JPH0724822Y2 - TV audio multiplex mute circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial field of application The present invention relates to a mute circuit for television sound multiplexing, and in particular, mute the sound output when the electric field strength of the receiving channel decreases and the multiplexed signal cannot be demodulated. The present invention relates to a television audio multiplex mute circuit suitable for the operation.

(B) Prior Art As a conventional television audio multiplex signal receiving device, for example,
As shown in FIG. 6, it is composed of a television audio receiving section and a television audio multiplex signal demodulation circuit.

In the figure, 20 is a television audio multiplex signal demodulation circuit, 21 is a television audio receiving section, and 22 is a television receiving antenna.

The block configuration is such that the TV audio multiplex broadcast signal received by the TV receiving antenna 22 is added to the TV audio receiving unit 21, and is processed by the front end, the IF amplification circuit, and the FM detection circuit into the main channel signal, the sub-channel signal, and the control signal (pilot). It is output as an MPX signal in which the three signals of (carrier) are combined and input to the television audio multiplex signal demodulation circuit 20.

In the TV audio multiplex signal demodulation circuit 20 to which the MPX signal is added, the main audio signal, the sub-channel signal and the control signal (pilot carrier) are separated separately after amplifying the MPX signal to a predetermined level, and only the sub-channel signal FM detection is performed and demodulated into an audio signal, and the demodulated sub-channel audio signal and main channel signal are subjected to a matrix operation according to a control signal to extract an output audio signal in two languages.

The control signal (pilot carrier) is an AM modulation signal whose modulation frequency is different between bilingual and stereo broadcasting, and the modulation frequency is identified to determine whether bilingual broadcasting or stereo broadcasting. There is.

Therefore, if the electric field strength of the receiving channel is weak, the control signal level cannot be detected, and the sub-channel signal is not FM-detected either. Therefore, only the main channel signal is output and a so-called monaural signal is output.

(C) Problems to be Solved by the Invention However, in the above-mentioned conventional television audio multiplex signal receiving apparatus, as shown in FIG. 6, it is configured by the television audio receiving section 21 and the television audio multiplex signal demodulating circuit 20. Since the main channel signal and the sub-channel signal of the television multiplex broadcast are demodulated and separated by the television audio multiplex signal demodulation circuit 20 and output, the electric field strength of the receiving channel decreases and the control signal (pilot carrier) can be detected. When it disappears, the sub-channel signal is not demodulated, and even if the sub-channel is selected, a monaural signal of only the main channel is output, which gives the viewer a feeling of strangeness.

The present invention has been made in view of the above points, and the purpose thereof is to solve the drawbacks of the conventional example, and when the sub-channel signal is selected and the electric field strength of the audio multiplex broadcasting decreases, the main channel The present invention provides a mute circuit for multiplexing television sound, which is configured so as to mute an output signal that has become a so-called monaural signal and not output it so as not to give a viewer a feeling of strangeness.

(D) Means for Solving the Problem A mute circuit for multiplexing television sound according to the present invention comprises a television receiver for receiving television broadcasting, and a television sound multiplex signal demodulating circuit for demodulating an audio multiplex signal for television broadcasting. In the television audio multiplex broadcasting receiver configured by, a mute drive circuit and a mute circuit are provided between the audio signal output circuit output from the television audio multiplex signal demodulation circuit and the bilingual discrimination signal output circuit, A monophonic audio signal output from the TV audio multiplex signal demodulation circuit when the bilingual discrimination pilot carrier is deteriorated due to the decrease in the electric field strength of the reception channel frequency while receiving the bilingual broadcast and selecting the sub signal. It is configured to be muted.

(E) Operation According to the present invention, in a television sound multiplex broadcast receiving apparatus including a television receiver for receiving a television broadcast and a television sound multiplex signal demodulation circuit for demodulating a television multiplex audio multiplex signal. , A mute drive circuit and a mute circuit are provided between the audio signal output circuit output from the TV audio multiplex signal demodulation circuit and the bilingual discrimination signal output circuit, and the bilingual broadcast is received and the sub signal is selected. In this condition, the monaural audio signal output from the TV audio multiplex signal demodulation circuit is muted when the bilingual discrimination pilot carrier deteriorates due to the decrease in the electric field strength of the receiving channel frequency. When receiving a word broadcast and selecting a sub signal, the electric field strength becomes weaker and the audio signal changes from the sub channel signal to the main channel. Even if the signal is switched to the channel signal, the main channel signal which is a monaural audio signal can be prevented from being output.

(F) Embodiment An embodiment of the mute circuit for multiplexing television sound according to the present invention will be described with reference to FIGS.

1 is a circuit diagram of the first embodiment of the present invention, FIG. 2 is a circuit diagram of the second embodiment, FIG. 3 is a block diagram of the third embodiment, and FIG. 4 is an S meter output and an attenuator with respect to an antenna input level. FIG. 5 is a characteristic diagram showing the damping ratio of FIG.

In the figure, 1 is a television audio multiplex signal demodulation circuit, 2 is 2
National language discrimination signal, 3 is a sub-channel mode selection signal,
4 is an AND gate circuit, 5 is a mute circuit, 6 is a front end circuit, 7 is an audio intermediate frequency detection circuit, 8 is a comparator, 9 is an analog switch, 10 is an S meter signal, 11
Is a composite audio signal, 12 is an attenuator, 13 is an A / D converter, 1
4 is a microcomputer.

As for the circuit configuration, the bilingual discrimination signal 2 output from the TV audio multiplex signal demodulation circuit 1 is connected to the gate a of the AND gate circuit 4, and the other gate b is selected when the sub-channel mode is selected. Is connected to the sub-channel mode selection signal 3 and the output of the AND gate circuit 4 is connected to the mute circuit 5.

On the other hand, the mute signal output from the mute circuit 5 is connected to each of the main audio signal output and the sub audio signal output of the bilingual broadcast output from the television audio multiplex signal demodulation circuit 1.

The operation of the circuit block configured as described above will be described. The low level and high level of the bilingual discrimination signal 2 output from the television audio multiplex signal demodulation circuit 1 are switched depending on whether bilingual broadcasting is detected. It is designed to be replaced, and outputs a low level when receiving a bilingual broadcast.

In addition, the sub-channel mode selection signal 3 for selecting the bilingual broadcasting is obtained by switching the matrix control circuit provided in the television audio multiplex signal demodulation circuit 1 to the bilingual mode by a mode select switch (not shown).
High level is output.

Therefore, the mode selection switch is set to the bilingual mode, and the sub-channel mode selection signal 3 is High.
In addition to the gate b of the AND gate circuit at the level, and when receiving the bilingual broadcast of the TV audio multiplex broadcast, the bilingual discrimination signal 2 from the TV audio multiplex signal demodulation circuit 1 is at the low level. Since it outputs and is added to the gate a of the AND gate circuit 4, the gate a of the AND gate circuit 4 does not open, the output of the AND gate circuit 4 also becomes Low level, the operation of the mute circuit 5 is not performed, and only the two languages of the sub-channel are Is output.

If the control signal in the composite signal output after FM detection cannot be detected due to the decrease in the electric field strength of the receiving channel of the TV audio multiplex broadcast, the bilingual discrimination signal 2 will also not be output and the high level will be AND gate. Since it is added to the gate a of the circuit 4, the gates a and b of the AND gate circuit 4 are at the high level, both gates are opened, the high level is output to the output of the AND gate circuit 4, and the mute circuit 5 is operated. .

When the mute circuit 5 operates, the output of the mute circuit 5 is
Both the main and sub audio signals output from the TV audio multiplex signal demodulation circuit 1 are pulled to the ground level to set the output of the audio signal to 0 level and perform the mute operation.

By performing the above operation, the electric field strength is lowered during the reception of the television audio multiplex broadcast, the bilingual audio signal of the sub-channel is not output, and the main channel audio signal is output from the speaker in a monaural state. It is possible to prevent discomfort that the main voice signal is heard or the foreign language of the sub-channel is heard due to the change of the electric field strength.

The second embodiment will be described. The IF signal output from the front end 6 of the television audio receiving unit is output as an audio multiplex composite signal 11 in the audio intermediate frequency detection circuit 7 and is output at a DC level proportional to the electric field strength. Outputs S meter signal 10.

The S meter signal 10 is applied to the-input terminal of the comparator 8 and the reference voltage V _REF is applied to the + input terminal of the comparator 8 in a resistance-divided manner.

The output of the comparator 8 is applied to the gate of the AND gate circuit 4, and the sub-channel mode selection signal 3 is connected to the other gates.

The output of the AND gate circuit 4 is connected to the mute circuit 5, and the output of the mute circuit 5 is connected to the main and sub-channel audio signal output circuits.

Explaining the mute operation, the electric field strength of the television audio multiplex broadcast is reduced, the DC level S meter signal 10 output from the audio intermediate frequency detection circuit 7 is reduced, and the +
When it becomes lower than the reference voltage V _REF applied to the input terminal, the output of the comparator 8 goes from the low level to the high level and is output.

When the comparator 8 outputs at the high level, the AND gate circuit 4 opens the AND gate and outputs the high level at the output when the sub-channel mode signal 3 is selected and is added to the gate at the high level, and the mute circuit 5 operates. .

While the mute circuit 5 is operating, the output of the mute circuit 5 pulls the main and sub-channel audio signal output circuits to 0 level to perform the mute operation.

Further, the third embodiment will be described. In the same manner as in the second embodiment, the audio intermediate frequency detection circuit 7 outputs a composite audio signal.
11 is output and added to the input side of the attenuator 12, and
The S meter signal 10 is connected to the terminal of the analog switch 9.

The other terminal of the analog switch 9 is connected to the control terminal of the attenuator 12, and the composite audio signal 11 is output from the output terminal of the attenuator 12 to the television audio multiplex signal demodulation circuit 1.

To explain the mute operation, the audio intermediate frequency detection circuit 7
When the sub-channel mode signal 3 is selected and is applied at a high level, the S meter signal 10 output from is turned on to the analog switch 9 and applied to the control terminal of the attenuator 12.

The operation of the attenuator 12 reduces the attenuation ratio when the level of the S meter signal 10 output from the audio intermediate frequency detection circuit 7 is large in proportion to the electric field strength of the television audio multiplex broadcast, and the level of the S meter signal 10 decreases the electric field strength. When it becomes smaller, the damping ratio is controlled to increase.

The relationship between the output level of the S meter signal 10 and the attenuation ratio of the attenuator 12 will be described. As shown in FIG. 4, the S meter signal output level 10 also increases or decreases in proportion to the antenna input level.

The S input signal at this time is defined as the discrimination sensitivity at the point of the antenna input level at which the sub-channel audio signal is not demodulated.
At 10, the attenuator 12 has the maximum attenuation ratio, and conversely, when the antenna input level increases and the level of the S meter signal 10 becomes maximum, the attenuation ratio of the attenuator 12 is set to 0.

With the above configuration, the electric field strength of the television audio multiplex broadcast is lowered, and the attenuation ratio of the attenuator 12 is increased in response to the decrease in the level of the S meter signal 10 accompanying the antenna input, thereby gradually increasing the composite. So-called soft mute can be performed in which the level of the audio signal 11 is reduced.

Explaining Example 4 to which a microcomputer is applied, the S meter signal 10 output from the audio intermediate frequency detection circuit 7 is added to an A / D converter 13 and converted into a digital signal and input to an input port of a microcomputer 14. Has been done.

Further, a bilingual discrimination signal 2 output from the television sound multiplex signal demodulation circuit 1 and a sub mode selection signal 3 from a mode selection switch (not shown) are input to the input port of the microcomputer 14, and the microcomputer 14
A signal for turning ON / OFF the operation of the mute circuit 5 is output from the output port of.

The microcomputer 14 is designed to monitor and control the digital S signal 10 output from the A / D converter 13 with reference to a threshold voltage of a level higher than the discrimination sensitivity that can output a bilingual discrimination signal. There is.

An output terminal of the mute circuit 5 is connected to the L and R audio signal output terminals output from the television audio multiplex signal demodulation circuit 1.

When receiving the bilingual broadcast with the above configuration, when the mode switch is selected to the submode and the submode selection signal is output, if the electric field strength weakens and the pilot carrier signal cannot be detected, the bilingual language will be detected. At the same time that the discrimination signal 2 is no longer output, the S meter signal 10 drops below the threshold voltage set in the microcomputer 14, and a signal for turning on the operation of the mute circuit 5 is output from the output port of the microcomputer 14.

Therefore, the mute circuit 5 is in the mute operation state,
It functions to mute the L and R audio signals output from the television audio multiplex signal demodulation circuit 1.

Next, when the electric field strength rises and the S meter signal 10 increases above the threshold voltage set in the microcomputer 14, the bilingual discrimination signal 2 is restored and output, so the mute operation is canceled and bilingual The signals are output from the L and R audio output terminals of the television audio multiplex signal demodulation circuit 1.

Further, when the broadcasting of the receiving channel is changed from the bilingual broadcasting to the monaural (or stereo) broadcasting when the electric field strength is below the discrimination sensitivity, the bilingual discrimination signal 2 is not output. However, the microcomputer 14 works to release the mute operation when the electric field strength is restored and the S meter signal 10 exceeds the discrimination sensitivity, and the monaural (or stereo) broadcasting can be output from the television sound multiplex signal demodulation circuit 1. it can.

(G) Effect of the Invention According to the mute circuit for multiplexed television audio according to the present invention, the mute drive circuit is provided between the audio signal output circuit output from the multiplexed television audio signal demodulation circuit and the bilingual discrimination signal output circuit. , A mute circuit is provided, and when the electric field strength of the TV audio multiplex broadcasting is lowered, the monaural audio signal output from the TV audio multiplex signal demodulating circuit is muted, so that the bilingual sub signal is selected. In addition, there is an effect that it is possible to prevent a feeling of strangeness and a feeling of strangeness that may become a main signal or a sub signal depending on the reception sensitivity.

Moreover, it has excellent features such as a simple structure and easy implementation because it can be constructed at low cost.

[Brief description of drawings]

1 to 5 show an embodiment of a mute circuit for television sound multiplexing according to the present invention, FIG. 1 is a circuit diagram of the first embodiment of the present invention, FIG. 2 is a circuit diagram of the second embodiment, and FIG. 3 is a block diagram of the third embodiment, FIG. 4 is a characteristic diagram showing the S meter output with respect to the antenna input level, and FIG. 5 is a block diagram of the fourth embodiment. FIG. 6 is a block diagram of a device for receiving a television audio multiplex broadcast of a conventional example. Explanation of main symbols 1: TV audio multiplex signal demodulation circuit 2: Bilingual discrimination signal 3: Sub-channel mode selection signal 4: AND gate circuit 5: Mute circuit 6: Front end circuit 7: Audio intermediate frequency detection circuit 8: Comparator 9: Analog switch 10: S meter signal 11: Composite audio signal 12: Attenuator 13: A / D converter 14: Microcomputer

Claims (1)

[Scope of utility model registration request] 1. A television sound multiplex broadcast receiving apparatus comprising a television receiver for receiving a television broadcast and a television sound multiplex signal demodulation circuit for demodulating a television multiplex sound multiplex signal, wherein the television sound multiplex is provided. A mute drive circuit and a mute circuit are provided between the audio signal output circuit output from the signal demodulation circuit and the bilingual discrimination signal output circuit, and in the state where the bilingual broadcast is received and the sub signal is selected, When the pilot carrier for bilingual discrimination is deteriorated due to the decrease in the electric field strength of the reception channel frequency, the monaural audio signal output from the TV audio multiplex signal demodulation circuit is muted. Mute circuit.