JPH0748622B2 - AGC amplifier - Google Patents

Description

The present invention relates to an AGC (automatic gain control) amplifier, and more particularly to an AGC amplifier for large capacity digital microwave communication.

[Conventional technology]

Conventionally, this type of AGC amplifier has its gain controlled according to a control signal received at a control terminal 31, an input signal received at an input terminal IN is amplified according to the gain, and output as shown in FIG. It has a variable gain amplifier 1 for outputting as an output signal to the terminal OUT.

The first control circuit 51 outputs a first control signal for automatically controlling the gain of the variable gain amplifier 1 so as to keep the level of the output signal of the variable gain amplifier 1 at a constant value. First
The control circuit 51 of FIG. 2 includes a level detection circuit 2 that detects the level of the output signal of the variable gain amplifier 1, a comparison value setting device that outputs a comparison value, an output signal of the level detection circuit 2 and an output of the comparison value setting device 4. And a gain controller 3 that outputs the first control signal so that the output signal of the level detection circuit 2 matches the comparison value.

On the other hand, the second control circuit 52 includes a reference voltage setting device 5 that sets a reference voltage, and outputs the reference voltage as a second control signal for manually controlling the gain of the variable gain amplifier 1.

The switch 6 is a change-over switch that can manually apply one of the first and second control signals to the control terminal 31.

Thus, the conventional AGC amplifier is equipped with the switch 6,
Normally, the control voltage of the control terminal 31 is automatically controlled so that the output level becomes constant even when the input signal level fluctuates by closing the AGC loop. On the other hand, when adjusting or measuring equipment,
For example, when measuring the amplitude frequency characteristics of the main signal system,
The switch 6 is operated to open the AGC loop, and instead, a fixed bias is applied to the control terminal 31 of the variable gain amplifier 1.

[Problems to be solved by the invention]

However, in this conventional circuit, the control voltage at the control terminal 31 is instantaneously interrupted or abruptly changed stepwise at the moment the switch is operated, so that the main signal output from the variable gain amplifier is interrupted. ， Rapidly increase. Therefore, when this is used in a digital communication device, there has been a problem that a bit error occurs.

The object of the present invention is to eliminate the above-mentioned drawbacks and to make the switching device an AGC.
When switching from the loop to the reference voltage, the output level of the variable gain amplifier is not interrupted or suddenly increases.
It is to provide a C amplifier.

[Means for solving problems]

According to the present invention, a gain is controlled according to a control signal received at a control terminal, a variable gain amplifier that amplifies an input signal according to the gain and outputs as an output signal, and a level of the output signal to a constant value. A first control circuit that outputs a first control signal for automatically controlling the gain so as to keep it, and a second control circuit that outputs a second control signal for manually controlling the gain.
An AGC amplifier comprising: a control circuit and a switch for applying one of the first and second control signals to the control terminal, and integrating between the switch and the control terminal of the variable gain amplifier. An AGC amplifier characterized by connecting circuits is obtained.

〔Example〕

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

Referring to FIG. 1, an AGC amplifier according to an embodiment of the present invention mitigates a sudden change in control voltage between a switch 6 and a control terminal 31 of a variable gain amplifier 1 in order to solve the above problems. It has an integrator 7 for performing the operation.

FIG. 3 shows a concrete circuit configuration of the embodiment shown in FIG. Of these, 8,9,10,11,12 correspond to 1 in Fig. 1, 13,1
4,15,16,17 corresponds to 2, 18,19,20 corresponds to 3, and 21 corresponds to 4.
Also, 22 corresponds to 5, 23 corresponds to 6, and 24, 25, 26, 27, 28, 29, 30 correspond to 7. The operation of this example will be described below step by step.

When the signal level applied to the input terminal IN increases, the detection voltage at the point A increases and becomes higher than the voltage at the point B determined by the variable resistor 21, so the output of the inverting amplification operational amplifier 18 having a large gain. Becomes -V. Therefore, the voltage at point D is
As the voltage at the point C determined by the resistors 29 and 30 approaches, the output of the inverting amplification operational amplifier 24 increases.

This reduces the current flowing in the PIN diode 10,
The gain decreases. When the input level decreases, the detection voltage at point A decreases, and the output of the inverting amplification operational amplifier 18 is + V.
Therefore, the voltage at point D is higher than the voltage at point C, so 24
Output is -V. This is in the direction of increasing the current flowing through the PIN diode 10, so the gain increases and automatic control is performed so that the output level becomes constant. Up to this point, the normal AGC operation has been described.

Here, considering the moment when the switch 23 is switched, the voltage of the movable piece of the switch 23 suddenly changes because it is released from the output voltage of the operational amplifier 18 at the moment of switching and then becomes equal to the set voltage of 22. , 24, 25, 26, and 27 constitute a Miller integrator, so that the voltage at the point D and the voltage at the control terminal E change slowly with a time constant determined by 27 and 25.

Therefore, the main signal obtained at the output terminal OUT can complete the switching without causing a momentary interruption or the like and without causing a bit error.

〔The invention's effect〕

As described above, according to the present invention, by providing the integrator between the switch and the variable gain amplifier, when the switch is switched from the AGC loop to the reference voltage, the output signal of the variable gain amplifier is interrupted or its output level is changed. It is possible to provide an AGC amplifier which does not rapidly increase.

[Brief description of drawings]

FIG. 1 is a block diagram of an AGC amplifier of the present invention, FIG. 2 is a block diagram of a conventional AGC amplifier, and FIG. 3 is a circuit diagram of the AGC amplifier of the present invention. 1 ... Variable gain amplifier, 2 ... Level detector, 3 ... Comparator and gain controller, 4 ... Comparison value setting device, 5 ... Reference voltage setting device, 6 ... Switching device, 7 ... Integrator, 8, 9 ... Fixed Gain amplifier, 10… PIN diode, 11,12… Current limiting resistor, 13,14… Detection diode, 1
6,17,19,20,26,27,29,30 ... Fixed resistor, 18,24 ... Operational amplifier, 21,22 ... Variable resistor, 23 ... Switch, 31 ... Control terminal.

Claims (1)

[Claims] 1. A variable gain amplifier whose gain is controlled according to a control signal received at a control terminal, which amplifies an input signal according to the gain and outputs as an output signal, and a level of the output signal is kept at a constant value. First for automatically controlling the gain
A first control circuit for outputting the control signal, a second control circuit for outputting the second control signal for manually controlling the gain, and one of the first and second control signals. An AGC amplifier comprising a switch provided to the control terminal, wherein an integrating circuit is connected between the switch and the control terminal of the variable gain amplifier.