US2393709A - Distortion reduction on modulated amplifiers - Google Patents

Distortion reduction on modulated amplifiers Download PDF

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Publication number
US2393709A
US2393709A US465712A US46571242A US2393709A US 2393709 A US2393709 A US 2393709A US 465712 A US465712 A US 465712A US 46571242 A US46571242 A US 46571242A US 2393709 A US2393709 A US 2393709A
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US
United States
Prior art keywords
amplifier
impedance
modulated
circuit
output
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US465712A
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English (en)
Inventor
Romander Hugo
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Federal Telephone and Radio Corp
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Federal Telephone and Radio Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to BE470453D priority Critical patent/BE470453A/xx
Application filed by Federal Telephone and Radio Corp filed Critical Federal Telephone and Radio Corp
Priority to US465712A priority patent/US2393709A/en
Priority to GB14867/43A priority patent/GB566844A/en
Application granted granted Critical
Publication of US2393709A publication Critical patent/US2393709A/en
Priority to CH270144D priority patent/CH270144A/de
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C1/00—Amplitude modulation
    • H03C1/16—Amplitude modulation by means of discharge device having at least three electrodes
    • H03C1/18—Amplitude modulation by means of discharge device having at least three electrodes carrier applied to control grid
    • H03C1/22—Amplitude modulation by means of discharge device having at least three electrodes carrier applied to control grid modulating signal applied to same grid
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C1/00—Amplitude modulation
    • H03C1/16—Amplitude modulation by means of discharge device having at least three electrodes
    • H03C1/18—Amplitude modulation by means of discharge device having at least three electrodes carrier applied to control grid
    • H03C1/20—Amplitude modulation by means of discharge device having at least three electrodes carrier applied to control grid modulating signal applied to anode
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03C—MODULATION
    • H03C7/00—Modulating electromagnetic waves
    • H03C7/02—Modulating electromagnetic waves in transmission lines, waveguides, cavity resonators or radiation fields of antennas
    • 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
    • H03F1/02—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation
    • H03F1/04—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in discharge-tube amplifiers
    • H03F1/06—Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation in discharge-tube amplifiers to raise the efficiency of amplifying modulated radio frequency waves; to raise the efficiency of amplifiers acting also as modulators
    • 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
    • H03F1/08—Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H7/00—Multiple-port networks comprising only passive electrical elements as network components
    • H03H7/38—Impedance-matching networks
    • H03H7/383—Impedance-matching networks comprising distributed impedance elements together with lumped impedance elements

Definitions

  • DISTORTION REDUCTION ON MODULATED AMPLIFIERS Filed NOV. 16, 1942 INVENTOR. flue-o IPOMAA/DEI? atented Jan. 29,. 1946 DISTORTION REDUCTION ON MODULATED AMPLIFIERS Hugo Romander, North Caldwell, N. J., assignor to Federal Telephone & Radio Corporation, New York, N. Y., a corporation of Delaware Application November 16, 1942, Serial No. 465,712
  • This invention relates to the prevention of distortion and in particular to the use of impedance inverting circuits as a means for preventing distoltion in modulated class C amplifiers.
  • the prior art discloses the use of impedance inverting networks in linear power amplifiers wherein a modulated carrier wave is applied to the input of the amplifier and a constant D.-C. potential is applied to the anode of the amplifier tube.
  • the input impedance decreases on the positive peaks of the modulation cycle, caused, as is Well known, by the grid current which flows as the grid swings positively.
  • One well known method of correcting, for distortion in amplifiers of this type is to employ two tubes in parallel branched circuits, one tube operating continuously and the other tube operating only on the positive modulation peaks at which the distortion occurs.
  • Another object of my invention is to vary the driving voltage of a modulated class C amplifier during periods of modulation in which the amplifier output is not a true reproduction of the amplifier input.
  • Another object of my invention is to increase the operating efiiciency of a modulated class C amplifier.
  • Fig. i is a circuit diagram illustrating one embodiment of my invention wherein a quarterwavelength line is employed as an impedance in verting element; a
  • Fig. 2 is a circuit diagram illustrating a second embodiment of my invention wherein a balanced T-section is employed as an impedance inverting element, and;
  • Fig. 3 is a circuit diagram illustrating a third embodiment wherein a balanced 1r-S8Ctio-11 is employed as an impedance inverting means.
  • D represents a carrier wave amplifier employed to excite or drive the input of a modulated class C amplifier, A, through an impedance inverting network, N.
  • the driver stage consists of two tubes, l and I, connected in a push-pull circuit.
  • the input circuit of the driver consists of an inductor 2 and a capacitor 3 tuned to the operating carrier frequency. The extremities of the input circuit are connected to the grids 4 and 4' of the tubes i and I respectively.
  • the center point of the inductor 2 is connected to grounded cathodes 5 and 5 through a biasing means shown as a capacitor and grid leak combination 6.
  • the inductor 2 acts as the secondary of a transformer of which the primary is the inductor l and which may be connected to the output of a previous amplifier stage, not shown.
  • the anodes d and 8' are connected to the output circuit of the driver through blocking capacitors 9 and. 9 and to a source of positive potential through choke coils l and Ill.
  • the output circuit i I consists of a balanced 1r-network composed of capacitors l2 and L3 and inductors l4 and I4,
  • the output circuit is coupled to an impedance inverting network, N, which is illustrated as a quarter wavelength line.
  • N an impedance inverting network
  • the output of the quarter wave line is connected to the input circuit l5 of the '20 and 20' are connected across the output of circuit I5.
  • Biasing voltage for the grids 20 and 20' is obtained in any suitablemanner such as for example by means of the condenser and grid leak combinations 2I-22 and 2l'--22'. I also prefer to employ a fixed bias in addition to the self bias. The fixed. bias.
  • a load circuit for example, an antenna not shown, may be coupled to the output circuit 25 through blocking condensers 28 and 28'.
  • the center point of the inductor 26, which is substantially at a radio frequency ground potential, is connected to the positive terminal of a power source through the secondary winding 29 of a modulation transformer 30.
  • the power for modulating the class C amplifier is obtained from the final stageiof a voice or signal amplifier schematically shown at B. This final stage is usually operated class B, but the circuits therefor are not shown in detail since they form no part of the present invention.
  • the voice amplifier as a whole is designed to develop a maxi- I mum undistorted modulating potential across the secondary winding 29 equal in value to the potential of the direct current power source supplying the amplifier A. This is desirable in order to obtain 100% modulation of the carrier wave.
  • the line N is a quarter wave length long and functions as an impedance inverting network.
  • Zo /Z where Z0 is the surge impedance
  • the impedance Z is the impedance looking into the network IS without modulation and is made from the tube ratings as supplied by tube manu- "latter is suitable for giving the required voltage swing to the grids of amplifier A. These adjustments are made at carrier frequency and with no modulation voltages applied to the anodes of the amplifier.
  • the network II is next adjusted until its outequal to Z0.
  • the impedance looking into the line N is therefore also Z0 and the line is flat, that is, contains no standing waves and there are no reflections from the output to the imflit end of the line.
  • a modulating voltage is applied as above described and as shownin Fig. 1.
  • the envelope of.the modulated carrier wave is substantially a replica of the modulation voltage. This is true whether or not the impedance inverting network is inserted in the coupling between the driver and the amplifier stages. However, if the impedance inverting network were omitted there would be a decided distortion of the output as modulation is approached. But with the impedance inverting network, the following operation takes place.
  • the input impedance of the modulated amplifier increases on the positive peaks and decreases on the valleys or negative peaks.
  • the line is now no longer fiat and the increased impedance is reflected to the input end of the quarter wave line as a reduction of impedance.
  • This reduction in impedance is passed on to the output of the driver stage through the impedance transforming net-' work II with the result that the radio frequency output of the driver stage increases.
  • This increased output produces a greater radio frequency voltage swing on the grids-of the modulated amplifier with the result that the amplifier output also increases and tends to compensate for what would otherwise be a distortion in i the modulated carrier wave.
  • the reduced input impedance of the modulated amplifier is reflected into the input end of the quarter wave line as an increased impedance with the result that the driver stage suffers a reduction in output, and the radio frequency driveto the grids of the amplifier is likewise reduced.
  • the impedance inverting network as a quarter wave length line.
  • This network may have either distributed or lumped constants, the only limitation being that it functions electrically as a means for inverting any impedance or impedance variation which may occur on its output side and for reflecting this inverted impedance into the output circuit of the driver amplifier.
  • Fig. 2 shows a network N in which the impedance inverting means consists of a balanced T-section in which the constants of the inductors 30, 30', 3
  • the figure also illustrates a different type of impedance transforming network from that shown in Fig. 1 as networks ii and I5.
  • the radio frequency transformers Ill] and I50 serve the same purpose as do the networks i I and I5 of Fig. 1.
  • Fig. 3 shows a network N" which takes the form of a balanced 1r-section, in which the electrical constants of the inductors 33 and 33 and the capacitors 34 and 35 are so chosen that the section functions as a quarter wave length line.
  • the separate capacitors i3 and 34 may be combined into one unit, and that the same is also true of the capacitors 35 and IS.
  • the impedance inverting network N" and the impedance transforming networks II and IE will then lose their separate identities but the operation of the circuits will be the same as before.
  • a driver amplifier capable of supplying an excitation voltage of sufiicient magnitude to drive the grid of said amplifier positive during a portion of the excitation voltage cycle and an impedance inverting network connected between said driver amplifier and said first mentioned amplifier.
  • a modulated amplifier of the class C type having an input circuit, means for modulating solely the anode thereof, a driver amplifier having an output circuit for supplying unmodulated excitation voltage solely to the grid of said modulated amplifier, and an impedance inverting circuit carrying only unmodulated excitation voltage and coupling the output circuit of said driver amplifier to the input circuit or said modulated amplifier, said input circuit having characteristics for matching the impedance of said inverting circuit to the input impedance of said modulated amplifier, and for automatically reflecting changes in said input impedance, via said inverting circuit, to the output circuit of said driver amplifier.
  • a modulated amplifier of the class C type means for modulating solely the anode thereof, a driver amplifier having an output circuit for supplying unmodulated excitation voltage solely to the grid of said modulated amplifier, a plurality of circuits for coupling the output circuit of said driver amplifier to the grid of said modulated amplifier, one of said plurality of circuits comprising an impedance inverting network and another of said circuits being an impedance transforming circuit for matching the impedance of said inverting network to the input impedance of said modulated amplifier, and for automatically reflecting changes in said input impedance, via said inverting circuit, to the output circuit of said driver amplifier.
  • a modulated amplifier of the type wherein the modulating voltage is applied solely to the plate of the amplifier a driver amplifier having an output circuit for supplying an unmodulated excitation potential to the input of said modulated amplifier, a line having an odd multiple of quarter wave lengths at the excitation frequency connected between the output 01' said driver amplifier and the input of said modulated amplifier and means for matching the surge impedance oi. said line to the input impedance of said modulated amplifier, and for automatically reflecting changes in said input impedance, via said inverting circuit, to the output circuit of said driver amplifier.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Amplifiers (AREA)
  • Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
US465712A 1942-11-16 1942-11-16 Distortion reduction on modulated amplifiers Expired - Lifetime US2393709A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE470453D BE470453A (en, 2012) 1942-11-16
US465712A US2393709A (en) 1942-11-16 1942-11-16 Distortion reduction on modulated amplifiers
GB14867/43A GB566844A (en) 1942-11-16 1943-09-10 Distortion reduction on modulated amplifiers
CH270144D CH270144A (de) 1942-11-16 1947-11-10 Hochfrequenzsender mit einer Modulationsstufe und Mitteln zur Verzerrungsverminderung.

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US465712A US2393709A (en) 1942-11-16 1942-11-16 Distortion reduction on modulated amplifiers

Publications (1)

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US2393709A true US2393709A (en) 1946-01-29

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US465712A Expired - Lifetime US2393709A (en) 1942-11-16 1942-11-16 Distortion reduction on modulated amplifiers

Country Status (4)

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US (1) US2393709A (en, 2012)
BE (1) BE470453A (en, 2012)
CH (1) CH270144A (en, 2012)
GB (1) GB566844A (en, 2012)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2571045A (en) * 1945-08-08 1951-10-09 Alan B Macnee Amplifier coupling circuit
US2574868A (en) * 1946-10-18 1951-11-13 Rca Corp Electron discharge tube circuit arrangement
US2606284A (en) * 1943-03-27 1952-08-05 Hartford Nat Bank & Trust Co Mixing circuit arrangement
US2743356A (en) * 1949-06-25 1956-04-24 Rca Corp Tunable frequency systems of constant band width
US2786903A (en) * 1950-11-06 1957-03-26 Marconi Wireless Telegraph Co Tuned thermionic valve amplifiers
US2994832A (en) * 1958-04-08 1961-08-01 Bell Telephone Labor Inc Transistor amplifier
US3290653A (en) * 1963-01-10 1966-12-06 Control Data Corp Single ended to double ended to single ended communication system

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2606284A (en) * 1943-03-27 1952-08-05 Hartford Nat Bank & Trust Co Mixing circuit arrangement
US2571045A (en) * 1945-08-08 1951-10-09 Alan B Macnee Amplifier coupling circuit
US2574868A (en) * 1946-10-18 1951-11-13 Rca Corp Electron discharge tube circuit arrangement
US2743356A (en) * 1949-06-25 1956-04-24 Rca Corp Tunable frequency systems of constant band width
US2786903A (en) * 1950-11-06 1957-03-26 Marconi Wireless Telegraph Co Tuned thermionic valve amplifiers
US2994832A (en) * 1958-04-08 1961-08-01 Bell Telephone Labor Inc Transistor amplifier
US3290653A (en) * 1963-01-10 1966-12-06 Control Data Corp Single ended to double ended to single ended communication system

Also Published As

Publication number Publication date
CH270144A (de) 1950-08-15
BE470453A (en, 2012)
GB566844A (en) 1945-01-16

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