JPS6326014A - Voltage feedback type automatic gain control circuit - Google Patents

Abstract

PURPOSE:To stabilize a processing circuit at the post-stage by inputting an input signal to an amplifier circuit through a variable resistance attenuation circuit, giving its output signal also to a full-wave rectifier circuit and using an output signal of the full-wave rectifier circuit so as to control the attenuation of the variable resistance attenuation circuit. CONSTITUTION:A level of an output signal (f) of a level detection circuit 1 is zero at input non-signal before a time T1, a switch circuit 3 is turned on at this time and a reference voltage Vs of a reference voltage generating circuit 2 is inputted to a full wave rectifier circuit 10. In this case, the gain of a voltage feedback type automatic gain control circuit is minimized. When an input signal (a) rises at the time T1, the level detection circuit 1 detects it and its output signal (f) rises at a time T2 with a small delay. Thus, the switch circuit 3 is turned off, no reference voltage VS is given to the full wave rectifier circuit 10, which applies full wave rectification to an output signal (d) of an amplifier circuit 6, the output signal (e) of which is inputted to a variable resistance attenuation circuit 5. Thus, the gain of the voltage feedback type automatic gain control circuit is controlled to be constant.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage feedback type automatic gain control circuit.

[Conventional technology]

As shown in FIG. 2, the conventional voltage feedback type automatic gain control circuit is comprised of a variable resistance attenuation circuit 5, an amplifier circuit 6, and a double-wave rectifier circuit 7.

In such a voltage feedback type automatic gain control circuit, a signal applied to the input terminal 8 is input to the amplifier circuit 6 through the variable resistance attenuation circuit 5, where it is amplified and output from the output terminal 9. The output signal of the amplifier circuit 6 is sent to the double wave rectifier circuit 7.
The signal is also inputted thereto, where it is double-wave rectified and applied to the variable resistance attenuation circuit 5. The output signal of the double-wave rectifier circuit 7 is a control signal for the variable resistance attenuation circuit 5, and the amount of attenuation of the variable resistance attenuation circuit 5 is controlled by this control signal. For example, if a high-level signal is applied to the input terminal 8 as an input signal, this signal is input to the amplifier circuit 6 through the variable resistance attenuation circuit 5, and the amplifier circuit 6 outputs a high-level signal, so it can be converted into a double-wave rectifier. The circuit 7 outputs a high voltage control signal. And is the variable resistance attenuation circuit 5 controlled? The higher the voltage of the signal No. 11 is, the more the amount of attenuation changes. Therefore, the gain of the voltage feedback automatic gain control circuit is reduced and the level of the signal at the output terminal 9 is suppressed. Conversely, when the level of the input signal is low, the amount of attenuation in the variable resistance attenuation circuit 5 becomes small, so the gain becomes large, and a signal with a high level is output to the output terminal 9. Gain control is automatically performed as described above, and a signal at a constant level is output regardless of fluctuations in the level of the input signal.

[Problem that the invention seeks to solve]

The problems of the above-mentioned conventional voltage feedback type automatic gain control circuit will be explained with reference to FIG. FIG. 3 is a waveform diagram of each part of the voltage feedback automatic gain control circuit shown in FIG. The waveform of the output signal C of the circuit 7 is shown.

When there is no input signal before time T, the level of the output signal C of the double-wave rectifier circuit 7 is O, so the attenuation amount of the variable resistance attenuation circuit is minimum and the gain of the voltage feedback automatic gain control circuit is maximum. There is. When the input signal a rises at time T, the gain of the voltage feedback automatic gain control circuit is at its maximum, so the output signal of the amplifier circuit 6 changes in the direction of increasing the amount of attenuation of the variable resistance attenuation circuit 5. do.

On the other hand, the time constant at which the output voltage C of the double-wave rectifier circuit 7 changes is set to have a constant time, since the output signal level will become unstable if it is shorter than the ripple period of the output signal of the double-wave rectifier circuit 7. has been done.

Within this certain period of time, the gain of the voltage feedback automatic gain control circuit becomes greater than the gain when the output signal level is stable, and the level of the first part of the output signal becomes higher than when it is stable, as shown. This has the problem that the first part of the output signal is colored, and the subsequent processing circuit becomes unstable due to the generation of transient phenomena due to fluctuations in the DC offset due to the difference between the positive and negative saturation levels.

An object of the present invention is to provide a voltage feedback automatic gain control circuit that solves these problems.

[Means for Solving the Problems] The voltage feedback automatic gain control circuit of the present invention includes a variable attenuation circuit, an amplifier circuit connected to the variable attenuation circuit, and an input signal to the variable attenuation circuit. a level detection circuit for detecting; a reference voltage generation circuit for generating a base voltage; a switch circuit connected to the reference voltage generation circuit and turned on/off based on the detection result of the level detection circuit; and the amplifier circuit. and connected to the switch circuit, and when the level detection circuit detects an input signal, the level detection circuit detects the reference voltage inputted from the reference voltage generation circuit via the switch circuit. a rectifier circuit that outputs a voltage obtained by rectifying the output signal from the amplifier circuit as a control signal to the variable attenuation circuit when the reference voltage is not in the range of gain variation; It is set to be a gain.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of the voltage feedback type automatic gain control circuit of this embodiment. This voltage feedback automatic gain control circuit includes a variable resistance attenuation circuit 5, an amplifier circuit 6, a double wave rectifier circuit 10, a level detection circuit 1, a reference voltage generation circuit 2, and a switch circuit 3. There is.

The input signal applied to the input terminal 8 is transmitted to the variable resistance attenuation circuit 5.
The signal is inputted to the amplifier circuit 6 through the signal line, where it is amplified and outputted from the output terminal 9. The output signal of the amplifier circuit 6 is also input to a double-wave rectifier circuit 10, where it is double-wave rectified and input to the variable resistance attenuation circuit 5. The output signal of the double-wave rectifier circuit 10 is a control signal for the variable resistance attenuation circuit 5, and the amount of attenuation of the variable resistance attenuation circuit 5 is controlled by this signal.

The level detection circuit 1 is for detecting whether or not a signal is input to the input terminal 8, and turns on/off the switch circuit 3 based on the detection result. The switch circuit 3 is turned on when the level detection circuit 1 is not detecting an input signal, and is turned off when the level detection circuit 1 is detecting an input signal. The reference voltage generation circuit 2 generates a reference voltage (1), which is input to the double-wave rectifier circuit 10 via the switch circuit 3 when the switch circuit 3 is on. The value of the reference voltage (2) is initially set so that the gain of the voltage feedback automatic gain control circuit of this embodiment is the gain for the maximum human power level in the input level response range, that is, the minimum gain in the gain variation range. When the reference voltage (2) is input to the double-wave rectifier circuit 10, it is configured to manually input this to the variable resistance attenuation circuit 5 as a control signal.

Next, the operation of this embodiment will be explained with reference to FIG. FIG. 4 shows the waveforms of the input signal a at the input terminal 8, the output signal d of the amplifier circuit 6, the output signal e of the double-wave rectifier circuit 10, and the output signal r of the level detection circuit 1, respectively. When there is no input signal before time T1, the level of the output signal f of the level detection circuit 1 is O, and at this time, the switch circuit 3 is on, and the reference voltage V of the reference voltage generation circuit 2.

is input to the double wave rectifier circuit 10. At this time, the gain of the voltage feedback automatic gain control circuit becomes minimum.

When the input signal a rises at time T1, the level detection circuit 1 detects this, and its output signal f rises at a slightly delayed time T2. As a result, the switch circuit 3 is turned off, and the reference voltage (2) is not input to the double-wave rectifier circuit 10. Therefore, the double-wave rectifier circuit 10 double-wave rectifies the output signal d of the amplifier circuit 6 to make the output signal e variable. It is input to the resistance attenuation circuit 5. Thereby, the gain of the voltage feedback automatic gain control circuit is controlled to be constant.

When the input signal a becomes a no-signal state again at time T3, the voltage of the output signal e of the double-wave rectifier circuit 10 decreases, but since the level detection circuit 1 detects no input signal and turns on the switch circuit 3, The voltage of the output signal e returns to V.

As described above, according to this embodiment, by initially setting the gain of the voltage feedback automatic gain control circuit to the minimum value when there is no input signal, the double-wave rectifier circuit 10 at the rising edge of the input signal a
The output voltage is set so that the gain of the voltage feedback automatic gain control circuit increases from the initial value of the gain for the maximum input level in the input level response range, that is, the minimum gain of the gain fluctuation range, to the gain when the output signal level is stable. Change. As a result, by setting the gain of the voltage feedback automatic gain control circuit at the rise of input signal a to be less than the gain when the output signal level is stable, it is possible to prevent the output signal from becoming higher than the level when it is stable. .

Although the above embodiment uses a double-wave rectifier circuit,
It is also possible to use a single-wave rectifier circuit. Furthermore, the attenuation circuit is not limited to a resistive attenuation circuit, and may be any other attenuation circuit.

〔Effect of the invention〕

As explained above, according to the present invention, by preventing saturation of the output signal at the rise of the input signal in a voltage feedback type automatic gain control circuit, it is possible to eliminate fluctuations in the DC offset of the output signal at the rise of the input signal. It has the effect of

[Brief explanation of drawings]

Figure 1 is a block diagram of a voltage feedback type automatic gain control circuit which is an embodiment of the present invention, Figure 2 is a block diagram of a conventional voltage feedback type automatic gain control circuit, and Figure 3 is a block diagram of a conventional voltage feedback type automatic gain control circuit. 4 is a waveform diagram showing signals of various parts of the gain control circuit. FIG. 4 is a waveform diagram showing signals of various parts of the voltage feedback automatic gain control circuit of FIG. 1...Level detection circuit 2...Reference voltage generation circuit 3...Switch circuit 5...Variable resistance attenuation circuit 6...Amplification circuit 7.10...・Dual wave rectifier circuit 8... Input terminal 9... Output terminal

Claims (1)

[Claims] (1) a variable attenuation circuit; an amplifier circuit connected to this variable attenuation circuit; a level detection circuit that detects the presence or absence of an input signal to the variable attenuation circuit; and a reference voltage generation circuit that generates a reference voltage; a switch circuit connected to the reference voltage generation circuit and turned on/off based on the detection result of the level detection circuit; and a switch circuit connected to the amplifier circuit and the switch circuit when the level detection circuit detects an input signal. , when the level detection circuit detects no input signal, the reference voltage inputted from the reference voltage generation circuit via the switch circuit is converted into a voltage obtained by rectifying the output signal from the amplifier circuit. and a rectifier circuit that outputs a control signal to the variable attenuation circuit, wherein the reference voltage is set so that the gain is a minimum gain in a gain variation range.