JPH0779518B2 - Electrostatic microphone device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrostatic microphone device suitable for use as a noise compression microphone or a zoom microphone that detects a sound pressure signal as a change in electrostatic capacitance. .

[Conventional technology]

The electrostatic microphone device is provided with a detection electrode facing a vibrating plate that vibrates when receiving a sound pressure signal, and electrically detects a change in electrostatic capacitance between the vibrating plate and the detection electrode, which changes due to an amplitude displacement of the vibrating plate. It is converted into a signal and taken out. Recently, there has been a movement to expand such devices to zoom microphones and noise compression microphones.

[Problems to be Solved by the Invention]

However, the conventional electrostatic microphone device does not have very high detection sensitivity for minute electrostatic capacitance, and is not sufficiently satisfactory in terms of characteristics.

In addition, the circuits of the zoom microphone and the noise compression microphone are very complicated, resulting in low device manufacturing efficiency and high manufacturing cost.

The present invention has been made to solve the above-described conventional problems, and an object thereof is to be able to detect a minute sound pressure signal under ultrahigh sensitivity, which is sufficiently satisfactory as a noise compression microphone or a zoom microphone. An object of the present invention is to provide a simple electrostatic microphone device having a circuit configuration having a power characteristic.

[Means for Solving the Problems]

The present invention is configured as follows to achieve the above object. That is, the electrostatic microphone device of the present invention includes a main sound detection electrode that detects an amplitude displacement of a main sound diaphragm that vibrates in response to a sound pressure signal of the main sound as a change in capacitance.
A side tone detection electrode that detects an amplitude displacement of a side tone diaphragm that vibrates in response to a sound pressure signal of a side tone as a change in capacitance, and a main tone that receives a change in capacitance detected by the main tone detection electrode. A first ceramic resonator type electrostatic sensor circuit that outputs a detection signal, an operational amplifier that amplifies a signal of the first ceramic resonator type electrostatic sensor circuit, and an electrostatic capacitance detected by the side sound detection electrode. A second ceramic resonator type electrostatic sensor circuit that outputs a side sound detection signal in response to a change in capacitance, and a feedback amount of the operational amplifier is controlled by a signal from the second ceramic resonator type electrostatic sensor circuit. And a variable resistance element for adjusting sidetone cancellation are provided in the feedback control circuit, which is also a characteristic configuration of the present invention. .

[Action]

According to the present invention, when the sound pressure signal of the main sound coming from the front side of the device enters, the main sound diaphragm vibrates by receiving the sound pressure, and the change in the capacitance due to the vibration displacement is detected by the main sound detecting electrode. , The detected change in capacitance is applied to the first ceramic resonator type electrostatic sensor circuit.
The first ceramic resonator type electrostatic sensor circuit converts a change in electrostatic capacitance into a voltage signal and outputs it as a detection signal. Then, this detection signal is amplified by the operational amplifier and taken out. Similarly, when a sound pressure signal of a side sound is input from the lateral direction of the device, the side sound diaphragm vibrates in response to the sound pressure, and this amplitude displacement is detected by the side sound detection electrode, and the second ceramic resonance The side-tone detection signal is output as a voltage signal from the container-type electrostatic sensor circuit. This sidetone detection signal acts on the feedback control circuit to change the feedback amount of the operational amplifier. For example, the feedback amount is increased when the voltage value of the side sound detection signal is large, and the feedback amount is decreased when the voltage value of the side sound detection signal is small. Thus, the feedback amount changes according to the magnitude of the sidetone detection signal, and the sensitivity of the operational amplifier is automatically adjusted.

In addition, in the configuration in which the feedback control circuit is provided with a variable resistance element for adjusting sidetone, if the resistance value of the variable resistance element is adjusted to the maximum, the feedback amount becomes zero and the sidetone is eliminated. , Only the tonic is extracted.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a circuit diagram of an embodiment of the electrostatic microphone device according to the present invention, and FIGS. 2 and 3 show a structure of a sound pressure detecting portion constituting the device of the embodiment. An example is shown. The device of this embodiment includes a first ceramic resonator type electrostatic sensor circuit 9a, a second ceramic resonator type electrostatic sensor circuit 9b, a sound pressure detection unit 3, an operational amplifier 12, and a feedback control circuit. 13 and the main circuit.

The first ceramic resonator type electrostatic sensor circuit 9a includes an oscillation circuit 1 having a ceramic resonator, and the oscillation circuit 1
The main resonator 2 is composed of a ceramic resonator that is independent of the ceramic resonator and a detection circuit 4, and the output electrodes of the oscillation circuit 1 and the main resonator 2 are a resistor 5 and a cup. They are connected via a ring capacitor 6, and the output electrode of the main tone resonator 2 and the detection circuit 4 are connected via a high impedance circuit composed of a coupling capacitor 7 and an inductance element 8.

The second ceramic resonator type electrostatic sensor circuit 9b includes an oscillation circuit 1, a side-tone resonator 10 which is a ceramic resonator independent of the ceramic resonator of the oscillation circuit 1, and a detection circuit 4 '. And has a circuit configuration similar to that of the first ceramic resonator type electrostatic sensor circuit 9a.
The circuit parts corresponding to the ceramic resonator type electrostatic sensor circuit 9a are distinguished by adding a dash to the number.

The positive side input terminal (non-inverting input terminal) of the operational amplifier 12 is connected to the output side of the detection circuit 4 of the first ceramic resonator type electrostatic sensor circuit 9a via a resistor 11. A first feedback resistor 14 is connected between the output side of the operational amplifier 12 and the negative side input terminal (inverting input terminal). The feedback control circuit 13 is connected to the negative input terminal of the operational amplifier 12. The feedback control circuit 13 includes a MOS FET 15, a feedback resistor 16, and
It comprises a variable resistor 17 as a variable resistance element and a second feedback resistor 18.

A variable resistor 17 and a second feedback resistor 18 are connected in series between the negative input terminal of the operational amplifier 12 and the source of the MOS FET 15. The feedback resistor 16 is provided between the source and the base of the MOS FET 15, and the drain of the MOS FET 15 is connected to the ground.
The base of the MOS FET 15 is provided with a detection circuit 4'in the second ceramic resonator type electrostatic sensor circuit 9b via a resistor 20.
Is connected to the output side of.

2 and 3 show the configuration of the sound pressure detector 3. In these figures, a frame body 21 made of a silicon material has an outer diaphragm forming frame portion 22 and a back pole frame portion 23 combined therewith, as shown in FIG. A tonic window 24 for taking in the sound pressure signal of the tonic is formed on the plane side of the diaphragm forming frame portion 22, and a tonic diaphragm 25 formed by diffusing fluorine into silicon is formed in the tonal window 24. It is formed integrally. Further, a plurality of sidetone windows 26 for taking in sidetones are formed on the side surface of the diaphragm forming frame portion 22, and sidetone diaphragms 27 are also integrally formed in each sidetone window 26 so as to close the windows. Is formed in.

The back pole frame portion 23 has an opposing surface that opposes the main tone vibration plate 25 and the side tone vibration plate 27 with a constant gap therebetween, and the main tone detection electrode 28 is provided on the opposite face to the main tone vibration plate 25. Is similarly formed of a fluorinated film or the like. Also, side tone diaphragm
Similarly, on the circumferential side surface of the back electrode frame portion 23 facing the back electrode frame portion 27, a side sound detecting electrode 30 is formed of a fluoride film or the like. An acoustic adjustment hole 31 for adjusting the acoustic coefficient is formed in the contact wall surface of the back electrode frame portion 23 with which the main sound detection electrode 28 and the side sound detection electrode 30 are respectively in contact. These acoustic adjustment holes 31
It is possible to process the window and the like by using micromachining technology using anisotropic etching or selective etching of silicon, and in order to facilitate the processing, the frame 21 is separated from the separation line 21a. It can be obtained by dividing and forming into a plurality of blocks, and finally incorporating and connecting them integrally.

The main sound diaphragm 25 is connected to the output electrode of the main sound resonator 2, and the side sound detection electrode 30 is connected to the output electrode of the side sound resonator 10. These main tone resonator 2 and side tone resonator
As shown in FIG. 4, each of the resonance frequencies f _{0 of} 10 is set at a position slightly deviated from the fixed frequency f _{1 of the} carrier signal oscillated from the common oscillating circuit 1. Is applied to the output electrode, the resonance frequency is biased by Δf, the tuning point is changed from A ₁ to A ₂ , and Δv
The voltage change component of is extracted. This voltage change component Δv
Is carried on the carrier signal to generate an amplitude modulation signal in each of the resonators 2 and 10, and this is added to the corresponding detection circuit 4 or 4 '.

The present embodiment is configured as described above, and its operation will be described below.

When the device is driven, a carrier signal having a fixed ultrahigh frequency of, for example, 1 GHz to 3 GHz from the oscillation circuit 1 is used as a selected carrier. This carrier signal is distributed and supplied to the main tone resonator 2 and the side tone resonator 10. In this state, when the main sound enters the main sound vibration plate 25, the main sound vibration plate 25 receives the sound pressure and vibrates, and its amplitude displacement is detected by the main sound detection electrode 28 as a change in the capacitance, and the detection is performed. A change in capacitance is applied to the main tone resonator 2.

In response to this change in capacitance, the main tone resonator 2 biases the resonance frequency by, for example, Δf in FIG. 4, changes the tuning point with the oscillation frequency f ₁ of the oscillation circuit ₁ from A ₁ to A _2, and The change in capacitance is taken out as the change in voltage Δv. Specifically, the main tone resonator 2 multiplies the frequency of the carrier signal by the change Δf of the resonance frequency due to the change of the capacitance, multiplies the carrier signal by the voltage Δv of the change component of the tuning point, and performs amplitude modulation. (AM (Am
plitude Modulation) signal is generated and added to the detection circuit 4. The detection circuit 4 envelope-detects this AM-modulated signal and converts it into a signal corresponding to the sound pressure signal of the tonic,
This is added to the operational amplifier 12. The operational amplifier 12 amplifies the detected output signal and sends it to a desired signal processing circuit such as a loudspeaker or a recorder.

On the other hand, when the sound pressure signal of the side sound enters the side sound diaphragm 27, the side sound diaphragm 27 receives the sound pressure and vibrates, and the amplitude displacement of the side sound diaphragm 27 is caused by the side sound detection electrode 30. Detected as a change in capacitance, the detection signal is applied to the sidetone resonator 10. Similarly to the main tone resonator 2, the side tone resonator 10 biases the resonance frequency in response to the change in the capacitance detected by the side tone detection electrode 30, and changes the tuning point with the oscillation frequency f ₁ . A voltage change corresponding to the change of the tuning point is produced as an AM modulation signal using the carrier wave, and this is added to the detection circuit 4 '.

The detection circuit 4'performs envelope detection similarly to the detection circuit 4 and applies the detection output to the base of the MOS FET 15. MOS
The FET 15 increases the base current to decrease the resistance between the source and drain as the signal applied from the detection circuit 4'increases, and reduces the feedback amount of the operational amplifier 12. On the other hand, when the detection output signal from the detection circuit 4'becomes small, the resistance between the source and drain of the MOS FET 15 becomes large, and the feedback amount of the operational amplifier 12 becomes large. Thus, the feedback amount of the operational amplifier 12 is controlled according to the magnitude of the side sound detection signal added from the detection circuit 4 ', and the sensitivity of the operational amplifier 12 is automatically adjusted.

When the variable resistor 17 is manually operated during this circuit operation to increase the resistance value to the maximum (almost infinity), the MOS FET 15 and the operational amplifier 12 are cut off in a circuit manner, and the side tone detection signal is erased. .

The side tone detection signal is erased when the device of the present embodiment is used as a zoom microphone, when the microphone is zoomed to obtain a sound pressure signal of a distant tonic,
In addition to manually operating the variable resistor 17, this sidetone elimination is linked to the zoom movement of the camera when, for example, when using a video device, the video camera is zoomed to shoot a distant object. The sliding terminal of the sliding resistor may be moved to change the resistance value of the variable resistor 17, or a sensor for detecting the zoom movement of the camera lens may be provided and linked with the signal of this sensor. The resistance value of the variable resistor 17 may be changed, and the resistance value of the variable resistor 17 can be adjusted by various means.

Since the device of this embodiment can detect a minute sound pressure from a low frequency region to a high frequency region under high characteristics, it is also suitable for use as a microphone device for detecting an abnormal sound of a stethoscope or a machine. Become.

The present invention is not limited to the above-mentioned embodiments, and can take various modes.

〔The invention's effect〕

The present invention, since it is intended to detect by using a ceramic resonator forms electrostatic sensor a change in electrostatic capacity corresponding to the amplitude displacement of the vibration plate that vibrates by acoustic pressure signal, ultra-sensitive as 10 ^-7 PF It is possible to detect the original minute electrostatic capacitance, which enables accurate detection of weak sound pressure signals with high sensitivity, and has a wide range of frequency characteristics in the voice sound band of 10 Hz to 100 KHz. It is possible to provide a high-performance microphone device.

Further, since the microphone device of the present invention uses the ceramic resonator type electrostatic sensor, the device is small and lightweight, and the handling is very convenient.

Further, it becomes possible to operate the feedback control circuit in response to the side tone detection signal and automatically adjust the sensitivity of the operational amplifier that amplifies the sound pressure detection signal, and it is possible to achieve higher functionality of the device.

Furthermore, by adjusting the resistance value of the variable resistance element provided in the feedback control circuit, the side-tone detection signal can be erased appropriately, so it is extremely useful when used as a zoom microphone or a noise compression microphone. It is convenient, and it is possible to develop various systems of the electrostatic microphone device by providing the side tone elimination function, the super-sensitive detection capability, and the automatic sensitivity adjustment capability of the operational amplifier.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of an electrostatic microphone device according to the present invention, FIG. 2 is a vertical cross-sectional view of a sound pressure detecting portion constituting the same embodiment, and FIG. 3 is a perspective view of the sound pressure detecting portion. , FIG. 4 is an operation explanatory view of the resonator functioning as a tuning circuit in the embodiment. 1 ... Oscillation circuit, 2 ... Main tone resonator, 3 ... Sound pressure detector, 4,4 '... Detection circuit, 5,5' ... Resistor, 6,6 '...
Coupling capacitor, 7,7 '... Coupling capacitor, 8,8' ... Inductance element, 9a ... First ceramic resonator type electrostatic sensor circuit, 9b ... Second ceramic resonator type electrostatic Sensor circuit, 10 ... Side tone resonator, 11
...... Resistor, 12 ...... Operational amplifier, 13 ...... Feedback control circuit,
14 …… first feedback resistor, 15 …… MOS FET, 16 …… feedback resistor, 17 …… variable resistor, 18 …… second feedback resistor, 20 …… resistor, 21 …… frame Body, 22 …… Vibration plate forming frame, 23 …… Back pole frame part, 24 …… Main tone window, 25 …… Main tone diaphragm, 26 …… Side tone window, 27 …… Side tone diaphragm, 28… … Main sound detection electrode, 30 …… Side sound detection electrode, 31 …… Sound adjustment hole.

Claims (2)

[Claims] 1. A main sound detection electrode for detecting an amplitude displacement of a main sound diaphragm vibrating in response to a sound pressure signal of a main sound as a change in capacitance, and a side sound diaphragm vibrating in response to a sound pressure signal of a side sound. Sound detection electrode for detecting the amplitude displacement of the sound as a change in capacitance, and a first ceramic resonator type electrostatic sensor for outputting a main sound detection signal in response to a change in capacitance detected by the main sound detection electrode. A circuit, an operational amplifier that amplifies a signal of the first ceramic resonator type electrostatic sensor circuit, and a second side sound detection signal that is output in response to a change in capacitance detected by the side sound detection electrode. Of the ceramic resonator type electrostatic sensor circuit, and a feedback control circuit for controlling the feedback amount of the operational amplifier by a signal from the second ceramic resonator type electrostatic sensor circuit. 2. The electrostatic microphone device according to claim 1, wherein the feedback control circuit is provided with a variable resistance element for adjusting sidetone cancellation.