JP2007005913A - Electrostatic electroacoustic transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high S/N by reducing parasitic capacitance and increasing an essentially required capacitance thereby enhancing sensitivity. <P>SOLUTION: A fixed electrode 6f is formed to have a size substantially equal to that of a vibrating membrane 3 so that the fixed electrode 6f is superposed on the vibrating membrane 3, and a plurality of supporting pieces 6s held by a holder 7 are formed integrally around the fixed electrode 6f. When attraction acts by a voltage applied between the vibrating membrane 3 and the fixed electrode 6f, interval between the vibrating membrane 3 and the fixed electrode 6f is sustained by an opening 6x made in the fixed electrode 6f at a portion where the vibrating membrane 3 and the fixed electrode 6f touch each other. The fixed electrode 6f is provided with a micropore 6h small enough not to impact on variation in capacitance between the vibrating membrane 3 and the fixed electrode 6f. A gate pattern 9 is a closed path pattern consisting of thin lines intersecting a gate ring 8 at a plurality of positions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrostatic electroacoustic transducer having high sensitivity characteristics such as a condenser microphone with improved sensitivity.

  For example, taking a condenser microphone (hereinafter, generically referred to as a condenser microphone) as an example, the microphone takes out a change in capacitance due to the capacitor as a voltage change and converts the impedance to obtain an output. FIG. 8 shows a cross section of an example of a conventional microphone. The diaphragm 2 has a capsule 2 having a sound hole 1 on the front surface, and a diaphragm 3 that vibrates due to sound pressure in the capsule 2. , A spacer 5, a back electrode 6, a holder 7, a gate ring 8, a conductive pattern such as a gate pattern 9 and a ground pattern 12, and a substrate 11 on which a circuit element 10 is mounted are incorporated. The structure of fixing these built-in components by caulking at the end of the is shown. A terminal portion 13 such as an output terminal or a ground terminal is provided outside the substrate 11. In this case, factors affecting the sensitivity of the microphone include the stiffness of the vibrating membrane 3 (difficult to vibrate or easy to vibrate), electrostatic capacitance between the vibrating membrane 3 and the back electrode 6, parasitic capacitance, high range or low The volume of the front chamber or the back chamber for capturing the sound pressure vibration in the region, the magnitude of the voltage (bias) applied between the vibrating membrane 3 and the back electrode 6, etc. are among the factors that improve the sensitivity. What is important is an increase in capacitance between the vibrating membrane 3 and the back electrode 6 and a reduction in parasitic capacitance.

  FIG. 9 is a plan view of a part of FIG. 8, and shows the positional relationship between the vibrating membrane 3 and the vibrating membrane ring 4 that overlap with the back electrode 6 in a state where the back electrode 6 is arranged. Here, the outer periphery of the back electrode 6 partially overlaps with the diaphragm ring 4, and hatching is an overlapping part of the diaphragm 3 and the back electrode 6 stretched inside the diaphragm ring 4, The hole has a structure that is a vent hole 14 formed in the back electrode 6. In this case, the capacitance due to the overlap between the back electrode 6 and the diaphragm ring 4 is a parasitic capacitance unrelated to the electrostatic capacitance formed by the back electrode 6 and the diaphragm 3 related to the output signal. Such parasitic capacitance exists throughout the microphone, and the parasitic capacitance in question is mainly the parasitic capacitance between the back electrode 6 and the diaphragm ring 8 and the gate pattern 9 formed on the substrate 11. This is a parasitic capacitance with the ground pattern 12.

FIG. 10 shows an equivalent circuit of an example of a microphone. That is, a voltage change due to the electrostatic capacitance C0 between the vibrating membrane 3 and the back electrode 6 is applied to the gate of the FET 10a that is a part of the circuit element 10, and impedance conversion is performed to obtain an output. Further, the output side of the FET 10a constitutes a noise removal filter including a capacitor C. However, as shown in FIG. 10, the gate of the FET 10a that is input as a voltage change accompanying the capacitance change has an electrostatic capacitance that is originally required between the vibrating membrane 3 and the back electrode 6 as illustrated in FIG. 8B. In addition to the capacitance C0, a parasitic capacitance C1 between the back electrode 6 and the diaphragm ring 8 and a parasitic capacitance C1 between the gate pattern 9 formed on the substrate 11 and the ground pattern 12 exist. This parasitic capacitance C1 divides the bias voltage applied to the originally required capacitance C0. Since this parasitic capacitance C1 is present, it is difficult to obtain a desired change in the capacitance C0. As a result, the output signal is attenuated.
JP 2003-209899 A JP 2003-348696 A

Japanese Patent Laid-Open No. 2004-133867 provides a spacer between a diaphragm ring and a back electrode built in a capsule with spacer pieces arranged at equal intervals in the circumferential direction to reduce a reactive capacitance and obtain a good S / N. Technology is disclosed. Patent Document 2 discloses a technique for improving the sensitivity by reducing the stray capacitance by depositing an electrode film only on the vibrating part of the vibrating film.
Conventionally, various measures for reducing the parasitic capacitance C1 have been proposed. Techniques for sufficiently reducing the parasitic capacitance C1 or increasing the necessary capacitance C0 related to the original output signal. Improvements are still in progress.

  The present invention has been invented in view of the above-mentioned problems, and is an electrostatic electroacoustic conversion in which parasitic capacitance is reduced, inherently necessary capacitance is increased, sensitivity is improved, and high S / N is obtained. The purpose is to provide vessels.

  The present invention which achieves this object is to connect a diaphragm ring with a diaphragm inside the capsule, a fixed electrode disposed opposite the diaphragm, a holder for holding the fixed electrode, and the fixed electrode. A built-in component comprising a gate ring formed on the gate ring and a substrate on which a gate pattern connected to the gate ring is formed, and the built-in component is fixed by caulking the substrate by an end of the capsule, and the vibration membrane is fixed. In the electrostatic electroacoustic transducer, a change in electrostatic capacitance with an electrode is input as a voltage signal to the impedance converter through the gate ring and gate pattern to obtain an output corresponding to the vibration of the vibration membrane. The size of the fixed electrode is formed to be substantially equal to the size of the vibrating membrane so as to overlap, and a plurality of pieces held by the holder around the fixed electrode The supporting pieces, characterized in that integrally formed.

  According to the present invention, the configuration is such that the back pole of the portion overlapping the diaphragm ring causing the parasitic capacitance is removed except for the support piece, so that the parasitic capacitance itself can be greatly reduced, and the sensitivity is increased and the signal is increased. To obtain a high S / N.

Hereinafter, embodiments of the electrostatic electroacoustic transducer of the present invention will be described with reference to the drawings. In the following drawings, the same parts as those in FIG. 8 are denoted by the same reference numerals, and the description thereof is omitted if not necessary.
[First embodiment]
FIG. 1 shows an electret condenser microphone according to the first embodiment. In this embodiment, a so-called back electret type in which the electret 15 is covered on the front side of the back electrode 6 is shown, but a so-called front electret type is also applicable. 1 has the same cross-sectional configuration as that of FIG. 8 except for the back electrode 6, and the back electrode 6 is configured as shown in FIG. Further, as shown in FIG. 3, the gate pattern 9 formed on the substrate 11 in contact with the gate ring 8 is thinned to reduce the parasitic capacitance between the gate pattern 9 and the ground pattern 12. It is to reduce.

  FIG. 2A shows a plane of the arrangement state of the back electrode 6 with respect to the diaphragm ring 4. In FIG. 2, the back electrode 6 has a shape in which a circular back electrode plate is equally cut out at three locations in the circumferential direction, and a portion that overlaps the cutout diaphragm 4 is a support piece 6 s. ing. Further, the portion other than the support piece 6s has a fixed electrode 6f (hatched portion in FIG. 2) having substantially the same area as the vibrating membrane 3. As a result, the portion (projected portion) where the back electrode 6 overlaps with the diaphragm ring 4 is only three support pieces 6s, and the parasitic capacitance is generated only in the portion corresponding to the support piece 6s. Decrease significantly.

  The configuration shown in FIG. 2A is a structure in which the circumferential length of the notched portion is slightly longer than the circumferential length of the support piece 6s. However, in order to further reduce the parasitic capacitance, the notched portion is formed. This can be realized by further shortening the circumferential length of the support piece 6s by cutting out the portion further in the circumferential direction. For this reason, if the circumferential length of the support piece 6s is extremely shortened and the support piece 6s is configured like a rod, for example, the parasitic capacitance becomes very small. However, as the caulking force is generated at the end of the capsule 2, the gate ring 8 structurally pushes the back electrode 6 toward the vibrating membrane 3 through the substrate 11, and the pushing force causes the fixed electrode 6 f to move. Since the support piece 6s is deformed to cause a defect, the support piece 6s having a length that does not deform with respect to the push-up force due to the caulking is required. Therefore, the circumferential length of the support piece 6s is preferably as short as possible in the circumferential direction within a range that can withstand the caulking force in order to reduce parasitic capacitance.

FIG. 2B shows a structural example in which four support pieces 6s are evenly arranged in the circumferential direction. In the case shown in FIG. 2B, the number of support pieces 6s is larger than that in the case of FIG. 2A, but the example shown in FIG. 2B is also supported within the range that can withstand the caulking force. Needless to say, the circumferential length of the piece 6s is preferably as short as possible in order to reduce the parasitic capacitance.
In this way, the parasitic capacity is greatly reduced by the support piece 6s than before, and if the number of the support pieces 6s is increased or the length in the circumferential direction is increased or decreased, the reduction of the parasitic capacity can be suppressed and the large caulking force can be obtained. On the other hand, if the number of support pieces 6s is reduced or the length in the circumferential direction is reduced, the parasitic capacitance is greatly reduced, but it is difficult to face the caulking force. Therefore, the parasitic capacitance can be reduced as much as possible by reducing the parasitic capacitance by changing the number of support pieces 6s and the circumferential length according to the caulking force. In addition, the notch portion other than the support piece 6 s of the back electrode 6 extends not only to the vibrating membrane ring 4 but also to the facing portion of the vibrating membrane 3 in the radial direction. This is because the vibration film 3 near the vibration film ring 4 is less likely to contribute to the vibration associated with the sound pressure than the center of the vibration film 3 and thus is difficult to take out a change in capacitance. This allows air to flow between the poles 6 and has a function of urging vibration according to the sound pressure of the vibrating membrane 3.

As a result, a plurality of support pieces 6s are formed integrally with the fixed electrode 6f in the back electrode 6 having the fixed electrode 6f having the same size as that of the vibrating membrane 3, and the support piece 6s can withstand the strength against the caulking force. By making the circumferential length as short as possible, the parasitic capacitance can be extremely reduced.
3 is an exploded perspective view of the microphone shown in FIG. As shown in FIG. 3, the capsule 2 is disposed in the capsule 2 in order from the top, the diaphragm ring 4 with the diaphragm 3 stretched, the spacer 5, the back electrode 6 illustrated in FIG. 2B, the holder 7, and the holder 7. A gate ring 8 whose upper end is in contact with the back electrode 6, a gate pattern 9 and circuit element 10 in contact with the lower end of the gate ring 8, and a substrate 11 having an external ground pattern 12 and a terminal portion 13 are disposed. . Here, the relationship between the back electrode 6 and the diaphragm 3 and the diaphragm ring 4 is that the support piece 6s of the back electrode 6 overlaps the diaphragm ring 4 as shown in FIG. 6 f overlaps with the vibration film 3.

Further, the gate pattern 9 formed on the substrate 11 by plating, for example, has a line width of 0.15 mm, for example, and is formed in a regular hexagonal shape as shown in FIG. The regular hexagonal shape is such that when the gate ring 8 is at a normal position of the substrate 11, it contacts six fine lines (six sides (segments)), and the gate ring 8 slightly moves over the substrate 11. This is because a plurality of portions of the gate pattern 9 made of fine lines are brought into contact with the lower end of the gate ring 8 even when moved (shifted). Therefore, even when the gate ring 8 is most displaced within the movement (displacement) range on the substrate 11, the apex angle and the side (line segment) are in contact with somewhere in the gate pattern 9 at a plurality of regular hexagonal locations. Here, a regular hexagonal gate pattern 9 is formed. In the present embodiment, the gate pattern 9 is formed in a regular hexagonal shape as shown in FIG. 3, but it may be a polygon including a regular polygon formed within the movement (shift) range of the gate ring 8, Various shapes are conceivable on the condition that the apex angle and side (line segment) of the pattern 9 are in contact with somewhere. Furthermore, the gate pattern 9 may be formed by connecting zigzag fine lines in the moving range of the gate ring 8, for example, even if it is not a polygon. Thus, by forming a closed circuit pattern made of a thin line within the moving range of the gate ring 8, the parasitic capacitance between the gate pattern 9 and the ground pattern 12 can be reduced. Incidentally, as shown in FIG. 8, the gate pattern 9 is conventionally formed in a ring shape having a width of about 0.65 mm in accordance with the width of the gate ring 8 as an example.
[Second Embodiment]
Although the above description has described the reduction of the parasitic capacitance, it is also important to increase the capacitance itself composed of the vibrating membrane 3 and the back electrode 6 in order to improve the sensitivity of the microphone. In order to increase the capacitance, it is effective to bring the vibrating membrane 3 and the back electrode 6 as close as possible. Conventionally, the gap between the center of the vibrating membrane 3 and the back electrode 6 is 25 μm to 30 μm. However, the present inventors have reduced the gap size to about 12.5 μm by about half. In this case, the air gap is in the condenser microphone, and even if an attractive force is applied by the voltage applied between the vibrating membrane 3 and the back electrode 6 and vibration due to sound pressure is applied, the center of the vibrating membrane 3 and the back electrode 6 Therefore, the shortening of the air gap is epoch-making including an increase in capacitance.

However, the shortening of the air gap shortens the space between the vibrating membrane 3 and the back electrode 6 and impairs the ease of movement of the vibrating membrane 3. In this embodiment, as shown in FIG. 4, minute holes 6h are formed in the back electrode 6 substantially evenly, and these minute holes 6h function as air circulation ports. The large number of fine holes 6h have a size that does not affect the acquisition of the capacitance change of the capacitor constituted by the vibrating membrane 3 and the back electrode 6, and has a diameter of 0.2 mm or less, for example. It is a micropore. Here, although a large number of fine holes are formed in the back electrode 6, the capacitance value proportional to the area is slightly reduced, but the electrostatic capacitance due to the proximity of the vibrating membrane 3 and the back electrode 6 is reduced. The diameter is 0.2 mm from the viewpoint that it is sufficient to obtain a sufficient voltage change from the capacitor as a change in capacitance due to the sound pressure. Therefore, even if, for example, the size of the fine hole 6h is taken, if the hole is, for example, 0.2 mm or less, the limit of the size can be obtained as much as it does not affect the acquisition of the capacitance change. 4 (a) and 4 (b) are illustrated using the example of FIG. 2 in which the back pole 6 is notched to form the support piece 6s. However, the present embodiment in which the fine hole 6h is formed is to shorten the above-mentioned gap and open the fine hole so as to increase the capacitance, and also applies to the example shown in FIG. be able to. In this case, both of the structures having only the fine holes and eliminating the air holes 14 are conceivable even when the air holes 14 of FIG. 9 are provided.
[Third Embodiment]
FIG. 5 shows still another embodiment. In this embodiment, the capacitance is further increased by bringing the vibrating membrane 3 and the back electrode 6 closer to each other based on the second embodiment. That is, when the vibrating membrane 3 and the back electrode 6 are brought close to each other, the center of the vibrating membrane 3 and the back electrode 6 come into contact with each other. The vibrating membrane 3 and the back electrode 6 are brought close to each other by opening an opening 6x in the back electrode 6 of the contact portion so that the back electrode 6 and the vibrating membrane 3 have a slight gap. The vibrating membrane 3 is stretched to the vibrating membrane ring 4 with a certain tension so as to be vibrated by sound pressure, but the portion where the vibrating membrane 3 is loosened is the center of the vibrating membrane ring 4. Therefore, by forming the opening 6x in anticipation of the portion of the vibrating membrane 3 that comes into contact with the back electrode 6, the vibrating membrane 3 can be brought very close without contacting the back electrode 6. In addition, as shown in FIG. 5, the opening 6x is formed in the back pole 6 which hits the center of the diaphragm ring 4, but this opening 6x can also be a vent hole. However, the opening 6x is not formed in an opening having a diameter large enough to decrease the capacitance because of having a function of increasing the capacitance by bringing the vibrating membrane 3 closer to the back electrode 6.

5 (a) and 5 (b) are illustrated using the example of FIG. 2 in which the back pole 6 is notched and the support piece 6s is formed. However, the present embodiment in which the opening 6x is formed is to shorten the gap so as to increase the capacitance, and can also be applied to the example shown in FIG. 9 in which the back electrode 6 is not cut out.
The description so far has described a microphone having a structure including an electret among condenser microphones. However, the structure of the vibrating membrane 3 and the back electrode 6 described above can also be applied to a so-called bias type condenser microphone. FIG. 6 illustrates a microphone having a structure in which a bias voltage is applied to the vibrating membrane 3 via the bias ring 16. Further, in the structure having a bias voltage applied to the back electrode 6, the bias ring 16 in FIG. 6 and the insulator film 17 stretched inside the capsule become unnecessary, and the bias voltage is applied to the back electrode 6 through the gate ring 8. It is done. FIG. 7 shows a gate pattern formed on the substrate 11 for this bias type condenser microphone. The circuit element 10 mounted on the substrate 11 in FIG. 7 includes a bias IC and a high frequency cut capacitor Cc in addition to the FET and the two capacitors C. Thus, the first, second and third embodiments can be applied to the bias condenser microphone.

It is sectional drawing of the microphone of 1st Embodiment of this invention. It is a positional relationship figure of a diaphragm ring and a back pole. It is a disassembled block diagram of 1st Embodiment. It is a positional relationship figure of the diaphragm ring and back pole of a 2nd embodiment. It is a positional relationship figure of a diaphragm ring and a back pole of a 3rd embodiment. It is sectional drawing of an example of a bias type | mold condenser microphone. It is a perspective view of the board | substrate which illustrates a gate pattern. It is sectional drawing of the microphone for conventional description. It is a positional relationship figure of the conventional diaphragm ring and a back pole. It is an equivalent circuit diagram of an example of a microphone.

Claims (4)

A vibrating membrane ring in which a vibrating membrane is stretched inside a capsule, a fixed electrode disposed opposite to the vibrating membrane, a holder for holding the fixed electrode, a gate ring connected to the fixed electrode, and the gate ring A built-in component composed of a substrate on which a connected gate pattern is formed, and the substrate is squeezed by the end of the capsule to fix the built-in component, and the capacitance of the vibrating membrane and the fixed electrode is changed. In the electrostatic electroacoustic transducer that obtains an output corresponding to the vibration of the diaphragm by inputting the voltage signal to the impedance converter through the gate ring and the gate pattern.
The size of the fixed electrode is formed substantially equal to the size of the vibration membrane so as to overlap the vibration membrane, and a plurality of support pieces held by the holder are integrally formed around the fixed electrode. An electrostatic electroacoustic transducer characterized by the above. A vibrating membrane ring in which a vibrating membrane is stretched inside a capsule, a fixed electrode disposed opposite to the vibrating membrane, a holder for holding the fixed electrode, a gate ring connected to the fixed electrode, and the gate ring A built-in component composed of a substrate on which a connected gate pattern is formed, and the substrate is squeezed by the end of the capsule to fix the built-in component, and the capacitance of the vibrating membrane and the fixed electrode is changed. In the electrostatic electroacoustic transducer that obtains an output corresponding to the vibration of the diaphragm by inputting the voltage signal to the impedance converter through the gate ring and the gate pattern.
When a suction force is applied between the vibrating membrane and the fixed electrode, an opening is formed in the fixed electrode at a portion where the vibrating membrane and the fixed electrode are in contact with each other. An electrostatic electroacoustic transducer characterized by maintaining a distance from a fixed electrode. A vibrating membrane ring in which a vibrating membrane is stretched inside a capsule, a fixed electrode disposed opposite to the vibrating membrane, a holder for holding the fixed electrode, a gate ring connected to the fixed electrode, and the gate ring A built-in component composed of a substrate on which a connected gate pattern is formed, and the substrate is squeezed by the end of the capsule to fix the built-in component, and the capacitance of the vibrating membrane and the fixed electrode is changed. In the electrostatic electroacoustic transducer that obtains an output corresponding to the vibration of the diaphragm by inputting the voltage signal to the impedance converter through the gate ring and the gate pattern.
An electrostatic electroacoustic transducer characterized in that the fixed electrode is provided with micropores that do not affect the acquisition of a change in capacitance between the vibrating membrane and the fixed electrode. A vibrating membrane ring in which a vibrating membrane is stretched inside a capsule, a fixed electrode disposed opposite to the vibrating membrane, a holder for holding the fixed electrode, a gate ring connected to the fixed electrode, and the gate ring A built-in component composed of a substrate on which a connected gate pattern is formed, and the substrate is squeezed by the end of the capsule to fix the built-in component, and the capacitance of the vibrating membrane and the fixed electrode is changed. In the electrostatic electroacoustic transducer that obtains an output corresponding to the vibration of the diaphragm by inputting the voltage signal to the impedance converter through the gate ring and the gate pattern.
The electrostatic electroacoustic transducer according to claim 1, wherein the gate pattern is a closed circuit pattern composed of fine lines intersecting with the gate ring at a plurality of locations.

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