JP2910530B2 - Composite audio demodulation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a composite audio demodulation circuit for television audio multiplex broadcasting. In particular, the present invention relates to a composite audio demodulation circuit which does not switch to another audio mode such as stereo or bilingual due to malfunction even if a monaural audio signal is input from a noisy composite audio signal.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a conventional complex sound demodulation circuit.

Conventionally, a composite audio demodulation circuit has a configuration as shown in FIG. In FIG. 4, a composite audio demodulation circuit includes an input terminal 1 for inputting a composite audio signal and an input terminal 1.
A band-pass filter 2 for extracting a center frequency (about 31.5 kHz) of an audio subcarrier transmitted during stereo audio broadcasting and bilingual audio broadcasting from a composite audio signal; a monostable multivibrator circuit 18 for prolonging the output signal of the pass filter 2, the other are different at the time of the control signal sub-carrier from the composite audio signal is AM modulated control channel signal [stereo audio broadcasting time and Nike language audio broadcasting Frequency (982.5
Hz and 922.5 Hz), a control channel signal that is AM-modulated is transmitted, and during monaural audio broadcasting, neither the audio subcarrier nor the control signal is transmitted. ], A demodulator 4 for demodulating an AM-modulated control channel signal, a band-pass filter 5 for extracting a control signal from an output signal of the demodulator 4, and a frequency of a reference frequency oscillator 7. A frequency comparator 8 for comparing the output frequency of the band-pass filter 5, a logical NOT circuit 9 for inverting an output signal of the band-pass filter 5, and an output signal of the mono-multi circuit 18 and an output signal of the logical NOT circuit 9; An AND circuit 10 for performing an AND operation and outputting that both the sub-channel signal and the control channel signal are detected, and a logical NOT circuit 11 for inverting the output signal of the frequency comparator 8
AND circuit 13 for calculating the logical product of the output signal of the logical AND circuit 10 and the output signal of the logical NOT circuit 11; a logical NOT circuit 12 for inverting the output signal of the logical NOT circuit 11; An AND circuit 14 for ANDing the output signal and the output signal of the logical NOT circuit 12; an output terminal 15 connected to the output of the AND circuit 10 for outputting a monaural audio mode discrimination signal during monaural audio broadcasting; Integrated circuit 13
And an output terminal 16 connected to an output of the AND circuit for outputting a stereo audio mode discrimination signal during stereo audio broadcasting, and an output connected to the output of the AND circuit 14 for outputting a bilingual audio mode discrimination signal during bilingual audio broadcasting And a terminal 17.

[0004]

However, in such a conventional composite audio demodulation circuit, when a composite audio signal having a large amount of noise is input to an input terminal, particularly when the audio mode is a monaural signal, the audio mode is not changed. The control signal after the AM demodulation of the control signal to be discriminated also has a noise component, and the frequency comparator 8 for discriminating the voice mode malfunctions due to the noise component, and the switching between the stereo voice mode and the bilingual voice mode malfunctions. There was a problem to do.

[0005] Here, there is a proposal in which the audio circuit of the television receiver is adapted to a bilingual audio mode of audio multiplex broadcasting with a simple configuration according to a control signal (Japanese Patent Laid-Open No. 59-30).
381), this does not prevent erroneous switching of the audio mode due to the control signal. In addition, the control signal is discriminated in the electronic circuit using the carrier of the control channel signal, and the control signal is stably discriminated against mechanical vibrations and the like without using components such as a lead filter. There is a proposal to extract a control signal from a voice multiplex signal (Japanese Unexamined Patent Publication No.
This has a different circuit configuration and does not prevent erroneous switching of the audio mode due to a control signal.

The present invention solves the above problems,
It is an object of the present invention to provide a composite audio demodulation circuit which does not malfunction in audio mode switching even in a monaural audio mode of a noisy composite audio signal.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a sub-channel signal detecting means (21) for detecting a sub-channel signal transmitted from a composite audio signal during stereo audio broadcasting and bilingual audio broadcasting. Control signal extracting means (2) for extracting a control channel signal from the composite audio signal and demodulating the control signal.
2) and the sub-channel signal detecting means (21)
When the control signal extracting means detects the channel signal,
A first AND circuit (6) for passing an output signal;
The output of the control signal extracting means passing through the first AND circuit
The frequency of the control signal to be input is compared with a predetermined reference frequency.
A frequency comparator (8), and an output of the control signal extracting means.
ANDing means (23) for ANDing a signal with an output signal of the sub-channel signal detecting means , and an audio mode is determined from an output signal of the frequency comparator and an output signal of the ANDing means (23). Voice mode determination means (24).

Further, the present invention is characterized in that the sub- channel signal detecting means extracts a center frequency of an audio sub-carrier transmitted during stereo audio broadcasting and bilingual audio broadcasting from the composite audio signal. Filter (2),
A mono-multi circuit (18) for extending the output signal of the band-pass filter;
A second bandpass filter (3) for extracting a control channel signal whose control signal subcarrier is amplitude-modulated from the composite audio signal, and a demodulator (4) for demodulating an output signal of the second bandpass filter. And a third band-pass filter (5) for extracting a control signal from the output signal of the demodulator, wherein the logical product means inverts the output signal of the control signal extracting means (1). 9) and the sub
A second logic for performing an AND operation on the output signal of the channel signal detection means and the output signal of the first logical NOT circuit to output that the sub- channel signal and the control channel signal have been detected; A second logical NOT circuit (11) for inverting an output signal of the frequency comparator; an output signal of the second logical product circuit; A third logical AND circuit (13) for performing a logical AND operation with the output signal of the second logical NOT circuit, a third logical NOT circuit (12) for inverting the output signal of the second logical NOT circuit,
A fourth AND circuit (1) which performs an AND operation on the output signal of the second AND circuit and the output signal of the third logical NOT circuit
4) and a first output terminal (1) connected to the output of the second AND circuit and outputting a monaural audio mode determination signal.
5) and a second output terminal (1) which is connected to the output of the third AND circuit and outputs a stereo audio mode determination signal.
6) and a third output terminal (1) which is connected to the output of the fourth AND circuit and outputs a bilingual voice mode determination signal.
7).

Further, the present invention can include a reference frequency oscillator (7) for generating the predetermined reference frequency.

Further, according to the present invention, the composite audio signal includes 5
A main channel signal in a frequency band of 0 Hz to 15 kHz;
31.5 for stereo and bilingual audio broadcasting
A sub-channel signal frequency-modulated at a frequency of 16 kHz to 47 kHz with kHz as an audio sub- carrier, and a control signal sub- carrier at 55.125 kHz is amplitude-modulated with a control signal of 982.5 Hz during stereo audio broadcasting, 922.5HZ for bilingual audio broadcasting
And a control channel signal amplitude-modulated with a control signal having a frequency of

[0011]

The output signal of the control signal extracting means and the sub- channel signal
By taking the logical product of the output signal of the detection means and masking the noise from the control signal extraction means at the time of broadcasting the monoler signal, erroneous operation of the audio mode switching is prevented even in the monaural audio mode of the noisy composite audio signal. it can.

[0012]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a composite audio demodulation circuit according to one embodiment of the present invention. FIG. 2 is a diagram showing a frequency spectrum and a frequency shift of a composite audio signal of the composite audio demodulation circuit of the present invention. 1 and 2, a composite audio demodulation circuit includes an input terminal 1 for inputting a composite audio signal, and a sub- channel signal transmitted during stereo audio broadcast and bilingual audio broadcast from the composite audio signal from the input terminal 1. Detect
Sub-carrier extracting means 21 which is a sub-channel detecting means
Control signal extracting means 22 for extracting a control channel signal from the composite audio signal from input terminal 1 and demodulating the control signal.
A frequency comparator 8 for comparing a predetermined reference frequency with an output frequency of the control signal extracting means;
ANDing means 23 for calculating the logical product of the output signal of the subcarrier extracting means 21 and the output signal of the subcarrier extracting means 21, and the voice mode determining means for determining the voice mode from the output signal of the frequency comparator 8 and the output signal of the logical product means 23 24.

The feature of the present invention is that the output signal of the sub-carrier extracting means 21 and the control signal extracting means 2
That is, the AND circuit 6 is inserted into the circuit that supplies the output signal of No. 2 to the frequency comparator 8.

That is, the sub-carrier extraction means 21 outputs the sound of the sub-channel signal transmitted during the stereo audio broadcast and the bilingual audio broadcast from the composite audio signal from the input terminal 1.
The control signal extracting means 22 includes a band-pass filter 2 as a first band-pass filter for extracting the center frequency of the voice subcarrier, and a mono-multi circuit 18 for extending the output signal of the band-pass filter 2. A band-pass filter 3 as a second band-pass filter for extracting a control channel signal in which a control signal sub-carrier is amplitude-modulated from the composite audio signal, a demodulator 4 for demodulating an output signal of the band-pass filter 3, and a demodulator 4 includes a band-pass filter 5 as a third band-pass filter for extracting a control signal from the output signal of the control signal extracting unit 4, and a logical product unit 23 performs a logical operation as a first logical NOT circuit for inverting the output signal of the control signal extracting unit 22. The logical AND of the output signal of the NOT circuit 9 and the output signal of the logical NOT circuit 9 with the output signal of the subcarrier extraction means 21 is obtained.
AND circuit 1 as a second AND circuit for outputting that both the channel signal and the control channel signal are detected
0, the audio mode discriminating means 24 includes a logical NOT circuit 11 as a second logical NOT circuit for inverting an output signal of the frequency comparator 8, an output signal of the AND circuit 10, and an output signal of the logical NOT circuit 11 AND circuit 13 as a third AND circuit for obtaining a logical AND of the logical AND circuit, and logical NOT circuit 12 as a third logical NOT circuit for inverting the output signal of logical NOT circuit 11
AND circuit 14 as a fourth AND circuit for performing a logical AND operation between the output signal of the AND circuit 10 and the output signal of the logical NOT circuit 12, and a determination of the monaural audio mode connected to the output of the AND circuit 10 An output terminal 15 as a first output terminal for outputting a signal; an output terminal 16 as a second output terminal connected to the output of the AND circuit 13 for outputting a determination signal of a stereo sound mode; and an output of the AND circuit 14 And an output terminal 17 as a third output terminal connected to the output terminal for outputting a bilingual voice mode determination signal.

Further, a reference frequency oscillator 7 for generating a predetermined reference frequency is provided.

Further, the composite audio signal is 50 Hz to 15 Hz.
Main channel signal in the frequency band of kHz and 31.5 kHz
a sub-channel signal frequency-modulated at a frequency of 16 kHz to 47 kHz as an audio sub- carrier of
5.125 kHz is used as a control signal subcarrier, and is amplitude-modulated with a control signal having a frequency of 982.5 Hz during stereo audio broadcasting, and is modulated with a control signal having a frequency of 922.5 Hz during bilingual audio broadcasting. Be composed.

A composite audio demodulation circuit having such a configuration will be described.

In FIG. 1 and FIG. 2, an input terminal 1 inputs a composite audio signal composed of a main channel signal, a sub channel signal and a control channel signal. The band pass filter 2 is a sub-channel which is transmitted from the composite audio signal from the input terminal 1 during stereo audio broadcasting and bilingual audio broadcasting.
The center frequency (approximately 31.5 kHz) of the audio sub-carrier of the channel signal (not transmitted during mono-rel audio broadcasting) is extracted. The mono-multi circuit 18 extends the output signal of the band-pass filter 2 and outputs a pulse signal. The band-pass filter 3 is a control channel signal in which the control signal subcarrier is AM-modulated from the composite audio signal from the input terminal 1 (a control signal of 982.5 Hz for stereo audio broadcasting and 922.5 Hz for bilingual audio broadcasting). , A control channel signal that is AM-modulated is transmitted, and neither audio subcarrier nor control signal is transmitted during monaural audio broadcasting.) The demodulator 4 demodulates the modulated control channel signal, and the bandpass filter 5 extracts a control signal from the output signal of the demodulator 4. The logical product circuit 6 calculates the logical product of the output signal of the mono-multi circuit 18 and the output signal of the bandpass filter 5. The frequency comparator 8 compares a predetermined reference frequency from the frequency oscillator 7 with an output frequency of the AND circuit 6. Here, for example, the predetermined reference frequency is 92
At 2.5Hz, 982.5H at the time of stereo sound broadcasting now
"1" is output when z is input, "0" is output when 922.5 Hz for bilingual audio broadcasting is input, and "0" is output for monaural audio broadcasting. The logical NOT circuit 9 inverts the output signal of the band-pass filter 5 to output a pulse signal, and the logical AND circuit 10 calculates the logical product of the output signal of the mono-multi circuit 18 and the output signal of the logical NOT circuit 9 to obtain a sub- channel. It outputs that both the signal and the control channel signal have been detected. The logical NOT circuit 11 inverts the output signal of the frequency comparator 8, and the logical AND circuit 13 calculates the logical product of the output signal of the logical AND circuit 10 and the output signal of the logical NOT circuit 11. The logical NOT circuit 12 inverts the output signal of the logical NOT circuit 11, and the logical AND circuit 14 calculates the logical product of the output signal of the logical AND circuit 10 and the output signal of the logical NOT circuit 12. The output terminal 15 is connected to the output of the AND circuit 10 and outputs a monaural audio mode determination signal during monaural audio broadcasting. The output terminal 16 is the AND circuit 1
3 and outputs a stereo audio mode discrimination signal during stereo audio broadcasting. The output terminal 17 is connected to the output of the AND circuit 14 and outputs a bilingual audio mode discrimination signal during bilingual audio broadcasting.

Here, if a complex audio signal having a large amount of noise is input, the sub- channel signal is input in the monaural audio mode.
Since the signal is not transmitted, even if there is a noise component that has passed through the band-pass filter 5, it is masked by the AND circuit 6, so that the frequency comparator 8 does not malfunction. Therefore, even in the monaural audio mode of the noisy composite audio signal, malfunction of audio mode switching can be prevented.

FIG. 3 is a block diagram of a composite audio demodulation circuit according to another embodiment of the present invention. The present embodiment is different from the circuit configuration of the above-described embodiment in that the output signal of the AND circuit 6 is input to the logical NOT circuit 9 instead of the output signal of the band-pass filter 5, and the frequency comparator Malfunction can be prevented.

[0022]

As described above, the present invention has an excellent effect that the malfunction of the sound mode switching can be eliminated even in the monaural sound mode of the noisy composite sound signal.

[Brief description of the drawings]

FIG. 1 is a block diagram of a composite audio demodulation circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a frequency spectrum and a frequency shift of a composite audio signal of the composite audio demodulation circuit of the present invention.

FIG. 3 is a block diagram of a composite audio demodulation circuit according to another embodiment of the present invention.

FIG. 4 is a block diagram of a conventional complex audio demodulation circuit.

[Description of Signs] 1 Input terminal 2, 3, 5 Band-pass filter 4 Demodulator 6, 10, 13, 14 Logical product circuit 7 Reference frequency oscillator 8 Frequency comparator 9, 11, 12 Logical NOT circuit 15, 16, 17 Output terminal 18 Mono-multi circuit 21 Sub-carrier extraction means 22 Control signal extraction means 23 Logical product means 24 Voice mode discrimination means

Claims (4)

(57) [Claims] 1. A sub-channel signal transmitted during stereo audio broadcasting and bilingual audio broadcasting from a composite audio signal.
A sub-channel signal detecting means (21) for detecting , a control signal extracting means (22) for extracting a control channel signal from the composite audio signal and demodulating a control signal, and a sub-channel signal detecting means (21)
Output signal of the control signal extracting means when
And a control signal extracting means passing through the first AND circuit
The frequency of the control signal output from the
A frequency comparator to be compared, an output signal of the control signal extracting means, and the sub-channel signal.
AND means (2) for performing an AND operation with the output signal of the detecting means
3), the output signal of the frequency comparator and the logical product means (23)
And a sound mode discriminating means (24) for discriminating a sound mode from the output signal of the composite sound demodulation circuit. Wherein said sub-channel signal detection means, the first band-pass filter for extracting a center frequency of the audio subcarrier that is transmitted from the composite audio signal at the stereo audio broadcasting time and Nike language audio broadcasting (2) And a mono-multi circuit (1) for extending the output signal of this bandpass filter.
8), wherein the control signal extracting means controls the control signal from the composite audio signal.
A second bandpass filter (3) for extracting a control channel signal whose signal subcarrier is amplitude-modulated, and a demodulator (4) for demodulating an output signal of the second bandpass filter.
A third band-pass filter (5) for extracting a control signal from the output signal of the demodulator, wherein the logical AND means inverts an output signal of the control signal extracting means (9) ) And said secondary channel
A second AND circuit (1) outputs the AND of the output signal of the signal detecting means and the output signal of the first logical NOT circuit to output the detection of the subcarrier and the control channel signal.
0), wherein the audio mode determination means includes: a second logical NOT circuit (11) for inverting an output signal of the frequency comparator; an output signal of the second AND circuit; A third AND circuit (13) for performing an AND operation with the output signal of the NOT circuit;
A third logical NOT circuit (12) for inverting an output signal of the second logical NOT circuit; and a logical product of an output signal of the second logical AND circuit and an output signal of the third logical NOT circuit. A fourth logical product circuit (14), a first output terminal (15) connected to an output of the second logical product circuit and outputting a monaural audio mode determination signal, and the third logical product circuit A second output terminal (16) connected to the output of the fourth AND circuit for outputting a determination signal of the stereophonic mode, and a third output terminal connected to the output of the fourth AND circuit and outputting a determination signal of the bilingual voice mode. 2. The composite audio demodulation circuit according to claim 1, further comprising an output terminal. 3. The composite audio demodulation circuit according to claim 1, further comprising a reference frequency oscillator for generating said predetermined reference frequency. 4. The composite audio signal has a frequency of 50 Hz to 15 k.
Hz main band signal and 31.5kHz
Is the center frequency voice subcarrier and 16 kHz to 47 kHz.
Stereo sound frequency-modulated with frequency in the z frequency band
Voice broadcast and bilingual voice broadcast sub-channel signals;
5.125 kHz is used as a subcarrier, and is amplitude-modulated by a control signal having a frequency of 982.5 Hz during stereo audio broadcasting.
2. The composite audio demodulation circuit according to claim 1, comprising a control signal having a frequency of 922.5 Hz and a control channel signal amplitude-modulated during bilingual audio broadcasting.