An amplifier circuit for an electret condenser microphone includes an

Рубрика: Articles. Автор: admin. Вторник 25 Окт 2011 в 10:46 дп

An amplifier circuit for an electret condenser microphone includes an operational amplifier, an operational amplifier, a bias circuit, and a power supply circuit. The operational amplifier has an inverting input terminal for receiving an output of a two-wire lead electret condenser microphone and a noninverting input terminal for receiving a bias voltage. The bias circuit divides a power supply voltage to generate the bias voltage. The power supply circuit applies the power supply voltage to the electret condenser microphone through the bias circuit and a first resistor. Condenser microphone, and method of construction, is disclosed. The microphone comprises a cup-shaped housing having a base surface and an upstanding peripheral wall. The wall terminates at a distal edge defining an opening. The microphone further comprises a diaphragm and ring assembly disposed on the base surface and having a peripheral edge, a backplate having a peripheral edge, and a spacing washer disposed between the diaphragm and ring assembly and the backplate for separating the diaphragm and ring assembly from the backplate. The microphone also comprises a substrate closing the housing opening. The spacer is disposed between the peripheral housing wall and the peripheral edges of the diaphragm and ring assembly and the backplate. The spacer includes a radially inwardly directed flange which engages an upper peripheral surface of the backplate. In these lower-end ECM’s, the parts are dropped into an aluminum housing, or can. Because of part tolerance problems, the parts may not be properly centered within the can, and this results in the active portion of the moving diaphragm being touched by elements that are not supposed to touch it, thus adversely effecting performance and production yield. The main problem, however, is that the top of such ECM cans are rolled closed at the upper edge. The forces used to roll the microphone closed and sealed can be very large, and this force is transmitted though all the internal parts. All ECM’s use the product TEFLON «FEP» somewhere in their design to hold the electrostatic charge. Sometimes it is used as the moving diaphragm and sometimes it is used to coat the backplate. But TEFLON is soft, and under the rolling/sealing force, it becomes distorted and changes its thickness. As the thickness changes, the performance and yield of the microphone changes due to changes in the critical space between the moving diaphragm and the backplate. In accordance with this aspect of the invention, the method comprises providing a cup-shaped housing having a base surface and an upstanding peripheral wall. The wall terminates at a distal edge defining an opening. The method further comprises inserting a diaphragm and ring assembly on the base surface. The diaphragm and ring assembly has a peripheral edge. The method still further comprises placing a spacing washer on the peripheral edge of the diaphragm and ring assembly, placing a backplate on the spacing washer, the backplate having a peripheral edge, and placing a spacer between the peripheral housing wall and the peripheral edges of the diaphragm and ring assembly and the backplate, the spacer having an upper surface. The method further comprises placing a substrate across the housing opening and on the spacer upper surface, and rolling the housing distal edge into engagement with the substrate to seal the microphone. The spacer transfers the rolling force from the substrate to the housing base surface. Conventional condenser microphones of this kind comprise a diaphragm, a back electrode disposed under the diaphragm, a back-chamber-constituting plate disposed under the back electrode, a circuit assembling plate disposed under theback-chamber-constituting plate, a plurality of electronic circuit elements including a preamplifier attached to the upper surface of the circuit assembling plate, and a space between the back electrode and the back-chamber-constituting plate forming aback chamber. Such conventional condenser microphone can advantageously obtain the optimum characteristics of microphone frequency response, since the back-chamber-constituting plate so disposed as to permit the distance between the back electrode and theback-chamber-constituting plate, i.e. the capacity of the back chamber, to be freely changed. On the other hand, however, such conventional condenser microphones are deficient in that the microphone structure is complicated. The electronic circuit elements are soldered to that lower surface of the circuit assembling plate to which such electronic circuit elements are not attached. This soldering lower surface is not faced toward the inside of the microphone or theback electrode, but is faced toward the outside with respect to the microphone. Thus, such a soldering lower surface is susceptible to adverse influences from external noise, and therefore should be covered with a shield plate. Accordingly, in addition to the back-chamber-constituting plate, such a shield plate is necessarily required, thereby disadvantageously increasing the number of members constituting the microphone. Conventional condenser microphones of another type are known in which the back-chamber-constituting plate in the conventional condenser microphone above-mentioned, is eliminated. In such a condenser microphone, the back chamber is formed between the back electrode and the circuit assembling plate. Thus, such a condenser microphone is advantageously constructed in such a manner as not to require theback-chamber-constituting plate. However, due to the presence of the electronic circuit elements, the distance between the back electrode and the circuit assembling plate cannot be reduced below a predetermined distance, so that the capacity of the backchamber cannot be reduced below a predetermined value. Thus, there is a case where the optimum characteristics of microphone frequency response cannot be obtained. Furthermore, such a conventional condenser microphone necessarily requires a shield plate, so that reduction in the number of members constituting the microphone and simplification of the microphone structure cannot be realized. An amplifier circuit for an electret condenser microphone includes an operational amplifier, an operational amplifier, a bias circuit, and a power supply circuit. The operational amplifier has an inverting input terminal for receiving an output of a two-wire lead electret condenser microphone and a noninverting input terminal for receiving a bias voltage. The bias circuit divides a power supply voltage to generate the bias voltage. The power supply circuit applies the power supply voltage to the electret condenser microphone through the bias circuit and a first resistor. Condenser microphone, and method of construction, is disclosed. The microphone comprises a cup-shaped housing having a base surface and an upstanding peripheral wall. The wall terminates at a distal edge defining an opening. The microphone further comprises a diaphragm and ring assembly disposed on the base surface and having a peripheral edge, a backplate having a peripheral edge, and a spacing washer disposed between the diaphragm and ring assembly and the backplate for separating the diaphragm and ring assembly from the backplate. The microphone also comprises a substrate closing the housing opening. The spacer is disposed between the peripheral housing wall and the peripheral edges of the diaphragm and ring assembly and the backplate. The spacer includes a radially inwardly directed flange which engages an upper peripheral surface of the backplate. In these lower-end ECM’s, the parts are dropped into an aluminum housing, or can. Because of part tolerance problems, the parts may not be properly centered within the can, and this results in the active portion of the moving diaphragm being touched by elements that are not supposed to touch it, thus adversely effecting performance and production yield. The main problem, however, is that the top of such ECM cans are rolled closed at the upper edge. The forces used to roll the microphone closed and sealed can be very large, and this force is transmitted though all the internal parts. All ECM’s use the product TEFLON «FEP» somewhere in their design to hold the electrostatic charge. Sometimes it is used as the moving diaphragm and sometimes it is used to coat the backplate. But TEFLON is soft, and under the rolling/sealing force, it becomes distorted and changes its thickness. As the thickness changes, the performance and yield of the microphone changes due to changes in the critical space between the moving diaphragm and the backplate. In accordance with this aspect of the invention, the method comprises providing a cup-shaped housing having a base surface and an upstanding peripheral wall. The wall terminates at a distal edge defining an opening. The method further comprises inserting a diaphragm and ring assembly on the base surface. The diaphragm and ring assembly has a peripheral edge. The method still further comprises placing a spacing washer on the peripheral edge of the diaphragm and ring assembly, placing a backplate on the spacing washer, the backplate having a peripheral edge, and placing a spacer between the peripheral housing wall and the peripheral edges of the diaphragm and ring assembly and the backplate, the spacer having an upper surface. The method further comprises placing a substrate across the housing opening and on the spacer upper surface, and rolling the housing distal edge into engagement with the substrate to seal the microphone. The spacer transfers the rolling force from the substrate to the housing base surface. Conventional condenser microphones of this kind comprise a diaphragm, a back electrode disposed under the diaphragm, a back-chamber-constituting plate disposed under the back electrode, a circuit assembling plate disposed under theback-chamber-constituting plate, a plurality of electronic circuit elements including a preamplifier attached to the upper surface of the circuit assembling plate, and a space between the back electrode and the back-chamber-constituting plate forming aback chamber. Such conventional condenser microphone can advantageously obtain the optimum characteristics of microphone frequency response, since the back-chamber-constituting plate so disposed as to permit the distance between the back electrode and theback-chamber-constituting plate, i.e. the capacity of the back chamber, to be freely changed. On the other hand, however, such conventional condenser microphones are deficient in that the microphone structure is complicated. The electronic circuit elements are soldered to that lower surface of the circuit assembling plate to which such electronic circuit elements are not attached. This soldering lower surface is not faced toward the inside of the microphone or theback electrode, but is faced toward the outside with respect to the microphone. Thus, such a soldering lower surface is susceptible to adverse influences from external noise, and therefore should be covered with a shield plate. Accordingly, in addition to the back-chamber-constituting plate, such a shield plate is necessarily required, thereby disadvantageously increasing the number of members constituting the microphone. Conventional condenser microphones of another type are known in which the back-chamber-constituting plate in the conventional condenser microphone above-mentioned, is eliminated. In such a condenser microphone, the back chamber is formed between the back electrode and the circuit assembling plate. Thus, such a condenser microphone is advantageously constructed in such a manner as not to require theback-chamber-constituting plate. However, due to the presence of the electronic circuit elements, the distance between the back electrode and the circuit assembling plate cannot be reduced below a predetermined distance, so that the capacity of the backchamber cannot be reduced below a predetermined value. Thus, there is a case where the optimum characteristics of microphone frequency response cannot be obtained. Furthermore, such a conventional condenser microphone necessarily requires a shield plate, so that reduction in the number of members constituting the microphone and simplification of the microphone structure cannot be realized.


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