JPH0516790Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to a demodulation device for a two-carrier audio multiplex system, which is the main system for audio multiplex broadcasting in Europe.

(Prior art) The audio multiplex broadcasting system adopted in European countries uses two types of carrier waves, so-called
This is a carrier audio multiplexing method. This 2-carrier audio multiplexing method frequency-modulates (FM) the 5.5MHz first carrier (main audio carrier) with the main (or (L+R)/2) audio, and transmits the 5.74MHz
A second carrier wave (sub-audio carrier) of Hz is frequency-modulated and carried by a sub-channel signal in which the sub-(or R) audio and the pilot carrier are superimposed.

The pilot carrier is used to enable the receiver to determine whether the broadcast being received is a stereo broadcast or a bilingual broadcast. The pilot carrier has a frequency of 3.5× _H ( _H is the horizontal scanning frequency) and is amplitude modulated (AM) with a discrimination signal for discriminating each of the broadcasts. The discrimination signal is 117.5Hz ( _H /133) for stereo broadcasting and 274.1Hz ( _H /57) for bilingual broadcasting.

By the way, in the case of monaural broadcasting, it is possible to transmit with the sub-audio carrier in the OFF state, but when switching from stereo broadcasting or bilingual broadcasting to monaural broadcasting, the sub-audio carrier
This causes the inconvenience that the noise is noticeable when it is OFF (cutting is not possible). Therefore, even in monaural broadcasting, the main audio carrier and the sub audio carrier are frequency-modulated and transmitted using the same audio signal. Such a monaural broadcast signal is called a Mono-Mono signal. And this Mono−Mono
By superimposing an unmodulated pilot carrier on the sub-audio carrier of the signal, the receiver can determine that the broadcast is monaural.

A demodulation device included in a television receiver that receives such audio multiplex broadcasting includes a first FM detector that performs FM detection on the main audio carrier, and a second FM detector that performs FM detection on the sub audio carrier.
The main (or (L+R)/2) audio signal and sub (or R) audio signal output from each FM detector are appropriately converted in a matrix circuit and then given to the audio output circuit of each channel. .
On the other hand, a pilot carrier is extracted from the output signal of the second FM detector, and a discrimination signal is reproduced by performing AM detection on this. By detecting the frequency of this discrimination signal, it is determined whether the broadcast is monaural, stereo, or bilingual, and the matrix is A circuit switching operation is being performed.

However, the pilot carrier obtained when the secondary audio carrier is FM detected by the second FM detector is susceptible to AM modulation by the secondary (or R) audio due to the vertical asymmetry of the FM detection characteristics. Such a tendency is particularly noticeable in areas where the frequency shift of the sub (or R) voice is set to be large. Therefore, for example, the pilot carrier obtained when a mono-mono signal is received and subjected to FM detection should originally be a flat, unmodulated carrier, but due to the asymmetry of the FM detection characteristics, the sub (or R) The audio signal components are superimposed. In this way, the sub (or R) audio signal component superimposed on the pilot carrier is
If it has a frequency component close to the frequency of the stereo/bilingual discrimination signal, due to this frequency component,
If the broadcast is incorrectly determined, problems such as the matrix circuit being switched to stereo broadcast even though it is a monaural broadcast occur, making normal reception impossible.

(Purpose of the invention) The present invention was developed in view of the above circumstances, and aims to eliminate the influence of the sub-audio signal component superimposed on the pilot carrier to enable normal reception. The purpose is

(Structure of the invention) In order to achieve the above purpose, the invention has the following features:
It has the following structure.

That is, the present invention transmits a first carrier wave by frequency modulating it with (L+R)/2 during stereo broadcasting and with the main audio during bilingual broadcasting, and transmits a second carrier wave having a frequency different from the frequency of the first carrier wave. In a demodulator of a two-carrier audio multiplexing system, the demodulator uses a two-carrier audio multiplexing system that frequency-modulates and transmits a signal in which a pilot carrier is superimposed on each signal of R during stereo broadcasting and sub-audio during bilingual broadcasting. A first bandpass filter passes the sub-audio carrier included in the audio multiplexed signal, and performs FM detection on the sub-audio carrier from the first band-pass filter to generate a sub-channel signal. FM detector for FM demodulation;
No modulation (no AM modulation) compatible with monaural broadcasting included in the sub-channel signal from the FM detector
1st pilot carrier and other broadcast compatible
A second bandpass filter that passes the AM modulated second pilot carrier, each pilot carrier from the first bandpass filter, and the subchannel signal from the FM detector provided via the correction circuit described later are added. The adder is connected between the FM detector and the adder to output a sum signal, and is connected between the FM detector and the adder to determine the level and phase of the sub-channel signal from the FM detector which is added to the first pilot carrier in the adder. a correction circuit that flattens the envelope of the added signal output from the adder by applying correction to the adder, and performs AM detection on the added signal from the adder.
It is characterized by being equipped with an AM detector and a discrimination circuit that discriminates the type of broadcast based on the output of the AM detector.

Next, the operation of the present invention will be explained.

When the output signal of the correction circuit as described above is added to the output signal of the bandpass filter, the adder outputs a pilot carrier from which the sub-audio signal component has been removed. Therefore, by performing AM detection on the output signal of this adder, it is possible to reproduce a correct discrimination signal that is not affected by the sub-audio signal component.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram schematically showing the configuration of a two-carrier audio multiplexing demodulator according to an embodiment of the present invention.

The audio multiplexed signal transmitted by the two-carrier audio multiplexing method is applied to bandpass filters 2 and 4. The bandpass filter 2 passes the 5.5MHz main audio carrier included in the audio multiplex signal. This main audio carrier is given to the FM detector 6. FM detector 6 detects the main audio carrier.
Main (or (L+R)/
2) Demodulate the audio signal. On the other hand, the bandpass filter 4 filters the 5.74MHz included in the audio multiplexed signal.
The secondary audio carrier is passed through. This sub-audio carrier is given to the FM detector 8. FM detector 8
demodulates the sub channel signal by performing FM detection on the sub audio carrier. Each detection output of the FM detectors 6 and 8 is given to a matrix circuit 10. The matrix circuit 10 receives the determination result of the determination signal and an external control signal (for example,
MAIN, SUB, MAIN/SUB selection signal),
The input detection outputs are appropriately converted. The output signal of the matrix circuit 10 is given to the audio output circuit of each channel via the de-emphasis circuit 12.

On the other hand, a part of the sub-channel signal output from the FM detector 8 is given to a bandpass filter 14 and a level/phase correction circuit 16. The bandpass filter 14 passes the 3.5× _H pilot carrier included in the sub-channel signal.
The level/phase correction circuit 16 is a circuit that appropriately corrects and outputs the level and phase of the sub-channel signal as described later. Bandpass filter 14
and the output signals of the level/phase correction circuit 16 are respectively given to an adder 18.

The output signal of adder 18 is given to AM detector 20. The output signal of the AM detector 20 is applied to bandpass filters 22 and 24, respectively. The bandpass filter 22 passes the 117.5Hz stereo broadcast discrimination signal. On the other hand, the band pass filter 24 passes the 274.1 Hz bilingual broadcast discrimination signal.

The signals passed through the bandpass filters 22 and 24 are applied to a phase comparator 28 via an adder 26. The output signal of phase comparator 28 is provided to stereo bilingual detector 30. The phase comparator 28 and the stereo bilingual detector 30 correspond to the aforementioned discrimination circuit for discriminating the type of broadcast. The output signal of the stereo bilingual detector 30 is provided to a mode switching circuit 32. The mode switching circuit 32 switches the matrix circuit 10 based on the output signal of the stereo bilingual detector 30 and the external control signal so that the type of broadcasting and use are compatible with the selected mode.

Next, the operation of the demodulator having the above-described configuration will be explained.

FIG. 2 shows operating waveforms of each part of the demodulator shown in FIG. 1.

Now, assume that a Mono-Mono signal is input to this demodulator. Then, the FM detector 8 outputs the sub (or R) signal as shown in Figure 2a.
A subchannel signal a in which a pilot carrier is superimposed on an audio signal is output. If the pilot carrier is not subjected to any AM modulation by the sub (or R) audio signal, the output signal b of the bandpass filter 14 given this sub channel signal a will be as shown by the broken line in Fig. 2b. This results in a flat unmodulated carrier signal like this. However, in reality, due to the vertical asymmetry of the FM detection characteristics of the FM detector 8, the output signal b of the bandpass filter 14
is a sub (or R) as shown by the solid line in Figure b.
The waveform is AM modulated with the audio signal component.

On the other hand, the level/phase correction circuit 16 described above is
When the output signal is added to the output signal b of the bandpass filter 14, the level and phase of the sub-channel signal a are appropriately corrected so that, for example, the upper envelope of the added signal becomes flat. It is composed of Therefore, when a monaural broadcast is being received, the output signal c of the adder 18 which is given the output signal b of the bandpass filter 14 and the output signal of the level/phase correction circuit 16 is
As shown in FIG. 2c, the waveform has a flat upper envelope.

The AM detector 20 detects the upper side of the output signal c.
By performing AM detection, as shown in FIG. 2d, a DC level discrimination signal d that does not contain the sub (or R) audio signal component is output. This discrimination signal d
does not pass through the bandpass filters 22 and 24, so the phase comparator 28 outputs a first level DC voltage corresponding to its internal oscillation frequency. That is, this first level DC voltage indicates that the broadcast at that time is monaural broadcast.

On the other hand, when stereo broadcasting or bilingual broadcasting is being received, as described above,
Since the sub (or R) audio signal component is removed from the pilot carrier that has passed through the bandpass filter 14, the AM detector 20 extracts a discrimination signal that does not include the sub (or R) audio signal component. For example, when receiving a stereo broadcast, the AM detector 20 outputs a 117.5Hz discrimination signal that is not affected by the sub (or R) audio signal component, and this discrimination signal is passed to the bandpass filter 22 and the addition signal. The signal is applied to a phase comparator 28 via a device 26. The phase comparator 28 outputs a second level DC voltage according to the frequency of the input discrimination signal. By detecting the level of this DC voltage, the stereo bilingual detector 30 provides a signal indicating stereo broadcasting to the mode switching circuit 32. The mode switching circuit 32 is
Based on this signal and an external control signal,
For example, if the external control signal is a STEREO selection signal, the matrix circuit 10 is switched to suit stereo broadcasting.

Similarly, during bilingual broadcasting, 274.1
The Hz discrimination signal is applied to a phase comparator 28 via a bandpass filter 24 and an adder 26. The phase comparator 28 outputs a third level DC voltage according to the frequency of the input discrimination signal. Based on the result of determining the level of this DC voltage by the stereo bilingual detector 30 and the external control signal, for example, an external control signal is detected.
In the case of the MAIM/SUB selection signal, the matrix circuit 10 is switched to output the MAIM/SUB output signal for bilingual broadcasting.

In the above embodiment, in order to detect the upper side of the output signal c of the adder 18, the level/phase correction circuit 1 is configured so that the upper side of the output signal c is flat.
6. However, when the lower side of the output signal c of the adder 18 is detected, it goes without saying that the level/phase correction circuit 16 is constructed so that the lower side of the output signal c is flat.

Furthermore, in the above embodiment, demodulation of the sub (or R) audio and the pilot carrier are performed by the FM detector 8, but in some television receivers, the demodulation of the sub (or R) audio and the pilot carrier are performed. Vice (or R)
In addition to the FM detector 8 for audio, an FM detector 34 for the pilot carrier is provided. This FM
The detector 34 is provided to adjust its detection coil in order to minimize the influence of sub (or R) audio on the pilot carrier. FM for pilot carriers like this
The present invention can also be applied to a demodulator equipped with a detector 34. In this case, as shown by the chain line in the figure, the pilot carrier FM detector 34
The detected outputs are given to a bandpass filter 14 and a level/phase correction circuit 16, respectively.

(Effects of the invention) As is clear from the above explanation, the two-carrier audio multiplexing demodulator according to the invention corrects the level and phase of the output signal of the FM detector for demodulating the pilot carrier. By adding this to the output of a bandpass filter for extracting the pilot carrier from the output signal of the FM detector, the auxiliary audio signal component superimposed on the pilot carrier extracted from the bandpass filter is added. is being removed.

Therefore, according to the present invention, since it is possible to extract a pilot carrier that is not affected by the sub-audio signal component, the type of broadcast can be correctly determined based on the discrimination signal obtained from this pilot carrier. This allows normal reception depending on the type of broadcast.

In addition, recently, on-screen displays have become popular, but when switching between stereo and bilingual broadcasts on-screen, the result of the pilot carrier discrimination signal described above is generally used as an input signal to a microcomputer for channel selection. Therefore, according to the present invention, such on-screen display can be performed correctly.

[Brief explanation of the drawing]

FIG. 1 is a block diagram schematically showing the configuration of a two-carrier audio multiplexing demodulator according to an embodiment of the present invention, and FIG. 2 is an operational waveform diagram of the embodiment. 2, 4, 14, 22, 24... Band pass filter, 6, 8, 34... FM detector, 10... Matrix circuit, 18, 26... Adder, 20...
AM detector, 28...phase comparator, 30...stereo bilingual detector.

Claims (1)

[Scope of claim for utility model registration] The first carrier wave is (L+R)/
2. Then, during bilingual broadcasting, the main audio is frequency modulated and transmitted, and a second carrier wave with a frequency different from the frequency of the first carrier wave is piloted to each signal of R during stereo broadcasting and sub audio during bilingual broadcasting. In a demodulator for a two-carrier audio multiplex system that frequency-modulates and transmits a signal in which carriers are superimposed together, an audio multiplex signal transmitted by the two-carrier audio multiplex system is given, and the audio multiplex signal included in this audio multiplex signal is a first bandpass filter that passes the sub-audio carrier transmitted through the first band-pass filter; and FM-detects the sub-audio carrier from the first band-pass filter to FM demodulate the sub-channel signal.
An FM detector, an unmodulated (no AM modulation) first pilot carrier compatible with monaural broadcasting included in the sub-channel signal from the FM detector, and an AM-modulated second pilot carrier compatible with other broadcasting. A second band pass filter that passes the FM signal, each pilot carrier from the first band pass filter, and an FM signal provided via a correction circuit described later.
An adder that adds the sub-channel signal from the wave detector and outputs a sum signal; and an FM wave detector that is connected between the FM detector and the adder and is added to the first pilot carrier in the adder. a correction circuit that flattens the envelope of the added signal output from the adder by correcting the level and phase of the sub-channel signal; and an AM that performs AM detection on the added signal from the adder.
A two-carrier audio multiplexing demodulator comprising: a wave detector; and a discrimination circuit that discriminates the type of broadcast based on the output of the AM detector.