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JP2014229917

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DESCRIPTION JP2014229917
Abstract: While having a simple configuration and capable of outputting to a speaker in a BTL
type output format, noise due to transient fluctuation of an output signal to a headphone at the
time of headphone connection is suppressed. SOLUTION: In an audio output circuit A that
outputs BTL format to speakers 41 and 42 and outputs SE format to headphones 7, right and left
audio signals on which DC bias voltage is superimposed or DC bias voltage And a ground control
circuit 6 for controlling the ground terminal 55 of the headphone terminal 5 to be at the ground
potential on the basis of any one of the left and right inverted signals superimposed. [Selected
figure] Figure 1
Voice output circuit
[0001]
The present invention relates to an audio output circuit, and more particularly, to an audio
output circuit that can use a speaker signal output by BTL (Bridged Transformer Less) output as
an output of a headphone.
[0002]
The audio output circuit is roughly classified into an SE type (Single End) type and a BTL (Bridged
Transformer Less) type according to its output format.
The SE type audio output circuit is configured such that the output of the amplifier is connected
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to the positive electrode of the speaker and the negative electrode is grounded. Further, the BTL
type audio output circuit is configured to include two amplifiers, and to input a non-inverted
signal passed through one amplifier and an inverted signal passed through the other amplifier to
the speaker. The audio output circuit superimposes a DC bias voltage on an AC audio signal and
inputs it to the speaker. When audio is output from a speaker, any of the above-described SE type
and BTL type output formats can be used.
[0003]
On the other hand, when outputting audio from headphones, the audio output circuit needs to be
an SE type. When the electronic device has a BTL type audio output circuit, it is impossible to
connect headphones as it is. Then, although there was a thing provided separately with SE type
audio ¦ voice output circuit for headphones, there existed a problem that a circuit structure was
complicated.
[0004]
Therefore, Patent Document 1 proposes a BTL type audio output circuit provided with a
headphone output. The audio output circuit of Patent Document 1 is formed so that the first
section of the headphone jack can be bent, and is supplied with a forward rotation signal and
connected to the positive electrode of the speaker. Then, the forward rotation signal is supplied
also to the second section, and the inverting amplifier is connected to the negative electrode of
the speaker.
[0005]
When the headphone plug is not connected to the headphone jack, the wire to which the forward
rotation signal from the forward rotation amplifier is supplied and the first section are connected.
Thereby, the non-inverted signal from the non-inverted amplifier is supplied to the positive
electrode of the speaker through the first section, and the inverted signal from the inverted
amplifier is directly supplied to the negative electrode of the speaker to output BTL type audio
output It constitutes a circuit.
[0006]
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In addition, when the headphone plug is connected to the headphone jack, the wiring to which
the forward rotation signal from the forward rotation amplifier is supplied and the first section
are separated, and the forward rotation signal is supplied to the speaker Is stopped. Thereby, the
output of the sound from the speaker is stopped. On the other hand, since the positive signal is
supplied to the second section, sound is output from the headphones.
[0007]
However, in such an audio output circuit, due to a transient fluctuation of a direct current bias
immediately after power on, for example, short noise called pop noise such as "pop" or pop noise
(hereinafter referred to as pop noise). ) Occurs. In order to suppress such pop noise, for example,
an IC for audio output processing as shown in Patent Document 2 has been proposed. The IC for
audio output processing of Patent Document 2 makes the bias circuit and the amplifier circuit
independent, and outputs the output of the audio signal to the speaker from the amplifier circuit,
and activates the bias circuit and the amplifier circuit at different timings. The popping sound is
suppressed by
[0008]
JP, 2005-269291, A JP, 2002-78064, A
[0009]
However, in the configuration of Patent Document 2, in addition to the audio output processing
IC, a control IC is required to suppress pop noise, and a shutdown signal for driving the control
IC is required. It is.
That is, not only the configuration of the audio output circuit is complicated but also the control
is complicated and the manufacturing cost is increased.
[0010]
SUMMARY OF THE INVENTION In order to solve the problems as described above, it is an object
of the present invention to have a simple configuration and be able to output sound from a
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speaker in a BTL type output format, and at the time of headphone connection It is to suppress
the noise due to the transient fluctuation of the output signal to the headphones.
[0011]
The audio output circuit according to one aspect of the present invention is a BTL type audio
output circuit in which a DC bias voltage is superimposed on the left and right audio signals and
the left and right inverted signals obtained by inverting the phases of the left and right audio
signals. A headphone terminal for outputting left and right audio signals or left and right inverted
signals to headphones, and the headphone terminal is superimposed with the left and right audio
signals on which the DC bias voltage is superimposed or the DC bias voltage is superimposed A
terminal for independently outputting left and right inverted signals and a ground terminal, the
left and right audio signals on which the DC bias voltage is superimposed or the left and right
inversion signals on which the DC bias voltage is superimposed And a ground control circuit for
controlling whether or not the ground terminal is set to the ground potential based on any one of
the signals.
[0012]
In the audio output circuit according to one aspect of the present invention, an output signal of a
BTL type output format can be output to the speaker, and pop noise is generated in the
headphone even if the output signal to the headphone transiently fluctuates. It can be
suppressed.
Then, in order to suppress the generation of the pop noise, by using the ground control circuit, a
separate circuit is provided for the speaker and the headphone, or an oscillation circuit which
outputs a signal for suppressing the pop noise is provided. There is no need to make it possible
to simplify the circuit.
[0013]
In the audio output circuit according to the above aspect, the ground control circuit detects a
rising edge of the bias voltage and a switching element disposed between the ground terminal
and the ground potential, and a predetermined time from the rise of the bias voltage The
switching element is turned on at a delayed timing, and the switching element is kept on while
the left and right audio signals on which the bias voltage is superimposed or the left and right
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inversion signals on which the bias voltage is superimposed are output. And the circuit to be
configured.
With this configuration, it is possible to suppress the generation of pop noise in the headphones
with a simple configuration.
[0014]
In the audio output circuit according to the above aspect, the ground control circuit is a circuit
that outputs left and right audio signals on which the bias voltage is superimposed or a circuit
that outputs left and right inversion signals on which the bias voltage is superimposed. A signal is
detected as a voltage from any one circuit, and a smoothing circuit is provided to smooth the
voltage. If configured in this way, this configuration makes it possible to suppress the generation
of pop noise in headphones with a simple configuration.
[0015]
In the audio output circuit according to the above aspect, the ground control circuit includes a
smoothing circuit combining a resistor and a capacitor, and the ground control circuit is stored in
the capacitor after the voltage signal is stopped. It is in love with the reset circuit to release the
charge. According to this structure, pop noise based on the transient fluctuation of the output
signal to the headphone which is generated whenever the power is supplied to the audio output
circuit can be effectively suppressed. .
[0016]
In the audio output circuit according to the above aspect, the ground control circuit is a signal
from the circuit to which the left and right audio signals on which the bias voltage is
superimposed is output or from the circuit to which the left and right inversion signals on which
the bias voltage is superimposed are output. The diode is configured to be connected in a
forward direction from the connection point to the smoothing circuit in a portion from the
connection point for detecting the signal to the smoothing circuit. According to this structure, the
current from the ground control circuit to the audio output circuit can be suppressed, and the
generation of noise at the time of reset can be suppressed.
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[0017]
According to the present invention, while having a simple configuration, it is possible to output
sound from a speaker in a BTL type output format, and to suppress noise due to transient
fluctuation of an output signal to headphones when headphones are connected. Can provide an
audio output circuit that can
[0018]
It is a circuit diagram of an example of the audio output circuit concerning the present invention.
FIG. 7 is a circuit diagram of another example of the audio output circuit according to the present
invention. FIG. 7 is a circuit diagram of still another example of the audio output circuit
according to the present invention. FIG. 7 is a circuit diagram of still another example of the
audio output circuit according to the present invention. FIG. 7 is a circuit diagram of still another
example of the audio output circuit according to the present invention.
[0019]
Embodiments of the present invention will be described below with reference to the drawings.
First Embodiment FIG. 1 is a circuit diagram of an example of an audio output circuit according
to the present invention. The audio output circuit A shown in FIG. 1 is a circuit that receives left
and right audio signals independently and outputs audio independently from the left and right
speakers or headphones. The audio output circuit A includes an input unit 1 to which left and
right audio signals are independently input, an amplification unit 2 to independently amplify left
and right audio signals, a filter circuit 31, speakers 41 and 42, and headphones. A terminal 5 and
a ground control circuit 6 are provided. The audio output circuit A has an Rch system for
processing a right audio signal (hereinafter referred to as Rch signal) and an Lch system for
processing a left audio signal (hereinafter referred to as Lch signal). . Rch and Lch are signals
including AC components. Further, FIG. 1 shows a headphone equivalent circuit 7 equivalent to
the configuration of the headphones.
[0020]
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First, the headphone equivalent circuit 7 will be described. The headphone equivalent circuit 7
includes a resistor 71 replaced with an Rch headphone and a resistor 72 replaced with an Lch
headphone. One of the resistors 71 is connected to the R input end 711, and one of the resistors
72 is connected to the L input end 721. The other of the resistor 71 and the resistor 72 is
connected to the ground terminal 73, respectively. As shown in FIG. 1, the headphone equivalent
circuit 7 has a circuit configuration corresponding to the SE type output format. The R input end
711, the L input end 721, and the ground terminal 73 are included in the headphone plug
connected to the headphone terminal 5.
[0021]
The input unit 1 of the audio output circuit A includes an R input terminal 11 to which the right
Rch signal is input and an L input terminal 12 to which the Lch signal is input. The R input
terminal 11 and the L input terminal 12 are connected to the amplification unit 2 via capacitors
C11 and C21, respectively. The capacitors C10 and C20 are AC coupling capacitors and remove
direct current components.
[0022]
The amplification unit 2 receives the Rch signal and the Lch signal independently. A distribution
unit is provided to distribute the Rch signal into two signals. The Rch signal distributed by the
distribution unit is provided with an amplifier circuit 211 which amplifies a DC bias and
superposing it, and an amplifier circuit 212 which superimposes a DC bias and amplifies it on an
inverted Rch signal whose phase is inverted. The amplification unit 2 outputs the amplified Rch
signal and the amplified inverted Rch signal. Further, the Lch system has a similar configuration,
and a distribution unit, an amplifier circuit 221 which superimposes and amplifies a DC bias on
an Lch signal, and an amplifier circuit 222 which superimposes and amplifies a DC bias on an
inverted Lch signal Is equipped.
[0023]
The amplification unit 2 is configured to output each of the amplified Rch signal, the inverted
Rch signal, the Lch signal, and the inverted Lch signal. An R output circuit 101, which outputs an
Rch signal, is connected to an R speaker signal input unit 511, which will be described later, of
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the headphone terminal 5 via a low pass filter configured of a coil L11 and a capacitor C11. The
inverted R output circuit 102, which outputs the inverted Rch signal, is connected to the negative
electrode of the Rch speaker 41 via a low pass filter formed of a coil L12 and a capacitor C12.
[0024]
That is, the high frequency component of the Rch signal from the amplification unit 2 is removed
by a low pass filter, and the Rch signal is input to the R speaker signal input unit 511 of the
headphone terminal 5. The high frequency component of the inverted Rch signal from the
amplification unit 2 is removed by a low pass filter, and the inverted Rch signal is input to the
negative electrode of the Rch speaker 41. Further, a bypass capacitor C13 for connecting the R
output circuit 101 and the inverted R output circuit 102 is also provided.
[0025]
The L output circuit 201 through which the Lch signal is output from the amplification unit 2 is
connected to an L speaker signal input unit 521, which will be described later, of the headphone
terminal 5 via a low pass filter configured of a coil L21 and a capacitor C21. The inverted L
output circuit 202 from which the inverted Lch signal is output is connected to the negative
electrode of the Lch speaker 42 via a low pass filter formed of a coil L22 and a capacitor C22.
[0026]
That is, the high frequency component of the L signal from the amplification unit 2 is removed
by the low pass filter, and the L signal is input to the L speaker signal input unit 521 of the
headphone terminal 5. Further, high frequency components of the inverted Lch signal from the
amplification unit 2 are removed by a low pass filter, and the inverted Lch signal is input to the
negative electrode of the Lch speaker 42. In addition, a bypass capacitor C23 for connecting the
L output circuit 201 and the inverted L output circuit 202 is also provided.
[0027]
The Rch speaker 41 and the Lch speaker 42 are conventionally known speakers, and the details
will be omitted.
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[0028]
The headphone terminal 5 includes an R speaker signal input unit 511, an R bypass connection
unit 512, an R headphone signal input unit 513, an L speaker signal input unit 521, an L bypass
connection unit 522, and an L headphone signal input unit 523. Is equipped.
The headphone terminal 5 further includes an R contact piece 514, an L contact piece 524, an R
switch 53, an L switch 54, and a ground terminal 55.
[0029]
As described above, the R output circuit 101 is connected to the R speaker signal input unit 511.
The R bypass connection unit 512 is connected to the positive electrode of the Rch speaker 41.
The R headphone signal input unit 513 is connected to the R headphone signal circuit 103
branched from the R output circuit 101. Here, the R headphone signal circuit 103 will be
described. The R headphone signal circuit 103 receives the amplified Rch signal demultiplexed
from the R output circuit 101. The R headphone signal circuit 103 includes a bias removing and
gain adjusting circuit 32 including a capacitor C14, a resistor R11 and a resistor R12. The Rch
signal demultiplexed from the R output circuit 101 and sent to the R headphone signal circuit
103 is subjected to the bias removal and gain adjustment circuit 32 to remove the DC bias
superimposed thereon, and is used as the R headphone headphone signal with gain adjustment.
Input to the signal input unit 513.
[0030]
As described above, the L speaker signal input unit 521 is connected to the L output circuit 201.
The L bypass connection unit 522 is connected to the positive electrode of the Lch speaker 42.
An L headphone signal circuit 203 branched from the L output circuit 201 is connected to the L
headphone signal input unit 523. Here, the L headphone signal circuit 203 will be described. The
L headphone signal circuit 203 receives the amplified Lch signal demultiplexed from the L
output circuit 201. The L headphone signal circuit 203 includes a bias removal and gain
adjustment circuit 32 including a capacitor C24, a resistor R21, and a resistor R22. The Lch
signal demultiplexed from the L output circuit 201 and sent to the L headphone signal circuit
203 is subjected to the bias removal and gain adjustment circuit 32 to remove the DC bias
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superimposed thereon, and the L headphone signal is obtained as a Gain adjusted Lch headphone
signal. Input to the signal input unit 523.
[0031]
The R speaker signal input unit 511 and the R bypass connection unit 512 are connected to the
R switching switch 53, and the R headphone signal input unit 513 is connected to the R contact
piece 514. The R contact piece 514 is an elastically deformable conductive member, and contacts
the R input end 711 when the headphone plug is connected to the headphone terminal 5. Also, at
this time, the R contact piece 514 is pushed by the R input end portion 711 and bends.
[0032]
The R switching switch 53 is provided at the tip of the movable piece 531 which can be
elastically deformed, a conductive contact portion 532 which contacts the movable piece 531 in
a conductive state, and the movable piece 531. And a non-conductive pressing portion 533 to be
in contact. In place of the pressing portion 533, a non-conductive contact portion may be
provided at a portion of the R contact piece 514 that is in contact with the tip of the movable
piece 531. As shown in FIG. 1, the movable piece 531 is connected to the R speaker signal input
unit 511, and the contact unit 532 is connected to the R bypass connection unit 512. When the
headphone plug is not connected to the headphone terminal 5, the movable piece 531 and the
contact portion 532 are in contact. Thus, the R output circuit 101 is connected to the positive
electrode of the Rch speaker 41 via the R speaker signal input unit 511, the movable piece 531,
the contact unit 532, and the R bypass connection unit 512. Further, when the R contact piece
514 is pushed by the R input end portion 711 and bent, the pressing portion 533 is pushed by
the R contact piece 514, the movable piece 531 is bent, and the connection between the movable
piece 531 and the contact portion 532 is disconnected. .
[0033]
The L speaker signal input unit 521 and the L bypass connection unit 522 are connected to the L
switching switch 54, and the L headphone signal input unit 523 is connected to the L contact
piece 524. The L contact piece 524 is an elastically deformable conductive member, and when
the headphone plug is connected to the headphone terminal 5, the L contact piece 524 contacts
the L input end portion 721. Also, at this time, the L contact piece 524 is pushed by the L input
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end portion 721 and is bent.
[0034]
The L switching switch 54 is provided at the tip of the movable piece 541 and the conductive
contact portion 542 in contact with the movable piece 541 in the conductive state and in the
nonconductive state with the L contact piece 524. And a non-conductive pressing portion 543 to
be in contact. Note that, instead of the pressing portion 543, a non-conductive contact portion
may be provided at a portion of the L-contacting piece 524 that is in contact with the tip of the
movable piece 541. As shown in FIG. 1, the movable piece 541 is connected to the L speaker
signal input unit 521, and the contact portion 542 is connected to the L bypass connection unit
522. When the headphone plug is not connected to the headphone terminal 5, the movable piece
541 and the contact portion 542 are in contact. Thus, the L output circuit 201 is connected to
the positive electrode of the Lch speaker 42 via the L speaker signal input unit 521, the movable
piece 541, the contact unit 542, and the L bypass connection unit 522. Further, when the L
contact piece 524 is pushed by the L input end portion 721 and bent, the pressing portion 543 is
pushed by the L contact piece 524, the movable piece 541 is bent, and the connection between
the movable piece 541 and the contact portion 542 is disconnected. .
[0035]
As described above, when the headphone plug is not connected to the headphone terminal 5, the
R speaker signal input unit 511 and the R bypass connection unit 512 are connected by the
contact between the movable piece 531 and the contact unit 532. The R output circuit 101 is
connected to the R speaker signal input unit 511, and the R bypass connection unit 512 is
connected to the positive electrode of the Rch speaker 41. As a result, the amplified Rch signal
transmitted via the R output circuit 101 is input to the positive electrode of the Rch speaker 41.
[0036]
Similarly, by the contact between the movable piece 541 and the contact portion 542, the L
speaker signal input portion 521 and the L bypass connection portion 522 are connected. The L
output circuit 201 is connected to the L speaker signal input unit 521, and the L bypass
connection unit 522 is connected to the positive electrode of the Lch speaker 42. As a result, the
amplified Lch signal transmitted through the L output circuit 201 is input to the positive
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electrode of the Lch speaker 42. Thereby, an audio signal can be input to the Rch speaker 41 and
the Lch speaker 42 in the BTL type output format.
[0037]
Further, when the headphone plug is connected to the headphone terminal 5, the movable piece
531 and the contact portion 532 are separated. Since the circuit for inputting the amplified Rch
signal to the positive electrode of the Rch speaker 41 is opened, the output from the Rch speaker
41 is stopped. The R contact piece 514 is connected to the R headphone signal input unit 513,
and the R headphone signal input unit 513 is connected to the R headphone signal circuit 103.
Thus, the Rch headphone signal from the R headphone signal circuit 103 is supplied to the R
input end 711 connected to the R contact piece 514.
[0038]
Similarly, since the circuit for inputting the amplified Lch signal to the positive electrode of the
Lch speaker 42 is opened, the output from the Lch speaker 42 is stopped. The L contact piece
524 is connected to the L headphone signal input unit 523, and the L headphone signal input
unit 523 is connected to the L headphone signal circuit 203. Thus, the Lch headphone signal
from the L headphone signal circuit 203 is supplied to the L input end 721 connected to the L
contact piece 524.
[0039]
Further, the ground terminal 73 of the headphone equivalent circuit 7 is connected to the ground
terminal 55 of the headphone terminal 5 and is grounded. As described above, audio can be
output with headphones (here, an equivalent circuit of headphones) in the SE type output format.
[0040]
In a circuit including such an amplification circuit that performs amplification by superimposing
a DC bias, for example, when the operation is switched immediately after turning on the power, a
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signal for the DC bias voltage is output from the amplification unit 2. As a result, voltage signals
that rise sharply are output to the output circuits 101, 102, 201, 202, that is, the output signals
exhibit transient fluctuations. When BTL output is performed, for example, since the signal from
the R output circuit 101 is input to the positive electrode and the signal from the inverting R
output circuit 102 is input to the negative electrode to the Rch speaker 41, both input signals are
Even if it rises rapidly, a potential difference between the positive electrode and the negative
electrode does not occur or hardly occurs. That is, the state is the same as when the audio signal
is not input, and noise due to transient fluctuation of the output signal is not generated or hardly
generated. Similarly to the Rch system, the Lch system does not generate noise from the Lch
speaker 42 or hardly generates noise.
[0041]
On the other hand, when a headphone plug is connected to the headphone terminal 5, the R
output circuit 101 is connected to the R input end portion 711, so that it is connected to the
resistor 71 replaced equivalent to the Rch headphone. When a signal that rises sharply from the
amplification unit 2 is output in a state where headphones are connected, the bias removal and
gain adjustment circuit 32 has a rapid change, and thus the bias component can not be removed
reliably, and a transient change is generated. Is input to the R input terminal 711. Since the
transient fluctuation of this signal occurs instantaneously immediately after the rise of the signal,
the Rch headphone outputs pop sound. The Lch headphones also output pop sound, like the Rch
headphones.
[0042]
In order to suppress the generation of pop noise when headphones are connected, the audio
output circuit A includes a ground control circuit 6. The ground control circuit 6 will be
described below. The ground control circuit 6 suppresses the operation of the headphone by
controlling the ground of the ground terminal 55 of the headphone terminal 5 to suppress the
output of pop sound from the headphone due to the transient fluctuation of the signal input to
the headphone. There is.
[0043]
The ground control circuit 6 includes a diode 61, a smoothing circuit 62, a reset circuit 63, and
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an n-type MOSFET 64. The ground control circuit 6 is connected to the inverted L output circuit
202 and detects an inverted Lch output signal.
[0044]
The drain of the n-type MOSFET 64 is connected to the ground terminal 55 of the headphone
terminal 5, and the source is grounded. A signal (voltage) transmitted by the inverted L output
circuit 202 is input to the gate. A diode 61, a smoothing circuit 62, and a reset circuit 63 are
connected in series to a circuit from the connection portion to the inverted L output circuit 202
to the gate of the n-type MOSFET 64. In the n-type MOSFET 64, when no signal is input to the
gate, the drain and the source are nonconductive (OFF). In the n-type MOSFET 64, when the
voltage of the signal input to the gate becomes equal to or higher than a predetermined voltage
value, the drain and the source become conductive (that is, ON). The ground control circuit 6
controls the ON timing of the n-type MOSFET 64 and controls the timing at which the ground
terminal 55 becomes the ground potential.
[0045]
The anode of the diode 61 is connected to the inverting L output circuit 202. The diode 61
suppresses the drop of the gate voltage of the n-type MOSFET 64 by the voltage when the
amplitude of the inverted Lch output signal detected from the inverted L output circuit 202 is
low. That is, the diode 61 is disposed to hold the gate voltage and to keep the n-type MOSFET 64
in the ON state at all times. As a result, it is possible to suppress the repetition of ON / OFF of the
n-type MOSFET 64 due to the change in the amplitude of the inverted Lch output signal, and to
suppress the occurrence of a defect such as the interruption of the sound from the headphones.
[0046]
Smoothing circuit 62 includes a resistor 621 disposed between the cathode of diode 61 and the
gate of n-type MOSFET 64, one terminal connected to a portion between resistor 621 and the
gate of n-type MOSFET 64, and the other terminal connected to ground The capacitor 622 is
provided. The reset circuit 63 is formed of a resistor, one end of which is connected between the
resistor 621 and the gate of the n-type MOSFET 64, and the other end is grounded.
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[0047]
The operation of the ground control circuit 6 configured as described above will be described.
For example, when the power of the audio output circuit A is turned on, a signal that rapidly rises
(voltage) is output from the amplifier circuit 222 to the inverting L output circuit 202 because a
DC bias is superimposed. At this time, the signal that rises rapidly is input to the ground control
circuit 6. On the other hand, in the ground control circuit 6, the smoothing circuit 62 smoothes
the signal input from the inverting L output circuit 202. In the smoothing circuit 62, when a
signal is input, charge is accumulated in the capacitor 622. While charge is stored in the
capacitor 622, the voltage at the gate of the n-type MOSFET 64 gradually increases. Therefore,
the n-type MOSFET 64 does not turn on immediately, but turns on late (delayed).
[0048]
Since the n-type MOSFET 64 is turned off immediately after the signal that rises sharply from the
amplification unit 2 is output to the R output circuit 101 and the L output circuit 201, the
ground terminal 55 is also not at the ground potential. As a result, since the headphones
(headphone equivalent circuit 7) are open circuits, no sound is output from the headphones even
if a signal is input. And, as described above, the pop noise is due to a transient fluctuation that
occurs for a short time immediately after the fluctuation of the signal, so when the n-type
MOSFET 64 is turned on, it is not input to the headphones. Thus, the audio output circuit A
according to the present invention suppresses the output of pop sound from the headphones.
[0049]
Further, in the ground control circuit 6, since the smoothing circuit 62 is a general smoothing
circuit, while the signal is being output from the amplification unit 2 (the amplification circuit
222), the signal is periodically varied. Also, a voltage smoothed by the diode 61 and the
smoothing circuit 62 is output to the gate of the n-type MOSFET 64. That is, in the audio output
circuit A, the ground terminal 55 of the headphone terminal 5 is at the ground potential while
the signal is being output from the amplifier unit 2 (amplifying circuit 222) except immediately
after the power is turned on. It is possible to output.
[0050]
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To summarize the above, the audio output circuit A detects the rise (transient fluctuation) of the
output signal (DC bias) output from the amplification unit 2 and becomes the ground potential of
the ground terminal 55 of the headphone terminal 5 Delay (control) and suppress the pop sound
output from the headphones. The audio output circuit A according to the present invention can
suppress the output of pop sound from headphones and can output audio from the speakers 41
and 42 as a signal in the BTL type output format. As a result, it is possible to output to the
speaker in a BTL type output format with a simple circuit configuration, and to suppress noise
due to transient fluctuation of the audio signal at the time of headphone connection.
[0051]
In addition, when the above operation is performed using the ground control circuit 6, it is
preferable that the charge is not accumulated in the capacitor 622 of the smoothing circuit 62
when there is a transient fluctuation of the output signal. Therefore, in the ground control circuit
6, the charge accumulated in the capacitor 622 is grounded via the reset circuit 63, and the
charge is removed (reset).
[0052]
As a result, the ground control circuit 6 opens the capacitor 622 in preparation for the input of
the next voltage, so that the ground terminal 55 is delayed to the ground potential also at the
time of the transient fluctuation (rise) of the next output signal. It is possible to suppress pop
noise reliably.
[0053]
In addition, the resistance value of the resistor 621 of the smoothing circuit 62 and the
capacitance of the capacitor 622 are the magnitude of the signal input to the gate of the n-type
MOSFET 64, and the delay from the transient fluctuation until the ground terminal 55 becomes
the ground potential. Determined by time.
[0054]
That is, in the audio output circuit according to the present invention, audio can be output from
the speaker in the BTL type output format.
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Then, by controlling the grounding of the headphones by the grounding control circuit 6 that
detects the output signal, it is possible to effectively suppress the output of pop sound from the
headphones due to the transient fluctuation of the audio signal when the headphones are
connected.
[0055]
Since the ground control circuit 6 has a simple configuration of a diode, a resistor, a capacitor,
and a switching element, the conventional voice of a configuration having a separate circuit for
speaker and headphone and a configuration having a circuit for separately outputting a control
signal The configuration can be simplified compared to the output circuit.
[0056]
Second Embodiment Another example of the audio output circuit according to the present
invention will be described with reference to the drawings.
FIG. 2 is a circuit diagram of another example of the audio output circuit according to the present
invention.
Audio output circuit B shown in FIG. 2 has the same configuration as audio output circuit A
shown in FIG. 1 except that the ground control circuit is different. Detailed description is omitted.
[0057]
The ground control circuit 6 b of the audio output circuit B includes an npn bipolar transistor 65
instead of the n-type MOSFET 64. The collector of the npn bipolar transistor 65 is connected to
the ground terminal 55 of the headphone terminal 5, the emitter is grounded, and the base
receives a signal from the inverting L output circuit 202.
[0058]
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Similar to the ground control circuit 6 of the audio output circuit A shown in FIG. 1, the ground
control circuit 6b of this configuration delays the ground terminal 55 from becoming the ground
potential when there is a transient change in the output signal. Can. As a result, the audio output
circuit B can suppress pop noise even if the output signal output from the amplification unit 2
has a transient change in a state where headphones are connected.
[0059]
The npn bipolar transistor is an element whose ON / OFF is controlled by the current input to the
gate. Therefore, the resistance value of the resistance (the resistance 621 of the smoothing
circuit 62 and the resistance of the reset circuit 63) included in the middle of the circuit
connected to the gate is adjusted to be a current that can turn on the npn bipolar transistor. .
[0060]
The audio output circuit B of this embodiment has the same features as the audio output circuit A
of the first embodiment.
[0061]
Third Embodiment Still another example of the audio output circuit according to the present
invention will be described with reference to the drawings.
FIG. 3 is a diagram showing still another example of the audio output circuit according to the
present invention. In the audio output circuit C shown in FIG. 3, the ground control circuit 6c is
connected to the R output circuit 101, and detects an amplified Rch output signal. The other
configuration is the same as that of the audio output circuit A, and substantially the same parts
are denoted by the same reference numerals.
[0062]
The ground control circuit 6c delays the ground terminal 55 from becoming the ground potential
based on the amplified Rch output signal. The ground control circuit 6c is configured to use the
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n-type MOSFET 64. However, like the ground control circuit 6b, the npn-type bipolar transistor
65 may be used. The audio output circuit C of the present embodiment has the same features as
the audio output circuit A of the first embodiment.
[0063]
Fourth Embodiment Still another example of the audio output circuit according to the present
invention will be described with reference to the drawings. FIG. 4 is a diagram showing still
another example of the audio output circuit according to the present invention. In the audio
output circuit C shown in FIG. 4, the ground control circuit 6d is connected to the inverted R
output circuit 102, and detects the amplified inverted Rch output signal. The other configuration
is the same as that of the audio output circuit A, and substantially the same parts are denoted by
the same reference numerals.
[0064]
The ground control circuit 6d delays the ground terminal 55 from becoming the ground potential
based on the amplified inverted Rch output signal. The ground control circuit 6d is configured to
use the n-type MOSFET 64. However, like the ground control circuit 6b, the npn-type bipolar
transistor 65 may be used. The audio output circuit C of the present embodiment has the same
features as the audio output circuit A of the first embodiment.
[0065]
Fifth Embodiment Still another example of the audio output circuit according to the present
invention will be described with reference to the drawings. FIG. 5 is a diagram showing still
another example of the audio output circuit according to the present invention. In the audio
output circuit E shown in FIG. 5, the ground control circuit 6e is connected to the L output circuit
201, and detects an amplified Lch output signal. The other configuration is the same as that of
the audio output circuit A, and substantially the same parts are denoted by the same reference
numerals.
[0066]
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The ground control circuit 6e delays the ground terminal 55 from becoming the ground potential
based on the amplified Lch output signal. The ground control circuit 6e is configured to use the
n-type MOSFET 64. However, like the ground control circuit 6b, the npn-type bipolar transistor
65 may be used. The audio output circuit C of the present embodiment has the same features as
the audio output circuit A of the first embodiment.
[0067]
As described above, this is an audio output circuit that outputs a signal in the BTL type output
format when outputting to speakers or in the SE type output format when outputting to
headphones. It is possible to suppress the generation of pop noise due to various fluctuations. In
addition, the configuration can be simpler than that of the conventional audio output circuit in
which the BTL audio output circuit and the SE audio output circuit are provided, or a separate
control circuit is provided to determine the timing of interrupting the signal.
[0068]
As described above, in the audio output circuit according to the present invention, the headphone
terminal is selected based on any one of the Rch output signal of the BTL type output format, the
inverted Rch output signal, the Lch output signal, and the inverted Lch output signal. It controls
(delays) that the ground terminal is at the ground potential. The generation of pop noise can be
suppressed in the same or substantially the same manner using any of the signals. The ground
control circuit detects an inverted Rch output signal or an inverted Lch output signal, thereby
suppressing noise being applied to the Rch output signal and the Lch output signal used as audio
signals when headphones are connected. It is possible.
[0069]
In the audio output circuit of each of the above embodiments, the ground control circuit is one
that performs ON / OFF control of the switching element in combination with the smoothing
circuit and the reset circuit, but is not limited to this. The ground control circuit can delay that
the ground terminal of the headphone terminal becomes the ground potential later than the time
when pop noise occurs due to transient fluctuation of the output signal, while the output signal is
being output, A circuit that maintains the ON of the switching element can be widely employed.
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[0070]
Although the Rch output signal and the Lch output signal are output to the headphones in each
embodiment described above, the present invention is not limited to this, and an inverted Rch
output signal and an inverted Lch output signal may be output. . Furthermore, either the Rch
output signal or the inverted Rch output signal may be output to the Rch headphone, or the Lch
output signal or the inverted Lch output signal may be output to the Lch headphone.
[0071]
As mentioned above, although embodiment of this invention was described, this invention is not
limited to this content. Moreover, the embodiment of the present invention can add various
modifications without departing from the spirit of the invention.
[0072]
DESCRIPTION OF SYMBOLS 1 input part 11 R input terminal 12 L input terminal 101 R output
circuit 102 inverted R output circuit 103 R headphone signal circuit 201 L output circuit 202
inverted L output circuit 203 L headphone signal circuit 2 amplification part 211 amplification
circuit 212 amplification circuit 221 amplification circuit Circuit 222 amplification circuit 31
filter circuit 32 bias removal circuit 41 speaker (speaker for Rch) 42 speaker (speaker for Lch) 5
headphone terminal 511 R speaker signal input section 512 R bypass connection section 513 R
headphone signal input section 514 R contact piece 521 L speaker signal input section 522 L
bypass connection section 523 L headphone signal input section 524 L contact piece 53 R
switching switch 531 movable piece 532 contact portion 533 pressing portion 54 L switching
switch 541 movable piece 54 Contact portion 543 Pressing portion 6, 6b, 6c, 6e Ground control
circuit 61 Diode 62 Smoothing circuit 621 Resistance 622 Capacitor 63 Reset circuit 64 n-type
MOSFET (switching element) 65 npn-type bipolar transistor (switching element) 711 R input end
721 L input end 73 ground terminal
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