JP2924198B2 - CS broadcast receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for distribution and broadcasting of television signals by a communication satellite and audio PCM broadcasting.

[0002]

2. Description of the Related Art In recent years, services using communication satellites (CS) are expanding, and satellite television receivers used for purposes such as satellite-based video distribution and television broadcast reception are shown in FIG. Configuration. In FIG. 3, reference numeral 40 denotes an input terminal for the first intermediate frequency signal. To this terminal 40, a first intermediate frequency signal which is converted into a frequency of 1GHz by a 12GHz band radio wave from a satellite received by an antenna by a down converter and guided indoors by a coaxial cable is applied. 41 is a first intermediate frequency amplifier circuit, 12 is an image filter, 13 is a frequency converter, 30 is a local oscillator, 31 is a PLL frequency control circuit, 14 is a band pass filter,
5 is an FM demodulator, 33 is an AFC detection circuit, 32 is an AFC
A microcomputer circuit for controlling the QPS 16 is a QPS
A K demodulation circuit, 17 is an audio signal processing circuit, 18 and 19 are audio signal output terminals, 20 is a video signal processing circuit, and 21 is a video signal output terminal.

A first intermediate frequency amplifier circuit 41, an image filter 12, a frequency converter 13, a local oscillator 30, a PLL
The frequency control circuit 31 forms a tuning circuit. The FM signal in the 1 GHz band is converted to the second intermediate frequency by the tuning circuit. At this time, the first intermediate frequency amplifying circuit 41
Is a low NF broadband amplifier for preventing the subsequent stage NF from affecting the input terminal. The image filter 12 is a filter for preventing image interference, and is for removing a component of an image frequency which is a sum of twice the first intermediate frequency and the second intermediate frequency. The frequency converter 13, the local oscillator 30, and the PLL frequency control circuit 31 constitute a frequency conversion circuit with high frequency accuracy using a frequency synthesizer method. The tuning circuit has a function of tuning from a number of first intermediate frequency signals and receiving one channel. The second intermediate frequency that is obtained by tuning is, in recent years, due to advances in IC technology and ease of image processing,
The 400 MHz band has been adopted. Numeral 14 denotes a channel filter, which is a band pass filter for passing only one wave, and a SAW filter or the like is generally used. Numeral 15 demodulates the FM signal selected by the FM demodulator to obtain a detection output signal. Reference numeral 20 denotes a video signal processing circuit that performs processing such as de-emphasis on the demodulated detection output signal, and outputs a 1Vp-p video signal to a video signal output terminal 21. 16 is a QPSK demodulator 5.7M
It plays a role of demodulating a QPSK-modulated audio signal on a subcarrier of Hz and extracting I and Q baseband signals orthogonal to each other. The I and Q baseband signals are converted into PCM-coded digital signals by differential conversion. The audio signal processing circuit 17 receives the separated digital signal for one channel and performs PCM demodulation processing such as interleaving, range bits, and control signals. The D / A converter converts the digital signal into an analog signal, and outputs the audio baseband signals (R, L) to the output terminals 18 and 19 via the LPF.

[0004] The AFC detection circuit 33 is a detection circuit for setting the second intermediate frequency to a predetermined frequency. A
The FC detection circuit 33 provides an output signal to the microcomputer 32 when the second intermediate frequency has a frequency deviation of about ± 200 kHz from its center frequency. Using this signal, the microcomputer 32 controls the frequency synthesizer circuit to set the second intermediate frequency to a predetermined frequency.
The demodulation characteristics of the FM demodulator 15 hardly change even when a frequency shift of about ± 400 kHz occurs. Therefore, the frequency converter 13, the local oscillator 30, the PLL frequency control circuit 3
Generally, the frequency step of the frequency synthesizer composed of 1 is set to about 200 kHz.

On the other hand, audio PCM broadcasting is about to start service using CS. This system occupies a band (27 MHz) for one transponder, which is usually used for transmitting a television signal including video and audio for one channel, and has a high quality PCM audio equivalent to satellite broadcasting (BS). Are digitally multiplexed and transmitted. In this system, it is planned to transmit a digitally multiplexed PCM audio signal after performing MSK modulation in consideration of input / output nonlinear characteristics of a transponder of a communication satellite. An audio PCM broadcast receiver for receiving this is configured with a block diagram as shown in FIG. (Reference: "Multi-channel PCM audio satellite broadcasting" NHK Giken R & D, published February 15, 1990 by Kameda and Kawai) In FIG. 4, reference numeral 40 denotes an IF input terminal of an audio PCM broadcast receiver. To this terminal 40, a first intermediate frequency signal which is converted into a frequency of 1GHz by a 12GHz band radio wave from a satellite received by an antenna by a down converter and guided indoors by a coaxial cable is applied. 41 is a first intermediate frequency amplifier circuit, 42 is an image filter, 43 is a frequency converter, 50 is a local oscillator, 51 is a PLL frequency control circuit, 52 is a microcomputer circuit for controlling AFC, 53 is an AFC detection circuit, 44 Is a bandpass filter, 45 is an MSK demodulator, 46 is a high-order multiplex decoder, 47 is an audio signal processing circuit, and 48 and 49 are audio output signal terminals.

A first intermediate frequency amplifier circuit 41, an image filter 42, a frequency converter 43, a local oscillator 50, a PLL
A frequency selection circuit is configured by the frequency control circuit 51. The 1 GHz band MSK signal is converted to the second intermediate frequency by the tuning circuit. At this time, the first intermediate frequency amplifying circuit 41
Is a low NF broadband amplifier for preventing the subsequent stage NF from affecting the input terminal. The image filter 42 is a filter for preventing image interference, and is for removing a component of an image frequency which is a sum of twice the first intermediate frequency and the second intermediate frequency. The frequency converter 43, the local oscillator 50, and the PLL frequency control circuit 51 constitute a high-accuracy frequency conversion circuit using a frequency synthesizer method. Image filter 42
When the second intermediate frequency is selected in the 140 MHz band, since the image frequency falls within the band of the first intermediate frequency, it is necessary to change the image frequency following the first intermediate frequency signal to be selected. This is called frequency tracking of the image filter, and it is important that the frequencies are accurately matched and that the frequency characteristics do not change.

The band-pass filter 44 is a filter for extracting only the MSK signal and removing noise and signals of other channels. Generally, a filter having a Gaussian characteristic having excellent phase group delay characteristics is employed. This filter plays an important role in determining the demodulation characteristics of the receiver, and a surface acoustic wave bandpass filter (SAW BPF) is suitable in consideration of the stability of the frequency characteristics and the phase group delay characteristics.

[0008] The MSK demodulator 45 has I,
It plays the role of extracting the Q baseband signal. The demodulation stage of the MSK demodulation divides the reproduced carrier signal into two components, in-phase and quadrature, and synchronously detects the input signal with each component. Signal distribution and synchronous detection are performed at the second intermediate frequency. The 140 MHz band is suitable as the frequency in consideration of the phase stability of the signal distributor and the like.

The high-order multiplex decoder 46 receives the baseband signal and separates the MSK-demodulated digitally multiplexed audio signals for the six channels into respective channels. It performs the function of correcting the accompanying bit error. Audio signal processing circuit 4
Reference numeral 7 inputs the separated digital signals of one channel, and performs processing of interleaving, range bits, and control signals as PCM decoding processing. The digital signal is converted into an analog signal by a D / A converter, and the LPF is converted.
And outputs the audio baseband signals (R, L) to the output terminals 48 and 49 via.

The AFC detection circuit 53 is a detection circuit for setting the second intermediate frequency to a predetermined frequency. M
The SK demodulator 45 has a large deterioration in demodulation characteristics due to a frequency shift. Therefore, the frequency deviation of the second intermediate frequency is ± 10
It is necessary to set the frequency to 0 kHz or less. Therefore, the frequency step of the frequency synthesizer including the frequency converter 43, the local oscillator 50, and the PLL frequency control circuit 51 is 30
It should be set to about kHz. AFC detection circuit 53
Is a microcomputer 5 when the second intermediate frequency has a frequency deviation of about ± 20 kHz from its center frequency.
2 to give an output signal. Using this signal, the microcomputer 52 controls the frequency synthesizer circuit to set the second intermediate frequency to a predetermined frequency.

[0011]

As described above, the voice P
Since both the CM broadcast receiver and the satellite television receiver are terminals of a system for transmitting data using satellites, a receiver that can be integrated and enjoy both media can be considered. At this time, there is a problem that the second intermediate frequency and the frequency step of the frequency synthesizer are different.

The present invention has been made in view of the above problems, and has as its object to share an audio PCM broadcast receiver and a satellite television receiver.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a CS broadcast receiver according to the present invention selects a first intermediate frequency signal obtained by receiving a radio wave from a satellite and frequency-converting the same as an input signal. Circuit, a first band-pass filter that receives an output signal of the tuning circuit as an input, and passes only a desired FM signal, an FM demodulator that receives an output signal of the first band-pass filter as an input, and an FM demodulator. A video signal processing circuit that inputs a detection output signal and outputs a video signal, and a QP that inputs a detection output signal of an FM demodulator and demodulates an audio subcarrier
Inputting the output signals of the SK demodulator and the QPSK demodulator,
A first audio signal processing circuit that decodes the CM-encoded audio signal to obtain an audio signal, a second bandpass filter that receives an output signal of the channel selection circuit as an input, and passes only a desired MSK signal, A frequency conversion circuit that receives an output signal of the second bandpass filter, an MSK demodulator that receives an output signal of the frequency conversion circuit, and a high-order multiplexing that receives an output signal of the MSK demodulator and selects one channel A decoder, a second audio signal processing circuit that receives an output signal of the higher-order multiplex decoder and decodes a PCM-encoded audio signal to obtain an audio signal, and an output signal of a frequency conversion circuit. An AFC detection circuit for detecting a frequency shift, a circuit for receiving an output signal thereof, and controlling an oscillation frequency of a first local oscillator included in a channel selection circuit and a second local oscillator included in a frequency conversion circuit; It is those having the frequency step of the oscillation frequency of the first local oscillator approximately 200kHz
The frequency step of the oscillation frequency of the second local oscillator is set to about 30 kHz, and the variation width of the oscillation frequency of the second local oscillator is set to be equal to or less than the frequency step of the oscillation frequency of the first local oscillator.

[0014]

According to the present invention, a desired channel is selected by the channel selection circuit from the input first intermediate frequency signals from the satellite and the second intermediate frequency signal is obtained. After the TV signal and the FM signal by the audio subcarrier are tuned, they pass through a first band-pass filter, and are guided to an FM demodulator after removing noise and the like. The FM signal selected by the FM demodulator is demodulated to obtain a detection output signal.
Upon input of this signal, the video signal processing circuit performs processing such as de-emphasis to obtain a video signal. The detection output signal is also input to the QPSK demodulator, where the audio subcarrier is demodulated to obtain I and Q baseband signals orthogonal to each other. The I and Q baseband signals are differentially converted to 1
A PCM encoded audio digital signal for the channel is obtained. This audio digital signal is guided to an audio signal processing circuit, and the audio signal subjected to PCM encoding is decoded to obtain an audio baseband signal.

Since the frequency accuracy of the second intermediate frequency inputted to the FM demodulator is about 300 kHz is sufficient, the frequency step of the oscillation frequency of the first local oscillator included in the channel selection circuit is set to about 200 kHz.

The MSK signal of the PCM audio broadcast passes through a second band-pass filter to remove noise and the like, and is input to a frequency conversion circuit. The output signal is input to the MSK demodulator and subjected to MSK demodulation. The mutually orthogonal I and Q baseband signals output from the MSK demodulator are guided to a high-order multiplex decoder. The high-order multiplex decoder has functions of separating digitally multiplexed audio signals of six channels into respective channels and correcting bit errors due to deterioration of the transmission system. The separated audio digital signal for one channel is guided to an audio signal processing circuit,
The encoded audio signal is decoded to obtain an audio baseband signal.

Since the frequency shift of the third intermediate frequency input to the MSK demodulator needs to be 100 kHz or less, the frequency step of the oscillation frequency of the second local oscillator is set to about 30 kHz. The frequency deviation of the third intermediate frequency is detected by the AFC detection circuit, and the microcomputer circuit controls the frequencies of the first and second local oscillators in conjunction with each other. At this time, the change width of the frequency of the second local oscillator is limited to a frequency step of the first local oscillator or less. Even under this condition, the third intermediate frequency can be continuously changed at a frequency step of about 30 kHz with respect to the deviation of the first intermediate frequency. Further, when the third intermediate frequency is pulled to its center frequency by the AFC operation, the frequency shift of the second intermediate frequency is at most 100
kHz. With such a frequency shift, deterioration of the demodulation characteristics due to the first and second bandpass filters hardly occurs.

In this manner, the satellite television receiver and the PC
The channel selection circuit and the AFC circuit can be shared with the M audio broadcast receiver.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a CS broadcast receiver according to one embodiment of the present invention. In FIG. 1, reference numeral 40 denotes an input terminal of a first intermediate frequency signal, 41 denotes a first intermediate frequency amplifier circuit, 12 denotes an image filter, 13 denotes a first frequency converter, 30 denotes a first local oscillator, and 31 denotes a first local oscillator. PLL frequency control circuit, 14 is a first band-pass filter, 15 is an FM demodulator, 33 is an AFC detection circuit, 16 is a QPSK demodulation circuit, 17 is a first audio signal processing circuit, and 18 and 19 are audio signal outputs. Terminal, 20 is a video signal processing circuit, 21 is a video signal output terminal, 44 is a second band pass filter, 6
4 is a second frequency converter, 60 is a second local oscillator, 6
1 is a second PLL frequency control circuit, 62 is a microcomputer circuit for controlling AFC, 63 is an AFC detection circuit, 45 is an MSK demodulator, 46 is a high-order multiplex decoder, 47
Is a second audio signal processing circuit, and 48 and 49 are audio output signal terminals.

The operation of the above configuration will be described below. The input terminal 40 is applied with a first intermediate frequency signal which is converted from a 12 GHz band radio wave from a satellite received by an antenna to a 1 GHz band by a down converter and guided indoors by a coaxial cable. The first intermediate frequency signal that has received video distribution or television broadcast using a satellite is guided to an input terminal 40. The first intermediate frequency amplifying circuit 41, the image filter 12, the first frequency converter 13, the first local oscillator 30, and the first PLL frequency control circuit 31 constitute a tuning circuit 70. The channel selection circuit 70 has a function of selecting one of the first intermediate frequency signals and receiving one channel, and has a function of 402.7.
A second intermediate frequency signal having a center frequency of 8 MHz is generated. At this time, the first intermediate frequency amplifying circuit 41
Are low-NF broadband amplifiers that do not affect the input terminal. The image filter 12 is a filter for preventing image interference, and is for removing a component of an image frequency which is a sum of twice the first intermediate frequency and the second intermediate frequency. When selecting the second intermediate frequency in the 400 MHz band, since the image frequency does not fall within the band of the first intermediate frequency, the image filter 12 needs to change the image frequency following the first intermediate frequency signal to be selected. There is no. The first frequency converter 13, the first local oscillator 30, and the first PLL frequency control circuit 31 constitute a frequency conversion circuit with high frequency accuracy using a frequency synthesizer method. The demodulation characteristics of the FM demodulator 15 hardly change even when a frequency shift of about ± 400 kHz occurs. Therefore, the frequency step of the frequency synthesizer may be set to about 200 kHz.

Reference numeral 14 denotes a band-pass filter for passing only one wave of a television signal FM-modulated by a channel filter, and a SAW filter or the like is generally used. 15 demodulates the FM signal selected by the FM demodulator,
Obtain the detection output signal. Reference numeral 20 denotes a video signal processing circuit that performs processing such as de-emphasis on the demodulated detection output signal, and outputs a 1Vp-p video signal to a video signal output terminal 21. 16 is a QPSK demodulator, 5.7 MHz
And demodulates a QPSK-modulated audio signal on the sub-carriers and extracts the I and Q baseband signals orthogonal to each other. The I and Q baseband signals are converted into PCM-coded digital signals by differential conversion. The digital signal for one channel is guided to the first audio signal processing circuit 17. The audio signal processing circuit 17 outputs audio baseband signals (R, L) to output terminals 18 and 19.

On the other hand, the 1 GHz band MSK signal is converted by the tuning circuit 70 into a second intermediate frequency in the 400 MHz band. The second band-pass filter 44 is a channel filter for extracting only the MSK signal and removing noise and signals of other channels. Generally, a filter having a Gaussian characteristic having excellent phase group delay characteristics is employed. A second frequency converter 64, a second local oscillator 60, a second P
The second intermediate frequency signal of the 400 MHz band is converted to 14 by the frequency conversion circuit composed of the LL frequency control circuit 61.
It is converted to a third intermediate frequency signal in the 0 MHz band. Also here, a frequency conversion circuit with high frequency accuracy based on the frequency synthesizer method is configured. Set the bandpass filter 44 to 1
The reason why the frequency band is set in the 400 MHz band instead of the 40 MHz band is that cross-modulation does not occur by extracting only the MSK signal from many CS IF signals. Thereby, the intercept point of the second frequency converter 64 and the like can be lowered.

The AFC detection circuit 63 is a detection circuit for setting the third intermediate frequency to a predetermined frequency. M
The SK demodulator 45 has a large deterioration in demodulation characteristics due to a frequency shift. Therefore, the frequency deviation of the third intermediate frequency is ± 10
It is necessary to set the frequency to 0 kHz or less. For this reason, the frequency step of the frequency synthesizer including the second frequency converter 64, the second local oscillator 60, and the second PLL frequency control circuit 61 is set to about 30 kHz. The AFC detection circuit 63 determines that the third intermediate frequency is within ± 20 of its center frequency.
An output signal is supplied to the microcomputer 62 when a frequency shift of about kHz occurs. Using this signal, the microcomputer 62 controls the frequency synthesizer circuit to set the third intermediate frequency to a predetermined frequency. At this time, since the band pass filter 44 exists in the second intermediate frequency band,
It is desirable that the second intermediate frequency does not change from a predetermined center frequency. For this reason, the frequency change width of the second local oscillator 60 is preferably selected to be about the frequency step of the frequency synthesizer of the tuning circuit.

FIG. 2 shows a state when the AFC operation is performed under such conditions. In FIG. 2, the frequency steps by the frequency synthesizer are 200 kHz and 25 kHz by the first local oscillator 30 and the second local oscillator 60, respectively.
The frequency of the first intermediate frequency signal was set to 1400 MHz. The numbers shown in the figure indicate the order in which the frequencies of the local oscillators 30 and 60 are set by the frequency synthesizer. At the same time, changes in the second and third intermediate frequencies are shown. First, the number 1 indicates an initial state. At this time, since a signal indicating that the third intermediate frequency is high is output from the AFC detection circuit 63, the frequency of the second local oscillator 60 is reduced in 25 kHz steps. As a result, the frequency of the third intermediate frequency decreases to 1, 2, 3, and 4 as indicated by the numbers. Next number 5
Then, the frequencies of the first and second local oscillators 30 and 60 are simultaneously changed to lower the third intermediate frequency. After the number 6, the third intermediate frequency is lowered by changing only the frequency of the second local oscillator 60. Thus, the third intermediate frequency approaches the predetermined center frequency. When the frequency of the first intermediate frequency signal is shifted low, the reverse operation can be performed using a frequency synthesizer.

When the operation of pulling in the frequency of the AFC is completed as described above, the third intermediate frequency is at most ± 20 kHz from the predetermined center frequency. Since the frequency of the second local oscillator 60 changes only by 180 kHz,
The frequency deviation at the completion of the AFC operation of the second intermediate frequency is
It is at most about ± 100 kHz. With such a frequency shift, the demodulation characteristics of the band-pass filters 14 and 44 are hardly affected.

The MSK demodulator 45 has an M of 140 MHz band.
It plays the role of inputting an SK signal and extracting I and Q baseband signals that are orthogonal to each other. The high-order multiplexing decoder 46 receives the baseband signal and separates the MSK-demodulated digitally multiplexed audio signals for the six channels into respective channels. Performs the function of correcting The digital signal output from the high-order multiplex decoder 46 is guided to an audio signal processing circuit 47. The audio signal processing circuit 47 performs PCM decoding processing such as interleaving, range bit processing, and control signal processing. The digital signal is converted into an analog signal by a D / A converter, and the audio baseband signal (R, L) is converted via an LPF.
To the output terminals 48 and 49.

The range bit format of the PCM-coded audio digital signal is slightly different between the audio PCM broadcast signal and the satellite television signal. That is, the range bits are transmitted from 0 to 7 in the audio PCM broadcast signal, but from 0 to 4 in the satellite TV signal. However, the basic concept of the range bit method is the same, and both systems can be dealt with by processing as if they are transmitted from 0 to 7. In this way, the audio signal processing circuits 17 and 47 can be integrated.

In this embodiment, the description of the AGC system not directly related to the present invention is omitted.

[0029]

As described above, according to the present invention, a channel selecting circuit and an AF are provided between a satellite television receiver and an audio PCM broadcast receiver.
The C circuit can be shared.

[Brief description of the drawings]

FIG. 1 is a block diagram of a CS broadcast receiver according to an embodiment of the present invention.

FIG. 2 shows A of a CS broadcast receiver according to an embodiment of the present invention.
FC operation explanatory diagram

FIG. 3 is a block diagram of a satellite television receiver in a conventional example.

FIG. 4 is a block diagram of a conventional audio PCM broadcast receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Image filter 13 1st frequency converter 14 1st band pass filter 15 FM demodulator 16 QPSK demodulation circuit 17 1st audio signal processing circuit 18, 19 Audio signal output terminal 20 Video signal processing circuit 21 Video signal output terminal Reference Signs List 30 first local oscillator 31 first PLL frequency control circuit 33 AFC detection circuit 40 input terminal of first intermediate frequency signal 41 first intermediate frequency amplifier 44 second bandpass filter 45 MSK demodulator 46 high-order multiplex decoder 47 second audio signal processing circuit 48, 49 audio output signal terminal 60 second local oscillator 61 second PLL frequency control circuit 62 microcomputer circuit for controlling AFC 63 AFC detection circuit 64 second frequency converter 70 Tuning circuit

Continuation of the front page (56) References JP-A-4-242323 (JP, A) JP-A-4-53312 (JP, A) JP-A-4-29417 (JP, A) JP-A-1-133377 (JP) , A) Hikaru Hei 3-70433 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04B 1/16 H04B 7/15 H04N 5/60 H04N 7/20

Claims (1)

(57) [Claims] 1. A tuning circuit for receiving a radio wave from a satellite and frequency-converting the first intermediate frequency signal as an input signal, and an output signal of the tuning circuit as an input to pass only a desired FM signal. A first band-pass filter, an FM demodulator that receives an output signal of the first band-pass filter, a video signal processing circuit that receives a detection output signal of the FM demodulator, and outputs a video signal; QPSK demodulator for inputting a detection output signal of a demodulator and demodulating an audio subcarrier, and a first audio signal for receiving an output signal of the QPSK demodulator and decoding a PCM-coded audio signal to obtain an audio signal A processing circuit; a second band-pass filter that receives an output signal of the tuning circuit as an input and passes only a desired MSK signal; a frequency conversion circuit that receives an output signal of the second band-pass filter as an input; An MSK demodulator for inputting an output signal of the number conversion circuit, a high-order multiplex decoder for inputting an output signal of the MSK demodulator and selecting one channel, and a PCM for inputting an output signal of the high-order multiplex decoder A second audio signal processing circuit that decodes the encoded audio signal to obtain an audio signal, an AFC detection circuit that receives an output signal of the frequency conversion circuit to detect a frequency shift, and inputs the output signal. A circuit for controlling the oscillation frequency of the first local oscillator included in the tuning circuit and the second local oscillator included in the frequency conversion circuit, the frequency step of the oscillation frequency of the first local oscillator is set to about 200 kHz, The frequency step of the oscillation frequency of the second local oscillator is approximately 30 kHz,
A CS broadcast receiver characterized in that the variation width of the oscillation frequency of the second local oscillator is set to be equal to or less than the frequency step of the oscillation frequency of the first local oscillator.