JPH05268110A - Pcm music broadcast receiver for catv - Google Patents

Abstract

PURPOSE:To provide the inexpensive PCM music broadcast receiver for a CATV able to receive a PCM music broadcast signal broadcast via the CATV or the like. CONSTITUTION:An input terminal 41, a channel selection tuner 43, an intermediate frequency filter 44, a demodulator 45, a decoder 46, a D/A converter 47, an output terminal 48 are connected in series in this order, a single super-tuner is adopted for the tuner 43, an output frequency of the tuner 43 is set to an intermediate value between a standard audio frequency and a standard video intermediate frequency of the television receiver and the receiver receives and selects a channel of a CATV use multi-channel music broadcast wave subject to phase modulation having same upper and lower bands with respect to a carrier. Since only one local oscillator and one frequency converter each are enough for the single super tuner 43, the inexpensive PCM music broadcast receiver is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV PCM music broadcast receiver for receiving a PCM music broadcast broadcast via CATV or the like.

[0002]

2. Description of the Related Art In recent years, compact discs and satellite broadcasting have become widespread, and it has become easy to enjoy high-quality sounds that could not be realized by conventional LP record or AM or FM broadcasting.

[0003] In addition, CATV has reached the end of the sophistication of services due to the increase in the number of channels of video, and there is an urgent need to develop the CATV industry and business by opening up new services.

Against this background, the current CATV
A new service has begun to send the high-quality music of the compact disc to the individual subscribers via the CATV cable by using the free channels of the channels allocated to the subscribers by using the digital modulation technology. In order to smoothly spread this service, development of an optimum receiver capable of receiving multi-channel PCM music broadcasting transmitted via a cable for CATV is desired.

A conventional CATV PCM music broadcast receiver and its peripherals will be described below with reference to the drawings.

FIG. 13 shows a block diagram of the entire CATV receiving system. In FIG. 13, reference numeral 30 is a CATV broadcasting company, and C broadcast from this CATV broadcasting company 30.
The ATV broadcast is distributed from the cable main line 31 by the distributor 34 and sent to each individual contractor's house 33 via the branch line 32.

At each individual contractor's house 33, as shown in FIG. 14, the broadcast signal sent from the branch line 32 is further distributed by the distributor 21, and one of the output signals is CATV.
The image is supplied to the television receiver 23 via the receiver 22 and received. The other output signal of the distributor 21 is input to the CATV PCM music broadcast receiver 20. The two output signals 8a and 8b are respectively fed to the audio amplifier 24.
Is amplified and drives the speakers 25 and 26.

Further, a PCM music broadcast receiver 2 for CATV
As shown in FIG. 15, 0 indicates an input terminal 1, a tuning tuner 3 connected to the input terminal 1, and the tuner 3
Of the intermediate frequency filter 4 connected to the output of the demodulator 5, the demodulator 5 connected to the output of the intermediate frequency filter 4, the decoder 6 connected to the output of the demodulator 5, and the output of the decoder 6. The connected D / A converter 7 and this D / A converter 7
The output terminal 8a and 8b respectively connected to the two outputs of the above, and the tuner 3 used the double super tuner. The reason is that the local oscillation generated from the tuner 3 itself is transmitted to the CATV via the input terminal 1 of the tuner 3.
This is to prevent the cables 31 and 32 from leaking and interfering with the entire CATV system.

[0009]

However, according to such a conventional structure, the double super tuner 3 first raises the selected frequency and then lowers it to a predetermined frequency. As shown in FIG.
The first frequency converter 2e and the first frequency converter 2
A voltage controlled oscillator 2k for inputting to the mixing terminal of e, a second frequency converter 2i, a fixed oscillator 2n for inputting to the mixing terminal of the second frequency converter 2i, etc. are required, Each required two frequency converters, an oscillator and its peripherals. The double super tuner 3 has a problem that the price is higher than that of a tuner used for general television reception because it takes measures against complicated frequency interference caused by having two local oscillation frequencies and two frequency converters. There was a point.

Therefore, the present invention is a low-priced P for CATV.
It is intended to provide a CM music broadcast receiver.

[0011]

In order to achieve this object, the CATV PCM music broadcasting receiver of the present invention comprises:
The tuner is a single super tuner, and the output frequency of the tuner is set to a value between the standard audio frequency and the standard video intermediate frequency of the television receiver.

[0012]

With this configuration, since the output frequency of the single super tuner is set to a value between the standard audio frequency and the standard video intermediate frequency of the television receiver, the phase modulation that occupies the same band above and below the carrier wave is occupied. CAT
It is possible to receive and tune in to a V multi-channel music broadcast wave. Here, since the single super tuner only needs to have one local oscillation frequency and one frequency converter,
It is possible to provide a low-priced CATV PCM music broadcast receiver.

In this case, considering the entire CATV system, since the distributor is inserted at the branch point of the signal, even if the local oscillation frequency of the single super tuner leaks through the input terminal, the leaked signal is Since it is attenuated by this distributor, a third party CA connected to the main line 31
It does not interfere with TV equipment.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a CATV according to an embodiment of the present invention.
FIG. 3 is a block diagram of a PCM music broadcast receiver 40 for use. Figure 1
In, 43 is a single super tuner. Reference numeral 44 denotes an intermediate frequency filter. As the intermediate frequency filter 44, a SAW filter having a bandwidth (for example, 3 MHz) determined by the digital modulation method of the transmission system is used, and is separated from the intermediate frequency band (for example, 44M for US specifications
Hz is set).

Reference numeral 45 is a demodulator for demodulating a signal modulated into QPSK or the like. It may also be a BPSK or QPR demodulator. 46 is the PCM demodulated by the demodulator 45
Decoder for decoding the code of the signal (for example, digital multiplexing of a plurality of channels, error correction code, etc.), and D for converting the PCM code for the decoded channel into an analog signal
A / A converter, whose outputs 47a and 47b are D using MASH (trademark of NTT) technology as a 1-bit DAC.
AC is used. Further, 11 is an input unit for instructing channel selection and the like, 12 is a control unit for controlling input signal processing and the single super tuner 43, and 13 is a remote control transmitter.

The configuration is such that the input terminal 41, the tuning tuner 43 connected to the input terminal 41, and the intermediate frequency filter 4 connected to the output of the tuner 43.
4, a demodulator 45 connected to the output of the intermediate frequency filter 44, a decoder 46 connected to the output of the demodulator 45, and a D / A converter 47 connected to the output of the decoder 46. And the two outputs 47a of the D / A converter 47,
47b and output terminals 48a and 48b respectively connected to the tuner 47b.
3 and this single super tuner 43
Is set to a value between the standard audio frequency of the television receiver 23 (FIGS. 13 and 14) and the standard video intermediate frequency.

As shown in FIG. 2, this single super tuner 43 has an input terminal 43a, a filter 43p connected to the input terminal 43a, an amplifier 43q connected to the output of the filter 43p, and an amplifier 43q. A filter 43r connected to the output of the amplifier 43q, a mixer 43s connected to the output of the filter 43r, and an oscillator 43u connected to the mixing input of the mixer 43s.
And a filter 43 connected to the output of the mixer 43s.
t, an output terminal 43c connected to the output of the filter 43t, and a PLL circuit section 43v for controlling the oscillator 43u from the signal of the oscillator 43u and the crystal oscillator 43w based on the signal of the tuning command input terminal 43b. It is configured.

CATV PCM configured as described above
Regarding the music broadcast receiver 40, the reason why the single super tuner 43 can be used as a tuner for tuning will be described below.

FIG. 3 shows a typical measurement example of S / N vs. input signal voltage of a video receiver. The input signal voltage at which S / N = 30 dB is called noise limiting sensitivity.

FIG. 4 shows a video signal waveform used in the above measurement. On the other hand, QPSK for multi-channel PCM music broadcasting
Etc. are digitally modulated and transmitted using the empty channel of CATV. FIG. 5 shows the bit error rate (B
ER) to C / N. The solid line shows the case where no processing such as error correction is performed. When designing an actual device, BER ≦ 10 ⁻⁶ with a 3 dB margin (dotted line) may be set as a design target, depending on the error correction code capability. Good. From Figure 53 dB margin, the required C / N for BER = 10 ^-6 is 1.
It becomes 6.5 dB.

S / N of FIG. 3 has a relationship of C / N with (Equation 1), and FIG. 6 shows a relationship of C / N with the input signal voltage using (Equation 2). is there.

[0023]

[Equation 1]

Bo: C / N reference bandwidth (4 MHz) B: Receiver bandwidth (above, Broadcasting Technology P201 edited by the Japan Broadcasting Corporation) When Bo = B, the following equation is approximated.

S / N = (C / N) dB−7dB ... (2) From FIG. 6, C / necessary to secure BER = 10 ^−6.
The input signal voltage at N = 16.5 dB is -38 dB.
It becomes mV. On the other hand, the noise limit sensitivity of the image is -17 dBm.
The input signal voltage of the QPSK signal can be set to 38-17 = 21 dB lower than the video input signal voltage. When the input signal voltage at the CATV receiver input terminal of the individual contractor is guaranteed at -10 dBmV, the input signal voltage at the input terminal of the multi-channel PCM receiver of the QPSK signal is relative to the video input signal voltage. It can be seen that the setting can be made 28 dB lower.

FIG. 7 shows the receivable frequency range of the CATV receiving double super tuner and the television built-in single super tuner, FIG. 8 shows the respective local oscillation frequency ranges, and FIG. 9 shows the single super tuner. R
The actual measured value of the local leakage voltage to the F input terminal is shown. The fourth harmonic and the fifth harmonic are at the same level or lower than the third harmonic, and are not described because they are unnecessary for the description here.

FIG. 10 shows a typical characteristic of the reverse attenuation characteristic of a directional coupler having a forward loss of 10 dB.

Applying the results previously discussed using FIG. 6 to FIG. 14, the distributor 21 of FIG. 14 allows more than 21 dB of attenuation from the cable 32 to the receiver 20, which is Two directional couplers having the characteristics of FIG. 10 can be inserted, and the reverse attenuation characteristic when using the two-stage directional coupler is 29 × 2 = 58 dB at 550 MHz.
As a result, the local leakage voltage of the fundamental wave in FIG. 9 is calculated as −18−58 = −76 dBm.
It is possible to suppress V to a sufficiently low level for practical use.

The intermediate frequency (IF) spectrum distribution of a single super tuner for NTSC television reception is
It is shown in FIG.

FIG. 12 shows a phase-modulated IF spectrum used in CATV multi-channel PCM music broadcasting and the like. Since the video signal of the NTSC system and the like effectively uses the limited channel frequency band (for example, 6 MHz) by using the vestigial sideband system, the video carrier and the audio subcarrier are set by shifting from the center of the band. However, in the case of a phase-modulated IF spectrum, since it occupies the same band above and below the carrier frequency, CA
The intermediate frequency f _IFPCM of the single super tuner used for the multi-channel PCM music broadcasting receiver for TV is set at the center of the channel frequency band. For example, in the case of the US specification, f _VIF = 45.75 MHz, f _SIF = 41.25 MHz, and f _IFPCM = 44.0 MHz.

As a result, the single super tuner 43
The local leakage voltage of is used with the directional couplers 21 and 34.
It becomes possible to take countermeasures, and the intermediate frequency
F _SIF<F_IFPCM<F_VIFSet to to receive TV
Credit single super system tuner, PCM music broadcasting
It can be effectively used for the phase modulation used in.

[0032]

As described above, according to the present invention, since the output frequency of the single super tuner is set to a value between the standard audio frequency and the standard video intermediate frequency of the television receiver, It is possible to receive and select a channel-modulated multichannel music broadcasting wave for CATV having the same upper and lower bands exclusively. Since this single super tuner needs only one local oscillation frequency and one frequency converter, it is possible to provide a low-priced PCM music broadcasting receiver for CATV.

In this case, considering the entire CATV system, since the distributor is inserted at the branch point of the signal, even if the local oscillation frequency of the single super tuner leaks through the input terminal, the leaked signal is It is attenuated by this distributor, so a third party CATV connected to the main line
It does not interfere with the equipment.

Since the single super tuner has one local oscillation frequency and one frequency converter, the C / N ratio is improved as compared with the double super tuner.

Furthermore, since the circuit structure is simpler than that of the double super tuner, the yield of parts is high, and it is effective in improving the quality.

[Brief description of drawings]

FIG. 1 is a block diagram of a PCM music broadcasting receiver for CATV according to an embodiment of the present invention.

[Figure 2] Block diagram of the same single super tuner

FIG. 3 is a characteristic diagram of input signal vs. video output S / N.

FIG. 4 is an explanatory diagram of a video signal waveform for sensitivity measurement.

FIG. 5 is an explanatory diagram of bit error rate vs. C / N of QPSK modulation.

FIG. 6 is a relationship diagram of C / N vs. input signal voltage.

FIG. 7 is an explanatory diagram showing a receivable frequency range of a CATV receiver.

FIG. 8 is an explanatory diagram showing the local oscillation frequency range.

FIG. 9 is an explanatory diagram showing measured values of a local oscillation leakage voltage to an RF input terminal.

FIG. 10 is a reverse attenuation characteristic diagram of the directional coupler.

FIG. 11 is an NTSC IF spectrum distribution map.

FIG. 12 is a phase-modulated IF spectrum distribution map.

FIG. 13 is a block diagram of the entire CATV system.

FIG. 14 is a block diagram of a PCM music broadcasting system for CATV.

FIG. 15 is a block diagram of a conventional PCM music broadcast receiver.

FIG. 16 is a block diagram of a double super tuner.

[Explanation of symbols]

 41 Input Terminal 43 Single Super Tuner 44 Intermediate Frequency Filter 45 Demodulator 46 Decoder 47 D / A Converter 48a, 48b Output Terminal

Claims (1)

[Claims] 1. An input terminal, a tuning tuner connected to this input terminal, an intermediate frequency filter connected to the output of this tuner, a demodulator connected to the output of this intermediate frequency filter, and A decoder connected to the output of the demodulator, a D / A converter connected to the output of the decoder, and an output terminal connected to the output of the D / A converter,
The tuner is a single super tuner, and the output frequency of the tuner is set to a value between the standard audio frequency and the standard video intermediate frequency of the television receiver.