JPH0482305A - Logarithmic amplification rectifier circuit and AGC circuit for telephones using it - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a logarithmic amplification rectification circuit for a telephone that includes an amplifier in the communication circuit, and an AGC circuit using the same, and particularly to , relates to a logarithmic amplification rectifier circuit and an AGC circuit for telephones that operate on a low voltage power supply.

[Prior Art 1] Conventionally, a circuit as shown in FIG. 7 has been used as a logarithmic amplification and rectification circuit that logarithmically amplifies an audio signal and rectifies it into a voltage corresponding to the signal level.

In this figure, 1 is an audio signal input terminal, 2 is a rectified voltage output terminal, 11 is a differential amplifier, 12.13 is a diode that performs logarithmic conversion, 14 is a resistor that adjusts the gain, and 15 is a diode that performs rectification. be.

The differential amplifier 11, diodes 12, 13, and resistor 14 constitute a logarithmic amplifier circuit that logarithmically amplifies an audio signal, and this logarithmic amplifier circuit and diode 15 constitute a logarithmic amplification rectifier circuit 10A. . The output signal of the logarithmic amplifier circuit is half-wave rectified by the diode 15, but if the forward voltage of the diode 15 is 0.7V, the output voltage of the rectified voltage output terminal 2 is 0.
．． The voltage will be 7v lower. Therefore, in a region where the output signal of the logarithmic amplifier circuit is 0.7V or less, an insensitivity region occurs in which the output voltage of the rectified voltage output terminal 2 becomes o■, and the output signal of the logarithmic amplifier circuit is There was a drawback that an amplitude voltage higher than the output voltage required in No. 2 by 0.7 V or more was required.

FIG. 8 is a circuit example of a conventional telephone AGC circuit using the logarithmic amplification and rectification circuit 10A of FIG. In this diagram, 2
o smoothes the output voltage of the logarithmic amplification rectifier circuit 1°A,
Further, a smoothing circuit whose time constant can be set; 3o is a variable gain circuit having a gain that changes according to the output voltage of the smoothing circuit 20; 41 is an audio signal input terminal of the front-filling variable gain circuit 3o; 42 is an audio signal output terminal of the variable gain circuit 3o.

In FIG. 8, if 0.7V or more is required as the control voltage for controlling the gain of the variable gain circuit 30, as explained in FIG.
An amplitude voltage of V or more is required. Therefore, if the ground potential of the logarithmic amplifier circuit is set to an intermediate voltage of the power supply voltage, the power supply voltage of the logarithmic amplifier circuit must be at least 2.8V or more.

[Problem to be solved by the invention] As described above, in the conventional logarithmic amplification rectifier circuit 10A,
The output signal of the logarithmic amplification circuit 10 constituting this circuit has the drawback that an amplitude voltage that is 0.7 V or more higher than the required output voltage is required.
An AGC circuit for a telephone using A requires an amplitude voltage of 1.4 V or more, and therefore cannot be used because it cannot perform low-voltage power supply operation.

The present invention has been made to solve these drawbacks, and provides a logarithmic amplification rectifier circuit that has a rectification action that does not reduce the output voltage and has no insensitive region, and is configured using the logarithmic amplification rectifier circuit. By doing so, it is an object of the present invention to obtain an AGC circuit for a telephone that is capable of operating on a low voltage power supply.

Means for Solving Problems] A logarithmic amplification rectifier circuit according to the present invention comprises: a differential amplifier into which an audio signal is input; a transistor whose base is connected to the output of the differential amplifier and whose collector is the output; It consists of a diode that forms a feedback loop from the collector of the transistor to one end of the input of the differential amplifier, and a resistor that is connected to one end of the input of the differential amplifier to adjust the gain.

Further, the AGC circuit for a telephone according to the present invention has the above-mentioned logarithmic amplification rectifier circuit, a smoothing circuit that smoothes the output voltage of the logarithmic amplification rectifier circuit, and a gain that changes according to the output voltage of the smoothing circuit. It is equipped with a variable gain circuit.

C Effect J In the logarithmic amplification rectifier circuit of the present invention, when a voltage more negative or positive than the ground potential is applied to the audio signal input terminal, the transistor turns on or off depending on the polarity of the diode in the feedback loop, so that the output A logarithmic amplification rectifier circuit having a rectification function without voltage drop can be obtained.

Further, since the AGC circuit for a telephone according to the present invention uses the above-mentioned logarithmic amplification rectifier circuit, it can operate with a low voltage power supply.

〔Example〕

Hereinafter, this invention will be explained using the drawings.

FIG. 1 shows a first embodiment of a logarithmic amplification rectifier circuit 1° according to the present invention. 1 is an audio signal input terminal, 2 is a rectified voltage output terminal, 3 is a differential amplifier, 4 is a transistor that performs rectification and amplification, 5 is a diode that performs logarithmic conversion, 6 and 7 are resistors that adjust the gain, and 8 is a This is a power supply connection terminal for the transistor 4. The resistor 7 is for stabilizing the circuit operation, and there is no problem in operation even if it is absent. Hereinafter, the circuit operation in the case where the resistor 7 is not provided will be explained.

In FIG. 1, when an audio input signal is input to the audio signal input terminal 1 and a voltage negative than the ground potential is applied,
The signal is input to the non-inverting input terminal of the differential amplifier 3,
The output of the differential amplifier 3 swings to the negative side. At that time, a collector current flows through the transistor 4 whose pace is connected to the output terminal of the differential amplifier 3, and the current flows through the diode 5 connected to the feedback loop, so that the potential at the non-inverting input terminal of the differential amplifier 3 is inverted. It acts so that the potential is the same as that of the input terminal. Therefore, the negative voltage input to the audio signal input terminal 1 is logarithmically converted and output to the rectified voltage output terminal 2 as a positive voltage. At this time, the input voltage -E and the output voltage E. The relationship is expressed by the following formula % Formula % Here, Is is the reverse saturation current of the diode 5, k is the Boltzmann constant, q is the amount of electron charge, T is the absolute temperature, and R is the resistance value of the resistor 6.

On the other hand, when a voltage more positive than the ground potential is applied to the audio signal input terminal 1, the output terminal of the differential amplifier 3 swings to the positive side, but even if the transistor 4 becomes 0FF (state where no collector current flows). , the rectified voltage output terminal 2 does not have a voltage lower than the ground potential. Therefore, the potential at the non-inverting input terminal of the differential amplifier 3 is higher than the potential at the inverting input terminal (the transistor 4 acts to maintain the OFF state).

In this way, according to the circuit shown in Fig. 1, when a negative voltage is input to the audio signal input terminal 1, it is logarithmically amplified and a positive voltage is output, and when a positive voltage is input, the transistor 4 is 0FFL, the output does not fall below the ground potential and is half-wave rectified. Therefore, it is possible to obtain a logarithmic amplification rectifier circuit 1o without a negative sensitivity region, which has a rectification effect that does not cause a drop in output voltage.

FIG. 2 shows a logarithmic amplification and rectification circuit 1o according to the present invention in which an audio signal input terminal 1 is connected to an inverting input terminal of a differential amplifier 3.
This is a second example. In this case, audio signal input terminal 1
When a positive voltage is input to the circuit, it is logarithmically amplified and a positive voltage is output, and when a negative voltage is input, the transistor 4 is turned off, and the output is not lower than the ground potential and is half-wave rectified. When a positive voltage is input to the audio signal input terminal 1, the relationship between the input voltage E and the output voltage E0 is as shown in the following equation.

FIG. 3 shows a third circuit of the logarithmic amplification rectifier circuit 10 according to the present invention, which has a polarity opposite to that of the circuit shown in FIG. 1 and obtains a negative voltage as an output.
This is an example. 9 is a transistor having a polarity opposite to that of the transistor 4; In other words, if a positive voltage is input to the audio signal input terminal 1, it will be logarithmically amplified and a negative voltage will be output. If a negative voltage is input, the transistor 9 will be turned off, and the output will not exceed the ground potential. It is half-wave rectified.

FIG. 4 shows the fourth logarithmic amplification rectifier circuit 1o according to the present invention, which has a polarity opposite to that of the circuit shown in FIG. 2 and obtains a negative voltage as an output.
This is an example. That is, when a negative voltage is input to the audio signal input terminal 1, it is logarithmically amplified and a negative voltage is output, and when a positive voltage is input, the transistor 9 becomes 0.
FFL, the output does not exceed ground potential and is half-wave rectified.

FIG. 5 shows an embodiment of an AGC circuit for a telephone according to the present invention using the logarithmic amplification and rectification circuit 1o of FIG. Fifth
FIG. 6 shows a detailed circuit example of the smoothing circuit 20 and variable gain circuit 3o shown in the figure. In Figure 6, 21
is an input terminal of the smoothing circuit 2°, 22.23 is a resistor for setting a time constant, and 24 is a smoothing capacitor. Further, 31 is a transistor for variable gain control, 32 is a resistor that sets the width of the variable gain, 33 and 34 are resistors that set the gain of this variable gain circuit 30, and 35 is a differential amplifier.

As shown in the circuit of FIG. 6, a transistor is used to control the gain of the variable gain circuit 30 for boat fishing;
A control voltage of 0.7V or more is required. therefore,
The output voltage of the logarithmic amplification rectifier circuit 10 in FIG. 5 is 0.
7V or more is required, but as explained in FIG. Assuming that it is the intermediate voltage of the power supply voltage,
Operation is possible when the power supply voltage is 1.4 µ or higher.

As explained in the section on the conventional circuit, in the conventional example shown in FIG. It is necessary to connect the two in series to increase the output voltage of the logarithmic amplifier circuit by 0.7V. On the other hand, in the embodiments shown in FIGS. 1 to 5, there is no voltage drop, so
Output voltage can be obtained with 51 diodes.

[Effects of the Invention] As described above, according to the logarithmic amplification rectifier circuit of the present invention, the transistors connected to the differential amplifier provide a rectifying action that does not reduce the output voltage and provide an operation without an insensitive region. Further, the AGC circuit for a telephone according to the present invention includes:
By configuring using the above logarithmic amplification rectifier circuit,
It is possible to obtain an AGC circuit for a telephone that can lower the power supply voltage by 1.4 cm compared to the conventional circuit.

In a telephone circuit that receives current supply from a telephone line and operates on a low voltage power supply, a reduction in operating voltage of 1.4 square meters has a very large effect.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of a logarithmic amplification rectifier circuit according to the present invention, and FIG. 2 is a circuit diagram showing a second embodiment of the present invention in which an audio signal input terminal is connected to an inverting input terminal of a differential amplifier. FIG. 3 is a circuit diagram showing a third embodiment in which a negative voltage is obtained as an output with the opposite polarity to the circuit in FIG. 1, and FIG. 4 is a circuit diagram with the opposite polarity to the circuit in FIG. 5 is a circuit diagram showing an embodiment of the AGC circuit for a telephone according to the present invention, and FIG. 6 is a circuit diagram showing an embodiment of the AGC circuit for a telephone according to the present invention. FIG. 7 is a diagram showing details of the smoothing circuit and variable gain circuit in the example, FIG. 7 is a diagram showing a circuit example of a conventional logarithmic amplification rectifier circuit, and FIG. 8 is a diagram showing a circuit example of a conventional AGC circuit for a telephone. . In the figure, 1 is an audio signal input terminal, 2 is a rectified voltage output terminal,
3 is a differential amplifier, 4 is a transistor, 5 is a diode,
6 and 7 are resistors, 8 is a power supply connection terminal, 9 is a reverse polarity transistor, 1o is a logarithmic amplification rectifier circuit, 20 is a smoothing circuit,
30 is a variable gain circuit, 41 is an audio signal input terminal of the variable gain circuit, and 42 is an audio signal output terminal of the variable gain circuit. Figure 1 Figure 2 Funeral diagram Funeral diagram Figure A

Claims (2)

[Claims] (1) A logarithmic amplification and rectification circuit that logarithmically amplifies an audio signal from an audio signal input terminal, rectifies it to a voltage according to the signal level, and outputs it from a rectified voltage output terminal. a transistor having a base connected to the output of the differential amplifier and having a collector as an output; a diode forming a feedback loop from the collector of the transistor to one end of the input of the differential amplifier; A logarithmic amplification rectifier circuit comprising: a resistor connected to one end of the input to adjust gain; (2) The logarithmic amplification rectifier circuit according to claim (1), a smoothing circuit that smoothes the output voltage of the logarithmic amplification rectifier circuit, and a variable gain circuit having a gain that changes according to the output voltage of the smoothing circuit. An AGC circuit for a telephone, characterized by comprising: