JPS62261207A - Agc circuit - Google Patents

Abstract

PURPOSE:To expand the proportional region in the input/output characteristic by providing a variable resistor connected between an output of an amplifier and ground and a detection circuit converting a signal obtained from a slider of the variable resistor into a DC and supplying the DC output to a base of a transistor (TR). CONSTITUTION:An AGC circuit is provided with an amplifier 4, a TR 6 whose collector and emitter are connected between the input of the amplifier and ground, the variable resistor 7 connected between the output of the amplifier and ground and the detection circuit converting a signal obtained from the slider of the variable resistor into a DC and supplying the DC output to a base of the TR. Suppose that the slider of the variable resistor 7 is set to a point (a), the input/output characteristic in this case has a characteristic shown in figure A'. When the slider of the variable resistor 7 is set to a point (b), even when the input signal is increased, the signal level inputted to the detection circuit 3 is lowered more than that when the slider is set to the point (a), then the input voltage starting the AGC is increased, resulting that the input/output characteristic as shown figure B' is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an AGC circuit that operates to suppress an increase in output when the input signal level exceeds a certain level.

BACKGROUND OF THE INVENTION In recent years, AGC circuits have been widely used in audio products such as microphone amplifier circuits and recording circuits.

An example of the above-mentioned conventional ACiC circuit will be described below with reference to the drawings.

Figure 3 is a block diagram of a conventional AGC circuit, and Figure 4 is a block diagram of a conventional AGC circuit.
2 shows an input/output characteristic diagram of the block diagram in the figure. Third
In the figure, 1 is a microphone, which is connected to the input of an amplifier 4 via a resistor 2.

A collector-emitter of a transistor 6 is connected between the input of the amplifier 4 and ground. A variable resistor 7 is connected between the output of the amplifier 4 and ground, and a slider of the variable resistor 7 is connected to the input of the amplifier 6. Further, the output of the amplifier 4 is connected to the base of the transistor 6 via the detection circuit 3.

The operation of the AGC circuit configured as described above will be explained below with reference to FIG. 4.

First, when the slider of the variable resistor 7 in FIG. The signal is amplified by the amplifier 5 and output to the output terminal 8. On the other hand, the output signal of the amplifier 4 is converted into direct current by the detection circuit 3, supplies the base current of the transistor 6, and operates the transistor 6 so as to attenuate the input signal. Here, in a range where the input voltage is low, the detection output is low, so the transistors do not operate at all, and the input/output characteristics are proportional, but when the input voltage exceeds a certain level, transistor 6 begins to operate. , the input/output characteristics are no longer proportional, and even if the input increases, the output does not increase much, resulting in the input/output characteristics as shown in FIG. 4A. Since the output voltage of the amplifier 2 has not reached the saturation level, an output waveform without distortion can be obtained.

Next, when the slider of the variable resistor 7 in FIG. 3 is at point b, the input voltage level at which the AGC starts to turn does not change, and the overall output level only decreases.
The input/output characteristics are as shown in FIG. 4B.

Problems to be Solved by the Invention However, in the above configuration, when the slider of the variable resistor 7 is set to bAK, the output voltage has a margin up to the output voltage saturation level of the amplifier 2, so the input/output There is no need to intentionally set the characteristics to AGC characteristics. That is, A.G.
The use of C characteristics has the problem of deteriorating the voltage utilization rate.

In view of the above-mentioned problems, the present invention provides a case in which a variable resistor that controls the output voltage level is set in a direction that lowers the output.
The present invention provides an AGC circuit that increases the input voltage level at which GC starts to be applied and increases the proportional region of input/output characteristics.

Means for Solving the Problems In order to solve the above problems, the AGC circuit of the present invention includes an amplifier, a transistor whose collector-emitter is connected between the input of the amplifier and ground, and an output of the amplifier. It is equipped with a variable resistor connected between the ground and a detection circuit that converts the signal obtained from the slider of the variable resistor into direct current and supplies this direct current output to the base of the transistor. .

Effects According to the present invention, when the variable resistor that controls the output voltage level is set in the direction of decreasing the output, the level of the signal input to the detection circuit also decreases at the same time, so that AGC starts to apply. The input voltage level increases, increasing the proportional region of the input/output characteristics.

Embodiment Hereinafter, an AGC circuit according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an AGC circuit in an embodiment of the present invention, and FIG. 2 is an input/output characteristic diagram of the block diagram of FIG. 1. In FIG. 1, the same reference numerals as in the description of the conventional example above indicate the same things,
Except for the point that the input of the detection circuit 3 is directly connected to the slider of the variable resistor 7, it is completely the same as the conventional example, so a description of its configuration will be omitted.

The operation of the AGC circuit configured as described above will be explained below with reference to FIGS. 1 and 2.

First, in FIG. 1, assuming that the slider of the variable resistor 7 is set at point a, the operation in this case is exactly the same as when the variable resistor 7 is set at point a in the conventional example. However, the input/output characteristics in this case are as shown in FIG. 2A'.

Next, when the slider of the variable resistor 7 in FIG. 1 is at point b, even if the input signal increases, the signal level input to the detection circuit 3 will be the same as when the slider is at point a. Since the input voltage is lower than that in comparison, the input voltage at which AGC starts to apply increases, resulting in the input/output characteristics as shown in FIG. 2B'. Therefore, the proportional region of the input/output characteristics increases.

Effects of the Invention As described above, the present invention comprises an amplifier, a transistor whose collector-emitter is connected between the input of the amplifier and ground, a variable resistor connected between the output of the amplifier and ground, and the above-mentioned transistor. and a detection circuit that converts the signal obtained from the slider of the variable resistor into direct current and supplies this direct current output to the base of the transistor, and the variable resistor is set in a direction to lower the output. if you did this,
It is possible to increase the input voltage level at which the AGC starts flowing and increase the proportional region of the input/output characteristics. Normally, variable resistors used for volume adjustment, etc. are rarely used with the maximum output, but are often used with the volume reduced to a certain extent, so the expansion of the proportional range of input/output characteristics by the present invention is extremely effective. It's large.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the AGC circuit according to the embodiment of the present invention, Fig. 2 is a doujin output characteristic diagram, Fig. 3 is a block diagram of a conventional AGC circuit, and Fig. 4 is an input/output characteristic diagram of Fig. 3. be. 3...Detection circuit, 4...Amplifier, 6...
...Transistor, 7...Variable resistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. Z
Illustration 77, Figure 8

Claims (1)

[Claims] an amplifier, a transistor whose collector-emitter is connected between the input of the amplifier and ground, a variable resistor connected between the output of the amplifier and ground, and a signal obtained from the slider of the variable resistor. and a detection circuit that converts the DC output into DC and supplies the DC output to the base of the transistor.