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JP2002345064

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DESCRIPTION JP2002345064
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
audio output amplifier, for example, a headphone amplifier suitable for use in a portable
electronic device connected to headphones for listening to audio. is there.
[0002]
[0002] Generally, portable players such as CD (compact disc), MD (mini disc), DVD (digital video
disc), and compression methods such as MP3 (MPEG audio-layer 3) and ATRAC (Adaptive
Transform Acoustic Coding) In portable audio devices compatible with the above, mobile devices
such as mobile phones and PDAs (Personal Digital Assistants), etc., audio is often output through
headphones connected to these devices. In this case, a DA converter and a headphone amplifier
are used to convert reproduced digital audio data into an analog signal and output it to a
headphone.
[0003]
FIG. 5 is a diagram showing a configuration example of a conventional DA converter and
headphone amplifier. FIG. 5 shows a configuration for converting digital audio data of the 1-bit
system described below into an analog audio signal and outputting it. The 1-bit system is a
system in which the recovery from digital data to the original analog signal is improved by
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controlling the distribution of quantization noise using ΔΣ modulation, compared to the PCM
system currently widely used. In particular, it has recently attracted attention.
[0004]
In FIG. 5, a digital interface (I / F) 1, a digital filter 2 and a ΔΣ modulation processing unit 3 are
provided to constitute a DA converter. In addition, a headphone amplifier is configured by
including the drivers 4 and 5, coils L1 and L3, capacitors C1 to C3, C4 and C5, and resistors R1
and R3.
[0005]
The DA converter generates a modulation signal based on digital audio data reproduced from a
digital recording medium such as a CD. The headphone amplifier connected to the rear stage of
the DA converter is driven based on this modulation signal, and an amplified analog audio signal
is obtained by supplying a current of an amount according to the pulse width of the modulation
signal.
[0006]
The digital I / F 1 inputs a digital 1-bit signal reproduced from a digital recording medium (not
shown) or the like. The digital filter 2 performs low-pass filter processing on the 1-bit signal
input by the digital I / F 1, and outputs the result to the ΔΣ modulation processing unit 3. The
ΔΣ modulation processing unit 3 performs conversion processing based on ΔΣ modulation on
the signal output from the digital filter 2 to generate a modulation signal.
[0007]
The drivers 4 and 5 drive based on the modulation signal output from the ΔΣ modulation
processing unit 3 and output a current of an amount according to the pulse width of the
modulation signal. One driver 4 is in charge of the left (L) channel of stereo sound, and the other
driver 5 is in charge of the right (R) channel of stereo sound. These drivers 4 and 5 are formed of
a switching amplifier (inversion amplifier) using a pMOS transistor and an nMOS transistor.
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[0008]
The power supply unit 6 supplies a power supply voltage to the digital I / F 1, the digital filter 2,
the ΔΣ modulation processing unit 3 and the drivers 4 and 5 described above. At this time,
digital power supply voltages (VDD, DGND) are supplied to the digital I / F 1 constituting the DA
converter, the digital filter 2 and the ΔΣ modulation processing unit 3, and the analog power
supply voltages are supplied to the drivers 4 and 5 constituting the headphone amplifier. Supply
(VCC, AGND). In the case of a portable electronic device, the power supplied to the circuits from
the power supply unit 6 is obtained from a battery or the like (not shown).
[0009]
The coil L1 and the capacitor C1 constitute a low pass filter for L channel, and the coil L3 and the
capacitor C3 constitute a low pass filter for R channel. The resistor R1 constitutes a bias circuit
for L channel, and the resistor R3 constitutes a bias circuit for R channel. The left and right
analog audio signals generated by passing through these low pass filters are output from the
output terminal 11 through the capacitors C4 and C5, respectively.
[0010]
Headphones widely used at present include three signal lines (L channel, R channel, and ground),
and the output terminal 11 also has three terminals 11 a to 11 c correspondingly. The first
terminal 11a is for L channel, the second terminal 11b is for ground (GND), and the third
terminal 11c is for R channel. The ground line connected to the second terminal 11 b is
commonly used for the left headphone 12 and the right headphone 13.
[0011]
When outputting audio signals from the left and right headphones 12 and 13, it is necessary to
swing the output voltage to the headphones 12 and 13 in a positive and negative manner
centering on the ground zero voltage. However, in the case of a single power source of direct
current having no plus or minus, such as a battery used for a portable device, the output voltage
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is shaken in a form biased to one side of only the plus side, for example. The output voice in this
case does not have a low tone, and becomes a kinky sound.
[0012]
In order to prevent this, it is essential to provide capacitors C4 and C5 for DC cutting. However,
since the impedance of headphones used in portable electronic devices is generally as low as a
few tens of ohms to several tens of ohms, the capacitance of the capacitors for DC cut-off C4, C5
is required to output low frequency bass sounds. Must be as large as several hundred μF. In this
case, the outer shape of the capacitor becomes very large.
[0013]
In order to avoid this, it is common practice to amplify the low frequency bass to reduce the
capacity of the DC cut capacitor. However, in this case, the frequency characteristic is changed,
so that the deterioration of the sound quality can not be avoided. Also, with this method,
although there is a possibility of downsizing the DC cut capacitor, it can not be completely
eliminated. This has been a factor that hinders the reduction in size, weight and cost of portable
devices.
[0014]
The present invention has been made to solve such a problem, and enables the output voltage to
the headphone to be oscillated in the positive and negative directions without using a capacitor
for DC cut, thereby making it possible to use the electronic device. The purpose is to reduce the
size, weight and cost.
[0015]
The audio output amplifier according to the present invention is a standard used to output a
difference between a first signal line to which an audio signal is supplied and the audio signal to
an audio output unit. A second signal line to which a signal is supplied, and generating an
intermediate voltage of a power supply voltage used to amplify the audio signal of the first signal
line, and the reference signal of the second signal line And an intermediate voltage generation
circuit for applying the voltage.
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[0016]
In another aspect of the present invention, a driver for amplifying an audio signal based on a
power supply voltage and supplying the amplified signal to a first signal line, and an intermediate
voltage of the power supply voltage, and supplying a reference signal for the audio signal And an
intermediate voltage generation circuit for applying the intermediate voltage to the second signal
line.
[0017]
In another aspect of the present invention, the first signal line includes two signal lines for
supplying audio signals of at least two channels, and the reference signal supplied to the second
signal line is The present invention is characterized in that it is commonly used for the two
channels of audio signals supplied to the two signal lines.
[0018]
Another aspect of the present invention is characterized in that the intermediate voltage
generation circuit is configured using an operational amplifier.
For example, the intermediate voltage generation circuit includes a voltage dividing circuit that
divides the power supply voltage into approximately one half, and an operational amplifier that
operates using the divided voltage as an input.
[0019]
According to the present invention configured as described above, the difference between the
audio signal output to the first signal line and the reference signal output to the second signal
line is taken, and an audio output unit such as headphones, for example, is obtained. It is emitted
from
At this time, since an intermediate voltage of the power supply voltage is always applied to the
second signal line, the output voltage between (−power supply voltage / 2) and (+ power supply
voltage / 2) when viewed from the audio output unit Works as if it is swinging to the positive or
negative.
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Therefore, it is possible to properly swing the output voltage to the audio output unit to positive
or negative without providing a capacitor for DC cut on the first signal line to which the audio
signal is supplied.
[0020]
Further, according to another feature of the present invention in which the intermediate voltage
of the reference signal is generated by the operational amplifier, the impedance of the second
signal line viewed from the audio output unit can be made as small as negligible.
Therefore, the voltage fluctuation of the second signal line can be suppressed, and the potential
can be constantly maintained at the intermediate voltage.
[0021]
DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) First, a first embodiment
of the present invention will be described based on the drawings. FIG. 1 is a view showing a
configuration example of a headphone amplifier according to a first embodiment in which the
audio output amplifier of the present invention is implemented. Here, in addition to the
headphone amplifier, the configuration of the DA converter is also shown. In FIG. 1, components
having the same functions as the components shown in FIG. 5 are assigned the same reference
numerals.
[0022]
In FIG. 1A, reference numeral 10 denotes an IC chip, which includes a digital I / F 1, a digital
filter 2, a ΔΣ modulation processing unit 3, drivers 4 and 5 operating as a class D amplifier, a
power supply unit 6, and a reference voltage generation circuit 7. And an operational amplifier 8
operating as a class B amplifier.
[0023]
The digital I / F 1 inputs a digital 1-bit signal reproduced from a digital recording medium (not
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shown) or the like into the IC chip 10.
At this time, the digital I / F 1 alternately inputs digital data for the L channel and digital data for
the R channel in the form of serial data DIN. Further, a clock LRCK for identifying L channel
digital data and R channel digital data, a clock BCK for synchronizing L channel digital data and R
channel digital data, and the like are also input.
[0024]
The digital filter 2 performs low-pass filter processing on the 1-bit signal input by the digital I / F
1, and outputs the result to the ΔΣ modulation processing unit 3. The ΔΣ modulation
processing unit 3 performs conversion processing based on ΔΣ modulation on the signal output
from the digital filter 2 to generate a modulation signal.
[0025]
The drivers 4 and 5 amplify the L channel and R channel modulation signals output from the
ΔΣ modulation processing unit 3 using the analog power supply voltage VCC, and output them
to the first signal lines OUTL and OUTR. . One driver 4 is in charge of L channel audio, and the
other driver 5 is in charge of R channel audio. These drivers 4 and 5 are formed of switching
amplifiers using pMOS transistors and nMOS transistors.
[0026]
The power supply unit 6 supplies a power supply voltage to the digital I / F 1, the digital filter 2,
the ΔΣ modulation processing unit 3 and the drivers 4 and 5 described above, and a reference
voltage generation circuit 7 and an operational amplifier 8 described below. At this time, digital
power supply voltages (VDD, DGND) are supplied to the digital I / F 1 constituting the DA
converter, the digital filter 2 and the ΔΣ modulation processing unit 3, and the drivers 4 and 5
constituting the headphone amplifier The analog power supply voltages (VCC, AGND) are
supplied to the operational amplifier 7 and the operational amplifier 8.
[0027]
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In the case of a portable electronic device, the power supplied from the power supply unit 6 to
each circuit is obtained from the battery 14 or 15. The battery 14 is one in which the digital
power supply voltage VDD and the analog power supply voltage VCC are both set to 3.3V. The
battery 15 is set to 3.3 V for the digital power supply voltage VDD and 5 V for the analog power
supply voltage VCC. These two batteries 14 and 15 can be arbitrarily replaced and used. When
the battery 15 having a large analog power supply voltage VCC is used, the amplitude of the
audio signal to be amplified becomes large, so that it is possible to obtain higher output.
[0028]
As shown in FIG. 1 (b), the reference voltage generation circuit 7 has two resistors R and R of the
same resistance value connected in series between the analog power supply voltage VCC and the
analog ground AGND, and one of the resistors And a capacitor C connected in parallel to R. With
such a configuration, the reference voltage generation circuit 7 generates an intermediate
voltage (VCC / 2) which is 1/2 the potential of the analog power supply voltage VCC, and outputs
it to the positive terminal of the operational amplifier 8.
[0029]
The operational amplifier 8 performs an amplification operation based on the intermediate
voltage generated by the reference voltage generation circuit 7, and the intermediate voltage as a
reference signal for audio signals of L and R channels supplied to the first signal lines OUTL and
OUTR. Signal is supplied to the second signal line COM. Since the output of the operational
amplifier 8 is fed back to its own negative terminal, a constant intermediate voltage (VCC / 2) is
always applied to the second signal line COM. The reference voltage generation circuit 7 and the
operational amplifier 8 constitute an intermediate voltage generation circuit of the present
invention.
[0030]
The coil L1 and the capacitor C1 constitute a low pass filter for an L channel audio signal, and
the coil L3 and the capacitor C3 constitute a low pass filter for an R channel audio signal. The
resistors R1, R2 and R3 respectively constitute a bias circuit for L channel audio signal, a bias
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circuit for reference signal, and a bias circuit for R channel audio signal.
[0031]
The pulse signals output from the drivers 4 and 5 pass through the respective low pass filters to
become analog audio signals of L and R channels, and are output to the left headphone 12 and
the right headphone 13 through the output terminals 11a and 11c. Further, the signal of the
intermediate voltage for the reference signal is output to both the left headphone 12 and the
right headphone 13 through the output terminal 11 b.
[0032]
The left headphone 12 outputs a difference between an audio signal of L channel supplied from
the output terminal 11a and a reference signal of an intermediate voltage supplied from the
output terminal 11b. Further, the right headphone 13 obtains the difference between the audio
signal of the R channel supplied from the output terminal 11c and the reference signal of the
intermediate voltage supplied from the output terminal 11b, and outputs it.
[0033]
When the headphone amplifier is configured as described above, since the intermediate voltage
VCC / 2 is always applied to the second signal line COM, for example, when the maximum
voltage VCC is applied to the L channel, from the left headphone 12 As seen, the output voltage
is swung to the positive side by + VDD / 2 (= VCC−VCC / 2). Further, for example, when the
minimum zero volt is applied to the L channel, the output voltage is swung to the negative side
by −VDD / 2 (= 0−VCC / 2) when viewed from the left headphone 12.
[0034]
That is, as shown in FIG. 2, from the left headphone 12, it operates so that the output voltage is
oscillated in the positive and negative directions between -VCC / 2 and + VCC / 2. The same
applies to the right headphone 13. Therefore, according to the present embodiment, the output
voltage to the left and right headphones 12 and 13 is provided without providing a capacitor for
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DC cut on the first signal lines OUTL and OUTR to which the audio signals of L and R channels
are supplied. Can be shaken positive or negative. As a result, it is possible to omit a very large
capacitor, which has conventionally been essential, and to reduce the size, weight and cost of
portable devices.
[0035]
Further, in the present embodiment, the intermediate voltage (VCC / 2) of the reference signal
used when taking the difference from the audio signals of the L and R channels and outputting it
to the left and right headphones 12 and 13 is the same as the drivers 4 and 5 The switching
amplifier is generated by the operational amplifier 8 instead of the switching amplifier. As
described above, when the operational amplifier 8 is used, the impedance of the second signal
line COM can be reduced to a negligible level as viewed from the left and right headphones 12
and 13.
[0036]
Although it is conceivable to smooth the 50% duty pulse output from the switching amplifier with
an LC filter to generate an intermediate voltage (VCC / 2), in this case, the IC chip 10 side is
connected to the second signal line COM. Since the impedance at the time of viewing becomes
large, the output voltage to the second signal line COM largely fluctuates due to the flowing
current.
[0037]
Therefore, the separation between the L channel and the R channel is deteriorated, and there
arises a problem that one of the audio signals of the L and R channels is mixed in the other.
In addition, since the switching amplifier outputs a pulse, noise is generated to some extent even
if smoothed, which causes a problem that the S / N becomes worse.
[0038]
On the other hand, by performing the amplification operation linearly using the operational
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amplifier 8 as in the present embodiment, the voltage fluctuation of the second signal line COM
is suppressed, and the potential is always maintained at VCC / 2. it can. As a result, separation
and S / N of the L channel and the R channel can be kept good, and the output voltage to the left
and right headphones 12 and 13 can be properly shaken positive and negative.
[0039]
As described above, when the operational amplifier 8 is used, much higher performance can be
realized as compared with the case where the intermediate voltage is generated using a
smoothing circuit such as an LC filter. Therefore, the configuration of the operational amplifier 8
may be simple, and the operational amplifier 8 may be incorporated without increasing the chip
area.
[0040]
In the case of the present embodiment, the output voltage to the left and right headphones 12
and 13 is oscillated in the positive and negative directions in the range of -VCC / 2 to + VCC / 2,
compared with the conventional case in which the output voltage is Power is decreasing.
However, with regard to the sound heard from the left and right headphones 12 and 13 in
mobile devices such as CD / MD / DVD players, portable audio devices compatible with MP3 and
ATRAC, mobile phones and PDAs, it is sufficient if there is output power as in this embodiment. is
there. Further, if desired, a larger output can be obtained by using the battery 15.
[0041]
Second Embodiment Next, a second embodiment of the present invention will be described. The
second embodiment shows an example in which an amplifier used for a headphone amplifier is
configured only by a class B amplifier. The second embodiment is applicable to both the PCM
method and the 1-bit method.
[0042]
FIG. 3 is a view showing an example of the configuration of a headphone amplifier according to
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the second embodiment. In FIG. 3, 12 V is used as the analog power supply voltage VCC. R11 and
R12 are resistors for voltage division and have equal resistance values. In addition, a capacitor
C21 is connected in parallel to the resistor R12. As a result, an intermediate voltage VCC / 2
obtained by dividing the analog power supply voltage VCC by 1/2 appears at an intermediate
node between the resistors R11 and R12.
[0043]
The operational amplifier 21 operates with the intermediate voltage VCC / 2 generated by this
voltage division as an input to the plus terminal. The output of this operational amplifier 21 is
fed back to its own negative terminal. Thereby, the operational amplifier 21 stably supplies a
voltage of VCC / 2 = 6V.
[0044]
On the other hand, the L channel audio signal and the R channel audio signal input from the
signal lines INL and INR are input to the positive terminals of the operational amplifiers 22 and
23 through the DC cut capacitors C11 and C12. Bias resistors R15 and R16 are provided at the
input stage of each of the operational amplifiers 22 and 23, and the output signal of the
operational amplifier 21 is supplied thereto.
[0045]
As these bias resistors R15 and R16, one having a large resistance value (for example, 100 KΩ)
is used. By thus providing a high resistance bias circuit at the input stage of each of the
operational amplifiers 22 and 23, the plus terminals of the operational amplifiers 22 and 23
have high impedance. In this way, low-frequency audio signals can be passed without increasing
the capacitances of the capacitors C11 and C12 for cutting off direct current. That is, the
capacitances of the capacitors C11 and C12 may be at most 1 μF (eg, 0.1 μF).
[0046]
The audio signals of the L and R channels amplified by the operational amplifiers 22 and 23 are
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inputted to the minus terminals of the operational amplifiers 24 and 26 at the next stage through
the resistors R25 and R26. These operational amplifiers 24 and 26 operate as inverting
amplifiers, and output their amplified signals to the first signal lines OUTL and OUTR. At this
time, the audio signal output from each of the operational amplifiers 24 and 26 is oscillated
between 0 and 12 V in accordance with the power supply voltage VCC supplied to the control
end of each of the operational amplifiers 24 and 26.
[0047]
The operational amplifier 25 operates with the intermediate voltage VCC / 2 supplied from the
operational amplifier 21 as an input to the plus terminal. The output of this operational amplifier
25 is also fed back to its own negative terminal. Thereby, the operational amplifier 25 stably
supplies an intermediate voltage of VCC / 2 = 6V to the second signal line COM.
[0048]
When configured in this way, as in the first embodiment, from the headphone, it operates so that
the output voltage is oscillated between positive and negative between −VCC / 2 and + VCC / 2.
Therefore, the output voltage to the headphone can be oscillated in the positive and negative
directions without providing a DC cut capacitor on the first signal lines OUTL and OUTR to which
the audio signals of the L and R channels are supplied. As a result, it is possible to omit a very
large capacitor, which has conventionally been essential, and to reduce the size, weight and cost
of portable devices.
[0049]
Further, in the present embodiment, only the operational amplifier is used, so the impedance of
the second signal line COM can be made as small as can be ignored from the headphone.
Thereby, voltage fluctuation of the second signal line COM can be suppressed, separation and S /
N of L channel and R channel can be maintained well, and output voltage to the headphone can
be properly shaken positive and negative. .
[0050]
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Third Embodiment Next, a third embodiment of the present invention will be described. This
third embodiment is also applicable to both the PCM method and the 1-bit method. FIG. 4 is a
view showing a configuration example of a headphone amplifier according to the third
embodiment. In FIG. 4, components having the same functions as the components shown in FIG.
3 will be assigned the same reference numerals and overlapping descriptions will be omitted.
[0051]
In the third embodiment shown in FIG. 4, two operational amplifiers 31, 32 are used instead of
the operational amplifier 25 shown in FIG. The operational amplifier 31 operates with the output
signal of the operational amplifier 24 for L channel as the input to the negative terminal. Further,
the operational amplifier 32 operates with the output signal of the operational amplifier 26 for R
channel as the input to the negative terminal. That is, these operational amplifiers 31 and 32 also
operate as inverting amplifiers.
[0052]
The operational amplifier 24 outputs an L channel audio signal oscillated between 0 and 12 V to
the signal line OUTL-, and the operational amplifier 31 outputs an L channel audio signal whose
phase is opposite to that of the output signal to the signal line OUTL- Output to the signal line
OUTL +. In this embodiment, the difference between the audio signals output to the signal lines
OUTL− and OUTL + is taken and output to the left headphone.
[0053]
Further, the operational amplifier 26 outputs an R channel audio signal oscillated between 0 and
12 V to the signal line OUTR-, and the operational amplifier 32 generates an R channel audio
whose phase is opposite to that of the output signal to the signal line OUTR-. A signal is output to
the signal line OUTR +. In this embodiment, the difference between the audio signals output to
the signal lines OUTR− and OUTR + is taken and output to the right headphone.
[0054]
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In this case, for example, when the output voltage of one of the L-channel signal lines OUTL− is
12 V at the maximum, the output voltage of the other signal line OUTL + is 0 V and the
differential voltage applied to the left headphone is 12 V. When the output voltage of one signal
line OUTL− is 0 V which is the minimum, the output voltage of the other signal line OUTL + is
12 V, and the differential voltage applied to the left headphone is −12 V. Therefore, in the case
of the left headphone, it operates so that the output voltage is oscillated in the positive and
negative directions between -12 and +12 V (-VCC and + VCC). The same is true for the right
headphone.
[0055]
As described above, according to the third embodiment, although four output terminals to
headphones are required and lack in versatility, an output power about twice as large as that of
the second embodiment can be obtained. It has the merit of being able to
[0056]
In the first to third embodiments, the reference voltage generation circuit 7 or the voltage
dividing resistors R11 and R12 are used as a configuration for generating the intermediate
voltage of the power supply voltage VCC, but the present invention is limited to this. It is not a
thing.
That is, any configuration that can generate an intermediate voltage is applicable.
[0057]
Further, in the first and second embodiments, the voltage supplied to the second signal line COM
is a voltage exactly 1/2 of the analog power supply voltage VCC, but may not be exactly 1/2.
That is, as long as a desired maximum amplitude voltage can be obtained, it may be slightly offset
to the GND side or the VCC side.
[0058]
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15
In the first to third embodiments, the stereo audio compatible headphones having two channels
of L and R have been described, but the present invention may be similarly applied to monaural
headphones or earphones. It is possible. Moreover, although the thing provided with the
headphones 12 and 13 on either side was demonstrated to the example in the said embodiment,
it is also possible to apply to the earphone which has only one audio | voice output part.
[0059]
The first to third embodiments are preferable when applied to portable electronic devices that
are particularly required to be reduced in size and weight, but it goes without saying that the first
to third embodiments may be applied to stationary electronic devices.
[0060]
In addition, each embodiment described above is only an example of embodiment for carrying
out the present invention, and the technical scope of the present invention should not be
interpreted limitedly by these.
That is, the present invention can be implemented in various forms without departing from the
spirit or main features of the present invention.
[0061]
As described above in detail, according to the present invention, by applying an intermediate
voltage of the power supply voltage to the second signal line, it can be seen from the audio
output unit as (-power supply voltage / 2) to (-) It can be operated such that the output voltage is
oscillated in the positive and negative directions between + power supply voltage / 2). As a result,
the output voltage to the audio output unit can be oscillated in the positive and negative
directions without providing a capacitor for DC cutting on the first signal line to which the audio
signal is supplied. Therefore, it is possible to omit a very large capacitor, which is conventionally
required to output low-frequency sound, and to reduce the size, weight and cost of the electronic
device.
[0062]
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Further, according to another feature of the present invention, since the intermediate voltage of
the reference signal is generated by the operational amplifier, the impedance of the second signal
line can be reduced to a negligible level when viewed from the audio output unit. This makes it
possible to suppress the voltage fluctuation of the second signal line and to maintain the
potential at the intermediate voltage at all times. Therefore, when the present invention is applied
to stereo audio having two channels of the left channel and the right channel, separation and S /
N of the left and right channels can be kept good, and output voltages of the left and right
channels can be properly made positive and negative. You will be able to shake.
[0063]
Brief description of the drawings
[0064]
1 is a diagram showing a configuration example of a headphone amplifier according to the first
embodiment in which the audio output amplifier of the present invention is implemented.
[0065]
2 is a diagram showing the movement of the output voltage seen from the headphones in the
present embodiment.
[0066]
3 is a diagram showing a configuration example of a headphone amplifier according to a second
embodiment in which the audio output amplifier of the present invention is implemented.
[0067]
4 is a diagram showing a configuration example of a headphone amplifier according to a third
embodiment in which the audio output amplifier of the present invention is implemented.
[0068]
5 is a diagram showing the configuration of a conventional headphone amplifier.
[0069]
Explanation of sign
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[0070]
REFERENCE SIGNS LIST 1 digital I / F 2 digital filter 3 Δ4,5 modulation processing unit 4, 5
driver 6 power supply unit 7 reference voltage generation circuit 8 operational amplifier 10 IC
chip 11 output terminal 12 left headphone 13 right headphone 14, 15 battery 21 to 26
operational amplifier 31, 32 Op amp R11, R12 Resistor for voltage dividing R15, R16 Bias
resistance
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