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JP2008258719

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DESCRIPTION JP2008258719
A speaker which is small in size and capable of eliminating distortion due to magnetic saturation
without requiring an H-bridge driver or an output filter having a complicated electrical
configuration while having a class D amplifier and eliminating a toroidal core or coil. Get A super
magnetostrictive member (20) displaced according to a variation of a magnetic field, and a
magnetic field arranged at intervals around the giant magnetostrictive member (20) and directed
along a displacement direction of the giant magnetostrictive member according to a drive
current. And a diaphragm 30 supported at one end of the giant magnetostrictive member 20, and
a class D amplifier for supplying a drive current to the coil, the coil being driven by the up side
drive current of the class D amplifier And a down side coil 24 driven by the down side drive
current of the class D amplifier. [Selected figure] Figure 1
スピーカ
[0001]
The present invention relates to a speaker driven by a class D amplifier, and is particularly
characterized by a driving method.
[0002]
Switching amplifiers called class D amplifiers are known.
Class D amplifiers are characterized by high power efficiency, and are also used as audio
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1
amplifiers for driving speakers. Class D amplifiers include digital amplifiers that receive digital
signals. A digital amplifier inputs a PWM signal generated by applying a pulse width modulation
to the quantization signal and quantizing with a low resolution of several bits while making the
sampling frequency of the input signal as high as 16 times or 32 times It is a signal. The digital
amplifier performs switching operation corresponding to the input PWM signal, and its output
signal is passed through a low pass filter, and only the power component is input to the speaker
to drive the speaker (for example, Patent Document) 1, Patent Document 2).
[0003]
In addition, pulse width modulation is performed by predicting in advance the harmonic
distortion generated in the process of generating the PWM signal input to the class D amplifier
as described above, subtracting the harmonic component from the original signal, and then
performing pulse width modulation. A PWM signal generator that cancels out the harmonic
distortion generated by the above has also been proposed (see, for example, Patent Document 3).
[0004]
Japanese Utility Model Application Publication No. 5-55691 Japanese Patent Application LaidOpen No. 6-29857 Japanese Patent Application Laid-Open No. 2005-218070
[0005]
FIG. 2 shows an example of a speaker provided with a conventional class D amplifier.
In FIG. 2, for example, a PWM signal obtained by pulse width modulation of an audio signal is
input to the H bridge driver 42 through the gate driver 40, and an output of the H bridge driver
42 is input to the speaker 46 through the output filter 44. It is supposed to drive 46.
A portion including the gate driver 40 and the H bridge driver 42 constitutes a class D amplifier.
The speaker 46 is generally dynamic. That is, a magnetic circuit including a permanent magnet, a
voice coil disposed in a magnetic gap in which a magnetic field is formed in the magnetic circuit,
a diaphragm to which one end of the voice coil is fixed, an outer peripheral edge of the
diaphragm and It has a frame holding the above-mentioned magnetic circuit.
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2
[0006]
A conventional class D amplifier used to drive a speaker as described in Patent Documents 1 and
2 or as shown in FIG. 2 has an active element such as a transistor in an H shape in order to
obtain a single-ended output. The circuit configuration is complicated because a connected Hbridge driver is required, and additionally, the active elements need to be complementarily
connected. Also, in order to make the class D amplifier single-ended output, an output filter
consisting of a low pass filter for removing unnecessary high frequency is required.
[0007]
In addition, although a toroidal core and a coil wound around this core are used to obtain a
sufficiently large inductance in a conventional class D amplifier, a large toroidal core is required
so that distortion does not occur in a signal due to magnetic saturation. In addition, it is desirable
that the direct current resistance of the coil be as low as possible, and for that purpose, it is
desirable to form the coil with a thick wire. However, if a coil composed of a large toroidal core
and a thick wire is used, these become bulky, and a speaker equipped with a class D amplifier
becomes large in size and also expensive.
[0008]
The present invention has been made to solve the problems of the prior art, and while having a
class D amplifier, it does not require an H bridge driver or an output filter having a complicated
electrical configuration. It is an object of the present invention to provide a small-sized speaker
capable of eliminating distortion due to magnetic saturation by eliminating the need for coils and
coils.
[0009]
The loudspeaker according to the present invention is disposed at intervals around the giant
magnetostrictive member displaced according to the variation of the magnetic field and the giant
magnetostrictive member, and the magnetic field oriented in the direction of displacement of the
giant magnetostrictive member according to the drive current. , A diaphragm supported at one
end of the giant magnetostrictive member, and a class D amplifier for supplying a drive current
to the coil, wherein the coil is driven by the up side drive current of the class D amplifier The
most important feature of the present invention is to provide an up-side coil and a down-side coil
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driven by the down-side drive current of the class D amplifier.
One end of the direction of displacement of the giant magnetostrictive member may be coupled
to the base via a mechanical filter, and the other end of the direction of displacement of the giant
magnetostrictive member may be coupled to a diaphragm via another mechanical filter.
[0010]
The mechanical driving principle of the diaphragm of the speaker is due to the giant
magnetostriction phenomenon caused by the giant magnetostrictive member. When a current
corresponding to the audio signal is supplied to the coil wound around the giant magnetostrictive
member, a magnetic field corresponding to the current is generated in the coil, and the giant
magnetostrictive member expands and contracts in accordance with the change of the magnetic
field. This expansion and contraction motion is transmitted to the diaphragm to vibrate the
diaphragm, and a sound wave corresponding to the sound signal is emitted from the diaphragm.
[0011]
The coil wound around the giant magnetostrictive member is divided into the up side and the
down side, and the drive current corresponding to each is supplied from the class D amplifier to
each coil, and the drive on the up side and the drive on the down side are To be done. Therefore,
since the class D amplifier does not have to be a single-ended output as in the prior art, a
complicated H bridge driver having a configuration is not necessary. In addition, there is no need
to use an inductor, and no distortion of sound due to magnetic saturation of the inductor occurs.
[0012]
Mechanical filters are provided at both ends of the direction of displacement of the giant
magnetostrictive member, and by coupling each end of the giant magnetostrictive element to the
base and the diaphragm via these mechanical filters, unnecessary high frequency waves are
removed by the mechanical filter and harmful. It is possible to prevent the generation of sound
waves.
[0013]
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Hereinafter, an embodiment of a loudspeaker according to the present invention will be
described with reference to FIG.
In FIG. 1, the mechanical configuration of the speaker is shown on the right side, and the
configuration of the drive circuit is shown on the left side. The speaker is provided with a giant
magnetostrictive member 20 formed in a cylindrical shape. The giant magnetostrictive member
20 is formed of a giant magnetostrictive element that has the property of being displaced
(stretched) according to the variation of the magnetic field, and is disposed in an appropriate
housing. The giant magnetostrictive element is, for example, an element made of a single crystal
alloy mainly composed of terbium, dysprosium, iron and the like, and along the direction of the
external magnetic field by the Joule effect when a magnetic field is applied from the outside It
has the property of causing a change in the dimension to stretch. In addition, when stress is
applied from the outside, it has a property of causing a change in the amount of magnetization
due to a billy effect and causing compressive deformation. The giant magnetostrictive element is
made of powder metallurgy and has extremely high mechanical strength such as compressive
strength of 600 × 10 <6> (Pa) and tensile strength of 20 × 10 <6> (Pa). The Young's modulus is
also extremely high at 2.0 × 10 <6> (N / m <2>).
[0014]
Two coils 22 and 24 are disposed around the giant magnetostrictive member 20 at a distance
from the outer circumferential surface of the giant magnetostrictive member 20, and the coils 22
and 24 are wound around the giant magnetostrictive member 20. It has become. The two coils
22 and 24 are supplied with drive current from a class D amplifier described later, and generate
a magnetic field oriented along the displacement direction of the giant magnetostrictive member
20 according to the drive current. The coil 22 is a drive coil on the up side, and the coil 24 is a
drive coil on the down side. The super magnetostrictive member 20 is driven to the up side and
the down side according to the drive current supplied to each drive coil.
[0015]
Mechanical filters 26 and 28 are fixed to both ends in the longitudinal direction which is the
displacement direction of the giant magnetostrictive member 20. The mechanical filters 26 and
28 are made of, for example, an elastic material such as rubber, and have a function of absorbing
the high frequency components and cutting them out to be transmitted to the outside. One end
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(the lower end in FIG. 1) of the giant magnetostrictive member 20 in the displacement direction
is coupled to a base 29 forming a part of the casing of the speaker via a mechanical filter 26. A
diaphragm 30 is coupled to the other end (upper end in FIG. 1) of the giant magnetostrictive
member 20 in the displacement direction via a mechanical filter 28. The diaphragm 30 has a
cone shape, the base of the cone diaphragm 30 is coupled to the mechanical filter 28, and the
outer periphery of the open end of the cone diaphragm 30 is a frame or the like that forms a part
of the speaker housing It is combined. The magnetostrictive member 20 expands and contracts
due to the magnetic field generated corresponding to the audio signal input to the coils 22 and
24, and this expansion and contraction motion is transmitted to the diaphragm 30, the
diaphragm 30 vibrates, and the acoustic wave from the diaphragm 30 It is emitted.
[0016]
Next, a drive circuit for driving the mechanical component of the speaker configured as
described above will be described. The drive circuit constitutes a class D amplifier, and in the
example shown in FIG. 1, it comprises a gate driver 10 and a MOS-FET driver 12. In the gate
driver 10, for example, as described above, the sampling frequency of the input signal is set to a
high frequency such as 16 times or 32 times, and the pulse width modulation is performed on
the quantized and quantized signal with low resolution of several bits. The generated PWM signal
is used as an input signal. The MOS-FET driver 12 includes an up-side MOS-FET 14 for driving
the up-side coil 22 and a down-side MOS-FET 16 for driving the down-side coil 24. The MOS-FET
14 and the coil 22 are connected in series between the power supply 18 and the ground, and the
MOS-FET 16 and the coil 24 are connected in series between the power supply 18 and the
ground. The PWM signal is divided into the up side and the down side and input to the gate
driver 10. The gate driver 10 inputs a switching signal to the gates of the MOS-FETs 14 and 16
based on the PWM signal on the up side and the down side. -It is comprised so that FET14 and
16 may be driven. The MOS-FETs 14 and 16 perform switching operation according to a signal
input to the gate, and supply drive current to the coils 22 and 24.
[0017]
According to the embodiment described above, the drive current is supplied from the MOS-FET
14 on the up side to the coil 22 on the up side, and the drive current is supplied from the MOSFET 16 on the down side to the coil 24 on the down side. The coils 22 and 24 generate a
magnetic field according to the drive current supplied to each, and the super magnetostrictive
member 20 expands and contracts to the up side and the down side according to each magnetic
field. The diaphragm 30 vibrates according to the expansion and contraction of the giant
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magnetostrictive member 20, and a sound wave is emitted.
[0018]
Thus, the diaphragm 30 is driven to the up side and the down side by the combination of the two
coils 22 and 24 and the super magnetostrictive member 20, and in order to mechanically
combine up and down, a conventional class D amplifier is used. Unlike a speaker, there is no need
for a class D amplifier to have a single-ended output, and no complicated H bridge driver is
required. In addition, since it is not necessary to use an inductor, distortion of sound due to
magnetic saturation of the inductor does not occur.
[0019]
The unnecessary high frequency components are removed by the mechanical filters 26 and 28 to
prevent the high frequency components from being transmitted to the diaphragm 30 and the
base 29, so that the generation of harmful sound waves due to the high frequency components
can be prevented. In addition, since it is not necessary to use an electrically complex output filter
as in the prior art, the cost can be reduced.
[0020]
As described above, the physical size of the class D amplifier can be reduced because the
inductor is not necessary, and the class D amplifier can be easily incorporated in the speaker
casing. In addition, it is easy to incorporate a class D amplifier in the housing of the speaker and
arrange it in the vicinity of the coils 22 and 24, thereby shortening the electrical wiring of the
digital signal portion and preventing unnecessary radiation. be able to.
[0021]
It is a circuit diagram showing the example of the speaker concerning the present invention with
the sectional view of the speaker part. It is a block diagram showing an example of a speaker
provided with the conventional class D amplifier.
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Explanation of sign
[0022]
DESCRIPTION OF SYMBOLS 10 Gate driver 12 MOS-FET driver 14 MOS-FET 16 MOS-FET 20
super magnetostrictive member 22 coil 24 coil 26 mechanical filter 28 mechanical filter 29 base
30 diaphragm
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