Abstract:
An exemplary condenser microphone includes a printed circuit board, a first via, a second via, and a number of through holes. The first and second vias are formed in the printed circuit board for the signal line and ground line respectively passing therethrough. The through holes are formed surrounding the first and second vias. Inner walls of the through holes are coated with a conductive material.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to condenser microphones and, more particularly, to a condenser microphone capable of reducing acoustic noise from high-frequency sources. 
     2. Description of the Related Art 
     Condenser microphones are used in many portable electronic devices, such as digital video cameras, digital still cameras, and mobile phones. One of the challenges of utilizing condenser microphones in electronic devices is that noise generated by high-frequency components in the electronic devices may affect recording quality. 
     What is needed, therefore, is a condenser microphone that can overcome the above-described shortcoming. 
     SUMMARY 
     An exemplary condenser microphone apparatus includes a printed circuit board, a first via, a second via, and a number of through holes. The first and second vias are formed in the printed circuit board for the signal line and ground line respectively passing therethrough. The through holes are formed surrounding the first and second vias. Inner walls of the through holes are coated with a conductive material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present condenser microphone can be better understood with reference to the accompanying drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present condenser microphone. 
         FIG. 1  is a schematic view of a condenser microphone. 
         FIG. 2  is an isometric, schematic view of one printed circuit board embedded in the condenser microphone of  FIG. 1 , according to a first exemplary embodiment. 
         FIG. 3  is an isometric, schematic view of another print circuit board embedded in the condenser microphone of  FIG. 1 , according to a second exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present condenser microphone will now be described in detail below, with reference to the drawings. 
     Referring to  FIG. 1 , a condenser microphone  100  is shown. The condenser microphone  100  is formed by successively inserting a polar ring  102 , a diaphragm  104 , a spacer  103 , an insulating ring  105 , an electrode plate  106 , a conductive pattern  107 , and a printed circuit board (PCB)  130  into a cylindrical case  110 . The polar ring  102  is disposed on the top end of the cylindrical case  110  and the diaphragm  104  is disposed on one side of the polar ring  102 . The electrode plate  106  is disposed on the diaphragm  104  with the spacer  103  positioned therebetween. The top end of the cylindrical case  110  is provided with a number of sound holes  101 . The diaphragm  104  is electrically connected to the cylindrical case  110  through the polar ring  102  that is formed of a conductive material. The diaphragm  104  and the polar ring  102  may be integrally formed as a single body. 
     The electrode plate  106  is formed of a metal plate coated with an organic (polymer) film on which the electrode is formed. The electrode plate  106  is insulated from the cylindrical case  110  by the insulating ring  105 . Moreover, the electrode plate  106  is supported by the conductive pattern  107  and is electrically connected to the PCB  130  via the conductive pattern  107 . A circuit component  108 , such as a junction field effect transistor (JFET), is embedded in the PCB  130 . The electrode plate  106 , the conductive pattern  107 , and the PCB  130  cooperatively define a back chamber  120 . In this embodiment, when sound waves strike the condenser microphone  100  through the sound holes  101 , the diaphragm  104  vibrates. The sound waves also enter the back chamber  120 . When the diaphragm  104  vibrates, the interval between the diaphragm  104  and the electrode plate  106  varies thereby varying electrostatic capacity generated by the diaphragm  104  and the electrode plate  106 . As a result, a voltage signal is varied according to the sound waves. The voltage signal is transmitted to the circuit component  108  such as the JFET embedded in the PCB  130  and amplified. The amplified voltage signal is externally transmitted through a connection terminal (not shown). 
     Referring to  FIG. 2 , the PCB  130  embedded in the condenser microphone  100  is shown according to a first exemplary embodiment. The PCB  130  defines a first via  131 , and a second via  132  therein. A signal line  140  and a ground line  150  corresponding to the first via  131  and the second via  132  are inserted through the PCB  130  respectively and soldered thereto, thereby electrically connecting a digital signal processor (DSP) (not shown) to the PCB  130 . The PCB  130  defines a number of through holes  133  arranged around the signal line  140  and the ground line  150  along the edge of the PCB  130 . In this embodiment, the signal line  140  and the ground line  150 , each has three through holes  133  therearound, and the distances from the first via  131  or the second via  132  to their corresponding through holes  133  are the same. Inner walls of the through holes  133  are formed with a conductive coating such as copper. Induction/capacitance introduced in the through holes  133  corresponding to the signal line  140  can shorten a backflow route of the signal line  140 , thereby reducing characteristic impedance of signals transmitted via the signal line  140  and edge rate of the signals. Characteristics of the capacitance can be manipulated by adjusting the number, shape, and dimensions of the coated through holes  133  to reduce noise interference from the high frequency signals transmitted through the signal line  140  that might interfere with the microphone  100 . In this embodiment, the number of the through holes  133  is six and cross-sectional shape of each through hole  133  is circular shape. In other embodiments, more or less through holes can be used and cross-sectional shapes other than circular, such as hexagonal may be used. 
     Referring to  FIG. 3 , another PCB  230  embedded in the condenser microphone  100  is shown according to a second exemplary embodiment. The second exemplary embodiment is identical to the first exemplary embodiment except that the PCB  230  has a number of through holes  233  distributed between the first via  131  and the second via  132  of the PCB  230 . The number of the through holes  233  is four and they form a square pattern. Other aspects of the second embodiment are the same as that of the first embodiment, and are not described in detail. 
     The present condenser microphone  100  has the through holes  133 ,  233 , with the conductive coating formed on the inner wall thereof, positioned adjacent to the signal line  140  and the ground line  150 . Thus, noise interference to the microphone  100  from the high frequency signals transmitted through the signal line  140  is reduced. 
     While certain embodiments have been described and exemplified above, various other embodiments will be apparent to those skilled in the art from the foregoing disclosure. The present invention is not limited to the particular embodiments described and exemplified but is capable of considerable variation and modification without departure from the scope of the appended claims.