JP2809441B2 - Satellite receiver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite broadcast receiver for demodulating an FM signal of a video signal and an audio subcarrier signal and an audio-only subcarrier signal transmitted by satellite broadcasting. It is about.

2. Description of the Related Art In recent years, it has been desired that a satellite broadcast receiver incorporate a demodulator for video and various types of audio.

FIG. 2 shows a signal spectrum transmitted by satellite broadcasting. FIG. 2A shows the channel arrangement of the first intermediate frequency band, and FIG. 2B shows the channel arrangement of the first intermediate frequency band.
FIG. 2 (c) shows an arrangement of a video signal and an audio subcarrier signal which are FM-modulated to one channel of the first intermediate frequency.

FIG. 3 shows a block diagram of a conventional satellite broadcast receiver.
In FIG. 3, reference numeral 1 denotes a first intermediate frequency input terminal of a satellite broadcast, which is a frequency converter 2, a VHF band intermediate frequency band-pass filter 3, and a dedicated voice through a tuning type band-pass filter 8. The demodulators 4 are sequentially connected, and the demodulated audio-only signal is output from the audio demodulation output terminal 5. Reference numeral 6 denotes a voltage or current control oscillator connected to the frequency converter 2, and a tuning control signal generator 7 controls a band-pass filter 8 tuned to the voltage or current control oscillator 6 for tuning. I do.

On the other hand, the first intermediate frequency input terminal 1 for satellite broadcasting further includes a first frequency converter 9, a first intermediate frequency bandpass filter 10 in the UHF band, a second frequency converter 11, and a UHF band. 1
VH with a narrower passband than the intermediate frequency bandpass filter 10
F band second intermediate frequency band-pass filter 12, phase comparator 1
3. The DC amplifier / distributor 14 is sequentially connected, and the demodulated composite signal of the video signal and the audio signal is output from the demodulation output terminal 15. In addition, the first frequency converter 9 connected to the first frequency converter 9
The voltage or current control oscillator 16 is a control signal generator for channel selection.
The second voltage or current controlled oscillator 18 controlled by the second frequency converter 11 and controlled by the second frequency converter 11
Controlled by 14. The third voltage or current control oscillator 19 connected to the phase comparator 13 is a DC amplifier / distributor.
Controlled by the demodulated output output from 14.

The operation of the satellite broadcast receiver thus configured will be described below. The audio modulation dedicated signal of the satellite broadcast first intermediate frequency band input from the satellite broadcast first intermediate frequency input terminal 1 is a band controlled by a control signal corresponding to a desired station from a tuning control signal generator 7. The image frequency band of the desired signal is attenuated by the pass filter 8, and the frequency is converted to the second intermediate frequency of the VHF band in the frequency converter 2 by the local signal from the voltage or current control oscillator 6. . The second intermediate frequency signal is attenuated by the intermediate frequency band-pass filter 3 for undesired signals, input to the audio demodulator 4, and output to the audio demodulation output terminal 5.
Are demodulated and output.

On the other hand, the video signal of the first intermediate frequency band of the satellite broadcast and the FM signal of the audio subcarrier signal are also input from the first intermediate frequency input terminal 1 of the satellite broadcast, and correspond to the desired station from the channel selection control signal generator 17. The frequency is converted to a second intermediate frequency in the UHF band in the first frequency converter 9 by the first voltage converter 9 controlled by the control signal or the local oscillator signal from the current control oscillator 16. The second intermediate frequency signal is attenuated by a first intermediate frequency band-pass filter 10 for undesired signals, and is input to a second frequency converter 11. This second frequency converter 11 is frequency-converted to a third intermediate frequency in the VHF band by a signal from the second voltage or current control oscillator 18, and
The undesired signal is suppressed by the intermediate frequency band-pass filter 12 and input to the phase comparator 13. The phase comparator 13 compares the phase of the third intermediate frequency signal with the signal from the third voltage or current control oscillator 19, and outputs the phase difference signal to the DC amplifier / divider 14, where the DC difference is amplified. It becomes a control signal of the third voltage or current control oscillator 19 and a demodulation output signal at the same time. In addition, by the DC amplification and distribution unit 14,
A part of the phase difference signal is distributed and becomes a control signal for the second voltage or current control oscillator 18, and changes the oscillation frequency of the second voltage or current control oscillator 18. At this time, FM
Since the FM deviation of the third intermediate frequency is smaller than the FM deviation of the second intermediate frequency by selecting the polarity to change the frequency in the in-phase with respect to the modulation phase of the signal, the second intermediate frequency The pass bandwidth of the band pass filter 12 is narrower than the pass bandwidth of the first intermediate frequency band pass filter 10,
Further, the band characteristics of the FM demodulation systems 13, 14, and 19 can be narrowed, and the noise suppression capability outside the signal band is improved.

Problems to be Solved by the Invention However, in the above-described conventional configuration, since the dedicated signal for audio modulation and the FM signal of the video signal and the audio subcarrier signal must be demodulated by separate receiving circuits, the circuit configuration is complicated. Had the problem of becoming

An object of the present invention is to solve the above-mentioned conventional problems and to provide a satellite broadcast receiver capable of demodulating an FM signal of an audio modulation dedicated signal and a video signal and an audio subcarrier signal with a small circuit configuration. It is intended for.

Means for Solving the Problems To solve the above problems, a satellite broadcast receiver according to the present invention comprises: a first demodulation means including a phase comparator, a voltage or current control oscillator, and a phase locked demodulation circuit having a DC amplifier;
The frequency of an input signal in the UHF band is converted into an intermediate frequency signal in the VHF band as an input signal of the phase comparator by an oscillator signal whose oscillation frequency is controlled by the demodulated output.
M negative feedback loop, second demodulation means for selecting and demodulating a desired audio channel from VHF band intermediate frequency signals,
The divided signal of the oscillator output and the second
And a reference signal for tuning obtained from the demodulation means of
The FM negative feedback loop is selected as a phase-locked oscillation circuit loop, and VH as an input signal of the second demodulation means is used.
Means for obtaining an F-band intermediate frequency signal.

Operation According to the above configuration, since the image frequency band is outside the intermediate frequency band by performing frequency conversion from the first intermediate frequency of the satellite broadcasting to the VHF band via the UHF band, the conventional tuning type band that attenuates the image frequency band. The need for a pass filter is eliminated, and the first frequency converter including the tuning circuit can be shared.
Further, the second demodulation means needs to select a desired station of the voice. By performing this operation in the FM negative feedback loop of the first demodulation means, the second demodulation means can select the desired station. No circuit is required. Thus, the circuit configuration can be reduced, and a low-cost receiver can be realized.

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

FIG. 1 is a block diagram of a satellite broadcast receiver according to one embodiment of the present invention. In FIG. 1, reference numeral 21 denotes satellite broadcasting No. 1.
An intermediate frequency input terminal, a first frequency converter 22, a second intermediate frequency band-pass filter 23, a second frequency converter 24,
A third intermediate frequency band-pass filter 25 and an audio-only demodulator 26 are sequentially connected. Reference numeral 27 denotes a first voltage or current control oscillator connected to the first frequency converter 22, which is controlled by a tuning control signal generator. Reference numeral 29 denotes a second voltage or current control oscillator connected to the second frequency converter 24, which is controlled by the output from the distributor 30 via the DC amplifier 31. Reference numeral 32 denotes a phase comparator, which is switchably connected to a third intermediate frequency band-pass filter 25 and an audio-only demodulator 26 via an input switch 33, and has an output terminal connected to the distributor 30, Demodulation output terminal 35 via amplifier 34
It is connected to the. Further, the phase comparator 32 has a third input switch 36 interlocked with the input switch 33 for the third phase.
Is connected intermittently to the voltage or current control oscillator 37,
This third voltage or current controlled oscillator 37 is a DC amplifier 34
Is controlled by the demodulated output output from. Further, the phase comparator 32 is connected to a second voltage or current control oscillator 29 via a frequency divider 38, and the phase comparator 32 outputs a divided signal obtained by dividing the output of the second voltage or current control oscillator 29. The phase comparison with the signal obtained from the audio-only demodulator 26 is also performed.

The operation of the thus configured satellite broadcast receiver will be described below. Satellite broadcasting first intermediate frequency input terminal
The first intermediate frequency of the satellite broadcast input from 21 is a local oscillation signal corresponding to a desired channel generated from a first voltage or current control oscillator 27 controlled by a control signal from a channel selection control signal generator 28. Using the first frequency converter
At 22 the frequency is converted to a second intermediate frequency. Next, an undesired signal is attenuated by the second intermediate frequency band-pass filter 23,
The signal is input to the second frequency converter 24. If the desired channel is a composite FM signal of a video signal and an audio subcarrier signal, the input switch 33 is connected to the a side, and the input switch 36 is connected to the b side, and the second frequency conversion is performed. The third intermediate frequency output from the filter 24 is input to the phase comparator 32 via the third intermediate frequency band-pass filter 25 having a narrower pass bandwidth than the second intermediate frequency band-pass filter 23.
In the phase comparison 32, a phase difference signal between the third intermediate frequency and a signal from the third voltage or current control oscillator 37 is output to the distributor 30. This phase difference signal is distributed at an arbitrary ratio by the distributor 30 and output to the DC amplifiers 31 and 34. The output of the DC amplifier 34 becomes a demodulated output and the oscillation frequency of the third voltage or the oscillation frequency of the current control oscillator 37. It becomes a control signal. These 32,30,34,3
7 constitutes a phase synchronous demodulation circuit. Further, the output of the DC amplifier 31 becomes a control signal of the oscillation frequency of the second voltage or current control oscillator 39. At this time, the oscillation frequency of the second voltage or current control oscillator 29 is the second intermediate frequency.
Since the FM shift of the third intermediate frequency is selected to be in phase with the FM shift, an FM negative feedback loop is configured such that the FM shift of the third intermediate frequency is smaller than the FM shift of the second intermediate frequency.

Next, if the desired channel is a signal dedicated to audio modulation,
The input changeover switch 33 is connected to the b side, the input changeover switch 36 is connected to the a side, and the third intermediate frequency output from the second frequency converter 24 is applied to the third intermediate frequency bandpass filter 25. Is input to the audio-only demodulator 26 via the. The audio-only demodulator 26 outputs a distribution frequency signal having a frequency corresponding to a desired audio channel. The phase comparator 32 outputs a frequency-divided signal of the second voltage from the frequency divider 38 or the oscillation frequency of the current control oscillator 29. And a phase difference signal is generated. This phase difference signal becomes a control signal for the second voltage or current control oscillator 29 via the distributor 30 and the DC amplifier 31.
That is, it operates as a phase-locked channel selecting circuit, and makes the second frequency converter 24 output a frequency corresponding to channel selection of a desired audio channel from the second voltage or current control oscillator 29, thereby demodulating the audio only. A desired audio channel signal is input to the device 26, and a demodulated output is obtained.

As described above, according to the present invention, an oscillator whose oscillation frequency is controlled by the demodulation output of the first demodulation means comprising a phase comparator, a voltage or current control oscillator, and a phase locked demodulation circuit having a DC amplifier is provided. UHF band input signal to V
Construct an FM negative feedback loop for converting the frequency to an HF band intermediate frequency signal, and select and demodulate a desired audio channel from the frequency-divided signal from the oscillator and the VHF band intermediate frequency signal in the phase comparator. A reference signal for channel selection from the second demodulator is input, the FM negative feedback loop is operated as a phase-locked oscillation circuit loop, and an intermediate VHF band as an input signal of the second demodulation means is input. Due to the configuration in which the frequency signal is obtained, one of the composite signal of the video signal and the audio subcarrier signal and one of the audio only channels are selected.
Tuning can be performed by one tuning circuit, and by using the FM negative feedback loop of the first demodulating means for tuning a dedicated audio channel, an independent tuning circuit becomes unnecessary. Further, by using the first frequency converter to obtain the intermediate frequency of the VHF band for demodulating the audio-only channel via the intermediate frequency of the UHF band, the image frequency is attenuated as in the prior art. Since a tunable band-pass filter is not required, a very small circuit configuration can be achieved, and an excellent satellite broadcast receiver can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a satellite broadcast receiver in one embodiment of the present invention, FIG. 2 is a spectrum diagram of a satellite broadcast intermediate frequency band, and FIG. 3 is a block diagram of a conventional satellite broadcast receiver. 21 ... satellite broadcast first intermediate frequency input terminal, 22 ... first frequency converter, 23 ... second intermediate frequency band-pass filter,
24 second frequency converter 25 third intermediate frequency bandpass filter 26 demodulator for voice only 27 first voltage or current controlled oscillator 28 control for channel selection Signal generator,
29 second voltage or current controlled oscillator, 30 distributor, 31, 34 DC amplifier, 32 phase comparator, 33, 36
... Input selector switch, 35 ... Demodulation output terminal, 37 ... Third
Voltage or current controlled oscillator, 38 ... frequency divider.

Claims (1)

(57) [Claims] A first frequency converter for converting a first intermediate frequency of a satellite broadcast into a second intermediate frequency; and a second frequency converter for converting the second intermediate frequency to a third intermediate frequency by a superheterodyne method. Frequency conversion means, first demodulation means for demodulating the third intermediate frequency by a phase-locked FM demodulation circuit having a phase comparator, a voltage or current control oscillator and a DC amplifier, and second frequency conversion by the demodulated output. Means for controlling a voltage or current controlled oscillator of the means;
A second demodulator for selecting and demodulating a desired audio channel from the third intermediate frequency, and a switch for inputting a reference signal to the first demodulator for channel selection of the audio channel. Means for dividing the voltage of the voltage or current controlled oscillator of the second frequency conversion means and inputting the divided signal to the first demodulation means; and operating the first demodulation means as channel selection means. Switching means for inputting a station control signal to the voltage or current control oscillator of the second frequency converter;
A satellite broadcast receiver comprising: means for extracting the output signal of the first demodulation means to the outside; and means for extracting the output signal of the second demodulation means to the outside.