JPH0794984A - Automatic gain control device - Google Patents

Abstract

PURPOSE:To always effectively obtain a demodulated output by efficiently following up sudden level variation generated in a received signal. CONSTITUTION:When sudden level variation is generated in a received signal, a level variation detecting circuit 2 and a judging circuit detect the variation and the circuit 3 judges the validity of the response speed of an automatic gain control circuit 1. A loop band control circuit 4 swiches a loop band to a wider band in accordance with the judged result. After counting the lapse of fixed time by a timer circuit 5, the circuit 4 returns the switched band to the original loop band to hold a normal control state. When a level judging circuit 6 judges that the received signal is weak, the loop band is held at a narrow band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver automatic gain control device, and more particularly to a receiver automatic gain control device having a function of automatically switching an automatic gain control loop band.

[0002]

2. Description of the Related Art As shown in FIG. 2, a conventional automatic gain control device for an artificial satellite receiver has an amplitude detector 11 for detecting the amplitude of a signal obtained by converting a received signal into an intermediate frequency.
And an automatic gain control loop filter 12 that removes high frequency components in order to make this detection signal a stable gain control signal.
And an automatic gain control amplifier 13. Further, the intermediate frequency amplifier 14 is provided with a voltage control type variable attenuator capable of controlling the gain according to the gain control voltage.

With such a configuration, it operates so as to maintain a stable gain with respect to variations in the received signal level.

[0004]

In the conventional automatic gain control circuit, the cutoff of the automatic gain control loop filter is performed in order to improve the loop S / N or prevent the automatic gain control circuit from responding to noise of high frequency components. The frequency is set to a low value. For this reason, when a sudden level change occurs in the received signal, the automatic gain control circuit cannot sufficiently follow up, the output signal demodulated by the demodulation circuit has a large level change, and the data decoder for decoding the data There were cases where problems such as out-of-synchronization of occurred.

It is possible to widen the automatic gain control loop band at the time of a strong signal, but the altitude of the artificial satellite is constantly different, its variation range is wide, and the receiving state also differs depending on the propagation condition, and the optimum setting of the loop band is made. Was a difficult problem.

For example, as shown in FIG. 3, a method adopted for good communication with an artificial satellite that is put into an elliptical orbit around the earth (also used when launching a geostationary satellite) is used. , In general, system specifications are set so that the maximum gain direction of the antenna at the apogee is oriented toward the earth.

In this case, since the communication in the area where the artificial satellite is relatively close to the earth is the communication in the side beam region of the satellite antenna, the reception level is relatively high and the level fluctuations are large.

In the case of a spin-stabilized satellite, the gain of the satellite-mounted antenna constantly changes with the spin. Therefore, when the spin rate increases, the level change rate increases. In addition, the level change rate also increases when communication is performed in a region where the antenna gain changes greatly due to the tilt of the satellite. In such a case, the fluctuation of the received signal level becomes a problem.

Therefore, the present invention has been made to solve the above-mentioned drawbacks of the prior art, and its object is to have a good follow-up characteristic even for a sudden change in the received signal level. An object is to provide an automatic gain control device for a receiver.

[0010]

An automatic gain control apparatus according to the present invention comprises an automatic gain control loop circuit for setting a gain according to a received signal level, and a level fluctuation detection circuit for detecting a sudden fluctuation of the received signal level. A level determination circuit for determining the level strength of the received signal, and a loop of the automatic gain control loop circuit based on the determination output, the gain control voltage of the automatic gain control loop circuit, and the detection output of the level fluctuation detection circuit. And a loop band control circuit that performs automatic band switching control.

[0011]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. First, the overall configuration of the block diagram of FIG. 1 will be described. In the figure, an automatic gain control circuit 1 includes an amplitude detector 11, an automatic gain control loop filter 15, an automatic gain control amplifier 13, and an intermediate frequency amplifier 14 in order to stabilize the gain against variations in the level of a received signal. This is the same as the prior art.

The present invention is one of the features of the present invention, which is different from the prior art in that the band of the loop filter is switched in multiple stages and the setting can be automatically performed. Further, the provision of the level fluctuation detection circuit 2 is also one of the features of the present invention, and has a function of detecting the amplitude of the signal converted to the intermediate frequency and detecting a rapid level fluctuation of the received signal. It includes an intermediate frequency amplifier 21, an amplitude detector 22, a low pass filter 23, and a level fluctuation detection amplifier 24. The response characteristic of the level fluctuation detection circuit 2 is determined by the low pass filter 23.

The determination circuit 3 determines the validity of the response characteristic of the automatic gain control circuit 1 based on the output signal of the level fluctuation detection circuit 2. The loop band control circuit 4 has a function of controlling the band of the automatic gain control loop filter 15 by the signal from the determination circuit 3.

After the loop band is switched to the wide band, the timer circuit 5 outputs a signal to the loop band control circuit 4 so as to restore the narrow band again after a predetermined time. The level determination circuit 6 determines whether the received signal level is a strong signal or a weak signal.

Next, the operation of the block diagram of FIG. 1 will be described. When the received signal level fluctuates sharply during a strong signal, the gain control voltage V generated by the automatic gain control circuit 1
The difference between 1 and the output voltage V2 amplitude-detected by the level fluctuation detection circuit 2 is calculated by the subtractor 31 of the judgment circuit 3, and when this value exceeds a predetermined value, that is, a sudden level fluctuation occurs. On the other hand, when the automatic gain control circuit 1 does not respond sufficiently, the voltage comparator 32 of the determination circuit 3 outputs "1".

When the decision circuit 3 outputs "1", the loop band control circuit 4 switches the automatic gain control loop filter 15 to a band one step wider. At the same time, a reset signal is output to the timer circuit 5. To switch the loop band, a switch is provided in the resistor for setting the cutoff frequency, and these resistors are changed by open or short circuit according to the signal from the determination circuit 3.

Further, the timer circuit 5 uses charging and discharging of a capacitor, and is reset when the loop band is switched to a wide band to start timing. If "1" is output again from the determination circuit 3 before the timer is stopped, the loop band is switched to a wider band and the timer is reset again. Also, when the timer stops, it is returned to the narrowest loop band.

The band of the automatic gain control loop filter 15 is considered to be effectively switched in two stages or three stages.

The level judgment circuit 6 judges the gain control voltage V1 by the voltage comparator, and when it is a weak signal, the loop band control circuit 4 causes the automatic gain control loop filter 15 to operate regardless of the output of the judgment circuit 3. Keep the band in the narrowest band.

Further, the control of the loop band is forcibly switched to the minimum band depending on the lock-off status of the receiver. Further, in the case of the receiver on the satellite side, it also has a function of selecting or fixing an arbitrary loop band by a command signal from the ground.

In the configuration of the first embodiment, the rate of change of the received signal level fluctuation suddenly increases, and the narrowest loop band among the loop bands set in multiple stages is switched to the widest loop band. If such a situation frequently occurs, it may take a long time to switch the loop band.

In such a case, the determination circuit 3 is selected so that the required loop band can be selected according to the degree of difference between the gain control voltage V1 and the output voltage V2 of the level fluctuation detection circuit 2.
Output state is changed, and the loop band control circuit 4 is configured accordingly.

With this, it is possible to directly switch to the loop band according to the degree of the fluctuation of the received signal level, and it is possible to save the dead time. Also in this case, the timer circuit 3 is operated as in the first embodiment.

The method of directly switching to the required loop band shown in the second embodiment or the method of switching the loop band step by step shown in the first embodiment is terrestrial in the case of a satellite receiver. It is also possible to select either method by a command from. Also, the set time of the timer circuit 3 can be changed by a command from the ground.

[0026]

As described above, since the automatic gain control circuit of the receiver according to the present invention automatically controls the loop band according to the degree of change rate of the level fluctuation of the received signal, the received signal is drastically changed. Even if a level change occurs, there is an effect that the signal can be reliably received and demodulated by following the level change and without outputting an abnormal demodulated signal in the demodulator.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a conventional automatic gain control device.

FIG. 3 is a diagram showing a concept of communication between an artificial satellite and an earth station.

[Explanation of symbols]

 1 Automatic Gain Control Circuit 2 Level Fluctuation Detection Circuit 3 Judgment Circuit 4 Loop Bandwidth Control Circuit 5 Timer Circuit 6 Level Judgment Circuit 11, 22 Amplitude Detector 13 Automatic Gain Control Amplifier 14, 21 Intermediate Frequency Amplifier 15 Automatic Gain Control Loop Filter 23 Low Pass Filter 24 Level fluctuation detection amplifier 31 Subtractor 32 Voltage comparator

Claims (4)

[Claims] 1. An automatic gain control loop circuit that sets a gain according to a received signal level, a level fluctuation detection circuit that detects a sudden fluctuation of the received signal level, and a level judgment circuit that judges the level strength of the received signal. A loop band control circuit that performs automatic switching control of the loop band of the automatic gain control loop circuit based on the determination output, the gain control voltage of the automatic gain control loop circuit, and the detection output of the level fluctuation detection circuit. An automatic gain control device comprising: 2. The automatic gain control according to claim 1, further comprising means for controlling the return to the loop band immediately before switching when the loop band is switched to a wider band by the loop band control circuit after a fixed time. apparatus. 3. A means for controlling the return of the loop band to a narrow band narrower than the wide band when the loop band is switched to the wide band by the loop band control circuit and the receiver is out of synchronization. The automatic gain control device according to claim 1 or 2, further comprising: 4. The automatic gain control device according to claim 1, wherein the loop band control circuit is configured to switch and control the loop band in response to an external command.