JPS6161312B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio multiplex tuner. TV audio multiplex broadcasts include stereo broadcasts and bilingual broadcasts, and in the case of stereo broadcasts, FM
Main signal M [L+R] (sum signal of left channel signal L and right channel signal R, frequency band is 50~
15KHz) and sub-signal S [L-R] (difference signal between left channel signal L and right channel signal R. In a composite signal, this difference signal creates a subcarrier
31.5KHz FM modulated signal) in an FM stereo demodulation circuit, as shown in the following formula: [M] (L + R) + [S] (L - R) = 2L [M] (L + R) + [-S] ( -L+R)=2R The left channel signal 2L is obtained by adding the main signal M and the sub signal S, and the right channel signal 2R is obtained by adding the main signal M and the sub signal -S whose phase is inverted. On the other hand, in the case of bilingual broadcasting, the main signal M is Japanese audio and the sub signal is foreign language audio, and either or both can be selectively listened to.

By the way, when receiving and listening to audio multiplex broadcasting, there is a problem in that the main signal is mixed into the sub signal or the sub signal is mixed into the main signal, causing crosstalk, and when the amount of crosstalk increases, the sound quality deteriorates significantly. Particularly in the case of bilingual broadcasting, the main signal and sub-signal have completely different content, so even a small amount of crosstalk can have a very large effect, effectively causing the high-frequency components of the main signal to mix into the sub-signal, resulting in poor sound quality. This has become a major problem, and as a countermeasure to this problem, conventional methods have been used to reduce the high frequencies of sub-signals in order to reduce the audible crosstalk. On the other hand, in the case of stereo broadcasting, music programs are the main content and high-fidelity reproduction characteristics are required, so it is not preferable to reduce the high frequencies of the audible band as described above. Therefore, the above-mentioned method has been made to be selectable using a manual switch, but it is cumbersome to operate as the listener has to switch each broadcast mode one by one, and there is a risk of erroneous operation by the listener. This was one of the causes that had a negative impact on the spread of audio multiplex broadcasting.

This invention solves the above-mentioned drawbacks. When receiving stereo broadcasts, both left and right channel signals obtained by stereo demodulation are mixed through a high-pass filter, and the audible signals contained in both channel signals in an antiphase relationship are mixed. It cancels out the high frequency noise components of the frequency band, improving the S/N without deteriorating the frequency characteristics, and reduces the high frequency components of the sub signal using a low pass filter when receiving bilingual broadcasts to prevent crosstalk. In addition to improving the audible sound quality by removing
To provide an audio multiplex tuner which automatically switches by detecting Hz (2-language broadcast identification signal: 922.5 Hz) and allows listeners to enjoy audio multiplex broadcasting without bothersome operations.

Hereinafter, one embodiment of the present invention will be described in detail.

FIG. 1 shows a block diagram of an audio multiplex tuner, where 1 is a front end, 2 is an IF amplification stage, and 3 is an FM detector. 4 is a bandpass filter (BPF) that filters the subchannel band signal (16KHz~) from the composite signal from the FM detector 3.
47KHz), and 5 is the subchannel band signal that has passed through bandpass filter 4.
An FM detector 6 for demodulating to obtain a sub-signal [S] is a phase inversion circuit which inverts the phase of the sub-signal [S] to obtain a phase-inverted sub-signal [-S] necessary for stereo demodulation. 7 is a crosstalk cancel circuit configured with an LPF consisting of a resistor R and a capacitor _C1 , and removes high-frequency crosstalk mixed into the sub-signal S. As will be explained later, the first electronic switch 1
Operation/non-operation is controlled by 5. 8 is a control signal from the composite signal from the FM detector 3 (stereo broadcasting identification signal 982.5Hz or two language broadcasting identification signal 922.5Hz)
9 is an AM detector for extracting and amplifying the AM modulated signal (55.125KHz); 9 is an AM detector for demodulating the control signal to obtain an identification signal;
1 is a lead filter that passes only identification signals of 982.5 Hz and 922.5 Hz, respectively, and 12 is a logic circuit configuration that can be set by inputting a stereo broadcast identification signal of 982.5 Hz or two language broadcast identification signals of 922.5 Hz and setting the mode switch 13. 1st electronic switch 1
5. A mode switching circuit that controls the opening and closing of the matrix switches 16 to 20 and the second electronic switch 21 to instruct stereo demodulation or bilingual audio demodulation; mode switch 13 is operated when receiving bilingual broadcasting; This is to arbitrarily set the operation mode of Japanese audio (main signal), foreign language audio (sub signal), or both Japanese audio and foreign language audio. At contact point b, foreign language voice is selected, and at contact point c, both Japanese voice and foreign language voice are selected, and the mode switching circuit is set to each of the above modes. Reference numeral 14 is a high-blend switch, which is a high-blend switch that can be used when receiving radio waves in good condition and without performing the above-mentioned high-blend operation (mixing both left and right channel signals through a high-pass filter) when receiving stereo broadcasts. If S/N characteristics are obtained, turning this switch OFF turns the second electronic switch ON from the mode switching circuit.
No instruction is given, and the left and right channel signals are output without being mixed.

Next, reference numeral 15 denotes a first electronic switch, which is closed in response to an instruction from the mode switching circuit 12 when listening to a bilingual broadcast, and serves to operate a crosstalk cancel circuit.

The matrix switches 16 to 20 are controlled to open and close by the mode switching circuit 12. For example, when receiving a stereo broadcast, switches 16, 17, 18, and 19 are closed, switch 20 is open, and switch 1 is closed.
The main signal M and the sub-signal S are added through switches 6 and 17 to obtain a left channel signal, and the main signal M and the phase-inverted sub-signal -S are added together via a switch 18 and a switch 19 to obtain a right channel signal. ,
When receiving foreign language audio (sub signal) of bilingual broadcasting, switches 17 and 20 are closed, and switch 1 is closed.
6, 18, and 19 are open, and sub signals can be obtained from both left and right channels.

The second electronic switch 21 closes according to instructions from the mode switching circuit 13 when receiving stereo broadcasting, and combines the stereo demodulated left channel signal L and right channel signal R via the capacitor _C2 , and performs other operations. In mode, it is an open operation.
The operating states of the first electronic switch 15, matrix switches 16-20, and second electronic switch 21 in each operating mode are shown in the table of FIG. 2
Negative feedback amplifiers 2 and 23 amplify the left and right channel signals, respectively, and also perform de-emphasis by imparting frequency selectivity to the negative feedback loop. 24 and 25 are low-pass filters (LPFs) that remove unnecessary high-frequency signal components (subchannel band signals, control signals, etc.) mixed into the left and right channel signals.

Next, the operation of this embodiment in stereo broadcast reception will be explained.

The composite signal demodulated by the FM detector 3 is sent to the matrix switches 16, 19 and the BPF.
4. The subchannel band signals distributed to the control signal selection amplification circuits 8 and extracted by the BPF 5 are demodulated by the FM detector 6 to become subsignals S, which are directly transmitted to the matrix switch 17.
At the same time, the signal is phase inverted (-S) by the phase inversion circuit 6, and is also transmitted to the matrix switch 18.

On the other hand, the control signal extracted from the composite signal by the control signal selection amplification circuit 8 is subjected to AM detection and passed through the read filter 10 to obtain a stereo broadcast identification signal of 982.5 Hz, and this identification signal is input to the mode switching circuit. Upon receiving the identification signal, the mode switching circuit closes the matrix switches 16 to 19 and the second electronic switch 21 as shown in the stereo broadcast section of the table in FIG. After passing through a negative feedback amplifier, both channel signals are mixed through a capacitor C ₂ to remove high-frequency noise having an antiphase relationship. In this case, since only the high frequency bands of the left and right channel signals are mixed, the S/N and distortion ratio can be improved without deteriorating the frequency characteristics.

Next, when listening to a foreign language broadcast (sub signal) in a bilingual broadcast, switch the mode switch 13.
is switched to contact b, and the two-language broadcast identification signal (922.5
Hz) to the mode switching circuit,
As shown in the sub-signal section of the table in Figure 2,
electronic switch 15, matrix switch 17,
20 is in a closed state. On the other hand, the sub-signal obtained by the FM detector 5 is input to the crosstalk cancel circuit 7, the crosstalk in the sub-signal is removed, and the sub-signal is transmitted to the matrix switches 17 and 20. Supplies sub-signals to the channel signal transmission system.

As described above, the present invention includes a low-pass filter provided in a sub-signal transmission line, a first switch means for controlling the operation/inoperation of the low-pass filter, a left channel signal transmission line, and a right channel signal transmission line. A high pass established between the route and the
a filter, a second switch means for controlling the operation/non-operation of the high-pass filter, and a second switch means whose operation is determined by the audio multiplex identification signal,
and a mode switching circuit for controlling activation/deactivation of the switch means, which operates the low-pass filter to reduce high frequency components in the sub-signal when receiving bilingual broadcasting, and when receiving stereo broadcasting, operates the low-pass filter to reduce high frequency components in the sub-signal. Since both left and right channel signals are mixed through a high-pass filter, high-frequency crosstalk in the sub signal can be removed when receiving bilingual broadcasts, improving the perceived sound quality.
When receiving stereo broadcasts, the high-frequency noise in the left and right channel signals can be canceled out, so the S/N ratio can be improved without deteriorating the frequency characteristics. Moreover, each of the above operations can be performed by detecting the audio multiplex broadcast identification signal. Since the switching operation is performed automatically, it does not impose an excessive burden on the listener, and it has excellent features in that it enables reliable switching operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 shows operating modes of the mode switching circuit according to the present invention. Explanation of symbols, 1...Front end, 2...IF amplification stage, 3...FM demodulator, 4...Band pass filter, 5...FM demodulator, 6...Phase inversion circuit, 7...Low pass filter, 8...Control signal selective amplification circuit,
9... AM detector, 10, 11... Lead filter, 12... Mode switching circuit, 13... Mode switch, 14... High blend switch, 15... First electronic switch, 16, 17, 18, 19, 20... Matrix switch , 21...second electronic switch.

Claims (1)

[Claims] 1. Between a low-pass filter provided in the sub-signal transmission line, a first switch means for controlling operation/non-operation of the low-pass filter, and the left channel signal transmission line and the right channel signal transmission line. A high-pass filter provided, a second switch means for controlling operation/inoperation of the high-pass filter, and a mode switching means for controlling operation/inoperation of the first and second switch means based on the audio multiplex identification signal. When receiving a broadcast in two languages, the low-pass filter is operated to attenuate high frequency components in the sub-signal, and when receiving a stereo broadcast, the left and right channel signals are mixed through the high-pass filter. An audio multiplex tuner characterized by: