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DESCRIPTION JP2008271283

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DESCRIPTION JP2008271283
An object of the present invention is to provide a phase modulation type oscillation detection
capable of stably performing oscillation and resonance and eliminating an increase factor of DC
resistance of a resonance circuit without strictly and finely adjusting a coupling relationship
between an oscillation coil and a resonance coil. Get a system condenser microphone. An
oscillation circuit (1) including an oscillation coil (12) and a crystal oscillator (3) and an
oscillation circuit (1) are coupled via a coupling means to be biased by a high frequency
generated by the oscillation circuit (1). And a demodulation circuit that demodulates an output
signal of the resonance circuit to an audio signal corresponding to a change in capacitance of the
condenser microphone unit, and the coupling means is a dielectric circuit. It is the capacitor |
condenser 14 comprised between the electrodes provided in front and back both surfaces of the
fixed electrode holding body which consists of bodies. [Selected figure] Figure 1
コンデンサーマイクロホン
[0001]
The present invention relates to an oscillation detection type condenser microphone, and in
particular, a condenser is used for coupling between an oscillation coil and a resonance coil, and
further, this condenser is characterized by using a unique structure of the condenser microphone
unit. It is said that.
[0002]
Since a microphone unit used for a condenser microphone has a high output impedance,
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generally, an impedance converter is connected, and the impedance is lowered to be output.
As another system capable of low impedance output without using an impedance converter,
there is a condenser microphone of an oscillation detection system. Although there is a problem
that the circuit configuration is complicated and the adjustment is difficult, the oscillation
detection type condenser microphone has a merit that the intrinsic noise is small, and it is
commercialized even now.
[0003]
There are a phase modulation type and an amplitude modulation type as the condenser
microphone of the oscillation detection method. The phase modulation type can use a crystal
oscillator as an oscillator, and has been used for a long time because the circuit configuration is
relatively simple. The amplitude modulation type uses a high frequency bridge and operates even
if the oscillation frequency moves slightly, but the circuit configuration is more complicated than
the phase modulation type, and the push-pull type microphone unit is preferable. There is.
[0004]
Since the condenser microphone according to the present invention is a phase modulation
oscillation detection method, an example of a conventional phase modulation oscillation
detection condenser microphone will be described in more detail below. In FIG. 5, reference
numeral 1 denotes an oscillation circuit, 4 denotes an oscillation coil, 10 denotes a ratio
detection circuit, and 6 denotes a resonance coil. The oscillating coil 4 comprises three coils L1,
L2 and L3 magnetically coupled to one another.
[0005]
The oscillation circuit 1 includes a transistor 2, a crystal unit 3, and the coil L1 (tank coil). A
capacitor C1 is connected in parallel to the coil L1, a power source PS is connected to one end of
the coil L1, and the other end of the coil L1 is connected to the collector of the transistor 2. A
resistor R1 is connected between the collector and the base of the transistor 2, a crystal unit 3 is
connected between the base and the ground, and a resistor R2 is connected in parallel with the
crystal unit 3. Capacitors C7 and C8 are also connected in series between the collector and base
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of transistor 2, the junction of capacitors C7 and C8 is connected to the emitter of transistor 2,
and the emitter is connected to ground through resistor R3. ing. The coils L2 and L3 are
connected in series and this connection point is connected to ground. The oscillation circuit 1
stabilizes the oscillation frequency by configuring an oscillation circuit including the crystal
oscillator 3.
[0006]
The resonant coil 6 comprises three coils L4, L5 and L6 magnetically coupled to one another.
The ratio detection circuit 10 is one of the demodulation methods for phase-modulated signals,
and is a circuit method for creating a phase difference by combining the coils L5 and L6 and a
capacitor and performing vector-like demodulation. The capacitor is formed between the
condenser microphone unit 5, more specifically, the diaphragm constituting the condenser
microphone unit, and the fixed electrode facing the diaphragm with a gap. It is a capacitor. The
coils L5 and L6 are connected in series, the other end of the coil L5 is connected to the
microphone output terminal OUT via the diode 7, and the other end of the coil L6 is connected to
the microphone output terminal OUT via the diode 8. The diodes 7 and 8 are in the opposite
direction to each other.
[0007]
The oscillation circuit 1 oscillates a high frequency of, for example, 8 MHz to 12 MHz, and one
end of the coil L2 and one end of the coil L4 are connected in order to supply the oscillated high
frequency to the resonant coil 6 from the oscillation coil 4 Are connected to the connection point
of the coils L5 and L6. The high frequency oscillated by the oscillation circuit 1 is supplied from
the coils L2 and L3 to the resonant coil 6. The electrostatic capacitance of the microphone unit 5
is connected in series to the coil L4 constituting the resonant coil 6. The capacitance of the
condenser microphone unit 5 is changed by vibrating according to the sound wave received by
the diaphragm. The capacitance of the microphone unit 5 and the inductance of the resonant coil
6 constitute a resonant circuit, to which a high frequency signal generated by the oscillator
circuit 1 is added as a bias. The high frequency is phase-modulated with the audio signal
electroacoustically converted by the microphone unit 5. The modulated signal is demodulated by
the ratio detection circuit 10 and output from the microphone output terminal OUT. The coil L4
constituting the resonance coil 6 resonates in series with the capacitance of the microphone unit
5, so the impedance at the resonance frequency becomes extremely low. If the impedance at the
resonance frequency is not lowered as described above, the sensitivity is lowered.
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[0008]
In the above-described example of the conventional phase modulation type oscillation detection
type condenser microphone, a high frequency is supplied from the coil L2 constituting the
oscillation coil 4 to the resonance coil 6. Therefore, if the coupling between the coil L2 and the
resonant coil 6 becomes too tight, the impedance lowered by series resonance becomes the load
of the oscillation circuit 1, so the oscillation tends to be unstable, and the oscillation stops when
it becomes overloaded. was there. When the coupling between the coil L2 and the resonant coil 6
is shallow, the load on the oscillation circuit 1 is small, but the signal output may be weak and no
sound may be produced. Therefore, the coil L2 constituting the oscillation coil 4 needs to finely
adjust the number of turns and the winding position with respect to the other oscillation coil, and
the adjustment is troublesome. Furthermore, the coil L2 is a part of the DC resistance of the
resonant circuit for the resonant coil L4, reduces the resonance acuity of the resonant circuit,
and causes a reduction in sensitivity.
[0009]
By the way, although the prior art similar to the technical idea of the present invention could not
be found, the invention described in Patent Document 1 is one that seems to be relatively close to
the present invention. The invention described in Patent Document 1 relates to a digital
microphone, and an oscillator for converting vibration of a vibrating plate that receives an
acoustic wave and vibrates to an oscillation frequency change, that is, an FM wave, and an FM
signal output from the oscillator as a digital audio signal. A difference between a reference value
of the same frequency as that at the time of no modulation of FM and the above-mentioned
counted value is calculated, a gate circuit which gates at a clock cycle of sampling frequency, a
pulse count section which counts the number of gated FM signals. And a digital signal is output
according to the period of the sampling frequency. Japanese Patent Application Laid-Open No. 723492
[0010]
The invention described in Patent Document 1 is similar to the configuration of the invention of
the present invention described later, insofar as it has an oscillator for converting the vibration of
the diaphragm to an FM wave, but the circuit configuration after conversion to an FM wave Also,
the signal processing is completely different, and the present invention does not have a circuit
configuration for outputting as a digital signal.
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[0011]
An object of the present invention is to solve the problems found in the conventional phase
modulation type oscillation detection condenser microphone as described with reference to FIG.
That is, oscillation and resonance can be stably performed without strictly and finely adjusting
the coupling relationship between the oscillation coil and the resonance coil, and problems such
as stop of oscillation and resonance and no sound can be solved. The purpose is to provide a
condenser microphone. Another object of the present invention is to provide a condenser
microphone capable of enhancing the sensitivity of the resonance circuit by increasing the
resonance sharpness of the resonance circuit by eliminating the factor that increases the direct
current resistance of the resonance circuit.
[0012]
According to the present invention, an oscillation circuit including an oscillation coil and a quartz
oscillator, and the oscillation circuit coupled with the oscillation circuit via the coupling means
and biased by a high frequency generated by the oscillation circuit, and the capacitance and
resonance of the condenser microphone unit A condenser microphone comprising: a resonance
circuit constituted by a coil; and a demodulation circuit for demodulating an output signal of the
resonance circuit into an audio signal corresponding to a change in capacitance of the condenser
microphone unit, the coupling means being The main feature of the present invention is that it is
a capacitor configured between electrodes provided on both the front and back sides of a fixed
electrode holder made of a dielectric.
[0013]
The coupling means between the oscillation circuit and the resonance circuit is a capacitor,
unlike the coupling between the coils of the oscillation circuit and the resonance circuit as in the
prior art, the degree of coupling is stable, and oscillation and resonance are stably performed. It
is possible to solve the problems such as stop of resonance and no sound.
Further, unlike the coupling of the coils of the oscillation circuit and the resonance circuit, an
increase factor of the direct current resistance of the resonance circuit can be eliminated,
whereby the resonance sharpness of the resonance circuit can be enhanced to enhance the
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sensitivity.
[0014]
The present invention also makes use of the structural features of the condenser microphone
unit to form a capacitor between the electrodes provided on the front and back sides of the fixed
electrode holder made of dielectric material, and this capacitor is used as a coupling means.
There is no need to separately provide a condenser as a means, and the condenser microphone
can be miniaturized.
[0015]
Hereinafter, embodiments of a condenser microphone according to the present invention will be
described with reference to FIGS. 1 to 4.
The same components as those of the conventional example shown in FIG. 5 are denoted by the
same reference numerals. In FIG. 1, reference numeral 1 denotes an oscillation circuit, 12
denotes an oscillation coil, 10 denotes a ratio detection circuit which is a demodulation circuit,
and 6 denotes a resonance coil. The oscillation coil 12 has two coils L1 and L3 magnetically
coupled to each other, and unlike the oscillation coil 4 in the conventional example shown in FIG.
5, the coil L2 is not provided.
[0016]
The oscillation circuit 1 includes a transistor 2, a crystal unit 3, and the coil L1 (tank coil). A
capacitor C1 is connected in parallel to the coil L1, a power source PS is connected to one end of
the coil L1, and the other end of the coil L1 is connected to the collector of the transistor 2. A
resistor R1 is connected between the collector and the base of the transistor 2, a crystal unit 3 is
connected between the base and the ground, and a resistor R2 is connected in parallel with the
crystal unit 3. Capacitors C7 and C8 are also connected in series between the collector and base
of transistor 2, the junction of capacitors C7 and C8 is connected to the emitter of transistor 2,
and the emitter is connected to ground through resistor R3. ing. The coils L2 and L3 are
connected in series and this connection point is connected to ground. The oscillation circuit 1
stabilizes the oscillation frequency by configuring an oscillation circuit including the crystal
oscillator 3.
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[0017]
The resonant coil 6 comprises three coils L4, L5 and L6 magnetically coupled to one another.
The ratio detection circuit 10 is one of the demodulation methods for phase-modulated signals,
and is a circuit method for creating a phase difference by combining the coils L5 and L6 and a
capacitor and performing vector-like demodulation. The capacitor is formed between the
condenser microphone unit 5, more specifically, the diaphragm constituting the condenser
microphone unit, and the fixed electrode facing the diaphragm with a gap. It is a capacitor. The
coils L5 and L6 are connected in series, the other end of the coil L5 is connected to the
microphone output terminal OUT via the diode 7, and the other end of the coil L6 is connected to
the microphone output terminal OUT via the diode 8. The diodes 7 and 8 are in the opposite
direction to each other.
[0018]
The oscillation circuit 1 oscillates, for example, a high frequency of about 8 MHz to 12 MHz, and
one end of the tank coil L1 is connected to one of the resonant coils 6 via the capacitor 14 in
order to supply the oscillated high frequency to the resonant coil 6 from the oscillating coil 4. It
is connected to the connection point between the coil L 4 and the microphone unit 5. Further,
one end of the coil L3 is connected to the connection point of the coils L5 and L6, and the other
end of the coil L3 is connected to the ground. The high frequency oscillated by the oscillation
circuit 1 is supplied to the resonance coil 6 through the capacitor 14. The electrostatic
capacitance of the microphone unit 5 is connected in series to the coil L4 constituting the
resonant coil 6. The capacitor microphone unit 5 vibrates in accordance with the sound wave
received by the diaphragm, thereby changing the capacitance and converting it into an electric
signal. The capacitance of the microphone unit 5 and the inductance of the resonant coil 6
constitute a resonant circuit, to which a high frequency signal generated by the oscillator circuit
1 is added as a bias. The high frequency is phase-modulated with the audio signal
electroacoustically converted by the microphone unit 5. The modulated signal is demodulated by
the ratio detection circuit 10 and output from the microphone output terminal OUT.
[0019]
The embodiment shown in FIG. 1 is characterized in that the coupling means between the
oscillation coil 12 and the resonance coil 6 is constituted by a capacitor 14, and this capacitor 14
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has the feature of the structure of the condenser microphone unit 5. Another feature is that it is
configured to take advantage of. Hereinafter, the configuration of the capacitor 14 will be
described with reference to FIGS. 2 to 4.
[0020]
As is well known, the condenser microphone unit includes a diaphragm and a fixed electrode
disposed opposite to the diaphragm with a gap. When the diaphragm receives a sound wave and
vibrates, the capacitance between the diaphragm and the fixed electrode changes and is output
as an electrical signal. The present invention forms a capacitor by forming electrodes on both the
front and back sides of the fixed electrode as a dielectric separately from the capacitor formed
between the diaphragm and the fixed electrode, and this capacitor is used as the coupling means.
The capacitor 14 is used.
[0021]
In FIGS. 3 and 4, reference numeral 51 denotes a diaphragm, 53 denotes a fixed electrode holder,
and 54 denotes a fixed electrode. The diaphragm 51 is, for example, one obtained by depositing a
conductive metal film such as gold on a synthetic resin film made of polyphenylene sulfide (PPS)
with a thickness of about 2 μm as a base. The diaphragm 51 is formed in a circular shape, and is
held by fixing its peripheral portion to the ring-shaped diaphragm holder 52. The diaphragm 51
is disposed so as to face the fixed electrode holder 53 with a ring-shaped spacer interposed in a
state where the diaphragm 51 is held by the diaphragm holder 52. The fixed electrode holder 53
is made of a dielectric and formed in a disk shape, and the fixed electrode 54 is formed over the
substantially entire surface on the side facing the diaphragm. A gap corresponding to the
thickness of the spacer is formed between the fixed electrode 54 and the diaphragm 51. The
diaphragm 51 can receive an acoustic wave and vibrate within the gap, and can output a change
in capacitance between the fixed electrode 54 and the diaphragm 51 as a sound signal. The audio
signal is output from a terminal 55 connected to the fixed electrode 54 and a terminal 58
connected to the diaphragm holder 52. The output terminals of the condenser microphone unit 5
shown in FIG.
[0022]
As shown in FIGS. 2 and 3, on the surface of the fixed electrode holder 53 opposite to the surface
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facing the diaphragm 51, a capacitor that functions as a capacitor of a condenser microphone
unit with the fixed electrode 54. The electrode which comprises another capacitor | condenser is
formed. Hereinafter, this other capacitor is referred to as a "second capacitor", and an electrode
formed on the opposite side to the surface on which the fixed electrode 54 is formed and
constituting the second capacitor together with the fixed electrode 54 is referred to as a second
electrode. Like the fixed electrode 54, the second electrode may be formed on substantially the
entire surface of the fixed electrode holder 5 to constitute one second capacitor, but in the
illustrated embodiment, the second electrode is divided into four. It is formed. The reference
numerals 61, 62, 63, and 64 respectively indicate second electrodes, and these second electrodes
face one fixed electrode 54 to constitute four second capacitors. In the illustrated example, one
surface of the fixed electrode holder 5 is divided into four along a cross line orthogonal to each
other, so as to form a symmetrical shape radially outward from the outer periphery of the fixed
electrode holder 5 Terminals 71, 72, 73, 74 electrically connected to the respective second
electrodes 61, 62, 63, 64 are formed in the projections formed in the above. In the illustrated
example, the second electrode is equally divided into four, but the number of second electrodes,
that is, the number of second capacitors is arbitrary, and a plurality of second capacitors are
formed. The areas of the plurality of second electrodes may be made different, and the
capacitances of the plurality of second capacitors may be made different.
[0023]
The second capacitor corresponds to the coupling capacitor 14 in the circuit example shown in
FIG. The optimum value of the capacitance of the capacitor 14 may differ depending on the
design of the circuit or due to variations in individual circuit constants. Therefore, the terminals
71, 72, 73, 74 connected to the second electrode are appropriately selected to The value of
capacitance can be set. In the illustrated embodiment, since the areas of the second electrodes
61, 62, 63, 64 are equal to each other and the capacitances are also equal, one or more of the
terminals 71, 72, 73, 74 are selected to The capacity will be set appropriately.
[0024]
In the case of an electret type condenser microphone unit, an electret layer is formed on the side
of the fixed electrode 54 facing the diaphragm 51.
[0025]
According to the embodiment described above, by taking advantage of the structural features of
the condenser microphone unit, the second capacitor is formed between the electrodes provided
on the front and back sides of the fixed electrode holder 53 made of dielectric material, and this
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second capacitor Since the capacitor 14 is used as the coupling means in the circuit example
shown in FIG. 1, it is not necessary to separately provide a capacitor as the coupling means, and
the condenser microphone can be miniaturized.
[0026]
It is a circuit diagram showing an example of a condenser microphone concerning the present
invention.
It is a front view which shows the example of the electrode pattern in the single side | surface
side of the fixed electrode holding body which comprises the condenser microphone unit in the
said Example.
It is a front view which shows the example of the electrode pattern in the other surface side of
the said fixed electrode holder. FIG. 6 is a side cross-sectional view showing the fixed electrode
holder and the diaphragm in an exploded state. It is a circuit diagram showing an example of a
conventional condenser microphone.
Explanation of sign
[0027]
DESCRIPTION OF SYMBOLS 1 oscillator circuit 2 transistor 3 crystal oscillator 5 condenser
microphone unit 6 resonant coil 10 demodulation circuit 12 oscillation coil 14 capacitor as a
coupling means 51 diaphragm 53 fixed electrode holder 54 fixed electrode 61, 62, 63, 64
second electrode
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