US2760009A - Negative feed-back amplifier - Google Patents

Negative feed-back amplifier Download PDF

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Publication number
US2760009A
US2760009A US384568A US38456853A US2760009A US 2760009 A US2760009 A US 2760009A US 384568 A US384568 A US 384568A US 38456853 A US38456853 A US 38456853A US 2760009 A US2760009 A US 2760009A
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United States
Prior art keywords
impedance
cathode
tube
grid
negative feed
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Expired - Lifetime
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US384568A
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English (en)
Inventor
Boer Sjoerd De
Winkel Jan Te
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Hartford National Bank and Trust Co
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Hartford National Bank and Trust Co
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Publication date
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Publication of US2760009A publication Critical patent/US2760009A/en
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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 comprising an odd number, preferably three, cascadeconnected tube stages and a negative feed-back impedance which is common to the cathode circuits of the first and the last tube-stages of the cascade. It has for its purpose to compensate for the undesirable current passing from the anode of the penultimate tube-stage ofthe cascade via the impedance, comprising the internal grid-cathode capacity between the grid and the cathode of the last tubestage, through the negative feed-back impedance. As is well known, this current permtis the reduction of distortion of the amplifier to be improved only to a given limit.
  • the present invention provides an extremely simple solution.
  • the grid of said last tube-stage is connected by way of a suitably proportioned compensation-impedance to the grid of the first tubestage of the cascade.
  • the input impedance of the amplifier, said compensation impedance, said grid-cathode impedance and said negative feed-back impedance constitute a capacitatively balanced Wheatstone bridge at least within the frequency pass-band of the amplifier.
  • an amplifier comprises three cascadeconnected tubes 1, 2 and 3, that is to say that the output circuit of tube 1 is coupled to the input circuit of tube 2, and the output circuit of tube 2 is coupled to the input circuit of tube 3.
  • the input circuit of the first tube 1 of the cascade comprises a source 5 of oscillations to be amplified, in series with an input impedance Z1 which may entirely or partly consist of the internal resistance of source 5, the output circuit of the last tube 3 of the cascade comprising a load impedance Zu.
  • the cathode circuits of the tubes 1 and 3 comprise a common negative feedback impedance Z1; bringing about negative feed-back of the amplifier.
  • the lastmentioned current should be compensated for, which, according to the invention, is achieved by means of a properly proportioned compensation impedance Zc.
  • the impedance Zc together with the input 2 impedance Z1, the negative feed-back impedance Z1: and the grid-cathode impedance Z4 constitute a Wheatstone bridge which is capacitatively in equilibrium with respect to the frequency pass-band of the amplifier, that is to say Z 'Z as a result of which the voltage between the grid and the cathode of the first tube 1 of the cascade is exactly equal to the difference between the voltage of source 5 and the voltage producing the cathode current of tube 3 via the negative feed-back impedance Zt.
  • Z1 and Z1; are mostly resistive, whereas Z4 is substantially of a capacitative character, a capacitor, whose c pacit t ve v lue is Z I times as low as the capacity between the grid and the cathode of the tube 3, should be chosen for Z0. In practice, this value is usually lower than 21.6,Ltf. On the other hand, this capacity causes a low negative capacity parallel to the input circuit 5-21 of tube 1. Sometimes, it may therefore be desirable to choose other frequencydependent impedances for the impedances Z0 and Zt, particularly if the input impedance Zr itself is frequencydependent.
  • circuit-arrangement may alternatively comprise five or, in general, an odd number of cascadeconnected tubes in exactly the same manner, but in this case the risk of self-oscillation is much greater than in the case of three tubes.
  • a tube-stage comprising two push-pull connected tubes may alternatively be substituted for one or each of a plurality of the tubes.
  • the negative input capacity brought about by Zc was 1.5 to 3 .L,uf, in accordance with the mutual conductance (9 to 19 ma./V) of the last push-pull stage of the cascade.
  • a negative feed-back amplifier comprising an odd number of cascade-connected stages each having an electron discharge tube provided with a cathode, a grid and an anode and circuits therefor and the last stage having an internal grid-cathode impedance, a negative feed-back impedance connected in common to the cathode circuits of the first and last tube-stages, and a compensation im pedance connected between the grid of the first tube-stage and the grid of the last tube-stage and having a value which compensates for the anode current of the penultimate tube-stage which flows through said grid-cathode impedance to said negative feed-back impedance, thereby reducing distortion in said amplifier.
  • An amplifier as set forth in claim 1, further including an input impedance coupled to the first tube-stage and wherein said input impedance, said compensation impedance, said grid-cathode impedance and said negative feedback impedance comprise a capacitatively balanced Wheatstone bridge at least within the frequency passband of the amplifier.
  • said compensation impedance is a capacitor having a value less than two micro-microfarads.
  • a negative feed-back amplifier comprising three electron discharge devices, each having a cathode, an anode and a control grid, a first impedance connected between the control grid and cathode of the first device, a

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
US384568A 1952-10-22 1953-10-07 Negative feed-back amplifier Expired - Lifetime US2760009A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL725534X 1952-10-22

Publications (1)

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US2760009A true US2760009A (en) 1956-08-21

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US384568A Expired - Lifetime US2760009A (en) 1952-10-22 1953-10-07 Negative feed-back amplifier

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US (1) US2760009A (en(2012))
BE (1) BE523683A (en(2012))
FR (1) FR1085318A (en(2012))
GB (1) GB725534A (en(2012))
NL (2) NL173310B (en(2012))

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2931956A (en) * 1956-02-06 1960-04-05 Elliott & Evans Inc Regenerative radio receiver for remotely controlled relay
US2955261A (en) * 1956-12-03 1960-10-04 Lon E Edwards Audio amplifier
US3162821A (en) * 1960-03-16 1964-12-22 Motorola Inc Electronic circuit

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2170645A (en) * 1938-01-03 1939-08-22 Bell Telephone Labor Inc High frequency amplifier
US2315040A (en) * 1940-12-28 1943-03-30 Bell Telephone Labor Inc Electric wave amplification
US2337423A (en) * 1942-10-01 1943-12-21 Bell Telephone Labor Inc Negative feed-back amplifier

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2170645A (en) * 1938-01-03 1939-08-22 Bell Telephone Labor Inc High frequency amplifier
US2315040A (en) * 1940-12-28 1943-03-30 Bell Telephone Labor Inc Electric wave amplification
US2337423A (en) * 1942-10-01 1943-12-21 Bell Telephone Labor Inc Negative feed-back amplifier

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2931956A (en) * 1956-02-06 1960-04-05 Elliott & Evans Inc Regenerative radio receiver for remotely controlled relay
US2955261A (en) * 1956-12-03 1960-10-04 Lon E Edwards Audio amplifier
US3162821A (en) * 1960-03-16 1964-12-22 Motorola Inc Electronic circuit

Also Published As

Publication number Publication date
NL93262C (en(2012))
FR1085318A (fr) 1955-01-31
GB725534A (en) 1955-03-02
BE523683A (en(2012))
NL173310B (nl)

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