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DESCRIPTION JP2010157958

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DESCRIPTION JP2010157958
A capacitor microphone that requires a polarization voltage is configured to obtain a high
polarization voltage from a part of a voltage supplied from a phantom power source or the like
without using a booster circuit such as a DC-DC converter. An electrostatic-type acoustoelectric
converter 10 including a diaphragm 10a and a fixed pole 10b disposed opposite to each other,
and a polarization providing a polarization voltage to the fixed pole 10b of the acoustoelectric
converter 10. In the condenser microphone having the power supply unit 30, as the polarized
power supply unit 30, the PLZT element 31 connected to the fixed pole 10b via the
predetermined resistance element R01, and the ultraviolet light emission optically coupled to the
PLZT element 31 A diode 32 and a drive circuit 33 for driving the ultraviolet light emitting diode
32 are provided, and the PLZT element 31 is irradiated with ultraviolet light of a predetermined
wavelength from the ultraviolet light emitting diode 32 to cause the PLZT element 31 to
generate a voltage by the photovoltaic effect. The polarization voltage for the fixed pole 10b is
obtained. [Selected figure] Figure 1
コンデンサマイクロホン
[0001]
The present invention relates to a condenser microphone, and more particularly, to a technique
for obtaining a polarization voltage of a condenser microphone by the photovoltaic effect of a
PLZT element.
[0002]
The condenser microphone has an electrostatic type acoustoelectric converter (also referred to
as a condenser microphone capsule) in which a diaphragm and a fixed pole are disposed opposite
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to each other through an electrically insulating spacer ring as a sound pickup unit. .
[0003]
The diaphragm is stretched on the diaphragm support ring with a predetermined tension, the
fixed pole is supported by the insulating seat, and is disposed opposite to each other through the
insulating spacer, thereby forming a type of capacitor, By vibrating the diaphragm with the
incoming sound wave, the capacitance is changed, and the amount of change is output as an
audio signal.
[0004]
Therefore, when driving a condenser microphone, it is usually necessary to apply a polarization
voltage to the acoustoelectric converter.
[0005]
In the case of an electret condenser microphone having an electret dielectric film, the electret
dielectric film is semipermanently charged, so it is not necessary to apply a polarization voltage
from the outside.
[0006]
However, in the electret condenser microphone, it is difficult to uniformly charge the electret
dielectric film by corona discharge or the like, and to control the polarization voltage uniformly,
so that the sensitivity is likely to vary.
[0007]
Therefore, for example, a condenser microphone for emphasizing sound quality such as a studio
sound pickup application is provided with a polarized power supply unit, and a predetermined
polarized voltage is applied to the fixed pole of the acoustoelectric converter from the polarized
power supply unit to achieve high sensitivity. I am trying to get
[0008]
One of the methods for obtaining the polarization voltage is a method using a voltage of 48 V
supplied from a phantom power supply (see, for example, Patent Document 1).
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According to this method, a high polarization voltage can be obtained by reducing the current
consumed by the main circuit such as the audio output circuit.
However, since there is a limit to reducing the current consumption in the main circuit, the
sensitivity can not be made very high.
[0009]
Another method is to use a DC-DC converter (see, for example, Patent Document 2).
That is, in this method, a high polarization voltage is obtained by converting direct current into
alternating current using an oscillation circuit, boosting it with a transformer, and rectifying it.
[0010]
However, the oscillation frequency output from the oscillation circuit may be superimposed on
the microphone output, which may generate noise.
In addition, when an exciter is used for the oscillation circuit, an induction magnetic field is
generated, and noise may be induced in other electronic devices by magnetic coupling.
[0011]
JP, 2005-287000, A JP, 09-121533, A
[0012]
Therefore, an object of the present invention is to provide a condenser microphone that requires
a polarization voltage in an acoustoelectric converter, and does not use a booster circuit such as
a DC-DC converter, but uses a part of the voltage supplied from a phantom power supply etc. It is
about making it possible to obtain a polarization voltage.
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[0013]
In order to solve the above problems, the present invention relates to an electrostatic
acoustoelectric transducer including a diaphragm and a fixed pole disposed opposite to each
other, and a polarization voltage to the fixed pole of the acoustoelectric transducer. A condenser
microphone having a polarized power supply unit, wherein the polarized power supply unit
includes a PLZT element connected to the fixed pole via a predetermined resistance element, and
an ultraviolet light emitting diode optically coupled to the PLZT element. And a driving circuit for
driving the ultraviolet light emitting diode, wherein the PLZT element is irradiated with
ultraviolet light of a predetermined wavelength from the ultraviolet light emitting diode, and a
voltage is generated in the PLZT element by the photovoltaic effect, and the fixed electrode is
generated. To obtain a polarization voltage for
[0014]
According to a preferred aspect of the present invention, a switched capacitor type voltage
converter that converts a part of the voltage supplied from the phantom power supply into a
predetermined voltage is used in the drive circuit.
[0015]
According to the present invention, the polarized power supply unit for the acoustoelectric
converter, the PLZT element connected to the fixed pole through the predetermined resistance
element, the ultraviolet light emitting diode optically coupled to the PLZT element, and the
ultraviolet light emission The PLZT element is irradiated with ultraviolet light of a predetermined
wavelength from the ultraviolet light emitting diode, and a voltage is generated in the PLZT
element by the photovoltaic effect to obtain a polarization voltage for the fixed electrode. Thus,
without using a boosting circuit such as a DC-DC converter, a high polarization voltage can be
obtained from a part of the voltage supplied from a phantom power source or the like.
[0016]
FIG. 1 is a circuit diagram showing a condenser microphone according to an embodiment of the
present invention.
[0017]
Next, an embodiment of the present invention will be described with reference to FIG.
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FIG. 1 is a circuit diagram showing a condenser microphone according to an embodiment of the
present invention.
Although the condenser microphone according to this embodiment operates with a phantom
power supply, the phantom power supply itself has two 6.8 kΩ resistors connected in series
between hot and cold of balanced transmission, and The illustration is omitted because it is a
known one having a direct current 48 V power source connected between the connection point
of the resistor and the ground.
[0018]
As shown in FIG. 1, this condenser microphone is an acoustoelectric converter (capacitor as a
sound pickup unit in which the diaphragm 10a and the fixed pole 10b are disposed opposite to
each other through an electrically insulating spacer ring (not shown). Microphone capsule 10 is
provided.
[0019]
The diaphragm 10a is stretched on a diaphragm support ring (not shown) with a predetermined
tension, and the fixed electrode 10b is supported by an insulating seat and arranged oppositely
through the spacer ring. A capacitor is formed, and the vibrating plate vibrates with an incoming
sound wave to change the capacitance, and the amount of change is output as an audio signal.
[0020]
The diaphragm 10a is connected to the microphone case (ground 11) via the diaphragm support
ring, and the fixed electrode 10b is connected to the gate of an FET (field effect transistor) 40 as
an impedance converter.
[0021]
The microphone output unit 50 is provided with a terminal H connected to the hot side of the
phantom power supply, a terminal C connected to the cold side, and a terminal G connected to
the ground side.
[0022]
The hot side terminal H is connected to the drain of the FET 40 through the constant current
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diode D03, and the cold side terminal C is connected to the source of the FET 40.
The output side of the FET 40 is connected to the hot terminal H and the cold terminal C via the
output transformer TRS.
[0023]
The condenser microphone includes a polarized power supply unit 30 which applies a polarized
voltage to the fixed pole 10b.
The polarization power supply unit 30 includes a PLZT element 31, an ultraviolet light emitting
diode 32 for irradiating the PLZT element 31 with ultraviolet light, and a drive circuit 33 for
driving the ultraviolet light emitting diode 32.
[0024]
The PLZT element 31 is a lead lanthanum zirconate titanate which is sintered by adding
lanthanum oxide (La 2 O 3) to a solid solution of lead titanate (PbTiO 3) and lead zirconate
(PbZrO 3), and emits ultraviolet light having a wavelength of about 365 nm. Then, the
photovoltaic effect generates a very high voltage (the generated voltage per electrode distance is
3.3 kV / cm).
[0025]
The PLZT element 31 is connected to the fixed pole 10b via the resistance element R01.
As the ultraviolet light emitting diode 32, one that emits ultraviolet light of about 365 nm is used,
and for this type of ultraviolet light emitting diode, for example, part number NSHU550B (peak
wavelength 365 nm, light output 2,000 μW, drive by Nichia Chemical Industry Co., Ltd.) There
is a voltage Max 4V).
[0026]
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In this embodiment, the drive circuit 33 may be abbreviated as a switched capacitor type voltage
converter IC (hereinafter simply referred to as "converter IC").
)からなる。
In this example, three converters IC01, IC02, and IC03 are connected in series in three stages,
and each of them uses an LM 2665 manufactured by NATIONAL SEMICONDUCTOR, USA.
[0027]
This LM2665 converter IC has six pins from No. 1 to No. 6. When a positive voltage is input from
the No. 1 pin, a double boosting type in which a double voltage is output from the No. 5 pin On
the other hand, when a positive voltage is input from the fifth pin, it operates as a 1/2 step-down
type in which a half voltage is output from the first pin.
[0028]
In this embodiment, each of the converters IC01, IC02 and IC03 is supplied with a positive
voltage from the fifth pin so as to be used as a half-time step-down type, and an output voltage of
one half of that is obtained from the first pin. There is.
[0029]
The second pin is the ground pin, the fourth pin is the shutdown control pin, and the charge
pump capacitors C01, C02 and C03 are connected between the third and sixth pins, respectively.
The positive terminal of the capacitor is connected to the third pin in order to make it a stepdown type.
In the case of operation as a double boosting type, the negative terminal of the capacitor is
connected to the third pin.
Further, capacitors C010, C20 and C30 for smoothing and alternating current grounding are
connected to each of the first pins on the output side.
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[0030]
The drive circuit 33 includes an input circuit 33a formed of a series circuit of a current limiting
resistor R02 and a Zener diode D01.
A predetermined constant current is supplied to the input circuit 33a from the terminal H on the
hot side and the terminal C on the cold side via the constant current diodes D02 and D03.
[0031]
In this example, the input voltage to the drive circuit 33 is 32 V by the zener diode D01 of the
input circuit 33a, and the input current to the drive circuit 33 is limited to 2.5 mA by the current
limiting resistor R02.
A capacitor C40 connected in parallel to the Zener diode D01 is a smoothing capacitor.
[0032]
As a result, while the voltage is stepped down from 16 V to 8 V to 4 V in the order of the first
stage converter IC03, the second stage converter IC02 and the third stage converter IC01, the
current is 5 mA to 10 mA to 20 mA. The driving power of 4 V and 20 mA is finally applied to the
ultraviolet light emitting diode 32 from the first pin of the converter IC01 of the third stage.
[0033]
As a result, ultraviolet light (ultraviolet light) having a wavelength of 365 nm is emitted from the
ultraviolet light emitting diode 32 to the PLZT element 31, so that a high voltage is generated
from the PLZT element 31 by its photovoltaic effect, and the high voltage is a fixed electrode.
10b is applied as a polarization voltage.
[0034]
As described above, according to the present invention, the ultraviolet light emitting diode 32
emits ultraviolet light of a specific wavelength that causes the PLZT element 31 to exhibit the
photovoltaic effect, and the PLZT element 31 obtains polarization voltage to the fixed electrode
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10b. By doing this, it is possible to apply a higher polarization voltage to the fixed pole without
using a transformer such as a DC-DC converter including an oscillation circuit which becomes a
noise source, and to increase the sensitivity of the capacitor microphone accordingly. Is possible.
[0035]
DESCRIPTION OF SYMBOLS 10 Electrostatic-type acoustic-electric converter (capacitor
microphone capsule) 10a diaphragm 10b fixed pole 11 grounding (microphone case) 30
polarized power supply part 31 PLZT element 32 ultraviolet light emitting diode 33 drive circuit
40 impedance converter (FET) 50 microphone Output part IC01, IC02, IC03 Switched capacitor
type voltage converter C01, C02, C03 Charge pump capacitor H Hot side terminal C Cold side
terminal G Ground (ground) side terminal
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