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DESCRIPTION JP2018042086

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DESCRIPTION JP2018042086
Abstract: To detect the impedance of headphones without deteriorating the sound quality.
SOLUTION: A DAP1 comprises a resistor R1 connected between a bipolar transistor Q1 and a
power supply V1, a resistor R2 connected between a bipolar transistor Q2 and a power supply
V2, and a test signal as an analog audio signal. The voltage detection circuit 11 detects a voltage
generated by the resistor R1 and the resistor R2 when the transistor Q1 and the bipolar
transistor Q2 are input. [Selected figure] Figure 2
Music playback device
[0001]
The present invention relates to a music reproduction apparatus that outputs an audio signal to
headphones.
[0002]
In headphones used to listen to sound, the impedance differs depending on the headphones.
For this reason, it is necessary to change the gain of the music player according to the impedance
of the headphones. A technique is disclosed for detecting the impedance of headphones in order
to automatically change the gain of the music player. Patent Document 1 discloses that a series
resistance is provided in a signal line and the impedance of a headphone is measured from the
voltage of the resistance. Further, Patent Document 2 discloses that a DC voltage is applied from
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a headphone jack and a voltage at a headphone terminal is read by an A / D converter.
[0003]
Patent No. 3659349 JP, 2013-126142, A
[0004]
As described above, when the voice signal line is provided with a series resistance or an
impedance detection IC is provided, there is a problem that the sound quality is deteriorated.
[0005]
An object of the present invention is to make it possible to detect the impedance of headphones
without deteriorating the sound quality.
[0006]
According to a first aspect of the present invention, there is provided a music reproducing
apparatus comprising: a first amplifier for amplifying a positive analog audio signal; a second
amplifier for amplifying a negative analog audio signal; and a positive power supply voltage to
the first amplifier. A first power supply, a second power supply for supplying a negative power
supply voltage to the second amplifier, a first resistor connected between the first amplifier and
the first power supply, the second amplifier and the second power supply A second resistor
connected between two power supplies, and a first resistor and a second resistor when a test
signal is input to the first amplifier and the second amplifier as an analog audio signal And V. a
voltage detection circuit that detects a voltage generated.
[0007]
In the present invention, the voltage detection circuit detects, as an analog audio signal, a voltage
generated by the first resistor and the second resistor when the test signal is input to the first
amplifier and the second amplifier.
Further, the impedance of the headphone can be calculated from the voltage generated by the
first resistor and the second resistor.
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In the present invention, since the detection means for detecting the impedance of the
headphones is provided only in the power supply line, it is not necessary to provide the detection
means in the audio signal line.
Thereby, the impedance of the headphone can be detected without deteriorating the sound
quality.
[0008]
Further, since the voltage generated by the positive first resistor and the negative second resistor
is detected, the detection sensitivity is high.
[0009]
A music reproducing apparatus according to a second aspect of the present invention is the
music reproducing apparatus according to the first aspect, wherein one end of the voltage
detection circuit is connected between the first power supply and the first resistor, and the other
end is A third resistor connected to one end of the four resistors, and one end connected to the
other end of the third resistor, and the other end connected between the second resistor and the
second amplifier A fourth resistor, a fifth resistor having one end connected between the first
resistor and the first amplifier and a second end connected to one end of the sixth resistor, and
one end having the fifth resistor The sixth resistor is connected to the other end of the second
resistor and the other resistor is connected between the second power supply and the second
resistor.
[0010]
A music reproducing apparatus according to a third aspect of the present invention is the music
reproducing apparatus according to the first or second aspect, wherein a voltage-current
conversion circuit converts the voltage detected by the voltage detection circuit into a current,
and the voltage-current conversion circuit converts And an integrating circuit for integrating the
current.
[0011]
In the present invention, the integration circuit integrates the current converted by the voltagecurrent conversion circuit.
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Therefore, based on the integral value by the integrating circuit, it can be determined whether
the headphone has a predetermined impedance or less.
[0012]
A music reproduction apparatus according to a fourth aspect of the invention is the music
reproduction apparatus according to the third aspect, wherein the voltage-current conversion
circuit comprises: between the third resistance and the fourth resistance, the fifth resistance, and
the sixth resistance. And between and.
[0013]
A music reproducing apparatus according to a fifth invention is the music reproducing apparatus
according to the fourth invention, wherein one end is connected between the third resistor and
the fourth resistor, and the other end is connected to the voltage-current conversion circuit. A
seventh capacitor, a seventh resistor connected at one end between the first capacitor and the
voltage-current conversion circuit, and a seventh resistor connected at the other end to the
ground potential; A second capacitor connected between the resistor and the sixth resistor and
the other end connected to the voltage-current conversion circuit, and one end connected
between the second capacitor and the voltage-current conversion circuit And an eighth resistor,
the other end of which is connected to the ground potential.
[0014]
In the present invention, the low pass is cut because the bias current flowing in steady state is
canceled by the filter circuit of the first capacitor and the seventh resistor and the filter circuit of
the second capacitor and the eighth resistor. .
[0015]
A music reproduction apparatus according to a sixth invention is the music reproduction
apparatus according to any one of the third to fifth inventions, wherein an integral value of the
integration circuit is compared with a predetermined threshold value, and the integral value is
the predetermined value. And a comparator that supplies a detection signal when the threshold
value is or above.
[0016]
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In the present invention, the comparator supplies a detection signal when the integral value is
greater than or equal to a predetermined threshold.
Therefore, when the comparator supplies the detection signal, it can be determined that the
headphones have a predetermined impedance or less.
[0017]
A music reproduction apparatus according to a seventh invention is characterized in that the
music reproduction apparatus according to the sixth invention further comprises a holding
circuit for holding the detection signal supplied by the comparator.
[0018]
A music reproduction apparatus according to an eighth invention is the music reproduction
apparatus according to any one of the first to seventh inventions, further comprising a terminal
detection circuit for detecting insertion of a terminal into the own apparatus, and a control unit,
The control unit is characterized in that, when the terminal detection circuit detects insertion of
the terminal, the test signal is input to the first amplifier and the second amplifier.
[0019]
In the present invention, the control unit inputs a test signal to the first amplifier and the second
amplifier when the terminal detection circuit detects insertion of a terminal.
Thereby, when the terminal is connected to the music player, the impedance of the headphone
can be detected.
[0020]
The music reproduction apparatus according to a ninth aspect of the present invention is the
music reproduction apparatus according to the sixth or the seventh aspect, wherein the
comparator sets the gain to low gain when the detection signal is supplied, and the comparator
performs the comparison. The control apparatus may further include a control unit that sets the
gain to a high gain when the detection signal is not supplied.
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[0021]
In the present invention, the control unit sets the gain to high gain or low gain according to the
presence or absence of the detection signal.
Thereby, for example, gain setting corresponding to the European sound pressure regulation can
be performed.
[0022]
A music reproducing apparatus according to a tenth invention is the music reproducing
apparatus according to any one of the first to ninth inventions, wherein one end is connected
between the first resistor and the first amplifier, and the other end is grounded. A third capacitor
for decoupling connected to a potential, and one end connected between the second resistor and
the second amplifier, and a fourth capacitor for decoupling connected to the ground potential at
the other end And the first resistor and the second resistor are used for decoupling.
[0023]
In the present invention, a resistor for decoupling is used as a resistor for impedance detection.
For this reason, it is not necessary to add a new part for impedance detection of headphones.
[0024]
According to the present invention, it is possible to detect the impedance of headphones without
deteriorating the sound quality.
[0025]
It is a block diagram showing composition of a digital audio player concerning an embodiment of
the present invention.
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It is a figure which shows an amplifier circuit and its periphery circuit.
It is a graph which shows the simulation result when the headphones whose impedance is 32
ohms are connected and a test signal is inputted.
It is a graph which shows the simulation result when headphones with an impedance of 62 Ω are
connected and a test signal is input.
[0026]
Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a digital audio player according to an embodiment of the present invention (hereinafter
referred to as "DAP").
Is a block diagram showing the configuration of.
The DAP 1 (music playback device) outputs analog audio data (analog audio signal) to the
headphone 101.
The headphone 101 outputs sound to the outside based on analog audio data.
[0027]
As shown in FIG. 1, DAP 1 is a CPU 2, a storage unit 3, a display unit 4, an operation unit 5, a
DSP 6, and a D / A converter (hereinafter referred to as “DAC”).
7) amplifier circuit 8, wireless module 9, USB interface (hereinafter referred to as "USB I / F". )
Provided.
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[0028]
A central processing unit (CPU) 2 (control unit) controls each unit constituting the DAP 1 in
accordance with a control program, an OS program, and an application program. The storage
unit 3 stores various data such as a RAM (Random Access Memory) functioning as a main
memory of the CPU 2, a ROM (Read Only Memory) storing a control program, an OS program, a
program such as an application program, and digital audio data. It consists of flash memory. The
storage unit 3 is not limited to the illustrated configuration, and may include an HDD (Hard Disk
Drive) or the like.
[0029]
The display unit 4 displays various images (including a still image and a moving image), and is
constituted by a liquid crystal panel. The operation unit 5 includes operation keys for performing
various settings, and a touch panel interlocked with the display unit 4. The user can perform
various character inputs, settings, and the like through the operation unit 5.
[0030]
A DSP (Digital Signal Processor) 6 performs signal processing such as equalizer processing on
digital audio data. The DAC 7 D / A converts digital audio data (digital audio signal) into analog
audio data (analog audio signal). The amplification circuit 8 amplifies analog audio data D / A
converted by the DAC 7 and outputs the amplified data to the headphone 101. The wireless
module 9 is for performing wireless communication in accordance with the Bluetooth (registered
trademark) standard and the Wi-Fi standard. The USB I / F 10 is for performing communication
in accordance with the USB standard.
[0031]
FIG. 2 is a diagram showing an amplifier circuit and its peripheral circuit. As shown in FIG. 2,
DAP 1 further includes power supplies V 1 and V 2, voltage detection circuit 11, resistors R 1
and R 2, voltage-current conversion circuit 12, integration circuit 13, comparator 14, holding
circuit 15, resistors R 7 and R 8, R10 to R13 and capacitors C1 to C4 and C6 are provided. In FIG.
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2, the headphone 101 is shown as a load resistor RL.
[0032]
The amplifier circuit 8 includes bipolar transistors Q1 and Q2. The bipolar transistor Q1 (first
amplifier) amplifies positive side analog audio data (analog voice signal). The bipolar transistor
Q1 is an npn bipolar transistor. Analog audio data is input to the base of the bipolar transistor
Q1. The collector of the bipolar transistor Q1 is connected to the positive power supply V1. The
emitter of the bipolar transistor Q1 is connected to the headphone RL via a resistor R10 which is
an emitter resistor.
[0033]
The bipolar transistor Q2 (second amplifier) amplifies negative side analog audio data (analog
voice signal). The bipolar transistor Q2 is a pnp bipolar transistor. Analog audio data is input to
the base of the bipolar transistor Q2. The collector of the bipolar transistor Q2 is connected to
the negative side power supply V2. The emitter of the bipolar transistor Q2 is connected to the
headphone RL via a resistor R11 which is an emitter resistor.
[0034]
The power supply V1 (first power supply) supplies a positive power supply voltage to the bipolar
transistor Q1. The power supply V2 (second power supply) supplies a negative power supply
voltage to the bipolar transistor Q2. The resistor R1 (first resistor) is connected between the
bipolar transistor Q1 and the power supply V1. The resistor R2 (second resistor) is connected
between the bipolar transistor Q2 and the power supply V2. The resistors R1 and R2 are
resistors for decoupling, but also serve as a resistor for detecting the impedance of the
headphone RL.
[0035]
The capacitor C3 (third capacitor) and the capacitor C4 (fourth capacitor) are capacitors for
decoupling. One end of the capacitor C3 is connected between the resistor R1 and the bipolar
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transistor Q1. The other end of the capacitor C3 is connected to the ground potential. One end of
the capacitor C4 is connected between the resistor R2 and the bipolar transistor Q2. The other
end of the capacitor C4 is connected to the ground potential.
[0036]
The voltage detection circuit 11 detects a voltage generated by the resistors R1 and R2 when the
test signal is input to the bipolar transistor Q1 and the bipolar transistor Q2 as an analog voice
signal. The voltage detection circuit 11 includes a resistor R3 (third resistor), a resistor R4
(fourth resistor), a resistor R5 (fifth resistor), and a resistor R6 (sixth resistor). One end of the
resistor R3 is connected between the power supply V1 and the resistor R1. The other end of the
resistor R3 is connected to one end of the resistor R4. One end of the resistor R4 is connected to
the other end of the resistor R3. The other end of the resistor R4 is connected between the
resistor R2 and the bipolar transistor Q2.
[0037]
One end of the resistor R5 is connected between the resistor R1 and the bipolar transistor Q1.
The other end of the resistor R5 is connected to one end of the resistor R6. One end of the
resistor R6 is connected to the other end of the resistor R5. The other end of the resistor R6 is
connected between the power supply V2 and the resistor R2.
[0038]
The voltage-current conversion circuit 12 converts the voltage detected by the voltage detection
circuit 11 into a current. The voltage-current conversion circuit 12 is connected between the
resistors R3 and R4 and between the resistors R5 and R6. The voltage on the positive side is
input to the voltage-current conversion circuit 12 via the resistors R3 and R5. In addition, the
voltage on the negative side is input to the voltage-current conversion circuit 12 through the
resistors R4 and R6.
[0039]
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One end of the capacitor C1 (first capacitor) is connected between the resistor R3 and the
resistor R4. The other end of the capacitor C1 is connected to the voltage-current conversion
circuit 12. One end of the resistor R7 (seventh resistor) is connected between the capacitor C1
and the voltage-current conversion circuit 12. The other end of the resistor R7 is connected to
the ground potential. The capacitor C1 and the resistor R7 constitute a filter circuit.
[0040]
One end of the capacitor C2 (second capacitor) is connected between the resistor R5 and the
resistor R6. The other end of the capacitor C2 is connected to the voltage-current conversion
circuit 12. One end of the resistor R8 (eighth resistor) is connected between the capacitor C2 and
the voltage-current conversion circuit 12. The other end of the resistor R8 is connected to the
ground potential. The capacitor C2 and the resistor R8 constitute a filter circuit. In order to
cancel the bias component flowing at the time of steady state, the low band is cut by the filter
circuit of the capacitor C1 and the resistor R7 and the filter circuit of the capacitor C2 and the
resistor R8.
[0041]
The integration circuit 13 integrates the current converted by the voltage-current conversion
circuit 12. The comparator 14 compares the integration value of the integration circuit 13 with a
predetermined threshold. Then, the comparator 14 supplies a detection signal when the integral
value is equal to or greater than a predetermined threshold. Here, when the integral value is
large, headphones with low impedance are connected, and the voltage generated by the resistors
R1 and R2 is large. When the integral value is small, the headphone RL having a high impedance
is connected, and the voltage generated by the resistors R1 and R2 is small. For example, the
threshold is set to a value between an integral value when the headphone RL having an
impedance of 32Ω is connected and an integral value when the headphone RL having an
impedance of 62Ω is connected. In this case, when the headphone RL having an impedance of
32Ω is connected, the comparator 14 supplies a high level signal as a detection signal. The
holding circuit 15 holds the detection signal supplied by the comparator 14.
[0042]
Although not illustrated, the DAP 1 further includes a terminal detection circuit that detects
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insertion of a headphone terminal into the DAP 1. When the terminal detection circuit detects
insertion of the headphone terminal, the CPU 2 inputs a test signal to the bipolar transistors Q1
and Q2. Then, when the comparator 14 supplies the detection signal, the CPU 2 sets the gain to
low gain. Further, when the comparator 14 does not supply a detection signal, the CPU 2 sets the
gain to a high gain.
[0043]
FIG. 3 is a graph showing simulation results in the case where a headphone RL having an
impedance of 32Ω is connected and a test signal is input. FIG. 3A is a graph showing the
charging current of the capacitor C5. The horizontal axis shows time (ms). The vertical axis
shows current (mA). FIG. 3B is a graph showing the integration voltage of the integration circuit
13 and the output of the comparator 14. The horizontal axis shows time (ms). The vertical axis
represents voltage (V). FIG. 3 (c) is a graph showing a test signal. The horizontal axis shows time
(ms). The vertical axis represents voltage (V).
[0044]
As shown in FIG. 3A, two charging currents are generated by the positive side test signal and the
negative side test signal. Then, as shown in FIG. 3B, the comparator 14 outputs a high level signal
(detection signal) by integration in the integration circuit 13 by the second charging current.
[0045]
FIG. 4 is a graph showing simulation results in the case where a headphone RL having an
impedance of 62Ω is connected and a test signal is input. FIG. 4A is a graph showing the
charging current of the capacitor C5. The horizontal axis shows time (ms). The vertical axis
shows current (mA). FIG. 4B is a graph showing the integration voltage of the integration circuit
13 and the output of the comparator 14. The horizontal axis shows time (ms). The vertical axis
represents voltage (mV). FIG. 4 (c) is a graph showing a test signal. The horizontal axis shows
time (ms). The vertical axis represents voltage (V).
[0046]
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As shown in FIG. 4A, two charging currents are generated by the positive side test signal and the
negative side test signal. However, since the charging current is small, as shown in FIG. 4B, the
integrated voltage in the integration circuit 13 does not reach the predetermined threshold or
more, and the output from the comparator 14 is at the low level.
[0047]
As described above, in the present embodiment, the voltage detection circuit 11 generates the
voltage generated by the resistors R1 and R2 when the test signal is input to the bipolar
transistor Q1 and the bipolar transistor Q2 as an analog voice signal. To detect Further, the
impedance of the headphone 101 can be calculated from the voltage generated by the resistors
R1 and R2. In the present embodiment, since the detection means for detecting the impedance of
the headphone 101 is provided only in the power supply line, it is not necessary to provide the
detection means in the audio signal line. Thereby, the impedance of the headphone 101 can be
detected without degrading the sound quality.
[0048]
Further, since the voltage generated by the positive side resistance R1 and the negative side
resistance R2 is detected, the detection sensitivity is high.
[0049]
Further, in the present embodiment, the integration circuit 13 integrates the current converted
by the voltage-current conversion circuit 12.
Therefore, based on the integration value by the integration circuit 13, it can be determined
whether the headphone 101 is less than or equal to a predetermined impedance.
[0050]
Further, in the present embodiment, the low pass is cut because the bias component flowing in
the steady state is canceled by the filter circuit including the capacitor C1 and the resistor R7 and
the filter circuit including the capacitor C2 and the resistor R8.
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[0051]
Further, in the present embodiment, the comparator 14 supplies a detection signal when the
integral value is equal to or greater than a predetermined threshold value.
Therefore, when the comparator 14 supplies the detection signal, it can be determined that the
headphone 101 has a predetermined impedance or less.
[0052]
Further, in the present embodiment, when the terminal detection circuit detects insertion of a
terminal, the CPU 2 inputs a test signal to the bipolar transistor Q1 and the bipolar transistor Q2.
Thereby, when the terminal is connected to DAP1, the impedance of the headphone 101 can be
detected.
[0053]
Further, in the present embodiment, the CPU 2 sets the gain to high gain or low gain according to
the presence or absence of the detection signal. Thereby, for example, gain setting corresponding
to the European sound pressure regulation can be performed.
[0054]
Further, in the present embodiment, decoupling resistors R1 and R2 are used as the impedance
detection resistors. For this reason, it is not necessary to add a new component for detecting the
impedance of the headphone 101.
[0055]
As mentioned above, although embodiment of this invention was described, the form which can
apply this invention is not restricted to the above-mentioned embodiment, As it illustrates below,
it is suitably in the range which does not deviate from the meaning of this invention. It is possible
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to make changes.
[0056]
In the above-described embodiment, it is determined based on the voltage detected by the
voltage detection circuit 11 whether or not the connected headphone 101 is less than or equal to
a predetermined impedance.
Instead of this, the voltage detected by the voltage detection circuit 11 may be A / D converted to
calculate the impedance of the headphone 101. Also, gain setting may be performed based on
the calculated impedance of the headphone 101.
[0057]
In the above-mentioned embodiment, DAP was illustrated as a music reproduction device. Not
limited to this, it may be a smartphone, a tablet PC, a USB DAC, or the like.
[0058]
The present invention can be suitably adopted for a music reproduction apparatus that outputs
an audio signal to headphones.
[0059]
DESCRIPTION OF SYMBOLS 1 DAP (music reproducing apparatus) 2 CPU (control part) 8
amplifier circuit 11 voltage detection circuit 12 voltage current conversion circuit 13 integration
circuit 14 comparator 15 holding circuit C1 capacitor (1st capacitor) C2 capacitor (2nd
capacitor) C3 capacitor (Third capacitor) C4 capacitor (fourth capacitor) R1 resistance (first
resistance) R2 resistance (second resistance) R3 resistance (third resistance) R4 resistance
(fourth resistance) R5 resistance (fifth resistance) R6 resistance (6th resistance) Sixth resistance)
R7 resistance (seventh resistance) R8 resistance (eighth resistance) Q1 bipolar transistor (first
amplifier) Q2 bipolar transistor (second amplifier) V1 power supply (first power supply) V2
power supply (second power supply) 101 headphones
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