JPH08237620A - Television signal converter - Google Patents

Abstract

PURPOSE: To provide a television signal converter in which an audio signal is surely muted without noise and simple configuration and which is used for a dual carrier audio multiplex system audio multiplex broadcast or stereo broadcast receiver. CONSTITUTION: This converter is provided with a 1st audio muting circuit 106 muting a 1st audio signal A1 demodulated from a television signal in response to an audio muting signal, a 2nd audio carrier muting circuit 11 muting a 2nd audio carrier S2 separated from the television signal in response to the audio muting signal, a 1st carrier modulation circuit 107 modulating a carrier of a frequency corresponding to the 1st audio carrier S1, and with a modulation circuit 114 summing the video signal, a signal outputted from the 1st carrier modulation circuit 107, and a signal outputted from the 2nd audio carrier separation circuit and modulating a main carrier corresponding to a prescribed channel to provide an output of a television signal of a prescribed channel.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

The present invention relates to a CATV (community an
Suitable for CATV terminals installed on the receiving side of a tenna television or cable television system, especially 2
The present invention relates to improvement of audio signal processing of a television signal conversion device used for receiving a carrier wave audio multiplex broadcast or a stereo broadcast.

[0003]

[0002]

[0004]

2. Description of the Related Art FIG. 3 shows a general structure of a CATV system. The broadcast center 303 receives a commercial broadcast program by the BS antenna 304, the BS converter 305, or the television antenna 306 and relays it, or delivers a self-produced broadcast program by a television camera 307 and a VTR 308 via a transmission cable 309. On the side of each user, the CATV terminal devices 3011 to 301n receive the transmitted television signals, descramble the television signals scrambled to prevent wiretapping, and then receive the television receivers 3021 to 302n.
Send to

[0005]

In the two-carrier system audio multiplex (or stereo) broadcasting, in addition to the conventional audio carrier (first audio carrier), another audio carrier (second audio carrier) is added to a frequency higher than the first audio carrier. This is a method of adding and transmitting. In the case of the West German system, the primary audio (the (L + R) / 2 signal in stereo broadcasting) is assigned to the first audio carrier, and the secondary audio (the R signal in stereo broadcasting) is assigned to the second audio carrier.

[0006]

The second voice carrier further includes a voice multiplex control signal. This audio multiplex control signal indicates that the signal being broadcast is audio multiplex (or stereo) broadcasting.
During the broadcast, the receiving circuits on the side of the television receivers 3021 to 302n detect the audio multiplex control signal, thereby determining that the signal transmitted is the audio multiplex (or stereo) broadcast, and the desired reproduction mode is set. Accordingly, the predetermined sound is reproduced from the left and right speakers, respectively. However, if the television receiver does not support audio multiplexing, it is inevitably equipped with only a receiving circuit for the first audio carrier wave, and therefore, inevitably only the main audio ((L + R) in stereo broadcasting).
/ 2 or monaural) is reproduced.

[0007]

FIG. 4 is a block diagram of an audio muting circuit of a conventional receiving terminal device for two-carrier audio multiplex broadcasting.

Reference numeral 401 in the drawing denotes an input terminal, and 402
Is a tuner. 403 and 404 are band pass filters, and 405 is an audio / video detection IC. Again 4
Reference numerals 06 and 407 are bandpass filters, and 408 is a two-carrier television audio multiplex demodulation IC. Again 409
Is a matrix circuit, 410 is a first carrier modulation circuit, and 411 is a second carrier modulation circuit. Again 4
12 is an adding circuit, 413 is a modulating circuit, 41
Reference numeral 4 is a microcomputer, and 415 is an output terminal.

[0009]

The input terminal 401 is connected to a broadcasting center as a head end via a transmission line such as a coaxial cable (not shown). The tuner 402 selects one desired channel from the multi-channel television signals transmitted to the input terminal 401 and frequency-converts it to obtain an intermediate frequency signal (IF signal). Bandpass filter 40
3 separates the video carrier from the IF signal to obtain the video IF signal IFV. Further, the bandpass filter 404 uses the IF
An audio IF signal IFA is obtained by separating the audio carrier from the signal.

[0010]

The audio / video detection IC 405 includes a video demodulation circuit 405a and an audio demodulation circuit 405b.
The video demodulation circuit 405a demodulates the video IF signal IFV and outputs the baseband video signal V from the video output terminal 405c. The audio demodulation circuit 405b is an audio IF signal IFA.
To demodulate the first audio signal A1 into the first audio output terminal 405.
Output from e. Further, the audio carrier of the audio IF signal IFA is frequency-converted and output from the split output terminal 405d. The sound carrier includes the first sound carrier S1 and the second sound carrier S2 when the television signal is a signal obtained by sound multiplexing, and includes only the first sound carrier S1 when the television signal is a single sound signal.

In the case of the West German system, the first voice carrier S1 is 5.5 MHz and the second voice carrier S2 is 5.74 M.
Hz, and the audio IF signal IFA is the IF corresponding to S1.
A1 is 33.4MHz, IF2 corresponding to S2 is 3
3.16 MHz. The video IF signal IFV is 3
It is 3.9 MHz.

[0012]

The bandpass filter 406 is connected to the split output terminal 405d and removes the second sound carrier S2 from the sound carrier to obtain the first sound carrier S1. Similarly, the band pass filter 407 also has a split output terminal 40.
5d, the first sound carrier S1 is removed from the sound carrier to obtain the second sound carrier S2.

[0013]

2 carrier television sound multiplex demodulation IC4
Reference numeral 08 denotes the first voice carrier FM detection circuit 408a and the second voice carrier FM detection circuit 408a.
An audio carrier FM detection circuit 408b and an audio multiplex demodulation circuit 408c are provided. The first voice carrier FM detection circuit 408a FM-detects the first voice carrier S1 separated by the band-pass filter 406 and outputs the first voice signal A1. Further, the second voice carrier FM detection circuit 408b outputs the second voice carrier S2 separated by the band pass filter 407 to F
M detection is performed and the second audio signal A2 is output.

[0014]

The audio multiplex demodulation circuit 408c outputs the first audio signal A output from the first audio carrier FM detection circuit 408a.
1 and the second audio signal A2 output from the second audio carrier FM detection circuit 408b are demodulated to output the L signal and the R signal.

The matrix circuit 409 is connected to the two-carrier television audio multiplex demodulation IC 408 and synthesizes the L signal and the R signal to output the (L + R) / 2 signal and the R signal.

[0016]

The first carrier modulation circuit 410 modulates the (L + R) / 2 signal output from the matrix circuit 409 and outputs a first audio carrier S1. The second carrier modulation circuit 411 modulates the R signal output from the matrix circuit 409 and outputs the second audio carrier S2.

The output first sound carrier S1 and second sound carrier S2 are added to each other by the adder circuit 412 and input to the modulation circuit 413.

[0018]

The modulation circuit 413 is a video processing IC 413a.
And an adder circuit 413b and an AM modulator 413c.

The image processing IC 413a performs image processing (image clamp, white clip) on the image signal V output from the image output terminal 405c, and then outputs the image signal.

The output video signal and the output of the adder circuit 412 are added to each other by the adder circuit 413b, modulated by the AM modulator 413c to the frequency of a predetermined channel, and output from the output terminal 415.

[0021]

Conventionally, audio and video are reproduced with the above-mentioned configuration. However, when a user switches a channel with the tuner 402 for channel selection or forcibly switches an audio signal from stereo to monaural, it is temporarily stopped. Since the audio carrier wave is lost in, it is necessary to mute the audio to prevent the occurrence of audio reproduction noise. It is also necessary to mute the voice and noise when displaying the text information on screen when setting a timer or applying for a pay program, or when cutting the voice when an uncontracted channel is received. is there.

[0022]

Therefore, at the time of switching, the microcomputer 4
14 receives a voice mute command and outputs a voice muting signal, and a two-carrier television voice multiplex demodulation IC4
The L signal and the R signal demodulated by the audio multiplex demodulation circuit 408c of No. 08 were muted at the baseband stage.

[0023]

[0015]

[0024]

With the above configuration, the audio mute process is conventionally performed after demodulating the first audio carrier S1 and the second audio carrier S2. Therefore, in addition to the demodulating circuit, the matrix circuit and There is a drawback that a modulation circuit is required and the circuit configuration becomes complicated.

[0025]

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and is for receiving audio multiplex broadcasts or stereo broadcasts of a two-carrier audio multiplex system capable of reliably muting audio without noise with a simple structure. The present invention provides a television signal conversion device used in.

[0026]

[0017]

[0027]

According to the first aspect of the present invention,
A first channel including a video signal and a first audio signal on one channel;
A television signal conversion device for receiving a television signal including an audio carrier wave and a second audio carrier wave including a second audio and converting the television signal into a television signal of a predetermined channel, A video demodulation circuit for demodulating a video signal and a first
A first audio demodulation circuit for demodulating an audio signal, a first audio muting circuit for muting the first audio signal according to the audio muting signal, and a second audio carrier separating circuit for separating a second audio carrier from a television signal. A second sound carrier muting circuit for muting the second sound carrier according to the sound muting signal, and a first carrier for modulating a carrier having a frequency corresponding to the first sound carrier by the output signal of the first sound muting circuit. The modulation circuit, the video signal, the signal output from the first carrier wave modulation circuit, and the signal output from the second sound carrier wave separation circuit are added, and the main carrier wave corresponding to the predetermined channel is modulated to add the predetermined channel. And a modulation circuit for outputting the television signal of.

[0028]

According to a second aspect of the present invention, in the television signal conversion apparatus according to the first aspect, a second audio carrier wave detection circuit for detecting a second audio carrier wave is further provided, and the second audio carrier wave muting circuit comprises: When the second audio carrier wave detection circuit does not detect the second audio carrier wave, the signal output from the second audio carrier wave separation circuit is muted.

[0029]

According to a third aspect of the present invention, a television signal including a video signal on one channel, a first audio carrier wave including a first audio signal, and a second audio carrier wave including a second audio signal is received, A television signal conversion device for converting the television signal into a television signal of a predetermined channel, comprising a video demodulation circuit for demodulating a video signal from the television signal and a first audio signal for demodulating the first audio signal from the television signal. An audio demodulation circuit, a first audio muting circuit that mutes a first audio signal according to an audio muting signal, a second audio carrier separating circuit that separates a second audio carrier from a television signal, and an audio muting signal In response to the second audio carrier muting circuit for muting the second audio carrier and the first audio carrier by the output signal of the first audio muting circuit. A first carrier wave modulation circuit that modulates a carrier wave having a frequency corresponding to a wave, a pseudo second carrier wave oscillator that oscillates at a second sound carrier wave frequency, and an output signal of the pseudo second carrier wave oscillator according to a sound muting signal The pseudo second carrier muting circuit, the video signal, the signal output from the first carrier modulation circuit, the signal output from the second audio carrier separation circuit, and the signal output from the pseudo second carrier oscillator. And a modulation circuit for modulating the main carrier wave corresponding to the predetermined channel and outputting the television signal of the predetermined channel.

[0030]

According to a fourth aspect of the present invention, in the television signal converting apparatus according to the third aspect, a second audio carrier wave detecting circuit for detecting the second audio carrier wave is further provided, and the second audio carrier wave muting circuit is When the second audio carrier wave detection circuit does not detect the second audio carrier wave, the signal output from the second audio carrier wave separation circuit is muted, and the pseudo second carrier wave muting circuit is unmuted to cancel the pseudo second carrier wave. It is configured to output the output signal of the oscillator.

[0031]

[0021]

[0032]

In the present invention, the first audio signal output from the first audio output terminal of the audio / video detection IC is muted in the baseband by the first audio muting circuit in response to the audio muting signal. With
Since the second audio carrier wave obtained from the audio carrier wave output from the split output terminal of the audio / video detection IC is muted by the second audio carrier wave muting circuit, the sound can be muted with a simple circuit configuration. it can.

In addition, according to the voice muting signal, the second
When there is no output from the audio carrier muting circuit, by adding the pseudo second carrier, it is possible to prevent the occurrence of audio reproduction noise even if the carrier is temporarily lost.

In addition to the above, if the second sound carrier wave is not detected by the second sound carrier wave detection circuit, the second sound carrier wave is detected.
Since the signal output from the audio carrier wave separation circuit, especially the noise component is also muted, the second audio can be surely muted.

[0035]

[0022]

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram of an audio muting circuit of a two-carrier audio multiplex system CATV terminal according to an embodiment of the present invention.

In the figure, reference numeral 101 is an input terminal, and 10
2 is a tuner. Reference numerals 103 and 104 are bandpass filters, and 105 is an audio / video detection IC. Further, 106 is a first audio muting circuit,
7 is a first carrier modulation circuit, and 108 is an amplifier. 10
9 is a trap filter, 110 is an amplifier, 111
Is a second voice carrier muting circuit. Also, 1
Reference numeral 12 is a second voice carrier detection circuit, and 113 is an addition circuit. Further, 114 is a modulation circuit, and 114c is an AM modulator. Further, 115 is a microcomputer, and 1
16 is an output terminal.

[0038]

The input terminal 101 receives a multi-channel television signal transmitted from the center as a head end using the frequency band of 50 to 500 MHz. The tuner 102 selects one desired channel from the multi-channel television signals transmitted to the input terminal 101 and frequency-converts it to obtain an intermediate frequency signal (IF signal). The band pass filter 103 separates the video carrier from the IF signal to obtain the video IF signal IFV. The bandpass filter 104 separates the audio carrier from the IF signal to obtain the audio IF signal IFA.

[0039]

The audio / video detection IC 105 includes a video demodulation circuit 105a and an audio demodulation circuit 105b.
The video demodulation circuit 105a demodulates the video IF signal IFV to convert the baseband video signal V into the audio / video detection IC 10
5 from the video output terminal 105c. The audio demodulation circuit 105b demodulates the audio IF signal IFA and outputs the first audio signal A1 from the first audio output terminal 105e. Further, the audio carrier of the audio IF signal IFA is frequency-converted and output from the split output terminal 105d.

The voice carrier is the first voice carrier S1 when the television signal is a voice multiplex (or stereo) broadcast.
And the second audio carrier S2, and only the first audio carrier S1 in the case of single audio (or monaural) broadcasting.

[0041]

The first audio output terminal 105e of the audio / video detection IC 105 is connected to the first audio muting circuit 106, and the first carrier modulation circuit 107 and the amplifier 10 are connected.
It is connected via 8 to the adder circuit 113.

The first carrier modulation circuit 107 receives the output signal from the first audio muting circuit 106 and outputs the first signal.
A carrier wave having a frequency corresponding to the sound carrier wave S1 is modulated and output to the amplifier 108.

The amplifier 108 amplifies the input signal to obtain the first audio carrier wave S1 and outputs it to the adder circuit 113.

[0044]

The split output terminal 105d of the audio / video detection IC 105 is connected to the trap filter 109. The trap filter 109 constitutes a second audio carrier wave separation circuit, removes the first audio carrier wave S1 from the audio carrier wave output from the split output terminal 105d, and takes out only the second audio carrier wave S2.

The output of the trap filter 109 is supplied to the amplifier 110 and the second voice carrier detection circuit 112. The output of the second voice carrier detection circuit 112 is connected to the second voice carrier muting circuit 111. The microcomputer 115 is connected to the first audio muting circuit 106 and the second audio carrier muting circuit 111. The output of the amplifier 110 is connected to the adder circuit 113 via the second voice carrier muting circuit 111.

[0046]

The adder circuit 113 adds the output of the amplifier 108 and the output of the second voice carrier muting circuit 111 to each other and outputs the result to the modulation circuit 114.

The modulation circuit 114 is a video processing IC 114a.
And an adder circuit 114b and an AM modulator 114c. The video processing IC 114a has a video output terminal 1
The video signal V output from 05c is subjected to video processing (video clamp, white clip) and output.

The output video signal and the signal output from the addition circuit 113 are added to each other in the addition circuit 114b,
The signal is modulated to a frequency of a predetermined channel by the AM modulator 114c and output from the output terminal 116.

[0049]

The second voice carrier detecting circuit 112 is a circuit for detecting that the second voice carrier S2 of a predetermined level or more does not exist in the voice carrier, and when the tuner 102 is tuning between stations or a television. When this is detected when the signal is a single voice (or monaural) broadcast, the second voice carrier muting circuit 111 is muted on, and noise of the frequency component of the second voice carrier S2 output from the split output terminal 105d. The noise generated from the amplifier 110 is not output to the adder circuit 113. That is, the second voice carrier muting circuit 11
1 is in the mute on state when the television signal is a single audio (or monaural) broadcast.

When the television signal is audio multiplex (or stereo) broadcast, the second audio carrier muting circuit 111 is in the mute off state by the second audio carrier detecting circuit 112.

[0051]

The microcomputer 115 displays a predetermined period until the operation of the tuner 102 or the like becomes stable when the user switches channels on the tuner 102 for channel selection, or when a timer setting screen or a pay program application screen is displayed. Alternatively, when it is necessary to cut the voice, for example, when a channel that has not been contracted is selected, the voice muting signal is output in response to the voice mute command. While the audio muting signal is being output, the first audio muting circuit 106 and the second audio carrier muting circuit 1
Mute 11 on. That is, the first audio output terminal 10
The output of 5e is muted, and the second sound carrier S2 or noise output from the amplifier 110 is prevented from being output to the adder circuit 113.

Second voice carrier muting circuit 111
Is a mute on state when the television signal is a single audio (or monaural) broadcast as described above,
In the case of audio multiplex (or stereo) broadcasting, it is in the mute off state. Further, while the microcomputer 115 is outputting the audio muting signal in response to the audio mute command, the mute is on regardless of whether the television signal is a single audio (or monaural) broadcast or an audio multiplex (or stereo) broadcast. .

[0053]

That is, when the microcomputer 115 is not outputting the audio muting signal, the tuner 102
When the television signal tuned in is audio multiplex broadcasting (or stereo broadcasting), the addition circuit 114b of the modulation circuit 114 adds the video signal to the first audio carrier S1 and the second audio carrier S2, The AM modulator 114c modulates the frequency of a predetermined channel.

As described above, the output terminal 116 outputs a television signal by audio multiplex (or stereo) broadcasting.

[0055]

Next, the operation of the second audio carrier wave detecting circuit 112 when the audio multiplex (or stereo) broadcast is switched to the single audio (or monaural) broadcast will be described.

When the television signal selected by the tuner 102 is switched from the audio multiplex (or stereo) broadcast to the single audio (or monaural) broadcast, the second audio carrier wave detection circuit 112 causes the second audio carrier wave S2. Is not detected, the second voice carrier muting circuit 11
Mute 1 Therefore, the output of the amplifier 110 is muted and is not input to the adder circuit 113.

Therefore, the adder circuit 11 of the modulation circuit 114
In 4b, only the video signal and the first audio carrier S1 are added and converted into a frequency of a predetermined channel by the AM modulator 114c. Therefore, a single audio (or monaural) broadcast television signal is output from the output terminal 116.

[0058]

Next, the process in which the audio signal is muted in response to the audio muting signal will be described.

When the microcomputer 115 receives the audio mute command and outputs the audio muting signal, the first audio muting circuit 106 and the second audio carrier muting circuit 111 are muted on. Therefore, the first audio muting circuit 106 is connected to the first audio output terminal 105.
Since the output of e is muted, the first audio output terminal 105
The first audio signal A1 output from e is not input to the first carrier modulation circuit 107. Therefore, the first carrier wave modulation circuit 107 outputs a carrier wave having a frequency corresponding to the first sound carrier wave S1 and inputs the carrier wave to the amplifier 108. Amplifier 108
Amplifies the input signal into a first carrier wave S1a,
Output to the adder circuit 113. Here, the first carrier wave S1a
Is the unmodulated first voice carrier S1.

[0060]

Further, since the second sound carrier muting circuit 111 mutes the output of the amplifier 110, the second sound carrier S2 outputted from the amplifier 110 is not inputted to the adding circuit 113. Therefore, in the adder circuit 114b of the modulator circuit 114, the video signal and the first carrier wave S1a.
Only the signals are added and modulated by the AM modulator 114c to a frequency of a predetermined channel.

As described above, the television signal including the unmodulated first audio carrier wave component and the video signal component is output from the output terminal 116.

[0062]

Another embodiment of the present invention will be described below with reference to FIG. 2. The same parts as those of the conventional one described with reference to FIG. 1 are designated by the same reference numerals.

FIG. 2 is a block diagram of a voice muting circuit of a CATV terminal device of a two-carrier voice multiplex system according to another embodiment of the present invention.

In the figure, reference numeral 201 is a pseudo second carrier oscillator, and 202 is an amplifier. Further, 203 is a pseudo second carrier wave muting circuit, and 204 is an adding circuit.

[0065]

The pseudo second carrier oscillator 201 is an amplifier 20.
2 and the pseudo second carrier wave muting circuit 203, and is connected to the adding circuit 204.

The pseudo second carrier wave oscillator 201 oscillates at the frequency of the carrier wave corresponding to the second sound carrier wave S2, and the amplifier 2
Enter in 02. The amplifier 202 amplifies the input signal, outputs the pseudo second carrier S2a, and outputs the pseudo second carrier S2a to the pseudo second carrier muting circuit 203.

The adder circuit 204 outputs the output of the amplifier 108,
The output of the second voice carrier muting circuit 111 and the output of the pseudo second carrier muting circuit 203 are added to each other and input to the modulation circuit 114. Modulation circuit 114
Then, the video signal output from the video processing IC 114a and the signal output from the addition circuit 204 are added to the addition circuit 114b.
Are added to each other, modulated by the AM modulator 114c to a frequency of a predetermined channel, and output from the output terminal 116.

[0068]

The second audio carrier wave detection circuit 112 is used when the television signal is a single audio (or monaural) broadcast or when the tuner 102 is tuned between stations. This is a circuit for detecting the absence of the two audio carrier waves S2. When this is detected, the second audio carrier wave muting circuit 111 is muted on, and the second output signal is output from the split output terminal 105d.
The noise of the frequency component of the sound carrier S2 and the noise generated from the amplifier 110 are prevented from being output to the adding circuit 204, and the pseudo second carrier muting circuit 2
03 is muted off, and the pseudo second carrier wave S2a output from the amplifier 202 is output to the adding circuit 204. That is, the second audio carrier wave muting circuit 111 is in the mute on state, and the pseudo second carrier wave muting circuit 203 is in the mute off state.

When the television signal is a voice multiplex (or stereo) broadcast, the voice carrier output from the amplifier 110 is output to the adding circuit 204, and
The pseudo second carrier wave S2a is not output to the adder circuit 204. That is, the second audio carrier wave muting circuit 111 is in the mute off state, and the pseudo second carrier wave muting circuit 203 is in the mute on state.

[0070]

The microcomputer 115 outputs a sound for a predetermined period until the operation of the tuner or the like becomes stable when the user switches channels with the tuner 102 for channel selection, or when a timer setting screen or a pay program application screen is displayed. Receiving the mute command, it outputs the audio muting signal. While the audio muting signal is being output, the first audio muting circuit 106 and the second audio carrier muting circuit 111 are muted on, and the pseudo second
The carrier wave muting circuit 203 is muted off. That is, the output of the first audio output terminal 105e is muted so that the second audio carrier wave S2 or noise output from the amplifier 110 is not output to the adding circuit 204, and the pseudo second carrier wave S2a is output to the adding circuit 204. .

[0071]

As described above, when the television signal is a single audio (or monaural) broadcast, the second audio carrier muting circuit 111 is in the mute on state, and the pseudo second carrier muting circuit 203 is muted. It is off.

In the case of audio multiplex (or stereo) broadcasting, the second audio carrier muting circuit 111.
Is in the mute off state, and the pseudo second carrier wave muting circuit 203 is in the mute on state.

Further, while the microcomputer 115 is outputting the audio muting signal in response to the audio mute command, the second audio carrier wave is generated regardless of whether the television signal is a single audio (or monaural) broadcast or an audio multiplex (or stereo) broadcast. The muting circuit 111 is in the mute on state, and the pseudo second carrier wave muting circuit 203 is in the mute off state.

[0074]

Here, in the case where the microcomputer 115 is not outputting the audio muting signal, the tuner 10
The television signal output to the output terminal 116 when the television signal selected in 2 is a voice multiplex (or stereo) broadcast will be described.

When the television signal selected by the tuner 102 is audio multiplex (or stereo) broadcasting, the split output terminal 105d outputs the first audio carrier S1 and the second audio carrier S2, and the first audio carrier S1 is output. The first audio signal A1 is output from the output terminal 105e. Therefore, the first carrier modulation circuit 107 receives the first audio signal A1 and modulates the carrier of the frequency corresponding to the first audio carrier S1 and outputs it to the amplifier 108. The amplifier 108 amplifies the input signal to form the first audio carrier wave S1 and outputs it to the adder circuit 204.

[0076]

The second audio carrier wave detecting circuit 112 detects the second audio carrier wave S2 to mute off the second audio carrier wave muting circuit 111, and turns on the pseudo second carrier wave muting circuit 203.

Second audio carrier muting circuit 111
Is muted off, the second audio carrier muting circuit 111 passes the second audio carrier S2 and outputs it to the adder circuit 204.

When the pseudo second carrier wave muting circuit 203 is muted on, the pseudo second carrier wave muting circuit 203 mutes the pseudo second carrier wave S2a output from the amplifier 202 and passes it to the adding circuit 204. Do not let

Therefore, in the adding circuit 204, the first sound carrier S1 and the second sound carrier S2 are added to each other.

[0080]

Therefore, the adder circuit 11 of the modulation circuit 114 is used.
4b, the video signal and the first audio carrier S1 and the second
The voice carrier S2 is added and modulated by the AM modulator 114c to a frequency of a predetermined channel.

As described above, the output terminal 116 outputs a television signal by audio multiplex (or stereo) broadcasting.

[0082]

Next, the operation of the second audio carrier wave detection circuit 112 when the audio multiplex (or stereo) broadcast is switched to the single audio (or monaural) broadcast will be described.

When the television signal selected by the tuner 102 is switched from the audio multiplex (or stereo) broadcast to the single audio (or monaural) broadcast, the second audio carrier detection circuit 112 outputs the second audio carrier S2. Is not detected, the second voice carrier muting circuit 11
1 is muted on, and the pseudo second carrier wave muting circuit 203 is muted off. When the second audio carrier muting circuit 111 is muted on,
The output of the amplifier 110 is muted and is not input to the adder circuit 204.

When the pseudo second carrier wave muting circuit 203 is muted off, the pseudo second carrier wave S2a output from the amplifier 202 is input to the adding circuit 204.

Therefore, the adder circuit 11 of the modulation circuit 114 is
4b, the video signal, the first audio carrier S1 and the pseudo second
The carrier wave S2a is added and modulated by the AM modulator 114c to a frequency of a predetermined channel.

As described above, the output terminal 116 outputs a television signal by a single audio (or monaural) broadcast.

[0087]

On the other hand, in the television receiver (302 in FIG. 3) connected to the output terminal 116, the output terminal 11
When the signal output from 6 is switched from a television signal for audio multiplex (or stereo) broadcasting to a television signal for single audio (or monaural broadcasting), the control signal disappears (the control signal is superimposed. The second sound carrier itself disappears)
The receiver circuit on the receiver side is switched so as to reproduce only the first audio signal A1.

However, if this detection takes a long time (for example, about 300 to 500 msec), the second audio carrier wave S2 is output to the output terminal 116 in the television receiver during that time.
Continues to try to demodulate the second audio signal A2 in a state where no signal exists.

However, since the second voice carrier detection circuit 112 no longer detects the second voice carrier S2, the second voice carrier muting circuit 111 is muted on and the pseudo second carrier muting circuit 203 is muted off. The pseudo second carrier wave S2a is added to the adding circuit 204.
Output to.

Therefore, in the television receiver, the second
Even if the sound carrier S2 does not exist, the unmodulated pseudo second carrier S2a exists, so that sound reproduction noise does not occur.

[0091]

Next, the process in which the audio signal is muted in response to the audio muting signal will be described.

When the microcomputer 115 receives the audio mute command and outputs the audio muting signal, the first audio muting circuit 106 and the second audio carrier muting circuit 111 are muted on, and the pseudo second
The carrier wave muting circuit 203 is muted off.
Therefore, the first audio signal A1 output from the first audio output terminal 105e is not output to the first carrier modulation circuit 107.

Therefore, the first carrier modulation circuit 107
Outputs a carrier wave having a frequency corresponding to the first sound carrier wave S1 and inputs the carrier wave to the amplifier 108.

The amplifier 108 amplifies the input signal to form the first carrier wave S1a and outputs it to the adder circuit 204.
The second audio carrier muting circuit 111 mutes the output of the amplifier 110.

[0095]

Therefore, the second voice carrier S2 output from the amplifier 110 is not input to the adder circuit 204.

Further, the pseudo second carrier wave muting circuit 203 allows the pseudo second carrier wave S2a output from the amplifier 202 to pass through and input to the adder circuit 204.

Therefore, the adder circuit 11 of the modulation circuit 114 is
In 4b, the video signal and the first carrier wave S1a and the pseudo second carrier wave S2a are added and modulated by the AM modulator 114c to a frequency of a predetermined channel.

As described above, the output terminal 116 outputs the television signal including the unmodulated first and second audio carrier components and the video signal component.

[0099]

Here, when the microcomputer 115 receives an audio mute command and outputs an audio muting signal while the television signal selected by the tuner 102 is audio multiplex (or stereo) broadcast, it is output from the amplifier 110. The second audio carrier wave S2 to be generated is not input to the adder circuit 204, but instead is a pseudo second carrier wave S that is not modulated.
Since 2a is input, no audio reproduction noise is generated in the television receiver as described above.

In the above description, the West German system is assumed as the two-carrier system, but it can be applied to the Korean system. Further, the modulation system may not be the FM-AM system.

Further, the present invention can be applied to not only CATV terminal devices but also all devices relating to frequency conversion of television signals, for example, VCR channel converters and the like.

[0102]

[0047]

[0103]

According to the present invention, the first audio signal output from the first audio output terminal of the audio / video detection IC is muted by the first audio muting circuit in accordance with the audio muting signal. IC for audio / video detection
Since the second sound carrier wave obtained from the sound carrier wave output from the split output terminal is muted by the second sound carrier muting circuit, the sound can be muted with a simple circuit configuration.

In addition to the video signal, the first carrier wave, and the output signal of the second sound carrier wave muting circuit, in addition to the pseudo second carrier wave in accordance with the sound muting signal, the carrier wave is temporarily lost. Also, it is possible to prevent the occurrence of voice reproduction noise.

Further, since the second audio carrier wave detection circuit is provided so that the signal output from the second audio carrier wave separation circuit is muted when the second audio carrier wave is not detected, the second audio is surely muted. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of an audio muting circuit of a two-carrier audio multiplex system CATV terminal according to an embodiment of the present invention.

FIG. 2 is a block diagram of an audio muting circuit of a CATV terminal device of a two-carrier audio multiplex system according to another embodiment of the present invention.

FIG. 3 is a general configuration of a CATV system.

FIG. 4 is a block diagram of an audio muting circuit of a conventional receiving terminal device for two-carrier audio multiplex broadcasting.

[Explanation of symbols]

 101 ... Input terminal 102 ... Tuner 103 ... Band pass filter 104 ... Band pass filter 105 ... Audio / video detection IC 105a ... Video demodulation circuit 105b ... Audio demodulation circuit 105c ... Video output terminal 105d ... Split output terminal 105e ... First audio output terminal 106 ... First audio muting circuit 107 ... First carrier modulation circuit 108 ... Amplifier 109 ... Trap filter 110 ... -Amplifier 111 ... 2nd audio | voice carrier muting circuit 112 ... 2nd audio | voice carrier detection circuit 113 ... Addition circuit 114 ... Modulation circuit 114a ... Video processing IC 114b ... Addition circuit 114c ... AM modulator 115 ... Microcomputer 116 ... Output terminal 201 ... Pseudo second carrier oscillator 2 02 ... Amplifier 203 ... Pseudo second carrier muting circuit 204 ... Addition circuit 3011-301n ... CATV terminal device 3021-302n ... Television receiver 303 ... Broadcast center 304 ... BS antenna 305 ... BS converter 306 ... Television antenna 307 ... Television camera 308 ... VTR 309 ... Transmission cable 401 ... Input terminal 402 ... Tuner 403 ... Band Pass filter 404 ... Band pass filter 405 ... IC for audio / video detection 405a ... Video demodulation circuit 405b ... Audio demodulation circuit 405c ... Video output terminal 405d ... Split output terminal 405e ... First audio output Terminal 406 ... Band pass filter 407 ... Band pass filter 408 ... Two-carrier television audio multiplex demodulation IC 408a ... First audio carrier FM detection circuit 408b ... Second audio carrier FM detection circuit 408c ... Multiplex audio demodulation circuit 409 ... Matrix circuit 410 ... 1 carrier wave modulation circuit 411 ... Second carrier wave modulation circuit 412 ... Addition circuit 413 ... Modulation circuit 413a ... Video processing IC 413b ... Addition circuit 413c ... AM modulator 414 ... Microcomputer 415 ... ..Output terminals

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Horie 4-15-5 Omorinishi, Ota-ku, Tokyo Pioneer Co., Ltd. Omori Plant (72) Inventor Yuichi Nishina 4-15 Omorinishi, Ota-ku, Tokyo No. 5 Pioneer Co., Ltd. Omori Factory

Claims (4)

[Claims] 1. A television signal including a video signal, a first audio carrier including a first audio signal, and a second audio carrier including a second audio in one channel is received, and the television signal is predetermined. A television signal conversion device for converting a television signal of a channel, comprising: a video demodulation circuit for demodulating the video signal from the television signal; and a first audio demodulation for demodulating the first audio signal from the television signal. A circuit, a first audio muting circuit that mutes the first audio signal according to an audio muting signal, a second audio carrier separation circuit that separates the second audio carrier from the television signal, and the audio muting A second audio carrier muting circuit for muting the second audio carrier according to a signal; and the first audio muting circuit The output signal of the first
A first carrier modulation circuit that modulates a carrier having a frequency corresponding to an audio carrier; the video signal; a signal output from the first carrier modulation circuit; and a signal output from the second audio carrier separation circuit. A television signal conversion apparatus comprising: a modulation circuit for adding and modulating a main carrier wave corresponding to the predetermined channel to output a television signal of the predetermined channel. 2. The television signal conversion device according to claim 1, further comprising a second audio carrier detection circuit for detecting the second audio carrier, wherein the second audio carrier muting circuit includes the second audio carrier. A television signal conversion device, wherein the signal output from the second audio carrier wave separation circuit is muted when the second audio carrier wave is not detected by the detection circuit. 3. A television signal including a video signal, a first audio carrier including a first audio signal, and a second audio carrier including a second audio on one channel is received, and the television signal is predetermined. A television signal conversion device for converting a television signal of a channel, comprising: a video demodulation circuit for demodulating the video signal from the television signal; and a first audio demodulation for demodulating the first audio signal from the television signal. A circuit, a first audio muting circuit that mutes the first audio signal according to an audio muting signal, a second audio carrier separation circuit that separates the second audio carrier from the television signal, and the audio muting A second audio carrier muting circuit for muting the second audio carrier according to a signal; and the first audio muting circuit The output signal of the first
A first carrier wave modulation circuit that modulates a carrier wave having a frequency corresponding to an audio carrier wave, a pseudo second carrier wave oscillator that oscillates at the frequency of the second audio carrier wave, and an output of the pseudo second carrier wave oscillator according to the audio muting signal A pseudo second carrier muting circuit for outputting a signal, the video signal, a signal output from the first carrier modulating circuit, a signal output from the second audio carrier separating circuit, and the pseudo second carrier A television signal conversion device, comprising: a modulation circuit that adds a signal output from an oscillator and modulates a main carrier wave corresponding to the predetermined channel to output a television signal of the predetermined channel. 4. The television signal conversion apparatus according to claim 3, further comprising a second audio carrier detection circuit for detecting the second audio carrier, wherein the second audio carrier muting circuit includes the second audio carrier. When the detection circuit does not detect the second audio carrier wave, the signal output from the second audio carrier wave separation circuit is muted, and the pseudo second carrier wave muting circuit is unmuted to cancel the pseudo second carrier wave. A television signal converter, which outputs an output signal of an oscillator.