JP2008271283A - Condenser microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a condenser microphone of a phase modulated oscillation detecting system, which stably generates oscillation and resonance without strictly nor delicately adjusting coupling relation between an oscillation coil and a resonance coil to eliminate a factor of increase in DC resistance of a resonance circuit. <P>SOLUTION: The condenser microphone has: an oscillation circuit 1 having an oscillation coil 12 and a crystal vibrator 3; a resonance circuit which is coupled to the oscillation circuit 1 via a coupling means to be biased at a high frequency generated by the oscillation circuit 1, and is composed of the electrostatic capacitance of a condenser microphone unit 5 and a resonance coil 6; and a demodulation circuit 10 which demodulates the output signal of the resonance circuit into an audio signal corresponding to variation in electrostatic capacitance of the condenser microphone unit 5, wherein the coupling means is a capacitor 14 constituted between electrodes provided on both the top and reverse surfaces of a fixed electrode holder made of a dielectric. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an oscillation detection type condenser microphone. In particular, the present invention is characterized in that a condenser is used for coupling an oscillation coil and a resonance coil, and further, this condenser is configured using a unique structure of a condenser microphone unit. It is what.

  Since the microphone unit used for the condenser microphone has a high output impedance, an impedance converter is generally connected to output the microphone unit with a low impedance. There is an oscillation detection type condenser microphone as another method capable of outputting a low impedance without using an impedance converter. Oscillation detection type condenser microphones have the problem that the circuit configuration is complicated and difficult to adjust, but are still commercialized because they have the advantage of low inherent noise.

  Oscillation detection type condenser microphones include a phase modulation type and an amplitude modulation type. The phase modulation type can use a crystal resonator as an oscillator and has been used for a long time because of its relatively simple circuit configuration. The amplitude modulation type uses a high-frequency bridge and operates even if the oscillation frequency moves slightly, but the circuit configuration is more complex than the phase modulation type, and the push-pull type microphone unit is preferred. There is.

  Since the condenser microphone according to the present invention is a phase modulation type oscillation detection system, an example of a conventional phase modulation type oscillation detection system condenser microphone will be described in more detail below. In FIG. 5, reference numeral 1 is an oscillation circuit, 4 is an oscillation coil, 10 is a ratio detection circuit, and 6 is a resonance coil. The oscillation coil 4 includes three coils L1, L2, and L3 that are magnetically coupled to each other.

  The oscillation circuit 1 includes a transistor 2, a crystal resonator 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 R 1 is connected between the collector and base of the transistor 2, a crystal resonator 3 is connected between the base and ground, and a resistor R 2 is connected in parallel with the crystal resonator 3. Capacitors C7 and C8 are also connected in series between the collector and base of the transistor 2, the connection point of the capacitors C7 and C8 is connected to the emitter of the transistor 2, and the emitter is connected to the ground via the resistor R3. ing. The coils L2 and L3 are connected in series, and this connection point is connected to the ground. The oscillation circuit 1 stabilizes the oscillation frequency by configuring an oscillation circuit including the crystal resonator 3.

  The resonance coil 6 includes three coils L4, L5, and L6 that are magnetically coupled to each other. The ratio detection circuit 10 is one of demodulation methods for phase-modulated signals, and is a circuit method for generating a phase difference by coupling coils L5 and L6 and a capacitor and demodulating in a vector manner. The condenser is formed between a condenser microphone unit 5, more specifically, a diaphragm constituting the condenser microphone unit and a fixed electrode facing the diaphragm with a gap. It is a condenser. 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 opposite to each other.

  The oscillation circuit 1 oscillates a high frequency of about 8 MHz to 12 MHz, for example, and in order to supply the oscillated high frequency from the oscillation coil 4 to the resonance coil 6, one end of the coil L2 and one end of the coil L4 are connected, and one end of the coil L3 is connected. Is 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 resonance coil 6. The capacitance of the microphone unit 5 is connected in series to the coil L4 constituting the resonance coil 6. The condenser microphone unit 5 vibrates in accordance with the sound wave received by the diaphragm, so that the capacitance changes. A resonance circuit is constituted by the capacitance of the microphone unit 5 and the inductance of the resonance coil 6, and a high frequency signal generated by the oscillation circuit 1 is added to the resonance circuit as a bias. The high frequency is phase-modulated by an audio signal that has been electroacoustic converted by the microphone unit 5. This modulation signal is demodulated by the ratio detection circuit 10 and output from the microphone output terminal OUT. Since the coil L4 constituting the resonance coil 6 resonates in series with the capacitance of the microphone unit 5, the impedance at the resonance frequency becomes extremely low. Thus, unless the impedance at the resonance frequency is lowered, the sensitivity is lowered.

  In the example of the conventional phase modulation type oscillation detection system condenser microphone, a high frequency is supplied from the coil L 2 constituting the oscillation coil 4 to the resonance coil 6. For this reason, if the coupling between the coil L2 and the resonance coil 6 becomes too dense, the impedance reduced by the series resonance becomes a load of the oscillation circuit 1, so that the oscillation is likely to be unstable, and the oscillation stops when it becomes overloaded. was there. When the coupling between the coil L2 and the resonance coil 6 is shallow, the load on the oscillation circuit 1 is reduced, but the signal output may be weak and no sound may be produced. Accordingly, the coil L2 constituting the oscillation coil 4 needs to be finely adjusted in the number of windings and the winding position with respect to other oscillation coils, and the adjustment is troublesome. Further, the coil L2 becomes a part of the direct current resistance of the resonance circuit for the resonance coil L4, reducing the resonance sharpness of the resonance circuit and causing a decrease in sensitivity.

By the way, although a prior art similar to the technical idea of the present invention could not be found, there is an invention described in Patent Document 1 that seems to be relatively close to the present invention. The invention described in Patent Document 1 relates to a digital microphone. An oscillator that converts vibrations of a diaphragm that receives and vibrates a sound wave into an oscillation frequency change, that is, an FM wave, and an FM signal that is output from the oscillator are converted into digital audio signals. A gate circuit that gates at a sampling frequency clock period, a pulse count unit that counts the number of gated FM signals, and a difference between the reference value and the counted value at the same frequency as when FM is not modulated. And an arithmetic unit, which outputs digital data according to a sampling frequency period.
Japanese Patent Laid-Open No. 7-23492

  The invention described in Patent Document 1 has the same configuration as that of the present invention described later as long as it includes an oscillator that converts vibrations of the diaphragm into FM waves, but the circuit configuration after conversion to FM waves In addition, the signal processing is completely different, and the present invention does not include a circuit configuration for outputting as a digital signal.

An object of the present invention is to eliminate the problems found in the conventional phase modulation type oscillation detection type condenser microphone as described with reference to FIG. In other words, even if the coupling relationship between the oscillation coil and the resonance coil is not strictly and delicately adjusted, the oscillation and resonance can be performed stably, and the problems such as oscillation and resonance stop and no sound can be solved. An object is to provide a condenser microphone.
Another object of the present invention is to provide a condenser microphone that can increase the sensitivity of the resonance circuit by increasing the resonance sharpness of the resonance circuit by eliminating the increase factor of the DC resistance of the resonance circuit.

  The present invention relates to an oscillation circuit including an oscillation coil and a crystal resonator, and is coupled to the oscillation circuit via a coupling means and biased at a high frequency generated by the oscillation circuit, and also to electrostatic capacitance and resonance of the condenser microphone unit. A condenser microphone comprising: a resonance circuit configured by a coil; and a demodulation circuit that demodulates an audio signal corresponding to a change in capacitance of the capacitor microphone unit from an output signal of the resonance circuit, wherein the coupling means The most important feature is that the capacitor is composed of electrodes provided on both the front and back surfaces of a fixed electrode holder made of a dielectric.

  Since the coupling means between the oscillation circuit and the resonance circuit is a capacitor, unlike the conventional coupling between the coils of the oscillation circuit and the resonance circuit, the degree of coupling is stable, and oscillation and resonance are performed stably. In addition, problems such as resonance stoppage and no sound can be solved. Further, unlike the coupling between the coils of the oscillation circuit and the resonance circuit, it is possible to eliminate the cause of increasing the DC resistance of the resonance circuit, thereby increasing the resonance sharpness of the resonance circuit and enhancing the sensitivity.

  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 surfaces of the fixed electrode holder made of a dielectric, and this capacitor is used as a coupling means. It is not necessary to separately provide a condenser as a means, and the condenser microphone can be reduced in size.

Hereinafter, an embodiment of a condenser microphone according to the present invention will be described with reference to FIGS. In addition, the same code | symbol is attached | subjected to the same component as the structure of the prior art example shown in FIG.
In FIG. 1, reference numeral 1 is an oscillation circuit, 12 is an oscillation coil, 10 is a ratio detection circuit which is a demodulation circuit, and 6 is a resonance coil. The oscillation coil 12 includes two coils L1 and L3 that are magnetically coupled to each other. Unlike the oscillation coil 4 in the conventional example shown in FIG. 5, the oscillation coil 12 does not include the coil L2.

  The oscillation circuit 1 includes a transistor 2, a crystal resonator 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 R 1 is connected between the collector and base of the transistor 2, a crystal resonator 3 is connected between the base and ground, and a resistor R 2 is connected in parallel with the crystal resonator 3. Capacitors C7 and C8 are also connected in series between the collector and base of the transistor 2, the connection point of the capacitors C7 and C8 is connected to the emitter of the transistor 2, and the emitter is connected to the ground via the resistor R3. ing. The coils L2 and L3 are connected in series, and this connection point is connected to the ground. The oscillation circuit 1 stabilizes the oscillation frequency by configuring an oscillation circuit including the crystal resonator 3.

  The resonance coil 6 includes three coils L4, L5, and L6 that are magnetically coupled to each other. The ratio detection circuit 10 is one of demodulation methods for phase-modulated signals, and is a circuit method for generating a phase difference by coupling coils L5 and L6 and a capacitor and demodulating in a vector manner. The condenser is formed between a condenser microphone unit 5, more specifically, a diaphragm constituting the condenser microphone unit and a fixed electrode facing the diaphragm with a gap. It is a condenser. 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 opposite to each other.

  The oscillation circuit 1 oscillates a high frequency of about 8 MHz to 12 MHz, for example, and supplies one of the resonance coils 6 via the capacitor 14 to one end of the tank coil L1 in order to supply the oscillated high frequency from the oscillation coil 4 to the resonance coil 6. A connection point between the coil L4 and the microphone unit 5 is connected. One end of the coil L3 is connected to a connection point between 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 capacitance of the microphone unit 5 is connected in series to the coil L4 constituting the resonance coil 6. The condenser microphone unit 5 vibrates according to the sound wave received by the diaphragm, so that the capacitance changes and is converted into an electric signal. A resonance circuit is constituted by the capacitance of the microphone unit 5 and the inductance of the resonance coil 6, and a high frequency signal generated by the oscillation circuit 1 is added to the resonance circuit as a bias. The high frequency is phase-modulated by an audio signal that has been electroacoustic converted by the microphone unit 5. This modulation signal is demodulated by the ratio detection circuit 10 and output from the microphone output terminal OUT.

  The embodiment shown in FIG. 1 is characterized in that the coupling means of the oscillation coil 12 and the resonance coil 6 is constituted by a capacitor 14. This capacitor 14 is characterized by the structure of the condenser microphone unit 5. Another feature is that it is constructed by utilizing it. Hereinafter, the configuration of the capacitor 14 will be described with reference to FIGS. 2 to 4.

  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 vibration plate receives a sound wave and vibrates, the capacitance between the vibration plate and the fixed electrode changes and is output as an electric signal. In the present invention, apart from the capacitor formed between the diaphragm and the fixed electrode, a capacitor is formed by forming electrodes on both the front and back surfaces of the fixed electrode as a dielectric, and this capacitor is used as the coupling means. The capacitor 14 is used.

  3 and 4, reference numeral 51 denotes a diaphragm, 53 denotes a fixed electrode holder, and 54 denotes a fixed electrode. As the diaphragm 51, for example, a synthetic resin film made of polyphenylene sulfite (PPS) having a thickness of about 2 μm is used as a base, and a conductive metal film such as gold is deposited thereon. The diaphragm 51 is formed in a circular shape, and the periphery thereof is held by being fixed to a ring-shaped diaphragm holder 52. The diaphragm 51 is disposed in a state of being held by the diaphragm holder 52 and facing the fixed electrode holder 53 with a ring-shaped spacer interposed therebetween. The fixed electrode holder 53 is made of a dielectric material and is formed in a disk shape, and a fixed electrode 54 is formed over substantially the entire surface on the side facing the diaphragm. A gap corresponding to the thickness of the spacer is generated between the fixed electrode 54 and the diaphragm 51. The diaphragm 51 can receive a sound wave and vibrate in the gap, and can output a change in electrostatic capacitance between the fixed electrode 54 and the diaphragm 51 due to the vibration as an audio signal. This 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.

  As shown in FIGS. 2 and 3, a condenser that functions as a condenser of a condenser microphone unit between the fixed electrode holder 53 and the fixed electrode 54 on the surface opposite to the face facing the diaphragm 51. An electrode constituting another capacitor is formed. Hereinafter, this other capacitor is referred to as a “second capacitor”, and an electrode that is formed on the side opposite to the surface on which the fixed electrode 54 is formed and constitutes the second capacitor together with the fixed electrode 54 is referred to as a second electrode. Similarly to 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. However, in the illustrated embodiment, the second electrode is divided into four parts. Is formed. Reference numerals 61, 62, 63, and 64 denote second electrodes, respectively. These second electrodes face one fixed electrode 54 to constitute four second capacitors. In the illustrated example, one side of the fixed electrode holder 5 is divided into four along a cross-shaped line that is orthogonal to each other so as to be symmetrical from the outer periphery of the fixed electrode holder 5 radially outward. Terminals 71, 72, 73, and 74 that are electrically connected to the second electrodes 61, 62, 63, and 64 are formed on the protrusions formed on the surface. In the illustrated example, the second electrode is divided into four equal parts, but the number of the second electrodes, that is, the number of the second capacitors is arbitrary, and a plurality of second capacitors are formed. The capacitances of the plurality of second capacitors may be varied by varying the areas of the plurality of second electrodes.

  The second capacitor corresponds to the coupling capacitor 14 in the circuit example shown in FIG. The optimum capacitance of the capacitor 14 may vary depending on the circuit design or due to variations in individual circuit constants. Therefore, the terminals 71, 72, 73, 74 connected to the second electrode are appropriately selected to be static. The capacitance value can be set. In the illustrated embodiment, the areas of the second electrodes 61, 62, 63, and 64 are equal to each other and the capacitance is also equal. Therefore, one or a plurality of the terminals 71, 72, 73, and 74 are selected and electrostatically selected. The capacity is set appropriately.

  In the case of an electret type condenser microphone unit, an electret layer is formed on the surface of the fixed electrode 54 facing the diaphragm 51.

  According to the embodiment described above, the second condenser is formed between the electrodes provided on both the front and back surfaces of the fixed electrode holder 53 made of a dielectric, taking advantage of the constitutional features of the condenser microphone unit. 1 is used as the condenser 14 as the coupling means in the circuit example shown in FIG. 1, it is not necessary to separately provide a condenser as the coupling means, and the condenser microphone can be miniaturized.

It is a circuit diagram which shows the Example of the condenser microphone which concerns on this 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 holding body. It is side surface sectional drawing shown in the state which decomposed | disassembled the part of the said fixed electrode holder and a diaphragm. It is a circuit diagram which shows the example of the conventional condenser microphone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Oscillation circuit 2 Transistor 3 Crystal oscillator 5 Condenser microphone unit 6 Resonance coil 10 Demodulation circuit 12 Oscillation coil 14 Capacitor as coupling means 51 Diaphragm 53 Fixed electrode holder 54 Fixed electrodes 61, 62, 63, 64 Second electrode

Claims (6)

An oscillation circuit including an oscillation coil and a crystal unit;
A resonance circuit coupled with the oscillation circuit via a coupling means and biased at a high frequency generated by the oscillation circuit and configured by a capacitance of a condenser microphone unit and a resonance coil;
A demodulator circuit that demodulates an audio signal corresponding to a change in capacitance of the condenser microphone unit from the output signal of the resonance circuit, and a condenser microphone comprising:
The condenser microphone is characterized in that the coupling means is a condenser configured between electrodes provided on the front and back surfaces of a fixed electrode holder made of a dielectric.   The electrode on at least one side of the front and back electrodes of the fixed electrode holder is divided into a plurality of parts, and by selecting the divided electrodes, it is possible to change the capacitance of a capacitor as a coupling means Item 10. The condenser microphone according to Item 1.   The condenser microphone according to claim 2, wherein the divided electrodes have the same area.   3. The condenser microphone according to claim 2, wherein the plurality of divided electrodes are formed on a surface of the fixed electrode holder opposite to the surface facing the diaphragm.   2. The capacitor according to claim 1, wherein the electrode on the surface opposite to the diaphragm among the electrodes on the front and back surfaces of the fixed electrode holder constitutes a capacitor together with the diaphragm, and the capacitance of the capacitor is changed by vibration of the diaphragm. Microphone.   2. The condenser microphone according to claim 1, wherein the demodulation circuit is a ratio detection circuit.

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