JPH0520007B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in an automatic frequency gain control method for a satellite communications earth station receiving device.

[Conventional technology]

Receiving devices for satellite communication earth stations have automatic gain and frequency control (automatic frequency control) that performs automatic gain control and automatic frequency control in one circuit.
automatic gain control, hereinafter referred to as AFC/AGC. ) circuit, which performs AFC and AGC on the incoming reference wave (pilot signal, etc.) and supplies a signal with frequency deviation and level fluctuation compensated for to the demodulator. . Conventionally, in order to prevent the reference wave detection circuit in this AFC/AGC circuit from malfunctioning when detecting the presence or absence of a reference wave, a bandpass filter was used.
BPF) was required.

FIG. 3 is a block diagram of a conventional AFC and AGC circuit. In FIG. 3, a received signal that has undergone frequency deviation and level fluctuation has its frequency deviation removed by an AFC mixer 1, passes through a bandpass filter 2 for removing unnecessary waves, and then passes through a voltage-controlled variable gain amplifier 3. Level fluctuations are compensated for and the signal is sent to a demodulator (not shown) via a distributor 4.

On the other hand, the other output signal of the distributor 4 is input to the bandpass filter 5, where only the reference wave is extracted and sent by the distributor 6 to the AGC detector 7 and the AFC bandpass filter 101. The output signal of the AFC bandpass filter 101 is distributed by a distributor 9 to a phase comparator 10 and a reference wave detector 12. The phase comparator 10 performs a phase comparison with the output signal of the local reference oscillator 11, and the output signal is sent to the AFC controller 102. On the other hand, the AFC switch 10
3, when a reference wave appears within the band of the AFC band-pass filter 101, the sweep signal from the AFC sweeper 104 is transferred to the output signal side of the AFC controller 102 using the output signal of the reference wave detector 12. Switch to
The output signal of the AFC switch 103 is supplied to the voltage controlled oscillator 18 to determine the AFC local frequency.

However, in the conventional circuit, the AFC bandpass filter 101 was required to prevent the AFC reference wave detector 12 from malfunctioning. The necessity of the AFC bandpass filter 101 will be explained below. Now, the received signal-to-noise power density is C/N ₀ ,
Let the band of the band pass filter ₅ be B1 or the band of the AFC band pass filter 101 be _B2 , and the received signal-to-noise power of the output signals of the band pass filter 5 and the AFC band pass filter 101 are respectively C. /N ₁ and C/N ₂ , C/N ₁ = C/N ₀ B ₁ ...(1) C/N ₂ = C/N ₀ B ₂ ...(2).

On the other hand, since the voltage-controlled variable gain amplifier 3 operates with the full power of the output of the bandpass filter 5, if the output of the voltage-controlled variable gain amplifier 3 is P ₁ , then P ₁ = C + N ₁ ...(3) . Furthermore, when there is no reception reference signal, if the control range of the voltage-controlled variable gain amplifier 3 is sufficiently large, P ₁ =N ₁ (4). On the other hand, if the total power of the output of the AFC bandpass filter 101 is P ₂ , then P ₂ = C + N ₂ ...(5), and when there is no reception reference signal, P ₂ '=N ₂ ...(6). Become. If there is no AFC bandpass filter 101, the power input to the reference wave detector 12 is calculated using the formula
From (3) and (4), P is ₁ regardless of the presence or absence of the reference wave,
It is not possible to detect the presence or absence of a reference wave. A.F.C.
When the band-pass filter 101 for AFC is used, when there is no reference wave in the output of the band-pass filter 101 for AFC, the output is P ₂ '(=N ₂ ) from equation (6), which is expressed by the following equation. Bandpass filter 5 and AFC as shown in
output by the band ratio α with the bandpass filter 101 for
It decreases from P ₁ (=N ₁ ).

α＝P ₂ ′／P ₁ ＝N ₂ ／N ₁ ＝N ₀ B ₂ ／N ₀ B ₁ ＝B ₂ ／B ₁ ...(7) On the other hand, when the reference wave exists, band-pass filtering The output ratio β between the filter 5 and the AFC band-pass filter 101 is expressed by the following equation from equations (3) and (5).

β=P ₂ /P ₁ =C+N ₂ /C+N ₁ =C+N ₀ B ₂ /C+N ₀ B ₁ =1+N ₀ B ₂ /C/1+N ₀ B ₁ /C ...(8) Therefore, P ₂ ′=αP ₁ = (B ₂ /B ₁ )P ₁ ...(9) P ₂ =βP ₁ = (1+N ₀ B ₂ /C/1+N ₀ B ₁ /C)P ₁ ...(1
0) Here, if P ₂ > P ₂ ', the reference wave detector 12 can detect the presence or absence of the reference wave. We will explain below that if B ₁ > B ₂ then P ₂ > P ₂ ′.

P ₂ −P ₂ ′=(β−α)P ₁ =(1+N ₀ B ₂ /C/1+
N ₀ B ₁ /C-B ₂ /B ₁ )P ₁ = {B ₁ -B ₂ /B ₁ (1+N ₀ B ₁ /C)
}P ₁ ...(25) Here, since the bands B ₁ , B ₂ , received signal power C, noise power density N ₀ and output P ₁ are all positive, if B ₁ > B ₂ then P ₂ > P ₂ ′.

[Problem that the invention seeks to solve]

As mentioned above, the conventional analog AFC
In the AGC circuit, the AFC bandpass filter 101 was required to prevent the reference wave detector 12 from malfunctioning. Therefore, there were problems in that the circuit scale became large and the reliability was not high.

The present invention solves the above problems,
The purpose of the present invention is to provide an automatic frequency gain control circuit that can operate a reference wave detector normally without using an AFC bandpass filter, has a small circuit scale, and has high reliability.

[Means for solving problems]

The present invention provides an automatic frequency control mixer that removes frequency deviations of an input reference wave, a variable gain amplifier that compensates for level fluctuations in the output signal of the automatic frequency control mixer, and a local frequency control mixer for the automatic frequency control mixer. a reference wave detector that detects a reference wave from the output signal of the variable gain amplifier; and a sweeper that applies a sweep voltage to the voltage controlled oscillator when there is no detection output of the reference wave detector. In an automatic frequency gain control circuit for an earth station receiver for satellite communications, the automatic frequency gain control circuit includes an initial sweep means for applying a sweep voltage to the voltage controlled oscillator at the time of initial setting, and an initial stage for setting a predetermined level to the variable gain amplifier at the time of initial setting. level setting means, and digital control means that receives the detection output of the reference wave detector as input and program-controls the initial sweep means and the initial level setting means. Sweeping at predetermined frequency intervals by a means and determining the presence or absence of the reference wave by majority vote based on the detection output of the reference wave detector;
The present invention is characterized by comprising a control means for sequentially lowering the initial level setting value of the initial level setting means until the reference wave is no longer detected by a majority vote.

[Effect]

In the present invention, the control means performs a frequency sweep at predetermined frequency intervals by the initial sweep means during a period in which there is a detection output of the reference wave detector at the time of initial setting. The presence or absence of a reference wave is determined by majority vote on the detection output of the reference wave detector during this frequency sweep. When the reference wave is detected, the initial level setting means of the AGC circuit sequentially sets lower initial setting values, and this is repeated until the presence of the reference wave is no longer determined by majority vote. As a result, when the reference wave detector is able to detect the reference wave normally without malfunctioning due to noise, the normal reference wave capturing operation is started.

As a result, the reference wave detector can be operated normally without using an AFC bandpass filter as in the conventional case.

〔Example〕

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

FIG. 1 is a block diagram of an automatic frequency gain control circuit according to an embodiment of the present invention. FIG. 2 is a block diagram of the digital AGC circuit. In FIG. 1, a received signal is input to an AFC mixer 1 after receiving frequency deviation and level fluctuation from outside the figure. The received signal from the AFC mixer 1 from which the frequency deviation has been removed is connected to the input of the voltage-controlled variable gain amplifier 3 via the band-pass filter 2 for removing unnecessary waves. A received signal whose level fluctuations have been compensated for from the voltage-controlled variable gain amplifier 3 is sent via a distributor 4 to a demodulator (not shown). The other output signal of the divider 4 is connected to the input of a bandpass filter 5, and a reference wave is taken out. A reference wave from the bandpass filter 5 is connected to an AGC detector 7 and a distributor 9 via a distributor 6. The output signal of the AGC detector 7 is connected to the input of a digital AGC circuit 8 shown in FIG.

Here, the feature of the present invention is the digital circuit portion surrounded by a dashed line. That is,
The output signal of the AGC detector 7 is connected to the input of an analog-to-digital converter 201 in the digital AGC circuit 8 shown in FIG. 2, and the analog signal is converted into a digital signal. A digital output signal from the analog-to-digital converter 201 is connected to one input of the AZC switch 203 via the AGC digital low-pass filter 202. In addition, the output signal of the initial level setter 205 is
Connected to the other input of 3. AGC switch 203
Then, the output signals from the AGC digital low-pass filter 202 and the initial level setter 205 are selected, and the output signal of the AGC switch 203 is connected to the input of the digital-to-analog converter 204.
The output signal of the digital-to-analog converter 204 is connected to the control input of the voltage-controlled variable gain amplifier 3 shown in FIG. 1, and gain control is performed. Further, the reference wave from the distributor 9 and the output signal from the local reference oscillator 11 are connected to respective inputs of the phase comparator 10. Also, the reference wave from the distributor 9 is sent to the reference wave detector 1.
2 input. The output signal of the phase comparator 10 is connected to the input of an analog-to-digital converter 13, and is converted from an analog signal to a digital signal. The digital output signal from the analog-to-digital converter 13 is sent to the digital low-pass filter 14 for AFC.
It is connected to one input of the AFC switch 15 via. For other inputs of the AFC switch 15,
The output signal of the AFC digital sweeper 16 is connected. The AFC switch 15 includes an AFC digital low-pass filter 14 and an AFC digital sweeper 1.
6 is selected, and the output signal of the AFC switch 15 is sent to the digital-to-analog converter 17.
connected to convert the digital signal into an analog voltage. The analog output voltage from the digital-to-analog converter 17 is connected to the voltage controlled oscillator 18, and the AFC local frequency from the voltage controlled oscillator 18 is connected to the AFC mixer 1 to remove frequency deviations from the received signal.

In the initial state, AFC is activated from the digital controller 19.
The AFC switch signal 20 is connected to the AFC switch 15, and the AFC switch 15 selects and outputs the output signal of the AFC digital sweeper 16. In addition, the AGC switching signal 2 is sent from the digital controller 19.
2 is connected to the AGC switch 203 shown in FIG. 2, and the output signal of the initial level setter 205 is selected. In addition, the initial level setting signal 23 for AGC is sent from the digital controller 19 to the initial level setting device 205.
The voltage controlled variable gain amplifier 3 is connected to and set by program control so that the voltage controlled variable gain amplifier 3 has the maximum gain.

Here, an output signal with a reference wave from the reference wave detector 12 is connected to the digital controller 19, an AFC digital sweep control signal 21 is connected from the digital controller 19 to the AFC digital sweeper 16, and a predetermined signal is output. Sweeps are performed a set number of times at frequency intervals. Each time the sweep is performed, the presence or absence of a reference wave is checked using the output signal of the reference wave detector 12, and after the sweep is completed, the presence or absence of the reference wave is determined by majority vote. As a result, if it is determined that there is a reference wave, the digital controller 19
The AGC initial level setting signal 23 is connected to the initial level setting device 205 shown in FIG. 2, and its data value is reset. After that, the reference wave detector 1 is again
When it is determined that the reference wave is present based on the output signal No. 2, the data value of the initial level setter 205 is reset again. The above operation is repeated until it is determined that there is no reference wave.

After the initial settings described above have been made,
When the AFC digital sweeper 16 sweeps and the reference wave detector 12 detects the reference wave, the output signal of the reference wave detector 12 is sent to the digital controller 1.
9 and the AFC from the digital controller 19.
The AFC switch signal 20 is connected to the AFC switch 15, the output signal of the AFC digital low-pass filter 14 is selected, and the AFC mixer 1 removes the frequency deviation of the received signal. Also, digital controller 1
9 to AGC switch signal 22 is AGC switch 2
03, the output signal of the AGC digital low-pass filter 202 is selected, and level fluctuations are compensated for by the voltage controlled variable gain amplifier 3.

The operation of the automatic frequency gain control circuit having such a configuration will be explained. In FIG. 1, a phase comparator 10
The output signal is input to the analog-to-digital converter 13, and after being converted to a digital signal, the AFC
The signal is inputted to the AFC switch 15 via the digital breath filter 14. In addition, the AFC switch 15 is
AFC digital sweeper 16 output signal and AFC
A selection of the output signal of the digital low pass filter 14 is performed. The output signal of the AFC switch 15 is converted into an analog voltage by a digital-to-analog converter 17 and input to a voltage controlled oscillator 18.

On the other hand, the output signal of the AGC detector 7 is input to the digital AGC circuit 8. In Figure 2,
The output signal of the AGC detector 7 is input to an analog-to-digital converter 201, converted into a digital signal, and then input to an AGC switch 203 via an AGC digital low-pass filter 202.
Initial level setter 20 in AGC switch 203
5 output signal and digital low-pass filter 2 for AGC
02 is selected as the output signal. Also,
The output signal of the AGC switch 203 is converted into an analog voltage by a digital-to-analog converter 204 and input to the voltage-controlled variable gain amplifier 3.

First, an initial setting operation is started to prevent malfunctions in determining whether or not a reference wave has been received due to noise. This corresponds to the step in FIG. 4 and is the characteristic operation of the present invention.

In the digital AGC circuit 8, the output signal of the AGC switch 203 is first set to the initial level setter 205 side by the AGC switch signal 22, and the data of the initial level setter 205 is set to the initial level setting signal 23 for AGC. Therefore, the voltage controlled variable gain amplifier 3 is set to have the maximum gain.

On the other hand, in Fig. 1, the AFC switch signal 2
0, the AFC switch 15 selects the AFC digital sweeper 16 side, and the digital controller 19 selects the AFC digital sweeper 16 side.
When it is determined that the reference wave is present based on the output signal of the reference wave detector 12, the digital sweep control signal 21 for AFC performs a sweep at a predetermined frequency interval a set number of times. For each sweep, the digital controller 19 checks the output signal of the reference wave detector 12, and after the sweep is completed, determines the presence or absence of the reference wave by majority vote. As a result, if it is determined that the reference wave is present, it is determined that the reference wave detector 12 is malfunctioning due to noise even though the reference wave is not entering the bandpass filter 5.
The digital controller 19 uses the AGC initial level setting signal 23 to reset the data value of the initial level setter 205 in the digital AGC circuit 8. Thereafter, the data value of the initial level setter 205 is reset again based on the output signal of the reference wave detector 12 if it is determined that the reference wave is present. This operation is repeated until it is determined that there is no reference wave based on the output signal of the reference wave detector 12.

Generally, the reference wave detector 12 has a hysteresis characteristic, so if the level of the voltage-controlled variable gain amplifier 3 is lowered until it is determined that there is no reference wave, the reference wave detector 12 will be affected by noise alone. 12 will no longer malfunction. In this state, if the AFC digital sweeper 16 performs sweeping, the reference wave detector 12 can operate accurately when the reference wave enters the band of the bandpass filter 5.

As a result, the noise level from the voltage-controlled variable gain amplifier 3 can be set below the detection threshold of the reference wave detector, without using a narrow-band band-pass filter for AFC as in the past. Therefore, it is possible to prevent erroneous detection of the reference wave from occurring.

On the other hand, when it is determined by majority vote that there is no reference wave, an operation is performed to capture the reference wave, and the operation of the step in FIG. 4 is started.

On the other hand, if it is determined by majority vote that there is no reference wave, the reference wave is coincidentally present in the bandpass filter 5 when the initial reference wave is determined to be present, and this reference wave is filtered by the bandpass filter. This indicates that it was determined that there was no reference wave when the reference wave went out of the band of the device 5. This also means that when the reference wave does not exist within the band of the bandpass filter 5, the reference wave detector 12 does not malfunction due to noise alone. Therefore, the reference wave can be detected correctly by sweeping with the level setting of the voltage controlled variable gain amplifier 3 as it is. In addition, if it is determined that the output signal of the reference wave detector 12 does not have a reference wave in the initial state, it is immediately determined that the reference wave detector 12 is not malfunctioning due to noise, and the digital controller 19 immediately starts the sweep operation. AFC switch signal 20 and AFC digital sweep control signal 21 from
This is done by

As a result, when the reference wave is detected, the initial setting operation is completed and automatic frequency gain control by closed loop is started, resulting in the operation of the step in FIG. 4.

〔Effect of the invention〕

As explained above, the present invention programmatically controls the AFC digital sweeper and the digital AGC circuit using a digital controller during initial setting to adjust the gain of the variable gain amplifier so that the reference wave detector does not malfunction due to noise. By setting appropriately, it is possible to correctly determine whether or not the reference wave has been received, so the reference wave detector can be operated normally without using a narrow-band AFC band-pass filter. Therefore, there are advantages of reducing the circuit scale and increasing reliability.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an automatic frequency gain control circuit according to an embodiment of the present invention. FIG. 2 is a block diagram of the digital automatic gain control circuit. FIG. 3 is a block diagram of a conventional automatic frequency gain control circuit.
Figure 4 shows AFC/
Flowchart explaining the initial setting control operation of AGC. 1... mixer for AFC, 2... bandpass filter for unnecessary wave removal, 3... voltage controlled variable gain amplifier,
4...Distributor, 5...Band pass filter, 6...Distributor, 7...AGC detector, 8...Digital
AGC circuit, 9...distributor, 10...phase comparator,
11...Local reference oscillator, 12...Reference wave detector, 13...Analog-digital converter, 14...
...Digital low-pass filter for AFC, 15...AFC
16...Digital sweeper for AFC,
17... Digital analog converter, 18... Voltage controlled oscillator, 19... Digital controller, 20
...AFC switch signal, 21...AFC digital sweep control signal, 22...AGC switch signal,
23...AGC initial level setting signal, 101...
... Bandpass filter for AFC, 102 ... Controller for AFC, 103 ... Switcher for AFC, 104 ...
Sweeper for AFC, 201...Analog-digital converter, 202...Digital low-pass filter for AGC, 203...Switcher for AGC, 204...Digital-to-analog converter, 205...Initial level setter.

Claims (1)

[Claims] 1. An automatic frequency control mixer that removes frequency deviations of an input reference wave; a variable gain amplifier that compensates for level fluctuations in the output signal of the automatic frequency control mixer; and the above automatic frequency control mixer. a voltage controlled oscillator that provides a local frequency to the voltage controlled oscillator; a reference wave detector that detects a reference wave using the output signal of the variable gain amplifier; and a voltage controlled oscillator that applies a sweep voltage to the voltage controlled oscillator when there is no detection output from the reference wave detector. In an automatic frequency gain control circuit for a satellite communication earth station receiver equipped with a sweeper, an initial sweep means for applying a sweep voltage to the voltage controlled oscillator at the time of initial setting, and a predetermined level setting for the variable gain amplifier at the time of initial setting. and digital control means that receives the detection output of the reference wave detector and programmatically controls the initial sweep means and the initial level setting means. The frequency is swept by the initial sweep means at predetermined frequency intervals, and the presence or absence of the reference wave is determined by majority vote based on the detection output of the reference wave detector, and the initial level setting means An automatic frequency gain control circuit comprising control means for sequentially lowering a level setting value.