JPS589412A - Agc circuit - Google Patents

Abstract

PURPOSE:To facilitate the formation of an IC and to obtain the distortionless maximum input level which is enough to both the 1st and 2nd amplifiers, by securing an AGC operation for the 1st and 2nd amplifiers with the AGC control voltage of a control voltage generating circuit. CONSTITUTION:The 1st voice signal supplied to an input terminal is amplified by the 1st amplifier 3. The 1st voice signal and the 2nd voice signal supplied to an input terminal 2 are amplified by the 2nd amplifier 4. A control voltage generating circuit 9 produces the AGC control voltage curresponding to the level of the output voice signal. The 1st and 2nd level control means 7 and 10 control the output voice signals of the amplifiers 3 and 4 at a certain level respectively by the AGC control voltage. As a result, a circuit can be converted into an IC without increasing the number of terminal pins. At the same time, the sufficient distortionless maximum input level is obtained for both amplifiers 3 and 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AGO circuit, and the control voltage of the AGO circuit to which the first audio signal and/or the second audio signal is supplied,
It is an object of the present invention to provide an AGO circuit that can obtain a sufficient distortion-free maximum input level for both audio signals with a simple circuit configuration by sharing the control voltage of the AGO circuit to which the first audio signal is supplied. purpose.

FIG. 1 shows a circuit diagram of an example of a conventional AGO circuit.

In the figure, an audio signal from a microphone is input to an input terminal 1, and an audio signal from another device (for example, a tape recorder, a VTR, etc.) is input as a line input audio signal to an input terminal 2. These audio signals may arrive at the same time or only one of them may arrive. first,
To explain the case where a microphone audio signal comes in, the microphone audio signal that comes into input terminal 1 is connected to a resistor R.
An operational amplifier (so-called microphone amplifier) 3 is connected through a circuit consisting of P and a high frequency removal capacitor O4 and a capacitor C2.
is supplied to the non-inverting input terminal of

The operational amplifier 3 has its inverting input terminal grounded via the resistor R2, and is connected to the feedback resistor R3. C6, variable resistor vR1
A capacitor C and a resistor R5 are respectively connected to a non-inverting input terminal of an operational amplifier (so-called line amplifier) 4.

The line amplifier 4 has its inverting input terminal grounded via a resistor R6, and is connected to a feedback resistor R7, which non-inverts and amplifies the input microphone audio signal and supplies it to the control voltage generation circuit 6 via the amplifier 5. do. Control voltage generation circuit 6
rectifies and smoothes the input microphone audio signal at a predetermined attack time and recovery time, and applies the rectified voltage as a control voltage to the variable impedance element T to variably control its impedance. Here, in the case of 2-in-1, the impedance of the variable impedance element 7 is made small and the input audio signal level of the line amplifier 4 is controlled to be a constant value.

When the input audio signal of this line amplifier 4 is inputted from the input terminal 2 in addition to the microphone audio signal, this line input audio signal is input to the capacitor C.
4. Since it is mixed with the microphone audio signal via the resistor R4, it is a mixed signal of the line input audio signal and the microphone audio signal, and when the microphone audio signal does not come in and the line input audio signal comes in, It is clear that it is a line input audio signal. In this way, even if the level of the microphone audio signal and/or line input audio signal supplied to the line amplifier 4 changes, it is automatically controlled to a constant level and output to the output terminal 8).

However, although the conventional AGC circuit described above can obtain a sufficient AGO effect for the line input audio signal, the microphone audio signal enters the input terminal 1 at an excessive level that exceeds the undistorted maximum output level of the microphone amplifier 3. When this happens, there is a drawback that the microphone amplifier 3 picks up the signal with distortion and outputs it to the output terminal 8. In order to prevent the above phenomenon, it is conceivable to lower the gain of the microphone amplifier 3 and obtain the gain to a required value in the subsequent stage circuit, but this would deteriorate the performance of the line amplifier 4 when the microphone is not used. Therefore, in the conventional AGC circuit, it was not possible to use a microphone amplifier with a sufficient undistorted maximum input level.

The present invention eliminates the above-mentioned drawbacks, and will be described below with reference to FIG. 2.

FIG. 2 shows a circuit diagram of an embodiment of the AGC circuit according to the present invention. In the figure, the same components as in FIG. 1 are denoted by the same reference numerals, and their explanations will be omitted. In FIG. 2, a rectifier circuit 9 generates a control voltage to a variable impedance element T that causes the line amplifier 4 to perform an AGO operation, and at the same time generates a control voltage to a variable impedance element T that causes the microphone amplifier 3 to perform an AGO operation. This circuit also applies voltage to 10. That is, according to this embodiment, the control voltage generation circuit 9 is created by adding a resistor R8 and a variable impedance element 10 to the conventional circuit shown in FIG. 1, and by slightly changing the configuration of the control voltage generation circuit 6. ), microphone amplifier 3
and line amplifier 4 are configured to perform the fiAGo operation using a common AGO control voltage from the control voltage generation circuit 9. Now, the level of the microphone audio signal entering the input terminal 1 is such that the microphone is If the level becomes too thick due to reasons such as this, the output level of the line amplifier 4 will increase accordingly, and the impedance values of the 0 variable impedance regulators T and 10 from the control voltage generation circuit 9 will be reduced. The AGO control voltage is taken out. This results in
The excessively high level microphone audio signal that has entered the input terminal 1 is lowered to a predetermined level by changing the voltage division ratio of the rolled rod voltage dividing circuit made up of the resistor R8 and the variable impedance element 10, and then sent to the microphone amplifier 3. This signal is then output as an amplified microphone audio signal with no distortion. At the same time, the input level of the line amplifier 4 is also lowered by changing the voltage dividing ratio of the resistive voltage dividing circuit made up of the resistor R5 and the variable impedance element 7. In this way, a distortion-free microphone audio signal and/or line audio signal is output to the output terminal 8.

By the way, the control voltage generation circuit 9 operates to reduce the impedance value of the variable impedance element 10 more quickly than the operation of reducing the impedance value of the variable impedance element 7.
AGO control voltages having a constant level difference are applied to each of the AGO control voltages 10 and 10, respectively. With this, when the microphone audio signal and the line human input audio signal are mixed and supplied to the line amplifier 4, when only the microphone audio signal is at an excessive level, the line input audio at an appropriate level Similarly to the microphone audio signal, the signal can be prevented from being set to a low level, and only the microphone audio signal that is at an excessive level can be lowered. This is particularly suitable for application to an AGC circuit for audio signals, such as microphone audio signals, where excessive levels are often input.

According to this embodiment, since the AGO control voltage of the microphone amplifier 3 is shared with the AGO control voltage of the line amplifier 4, a circuit section corresponding to the amplifier 5 and the control voltage generation circuit 6 is provided independently for the microphone amplifier. Therefore, when the AGC circuit shown in FIG. 2 is integrated into an integrated circuit, it can be configured with the same number of terminal pins as the conventional one without increasing the number of terminal pins.

In addition, in the above embodiment, the AGO circuit, which is a circuit in which a microphone audio signal and a line input audio signal can be mixed, is explained (1, but the audio signals may be of different types. Also, as the AGO means, Although the means for controlling the input levels of the amplifiers 3 and 4 by changing the resistor voltage division ratio has been described, other AGO means, such as changing the gains of the amplifiers 3 and 4, may be used.

As described above, the AGC circuit according to the present invention includes a first amplifier that amplifies the first audio signal, and a first audio signal and/or a second audio signal taken out from the amplifier in the ship 1. a second amplifier that is supplied with an audio signal and amplifies it; a voltage generating circuit that generates an AGO control voltage according to the output audio signal level of the second amplifier; Since the first and second level control amount stages control all the output audio signals of the second amplifier and the second amplifier to a constant level, the first. Compared to the case where each of the second amplifiers has a circuit that generates the AGO control voltage, the circuit configuration is simpler and cheaper, and when integrated, it can be integrated without increasing the number of terminal pins compared to the conventional case. can be made into
Further, it is possible to obtain a sufficient undistorted maximum input level for both the first and second amplifiers, and furthermore, the voltage generating circuit controls the M10 level control means when the output audio signal level of the second amplifier is equal to or higher than a predetermined value. Since the level control is configured to be performed with priority over the level control by the second level control means, when the first and second audio signals are mixed and supplied to the second amplifier, the first audio signal Only the level control of this first audio signal can be performed when only the signal has an excessive level, and therefore,
If the first audio signal is a microphone audio signal and the second audio signal is a line input audio signal, this is particularly suitable since the microphone audio signal often has an excessive level. .

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional circuit, and FIG. 2 is a circuit diagram showing an embodiment of the circuit of the present invention. 1... Microphone audio signal input terminal, 2... Line input audio signal input terminal, 3... Operational amplifier (microphone amplifier), 4... Operational amplifier (line amplifier), 6.
9... Control voltage generation circuit, 7.10... Variable impedance element. Continued from page 1 0 Inventor: Takashi Maki - Inside Victor Company of Japan, 3-12 Moriyamachi, Kanayō-ku, Yokohama City

Claims (1)

[Claims] 1. A first amplifier that amplifies a first audio signal, and a first audio signal and/or a second audio signal extracted from the first amplifier, which is supplied with the first audio signal and/or the second audio signal. and an AG according to the output audio signal level of the second amplifier.
a voltage generating circuit that generates an AGO control voltage; and first and second amplifiers that control the output audio signals of the first and second amplifiers to a constant level according to the output AGO control voltage of the voltage generating circuit.
An AGO circuit characterized in that it is similar to a level control means. 2. The voltage generating circuit performs level control by the first level control means with priority over level control by the second level control means when the output audio signal level of the second amplifier is equal to or higher than a predetermined value. 2. The AGO circuit according to claim 1, wherein the AGO circuit generates an AGO control voltage. 3. The first audio signal is a microphone audio signal;
The AGO according to claim 1 or 2, wherein the second audio signal is a line input audio signal.
circuit.