JPH0837629A - Satellite broadcast receiving device - Google Patents

Abstract

PURPOSE:To evade the increase of cost due to addition of a reference crystal oscillator and also to attain the application of a highly accurate digital AFC (automatic frequency control) circuit by using the PLL crystal oscillator of a channel selection circuit in common to an FM modulation circuit which applies the digital AFC circuit. CONSTITUTION:An AFC circuit always outputs the DC voltage 20 corresponding to a frequency error to a microcomputer 18 through an output terminal 17 of a 2nd converter 19. The microcomputer 18 controls the variance of frequency based on the received voltage 20. Then an FM modulation circuit 22 including a digital AFC circuit needs a crystal oscillator for generation of a reference signal. The converter 19 uses in common a crystal oscillator 15 which is used for generation of the PLL reference signal of a channel selection circuit 14 as the crystal oscillator needed for generation of the reference signal of the digital AFC circuit. In a system of such a constitution, the adjustment of frequency is not required and the control accuracy is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite broadcast receiving device, and more particularly to a device for improving receiving performance in a satellite broadcast and a second converter of the satellite broadcast receiving device for receiving the satellite broadcast.

[0002]

2. Description of the Related Art In satellite broadcasting and satellite communication, a broadcasting satellite (BS: Broadcasting Satellite) or a communication satellite (C) is used.
Radio waves from an S: Communication Satellite) are received by a parabolic antenna (parabolic antenna), and this is a first converter to generate a first intermediate frequency signal (hereinafter referred to as a first I signal).
It is supplied to the second converter after being converted into the F signal). The second converter has a mechanism for selecting a receiving channel and performing FM demodulation.

FIG. 4 shows a block diagram of a general second converter for receiving satellite broadcast and satellite communication.

In FIG. 4, an input terminal 1 receives a parabolic antenna (not shown) and amplifies and converts it into a first intermediate frequency (hereinafter, referred to as a first IF frequency) by a fast converter (generally a BS converter). The input signal is input. The first intermediate frequency is 950-1,880M
It is in the range of Hz. The first IF input to the input terminal 1
The signal is supplied to one input end of the mixer 6 via the input amplifier circuit 2, the AGC circuit 3, the first intermediate frequency amplifier circuit 4, and the pre-selector 5 for removing the image interference signal.
The local oscillation signal from the local oscillator 8 is supplied to the other input terminal of the mixer 6 via the buffer 7. The frequency of the local oscillation signal of the local oscillator 8 is made variable by the tuning data from the tuning circuit 14 controlled by a microcomputer (hereinafter referred to as a microcomputer) 18. The tuning circuit 14 is composed of a tuning circuit PLL and uses a reference signal from the crystal oscillator 15. In the mixer 6, the second intermediate frequency (402.78MHz)
Is converted to. The second intermediate frequency (hereinafter referred to as the second IF signal) from the mixer 6 is amplified by the second intermediate frequency amplifier circuit 9 and then input to the dual SAW filter 10. The dual SAW filter 10 is composed of two SAW filters (surface acoustic wave filters) having different pass bands (band 16 MHz and band 27 MHz), and outputs the input FM signal in two types of bands. is there. Here, two pass bands are prepared for the SAW filter because the CN of the signal entering the second converter 19 is used.
When the ratio (carrier level to input noise level ratio) decreases, the reception band is switched from the normal band of 27 MHz to a narrow band of 16 MHz to reduce the noise component entering the FM modulation circuit 13 and improve the deterioration of image quality. Is. SAW
The signals of the two pass bands from the filter 10 are switched to one of the bands by the band switching circuit 11 and supplied to the post amplifier 12, and after amplification, the FM modulation circuit 13 performs FM
It is detected and output from the output terminal 16 of the second converter 19.

The band switching circuit 11 is switched by a control signal from the channel selection circuit 14 controlled by the microcomputer 18.

Further, the FM demodulation circuit 13 uses the second I
In order to correct the deviation of the center frequency of the F signal, the DC voltage 20 corresponding to the deviation of the frequency is always output from the output terminal 17 of the second converter 19 and sent to the microcomputer 18. Based on this signal, the microcomputer 18 adjusts the fluctuation of the frequency. This is the operation of the AFC circuit. Further, the FM demodulation circuit 13 sets the level information of the detection output to A
The AGC circuit 3 is fed back to the GC circuit 3.
On the basis of the information, the gain of the receiver is automatically controlled according to the strength of the received radio wave so that the FM demodulation circuit 13 can always obtain a constant detection output without distortion. still,
The FM demodulation circuit 13 is composed of an IC (integrated circuit).

By the way, in the FM demodulation circuit in the apparatus described above, an analog system has been conventionally used as the AFC circuit. This is a method in which the DC component of the FM modulation output is used as a frequency shift signal, which requires fine adjustment and is somewhat problematic in terms of accuracy.

Therefore, it is conceivable to change the AFC circuit from the analog system to the digital system. By the way, the operation of the digital AFC circuit requires a highly accurate reference frequency, which requires a crystal oscillator. As a result, there is a problem (defect) that the cost of the FM demodulation circuit (IC) including the crystal oscillator increases, and the cost of the entire device increases.

[0009]

As described above, if an IC adopting a high-performance digital AFC circuit is used as the FM modulation IC in the second converter of the satellite broadcast receiving apparatus in order to improve the performance of the AFC circuit, the entire apparatus will be used. There was a problem that the cost would increase.

In order to solve such a problem, the present invention uses a high-performance digital AFC as an FM modulation IC.
An excellent (high cost performance) satellite broadcast receiving device that does not cause an increase in the cost of the second converter in the satellite broadcast receiving device and does not cause interference with peripheral circuits even if an IC adopting the circuit is used. It is intended to provide.

[0011]

A satellite broadcast receiving apparatus according to the present invention comprises a local oscillator and a mixer, mixes an input signal and an oscillation frequency from the local oscillator, and outputs a second intermediate frequency. A frequency converting means for generating, a tuning circuit having a crystal oscillator for controlling the frequency of the local oscillator by a PLL synthesizer system, and a digital AF for performing FM detection of the signal converted to the second intermediate frequency.
The FM demodulation circuit adopting the C circuit and the tuning data of the broadcasting station are supplied to the tuning circuit, and the frequency of the second intermediate frequency is controlled by the AFC DC voltage from the FM demodulation circuit adopting the digital AFC circuit. It is characterized by including a control means for performing control (AFC), and the crystal unit used in the tuning circuit is shared with the FM demodulation circuit adopting the digital AFC circuit.

A satellite broadcast receiving apparatus according to a second aspect of the present invention comprises a local oscillator and a mixer, and frequency conversion means for mixing an input signal and an oscillation frequency from the local oscillator to generate a second intermediate frequency. , A frequency tuning circuit having a crystal oscillator for controlling the frequency of the local oscillator by a PLL synthesizer system, and an FM adopting a digital AFC circuit for performing FM detection of the signal converted to the second intermediate frequency.
The demodulation circuit and the tuning circuit are supplied with tuning data of the broadcasting station, and frequency control (AFC) of the second intermediate frequency is performed by the AFC DC voltage from the FM demodulation circuit adopting the digital AFC circuit. And a crystal unit used in the channel selection circuit for controlling the digital A
The FM demodulation circuit adopting an FC circuit is also used, and the tuning circuit and the FM demodulation circuit adopting the digital AFC circuit are arranged close to each other, and an electromagnetic shield is provided therebetween.

[0013]

In the invention described in claim 1, the digital AF is newly added.
An FM demodulation circuit (IC) incorporating C is introduced. In the digital method, data is processed by a digital signal and a crystal oscillator (for example, 4 MHz) is used as a reference for accuracy, so that there is no variation and stable and good AFC accuracy can be obtained. In the present invention, the crystal oscillator (4 MHz) used as the reference signal in the tuning circuit is used without newly preparing the crystal oscillator (4 MHz) used as the reference signal in the digital AFC circuit, That is, since the digital AFC circuit is commonly used, it is possible to avoid the cost increase due to the introduction of a new crystal oscillator and to achieve high-performance AFC (automatic frequency control).

In a second aspect of the present invention, a crystal oscillator (4) used as a reference signal of a digital AFC circuit is used.
(MHz) with the crystal oscillator (4 MHz) used for the reference signal in the tuning circuit, the tuning circuit, the FM demodulation circuit (IC) with a built-in digital AFC, and the crystal Depending on the arrangement of the oscillator, there may be a long pattern of wiring. Therefore, first, the FM demodulation circuit (IC) incorporating the digital AFC and the tuning circuit are arranged close to each other so that the pattern with the crystal oscillator does not become long. This makes it possible to prevent interference with other blocks (input unit, local oscillator, etc.).

Further, since the shield is provided between the FM demodulation circuit (IC) incorporating the digital AFC and the tuning circuit,
It was possible to reduce the interference of the crystal oscillator (4 MHz) signal with the baseband signal. Further, by providing this shield, it is possible to suppress the influence of 4 MHz spurious (harmonic) on the image.

[0016]

EXAMPLES Examples will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, an input terminal 1 receives a parabolic antenna (not shown) and amplifies and converts it into a first intermediate frequency (hereinafter, referred to as a first IF frequency) by a fast converter (generally a BS converter). The input signal is input. The first intermediate frequency is 950-1,880M
It is in the range of Hz. The first IF input to the input terminal 1
The signal is supplied to one input end of the mixer 6 via the input amplifier circuit 2, the AGC circuit 3, the first intermediate frequency amplifier circuit 4, and the pre-selector 5 for removing the image interference signal.
The local oscillation signal from the local oscillator 8 is supplied to the other input terminal of the mixer 6 via the buffer 7.

The frequency of the local oscillation signal of the local oscillator 8 is
It is controlled by a microcomputer (hereinafter, referred to as a microcomputer) 18 and can be changed by tuning data from a tuning circuit 14. In addition, the tuning circuit 14
Is composed of a PLL for a tuning circuit, and uses a crystal oscillator 15 to generate a reference signal. As the crystal oscillator 15, for example, one having a frequency of 4 MHz is used.

The configuration of the tuning circuit PLL of the tuning circuit 14 will be described with reference to FIG. Tuning circuit 14
Is a PLL for a tuning circuit. The oscillation frequency (fi) of the local oscillator 8 is divided by the prescaler 23 to 1 / Np, and further divided by the programmable counter 24 to 1 / N, and the oscillation frequency of the reference crystal oscillator 15 (fo). The frequency divided by 1 / n by the reference oscillator 26 is applied to the phase comparator 25, and the result is returned to the local oscillator 8 through an LPF (low pass filter) 27. Then lock this loop. As a result, f is equivalently
Since i is set to N times fo, it is possible to change fi (local oscillation frequency) by appropriately changing N and tune to any channel. In the case of this embodiment, the frequency division ratio (N) of the programmable counter 24 is changed by the tuning data from the microcomputer.

The microcomputer 1
The local oscillation signal from the local oscillator 8 and the signal from the pre-selector 5, which are controlled by 8 and are changed by the tuning data from the tuning circuit 14, are mixed in the mixer 6 by a second intermediate signal. The frequency is converted to the frequency (402.78MHz).

The second intermediate frequency (hereinafter referred to as the second IF signal) from the mixer 6 is amplified by the second intermediate frequency amplifier circuit 9 and then input to the dual SAW filter 10. The dual SAW filter 10 is composed of two SAW filters (surface acoustic wave filters) having different pass bands (band 16 MHz and band 27 MHz), and outputs an input FM signal in two types of bands. is there. Here, two pass bands are prepared for the SAW filter because the CN of the signal entering the second converter 19 is used.
When the ratio (carrier level to input noise level ratio) decreases, the reception band is changed from the normal band of 27 MHz to 16 MHz.
This is because the noise component entering the FM modulation circuit 22 with a built-in digital AFC is reduced by switching to a narrow band of z and the deterioration of image quality is improved. The signals of the two pass bands from the SAW filter 10 are switched to one of the bands by the band switching circuit 11 and supplied to the post amplifier 12, and after amplification,
FM detection by the FM modulation circuit 22 with a built-in digital AFC,
It is output from the output terminal 16 of the second converter 19.

The band switching circuit 11 is switched by a control signal from the channel selection circuit 14 controlled by the microcomputer 18.

Here, a supplementary explanation will be given on the functions (operations) of the AFC circuit and the FM demodulation circuit of the digital AFC built-in FM modulation circuit 22.

First, the AFC circuit will be described. In order to correct the deviation of the center frequency of the second IF signal, the conventional AFC circuit always outputs the DC voltage 20 corresponding to the deviation of the frequency from the output terminal 17 of the second converter 19 and sends it to the microcomputer 18. ing. The microcomputer 18 adjusts the fluctuation of the frequency based on this signal. This is the operation of the AFC circuit. By the way, A according to the present embodiment
Since the FC circuit (the FM modulation circuit 22 with a built-in digital AFC) is a digital system, a crystal oscillator for generating a reference signal is required. In this embodiment, the tuning circuit 14 is used as the crystal oscillator for generating the reference signal of the digital AFC circuit.
The crystal oscillator 15 used for generating the reference signal of the PLL for the tuning circuit is used (shared). The digital AFC circuit according to this digital system is operated by the input signal (the second
The frequency of the IF signal) is directly detected by a counter to detect the frequency deviation. When compared with the analog method (method in which the DC component of the FM demodulated output is used as the frequency deviation signal), the adjustment is It is unnecessary and has achieved a marked improvement in accuracy.

Next, the FM demodulation circuit will be described. F
As described above, the M demodulation circuit performs FM detection on the input signal (the second IF signal) from the post amplifier 12 and feeds back the level information of the detection output to the AGC circuit 3. Based on the information, the AGC circuit 3 controls the gain of the receiver according to the strength of the received radio wave, and the digital AFC built-in FM demodulation circuit 22 can always obtain a constant detection output without distortion. ing.

Further, in this embodiment, the AFC circuit and the FM demodulation circuit are the digital AFC built-in FM demodulation circuit 2
2 is composed of one IC (integrated circuit).

By the way, according to the above configuration, the tuning circuit 1
4, FM demodulation circuit (IC) 2 with built-in digital AFC
2, and depending on the arrangement of the crystal oscillator (4 MHz) 15, a long pattern can be routed.

Therefore, an example of the chassis structure including these arrangements is shown in FIG. First, the FM demodulation circuit (IC) 22 having a built-in digital AFC and the tuning circuit 14 are arranged close to each other so that the pattern of the crystal oscillator (4 MHz) 15 does not become long. This allows other blocks (input section,
Interference interference to local oscillators, etc.) can be prevented. Next, between the FM demodulation circuit (IC) 22 incorporating the digital AFC and the tuning circuit 14, the electromagnetic shield means 21 formed of a metal plate is provided. This allows the baseband video signal (4
It is possible to reduce the interference of the crystal oscillator (4 MHz) signal to the (MHz band). Further, by providing this electromagnetic shield means 21, it is possible to suppress the influence of 4 MHz spurious (harmonics) on the image.

In the above embodiment, a plurality of PLLs in the second converter for receiving satellite broadcast and satellite communication are used.
The sharing of the reference crystal oscillator in the synthesizer type circuit (or IC) has been described, but the present invention is not limited to this, and can be applied to various devices using a plurality of reference crystal oscillators.

[0030]

As described above, according to the present invention, the FM
An IC using a digital AFC circuit is used as the modulation IC, and the reference crystal oscillator of the PLL for the tuning circuit is set to the digital AFC circuit.
Since it was used (shared) with the FM modulation IC that adopted the FC circuit,
There is an effect that the cost increase due to the addition of the crystal oscillator can be avoided, and at the same time, it is possible to introduce a highly accurate digital AFC circuit.

Further, the FM modulator circuit (IC) is rearranged together with the crystal oscillator and the chassis structure is changed by the shield arrangement, so that other blocks (input section, local oscillator, etc.) due to spurious of the crystal resonator. It is possible to prevent interference of interference with the image and suppress the influence on the image.

[Brief description of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a PLL for a tuning circuit.

FIG. 3 is a diagram showing a circuit arrangement and a chassis structure according to the present invention.

FIG. 4 is a block diagram of a conventional general second converter.

[Explanation of symbols]

 5 ... Pre-selector 6 ... Mixer (MIXER) 8 ... Local oscillator (OSC) 14 ... Tuning circuit 15 ... Crystal oscillator 16 ... FM detection output 18 ... Micro computer (AFC means) 19 ... Second converter 20 ... AFC DC voltage 22 ... FM demodulation circuit with built-in digital AFC

Claims (2)

[Claims] 1. A frequency converter that includes a local oscillator and a mixer, mixes an input signal and an oscillation frequency from the local oscillator to generate a second intermediate frequency, and a frequency of the local oscillator by a PLL synthesizer method. A tuning circuit provided with a crystal oscillator for controlling, an FM demodulation circuit adopting a digital AFC circuit for performing FM detection of the signal converted to the second intermediate frequency, and a broadcasting station for the tuning circuit. AFC from the FM demodulation circuit adopting the digital AFC circuit
And a means for performing frequency control (AFC) of the second intermediate frequency by a DC voltage, wherein the crystal unit used in the tuning circuit is shared with the FM demodulation circuit employing the digital AFC circuit. A satellite broadcasting receiver characterized by. 2. A frequency converter for providing a second intermediate frequency by mixing an input signal and an oscillation frequency from the local oscillator with a local oscillator and a mixer, and a frequency of the local oscillator by a PLL synthesizer system. A tuning circuit provided with a crystal oscillator for controlling, an FM demodulation circuit adopting a digital AFC circuit for performing FM detection of the signal converted to the second intermediate frequency, and a broadcasting station for the tuning circuit. AFC from the FM demodulation circuit adopting the digital AFC circuit
Means for performing frequency control (AFC) of the second intermediate frequency by a DC voltage, wherein the crystal oscillator used in the tuning circuit is shared with the FM demodulation circuit employing the digital AFC circuit. A satellite broadcast receiving apparatus characterized in that the tuning circuit and the FM demodulation circuit adopting the digital AFC circuit are arranged close to each other, and an electromagnetic shield means is provided therebetween.