JP2008035310A - Electret condenser microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent sensitivity deterioration due to heat during reflow processing even when a condenser microphone provided with an IC chip is configured as an electret condenser microphone. <P>SOLUTION: The IC chip 14 includes an impedance converting circuit 42 for performing impedance conversion of a change in electrostatic capacitance of a condenser structure part 12, a reference value storage circuit 44 for storing the reference value of a potential difference of the condenser structure part 12 in advance, a potential difference detecting circuit 46 for detecting the potential difference of the condenser structure part 12, and a gain adjusting circuit 48 for adjusting gain of the impedance converting circuit 42 in accordance with a difference between the potential difference detected by the potential difference detecting circuit 46 and the reference value. Even through the potential difference of the condenser structure part 12 drops in accordance with electric charge missing by the heat during the reflow processing, execution of the gain adjustment prevents the sensitivity of the electret condenser microphone 10 from deteriorating. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electret condenser microphone provided with an IC chip.

  In general, a capacitor microphone has a capacitor structure portion in which a vibrating membrane and a back electrode plate are arranged to face each other as described in, for example, “Patent Document 1” and “Patent Document 2”. A change in the capacitance of the structural portion is converted into an electrical impedance by an impedance conversion element.

  At that time, the condenser microphone described in the above-mentioned “Patent Document 1” is configured as an electret condenser microphone, and the condenser structure portion is a back formed by forming an electret layer on the surface of the back electrode plate on the vibration film side. It is configured as an electret type capacitor structure.

  On the other hand, the capacitor microphone described in the above-mentioned “Patent Document 2” has a configuration in which an impedance conversion element is incorporated in an IC chip as an impedance conversion circuit, and a predetermined potential difference is applied to the capacitor structure by the IC chip. It has become.

JP 2006-41575 A JP 2006-157837 A

  The electret condenser microphone as described in the above "Patent Document 1" can be manufactured at low cost, but the reflow process is performed on the electret condenser microphone for surface mounting on an external substrate. In this case, the electret layer charges are removed to some extent due to the heat of 200 ° C. or more applied during the reflow process, so that the potential difference of the capacitor structure becomes smaller than the expected value, and thus the electret condenser microphone There is a problem that the sensitivity is reduced.

  On the other hand, the condenser microphone described in the above-mentioned “Patent Document 2” does not have an electret layer. Therefore, even if reflow processing is performed, sensitivity reduction due to charge loss of the electret layer does not occur. When such a configuration is adopted, it is necessary to always apply a predetermined potential difference to the capacitor structure.

  The present invention has been made in view of such circumstances, and even when a condenser microphone having an IC chip is configured as an electret condenser microphone, the sensitivity is reduced due to heat applied during the reflow process. An object of the present invention is to provide an electret condenser microphone capable of preventing the occurrence of such a problem.

  The present invention is intended to achieve the above object by devising the circuit configuration of the IC chip.

That is, the electret condenser microphone according to the first invention of the present application is:
In an electret condenser microphone comprising: a capacitor structure portion in which a vibration film and a back electrode plate are arranged to face each other; and an impedance conversion element that converts the capacitance of the capacitor structure portion into an electric impedance.
The impedance conversion element is incorporated in the IC chip as an impedance conversion circuit,
The IC chip stores in advance a reference value storage circuit that stores a reference value of a potential difference of the capacitor structure, a potential difference detection circuit that detects a potential difference of the capacitor structure, and a potential difference detected by the potential difference detection circuit. And a gain adjustment circuit that adjusts the gain of the impedance conversion circuit in accordance with a difference from the reference value.

The electret condenser microphone according to the second invention of the present application is
In an electret condenser microphone comprising: a capacitor structure portion in which a vibration film and a back electrode plate are arranged to face each other; and an impedance conversion element that converts the capacitance of the capacitor structure portion into an electric impedance.
The impedance conversion element is incorporated in the IC chip as an impedance conversion circuit,
A calibration waveform input circuit in which the IC chip inputs a calibration waveform signal to the capacitor structure section at a predetermined timing, and an output from the impedance conversion circuit when the calibration waveform signal is input to the capacitor structure section. A target voltage storage circuit that stores a target voltage to be performed in advance; an output voltage detection circuit that detects a voltage output from the impedance conversion circuit by inputting the calibration waveform signal; and a detection by the output voltage detection circuit And a gain adjustment circuit for adjusting the gain of the impedance conversion circuit in accordance with a difference between the measured voltage and the target voltage.

  The “capacitor structure” may be a back electret type capacitor structure formed by forming an electret layer on the surface of the back electrode plate on the vibration film side, or a foil formed by forming an electret layer on the vibration film. It may be an electret type capacitor structure.

  The specific configuration of the “electret condenser microphone” other than the capacitor structure and the IC chip is not particularly limited.

  As shown in the above configuration, in the electret condenser microphone according to the first invention of the present application, the impedance conversion element for converting the capacitance of the capacitor structure portion into electrical impedance is incorporated in the IC chip as an impedance conversion circuit. The IC chip includes a reference value storage circuit that stores a reference value of a potential difference of the capacitor structure portion in advance, a potential difference detection circuit that detects a potential difference of the capacitor structure portion, and the potential difference detection circuit. Since the gain adjustment circuit for adjusting the gain of the impedance conversion circuit according to the difference between the potential difference detected by the above and the reference value is provided, the following operational effects can be obtained.

  That is, when the reflow process is performed on the electret condenser microphone, the electric charge of the electret layer is released to some extent due to the heat of 200 ° C. or more applied during the reflow process, and the potential difference of the capacitor structure portion is expected. In the IC chip, the impedance adjustment is performed by the gain adjustment circuit according to the difference between the potential difference of the capacitor structure detected by the potential difference detection circuit and the reference value stored in the reference value storage circuit. Since the gain of the conversion circuit is adjusted, the impedance change of the capacitance of the capacitor structure can be accurately converted in the impedance conversion circuit, which may cause a decrease in sensitivity of the electret condenser microphone. Can be prevented.

  In addition, as shown in the above configuration, the electret condenser microphone according to the second invention of the present application has an impedance conversion element for converting the capacitance of the capacitor structure portion into an electrical impedance, and the IC chip as an impedance conversion circuit. Although this IC chip has a built-in configuration, this IC chip has a calibration waveform input circuit that inputs a calibration waveform signal to the capacitor structure portion at a predetermined timing, and when this calibration waveform signal is input to the capacitor structure portion. A target voltage storage circuit that stores in advance a target voltage to be output from the impedance conversion circuit, an output voltage detection circuit that detects a voltage output from the impedance conversion circuit by inputting the calibration waveform signal, and Depending on the difference between the voltage detected by the output voltage detection circuit and the target voltage, Since a gain adjustment circuit for adjusting the gain of the impedance converter, it is possible to obtain the following effects.

  That is, when the reflow process is performed on the electret condenser microphone, the electric charge of the electret layer is released to some extent due to the heat of 200 ° C. or more applied during the reflow process, and the potential difference of the capacitor structure portion is expected. In the IC chip, when the calibration waveform signal is input from the calibration waveform input circuit to the capacitor structure portion, the voltage output from the impedance conversion circuit by the calibration waveform signal Since the gain adjustment circuit adjusts the gain of the impedance conversion circuit according to the difference from the target voltage stored in advance in the target voltage storage circuit, the impedance conversion circuit accurately changes the capacitance of the capacitor structure. The electrical impedance can be converted. From desensitization to preparative let condenser microphone occurs can be prevented.

  Thus, according to the present invention, even when a condenser microphone including an IC chip is configured as an electret condenser microphone, it is possible to prevent a reduction in sensitivity from occurring due to heat applied during the reflow process. it can. By configuring as an electret condenser microphone in this way, it is possible to eliminate the need to always apply a predetermined potential difference to the capacitor structure.

  Moreover, since the electret condenser microphone according to the present invention is designed so that the gain of the impedance conversion circuit is adjusted in the IC chip, not only is the sensitivity lowered due to the heat applied during the reflow process, but also at the time of manufacture. Occurrence of a decrease in sensitivity due to variations in stiffness of the vibration film and changes with time after the start of use can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, a first embodiment of the present invention will be described.

  FIG. 1 is a side sectional view showing the electret condenser microphone 10 according to the present embodiment arranged in an upward direction, and FIG. 2 is a view taken in the direction of the arrow II in FIG.

  As shown in these drawings, the electret condenser microphone 10 according to the present embodiment is a small microphone having a rectangular outer shape of about 3 × 4 mm in plan view, and includes a capacitor structure portion 12, an IC chip 14, and the like. , The contact spring 16, the base substrate 18, the side substrate 20, and the cover substrate 22. The electret condenser microphone 10 is surface-mounted on an external substrate (not shown) on the lower surface of the base substrate 18.

  The capacitor structure 12 includes a diaphragm subassembly 32 and a back electrode plate 34.

  The vibrating membrane subassembly 32 has a vibrating membrane 32A stretched and fixed on the upper surface of a metal support ring 32B formed in a rectangular ring shape, and the vibrating membrane 32A is a polymer having a metal vapor deposition film formed on the upper surface. Consists of film.

  The back electrode plate 34 includes a metal electrode plate main body 34A and an electret layer 34B heat-sealed to the upper surface of the electrode plate main body 34A, and the electret layer 34B is given a predetermined surface potential by polarization treatment. Has been. The outer diameter of the back electrode plate 34 is set to a value slightly larger than the inner diameter of the support ring 32B.

  In this capacitor structure portion 12, the diaphragm 32A of the diaphragm subassembly 32 and the electret layer 34B of the back electrode plate 34 are spaced at a predetermined minute distance via the support ring 32B of the diaphragm subassembly 32. Thus, a predetermined potential difference is generated between the vibrating membrane 32A and the electret layer 34B.

  The base substrate 18 includes an insulating substrate 18A, conductive layers 18B1, 18B2, and 18B3 formed on the lower surface of the insulating substrate 18A, and the conductive layers 18B1, 18B2, and 18B3 exposed at the four corners. The insulating layer 18C covers the lower surface in a cross shape, conductive layers 18D1 and 18D2 formed on the upper surface of the insulating substrate 18A, and a conductive layer (not shown). The IC chip 14 is mounted on the base substrate 18 at the center of the upper surface.

  At that time, the conductive layer 18B1 constitutes a power supply terminal, the conductive layer 18B2 constitutes an output terminal, and the conductive layers 18B3 and 18B4 constitute a ground terminal. The conductive layer 18B1 is electrically connected to a conductive layer (not shown) formed on the upper surface of the insulating substrate 18A through a through hole (not shown), and is electrically connected to the power supply terminal 14a of the IC chip 14 in this conductive layer. The conductive layer 18B2 is electrically connected to a conductive layer (not shown) formed on the upper surface of the insulating substrate 18A through a through hole (not shown), and is electrically connected to the output terminal 14b of the IC chip 14 in this conductive layer. Further, the conductive layer 18B3 is electrically connected to a conductive layer (not shown) formed on the upper surface of the insulating substrate 18A through a through hole (not shown), and is electrically connected to the ground terminal 14c of the IC chip 14 in this conductive layer.

  The side substrate 20 is placed and fixed on the base substrate 18 so as to surround the IC chip 14.

  The side substrate 20 includes an insulating substrate 20A formed in a rectangular ring shape having an inner diameter slightly larger than that of the back electrode plate 34, and conductive layers 20B and 20C formed on the lower surface and the upper surface of the insulating substrate 20A, respectively. Yes. At this time, the conductive layers 20B and 20C are electrically connected to each other through a through hole (not shown).

  The cover substrate 22 has an insulating substrate 22A having the same outer shape as the base substrate 18 in plan view, a conductive layer 22B formed in a rectangular ring shape on the lower surface of the insulating substrate 22A, and a substantially entire surface on the upper surface of the insulating substrate 22A. The conductive layer 22 </ b> C is formed, and is placed and fixed on the side substrate 20 via the vibration film subassembly 32.

  At this time, in the cover substrate 22, the conductive layers 22 </ b> B and 22 </ b> C are electrically connected to each other through a through hole (not shown), whereby the metal vapor deposition film of the vibration film 32 </ b> A is located on the upper surface of the cover substrate 22. The conductive layer 22B is electrically connected to the ground terminal of the external substrate.

  A sound hole 22 a penetrating the cover substrate 22 in the vertical direction is formed at a position slightly deviated from the center of the cover substrate 22.

  The contact spring 16 is formed with a pair of projecting pieces projecting in parallel with each other at each corner portion of the frame portion formed in a square shape in plan view, and each pair of projecting pieces at two locations on the frame portion. In addition, it is composed of a metal leaf spring formed so as to be bent downward. The contact spring 16 is disposed in a state where the contact spring 16 is bent to some extent so as to surround the IC chip 14 in the frame portion. At this time, the contact spring 16 contacts the lower surface of the electrode plate body 34A of the back electrode plate 34 at the frame portion, and contacts the four conductive layers 18D1 of the insulating substrate 18A at the four protruding pieces. Yes. The electrode plate body 34A of the back electrode plate 34 and the input terminal 14d of the IC chip 14 are electrically connected via the contact spring 16 and the conductive layer 18D1.

  FIG. 3 is a block diagram showing a circuit configuration of the electret condenser microphone 10 according to the present embodiment, together with an external circuit to which the electret condenser microphone 10 is connected.

  As shown in the figure, the IC chip 14 of the electret condenser microphone 10 has an impedance conversion circuit 42 for converting the capacitance of the capacitor structure 12 into an electrical impedance, and a reference value for the potential difference of the capacitor structure 12 in advance. The stored reference value storage circuit 44, the potential difference detection circuit 46 for detecting the potential difference of the capacitor structure 12, and the impedance conversion circuit according to the difference between the potential difference detected by the potential difference detection circuit 46 and the reference value And a gain adjustment circuit 48 for performing gain adjustment of 42.

  Next, the effect of the electret condenser microphone 10 according to the present embodiment will be described.

  When the electret condenser microphone 10 according to the present embodiment is surface-mounted on an external substrate, a reflow process is performed on the electret condenser microphone 10, but due to the heat of 200 ° C. or more applied during the reflow process, Since the electric charge of the electret layer 34B of the back electrode plate 34 is removed to some extent, the potential difference of the capacitor structure 12 becomes smaller than an expected value.

  However, in the IC chip 14 of the electret condenser microphone 10 according to the present embodiment, the difference between the potential difference of the capacitor structure 12 detected by the potential difference detection circuit 46 and the reference value stored in advance in the reference value storage circuit 44 is detected. Accordingly, the gain adjustment of the impedance conversion circuit 42 is performed by the gain adjustment circuit 48, so that the change in the capacitance of the capacitor structure portion 12 can be converted into an electrical impedance with high accuracy by the impedance conversion circuit 42. It is possible to prevent the sensitivity of the microphone 10 from being lowered.

  In addition, by adjusting the gain of the impedance conversion circuit 42 in the IC chip 14 as described above, not only the sensitivity is reduced due to heat applied during the reflow process, but also the stiffness variation of the vibration film 32A at the time of manufacture is reduced. Occurrence of a decrease in sensitivity due to a change with time after the start of use can also be prevented.

  Next, a second embodiment of the present invention will be described.

  FIG. 4 is a view similar to FIG. 3 showing the electret condenser microphone 110 according to the present embodiment.

  As shown in the figure, the electret condenser microphone 110 according to the present embodiment has the same basic configuration as the electret condenser microphone 10 according to the first embodiment, but the circuit configuration of the IC chip 114 is the same. This is different from the case of the first embodiment.

  That is, the IC chip 114 of this embodiment includes an impedance conversion circuit 42 that converts the capacitance of the capacitor structure 12 into an electrical impedance, and a calibration waveform that inputs a calibration waveform signal to the capacitor structure 12 at a predetermined timing. An input circuit 52, a target voltage storage circuit 54 that stores in advance a target voltage to be output from the impedance conversion circuit 42 when the calibration waveform signal 52 is input to the capacitor structure 12, and the calibration An output voltage detection circuit 56 that detects a voltage output from the impedance conversion circuit 42 in response to the input of the waveform signal, and an impedance conversion circuit 42 according to the difference between the voltage detected by the output voltage detection circuit 56 and the target voltage. And a gain adjustment circuit 48 for performing the gain adjustment.

  At that time, the timing at which the calibration waveform signal is input from the calibration waveform input circuit 52 to the capacitor structure unit 12 can be set to a timing immediately after the start of power supply to the electret condenser microphone 10, for example.

  In the IC chip 114 of the electret condenser microphone 110 according to the present embodiment, when a calibration waveform signal is input from the calibration waveform input circuit 52 to the capacitor structure unit 12, an output from the impedance conversion circuit 42 is generated by the calibration waveform signal. The gain adjustment circuit 48 adjusts the gain of the impedance conversion circuit 42 in accordance with the difference between the voltage to be stored and the target voltage stored in the target voltage storage circuit 54. The impedance conversion circuit 42 can perform electrical impedance conversion with high accuracy, thereby preventing a decrease in sensitivity of the electret condenser microphone 110.

  In addition, by adjusting the gain of the impedance conversion circuit 42 in the IC chip 114 as described above, not only the sensitivity is reduced due to heat applied during the reflow process, but also the stiffness variation of the vibration film 32A at the time of manufacture is reduced. Occurrence of a decrease in sensitivity due to a change with time after the start of use can also be prevented.

  In addition, the numerical value shown as a specification in each said embodiment is only an example, and of course, you may set these to a different value suitably.

Sectional side view which shows the state which has arrange | positioned the electret condenser microphone which concerns on 1st Embodiment of this invention upwards II direction view of FIG. The block diagram which shows the circuit structure of the said electret condenser microphone with an external circuit The figure similar to FIG. 3 which shows the electret condenser microphone which concerns on 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 110 Electret condenser microphone 12 Capacitor structure part 14, 114 IC chip 14a Power supply terminal 14b Output terminal 14c Ground terminal 14d Input terminal 16 Contact spring 18 Base board 18A, 20A, 22A Insulation board 18B1, 18B2, 18B3, 18D1, 18D2, 20B, 20C, 22B, 22C Conductive layer 18C Insulating layer 20 Side substrate 22 Cover substrate 22a Sound hole 32 Vibration membrane subassembly 32A Vibration membrane 32B Support ring 34 Back electrode plate 34A Electrode plate body 34B Electret layer 42 Impedance conversion circuit 44 Reference value Memory circuit 46 Potential difference detection circuit 48 Gain adjustment circuit 52 Calibration waveform input circuit 54 Target voltage storage circuit 56 Output voltage detection circuit

Claims (2)

In an electret condenser microphone comprising: a capacitor structure portion in which a vibration film and a back electrode plate are arranged to face each other; and an impedance conversion element that converts the capacitance of the capacitor structure portion into an electric impedance.
The impedance conversion element is incorporated in the IC chip as an impedance conversion circuit,
The IC chip stores in advance a reference value storage circuit that stores a reference value of a potential difference of the capacitor structure, a potential difference detection circuit that detects a potential difference of the capacitor structure, and a potential difference detected by the potential difference detection circuit. An electret condenser microphone comprising: a gain adjustment circuit that adjusts the gain of the impedance conversion circuit according to a difference from the reference value. In an electret condenser microphone comprising: a capacitor structure portion in which a vibration film and a back electrode plate are arranged to face each other; and an impedance conversion element that converts the capacitance of the capacitor structure portion into an electric impedance.
The impedance conversion element is incorporated in the IC chip as an impedance conversion circuit,
A calibration waveform input circuit in which the IC chip inputs a calibration waveform signal to the capacitor structure section at a predetermined timing, and an output from the impedance conversion circuit when the calibration waveform signal is input to the capacitor structure section. A target voltage storage circuit that stores a target voltage to be performed in advance; an output voltage detection circuit that detects a voltage output from the impedance conversion circuit by inputting the calibration waveform signal; and a detection by the output voltage detection circuit An electret condenser microphone comprising: a gain adjustment circuit that adjusts a gain of the impedance conversion circuit according to a difference between the measured voltage and the target voltage.

Images