JPH10145895A - Capacitor microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the capacitor microphone with superior signal characteristics. SOLUTION: On the back of a conductive diaphragm 11, a back electrode plate 20 is provided. The back electrode plate 20 consists of an insulating plate 21 and an electrode plate 22 which is provided on the surface of the insulating plate 21 facing the diaphragm 11. The insulating plate 21 is provided with a prepositional circuit 40. The diaphragm 11 and back electrode plate 22 are connected to the prepositional circuit 40 through conductive patterns 23, 23A, and 22B formed on the insulating plate 40. The vibration of the diaphragm 11 caused by a sound wave is taken out as variation in the electrostatic capacity C10 between the diaphragm 11 and electrode plate 22 and the variation in the capacity C10 is taken out of the prepositional circuit 40 in the form of a signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a condenser microphone suitable for business use.

[0002]

2. Description of the Related Art A condenser microphone is known as a microphone.
The unit is configured as shown in FIG. 6, for example. That is, in FIG. 6, reference numeral 30 denotes the microphone unit, and the diaphragm 31 is formed in a circular shape by a conductive plate such as a metal plate, and is formed in an annular shape by an insulating material on the rear surface. A back electrode (fixed electrode) 33 is provided with the spacer 32 interposed therebetween.

The back electrode 33 is formed in a circular shape by a conductive member such as a metal plate, and has a plurality of through holes 34 formed therein.
Is open to the rear of the back electrode 33.

Further, an air chamber member 35 is formed in a cup shape as a whole with an insulating material, and a step 36 is formed inside an opening portion thereof, and a back electrode 33 is located here. Further, the case 37 is formed in a cup shape from a conductive material such as a metal, and a through hole 38 is formed in a bottom surface thereof, and the components 31, 32, and 33 described above such that the diaphragm 31 faces the through hole 38. , 35 are Case 3
7 is provided inside. Further, inside the case 37, an annular fixing member 39 is provided in contact with the rear portion of the air chamber member 35.
Are provided, and components provided inside the case 37 are fixed.

As an example, the diameter of the diaphragm 31 is 30
The distance between the diaphragm 31 and the back electrode 33 (the thickness of the spacer 32) is 30 to 50 μm.

Further, a pre-circuit 40 is provided outside the case 37.
For example, a resistor R40 and a DC power supply 43 are provided. The back electrode 33 is connected to one end of the DC power supply 43 through the lead 41 and further through the resistor R40, and the diaphragm 31 is connected to the other end of the DC power supply 43 through the case 37 and the fixing member 39 and further through the lead 42. Is done. Further, both ends of the resistor R40 are connected to the output terminal T4.
1, connected to T42.

According to such a configuration, the capacitor C30 is constituted by the diaphragm 31 and the back electrode 33, and the diaphragm 31 vibrates as shown by a broken line by a sound wave.
The capacitance of the capacitor C30 changes. At this time, since the rear part of the diaphragm 31 is open to the air chamber (the space formed by the rear electrode 33 and the air chamber member 35) behind the back electrode 33 through the through hole 34, the diaphragm 31
Can vibrate following sound waves.

When the change in the capacitance of the capacitor C30 changes in response to the sound wave, the resistor R40 has the capacitor C30.
Since the current corresponding to the capacitance change flows through the terminals T41 and T41,
A signal obtained by acoustically / electrically converting a sound wave obtained by vibrating the diaphragm 31, that is, an audio signal collected by the microphone unit 30 can be obtained at 42.

By the way, the diaphragm 31 and the back electrode 33
Is 50 to 60 pF in the case of the above numerical example, and the capacitance change due to the sound wave is several pF.

[0010]

The AC equivalent circuit of the microphone unit 30 and the pre-circuit 40 described above is as shown in FIG. 7, where the signal voltage V30 changes with the capacitance of the capacitor C30. And the signal voltage V30 is taken out to terminals T41 and T42 through a low-pass filter constituted by a capacitor C30 and a resistor R40.

Therefore, the signal voltage V40 taken out at the terminals T41 and T42 is as follows: V40 = ((1 + 1 / (ωC30R40) ** 2) ** (-0.5))
V30. Here, X ** Y indicates the value X raised to the Yth power (the same applies hereinafter).

The cut-off frequency fc is fc = 1 / (2πC30R40). Therefore, in a frequency band higher than the cutoff frequency fc, V40 = V30.

However, in practice, when the capacitance change of the capacitor C30 is taken out by the lead lines 41 and 42, a stray capacitance CS is generated between the lead lines 41 and 42 as shown by a broken line in FIG. I will. By the way, CS ≒ 10
pF.

Then, the signal voltage V40CS at this time is V40CS = (((1 + CS / C30) ** 2 + 1 / (ωC30R4)
0) ** 2)) ** (-0.5)) × V30, and in a frequency band higher than the cutoff frequency fc, V40CS = (C30 / (C30 + CS)). V30.

Therefore, the signal voltage V40CS with the stray capacitance CCS is reduced to V40CS / V40 = C30 / (C30 + CS) [times] compared to the signal voltage V40 without the stray capacitance CCS. In addition, the S / N of the signal decreases due to the decrease in the signal level.

An object of the present invention is to provide a condenser microphone that eliminates such problems.

[0017]

According to the present invention, there is provided an electroconductive diaphragm, a back plate provided on a rear surface of the diaphragm, and a front circuit. Has an insulating plate and an electrode plate provided on a surface of the insulating plate facing the vibration plate, and the pre-circuit is provided on the insulating plate and formed on the insulating plate. Connected to the diaphragm and the back electrode plate through the conductive pattern, the vibration of the diaphragm caused by sound waves is taken out as a change in capacitance between the diaphragm and the electrode plate, and the capacitance The change is taken out as a signal from the pre-circuit. Therefore, the diaphragm and the electrode plate,
The stray capacitance is minimized due to the shortest distance to the pre-circuit.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 10 denotes a microphone unit according to the present invention, and a diaphragm 11 is formed in a circular shape by a conductive plate such as a metal plate. A printed wiring board 20 is provided on the rear surface of the vibration plate 11 with a spacer 12 formed in an annular shape from metal or the like.

Although the details of the printed wiring board 20 will be described later, the printed wiring board 20 is formed in the same manner as a printed wiring board used for general circuit wiring. Functions as a back electrode (fixed electrode).

Further, on the rear surface of the printed wiring board 20,
Insulating member 1 made of a plastic material or the like
An air chamber member 15 is provided with 3 in between. The air chamber member 15 is formed of a conductive material such as metal as a whole in a cup shape, and the printed wiring board 20 is positioned so as to cover the opening.

On the front surface of the diaphragm 11, a holding member 16 formed in an annular shape by a conductive material such as metal is provided, and a screw 17 penetrating through the components 16, 11, 12, 20, and 13 is used. Parts 16 to 13 are fixed to the air chamber member 15.

Then, regarding the printed wiring board 20,
This is configured, for example, as also shown in FIGS. 2 is a front view of the printed wiring board 20 (a view from the front of the microphone unit 10, FIG.
FIG. 1 is a cross-sectional view of the printed wiring board 20 of FIG. 1, and FIG. 4 is a view of the printed wiring board 20 as viewed from the rear. The printed wiring board 20 is a so-called double-sided board.

The printed wiring board 20 has an insulating substrate 21 formed in a rectangular shape,
A through hole 24 is formed in a portion surrounded by 15, and a rear surface of the diaphragm 11 is opened to the air chamber member 15 through the through hole 24. Further, as shown in FIG. 4, a front circuit 40 is provided on the rear surface (the lower surface in FIGS. 1 and 3) of the printed wiring board 20 in a portion where the microphone unit 10 is not located. A specific example of the pre-circuit 40 will be described later.

Further, as shown in FIG. 2, on the front surface of the insulating substrate 21 (the upper surface in FIGS.
The wiring pattern 22 serving as the back electrode corresponding to 1 is formed in a circular shape with a size not reaching the spacer 12. The wiring pattern 22 is formed on the rear surface of the printed wiring board 20 through the through hole 22A.
B, and the wiring pattern 22B is
It is connected to the pre-circuit 40.

On the front surface of the insulating substrate 21, a wiring pattern 23 is formed annularly around the wiring pattern 22 at a position corresponding to the spacer 12, and the wiring pattern 23 is formed by the wiring patterns 23A and 23A. The through hole 23B is connected to the wiring pattern 23C on the rear surface of the insulating substrate 21. The wiring pattern 23
C is a part of the ground line (earth line) of the pre-circuit 40.

Further, a through hole 25 is formed in the printed wiring board 20 at the portion of the wiring pattern 23.
Each component is fixed as described above with the screw 17 penetrating therethrough.

The size of the main part of the microphone unit 10 is the same as that of FIG. Also,
The printed wiring board 20 as described above can be manufactured by exactly the same steps and operations as those of a generally used double-sided printed wiring board.

For example, the insulating substrate 21 is a porous ceramic plate impregnated with an epoxy resin, and a glass cloth layer (not shown) impregnated with an epoxy resin for reinforcement is formed on both surfaces thereof. can do. The wiring patterns used for wiring the wiring patterns 22, 22B, 23A, and 23C and the pre-circuit 40 can also be formed in a required shape by etching the copper foil.

According to such a configuration, the capacitor C10 is constituted by the diaphragm 11 and the wiring pattern 22, and the diaphragm 11 is vibrated by a sound wave as shown by a broken line in FIG. The capacitance changes.
At this time, since the rear part of the diaphragm 11 is open to the air chamber (the space formed by the printed wiring board 20 and the air chamber member 15) at the rear part of the printed wiring board 20 through the through hole 24, the vibration The plate 11 can vibrate following the sound waves.

In this case, the wiring pattern 22
The vibration plate 11 is connected to the pre-circuit 40 through the signal line of the through hole 22A → the wiring pattern 22B, and the diaphragm 11 is connected to the pre-circuit 40 through the signal line of the spacer 12 → the wiring pattern 23 → the wiring pattern 23A → the through hole 23B → the wiring pattern 23C. It is connected to the.

Therefore, in the pre-circuit 40, a change in the capacitance of the capacitor C10 can be converted into an electric signal, and the signal is exactly a signal obtained by acoustically / electrically converting a sound wave that has vibrated the diaphragm 11. That is,
An audio signal collected by the microphone unit 10 can be obtained.

According to the condenser microphone shown in FIG. 1, the back plate of the microphone unit 10 is constituted by the printed wiring board 20, and the printed circuit board 20 is provided with the pre-circuit 40. Signal lines connecting the microphone unit 10 to the pre-circuit 40 (wiring patterns 22B, 23A, etc.)
Can be minimized, resulting in a microphone
The stray capacitance of the signal line connecting the unit 10 to the pre-circuit 40 can be minimized.

Accordingly, it is possible to suppress a decrease in the level of the audio signal caused by the stray capacitance,
The reduction in S / N can be suppressed.

Further, since the signal line connecting the microphone unit 10 to the pre-circuit 40 is constituted by the wiring pattern of the printed wiring board 20, even if the stray capacitance remains, the variation of the stray capacitance is suppressed. Therefore, variation in characteristics can be suppressed.

Further, in order to lower the cutoff frequency fc, it is necessary to increase the value of the resistor R40. Therefore, it is necessary to increase the insulation of the signal line and the pre-circuit 40 corresponding to the resistance value. However, since the wiring pattern 22 acting as the back electrode, the signal lines, and the pre-circuit 40 are all provided on the insulating substrate 21 of the printed wiring board 20 from which sufficient insulation can be originally secured, it is necessary to secure sufficient insulation. Can be.

Further, the spacer 12 and the like for determining the capacitance of the capacitor C10 can be formed of any metal by any processing method, and can be formed with high accuracy. Therefore, since the variation in the capacitance of the capacitor C10 can be suppressed, the variation in the level of the output audio signal can be suppressed, and the signal level and S / N of the design target can be obtained.

Further, since the back electrode plate is constituted by the printed wiring board 20, the wiring pattern 22 acting as a back electrode can be formed into a shape required electrically and with sufficient accuracy, and at the same time, the insulating pattern can be formed. The substrate 21 can also be formed in a shape necessary to support the wiring pattern 22. Therefore, excellent characteristics can be obtained from this point as a microphone unit of the condenser microphone.

Further, even if the thickness of the insulating substrate 21 varies, the distance between the wiring pattern 22 and the diaphragm 11 is not affected, so that the variation in the thickness of the insulating substrate 21 does not matter.

Further, when the printed wiring board 20 is manufactured, a solder resist layer (solder resist layer) can be formed on the surface of the wiring pattern 22. In this case, the wiring pattern 22 is covered and hidden. Therefore, even if moisture adheres to the inner peripheral surface of the spacer 12 and the like, insulation between the diaphragm 11 and the wiring pattern 22 is ensured by the solder resist layer, thereby lowering the insulation resistance. Never do. Therefore, stable microphone operation is always realized even in a humid environment,
A good audio signal can be obtained.

FIG. 5 shows a specific example of the pre-circuit 40, which comprises a cascode-connected differential amplifier. That is, the high-value resistor R40 and the microphone unit 10 are connected in series between the high voltage terminal THV to which a high voltage, for example, a DC voltage of 200 V is supplied, and the ground. At this time, in the microphone unit 10, the wiring pattern 22B is connected to the resistor R40,
The wiring pattern 23C is connected to the ground, and audio signals are extracted from both ends of the microphone unit 10.

A connection point between the resistor R40 and the microphone unit 10 is a DC cut capacitor C.
It is connected to the gate of the FET (Q41) through 41. In this case, the source of the FET (Q41) is connected to the source of the FET (Q42), and the FET (Q41, Q42) forms a differential amplifier A40. In addition, FET (Q41,
The emitter and collector of the transistors Q43 and Q44 are connected in series between the drain of the transistor Q42) and its load resistors R41 and R42, and the elements Q41, Q43 and R41 constitute a first cascode circuit A41. , Elements Q42, Q4
4. A second cascode circuit A42 is constituted by R42.

Therefore, the microphone unit 1
The audio signals from 0 are amplified by the circuits A41 to A43, and audio signals having phases opposite to each other are extracted from the collectors of the transistors Q43 and Q44. At this time,
An audio signal obtained at the collector of the transistor Q43 is negatively fed back to the gate of the FET (Q41) through the capacitor C42.

The audio signals from the transistors Q43 and Q44 are supplied to the bases of the transistors Q45 and Q46 constituting the differential amplifier A43, and the output terminal T41 is connected to the collector of the transistor Q45. The collector of the transistor Q45 is connected to the gate of the FET (Q42) through the negative feedback resistor R46.

Therefore, the audio signal extracted from the microphone unit 10 is amplified and extracted from the terminal T41. Since the first stage of the pre-circuit 40 is the differential amplifier A40 and the cascode circuits A41 and A42, the noise can be reduced.

In the above description, the diaphragm 11 may be formed by, for example, depositing a conductive material on a plastic film by vapor deposition or the like. Also, as the pre-circuit 40, the capacitor C10 is connected to the resonance circuit of the oscillation circuit, the oscillation frequency is FM-modulated by the capacitance change of the capacitor C10, and the FM signal is FM-demodulated to obtain an audio signal. You can also.

[0046]

According to the present invention, since the back electrode of the microphone unit and the pre-circuit are provided on the common insulating substrate, the wiring between them can be minimized. In addition, it is possible to minimize the stray capacitance and suppress the reduction of the output signal level and S / N.

Further, since the back electrode is provided on the insulating substrate, it is not necessary to use an insulating component having a complicated shape in order to obtain insulation between the diaphragm and the back electrode, and the microphone unit can be simplified. It can be realized with a simple structure. Further, the positional relationship between the diaphragm and the back electrode can be obtained with sufficient accuracy, and a good output signal can be obtained.

Further, since the back electrode plate and the back electrode are formed of a printed wiring board, each can be formed in any shape, and the position of the back electrode on the back electrode plate can be arbitrarily set. Also, the air chamber member 1
For example, a through hole may be provided in the rear surface of the diaphragm 5 to open the rear surface of the diaphragm 11 to the outside through the printed wiring board 20.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating one embodiment of the present invention.

FIG. 2 is a front view showing an embodiment of a main part of the present invention.

FIG. 3 is a cross-sectional view showing one embodiment of a main part of the present invention.

FIG. 4 is a rear view showing an embodiment of a main part of the present invention.

FIG. 5 is a connection diagram illustrating one embodiment of a circuit that can be used in the present invention.

FIG. 6 is a cross-sectional view for explaining the present invention.

FIG. 7 is an equivalent circuit diagram of the unit of FIG.

[Explanation of symbols]

10 = microphone unit, 11 = diaphragm, 12
= Spacer, 13 = insulating member, 15 = air chamber member, 16 =
Holding member, 17 = screw, 20 = printed wiring board, 2
1 = insulating substrate, 22 and 23 = wiring pattern, 22A
And 23B = through hole, 24 and 25 = through hole,
40 = prefix circuit

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Takeshi Hara 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Ikue Akiba 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Kohei Asada 6-7-35 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation

Claims (4)

[Claims] An electroconductive diaphragm, a back plate provided on a rear surface of the diaphragm, and a pre-circuit, wherein the back plate is an insulating plate, of the insulating plate, An electrode plate provided on a surface facing the diaphragm, wherein the pre-circuit is provided on the insulating plate, and the diaphragm and the back electrode are formed through a conductive pattern formed on the insulating plate. The vibration of the vibration plate due to the sound wave is taken out as a change in capacitance between the vibration plate and the electrode plate, and the change in capacitance is taken out as a signal from the pre-circuit. Condenser microphone. 2. The capacitor microphone according to claim 1, wherein said back electrode plate is a printed wiring board, said insulating plate is an insulating substrate of said printed wiring board, and said electrode plate and said conductive pattern are A capacitor microphone having a wiring pattern formed on the insulating substrate. 3. The capacitor microphone according to claim 2, wherein the wiring pattern as the electrode plate is connected to a wiring pattern on an opposite surface of the insulating substrate through a through hole, and the wiring pattern is connected to the front circuit. Condenser microphone. 4. The condenser microphone according to claim 3, wherein the wiring pattern as the electrode plate is covered and hidden by a solder resist layer.