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DESCRIPTION JP2002271884

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DESCRIPTION JP2002271884
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
wireless microphone system, and more particularly, to a wireless transmission connecting a
microphone device for converting sound pressure change into an electric signal and a receiving
device installed at a distance from the microphone device. It relates to technology.
[0002]
2. Description of the Related Art A conventional wireless microphone system using radio wave
transmission transmits a microphone device that modulates and transmits an acoustic signal
obtained from collected sound and receives and demodulates a radio wave transmitted from the
microphone device. And a receiving unit for extracting an acoustic signal.
[0003]
The microphone device is, for example, a microphone unit that detects a sound wave and
converts it into an electrical signal (acoustic signal), such as a condenser type microphone unit
whose capacitance changes in response to sound pressure, Electronic circuit as a transmission
circuit that modulates and amplifies the sound signal, an antenna that radiates a transmission
signal supplied from the electronic circuit as a radio wave, and a battery as a power supply that
supplies driving power to the microphone unit and the transmission circuit. The
[0004]
SUMMARY OF THE INVENTION The present inventors have found the following problems as a
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result of examining the prior art.
[0005]
In recent years, the usage applications have been expanded along with the performance
improvement of wireless microphone systems, and in particular, professional wireless
microphone systems used in broadcasting etc. have microphone devices used at all positions
within a relatively wide venue. Even in the case where the person moves, good transmission and
reception of radio waves has been demanded in order to enable sound collection with the same
quality as that of the wired microphone.
For this purpose, it is necessary to secure a long transmission distance, and it is necessary to
increase the transmission output of the microphone device.
However, when the transmission output of the microphone device is increased, the power
consumption increases accordingly, and a battery with a large power capacity is required to
supply sufficient power.
As a result, the volume of the battery increases and the weight thereof also increases, and there
is a problem that the microphone device also becomes heavy and large.
[0006]
In addition, in order to prevent interruption during the broadcast or recording of a program, a
long-time continuous operation is required particularly in a professional wireless microphone
system, and the microphone device is also mounted to achieve this request. The battery required
power capacity, ie a large battery.
[0007]
On the other hand, in the conventional microphone device, there is a demand for further
improvement of mobility which is one of its features.
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As a means to improve mobility, it has been necessary to reduce the weight and size of the
microphone device. On the other hand, with the rapid progress of microfabrication technology in
recent years, miniaturization of microphone units and transmission circuits has been rapidly
achieved.
[0008]
Also in the battery, the size and capacity of the battery have been developed to meet the demand
for power capacity and miniaturization due to improvement of electrode material etc. However,
as mentioned above, the power consumption in the microphone device is increased. Therefore,
the reduction in size of the battery is delayed compared to the reduction in size of the
microphone unit and the electronic circuit, making it difficult to further reduce the size of the
microphone device.
[0009]
Furthermore, the size of the antenna is determined according to the transmission frequency,
which makes it difficult to miniaturize the microphone device.
[0010]
An object of the present invention is to provide a technology capable of miniaturizing a
microphone device of a wireless microphone system.
[0011]
Another object of the present invention is to provide a technology capable of reducing the weight
of a microphone device of a wireless microphone system.
[0012]
The above and other objects and novel features of the present invention will become apparent
from the description of the present specification and the accompanying drawings.
[0013]
Among the inventions disclosed in the present application, the outline of typical ones will be
briefly described as follows.
[0014]
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(1) An LC circuit comprising a capacitor whose capacity changes in response to a change in
sound pressure, and a coil connected in parallel to the capacitor, the LC circuit comprising the
radio wave received from the coil by the LC circuit It absorbs radio waves of a frequency
corresponding to the resonance frequency.
[0015]
(2) A radiation means for radiating a radio wave having a predetermined bandwidth, a
discrimination means for receiving a radio wave radiated from the radiation means, and
discriminating the center frequency of the attenuation region from the received radio wave, and
discrimination by the discrimination means And means for reading out the change in the center
frequency as frequency modulation.
[0016]
(3) In a wireless microphone system in which a signal wirelessly transmitted from a microphone
device that converts a sound pressure change into an electrical signal is demodulated by a
receiving device, the microphone device includes a capacitor whose capacity changes in response
to the sound pressure change. The receiving device includes an LC circuit, and the emitting unit
generates an electric wave and radiates toward the microphone device, the electric wave passing
through the microphone device or the resonance absorbed by the LC circuit from the electric
wave reflected by the microphone device A demodulation means is provided for discriminating a
frequency and demodulating an electrical signal corresponding to a change in capacitance of the
capacitor from a change in the discriminated resonant frequency.
[0017]
(4) In the wireless microphone system according to (3) described above, the LC circuit receives a
radio wave emitted from the radiation means by a coil formed in a spiral shape.
[0018]
(5) In the wireless microphone system according to (4) described above, the capacitor and the
coil are formed on the same substrate.
[0019]
(6) In the wireless microphone system according to any one of (3) to (5) described above, the
capacitor uses part or all of the capacitance of the capacitor type microphone unit.
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[0020]
(7) In the wireless microphone system according to any one of (3) to (6) described above, the
demodulation means demodulates the change of the discriminated resonant frequency as an FM
modulation, and changes the capacitance of the capacitor Read out.
[0021]
According to the above-described means, the microphone device is configured to have an LC
circuit, so when the radio wave including the resonance frequency of the LC circuit is emitted
from the radiation means of the receiving device toward the microphone device, the microphone
device The radio wave that has passed through or the radio wave reflected by the microphone
device is such that spectral components in the vicinity of the resonance frequency are attenuated.
At this time, since the LC circuit includes a capacitor whose capacity changes in response to the
change in sound pressure, the resonance frequency changes in response to the change in sound
pressure.
[0022]
On the other hand, the demodulation means of the receiving apparatus discriminates the
resonance frequency absorbed by the LC circuit from the radio wave passing through the
microphone apparatus or the radio wave reflected by the microphone apparatus, and changes in
the discriminated resonance frequency Since the electric signal corresponding to the capacity
change is demodulated, the power supply of the microphone device is not required, and as a
result, the microphone device can be made compact and lightweight.
[0023]
In addition, by forming the coil of the LC circuit in a spiral shape, the reception area of the radio
wave radiated from the radiation means can be enlarged, so that the radio wave reception
performance of the microphone device can be improved.
As a result, it is possible to improve the accuracy of discrimination of the resonance frequency in
the demodulation means of the receiving apparatus, so it is possible to improve the S / N of the
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wireless microphone system.
[0024]
In addition, since the capacitor and the coil are formed on the same substrate, the LC circuit can
be formed using a micromachine processing technique which is a semiconductor manufacturing
technique, so that the microphone device can be made smaller and lighter.
[0025]
Furthermore, by using a part or all of the capacity of the capacitor type microphone unit as the
capacitor, the size of the coil for receiving the radio wave radiated from the radiation means can
be set arbitrarily, so LC It is possible to easily improve the reception performance of the circuit.
As a result, it is possible to improve the accuracy of discrimination of the resonance frequency in
the demodulation means of the receiving apparatus, so it is possible to improve the S / N of the
wireless microphone system.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in
detail with reference to the drawings together with embodiments (examples) of the invention.
[0027]
Note that components having the same function are denoted by the same reference symbols
throughout the drawings for describing the embodiments of the present invention, and the
repetitive description thereof will be omitted.
[0028]
FIG. 1 is a view for explaining a schematic configuration of a microphone device according to an
embodiment of the present invention.
In particular, FIG. 1A is a perspective view of the microphone device, and one side surface shows
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a cross-sectional structure.
Moreover, (b) of FIG. 1 is a cross-sectional view taken along the line A-A 'shown in (a) of FIG.
[0029]
As is clear from FIGS. 1A and 1B, in the microphone device of the present embodiment, the
substrate 6 is disposed so as to close the opening of the case 4 in which the upper surface is
open. There is.
Further, a leakage hole 25 is provided on the bottom surface facing the upper surface of the case
4 so that the vibration electrode 1 is not deformed due to the pressure difference between the
inside and the outside of the case.
[0030]
Further, the substrate 6 is provided with a hole of a predetermined size, and the vibrating
electrode 1 is disposed at the opening of the hole.
Around this opening portion, a rectangular ridge-shaped coil 5 which is a spiral flat curve along
the opening shape of the hole is formed.
One end of the coil 5 is connected to the vibrating electrode 1 via the first connection wiring 3a,
and the other end is connected to the back electrode 2 via the second connection wiring 3b.
Particularly, in the present embodiment, in order to connect back electrode 2 and the other end
of coil 5, a hole penetrating from the surface of substrate 6 to spacer 23 is formed, and second
connection wiring 3b is provided in this hole. It is done.
The shapes of the holes and the coils 5 formed in the substrate 6 are not limited to rectangles,
and it is needless to say that curved shapes such as circles and polygons such as triangles and
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pentagons may be used.
In addition, the coil 5 is not limited to a planar shape, and may be formed in, for example, a spiral
having the same length from the central axis to the outer periphery or a gradually changing
length from the central axis to the outer periphery Needless to say.
[0031]
The back electrode 2 is formed on the back surface side of the substrate 6, that is, inside the
container formed by the substrate 6 and the case 4, and in particular, a spacer 23 for
maintaining the distance to the vibrating electrode 1 at a predetermined distance. It is configured
to be fixed to the substrate 6 via the same.
With such a configuration, the vibrating electrode 1 and the back electrode 2 form a capacitor.
[0032]
Therefore, in the present embodiment, the coil 5 is connected in parallel to the capacitor formed
by the vibrating electrode 1 and the back electrode 2 to form an LC circuit (LC resonant circuit).
However, in the present embodiment, even if the vibration electrode 1 vibrates with the
application of the sound pressure, the hole 24 is formed in the back electrode 2 in order to
prevent the vibration from being transmitted to the back electrode 2 as much as possible. A
plurality of are provided.
That is, the capacitance change of the capacitor formed by the vibrating electrode 1 and the back
electrode 2 is performed only by the vibration of the vibrating electrode 1 and by preventing the
change of the capacitance of the capacitor due to the vibration of the back electrode 2, sound
collection performance and sound collection It prevents deterioration of the characteristics.
[0033]
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Further, since the structure described above can be manufactured using a micromachine
processing technology which is a well-known semiconductor manufacturing technology, the
microphone apparatus of the present embodiment can be miniaturized by using this
micromachine processing technology. And it can be made lightweight.
In addition, since it can be manufactured in large quantities by micromachining technology, the
manufacturing cost can be significantly reduced.
[0034]
FIG. 2 is a view for explaining a schematic configuration of a coil according to the present
embodiment.
[0035]
As apparent from FIG. 2, in the present embodiment, radio waves radiated from the transmission
unit described later are formed by forming the coil 5 in the form of a rectangular ridge, which is
a spiral flat curve along the opening shape of the hole. It is configured to improve the sensitivity
to
That is, in the present embodiment, the coil 5 has a function as a coil constituting an LC resonant
circuit and a function as an antenna for receiving radio waves radiated from the transmitting
unit.
[0036]
In addition, the coil 5 of the present embodiment is a coil whose outer peripheral shape formed
of a metal material is square and the number of turns is five.
For example, the number of turns is N, the thickness of the pattern forming the coil 5 is t
centimeters [cm], the volume resistivity of this pattern is ρ ohm centimeters [Ω · cm], the width
of the coil 5 or the outermost periphery When the width is A1, the width of the innermost
circumference is A2, the distance from the innermost pattern position to the outermost pattern
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position is D, and the pattern width is W, the inductance L [μH] of the coil 5 and Equivalent
resistance r [Ω] means “K. Inui, M. Kominami, H. Kusaka,“ Simulation and Design of LC
Resonant Circuit Security Tags ”, IEICE Trans.
Fund.,Vol. E78-A, no. 10, pp. 1412-1414 (1995) ", it is known to be calculated by the
following equation (1).
[0037]
L = 1.2 · (39/1000) · (A 2 · N 2 / (8 A + 11 D)) [μ H] r = / / (t · W) · 8 A · N [Ω] (1) where A = It is
(A1 + A2) / 4 [mm].
[0038]
On the other hand, when the capacitance of the microphone device 20 is C microfarad [μF] and
the equivalent series resistance of the entire LC resonant circuit is r ohm [Ω] to simplify the
explanation, “Negishi,“ Basic radio knowledge ”, sincerity As described in Bundo Shinko, pp.
83-95 (1953), the resonance frequency f0 megahertz [MHz] of the LC resonant circuit and its
selectivity Q are determined by the following equation (2) Are known.
[0039]
f0 = 1 / (2π (L · C) 1/2) [MHz] Q = (1 / r) · (L / C) 1/2 (2) The capacitance C of the capacitor type
IC microphone is Depending on its design, for example, according to "GM Sessler," NEW
ACOUSTIC SENSORS ", Proc. 15th International Congresson Acoustics, pp. 253-260 (1995), it is
several picofarads [pF]. .
[0040]
Therefore, for example, when the capacitance C of the capacitor type IC microphone is 2.5 pF
and aluminum (ρ = 2.2 × 10 −6 Ω · cm) is used for the electrode pattern forming the coil 5, A1
= 8. 32 [mm], A2 = 2.32 [mm], W = 0.1 [mm], D = 3.0 [mm], coil number of turns N = 4 where t =
0.01 [cm] The resonance frequency f0 and the selectivity Q of the LC resonant circuit formed by
the coil 5 and the capacitor are f0 = 322.2 [MHz] according to the above formulas (1) and (2). Q
becomes 1055.
[0041]
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That is, the resonance frequency f0 can be set with high selectivity in the specific low power
wireless microphone frequency band of the C standard.
The resonance frequency f0 and the selectivity Q can be largely changed by changing each size
of the coil 5, or by designing a microphone device or connecting a plurality of LC resonance
circuits in parallel, etc. Absent.
[0042]
As described above, in the microphone device according to the present embodiment, the
microphone device includes the capacitor for realizing a desired capacitance by the vibrating
electrode 1 and the back electrode 2 and the coil 5 connected in parallel to the capacitor. It has
become.
[0043]
Next, FIG. 3 illustrates a schematic configuration of a wireless microphone system using the
microphone device of the present embodiment.
[0044]
In FIG. 3, 1 is a vibrating electrode, 2 is a back electrode, 5 is a coil, 7 is a sound pressure
waveform, 8 is a transmitting antenna, 9 is a receiving antenna, 10 is an oscillation transmitting
unit, 11 is a high frequency amplification unit, 12 is amplitude control 13, 13 is a resonance
frequency discriminator, 14 is an audio signal demodulator, 15 is a transmission spectrum, 16 is
a reception spectrum, 17 is an amplitude controlled reception spectrum, 18 is a fluctuation
signal, 19 is an audio signal waveform, and 20 is a microphone device , 21 denotes a transmitter,
and 22 denotes a receiver.
[0045]
As apparent from FIG. 3, in the wireless microphone system of the present embodiment, a
microphone device 20 having an LC resonant circuit, a transmitter 21 for emitting radio waves
toward the microphone device 20, and radiation from the transmitter 21 And a receiving unit 22
for receiving radio waves of which a part of the spectrum is absorbed by the microphone device
20 and converting a change in sound pressure captured by the microphone device 20 into an
audio signal.
[0046]
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As described above, the microphone device 20 has one end connected to the capacitor (C) formed
of the vibrating electrode 1 and the back electrode 2 and the vibrating electrode 1 serving as one
electrode of the capacitor, and the other of the capacitors An LC resonance circuit is formed by
the coil (L) 5 whose other end is connected to the back electrode 2 which is the electrode of
At this time, in the microphone device 20 of the present embodiment, since the vibrating
electrode 1 is formed to vibrate according to the sound pressure, the distance between the
vibrating electrode 1 and the back electrode 2 is changed by this vibration, The capacitance C
between the vibrating electrode 1 and the back electrode 2 is changed.
As a result, the resonance frequency f0 of the LC resonance circuit consisting of the vibrating
electrode 1 and the back electrode 2 constituting the microphone device 20 and the coil 5
changes according to the sound pressure.
[0047]
The transmission unit 21 generates a transmission signal having a frequency spectrum that
spreads in the vicinity of the resonance frequency f0 of the transmission antenna 8 that radiates
radio waves toward the microphone device 20 and the LC resonance circuit of the microphone
device 20, and feeds the transmission signal to the transmission antenna 8 The transmission unit
10 is configured.
Even if the resonant frequency f0 changes due to the vibration of the vibrating electrode 1 that
constitutes the LC resonant circuit, the oscillation transmitting unit 10, for example, as shown in
FIG. 3 causes the changed resonant frequency f0 to fall within the band of the transmission
signal. As shown in the middle transmission spectrum 15, the transmission spectrum has a
predetermined bandwidth, and a transmission signal whose output is within the predetermined
range in the frequency range is generated.
[0048]
However, as a method of generating a transmission signal having such a predetermined
bandwidth, for example, a method of sweeping a single frequency within a predetermined band
sufficiently fast, or a combination of a frequency multiplying circuit and a resonant circuit In the
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prior art, it is possible to use known techniques such as a method of transmitting on a large
number of frequencies and artificially broadening the bandwidth.
[0049]
The oscillation transmitter unit 10 is the same as the conventional one except that the frequency
spectrum (transmission spectrum) of the transmission signal has a predetermined frequency
width and the output is within the predetermined range in the frequency range. Detailed
description will be omitted.
[0050]
The receiving unit 22 includes a well-known receiving antenna 9 for receiving radio waves of
which a part of the spectrum is absorbed by the LC resonance circuit of the microphone device
20, and a known high frequency amplifying unit 11 for amplifying the radio waves received by
the receiving antenna 9. And an amplitude control unit 12 for controlling the amplitude of the
reception signal so that the spectrum level of the reception signal amplified by the high
frequency amplification unit 11 becomes constant, and an LC resonance circuit of the
microphone device 20 from the reception signal whose amplitude is controlled. And a voice
signal demodulation unit 14 that demodulates the voice signal by regarding the fluctuation of the
resonance frequency f0 as the FM modulation.
In the present embodiment, a case will be described in which the transmission unit 21 and the
reception unit 22 configured integrally form a reception apparatus, but the transmission unit 21
and the reception unit 22 forming the reception apparatus are separately configured. In this case,
the degree of freedom of each installation place can be increased.
Further, even if any of the radio wave that has passed through the microphone device 20 or the
radio wave reflected by the microphone device 20 is received by the receiving antenna 9, it goes
without saying that the audio signal waveform can be read out by the receiving unit 22. Absent.
[0051]
Next, the sound collecting operation by the wireless microphone system of the present
embodiment will be described based on FIG.
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However, in the following description, although the case where one microphone device 20 is
provided will be described, it goes without saying that two or more microphone devices may be
provided.
[0052]
First, the oscillation transmission unit 10 of the transmission unit 21 radiates a radio wave
having a transmission spectrum 15 spreading in the vicinity of the resonance frequency f 0 of
the microphone device 20 from the transmission antenna 8 toward the microphone device 20.
The radio wave radiated from the transmission antenna 8 is absorbed by the LC resonance circuit
of the microphone device 20 at a portion of the resonance frequency f0 as described above.
[0053]
At this time, as shown in the equation (2) described above, in the microphone device 20 of the
present embodiment, the distance between the vibrating electrode 1 and the back electrode 2 is
changed by the sound pressure applied to the vibrating electrode 1. Because of this, the
capacitance of the capacitor C constituted by the vibrating electrode 1 and the back electrode 2
also changes.
Therefore, in the present embodiment, the resonance frequency f0 changes in accordance with
the sound pressure applied to the vibrating electrode 1, and the absorption frequency of the
radio wave emitted from the transmission antenna 8 also changes.
At this time, assuming that the change of the resonance frequency f0 caused by the sound
pressure is Δf0, Δf0 is expressed by the following equation (3).
[0054]
Here, ΔC represents a change in capacitance of the capacitor C caused by the sound pressure, s
represents a distance between the vibrating electrode 1 and the back electrode 2, and Δs
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represents a change in distance between the vibrating electrode 1 and the back electrode 2.
[0055]
The radio wave in which the portion of the resonance frequency f 0 of the microphone device 20
is absorbed is received by the receiving antenna 9 of the receiving unit 22.
As shown in the reception spectrum 16 of FIG. 3, the component of the resonant frequency f0 of
the microphone device 20 is attenuated, and the received radio wave becomes a spectrum having
a dip at the resonant frequency f0. The received signal having a dip at the resonance frequency
f0 of the microphone device 20 is input from the receiving antenna 9 to the high frequency
amplification unit 11, and only the high frequency component is amplified by the high frequency
amplification unit 11.
[0056]
The reception signal output from the high frequency amplification unit 11 is input to the
amplitude control unit 12, and amplitude control is performed so that the spectrum level
becomes constant as shown in the reception spectrum 17 whose amplitude is controlled. The
reception signal output from the amplitude control unit 12 is input to the resonance frequency
discrimination unit 13, and the fluctuation signal 18 of the resonance frequency f0 of the
microphone device 20 is discriminated from the dip of the amplitude controlled reception
spectrum 17.
[0057]
The fluctuation signal output from the resonance frequency discrimination unit 13 is input to the
audio signal demodulation unit 14, and as shown in the audio signal waveform 19, the electric
corresponding to the capacitance change of the capacitor composed of the vibrating electrode 1
and the back electrode 2 It is converted to a signal. In particular, in the present embodiment,
since the resonance frequency f0 of the LC resonance circuit of the microphone device 20
fluctuates according to the sound pressure applied to the vibrating electrode 1, the fluctuation of
the resonance frequency f0 is regarded as FM modulation to be an audio signal The demodulator
14 is configured to obtain an audio signal waveform 19.
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[0058]
As described above, in the wireless microphone system according to the present embodiment, the
fluctuation signal 18 is obtained by discrimination of the resonant frequency f0 of the LC
resonant circuit. Therefore, the absorption of the resonant frequency in the LC resonant circuit,
the receiving antenna 8 It is possible to demodulate an audio signal without being influenced by
the level (reception level) of the radio wave received by.
[0059]
Further, in the wireless microphone system of the present embodiment, the variation signal 18 is
obtained by discrimination of the resonance frequency f0 of the LC resonance circuit, so that one
reception consisting of the pair of transmission unit 21 and reception unit 22 is performed. The
device makes it possible to demodulate an audio signal collected by microphone devices 20 of
different resonance frequencies.
It goes without saying that two or more transmitting units 21 may be used, or two or more
receiving units 22 may be used.
[0060]
As described above, in the wireless microphone system of the present embodiment, the
microphone device 20 is provided with an LC resonance circuit in which the resonance
frequency f0 changes according to the sound pressure, and the microphone unit 20 emits
radiation toward the microphone device 20 from the transmission unit 21. A radio wave is
received by the receiver 22. At this time, the center frequency of the dip of the received signal is
discriminated by the resonance frequency discriminator 13, and the voice signal demodulator 14
demodulates the fluctuation of the discriminated center frequency as the modulation of the
resonance frequency f0 of the microphone device 20. Then, since the audio signal waveform 19
is obtained, the power supply of the microphone device 20 becomes unnecessary, and the
microphone device 20 can be miniaturized. As a result, the weight of the conventional
microphone device 20 can be reduced.
[0061]
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Further, in the wireless microphone system according to the present embodiment, the distance
between the microphone device 20 and the transmitting unit 21 and the receiving unit 22 is
variable according to the intensity of the radio wave emitted from the transmitting unit 21. Since
the receiver 22 can use a commercial power source or the like, the distance between the
microphone device 20 and the transmitter 21 and the receiver 22 can be extended without
increasing the size of the microphone device 20.
[0062]
In the microphone device according to the present embodiment, only the capacitance formed by
the vibrating electrode 1 and the back electrode 2 is used as a capacitor of the LC resonance
circuit, but the present invention is not limited to this. , A combined capacitance in which one or
more capacitors formed in different regions, one or more chip capacitors, etc., and the
capacitance formed by the vibrating electrode 1 and the back electrode 2 are connected in series
or in parallel to each other. It goes without saying that it is good as well.
Furthermore, although only the coil 5 is used as the inductance of the LC resonant circuit, the
present invention is not limited to this. For example, one or more coils formed in another region,
one or more chip coils, etc. It goes without saying that a combined inductance in which 5 and 5
are connected in series or in parallel may be used as the inductance of the LC circuit. When the
LC circuit is configured in this manner, the size of the coil 5 for receiving radio waves can be set
arbitrarily, so that it is possible to easily improve the reception performance of the LC circuit. As
a result, since it is possible to improve the discrimination accuracy of the resonance frequency f0
in the resonance frequency discrimination unit 13, it is possible to obtain the special effect that
the S / N of the whole wireless microphone system can be improved.
[0063]
Further, in the microphone device of the present embodiment, the change of the capacitance
formed by the vibrating electrode 1 and the back electrode 2 is detected by the change of the
resonance frequency f0 of the LC resonant circuit, but the invention is limited thereto For
example, as shown in FIG. 4, the inductance of the coil 5 of the LC resonance circuit of the
microphone device may be changed according to the sound pressure. However, FIG. 4A is a
perspective view of the microphone device, and one side surface shows a cross-sectional
structure. 4B is a cross-sectional view taken along the line B-B 'shown in FIG. 4A.
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[0064]
In the microphone device 20 shown in (a) and (b) of FIG. 4, the coil 5 is formed on the upper
surface of the vibrating electrode 1, and the magnetic body 26 is disposed in the vicinity of the
coil 5. A capacitor 27 is connected to the coil 5 to form an LC resonant circuit. In the microphone
device 20 configured in this manner, the inductance of the coil 5 changes due to the
displacement of the vibrating electrode 1, and therefore, the pressure changes according to the
sound pressure as in the above-described microphone device 20 that detects the change in
capacitance. The displacement of the vibrating electrode 1 can be detected as a change in the
resonant frequency f0 of the LC resonant circuit. As a result, it is possible to obtain the same
effect as the microphone device 20 that detects the change in capacitance described above.
[0065]
As mentioned above, although the invention made by the present inventor was concretely
explained based on the embodiment of the above-mentioned invention, the present invention is
not limited to the embodiment of the above-mentioned invention, The range which does not
deviate from the gist Of course, various modifications are possible.
[0066]
The effects obtained by the typical ones of the inventions disclosed in the present application will
be briefly described as follows.
[0067]
(1) Since a power supply of the microphone device is not required, management of a battery or
the like is unnecessary, and long-term operation is possible.
[0068]
(2) Since the power supply of the microphone device is not required, the microphone device can
be miniaturized and reduced in weight.
[0069]
(3) The transmitting unit and the receiving unit can use a commercial power supply or the like,
so the distance between the microphone device and the transmitting unit and the receiving unit
can be increased without increasing the size of the microphone device. .
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[0070]
(4) By forming the capacitor and the coil on the same substrate, the LC circuit can be formed
using the micromachine processing technology which is a semiconductor manufacturing
technology, so the microphone device can be made smaller and lighter.
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