US3617777A

US3617777A - Automatic sensitivity-regulating device

Info

Publication number: US3617777A
Application number: US887302A
Authority: US
Inventors: Stefan Kudelski
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-12-26
Filing date: 1969-12-22
Publication date: 1971-11-02
Anticipated expiration: 1988-11-02
Also published as: CH501338A; DE1965100B2; FR2027131A1; DE1965100A1; AT303413B; GB1290520A; JPS504304B1

Abstract

Automatic sensitivity-regulating device, characterized by the fact that it has two sensitivity recovery time constants, one a slow one which is applied permanently in case of the presence of a signal and the other a rapid one which is placed in operation if the signal remains less than a selected level during a selected period of time.

Description

United States Patent Inventor Stefan Kudelski CH. de la Croix-l052 Le Mont-sur- Lausanne, Chemin de la Croix, Switzerland Appl. No. 887,302 Filed Dec. 22, 1969 Patented Nov. 2, 1971 Priority Dec. 26, 1968 Switzerland 19,289/68 AUTOMATIC SENSITIVITY-REGULATING DEVICE 6 Claims, 3 Drawing Figs.

Int. Cl l-l03k 17/28 Field of Search 307/293;

[56] References Cited UNITED STATES PATENTS 2,719,226 9/1955 Gordon et al 328/120 X 3,019,396 l/1962 Heine et al 330/28 3,068,367 12/1962 Brown et al 328/120 3,119,970 1/1964 Thompson et al. 330/138 X 3,202,929 8/1965 Benger etal 330/138 3,284,713 11/1966 Bailey 330/138 X Primary Examiner-Donald D. Forrer Assistant Examiner-R. C. Woodbridge Attorneys-James M. Heilman and Heilman & Heilman ABSTRACT: Automatic sensitivity-regulating device, characterized by the fact that it has two sensitivity recovery time constants, one a slow one which is applied permanently in case of the presence of a signal and the other a rapid one which is placed in operation if the signal remains less than a selected level during a selected period of time.

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This invention relates to a variable impedance, and more particularly, to a variable impedance device providing different recovery time constants.

It is known that a microphone supplies a signal which is proportional to the acoustic levelwhich it picks up. This level may vary within wide proportions in actual sound recording and to a lesser extent in the case of a telecommunications transmitting microphone. Now, in order to record a signal or modulate a transmitter, it is necessary to have signal levels which are relatively constant. Regulation can be effected manually by means of a potentiometer and a voltmeter which measures the amplitude of the signal or automatically by means of a device which measures the amplitude of the signal and acts on a variable gain device. The known automatic regulators in general comprise a memory which ordinarily consists of a capacitor, the gain being'related to the voltage to which said capacitor is charged. The charging of this capacitor, which corresponds to a decrease in gain, takes place very rapidly so that the first syllable of a word is regulated, but the recovery time is much slower, presenting certain problems. If one uses a rapid recovery time, the sensitivity increases between the words, and this results in a very disagreeable effect due to increase in the background noise between the words. If the time constant is long, that is, the recovery time is slow, this phenomenon is no longer disturbing, but the readaptation of the gain to a weak signal which may have been preceded by a strong signal, is too slow.

SUMMARY OF THE INVENTION In order to overcome these drawbacks, an object of the present invention is to provide automatic sensitivity regulating device which is characterized by the fact that it has two sensitivity recovery time constants, namely, a slow one which is applied permanently in case of the presence of a signal, and the other a rapid one which is placed in operation if the signal remains below a selected level during a selected period of time.

Another object of the present invention is to provide an improved automatic sensitivity regulating device.

FIGURES FIG. 1 is a schematic diagram of the present invention; FIG. 2 is an explanatory graph therefor;

FIG. 3 is a schematic diagram of a detail of FIG. 1.

DETAILED DESCRIPTION In the arrangement shown in FIG. 1, an input signal is applied in the form of current to

terminals

23, 26, through a series connection of resistor 8 and capacitor 9 to a device 10, the impedance of which varies as a function of a control voltage E which is applied to another input 25 of device 10. As soon as the voltage E exceeds a given threshold value, for instance 3 v., the impedance decreases, for instance by 6 db. per 95 v. applied. The signal affected by the variable impedance 10 is supplied to an amplifier ll. phase shifter 12 located at the output of amplifier l 1 comprising a relatively standard capacitor resistor combination enables the signal amplified by amplifier 11 to be provided as two equal signals in phase opposition. The first of these two signals is supplied to the base of transistor T,, while the other is applied to the base of transistor T,. Transistors T, and T, forma peak rectifier l3 and a capacitor C, connected between their interconnected emitters and a point of reference potential is charged to a voltage, the value of which is related to the peak voltage of the input signal. This voltage on the capacitor C, constitutes the control signal E of the variable impedance 10. The capacitor C, is discharged by the resistor R, of high value, which causes this discharge to be slow and to last several seconds (slow recovery, for instance I to 2 db. per second on the average).

Simultaneously, the presence of a signal of sufiicient amplitude is coupled to the base of transistor T through capacitor C, and causes the transistor T to conduct and discharge the capacitor C, which is connected to the collector of transistor T The base of transistor T. is connected to the collector of transistor T and upon the discharge of capacitor C, is rendered nonconductive. If the amplitude of the signal drops below the value necessary to make the transistor '1', conduct, the resistor R connected between the collector of T, to a source of reference potential charges the capacitor C, and, at the end of a period of time t, (FIG. 2), the transistor T starts to conduct and rapidly discharges the capacitor C, through the resistor R (rapid recovery, for instance 10 db. per second).

The graph of FIG. 2 illustrates this operation and shows the decrease of the gain at the time of the appearance of the signal, its slow increase during the time t,, and its rapid increase subsequently.

The variable impedance device 10 can be developed in the manner shown in FIG. 3. In this circuit, 21 is a diode bridge constituting a variable, nonlinear impedance, 22 is a positive source of potential, 23 the signal input, 24 the signal output, 25 the terminal for the application of the control voltage, 26 the common ground terminal, 27 and 28 the transistors T, and T, respectively, and 29 a logarithmic circuit. The diagram also shows the currents I, and I the current I the direct current I controlled establishing the operating point and the constant alternating current I What is claimed is:

1. An automatic sensitivity regulating device responsive to the level and duration of an input signal comprising:

a. an input circuit including a series resistor;

b. an amplifier coupled to the input circuit for receiving and transmitting a signal;

c. a variable impedance circuit connected to the input circuit for varying the amplitude of the signal applied to the amplifier, said variable impedance including a control terminal, the voltage of which determines the circuit impedance;

d. A capacitor coupled to the amplifier output terminals and to said control terminal, said capacitor chargeable to a DC voltage responsive to the input signal;

e. a first resistor connected across said capacitor for discharging it at a first predetermined rate;

f. a second resistor coupled to the capacitor in series with a transistor for discharging the capacitor at a second predetermined rate;

g. and a coupling circuit between the amplifier output and the transistor for making the transistor conductive when the input voltage exceeds a predetermined value, thereby permitting current to flow through the second resistor.

2. A regulating device according to claim 1 wherein said variable impedance circuit includes a four armed bridge circuit having a diode rectifier in each of its four arms.

3. A regulating device according to claim 2 wherein said bridge circuit is connected to a transistor having base, collector, and emitter electrodes, said collector and emitter electrodes connected in series with the bridge, and the base connected to said control terminal.

4. A regulating device according to claim 1 wherein said amplifier circuit includes output terminals connected to a pair of phase-shifting means with the first of said pair providing a first phase shift and the second of said phase-shifting means providing a second phase shift, said second phase shift being complementary to said first phase shift.

5. A regulating device according to claim I wherein said transistor in series with the second resistor is normally nonconducting and is made conducting by a voltage derived from the output of said amplifier.

6. A regulating device according to claim 1 wherein the output terminals of said amplifier are connected to a full wave rectifier for charging said capacitor.

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Claims

1. An automatic sensitivity regulating device responsive to the level and duration of an input signal comprising: a. an input circuit including a series resistor; b. an amplifier coupled to the input circuit for receiving and transmitting a signal; c. a variable impedance circuit connected to the input circuit for varying the amplitude of the signal applied to the amplifier, said variable impedance including a control terminal, the voltage of which determines the circuit impedance; d. A capacitor coupled to the amplifier output terminals and to said control terminal, said capacitor chargeable to a DC voltage responsive to the input signal; e. a first resistor connected across said capacitor for discharging it at a first predetermined rate; f. a second resistor coupled to the capacitor in series with a transistor for discharging the capacitor at a second predetermined rate; g. and a coupling circuit between the amplifier output and the transistor for making the transistor conductive when the input voltage exceeds a predetermined value, thereby permitting current to flow through the second resistor.

5. A regulating device according to claim 1 wherein said transistor in series with the second resistor is normally nonconducting and is made conducting by a voltage derived from the output of said amplifier.