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JPH06113393

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPH06113393
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
FM stereo receiver.
[0002]
2. Description of the Related Art By using an IC, an FM stereo receiver can be miniaturized and
thinned to, for example, a size of a business card. However, in this case, it is difficult to
incorporate two speakers in the receiver for stereo if it is miniaturized as such, and even if it can
be provided, stereo feeling can not be obtained. Therefore, in a small FM stereo receiver, the
number of built-in speakers is one.
[0003]
When the FM stereo receiver has one built-in speaker, the stereo may be left as it is when
listening to the broadcast by the earphone, but it is necessary to be monaural when listening to
the broadcast by the built-in speaker.
[0004]
Also, when listening to the broadcast with earphones, it is naturally necessary to turn off the
built-in speaker.
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1
[0005]
Furthermore, since the built-in speaker is small and can not reproduce low frequencies, it is
necessary to cut high frequencies to balance the frequency of the reproduced sound and to
adjust the reproduced sound to be easy to hear.
[0006]
However, in order to satisfy the above-mentioned requirements, it is necessary to provide a low
pass filter for cutting the stereo / monaural switching switch earphone / speaker switching
switch high band.
[0007]
However, to provide two switches and a low pass filter in a business card sized FM stereo
receiver is difficult in space, which hinders downsizing and thinning of the receiver.
[0008]
The present invention is intended to solve such problems.
[0009]
By the way, in FM stereo broadcasting, balanced modulation by the sum signal (L + R) of audio
signals L and R of left and right channels, a pilot signal, and a difference signal (LR) A frequency
multiplexed signal with the signal, that is, a stereo composite signal is being transmitted.
Then, in the FM stereo receiver, a subcarrier signal is formed from the pilot signal of the stereo
composite signal and used for stereo demodulation.
[0010]
Also, the audio amplifier used in a small radio receiver is integrated into an IC, and its final stage
is generally push-pull connected in order to improve the efficiency of the battery as a power
supply.
[0011]
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2
And if it is an audio amplifier of a general stereo device, although the power supply of the last
stage is made into plus / minus 2 power supplies, in the small radio receiver, since the battery is
used as the power supply, the power supply of the last stage is , Plus or minus one power supply.
[0012]
Therefore, from the final stage of the audio amplifier used for a small radio receiver, at the same
time as the audio signal is outputted, the DC voltage of 1/2 the power supply voltage is also
outputted together.
That is, the DC voltage is superimposed on the audio signal.
[0013]
The present invention is made to solve the above-mentioned problems, paying attention to the
above points.
[0014]
That is, in the present invention, when the reference numerals of the respective parts correspond
to the embodiments described later, they are connected to the tuner circuit 11 for receiving a
broadcast and the output terminal of the tuner circuit 11, and the stereo composite signal SST
from the tuner circuit 11 Are supplied from the stereo composite signal SST to the stereo
demodulation circuit 13 for demodulating the left and right channel audio signals L and R, and to
the stereo demodulation circuit 13 so that the left and right channel audio signals are supplied
respectively. Audio amplifiers 14L and 14R for the left and right channels, a stereo earphone jack
16 to which audio signals for the left and right channels from the audio amplifiers 14L and 14R
are supplied, a speaker 15, a speaker / earphone changeover switch 17A, 17B and stereo A
switching element Q11 for controlling whether the demodulation circuit 13 performs stereo
demodulation or monaural operation is provided, and the output terminal T4R of one of the left
and right channel audio amplifiers 14L and 14R is switched to the speaker / earphone A direct
current voltage obtained at the output terminal T4R of one audio amplifier 14R is connected to
the switching element Q11 through the speaker / earphone changeover switch 17A when the
speaker / earphone changeover switch 17A, 17B is on via the switch 17A. This switching element
Q11 is turned on to turn on the switching element Q11, thereby causing the stereo demodulation
circuit 13 to perform monaural operation and outputting the audio amplifiers 14L and 14R of
the left or right channel. When the speaker / earphone changeover switch 17A, 17B is supplied
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3
to the speaker 15, the DC voltage obtained at the output terminal T4R of one of the audio
amplifiers 14R is turned off and the switching element Q11 is turned off. Since the switching
element Q11 is turned off and the switching element Q11 is turned off, the stereo demodulation
circuit 13 performs stereo demodulation, and the outputs of the left and right channel audio
amplifiers 14L and 14R are supplied to the stereo earphone jack 16, and The supply of the signal
to the speaker 15 is turned off.
[0015]
When the switches 17A and 17B are turned on, the transistor Q11 is turned on to form the low
pass filter 18, the stereo demodulation circuit 13 performs a monaural operation, and a
monaural audio signal is supplied to the speaker 15.
When the switches 17A and 17B are off, the transistor Q11 is off and the low pass filter 18 is not
configured, and the stereo demodulation circuit 13 performs stereo demodulation to supply a
stereo audio signal to the jack 16.
[0016]
DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 11 denotes an
FM.AM tuner circuit having an antenna tuning circuit to a demodulation circuit, and from this
tuner circuit 11, a stereo composite signal SST, ie, when receiving an FM stereo broadcast, is
shown. The frequency multiplexed signal SST of the sum signal SMN (= L + R) of the audio signals
L and R of the left and right channels, the pilot signal SPLT, and the balanced modulation signal
SSUB by the difference signal (LR) is output When receiving monaural broadcast and AM
broadcast, a monaural audio signal SMN is output.
Actually, although not shown, the tuner circuit 1 is integrated into a single chip IC except for the
antenna tuning circuit, the resonance circuit of the local oscillation circuit, the intermediate
frequency filter, and the like.
[0017]
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Reference numeral 13 denotes a stereo demodulation circuit. The output signal of the tuner
circuit 11 is supplied to the demodulation circuit 13 through the signal line 12, and when the
output signal is a stereo composite signal SST, left and right from the signal SST. The channel
audio signals L and R are demodulated and extracted, and when the output signal is a monaural
audio signal, the audio signal is extracted as it is as an audio signal of the left and right channels.
The demodulation circuit 13 is also made into a one-chip IC.
[0018]
Further, reference numerals 14L and 14R denote left and right channel audio amplifiers, and in
the final stages of these amplifiers 14L and 14R, the output transistors Q1 and Q2 are push-pull
connected as described above, and the collectors thereof are output terminals T4R (and It is
connected to T4L).
These amplifiers 14L and 14R are also integrated into one chip IC.
[0019]
Further, reference numeral 15 denotes a built-in speaker, 16 denotes a stereo earphone jack, and
17A and 17B denote speaker-earphone changeover switches interlocked with each other.
[0020]
The output terminal T4R of the amplifier 14R is connected to the contact 16R of the right
channel of the jack 16 through the small protection resistor R11, and the output terminal T4L of
the amplifier 14L is connected to the left of the jack 16 through the small protection resistor
R12. It is connected to the contact 16L of the channel.
In addition, the speaker 15, the switch 17B, and the capacitor C11 for direct current cut (bypass)
are connected in series between the output terminal T4L of the amplifier 14L and the ground,
and the common contact 16C of the jack 16 is It is connected to the connection point between
the speaker 15 and the capacitor C11.
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[0021]
Further, between the tuner circuit 11 and the demodulation circuit 13, between the signal line 12
of the signal SST and the ground, a high frequency cut capacitor C12 and a collector / emitter of
the switching transistor Q11 are connected in series. Be done.
The output terminal T4R of the amplifier 14R is connected to the base of the transistor Q11
through the switch 17A and further through the resistor R13, and a resistor R14 and a bypass
capacitor C13 are connected in parallel between the base and the ground. The circuit is
connected.
[0022]
Although not shown, the power supply of this receiver is, for example, two AA batteries, that is,
3V batteries. Therefore, the DC potential of the output terminal T4R of the amplifier 14R (and
14L) is 1.5V. Become.
[0023]
In such a configuration, when listening to the broadcast by the speaker 15, the switches 17A and
17B are turned on.
Then, the DC voltage of the terminal T4R of the amplifier 14R is supplied to the base of the
transistor Q11 through the switch 17A and further through the resistor R13, so that the
transistor Q11 is turned on and the output terminal of the tuner circuit 11 is grounded through
the capacitor C12. At this time, the low-pass filter 18 is configured by the output impedance of
the tuner circuit 11 and the capacitor C12.
[0024]
Therefore, the low-pass filter 18 attenuates the high-frequency component of the sum signal
SMN of the stereo composite signal SST from the tuner circuit 11, and removes (or sufficiently
attenuates) the pilot signal SPLT and the balanced modulation signal SSUB. ).
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[0025]
Then, since the pilot signal SPLT and the signal SST from which the balanced modulation signal
SSUB has been removed are supplied to the demodulation circuit 13, stereo demodulation is not
performed in the demodulation circuit 13, and the demodulation circuit 13 outputs the sum
signal SMN, That is, the monaural audio signal SMN is output as it is as the audio signal of the
left and right channels, and is supplied to the amplifiers 14L and 14R.
[0026]
Then, the monaural audio signal SMN supplied to the amplifier 14L is supplied to the speaker 15
through the signal line of the amplifier 14L, the speaker 15, the switch 17B, and the capacitor
C11. Can.
At this time, the high frequency band of the monaural audio signal SMN supplied to the amplifier
14L is attenuated by the low pass filter 18 constituted by the output impedance of the tuner
circuit 11 and the capacitor C12. Even if the bass can not be reproduced, the reproduced sound
is an audible sound with well-balanced frequencies in the low and high frequencies.
[0027]
On the other hand, when listening to the FM stereo broadcast in stereo by stereo earphones (not
shown), the switches 17A and 17B are turned off and the plug of the stereo earphones is inserted
into the jack 16.
すると、スイッチ17Aがオフなので、トランジスタQ11はバイアスされずオフである。
Therefore, the stereo composite signal SST from the tuner circuit 11 is supplied as it is to the
demodulation circuit 13 through the signal line 12, and the stereo audio signals L and R of the
left and right channels are demodulated.
[0028]
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Then, the stereo audio signals L and R are supplied to the contacts 16L and 16R of the jack 16
through the amplifiers 14L and 14R and the resistors R12 and R11.
At this time, the common contact 16C of the jack 16 is grounded via the capacitor C11.
Therefore, the signals L and R are supplied to the earphone through the plug inserted into the
jack 16, and the stereo broadcast can be listened to in stereo.
[0029]
At this time, the transistor Q11 is off, and the high frequency band of the sum signal SMN of the
stereo composite signal SST supplied to the demodulation circuit 13 is not attenuated. You can
get In addition, since the switch 17B is off, the reproduction sound is not output from the
speaker 15.
[0030]
Thus, according to the present invention, when listening to an FM stereo broadcast with the builtin speaker 15, it can listen in monaural, and when listening in stereo earphones, it can listen in
stereo.
[0031]
Moreover, in that case, monaural stereo switching, built-in speaker 15 and earphone switching,
and frequency balance correction at the time of reproduction by the speaker 15 are performed
by one interlocking switch 17A, 17B, transistor Q11 and capacitor C12. Can.
Therefore, a large space is not required, and when the FM stereo receiver is miniaturized and
thinned to a business card size, there is no hindrance.
[0032]
Further, when listening to a stereo broadcast in monaural by the built-in speaker 15, it is realized
by removing the pilot signal SPLT of the stereo composite signal SST supplied to the stereo
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8
demodulation circuit 13 by the low pass filter 18, so stereo monaural Switching is reliable.
[0033]
Furthermore, since the low-pass filter 18 for removing the pilot signal SPLT is configured by the
output impedance of the tuner circuit 11 and the capacitor C12, the configuration is simple,
which is advantageous for downsizing and thinning of the receiver. And the cost can be reduced.
[0034]
Further, at the time of stereo broadcast reception, not only the pilot signal SPLT is removed by
the capacitor C12, but also the high region of the sum signal (monaural audio signal) SMN is
attenuated. When listening, even if the speaker 15 can not reproduce the bass, the frequency
balance of the reproduced sound can be adjusted, and the reproduced sound can be made easy to
hear.
[0035]
Further, since the transistor Q11 is on / off controlled to realize the effectiveness /
ineffectiveness of the low pass filter 18, the transistor Q11 should be provided beside the signal
line 12 between the tuner circuit 11 and the stereo demodulation circuit 13. Can.
Therefore, since it is not necessary to route the signal line 12 around, the frequency
characteristics and phase characteristics of the stereo composite signal SST supplied to the
demodulation circuit 13 may be affected, or interference with other circuits may be generated.
Absent.
[0036]
In addition, the pattern of the printed circuit board is not aggravated due to the routing of the
signal line 12.
Furthermore, since the transistor Q11 is turned on and off using the DC voltage at the output
terminal T4R of the amplifier 14R, it is not necessary to provide a special voltage source for the
turning on and off. It is effective for size reduction, weight reduction or cost reduction.
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9
[0037]
In the example shown in FIG. 2, by using a jack with a switch contact as the jack 16, the speakerearphone changeover switch 17 of FIG. 1 is omitted.
[0038]
That is, the jack 16 is provided with a switch contact 16S that is always on, and the built-in
speaker 15 and the capacitor C21 for cutting off direct current are connected in series between
the contact 16S and the ground. Are connected to the connection point between the speaker 15
and the capacitor C21 through the capacitor C22 for direct current cut.
Further, the output terminals T4L and T4R of the amplifiers 14L and 14R are connected to the
contacts 16L and 16R of the jack 16, respectively.
[0039]
Furthermore, the contact 16S is connected to the base of the first switching transistor Q21
through the low pass filter 21 for removing the audio signal, and its collector is connected to the
base of the second switching transistor Q22, The collector is connected to the stereo
demodulation / mono demodulation mode switching terminal of the stereo demodulation circuit
13.
The demodulation circuit 13 is in the monaural mode when the transistor Q22 is on, and in the
stereo mode when the transistor Q22 is off.
[0040]
In such a configuration, when listening to a broadcast by the speaker 15, the earphone plug is
not inserted into the jack 16. Then, since the contact 16R and the contact 16S are turned on, the
DC voltage of the terminal T4R of the amplifier 14R is supplied to the base of the transistor Q21
through the voltage line of the contact 16R → the contact 16S → the low pass filter 21, whereby
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the transistor Q21 is The transistor Q22 is also turned on.
[0041]
Then, since the transistor Q22 is on, even if the stereo composite signal SST is supplied from the
tuner circuit 11 to the demodulation circuit 13, the demodulation circuit 13 is in the monaural
mode, and the demodulation circuit 13 outputs the monaural audio signal SMN in the stereo
composite signal SST. Are output and supplied to the amplifiers 14L and 14R.
[0042]
Then, the monaural audio signal SMN supplied to the amplifier 14R is supplied to the speaker 15
through the signal line of the amplifier 14R → the contact 16R → the contact 16S → the contact
16S → the speaker 15 → the capacitor C21. I can listen in monaural.
[0043]
On the other hand, when listening to an FM stereo broadcast in stereo by stereo earphones, the
plug of the stereo earphones is inserted into the jack 16.
Then, since the contact 16R and the contact 16S are turned off, no voltage is supplied to the base
of the transistor Q21, the transistor Q21 is turned off, and the transistor Q22 is also turned off.
[0044]
Then, since the transistor Q22 is off, the demodulation circuit 13 is in the stereo mode, and the
stereo audio signals L and R of the left and right channels stereo-demodulated from the stereo
composite signal SST are output from the demodulation circuit 13 and these signals L and R are
output. Are supplied to the amplifiers 14L and 14R, respectively, and are further supplied from
the amplifiers 14L and 14R to the contacts 16L and 16R of the jack 16.
At this time, the common contact 16C of the jack 16 is grounded through the capacitor C21.
Therefore, the signals L and R are supplied to the earphone through the plug inserted into the
jack 16, and the stereo broadcast can be listened to in stereo.
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[0045]
Therefore, also in this example, when listening to the FM stereo broadcast with the built-in
speaker 15, it can be listened in monaural, and when listening in stereo earphones, it can be
heard in stereo. Moreover, there is no need to switch between the case of listening with the
speaker 15 and the case of listening with the earphone.
[0046]
The circuit of FIG. 1 described above can be combined with the circuit of FIG. 2. For example,
instead of connecting the elements 15 to 17B of FIG. 1, the contact 16S of the jack 16 of FIG. If
connected to the device R13, the switches 17A and 17B can be omitted as well, and there is no
need to switch the switch between listening to the speaker 15 and listening to the earphone.
Also, in FIG. 2, a capacitor C22 can be connected between the contact 16C and the ground.
[0047]
According to the present invention, in the case of listening to the FM stereo broadcast with the
built-in speaker 15, it can be listened in monaural, and in the case of listening with the stereo
earphone it can be heard in stereo.
[0048]
In addition, it is possible to perform monaural stereo switching, switching between the built-in
speaker 15 and the earphone, and correct the frequency balance at the time of reproduction by
the speaker 15 with few elements, thus miniaturizing the FM stereo receiver to a business card
size.・ There is no hindrance when thinning.
[0049]
Further, when listening to a stereo broadcast in monaural by the built-in speaker 15, switching to
monaural is certain.
[0050]
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12
Furthermore, since the low-pass filter 18 for removing the pilot signal SPLT is configured by the
output impedance of the tuner circuit 11 and the capacitor C12, the configuration is simple,
which is advantageous for downsizing and thinning of the receiver. And the cost can be reduced.
In addition, even if the speaker 15 can not reproduce the bass, the frequency balance of the
reproduced sound can be adjusted, and the reproduced sound can be easily heard.
[0051]
Furthermore, since it is not necessary to lead the signal line 12 between the tuner circuit 11 and
the stereo demodulation circuit 13 around, the frequency characteristic and the phase
characteristic of the stereo composite signal SST supplied to the demodulation circuit 13 are
affected. There is no interference with the circuit.
[0052]
In addition, the pattern of the printed circuit board is not aggravated due to the routing of the
signal line 12.
Furthermore, since switching between stereo and monaural is performed using the DC voltage at
the output terminal T4R of the amplifier 14R, there is no need to provide a special voltage source
for the switching, which also reduces the size of the receiver.・ It is effective for weight reduction
or cost reduction.
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