WO2014107843A1 - Microphone à condensateur et son adaptateur d'impédance - Google Patents

Microphone à condensateur et son adaptateur d'impédance Download PDF

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Publication number
WO2014107843A1
WO2014107843A1 PCT/CN2013/070233 CN2013070233W WO2014107843A1 WO 2014107843 A1 WO2014107843 A1 WO 2014107843A1 CN 2013070233 W CN2013070233 W CN 2013070233W WO 2014107843 A1 WO2014107843 A1 WO 2014107843A1
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WO
WIPO (PCT)
Prior art keywords
direct voltage
jfet
active element
condenser
output terminal
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Ceased
Application number
PCT/CN2013/070233
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English (en)
Inventor
Zhihao Yang
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Individual
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Individual
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Priority to CN201380004917.2A priority Critical patent/CN104685904B/zh
Priority to PCT/CN2013/070233 priority patent/WO2014107843A1/fr
Publication of WO2014107843A1 publication Critical patent/WO2014107843A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00—Electrostatic transducers
    • H04R19/04—Microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R2410/00—Microphones
    • H04R2410/03—Reduction of intrinsic noise in microphones

Definitions

  • the present invention relates to condenser microphones using a direct coupling impedance converter.
  • the transducer of externally polarized condenser microphones experiences a change in capacitance in correlation with the acoustic sound pressure applied to the diaphragm of the transducer (i.e. sound of a voice of a singer).
  • the transducer is electro-statically charged with a constant direct voltage.
  • Uc represents the direct voltage at the condenser
  • Qc represents the electrostatic charge of the condenser
  • C represents the capacitance of the condenser
  • Such impedance converter needs to have a very high input impedance and a very low output impedance.
  • microphones require a high dynamic range and therefore this impedance converter needs to handle high signals of more than 10V peak to peak while adding minimum noise of typically 1uV or less.
  • a high direct current needs to be applied to the transducer in order to ensure a high electrostatic charge which in return will result in a high acoustic sensitivity (change of capacitance of the transducer at a change of sound pressure level). All of the above requirements are met in a circuit of Fig. 2 which reflects a present state of the art.
  • a condenser transducer KAP in order to realize various polar patterns, usually consists of two diaphragms which are positioned one on each side of an electrode. Polar patterns can be generated by changing the electrostatic charges of each diaphragm while keeping the electrode in the center electrostatically charged at a constant level.
  • the example of the circuit diagram in Fig. 2 shows that the electrode which is shared by both diaphragms is charged with a direct voltage of 60V. This direct voltage of 60V is applied to the transducer electrode via a resistor R1 which needs to have a high resistance value (6G Ohm in the example) in order to keep the electrostatic charge stable.
  • a JFET is the best choice in order to build the impedance converter because it can handle high signal voltages while maintaining a very low noise.
  • High signal voltages are achieved by setting the bias point of the JFET to 50% of the supply voltage.
  • Fig. 2 shows a bias point at 15V supplied via a resistor R2 which as well needs to have a high resistance value (6G Ohm in the example).
  • Output terminal AF-Out outputs a voice signal.
  • the maximum voltage a JFET can handle is usually limited to 50V. Therefore a direct connection to the transducer KAP is not possible as it is charged with 60V.
  • present designs use a capacitor C1.
  • the circuit design in FIG. 2 has several disadvantages.
  • One of them is that the noise of the impedance converter results from the resistance value of the bias resistors R1, R2 and the transducer capacitance following an arctan function.
  • noise 2,16uV at a frequency range of 20Hz to 20kHz
  • the transducer capacitance and bias resistors form a high pass filter. It is this high pass filter effect which causes the arctan correlation between noise, resistance value of bias resistors and transducer capacitance.
  • the corner frequency of this high pass filter needs to be in the sub audio area of the frequency response (not audible to human ears) in order to achieve a minimum noise performance.
  • Adjusting the transducer capacitance is very limited due to physical / acoustic constraints. Therefore the only parameter left for adjusting is the value of the bias resistor. However, adjusting the bias resistor is limited by the following design constraints:
  • the capacitor C1 has to be charged by the bias resistors R1, R2.
  • a high resistance value of these bias resistors will result in a long charging time ((R1+R2)xC1), up to 90 seconds.
  • the microphone does not provide the specified performance which is not accepted by the market for obvious reasons. This results in an upper limit of the capacitance of the capacitor.
  • choosing a small capacitance value for C1 will create a capacitive potential divider together with the inherent capacitance of JFET T1 which will result in signal loss.
  • An object of the present invention is to provide a condenser microphone using a direct coupling impedance converter, the coupling capacitor between the condenser transducer and the amplifier is eliminated.
  • the condenser microphone includes a condenser transducer and an impedance converter.
  • the condenser transducer includes an electrode and at least one diaphragm which is positioned on one side of the electrode, the electrode being charged with a bias direct voltage via a bias resistor.
  • the impedance converter includes an active element for impedance conversion with its input terminal directly connected to the electrode; a low-pass filter for filtering an AF output signal from the active element in order to obtain a direct voltage component from the AF output signal; and an operation amplifier with its non-inverting input being applied with a constant direct voltage, its inverting input connected to an output terminal of the low-pass filter, its output terminal connected to the bias resistor, and its inverting input connected to the output terminal via a second resistor .
  • the active element can be a JFET, a MOSFET, a transistor, a tube, an operation amplifier or a combination of these in a parallel circuit for impedance conversion.
  • the active element is an N-channel JFET
  • a gate of the JFET acts as the input terminal
  • a drain of the JFET is applied with a direct voltage larger than the constant direct voltage applied to the operation amplifier
  • a source of the JFET acts as the output terminal.
  • Another object of the present invention is to provide an impedance converter for condenser microphones, includes an active element for impedance conversion with its input terminal directly connected to a condenser transducer of the condenser microphones; a bias resistor with one terminal connected to the connection point between the active element and the condenser transducer; and a control circuit for filtering an AF output signal outputted from the active element in order to retrieve a bias direct voltage as a set value, the bias direct voltage being supplied to the other terminal of the bias resistor; wherein the set value is used to adjust a supply voltage for the bias resistor in order to assure a desired bias direct voltage at the output of the active element.
  • the control circuit includes a low-pass filter for obtaining a direct voltage component from the AF output signal; and an operation amplifier with its non-inverting input being applied with a constant direct voltage, its inverting input connected to an output terminal of the low-pass filter, its output terminal connected to the other terminal of the bias resistor, and its inverting input connected the its output terminal via a second resistor .
  • FIG.1 is a block diagram showing an impedance converter for a condenser microphone in accordance with an exemplary embodiment of the present invention.
  • FIG.2 is a block diagram showing a conventional impedance converter.
  • An condenser microphone shown in Fig. 1 in accordance with an embodiment of the present invention mainly includes a condenser transducer 10, a bias resistor 11, an active element (a JFET 12 in the embodiment), a low pass filter 13 and a operation amplifier 14.
  • the active element is selected from a JFET, a MOSFET, a transistor, a tube, an operation amplifier or a combination of these in a parallel circuit for impedance conversion.
  • the active element use an N-channel JFET.
  • a gate of the JFET 12 is directly connected to the condenser transducer 10, a drain of the JFET 12 is supplied with a direct voltage (usually twice of the bias voltage of the JFET 12) via a terminal 18.
  • a source of the JFET 12 acts as the output terminal 17 of the impedance converter for outputting an amplified AF output signal.
  • the source of the JFET 12 is connected to earth via a current source which is used to stabilize the work current of the JFET 12.
  • a non-inverted input of the operation amplifier 14 is supplied with a direct voltage via an input terminal 16.
  • the inverted input of the operation amplifier 14 is connected to an output of the low pass filter 13.
  • the output of the The operation amplifier 14 is connected to the gate of the JFET 12 (and the output of the transducer 10).
  • the inverted input is also connected to the output terminal of the operation amplifier 14 via a resistor 19.
  • the low pass filter 13 is connected between the source 17 of the JFET 12 and the inverted input of the operation amplifier 14, for filtering the AF output signal in order to obtain a direct voltage component from the AF output signal.
  • the condenser transducer 10 in the embodiment includes a fixed electrode and two diaphragms which are positioned one on each side of the electrode.
  • the electrode is charged with a direct voltage of 15V (from the terminal 16) via the bias resistor 11 and the operation amplifier 14 in the embodiment.
  • one diaphragm is charged with -45V (via an input terminal 15) and the other one with 75V.
  • Such polarization of the condenser transducer makes it possible to connect the gate of the of the JFET 12 directly to the electrode of the transducer 10 without the need for a coupling capacitor. Rely on this configuration, a coupling capacitor is eliminated, thus the bias resistor 11 can be increased.
  • a resistance value of the bias resistor 11 is 18G Ohm.
  • the +15V in our example happens to be the bias voltage for the JFET 12. It is easily understood, in other embodiment, the condenser transducer for outputting an AF (Audio Frequency) signal can only include a fixed electrode and one diaphragm which is positioned on one side of the electrode.
  • a control circuit 100 is used in order to safely increase the bias resistor 11 without running at risk that the circuit fails due to the system inherent leaking currents.
  • the set value for this control circuit are the +15V bias voltage at the non-inverted input 16 of the control amplifier 14.
  • the set value is retrieved via the low-pass filter 13 from the output voltage (the AF output signal from the output terminal 17) of the impedance converter.
  • the corner frequency of this low-pass filter 13 is set as low as possible so that only the direct voltage component of the AF output signal can pass through to the operation amplifier 14.
  • the voltage at the gate is only a few 100 mV smaller than the voltage at the source pin (output terminal 17 of the impedance converter).
  • the invented control circuit now ensures that at all times the output of the operation amplifier 14 (bias for the resistor 11) is adjusted to the correct voltage so that the output terminal 17 (source) of the JFET 12 always provides the correct bias voltage. Therefore leak currents at the input of the JFET 12 are effectively eliminated and the charging voltage of the transducer electrode is always adjusted to the right value.
  • the operation amplifier 14 there are no special requirements for the operation amplifier 14 in regard to noise or speed.
  • the only important specification is the maximum power supply voltage for the operation amplifier 14 as this determines the control range of the circuit. It is understandably, a power supply voltage of the operation amplifier can not exceed the maximum voltage that a JFET can handle.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)

Abstract

La présente invention porte sur un microphone à condensateur muni d'un convertisseur d'impédance couplé directement au transducteur dudit microphone à condensateur. Le convertisseur d'impédance comprend un élément actif destiné à l'adaptation d'impédance, et un circuit de commande conçu pour filtrer un signal de sortie AF émis par l'élément actif, dans le but de récupérer une tension continue de polarisation qui fait office de valeur définie, cette tension continue de polarisation étant fournie à l'autre borne de la résistance de polarisation. Un condensateur de couplage se trouvant entre le transducteur du condensateur et l'élément actif est supprimé, de sorte qu'une résistance de polarisation qui se comporte comme une source de bruit peut être supprimée elle aussi, et que la résistance de polarisation qui reste peut être agrandie.
PCT/CN2013/070233 2013-01-08 2013-01-08 Microphone à condensateur et son adaptateur d'impédance Ceased WO2014107843A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
CN201380004917.2A CN104685904B (zh) 2013-01-08 2013-01-08 电容式麦克风及其阻抗变换器
PCT/CN2013/070233 WO2014107843A1 (fr) 2013-01-08 2013-01-08 Microphone à condensateur et son adaptateur d'impédance

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/CN2013/070233 WO2014107843A1 (fr) 2013-01-08 2013-01-08 Microphone à condensateur et son adaptateur d'impédance

Publications (1)

Publication Number Publication Date
WO2014107843A1 true WO2014107843A1 (fr) 2014-07-17

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PCT/CN2013/070233 Ceased WO2014107843A1 (fr) 2013-01-08 2013-01-08 Microphone à condensateur et son adaptateur d'impédance

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CN (1) CN104685904B (fr)
WO (1) WO2014107843A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017083679A1 (fr) * 2015-11-12 2017-05-18 Knowles Electronics, Llc Procédé et appareil pour augmenter la sensibilité d'un microphone en bande audio
US9843292B2 (en) 2015-10-14 2017-12-12 Knowles Electronics, Llc Method and apparatus for maintaining DC bias
US10516935B2 (en) 2015-07-15 2019-12-24 Knowles Electronics, Llc Hybrid transducer
CN113132854A (zh) * 2019-12-30 2021-07-16 楼氏电子(苏州)有限公司 微机电系统换能器和麦克风组件

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN109862497B (zh) * 2017-11-30 2025-02-25 北京七九七华音电子有限责任公司 一种传声器
CN109618270B (zh) * 2018-12-04 2020-12-08 珠海市杰理科技股份有限公司 麦克风输入偏置校准方法及麦克风偏置装置
KR102350882B1 (ko) * 2020-10-29 2022-01-13 (주)다빛센스 마이크로폰 장치

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CN1280454A (zh) * 1999-07-08 2001-01-17 松下电器产业株式会社 电容式麦克风装置及其连接装置
CN101188406A (zh) * 2006-11-21 2008-05-28 财团法人工业技术研究院 低频模拟电路的设计方法及其低频模拟电路
US20090279717A1 (en) * 2008-05-12 2009-11-12 Udid Technology Co., Ltd. Circuit module for a condenser microphone
CN202135318U (zh) * 2011-06-29 2012-02-01 歌尔声学股份有限公司 电容式麦克风装置

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AT386303B (de) * 1986-07-31 1988-08-10 Akg Akustische Kino Geraete Schaltungsanordnung fuer kapazitive spannungsquellen hoher ausgangsimpedanz, insbesondere fuer kondensatormikrophone
US5978491A (en) * 1996-11-21 1999-11-02 Vxi Corporation Circuitry for improving performance of electret microphone
TWI221196B (en) * 2001-09-06 2004-09-21 Tokyo Electron Ltd Impedance measuring circuit, its method, and electrostatic capacitance measuring circuit
JP4799577B2 (ja) * 2008-03-13 2011-10-26 株式会社オーディオテクニカ コンデンサーマイクロホン
CN101887626B (zh) * 2010-04-28 2011-12-21 周玉林 家禽育雏孵出电子提醒装置

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1280454A (zh) * 1999-07-08 2001-01-17 松下电器产业株式会社 电容式麦克风装置及其连接装置
CN101188406A (zh) * 2006-11-21 2008-05-28 财团法人工业技术研究院 低频模拟电路的设计方法及其低频模拟电路
US20090279717A1 (en) * 2008-05-12 2009-11-12 Udid Technology Co., Ltd. Circuit module for a condenser microphone
CN202135318U (zh) * 2011-06-29 2012-02-01 歌尔声学股份有限公司 电容式麦克风装置

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10516935B2 (en) 2015-07-15 2019-12-24 Knowles Electronics, Llc Hybrid transducer
US9843292B2 (en) 2015-10-14 2017-12-12 Knowles Electronics, Llc Method and apparatus for maintaining DC bias
WO2017083679A1 (fr) * 2015-11-12 2017-05-18 Knowles Electronics, Llc Procédé et appareil pour augmenter la sensibilité d'un microphone en bande audio
US10616691B2 (en) 2015-11-12 2020-04-07 Knowles Electronics, Llc Method and apparatus to increase audio band microphone sensitivity
CN113132854A (zh) * 2019-12-30 2021-07-16 楼氏电子(苏州)有限公司 微机电系统换能器和麦克风组件

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CN104685904A (zh) 2015-06-03
CN104685904B (zh) 2017-10-03

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