JPH1188795A - Automatic frequency tuner for satellite broadcast tuner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely and quickly attain optimum tuning of a concerned channel by reading offset data to shift an oscillated frequency of a local oscillator stored in advance by a prescribed value so as to shift an oscillated frequency of the local oscillator in the case that a carrier frequency of an IF signal is deviated not to be controlled even by an AFT control means. SOLUTION: A channel selection microcomputer 29 generates a control signal for a local oscillator 16 based on initial value data corresponding to a channel selection request signal to set an oscillated frequency to a reference carrier frequency f0. Then the standard carrier frequency f0 is searched and when it is discriminated that no locking is made to the frequency f0, to which of high and low carrier frequency a 2nd IF signal is deviated is discriminated and-≃0 and +f0 offset data are read from an offset data storage section 32 to shift an oscillated frequency of the local oscillator 16 to conduct ATF search. Thus, the reception of a desired broadcast channel is surely and excellently 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 receiving a satellite broadcast signal, and more particularly to an automatic frequency tuning apparatus using digital signal processing.

[0002]

2. Description of the Related Art In recent years, digital technologies have been used for various circuit processes for processing television signals in video equipment such as television receivers and video recorders for receiving and reproducing analog television signals.

In particular, when a specific broadcast channel of a broadcast signal is selectively received, operation of a device by a remote device is performed from a position distant from the video device. In order to ensure the operation, a controlled device whose operation is controlled by a digital signal is mainly used.

[0004] On the other hand, satellite broadcasting has been adopted in addition to terrestrial broadcasting due to the variety of customer needs, and the number of broadcasting channels tends to increase.

[0005] A broadcast signal selecting device of a satellite broadcast video device for receiving and reproducing the satellite broadcast signal will be described with reference to FIG.
explain.

FIG. 4 is a block diagram showing a circuit configuration of a satellite broadcasting channel selecting device. Reference numeral 51 in the figure denotes a broadcasting satellite (hereinafter, referred to as B
S), which receives a broadcast signal transmitted from the BS, uses radio waves in the 12 GHz band from the BS,
Receive a modulated and transmitted television signal. This BS
A BS converter 52 is attached to the antenna 51, and converts the 12 GHz band signal into a 1.2 GHz band IF signal (hereinafter, referred to as a 1st IF signal). The 1st IF signal converted by the BS converter 52 is guided to the BS tuner 53 via a cable. This BS tuner 53
Comprises an IF amplifier 54, a mixer 55, a local oscillator 56, and a prescaler 57.

[0007] The first IF signal guided from the BS converter 52 to the BS tuner 53 is amplified to a predetermined signal size by an IF amplifier 54 and output to a mixer 55. In the mixer 55, the signal from the IF amplifier 54 and the signal from the local oscillator 56 are mixed, and
The signal is converted into an IF signal of a MHz band (hereinafter, referred to as a second IF signal). The local oscillator 56 includes a prescaler 57
, An oscillation frequency control signal to be described later for generating an oscillation frequency corresponding to a channel desired to be tuned is supplied.

The 2nd IF signal converted by the mixer 55 is output to the PLL type FM demodulator 58. This P
The LL type FM demodulator 58 includes a phase comparator 59, a loop filter 60, an error amplifier 61, and a voltage controlled oscillator (hereinafter, referred to as VCO) 62.

The FM demodulator 58 compares the phase of the 2nd IF signal from the mixer 55 with the reference frequency signal from the VCO 62, and supplies a control signal to the VCO 62 if there is an error as a result of the phase comparison. Thus, the oscillation frequency is controlled so as to match the frequency of the second IF signal.
As a result, an output corresponding to the frequency shift of the second IF signal, that is, an FM demodulated baseband television signal is obtained as the output of the error amplifier 16.

The baseband television signal FM-demodulated by the FM demodulator 58 is subjected to de-emphasis and dispersal removal processing by a circuit (not shown) to generate a video signal, and further QPSK demodulation processing to generate an audio signal. Is done.

On the other hand, in order to select a broadcast signal of a specific channel from the signals of a plurality of channels received by the BS antenna 51, the local oscillator 56 transmits the signal to the mixer 5.
5 is selected by associating the signal frequency supplied to 5 with the specific channel. As the control of the oscillation frequency of the local oscillator 56, a voltage synthesizer system and a frequency synthesizer system are generally used in many cases. A tuning microcomputer 63 is used to generate a voltage or frequency signal for controlling the local oscillator 56.

The tuning microcomputer 63 includes an input processing unit 64 for receiving and processing a tuning request signal such as desired channel number data input from a terminal (not shown) by a user using a numeric keypad, etc., and an initial value data storage unit. 65, an offset data storage unit 66, an output processing unit 67, and a control unit 68 for controlling transmission and reception of signals or data between the input / output processing units 64 and 67 and the data storage units 65 and 66.

When a tuning request signal such as desired channel number data is input to the input processing unit 64, the control unit 68 reads data of the corresponding channel from the initial value data storage unit 65 in response to the tuning request signal. , To the output processing unit 67. The output processing section 67 generates a voltage or a frequency control signal for controlling the oscillation frequency of the local oscillator 56 based on the transferred data, and supplies the generated voltage or frequency control signal to the prescaler 57. The prescaler 57 divides the oscillation output of the local oscillator 56 and compares it with the frequency control signal.
The oscillation of the local oscillator 56 is controlled based on the comparison result, and the oscillation frequency is made to correspond to the frequency control signal.

Based on a control signal from the prescaler 57, a signal having a frequency corresponding to a channel selected by the local oscillator 56 and the 1st IF signal are mixed by the mixer 55 to generate a 2nd IF signal of a desired channel. The signal is supplied to the FM demodulator 58.

On the other hand, 1s from the BS converter 52
When the carrier frequency f0 of the tIF signal shifts, the 2nd IF converted by the mixer 55 of the BS tuner 53 is used.
Since the carrier frequency f0 of the signal also shifts, a correct baseband television signal cannot be obtained from the FM demodulator 58.
Therefore, the error amplifier 61 of the FM demodulator 58 includes:
A circuit is provided for generating and outputting a signal indicating in which of the plus and minus directions a shift has occurred with respect to the carrier frequency f0. The plus and minus output terminals are connected to the tuning microcomputer 63. Is done. An analog-to-digital converter 69 for analog-to-digital conversion of a signal from the plus / minus output terminal of the error amplifier 61,
A comparing unit 70 is provided for comparing the plus and minus signals converted into digital signals with reference levels.
The comparison unit 70 generates displacement data indicating whether the carrier frequency f0 is shifted in the plus direction or the minus direction, and via the control unit 68,
It is supplied to the output processing unit 67. In the output processing unit 67, the local oscillator 56 is adjusted in a direction to correct the deviation based on the deviation data.
A frequency control signal for gradually changing the oscillation frequency is output to the prescaler 57. As a result, a so-called search is performed, and the search is stopped when the output of the comparator 70 indicates no shift, so that the shift of the carrier frequency of the second IF signal is automatically corrected (hereinafter, this control is referred to as "control"). AFT control). Further, the data corresponding to the frequency control signal output from the output processing unit 67 at the time when the seach ends, is stored in the offset data storage unit 66 by the control unit 68 as offset data. From then on, by selecting a channel based on this offset data, a quick and reliable tuning operation can be performed.

In order to eliminate the deviation of the carrier frequency f0 of the 1st IF signal, it is necessary to accurately capture the BS broadcast radio wave transmitted from tens of thousands km from the ground, and attention has been paid to the installation of the antenna. However, depending on the installation state, the mounting angle of the antenna may be slightly deviated, thereby causing the carrier frequency to be weak and causing a frequency shift,
In addition, a frequency shift occurs due to poor performance of the BS converter itself and fluctuations in the operating power supply voltage supplied to the BS converter. Even if a frequency shift occurs due to such factors, the AFT control is performed to accurately detect the carrier frequency. However, the analog output from the plus / minus output terminal of the error amplifier 61 of the FM demodulator 58 is output. As shown in FIG. 5A, the signal has an S-shaped characteristic centered on the reference carrier frequency f0, and a straight line portion of the S-shaped characteristic is drawn into a pull-in range (hereinafter, referred to as an AFT pull-in range) t.
An AFT control signal of 1 is generated. The difference between the positive and negative output of this analog AFT control signal is calculated by the BS.
By directly supplying the signal to the local oscillator 56 of the tuner 53 and controlling the transmission frequency to perform the AFT pull-in, the carrier frequency f0 located within the AFT pull-in range t1 can be pulled in.

However, when the analog AFT control signal from the error amplifier 61 of the PLL type FM demodulator 58 is converted into a digital signal by the analog / digital converter 69 of the tuning microcomputer 63, the digitally converted AFT control signal becomes As shown in FIG.
The T pull-in range t2 is narrower than the analog AFT pull-in range t1 (t1> t2).

For this reason, once the BS antenna is installed in the analog-compatible tuning device and the digital-compatible tuning device is used from a state where the BS broadcast can be sufficiently received and reproduced, the AF
Since the T pull-in range becomes narrow, a sufficient BS broadcast signal cannot be received, and it is necessary to adjust the mounting of the antenna again. In addition, if the position is not accurately adjusted at the time of the installation adjustment of the antenna or the installation adjustment of the new antenna again, there is a problem that the reception and reproduction are noisy or noisy.

[0019]

SUMMARY OF THE INVENTION In channel selection for satellite broadcasting reception, the first BS converter installed on the antenna is used.
The deviation of the carrier signal f0 of the IF signal is corrected by the AFT control in the BS tuner, but the AFT search and the pull-in range are set to a practically acceptable range in the analog processing. When digital processing is performed, the AFT output range and the pull-in range are narrowed, and the broadcast channel frequency cannot be received, or a sufficient broadcast signal amount cannot be received, and a TV signal with a large amount of noise noise is not received. There was a problem that the antenna had to be regenerated or the antenna had to be reattached and adjusted.

The present invention provides a carrier signal f of the first IF signal.
It is an object of the present invention to provide a digital automatic frequency tuning apparatus capable of performing the optimum tuning of a corresponding channel reliably and quickly by providing a plurality of AFT pull-in ranges even if the zero is shifted.

[0021]

SUMMARY OF THE INVENTION A satellite broadcast signal is received,
A BS tuner having at least a local oscillator and a mixer for generating a second IF signal of a desired channel from the first IF signal generated by the BS converter; and a second IF signal generated by the BS tuner. A frequency detecting means for generating an AFT signal indicating a deviation of the carrier frequency of the second IF signal; and a predetermined frequency pull-in control range, wherein the oscillation frequency of the local oscillator is controlled based on the AFT signal from the frequency detecting means. AFT control means for automatically controlling the carrier frequency of the second IF signal to a predetermined value, and AFT signal from the frequency detection means,
Determining means for determining that the carrier frequency of the second IF signal has shifted to a state where it cannot be controlled by the AFT control means; and data for shifting the oscillation frequency of the local oscillator by a predetermined value. Automatic frequency tuning of a satellite broadcast tuner, comprising: offset data storage means stored in advance; and offset means for reading offset data from the storage means and shifting the oscillation frequency of the local oscillator according to the determination result of the determination means. Device.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a circuit configuration of an embodiment of an automatic frequency tuning device for a satellite broadcast tuner according to the present invention.

A 12 GHz band television signal transmitted from a broadcasting satellite is received by an antenna 11.
Is converted to a 1.2 GHz band first IF signal by a BS converter 12 attached to the
It is supplied to the tuner 13. This BS tuner 13
It comprises an IF amplifier 14, a mixer 15, a local oscillator 16 and a prescaler 17.

The 1st IF signal supplied from the BS converter 12 to the BS tuner 13 is amplified by the IF amplifier 14 to a predetermined signal size and output to the mixer 15. In the mixer 15, the 1st IF signal is mixed with the local oscillation signal from the local oscillator 16 and
A 2nd IF signal in a Hz band is generated.

In the BS tuner 13, in order to selectively receive a desired broadcast channel from television signals transmitted from the BS, a tuning control signal for displacing the oscillation frequency of the local oscillator 16 for each channel is provided. It is supplied from the prescaler 17.

The 2nd generated by the BS tuner 13
The IF signal is output to the PLL type FM demodulator 18.
The FM demodulator 18 includes a phase comparator 19, a loop filter 20, an error amplifier 21, and a voltage controlled oscillator (hereinafter, V
22).

The FM demodulator 18 receives the 2nd IF signal from the mixer 15 and the VCO as in the circuit shown in FIG.
22 is compared with the reference frequency from the reference frequency 22. The VCO 22 is controlled in accordance with the comparison result, and the oscillation frequency is set to 2nd
Match the frequency of the IF signal, thereby providing an error amplifier
An FM demodulated baseband television signal is obtained as 21 output. Further, the error amplifier 21 has a plus terminal and a minus terminal for deriving an S-shaped characteristic output according to the deviation of the carrier frequency f0 of the second IF signal.

The baseband television signal FM-demodulated by the FM demodulator 18 passes through a low-pass filter 23 and a de-emphasis / dispersal remover 24.
A video signal is generated, and a high-pass filter 25, Q
PSK demodulator 26, PCM decoder 27 and digital
An audio signal is generated via the analog converter 28. On the other hand, the signal is received by the BS antenna 11 and the BS converter 1
In order for the BS tuner 13 to select a broadcast signal of a specific channel from the signal converted into a 1st IF signal in 2, the oscillation output frequency supplied from the local oscillator 16 to the mixer 15 is set to a frequency for selecting the specific channel. Is displaced to correspond to. The voltage or frequency displacement signal for controlling the oscillation frequency of the local oscillator 16 is supplied from the tuning microcomputer 29 via the prescaler 17.

The tuning microcomputer 29 is provided with an input processing unit 30 for receiving and processing a tuning request signal such as desired channel number data input by a user from a terminal (not shown) using a numeric keypad or the like, and storing initial value data. Unit 31, an offset data storage unit 32, an output processing unit 33, a control unit 34 for controlling the transfer of signals or data between the input / output processing units 30, 33 and the data storage units 31, 32, and the FM demodulation It comprises an analog-to-digital converter 35 for converting an AFT control signal from the plus / minus output terminal of the error amplifier 21 of the detector 18 from analog to digital, and a comparator 36.

When a channel selection request signal such as a desired channel number is input to the input processing unit 30, the control unit 34 sends the channel selection request signal from the initial value data storage unit 31 according to the input signal of the input processing unit 30. Read data,
Transfer to the output processing unit 33. In the output processing unit 33, the tuning data from the initial value data storage unit 31 is converted into a voltage or a frequency control signal (hereinafter, referred to as an oscillation control signal) for controlling the oscillation frequency of the local oscillator 16, and the prescaler 17 To supply. The prescaler 17 divides the oscillation output of the local oscillator 16 and compares it with the frequency control signal, controls the oscillation based on the comparison result, and makes the oscillation frequency of the local oscillator 16 correspond to the frequency control signal. The oscillation frequency of the local oscillator 16 is specified based on the oscillation control signal supplied from the output processing unit 33 of the tuning microcomputer 29 to the prescaler 17, and the oscillation output is supplied to the mixer 15. The signal is mixed with the 1st IF signal by the mixer 15 to generate a 2nd IF signal of a desired channel,
The signal is supplied to the LL type FM demodulator 18.

On the other hand, 1 s supplied to the mixer 15 due to poor performance of the BS converter 12 of the BS antenna 11 or the like.
If the carrier frequency f0 of the tIF signal deviates from the specified value, the carrier frequency of the 2nd IF signal output from the mixer 15 also deviates, and the deviation from the positive terminal and the negative terminal of the error amplifier 21 of the FM demodulator 18 shifts. A corresponding signal is output and supplied to the tuning microcomputer 29. The tuning microcomputer 29 converts the plus and minus outputs of the error amplifier 21 into a digital signal and supplies it to a comparator 36, which compares it with a reference level and outputs data indicating the direction of the shift.

The AFT control is performed based on this data. In the present invention, when the deviation cannot be corrected by the normal AFT control based on the channel selection operation based on the data from the initial value data storage unit 31, the AFT control is performed. Offset data for shifting the control center frequency by a predetermined value is stored in the offset data storage unit 32 in advance, and the offset data is read out and supplied to the output processing unit 33 to control the oscillation frequency of the local oscillator 16. Change the control signal.

The AFT operation will be described in detail with reference to FIG. 2. As shown in FIG. 2A, generally, the error amplifier of the FM demodulator 18 is used to correct the deviation of the carrier frequency f0 of the first IF signal. An oscillation frequency displacement range of the local oscillator 16 by a signal (hereinafter, referred to as an AFT signal) indicating a deviation supplied from the plus and minus output terminals of 21 to the tuning microcomputer 29, that is, a carrier frequency search range is a predetermined range. ± 6 for carrier frequency f0
It has a width of MHz. The carrier frequency search range ± 6 MHz corresponds to the AFT pull-in range t2 in FIG.
Is equivalent to

Therefore, within this ± 6 MHz range, the first
When the carrier frequency f0 of the IF signal shifts, the tuning microcomputer 29 causes the oscillation frequency of the local oscillator 16 to search for displacement, thereby obtaining the relationship (difference) between the frequency of the 1st IF signal and the oscillation frequency of the local oscillator 16. (Hereinafter referred to as f0 pull-in), and the mixer 15 can supply the FM demodulator 18 with a 2nd IF signal without any deviation of the corresponding channel.

However, as shown in FIG. 2A, the carrier frequency f0 of the first IF signal is + f0 or -f0, which is apart from ± 6 MHz of the carrier frequency search range.
If it exists at the position of, f0 cannot be pulled in.
Despite the presence of broadcast channels, satisfactory reproduction of baseband television signals will not be achieved.

In such a case, the offset data is read out to shift the AFT search range. However, the AFT control is executed naturally on the channel where the broadcast signal does not exist, because the AFT cannot be pulled in. Since this is meaningless, it is necessary to determine whether or not a broadcast signal exists when setting the offset data. In the present invention, it is determined whether or not a broadcast signal exists in a channel based on the presence or absence of a frame synchronization signal included in a bit stream signal from the PCM decoder 27 for reproducing an audio signal.

That is, the AFT cannot be pulled in,
Even if the carrier frequency of the first IF signal is shifted,
If the broadcast signal is present, the 2ndI
It is possible to demodulate the F signal as a television signal by the FM demodulator 18, and an audio subcarrier component is derived from the output of the high-pass filter 25. The PCM decoder 27 detects a frame pattern from the bit stream demodulated by the QPSK demodulator 26 and captures frame synchronization even if the C / N of the input signal is low and the number of bit errors is large. The operation is performed so that the error correction is performed more reliably while maintaining the stability. Therefore, the presence of the broadcast signal can be confirmed by using the frame synchronization signal.

Then, the frame processing signal of the bit stream detected by the PCM decoder 27 is taken into the input processing unit 30 of the microcomputer 29 to notify the presence / absence of the broadcast signal, and whether the AFT is pulled in by the output of the comparison unit 36. If the AFT is not performed despite the presence of the broadcast signal,
The offset data is read from the offset data storage unit 32 to shift the AFT pull-in range.

The offset data is set to such a value that the AFT search is performed in the same frequency range in the upper and lower frequency bands of the AFT search range in the channel selection operation based on the initial value data. As a result, AFT control having a pull-in range approximately three times as large as that of the related art is performed.

That is, FIG. 2A shows the AFT pull-in range in the channel selection operation based on the initial value data, with 6 MHz on the plus side and minus side with respect to the standard carrier frequency f0 of the first IF signal. The range is 6 MHz. FIG. 2B shows an AFT pull-in range based on offset data such that a search range of ± 6 MHz with a center frequency of −f0 shifted by 12 MHz to the minus side with respect to the carrier frequency f0 of FIG. FIG.
In (c), the carrier frequency f0 has 12
An AFT pull-in range based on offset data is shown such that a search range of ± 6 MHz with a center frequency of + f0 shifted by MHz.

In the state where the offset data shown in FIG. 2 is stored in the offset data storage unit 32, when a tuning request signal is input to the tuning microcomputer 29,
The channel selection operation is performed based on the initial value data, and the AFT control is also performed. At this time, whether or not the AFT has been pulled is determined by the output of the comparator 36. Comparator 36
The signal shown in FIG. 5B is supplied from the A / D converter 35 to the comparator 36, and the comparator 36 sets the plus side output and the minus side output to a high (Hi) state or a low (Lo) state. The data is compared with reference data and output. When both the plus side and the minus side are in the high (Hi) state, it is determined that the AFT has been pulled in. If both are not high (Hi) despite the AFT control being performed, it is determined that the pull-in is impossible, and the offset data is read from the offset data storage unit 32 to shift the AFT search range. That is, the plus side is high (Hi).
When the minus side is low (Lo), it is considered that the shift is out of the pull-in range in the high frequency direction, and the corresponding offset data is read out and output so that the AFT control is performed in the frequency range shown in FIG. It is supplied to the processing unit 33. As a result, the center of the oscillation frequency of the local oscillator 16 is lowered to -f0, and AFT control is performed within a frequency range of ± 6 MHz therefrom. (In this embodiment, the oscillation frequency of the local oscillator 16 is equal to the 1st IF signal. The carrier frequency is set higher than the carrier frequency (see Table 2 below), and the minus side is high (Hi) and the plus side is low (L).
In the case of o), the corresponding offset data is read out and supplied to the output processing unit 33 so that the AFT control is performed in the frequency range shown in FIG. Table 1 shows the relationship between the output of the comparator 36 and the offset data.

[0042]

[Table 1] Note that, as shown in FIG. 2 (d, e), the reference carrier frequency f
0 and the upper AFT pull-in range of the center carrier frequency −f0 are set so as to overlap by the frequency f1, and the upper AFT pull-in range of the reference carrier frequency f0 and the lower AFT of the center carrier frequency + f0. If the pull-in range is set to overlap by the frequency f1, any one of the upper and lower positions of the AFT pull-in range of the reference carrier frequency f0, or the lower limit of the center carrier frequency + f0 and -f
Even when the carrier frequency exists at the boundary of the upper limit of 0, the AFT pull-in can be sufficiently performed.

When the AFT cannot be pulled in the AFT pull-in range of the center carrier frequencies + f0 and -f0, the frame synchronization of the bit stream from the PCM decoder 27 supplied to the input processing unit 30 of the tuning microcomputer 29 is performed. After confirming the signal, the control unit 34
AFT control based on the initial value data and the offset data is repeatedly performed until the AFT control is completed.

In this way, in response to the AFT shift signal from the error amplifier 21 of the FM demodulator 18, the tuning microcomputer 29 uses the AFT pull-in data corresponding to the position where the carrier frequency f0 exists, and The oscillation frequency of the local oscillator 16 of the tuner 13 is sequentially shifted so that the signal of the broadcast channel requested to be tuned is always best received and reproduced.

As the AFT control, in addition to the control for pulling in the channel at the time of the channel switching as described above, once the pull-in is performed, the fluctuation of the carrier frequency of the 2nd IF signal is monitored, and the optimum tuning state is always maintained. It also has a control function for holding. The channel pull-in control requires a quick response, but the control in the normal state (just AFT) requires a minute response. For this reason, in the channel pull-in control, the data for the AFT control given to the prescaler 17 is set to, for example, 62.5 KHz in one step and is updated in two steps, and is updated in one step unit in a normal state. By doing so, the pull-in time when switching channels is reduced.

Next, the tuning microcomputer 29
Will be described with reference to the processing flowchart of FIG.

When a tuning request signal of a request channel is input to the tuning microcomputer 29, it is converted into tuning request data in S1, and initial value data (reference carrier frequency f0) corresponding to the tuning request data is obtained. Read in S2,
In S3, the local oscillator 16 is obtained from the read initial data.
And the oscillation frequency is set to the standard carrier frequency f
Set to 0. Next, in step S4, a search for the standard carrier frequency f0 is performed. As a result, it is determined in step S5 whether or not f0 has been pulled in. If it is determined that f0 has been pulled in, in step S6, the presence or absence of a frame synchronization signal is determined. If the data for changing the initial value data is supplied to the prescaler 17 at that time, the AFT data is stored in the offset data storage unit 32 in S7, and the initial value data is corrected based on it in S8. If it is determined in S6 that there is no frame synchronization signal, the process returns to S2, and the steps up to that are executed again.

When it is determined in step S5 that f0 has not been pulled in, it is determined whether the carrier frequency of the second IF signal is shifted in a high direction or a low direction.
If it is shifted to the higher side, -f0 offset data is read from the offset data storage unit 32 in S12,
In step S13, the oscillation frequency of the local oscillator 16 is shifted to -f0 to perform an AFT search. In step S14, it is determined whether or not the pull-in is performed. It is determined whether or not there is a synchronization signal.
Steps S2 to S15 are executed, and if no, the process returns to S2. Also,
If it is shifted to the lower side, + f0 offset data is read out in S16, and the oscillation frequency of the local oscillator 16 is set to +
f0, and AFT search is performed.
Steps S18 and S19 similar to steps S4 and S15 are executed. Note that there is a step of performing an AFT search between S13 and S14 and between S17 and S18, respectively, as in S4, but is omitted here.

After the pull-in has been performed, at S21,
A normal AFT control operation, that is, an operation (just AF) of always monitoring and controlling whether or not a deviation occurs in the carrier frequency of the second IF signal is executed. In this normal AFT operation, it is determined in S22 whether or not the AFT pull-in has been released.
It is determined whether or not a frame synchronization signal has been detected in S23.
When the pull-in is released or the frame synchronization signal is not detected anymore, the process returns to S2 and starts again from the above-described steps for the pull-in. Note that the initial value data when returning to S2 is data corrected in S8.

The channel selection microcomputer 29
As the AFT pull-in range data stored in the offset data storage unit 32, data as shown in Table 2 is stored.

[0051]

[Table 2] However, the data in Table 2 is H for controlling the local oscillator 16.
62.5K per step (bit) with EX data
It is hexadecimal data when changing the local transmission frequency in Hz.

As described above, according to the present invention, the search range of the digital AFT is provided with an offset point with respect to the reference carrier frequency f0, and the AFT pull-in search range data including three different center carrier frequencies is used for the AFT search.
The FT pull-in frequency can be expanded, and an automatic frequency tuning apparatus can be provided which can reliably capture the BS signal even if a weak input signal received by the antenna and a deviation occurs in the first IF signal.

[0053]

As described above, according to the present invention, an AFT pull-in frequency range corresponding to a frequency shifted from the standard carrier frequency by a predetermined value is set above and below the AFT pull-in frequency range corresponding to a predetermined standard carrier frequency. However, when the pull-in operation is not performed in the AFT pull-in operation corresponding to the standard carrier frequency, by shifting the pull-in frequency range, the AFT pull-in range can be expanded as a result. The deviation of the IF frequency of the received BS television signal due to the poor performance of the BS antenna itself can be tracked and corrected over a wide range, and the desired broadcast channel can be reliably received satisfactorily.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of an automatic frequency tuning device for a satellite broadcast tuner according to the present invention.

FIG. 2 is a frequency range diagram showing a carrier frequency search range for explaining the operation of the present invention.

FIG. 3 is a flowchart illustrating an operation processing procedure of a channel selection microcomputer constituting the present invention.

FIG. 4 is a block diagram showing a circuit configuration of a conventional automatic frequency tuning device for a satellite broadcast tuner.

FIG. 5 is a waveform chart for automatic frequency tuning illustrating a conventional problem.

[Explanation of symbols]

11 ... BS antenna, 12BS converter, 13BS tuner, 14IF amplifier, 15 mixer, 16 local oscillator, 17 prescaler, 18PLL FM demodulator, 1
9 phase comparator, 20 low-pass filter, 21 error amplifier, 22 voltage generator, 23 low-pass filter, 24 de-emphasis / dispar, 25 high-pass filter,
26 QPSK demodulator, 27 PCM decoder, 28 digital / analog converter, 29 channel selection microcomputer, 30 input processing unit, 31 initial value data storage unit, 32 offset data storage unit, 33 output processing unit, 34 control unit, 35 analog A digital conversion unit, a 36 comparison unit;

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Noriyuki Miyazaki 3-3-9, Shimbashi, Minato-ku, Tokyo Inside Toshiba AV EE Co., Ltd.

Claims (7)

[Claims] 1. A satellite broadcast signal is received, and a second channel of a desired channel is received from a first IF signal generated by a BS converter.
And a BS tuner having at least a local oscillator and a mixer, which generates an IF signal of the following. An AFT signal indicating a deviation of a carrier frequency of the second IF signal is generated from the second IF signal generated by the BS tuner. A frequency detection unit, having a predetermined frequency pull-in control range, controlling the oscillation frequency of the local oscillator based on the AFT signal from the frequency detection unit, and setting the carrier frequency of the second IF signal to a predetermined value AFT control means for automatically controlling as described above, and the AFT signal from the frequency detection means,
Determination means for determining that the carrier frequency of the IF signal has shifted to a state where it cannot be controlled by the AFT control means; and data for shifting the oscillation frequency of the local oscillator by a predetermined value are stored in advance. Offset data storage means, and offset means for reading the offset data from the storage means and shifting the oscillation frequency of the local oscillator according to the result of the determination by the determination means, and a satellite broadcast tuner characterized by comprising: Automatic frequency tuning device. 2. A BS tuner having at least a local oscillator and a mixer for receiving a satellite broadcast television signal and generating a second IF signal of a desired channel from the first IF signal generated by the BS converter. An FM demodulator for generating an AFT pull-in signal indicating a difference between a baseband television signal and a carrier frequency of the second IF signal from the second IF signal generated by the BS tuner, and a desired channel selection control by a channel selection request signal An input signal processing unit for generating a signal, and an AFT from the FM demodulator
An AFT signal processing unit for processing a pull-in signal, a data storage unit storing local oscillation frequency data and AFT pull-in search data for each channel in the satellite broadcast television signal, and data read from the data storage unit An output signal processing unit that outputs a control signal to a local oscillator of the BS tuner, and the input signal processing unit;
A tuning microcomputer having a control unit for controlling data transfer between the AFT signal processing unit, the data storage unit, and the output signal processing unit, wherein each channel is stored in the data storage unit of the tuning microcomputer. First AFT search data having a predetermined AFT pull-in range centered on each standard carrier frequency, and a predetermined centered on a carrier frequency different from the standard carrier frequency on the plus and minus sides of the first AFT search data. And third having the AFT pull-in range of
AFT search data of the first to third AFs according to the AFT pull-in signal from the FM demodulator.
An automatic frequency tuning apparatus for a satellite broadcast tuner, wherein an oscillation frequency of a local oscillator of the BS tuner is displaced by continuously using T search data. 3. The method according to claim 1, wherein the first AFT search is performed when a carrier frequency of a desired channel is searched using the first to third AFT search data in accordance with an AFT pull-in signal from the FM demodulator. The search is performed from the reference carrier frequency of the data to the plus side, and when the search reaches the plus limit, the carrier frequency search is performed with the second AFT search data, and the search is performed on the minus side from the reference carrier frequency of the first AFT search data. 3. The automatic frequency tuning apparatus for a satellite broadcast tuner according to claim 2, wherein a carrier frequency search is performed with the third AFT search data when the search reaches the lower limit. 4. An upper limit of a pull-in range of the first AFT search data, a lower limit of a pull-in range of the second AFT search data, a lower limit of a pull-in range of the first AFT search data, and a third AFT. 3. The automatic frequency tuning apparatus for a satellite broadcast tuner according to claim 2, wherein the upper limit of the search data pull-in range is overlapped. 5. An input signal processing unit of the channel selection microcomputer which detects a frame synchronization signal of a bit stream of an audio signal in a baseband television signal demodulated by the FM demodulator and detects the detected frame synchronization signal. Means for supplying a frame synchronization signal of a bit stream of an audio signal in the baseband television signal during a search for a carrier frequency of a desired channel signal in the pull-in range of the second or third AFT search data. 3. The satellite broadcast tuner according to claim 2, wherein, upon detection, the carrier frequency search is continuously performed within the same pull-in range of the second or third AFT search data from the tuning microcomputer. Automatic frequency tuning device. 6. When a carrier frequency of a signal of a desired broadcast channel is tuned in any one of the pull-in ranges of the first, second or third AFT search data, the tuning frequency is changed to the first AFT frequency. 3. The automatic frequency tuning apparatus according to claim 2, wherein the search data is offset. 7. A method for detecting the presence of a frame synchronization signal in a bit stream of an audio signal in synchronization with a carrier frequency of a desired broadcast channel in any one of the pull-in ranges of the first, second or third AFT search data. 7. The automatic frequency tuning device for a satellite broadcast tuner according to claim 2, wherein a tuning frequency with the carrier frequency is stored in a storage unit of the tuning microcomputer when the confirmation is made.