JPH05308234A - Automatic gain control amplifier - Google Patents

Abstract

PURPOSE:To prevent a fault in advance by outputting an alarm before an output level is reduced due to input fluctuation when a maximum gain is reduced due to a fault of an amplifier. CONSTITUTION:The amplifier consists of a variable attenuator 2, an amplifier 4 and a gain control circuit 7, an input and an output of the amplifier 4 are respectively provided with an input level detection circuit 3 and an output level detection circuit 5, and the amplifier is provided with a means receiving respective level detection signals and comparing them and outputting an alarm based on a set level difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control amplifier used in a transceiver.

[0002]

2. Description of the Related Art An example of a conventional automatic gain control amplifier is shown in FIG.
Will be described. In FIG. 3, reference numeral 1 denotes an input terminal to which an input signal is applied. The signal input from the input terminal 1 is a variable attenuator 2, an amplifier 4, and an output level detector 5.
The amplified signal is output to the output terminal 6. Then, the gain control circuit 7 controls the attenuation amount of the variable attenuator 2 by the signal detected by the output level detector 5 so that the output of the output terminal 6 becomes constant. In addition, a part of the detection signal of the output level detector 5 is input to the alarm detection circuit 10,
When the output level of the output terminal 6 becomes lower than a preset output level, an alarm signal is sent to the alarm output terminal 9.

FIG. 4 shows the input / output characteristics shown in FIG. The output level is A with respect to the standard input level, and the output level is kept constant even if the input level fluctuates.
When the output level drops due to the input level drop, an alarm is output.

[0004]

In this conventional automatic gain control amplifier, as shown by the dotted line in FIG. 3, the amplifier 4 in FIG.
When the maximum gain is lowered due to the abnormal condition, the output is normal at the standard input, but the dynamic range for keeping the output level constant with respect to the input level decreases. And, although the maximum gain is lowered due to the abnormality of the amplifier 4,
There is a problem that an abnormality cannot be detected unless the input level is lowered (alarm detection at point C).

[0005]

An automatic gain control amplifier according to the present invention comprises a variable attenuator, an amplifier and a gain control circuit, and the variable attenuator is provided so that the output of the output terminal is constant in the gain control circuit. In an automatic gain control amplifier to be controlled, an input level detection circuit and an output level detection circuit are provided at the input and output of the amplifier, and the level detection signals of the input level detection circuit and the output level detection circuit are received to compare the signal levels. An alarm output means for outputting an alarm according to the set level difference is provided.

[0006]

In the present invention, when the maximum gain is lowered due to the abnormality of the amplifier, the alarm is detected before the output level is lowered due to the input fluctuation, and the trouble is prevented in advance.

[0007]

1 is a block diagram showing an embodiment of an automatic gain control amplifier according to the present invention. In FIG. 1, FIG.
The same reference numerals denote corresponding parts, 3 is an input level detection circuit provided on the input side of the amplifier 4, and 5 is an output level detection circuit provided on the output side of the amplifier 4, which is detected by the output level detection circuit 5. The gain control circuit 7 is configured to control the attenuation amount of the variable attenuator 2 by the above signal so that the output is constant. Reference numeral 8 is a comparison circuit for comparing the input detection signal by the input level detection circuit 3 and the output detection signal by the output level detection circuit 5, 9 is an alarm output terminal, and these are the levels of the input level detection circuit 3 and the output level detection circuit 5, respectively. The alarm output means is configured to receive the detection signal, compare the signal levels, and output an alarm according to the set level difference.

Next, the operation of the embodiment shown in FIG. 1 will be described. First, the signal input from the input terminal 1 passes through the variable attenuator 2, the input level detection circuit 3, the amplifier 4, and the output level detection circuit 5, and the amplified signal is output to the output terminal 6. Then, the attenuation amount of the variable attenuator 2 is controlled by the gain control circuit 7 by the signal detected by the output level detection circuit 5 so that the output of the output terminal 6 becomes constant. Next, when the input detection signal from the input level detection circuit 3 and the output detection signal from the output level detection circuit 5 are input to the comparison circuit 8 and the gain of the amplifier 4 falls below a preset value, an alarm signal is sent to the output terminal 9. To do.

FIG. 2 is a characteristic diagram showing the input / output characteristics of the amplifier shown in FIG. Now, if an alarm point is set at the point B where the gain slightly decreases with respect to the maximum gain, the abnormality can be detected while the output level is constant even if the gain is reduced due to the abnormality of the amplifier 4 as shown by the dotted line. Therefore, the abnormality of the amplifier 4 can be detected and repaired in advance before a failure such as a decrease in the output level occurs.

[0010]

As described above, according to the present invention, when the maximum gain is lowered due to the abnormality of the amplifier, the alarm is detected before the output level is lowered due to the input fluctuation and the trouble is prevented in advance. In the gain control amplifier, when the gain is lowered due to the abnormality of the amplifier, the abnormality can be detected even in the state where the gain control is normally operating, and the failure that the output level is lowered when the allowable input level is changed can be prevented in advance. effective.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram showing input / output characteristics of the amplifier in FIG.

FIG. 3 is a block diagram showing an example of a conventional automatic gain control amplifier.

FIG. 4 is a characteristic diagram showing input / output characteristics of the amplifier in FIG.

[Explanation of symbols]

 1 Input Terminal 2 Variable Attenuator 3 Input Level Detection Circuit 4 Amplifier 5 Output Level Detection Circuit 6 Output Terminal 7 Gain Control Circuit 8 Comparison Circuit 9 Alarm Output Terminal

Claims (1)

[Claims] 1. An automatic gain control amplifier comprising a variable attenuator, an amplifier, and a gain control circuit, wherein the gain control circuit controls the variable attenuator so that the output at an output terminal is constant. An alarm output means for providing an output with an input level detection circuit and an output level detection circuit, receiving the level detection signals of the input level detection circuit and the output level detection circuit, comparing the signal levels, and outputting an alarm based on the set level difference. An automatic gain control amplifier comprising: