JPH07111491A - Catv receiver - Google Patents

Abstract

PURPOSE:To obtain a CATV receiver capable of receiving both a conventional broadcast and an HDTV broadcast whose occupied band differs. CONSTITUTION:A signal sent from a CATV transmission line is selected by a tuner 2 to obtain an intermediate frequency signal. An audio intermediate frequency signal included in a conventional broadcast wave is passed by a 1st band pass filter 5 and the audio signal is detected via an intermediate frequency amplifier circuit 7 and inputted to a monitor. Then the signal is branched simultaneously to use a voltage comparator circuit 14 to discriminate the presence of a signal V and a channel selection range of a tuner is selected via a microcomputer 15 to switch a changeover circuit 4 of a video signal. Thus, one receiver selects the reception of an HDTV broadcast or a conventional broadcast.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV receiver, and more particularly to a CATV receiver for receiving and demodulating broadcast waves of different systems such as HDTV broadcast and NTSC broadcast.

[0002]

2. Description of the Related Art Conventionally, demodulators are shared in color broadcasting and black-and-white broadcasting among television broadcasts because they occupy the same band. In recent years, in addition to terrestrial broadcast waves, satellite broadcasting using FM modulation and program supply to CATV using communication satellites have become widespread. In order for the terminal of CATV to receive the broadcast of the FM modulation system, the signal broadcast by the FM modulation system is received, demodulated once by the FM demodulator, and then modulated again by the AM modulator to be similar to the ground wave. It is multiplexed and transmitted on the frequency axis. On the other hand, as HDTV broadcasting becomes widespread, CATV is required to transmit HDTV signals. The HDTV broadcast wave is broadcast by the FM modulation method using satellites, and even if it is converted to the AM modulation method, the occupied band is twice as wide as the conventional broadcast wave, and it is necessary to use a dedicated reception demodulator. there were.

Therefore, until now, conventional reception demodulators and HD
A receiver for mounting and receiving a demodulator dedicated to TV broadcasting has been considered (for example, study of CATV-AM transmission system of MUSE signal: TV conference technical report, No. 13. PP73).
-78, 1990).

The above-mentioned conventional example will be described below with reference to the drawings. FIG. 2 is a block diagram showing the configuration of a receiver for receiving HDTV broadcast, in which HDTV signals are band-compressed by the MUSE method, via a CATV transmission line. CAT
Station V is VSB-AM modulated HDTV ground wave and NTSC
Terrestrial waves are multiplexed on the frequency axis and supplied from the terminal 31. The frequency spectrum of the NTSC broadcast wave at this time is as shown in FIG. 3A, the carrier wave 39 represents a video carrier wave, the carrier wave 40 represents an audio carrier wave, and the spectrum 41 represents a video signal. Also, as shown in FIG. 3B, the HDTV broadcast wave has a frequency spectrum 4 of the audio signal and the video signal with respect to the carrier wave 42.
Have three. These signals are input to the distributor 33 via the CATV transmission path 32. The HDTV broadcast wave is selected by the tuner 34 and demodulated into a MUSE signal by the VSB-AM demodulator 35. And MUSE decoder 3
The HDTV monitor 36
Displayed by. Also, the NTSC broadcast wave is selected and demodulated by the CATV terminal device 38, and then the NTSC-TV receiver 3
9 is supplied.

[0005]

However, when receiving with this configuration, the HDTV broadcast and the NTSC broadcast can be received by separate receivers, but when one of the broadcasts is being received, the other receiver operates. However, there is a problem in that redundancy and power consumption increase.

These problems will occur in future HD in CATV.
When trying to receive TV broadcasts or NTSC broadcasts, the scale of the receiving system becomes large and the cost becomes high. Moreover, since the number of system components increases, the user feels complicated.
It may also be a factor that hinders the spread of ATV and HDTV.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a CATV receiver capable of receiving HDTV broadcast and NTSC broadcast having different occupied bandwidths. .

[0008]

SUMMARY OF THE INVENTION The present invention is a CATV receiver for receiving a plurality of vestigial sideband amplitude modulated waves having different occupied bands, the tuner converting the vestigial sideband amplitude modulated wave into an intermediate frequency signal. A first band-pass filter that divides the signal tuned by the tuner into two and allows a predetermined audio frequency of the intermediate frequency to pass, and the intermediate frequency tuned by the tuner is input via a changeover switch. 2nd and 3rd bandpass filters that pass a predetermined intermediate frequency, and 1st, 2nd and 3rd intermediate frequencies that respectively amplify the signals that have passed the 1st, 2nd and 3rd bandpass filters. An amplification circuit, a first detection circuit that demodulates the signal that has passed through the first bandpass filter, and second and third detection circuits that detect the signals amplified by the second and third intermediate frequency amplification circuits. And the first van And signal determination means for determining the presence or absence of a signal passed through the pass filter, is characterized in that it comprises a band switching means for switching a selected frequency band of the tuner with the output from the signal discriminating means.

[0009]

According to the present invention having such features, the first
According to the presence / absence of a signal passing through the bandpass filter, the signal discriminating means discriminates which vestigial side wave amplitude modulated wave. Then, the required frequency band is selected by using the band switching means, and the receiving channel is selected by tuning. The signal thus output from the tuner is guided to the second or third bandpass filter by the switch.
The signal that has passed through the second or third bandpass filter is amplified and detected by the second and third intermediate frequency amplifier circuits, respectively, and the video signal or the video signal and the audio signal is demodulated.

[0010]

FIG. 1 is a block diagram showing a first embodiment. HDT sent from CATV transmission line to terminal 1
V broadcast wave and NTSC broadcast wave are input. These signals are frequency-arranged as shown in FIG. In FIG. 3C, carrier waves 44 and 46 represent video carrier waves of NTSC broadcast, carrier waves 45 and 47 represent audio carrier waves of NTSC broadcast, and carrier waves 48 and 49 represent carrier waves of HDTV broadcast. Also, spectra 50 and 51 are NTS
C and signal spectra 52 and 53 represent the spectrum of the HDTV signal.

When VSB-AM modulation is performed to transmit by the CATV transmission line using a compressed signal of the MUSE system as one of the HDTV broadcasts currently under study, one channel of HDTV is compared with the conventional NTSC broadcast. Requires twice as much transmission band. Therefore, the frequency interval between carrier 44 and carrier 46 is 6 MHz, but carrier 48
The frequency interval between carrier 49 and carrier 49 is 12 MHz.

These signals are tuned to a desired channel by the tuner 2 by the tuning signal from the tuning circuit 16 and converted to an intermediate frequency (for example, 58.75 MHz). At this time, the band limiting filter of the tuner 2 is HDTV broadcast or NT.
It is switched depending on whether it is SC broadcasting. The intermediate frequency signal is divided into two by the divider 3 and input to the changeover switch 4 and the first bandpass filter 5. Bandpass filter 5 is N
A filter for extracting a TSC audio IF signal, for example, a frequency of 54.25 MHz, the output of which is input to an intermediate frequency amplifier circuit 7 and a heterodyne detector 8 via a distributor 6. The intermediate frequency amplification circuit 7 amplifies the audio frequency, and its output is input to the audio detection circuit 9.
The voice detection circuit 9 demodulates the voice signal and outputs N through the terminal 10.
Output to the audio input terminal of the TV monitor 11 of the TSC.

On the other hand, a reference signal oscillator 12 is connected to the heterodyne detector 8. The reference signal oscillator 12 is, for example, 5
It is an oscillator that oscillates a frequency of 4.2 MHz. Therefore, when the NTSC signal is selected, the heterodyne detector 8 obtains a frequency of the difference between the oscillation frequency and the center frequency of the audio IF signal, that is, a signal of 50 KHz. This signal is input to the low pass filter 13. Low-pass filter 13
As for the output of, the signal of a constant level is output when the NTSC signal is selected, and the output is 0 level when the HDTV signal is selected. Therefore, by comparing this output with the voltage comparison circuit 14, it is determined whether it is NTSC or HDTV. This discrimination signal is input to the microcomputer 15. The microcomputer 15 switches between the tuner 2 and the switching circuit 4, and constitutes a band switching means. The channel selection circuit 16 switches the selected channel of the tuner 2 by the operation of the user.

On the other hand, the output side of the switching circuit 4 is connected with second and third band pass filters 17 and 18. The second bandpass filter 17 has a band of 12 MHz centered on an intermediate frequency (58.75 MHz), and the bandpass filter 18 has a band of 6 MHz centered on 58.75 MHz, which are respectively HDTV, The NTSC center frequency signal is extracted. The signals that have passed through these band pass filters are input to the center frequency amplifier circuits 19 and 20 and amplified. The signal amplified by the intermediate frequency amplifier 19 is supplied to the HDTV detection circuit 21. The HDTV detection circuit 21 is MUS
Since the E signal is VSB-AM modulated and transmitted through the CATV transmission line, this is a VSB-AM demodulator that demodulates the E signal. The output of the HDTV detection circuit 21 is input to the HDTV monitor 23 including the MUSE decoder 14 via the terminal 22.

When the desired signal is the NTSC signal, the NTSC signal is amplified by the intermediate frequency amplifier circuit 20. The output of the center frequency amplification circuit 20 is input to the NTSC detection circuit 24, detected and connected to the terminal 25. The video input terminal of the TV monitor 11 is connected to the terminal 25.

In this embodiment, the signal that has passed through the bandpass filter 5 is heterodyne-detected as a signal discriminating means into a low frequency component, and the level thereof is compared by a voltage comparison circuit. It is needless to say that the level may be detected in series in order to determine the presence or absence of the signal that has passed through the filter, and the presence or absence of the signal can be determined by various other methods. In this embodiment, the NTSC communication method and the HDTV communication method are the same CA.
Although it is assumed that the signal transmitted through the TV transmission path is received, the present invention is not limited to NTSC and is applied to other systems such as PAL and SECAM and a CATV receiver that receives a transmission signal obtained by multiplexing HDTV broadcast waves on the frequency spectrum. It goes without saying that you can do it.

[0017]

As described above in detail, according to the present invention, the tuner band and the detector can be switched by discriminating the HDTV broadcast from the conventional broadcast by one receiver. Therefore, it has higher performance and C than conventional receivers.
The effect that the ATV receiver can be realized at a low price is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a CATV receiver according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional CATV receiving system.

FIG. 3A is a spectrum diagram of an NTSC broadcast wave,
(B) is a spectrum diagram of HDTV broadcast wave, (c) is CA
It is a spectrum figure on a TV transmission line.

[Explanation of symbols]

 1 Input Terminal 2 Tuner 3,6 Distributor 4 Switching Circuit 5,17,18 Bandpass Filter 7,19,20 Intermediate Frequency Amplifier Circuit 8 Heterodyne Detector 9 Voice Detection Circuit 11 TV Monitor 12 Reference Signal Oscillator 13 Lowpass Filter 14 Voltage Comparison circuit 15 Microcomputer 16 Channel selection circuit 21 HDTV detection circuit 23 HDTV monitor 24 NTSC detection circuit

Claims (3)

[Claims] 1. A CATV receiver for receiving a plurality of vestigial sideband amplitude-modulated waves having different occupied bands, wherein the tuner converts the vestigial sideband amplitude-modulated wave into an intermediate frequency signal, and the tuner selects A first band-pass filter that divides a local signal into two and passes a predetermined audio frequency of the intermediate frequencies, and a predetermined intermediate frequency that is input via a changeover switch among the intermediate frequencies selected by the tuner. Second and third bandpass filters that pass frequencies, and first, second, and third intermediate-frequency amplifier circuits that amplify the signals that have passed through the first, second, and third bandpass filters, respectively. A first detection circuit that demodulates the signal that has passed through the first bandpass filter; and second and third detection circuits that detect the signals amplified by the second and third intermediate frequency amplification circuits. , The CATV reception, characterized by comprising: a signal discriminating means for discriminating the presence or absence of a signal that has passed through the first band pass filter; apparatus. 2. The first bandpass filter is NTS
A signal centered on a carrier of the audio frequency of the C signal is passed, and the second and third band pass filters pass the bands of the HDTV signal and the NTSC video intermediate frequency signal, respectively. 2. The CA according to claim 1, wherein the tuner changes the band to pass an NTSC signal and an HDTV signal based on the presence / absence of a received signal detected by the signal discriminating means.
TV receiver. 3. The signal discriminating means, a reference signal oscillator for generating a frequency close to a signal passing through the first bandpass filter, an output of the reference signal oscillator and the first bandpass filter. A heterodyne detector for heterodyne detection of the signal, a low pass filter for passing a low frequency component of the output obtained by the heterodyne detector, and a voltage comparison circuit for discriminating the signal based on the output level obtained by the low pass filter, The CATV receiver according to claim 1 or 2, further comprising: