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JPH08256017

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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 JPH08256017
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
audio amplification circuit in which the generation of shock noise is prevented.
[0002]
2. Description of the Related Art Conventionally, an audio amplification circuit for amplifying
stereo L and stereo R signals is known. FIG. 2 shows such an audio amplification circuit, which
comprises an amplifier (1) for amplifying a stereo L signal and an amplifier (2) for amplifying a
stereo R signal. In FIG. 2, the stereo L signal and stereo R signal amplified by the amplifiers (1)
and (2) are applied to the headphones (3) and (4), respectively, to drive the headphones (3) and
(4). Further, since the capacitor (5) is connected to the connection point of the headphones (3)
and (4), the DC voltage at the connection point is amplified by the amplifiers (1) and (2) by the
charging action of the capacitor (5) It becomes the same as the output DC voltage of). Therefore,
no direct current flows in the headphones (3) and (4), and between the output end of the
amplifier (1) and the headphones (3) and between the output end of the amplifier (2) and the
headphones (4) The output capacitor (not shown) that has been connected to can be eliminated.
[0003]
By the way, when the power is turned on, the amplifier of FIG. 2 is turned on in order to prevent
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noise due to transient operation of the preceding circuit from being transmitted to the
headphones (3) and (4). A muting function is added to cause the amplifiers (1) and (2) to mutate
only for a predetermined period of time from time. That is, in FIG. 2, the amplifiers (1) and (2) are
turned off by turning off the switches (7) and (7 ') in response to the muting signal generated
from the muting signal generation circuit (6). I was doing a muting.
[0004]
However, since the bias voltage is generated using a CR parallel circuit (not shown) that removes
the ripple component of the power supply voltage, the bias voltage of the terminal (A) is from
FIG. Gradually increase as a). Also, the voltage at the connection point (B) of the headphones (3)
and (4) rises more gradually than the rise of the bias voltage as shown in (b) of FIG. Do. The
voltage at the connection point (C) in FIG. 2 is substantially equal to the voltage at the connection
point (B) because the resistance values of the headphones (3) and (4) are small. When muting is
turned off, the amplifiers (1) and (2) start operating and their output DC voltage becomes equal
to the bias voltage. Further, according to FIG. 3A, when the muting is off, a voltage difference
occurs between the reference voltage and the voltage of the connection point B according to FIG.
Therefore, there is a problem that the capacitor (5) is rapidly charged by the outputs of the
amplifiers (1) and (2) which has started operation, and a shock noise is generated.
[0005]
SUMMARY OF THE INVENTION The present invention has been made in view of the abovedescribed point, and amplifies an input signal and applies an output signal to one end of a load
whose other end is grounded via a capacitor. An amplifier, a muting signal generation circuit for
generating a muting signal, a muting circuit for muting the amplifier circuit according to the
muting signal, and a terminal voltage of the capacitor being output from the amplifier And a
charging circuit for charging so as to be a point voltage.
[0006]
Further, the present invention is characterized by comprising: another amplifier which amplifies
another input signal different from the input signal and applies an output signal to one end of
another load whose other end is grounded via the capacitor. I assume.
[0007]
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According to the present invention, muting is performed from the muting signal generation
circuit while the amplifier that amplifies the input signal and applies the output signal to one end
of the load whose other end is grounded via the capacitor is muted. A muting signal is generated,
and muting of the amplifier is performed by operating the muting circuit in response to the
muting signal.
During the muting signal generation period, the charging circuit operates, and the capacitor is
charged according to the output signal of the charging circuit so that the terminal voltage thereof
becomes equal to the output midpoint voltage of the amplifier.
Therefore, when muting is released, it is possible to prevent the rapid charging of the capacitor
by the output signal of the amplifier, and to prevent the generation of shock noise.
[0008]
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a view showing an embodiment of
the present invention, wherein (8) is an amplifier for amplifying a stereo L signal, (9) is an
amplifier for amplifying a stereo R signal, and (10) is an amplifier (8). Headphones for stereo L
signal to which the output signal of) is supplied, (11) headphones for stereo R signal to which the
output signal of amplifier (9) is supplied, (12) for headphones (10) and (11) Capacitors (13) and
(14) connected between the connection point and the ground, constant current sources for
generating operating currents of the amplifiers (8) and (9), and (15) and (16) muting signals (17)
is a muting signal generation circuit that generates the muting signal, (18) is a charging circuit
that performs a charging operation according to the output signal of the muting signal
generation circuit (17), 19) is a reference voltage generating circuit for generating a reference
voltage as a bias voltage of the amplifier (8) and (9).
[0009]
In FIG. 1, during steady operation, no muting signal is generated from the muting signal
generation circuit (17), so the switches (15) and (16) are turned on to operate the operating
current of the constant current sources (13) and (14). In response, the amplifiers (13) and (14)
perform an amplification operation.
Also, since the charging circuit (18) does not generate an output signal, the capacitor (12) is not
charged by the charging circuit (18). In such a state, the stereo L signal and stereo R signal are
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superimposed on the reference voltage generated from the reference voltage generation circuit
(19) and then applied to the amplifiers (8) and (9), respectively. The stereo L signal and stereo R
signal amplified by the amplifiers (8) and (9) are applied to the headphones (10) and (11). Also,
the capacitor (12) is charged so that its terminal voltage, that is, the voltage at the connection
point (A) becomes equal to the output DC voltage of the amplifiers (8) and (9). As a result, the DC
voltages at both ends of the headphones (10) and (11) become equal, so that no DC current flows
in the headphones (10) and (11), and the headphones (10) and (11) are prevented from being
broken.
[0010]
Next, the operation at the time of power on will be described. Before power-on, the capacitor (12)
is completely discharged, and the voltage at the connection point (A) is 0V. When the power is
turned on, a control signal generated by the detection of the power on is applied to the muting
generation circuit (17). Then, a muting signal is generated from the muting signal generation
circuit (17), and the switches (15) and (16) are turned off. Therefore, the operating current is not
supplied to the amplifiers (8) and (9), and the amplifiers (8) and (9) do not perform amplification
operation. As a result, the amplifiers (8) and (9) do not generate amplified stereo L and R signals,
and the output impedances of the amplifiers (8) and (9) become high to achieve the muting state.
[0011]
Here, while amplifiers (8) and (9) are in the muting state, that is, while the muting signal is
generated, the muting signal generation circuit (17) for operating the charging circuit (18) Other
output signals occur. The charging circuit (18) operates in response to the other output signal of
the muting signal generation circuit (17), and the terminal voltage thereof becomes
approximately equal to the reference voltage generated from the reference voltage generation
circuit (19). The capacitor (12) is charged by the charging current of the charging circuit (18).
Further, since the reference voltage generation circuit (19) utilizes a CR parallel circuit for
removing the ripple component of the power supply, the reference voltage gradually rises as
shown in FIG. Since the capacitor (12) is charged so that its terminal voltage becomes
approximately equal to the reference voltage by the charging operation of the charging circuit
(18), the voltage at the connection point (A) is also as shown in FIG. Ascend. Therefore, when
muting is released, the output DC voltages of the amplifiers (8) and (9) become the reference
voltage, which is approximately equal to the voltage at the connection point (A), so that the rapid
charging of the capacitor (12) disappears. The generation of shock noise due to the outputs of
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the amplifiers (8) and (9) is prevented. Incidentally, since the output impedance of the amplifiers
(8) and (9) is high, the charging current is supplied to the capacitor (5) through the headphones
(4) and (4 '), and the capacitor (5) can be charged rapidly. It becomes.
[0012]
Thereafter, when the generation of the muting signal is finished, the switches (15) and (16) are
turned on again, the amplifiers (8) and (9) perform amplification, and the operation of the
charging circuit (18) stops. The first amplification circuit performs a steady amplification
operation. Since the impedance of the capacitor (12) is smaller for alternating current, the
charging circuit (18) may always be operated even during steady operation. However, when the
charging circuit (18) is operated only during the muting operation, the current consumption does
not increase uselessly, and power saving can be achieved.
[0013]
FIG. 4 is a diagram showing a specific circuit example of the main part of the circuit of FIG. 1, and
the charging circuit (18) is a differential part (22) comprising transistors (22a) and (22b) whose
emitters are commonly connected. A constant current source (23) for generating an operating
current of the differential section (22), a switch (24) turned on / off according to the output
signal of the muting signal generation circuit (17) of FIG. And an output stage transistor (25)
connected to the collector of the transistor (22a).
[0014]
In FIG. 4, the reference voltage generated from the reference voltage generation circuit (19) in
response to power on is applied to the base of the transistor (22a) and to the amplifiers (8) and
(9) of FIG. .
Further, the switch (24) is turned on according to the output signal of the muting signal
generation circuit (17) generated with the power on, and the operating current of the constant
current source (23) flows to the differential section (22). The unit (22) starts operation. The
reference voltage applied to the base of transistor (22a) is compared to the base voltage of
transistor (22b). When the base voltage of the transistor (22a) becomes higher than the base
voltage of the transistor (22b), the transistor (22a) is turned on and the output stage transistor
(25) is turned on. Therefore, the collector current of the current source transistor (25) is supplied
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to the capacitor (12) connected to the connection point (A) to charge the capacitor (12). When
the base voltage of the transistor (22b) is higher than that of the transistor (22a), the transistor
(22b) is turned on and the transistor (22a) is turned off, so the output stage transistor (25) is
turned off. Therefore, charging of the capacitor (12) is not performed. Since the capacitor (12) is
completely discharged when the power is turned on, the operation of the differential section (22)
and the output stage transistor (25) follows so that the terminal voltage of the capacitor (12)
becomes approximately equal to the reference voltage Do.
[0015]
As described above, according to the present invention, in an amplifier for generating an output
amplification signal at one end of a load whose other end is grounded via a capacitor, the
capacitor is amplified during the muting period and the terminal voltage is amplified. By charging
the capacitor so as to be substantially equal to the output midpoint voltage of the capacitor, it is
possible to prevent the rapid charging of the capacitor due to the output of the amplifier at the
time of muting cancellation, and hence to prevent the generation of shock noise.
[0016]
Brief description of the drawings
[0017]
1 is a diagram showing an embodiment of the present invention.
[0018]
2 is a diagram showing a conventional example.
[0019]
3 is a characteristic diagram for explaining the operation of FIG. 1 and FIG.
[0020]
4 is a circuit diagram showing the main part of FIG.
[0021]
Explanation of sign
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[0022]
8, 9 amplifier 10, 11 headphone 12 capacitor 13, 14 constant current source 15, 16 switch 17
muting signal generating circuit 18 charging circuit 19 reference voltage generating circuit
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