JP2000216651A - Automatic gain controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an automatic gain controller where the time until an output signal level is settled constant while an input signal level is rapidly changed is made shorter and sufficient smoothing in a usual state is simultaneously realized. SOLUTION: A detection circuit 11 detects an output signal from an amplifier circuit 10 and a smoothing circuit 12 smoothes the detected signal. When a voltage between an input signal and an output terminal of this smoothing circuit 12 reaches a prescribed voltage or over, a bypass circuit 13 bypasses the signal to the output stage of the smoothing circuit 12. Thus, the bypass circuit 13 is connected between the input and the output of the smoothing circuit 12 so as to eliminate the delay of the signal in the smoothing circuit 12. Thus, sufficient smoothing is attained in a normal state, and in the case that the input signal level is rapidly changed, a time until the output signal level is settled constant can be made shorter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an automatic gain control device using a smoothing circuit.

[0002]

2. Description of the Related Art Conventionally, in an automatic gain control circuit, an amplifier circuit detects a part of an output signal of the amplifier circuit by a detection circuit, smoothes an output signal of the detection circuit by a smoothing circuit, and controls the output signal of the smoothing circuit. Have been. This automatic gain control circuit is applied and used, for example, in a television relay broadcasting device.

[0003]

However, in the above conventional configuration, when the input signal level fluctuates rapidly, it takes time until the output signal level becomes constant due to the influence of the smoothing circuit. On the other hand, if the time constant of the output signal level is reduced by reducing the time constant of the smoothing circuit, the smoothing operation is not sufficiently performed in normal times.

For this reason, when the input signal level fluctuates rapidly, it is impossible to simultaneously shorten the time during which the output signal level becomes constant and to perform a sufficient smoothing operation in normal times. With some problems.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and when the input signal level fluctuates rapidly, it is possible to shorten the time during which the output signal level becomes constant, and to achieve a sufficient smoothing action at normal times. Realizing what is done at the same time,
It is an object to provide an automatic gain control device.

[0006]

The present invention adopts the following constitution in order to solve the above problems.

The automatic gain control device according to the first aspect of the present invention bypasses the signal and connects it to the output stage when the potential difference between the input and output signals for smoothing the signal by the smoothing circuit exceeds a certain value. Therefore, when the input / output potential difference of the smoothing circuit becomes a certain value or more, the bypass circuit is connected, and the delay caused by the smoothing circuit is eliminated.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention relating to an automatic gain control device according to the first aspect of the present invention relates to a smoothing circuit for smoothing a signal and a smoothing circuit which bypasses the signal when the potential difference between the input and output signals of the smoothing circuit exceeds a certain value. And a bypass circuit connected to the output stage.

With this configuration, when the input / output potential difference of the smoothing circuit becomes equal to or more than a predetermined value, the bypass circuit is connected, and the delay caused by the smoothing circuit can be eliminated.

According to a second aspect of the present invention, the automatic gain control device according to the first aspect further includes an amplifier circuit, and a signal at an output stage of the smoothing circuit is input to an amplification control signal terminal of the amplifier circuit. And

With this configuration, the amplifier can be controlled based on the control signal with no delay.

According to a third aspect of the present invention, the automatic gain control device according to the second aspect further includes a detection circuit for detecting an output signal of the amplifier circuit, and the output signal of the detection circuit is input to the smoothing circuit. The configuration is a signal.

With this configuration, it is possible to obtain a control signal with no delay in the detected signal.

According to a fourth aspect of the present invention, the smoothing circuit according to any one of the first to third aspects includes a resistor and a capacitor.

Next, an automatic gain control device according to an embodiment of the present invention will be described in detail with reference to the drawings. 1 to 5 are diagrams for explaining a configuration of an automatic gain control device according to one embodiment of the present invention. 1 is a block diagram of a circuit configuration, FIG. 2 is a circuit diagram of a main part, and FIGS. 3 to 5 are voltage characteristic diagrams of a main part.

In FIG. 1, an automatic gain control device according to the present embodiment includes an amplifier circuit 10, a detection circuit 11, a smoothing circuit 12,
It has a bypass circuit 13.

FIG. 2 is a circuit diagram showing a specific example of the above-mentioned smoothing circuit 12 and bypass circuit 13 together with their peripheral circuits.

A feature of the automatic gain control circuit according to the present invention having the above-mentioned configuration is that the automatic gain control circuit is connected to the bypass circuit 13 when the input / output potential difference between the smoothing circuit 12 and the smoothing circuit exceeds a certain value. And according to the automatic gain control circuit of the present invention,
When the input / output potential difference of the smoothing circuit 12 becomes a certain value or more, the bypass circuit 13 is connected, and the delay by the smoothing circuit 12 is eliminated. This relationship will be described in detail below.

Reference numerals V1 to V3 in the system diagrams showing the present embodiment of FIGS. 1 and 2 denote a control voltage V2 of the automatic gain control circuit, an output voltage V3 of the smoothing circuit, and an output voltage V4 of the bypass circuit. I have. The bypass circuit 13 includes the smoothing circuit 1
The connection is made only when the input / output potential difference of No. 2 exceeds a certain value.

The smoothing circuit 12 and the bypass circuit 1
2, the resistor 14 and the capacitor 15 determine the time constant of the smoothing circuit 12, and the variable resistor 1
Numeral 8 is for determining a constant value of the input / output voltage difference.
The diodes 17, 17 are connected to the output voltage V2 of the smoothing circuit.
And the output voltage V4 of the bypass circuit is compared to output a higher voltage. FIGS. 3 and 4 are time charts showing examples of changes in the control voltage V2 of the automatic gain control circuit, the output voltage V3 of the smoothing circuit, and the output voltage V4 of the bypass circuit when the input voltage V1 fluctuates. FIG. 5 is a characteristic diagram of the output voltage V2.

When the input signal level does not change, the output voltage V3 of the smoothing circuit 12 is set higher than the output voltage V4 of the bypass circuit 13 by the variable resistor 16. In this state, the output voltage V which is the control voltage of the automatic gain control circuit
In No. 2, since the output voltage V3 of the smoothing circuit 12 is selected, a sufficient smoothing operation is performed.

On the other hand, when the input voltage fluctuates rapidly,
The output voltage V3 of the smoothing circuit 12 rises slowly due to the influence of the time constant of the smoothing circuit 12, but the output voltage V4 of the bypass circuit 13 rises in proportion to the input voltage V1, so that there is no time delay and the output voltage V3 is automatically increased. Control voltage V of gain control circuit
Output as 2.

After a lapse of time, the output voltage V3 of the smoothing circuit 12 rises slowly, becomes higher than the output voltage V4 of the bypass circuit 13, and the output voltage V3 of the smoothing circuit 12 is selected as the control voltage V2 of the automatic gain control circuit. Is done. Based on these operation results, the output voltage V5 shown in FIG. 5 is output.

According to the present invention, even if the input signal level fluctuates rapidly, a bypass circuit 13 connected in parallel with the smoothing circuit 12 is connected so that the output signal level can be kept at a constant value in a short time without delay due to the influence of the smoothing circuit 12. Converges. In a normal state, the bypass circuit 13 is not connected, and the smoothing circuit 12 performs a sufficient smoothing operation.

The above embodiment is an example of a preferred embodiment of the present invention. However, it is not limited to this.
Various modifications can be made without departing from the spirit of the present invention. For example, the amplification circuit may be replaced with an attenuation circuit. Note that the automatic gain control circuit can be applied to a television relay broadcasting device and used.

[0026]

As is apparent from the above description, according to the present invention, the bypass circuit is provided to bypass the signal when the potential difference between the input and output signals of the smoothing circuit exceeds a certain value, and to output the signal to the output stage of the smoothing circuit. Connect to According to this configuration, when the potential difference between the input and output signals of the smoothing circuit for smoothing the signal becomes equal to or more than a predetermined value, the signal is bypassed and connected to the output stage, whereby the bypass circuit is connected and the delay caused by the smoothing circuit is eliminated. be able to. Therefore, in a normal case, when a sufficient smoothing action is performed and the input signal level fluctuates rapidly, the time during which the output signal level becomes constant is shortened.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an automatic gain control device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a specific example of a main part of FIG. 1;

FIG. 3 is a diagram showing a variation example of an input voltage V1.

FIG. 4 is a time chart showing a variation example of the output voltage V3 of the smoothing circuit and the output voltage V4 of the bypass circuit.

FIG. 5 shows a control voltage V obtained from the voltage characteristics shown in FIGS.
Characteristic diagram of 2

[Explanation of symbols]

 Reference Signs List 10 amplifying circuit 11 detection circuit 12 smoothing circuit 13 bypass circuit 14 resistor 15 capacitor 16 variable resistor 17 diode 18 variable resistor V1 input voltage V2 control voltage V3 output voltage of smoothing circuit V4 output voltage of bypass circuit

Claims (4)

[Claims] 1. A smoothing circuit that smoothes a signal, and a bypass circuit that bypasses the signal and connects to an output stage of the smoothing circuit when a potential difference between an input signal and an output signal of the smoothing circuit becomes a predetermined value or more. An automatic gain control device comprising: 2. The automatic gain control device according to claim 1,
An automatic gain control device further comprising an amplifier circuit, wherein a signal at an output stage of the smoothing circuit is input to an amplification control signal terminal of the amplifier circuit. 3. The automatic gain control device according to claim 2,
Further comprising a detection circuit for detecting an output signal of the amplification circuit,
An automatic gain control device, wherein an output signal of the detection circuit is a signal input to a smoothing circuit. 4. The automatic gain control device according to claim 1, wherein the smoothing circuit includes a resistor and a capacitor.