JP4024213B2 - Impedance converter for condenser microphone - Google Patents

Impedance converter for condenser microphone Download PDF

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JP4024213B2
JP4024213B2 JP2003583055A JP2003583055A JP4024213B2 JP 4024213 B2 JP4024213 B2 JP 4024213B2 JP 2003583055 A JP2003583055 A JP 2003583055A JP 2003583055 A JP2003583055 A JP 2003583055A JP 4024213 B2 JP4024213 B2 JP 4024213B2
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capacitor
resistor
impedance converter
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source follower
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隆志 山崎
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/50—Amplifiers in which input is applied to, or output is derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower
    • H03F3/505—Amplifiers in which input is applied to, or output is derived from, an impedance common to input and output circuits of the amplifying element, e.g. cathode follower with field-effect devices
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/181—Low-frequency amplifiers, e.g. audio preamplifiers
    • H03F3/183—Low-frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
    • H03F3/185—Low-frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only with field-effect devices
    • H03F3/1855—Low-frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only with field-effect devices with junction-FET devices
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/03—Indexing scheme relating to amplifiers the amplifier being designed for audio applications
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/219—Follower transistors are added at the input of the amplifier, e.g. source or emitter followers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F2200/00—Indexing scheme relating to amplifiers
    • H03F2200/222—A circuit being added at the input of an amplifier to adapt the input impedance of the amplifier

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  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)

Description

本発明は、補聴器などに用いられる小型のコンデンサマイクロホンに組み込むインピーダンス変換器に関する。   The present invention relates to an impedance converter incorporated in a small condenser microphone used in a hearing aid or the like.

従来のコンデンサマイクロホンの電気信号に関する出力インピーダンスを低減するインピーダンス変換器としては、電界効果型トランジスタ（ＦＥＴ）を用いたソースフォロワ回路を備え、このソースフォロワ回路の電源線及び出力信号線とグランド線との間に夫々３０ｐＦのコンデンサを接続したものが知られている（例えば、特許文献１参照）。これらのコンデンサは基板上に直接誘電率の高い絶縁体を回路パターンで挟み込んで実装され、これにより高周波電磁波妨害を受け難くしている。   As an impedance converter for reducing the output impedance related to an electric signal of a conventional condenser microphone, a source follower circuit using a field effect transistor (FET) is provided. A power source line, an output signal line, a ground line of the source follower circuit, There is known one in which a capacitor of 30 pF is connected between each of them (for example, see Patent Document 1). These capacitors are mounted on a substrate by directly sandwiching an insulator having a high dielectric constant between circuit patterns, thereby making it difficult to receive high-frequency electromagnetic interference.

また、従来の補聴器用マイクロホンにおいて、そのインピーダンス変換器は、セラミックス基板上にＪＦＥＴまたはＭＯＳＦＥＴのトランジスタチップを搭載し、セラミックス基板上に焼成抵抗を形成し、コンデンサについてはチップ部品を搭載するか、または強誘電体の膜を蒸着層で挟み込むことによってセラミックス基板上に形成することによりハイブリット回路として実現していた。   Further, in a conventional hearing aid microphone, the impedance converter has a JFET or MOSFET transistor chip mounted on a ceramic substrate, a firing resistor is formed on the ceramic substrate, and a chip component is mounted on the capacitor. It has been realized as a hybrid circuit by forming a ferroelectric film on a ceramic substrate by sandwiching it between vapor deposition layers.

米国特許第６０８４９７２号明細書US Pat. No. 6,084,972

しかし、従来のインピーダンス変換器においては、高周波電磁波妨害を除去するために電源線、出力信号線及びグランド線の高周波電磁波に対する電位の変化を等しく低減することで、電源線、出力信号線及びグランド線の電位のアンバランスな変化をなくし、高周波電磁波によるソースフォロワ回路からの雑音の出力を防ぐ必要がある。そのため電源線とグランド線の間に設けたコンデンサの静電容量と、出力信号線とグランド線の間に設けたコンデンサの静電容量を等しくする必要がある。この状態では、インピーダンス変換器の端子に静電気放電などのサージ電圧が加わると、直接コンデンサに高電圧が印加することになるので、コンデンサの耐圧を上げる必要がある。   However, in the conventional impedance converter, the power line, the output signal line, and the ground line are reduced by equally reducing the potential change of the power line, the output signal line, and the ground line with respect to the high frequency electromagnetic wave in order to remove the high frequency electromagnetic wave interference. It is necessary to eliminate the unbalanced change in the potential of the source and prevent the output of noise from the source follower circuit due to high frequency electromagnetic waves. Therefore, it is necessary to make the capacitance of the capacitor provided between the power supply line and the ground line equal to the capacitance of the capacitor provided between the output signal line and the ground line. In this state, when a surge voltage such as electrostatic discharge is applied to the terminal of the impedance converter, a high voltage is directly applied to the capacitor, so that it is necessary to increase the breakdown voltage of the capacitor.

また、インピーダンス変換器をセラミックス基板上にハイブリット回路として形成した場合には、補聴器用マイクロホンを小型化する際に、そのセラミックス基板上に形成したハイブリット回路の基板寸法が小型化を妨げてしまうという問題がある。   In addition, when the impedance converter is formed as a hybrid circuit on the ceramic substrate, the size of the hybrid circuit formed on the ceramic substrate prevents the miniaturization when the hearing aid microphone is downsized. There is.

本発明は、従来の技術が有するこのような問題点に鑑みてなされたものであり、その目的とするところは、静電気放電などのサージ電圧がコンデンサに直接加わることがなく、耐圧が低いコンデンサでもサージ電圧に耐えられ、しかも小型化が図れるコンデンサマイクロホン用インピーダンス変換器を提供しようとするものである。   The present invention has been made in view of such problems of the prior art, and the object of the present invention is to prevent a surge voltage such as electrostatic discharge from being directly applied to the capacitor, even if the capacitor has a low breakdown voltage. An object of the present invention is to provide an impedance converter for a condenser microphone that can withstand a surge voltage and can be reduced in size.

上記課題を解決すべく請求項１に係る発明は、コンデンサマイクロホンの電気信号に関する出力インピーダンスを低減するインピーダンス変換器であって、電界効果型トランジスタ（ＦＥＴ）を用いたソースフォロワ回路を備え、このソースフォロワ回路の電源線及び出力信号線に夫々抵抗Ｒ1，Ｒ2を直列に接続し、これらの抵抗Ｒ1，Ｒ2の前記ソースフォロワ回路側の前記電源線及び出力信号線とグランド線との間に夫々コンデンサＣ1，Ｃ2を接続し、前記電源線に接続された抵抗Ｒ1とコンデンサＣ1により構成されるフィルタ回路のカットオフ周波数と、前記出力信号線に接続された抵抗Ｒ2とコンデンサＣ2により構成されるフィルタ回路のカットオフ周波数をほぼ等しくした。 In order to solve the above-mentioned problem, an invention according to claim 1 is an impedance converter for reducing an output impedance related to an electric signal of a condenser microphone, comprising a source follower circuit using a field effect transistor (FET), and the source Resistors R1 and R2 are connected in series to the power supply line and output signal line of the follower circuit, and capacitors are respectively connected between the power supply line and output signal line on the source follower circuit side of these resistors R1 and R2 and the ground line. C1 and C2 are connected to each other , and a cutoff frequency of a filter circuit constituted by a resistor R1 and a capacitor C1 connected to the power supply line, and a filter circuit constituted by a resistor R2 and a capacitor C2 connected to the output signal line. The cut-off frequencies of were made almost equal .

請求項２に係る発明は、請求項１に記載のコンデンサマイクロホン用インピーダンス変換器において、前記ソースフォロワ回路と、前記抵抗Ｒ1とコンデンサＣ1により構成されるフィルタ回路と、前記抵抗Ｒ2とコンデンサＣ2により構成されるフィルタ回路が、同一シリコン基板上にワンチップで形成される。 Configuration invention according to claim 2, in the capacitor impedance converter microphone according to claim 1, said source follower circuit, a filter circuit constituted by the resistor R1 and the capacitor C1, by the resistor R2 and the capacitor C2 The filter circuit to be formed is formed in one chip on the same silicon substrate.

請求項１に係る発明によれば、電源線及び出力信号線に静電気などによるサージ電圧が印加されたとしても、サージ電圧は先ず抵抗Ｒ1及び抵抗Ｒ2に加わり、抵抗Ｒ1，Ｒ2の内部で熱エネルギーとして消費され、サージ電圧はその波高値を減じてコンデンサＣ1，Ｃ2に印加されるため、コンデンサＣ1，Ｃ2には、サージ電圧が直接印加されないため高い耐圧を持たせる必要がなく、インピーダンス変換器の機能とは関係ない過剰な品質をコンデンサＣ1，Ｃ2に求めなくて済む。   According to the first aspect of the present invention, even if a surge voltage due to static electricity or the like is applied to the power supply line and the output signal line, the surge voltage is first applied to the resistor R1 and the resistor R2, and heat energy is generated inside the resistors R1 and R2. Since the surge voltage is applied to the capacitors C1 and C2 with its peak value reduced, the surge voltage is not directly applied to the capacitors C1 and C2. There is no need for the capacitors C1 and C2 to obtain excessive quality unrelated to the function.

また、抵抗Ｒ1とコンデンサＣ1により構成されるフィルタ回路のカットオフ周波数と、抵抗Ｒ2とコンデンサＣ2により構成されるフィルタ回路のカットオフ周波数をほぼ等しくしたので、電源線とグランド線との間の高周波電磁波による妨害電波と、出力信号線とグランド線との間の高周波電磁波による妨害電波を等しく低減し、高周波電磁波によるソースフォロワ回路からの雑音の出力を防ぐことができる。 Further, since the cutoff frequency of the filter circuit composed of the resistor R1 and the capacitor C1 and the cutoff frequency of the filter circuit composed of the resistor R2 and the capacitor C2 are substantially equal , the high frequency between the power supply line and the ground line The interference radio wave due to the electromagnetic wave and the interference radio wave due to the high frequency electromagnetic wave between the output signal line and the ground line can be equally reduced, and the output of noise from the source follower circuit due to the high frequency electromagnetic wave can be prevented.

請求項２に係る発明によれば、補聴器用マイクロホンの小型化を促進することが容易にできる。 According to the second aspect of the present invention, it is possible to easily promote downsizing of the hearing aid microphone.

以下に本発明の実施の形態を添付図面に基づいて説明する。ここで、図１は本発明に係るコンデンサマイクロホン用インピーダンス変換器の回路図である。   Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a circuit diagram of an impedance converter for a condenser microphone according to the present invention.

図１に示すように、本発明に係るコンデンサマイクロホン用インピーダンス変換器１は、電界効果型トランジスタ（ＦＥＴ）２と抵抗３，４からなるソースフォロワ回路５と、ソースフォロワ回路５の電源線６及び出力信号線７に夫々直列に接続した抵抗Ｒ1，Ｒ2と、これらの抵抗Ｒ1，Ｒ2のソースフォロワ回路５側の電源線６及び出力信号線７とグランド線８との間に夫々接続したコンデンサＣ1，Ｃ2を備えている。なお、９はコンデンサマイクロホン、１０は電源端子、１１は出力端子、１２はグランド端子である。   As shown in FIG. 1, an impedance converter 1 for a condenser microphone according to the present invention includes a source follower circuit 5 comprising a field effect transistor (FET) 2 and resistors 3 and 4, a power source line 6 of the source follower circuit 5, and Resistors R1 and R2 connected in series to the output signal line 7, respectively, and a capacitor C1 connected between the power supply line 6 and the output signal line 7 of the resistors R1 and R2 on the source follower circuit 5 side and the ground line 8, respectively. , C2. Note that 9 is a condenser microphone, 10 is a power supply terminal, 11 is an output terminal, and 12 is a ground terminal.

そして、電源線６に接続された抵抗Ｒ1とコンデンサＣ1によりローパスフィルタ回路１３を構成し、出力信号線７に接続された抵抗Ｒ2とコンデンサＣ2によりローパスフィルタ回路１４を構成する。ローパスフィルタ回路１３のカットオフ周波数と、ローパスフィルタ回路１４のカットオフ周波数は等しくなるよう且つ、カットオフ周波数が妨害電波として受ける高周波電磁波の周波数より低くなるよう、抵抗Ｒ1，Ｒ2の抵抗値とコンデンサＣ1，Ｃ2の静電容量の値が決定される。抵抗Ｒ1の抵抗値と抵抗Ｒ2の抵抗値は等しくなくてもよく、コンデンサＣ1の静電容量の値とコンデンサＣ2の静電容量の値は等しくなくてもよい。   The low-pass filter circuit 13 is constituted by the resistor R1 and the capacitor C1 connected to the power supply line 6, and the low-pass filter circuit 14 is constituted by the resistor R2 and the capacitor C2 connected to the output signal line 7. Resistance values of resistors R1 and R2 and capacitors so that the cut-off frequency of the low-pass filter circuit 13 and the cut-off frequency of the low-pass filter circuit 14 are equal and the cut-off frequency is lower than the frequency of the high-frequency electromagnetic wave received as an interference wave. The capacitance values of C1 and C2 are determined. The resistance value of the resistor R1 may not be equal to the resistance value of the resistor R2, and the capacitance value of the capacitor C1 and the capacitance value of the capacitor C2 may not be equal.

以上のように構成した本発明に係るコンデンサマイクロホン用インピーダンス変換器１の動作について説明する。
音響信号がコンデンサマイクロホン９で電気信号に変換され、得られた電気信号がソースフォロワ回路５のＦＥＴ２に入力する。すると、コンデンサマイクロホン９の電気信号に関する出力インピーダンスは、ＦＥＴ２によって低減される。電気信号は抵抗Ｒ2と出力信号線７を介して出力端子１１より出力される。 The operation of the condenser microphone impedance converter 1 configured as described above will be described.
The acoustic signal is converted into an electric signal by the condenser microphone 9, and the obtained electric signal is input to the FET 2 of the source follower circuit 5. Then, the output impedance regarding the electric signal of the condenser microphone 9 is reduced by the FET 2. The electric signal is output from the output terminal 11 via the resistor R2 and the output signal line 7.

抵抗Ｒ1とコンデンサＣ1によるローパスフィルタ回路１３と抵抗Ｒ2とコンデンサＣ2によるローパスフィルタ回路１４のカットオフ周波数は、妨害電波として受ける高周波電磁波の周波数より低く設定されているため、電源線６とグランド線８との間の高周波電磁波による妨害電波と、出力信号線７とグランド線８との間の高周波電磁波による妨害電波を等しく低減し、高周波電磁波によるソースフォロワ回路５からの雑音の出力を防ぐことができる。   Since the cut-off frequency of the low-pass filter circuit 13 composed of the resistor R1 and the capacitor C1 and the low-pass filter circuit 14 composed of the resistor R2 and the capacitor C2 is set lower than the frequency of the high-frequency electromagnetic wave received as an interference radio wave, the power line 6 and the ground line 8 Between the output signal line 7 and the ground line 8 can be equally reduced to prevent noise from being output from the source follower circuit 5 due to the high frequency electromagnetic wave. .

これによって、ソースフォロワ回路５は高周波電磁波による妨害電波を検波することなくコンデンサマイクロホン９からの電気信号をインピーダンス変換して出力端子１１より出力することができる。この時、電源端子１０及び出力端子１１に静電気などによるサージ電圧が印加されたとしても、サージ電圧は先ず抵抗Ｒ1及び抵抗Ｒ2に加わり、抵抗Ｒ1，Ｒ2の内部で熱エネルギーとして消費され、サージ電圧はその波高値を減じてコンデンサＣ1，Ｃ2に印加される。
従って、コンデンサＣ1，Ｃ2には、サージ電圧が直接印加されないため高い耐圧を持たせる必要がなく、インピーダンス変換器の機能とは関係ない過剰な品質をコンデンサＣ1，Ｃ2に求めなくて済む。 As a result, the source follower circuit 5 can impedance-convert the electrical signal from the condenser microphone 9 and output it from the output terminal 11 without detecting interference radio waves due to high-frequency electromagnetic waves. At this time, even if a surge voltage due to static electricity or the like is applied to the power supply terminal 10 and the output terminal 11, the surge voltage is first applied to the resistor R1 and the resistor R2, and is consumed as thermal energy inside the resistors R1 and R2, and the surge voltage Is applied to the capacitors C1 and C2 with its peak value reduced.
Therefore, since no surge voltage is directly applied to the capacitors C1 and C2, it is not necessary to have a high breakdown voltage, and it is not necessary to obtain excessive quality from the capacitors C1 and C2 regardless of the function of the impedance converter.

また、抵抗Ｒ1，Ｒ2の抵抗値を大きくすることによりサージ電圧に対して強靭になるが、電源線６に直列に大きな抵抗を接続するのは、インピーダンス変換器が電池駆動の補聴器などの機器に使用された場合、電池の内部抵抗を大きくするのと等価に作用するため、それらに適用するのは不利となる。従って、電源線６に設けた抵抗Ｒ1の抵抗値は、補聴器などの電池駆動の製品にインピーダンス変換器を適用する場合には、使用上不利にならない程度に小さくする必要がある。   Also, by increasing the resistance values of the resistors R1 and R2, it becomes strong against surge voltage. However, the impedance converter is connected to the power line 6 in series with a battery-driven hearing aid or the like. When used, it is equivalent to increasing the internal resistance of the battery, so it is disadvantageous to apply to them. Therefore, when the impedance converter is applied to a battery-driven product such as a hearing aid, it is necessary to make the resistance value of the resistor R1 provided on the power supply line 6 small enough not to be disadvantageous in use.

また、出力信号線７に設けた抵抗Ｒ2の抵抗値は、抵抗Ｒ1の抵抗値ほど小さくなくても適用する機器に影響を与えることが少ない。従って、抵抗Ｒ2の抵抗値は、サージ電圧に対してより強靭にするため大きくすることができる。よって、電源線６に設けた抵抗Ｒ1の抵抗値と出力信号線７に設けた抵抗Ｒ2の抵抗値は、等しくする必要はない。   Further, even if the resistance value of the resistor R2 provided on the output signal line 7 is not as small as the resistance value of the resistor R1, it hardly affects the device to be applied. Therefore, the resistance value of the resistor R2 can be increased to make it more robust against surge voltages. Therefore, the resistance value of the resistor R1 provided on the power supply line 6 and the resistance value of the resistor R2 provided on the output signal line 7 need not be equal.

また、本発明に係るコンデンサマイクロホン用インピーダンス変換器１は、ソースフォロワ回路５と、抵抗Ｒ1とコンデンサＣ1により構成されるローパスフィルタ回路１３と、抵抗Ｒ2とコンデンサＣ2により構成されるローパスフィルタ回路１４が、同一のシリコン基板上にワンチップで形成されるので、補聴器用マイクロホンの小型化を容易にすることができる。   The capacitor microphone impedance converter 1 according to the present invention includes a source follower circuit 5, a low-pass filter circuit 13 including a resistor R1 and a capacitor C1, and a low-pass filter circuit 14 including a resistor R2 and a capacitor C2. Since it is formed on the same silicon substrate with one chip, the hearing aid microphone can be easily downsized.

本願発明によれば、電源線及び出力信号線に静電気などによるサージ電圧が印加されたとしても、サージ電圧は先ず抵抗Ｒ1及び抵抗Ｒ2に加わり、抵抗Ｒ1，Ｒ2の内部で熱エネルギーとして消費され、サージ電圧はその波高値を減じてコンデンサＣ1，Ｃ2に印加されるため、コンデンサＣ1，Ｃ2には、サージ電圧が直接印加されないため高い耐圧を持たせる必要がなく、インピーダンス変換器の機能とは関係ない過剰な品質をコンデンサＣ1，Ｃ2に求めなくて済む。
また、抵抗Ｒ1とコンデンサＣ1により構成されるフィルタ回路のカットオフ周波数と、抵抗Ｒ2とコンデンサＣ2により構成されるフィルタ回路のカットオフ周波数をほぼ等しくしたので、電源線とグランド線との間の高周波電磁波による妨害電波と、出力信号線とグランド線との間の高周波電磁波による妨害電波を等しく低減し、高周波電磁波によるソースフォロワ回路からの雑音の出力を防ぐことができる。 According to the present invention, even if a surge voltage due to static electricity or the like is applied to the power supply line and the output signal line, the surge voltage is first applied to the resistor R1 and the resistor R2, and is consumed as thermal energy inside the resistors R1 and R2. Since the surge voltage is applied to the capacitors C1 and C2 with its peak value reduced, the capacitors C1 and C2 do not need to have a high breakdown voltage because the surge voltage is not directly applied, and this is related to the function of the impedance converter. There is no need to obtain excessive quality in the capacitors C1 and C2.
Further, since the cutoff frequency of the filter circuit composed of the resistor R1 and the capacitor C1 and the cutoff frequency of the filter circuit composed of the resistor R2 and the capacitor C2 are substantially equal , the high frequency between the power supply line and the ground line The interference radio wave due to the electromagnetic wave and the interference radio wave due to the high frequency electromagnetic wave between the output signal line and the ground line can be equally reduced, and the output of noise from the source follower circuit due to the high frequency electromagnetic wave can be prevented.

本発明に係るコンデンサマイクロホン用インピーダンス変換器の回路図Circuit diagram of impedance converter for condenser microphone according to the present invention

符号の説明Explanation of symbols

１…インピーダンス変換器、２…ＦＥＴ、５…ソースフォロワ回路、６…電源線、７…出力信号線、８…グランド線、９…コンデンサマイクロホン、１３，１４…ローパスフィルタ回路、Ｃ1，Ｃ2…コンデンサ、Ｒ1，Ｒ2…抵抗。   DESCRIPTION OF SYMBOLS 1 ... Impedance converter, 2 ... FET, 5 ... Source follower circuit, 6 ... Power supply line, 7 ... Output signal line, 8 ... Ground line, 9 ... Condenser microphone, 13, 14 ... Low-pass filter circuit, C1, C2 ... Capacitor , R1, R2 ... resistance.

Claims (2)

コンデンサマイクロホンの電気信号に関する出力インピーダンスを低減するインピーダンス変換器であって、電界効果型トランジスタ（ＦＥＴ）を用いたソースフォロワ回路を備え、このソースフォロワ回路の電源線及び出力信号線に夫々抵抗Ｒ1，Ｒ2を直列に接続し、これらの抵抗Ｒ1，Ｒ2の前記ソースフォロワ回路側の前記電源線及び出力信号線とグランド線との間に夫々コンデンサＣ1，Ｃ2を接続し、前記電源線に接続された抵抗Ｒ 1 とコンデンサＣ 1 により構成されるフィルタ回路のカットオフ周波数が、前記出力信号線に接続された抵抗Ｒ 2 とコンデンサＣ 2 により構成されるフィルタ回路のカットオフ周波数とほぼ等しいことを特徴とするコンデンサマイクロホン用インピーダンス変換器。An impedance converter for reducing an output impedance related to an electric signal of a condenser microphone, comprising a source follower circuit using a field effect transistor (FET), and a resistance R1, a power supply line and an output signal line of the source follower circuit, respectively. R2 is connected in series, and capacitors C1 and C2 are connected between the power supply line and output signal line on the source follower circuit side of these resistors R1 and R2 and the ground line, respectively, and connected to the power supply line. The cutoff frequency of the filter circuit constituted by the resistor R 1 and the capacitor C 1 is substantially equal to the cutoff frequency of the filter circuit constituted by the resistor R 2 and the capacitor C 2 connected to the output signal line. Impedance converter for condenser microphone. 請求項１に記載のコンデンサマイクロホン用インピーダンス変換器において、前記ソースフォロワ回路と、前記抵抗Ｒ1とコンデンサＣ1により構成されるフィルタ回路と、前記抵抗Ｒ2とコンデンサＣ2により構成されるフィルタ回路が、同一シリコン基板上にワンチップで形成されることを特徴とするコンデンサマイクロホン用インピーダンス変換器。2. The capacitor microphone impedance converter according to claim 1 , wherein the source follower circuit, the filter circuit composed of the resistor R1 and the capacitor C1, and the filter circuit composed of the resistor R2 and the capacitor C2 are made of the same silicon. An impedance converter for a condenser microphone, which is formed on a substrate in one chip.
JP2003583055A 2002-04-11 2002-04-11 Impedance converter for condenser microphone Expired - Lifetime JP4024213B2 (en)

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PCT/JP2002/003623 WO2003086014A1 (en) 2002-04-11 2002-04-11 Impedance converter for capacitor microphone

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US4280018A (en) * 1979-05-14 1981-07-21 Strobotronix, Inc. Integrated piezoelectric sound transducer and preamplifier
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