JP2005323288A - Digital microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital microphone, in which the noise is reduced from acoustic signals having been digital-modulated, that affects the acoustic detection signal of capacity detection type. <P>SOLUTION: The digital microphone comprises an acoustic detector which consists of a diaphragm 13, functioning as an electrode and a fixed electrode 15 arranged to face the diaphragm 13 at a prescribed interval and outputs changes of electrostatic capacity between the diaphragm 13 and the fixed electrode 15 as acoustic detection signal, a modulation circuit part 7 which digital-modulates the acoustic detection signal and outputs it as digital acoustic signal, and a substrate 1 which has conductor patterns on both surfaces and connects the acoustic detection part to the modulation circuit part 7 by the conductor pattern. A conductor pattern 2 of acoustic detection signal provided on one surface of the substrate 1 is formed so as not to overlap in the direction vertical to the surfaces of the substrate 1, with a conductor pattern 3 of digital acoustic signal being provided on the other surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention includes a vibrating membrane that functions as an electrode, and a fixed electrode that is disposed opposite to the vibrating membrane at a predetermined interval, and a change in capacitance between the vibrating membrane and the fixed electrode is used as an acoustic detection signal. An acoustic detection unit for outputting, a modulation circuit unit for digitally modulating the acoustic detection signal and outputting it as a digital acoustic signal, a conductor pattern on both sides, and the acoustic detection unit and the modulation circuit unit being formed by the conductor pattern The present invention relates to a digital microphone including a substrate to be connected.

  A microphone using the principle of converting an acoustic signal into an electric signal by changing the capacitance of the capacitor formed by the electret material of the electrode and changing the capacitance of the capacitor caused by the vibration of the electrode (hereinafter referred to as “ECM”). .) Is widely used in mobile phones and digital still cameras with a voice recording function because it can be easily downsized. In the ECM, since the output of the capacitor portion that converts the acoustic signal into the electric signal is capacitive, the output circuit is a high impedance circuit. This is excellent for transmitting output with a small amount of power, but is also susceptible to other effects such as external noise.

For this reason, for example, a method has been proposed in which a ground pattern is formed on the entire remaining surface of the printed circuit board constituting the ECM, excluding the land portion of the mounted component and the surrounding electrical insulating portion, to protect it from external noise and the like. (For example, Patent Document 1).
In addition, the source terminal (ground side) of the field effect transistor for impedance conversion of the output of the capacitor portion is connected by a conductor whose total width is 1/3 or more of the peripheral length of the printed circuit board, or the drain terminal (output after impedance conversion) ) And the source terminal, or a method of attenuating external noise by simultaneously performing both of these is proposed (for example, Patent Document 2).

Registered Utility Model No. 3011048 (FIG. 2, paragraphs 0021 to 0027) JP 2001-16676 (paragraphs 0004 to 0007)

  The above is for preventing or reducing the influence of external noise on the ECM, and is expected to have a certain noise attenuation effect. However, the ECM also includes a so-called digital microphone that has a digital modulation circuit inside the ECM and is configured to output a digitally modulated signal. In such a digital microphone, since the microphone itself has a digital signal that can be a noise source, the influence on the internal signal is more prominent than external noise. That is, the noise level of the output signal of the capacitor rises because the output signal of the capacitor part, which is easily affected by noise with high impedance, and the digital signal whose output level changes at high speeds are in close proximity. End up.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a digital microphone that reduces noise received by a capacitance detection type acoustic detection signal from a digitally modulated acoustic signal.

  In order to achieve the above object, the digital microphone according to the present invention includes a vibrating membrane functioning as an electrode, and a fixed electrode disposed opposite to the vibrating membrane at a predetermined interval. The vibrating membrane and the fixed electrode An acoustic detection unit that outputs a change in electrostatic capacitance as an acoustic detection signal, a modulation circuit unit that digitally modulates the acoustic detection signal and outputs it as a digital acoustic signal, and a conductor pattern on both sides, A board for connecting an acoustic detection unit and the modulation circuit unit by the conductor pattern, the conductor pattern of the acoustic detection signal provided on one surface of the board, and the digital sound provided on the other surface The signal conductor pattern is formed so as not to overlap in the direction perpendicular to the surface of the substrate.

  According to this characteristic configuration, the conductor pattern of the acoustic detection signal and the conductor pattern of the digital acoustic signal do not overlap in a direction perpendicular to the surface of the substrate, so that the stray capacitance generated between the two conductor patterns. (Stray capacitance) can be reduced. And electrostatic induction caused by this stray capacitance can be reduced. Since electrostatic induction is particularly affected when the impedance on the damaged side is high, an effect of reducing noise with respect to the acoustic detection signal can be obtained. In order to prevent electrostatic induction, a method of providing a guard electrode on the conductor pattern can be used. This can be realized by forming a guard electrode on the inner layer of the substrate, for example, but the structure of the substrate is complicated and the cost is increased. To do. According to this characteristic configuration, the stray capacitance that causes electrostatic induction is reduced and the electrostatic induction is reduced. Therefore, noise can be reduced without increasing the cost.

  In the above configuration, the conductor pattern of the digital acoustic signal is preferably formed in a sector shape, and the conductor pattern of the acoustic detection signal is preferably formed in an arc shape in which a portion corresponding to the central angle of the sector shape is cut out.

  That is, the conductor pattern of the acoustic detection signal is formed in an annular shape (arc shape) except for a portion where the conductor pattern of the digital acoustic signal is formed on the opposite surface of the substrate. It can be formed so as not to overlap with the conductor pattern of the signal. And since a stray capacitance can be made small in the state which maintained the contact with the said acoustic detection part enough, the effect which reduces noise is acquired, without having a big influence on conduction | electrical_connection of the said acoustic detection signal.

  In the digital microphone according to the present invention, the conductor pattern of the digital acoustic signal is formed in a fan shape, and the conductor pattern of the acoustic detection signal has an inner diameter larger than the diameter of the fan-shaped conductor pattern. Thus, it is preferable to form a ring.

  That is, the conductor pattern of the acoustic detection signal is formed in an annular shape having an inner diameter larger than the diameter of the fan-shaped conductor pattern of the digital acoustic signal, so that it does not overlap with the conductor pattern of the digital acoustic signal. it can. Further, the contact with the sound detection unit can be sufficiently ensured over the entire circumference. As a result, the stray capacitance can be reduced without affecting the conduction of the acoustic detection signal, so that an effect of reducing noise can be obtained. The fan-shaped conductor pattern of the digital acoustic signal has a diameter smaller than the inner diameter of the annular conductor pattern of the acoustic detection signal, but is in contact with the output signal line (including the connector) (including soldering). There is no problem because a sufficient area can be secured.

  In the digital microphone according to the present invention, the conductor pattern of the digital acoustic signal is formed in a fan shape, and the conductor pattern of the acoustic detection signal has an arc shape in which a portion corresponding to the central angle of the fan shape is cut out. It is preferable to form the conductor pattern and an annular conductor pattern that is continuous with the arc shape and has an inner diameter larger than the fan-shaped diameter.

  That is, since the conductor pattern of the acoustic detection signal is formed in an annular shape except for a portion where the conductor pattern of the digital acoustic signal is formed on the opposite surface of the substrate, the conductor pattern of the digital acoustic signal Can be formed so as not to overlap. The contact with the acoustic detector can be sufficiently ensured over almost the entire circumference. Even when the contact is not made over the entire circumference, since the conductor pattern of the acoustic detection signal is conducted over the entire circumference, the acoustic detection signal can be transmitted well by reducing the wiring resistance. In addition, the fan-shaped conductor pattern of the digital acoustic signal can secure a sufficient area for contact (including soldering) with the output signal line (including the connector). In this way, since the stray capacitance can be reduced without affecting the conduction of the acoustic detection signal and the wiring of the digital acoustic signal to the outside, an effect of reducing noise can be obtained.

[Description of basic structure]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Prior to that, a basic structure of a digital microphone will be described. FIG. 1 is a cross-sectional view of a digital microphone according to the present invention. As shown in FIG. 1, in this digital microphone, a sound hole 11 is formed in a cylindrical bottom part, and each functional part is stored in a capsule 10 which is an opening part 12 opened on the side opposite to the bottom part. It is configured. Each functional unit includes an acoustic detection unit that detects an acoustic signal, a modulation circuit unit that digitally modulates the detected acoustic signal, and a substrate that connects them.

  The acoustic detector is provided with a diaphragm ring 16 at the bottom of the capsule 10 and a diaphragm 13 that functions as an electrode is disposed. The diaphragm 13 is sandwiched between the diaphragm ring 16 and the spacer 14, and the spacer 14 is provided. The fixed electrode 15 functioning as a back electrode is disposed at a predetermined interval defined by the thickness of the electrode, and a change in capacitance between the vibrating membrane 13 and the fixed electrode 15 is output as an acoustic detection signal. ing. Then, the substrate 1 is supported by the holder 18 and the end of the crimped capsule 10 inside the opening 12 so as to face the acoustic detection unit. The substrate 1 includes an integrated circuit 7 (modulation circuit unit) that digitally modulates an acoustic detection signal and outputs it as a digital acoustic signal. The acoustic detection unit and the substrate 1 are electrically connected by the gate ring 17, and the acoustic detection signal is input to the modulation circuit unit by the gate ring 17. The modulation circuit section is composed of one integrated circuit and, if necessary, a bypass capacitor for stabilizing the power supply and passive components such as a resistor and a capacitor as a filter for removing signal noise, and is mounted on the substrate 1. The In this example, for ease of explanation, as shown in FIG. 5A, a single integrated circuit 7 forms a modulation circuit section.

  FIG. 5 is a diagram illustrating an example of a conductive pattern of a substrate for explaining a circuit configuration of the digital microphone. FIG. 5A shows one side of the substrate 1 on which the integrated circuit 7 is mounted, that is, a side called a component mounting surface. FIG. 5B shows a conductive pattern of a surface called a solder surface on the other surface of the substrate 1 in a perspective view from the component mounting surface. Although not shown in FIGS. 1 and 5, signals and power are transmitted from the pattern of the solder surface to the outside of the digital microphone via connectors, cables, and contacts. In this example, the integrated circuit 7 has five terminals. Each of the terminals 75 is a power supply terminal, the terminal 76 is a ground (hereinafter referred to as “GND”) terminal, the terminal 72 is an input terminal from the acoustic detection unit, and a terminal. Reference numeral 74 is an input terminal for supplying a digital modulation reference clock, and terminal 73 is an output terminal for the modulated digital acoustic signal. The integrated circuit 7 includes an impedance conversion circuit, an amplifier, a modulation circuit, and the like. The high impedance acoustic detection signal input from the acoustic detection circuit, which is a capacitive detection element, is impedance-converted, amplified to the required level, and digitally modulated using the input reference clock to achieve high speed and high speed. A digital audio signal whose output level changes with output is output.

  As shown in FIG. 5A, the terminal 72 of the integrated circuit 7 is connected to the conductive pattern 2 of the acoustic detection signal. The other terminals 73 to 76 of the integrated circuit 7 are respectively connected to the conductive patterns 3 to 6 on the solder surface shown in FIG. 5B through the via holes 3v, 4v, 5v, and 6v, respectively.

  The acoustic detection signal is transmitted from the acoustic detection unit to the substrate 1 via the gate ring 17 shown in FIG. 1 as described above, and is circularly connected to the component mounting surface of the substrate 1 as shown in FIG. Are input from the conductive pattern 2 to the integrated circuit 7. As shown in FIG. 5B, the GND signal is also provided in an annular shape on the solder surface of the substrate 1 so that the opening 12 comes into contact with the end of the capsule 10 that is caulked inside.

  In the above, the example in which the conductive pattern 2 of the acoustic detection signal is provided in a ring shape on the component mounting surface has been described. However, in consideration of the acoustic effect, for example, a ring-shaped conductive film with a part missing as shown in FIG. Pattern 2 may occur. Hereinafter, embodiments of the digital microphone according to the present invention will be described, and the description will be based on the conductive pattern shown in FIG. In the following description, the conductive pattern on the component mounting surface side will be described with reference to the conductive pattern of the connection path for connecting the acoustic detection signal to the integrated circuit 7 and the terminal of the integrated circuit 7 for ease of explanation. Except for the conductive pattern and the integrated circuit 7, only the conductive pattern of the annular portion is shown and described.

[First embodiment]
FIG. 2 is a diagram showing a conductive pattern of the substrate of the digital microphone according to the first embodiment. 2A shows the conductive pattern on the component mounting surface, FIG. 2B shows the conductive pattern on the solder surface shown in a perspective view from the component mounting surface, and FIG. 2C shows the AA line. FIG. In the first embodiment, as shown in FIGS. 2A and 2B, the conductor pattern 3 of the digital acoustic signal is formed in a fan shape on the solder surface of the substrate 1, and the conductor pattern 2 of the acoustic detection signal is The part mounting surface of the substrate 1 is formed in an arc shape in which a portion corresponding to the central angle of the fan shape is cut out. 2C, which is a cross-sectional view taken along line AA, shows that the conductor pattern 2 of the acoustic detection signal and the conductor pattern 3 of the digital acoustic signal are in a direction perpendicular to the surface of the substrate 1. It turns out that it forms so that it may not overlap. That is, since the dotted line portion 2a shown in FIGS. 2A and 2C is not formed, the conductor pattern 2 of the acoustic detection signal and the conductor pattern 3 of the digital acoustic signal overlap in a direction perpendicular to the surface of the substrate 1. Do not fit.

  As described above, in the ECM, since the output of the capacitor portion that converts an acoustic signal into an electrical signal, that is, the output of the acoustic detection unit is capacitive, the output circuit is a high impedance circuit. Therefore, the transmission of the acoustic detection signal can be performed with a small amount of power and a very small attenuation, but it is also susceptible to other influences such as external noise. The ECM type digital microphone has a digital signal whose output level changes at high speed and high output, which is likely to be a noise source for the sound detection signal. That is, the digital acoustic signal obtained by digitally modulating the acoustic detection signal is in an environment where it can easily work as a noise source.

  The substrate 1 is a base material having a thickness of about 0.2 to 0.3 mm. Therefore, for example, when the conductive pattern 2 of the acoustic detection signal, which is a signal susceptible to noise, and the conductive pattern 3 of the digital acoustic signal, which is likely to be a noise source, are provided so as to overlap in a direction perpendicular to the surface of the substrate 1. A large stray capacitance is generated between the two conductive patterns. Then, noise is easily applied to the acoustic detection signal by electrostatic induction via the stray capacitance.

  However, if the conductor pattern 2 of the acoustic detection signal and the conductor pattern 3 of the digital acoustic signal are not overlapped in the direction perpendicular to the surface of the substrate 1 as in the first embodiment, these two conductor patterns The stray capacitance generated between them can be reduced. And electrostatic induction caused by this stray capacitance can be reduced. Since electrostatic induction is particularly affected when the impedance on the damaged side is high, an effect of reducing noise with respect to the acoustic detection signal can be obtained. In order to prevent electrostatic induction, a method of providing a guard electrode on the conductor pattern can be used. This can be realized by forming a guard electrode on the inner layer of the substrate, for example, but the structure of the substrate is complicated and the cost is increased. To do. According to the first embodiment, the stray capacitance that causes electrostatic induction is reduced to reduce electrostatic induction, so noise can be reduced without increasing costs.

  In the configuration of the first embodiment, the conductor pattern 2 of the acoustic detection signal is formed in an annular shape (arc shape) except for a portion where the conductor pattern 3 of the digital acoustic signal is formed on the opposite surface of the substrate 1. Therefore, it can be formed so as not to overlap with the conductor pattern 3 of the digital acoustic signal. In addition, the stray capacitance can be reduced while maintaining sufficient contact with the gate ring 17 that transmits the output from the sound detection unit, so that noise is not greatly affected and the conduction of the sound detection signal is not greatly affected. Effect is obtained.

  The input terminal 74 for supplying the digital modulation reference clock of the integrated circuit 7 is connected to the conductor pattern 4, and the conductor pattern 4 and the conductor pattern 2 of the acoustic detection signal are perpendicular to the surface of the substrate 1. Although there is an overlap in the direction, this is not a problem for the following reasons. The reference clock is of course a digital signal, and the output level fluctuates at high speed. However, the integrated circuit 7 having a modulation circuit generally has a high input impedance, so that a large input current is not required. For this reason, the reference clock signal that flows on the conductor pattern 4 is a low-current signal and has low electrical energy, so that it is difficult to be a noise source.

[Second Embodiment]
FIG. 3 is a diagram showing a conductive pattern of the substrate of the digital microphone according to the second embodiment. 3A shows the conductive pattern on the component mounting surface, FIG. 3B shows the conductive pattern on the solder surface shown in a perspective view from the component mounting surface, and FIG. 3C shows the AA line. FIG. In the second embodiment, as shown in FIGS. 3A and 3B, the conductor pattern 3 of the digital acoustic signal is formed in a fan shape on the solder surface of the substrate 1, and the conductor pattern 2 of the acoustic detection signal. Has an inner diameter larger than the diameter of the fan-shaped conductor pattern, and is formed in an annular shape on the component mounting surface of the substrate 1. From FIG. 3 (b) and FIG. 3 (c), which is a cross-sectional view taken along the line AA, since the dotted line portion 3a is not formed, the conductor pattern 2 of the acoustic detection signal and the conductor pattern 3 of the digital acoustic signal are It can be seen that they are formed so as not to overlap in the direction perpendicular to the surface of the substrate 1.

  Moreover, since the conductor pattern 2 of the acoustic detection signal is formed over substantially the entire circumference, the contact between the acoustic detection unit and the substrate 1 via the gate ring 17 can be sufficiently ensured over the entire circumference. Thereby, since the stray capacitance can be reduced without affecting the conduction of the acoustic detection signal, an effect of reducing noise can be obtained. In addition, although the area of the fan-shaped conductor pattern of the digital acoustic signal is smaller than the inner diameter of the annular conductor pattern of the acoustic detection signal, the area is reduced, but contact with the output signal line (including the connector) (soldering) A sufficient area can be secured, and there is no problem.

[Third embodiment]
FIG. 4 is a diagram showing a conductive pattern of the substrate of the digital microphone according to the third embodiment. 4A shows the conductive pattern on the component mounting surface, FIG. 4B shows the conductive pattern on the solder surface shown in a perspective view from the component mounting surface, and FIG. 4C shows the AA line. FIG. In the third embodiment, as shown in FIGS. 4A and 4B, the conductor pattern 3 of the digital acoustic signal is formed in a fan shape on the solder surface of the substrate 1, and the conductor pattern 2 of the acoustic detection signal is An arc-shaped conductor pattern 21 in which a part corresponding to the central angle of the fan shape is cut out on the component mounting surface of the substrate 1, and a fan shape of the conductor pattern 3 of the digital acoustic signal that is continuous with the arc-shaped conductor pattern 21. And an annular conductor pattern 22 having an inner diameter larger than the inner diameter. 4C, which is a cross-sectional view taken along the line AA, shows that the conductor pattern 2 of the acoustic detection signal and the conductor pattern 3 of the digital acoustic signal are in a direction perpendicular to the surface of the substrate 1. It can be seen that they are formed so as not to overlap.

  That is, since the dotted line portion 2a shown in FIGS. 4A and 4C is not formed, the conductor pattern 2 of the acoustic detection signal is formed on the surface opposite to the substrate 1 of the conductor pattern 3 of the digital acoustic signal. Except for the portion, it can be formed in an annular shape so as not to overlap with the conductor pattern 3 of the digital acoustic signal. Further, the contact with the acoustic detection unit via the gate ring 17 can be sufficiently ensured over the entire circumference. Even if the portion that contacts the gate ring 17 is on the conductor pattern 21 side and does not contact the entire circumference, the conductor pattern 2 of the acoustic detection signal is conducted by the conductor pattern 22 over the entire circumference. The sound detection signal can be satisfactorily transmitted by lowering the wiring resistance. In addition, the fan-shaped conductor pattern 3 for the digital audio signal can secure a sufficient area for contact (including soldering) with the output signal line (including the connector). In this way, since the stray capacitance can be reduced without affecting the conduction of the acoustic detection signal and the wiring of the digital acoustic signal to the outside, the effect of reducing noise can be reduced by reducing electrostatic induction and the like. Is obtained.

Sectional drawing of the digital microphone according to the present invention The figure which shows the conductive pattern of the board | substrate of the digital microphone which concerns on 1st embodiment. The figure which shows the conductive pattern of the board | substrate of the digital microphone which concerns on 2nd embodiment. The figure which shows the conductive pattern of the board | substrate of the digital microphone which concerns on 3rd embodiment. The figure which shows an example of the conductive pattern of the board | substrate for demonstrating the circuit structure of a digital microphone The figure which shows the other example of the electroconductive pattern of the board | substrate of a digital microphone

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Conductive pattern of acoustic detection signal 3 Conductive pattern of digital acoustic signal 4 Conductive pattern of reference clock for digital modulation 5 Conductive pattern of power supply 6 Conductive pattern of GND 7 Integrated circuit

Claims (4)

Acoustic detection including a vibration film functioning as an electrode and a fixed electrode disposed opposite to the vibration film at a predetermined interval, and outputting a change in capacitance between the vibration film and the fixed electrode as an acoustic detection signal And
A modulation circuit unit that digitally modulates the acoustic detection signal and outputs it as a digital acoustic signal;
A substrate having a conductor pattern on both sides, and connecting the acoustic detection unit and the modulation circuit unit by the conductor pattern;
A digital microphone comprising:
The digital formed so that the conductor pattern of the acoustic detection signal provided on one surface of the substrate and the conductor pattern of the digital acoustic signal provided on the other surface do not overlap in a direction perpendicular to the surface of the substrate. Microphone. The conductor pattern of the digital acoustic signal is formed in a fan shape,
The digital microphone according to claim 1, wherein the conductor pattern of the acoustic detection signal is formed in an arc shape in which a portion corresponding to the central angle of the fan shape is cut out. The digital acoustic signal conductor pattern is formed in a fan shape,
The digital microphone according to claim 1, wherein the conductor pattern of the acoustic detection signal has an inner diameter larger than the diameter of the fan-shaped conductor pattern and is formed in an annular shape. The conductor pattern of the digital acoustic signal is formed in a fan shape,
The conductor pattern of the acoustic detection signal includes an arc-shaped conductor pattern in which a portion corresponding to the central angle of the fan shape is cut out, and an annular conductor that is continuous with the arc shape and has an inner diameter larger than the fan-shaped diameter. The digital microphone according to claim 1, wherein the digital microphone is formed of a pattern.

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