JPS5846587Y2 - FM receiver - Google Patents

Description

[Detailed Description of the Invention] Recently, an audio device incorporating a television receiver has been proposed.

In an audio device incorporating such a television receiver, the channel switching of the television receiver's tuner is FM.
Unlike the continuously variable tuner of a radio receiver, the tuning frequency moves rapidly, so even though a muting circuit is provided, this is detected by the frequency detection stage, and the sound corresponding to this frequency shift is detected through the muting circuit. It comes out for a moment.

In this case, the wider the dynamic range of the frequency detection stage, the louder the sound will be reproduced, resulting in a very unpleasant sound.

The present invention relates to an FM receiver such as a television receiver having a mechanical tuner that switches the tuning frequency at high speed, and is particularly designed to avoid generating unpleasant sounds when changing channels.

An example in which the FM receiver of the present invention is used in a television receiver will be explained below with reference to the drawings.

In the figure, reference numeral 1 indicates an antenna for receiving television broadcasting, and the signal from antenna 1 is supplied to tuner 2, which mechanically switches the reception channel. The output signal of the tuner 2 is supplied to the input side of the audio intermediate frequency amplifier 4, and the output signal of the audio intermediate frequency amplifier 4 is supplied to the frequency amplifier. Detection circuit 5
The output signal is supplied to an audio output circuit 7 via the drain and source of the field effect transistor 6a constituting the muting circuit 6, and the output signal of the audio output circuit 7 is supplied to an audio signal output terminal 8 that supplies an audio signal to a speaker or the like. do.

It is also connected to the base of an npn transistor 6b constituting the muting circuit 6 via a rectifier circuit 9 and an inverter circuit 10 that detect the output signal of the audio intermediate frequency amplifier 4, and the emitter of this transistor 6b is grounded. The collector of this transistor 6b is connected to the gate of a field effect transistor 6a through a parallel circuit of a resistor 6C and a capacitor 6d, and the collector of this transistor 6b is grounded through a capacitor 6e.

That is, when there is no output signal from the audio intermediate frequency amplifier 4, that is, when a broadcast signal is not being received, the muting circuit 6 turns on the transistor 6b and turns off the field effect transistor 6a, so that the output from the frequency detection circuit 5 is Muting is performed without supplying the signal to the audio output circuit 7.

When the audio intermediate frequency amplifier 4 has an output signal, that is, when it is receiving a broadcast signal, the transistor 6b is turned off and the field effect transistor 6a is turned on, so that the output signal of the frequency detection circuit 5 is transmitted to the audio output circuit. 7 and muting is turned off.

Further, in the present invention, the output side of the inverter circuit 10 is connected to one fixed contact 11b of a changeover switch 11 for switching between use and non-use of the muting circuit 6, and the output side of the audio output circuit 7 is connected to a clipper circuit 12. It is connected to the other fixed contact 11C of the changeover switch 11 through the switch 11, and the movable contact 11a of the changeover switch 11 is grounded.

In this case, when using the muting circuit 6, the movable contact 11a of the changeover switch 11 is the other fixed contact 11C.
, the clipper circuit 12 is in an operating state, and when the muting circuit 6 is not used, the movable contact 11a of the changeover switch 11 is connected to one fixed contact 11b.
Since the clipper circuit 12 is connected to , the clipper circuit 12 becomes inactive.

In the figure, 10B is a power supply terminal to which a positive DC voltage is supplied.

Since the present invention is constructed as described above, the changeover switch 1 normally switches between using and not using the muting circuit.
One movable contact 11a is connected to the other fixed contact 11C.

In this case, the muting circuit 6 operates, and when there is an audio carrier signal on the output side of the audio intermediate frequency amplifier 4, the transistor 6b is turned off and the field effect transistor 6a is turned on, and the muting circuit 6 is turned off and frequency detection is performed. The audio signal from the circuit 5 can be supplied to the audio output circuit 7 to reproduce the audio signal.

Furthermore, when there is no signal on the output side of the audio intermediate frequency amplifier 4, the transistor 6b is turned on and the field effect transistor 6a is turned off, and the output side of the frequency detection circuit 5 is muted. No unpleasant noise is generated.

Also, when switching channels of the tuner 2 of the television receiver, a noise signal corresponding to the frequency deviation is momentarily supplied from the frequency detection circuit 5 to the audio output circuit 7 through the muting circuit 6, but at this time the clipper circuit 12 is activated. Therefore, this noise does not exceed a predetermined level, and the unpleasant noise at this time is improved.

Further, if it is desired not to use the clipper circuit 12 after channel switching, it is possible to connect the movable contact 11a of the changeover switch 11 to one of the fixed contacts 11b.

At this time, the muting circuit 6 is also turned off. Since the audio carrier signal is on the output side of the audio intermediate amplifier 4, only unpleasant noise from the speaker is not generated.

When receiving a television broadcast signal with a weak electric field, move the movable contact 11a of the changeover switch 11 to one of the fixed contacts 11.
b, so that the transistor 6b is always turned off and the field effect transistor 6a is always turned on, so that the muting circuit 6 is not used.

At this time, the muting circuit 6 does not work, so it is possible to reproduce the audio signal with a weak electric field.

Also, at this time, the ripper circuit 12 becomes inoperative as it is unnecessary.

As described above, according to the present invention, it is possible to improve the unpleasant noise that occurs when switching channels on a television receiver.

Also, in order to improve the generation of this unpleasant noise, a frequency detection circuit 5 is installed.
It may be possible to avoid unnecessarily widening the dynamic range (S curve) of the system, but in reality, the transmission management of broadcasting stations is not perfect, so music programs and live broadcast programs that place emphasis on sound quality have large frequency deviations. -300% modulation is often the case, and unless the dynamic range of this frequency detection circuit 5 is unnecessarily expanded, there is an inconvenience that a broadcast signal with such a large frequency deviation will not be reproduced. For example, as described above, since the dynamic range of the frequency detection circuit 5 is not changed, even overmodulated signals can be faithfully reproduced.

It goes without saying that the present invention is not limited to the above-described embodiments, and that various other configurations may be adopted without departing from the gist of the present invention.

[Brief explanation of drawings]

The figure is a block diagram showing an embodiment of the FM receiver of the present invention. 2 is a television receiver tuner, 4 is an audio intermediate frequency amplifier, 5 is a frequency detection circuit, 6 is a muting circuit,
7 is an audio output circuit, 8 is an audio output terminal, 11 is a changeover switch, and 12 is a clipper circuit.

Claims (1)

[Scope of utility model registration request] The muting circuit is controlled depending on the presence or absence of the output signal of the audio intermediate frequency amplifier, and a changeover switch is provided to switch between use and non-use of the muting circuit. An FM receiver characterized in that, when the FM receiver is used, a clipper circuit for limiting large amplitude signals is operated by the changeover switch.