ends of said resistor.
  • a signal amplifying system comprising signal input and output circuits, a pair of electron discharge devices, each device having at least a control grid, a cathode and an output electrode, said input circuit being connected to said grids to apply signals thereto in phase opposition, a load impedance in the space current paths of both of said devices, a second pair of electron discharge devices each including at least a control grid, a cathode and an output electrode,
  • said signal output circuit connecting the output electrodes of said second pair of devices in pushpuli relation, the control grids of said second pair of devices being connected to respectively different points of said load impedance which are of opposite phase, and a degenerative signal voltage feedback path from said output circuit to said input circuit, said load impedance being a resistor connected between the cathodes of said first pair of devices, and means for applying negative bias to the control grids of said second pair of devices through said resistor.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US289408A 1938-09-23 1939-08-10 Negative feedback amplifier Expired - Lifetime US2273997A (en)

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NL2273997X 1938-09-23

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BE (1) BE436446A (ja)

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2481533A (en) * 1944-06-06 1949-09-13 Rca Corp Audio amplifier circuits for radio transmitters
US2516181A (en) * 1948-05-03 1950-07-25 Collins Radio Co High-power audio frequency amplifier
US2529459A (en) * 1948-11-02 1950-11-07 Gen Precision Lab Inc Low-frequency power amplifier
US2589617A (en) * 1947-07-07 1952-03-18 Alfred C Kowalski Pulse amplitude modulation communication system
US2623741A (en) * 1946-06-11 1952-12-30 American Mach & Foundry Electromagnetic balance
US2638401A (en) * 1953-05-12 Lukacs
US2641695A (en) * 1949-12-30 1953-06-09 Bell Telephone Labor Inc Linear rectifier
US2648727A (en) * 1949-10-04 1953-08-11 Crosley Broadeasting Corp Push-pull wide band amplifier
US2687935A (en) * 1948-02-10 1954-08-31 Western Union Telegraph Co Signal amplifying system for electrically actuated recording devices
US2747028A (en) * 1952-10-29 1956-05-22 California Research Corp Amplifier circuit
US2921266A (en) * 1955-02-14 1960-01-12 Jr Martin V Kiebert Self-balancing amplifier
US3098978A (en) * 1959-10-30 1963-07-23 Bell Telephone Labor Inc Nonreciprocal wave translating network
US3120645A (en) * 1959-10-30 1964-02-04 Bell Telephone Labor Inc Nonreciprocal wave translating device
US5498996A (en) * 1994-11-21 1996-03-12 Wavestream Kinetics High-power, high-fidelity tube amplifier

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2638401A (en) * 1953-05-12 Lukacs
US2481533A (en) * 1944-06-06 1949-09-13 Rca Corp Audio amplifier circuits for radio transmitters
US2623741A (en) * 1946-06-11 1952-12-30 American Mach & Foundry Electromagnetic balance
US2589617A (en) * 1947-07-07 1952-03-18 Alfred C Kowalski Pulse amplitude modulation communication system
US2687935A (en) * 1948-02-10 1954-08-31 Western Union Telegraph Co Signal amplifying system for electrically actuated recording devices
US2516181A (en) * 1948-05-03 1950-07-25 Collins Radio Co High-power audio frequency amplifier
US2529459A (en) * 1948-11-02 1950-11-07 Gen Precision Lab Inc Low-frequency power amplifier
US2648727A (en) * 1949-10-04 1953-08-11 Crosley Broadeasting Corp Push-pull wide band amplifier
US2641695A (en) * 1949-12-30 1953-06-09 Bell Telephone Labor Inc Linear rectifier
US2747028A (en) * 1952-10-29 1956-05-22 California Research Corp Amplifier circuit
US2921266A (en) * 1955-02-14 1960-01-12 Jr Martin V Kiebert Self-balancing amplifier
US3098978A (en) * 1959-10-30 1963-07-23 Bell Telephone Labor Inc Nonreciprocal wave translating network
US3120645A (en) * 1959-10-30 1964-02-04 Bell Telephone Labor Inc Nonreciprocal wave translating device
US5498996A (en) * 1994-11-21 1996-03-12 Wavestream Kinetics High-power, high-fidelity tube amplifier

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Publication number Publication date
BE436446A (ja)

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