JPH09321676A - Multicarrier automatic gain control system for non-reproducing station - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent adjacent carrier interference, to simplify a circuit and to reduce costs by constituting the circuit so as to select the control voltage of a control voltage circuit when the level of an input signal gets lower than a set level. SOLUTION: In the input signal, only the band of a self-carrier signal is selected by a band filter 11, amplified by a variable gain amplifier 12 and outputted as an amplified carrier signal. An input discriminator 13 detects the input level of the carrier signal inputted to the variable gain amplifier 12 and discriminates whether this input level is settled within the range set in advance or not. An automatic gain control(AGC) circuit 14 detects the output level of the variable gain amplifier 12 and controls the gain of the variable gain amplifier 12 so that this output level can be settled at a prescribed level set in advance. Based on the output of the input discriminator 13, a switcher 15 selects a control voltage Vc outputted from the AGC circuit 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-carrier automatic gain control (AGC) system for non-reproducing stations, and particularly to an AGC for preventing interference of non-reproducing station multi-carriers with adjacent carriers in a microwave digital radio transmitter / receiver.
Regarding the scheme.

[0002]

2. Description of the Related Art Generally, multi-carrier AGC for non-reproducing station
In the method, since the AGC gain control is performed based on the level of the input signal, the AGC gain becomes maximum when the input signal level is equal to or lower than a predetermined fixed value or is cut off. In this state, since the AGC gain is maximum at the moment when the input signal is input again, an excessive signal due to a transient response may be output at the time of combining multiple signals, which may cause interference with normal adjacent carriers. Conventionally, in order to prevent adjacent carrier interference caused by such an excessive AGC gain, for example, Japanese Patent Laid-Open No. 5-315 has been proposed.
The method described in Japanese Patent No. 978 has been adopted.

The system described in this publication, as shown in FIG. 4, has an input detector 20, an attenuator 21, and an output detector 22.
The input level detected by the input detector 20 is delayed by the first delay means 23, the output level detected by the output detector 22 is delayed by the second delay means 24, and both detection levels are compared and calculated. The calculation is performed by the unit 25, and the calculation result is stored in the memory 26.
To the control unit 28 via the switching means 27.
And the control unit 28 controls the attenuator 21. Further, it has a detection switching unit 29 that controls switching of the switching unit 27 based on the detection level of the input detector 20, and the memory 26 is output by the detection switching unit 29.
And the switching means 27 are controlled.

In this prior art, the detection switching section 29 sets the memory 26 in a writable state when an input signal is present, and controls the switching means 27 to switch the signal from the comparison operation section 25. When the input signal is cut off, the write operation of the memory 26 is stopped and the switching means 27 is controlled to switch the output of the memory 26. As a result, the attenuator 21 keeps the memory 26 during the input signal interruption period.
Based on the signal read from, the amount of attenuation immediately before the interruption of the input signal is fixed. Further, at the time of re-input, since the attenuator 21 is controlled based on the respective input and output levels delayed by the first delay means 23 and the second delay means 24, the excessive output due to the transient response of the attenuator 21. The signal can be controlled.

[0005]

In this conventional technique, the following problems occur. First, the first problem is that when one of the input signals of the multi-carrier becomes disconnected and the input signal is input again, an excessive output signal due to a transient response may be output. The reason is that the input signal disconnection period is fixed to the attenuation amount immediately before the input signal disconnection, so that when an input signal having a level higher than the level immediately before the disconnection is input, the excessive signal is output as it is.

The second problem is that the circuit structure becomes complicated and the cost becomes high. The reason is that the memory 26 for controlling the gain when the input is cut off, the switching means 27 for selecting the memory 26, and the memories 2
6 and the detection switching unit 29 for controlling the switching unit 27, and the first delay unit 2 for preventing the transient response at the time of restoration.
This is because the third delay means 24 is essential.

It is an object of the present invention to provide a multi-carrier AGC system for a non-reproducing station which is capable of surely preventing adjacent carrier interference, simplifies the circuit, and realizes cost reduction. And

[0008]

The AGC system of the present invention is
An input discriminator that detects the level of an input signal and discriminates whether it is higher than a predetermined level or not, and outputs a control voltage for controlling the output level of a variable gain amplifier that amplifies this signal to a predetermined level. An AGC circuit, a control voltage circuit for outputting a control voltage for controlling the output level of the variable gain amplifier to a minimum level, and the AGC circuit as a control voltage of the variable gain amplifier based on the discrimination result of the input discriminator. Or a switch for switching and selecting the control voltage of the control voltage circuit, wherein the control voltage of the control voltage circuit is selected when the input signal is lower than a set level. To do.

Here, it is preferable that the switching device is provided with a delay circuit for delaying at least the control voltage output from the automatic gain control circuit for a fixed time and inputting it to the variable gain amplifier. This delay time is set to the time required for the output fluctuation of the variable gain amplifier to stabilize in a steady state when the control voltage of the AGC circuit is switched from the control voltage circuit as the control voltage of the variable gain amplifier. . Further, in the present invention, a plurality of variable gain amplifiers are provided corresponding to a plurality of carrier signals, and the input discriminator and the AGC are individually provided to the plurality of variable gain amplifiers.
It is preferable that a circuit and a switch are provided, and that one control voltage circuit is provided commonly to the plurality of variable gain amplifiers.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram showing an embodiment of the present invention, and shows a non-reproducing station with three carriers. In this non-reproduction station, the multi-carrier signal received by the input antenna 1 is received by the receiver 2 and then distributed by the hybrid 3 to three, and the carrier amplifiers 4A,
It is amplified in 4B and 4C. Each carrier amplifier 4A-
The carrier signals amplified by 4C are combined by the hybrid 5 and transmitted from the transmitter 6 and the transmitting antenna 7.

Each of the carrier amplifiers 4A to 4C has the same structure, and FIG. 2 shows a block diagram of the internal structure of one carrier amplifier 4A. As for the input signal, only the band of its own carrier signal is selected by the bandpass filter 11,
The variable gain amplifier 12 amplifies and outputs the amplified carrier signal. The input level of the variable gain amplifier 12 is detected by detecting the input level of the carrier signal input to the variable gain amplifier 12 and determining whether the input level is within a preset setting range. An AGC circuit 14 that detects an output level and outputs a gain control voltage for controlling the gain of the variable gain amplifier 12 so that the output level becomes a preset predetermined level;
A switch 15 for selecting the control voltage Vc output from the AGC circuit 14 based on the output of the input discriminator 13 is provided.

The switch 15 has a built-in delay circuit 16 having a time constant T1 for delaying the gain control voltage input to the variable gain amplifier 12. Also, the above 3
Each of the variable gain amplifiers 1 is connected to the switch 15 provided in each of the carrier amplification units 4A to 4C.
The gain control voltage Vs for minimizing the gain of 2 is input from the control voltage circuit 17 provided separately from the carrier amplifiers 4A to 4C.

The operation of the above-configured AGC system will be described. The operation of one carrier signal will be described here. When the input level of the received input signal is within the preset setting range in the stationary state, the input discriminator 1
The switch 3 operates to select the gain control voltage Vc which is the output of the AGC circuit 14 as the input of the switch 15. As a result, the output level of the variable gain amplifier 12 is detected by the AGC circuit 14, and the AGC circuit 13 outputs the gain control voltage Vc based on the detected output level, so that the gain of the variable gain amplifier 12 is a constant gain set in advance. The carrier signal is output at a constant level.

Next, when the received input level is below a predetermined set value or when the input is cut off, the input discriminator 13 uses the AGC circuit 14 as the input of the switching device until then.
The switching operation is performed so that the gain control voltage Vs which is the output of the control voltage circuit 17 is selected instead of the output of This allows
The gain control voltage Vs for minimizing the gain from the control voltage circuit 17 is input to each variable gain amplifier 12, and the gain of each variable gain amplifier 12 is minimized. Therefore, thereafter, the reception input level becomes higher than the set value, or the carrier signal is input again, and the input discriminator 1
3 causes the input of the switch 15 to change from the control voltage circuit 17 to AG.
Even when the output is switched to the output of the C circuit 14, the variable gain amplifier 12 has the minimum gain at the instant of the switching, so that the received signal is amplified by the variable gain amplifier 12 with the minimum gain. Level fluctuation and transient response to a high level received input signal can be suppressed. As a result, it is possible to prevent adjacent carrier interference due to the excessive output signal of the variable gain amplifier 12.

Further, in this embodiment, since the switching circuit 15 has the delay circuit 16 having the time constant T1 built-in, the output from the control voltage circuit 17 at the time of recovery at the time of re-input is changed to the AG
When switching to the output of the C circuit 14, the AGC circuit 14
Even if the gain control voltage Vc is high, the gain control voltage Vc is delayed and input to the variable gain amplifier 12. Therefore, the gain of the variable gain amplifier 12 is kept at the minimum state at the moment of switching, and the output thereof becomes excessively high even when the level of the signal to be re-input is higher than the level of the input signal immediately before the disconnection. However, it is possible to further suppress the above-mentioned rapid level fluctuation and transient response to a high-level received input signal, and to more effectively prevent adjacent carrier interference due to the above-mentioned excessive output signal of the variable gain amplifier 12. You can

The time constant T1 of the delay circuit 16 is
As shown in FIG. 3, the input discriminator 13 changes the input of the switch 15 from the control voltage circuit 17 to the AGC according to the received input level.
By setting the time sufficient for the level fluctuation of the output generated when switching to the output of the circuit 14 to settle in the steady state, it is possible to ensure the action and effect of the delay described above.

[0017]

As described above, according to the present invention, as the control voltage of the variable gain amplifier, the control voltage of the AGC circuit and the control voltage of the control voltage circuit set to minimize the gain are set to the input level. The input signal level is restored because the gain is minimized by selecting the control voltage of the control voltage circuit when the input signal level is less than or equal to the set value or is cut off. Since the gain of the variable gain amplifier is in the minimum state when the voltage is restored to the control voltage of the AGC circuit by the above, it is possible to suppress the excessive output signal due to the transient response of the variable gain amplifier and prevent the adjacent carrier interference.

Further, since the delay circuit is provided in the switching path, a delay occurs when the control voltage of the selected AGC circuit is input to the variable gain amplifier, so that the gain of the variable gain amplifier instantaneously increases. Therefore, the excessive output signal can be suppressed and the adjacent carrier interference can be surely prevented regardless of the increase of the input signal level.
Furthermore, since only one control voltage circuit is provided for a plurality of variable gain amplifiers, the circuit can be simplified,
A low-cost multi-carrier AGC system for non-reproducing stations can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing an internal configuration of the configuration of FIG.

FIG. 3 is a diagram for explaining a time constant in a delay circuit.

FIG. 4 is a block diagram showing an example of a conventional AGC method.

[Explanation of symbols]

 1 Input Antenna 2 Receiver 3 Hybrid 4A, 4B, 4C Carrier Amplifying Unit 5 Hybrid 6 Transmitter 7 Transmitting Antenna 11 Band Pass Filter 12 Variable Gain Amplifier 13 Input Discriminator 14 AGC Circuit 15 Switcher 16 Delay Circuit 17 Control Voltage circuit

Claims (4)

[Claims] 1. In a multi-carrier automatic gain control system for a non-reproducing station, wherein an input signal is gain-controlled by a variable gain amplifier, the level of the input signal is detected to determine whether or not it is higher than a predetermined level. Input discriminator, an automatic gain control circuit for outputting a control voltage for controlling the output level of the variable gain amplifier to a predetermined level, and a control voltage for controlling the output level of the variable gain amplifier to a minimum level. A control voltage circuit for outputting and a switcher for switching and selecting the control voltage of the automatic gain control circuit or the control voltage circuit as the control voltage of the variable gain amplifier based on the discrimination result of the input discriminator are inputted. A multi-carrier for a non-reproducing station, characterized in that the control voltage of the control voltage circuit is selected when the signal is lowered below a set level. A automatic gain control method. 2. A multi-circuit for a non-reproducing station according to claim 1, wherein the switching device is provided with a delay circuit for delaying at least the control voltage output from the automatic gain control circuit by a fixed time and inputting it to the variable gain amplifier. Automatic carrier gain control method. 3. The delay time of the delay circuit is such that when the control voltage of the automatic gain control circuit is switched from the control voltage circuit as the control voltage of the variable gain amplifier, the output fluctuation of the variable gain amplifier is stabilized in a steady state. The multi-carrier automatic gain control system for a non-reproducing station according to claim 2, wherein the time is required. 4. A plurality of variable gain amplifiers are provided corresponding to a plurality of carrier signals, and an input discriminator, an automatic gain control circuit, and a switch are individually provided for each of the plurality of variable gain amplifiers. 4. The multi-carrier automatic gain control system for a non-reproducing station according to claim 1, wherein one control voltage circuit is commonly provided for the plurality of variable gain amplifiers.