US2053449A - Detector distortion control - Google Patents

Detector distortion control Download PDF

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Publication number
US2053449A
US2053449A US8614A US861435A US2053449A US 2053449 A US2053449 A US 2053449A US 8614 A US8614 A US 8614A US 861435 A US861435 A US 861435A US 2053449 A US2053449 A US 2053449A
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United States
Prior art keywords
detector
circuit
resistor
audio
tap
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Expired - Lifetime
Application number
US8614A
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English (en)
Inventor
Travis Charles
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RCA Corp
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RCA Corp
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Publication date
Application filed by RCA Corp filed Critical RCA Corp
Priority to US8614A priority Critical patent/US2053449A/en
Priority to FR801381D priority patent/FR801381A/fr
Priority to DER95656D priority patent/DE681056C/de
Application granted granted Critical
Publication of US2053449A publication Critical patent/US2053449A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03D—DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TO ANOTHER
    • H03D1/00—Demodulation of amplitude-modulated oscillations
    • H03D1/02—Details
    • H03D1/06—Modifications of demodulators to reduce distortion, e.g. by negative feedback

Definitions

  • My present invention relates to arrangements for minimizing distortion in radio receivers,and more particularly to a novel and improved type of detector circuit adapted for use in connection with radio broadcastreceivers.
  • the present tendency in the art of radio broadcasting is to approach as closely as possibleto modulation of the. radiated carrier wave.
  • the audio waves picked up bythe broadcasting station microphone are thus faithfully radiated by means of the radio frequency carrier wave.
  • the detector network One of the most importantflinks in the chain of networks comprising a high fidelity radio re-' 'ceiver is the detector network. It is essential in a receiver of this type that the detector network possess a substantially linear detection characteristic up to 100% modulation of the received carrier wave.
  • the only demodulation device known in the past which approximates this ideal operation is, the diode detector.
  • a diode detector possesses various inherent disadvantages which render it undesirable for use in high fidelity reception. j
  • Another important object of the invention is to providein a degenerative plate circuit detector network a device for varyingthe effective detection characteristic. of the detector network in such a manner that for local broadcast reception of carrier waves of strong amplitude thedetection characteristic issubstantially linear up-to quencies whereby the input electrodes of the detector network have an audio voltage impressed upon them in degenerative phase with respect to the useful audio output voltage wherebythe detection characteristic is substantially linear up to 100% modulation of the received carrier wave; the input circuit of the detector network, additionally, including a controldevice which functions to vary the degree of audio degeneration introduced into the input circuit of the detector whereby the linearity of the detection characteristic with respect to percentage modulation of the carrier wave is capable of being varied, the signal frequency network feeding the detector input circuit having associated therewith an automatic gain control circuit for maintaining the carrier amplitude at the detector input circuit substantially constant over a wide range of signal carrier amplitude variation at any predetermined setting of the audio degeneration control device.
  • the intermediate frequency amplifier and second detector networks of a superheterodyne receiver which embodies the present invention.
  • the input of the intermediate frequency amplifier l is connected tothe usually preceding networks of such a receiver, and such networks ordinarily comprise a signal collector, such as a grounded antenna circuit, and a first detector network.
  • a signal collector such as a grounded antenna circuit
  • a first detector network such as a grounded antenna circuit
  • the latter maybe of the composite local oscillatorfirst detector type, or ofthe type which uses independent local oscillator and first detector tubes.
  • the network I may'comprise one, or more,,stages-of intermediate frequency amplification, and each stage may utilize a screen grid, or pentode,tube I and these tubes may also be of the variable mu type, if desired.
  • the second detector network is shown as comprising a tube of the 51, or pentode, type, and the resonant input, circuit 2 of the detectortube 3 is fixedly-tuned to. the operating intermediate frequency.
  • the input circuit 2 is coupled, as at M1, to the resonant output circuit 4 of the intermediate frequency amplifier network I, and the circuit 4 is also tuned to the operating intermediate frequency.
  • the coupling M1 is optimum so that the overall resonance curve characteristic of the coupling network is substantially band pass in nature, this lending itself to high fidelity reception.
  • the detected output of the detector tube 3 is transmitted to the succeeding audio frequency transmission network through condenser 5, and it is to be understood that the audio network may comprise one, or more, stages of audio frequency amplification, and the final stage of the audio network may be coupled to anydesired type of reproducer. It is to be understood that the networks, other than the detector, are
  • Such design usually includes a control for regulating the selectivity characteristic of a signal selector network.
  • a control for regulating the selectivity characteristic of a signal selector network For example, those skilled in the art are aware that the I. F. network preceding the detector may have its selectivity adjustable so that when weak stations are received the said net work will be sharply selective; on the other hand when strong local stations are received the selectivity will be varied to impart a wide band pass characteristic to the network.
  • the demodulator characteristic varied at the same time, since for weak station reception it is more important to have maximum gain at the detector than minimum harmonic distortion.
  • the cathode circuit of the detector tube 3 includes a grid bias resistor 6 having one side of the detector input circuit 2.
  • the grounded screen grid lead of detector tube 3 includes the positive potential source S, and the anode of the detector tube is connected to ground through a path which includes the detector plate circuit resistor 8 and the positive plate potential source 13.
  • a condenser II is connected between the low alternating potential side of the detector input circuit 2 and an adjustable tap I2, the tap being slidable along the grid bias resistor 6.
  • the condenser II is an audio frequency by-pass condenser, and may have a magnitude of about 0.01 mfd.
  • the automatic volume control system I3 is provided.
  • This automatic volume control system is shown connected in such a manner that it derives its signal energy from the primary circuit of the coupling M1, and its variable bias output is applied to any of the stages preceding the second detector.
  • the signal input for the automatic volume control tube is not derived from the second detector network in order that the latter shall not be loaded, and also in order to have the selectivity at the detector input ofa higher degree than that at the automatic volume control input.
  • the automatic volume control arrangement I3 need not be described because any system well known to those skilled in the art may be utilized for this purpose. How-ever, in order to render the present disclosure complete, reference is made to the fact that there may be utilized for the automatic volume control system I3 the arrangement disclosed by Stuart Ballantine in application Serial No. 376,163, filed July 5, 1929. In this aforesaid application there is disclosed an automatic volume control arrangement which is highly suitable for the present purposes, and which will maintain the carrier amplitude at the detector input circuit'substantially uniform over a wide range of received carrier amplitude variation.
  • the tap I2 When the tap I2 is adjusted to'the grounded side of the grid bias resistor 6, the latter is substantially unby-passed for audio frequencies.
  • the detection characteristic In this position of the tap I2 the detection characteristic is substantially linear up to modulation of the received carrier waves.
  • the resistor 6 In such position of tap I2 the resistor 6 may have a magnitude of the order of 100,000 ohms, and. the condenser 9 is to be understood as furnishing solely radio frequency b y-passing, this by-passing action being negligibly small for audio frequencies.
  • the resistor I may have a magnitude of the order of 1 megohm, and the plate circuit resistor 8 is given a magnitude which is larger than the cathode resistor 6; the latter may be done if the screen electrode of tube 3 is by-passed to ground for radio frequencies.
  • the detector tube 3 then acts as a triode (cathode, control grid, screen) with the plate electronically coupled. This detector circuit reverts to the' ordinary type of screen grid detector when the tap I2 is adjusted to the cathode side of resistor 6 for maximum detector gain. When tap I2 is adjusted to the last position the significance of by-passing the screen grid to ground disappears.
  • the detector circuit When the tap I2 has been adjusted to give degenerative action, the detector circuit has been adjusted for minimum harmonic distortion.
  • the detection. characteristic is substantially linear up to 100% modulation of the received carrier, it will be seen that the operation is similar to that of a diode rectifier circuit without the disadvantages inherent in the latter.
  • the degenerative plate circuit detector acts like a peak rectifier in the manner of a diode, but unlike the diode it draws no input power. Its dynamic characteristic properties are identical with that of a diode detector circuit, with the exception that in a practical diode circuit the driver impedance is of the same order as the input impedance of the diode circuit.
  • the degenerative plate circuit detector In the case of the degenerative plate circuit detector increased gain and selectivity is secured due to the fact that a negligibly high input impedance is utilized. It can be readily demonstrated that for high quality detection, when the tap I2 is adjusted to the grounded side of grid bias resistor 6, the degenerative plate circuit detector more closely achieves ideal detection operation than a diode detector circuit. Furthermore, by virtue of the electronically coupled output, there is secured a higher gain while retaining the distortion-free detection characteristic.
  • the degenerative action of the plate circuit detector shown can be reduced, or removed, if it is desired to increase detection gain at the expense of harmonic distortion.
  • the detector circuit functions in the normal and well known plate rectification manner and gives high gain, as well as substantially linear detection up to 50 to 70% modulation of the received carrier wave.
  • the automatic volume control system l3 performs a highly desirable function in conjunction with the manually adjustable audio degeneration detector control device, aside from its well known function of counteracting fading effects. It is desired, at any setting of the adjustable tap 12, that the carrier amplitude at the detector input circuit be substantially constant. TlL's will now be explained.
  • the operating bias on the signal input grid of detector tube 3 is composed of two components; one of these is the direct current component developed by the carrier current flow through the bias resistor 6, and the other is the audio voltage component developed by the audio frequency currents flowing through the resistor 6. For any given setting of the tap 12 on resistor 6, there is a critical relation between the magnitude of that portion of the resistor 6 between tap l2 and the cathode terminal of resistor 6 and the carrier amplitude at the detector input circuit.
  • the carrier amplitude value at the detector input circuit is kept substantially constant, and the taplZ may be adjusted to a desired point on resistor 6 for a desired quality of detection, and it will not be necessary to shift the tap again because of carrier amplitude variation.
  • the operation of the automatic volume control system l3 in no way affects the functioning of the degenerative plate circuit detector.
  • a radio receiver including a signal amplifier and a detector of the plate rectification type, a grid bias resistor in the cathode circuit of the detector tube, said resistor being common to the detector input and output circuits, means for varying the audio frequency by-passing of'the said grid bias resistor whereby the degree of audio degeneration of the detector input circuit may be varied, and additional means for maintaining the received carrier amplitude at the detector input circuit of a substantially constant value for any desired setting of said audio frequency bypassing means.
  • a detector including a pentode tube, a grounded grid bias resistor in the cathode circuit of said tube, a signal input circuit connected between the signal input grid and the grounded side of said grid bias resistor, said resistor being common to the detector input and output circuits, an audio frequency by-pass condenser having one side thereof fixedly connected to the detector input circuit and the other side thereof connected to the said grid bias resistor through an adjustable tap whereby the degree of audio degeneration introduced into the detector input circuit may be varied at will.
  • a detector including a pentode tube, a grounded grid bias resistor in the cathode circuit of said tube, a signal input circuit connected between the signal input grid and the grounded side of said grid bias resistor, said resistor being common to the detector input and output circuits, and an audio frequency by-pass condenser having one side thereof fixedly connected to the detector input circuit and the other side thereof connected to the said grid bias resistor through an adjustable tap whereby the degree of audio degeneration introduced into the detector input circuit may be varied at will, and means for maintaining the received carrier amplitude at the detector input circuit substantially uniform over a wide range of received carrier amplitude variation.
  • the screen grid electrode of the detector tube being by-passed to ground for radio frequencies.
  • a detector circuit of the type including a tube, a signal input circuit and an audio output circuit, a grid bias resistor in the cathode circuit of the tube, said resistor being common to the detector input and output circuits, a resistive path connected between the low alternating potential side of the detector input circuit and the negative side of said grid bias resistor, and means for controlling the linearity of the detection characteristic with respect to percentage modulation of the received carrier wave, said means comprising an audio frequency by-pass condenser having one terminal thereof connected to the detector input circuit and the other terminal thereof connected to the grid bias resistor through an adjustable tap.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Amplifiers (AREA)
  • Circuits Of Receivers In General (AREA)
US8614A 1935-02-28 1935-02-28 Detector distortion control Expired - Lifetime US2053449A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US8614A US2053449A (en) 1935-02-28 1935-02-28 Detector distortion control
FR801381D FR801381A (fr) 1935-02-28 1936-01-29 Dispositif de contrôle de la distorsion dans un détecteur de radio-récepteur
DER95656D DE681056C (de) 1935-02-28 1936-02-29 Empfaenger mit Gegenkopplung zur Entzerrung des Empfangsgleichrichters

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US8614A US2053449A (en) 1935-02-28 1935-02-28 Detector distortion control

Publications (1)

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US2053449A true US2053449A (en) 1936-09-08

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Application Number Title Priority Date Filing Date
US8614A Expired - Lifetime US2053449A (en) 1935-02-28 1935-02-28 Detector distortion control

Country Status (3)

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US (1) US2053449A (fr)
DE (1) DE681056C (fr)
FR (1) FR801381A (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL64007C (fr) * 1943-03-03

Also Published As

Publication number Publication date
DE681056C (de) 1939-09-20
FR801381A (fr) 1936-08-03

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