JPS6129587B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for receiving audio multiplex signals in television.

As is well known, a television audio multiplex signal includes a main audio channel of 0 to 15 KHz, a sub audio channel of 16 to 47 KHz having a subcarrier of 31.5 KHz, and a control channel signal of 55.125 KHz. This control channel signal is modulated with a 982.5Hz control signal during stereo broadcasting, and is modulated with a 922.5Hz control signal during heterogeneous broadcasting. In a receiving device that receives such audio multiplexed signals, the broadcast mode is detected by detecting the presence or absence of the above-mentioned subcarriers and each control signal, and the matrix circuit is automatically switched accordingly. The audio multiplex signal is configured to receive the audio multiplex signal in a predetermined mode. However, since conventional receiving devices of this type have used reed filters to detect control signals, they have been disadvantageous in that they are extremely expensive and are prone to malfunction due to external shocks. In addition, when controlling by detecting the presence or absence of a subcarrier, the entire audio multiplexed signal is detected from the television signal by an FM detection circuit.
Since it uses FM detection, there is an extremely large amount of noise when the electric field is weak or there is no signal, and it also has the disadvantage that it generates a detection output even though there is no subcarrier, causing malfunctions.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a receiving device equipped with a mode switching means that eliminates such conventional drawbacks, prevents erroneous mode switching control, and can be implemented at low cost. It is something to do.

Therefore, in the present invention, the 982.5Hz control signal or the 922.5Hz control signal in the control channel signal is detected by a phase-locked loop type detection circuit without using a lead filter, and The mode is switched based on the output that detects the presence or absence of the subcarrier of the channel signal, and the electric field strength of the received signal is detected by detecting the DC component of the control channel signal, so that it can be used in weak electric fields. The present invention is characterized in that control is always performed to switch to monaural mode at certain times, regardless of the above-mentioned detection outputs.

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to the drawings showing one embodiment thereof.

In the figure, 1 performs FM detection on the audio intermediate frequency signal of the television signal to generate an audio multiplex signal.
The FM detection circuit extracts only the main audio signal of 15KHz or less from the output audio multiplexed signal using a low-pass filter 2. On the other hand, this audio multiplexed signal is added to a bandpass filter 3, where a sub channel signal of 16 to 47 KHz and a control channel signal of 55.125 KHz are separated and extracted. The extracted sub-channel signal is amplified by a buffer amplifier 4, and then added to a phase-locked loop type FM detection circuit 5 for FM detection to obtain a sub-audio signal. These main audio signals and sub audio signals are each added to the matrix circuit 6, where the signals are mixed and switched according to the designated reception mode, and outputted from output terminals 7L and 7R, respectively. In addition, after amplifying the sub-channel signal with the buffer amplifier 8,
A detection circuit 9 performs detection smoothing, and in addition to a switching circuit 10 such as a jammit circuit, a detection output that becomes high level when a sub-channel signal is present is generated. However, this switching circuit 10
Of course, the detection output from the receiver reaches a high level as described above when an audio multiplexed signal is being received and the sub-channel signal (10) is present, but there are also other When the electric field strength is small,
Since the FM detection circuit 1 performs FM detection on the signal, a large noise signal peculiar to FM detection may also be detected, resulting in a high level by mistake. Therefore, the detection output is reliably at a low level only when receiving monaural broadcasting where the electric field strength of the received signal is large, the detection noise is small, and there is no sub-channel signal.

On the other hand, the filter extracted using band pass filter 3
A control channel signal of 55.125 KHz is amplified by a tuning amplifier 12 having a tuning circuit 11 tuned to the frequency, and then detected and smoothed by a detection circuit 13 to extract a control signal. Then, the detection output is added to a phase-locked loop detection circuit 14 in which one of the control signal frequencies is set to either 982.5Hz or 922.5Hz, and a high-level detection output is output when the control signal is present. Occur. Here, it is assumed that this detection circuit 14 is 982.5
The stereo control signal frequency is set to Hz, so that a high level detection output is generated only when a stereo broadcast signal is received and the stereo control signal is detected. In this PLL type detection circuit 14, even if signals of other frequencies or noise signals are present, a low level detection output is generated as in the case of no signal. moreover. , the detected output of this control channel signal is further smoothed by a smoothing circuit 15, and
In addition to the switching inversion circuit 16, such as a Schmitt circuit, it is detected whether a large noise signal is present in the control channel signal. That is, due to the use of the above-mentioned FM detection circuit 1, when the electric field strength of the received signal is small, the detection noise signal increases extremely, so by detecting the presence or absence of the noise signal, the received signal It detects whether the electric field strength is a strong electric field or a weak electric field. However, what should be noted here is the relationship between the magnitude of the control signal and the magnitude of the noise signal in the detection output of the control channel. More than anything,
Utilizing the general property that the magnitude of the noise signal when the electric field becomes weak is sufficiently large (regardless of the presence or absence of a control signal in a weak electric field), The detection output is generated only when the sensor is detected. Therefore, by using such a circuit, it is possible to obtain an output from the switching inversion circuit 16 that detects the electric field strength depending only on the electric field strength of the received signal, regardless of the presence or absence of a control signal.

Therefore, each detection output obtained in this manner is applied to the mode switching circuit 17 to control mode switching of the matrix circuit 6. First, PLL type detection circuit 14
The detection output of is applied to gate 18, and the inverted version thereof is applied to gates 19 and 20. Further, the detection output of the switching circuit 10 and the detection output of the switching inversion circuit 16 are applied to the gate 21, the outputs are applied to the gates 18 to 20, and the inverted output is applied to the gate 22. Furthermore, designated inputs from mode designation switches 23 to 26 are input to gates 18, respectively.
~Add to 22.

With this configuration, when the switch 23 specifying the stereo reception mode is closed, the PLL type detection circuit 14 generates a detection output of a stereo control signal, and the switching circuit 10 generates a detection output of a multiple subchannel signal. is generated,
Further, when a strong electric field detection output is generated from the switching inversion circuit 16, only the gate 18 becomes conductive, and the matrix circuit 6 is switched to the stereo mode. Furthermore, when the switch 24 that specifies the mode in which both the main audio and the sub audio are received is closed, the PLL type detection circuit 14 does not generate a detection output of the stereo control signal, and the switching circuit 10 outputs the detection output of the sub channel. When a signal is being output and a strong electric field detection output is being generated from the switching inverting circuit 16, only the gate 19 is conductive, and the matrix circuit 6 is placed in a state where the main audio and sub audio are simultaneously received. Switch. In addition, switch 2 that specifies the mode for receiving only sub-audio
5 is closed, only the gate 20 is conductive under the same conditions as in the present case, and the matrix circuit 6 is closed.
Switch. Furthermore, when the switch 26 that specifies the main audio only reception mode and the monaural reception mode is closed, the gate 2
2, the matrix circuit 6 is switched to the moral receiving state. However, in this moral reception mode, the matrix circuit 6 is configured to output only the main audio.

In any case where any of the above modes is specified, when a detection output indicating a weak electric field is generated from the Schmidt inversion circuit 16, the gate 21 is cut off, and the control is switched to the reception mode. be done.

In this way, with this device, it is possible to accurately control the reception mode without using a read filter.

In the above embodiment, the PLL type detection circuit 14 detects a stereo broadcast control signal, but even if a different type of broadcast control signal is detected, the connection to the gate in the mode switching circuit 17 is not necessary. It goes without saying that similar control can be achieved with just a few changes.

As detailed above, according to the present invention, when receiving a television audio multiplex signal, it is possible to accurately detect the broadcast mode and control the reception mode switching without using a read filter, and at a low cost. This makes it possible to obtain a device that operates reliably.

Furthermore, in the present invention, a PLL type detection circuit for detecting either one of the two control signals (982.5Hz or 922.5Hz) in the audio multiplex signal, a circuit for detecting the sub-channel signal, and a circuit for detecting the sub-channel signal are included in the control signal. By controlling the switching of each mode using the signals obtained from the three circuits that detect the included noise components, the electric field of the television signal becomes particularly weak, which causes the S/N of the audio multiplex signal to decrease.
To eliminate the situation where the mode switching malfunctions when the signal deteriorates, and the mode switching malfunctions and the mode switches to stereo mode, giving a strange feeling to the listener, for example, when receiving a different type of broadcast in a weak electric field. This makes it possible to obtain a device that is easy to use.

[Brief explanation of the drawing]

The figure is a circuit diagram of an audio multiplex receiver according to an embodiment of the present invention. 1...FM detection circuit, 2...Low pass filter, 3
... Band pass filter, 5... Detection circuit, 6... Matrix circuit, 9... Detection circuit, 10... Switching circuit, 12... Tuning lamp, 13... Detection circuit, 14
...PLL type detection circuit, 15...Smoothing circuit, 16...Switching inversion circuit, 17...Mode switching circuit, 1
8-22...Gate, 23-26...Mode designation switch.

Claims (1)

[Claims] 1 A phase that demodulates the main audio signal and the sub audio signal from the audio multiplexed signal, detects the control channel signal of the audio multiplexed signal, and sets the wave output to the different broadcasting control signal frequency or the stereo broadcasting control signal frequency. In addition to a locked-loop detection circuit, it detects the presence or absence of one of the control signals, smoothes the detection output of the control channel signal, and in addition to a switching circuit, detects the strength of the electric field strength to detect the sub-audio channel signal. In addition to the smoothing switching circuit, the presence or absence of multiplex broadcasting is detected, and the mode switching of the matrix circuit is controlled by the detection output of the control signal and the detection output of the multiplex broadcasting, and the mode switching of the matrix circuit is controlled by the detection output of the electric field strength. ,
An audio multiplex reception device characterized in that the matrix circuit is controlled to be forced into a monaural mold in the case of a weak electric field, regardless of the detection output of the control signal and the detection output of multiplex broadcasting.