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JP2009017337

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2009017337
An electrostatic speaker in which a drive circuit and a fixed electrode are integrated. An
electrostatic speaker is formed on a vibrating electrode, a base material disposed to face the
vibrating electrode, a fixed electrode formed on the base material, and the base material. A DC
voltage line for applying a DC voltage of a fixed electrode, and a switching element interposed
between the DC signal line and the fixed electrode on the base material, having a control
terminal, the control It has switching means whose on / off is controlled by a signal inputted to a
terminal, and a tone signal line which is formed on the substrate and which supplies a tone signal
to the control terminal. [Selected figure] Figure 2
Electrostatic speaker
[0001]
The present invention relates to an electrostatic speaker.
[0002]
A speaker called an electrostatic speaker (capacitor speaker) is known.
The electrostatic loudspeaker has, as a basic structure, two parallel flat electrodes facing each
other across an air gap. One of the two parallel flat electrodes is fixed (referred to as a fixed
electrode or fixed plate), and the other is often movable (referred to as a movable electrode, a
vibrating electrode, or a diaphragm). When the input signal is superimposed on the bias voltage
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applied between the parallel flat electrodes, the attraction between the parallel flat electrodes
changes. The electrostatic speaker outputs a sound by vibrating the diaphragm by this suction
force.
[0003]
The electrostatic speaker is desired to be compact. Patent Documents 1 and 2 disclose an image
display device in which a display element, a sound generator and a drive circuit are integrated.
JP, 2004-173264, A Special table 2004-524574
[0004]
Patent documents 1 and 2 relate to the image display apparatus to the last, and the sounding
body was only an accessory thing to the last. That is, the speaker was too small to be used as a
speaker. Also, the sound generator was only driven directly by the actuator. As described above,
Patent Documents 1 and 2 do not have conditions such as frequency characteristics, sound
quality, directivity, sensitivity, and the like that the speaker should have in terms of sounding
structure, sound quality, area, and the like. On the other hand, the present invention provides an
electrostatic speaker in which a drive circuit and a fixed electrode are integrated.
[0005]
According to the present invention, a vibrating electrode, a base material disposed to face the
vibrating electrode, a fixed electrode formed on the base, and a DC voltage of the fixed electrode
formed on the base A DC voltage line for applying, and a switching element interposed between
the DC signal line and the fixed electrode on the base material, having a control terminal, and a
signal input to the control terminal According to the present invention, there is provided an
electrostatic speaker having switching means whose on / off is controlled, and a tone signal line
formed on the base material and for supplying a tone signal to the control terminal.
[0006]
In a preferred embodiment, the electrostatic speaker may be provided with a plurality of the
fixed electrodes and the switching means, and the plurality of switching means may be
respectively interposed between the DC voltage line and the respective fixed electrodes. .
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[0007]
In another preferred embodiment, the electrostatic speaker is provided with a plurality of tone
signal lines, the plurality of fixed electrodes are divided into a plurality of groups corresponding
to the tone signal lines, and the tone signal lines are provided. A different music signal may be
supplied to each group.
[0008]
In yet another preferred embodiment, in the electrostatic loudspeaker, the switching means may
be formed of a thin film transistor.
[0009]
In still another preferred embodiment, in the electrostatic loudspeaker, the base, the vibrating
electrode, the fixed electrode, and the thin film transistor may be formed of a transparent
material.
[0010]
According to the present invention, the drive circuit of the electrostatic speaker and the fixed
electrode are integrated.
[0011]
1.
Embodiment FIG. 1 is an external view of a speaker unit 1 according to an embodiment.
FIG. 2 is a cross-sectional view of the speaker unit 1 taken along the line II.
The speaker unit 1 is a so-called push-pull electrostatic speaker having fixed electrodes
(electrode film 20 and electrode film 60) on both sides of a vibrating electrode (vibration film
40).
The speaker unit 1 has a vibrating film 40 between the base 10 and the base 70.
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An electrode film 20 and an electrode film 60 are respectively formed on the surfaces of the base
10 and the base 70 facing the vibrating membrane 40.
Spacers 30 and 50 are provided between the base 10 and the vibrating membrane 40 and
between the base 70 and the vibrating membrane 40, respectively.
[0012]
The base 10 is a member to be a substrate on which the electrode film 20 is formed. The base
material 10 is formed of, for example, an insulating material such as PET (polyethylene
terephthalate, polyethylene terephthalate), glass, plastic, glass epoxy material, paper phenol
material (bake), vinyl chloride, acrylic (methyl methacrylate), rubber or the like. . The base 10 has
a plate shape, and is disposed apart from the vibrating membrane 40. The base 10 has a through
hole H in the direction perpendicular to the vibrating membrane 40. The through hole H is a hole
for transmitting the sound wave generated by the vibration of the vibrating membrane 40 to the
outside of the speaker unit 1. The cross sectional shape, size, number, and position on the
substrate 10 of the through holes H are designed to obtain desired propagation characteristics.
Further, on the surface of the substrate 10 on which the electrode film 20 is formed, a voltage
line for applying a DC voltage and a signal line for supplying an audio signal (musical tone signal)
(both in FIGS. 1 and 2) The transistor 100 is formed. Details of the pattern formed on the
substrate 10 will be described later. The configuration of the base 70 is the same as that of the
base 10.
[0013]
The electrode film 20 functions as a fixed electrode in the electrostatic speaker. The electrode
film 20 is made of metal or another conductive material. The electrode film 20 is formed as a
thin film on the substrate 10 using a process technique such as vapor deposition, sputtering,
photolithography and the like. Although the details will be described later, a plurality of electrode
films 20 are formed on the substrate 10. The configuration of the electrode film 60 is the same
as that of the electrode film 20.
[0014]
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The spacer 30 and the spacer 50 have a function of fixing the substrate 10 and the substrate 70
to each other. The spacer 30 and the spacer 50 are formed of, for example, an insulating material
such as Teflon (registered trademark), acrylic (methyl methacrylate), rubber or the like. Spacer
30 and spacer 50 are fixed to substrate 10 and substrate 70 using an adhesive or the like.
[0015]
The vibrating film 40 functions as a vibrating electrode in an electrostatic speaker. The vibrating
film 40 is formed of, for example, a film (thin film or sheet) using a polymer material such as
PET, PP (polypropylene, polypropylene), or polyester, and a material in which a conductive
material such as metal is vapor-deposited. Alternatively, the vibrating film 40 may be formed of a
material obtained by applying a conductive dye to a film. The vibrating film 40 is sandwiched
between the cushioning material 80 and the cushioning material 90. The vibrating membrane 40
is supported by the cushioning material 80 and the cushioning material 90. That is, the speaker
unit 1 has a so-called edgeless structure.
[0016]
The cushioning material 80 and the cushioning material 90 are made of insulating non-woven
fabric, cotton or the like to prevent the contact between the vibrating electrode and the fixed
electrode and to make the frequency characteristic of the speaker unit 1 a desired characteristic.
The cushion material 80 and the cushion material 90 are formed using an elastic body or an
elastic material having a predetermined elastic modulus (for example, can be represented by a
linear elastic modulus (Young's modulus) or the like in the thickness direction).
[0017]
FIG. 3 is a diagram illustrating the arrangement of the electrode film 20 and the transistor 100.
In the present embodiment, the transistor 100 functions as a drive circuit of a so-called class D
amplifier. The voltage line VDD is a wiring for applying a DC voltage for driving the electrostatic
speaker to the electrode film 20. The voltage line VDD and the signal line VAUDIO are isolated
from each other. The signal line VAUDIO is a wiring for transmitting an audio signal input to the
electrostatic speaker. Here, the audio signal is input to the speaker unit 1 as a PWM (Pulse Width
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Modulation) signal. The voltage line VDD and the signal line VAUDIO are formed as a pattern on
the substrate 10. In order to simplify the description, the voltage applied by the voltage line VDD
and the audio signal supplied by the signal line VAUDIO will be denoted as a voltage VDD and a
signal VAUDIO, respectively.
[0018]
The voltage line VDD branches into a plurality of lines, and the branched lines extend in parallel
to one another. The signal line VAUDIO also branches into a plurality of lines, and the branched
lines extend in parallel with one another. The voltage line VDD and the signal line VAUDIO
extend in directions orthogonal to each other to form a lattice pattern. Now, one square in this
grid is called a "cell". One electrode film 20 is formed in one cell. In each cell, the transistor 100
is disposed between the voltage line VDD and the electrode film 20. That is, in the present
embodiment, the electrode films 20 are arranged in a matrix.
[0019]
The transistor 100 is an element that drives the speaker unit 1, specifically, an element that
functions as a switching unit that controls a voltage applied to the electrode film 20. The
transistors 100 are provided one by one for the electrode film 20. In the present embodiment,
the transistor 100 is a thin film FET (Field Effect Transistor). The drain of the transistor 100 is
connected to the voltage line VDD, the source is connected to the electrode film 20, and the gate
is connected to the signal line VAUDIO. Thus, the transistor 100 is interposed between the
electrode film 20 and the voltage line VDD. Note that “interposed” between the electrode film
20 and the voltage line VDD means that it is inserted at any position on the electrical path
between the electrode film 20 and the voltage line VDD. An element other than the transistor
100 may be connected in series to the transistor 100 between the electrode film 20 and the
voltage line VDD. In the transistor 100, the potential difference between the source and the drain
changes in accordance with a signal input to the gate which is a control terminal. As described
above, the transistor 100 is controlled to be on / off in accordance with a signal input to the gate,
that is, performs switching control in accordance with the signal input to the gate.
[0020]
The area or the size of the electrode film 20 is determined according to the maximum value of
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the drive current of the transistor 100, for example, as follows. Now, a case where VDD = 100 V
and the capacitance of the entire speaker unit 1 is 2000 pF will be described as an example. The
capacitance is a value when the total area of the electrode film 20 is 30 cm × 30 cm = 900 cm
<2> and the gap between the fixed electrode and the vibrating electrode is 0.5 mm.
[0021]
Now, consider the case where the fixed electrode is divided into 1000, that is, the case where a
plurality of electrode films 20 are arranged in a matrix of 32 × 31 (note that 32 × 31 is not
strictly 1000, but this is for the purpose of explanation). Is an example). The capacitance per
electrode film 20 is 2 pF. Assuming that a 1 kHz audio signal is input, the impedance is about 80
MΩ, and the current flowing at this time is about 1.2 μA. Alternatively, assuming that a 10 kHz
audio signal is input, the impedance is about 8 MΩ, and the current flowing at this time is about
12 μA. With a current of this level, a so-called low temperature polysilicon TFT (Thin Film
Transistor) can be used as the transistor 100. If the current value is too large, the division
number may be increased. By increasing the division number, it is possible to use a transistor
with a lower allowable current value.
[0022]
Although the configurations of the substrate 10 and the electrode film 20 have been described
above, the configurations of the substrate 70 and the electrode film 60 are similar to this.
[0023]
FIG. 4 is a view showing a schematic configuration of a speaker system 3 using the speaker unit
1.
The speaker system 3 has a speaker unit 1 and an amplifier 2 for outputting an audio signal to
the speaker unit 1. The triangular wave oscillator 21 is a circuit that generates and outputs a
triangular wave. The comparator 22 is a circuit that outputs a voltage according to the
comparison result of the + input (triangular wave) and the − input (audio signal). Specifically, the
comparator 22 compares the + input with the − input, and when the voltage of the + input is
high, the voltage of high level (H) is low, and when the voltage of the − input is high, it is low.
Output voltage of level (L). Thus, a PWM signal is generated. The amplifier 23 is a circuit that
amplifies the input PWM signal. The amplifier 2 outputs the PWM signal thus generated. The
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PWM signal (that is, audio signal VAUDIO) output from the amplifier 2 is input to the speaker
unit 1 via the cable 4.
[0024]
Although the configuration of the speaker unit 1 shown in FIG. 4 is different from the
configurations shown in FIGS. 1 to 3 in some respects, it is basically the same as the one
described in FIGS. is there. In the present embodiment, the transistor 100a, the transistor 100b,
and the filter LPF are formed on the same surface as the surface of the base 10 on which the
electrode film 20 is formed. The capacitance CF is a capacitance constituted by a fixed electrode
and a vibrating electrode which are main parts of the electrostatic speaker. The filter LPF
functions as an integrating circuit that integrates the PWM signal and returns it to the original
audio signal. The transistor 100a and the transistor 100b form a switching circuit that is
switched on / off in response to the PWM signal. Thereby, a signal indicating a voltage of + VDD
or -VDD is applied to the capacitor CF, that is, the electrode film 20 via the filter LPF. Thus, the
sound is output from the speaker unit 1.
[0025]
As described above, according to the present embodiment, since the electrode film 20 and the
transistor 100 are formed on the base material 10, the speaker unit 1 becomes more compact as
compared with a device without such a configuration. . Also, when the class D amplifier is
separated from the electrostatic speaker as in the prior art, a high voltage signal of 200 VPP
flows in the cable between the class D amplifier and the electrostatic speaker in the above
example. become. On the other hand, according to the present embodiment, the signal flowing
through the cable 4 between the amplifier 2 and the speaker unit 1 may be, for example, a signal
of about 3 VPP. The standards for so-called alternating current signal routing wires are subject to
the regulations of the Electric Business Law, for example, but if low voltage signals are
propagated as in this embodiment, restrictions such as laws are relaxed and design freedom
Increase.
[0026]
2. Other Embodiments The present invention is not limited to the above-described
embodiments, and various modifications can be made. In addition, the description is abbreviate |
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omitted about the matter which is the same as the above-mentioned embodiment below. In
addition, one or more of the modifications described below may be applied in combination with
other modifications.
[0027]
2−1. Modified Example 1 The audio signals VAUDIO supplied to the plurality of electrode
films 20 may not all be the same. That is, the plurality of electrode films 20 may be divided into a
plurality of groups. In this case, the speaker unit 1 has a plurality of signal lines VAUDIO. The
plurality of signal lines VAUDIO correspond to the groups one to one. That is, the plurality of
signal lines VAUDIO are arranged to supply audio signals to different groups. With such a
configuration, for example, by supplying an audio signal whose directivity is controlled to each
group, the directivity of the sound output from the speaker unit 1 can be controlled.
[0028]
2−2. Modification 2 FIG. 5 is a view showing the flexibility of the speaker unit 1 according to
Modification 2. As shown in FIG. In this example, the substrate 10 and the substrate 70 are
formed of plastic, PET, bake, glass epoxy material, or another material having flexibility
(flexibility or flexibility). In order to form the transistor 100 on the substrate 10 and the
substrate 70, a material that can withstand the temperature given in the semiconductor process
may be selected as the material of the substrate 10 and the substrate 70. For example, in the
case of using a low-temperature polysilicon TFT as the transistor 100, a thermosetting material
which is cured at 350 ° C. or higher may be used for the base 10 and the base 70. Alternatively,
when an amorphous oxide semiconductor is used for the transistor 100, it is also possible to use
PET for the base 10 and the base 70. In this case, there is a possibility that the maximum drive
current of the transistor 100 may be reduced, but even then, the number of divisions of the
electrode film 20 may be increased. With such flexible materials, so-called "bent" speakers can be
produced.
[0029]
2−3. Modification 3 FIG. 6 is a view showing a display system 5 using an electrostatic
speaker formed of a transparent material. As a transparent material, glass and a transparent
plastic material are used as the base material 10 and the base material 70, for example. As the
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electrode film 20 and the electrode film 60, a transparent electrode material such as ITO (Indium
Tin Oxide), ZnO, SnO 2 or the like is used. As the transistor 100, for example, an In-Ga-Zn-Obased amorphous oxide semiconductor is used. As the vibrating film 40, one in which a film is
formed of a transparent electrode material on PET is used. By arranging such a transparent
speaker in front of the display device D, it is possible to make the user feel that "sounds are
output from the image surface". The display device D may be any display device such as, for
example, a liquid crystal display, a plasma display, or a CRT (Cathode Ray Tube). Here,
"transparent" means that the light transmittance is equal to or higher than a threshold value.
[0030]
2−4. Other Modifications The configuration of the circuit that performs switching in
accordance with the PWM signal is not limited to that illustrated in FIG. The point is that any
circuit may be used as long as it switches the voltage according to the PWM signal. In this case,
elements other than the transistor 100 in this circuit may be formed without being integrated
with the transistor 100. Further, the arrangement of the electrode films 20 is not limited to the
matrix as illustrated in FIG. It may be arranged in any manner, such as in a zigzag, concentric or
random arrangement. Alternatively, the speaker unit 1 may have only a single electrode film 20.
1 and 2 merely schematically show the configuration of the speaker unit 1, and the number, size
and position of the through holes H, the shape of the base 10, and the configuration of the
speaker unit 1 are It is not limited to what was illustrated in FIG. 1 and FIG. For example, the
cushions 80 and 90 may be omitted. That is, an air layer may be used instead of the cushioning
material. Alternatively, the vibrating membrane 40 may be supported by the spacer 30 and the
spacer 50.
[0031]
It is an outline view of speaker unit 1 concerning one embodiment. FIG. 2 is a cross-sectional
view of the speaker unit 1 at I-I. FIG. 6 is a diagram illustrating an arrangement of an electrode
film 20 and a transistor 100. FIG. 2 is a view showing a schematic configuration of a speaker
system 3 using the speaker unit 1; It is a figure which shows the flexibility of the speaker unit 1
which concerns on modification 2. FIG. FIG. 1 is a view showing a display system using a
transparent electrostatic speaker.
Explanation of sign
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[0032]
DESCRIPTION OF SYMBOLS 1 ... Speaker unit, 2 ... Amplifier, 3 ... Speaker system, 4 ... Cable, 5 ...
Display system, 10 ... Base material, 20 ... Electrode film, 21 ... Triangle wave oscillator, 22 ...
Comparator, 23 ... Amplifier, 30 ... Spacer, DESCRIPTION OF SYMBOLS 40 ... Vibrating film, 50 ...
Spacer, 60 ... Electrode film, 70 ... Base material, 80 ... Cushion material, 90 ... Cushion material,
100 ... Transistor
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