JP5331489B2 - Condenser microphone - Google Patents

Description

  The present invention relates to a condenser microphone, and more particularly to a technique for obtaining a polarization voltage of a condenser microphone by a photovoltaic effect of a PLZT element.

  The condenser microphone includes an electrostatic acoustoelectric transducer (also referred to as a condenser microphone capsule) in which a diaphragm and a fixed pole are arranged to face each other via an electrically insulating spacer ring as a sound collection unit. .

  The diaphragm is stretched on the diaphragm support ring with a predetermined tension, the fixed pole is supported by an insulating seat, and is disposed oppositely through an insulating spacer to form a kind of capacitor. When the diaphragm vibrates with the incoming sound wave, the capacitance is changed, and the change is output as an audio signal.

  Therefore, when driving a condenser microphone, it is usually necessary to apply a polarization voltage to the acoustoelectric converter.

  In the case of an electret condenser microphone having an electret dielectric film, the electret dielectric film is semi-permanently charged, so there is no need to apply a polarization voltage from the outside.

  However, in the electret condenser microphone, since it is difficult to uniformly charge the electret dielectric film by corona discharge or the like, and to maintain the polarization voltage constant, the sensitivity tends to vary.

  Therefore, for example, a condenser microphone that places importance on sound quality for studio sound collection applications, etc. has a polarization power supply unit, and a predetermined polarization voltage is applied from the polarization power supply unit to the fixed pole of the acoustoelectric converter to achieve high sensitivity. Like to get.

  As one method for obtaining the polarization voltage, there is a method using a voltage of, for example, 48 V supplied from a phantom power supply (see, for example, Patent Document 1). According to this method, a high polarization voltage can be obtained by reducing the current consumed in 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 cannot be increased very much.

  As another method, there is a method using 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 to alternating current using an oscillation circuit, boosting it with a transformer, and then rectifying.

  However, the oscillation frequency output from the oscillation circuit may be superimposed on the microphone output, which may cause noise. In addition, when an inductor is used in the oscillation circuit, an induced magnetic field is generated, and noise may be induced in other electronic devices by magnetic coupling.

JP 2005-287000 A JP 09-121533 A

  Therefore, the subject of the present invention is high in a part of a voltage fed from a phantom power source or the like without using a booster circuit such as a DC-DC converter in a condenser microphone that requires a polarization voltage for an acoustoelectric converter. The purpose is to obtain a polarization voltage.

In order to solve the above-described problems, the present invention provides an electrostatic acoustoelectric converter including a diaphragm and a fixed pole disposed opposite to each other, and a polarization power supply unit to which a predetermined voltage is supplied from a phantom power supply. have a, in Turkey capacitor microphone given polarization voltage with respect to the fixed electrode of the acoustoelectric transducer from the polarization power supply unit, as the polarization power supply unit, via a predetermined resistance element to the fixed pole A part of a voltage supplied from the phantom power source to the drive circuit, comprising: a connected PLZT element; an ultraviolet light-emitting diode optically coupled to the PLZT element; and a drive circuit for driving the ultraviolet light-emitting diode. A switched-capacitor converter that operates as a step-down converter that converts voltage into a predetermined voltage, and the ultraviolet light-emitting diode is output at the output current of the switched-capacitor converter. To drive the de-irradiated with ultraviolet rays of a predetermined wavelength to the PLZT elements from the ultraviolet light emitting diode, by generating a voltage by the photovoltaic effect to the PLZT element, as characterized by obtaining a polarization voltage with respect to the fixed pole Yes.

  According to the present invention, a polarization power source for an acoustoelectric converter, a PLZT element connected to a fixed pole via a predetermined resistance element, an ultraviolet light-emitting diode optically coupled to the PLZT element, and an ultraviolet light emission A drive circuit for driving the diode, and irradiating the PLZT element with ultraviolet light of a predetermined wavelength from the ultraviolet light emitting diode, and generating a voltage by the photovoltaic effect on the PLZT element to obtain a polarization voltage with respect to the fixed pole Thus, a high polarization voltage can be obtained from a part of the voltage supplied from a phantom power source or the like without using a booster circuit such as a DC-DC converter.

1 is a circuit diagram showing a condenser microphone according to an embodiment of the present invention.

  Next, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram showing a condenser microphone according to an embodiment of the present invention. The condenser microphone according to this embodiment operates with a phantom power source. The phantom power source itself includes two resistors of 6.8 kΩ connected in series between the hot and cold of the balanced transmission, and their resistance. Since it is a known device having a DC 48V power source connected between the connection point of the resistor and the ground, the illustration thereof is omitted.

  As shown in FIG. 1, this condenser microphone includes an acoustoelectric converter (condenser) as a sound collecting unit in which a diaphragm 10a and a fixed pole 10b are arranged to face each other via an electrically insulating spacer ring (not shown). (Microphone capsule) 10.

  The diaphragm 10a is stretched on a diaphragm support ring (not shown) with a predetermined tension, and the fixed pole 10b is supported by an insulating seat and is disposed so as to face the spacer ring. A capacitor is formed, and the diaphragm is vibrated by the incoming sound wave, thereby changing the electrostatic capacitance and outputting the change as an audio signal.

  The diaphragm 10a is connected to the microphone case (ground 11) through the diaphragm support ring, and the fixed pole 10b is connected to the gate of an FET (field effect transistor) 40 as an impedance converter.

  The microphone output unit 50 is provided with a terminal H connected to the hot side of the phantom power source, a terminal C connected to the cold side, and a terminal G connected to the ground side.

  The hot side terminal H is connected to the drain of the FET 40 through the constant current 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 a hot-side terminal H and a cold-side terminal C via an output transformer TRS.

  The condenser microphone includes a polarization power supply unit 30 that applies a polarization voltage to the fixed electrode 10b. The polarization power supply unit 30 includes a PLZT element 31, an ultraviolet light emitting diode 32 that irradiates the PLZT element 31 with ultraviolet light, and a drive circuit 33 that drives the ultraviolet light emitting diode 32.

  The PLZT element 31 is made of lead lanthanum zirconate titanate that is sintered by adding lanthanum oxide (La2O3) to a solid solution of lead titanate (PbTiO3) and lead zirconate (PbZrO3), and irradiates ultraviolet rays having a wavelength of about 365 nm. Then, a very high voltage (generated voltage per electrode distance is 3.3 kV / cm) is generated by the photovoltaic effect.

  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 with a wavelength of about 365 nm is used. Voltage Max4V).

  In this embodiment, the drive circuit 33 includes a switched capacitor type voltage converter IC (hereinafter sometimes simply referred to as “converter IC”). In this example, three converters IC01, IC02, and IC03 are connected in series in three stages, and LM2665 manufactured by US National SEMICONDUCTOR is used for each of them.

  This LM2665 converter IC has six pins from No. 1 to No. 6, and when a positive voltage is input from the No. 1 pin, a double voltage 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 5th pin, it operates as a 1 / 2-fold step-down type in which a 1 / 2-fold voltage is output from the 1st pin.

  In this embodiment, the converter IC01, IC02, IC03 is used as a ½ step-down type, so that a positive voltage is input from the 5th pin, and an output voltage that is ½ the output voltage is obtained from the 1st pin. Yes.

  Pin 2 is a ground pin, pin 4 is a shutdown control pin, and charge pump capacitors C01, C02 and C03 are connected between pins 3 and 6, respectively. In order to be a step-down type, the positive side of the capacitor is connected to the third pin. When operating as a double boost type, the negative side of the capacitor is connected to the third pin. Also, smoothing and AC grounding capacitors C010, C20, and C30 are connected to each of the first pins on the output side.

  The drive circuit 33 includes an input circuit 33a composed 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 hot side terminal H and the cold side terminal C via the constant current diodes D02 and D03.

  In this example, the input voltage to the drive circuit 33 is set to 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. The capacitor C40 connected in parallel with the Zener diode D01 is a smoothing capacitor.

  As a result, the voltage is stepped down from 16V → 8V → 4V in the order of the first stage converter IC03, the second stage converter IC02, and the third stage converter IC01, while the current is 5 mA → 10 mA → 20 mA. The drive 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 in the third stage.

  As a result, ultraviolet light (ultraviolet light) having a wavelength of 365 nm is irradiated 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 the photovoltaic effect, and the high voltage is fixed pole. 10b is applied as a polarization voltage.

  As described above, according to the present invention, the ultraviolet light emitting diode 32 irradiates the PLZT element 31 with ultraviolet light having a specific wavelength that exerts the photovoltaic effect, and the polarization voltage for the fixed electrode 10b is obtained from the PLZT element 31. As a result, a higher polarization voltage can be applied to the fixed pole without using a transforming means such as a DC-DC converter including an oscillation circuit that becomes a noise source, and the sensitivity of the condenser microphone is increased accordingly. Is possible.

10 Electrostatic acoustoelectric transducer (condenser microphone capsule)
10a Diaphragm 10b Fixed pole 11 Ground (microphone case)
30 Polarizing Power Supply Unit 31 PLZT Element 32 Ultraviolet Light Emitting Diode 33 Drive Circuit 40 Impedance Converter (FET)
50 Microphone output section 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

Claims (1)

Possess the acoustoelectric transducer of the electrostatic type and a counter arranged vibration plate and the fixed electrode, and a polarization power supply unit to which a predetermined voltage is supplied from the phantom power, the more the polarization power supply unit in Turkey capacitor microphone given polarization voltage relative to the fixed pole of the acousto-electric transducer,
As the polarized power supply section, a PLZT element connected to the fixed pole via a predetermined resistance element, an ultraviolet light emitting diode optically coupled to the PLZT element, and a drive circuit for driving the ultraviolet light emitting diode With
A switched capacitor type converter that operates as a step-down type that converts a part of a voltage supplied from the phantom power source into a predetermined voltage is used for the drive circuit, and the ultraviolet light is output by the output current of the switched capacitor type converter. A light emitting diode is driven to irradiate the PLZT element with ultraviolet light having a predetermined wavelength from the ultraviolet light emitting diode, and a voltage is generated in the PLZT element by a photovoltaic effect to obtain a polarization voltage with respect to the fixed electrode. Capacitor microphone.

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