US3681625A - Variable,nonlinear impedance - Google Patents

Variable,nonlinear impedance Download PDF

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Publication number
US3681625A
US3681625A US887301A US3681625DA US3681625A US 3681625 A US3681625 A US 3681625A US 887301 A US887301 A US 887301A US 3681625D A US3681625D A US 3681625DA US 3681625 A US3681625 A US 3681625A
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Prior art keywords
impedance
bridge
variable
current
direct current
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Expired - Lifetime
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US887301A
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English (en)
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Stefan Kudelski
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Individual
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Individual
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G1/00—Details of arrangements for controlling amplification
    • H03G1/0005—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal
    • H03G1/0035—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal using continuously variable impedance elements
    • H03G1/0052—Circuits characterised by the type of controlling devices operated by a controlling current or voltage signal using continuously variable impedance elements using diodes

Definitions

  • This invention relates generally to a variable impedance device, and more particularly, to a nonlinear variable impedance device.
  • FIG. 1 is a schematic diagram of the present invention.
  • FIG. 2 is an explanatory curve therefor
  • FIG. 3 is a schematic diagram of a recording device with distortion compensation and variable gain.
  • FIG. 4 is a schematic circuit of two symmetrical transistors for regulation within a wide range of gain.
  • FIG. 5 is a simplified schematic diagram.
  • FIG. 6 is a detailed schematic diagram of FIG. 3.
  • FIG. 7 is a schematic diagram of an application of the present invention.
  • FIG. 8 is a schematic diagram of a circuit which may be used with the schematic diagram of FIG. 7.
  • the circuit shown in FIG. 1 comprises a bridge 1 having four branches, each having a diode.
  • the bridge- 1 comprises four diagonal points A, B and C, D.
  • the points A and B are connected to a source of alternating current 3, while the points C and D are fed by a selected direct current I
  • This circuit, between the points A and B, has a symmetrical, nonlinear impedance the curve of which is shown in FIG. 2. It can be seen that as the alternate voltage E between A and B increases, the impedance also increases, becoming infinite at the moment when the alternate current I equals the direct current I passing through the bridge, provided that the feed device of the bridge also has an infinite AC impedance.
  • the impedance of the bridge is inversely proportional to the direct current which passes through it, it is possible to regulate the gain of the assembly by modifying the said current.
  • the curve of the voltage over the ratio of the signal current to the direct current of the bridge is constant for a wide range of currents. This curve is also substantially constant as a function of the temperature
  • Advantageous use may be made in the case of the recording circuit of a magnetic recorder.
  • the fact that the gain can be varied makes it possible to obtain a limiting device by means of which one can avoid the saturation of the magnetic tape without excessive distortion in the event that the input signal should happen to exceed the normal maximum value.
  • the complementary nature of the characteristics of the diode bridge and the magnetic tape make it possible to reduce the distortion of the recorded signal by one order of magnitude.
  • a sinusoidal oscillator is essentially a selective amplifier connected on itself. At the frequency at which the loop gain is greater than 1 (phase shift 0), the amplifier starts to oscillate. This oscillation increases until a regulating element decreases the gain andstabilizes the amplitude thereof.
  • Such a regulation has been effected by the saturation of an element, but the signal obtained was deformed by this saturation.
  • Use has also been made of an element heated by the signal and the impedance of which varies with the temperature so as to reduce the gain. This manner of procedure entails, however, drawbacks such as the slowness of the response and the dependence of the output signal on the room temperature.
  • the oscillator By inserting the diode bridge described into the circuit of the oscillator and causing the direct current which passes through it to depend on the amplitude of the signal produced, the oscillator is stabilized without difficulty with optimum time constants. Furthermore, as the base amplifier produces a certain distortion which is complementary to that of the diode bridge, the AC amplitude can be suitably selected on the bridge so as to decrease this distortion by one order of magnitude. In the case of a high quality oscillator, a second diode bridge can be added in a feedback chain of the amplifier in order to perfect the correction.
  • FIG. 3 is an example of an embodiment of a recording device with distortion compensation and variable gain.
  • This circuit which is a circuit with complementary transistors and 102, comprises a diode bridge 10, variable impedance means 11 for compensation of distortion by even harmonics, a resistor 12 for compensating for differences in the thresholds of the PNP and NPN transistors, an amplifier 13 acted on by voltage a series input resistor 18, and recording head 14 and a bias magnetization generator 15.
  • the diagram also shows the input terminals 16 and the terminals 17 for applying the gain control voltage to the base of a control transistor 103.
  • FIG. 4 shows an assembly with two symmetrical transistors T, and T for the regulation of sensitivity within a wide range of gain. There is concerned here another form of feed of the diode bridge which permits a variation of gain within a wide range. If one desires to I lating circuit.
  • the diode bridge is accompanied by a decrease in current of the transistor T, of identical absolute value.
  • the device X (FIG. 4) supplies a constant current, the result is that I, will be identical to I, in absolute value.
  • FIG. 7 shows a part of an automatic sensitivity regu- In this circuit, 21 is the diode bridge, 22 the positive source of potential, 23 the input of the signal (values of between 4 p. amp and 400 1. amp effective), 24 the output of the signal, 25 the terminal for the application of the control voltage (values of between 0 and 4 V), 26 the common terminal, 27 and 28 the transistors T, and T, respectively and 29 a logarithmic circuit.
  • the diagram also showsthe currents I, and I, the current I the direct current I,,, controlled to establish the operating point and the constant alternating current 1, It should be noted that the current gain of the transistors T, and T, must be very great in order to prevent the base current from disturbing the equilibrium. If the transistors available are of insufiicient gain, they are assisted by means of the amplifier circuit of FIG. 8.
  • the system has a nonlinearity which is very constant as a function of the temperature, and it is easy to determine the amount of this nonlinearity by the determination of the amount of current in the bridge, which makes it possible to vary it as a function of the temperature in order to adopt it to the required conditions. Furthermore, there is a very slight passage of control signal in the useful signal, and it is not necessary to use precision elements or elements of high stability.
  • the diode bridge can be used in a number of circuits to (1) limit the current in a non-distorting manner, (2) to' correct for distortion produced in many communication circuits, and (3) to control the current in a signal transmission circuit.
  • the preferred form of the bridge circuit is shown in FIG. 4 where the bridge controls the input voltage applied to an amplifier'by presenting a shunt circuit having a variable impedance.
  • the variable impedance controls the input current and varies the potential drop across an input resistor 18, thereby also controlling the applied voltage.
  • Wlilat is claime i l. n a contro a le nonlinear impedance connected to a pair of input terminals in series with a dropping impedance for conditioning the AC input voltage applied to a recording means, the improvement which comprises:
  • a compensating circuit for correcting the waveform distortion in a recording means, said 1 compensating circuit connected across said recording means and including a first series resistor, a four-armed bridge, and a second series resistor; said four-armed bridge including a rectifier diode in each arm for continuous passage of current having a nonlinear amplitude responsive to its applied voltage;
  • a direct current power source connected acro said compensating circuit for producing a direct current in all four bridge arms;
  • variable impedance connected i respectively across the first and second series resistance for varying the current through the bridge, said variable impedances each including the emitter-collector circuit of a transistor;
  • control means connected to the bases of said transistors for varying the values of said variable impedances.
  • control means for varying the variable impedance includes an adjustable direct current voltage applied to the bases of said transistors.

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  • Amplifiers (AREA)
  • Digital Magnetic Recording (AREA)
  • Networks Using Active Elements (AREA)
  • Control Of Amplification And Gain Control (AREA)
US887301A 1968-12-26 1969-12-22 Variable,nonlinear impedance Expired - Lifetime US3681625A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH1929068A CH505505A (fr) 1968-12-26 1968-12-26 Utilisation d'un circuit électronique constituant une impédance non-linéaire et variable

Publications (1)

Publication Number Publication Date
US3681625A true US3681625A (en) 1972-08-01

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ID=4438533

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Application Number Title Priority Date Filing Date
US887301A Expired - Lifetime US3681625A (en) 1968-12-26 1969-12-22 Variable,nonlinear impedance

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US (1) US3681625A (enrdf_load_stackoverflow)
CH (1) CH505505A (enrdf_load_stackoverflow)
DE (1) DE1965099B2 (enrdf_load_stackoverflow)
FR (1) FR2027130A1 (enrdf_load_stackoverflow)
GB (1) GB1294108A (enrdf_load_stackoverflow)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4401940A (en) * 1982-09-30 1983-08-30 Harris Corporation Voltage equalizer bridge

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5412714A (en) * 1977-06-29 1979-01-30 Matsushita Electric Ind Co Ltd Recorder-reproducer

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4401940A (en) * 1982-09-30 1983-08-30 Harris Corporation Voltage equalizer bridge

Also Published As

Publication number Publication date
FR2027130A1 (enrdf_load_stackoverflow) 1970-09-25
DE1965099C3 (enrdf_load_stackoverflow) 1975-06-05
DE1965099A1 (de) 1970-07-09
DE1965099B2 (de) 1974-08-01
CH505505A (fr) 1971-03-31
GB1294108A (en) 1972-10-25

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