JPH114431A - Tuner for digital satellite broadcast - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tuner for digital satellite broadcast by which stable reception performance is ensured, adjust even when a frequency deviation of a LNB becomes larger, and easily adjust the direction of an antenna is. SOLUTION: In a 1st local oscillator 17, whose frequency is changed by a control signal being a signal of channel selection, a frequency offset obtained by a QPSK demodulation circuit 22 is added to a control signal of a frequency, so as to cancel a frequency deviation in an LNB 14 and an AGC level obtained by a QPSK demodulation circuit 22 is displayed on a display device 26. Thus, the adjustment of an antenna 13 such as its direction is easily conducted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tuner for digital satellite broadcasting using a QPSK modulation system.
The present invention relates to a tuner for digital satellite broadcasting capable of ensuring stable reception performance even when the frequency shift of the NB becomes large and easily adjusting the direction of an antenna.

[0002]

2. Description of the Related Art Conventionally, a digital satellite broadcast receiver using a QPSK modulation system has been known. FIG. 2 shows a conventional QP
It is a figure which shows the structure of the tuner of the digital satellite broadcast receiver using the SK modulation method. As shown in FIG. 1, a conventional digital satellite broadcast receiver includes an antenna 1, an LNB 2,
The tuner section includes a broadband amplifier circuit (broadband amplifier) 3, a mixing circuit 4, a first local oscillator 5, a bandpass filter (BPF) 6, an IQ demodulation circuit 7, a second local oscillator 8, It comprises a / D conversion circuit 9, a QPSK demodulation circuit 10, an error correction circuit 11, and an output terminal 12. Then, the received signal of, for example, 12 GHz band received by the antenna 1 is frequency-converted in the LNB 2 to be a signal of a new band of, for example, 1 GHz. This signal is transmitted via a cable and input to a tuner unit which is an indoor unit.

[0003] In the tuner section, the signal obtained from the LNB 2 is amplified by the broadband amplifier 3 and corrected for transmission loss by the cable before being input to the mixing circuit 4. The mixing circuit 4 detects the received signal by using a signal from the first local oscillator 5 whose oscillation frequency fluctuates in conjunction with channel selection to obtain an intermediate frequency signal.

This intermediate frequency signal is a BPF 6 having a bandwidth about 3 to 4 MHz wider than the bandwidth of the signal to be transmitted.
Unnecessary frequency components are removed by the IQ demodulation circuit 7
Is converted into an IQ signal by the output signal of the second local oscillator 8. Then, after converting this IQ signal into a digital signal by the A / D conversion circuit 9, it is demodulated into a digital signal by the QPSK demodulation circuit 10 and the error correction circuit 11.

[0005] Further, regarding the installation of the antenna 1, the direction and direction of the antenna 1 are adjusted by trial and error so as to obtain the best image quality while checking the image quality of the received TV broadcast or the like. The frequency stability of LNB2 is ± 1.5
It is specified to be within MHz.

[0006]

SUMMARY OF THE INVENTION However, LNB
2 is required to be installed outdoors together with the antenna 1, and it is difficult to maintain the above-mentioned stability for many years because severe use environment conditions are required.
There may be a frequency shift of about Hz.

When such a frequency shift occurs, the output signal from the mixing circuit of the tuner section does not fall within the pass band of the succeeding BPF 6, so that the output signal is distorted as shown in FIG. For this reason, the demodulated signal is deteriorated, and in the worst case, a failure such as an inability to correctly demodulate occurs. Further, the adjustment of the direction of the antenna 1 is largely a matter of trial and error, and it often takes time to install the antenna 1 in the best condition.

In view of the above, the present invention solves the above-mentioned problems, and secures a stable reception performance even when the frequency deviation of the LNB becomes large, and can easily adjust the direction of the antenna for digital satellite broadcasting. The purpose is to provide a tuner.

[0009]

To achieve the above object, a first aspect of the present invention is directed to a first aspect of the present invention, wherein a received signal received by an antenna and a first signal are received.
And a signal having an oscillating frequency responsive to a predetermined control signal output by the local oscillator, and an IQ signal is obtained from the mixed signal and a signal output by the second local oscillator. In a tuner for digital satellite broadcasting demodulated by a demodulator circuit, an offset value from a normal value of a carrier frequency detected by the demodulation circuit is fed back to frequency control of the first local oscillator, and the first local oscillator is controlled. Is made to follow the offset value of the carrier frequency.

In a second aspect of the present invention, a control signal for controlling the oscillation frequency of the first local oscillator is provided by using an offset value detected by the demodulation circuit and regular frequency information used for channel selection. It is characterized by including a controller to be created.

Further, the third invention further comprises a storage means for storing the offset value detected by the demodulation circuit, and oscillating the first local oscillator using the offset value stored in the storage means. It is characterized in that the frequency is controlled.

A fourth invention is characterized in that the installation of the antenna is adjusted so that the level of the AGC signal detected by the demodulation circuit is maximized.

[0013]

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

FIG. 1 is a block diagram showing the configuration of a tuner of a digital satellite broadcast receiver used in the present embodiment. As shown in FIG. 1, the digital satellite broadcast receiver includes an antenna 13, an LNB 14, and a tuner unit. The tuner unit includes a broadband amplifier circuit (broadband amplifier) 15, a mixing circuit 16, a first local unit. Oscillator 17, BPF
18, IQ demodulation circuit 19, second local oscillator 20, A / D
Conversion circuit 21, QPSK demodulation circuit 22, Error correction circuit 2
3, a controller 24, a memory 25, a display device 26, and a demodulated signal output terminal 27.

That is, this digital satellite broadcast receiver has a first feature in that the controller 24 applies a control signal to the first local oscillator 17 so as to follow the offset value of the input signal. Thereby, the mixing circuit 1
The intermediate frequency signal detected at 6 is followed by a BPF 18
To reduce signal distortion and the like.

Further, this digital satellite broadcast receiver has
The second point is that the offset value from the normal value of the carrier frequency obtained by the QPSK demodulation circuit 22 is stored in the memory 25.
Thus, the carrier wave discovery time at the time of next and subsequent reception is shortened, thereby improving the tuning speed.

Further, in this digital satellite broadcasting receiver, a signal indicating the AGC level obtained from the QPSK demodulation circuit 22 is monitored on the display device 26, and the direction of the antenna is adjusted so that the value becomes maximum. There is a third feature in the configuration, whereby the best reception state can be easily obtained.

Specifically, for example, a signal in the 12 GHz band received by the antenna 13 is frequency-converted in the LNB 14 to become a signal in a new frequency band, for example, in the 1 GHz band.
The signal is transmitted to the tuner via a cable. Then, in the tuner section, after correcting the transmission loss of the cable in the broadband amplifier 15, the mixing circuit 16 performs detection using the signal from the first local oscillator 17 whose oscillation frequency changes according to the control signal, and converts the intermediate frequency signal. get.

In this tuner, the controller 24 applies a control signal to the first local oscillator 17 so as to follow the frequency offset of the input signal, and the control signal is used as a tuning signal. A value obtained by adding or subtracting the frequency offset value obtained by the QPSK demodulation circuit 22 from the given regular frequency value. Whether the offset value is added or subtracted depends on the sign of the detected offset value.

As a result, the intermediate frequency signal detected by the mixing circuit 16 falls within the band of the BPF 18 following the intermediate frequency signal, thereby preventing the occurrence of signal distortion and the like. Note that a microcomputer or the like can be used as the controller 24.

From the intermediate frequency signal detected by the mixing circuit 16, unnecessary frequency components are removed by a BPF 18.
The IQ demodulation circuit 19 outputs an IQ signal from the intermediate frequency signal and the signal generated by the second local oscillator 20. Then, after converting the IQ signal into a digital signal by the A / D conversion circuit 21, the QPSK demodulation circuit 22 and the error correction circuit 2
A digital signal is obtained by demodulation and decoding at step 3.

The offset value from the normal value of the carrier frequency obtained by the QPSK demodulation circuit 22 is stored in the memory 25.
By controlling the frequency of the first local oscillator 17 using the value of the memory 25 at the time of the next and subsequent reception, the time required for the QPSK demodulation circuit 22 to find a carrier is reduced, and as a result, The tuning speed can be improved.

By using a non-volatile memory such as a flash ROM or an EEPROM as the memory 25, the value is retained even when the power is turned off. Further, the signal indicating the AGC level obtained from the QPSK demodulation circuit 22 is monitored by the display device 26, and the direction of the antenna is adjusted so that the value is maximized, so that the best reception state can be easily obtained. it can.

As described above, in the present embodiment,
An offset value from the normal value of the carrier frequency detected by the QPSK demodulation circuit 22 is fed back to the frequency control of the first local oscillator 17 so that the frequency of the first local oscillator 15 follows the offset value of the carrier frequency. Therefore, even if the frequency shift of the LNB 14 becomes large,
Following this, stable reception performance can be ensured.

Further, the controller 24 controls the oscillation frequency of the first local oscillator 17 using the offset value detected by the QPSK demodulation circuit 22 and regular frequency information used for channel selection. Frequency control can be easily performed.

The offset value detected by the QPSK demodulation circuit is stored in the memory 25, and the oscillation frequency of the first local oscillator 17 is controlled using the offset value stored in the memory 25. Station time can be reduced.

Further, since the installation of the antenna 13 is adjusted so that the level of the AGC signal detected by the QPSK demodulation circuit 22 is maximized, the adjustment of the direction and the direction when the antenna is installed can be easily performed. be able to.

[0028]

As described in detail above, the first invention feeds back the offset value of the carrier frequency detected by the demodulation circuit from the normal value to the frequency control of the first local oscillator, and 1 so that the frequency of the local oscillator 1 follows the offset value of the carrier frequency.
Even if the frequency shift of the NB becomes large, it is possible to keep up with it and secure stable reception performance.

Further, according to a second aspect of the present invention, the controller uses the offset value detected by the demodulation circuit and regular frequency information used for tuning to control a control signal for controlling the oscillation frequency of the first local oscillator. Since it is configured to generate the oscillation frequency, the oscillation frequency can be easily controlled.

According to a third aspect of the present invention, the offset value detected by the demodulation circuit is stored in a storage means, and the oscillation frequency of the first local oscillator is controlled using the offset value stored in the storage means. With this configuration, it is possible to shorten the tuning time.

Also, in the fourth invention, the antenna installation is adjusted so that the level of the AGC signal detected by the demodulation circuit is maximized. This can be easily performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a digital satellite broadcast tuner used in the present embodiment.

FIG. 2 is a block diagram showing a configuration of a conventional digital satellite broadcast tuner.

FIG. 3 is a diagram illustrating a role of a BPF of a digital satellite broadcast tuner.

[Explanation of symbols]

 1,13 Antenna 2,14 LNB 3,15 Broadband Amplifier 4,16 Mixing Circuit 5,17 First Local Oscillator 6,18 BPF 7,19 IQ Demodulator 8,20 Second Local Oscillator 9,21 A / D conversion circuit 10,22 QPSK demodulation circuit 11,23 error correction circuit 12,27 output terminal 24 controller 25 memory 26 display device

Claims (4)

[Claims] 1. A reception signal received by an antenna is mixed with a signal having an oscillation frequency responsive to a predetermined control signal output by a first local oscillator, and the mixed signal is output by a second local oscillator. A digital satellite broadcast tuner for obtaining an IQ signal from the signal and demodulating the obtained IQ signal by a demodulator circuit, wherein the offset value from the normal value of the carrier frequency detected by the demodulation circuit is set to the first local area. A tuner for digital satellite broadcasting, wherein the tuner feeds back to frequency control of an oscillator to cause the frequency of the first local oscillator to follow the offset value of the carrier frequency. 2. A controller for generating a control signal for controlling an oscillation frequency of the first local oscillator using an offset value detected by the demodulation circuit and regular frequency information used for channel selection. 2. The method according to claim 1, wherein
The tuner for digital satellite broadcasting according to the description. 3. A storage unit for storing an offset value detected by the demodulation circuit, wherein the control unit controls the oscillation frequency of the first local oscillator using the offset value stored in the storage unit. 3. The method according to claim 1, wherein
The tuner for digital satellite broadcasting according to the description. 4. The tuner for digital satellite broadcasting according to claim 1, wherein the antenna installation is adjusted so that the level of the AGC signal detected by said demodulation circuit is maximized.