JPH0690116A - Fm demodulator - Google Patents

Abstract

PURPOSE:To unnecessitate manual control for optimizing an input level in the case of receiving the broadcasting program of a different C/N or temporarily degrading the C/N caused by rain fall or the like at an FM demodulator used for a receiver for satellite broadcasting. CONSTITUTION:The output of a PLL demodulator 3 is connected through a C/N detector 11 to the other input of a gain control part 5b. The gain control part 5b of an AGC 10b compares the input of the PLL demodulator 3 with the output of the C/N detector 11 and controls the output level of the AGC 10b corresponding to the difference. Therefore, the input level to the PLL demodulator 3 is optimumly changed corresponding to the C/N, and killifish noise can be prevented from being generated. Thus, since the output of the PLL demodulator 3 is fed back to a variable gain amplifier 2 and the amplification factor is controlled even in the case of receiving the broadcasting program of the different C/N or temporarily degrading the C/N because of rain fall or the like, the input level of the PLL demodulator 3 can be controlled to a suitable level corresponding to the C/N. Therefore, the killifish noise can be improved without any control and the manual control can be unnecessitated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an F receiver such as a satellite receiver.
It relates to an M demodulator.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing a conventional FM demodulator. The structure of a conventional FM demodulator will be described below with reference to the drawings. Reference numeral 1 denotes an input terminal, a variable gain amplifier 2 connected to the input terminal 1, a PLL demodulator 3 connected to the output of the variable gain amplifier 2, and an output connected to the output of the PLL demodulator 3. A terminal 4 for connecting the output of the variable gain amplifier 2 to one input of the gain control section 5a, connecting the gain control terminal of the variable gain amplifier 2 and the output of the gain control section 5a, and The other input of the gain control section 5a was connected to the sliding terminal of the variable resistor 6.

The PLL demodulator 3 has a loop filter 8 connected to the output of a phase comparator 7 having a variable gain amplifier 2 connected to one input, and a voltage controlled oscillator 9 connected to the output of the loop filter 8. The input is connected, and the output of the voltage controlled oscillator 9 is connected to the other comparison input of the phase comparator 7.

The operation of the FM demodulator configured as above will be described below. When the variable resistor 6 is changed, the control signal of the gain control section 5a changes according to this change, and the output level of the variable gain amplifier 2 is changed. Therefore, even if the C / N (signal carrier / noise) is lowered, if the variable resistor 6 is adjusted so that the input level of the PLL demodulator 3 is lowered, the loop gain of the PLL becomes smaller and the response becomes slower. As a result, the gain in the high frequency region where the PLL does not respond is reduced, and medaka-like noise (hereinafter referred to as medaka noise) on the screen can be prevented from occurring.
Further, once the variable resistor 6 is adjusted, the output level of the variable gain amplifier 2 is kept constant by the gain control section 5a,
It operates as an automatic gain control circuit (hereinafter referred to as AGC) 10a.

As a technique similar to this, Japanese Patent Laid-Open No. 2-305
No. 087 is available.

[0006]

However, in such a conventional structure, the C / N ratio is lowered when the input level is lowered.
If is improved, truncation noise deteriorates. In order to improve this, it is necessary to adjust the input level corresponding to each C / N each time. To solve this problem, a terminal for external adjustment is required. However, when a broadcast program with a different C / N is received, or when the C / N is temporarily deteriorated due to rainfall or the like, the input level must be adjusted to improve the medaka noise each time. I had a problem.

The present invention solves the above-mentioned conventional problems, and optimizes the input level when receiving a broadcast program having a different C / N or when the C / N is temporarily deteriorated due to rainfall or the like. The purpose is to eliminate the need for manual adjustment for the operation.

[0008]

In order to achieve this object, the FM demodulator of the present invention outputs the output of the PLL demodulation section to C / N.
It is connected to the other input of the gain control section through a detector.

[0009]

With this configuration, the output of the PLL demodulator is fed back to the variable gain amplifier even when a broadcast program having a different C / N is received or when the C / N is temporarily deteriorated due to rainfall or the like. Since it controls the degree of amplification,
The input level of the PLL demodulator can be controlled to the optimum level corresponding to C / N. Therefore, medaka noise can be improved without adjustment, and adjustment by manual operation can be eliminated.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an FM according to an embodiment of the present invention.
3 shows a block diagram of a demodulator. FIG. 2 is a block diagram of the C / N detector of the present invention.

The same parts as those of FIG. 3 shown in the conventional example are designated by the same reference numerals to simplify the description.

In FIG. 1, reference numeral 1 is an input terminal, a variable gain amplifier 2 connected to the input terminal 1, a PLL demodulator 3 connected to the output of the variable gain amplifier 2, and a PLL demodulator 3 And an output terminal 4 connected to the output of the variable gain amplifier 2, the output of the variable gain amplifier 2 is connected to one input of the gain control section 5b, and the output of the gain control section of the variable gain amplifier 2 and the output of the gain control section 5b. And connect
The output of the PLL demodulator 3 is connected to the other input of the gain controller 5b via a C / N detector 11. The output of the C / N detector 11 is the monitor terminal 1
Connected to 2.

The operation of the FM demodulator configured as described above will be described below. In FIG. 1, the variable gain amplifier 2 and the gain control unit 5b constitute an AGC 10b,
The output signal level is always kept constant with respect to the level fluctuation of the input signal. The output signal of this AGC 10b is PL
It is input to the L demodulator 3. The PLL demodulator 3 is a phase-locked loop type demodulator including a phase comparator 7, a loop filter 8 and a voltage controlled oscillator 9. The C / N detector 11 extracts a high-frequency noise component from the demodulated signal and performs voltage detection to output a voltage corresponding to C / N. The gain controller 5b of the AGC 10b is a PLL
The input of the demodulator 3 is compared with the output of the C / N detector 11, and the output level of the AGC 10b is controlled by the difference. Therefore, the input level to the PLL demodulator 3 is optimally changed corresponding to the C / N, and the generation of medaka noise can be prevented.

Next, a concrete example of the C / N detector 11 is shown in FIG.
Shown in. The bandpass filter 13, the amplifier 14, the detection circuit 15, and the DC amplifier 16 are connected in series in this order. Here, the center frequency of the bandpass filter 13 is selected to be higher than the signal.

[0015]

As described above, according to the present invention, C / N is received when a broadcast program having a different C / N is received, or when it is raining or the like.
Even when N is temporarily deteriorated, the output of the PLL demodulator is fed back to the variable gain amplifier to control its amplification degree. Therefore, the input level of the PLL demodulator is appropriate for C / N. You can control the level. Therefore, medaka noise can be improved without adjustment, and adjustment by manual operation can be eliminated.

Further, since it can be improved by adding only the C / N detector from the conventional structure, there is an effect that it can be easily coped with.

Further, in the above embodiment, the output from the C / N detector is divided into two, and one of them is connected to the monitor terminal, so that the function can be added as a C / N monitor.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an FM demodulator according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a C / N detector according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional FM demodulator.

[Explanation of symbols]

 1 Input Terminal 2 Variable Gain Amplifier 3 PLL Demodulator 4 Output Terminal 5b Gain Control Section 11 C / N Detector 12 Monitor Terminal

Claims (2)

[Claims] 1. An input terminal, a variable gain amplifier connected to the input terminal, a PLL demodulator connected to the output of the variable gain amplifier, and an output terminal connected to the output of the PLL demodulator. The output of the variable gain amplifier is connected to one input of a gain control unit, the gain control terminal of the variable gain amplifier is connected to the output of the gain control unit, and the output of the PLL demodulator is C / N detected. An FM demodulator connected to the other input of the gain control unit via an amplifier. 2. The FM demodulator according to claim 1, wherein the output of the C / N detector is connected to a monitor terminal.