JPH05175770A - Low frequency agc circuit - Google Patents

Abstract

PURPOSE:To prevent overshoot of a volume control signal even when an attack time is reduced by providing 1st and 2nd voltage control means controlling a voltage of a low frequency signal outputting the controlled signal. CONSTITUTION:A voltage of a low frequency signal from an input terminal 1 is controlled respectively by electronic volumes IC2, 10 and the result is outputted. Then an output signal of the IC2 is full-wave-rectified by a full rectifier circuit 4 and the result is outputted as a pulsating wave and the result is applied to both terminals of a variable resistor 5. Moreover, an output signal of a feedback amplifier 6 is fed to a first attack slow recovery circuit comprising a capacitor 12, a resistor 13 and a diode 14 via a buffer 11, smoothed and the result is fed to a control terminal of the IC 10 as a variable resistor control voltage. Thus, when the voltage of the low frequency signal is rapidly increased, the variable resistor control voltage is quickly decreased, and when the voltage of the low frequency signal is rapidly decreased, the variable resistor control voltage is gradually increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low frequency AGC circuit for inputting a low frequency signal in the audible frequency band or the like and always controlling and outputting it to a predetermined voltage regardless of the input voltage.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a configuration example of a conventional negative feedback type low frequency AGC circuit. In FIG. 3, 1 is an input terminal to which a low frequency signal such as an audible frequency band is input. _{Reference numeral} 2 denotes an electronic volume IC, which is a volume control voltage V _VOL applied to the control end T _VOL.
The voltage of the low frequency signal is controlled and output according to the. Here, an example of the characteristic of the attenuation amount ATT of the electronic volume IC2 with respect to the volume control voltage V _VOL is shown in FIG.

Further, 3 is an output terminal for outputting the output signal of the electronic volume IC 2, 4 is a double-wave rectification circuit for rectifying the output signal of the electronic volume IC 2 as a pulsating flow, and 5 is a pulsating flow. Volume, 6 is a feedback amplifier that inverts and amplifies the signal appearing at the tap of the volume 5,
Reference numeral 7 is a decay time capacitor, 8 is a diode for charging the capacitor 7 with a signal applied to the anode, and 9 is a resistor for discharging the electric charge charged in the capacitor 7. These circuit elements 7 to 9 form a fast attack / slow recovery circuit.

In such a configuration, when the low frequency signal shown in FIG. 5A is input from the input terminal 1, the low frequency signal is output with its voltage controlled by the electronic volume IC 2 (FIG. 5 (d)). The output signal of the electronic volume IC 2 is output from the output terminal 3, double-wave rectified in the double-wave rectification circuit 4, and output as a pulsating current as shown in FIG. Is applied.

Next, the signal appearing at the tap of the volume 5 is inverted and amplified by the feedback amplifier 6, and then smoothed by the fast attack / slow recovery circuit composed of the capacitor 7, the diode 8 and the resistor 9, as shown in FIG. The signal becomes the signal shown in c) and is applied as the volume control voltage V _VOL to the control terminal T _VOL of the electronic volume IC 2. The volume control voltage V _VOL controls the attenuation amount ATT so that the voltage of the output signal of the electronic volume IC 2 is always constant.

The fast attack / slow recovery circuit is a circuit that controls and outputs changes in the volume control voltage V _VOL so that the reproduced sound of the signal output from the output terminal 3 cannot be heard unnaturally. .. That is, the input terminal 1
When the voltage of the low-frequency signal input from is suddenly increased, the voltage is instantly decreased. Conversely, when the voltage of the low-frequency signal is rapidly decreased, the voltage is slowly reduced. Volume control voltage V _VOL to increase
Changes.

[0007]

By the way, in the above-mentioned conventional low frequency AGC circuit, due to the time delay in the negative feedback loop, FIG.
As shown in the portion p of, the overshoot occurs in the volume control voltage V _VOL . Then, when the extremely short attack time t _a which is determined by the output impedance of the capacitor 7 and the feedback amplifier 6, in the portion where the volume control voltage V _VOL overshot, momentarily, the attenuation of the electronic volume IC2 abnormal However, the signal to be output from the output terminal 3 is interrupted and the sound cannot be heard.

[0008] Therefore, in order to remove the adverse effects of overshoot described above, increasing the attack time t _a, instantly reducing the voltage when the voltage of the turn, especially high frequency signal becomes abruptly increases Therefore, there is a problem that when output from the output terminal 3, it sounds as a buzz sound (see FIG. 5D).
The present invention has been made under such a background, and an object thereof is to provide a low frequency AGC circuit in which the volume control voltage does not overshoot even if the attack time is shortened.

[0009]

According to the present invention, first and second voltage control means for inputting a low-frequency signal, controlling and outputting the voltage of the low-frequency signal, and the first voltage control are provided. A double-wave rectification circuit that rectifies the output signal of the means by double-wave rectification and outputs it as a pulsating flow, and outputs by inverting and amplifying the pulsation
A first amplifier that applies the output voltage as a control voltage to the control end of the first voltage control means, and a predetermined voltage source connected via a resistor, and a charging voltage is the control end of the second voltage control means. A capacitor applied as a control voltage to the second amplifier, a second amplifier for inputting and amplifying the output signal of the first amplifier, and a cathode connected to the output terminal of the second amplifier,
It is characterized by including a diode whose anode is connected to a connection point between the resistor and the capacitor.

[0010]

According to the above configuration, the input low frequency signal is
The voltages are respectively controlled and output by the first and second voltage control means. Then, the output signal of the first voltage control means is double-wave rectified in the double-wave rectification circuit and output as a pulsating current, and then inverted and amplified in the first amplifier, and the control terminal of the first voltage control means. Is applied as a control voltage. This control voltage controls the voltage of the output signal of the first voltage control means.

The output signal of the first amplifier is amplified by the second amplifier, smoothed by the capacitor, the resistor and the diode, and applied as a control voltage to the control terminal of the second voltage control means. .. This control voltage controls the voltage of the output signal of the second voltage control means.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of a low frequency AGC circuit according to an embodiment of the present invention. In this figure, parts corresponding to those in FIG. 3 are assigned the same reference numerals and explanations thereof are omitted. In FIG. 1, 10 is an electronic volume IC having the same volume control voltage-attenuation amount characteristic (see FIG. 4) as the electronic volume IC 2, 11 is a buffer amplifier for amplifying the output signal of the feedback amplifier 6, 12
Is a capacitor, 13 is a resistor for decay time, 14
Is a diode for discharging the electric charge charged in the capacitor 12. The circuit elements 12 to 14 form a fast attack / slow recovery circuit.

In such a configuration, when the low frequency signal shown in FIG. 2 (a) is input from the input terminal 1, this low frequency signal is output with its voltage controlled by the electronic volume ICs 2 and 10, respectively. It Then, the output signal of the electronic volume IC 2 is double-wave rectified in the double-wave rectification circuit 4, output as a pulsating current as shown in FIG. 2B, and applied to both ends of the volume 5.

Next, the signal appearing at the tap of the volume 5 is inverted and amplified by the feedback amplifier 6 and then the signal shown in FIG.
And the control end T of the electronic volume IC 2
_The volume control voltage V _VOL1 is applied to _VOL1 . With this volume control voltage V _VOL1 , the electronic volume I
The attenuation amount ATT is controlled so that the voltage of the output signal of C2 is always constant. Circuit elements 2 and 4 to 6
Constitute a real-time AGC circuit.

The output signal of the feedback amplifier 6 is amplified by the buffer amplifier 11 and then amplified by the capacitor 12,
2 is smoothed in the fast attack / slow recovery circuit composed of the resistor 13 and the diode 14.
The signal becomes as shown in (d) and is applied to the control terminal T _VOL2 of the electronic volume IC 10 as the volume control voltage V _VOL2 . The volume control voltage V _VOL2 controls the attenuation amount ATT so that the voltage of the output signal of the electronic volume IC 10 is always constant. The circuit elements 11 to 1
Reference numeral 4 constitutes a feedforward AGC circuit.

Then, as shown in FIG. 2 (a), when the voltage of the low frequency signal suddenly increases, the volume control voltage V _VOL1 and the output voltage of the buffer amplifier 11 immediately drop, the diode 14 becomes conductive and the capacitor 12 is turned on. Since the electric charge that has been charged is discharged, the volume control voltage V _VOL2 is rapidly decreased as shown in the part p of FIG. 2 (d). Further, as shown in FIG. 2A, when the voltage of the low frequency signal suddenly decreases, the volume control voltage V _VOL1 and the output voltage of the buffer amplifier 11 immediately rise, the diode 14 becomes non-conductive, and the capacitor 12 becomes Since the battery is gradually charged via the resistor, the volume control voltage V _VOL2 gradually rises as shown in the part q of FIG. 2 (d).

As described above, according to the above-described embodiment, the volume control voltage V _VOL1 is obtained by the real-time AGC circuit including the circuit elements 2 and 4 to 6,
An electronic volume IC 10 having the same characteristics as the electronic volume IC 2 by smoothing the volume control voltage V _VOL1.
Since the volume control voltage V _VOL2, as in the prior art, the volume control voltage V _VOL2 due to the time lag in the negative feedback loop does not overshoot. Therefore, even if the attack time is shortened, if the voltage of the low-frequency signal increases momentarily,
The output signal of this low frequency AGC circuit is not interrupted.

[0018]

As described above, according to the present invention, the volume control voltage does not overshoot even if the attack time is shortened. Therefore, even if the voltage of the low frequency signal increases momentarily, the output signal of the low frequency AGC circuit will not be interrupted.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a low frequency AGC circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a signal output from each unit of the circuit of FIG.

FIG. 3 is a circuit diagram showing a configuration example of a conventional low frequency AGC circuit.

FIG. 4 is a diagram showing an example of a characteristic of an attenuation amount ATT of an electronic volume IC2 with respect to a volume control voltage V _VOL .

5 is a diagram showing an example of a signal output from each unit of the circuit of FIG.

[Explanation of symbols]

 1 Input Terminal 2,10 Electronic Volume IC 3 Output Terminal 4 Double Wave Rectifier Circuit 5 Volume 6 Feedback Amplifier 7,12 Capacitor 8,14 Diode 9,13 Resistance

Claims (1)

[Claims] 1. A low-frequency signal is input to each of the first and second voltage control means for controlling and outputting the voltage of the low-frequency signal, and an output signal of the first voltage control means is double-wave rectified. A double-wave rectifier circuit that outputs a pulsating current, and a first amplifier that inverts and amplifies and outputs the pulsating current, and applies the output voltage to the control terminal of the first voltage control means as a control voltage. A second capacitor which is connected to a predetermined voltage source via a resistor and applies a charging voltage as a control voltage to the control terminal of the second voltage control means; and a second input for amplifying the output signal of the first amplifier. A low frequency AGC, comprising: an amplifier; and a diode having a cathode connected to an output terminal of the second amplifier and an anode connected to a connection point between the resistor and the capacitor.
circuit.