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EP0692921A1 - Sound pick-up device by an electret microphone - Google Patents

Sound pick-up device by an electret microphone Download PDF

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Publication number
EP0692921A1
EP0692921A1 EP95401674A EP95401674A EP0692921A1 EP 0692921 A1 EP0692921 A1 EP 0692921A1 EP 95401674 A EP95401674 A EP 95401674A EP 95401674 A EP95401674 A EP 95401674A EP 0692921 A1 EP0692921 A1 EP 0692921A1
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EP
European Patent Office
Prior art keywords
electret microphone
input
differential
preamplifier stage
symmetrical
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP95401674A
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German (de)
French (fr)
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EP0692921B1 (en
Inventor
Grégoire Le Tourneur
Marcel Clement
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Orange SA
Original Assignee
France Telecom SA
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Publication date
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Publication of EP0692921A1 publication Critical patent/EP0692921A1/en
Application granted granted Critical
Publication of EP0692921B1 publication Critical patent/EP0692921B1/en
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00Electrostatic transducers
    • H04R19/04Microphones
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00Details of transducers, loudspeakers or microphones
    • H04R1/02Casings; Cabinets ; Supports therefor; Mountings therein
    • H04R1/04Structural association of microphone with electric circuitry therefor
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04RLOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R19/00Electrostatic transducers
    • H04R19/01Electrostatic transducers characterised by the use of electrets
    • H04R19/016Electrostatic transducers characterised by the use of electrets for microphones

Definitions

  • the invention relates to a sound pickup device by electret microphone.
  • the final cost of the product essentially depends on the type of microphone used, the cost of this varying directly as a result of its quality.
  • the overall cost can become very high.
  • Dynamic microphones are generally used for sound recording in shows and in the studio, because of their very high quality, but their high price and their irreducible size do not make them suitable for sound recording for telephone terminals, or any making sound economic.
  • Electret microphones providing a weak useful signal, require a preamplifier in order to bring the output signal of the electret capsule at a level of the order of a volt.
  • the electret capsule must be supplied with electrical energy, since it incorporates a field effect transistor.
  • the electret microphone M comprising a point connected to ground and a point receiving the electrical supply and delivering the useful audio signal, the usual arrangement is shown in FIG. 1a.
  • the output level of the useful signal which varies from a few hundred microvolts to a few tens of millivolts, depending on the sensitivity of the capsules and the position of the microphone relative to the source, i.e.
  • this mounting requires the implementation of a high gain preamplification stage.
  • the presence of this significant gain makes the assembly very sensitive to power supply noise and electromagnetic disturbances. Indeed, if the supply voltage VM is not perfectly regulated, the variations thereof are seen as a useful signal by the preamplification stage. The same is true for electromagnetic radiation or parasites, which affect the useful input of the preamplification stage.
  • Such sound recording systems are said to be noisy, because these, on the one hand, have a low signal-to-noise ratio when the power supply is not perfectly regulated, rate of change less than or equal to 0.5% , and, on the other hand, are very sensitive to parasitic electromagnetic radiation, 50 Hz, if the assembly is not perfectly shielded.
  • the object of the present invention is to remedy the aforementioned drawbacks by using a device for picking up sound by an electret microphone of the differential type in which any transformer is omitted.
  • Another object of the present invention is also the implementation of a sound pickup device by good quality electret microphone, due to its operation in differential mode.
  • the device for taking sound from an electret microphone, object of the present invention in which signals delivered by the electret microphone are amplified by means of a differential preamplifier stage, is remarkable in that it comprises a link by connection capacity between each output terminal of the electret microphone and an input of the differential preamplifier stage.
  • a symmetrical bias circuit of the output terminals an electret microphone is provided, which comprises a first and a second voltage source, symmetrical with respect to a reference voltage, and each connected to an output terminal of the electret microphone.
  • the electret microphone sound pickup device finds application in the production of quality sound pickup systems in the field of telecommunications, voice recognition, acoustic antennas.
  • FIG. 2 it is indicated that the same references indicate the same elements as in FIGS. 1a and 1b relating to the prior art.
  • the sound pickup device comprises, as shown in FIG. 2 above, a link 1 per link capacity between each output terminal of the electret microphone M and an input of the differential preamplifier stage 3.
  • the link capacities bear the reference 11 and 12 on the figure 2.
  • a symmetrical bias circuit of the output terminals of the electret microphone M is provided, this circuit bearing the reference 2 in the aforementioned FIG. 2.
  • first 21 and a second 22 voltage source the voltages supplied by the sources 21 and 22 being symmetrical with respect to a reference voltage of the device, the mass of the sound pickup device.
  • Each voltage source 21, 22 is connected via a resistor 210, respectively 220, to an output terminal of the electret microphone M.
  • the polarization device 2 must be symmetrical, the supply voltages -VM and + VM delivered by sources 21 and 22 being opposite, resistors 210 and 220 and capacitors 11 and 12 being identical, for rejection in common mode.
  • the differential preamplifier stage 3 can advantageously comprise on each input channel a preamplifier device in non-differential mode, carrying the reference 30 respectively 31.
  • the preamplifiers in non-differential mode 30 and 31 can conventionally include a positive terminal forming an input terminal for the signals delivered by the connection capacitors 11 respectively. 12, and a resistive feedback coupling via resistors 301 and 311 respectively on the corresponding negative terminal.
  • the output resistors 302 and 312 make it possible to drive a differential output amplifier 32, which can conventionally include a positive terminal forming an input terminal connected to the output of the preamplifier 31 via a resistor 321 and d a capacitor 322 in parallel connected between the aforementioned positive input terminal and the reference voltage, and a negative input terminal connected on the one hand, in feedback by a 320 capacitor circuit 323 to the output terminal of the amplifier 32, and, on the other hand, to the resistor 302 of the output of the preamplifier device in non-differential mode 30.
  • each preamplifier device in non-differential mode 30 and 31 is connected to the reference voltage by means of an input resistor 300, respectively 310.
  • an adjustable resistor 313 is provided, this resistor connecting the two negative inputs of each preamplifier device in non-differential mode 30 and 31.
  • the resistor 313 may include a non-adjustable fixed resistor of non-zero value and thus allows to carry out a gain adjustment adjustment in non-differential mode of the aforementioned non-differential preamplifier devices 30 and 31.
  • a noticeable improvement of the device, object of the present invention, as shown in Figure 3, can then be made, as shown in Figure 4, in order to reduce the noise inherent in the two supply voltages 21 and 22 in the case in particular where non-symmetrical noise disturbances would appear on these supplies.
  • the electret microphone sound recording device further comprises, between the differential preamplifier stage 3 and the link by link capacity, on each input channels of the aforementioned differential preamplifier stage 3, an inverted coupling circuit of each of the input channels to the symmetrical bias circuit.
  • This inverted coupling circuit called supply rejection, makes it possible to reinject at each input terminal of the differential preamplifier stage the voltages delivered by the symmetrical inverted voltage sources, deprived of their continuous components.
  • each input of the differential amplifier stage 3 thus sees the sum of the noises of the two aforementioned supplies 21 and 22, this noise then disappearing at the output since the assembly effects the difference of the input signals.
  • the coupling circuit 4 comprises a first and a second circuit, each formed by a resistor and an electric capacitor in series, bearing the references 211, 212, respectively 221, 222.
  • the first circuit 211, 212 is connected between the second negative voltage source 21 and the first input of the differential amplifier stage 3, that is to say downstream of the connection capacity 11
  • the second circuit 221, 222 is connected between the first positive voltage source 20 and the second input of the differential preamplifier stage 3, that is to say downstream of the connection capacitor 12.
  • the power rejection circuit 4 must be identical to the bias circuit 2, the resistor 211 being identical to the resistor 210, the resistor 221 identical to the resistor 220, the capacity 212 identical at capacity 12 and capacity 222 identical to capacity 11.
  • Figure 5a the response of the assembly of the prior art shown in Figure la to a disturbance of the power supply sector, that is to say at a frequency of 50 Hz.
  • Figure 5a is graduated on the ordinate in decibels and, on the abscissa, in frequencies. The tests were carried out in the presence of a pink noise and a line at 50 Hz due to a disturbance of the sector as well as to the harmonic frequencies of the latter.
  • the response of the circuit as shown in FIG. 1 relating to the prior art, clearly exhibits parasitic noise at the frequency of the sector mentioned above.
  • the device for picking up sound by electret microphone, object of the present invention, previously described, is particularly advantageous insofar as, by the mere replacement of the transformer by a coupling circuit by capacitance link, the results, in terms of pick-up its, however, are identical to the circuits of the prior art comprising such transformers, while the cost price of implementation of these circuits have been known to be reduced.
  • circuits in accordance with the object of the present invention, is particularly advantageous in acoustic antennas or in complex circuits requiring quality sound recording.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)

Abstract

The sound pick-up (1) for an electret microphone comprises a capacitive link (11,12) between each output terminal of the electret microphone (M) and an input of a differential amplifier stage (3). A biasing circuit (2) which is symmetrical w.r.t. the output terminals of the electret microphone (M) includes a first and a second voltage source (21,22), symmetrical w.r.t. a reference voltage. Each terminal is connected to an output terminal for the microphone. <IMAGE>

Description

L'invention concerne un dispositif de prise de son par microphone électret.The invention relates to a sound pickup device by electret microphone.

Lors de la réalisation de systèmes de prise de son de qualité, le coût final du produit dépend essentiellement du type de microphone utilisé, le coût de celui-ci variant en raison directe de sa qualité. Lorsque la prise de son impose la mise en oeuvre de plusieurs microphones, comme dans le cas des terminaux de communication de groupe, des antennes acoustiques ou des salles de visio- ou audioconférence, le coût global peut devenir très élevé.When producing quality sound recording systems, the final cost of the product essentially depends on the type of microphone used, the cost of this varying directly as a result of its quality. When sound recording requires the use of several microphones, as in the case of group communication terminals, acoustic antennas or video or audio conference rooms, the overall cost can become very high.

A l'heure actuelle, il existe principalement deux grandes familles de microphones :

  • les microphones dynamiques, qui consistent en des capsules traduisant directement le mouvement de l'air, la pression acoustique, en signal électrique, ce type de capsule, passive car ne nécessitant aucune alimentation électrique, délivrant un signal très faible, lequel, de préférence, doit être amplifié au moyen d'un transformateur de très haute qualité ;
  • les microphones électret, lesquels fonctionnent selon le principe de variation de capacité entre deux membranes chargées électriquement, intègrent en sortie un transistor à effet de champ et qui, grâce à cet élément actif, délivrent un signal d'amplitude plus élevée que les précédents. En contrepartie toutefois, il est nécessaire de prévoir une alimentation électrique pour ce type de microphone.
Currently, there are mainly two main families of microphones:
  • dynamic microphones, which consist of capsules directly translating the movement of air, the acoustic pressure, into an electrical signal, this type of capsule, passive since it requires no electrical supply, delivering a very weak signal, which, preferably, must be amplified using a very high quality transformer;
  • electret microphones, which operate on the principle of varying capacity between two electrically charged membranes, incorporate a field effect transistor at the output and which, thanks to this active element, deliver a signal of higher amplitude than the previous ones. In return, however, it is necessary to provide an electrical supply for this type of microphone.

Les microphones dynamiques sont généralement utilisés pour les prises de son dans les spectacles et en studio, du fait de leur très haute qualité, mais leur prix élevé et leur encombrement irréductible ne les destinent pas à la prise de son pour terminaux téléphoniques, ou à toute prise de son économique.Dynamic microphones are generally used for sound recording in shows and in the studio, because of their very high quality, but their high price and their irreducible size do not make them suitable for sound recording for telephone terminals, or any making sound economic.

Les microphones électret, fournissant un signal utile faible, nécessitent un préamplificateur afin d'amener le signal de sortie de la capsule électret à un niveau de l'ordre du volt. La capsule électret doit être alimentée en énergie électrique, car elle intègre un transistor à effet de champ. Pour une capsule "deux points" telle que représentée en figure la, le microphone électret M comprenant un point relié à la masse et un point recevant l'alimentation électrique et délivrant le signal audio utile, le montage habituel est représenté sur la figure 1a. Compte tenu du niveau de sortie du signal utile, lequel varie de quelques centaines de microvolts à quelques dizaines de millivolts, selon la sensibilité des capsules et la position du microphone par rapport à la source, c'est-à-dire le locuteur, ce montage nécessite la mise en oeuvre d'un étage de préamplification à grand gain.
La présence de ce gain important rend le montage très sensible au bruit de l'alimentation et aux perturbations d'origine électromagnétique. En effet, si la tension d'alimentation VM n'est pas parfaitement régulée, les variations de celle-ci sont vues comme un signal utile par l'étage de préamplification. Il en est de même pour les rayonnements ou parasites électromagnétiques, lesquels affectent l'entrée utile de l'étage de préamplification.
Electret microphones, providing a weak useful signal, require a preamplifier in order to bring the output signal of the electret capsule at a level of the order of a volt. The electret capsule must be supplied with electrical energy, since it incorporates a field effect transistor. For a "two-point" capsule as represented in FIG. 1a, the electret microphone M comprising a point connected to ground and a point receiving the electrical supply and delivering the useful audio signal, the usual arrangement is shown in FIG. 1a. Given the output level of the useful signal, which varies from a few hundred microvolts to a few tens of millivolts, depending on the sensitivity of the capsules and the position of the microphone relative to the source, i.e. the speaker, this mounting requires the implementation of a high gain preamplification stage.
The presence of this significant gain makes the assembly very sensitive to power supply noise and electromagnetic disturbances. Indeed, if the supply voltage VM is not perfectly regulated, the variations thereof are seen as a useful signal by the preamplification stage. The same is true for electromagnetic radiation or parasites, which affect the useful input of the preamplification stage.

De tels systèmes de prise de son sont dits bruités, car ceux-ci, d'une part, présentent un faible rapport signal à bruit lorsque l'alimentation n'est pas parfaitement régulée, taux de variation inférieur ou égal à 0,5%, et, d'autre part, sont très sensibles au rayonnement électromagnétique parasite, 50 Hz, si le montage n'est pas parfaitement blindé.Such sound recording systems are said to be noisy, because these, on the one hand, have a low signal-to-noise ratio when the power supply is not perfectly regulated, rate of change less than or equal to 0.5% , and, on the other hand, are very sensitive to parasitic electromagnetic radiation, 50 Hz, if the assembly is not perfectly shielded.

Afin d'améliorer les performances de ce type de microphone, notamment leur rapport signal à bruit, on a proposé, ainsi que représenté en figure 1b, d'utiliser un montage différentiel. De cette façon, tout bruit en provenance de l'alimentation et toute perturbation influençant les deux voies, 50 Hz parasite, se retrouve, de par la symétrie du montage, sur les deux entrées du préamplificateur différentiel et se trouve donc sensiblement éliminé en sortie.In order to improve the performance of this type of microphone, in particular their signal to noise ratio, it has been proposed, as shown in FIG. 1b, to use a differential arrangement. In this way, any noise coming from the power supply and any disturbance influencing the two channels, 50 Hz parasitic, is found, by the symmetry of the assembly, on the two inputs of the preamplifier differential and is therefore substantially eliminated at the output.

Afin de mettre en oeuvre un tel montage, il est toutefois nécessaire d'ajouter un transformateur T en sortie de la capsule, afin de permettre le couplage de celle-ci en mode différentiel.In order to implement such an assembly, it is however necessary to add a transformer T at the outlet of the capsule, in order to allow the coupling thereof in differential mode.

L'utilisation d'un tel transformateur, de type élévateur, améliore la qualité de la prise de son mais présente l'inconvénient majeur d'augmenter le prix de revient et l'encombrement de ce type de dispositif. Une telle solution devient tout-à-fait irréaliste lorsqu'une pluralité de microphones doit être utilisée. En conséquence, il est difficile de réaliser des systèmes de prise de son de bonne qualité avec des microphones électret sans utiliser de transformateurs onéreux et sans l'adjonction d'un blindage électromagnétique conséquent, ce qui rend le coût des installations de prise de son correspondantes élevé, sans que le faible coût intrinsèque des microphones électret ne puisse être effectivement exploité.The use of such a transformer, of the booster type, improves the quality of the sound recording but has the major drawback of increasing the cost price and the size of this type of device. Such a solution becomes completely unrealistic when a plurality of microphones must be used. As a result, it is difficult to make good quality sound pickup systems with electret microphones without using expensive transformers and without the addition of substantial electromagnetic shielding, which makes the cost of the corresponding sound pickup installations expensive. high, without the low intrinsic cost of electret microphones being able to be effectively exploited.

La présente invention a pour but de remédier aux inconvénients précités, par la mise en oeuvre d'un dispositif de prise de son par microphone électret de type différentiel dans lequel tout transformateur est supprimé.The object of the present invention is to remedy the aforementioned drawbacks by using a device for picking up sound by an electret microphone of the differential type in which any transformer is omitted.

Un autre objet de la présente invention est également la mise en oeuvre d'un dispositif de prise de son par microphone électret de bonne qualité, en raison de son fonctionnement en mode différentiel.Another object of the present invention is also the implementation of a sound pickup device by good quality electret microphone, due to its operation in differential mode.

Le dispositif de prise de son à partir d'un microphone électret, objet de la présente invention, dans lequel des signaux délivrés par le microphone électret sont amplifiés au moyen d'un étage préamplificateur différentiel, est remarquable en ce qu'il comprend une liaison par capacité de liaison entre chaque borne de sortie du microphone électret et une entrée de l'étage préamplificateur différentiel.
Un circuit de polarisation symétrique des bornes de sortie du microphone électret est prévu, lequel comprend une première et une deuxième source de tension, symétriques par rapport à une tension de référence, et reliées chacune à une borne de sortie du microphone électret.
The device for taking sound from an electret microphone, object of the present invention, in which signals delivered by the electret microphone are amplified by means of a differential preamplifier stage, is remarkable in that it comprises a link by connection capacity between each output terminal of the electret microphone and an input of the differential preamplifier stage.
A symmetrical bias circuit of the output terminals an electret microphone is provided, which comprises a first and a second voltage source, symmetrical with respect to a reference voltage, and each connected to an output terminal of the electret microphone.

Le dispositif de prise de son à microphone électret, objet de la présente invention, trouve application à la réalisation de systèmes de prise de son de qualité dans le domaine des télécommunications, de la reconnaissance vocale, des antennes acoustiques.The electret microphone sound pickup device, object of the present invention, finds application in the production of quality sound pickup systems in the field of telecommunications, voice recognition, acoustic antennas.

Il sera mieux compris à la lecture de la description et à l'observation des dessins ci-après dans lesquels, outre les figures 1a et 1b relatives à l'art antérieur :

  • la figure 2 représente un schéma de principe d'un dispositif de prise de son à microphone électret, objet de la présente invention,
  • la figure 3 représente un schéma complet d'un dispositif de prise de son à microphone électret, conforme à l'objet de la présente invention, tel que représenté en figure 2,
  • la figure 4 représente une variante avantageuse de mise en oeuvre du dispositif de prise de son à microphone électret tel que représenté en figure 3,
  • les figures 5a et 5b représentent des courbes de réponse en fréquence du montage de la figure la, relatif à l'art antérieur, respectivement du descriptif de prise de son selon l'invention, tel que représenté en figure 4.
It will be better understood on reading the description and on observing the following drawings in which, in addition to FIGS. 1a and 1b relating to the prior art:
  • FIG. 2 represents a block diagram of a sound pickup device with an electret microphone, object of the present invention,
  • FIG. 3 represents a complete diagram of a sound pickup device with an electret microphone, in accordance with the object of the present invention, as represented in FIG. 2,
  • FIG. 4 represents an advantageous variant of implementation of the electret microphone sound pickup device as shown in FIG. 3,
  • FIGS. 5a and 5b represent frequency response curves of the assembly of FIG. 1a, relating to the prior art, respectively of the description of sound recording according to the invention, as represented in FIG. 4.

Une description plus détaillée d'un dispositif de prise de son à microphone électret, conforme à l'objet de la présente invention, sera maintenant donnée en liaison avec les figures 2 et suivantes.A more detailed description of a sound pickup device with an electret microphone, in accordance with the object of the present invention, will now be given in conjunction with FIGS. 2 and following.

Sur la figure 2 précitée, on indique que les mêmes références indiquent les mêmes éléments que dans les figures la et lb relatives à l'art antérieur.In FIG. 2 above, it is indicated that the same references indicate the same elements as in FIGS. 1a and 1b relating to the prior art.

Dans le but d'amplifier les signaux délivrés par le microphone électret M au moyen d'un étage préamplificateur différentiel 3, le dispositif de prise de son selon l'invention comprend, ainsi que représenté sur la figure 2 précitée, une liaison 1 par capacité de liaison entre chaque borne de sortie du microphone électret M et une entrée de l'étage préamplificateur différentiel 3. Les capacités de liaison portent la référence 11 et 12 sur la figure 2.In order to amplify the signals delivered by the electret microphone M by means of a differential preamplifier stage 3, the sound pickup device according to the invention comprises, as shown in FIG. 2 above, a link 1 per link capacity between each output terminal of the electret microphone M and an input of the differential preamplifier stage 3. The link capacities bear the reference 11 and 12 on the figure 2.

En outre, un circuit de polarisation symétrique des bornes de sortie du microphone électret M est prévu, ce circuit portant la référence 2 sur la figure 2 précitée.In addition, a symmetrical bias circuit of the output terminals of the electret microphone M is provided, this circuit bearing the reference 2 in the aforementioned FIG. 2.

Il comprend une première 21 et une deuxième 22 source de tension, les tensions délivrées par les sources 21 et 22 étant symétriques par rapport à une tension de référence du dispositif, la masse du dispositif de prise de son. Chaque source de tension 21, 22 est reliée par l'intermédiaire d'une résistance 210, respectivement 220, à une borne de sortie du microphone électret M. Le dispositif de polarisation 2 doit être symétrique, les tensions d'alimentation -VM et +VM délivrées par les sources 21 et 22 étant opposées, les résistances 210 et 220 et les capacités 11 et 12 étant identiques, pour une réjection en mode commun.It comprises a first 21 and a second 22 voltage source, the voltages supplied by the sources 21 and 22 being symmetrical with respect to a reference voltage of the device, the mass of the sound pickup device. Each voltage source 21, 22 is connected via a resistor 210, respectively 220, to an output terminal of the electret microphone M. The polarization device 2 must be symmetrical, the supply voltages -VM and + VM delivered by sources 21 and 22 being opposite, resistors 210 and 220 and capacitors 11 and 12 being identical, for rejection in common mode.

Compte tenu de la liaison par capacité de liaison et de la mise en oeuvre d'une alimentation symétrique par l'intermédiaire des sources de tension 21 et 22, une telle mesure permet d'alimenter par ce biais le transistor à effet de champ de la capsule électret M, ce transistor à effet de champ n'étant pas représenté aux dessins car ce dernier est intégré à la capsule elle-même, ainsi que de transformer le montage du microphone électret M en mode différentiel, ce qui permet d'utiliser en aval de la liaison par capacité de liaison un préamplificateur différentiel 3, tel que représenté sur la figure 2, en supprimant toutefois le transformateur représenté en figure 1b.Taking into account the link by link capacity and the implementation of a symmetrical supply via the voltage sources 21 and 22, such a measurement makes it possible to supply the field effect transistor of the electret capsule M, this field effect transistor not being shown in the drawings because the latter is integrated into the capsule itself, as well as transforming the mounting of the electret microphone M into differential mode, which makes it possible to use in downstream of the link by link capacity, a differential preamplifier 3, as shown in FIG. 2, however eliminating the transformer shown in FIG. 1b.

Afin de maintenir une propriété d'insensibilité au bruit d'alimentation, propriété qui existait dans le montage de l'art antérieur en raison de l'utilisation du transformateur tel que représenté en figure 1b, il est toutefois nécessaire d'utiliser des alimentations électriques 21 et 22 bien régulées et filtrées, afin de garantir un fonctionnement optimal.In order to maintain a property of insensitivity to supply noise, a property which existed in the assembly of the prior art due to the use of the transformer as shown in FIG. 1b, it is however necessary to use electrical supplies 21 and 22 well regulated and filtered, to guarantee optimal operation.

Afin toutefois d'améliorer le mode opératoire symétrique de l'ensemble, on indique que, ainsi que représenté en figure 3, l'étage préamplificateur différentiel 3 peut comprendre avantageusement sur chaque voie d'entrée un dispositif préamplificateur en mode non-différentiel, portant la référence 30 respectivement 31.In order, however, to improve the symmetrical operating mode of the assembly, it is indicated that, as shown in FIG. 3, the differential preamplifier stage 3 can advantageously comprise on each input channel a preamplifier device in non-differential mode, carrying the reference 30 respectively 31.

A titre d'exemple non limitatif, ainsi que représenté sur la figure 3, les préamplificateurs en mode non-différentiel 30 et 31 peuvent comporter de manière classique une borne positive formant borne d'entrée pour les signaux délivrés par les capacités de liaison 11 respectivement 12, et un couplage résistif en contre-réaction par l'intermédiaire de résistances 301 respectivement 311 sur la borne négative correspondante. Les résistances de sortie 302 et 312 permettent d'attaquer un amplificateur différentiel de sortie 32, lequel peut comporter de manière classique une borne positive formant borne d'entrée reliée à la sortie du préamplificateur 31 par l'intermédiaire d'une résistance 321 et d'une capacité 322 en parallèle connectées entre la borne d'entrée positive précitée et la tension de référence, et une borne d'entrée négative reliée d'une part, en contre-réaction par un circuit 320 capacité 323 à la borne de sortie de l'amplificateur 32, et, d'autre part, à la résistance 302 de la sortie du dispositif préamplificateur en mode non-différentiel 30.By way of nonlimiting example, as shown in FIG. 3, the preamplifiers in non-differential mode 30 and 31 can conventionally include a positive terminal forming an input terminal for the signals delivered by the connection capacitors 11 respectively. 12, and a resistive feedback coupling via resistors 301 and 311 respectively on the corresponding negative terminal. The output resistors 302 and 312 make it possible to drive a differential output amplifier 32, which can conventionally include a positive terminal forming an input terminal connected to the output of the preamplifier 31 via a resistor 321 and d a capacitor 322 in parallel connected between the aforementioned positive input terminal and the reference voltage, and a negative input terminal connected on the one hand, in feedback by a 320 capacitor circuit 323 to the output terminal of the amplifier 32, and, on the other hand, to the resistor 302 of the output of the preamplifier device in non-differential mode 30.

En outre, on indique que la borne d'entrée positive de chaque dispositif préamplificateur en mode non-différentiel 30 et 31 est reliée à la tension de référence par l'intermédiaire d'une résistance d'entrée 300, respectivement 310. En outre, une résistance ajustable 313 est prévue, cette résistance reliant les deux entrées négatives de chaque dispositif préamplificateur en mode non-différentiel 30 et 31. La résistance 313 peut comporter une résistance fixe non-ajustable de valeur non nulle et permet ainsi d'effectuer un réglage de rattrapage des différences de gain en mode non-différentiel des dispositifs préamplificateurs non-différentiels 30 et 31 précités.In addition, it is indicated that the positive input terminal of each preamplifier device in non-differential mode 30 and 31 is connected to the reference voltage by means of an input resistor 300, respectively 310. In addition, an adjustable resistor 313 is provided, this resistor connecting the two negative inputs of each preamplifier device in non-differential mode 30 and 31. The resistor 313 may include a non-adjustable fixed resistor of non-zero value and thus allows to carry out a gain adjustment adjustment in non-differential mode of the aforementioned non-differential preamplifier devices 30 and 31.

Le montage tel que représenté en figure 3 donne satisfaction. Toutefois, il nécessite, afin de garantir un fonctionnement optimal, l'utilisation d'alimentations électriques 21 et 22 bien régulées et filtrées, en raison du fait que, dans le cas où une perturbation non-symétrique apparaît sur les sources d'alimentation électrique 21 et 22 précitées, la différence des bruits d'alimentation ainsi formée se retrouve en sortie du montage, c'est-à-dire à la sortie du préamplificateur différentiel 3.The assembly as shown in Figure 3 gives satisfaction. However, in order to guarantee optimal operation, it requires the use of well regulated and filtered power supplies 21 and 22, due to the fact that, in the event that a non-symmetrical disturbance appears on the power supply sources 21 and 22 above, the difference in supply noise thus formed is found at the outlet of the assembly, that is to say at the outlet of the differential preamplifier 3.

Une amélioration notoire du dispositif, objet de la présente invention, tel que représenté en figure 3, peut alors être apportée, ainsi que représenté en figure 4, afin de diminuer le bruit inhérent aux deux tensions d'alimentation 21 et 22 dans le cas notamment où des perturbations de bruit non-symétriques apparaîtraient sur ces alimentations.A noticeable improvement of the device, object of the present invention, as shown in Figure 3, can then be made, as shown in Figure 4, in order to reduce the noise inherent in the two supply voltages 21 and 22 in the case in particular where non-symmetrical noise disturbances would appear on these supplies.

Dans ce but, ainsi que représenté sur la figure 4 précitée, le dispositif de prise de son à microphone électret, objet de la présente invention, comprend en outre, entre l'étage préamplificateur différentiel 3 et la liaison par capacité de liaison, sur chacune des voies d'entrée de l'étage préamplificateur différentiel 3 précité, un circuit de couplage inversé de chacune des voies d'entrée au circuit de polarisation symétrique. Ce circuit de couplage inversé, dit de réjection d'alimentation, permet de réinjecter au niveau de chaque borne d'entrée de l'étage préamplificateur différentiel les tensions délivrées par les sources de tension symétriques inversées, privées de leur composantes continues.For this purpose, as shown in FIG. 4 above, the electret microphone sound recording device, object of the present invention, further comprises, between the differential preamplifier stage 3 and the link by link capacity, on each input channels of the aforementioned differential preamplifier stage 3, an inverted coupling circuit of each of the input channels to the symmetrical bias circuit. This inverted coupling circuit, called supply rejection, makes it possible to reinject at each input terminal of the differential preamplifier stage the voltages delivered by the symmetrical inverted voltage sources, deprived of their continuous components.

De cette façon, on comprend que chaque entrée de l'étage amplificateur différentiel 3 voit ainsi la somme des bruits des deux alimentations 21 et 22 précitées, ce bruit disparaissant alors en sortie puisque le montage effectue la différence des signaux d'entrée.In this way, it is understood that each input of the differential amplifier stage 3 thus sees the sum of the noises of the two aforementioned supplies 21 and 22, this noise then disappearing at the output since the assembly effects the difference of the input signals.

Ainsi qu'on l'a représenté de manière plus détaillée sur la figure 4, on indique que le circuit de couplage 4 comporte un premier et un deuxième circuit, formés chacun par une résistance et un condensateur électrique en série, portant les références 211, 212, respectivement 221, 222. Le premier circuit 211, 212 est connecté entre la deuxième source de tension négative 21 et la première entrée de l'étage amplificateur différentiel 3, c'est-à-dire en aval de la capacité de liaison 11. Le deuxième circuit 221, 222 est connecté entre la première source de tension positive 20 et la deuxième entrée de l'étage préamplificateur différentiel 3, c'est-à-dire en aval de la capacité de liaison 12.As shown in more detail in FIG. 4, it is indicated that the coupling circuit 4 comprises a first and a second circuit, each formed by a resistor and an electric capacitor in series, bearing the references 211, 212, respectively 221, 222. The first circuit 211, 212 is connected between the second negative voltage source 21 and the first input of the differential amplifier stage 3, that is to say downstream of the connection capacity 11 The second circuit 221, 222 is connected between the first positive voltage source 20 and the second input of the differential preamplifier stage 3, that is to say downstream of the connection capacitor 12.

Pour un résultat optimum, on indique en outre que le circuit de réjection d'alimentation 4 doit être identique au circuit de polarisation 2, la résistance 211 étant identique à la résistance 210, la résistance 221 identique à la résistance 220, la capacité 212 identique à la capacité 12 et la capacité 222 identique à la capacité 11.For an optimum result, it is further indicated that the power rejection circuit 4 must be identical to the bias circuit 2, the resistor 211 being identical to the resistor 210, the resistor 221 identical to the resistor 220, the capacity 212 identical at capacity 12 and capacity 222 identical to capacity 11.

Des essais comparatifs ont été effectués afin de mettre en évidence la qualité du dispositif de prise de son à microphone électret, objet de la présente invention, et sa robustesse aux perturbations électro-magnétiques notamment par rapport aux dispositifs de l'art antérieur.Comparative tests have been carried out in order to demonstrate the quality of the electret microphone sound recording device, object of the present invention, and its robustness to electromagnetic disturbances, in particular compared to the devices of the prior art.

A cet effet, on a représenté sur la figure 5a, la réponse du montage de l'art antérieur représenté en figure la à une perturbation du secteur d'alimentation électrique, c'est-à-dire à une fréquence de 50 Hz. La figure 5a est graduée en ordonnées en décibels et, en abscisses, en fréquences. Les essais ont été effectués en présence d'un bruit rose et d'une raie à 50 Hz due à une perturbation du secteur ainsi qu'aux fréquences harmoniques de celui-ci. La réponse du circuit, tel que représenté en figure la relative à l'art antérieur, présente de manière manifeste un bruit parasite à la fréquence du secteur précédemment mentionné.To this end, there is shown in Figure 5a, the response of the assembly of the prior art shown in Figure la to a disturbance of the power supply sector, that is to say at a frequency of 50 Hz. Figure 5a is graduated on the ordinate in decibels and, on the abscissa, in frequencies. The tests were carried out in the presence of a pink noise and a line at 50 Hz due to a disturbance of the sector as well as to the harmonic frequencies of the latter. The response of the circuit, as shown in FIG. 1 relating to the prior art, clearly exhibits parasitic noise at the frequency of the sector mentioned above.

Au contraire, dans le cas de la figure 5b, la réponse du montage de la figure 4, tel que représenté précédemment dans la description, dans des conditions analogues de perturbation de bruit, montre clairement une diminution de 18 dB sur l'amplitude de la raie à 50 Hz, soit un niveau huit fois inférieur. La réponse en fréquence du dispositif, objet de la présente invention, n'est dans ce cas plus affectée par la présence du perturbateur.On the contrary, in the case of Figure 5b, the response of the assembly of Figure 4, as shown previously in the description, under analogous noise disturbance conditions, clearly shows a decrease of 18 dB on the amplitude of the line at 50 Hz, ie a level eight times lower. The frequency response of the device, object of the present invention, is in this case no longer affected by the presence of the disturbance.

Le dispositif de prise de son par microphone électret, objet de la présente invention, précédemment décrit, est particulièrement avantageux dans la mesure où, par le seul remplacement du transformateur par un circuit de couplage par liaison capacité, les résultats, en qualité de prise de son, sont toutefois identiques aux circuits de l'art antérieur comportant de tels transformateurs, alors que les coûts de prix de revient de mise en oeuvre de ces circuits ont été notoirement diminués.The device for picking up sound by electret microphone, object of the present invention, previously described, is particularly advantageous insofar as, by the mere replacement of the transformer by a coupling circuit by capacitance link, the results, in terms of pick-up its, however, are identical to the circuits of the prior art comprising such transformers, while the cost price of implementation of these circuits have been known to be reduced.

En outre, la mise en oeuvre de ces circuits, conformément à l'objet de la présente invention, est particulièrement avantageuse dans les antennes acoustiques ou dans des circuits complexes nécessitant une prise de son de qualité.In addition, the implementation of these circuits, in accordance with the object of the present invention, is particularly advantageous in acoustic antennas or in complex circuits requiring quality sound recording.

Claims (4)

Dispositif de prise de son à partir d'un microphone électret, dans lequel les signaux délivrés par le microphone électret sont amplifiés au moyen d'un étage préamplificateur différentiel, ce dispositif comprenant une liaison par capacité de liaison entre chaque borne de sortie du microphone électret et une entrée de l'étage préamplificateur différentiel, caractérisé en ce qu'il comprend des moyens de polarisation symétrique des bornes de sortie dudit microphone électret, comprenant une première et une deuxième source de tension, symétrique par rapport à une tension de référence, chacune reliée à une borne de sortie du microphone électret.Device for picking up sound from an electret microphone, in which the signals delivered by the electret microphone are amplified by means of a differential preamplifier stage, this device comprising a link by capacitance of link between each output terminal of the electret microphone and an input of the differential preamplifier stage, characterized in that it comprises means for symmetrical polarization of the output terminals of said electret microphone, comprising a first and a second voltage source, symmetrical with respect to a reference voltage, each connected to an electret microphone output terminal. Dispositif selon la revendication 1, caractérisé en ce que ledit étage préamplificateur différentiel comprend sur chaque voie d'entrée un dispositif préamplificateur en mode non différentiel.Device according to claim 1, characterized in that said differential preamplifier stage comprises on each input channel a preamplifier device in non-differential mode. Dispositif selon l'une des revendications 1 ou 2, caractérisé en ce que celui-ci comporte en outre, entre l'étage préamplificateur différentiel et ladite capacité de liaison, sur chacune des voies d'entrée de l'étage préamplificateur différentiel, des moyens de couplage inversé de chacune des voies d'entrée auxdits moyens de polarisation symétrique, de façon à réinjecter au niveau de chaque borne d'entrée de l'étage préamplificateur différentiel lesdites sources de tension symétriques inversées, privées de leur composante continue.Device according to one of claims 1 or 2, characterized in that it further comprises, between the differential preamplifier stage and said connection capacity, on each of the input channels of the differential preamplifier stage, means of inverted coupling of each of the input channels to said symmetrical polarization means, so as to reinject at each input terminal of the differential preamplifier stage said inverted symmetrical voltage sources, deprived of their direct component. Dispositif selon la revendication 3, caractérisé en ce que lesdits moyens de couplage comportent un premier et un deuxième circuit formé par une résistance et un condensateur électrique en série, le premier circuit étant connecté entre la deuxième source de tension négative et la première entrée de l'étage préamplificateur différentiel, et le deuxième circuit étant connecté entre la première source de tension positive et la deuxième entrée de l'étage préamplificateur différentiel.Device according to claim 3, characterized in that said coupling means comprise a first and a second circuit formed by a resistor and an electric capacitor in series, the first circuit being connected between the second source of negative voltage and the first input of the 'differential preamplifier stage, and the second circuit being connected between the first positive voltage source and the second input of the differential preamplifier stage.
EP19950401674 1994-07-15 1995-07-12 Sound pick-up device by an electret microphone Expired - Lifetime EP0692921B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9408807A FR2722636B1 (en) 1994-07-15 1994-07-15 SOUND DEVICE BY ELECTRET MICROPHONE
FR9408807 1994-07-15

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EP0692921A1 true EP0692921A1 (en) 1996-01-17
EP0692921B1 EP0692921B1 (en) 2001-10-04

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EP19950401674 Expired - Lifetime EP0692921B1 (en) 1994-07-15 1995-07-12 Sound pick-up device by an electret microphone

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EP (1) EP0692921B1 (en)
DE (1) DE69523004T2 (en)
ES (1) ES2164140T3 (en)
FR (1) FR2722636B1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2769164A1 (en) * 1997-09-26 1999-04-02 Alain Maurice Ange Magagnini Electrostatic microphone device with integrated circuit interface.
GB2382949A (en) * 2001-12-04 2003-06-11 Samsung Electronics Co Ltd Reducing echoes and noise caused by cross talk in a telephone handset connecting cord

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3778561A (en) * 1972-06-21 1973-12-11 Bell Canada Northern Electric Electret microphone
EP0055650A1 (en) * 1980-12-31 1982-07-07 Thomson-Csf Telephone Circuit for connecting an active microphone, in particular with an electret, to a telephone transmission circuit
DE3933870A1 (en) * 1989-10-11 1991-04-18 Neumann Gmbh Georg Controlling microphones supplied with current over cable audio cores - involves adjustment of supply voltage so that magnitude provides control information
EP0546571A1 (en) * 1991-12-12 1993-06-16 Nec Corporation Amplifier circuit for electret condenser microphone
US5315231A (en) * 1992-11-16 1994-05-24 Hughes Aircraft Company Symmetrical bipolar bias current source with high power supply rejection ratio (PSRR)

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3778561A (en) * 1972-06-21 1973-12-11 Bell Canada Northern Electric Electret microphone
EP0055650A1 (en) * 1980-12-31 1982-07-07 Thomson-Csf Telephone Circuit for connecting an active microphone, in particular with an electret, to a telephone transmission circuit
DE3933870A1 (en) * 1989-10-11 1991-04-18 Neumann Gmbh Georg Controlling microphones supplied with current over cable audio cores - involves adjustment of supply voltage so that magnitude provides control information
EP0546571A1 (en) * 1991-12-12 1993-06-16 Nec Corporation Amplifier circuit for electret condenser microphone
US5315231A (en) * 1992-11-16 1994-05-24 Hughes Aircraft Company Symmetrical bipolar bias current source with high power supply rejection ratio (PSRR)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2769164A1 (en) * 1997-09-26 1999-04-02 Alain Maurice Ange Magagnini Electrostatic microphone device with integrated circuit interface.
GB2382949A (en) * 2001-12-04 2003-06-11 Samsung Electronics Co Ltd Reducing echoes and noise caused by cross talk in a telephone handset connecting cord
AU2002302014B2 (en) * 2001-12-04 2004-08-19 Samsung Electronics Co., Ltd. Apparatus for reducing echoes and noises in telephone
GB2382949B (en) * 2001-12-04 2004-09-29 Samsung Electronics Co Ltd Apparatus for reducing echoes and noises in telephone equipment
AU2002302014B9 (en) * 2001-12-04 2005-03-24 Samsung Electronics Co., Ltd. Apparatus for reducing echoes and noises in telephone
US6934383B2 (en) 2001-12-04 2005-08-23 Samsung Electronics Co., Ltd. Apparatus for reducing echoes and noises in telephone

Also Published As

Publication number Publication date
FR2722636A1 (en) 1996-01-19
DE69523004T2 (en) 2002-06-06
EP0692921B1 (en) 2001-10-04
FR2722636B1 (en) 1996-09-20
DE69523004D1 (en) 2001-11-08
ES2164140T3 (en) 2002-02-16

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