JPS6111512B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the reception mode switching part of an audio multiplex signal receiver, particularly for reception of different types of broadcasts, reception of stereo broadcasts, and reception of monaural broadcasts. The purpose is to provide a device that can erase data.

In television audio multiplex broadcasting, a main audio signal, a sub audio signal, and a pilot signal for distinguishing between different types of broadcasting, stereo broadcasting, or monaural broadcasting are sent using the frequency domain shown in FIG.

The outline of a device for receiving such a signal is as shown in Fig. 2, which converts the main and sub audio signals from the audio multiplex demodulated composite signal applied to the input terminal 1 using a low pass filter 2 and a band filter 3. The sub-audio signals are further demodulated by the FM demodulation circuit 4. In the case of receiving a different type of broadcast, the main audio signal and sub audio signal thus demodulated are taken out as they are or selectively via the switching circuit 5, amplified by the amplifier circuit 6, and reproduced by the speakers 7L and 7R. In the case of stereo broadcast reception, the main audio signal is the sum of the stereo left channel signal L and right channel signal R (L+R), and the sub audio signal is the difference between the left channel signal L and right channel signal R (L+R). −
R) signal, the main audio signal and the sub audio signal are synthesized and separated into a stereo left channel signal L and a right channel signal R, which are extracted and sent to the speaker 7.
Play with L and 7R.

When receiving monaural broadcasting, only the main audio signal is present, so it is supplied to both speakers 7L and 7R for reproduction.

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To switch between these three types of broadcasts, a pilot signal extraction circuit 8 consisting of a narrow band filter extracts the pilot signal, and a different type detection circuit 9 including a 922.5 Hz read filter detects a pilot signal for identifying different types of broadcasts. However, the stereo detection circuit 10 including a 982.5Hz lead filter detects a pilot signal for stereo broadcast identification,
This is done by switching the switching circuit 5 based on these detection outputs.

However, in such devices, the reception mode is switched by switching the transmission path of the main audio signal and the sub audio signal using the detection output of the pilot signal, so noise is inevitably generated during the switching. This has the disadvantage of causing a problem. There are two main reasons why the noise occurs:
One of them is the noise generated by the switching element itself when switching. Another noise generation factor is due to a delay in the response of a high Q filter such as a reed filter that detects pilot signals of 922.5 Hz and 982.5 Hz. In other words, a high Q reed filter is used to ensure pilot signal detection even in reception conditions with poor S/N in weak electric fields, but this is due to the characteristic that the higher the Q, the greater the response delay. It is something.

This noise due to the delay in response of the reed filter is caused by the following reasons. That is, even when the transmission mode is switched from different type broadcasting or stereo broadcasting to monaural broadcasting, the detection outputs of the detection circuits 9 and 10 continue to be generated for the delay time of the response of the lead filter, so that the detection outputs of the sub-audio demodulation circuit 4 during that time are The output passes through the switching circuit 5, is amplified by the audio amplification circuit 6, and is generated from the speakers 7L and 7R. However, when the transmission mode is switched to monaural broadcasting, the sub-audio signal disappears at the same time, so only the noise signal is output from the sub-audio demodulation circuit 5, and as a result, the detection circuits 9 and 1
During the lead filter response delay time at 0, noise is output from the speakers 7L and 7R.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a device that can effectively eliminate noise generated during automatic switching of reception modes.

Hereinafter, the present invention will be described in detail with reference to FIGS. 3 and 4 showing one embodiment thereof. It should be noted that the same parts as in the prior art are denoted by the same reference numerals as in FIG. 2, and the explanation thereof will be omitted. This device includes a signal cutoff circuit 11 that cuts off the transmission of the audio signal (including one that attenuates it to a sufficiently effective degree) and eliminates noise when switching the reception mode, and a signal cutoff circuit 11 that generates a control signal for blocking the signal. a control signal generation circuit 12,
A third detection circuit 13 that detects the presence or absence of a 31.5 KHz subcarrier and detects a mode change of a broadcast signal to monaural broadcasting is newly provided as a noise canceling means. The cutoff circuit 11 includes analog gates 11L and 11 provided respectively in two transmission paths of audio signals.
Consists of R. Further, the third detection circuit 13 consists of a detection circuit that detects the output of the band filter 3 centered at 31.5 KHz.

A detailed configuration example of the control signal generation circuit 12 is shown in FIG. In this circuit, first, the detection outputs of the first detection circuit 9 and the second detection circuit 10 are
In addition to the OR gate 14, the output when any detection output is present is taken out, and this and the detection output of the third detection circuit 13 inverted by the inverter 15 are added to the AND gate 16. Therefore, the AND gate 16 generates an output only when there is no detection output from the third detection circuit 13 and only when there is a detection output from the first or second detection circuits 9, 10. This is because the 31.5KHz pilot signal disappears when a different type of broadcast or stereo broadcast changes to monaural broadcast, and the detection output of the third detection circuit 13 disappears, and the operation of the first detection circuit 9 or the second detection circuit 10 still stops. is delayed and its detection output is present, that is, a state where the above-mentioned noise occurs. Therefore, the output of the AND gate 16 is passed through the NOR gate 17 to the analog gates 11L and 11 of the cutoff circuit 11.
By blocking this in addition to R, noise at the time of mode switching is prevented from being emitted from the speakers 7L and 7R.

In addition, when the detection outputs of the first and second detection circuits 9 and 10 change, that is, when there is a mode change of different types of broadcasting or stereo broadcasting, and the mode change is detected a little later, the detection outputs are differentiated. The change is detected by differentiating it in circuits 18 and 19, and the differential output is sent to a monostable multivibrator 21 via an OR gate 20.
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Trigger in addition to . The output pulse width of the monostable multivibrator 21 is set to be longer than the period of noise generated when the switching circuit 5 switches based on the detection outputs of the detection circuits 9 and 10, and its output is also In addition to the analog gates 11L and 11R of the cutoff circuit 11,
This is blocked to prevent noise from being produced.

In this way, according to this device, even when switching the reception mode using pilot signal detection means with slow response characteristics such as a reed filter in a device that receives television audio multiplex broadcasting, noise is generated at the time of switching. This makes it possible to obtain an excellent device that does not require any additional effort.

In the above embodiment, a circuit using an inverter 15, an OR gate 14, an AND gate 16, a NOR gate 17, etc. was employed, but the present invention is not limited to this circuit, and similar circuits may be used. It goes without saying that any circuit configuration that produces the effect can be designed and used.

As detailed above, according to the present invention, by using the detection output of a subcarrier for audio multiplexing and the detection output of a pilot signal for different types of broadcasting or stereo broadcasting, there is no detection output of the former, and a detection output of the latter is used. Since the audio signal is cut off when the pilot signal is detected, even if there is a delay in the response of the detection operation due to the use of a reed filter etc. in the pilot signal detection circuit, the noise caused by switching the reception mode can be filtered out from the speaker etc. It is possible to achieve an excellent effect of not generating any oxidation.

[Brief explanation of the drawing]

FIG. 1 is a spectrum diagram of a television audio multiplex broadcast signal, FIG. 2 is a block diagram of a conventional audio multiplex broadcast receiver, and FIG. 3 is a block diagram of an audio multiplex broadcast receiver according to an embodiment of the present invention. 4 are circuit diagrams of the main parts of the device. 5...Switching circuit, 6...Audio amplification circuit, 7L,
7R... Speaker, 8... Pilot signal extraction circuit, 9... First detection circuit, 10... Second detection circuit, 11... Cutoff circuit, 12... Control signal generation circuit, 13... Third detection circuit , 14...OR gate, 15...Inverter, 16...AND gate, 1
7...NOR gate. 〓〓〓〓〓

Claims (1)

[Scope of Claims] 1. A demodulation circuit that demodulates an audio multiplexed signal to create a main audio signal and a sub audio signal, and detects the presence or absence of a pilot signal for different types of broadcasting or a pilot signal for stereo broadcasting from the audio multiplexed signal. A pilot signal detection circuit having a delayed response; a switching circuit for switching the main audio signal and the sub audio signal according to the detected output of the pilot signal and supplying the same to a subsequent circuit; A cutoff circuit provided in the transmission path, a subcarrier detection circuit for detecting the presence or absence of a subcarrier signal in the audio multiplexed signal, and a detection output of the pilot signal detection circuit, and a detection output of the subcarrier detection circuit. An audio multiplex signal receiving device comprising: a control signal generating circuit that generates a cutoff control signal to cut off the cutoff circuit when no output is present. 2. The control signal generation circuit includes means for generating a cutoff control signal to cut off the cutoff circuit for a predetermined period even when the detection output of the pilot signal detection circuit changes. Audio multiplex signal receiving device.