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DESCRIPTION JP2009212832

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DESCRIPTION JP2009212832
PROBLEM TO BE SOLVED: In an electret condenser microphone in which a conventional
condenser microphone and an impedance conversion circuit are connected by a series
capacitance, cost increases due to an increase in the number of parts for providing the series
capacitance and an increase in the number of mounting processes There is a problem that it
becomes an obstacle to thinning. SOLUTION: In an electret condenser microphone in which a
series capacitance is connected between an impedance conversion circuit on a circuit board and
a back electrode forming a condenser microphone or a diaphragm, the series capacitance is a
resin layer forming the electret condenser microphone It is formed of metal electrodes provided
on both sides of the resin layer. [Selected figure] Figure 1
エレクトレットコンデンサマイクロホン
[0001]
In the present invention, a circuit board on which an impedance conversion circuit is mounted, a
back electrode on which an electret layer is formed, and a diaphragm are disposed opposite to
each other to form a condenser microphone, and an impedance conversion circuit on the circuit
board and the condenser microphone are formed. An electret condenser microphone in which a
series capacitance is connected between the back electrode or the vibrating membrane, and in
particular, an electret condenser formed of a series layer by a resin layer forming the electret
condenser microphone and metal electrodes provided on both sides of the resin layer It relates to
a microphone.
[0002]
In recent years, electret condenser microphones are widely used as small-sized and high-
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performance microphones widely used for mobile phones, video cameras, digital cameras, etc.
Furthermore, a series capacitance is connected between the condenser microphone and the
impedance conversion circuit for various reasons. The configuration described above is adopted,
and is disclosed, for example, in Patent Document 1.
[0003]
The circuit configuration of the conventional electret condenser microphone disclosed in Patent
Document 1 will be described below.
FIG. 6 is a circuit diagram of a conventional electret condenser microphone. In FIG. 6, the
condenser microphone 100 is configured such that the vibrating membrane 107 and the back
electrode 104 having the electret layer 105 formed on the surface are opposed via a spacer not
shown. It is done.
[0004]
The FET 110 which is an impedance conversion circuit is provided with an output terminal OUT
at the source S by the source follower operation.
Further, voltage dividing resistors R1 and R2 are provided on the source S side of the FET 110,
and a bias voltage is supplied from the voltage dividing point to the gate G through the resistor
Rg, and the drain D is connected to the power supply voltage Vcc. There is. The back electrode
104 of the condenser microphone 100 and the gate G of the FET 110 are connected via a series
capacitance C, and the diaphragm 107 of the condenser microphone 100 is directly grounded,
and the back electrode 104 is grounded through a high resistance Ra. It is done.
[0005]
The series capacitance C in the electret condenser microphone shown in this patent document 1
has a function to cut DC between the back electrode 104 of the condenser microphone 100 and
the gate G of the FET 110 in order to adjust sensitivity as the microphone. However, in order to
prevent other bias variations in the impedance conversion circuit, the function of the series
capacitance C is required.
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[0006]
Unexamined-Japanese-Patent No. 2006-295357
[0007]
In the conventional electret condenser microphones described above, the configuration in which
the series capacitance is connected between the impedance conversion circuit and the back
electrode forming the condenser microphone or the vibrating membrane is an increasingly
necessary technology as the condenser microphones become more sophisticated. It will come.
However, considering that a conventional chip capacitance is mounted as this series capacitance,
not only the price of the capacitor microphones increases due to the increase of the number of
parts and the mounting cost but also the miniaturization of the capacitor microphones due to the
increase of the mounting area There is a problem of getting in the way.
[0008]
The object of the present invention has been made in view of the above circumstances, and by
providing an electret condenser microphone without increasing the price or increasing the shape,
by configuring the series capacitance using an element constituting the condenser microphone. is
there.
[0009]
The configuration of the electret condenser microphone in the present invention for solving the
above problems is that a condenser microphone is formed by opposingly arranging a circuit
board on which an impedance conversion circuit is mounted, a back electrode on which an
electret layer is formed, and a diaphragm. In an electret condenser microphone in which a series
capacitance is connected between an impedance conversion circuit on a circuit board and a back
electrode or a vibrating film forming the condenser microphone, the series capacitance is a resin
layer forming the electret condenser microphone and its resin layer It is characterized in that it is
formed by metal electrodes provided on both sides of.
[0010]
According to the above configuration, the series capacitance can be configured only by forming
the metal electrodes on both sides of the resin layer forming the electret condenser microphone
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as needed. Therefore, without changing the shape of the conventional condenser microphone,
Also, only a slight increase in the manufacturing cost of electrode formation allows the
construction of series capacitances.
[0011]
The resin layer is a back electrode substrate for holding the back electrode, and the series
capacitor is formed of the back electrode and the back electrode provided on both sides of the
back electrode substrate, and the impedance conversion circuit and the back electrode. It is
characterized in that it is connected between the electrodes.
[0012]
The series capacitance is formed on substantially the entire surface of the back electrode.
[0013]
The resin layer is a spacer stacked between the back electrode substrate holding the back
electrode and the circuit substrate, and the series capacitance is formed by metal electrodes
provided on both surfaces of the spacer, and the impedance conversion is performed. It is
characterized in that it is connected between a circuit and the back electrode.
[0014]
The resin layer is a spacer stacked between the back electrode substrate holding the back
electrode and the diaphragm supporting member holding the diaphragm, and the series capacity
is a metal electrode provided on both sides of the spacer , And is connected between the
impedance conversion circuit and the vibrating membrane.
[0015]
As described above, according to the present invention, since the series capacitance can be
configured only by forming metal electrodes on both sides of the resin layer forming the electret
condenser microphone as needed, the shape of the conventional condenser microphone is
changed In addition, it is possible to configure a series capacitance with only a slight increase in
production cost of electrode formation.
[0016]
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The configuration of an electret condenser microphone (hereinafter abbreviated as ECM)
according to a first embodiment of the present invention will be described below with reference
to FIGS. 1 and 2.
FIG. 1 is a cross-sectional view of an ECM, and FIG. 2 is a circuit diagram of the ECM shown in
FIG.
[0017]
Hereinafter, the configuration of the ECM in the first embodiment of the present invention will be
described with reference to FIG.
FIG. 1 is a cross-sectional view of an ECM according to a first embodiment of the present
invention, and in FIG. 1, 10 is an ECM.
Reference numeral 2 denotes a circuit board, the circuit board 2 is formed of an insulating
substrate, the connection wiring 2a is formed on the upper surface side, the output electrode 2b
is formed on the lower surface side, and an integrated circuit 11 which is an impedance
conversion circuit is mounted. .
Reference numeral 3 denotes a back electrode unit. The back electrode unit 3 has a back
electrode 4 formed of an electrode film formed on the top surface side of the back electrode
substrate 3a which is an insulating substrate, and an electret layer 5 is formed on the top surface
of the back electrode 4 In addition, on the outside of the back electrode 4 and the electret layer 5
of the back electrode substrate 3a, a through hole 3b penetrating the back electrode substrate 3a
is formed.
[0018]
6 is a vibrating membrane unit, and the vibrating membrane unit 6 is integrated by fixing the
conductive vibrating membrane 7 on the lower surface side of the vibrating membrane support
frame 6a having a metal film formed on the surface of a metal material or insulating member It is
done.
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Reference numeral 85 denotes a metal shield case, and an acoustic hole 85a is provided on the
upper surface side.
Furthermore, 8 is a first spacer, 9 is a second spacer.
[0019]
The structure of the ECM 10 is bonded after the first spacer 8 is interposed between the circuit
board 2 and the back electrode unit 3 and the second spacer 9 is interposed between the back
electrode unit 3 and the vibrating membrane unit 6. The ECM 10 is completed by fixing and
integrating with a material or the like to construct an ECM capsule, and covering the ECM
capsule with the shield case 85.
The through holes 3b are formed on the outer side of the back electrode 4 in the back electrode
unit 3, thereby ensuring ventilation of the upper and lower surfaces of the back electrode unit 3
without reducing the area of the back electrode 4 and thus achieving good acoustics. It comes to
get the effect.
[0020]
Next, the configuration of the series capacitance, which is a feature of the present invention, will
be described.
The configuration of the series capacitance Cs1 in the ECM 10 is as follows.
That is, in the ECM 10, the back electrode substrate 3a of the back electrode unit 3 is used as a
resin layer constituting the series capacitance Cs1, and the back electrode substrate 3a is
opposed to the back electrode 4 formed on the top surface of the back electrode substrate 3a.
The series capacitance Cs1 is formed in the range indicated by the dotted line by forming the
counter electrode 3c on the lower surface of
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[0021]
The series capacitance Cs1 is connected from one end of the counter electrode 3c to the
connection electrode 2a of the circuit board 2 through the through hole electrode 8a provided in
the first spacer 8, and the connection electrode 2a is provided in the integrated circuit 11. By
being connected to the input terminal of the impedance conversion circuit (to be described later),
the series capacitance Cs is connected in series between the impedance conversion circuit and
the back electrode 4 forming the capacitor microphone. Although not shown, the vibrating
membrane 7 is connected to the ground terminal of the integrated circuit 11 through the
conductive vibrating membrane supporting frame 6a and the shield case 85 made of metal.
Further, by using the entire surface of the back electrode 4, the series capacitance Cs1 can
constitute a series capacitance having a relatively large capacitance value.
[0022]
Next, the operation of the ECM 10 will be described. In the operation of the ECM 10 having the
above configuration, the diaphragm 7 having the conductive film on the surface and the back
electrode 4 having the electret layer 5 formed on the surface sandwich the second spacer 9 to
form a condenser microphone. When the diaphragm 7 is displaced by air vibration of the
acoustic input signal Ps input from the acoustic hole 85a, the capacitor of the condenser
microphone converts this displacement into an electrical signal, and this electrical signal is
transmitted from the back electrode 4 to the series capacitance Cs1. , And after being processed
by the integrated circuit 11, output from the output electrode 2b provided on the lower surface
of the circuit board 2. The vibrating action of the vibrating membrane 7 is smoothed by the
presence of the through hole 3b, and the acoustic characteristics are secured.
[0023]
Next, the impedance conversion circuit of the present invention will be described with reference
to FIG. 2 is a circuit diagram of the ECM 10 shown in FIG. 1. In FIG. 2, the condenser microphone
10a constituting the ECM 10 has the diaphragm 9 as shown in FIG. 1 and the diaphragm 7 and
the back electrode 4 having the electret layer 5 formed on the surface. It is arranged opposingly
through. (In the circuit diagram, only the diaphragm 7, the electret layer 5, and the back
electrode 4 are shown)
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[0024]
The impedance conversion circuit of this embodiment differs from the impedance conversion
circuit shown in FIG. 6 in that the conversion element in FIG. 6 is configured of the FET 110
having no amplification function, whereas in FIG. It is making high sensitivity using the amplifier
provided with and the amplification function.
[0025]
That is, voltage dividing resistors R1 and R2 are provided at the output terminal OUT of the
amplifier 10b, which is a conversion element, and feedback is made from the voltage dividing
point to the negative input terminal of the amplifier 10b, and the positive input terminal of the
amplifier 10b is high. It is grounded via a resistor R3 and is connected via a series capacitor Cs1
to the back electrode 4 of the condenser microphone 10a.
Furthermore, the vibrating membrane 7 of the condenser microphone 10a is connected to the
ground terminal of the integrated circuit 11 through the conductive diaphragm supporting frame
6a shown in FIG. 1 and the shield case 85 made of metal.
[0026]
Next, the operation of the impedance conversion circuit and the effect of the series capacitance
Cs1 will be described. In the normal operation of the impedance conversion circuit, even if there
is no series capacitance Cs1, the amplifier 10b which is an impedance conversion element is in a
stable and constant bias state, so that the acoustic input signal Ps detected by the capacitor
microphone 10a is processed correctly. It can be output.
[0027]
However, when the ambient temperature of the ECM 10 fluctuates, low frequency capacity
fluctuation occurs due to expansion or contraction of components such as the diaphragm 7, the
back electrode 4 and the electret layer 5 constituting the condenser microphone 10a. May. As a
result, the bias level of the input terminal of the amplifier 10b, which is a conversion element,
largely fluctuates due to the capacitance fluctuation, which causes a problem that the acoustic
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input signal Ps detected by the condenser microphone 10a can not be processed correctly. This
low frequency capacity fluctuation is not limited to temperature change, but also occurs when
low frequency air pressure vibration is applied to the condenser microphone 10a.
[0028]
As described above, since the input impedance of the amplifier 10b, which is an impedance
conversion element, is maintained at a very high level, the fluctuation of the bias level of the
amplifier 10b caused by the low frequency capacity fluctuation is long when there is no series
capacity. There is a problem that the detection operation of the ECM 10 becomes impossible,
because Further, the problem that the detection operation of the ECM 10 can not be performed
due to the above-mentioned low frequency capacity fluctuation is because the amplifier 10b
having an amplification factor is used as an impedance element as compared to the case where
an FET having no amplification factor is used as an impedance element. The more sensitive ECM
10 is more sensitive.
[0029]
On the other hand, when the series capacitance Cs1 is connected, since the series capacitance
Cs1 functions as a direct current cut capacitance, when a low frequency capacitance fluctuation
occurs, the variation of the capacitance fluctuation, that is, the AC component passes However,
since the DC component can not pass through, at the moment when the capacity fluctuation
occurs, the bias level of the input terminal of the amplifier 10b fluctuates and the detection
operation of the ECM 10 becomes impossible, but after a certain time, it returns to a stable
constant bias state Detection operation is possible. If the capacitance value of the series
capacitance Cs1 is too small, the acoustic input signal Ps is attenuated to cause a decrease in
sensitivity. Therefore, the capacitance value of the series capacitance Cs1 is equal to or equal to
the capacitance value of the main capacitance portion of the capacitor microphone 10a It is
desirable to set it as the above.
[0030]
Next, the configuration of an ECM according to a second embodiment of the present invention
will be described with reference to FIG. FIG. 3 is a cross-sectional view of the ECM 20 in the
second embodiment, the basic configuration is the same as the ECM 10 shown in FIG. 1, the same
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elements as the ECM 10 shown in FIG. . The difference between the ECM 20 in FIG. 3 and the
ECM 10 shown in FIG. 1 is the configuration of the series capacitance Cs2.
[0031]
That is, the configuration of the series capacitance Cs2 in the ECM 20 is as follows. In the ECM
20, a first spacer 8 stacked between the back electrode substrate 3a holding the back electrode 4
and the circuit substrate 2 is used as a resin layer constituting the series capacity Cs2. That is,
the first spacer 8 is slightly shortened, the auxiliary spacer 18 is provided, and the metal
electrodes 18a and 18b are provided on both sides of the auxiliary spacer 18, thereby forming a
series capacitance Cs2 in the range indicated by the dotted line.
[0032]
The series capacitance Cs2 is connected from the metal electrode 18a to the back electrode 4 via
the through hole electrode provided on the back electrode substrate 3a, and the through hole
electrode provided on one end of the metal electrode 18b to the first spacer 8 The series
capacitor Cs2 is connected to the connection electrode 2a of the circuit board 2 through 8a, and
the connection electrode 2a is connected to the input terminal of the amplifier 10b constituting
the impedance conversion circuit provided in the integrated circuit 11. It is connected in series
between the conversion circuit and the back electrode 4 forming a condenser microphone.
Although not shown, the vibrating membrane 7 is connected to the ground terminal of the
integrated circuit 11 through the conductive vibrating membrane supporting frame 6a and the
shield case 85 made of metal.
[0033]
The series capacitance Cs2 can form a series capacitance having a relatively large capacitance
value by using the entire surface of the ring-shaped auxiliary spacer 18. Further, as the resin
material of the auxiliary spacer 18, in order to increase the capacity value of the series capacity
Cs2, a resin material having a high dielectric constant (a printed substrate such as an epoxy resin
containing glass or a ceramic such as alumina) may be used. desirable.
[0034]
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Next, the configuration of an ECM according to a third embodiment of the present invention will
be described with reference to FIG. FIG. 4 is a cross-sectional view of the ECM 30 in the third
embodiment, the basic configuration is the same as the ECM 20 shown in FIG. 3, the same
elements as the ECM 20 shown in FIG. Do. The difference between the ECM 30 in FIG. 4 and the
ECM 20 shown in FIG. 3 is the configuration of a spacer provided between the circuit substrate 2
and the back electrode substrate 3a.
[0035]
That is, in the ECM 20, the spacer provided between the circuit board 2 and the back electrode
substrate 3a is constituted by the first spacer 8 and the auxiliary spacer 18 made of resin, and
the series capacitance Cs 2 formed by the auxiliary spacer 18 is provided in the first spacer 8 In
the ECM 30, a spacer provided between the circuit board 2 and the back electrode board 3a is
connected to the connection electrode 2a of the circuit board 2 through the through-hole
electrode 8a. And the auxiliary spacer 18, and the series capacitance Cs2 formed by the auxiliary
spacer 18 is directly connected to the connection electrode 2a of the circuit board 2 via the first
spacer 28 made of metal. According to this configuration, it is not necessary to provide the
through hole electrode 8 a in the first spacer 8, and furthermore, the entire first spacer 28 made
of metal can conduct electricity, so that the connection resistance can be significantly reduced.
[0036]
Next, the configuration of an ECM according to a fourth embodiment of the present invention will
be described with reference to FIG. FIG. 5 is a cross-sectional view of the ECM 40 in the fourth
embodiment, the basic configuration is the same as the ECM 10 shown in FIG. 1, and the same
elements as the ECM 10 shown in FIG. . The difference between the ECM 40 in FIG. 5 and the
ECM 10 shown in FIG. 1 is the configuration of the series capacitance Cs3.
[0037]
That is, the configuration of the series capacitance Cs3 in the ECM 40 is as follows. In the ECM
40, the second spacer 9 laminated between the back electrode unit 3 and the vibrating
membrane unit 6 is used as a resin layer constituting the series capacity Cs3, and metal
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electrodes 9a and 9b are formed on both sides of the second spacer 9. By forming the capacitor,
the series capacitor Cs3 is formed in the range indicated by the dotted line.
[0038]
The series capacitance Cs3 has the metal electrode 9a connected to the conductive vibrating film
7 and the metal electrode 9b provided in the back electrode substrate 3a and the through hole
electrode 8a provided in the first spacer 8 Is connected to the connection electrode 2a of the
circuit board 2 via the connection terminal 2a, and the connection electrode 2a is connected to
the input terminal of the amplifier 10b that constitutes the impedance conversion circuit
provided in the integrated circuit 11, thereby converting It is connected in series between the
circuit and the diaphragm 7 which forms a condenser microphone.
[0039]
Further, in the case of the ECM 40, since it is necessary to insulate the diaphragm 7 from the
metal shield case 85, the diaphragm support frame 6a is made of an insulating material such as
resin.
As a result, the ground terminals of the condenser microphone and the integrated circuit 11 are
connected to the through hole electrode and the first spacer 8 provided on the back electrode
substrate 3a from the back electrode 4 constituting the condenser microphone as shown in FIG.
The connection electrode 2 a is connected to the connection electrode 2 a of the circuit board 2
through the through hole electrode 8 b, and the connection electrode 2 a is connected to the
ground terminal of the integrated circuit 11.
[0040]
Then, by using the entire surface of the ring-shaped second spacer 6a also in this series
capacitance Cs3, a series capacitance having a relatively large capacitance value can be
configured. In addition, as the resin material of the second spacer 6a, in order to increase the
capacitance value of the series capacitance Cs3, a resin material having a high dielectric constant
(a printed substrate such as an epoxy resin containing glass or a ceramic such as alumina) is
used. Is desirable.
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[0041]
In each of the above embodiments, as the configuration of the condenser microphone, the back
electret type ECM in which the electret layer 5 is provided on the back electrode 4 on the back
electrode unit 3 side has been described, but it is not limited thereto. Of course, the present
invention can also be applied to a membrane electret type ECM in which the electret layer 5 is
provided on the vibrating membrane 7 on the sixth side.
[0042]
It is sectional drawing of ECM10 in 1st Embodiment of this invention.
It is a circuit block diagram of ECM10 shown in FIG. It is sectional drawing of ECM 20 in 2nd
Embodiment of this invention. It is sectional drawing of ECM30 in 3rd Embodiment of this
invention. It is sectional drawing of ECM40 in 4th Embodiment of this invention. It is a circuit
block diagram of the conventional ECM.
Explanation of sign
[0043]
Reference Signs List 2 circuit board 2a connection wiring 2b output electrode 3 back electrode
unit 3a back electrode substrate 3c counter electrode 4, 104 back electrode 5, 105 electret layer
6 vibrating membrane unit 6a vibrating membrane support frame 7, 107 vibrating membrane 8,
28 first spacer 8a through-hole electrode 9 second spacer 9a, 9b metal electrode 10, 20, 30, 40
ECM 10a, 100 condenser microphone 10b amplifier 11 integrated circuit 18 auxiliary spacer
18a, 18b metal electrode 85 shield case 85a acoustic hole 110 FET R1, R2 , R3, Ra, Rg
Resistance C, Cs1, Cs2, Cs3 Series capacitance
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