Title of Invention	A CONDENSER MICROPHONE EMPLOYING WIDE BAND STOP FILTER FOR WIDEBAND SIGNAL OF LOW FREQUENCY AND RADIO FREQUENCY
Abstract	A condenser microphone employing a wide band stop filter is disclosed. Said microphone has improved resistance to electrostatic discharge applied from outside. This has an object of providing a condenser microphone capable of being used for or a multi-band by comprising a wide band stop filter capable of efficiently blocking a wide band signal including low frequency and radio frequency used in a mobile communication. To this end, a condenser microphone comprises: an acoustic module (36) for converting sound pressure into variation of an electric signal; a FET for amplifying the electric signal inputted from the acoustic module (36); and a wide band stop filter for blocking a wide band signal including low frequency and radio frequency outputted from the FET, and being realized by any one or more of resistors and capacitors which are connected selectively according to the radio frequency band between the drain D and the source S of the FET.

Title of Invention

A CONDENSER MICROPHONE EMPLOYING WIDE BAND STOP FILTER FOR WIDEBAND SIGNAL OF LOW FREQUENCY AND RADIO FREQUENCY

Abstract

A condenser microphone employing a wide band stop filter is disclosed. Said microphone has improved resistance to electrostatic discharge applied from outside. This has an object of providing a condenser microphone capable of being used for or a multi-band by comprising a wide band stop filter capable of efficiently blocking a wide band signal including low frequency and radio frequency used in a mobile communication. To this end, a condenser microphone comprises: an acoustic module (36) for converting sound pressure into variation of an electric signal; a FET for amplifying the electric signal inputted from the acoustic module (36); and a wide band stop filter for blocking a wide band signal including low frequency and radio frequency outputted from the FET, and being realized by any one or more of resistors and capacitors which are connected selectively according to the radio frequency band between the drain D and the source S of the FET.

Full Text	A condenser microphone employing a wide band stop filter for wideband signals of low frequency and radio frequency FIELD OF THE INVENTION The present invention relates to a condenser microphone employing a wide band stop filter for wideband signals of low frequency and radio frequency, and more particularly to a condenser microphone capable of not only suppressing electromagnetic (EM) noise but also improving resistance to electrostatic discharge (ESD) applied from outside. BACKGROUND ART In general, microphones are classified as follows, according to methods converting mechanical vibration into an electrical signal: carbon microphones using electrical resistance characteristics of carbon particles; crystal microphones using the piezoelectric effect of Rochelle Salt; moving coil microphones generating induced current by vibrating a diaphragm, in which a coil of wire is attached, in a magnetic field; velocity microphones using induced current generated when a metal film installed in a magnetic field receives sound waves and is vibrated; and condenser microphones using capacitance varied according to vibration of a diaphragm caused by sound waves. Herein, the condenser microphone is universally used as a small microphone, but has a problem in that a DC power supply is necessarily required to apply a voltage to a condenser. Lately, to solve such a problem, an electret condenser microphone using electret, which has semi-permanent charge, is used, which has advantages in that a structure of a pre-amplifier is simplified because a bias power supply is not needed and also its performance can be improved at a low cost. Meanwhile, a transmission section of a mobile terminal radiates a radio frequency signal of a large instantaneous power, which is range of a few mW to a few W, through an antenna. The radio frequency signal is induced into a line between a microphone and an external sound pressure signal process circuit and then is applied to a junction field-effect transistor (hereinafter, referred to as "JFET'). which is a field-effect transistor (hereinafter, referred to as "FET"), installed in the inside or outside of the microphone. At this time, if a power of the radio frequency signal applied to the JFET is larger than a predetermined level, the JFET is nonlinearly operated, so as to generate noise component relative to a peak envelope together with a harmonic wave. Since the frequency band of the peak envelope overlaps with a sound pressure signal of audio frequency in general, the signal of the noise component is amplified with the sound pressure signal and is inputted to the sound pressure signal process circuit, thereby forming the largest noise of the microphone. Therefore, in order to remove such a noise, a microphone used in a mobile terminal, in the case of a single mode, comprises a notch filter using a LC resonator realized by one chip capacitor in the inside, so that radio frequency signals of a predetermined frequency range are blocked. Meanwhile, a conventional microphone 1 used in a dual-mode mobile terminal, as shown in FIG. 1, comprises a filter 14 generating resonance at two frequency bands in using two chip capacitors C1 and C2. That is, terminals for mobile communications, which are widely used today, can be classified into Mobile Subscriber Radio Telephones of 900MHz band and Personal Communication Systems (PCNs) of 1800MHz band. Therefore, the dual-mode terminal must have a function capable of blocking radio frequency signals of both 900MHz band and 1800MHz band. Referring to FIG. 1, an acoustic module is equivalently represented as a variable capacitor CECM and is connected to the gate G of a FET 12 realized by a JFET. A filter 14 realized by a first and a second capacitor C1 and C2 is connected in parallel between the drain D and the source S of the FET 12. Herein, the first capacitor C1 has a capacitance of about 10pF and functions to remove 1800MHz frequency components, and the second capacitor C2 has a capacitance of about 33pF and functions to remove 900MHz frequency components. In the case of using such a microphone in a mobile terminal, the output of the FET 12 is transmitted to a sound pressure signal process circuit 16 after passing the filter 14 designed with parallel connected capacitors C1 and C2, and the output of the sound pressure signal process circuit 16 passes a radio-frequency/intermediate- frequency circuit (RF/IF circuit) 18 and is radiated to the air through an antenna. Herein, the parallel connected capacitors C1 and C2 are designed with a chip capacitor C1 and C2, and each of the capacitors C1 and C2 forms a LC resonance circuit together with respective parasitic inductance L existed in the inside, thereby functioning as a notch filter. FIG. 2 is a graph showing transfer characteristic of each filter in several cases in which the filter shown in FIG. 1 is realized by one capacitor or two capacitors. In the graph shown in FIG. 2, the horizontal axis represents frequencies in GHz, the vertical axis represents attenuation levels. A dotted line gl represents a transfer characteristic in a case of having only the second capacitor C2 of 33pF and shows a rapid attenuation of a signal at about 900MHz band, and a solid line g2 represents a transfer characteristic in a case of having only the first capacitor C1 of 10pF and shows a rapid attenuation of a signal at about 1800MHz band. Also, a dashed-dot line g3 represents a transfer characteristic in a case of having the first and the second capacitor C1 and C2 connected parallel with each other, and shows a great attenuation of a signal at about 900MHz band and about 2.2GHz. However, such a conventional multi-band low-noise microphone has not only a problem in that only a little variation of the distance between two capacitors effects the resonance filter's center of 1800MHz to be moved but also another problem in that it is impossible effectively to remove or block noise in a super-radio frequency mode. That is, in a case of using a new mode such as a new frequency band for IMT-2000 service (for example, 2000MHz band or 2400MHz band), since having a narrowband blocking characteristic limited within a predetermined frequency band, a conventional circuit can attenuate only electromagnetic noise within a predetermined frequency band but cannot attenuate radio frequency (RF) noise and electromagnetic noise generated within other frequency bands with the exception of a predetermined frequency band. Such a problem is also generated in a mode below 1800MHz frequency band. Further, in order to improve reliability of a mobile terminal, each element of the terminal is required to have a strong resistance to electrostatic discharge. However, the conventional microphone is problematic in that the conventional microphone is easily affected by electrostatic discharge applied from outside. In other words, the mobile terminal must have no damaged internal circuit clement at all. either after it experiences electrostatic discharge in the air with a voltage of 15 kV applied thereto in a state where its microphone is grounded, or after it experiences electrostatic discharge with a voltage of 8 kV applied thereto in a state where it is in direct contact with a node for the electrostatic discharge. However, the conventional microphones cannot satisfy the above-mentioned requirement with respect to the ESD applied from outside. SUMMARY OF THE INVENTION Therefore, the present invention has been made in view of the above- mentioned problems, and it is an object of the present invention to provide a condenser microphone comprising a wide band stop filter capable of efficiently blocking a wide band signal including low frequency and radio frequency used in a mobile communication, thereby being able to be used for a multi-band. Another object of the present invention is to provide a condenser microphone having widened removal range of electromagnetic noise, improved blocking level of filtering, and improved resistance to electrostatic discharge applied from outside. According to an aspect of the present invention, there is provided a condenser microphone decreasing noise by blocking radio frequency interference for a mobile terminal, comprising: an acoustic module for converting sound pressure into variation of an electric signal; an amplification means for amplifying the electric signal inputted from the acoustic module; and an EM-noise-filtering/ESD-blocking section for blocking a wide band signal including low frequency and radio frequency outputted from the amplification means and for blocking electromagnetic-wave/radio- frequency noises and electrostatic discharge entered from outside. The amplification means is an FET, and the EM-noise-filtering/ESD- blocking section includes capacitors and resistors connected selectively between the gate G and the source S of the FET and/or between the drain D and the source S of the FET according to frequency band. In addition, the capacitor can be changed in a range of lpF to 100µF according to frequency band, and the resistor can be changed in a range of 100 to 1GΩ according to frequency band. The resistor can be replaced by a magnetic induction element such as an inductor, and also the value of the resistors connected serially or parallel can be changed selectively according to frequency band. These will be identically applied to each embodiment in the following description. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: FIG. 1 is a schematic view of a multi-band low-noise microphone, having capacitor array, used in a conventional mobile terminal; FIG. 2 is a graph showing transfer characteristic of each filter in several cases in which capacitance of the filter shown in FIG. 1 is changed variously; FIG. 3 is a circuit showing a microphone having an EM-noise-filtering/ESD- blocking section realized by one capacitor and one resistor according to a first embodiment of the present invention; FIGs. 4A to 4D are circuits each of which shows a microphone having one of various EM-noise-filtering/ESD-blocking sections realized by two capacitors and one resistor according to a second embodiment of the present invention; FIG. 4E is a graph for comparing noise characteristics of a condenser microphone according to the present invention with that of a conventional microphone in using direct RF injection; FIGs. 5A and 5B are circuits each of which shows a microphone having one of various EM-noise-filtering/ESD-blocking sections realized by two capacitors and two resistors according to a third embodiment of the present invention; FIG. 6 is a circuit showing a microphone having an EM-noise-filtcring/ESD- blocking section realized by only three capacitors according to a fourth embodiment of the present invention; and FIGs. 7A and 7B are circuits each of which shows a microphone having one of various EM-noise-filtering/ESD-blocking sections realized by three capacitors and one resistor according to a fifth embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention. First, a condenser microphone according to the present invention comprises: an acoustic module having a capacitance varying according to an acoustic signal inputted thereto; a FET for converting and amplifying varied capacitance of the- acoustic module into an electric signal; and an EM-noise-filtering/ESD-blocking section, which is connected to the output ports of the FET, for removing electromagnetic noise (EM noise) and for providing a function to block electrostatic discharge. For easy comprehension, according to the numbers of resistors and capacitors realizing the EM-noise-filtering/ESD-blocking section, embodiments will be classified and described as follows. Embodiment 1 FIG. 3 is a circuit showing a microphone having an EM-noise-filtering/ESD-blocking section realized by one capacitor C1 1 and one resistor R11 according to the present invention. Referring to FIG. 3, an acoustic module 36, which has a capacitance varying according to an acoustic signal inputted thereto, is equivalently represented as a variable capacitor CECM and is connected to the gate G of a FET 30. Also, an EM- noise-filtering/ESD-blocking section 32 for removing electromagnetic noise and blocking electrostatic discharge is connected in parallel between the source S and the drain D of the FET 30. According to a first embodiment, the EM-noise- filtering/ESD-blocking section 32 consists of a resistor Rl 1 and a capacitor C1 1, in which the resistor Rl 1 is connected serially to the drain D of the FET 30 in such a manner that one end of the resistor Rl 1 is connected to the drain D of the FET 30, and the capacitor C1 1 is connected between the other end of the resistor R11 and source S ofthe FET 30. With this construction, sound pressure of a user vibrates a diaphragm (not shown) to vary the capacitance of the variable capacitor CHCM. and such capacitance variation induces voltage variation at the gate G of the FET 30. The FET 30 includes a JFET, which has a gate G connected to the variable capacitor CECM, a source S connected to a common ground, and a drain D connected to the EM-noise-filtcring/ESD-blocking section 32, or an amplifier of a built-in-gain microphone, thereby amplifying an input signal. Such FETs 30 have a very high input impedance and a very low output impedance, so that it functions as an impedance transformer matching impedance of the acoustic module and circuit part. The output of the FET 30 is outputted to output ports 34a and 34b after passing the EM-noise-filtering/ESD-blocking section 32. Flere, the EM-noise- filtering/ESD-blocking section 32 functions as a wide band stop filter blocking high- frequency radio signals or EM noise which enters through the output ports 34a and 34b for connecting the microphone to an external device, while functioning to block electrostatic discharge which is applied from outside. That is, high pressure of electrostatic discharge applied through the output ports 34a and 34b from outside is discharged to ground through the capacitor C11 of large capacitance, and the resistor R11 prevents the electrostatic discharge from being directly applied to the inside circuit section. To achieve such a result, the capacitor CM must have a large capacitance, enough to store current caused by the high pressure of electrostatic discharge, that is, the capacitor C11 must be at least 1 nF. With the first embodiment, it is possible that the capacitance of the capacitor C11 is changed selectively from InF to 100µF according to conditions. For example, the capacitor C1 1 may have a capacitance selected from the group consisting of InF. I.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF. and the resistor R11 may have a resistance selected from the group consisting of 100Ω, 220Ω, 330ft, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩt. In a condenser microphone having a circuit as constructed according to the first embodiment described above, electromagnetic noise over a wide frequency band including low frequency and radio frequency can be blocked. Further, a condenser microphone according to the first embodiment has an improved blocking capability (resistance) enough to stand against electrostatic discharge of even above 8KV applied from outside when the microphone is grounded and high pressure of electrostatic discharge is applied directly to the output ports. Embodiment 2 FIGs. 4A to 4D are circuits each of which shows a microphone having one of various EM-noise-filtering/ESD-blocking sections 32 selectively including two capacitors C21 and C22 and one resistor R21 according to a second embodiment of the present invention. The EM-noise-filtering/ESD-blocking section 32 according to the second embodiment forms a shape of a character 'IT or a shape of a character 'inverted IT by connecting a resistor R21 between two capacitors C21 and C22 faced to each other, in which the a shape of a character 'inverted IT means a shape formed by inverting top and bottom of a shape of a character 'IT. Also, a noise-blocking resistor R22 for blocking electromagnetic noise inputted to the FET 30 is selectively added between the gate G of the FET 30 and the acoustic module 36. According to the second embodiment, FIG. 4A is a circuit showing a case in which the EM-noise-filtering/ESD-blocking section 32 has a shape of a character 'IT and a noise-blocking resistor for preventing electromagnetic noise from being inputted to the FET 30 is not between the gate G of the FET 30 and the acoustic module 36. FIG. 4B is another circuit showing another case in which the EM-noise-filtering/ESD- blocking section 32 has a shape of a character 'IT and a noise-blocking resistor R22 for blocking electromagnetic noise inputted to the FET 30 is connected between the gate G of the FET 30 and the acoustic module 36. Referring to FIG. 4A and 4B, A condenser microphone in accordance with the second embodiment of the present invention comprises: an acoustic module 36 having a capacitance varying according to an acoustic signal inputted thereto; a FET 30 for converting and amplifying varied capacitance of the acoustic module into an electric signal; and an EM-noise-filtering/ESD-blocking section 32, which is connected to the drain D of the FET 30, for removing electromagnetic noise (EM noise) and for providing a function to block electrostatic discharge. The acoustic module 36 is equivalently represented as a variable capacitor CECM and is connected to the gate G of the FET 30. Also, an F.M-noise- filtering/ESD-blocking section 32 for removing electromagnetic noise and blocking electrostatic discharge is connected in parallel between the source S and the drain D of the FET 30. The FET 30 includes a JFET, which has a gate G connected to the variable capacitor CECM, a source S connected to a common ground, and a drain D connected to the EM-noisc-filtering/ESD-blocking section 32. or an amplifier of a built-in-gain microphone, thereby amplifying an input signal. Such FETs 30 have a very high input impedance and a very low output impedance, so that it functions as an impedance transformer matching impedance of the acoustic module and circuit part. The EM-noise-filtering/ESD-blocking section 32 shown in FIG. 4A and 4B according to the second embodiment is realized by a first capacitor C21 connected between the drain D and the source S of the FET 30, a second capacitor C22 connected parallel to the first capacitor C21, and a first resistor R21 connected serially to between an upper signal-line end of the first capacitor C21 and an upper signal-line end of the second capacitor C22, thereby forming a shape of a character TE. With this construction of such a second embodiment, the acoustic module 36 and the FET 30 are operated identical to those in the first embodiment, therefore a detailed description of the acoustic module 36 and the FET 30 will be omitted so as to avoid repeated description and the following description will be laid out centering around the EM-noise-filtering/ESD-blocking section 32 according to the second embodiment. In the second embodiment, a filtering operation of the EM-noise- filtcring/ESD-b10cking section 32 is performed by the first capacitor C21 and the second capacitor C22, thereby b10cking high-frequency noise or electromagnetic noise which is inputted from outside through the output ports 34a and 34b. Also, the first resistor R21 performs not only a decoupling function separating the first capacitor C21 and the second capacitor C22 but also an electrostatic-discharge b10cking function preventing the electrostatic discharge from being directly applied to the inside circuit. The second capacitor C22 bypasses electrostatic discharge voltage applied through the output ports 34a and 34b to ground, thereby preventing the inside elements from being damaged by the electrostatic discharge. To achieve such a result, the second capacitor C22 must have a large capacitance, enough to store- current caused by the high pressure of electrostatic discharge, that is, the second capacitor C22 must be at least InF. Meanwhile, in FIG. 4B, the second resistor R22 connected serially between the acoustic module 36 and the gate G of the FET is a noise-b10cking resistor for preventing electromagnetic noise from being inputted to the FET 30. With the second embodiment, it is possible that the capacitance of the first capacitor C21 and the second capacitor C22 are changed selectively between 10pF and 100µF according to conditions. For example, the first capacitor C21 may be 10pF or 33pF, while the second capacitor C22 may be a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF. 22nF, 33nF, 47nF, 68nF and 100nF. Also, it is preferred that the first resistor R21 has a resistance selected from the group consisting of 100ft, 220ft, 330ft, 430ft, 620ft. 680ft, 820ft and IKft, and it is preferred that the second resistor R22 has a resistance selected from the group consisting of 100Ω, 1KΩ, 10KΩ, 100KΩ, and 1MΩt. In a condenser microphone having a circuit as constructed according to the second embodiment described above, electromagnetic noise over a wide frequency band including 10w frequency and radio frequency can be b10cked. Further, a condenser microphone according to the first embodiment has an improved b10cking capability (resistance) enough to stand against electrostatic discharge of even above 8KV applied from outside when the microphone is grounded and high pressure of electrostatic discharge is applied directly to the output ports. According to the second embodiment, FIG. 4C is still another circuit showing a case in which an EM-noise-filtering section 32 has a shape of a character "inverted IT and a noise-b10cking resistor for preventing electromagnetic noise from being inputted to the FET 30 is not between the gate G of the FET 30 and the acoustic module 36. FIG. 4D is still another circuit showing another case in which the EM- noise-filtering section 32 has a shape of a character 'inverted IT and a noise-b10cking resistor R22 for preventing electromagnetic noise from being inputted to the FET 30 is connected between the gate G of the FET 30 and the acoustic module 36. The EM-noise-filtering section 32 shown in FIG. 4C and 4D according to the second embodiment comprises a first capacitor C2I connected between the drain D and the source S of the FET 30, a second capacitor C22 connected parallel to the first capacitor C21, and a first resistor R21 connected serially to between a 10wer ground- line end of the first capacitor C21 and a 10wer ground-line end of the second capacitor C22, thereby forming a shape of a character 'inverted IT. With this construction of such a second embodiment, the acoustic module 36 and the FET 30 arc operated identical to those in the first embodiment, therefore a detailed description of the acoustic module 36 and the FET 30 will be omitted so as to avoid repeated description and the fol10wing description will be laid out centering around the EM-noise-filtering section 32 according to the second embodiment. In the second embodiment, a filtering operation of the EM-noise-filtering section 32 is performed by the first capacitor C21 and the second capacitor C22, thereby b10cking high-frequency noise or electromagnetic noise which is inputted from outside through the output ports 34a and 34b. Also, the first resistor R21 performs a decoupling function separating the first capacitor C21 and the second capacitor C22. To achieve such a result, the second capacitor C22 must be realized by a wide band stop filter having a large capacitance efficiently capable of b10cking a wide band signal including 10w frequency and radio frequency, that is. the second capacitor C22 must be at least 1 nF. Meanwhile, in FIG. 4D. a second resistor R22 connected serially between the acoustic module 36 and the gate G of the FET is a noise-b10cking resistor for preventing electromagnetic noise from being inputted to the FET 30. With such second embodiments, it is possible that the capacitance of the first capacitor C21 and the second capacitor C22 are changed selectively from 10pF to 100µF according to conditions. For example, the first capacitor C21 may be 10pF or 33pF, while the second capacitor C22 may have a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, l5nF, 22nF. 33nF, 47nF, 68nF and 100nF. Also, it is preferred that the first resistor R2I has a resistance selected from the group consisting of 100ft, 220ft, 330ft, 430ft, 620ft, 680ft, 820ft and IKft, and it is preferred that the second resistor R22 has a resistance selected from the group consisting of 100Ω, 1KΩ, 10KΩ, 100KΩ, and 1MΩ. In a condenser microphone having a circuit as constructed according to such second embodiment described above, electromagnetic noise over a wide frequency band including 10w frequency and radio frequency can be b10cked. In a circuit according to the second embodiments, an electric signal of the microphone inputted through the gate G of the FET 30 and the second resistor R22 is amplified in the FET 30 so as to have 10w noise, a radio frequency band of the electric signal is b10cked so that the noise is removed, and then the electric signal is transmitted to a sound process circuit of a mobile terminal through the output ports 34a and 34b. FIG. 4E is a graph showing a result of comparing RF noise characteristics of a conventional commercially-used condenser microphone and a condenser microphone according to the second embodiment of the present invention. Referring to FIG. 4E, (a) is a graph showing a filtering characteristic of a conventional microphone, and (b) is a graph showing a filtering characteristic of a microphone according to the second embodiment of the present invention. In the shown graphs, each horizontal axis represents frequency with a unit of MHz, and each vertical axis represents attenuation level with a unit of dB. in which a larger negative (-) value means a higher attenuation level. In a direct RF injection method for a commercially-used condenser microphone in a frequency range from 0.125MHz to 3.0GHz, RF noise characteristic (a) of the microphone module shows a RF noise level attenuation of -40dB generally at 900MHz (GSM) and 1.8MHz (DCS). However, the RF noise characteristic shows an RF noise level attenuation much smaller than -40dB in other frequency ranges. A vertical axis expressed on a measuring apparatus used in the above test has a minimum value of -40dB, thereby al10wing all values 10wer than -40dB to be expressed only as -40dB. On the other hand, in the case of applying a direct RF injection method to a condenser microphone according to the second embodiment of the present invention over frequency range from 0.125MHz to 3.0GHz, RF noise characteristic (b) of the microphone module shows an RF noise attenuation level of -40dB, which is the minimum value of an available measurement range, over all of the frequency band. That is, the microphone according to the second embodiment shows a result that its RF noise level is improved to maximum 45dB or more as compared to that of the commercially-used electret condenser microphone. This shows that the condenser microphone according to the present invention functions as an excellent EMI filter. Embodiment 3 FIGs. 5A and 5B are circuits each of which shows a microphone having one of various EM-noise-filtering/ESD-b10cking sections 32 including two capacitors C31 and C32 and two resistors R31 and R32 according to a third embodiment of the present invention. The EM-noise-filtering/ESD-b10cking section 32 according to the third embodiment forms a shape of a character '#' with two capacitors C31 and C32 faced to each other and two resistor R31 and R32 connected respectively between adjacent two ends of the capacitors C31 and C32. Also, a noise-b10cking resistor R33 for preventing electromagnetic noise from being inputted to the FET is selectively added between the gate G of the FET 30 and the acoustic module 36. As shown in FIG. 5A and 5B, a condenser microphone according to the third embodiment of the present invention comprises an equivalent capacitor CECM connected between the gate G and the source S of the FET 30 performing an amplification function, and also comprises an EM-noise-filtering/ESD-b10cking section 32 connected between the drain D and the source S of the FET 30, in which the equivalent capacitor CECM represents the capacitance of the microphone. In the case of FIG. 5B, a third resistor R33 is connected between the acoustic module 36 and the gate G of the FET 30. Also, the EM-noisc-filtering/ESD-b10cking section 32 according to the third embodiment forms a shape of a character '#' in such a manner that a first capacitor C31 and a second capacitor C32 arc parallel connected to each other and a first resistor R31 and a second resistor R32 are connected respectively between ends of the capacitors C31 and C32. Referring to FIG. 5A and 5B, sound pressure of a user vibrates a diaphragm of a sound module (not shown), so as to vary the capacitance of the variable capacitor CECM. and such capacitance variation induces voltage variation at the gate G of the FET 30. The FET 30 includes a JFET, which has a gate G connected to the variable capacitor CKCM. a source S connected to a common ground, and a drain D connected to the EM-noise-filtering/ESD-b10cking section 32, or an amplifier of a built-in-gain microphone, thereby amplifying an input signal. Such FETs 30 have a very high input impedance and a very 10w output impedance, so that it functions as an impedance transformer matching impedance of the acoustic module and circuit part. The output of the FET 30 is outputted to output ports 34a and 34b after passing the EM-noise-filtering/ESD-b10cking section 32. Here, the EM-noise- filtering/ESD-b10cking section 32 functions as a wide band stop filter b10cking high- frequency radio signals or EM noise which enters through the output ports 34a and 34b for connecting the microphone to an external device, while functioning to b10ck electrostatic discharge which is applied from outside. In the third embodiment, a filtering operation of the EM-noise-filtering/ESD- b10cking section 32 is performed by the first capacitor C31 and the second capacitor C32. thereby b10cking high-frequency noise or electromagnetic noise which is inputted from outside through the output ports 34a and 34b. Also, the first resistor R31 and the second resistor R32 performs not only a decoupling function separating the first capacitor C31 and the second capacitor C32 but also an electrostatic- discharge b10cking function preventing the electrostatic discharge from being directly applied to the inside circuit. The second capacitor C32 bypasses electrostatic discharge voltage applied through the output ports 34a and 34b to ground, thereby preventing the inside elements from being damaged by the electrostatic discharge. To achieve such a result, the second capacitor C32 must have a large capacitance, enough to store current caused by the high pressure of electrostatic discharge, that is, the second capacitor C32 must be at least I nF. Meanwhile, in FIG. 5B, the third resistor R33 connected serially between the acoustic module and the gate G of the FET 30 is a noise-b10cking resistor for preventing electromagnetic noise from being inputted to the FET 30. The capacitance of the first capacitor C31 and the second capacitor C32 can be changed selectively from 10pF to 100µF according to conditions. For example, the first capacitor C31 may be 10pF or 33pF, while the second capacitor C32 may have a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF. 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF. Also, it is preferred that each of the first resistor R31 and the second resistor R32 has a resistance selected from the group consisting of 100Ω, 220Ω, 330Ω. 430Ω. 620Ω, 680Ω, 820Ω and 1KΩ. and it is preferred that the third resistor R33 has a resistance selected from the group consisting of 100Ω, 1KΩ, 10KΩ, 100KΩ, and 1MΩ. In a condenser microphone having a circuit as constructed according to the third embodiment described above, electromagnetic noise over a wide frequency band including 10w frequency and radio frequency can be b10cked. Further, a condenser microphone according to the first embodiment has an improved b10cking capability (resistance) enough to stand against electrostatic discharge of even above 8K.V applied from outside when the microphone is grounded and high pressure of electrostatic discharge is applied directly to the output ports. Embodiment 4 FIG. 6 is a circuit showing a microphone having an EM-noise-filtering section realized by only three capacitors C41 to C43 according to a fourth embodiment of the present invention. Referring to FIG. 6, most of the construction is identical to that of the embodiments described above, therefore a detailed description will be omitted and the fol10wing description will be laid out centering around the EM-noise-filtering section 32. which has a different construction from the embodiments described above. The EM-noise-filtering section 32 according to the fourth embodiment comprises a first capacitor C41, a second capacitor C42, and a third capacitor C43 connected in parallel between the drain D and the source S of the FET 30. In the fourth embodiment, a filtering operation of the EM-noise-filtering section 32 is performed by the first to third capacitors C41 to C43, thereby b10cking high-frequency noise or electromagnetic noise which is inputted from outside through the output ports 34a and 34b. To achieve such a result, the third capacitor C43 must be realized by a wide band stop filter having a large capacitance efficiently capable of b10cking a wide band signal including low frequency and radio frequency, that is, the third capacitor C43 must be at least lnF. The capacitance of the capacitors C41 to C43 can be changed selectively from 10pF to l00µF according to conditions. Preferably, the first capacitor C41 is selected to have a capacitance between 10pF and 20pF according to conditions, the second capacitor C42 is selected to have a capacitance between 20pF and lnF according to conditions, and the third capacitor C43 is selected to have a capacitance between InF and 100µF according to conditions. More preferably, the third capacitor C43 has a capacitance selected from the group consisting of InF. 1.5nF. 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, l5nF, 22nF, 33nF, 47nF, 68nF and 100nF. In a condenser microphone having a circuit as constructed according to the fourth embodiment described above, electromagnetic noise over a wide frequency band including 10w frequency and radio frequency can be b10cked. Embodiment 5 FIGs. 7A and 7B are circuits each of which shows a microphone having one of various EM-noise-filtering/ESD-b10cking sections realized by three capacitors C41 to C43 and one resistor R51 according to a fifth embodiment of the present invention. FIG. 7A shows a construction in which the resistor R5! of the EM-noise- filtering/ESD-b10cking section is connected serially to the drain D of the FET 30, and FIG. 7B shows a construction in which the resistor R51 of the EM-noise- filtering/ESD-b10cking section is connected serially to the source S of the FET 30. Referring to FIG. 7A, a condenser microphone according to the fifth embodiment of the present invention comprises an equivalent capacitor Cecw connected between the gate G and the source S of the FET 30 performing an amplification function. Also, the condenser microphone according to the fifth embodiment comprises a first capacitor C41, a second capacitor C42, and a third capacitor C43 connected in parallel between the source S and the drain D of the FET 30, and comprises a first resistor R51 connected between the drain connection ends of the second capacitor C42 and the third capacitor C43, so that an EM-noise- filtcring/ESD-blocking section 32 is formed. Also, referring to FIG. 7B, an EM-noise-filtering/ESD-b10cking section 32 is realized in such a manner that a first capacitor C41, a second capacitor C42, and a third capacitor C43 are connected in parallel between the source S and the drain D of the FET 30, and a first resistor R51 is connected between the source connection ends of the second capacitor C42 and the third capacitor C43. In the fifth embodiment of the present invention, repeated description of the construction and the operation identical to those of the embodiments described above will be omitted, and the fol10wing description will be laid out centering around the operation of the EM-noise-filtering section 32. In the EM-noise-filtering/ESD-b10cking section 32 shown in FIG. 7A according to the fifth embodiment of the present invention, the first to the third capacitors C41 to C43 performs a filtering function b10cking high-frequency noise or electromagnetic noise which is inputted from outside through the output ports 34a and 34b, and the first resistor R51 performs not only a decoupling function separating the second capacitor C42 and the third capacitor C43 but also an b10cking function preventing the electrostatic discharge voltage, which is applied from outside, from directly affecting the inside circuit. Also, the third capacitor C43 bypasses electrostatic discharge voltage applied through the output ports 34a and 34b to ground, thereby preventing the inside elements from being damaged by the electrostatic discharge. To achieve such a result, the third capacitor C43 must have a large capacitance, enough to store current caused by the high pressure of electrostatic discharge, that is, the third capacitor C43 must be at least InF. The capacitance of the capacitors C41 to C43 can be changed selectively from 10pF to 100u.F according to conditions. Preferably, the first capacitor C41 is selected to have a capacitance between 10pF and 20pF according to conditions, the second capacitor C42 is selected to have a capacitance between 20pF and InF according to conditions, and the third capacitor C43 is selected to have a capacitance between InF and 100u.F according to conditions. More preferably, the third capacitor C43 has a capacitance selected from the group consisting of InF, l.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF. Also, it is preferred that the first resistor R51 has a resistance selected from the group consisting of 100ft, 220ft, 330ft, 430ft, 620ft, 680ft, 820ft and 1 Kft. In a condenser microphone having a circuit as constructed according to the fifth embodiment described above, electromagnetic noise over a wide frequency band including 10w frequency and radio frequency can be b10cked. Further, a condenser microphone according to the first embodiment has an improved b10cking capability (resistance) enough to stand against electrostatic discharge of even above 8KV applied from outside when the microphone is grounded and high pressure of electrostatic discharge is applied directly to the output ports. In the EM-noise-filtering section 32 shown in FIG. 7B according to the fifth embodiment of the present invention, the first to the third capacitors C41 to C43 performs a filtering function b10cking high-frequency noise or electromagnetic noise which is inputted from outside through the output ports 34a and 34b, and the first resistor R51 performs a decoupling function separating the second capacitor C42 and the third capacitor C43. To achieve such a result, the third capacitor C43 must be realized by a wide band stop filter having a large capacitance efficiently capable of b10cking a wide band signal including 10w frequency and radio frequency, that is, the third capacitor C43 must be at least InF. The capacitance of the capacitors C41, C42, and C43 can be changed selectively from 10pF to 100u.F according to conditions. Preferably, the first capacitor C41 is selected to have a capacitance between 10pF and 20pF according to conditions, the second capacitor C42 is selected to have a capacitance between 20pF and InF according to conditions, and the third capacitor C43 is selected to have a capacitance between InF and 100µF according to conditions. More preferably, the third capacitor C43 is selected to have a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF. Also, it is preferred that the first resistor R51 has a resistance selected from the group consisting of 100Ω, 220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ. In a condenser microphone having the circuit described above according to the fifth embodiment described above, electromagnetic noise over a wide frequency band including 10w frequency and radio frequency can be b10cked. Embodiment 6 Meanwhile, the first to the fifth embodiments described above can be applied to a variety of circuits for removing noise caused in a frequency band of 1.8GUz or more including a next-generation mobile communication system (1MT2000). That is, a circuit for removing noise caused in the frequency band of I.8GHz or more has the same construction as the circuit described above for removing noise corresponding to the frequency band of 900MHz and 1.8GHz, and has only a different feature in that capacitors C1 and C2 for performing a filtering function are realized by capacitors having a capacitance between lpF and 100µF. The capacitors having a capacitance between IpF and 100µF can filter electromagnetic noise of 5KHz to 6GFIz. For example, in a case of applying the EM-noise-filtering/ESD-b10cking section 32 using three capacitors and one resistor as shown in FIG. 7A to a circuit for removing noise of 1.8GFIz or more, the first to the third capacitors C41, C42, and C43 for performing a filtering function can be selected to have a capacitance between 1pF and 100µF according to conditions. For example, the first capacitor C41 is selected to have a capacitance between 1pF and 5pF according to conditions, and preferably 4.7pF, the second capacitor C42 is selected to have a capacitance between 5pF and InF according to conditions, and preferably 5.6pF, the third capacitor C43 is selected to have a capacitance between 1nF and 100µF according to conditions, and preferably a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF, and it is preferred that the first resistor R51 has a resistance selected from the group consisting of 100Ω, 220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ.. In the example described above, the capacitors C41, C42, and C43 and the resistor R51 form a wide band stop filter, while functioning to improve resistance to electrostatic discharge. High pressure of electrostatic discharge applied through the output ports from outside is discharged to ground port 34b through the third capacitor C43 having the largest capacitance, and the first resistor R51 prevents the electrostatic discharge from being applied directly to the inside circuit section. To achieve such a result, the third capacitor C43 must have a large capacitance, enough to store current caused by the high pressure of electrostatic discharge, that is, the third capacitor C43 must be at least InF. In a condenser microphone having a circuit as constructed according to the example described above, electromagnetic noise over a wide frequency band including 10w frequency and radio frequency can be reduced. Further, a condenser microphone according to the present invention has an improved resistance enough to stand against electrostatic discharge of even above 8KV applied from outside when the microphone is grounded and high pressure of electrostatic discharge is applied directly to the output ports. In such a sixth embodiment, an electric signal of the microphone inputted through the gate G of the FET 30 is amplified in the FET 30 so as to have 10w noise, and is transmitted to a sound process circuit of a mobile terminal through the output ports 34a and 34b with noise removed by a wide band stop filter b10cking signals of radio frequency band, in which the wide band stop filter is realized by the first capacitor C41, the second capacitor C42, the third capacitor C43, and the first resistor R51. INDUSTRIAL APPLICABILITY As can be seen from the foregoing, the condenser microphone according to the present invention has advantages of widening range capable of removing electromagnetic noise, obtaining an excellent filtering effect of electromagnetic noise with a circuit only including capacitors and resistors in a wide frequency band including 10w frequency and radio frequency, and largely improving b10cking capability (resistance) to electrostatic discharge applied from outside. While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disc10sed embodiment and the drawings, but, on the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims. WE CLAIM : 1. A condenser microphone emp10ying a wide band stop filter for wideband signals of 10w frequency and radio frequency, the condenser microphone having improved resistance to electrostatic discharge applied from outside and preventing radio frequency interference to decrease noise, the condenser microphone comprising: an acoustic module 36 for converting sound pressure into variation of an electric signal; an amplification means, such as described herein an amplifier used in a built- in-gain microphone or a field-effect transistor, for amplifying the electric signal inputted from the acoustic module 36 ; and an EM-noise-filtering/ESD-b10cking section 32 for b10cking a wideband signal having 10w frequency and radio frequency outputted from the amplification means, b10cking introduced electromagnetic waves, radio wave noise, and electrostatic discharge, the EM-noise-filtering/ESD-b10cking section 32 including one or combination of a resistor and a capacitor disposed between an input port of the amplification means and the acoustic module 36 and/or between an output port of the amplification means and a ground, the resistor and the capacitor being connected in parallel or in series to each other. 2. A condenser microphone as claimed in claim 1, wherein the capacitor and the resistor have a capacitance between lpF and 100µF and a resistance between 10Ω and 1GΩ, respectively, each of which can be selectively adjusted according to frequency band. 3. A condenser microphone as claimed in claim 1, wherein the EM-noise- filtering/ESD-b10cking section 32 comprises: a resistor R11 connected serially between output port of the amplification means and signal output port 34a; and a capacitor C1 1 connected between one end of the resistor Rl 1 and ground GND. 4. A condenser microphone as claimed in claim 3, wherein: the capacitor C11 has a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF; and the resistor R11 has a resistance selected from the group consisting of 100Ω, 220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ.. 5. A condenser microphone as claimed in claim 1, wherein the EM-noise- filtering/ESD-b10cking section 32 comprises: a first capacitor C21 connected in parallel between output port of the amplification means and ground port to function as a filter, a second capacitor C22 connected parallel to the first capacitor C21 to perform an EM-noise-filtering and ESD-b10cking function; and a first resistor R21 connected serially to between an output port of the first capacitor C21 and an output port of the second capacitor C22 to perform a decoupling function, so that the EM-noise-filtering/ESD-b10cking section has a shape of a character 'IT. 6. A condenser microphone as claimed in claim 5, wherein: the first capacitor C21 has a capacitance of 10pF or 33pF; the second capacitor C22 has a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF;and the first resistor R21 has a resistance selected from the group consisting of 100ft, 220ft, 330ft, 430ft, 620ft, 680ft, 820ft and lKft. 7. A condenser microphone as claimed in claim 1, wherein the EM-noise- filtering/ESD-b10cking section 32 comprises: a first capacitor C21 connected in parallel between output port of the amplification means and ground port to function as a filter; a second capacitor C22 connected parallel to the first capacitor C21 to perform an EM-noise-filtering function; and a first resistor R21 connected serially to between a ground port GND of the first capacitor C21 and a ground port GND of the second capacitor C22 to perform a decoupling function, so that the EM-noise-filtering/ESD-b10cking section has a shape of a character 'inverted IT. 8. A condenser microphone as claimed in claim 7, wherein: the first capacitor C21 has a capacitance of 10pF or 33pF; trie second capacitor C22 has a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nFand 100nF; and the first resistor R21 has a resistance selected from the group consisting of 100Ω, 220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ.. 9. A condenser microphone as claimed in claim 5 or claim 7, further comprising a noise-b10cking resistor R22 between the acoustic module 36 and input port of the amplification means so as to b10ck electromagnetic noise from being inputted. 10. A condenser microphone as claimed in claim 9, wherein the noise- b10cking resistor has a resistance selected from the group consisting of 100Ω, 1KΩ, 10KΩ, 100KΩ, and 1MΩ. 11. A condenser microphone as claimed in claim 1, wherein the EM-noise- filtering/ESD-b10cking section 32 comprises: a first and a second capacitor C31 and C32 connected in parallel between output port of the amplification means and ground port; and a first and a second resistor R31 and R32 connected respectively between adjacent ends of the two capacitors C31 and C32, so that the EM-noise-filtering/ESD- b10cking section has a shape of a character '#', wherein, the first capacitor C31 performs a filtering function, the second capacitor C32 faced to the first capacitor C31 performs an EM-noise-filtering and electrostatic- discharge-b10cking function, and the resistors R31 and R32 performs a decoupling function and an electrostatic-discharge-b10cking function. 12. A condenser microphone as claimed in claim 11, wherein: the first capacitor C31 has a capacitance of 10pF or 33pF; the second capacitor C32 has a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nFand 100nF;and each of the first and second resistors R31 and R32 has a resistance selected from the group consisting of 100Ω, 220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ. 13. A condenser microphone as claimed in claim 11, further comprising a noise-b10cking resistor R33 between the acoustic module 36 and input port of the amplification means so as to b10ck electromagnetic noise from being inputted. 14. A condenser microphone as claimed in claim 13, wherein the noise- b10cking resistor R33 has a resistance selected from the group consisting of 100ft, 1KΩ, 10KΩ, 100KΩ, and 1MΩ. 15. A condenser microphone as claimed in claim 1, wherein the EM-noise- filtering section 32 comprises a first capacitor C41, a second capacitor C42, and a third capacitor C43 connected in parallel with each other between ground port and output port of the amplification means. 16. A condenser microphone as claimed in claim 15, wherein: the first capacitor C41 can be selectively adjusted so as to have a capacitance between 10pF and 20pF; the second capacitor C42 can be selectively adjusted so as to have a capacitance between 20pF and InF; and the third capacitor C43 can be selectively adjusted so as to have a capacitance between InF and 100p-F. 17. A condenser microphone as claimed in claim 15, wherein, in the EM- noise-filtering/ESD-b10cking section 32, a resistor R51 is further connected serially between a signal output end of the second capacitor C42 and a signal output end of the third capacitor C43. 18. A condenser microphone as claimed in claim 17, wherein: the first capacitor C41 is selectively adjusted so as to have a capacitance between 10pF and 20pF; the second capacitor C42 is selectively adjusted so as to have a capacitance between 20pF and 1 nF; the third capacitor C43 has a capacitance selected from the group consisting of 1nF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF; and the resistor R51 has a resistance selected from the group consisting of 100Ω, 220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ. 19. A condenser microphone as claimed in claim 15, wherein, in the EM- noise-filtering section 32, a resistor R51 is further connected serially between a ground end of the second capacitor C42 and a ground end of the third capacitor C43. 20. A condenser microphone as claimed in claim 19, wherein: the first capacitor C41 is selectively adjusted so as to have a capacitance between 10pF and 20pF; the second capacitor C42 is selectively adjusted so as to have a capacitance between 20pF and 1 nF; die third capacitor C43 has a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF;and the resistor R51 has a resistance selected from the group consisting of 100Ω, 220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ A condenser microphone employing a wide band stop filter is disclosed. Said microphone has improved resistance to electrostatic discharge applied from outside. This has an object of providing a condenser microphone capable of being used for or a multi-band by comprising a wide band stop filter capable of efficiently blocking a wide band signal including low frequency and radio frequency used in a mobile communication. To this end, a condenser microphone comprises: an acoustic module (36) for converting sound pressure into variation of an electric signal; a FET for amplifying the electric signal inputted from the acoustic module (36); and a wide band stop filter for blocking a wide band signal including low frequency and radio frequency outputted from the FET, and being realized by any one or more of resistors and capacitors which are connected selectively according to the radio frequency band between the drain D and the source S of the FET.

Full Text

A condenser microphone employing a wide band stop filter for
wideband signals of low frequency and radio frequency
FIELD OF THE INVENTION
The present invention relates to a condenser microphone employing a wide
band stop filter for wideband signals of low frequency and radio frequency, and more
particularly to a condenser microphone capable of not only suppressing
electromagnetic (EM) noise but also improving resistance to electrostatic discharge
(ESD) applied from outside.
BACKGROUND ART
In general, microphones are classified as follows, according to methods
converting mechanical vibration into an electrical signal: carbon microphones using
electrical resistance characteristics of carbon particles; crystal microphones using the
piezoelectric effect of Rochelle Salt; moving coil microphones generating induced
current by vibrating a diaphragm, in which a coil of wire is attached, in a magnetic
field; velocity microphones using induced current generated when a metal film
installed in a magnetic field receives sound waves and is vibrated; and condenser
microphones using capacitance varied according to vibration of a diaphragm caused
by sound waves.
Herein, the condenser microphone is universally used as a small microphone,
but has a problem in that a DC power supply is necessarily required to apply a voltage
to a condenser. Lately, to solve such a problem, an electret condenser microphone
using electret, which has semi-permanent charge, is used, which has advantages in
that a structure of a pre-amplifier is simplified because a bias power supply is not
needed and also its performance can be improved at a low cost.
Meanwhile, a transmission section of a mobile terminal radiates a radio
frequency signal of a large instantaneous power, which is range of a few mW to a few
W, through an antenna. The radio frequency signal is induced into a line between a
microphone and an external sound pressure signal process circuit and then is applied

to a junction field-effect transistor (hereinafter, referred to as "JFET'). which is a
field-effect transistor (hereinafter, referred to as "FET"), installed in the inside or
outside of the microphone.
At this time, if a power of the radio frequency signal applied to the JFET is
larger than a predetermined level, the JFET is nonlinearly operated, so as to generate
noise component relative to a peak envelope together with a harmonic wave. Since
the frequency band of the peak envelope overlaps with a sound pressure signal of
audio frequency in general, the signal of the noise component is amplified with the
sound pressure signal and is inputted to the sound pressure signal process circuit,
thereby forming the largest noise of the microphone.
Therefore, in order to remove such a noise, a microphone used in a mobile
terminal, in the case of a single mode, comprises a notch filter using a LC resonator
realized by one chip capacitor in the inside, so that radio frequency signals of a
predetermined frequency range are blocked.
Meanwhile, a conventional microphone 1 used in a dual-mode mobile
terminal, as shown in FIG. 1, comprises a filter 14 generating resonance at two
frequency bands in using two chip capacitors C1 and C2. That is, terminals for
mobile communications, which are widely used today, can be classified into Mobile
Subscriber Radio Telephones of 900MHz band and Personal Communication Systems
(PCNs) of 1800MHz band. Therefore, the dual-mode terminal must have a function
capable of blocking radio frequency signals of both 900MHz band and 1800MHz
band.
Referring to FIG. 1, an acoustic module is equivalently represented as a
variable capacitor CECM and is connected to the gate G of a FET 12 realized by a
JFET. A filter 14 realized by a first and a second capacitor C1 and C2 is connected
in parallel between the drain D and the source S of the FET 12. Herein, the first
capacitor C1 has a capacitance of about 10pF and functions to remove 1800MHz
frequency components, and the second capacitor C2 has a capacitance of about 33pF
and functions to remove 900MHz frequency components.
In the case of using such a microphone in a mobile terminal, the output of the

FET 12 is transmitted to a sound pressure signal process circuit 16 after passing the
filter 14 designed with parallel connected capacitors C1 and C2, and the output of the
sound pressure signal process circuit 16 passes a radio-frequency/intermediate-
frequency circuit (RF/IF circuit) 18 and is radiated to the air through an antenna.
Herein, the parallel connected capacitors C1 and C2 are designed with a chip capacitor
C1 and C2, and each of the capacitors C1 and C2 forms a LC resonance circuit
together with respective parasitic inductance L existed in the inside, thereby
functioning as a notch filter.
FIG. 2 is a graph showing transfer characteristic of each filter in several cases
in which the filter shown in FIG. 1 is realized by one capacitor or two capacitors.
In the graph shown in FIG. 2, the horizontal axis represents frequencies in
GHz, the vertical axis represents attenuation levels. A dotted line gl represents a
transfer characteristic in a case of having only the second capacitor C2 of 33pF and
shows a rapid attenuation of a signal at about 900MHz band, and a solid line g2
represents a transfer characteristic in a case of having only the first capacitor C1 of
10pF and shows a rapid attenuation of a signal at about 1800MHz band. Also, a
dashed-dot line g3 represents a transfer characteristic in a case of having the first and
the second capacitor C1 and C2 connected parallel with each other, and shows a great
attenuation of a signal at about 900MHz band and about 2.2GHz.
However, such a conventional multi-band low-noise microphone has not only
a problem in that only a little variation of the distance between two capacitors effects
the resonance filter's center of 1800MHz to be moved but also another problem in that
it is impossible effectively to remove or block noise in a super-radio frequency mode.
That is, in a case of using a new mode such as a new frequency band for IMT-2000
service (for example, 2000MHz band or 2400MHz band), since having a narrowband
blocking characteristic limited within a predetermined frequency band, a conventional
circuit can attenuate only electromagnetic noise within a predetermined frequency
band but cannot attenuate radio frequency (RF) noise and electromagnetic noise
generated within other frequency bands with the exception of a predetermined
frequency band. Such a problem is also generated in a mode below 1800MHz

frequency band.
Further, in order to improve reliability of a mobile terminal, each element of
the terminal is required to have a strong resistance to electrostatic discharge.
However, the conventional microphone is problematic in that the conventional
microphone is easily affected by electrostatic discharge applied from outside. In
other words, the mobile terminal must have no damaged internal circuit clement at all.
either after it experiences electrostatic discharge in the air with a voltage of 15 kV
applied thereto in a state where its microphone is grounded, or after it experiences
electrostatic discharge with a voltage of 8 kV applied thereto in a state where it is in
direct contact with a node for the electrostatic discharge. However, the conventional
microphones cannot satisfy the above-mentioned requirement with respect to the ESD
applied from outside.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in view of the above-
mentioned problems, and it is an object of the present invention to provide a
condenser microphone comprising a wide band stop filter capable of efficiently
blocking a wide band signal including low frequency and radio frequency used in a
mobile communication, thereby being able to be used for a multi-band.
Another object of the present invention is to provide a condenser microphone
having widened removal range of electromagnetic noise, improved blocking level of
filtering, and improved resistance to electrostatic discharge applied from outside.
According to an aspect of the present invention, there is provided a condenser
microphone decreasing noise by blocking radio frequency interference for a mobile
terminal, comprising: an acoustic module for converting sound pressure into
variation of an electric signal; an amplification means for amplifying the electric
signal inputted from the acoustic module; and an EM-noise-filtering/ESD-blocking
section for blocking a wide band signal including low frequency and radio frequency
outputted from the amplification means and for blocking electromagnetic-wave/radio-
frequency noises and electrostatic discharge entered from outside.

The amplification means is an FET, and the EM-noise-filtering/ESD-
blocking section includes capacitors and resistors connected selectively between the
gate G and the source S of the FET and/or between the drain D and the source S of the
FET according to frequency band.
In addition, the capacitor can be changed in a range of lpF to 100µF
according to frequency band, and the resistor can be changed in a range of 100 to
1GΩ according to frequency band. The resistor can be replaced by a magnetic
induction element such as an inductor, and also the value of the resistors connected
serially or parallel can be changed selectively according to frequency band. These will
be identically applied to each embodiment in the following description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The foregoing and other objects, features and advantages of the present
invention will become more apparent from the following detailed description when
taken in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic view of a multi-band low-noise microphone, having
capacitor array, used in a conventional mobile terminal;
FIG. 2 is a graph showing transfer characteristic of each filter in several cases
in which capacitance of the filter shown in FIG. 1 is changed variously;
FIG. 3 is a circuit showing a microphone having an EM-noise-filtering/ESD-
blocking section realized by one capacitor and one resistor according to a first
embodiment of the present invention;
FIGs. 4A to 4D are circuits each of which shows a microphone having one of
various EM-noise-filtering/ESD-blocking sections realized by two capacitors and one
resistor according to a second embodiment of the present invention;
FIG. 4E is a graph for comparing noise characteristics of a condenser
microphone according to the present invention with that of a conventional microphone
in using direct RF injection;
FIGs. 5A and 5B are circuits each of which shows a microphone having one
of various EM-noise-filtering/ESD-blocking sections realized by two capacitors and

two resistors according to a third embodiment of the present invention;
FIG. 6 is a circuit showing a microphone having an EM-noise-filtcring/ESD-
blocking section realized by only three capacitors according to a fourth embodiment
of the present invention; and
FIGs. 7A and 7B are circuits each of which shows a microphone having one
of various EM-noise-filtering/ESD-blocking sections realized by three capacitors and
one resistor according to a fifth embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference will now be made in detail to the preferred embodiments of the
present invention.
First, a condenser microphone according to the present invention comprises:
an acoustic module having a capacitance varying according to an acoustic signal
inputted thereto; a FET for converting and amplifying varied capacitance of the-
acoustic module into an electric signal; and an EM-noise-filtering/ESD-blocking
section, which is connected to the output ports of the FET, for removing
electromagnetic noise (EM noise) and for providing a function to block electrostatic
discharge. For easy comprehension, according to the numbers of resistors and
capacitors realizing the EM-noise-filtering/ESD-blocking section, embodiments will
be classified and described as follows.
Embodiment 1
FIG. 3 is a circuit showing a microphone having
an EM-noise-filtering/ESD-blocking section realized by one capacitor C1 1 and one
resistor R11 according to the present invention.
Referring to FIG. 3, an acoustic module 36, which has a capacitance varying
according to an acoustic signal inputted thereto, is equivalently represented as a
variable capacitor CECM and is connected to the gate G of a FET 30. Also, an EM-
noise-filtering/ESD-blocking section 32 for removing electromagnetic noise and
blocking electrostatic discharge is connected in parallel between the source S and the

drain D of the FET 30. According to a first embodiment, the EM-noise-
filtering/ESD-blocking section 32 consists of a resistor Rl 1 and a capacitor C1 1, in
which the resistor Rl 1 is connected serially to the drain D of the FET 30 in such a
manner that one end of the resistor Rl 1 is connected to the drain D of the FET 30, and
the capacitor C1 1 is connected between the other end of the resistor R11 and source S
ofthe FET 30.
With this construction, sound pressure of a user vibrates a diaphragm (not
shown) to vary the capacitance of the variable capacitor CHCM. and such capacitance
variation induces voltage variation at the gate G of the FET 30.
The FET 30 includes a JFET, which has a gate G connected to the variable
capacitor CECM, a source S connected to a common ground, and a drain D connected
to the EM-noise-filtcring/ESD-blocking section 32, or an amplifier of a built-in-gain
microphone, thereby amplifying an input signal. Such FETs 30 have a very high input
impedance and a very low output impedance, so that it functions as an impedance
transformer matching impedance of the acoustic module and circuit part.
The output of the FET 30 is outputted to output ports 34a and 34b after
passing the EM-noise-filtering/ESD-blocking section 32. Flere, the EM-noise-
filtering/ESD-blocking section 32 functions as a wide band stop filter blocking high-
frequency radio signals or EM noise which enters through the output ports 34a and
34b for connecting the microphone to an external device, while functioning to block
electrostatic discharge which is applied from outside. That is, high pressure of
electrostatic discharge applied through the output ports 34a and 34b from outside is
discharged to ground through the capacitor C11 of large capacitance, and the resistor
R11 prevents the electrostatic discharge from being directly applied to the inside
circuit section. To achieve such a result, the capacitor CM must have a large
capacitance, enough to store current caused by the high pressure of electrostatic
discharge, that is, the capacitor C11 must be at least 1 nF.
With the first embodiment, it is possible that the capacitance of the capacitor
C11 is changed selectively from InF to 100µF according to conditions. For example,
the capacitor C1 1 may have a capacitance selected from the group consisting of InF.

I.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF.
and the resistor R11 may have a resistance selected from the group consisting of
100Ω, 220Ω, 330ft, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩt.
In a condenser microphone having a circuit as constructed according to the
first embodiment described above, electromagnetic noise over a wide frequency band
including low frequency and radio frequency can be blocked. Further, a condenser
microphone according to the first embodiment has an improved blocking capability
(resistance) enough to stand against electrostatic discharge of even above 8KV applied
from outside when the microphone is grounded and high pressure of electrostatic
discharge is applied directly to the output ports.
Embodiment 2
FIGs. 4A to 4D are circuits each of which shows a microphone having one of
various EM-noise-filtering/ESD-blocking sections 32 selectively including two
capacitors C21 and C22 and one resistor R21 according to a second embodiment of
the present invention. The EM-noise-filtering/ESD-blocking section 32 according to
the second embodiment forms a shape of a character 'IT or a shape of a character
'inverted IT by connecting a resistor R21 between two capacitors C21 and C22 faced
to each other, in which the a shape of a character 'inverted IT means a shape formed
by inverting top and bottom of a shape of a character 'IT. Also, a noise-blocking
resistor R22 for blocking electromagnetic noise inputted to the FET 30 is selectively
added between the gate G of the FET 30 and the acoustic module 36.
According to the second embodiment, FIG. 4A is a circuit showing a case in
which the EM-noise-filtering/ESD-blocking section 32 has a shape of a character 'IT
and a noise-blocking resistor for preventing electromagnetic noise from being inputted
to the FET 30 is not between the gate G of the FET 30 and the acoustic module 36.
FIG. 4B is another circuit showing another case in which the EM-noise-filtering/ESD-
blocking section 32 has a shape of a character 'IT and a noise-blocking resistor R22
for blocking electromagnetic noise inputted to the FET 30 is connected between the
gate G of the FET 30 and the acoustic module 36.

Referring to FIG. 4A and 4B, A condenser microphone in accordance with
the second embodiment of the present invention comprises: an acoustic module 36
having a capacitance varying according to an acoustic signal inputted thereto; a FET
30 for converting and amplifying varied capacitance of the acoustic module into an
electric signal; and an EM-noise-filtering/ESD-blocking section 32, which is
connected to the drain D of the FET 30, for removing electromagnetic noise (EM
noise) and for providing a function to block electrostatic discharge.
The acoustic module 36 is equivalently represented as a variable capacitor
CECM and is connected to the gate G of the FET 30. Also, an F.M-noise-
filtering/ESD-blocking section 32 for removing electromagnetic noise and blocking
electrostatic discharge is connected in parallel between the source S and the drain D of
the FET 30.
The FET 30 includes a JFET, which has a gate G connected to the variable
capacitor CECM, a source S connected to a common ground, and a drain D connected
to the EM-noisc-filtering/ESD-blocking section 32. or an amplifier of a built-in-gain
microphone, thereby amplifying an input signal. Such FETs 30 have a very high
input impedance and a very low output impedance, so that it functions as an
impedance transformer matching impedance of the acoustic module and circuit part.
The EM-noise-filtering/ESD-blocking section 32 shown in FIG. 4A and 4B
according to the second embodiment is realized by a first capacitor C21 connected
between the drain D and the source S of the FET 30, a second capacitor C22
connected parallel to the first capacitor C21, and a first resistor R21 connected serially
to between an upper signal-line end of the first capacitor C21 and an upper signal-line
end of the second capacitor C22, thereby forming a shape of a character TE.
With this construction of such a second embodiment, the acoustic module 36
and the FET 30 are operated identical to those in the first embodiment, therefore a
detailed description of the acoustic module 36 and the FET 30 will be omitted so as to
avoid repeated description and the following description will be laid out centering
around the EM-noise-filtering/ESD-blocking section 32 according to the second
embodiment.

In the second embodiment, a filtering operation of the EM-noise-
filtcring/ESD-b10cking section 32 is performed by the first capacitor C21 and the
second capacitor C22, thereby b10cking high-frequency noise or electromagnetic noise
which is inputted from outside through the output ports 34a and 34b. Also, the first
resistor R21 performs not only a decoupling function separating the first capacitor
C21 and the second capacitor C22 but also an electrostatic-discharge b10cking
function preventing the electrostatic discharge from being directly applied to the
inside circuit. The second capacitor C22 bypasses electrostatic discharge voltage
applied through the output ports 34a and 34b to ground, thereby preventing the inside
elements from being damaged by the electrostatic discharge. To achieve such a
result, the second capacitor C22 must have a large capacitance, enough to store-
current caused by the high pressure of electrostatic discharge, that is, the second
capacitor C22 must be at least InF.
Meanwhile, in FIG. 4B, the second resistor R22 connected serially between
the acoustic module 36 and the gate G of the FET is a noise-b10cking resistor for
preventing electromagnetic noise from being inputted to the FET 30.
With the second embodiment, it is possible that the capacitance of the first
capacitor C21 and the second capacitor C22 are changed selectively between 10pF
and 100µF according to conditions. For example, the first capacitor C21 may be
10pF or 33pF, while the second capacitor C22 may be a capacitance selected from the
group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF. 22nF, 33nF,
47nF, 68nF and 100nF. Also, it is preferred that the first resistor R21 has a resistance
selected from the group consisting of 100ft, 220ft, 330ft, 430ft, 620ft. 680ft, 820ft
and IKft, and it is preferred that the second resistor R22 has a resistance selected
from the group consisting of 100Ω, 1KΩ, 10KΩ, 100KΩ, and 1MΩt.
In a condenser microphone having a circuit as constructed according to the
second embodiment described above, electromagnetic noise over a wide frequency
band including 10w frequency and radio frequency can be b10cked. Further, a
condenser microphone according to the first embodiment has an improved b10cking
capability (resistance) enough to stand against electrostatic discharge of even above

8KV applied from outside when the microphone is grounded and high pressure of
electrostatic discharge is applied directly to the output ports.
According to the second embodiment, FIG. 4C is still another circuit showing
a case in which an EM-noise-filtering section 32 has a shape of a character "inverted
IT and a noise-b10cking resistor for preventing electromagnetic noise from being
inputted to the FET 30 is not between the gate G of the FET 30 and the acoustic
module 36. FIG. 4D is still another circuit showing another case in which the EM-
noise-filtering section 32 has a shape of a character 'inverted IT and a noise-b10cking
resistor R22 for preventing electromagnetic noise from being inputted to the FET 30 is
connected between the gate G of the FET 30 and the acoustic module 36.
The EM-noise-filtering section 32 shown in FIG. 4C and 4D according to the
second embodiment comprises a first capacitor C2I connected between the drain D
and the source S of the FET 30, a second capacitor C22 connected parallel to the first
capacitor C21, and a first resistor R21 connected serially to between a 10wer ground-
line end of the first capacitor C21 and a 10wer ground-line end of the second capacitor
C22, thereby forming a shape of a character 'inverted IT.
With this construction of such a second embodiment, the acoustic module 36
and the FET 30 arc operated identical to those in the first embodiment, therefore a
detailed description of the acoustic module 36 and the FET 30 will be omitted so as to
avoid repeated description and the fol10wing description will be laid out centering
around the EM-noise-filtering section 32 according to the second embodiment.
In the second embodiment, a filtering operation of the EM-noise-filtering
section 32 is performed by the first capacitor C21 and the second capacitor C22,
thereby b10cking high-frequency noise or electromagnetic noise which is inputted
from outside through the output ports 34a and 34b. Also, the first resistor R21
performs a decoupling function separating the first capacitor C21 and the second
capacitor C22. To achieve such a result, the second capacitor C22 must be realized
by a wide band stop filter having a large capacitance efficiently capable of b10cking a
wide band signal including 10w frequency and radio frequency, that is. the second
capacitor C22 must be at least 1 nF.

Meanwhile, in FIG. 4D. a second resistor R22 connected serially between the
acoustic module 36 and the gate G of the FET is a noise-b10cking resistor for
preventing electromagnetic noise from being inputted to the FET 30.
With such second embodiments, it is possible that the capacitance of the first
capacitor C21 and the second capacitor C22 are changed selectively from 10pF to
100µF according to conditions. For example, the first capacitor C21 may be 10pF or
33pF, while the second capacitor C22 may have a capacitance selected from the group
consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, l5nF, 22nF. 33nF, 47nF,
68nF and 100nF. Also, it is preferred that the first resistor R2I has a resistance
selected from the group consisting of 100ft, 220ft, 330ft, 430ft, 620ft, 680ft, 820ft
and IKft, and it is preferred that the second resistor R22 has a resistance selected
from the group consisting of 100Ω, 1KΩ, 10KΩ, 100KΩ, and 1MΩ.
In a condenser microphone having a circuit as constructed according to such
second embodiment described above, electromagnetic noise over a wide frequency
band including 10w frequency and radio frequency can be b10cked.
In a circuit according to the second embodiments, an electric signal of the
microphone inputted through the gate G of the FET 30 and the second resistor R22 is
amplified in the FET 30 so as to have 10w noise, a radio frequency band of the electric
signal is b10cked so that the noise is removed, and then the electric signal is
transmitted to a sound process circuit of a mobile terminal through the output ports
34a and 34b.
FIG. 4E is a graph showing a result of comparing RF noise characteristics of
a conventional commercially-used condenser microphone and a condenser
microphone according to the second embodiment of the present invention.
Referring to FIG. 4E, (a) is a graph showing a filtering characteristic of a
conventional microphone, and (b) is a graph showing a filtering characteristic of a
microphone according to the second embodiment of the present invention. In the
shown graphs, each horizontal axis represents frequency with a unit of MHz, and each
vertical axis represents attenuation level with a unit of dB. in which a larger negative
(-) value means a higher attenuation level.

In a direct RF injection method for a commercially-used condenser
microphone in a frequency range from 0.125MHz to 3.0GHz, RF noise characteristic
(a) of the microphone module shows a RF noise level attenuation of -40dB generally
at 900MHz (GSM) and 1.8MHz (DCS). However, the RF noise characteristic shows
an RF noise level attenuation much smaller than -40dB in other frequency ranges. A
vertical axis expressed on a measuring apparatus used in the above test has a
minimum value of -40dB, thereby al10wing all values 10wer than -40dB to be
expressed only as -40dB.
On the other hand, in the case of applying a direct RF injection method to a
condenser microphone according to the second embodiment of the present invention
over frequency range from 0.125MHz to 3.0GHz, RF noise characteristic (b) of the
microphone module shows an RF noise attenuation level of -40dB, which is the
minimum value of an available measurement range, over all of the frequency band.
That is, the microphone according to the second embodiment shows a result that its
RF noise level is improved to maximum 45dB or more as compared to that of the
commercially-used electret condenser microphone.
This shows that the condenser microphone according to the present invention
functions as an excellent EMI filter.
Embodiment 3
FIGs. 5A and 5B are circuits each of which shows a microphone having one
of various EM-noise-filtering/ESD-b10cking sections 32 including two capacitors C31
and C32 and two resistors R31 and R32 according to a third embodiment of the
present invention. The EM-noise-filtering/ESD-b10cking section 32 according to the
third embodiment forms a shape of a character '#' with two capacitors C31 and C32
faced to each other and two resistor R31 and R32 connected respectively between
adjacent two ends of the capacitors C31 and C32. Also, a noise-b10cking resistor
R33 for preventing electromagnetic noise from being inputted to the FET is
selectively added between the gate G of the FET 30 and the acoustic module 36.
As shown in FIG. 5A and 5B, a condenser microphone according to the third

embodiment of the present invention comprises an equivalent capacitor CECM
connected between the gate G and the source S of the FET 30 performing an
amplification function, and also comprises an EM-noise-filtering/ESD-b10cking
section 32 connected between the drain D and the source S of the FET 30, in which
the equivalent capacitor CECM represents the capacitance of the microphone. In the
case of FIG. 5B, a third resistor R33 is connected between the acoustic module 36 and
the gate G of the FET 30. Also, the EM-noisc-filtering/ESD-b10cking section 32
according to the third embodiment forms a shape of a character '#' in such a manner
that a first capacitor C31 and a second capacitor C32 arc parallel connected to each
other and a first resistor R31 and a second resistor R32 are connected respectively
between ends of the capacitors C31 and C32.
Referring to FIG. 5A and 5B, sound pressure of a user vibrates a diaphragm
of a sound module (not shown), so as to vary the capacitance of the variable capacitor
CECM. and such capacitance variation induces voltage variation at the gate G of the
FET 30.
The FET 30 includes a JFET, which has a gate G connected to the variable
capacitor CKCM. a source S connected to a common ground, and a drain D connected
to the EM-noise-filtering/ESD-b10cking section 32, or an amplifier of a built-in-gain
microphone, thereby amplifying an input signal. Such FETs 30 have a very high
input impedance and a very 10w output impedance, so that it functions as an
impedance transformer matching impedance of the acoustic module and circuit part.
The output of the FET 30 is outputted to output ports 34a and 34b after
passing the EM-noise-filtering/ESD-b10cking section 32. Here, the EM-noise-
filtering/ESD-b10cking section 32 functions as a wide band stop filter b10cking high-
frequency radio signals or EM noise which enters through the output ports 34a and
34b for connecting the microphone to an external device, while functioning to b10ck
electrostatic discharge which is applied from outside.
In the third embodiment, a filtering operation of the EM-noise-filtering/ESD-
b10cking section 32 is performed by the first capacitor C31 and the second capacitor
C32. thereby b10cking high-frequency noise or electromagnetic noise which is

inputted from outside through the output ports 34a and 34b. Also, the first resistor
R31 and the second resistor R32 performs not only a decoupling function separating
the first capacitor C31 and the second capacitor C32 but also an electrostatic-
discharge b10cking function preventing the electrostatic discharge from being directly
applied to the inside circuit. The second capacitor C32 bypasses electrostatic
discharge voltage applied through the output ports 34a and 34b to ground, thereby
preventing the inside elements from being damaged by the electrostatic discharge.
To achieve such a result, the second capacitor C32 must have a large capacitance,
enough to store current caused by the high pressure of electrostatic discharge, that is,
the second capacitor C32 must be at least I nF.
Meanwhile, in FIG. 5B, the third resistor R33 connected serially between the
acoustic module and the gate G of the FET 30 is a noise-b10cking resistor for
preventing electromagnetic noise from being inputted to the FET 30.
The capacitance of the first capacitor C31 and the second capacitor C32 can
be changed selectively from 10pF to 100µF according to conditions. For example,
the first capacitor C31 may be 10pF or 33pF, while the second capacitor C32 may
have a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF.
4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF. Also, it is preferred
that each of the first resistor R31 and the second resistor R32 has a resistance selected
from the group consisting of 100Ω, 220Ω, 330Ω. 430Ω. 620Ω, 680Ω, 820Ω and 1KΩ.
and it is preferred that the third resistor R33 has a resistance selected from the group
consisting of 100Ω, 1KΩ, 10KΩ, 100KΩ, and 1MΩ.
In a condenser microphone having a circuit as constructed according to the
third embodiment described above, electromagnetic noise over a wide frequency band
including 10w frequency and radio frequency can be b10cked. Further, a condenser
microphone according to the first embodiment has an improved b10cking capability
(resistance) enough to stand against electrostatic discharge of even above 8K.V applied
from outside when the microphone is grounded and high pressure of electrostatic
discharge is applied directly to the output ports.

Embodiment 4
FIG. 6 is a circuit showing a microphone having an EM-noise-filtering
section realized by only three capacitors C41 to C43 according to a fourth
embodiment of the present invention.
Referring to FIG. 6, most of the construction is identical to that of the
embodiments described above, therefore a detailed description will be omitted and the
fol10wing description will be laid out centering around the EM-noise-filtering section
32. which has a different construction from the embodiments described above.
The EM-noise-filtering section 32 according to the fourth embodiment
comprises a first capacitor C41, a second capacitor C42, and a third capacitor C43
connected in parallel between the drain D and the source S of the FET 30.
In the fourth embodiment, a filtering operation of the EM-noise-filtering
section 32 is performed by the first to third capacitors C41 to C43, thereby b10cking
high-frequency noise or electromagnetic noise which is inputted from outside through
the output ports 34a and 34b. To achieve such a result, the third capacitor C43 must
be realized by a wide band stop filter having a large capacitance efficiently capable of
b10cking a wide band signal including low frequency and radio frequency, that is, the
third capacitor C43 must be at least lnF.
The capacitance of the capacitors C41 to C43 can be changed selectively
from 10pF to l00µF according to conditions. Preferably, the first capacitor C41 is
selected to have a capacitance between 10pF and 20pF according to conditions, the
second capacitor C42 is selected to have a capacitance between 20pF and lnF
according to conditions, and the third capacitor C43 is selected to have a capacitance
between InF and 100µF according to conditions. More preferably, the third
capacitor C43 has a capacitance selected from the group consisting of InF. 1.5nF.
2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, l5nF, 22nF, 33nF, 47nF, 68nF and 100nF.
In a condenser microphone having a circuit as constructed according to the
fourth embodiment described above, electromagnetic noise over a wide frequency
band including 10w frequency and radio frequency can be b10cked.

Embodiment 5
FIGs. 7A and 7B are circuits each of which shows a microphone having one
of various EM-noise-filtering/ESD-b10cking sections realized by three capacitors C41
to C43 and one resistor R51 according to a fifth embodiment of the present invention.
FIG. 7A shows a construction in which the resistor R5! of the EM-noise-
filtering/ESD-b10cking section is connected serially to the drain D of the FET 30, and
FIG. 7B shows a construction in which the resistor R51 of the EM-noise-
filtering/ESD-b10cking section is connected serially to the source S of the FET 30.
Referring to FIG. 7A, a condenser microphone according to the fifth
embodiment of the present invention comprises an equivalent capacitor Cecw
connected between the gate G and the source S of the FET 30 performing an
amplification function. Also, the condenser microphone according to the fifth
embodiment comprises a first capacitor C41, a second capacitor C42, and a third
capacitor C43 connected in parallel between the source S and the drain D of the FET
30, and comprises a first resistor R51 connected between the drain connection ends of
the second capacitor C42 and the third capacitor C43, so that an EM-noise-
filtcring/ESD-blocking section 32 is formed.
Also, referring to FIG. 7B, an EM-noise-filtering/ESD-b10cking section 32 is
realized in such a manner that a first capacitor C41, a second capacitor C42, and a
third capacitor C43 are connected in parallel between the source S and the drain D of
the FET 30, and a first resistor R51 is connected between the source connection ends
of the second capacitor C42 and the third capacitor C43.
In the fifth embodiment of the present invention, repeated description of the
construction and the operation identical to those of the embodiments described above
will be omitted, and the fol10wing description will be laid out centering around the
operation of the EM-noise-filtering section 32.
In the EM-noise-filtering/ESD-b10cking section 32 shown in FIG. 7A
according to the fifth embodiment of the present invention, the first to the third
capacitors C41 to C43 performs a filtering function b10cking high-frequency noise or
electromagnetic noise which is inputted from outside through the output ports 34a and

34b, and the first resistor R51 performs not only a decoupling function separating the
second capacitor C42 and the third capacitor C43 but also an b10cking function
preventing the electrostatic discharge voltage, which is applied from outside, from
directly affecting the inside circuit. Also, the third capacitor C43 bypasses
electrostatic discharge voltage applied through the output ports 34a and 34b to ground,
thereby preventing the inside elements from being damaged by the electrostatic
discharge. To achieve such a result, the third capacitor C43 must have a large
capacitance, enough to store current caused by the high pressure of electrostatic
discharge, that is, the third capacitor C43 must be at least InF.
The capacitance of the capacitors C41 to C43 can be changed selectively
from 10pF to 100u.F according to conditions. Preferably, the first capacitor C41 is
selected to have a capacitance between 10pF and 20pF according to conditions, the
second capacitor C42 is selected to have a capacitance between 20pF and InF
according to conditions, and the third capacitor C43 is selected to have a capacitance
between InF and 100u.F according to conditions. More preferably, the third
capacitor C43 has a capacitance selected from the group consisting of InF, l.5nF,
2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF. Also, it
is preferred that the first resistor R51 has a resistance selected from the group
consisting of 100ft, 220ft, 330ft, 430ft, 620ft, 680ft, 820ft and 1 Kft.
In a condenser microphone having a circuit as constructed according to the
fifth embodiment described above, electromagnetic noise over a wide frequency band
including 10w frequency and radio frequency can be b10cked. Further, a condenser
microphone according to the first embodiment has an improved b10cking capability
(resistance) enough to stand against electrostatic discharge of even above 8KV applied
from outside when the microphone is grounded and high pressure of electrostatic
discharge is applied directly to the output ports.
In the EM-noise-filtering section 32 shown in FIG. 7B according to the fifth
embodiment of the present invention, the first to the third capacitors C41 to C43
performs a filtering function b10cking high-frequency noise or electromagnetic noise
which is inputted from outside through the output ports 34a and 34b, and the first

resistor R51 performs a decoupling function separating the second capacitor C42 and
the third capacitor C43. To achieve such a result, the third capacitor C43 must be
realized by a wide band stop filter having a large capacitance efficiently capable of
b10cking a wide band signal including 10w frequency and radio frequency, that is, the
third capacitor C43 must be at least InF.
The capacitance of the capacitors C41, C42, and C43 can be changed
selectively from 10pF to 100u.F according to conditions. Preferably, the first
capacitor C41 is selected to have a capacitance between 10pF and 20pF according to
conditions, the second capacitor C42 is selected to have a capacitance between 20pF
and InF according to conditions, and the third capacitor C43 is selected to have a
capacitance between InF and 100µF according to conditions. More preferably, the
third capacitor C43 is selected to have a capacitance selected from the group
consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF,
68nF and 100nF. Also, it is preferred that the first resistor R51 has a resistance
selected from the group consisting of 100Ω, 220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω
and 1KΩ.
In a condenser microphone having the circuit described above according to
the fifth embodiment described above, electromagnetic noise over a wide frequency
band including 10w frequency and radio frequency can be b10cked.
Embodiment 6
Meanwhile, the first to the fifth embodiments described above can be applied
to a variety of circuits for removing noise caused in a frequency band of 1.8GUz or
more including a next-generation mobile communication system (1MT2000). That is,
a circuit for removing noise caused in the frequency band of I.8GHz or more has the
same construction as the circuit described above for removing noise corresponding to
the frequency band of 900MHz and 1.8GHz, and has only a different feature in that
capacitors C1 and C2 for performing a filtering function are realized by capacitors
having a capacitance between lpF and 100µF. The capacitors having a capacitance
between IpF and 100µF can filter electromagnetic noise of 5KHz to 6GFIz.

For example, in a case of applying the EM-noise-filtering/ESD-b10cking
section 32 using three capacitors and one resistor as shown in FIG. 7A to a circuit for
removing noise of 1.8GFIz or more, the first to the third capacitors C41, C42, and C43
for performing a filtering function can be selected to have a capacitance between 1pF
and 100µF according to conditions. For example, the first capacitor C41 is selected
to have a capacitance between 1pF and 5pF according to conditions, and preferably
4.7pF, the second capacitor C42 is selected to have a capacitance between 5pF and
InF according to conditions, and preferably 5.6pF, the third capacitor C43 is selected
to have a capacitance between 1nF and 100µF according to conditions, and preferably
a capacitance selected from the group consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF,
6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and 100nF, and it is preferred that the
first resistor R51 has a resistance selected from the group consisting of 100Ω, 220Ω,
330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ..
In the example described above, the capacitors C41, C42, and C43 and the
resistor R51 form a wide band stop filter, while functioning to improve resistance to
electrostatic discharge. High pressure of electrostatic discharge applied through the
output ports from outside is discharged to ground port 34b through the third capacitor
C43 having the largest capacitance, and the first resistor R51 prevents the electrostatic
discharge from being applied directly to the inside circuit section. To achieve such a
result, the third capacitor C43 must have a large capacitance, enough to store current
caused by the high pressure of electrostatic discharge, that is, the third capacitor C43
must be at least InF.
In a condenser microphone having a circuit as constructed according to the
example described above, electromagnetic noise over a wide frequency band
including 10w frequency and radio frequency can be reduced. Further, a condenser
microphone according to the present invention has an improved resistance enough to
stand against electrostatic discharge of even above 8KV applied from outside when
the microphone is grounded and high pressure of electrostatic discharge is applied
directly to the output ports.

In such a sixth embodiment, an electric signal of the microphone inputted
through the gate G of the FET 30 is amplified in the FET 30 so as to have 10w noise,
and is transmitted to a sound process circuit of a mobile terminal through the output
ports 34a and 34b with noise removed by a wide band stop filter b10cking signals of
radio frequency band, in which the wide band stop filter is realized by the first
capacitor C41, the second capacitor C42, the third capacitor C43, and the first resistor
R51.
INDUSTRIAL APPLICABILITY
As can be seen from the foregoing, the condenser microphone according to
the present invention has advantages of widening range capable of removing
electromagnetic noise, obtaining an excellent filtering effect of electromagnetic noise
with a circuit only including capacitors and resistors in a wide frequency band
including 10w frequency and radio frequency, and largely improving b10cking
capability (resistance) to electrostatic discharge applied from outside.
While this invention has been described in connection with what is presently
considered to be the most practical and preferred embodiment, it is to be understood
that the invention is not limited to the disc10sed embodiment and the drawings, but, on
the contrary, it is intended to cover various modifications and variations within the
spirit and scope of the appended claims.

WE CLAIM :
1. A condenser microphone emp10ying a wide band stop filter for wideband
signals of 10w frequency and radio frequency, the condenser microphone having
improved resistance to electrostatic discharge applied from outside and preventing
radio frequency interference to decrease noise, the condenser microphone comprising:
an acoustic module 36 for converting sound pressure into variation of an
electric signal;
an amplification means, such as described herein an amplifier used in a built-
in-gain microphone or a field-effect transistor, for amplifying the electric signal
inputted from the acoustic module 36 ; and
an EM-noise-filtering/ESD-b10cking section 32 for b10cking a wideband signal
having 10w frequency and radio frequency outputted from the amplification means,
b10cking introduced electromagnetic waves, radio wave noise, and electrostatic
discharge, the EM-noise-filtering/ESD-b10cking section 32 including one or
combination of a resistor and a capacitor disposed between an input port of the
amplification means and the acoustic module 36 and/or between an output port of the
amplification means and a ground, the resistor and the capacitor being connected in
parallel or in series to each other.
2. A condenser microphone as claimed in claim 1, wherein the capacitor and
the resistor have a capacitance between lpF and 100µF and a resistance between 10Ω
and 1GΩ, respectively, each of which can be selectively adjusted according to
frequency band.
3. A condenser microphone as claimed in claim 1, wherein the EM-noise-
filtering/ESD-b10cking section 32 comprises:
a resistor R11 connected serially between output port of the amplification
means and signal output port 34a; and

a capacitor C1 1 connected between one end of the resistor Rl 1 and ground
GND.
4. A condenser microphone as claimed in claim 3, wherein:
the capacitor C11 has a capacitance selected from the group consisting of
InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and
100nF; and
the resistor R11 has a resistance selected from the group consisting of 100Ω,
220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ..
5. A condenser microphone as claimed in claim 1, wherein the EM-noise-
filtering/ESD-b10cking section 32 comprises:
a first capacitor C21 connected in parallel between output port of the
amplification means and ground port to function as a filter,
a second capacitor C22 connected parallel to the first capacitor C21 to
perform an EM-noise-filtering and ESD-b10cking function; and
a first resistor R21 connected serially to between an output port of the first
capacitor C21 and an output port of the second capacitor C22 to perform a decoupling
function, so that the EM-noise-filtering/ESD-b10cking section has a shape of a
character 'IT.
6. A condenser microphone as claimed in claim 5, wherein:
the first capacitor C21 has a capacitance of 10pF or 33pF;
the second capacitor C22 has a capacitance selected from the group
consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF,
68nF and 100nF;and
the first resistor R21 has a resistance selected from the group consisting of
100ft, 220ft, 330ft, 430ft, 620ft, 680ft, 820ft and lKft.
7. A condenser microphone as claimed in claim 1, wherein the EM-noise-
filtering/ESD-b10cking section 32 comprises:

a first capacitor C21 connected in parallel between output port of the
amplification means and ground port to function as a filter;
a second capacitor C22 connected parallel to the first capacitor C21 to
perform an EM-noise-filtering function; and
a first resistor R21 connected serially to between a ground port GND of the
first capacitor C21 and a ground port GND of the second capacitor C22 to perform a
decoupling function, so that the EM-noise-filtering/ESD-b10cking section has a shape
of a character 'inverted IT.
8. A condenser microphone as claimed in claim 7, wherein:
the first capacitor C21 has a capacitance of 10pF or 33pF;
trie second capacitor C22 has a capacitance selected from the group
consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF,
68nFand 100nF; and
the first resistor R21 has a resistance selected from the group consisting of
100Ω, 220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ..
9. A condenser microphone as claimed in claim 5 or claim 7, further
comprising a noise-b10cking resistor R22 between the acoustic module 36 and input
port of the amplification means so as to b10ck electromagnetic noise from being
inputted.
10. A condenser microphone as claimed in claim 9, wherein the noise-
b10cking resistor has a resistance selected from the group consisting of 100Ω, 1KΩ,
10KΩ, 100KΩ, and 1MΩ.
11. A condenser microphone as claimed in claim 1, wherein the EM-noise-
filtering/ESD-b10cking section 32 comprises:
a first and a second capacitor C31 and C32 connected in parallel between
output port of the amplification means and ground port; and
a first and a second resistor R31 and R32 connected respectively between

adjacent ends of the two capacitors C31 and C32, so that the EM-noise-filtering/ESD-
b10cking section has a shape of a character '#', wherein,
the first capacitor C31 performs a filtering function, the second capacitor C32
faced to the first capacitor C31 performs an EM-noise-filtering and electrostatic-
discharge-b10cking function, and the resistors R31 and R32 performs a decoupling
function and an electrostatic-discharge-b10cking function.
12. A condenser microphone as claimed in claim 11, wherein:
the first capacitor C31 has a capacitance of 10pF or 33pF;
the second capacitor C32 has a capacitance selected from the group
consisting of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF,
68nFand 100nF;and
each of the first and second resistors R31 and R32 has a resistance selected
from the group consisting of 100Ω, 220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ.
13. A condenser microphone as claimed in claim 11, further comprising a
noise-b10cking resistor R33 between the acoustic module 36 and input port of the
amplification means so as to b10ck electromagnetic noise from being inputted.
14. A condenser microphone as claimed in claim 13, wherein the noise-
b10cking resistor R33 has a resistance selected from the group consisting of 100ft,
1KΩ, 10KΩ, 100KΩ, and 1MΩ.
15. A condenser microphone as claimed in claim 1, wherein the EM-noise-
filtering section 32 comprises a first capacitor C41, a second capacitor C42, and a
third capacitor C43 connected in parallel with each other between ground port and
output port of the amplification means.
16. A condenser microphone as claimed in claim 15, wherein:
the first capacitor C41 can be selectively adjusted so as to have a capacitance
between 10pF and 20pF;

the second capacitor C42 can be selectively adjusted so as to have a
capacitance between 20pF and InF; and
the third capacitor C43 can be selectively adjusted so as to have a capacitance
between InF and 100p-F.
17. A condenser microphone as claimed in claim 15, wherein, in the EM-
noise-filtering/ESD-b10cking section 32, a resistor R51 is further connected serially
between a signal output end of the second capacitor C42 and a signal output end of the
third capacitor C43.
18. A condenser microphone as claimed in claim 17, wherein:
the first capacitor C41 is selectively adjusted so as to have a capacitance
between 10pF and 20pF;
the second capacitor C42 is selectively adjusted so as to have a capacitance
between 20pF and 1 nF;
the third capacitor C43 has a capacitance selected from the group consisting
of 1nF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and
100nF; and
the resistor R51 has a resistance selected from the group consisting of 100Ω,
220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ.
19. A condenser microphone as claimed in claim 15, wherein, in the EM-
noise-filtering section 32, a resistor R51 is further connected serially between a
ground end of the second capacitor C42 and a ground end of the third capacitor C43.
20. A condenser microphone as claimed in claim 19, wherein:
the first capacitor C41 is selectively adjusted so as to have a capacitance
between 10pF and 20pF;
the second capacitor C42 is selectively adjusted so as to have a capacitance
between 20pF and 1 nF;
die third capacitor C43 has a capacitance selected from the group consisting

of InF, 1.5nF, 2.2nF, 3.3nF, 4.7nF, 6.8nF, 10nF, 15nF, 22nF, 33nF, 47nF, 68nF and
100nF;and
the resistor R51 has a resistance selected from the group consisting of 100Ω,
220Ω, 330Ω, 430Ω, 620Ω, 680Ω, 820Ω and 1KΩ

A condenser microphone employing a wide band stop filter is disclosed. Said
microphone has improved resistance to electrostatic discharge applied from outside.
This has an object of providing a condenser microphone capable of being used for or a
multi-band by comprising a wide band stop filter capable of efficiently blocking a
wide band signal including low frequency and radio frequency used in a mobile
communication. To this end, a condenser microphone comprises: an acoustic module
(36) for converting sound pressure into variation of an electric signal; a FET for
amplifying the electric signal inputted from the acoustic module (36); and a wide band
stop filter for blocking a wide band signal including low frequency and radio
frequency outputted from the FET, and being realized by any one or more of resistors
and capacitors which are connected selectively according to the radio frequency band
between the drain D and the source S of the FET.

Documents:

1798-KOLNP-2005-FORM-27-1.pdf

1798-KOLNP-2005-FORM-27.pdf

1798-kolnp-2005-granted-abstract.pdf

1798-kolnp-2005-granted-assignment.pdf

1798-kolnp-2005-granted-claims.pdf

1798-kolnp-2005-granted-correspondence.pdf

1798-kolnp-2005-granted-description (complete).pdf

1798-kolnp-2005-granted-drawings.pdf

1798-kolnp-2005-granted-examination report.pdf

1798-kolnp-2005-granted-form 1.pdf

1798-kolnp-2005-granted-form 18.pdf

1798-kolnp-2005-granted-form 3.pdf

1798-kolnp-2005-granted-form 5.pdf

1798-kolnp-2005-granted-gpa.pdf

1798-kolnp-2005-granted-reply to examination report.pdf

1798-kolnp-2005-granted-specification.pdf

1798-KOLNP-2005-OTHER DOCUMENT.pdf

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Patent Number

231736

Indian Patent Application Number

1798/KOLNP/2005

PG Journal Number

11/2009

Publication Date

13-Mar-2009

Grant Date

09-Mar-2009

Date of Filing

12-Sep-2005

Name of Patentee

BSE CO., LTD.

Applicant Address

4 LOT, 58 BLOCK, 626-3, GOJAN-DONG, NAMDONG-GU, INCHEON,

Inventors:

#	Inventor's Name	Inventor's Address
1	SONG, CHUNG-DAM	236-6, GAYANG 1-DONG, GANGSEO-GU, SEOUL, 157-801
2	CHUNG, EEK-JOO	206-1906, CHEONGSONG MAEUL HYUNDAI APT JANGGIDONG, GIMPO-SI, KYUNGGI-DO, 415-748
3	KIM, HYUN-HO	508-1607, DODURI MAEUL DONGBO APT., JAKJEON 3-DONG, GYEYANG-GU, INCHEON, 407-772

PCT International Classification Number

H04R 19/04

PCT International Application Number

PCT/KR2003/001137

PCT International Filing date

2003-06-10

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10-2003-0017454	2003-03-20	Republic of Korea