Abstract:
A microphone assembly include a microphone housing unit having a cover and a base. The microphone assembly further includes a preamplifier circuit assembly attached to the base and protected by the cover. The protected preamplifier circuit assembly has at least one terminal unprotected by the cover. A radio frequency interference suppression device can be electrically coupled to the preamplifier circuit and includes at least one internal ground electrically coupled to the at least one terminal. The at least one internal ground provides a ground path between the cover and the base.

Description:
TECHNICAL FIELD  
       [0001]     This patent generally relates to microphones used in listening devices, such as hearing aids or the like, and more particularly, to a microphone assembly with preamplifier and a method of manufacturing the same.  
       BACKGROUND  
       [0002]     Hearing aid technology has progressed rapidly in recent years. Technological advancements in this field continue to improve the reception, wearing-comfort, life-span, and power efficiency of hearing aids. With these continual advances in the performance of ear-worn acoustic devices, ever-increasing demands are placed upon improving the inherent performance of the miniature acoustic transducers that are utilized. There are several different hearing aid styles known in hearing aid industry: Behind-The-Ear (BTE), In-The-Ear or All In-The-Ear (ITE), In-The Canal (ITC), and Completely-In-The-Canal (CTC).  
         [0003]     Generally, a listening device, such as a hearing aid or the like, includes a microphone portion, an amplification portion and a receiver (transducer) portion. The microphone portion receives vibration energy, i.e. acoustic sound waves in audible frequencies, and generates an electronic signal representative of these sound waves. The amplification portion accepts the electronic signal, increases the electronic signal magnitude, and communicates the increased electronic signal (e.g. the processed signal) to the receiver portion. The receiver portion, in turn, converts the increased electronic signal into vibration energy for transmission to a user.  
         [0004]     The electronic signals communicated from the microphone portion to the amplification portion, are susceptible to high frequency interference radiated, for example, in the range of 1-3 GHz. To reduce the sensitivity to low and high radio frequency interference signals (RFI), the conventional microphone assembly comprises a preamplifier assembly with capacitive couplings. In particular, the microphone portion can be communicatively coupled to the preamplifier assembly to reduce the RFI generated by communication devices such as cellular phones, web-enabled phones, personal digital assistants (PDAs), laptops, other devices that may be capable of communication over one or more public or private communication networks. Further, microphone assemblies include external ground wirings or electrical paths to connect the portions of the microphone casing and further reduce the sensitivity to low and high radio frequency interference (RFI) signals. However, known microphone assemblies provide poor RFI suppression in the presence of a communication device such as cellular phone and thereby making the microphone assembly less attractive to potential customers. In addition, known microphone assemblies that provide acceptable RFI suppression often require additional, and costly, assembly steps to connect and position ground wires between the individual external portions of the microphone casing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     For a more complete understanding of the invention, reference should be made to the following detailed description and accompanying drawings wherein:  
         [0006]      FIG. 1  is a perspective view of a microphone assembly;  
         [0007]      FIG. 2  is an exploded view illustrating a microphone assembly embodying the teachings of the present disclosure;  
         [0008]      FIG. 3  is an enlarged exploded view of the microphone assembly shown in  FIG. 2 ; and  
         [0009]      FIG. 4  is a cross-sectional view of the microphone assembly of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0010]     While the present invention is susceptible to various modifications and alternative forms, certain embodiments are shown by way of example in the drawings and these embodiments will be described in detail herein. It will be understood, however, that this disclosure is not intended to limit the invention to the particular forms described, but to the contrary, the invention is intended to cover all modifications, alternatives, and equivalents falling within the spirit and scope of the invention defined by the appended claims.  
         [0011]      FIG. 1  illustrates a perspective view of a microphone assembly generally indicated by the numeral  100 . The microphone assembly  100  includes a housing  102  having a cover  104  and a cup or base  106 . The housing  102  can be manufactured in a variety of configurations such as, a roughly square shape, a cylindrical shape, a rectangular shape or any other desired geometry. In addition, the scale and size of the housing  102  may be varied based on the intended application, operating conditions, required components, etc. Moreover, the housing  102  can be manufactured from a variety of materials such as, for example, stainless steel, alternating layers of conductive materials, alternating layers of non-conductive materials (e.g., metal particle-coated plastics).  
         [0012]     The microphone assembly  100  further includes a mounting frame  108  sized to engage a top edge  110  of the base  106 . The mounting frame  108  supports a printed circuit board (PCB)  112 . The mounting frame  108  may be a single layer of stainless steel, as shown, or may utilize alternating layers of conductive and/or non-conductive materials such as metal particle-coated plastics. Further, the mounting frame  108  may have various shapes and a number of different of sizes, corresponding to the overall shape of the housing  102 . The PCB  112  extends though an opening  114  formed in a bottom edge  116  of the cover  104 . An exposed portion  118  of the PCB  112  supports a plurality of contact points or electrical connection terminals  120 . The electrical connection terminals  120  provide an electrical connection to a preamplifier circuit assembly  122  shown in  FIG. 2 .  
         [0013]      FIG. 2  illustrates an exploded view of the microphone assembly  100 . The base  106  may include a plurality of supporting members  106   a - 106   b  to serve as a support for the diaphragm assembly  124 . It will be understood that a variety of supporting structures such as a U-shaped plate, two deformed corners, or a glue fillet, may be utilized to support the diaphragm assembly  124 .  
         [0014]     The base  106  further includes a sound inlet port  126  positioned distal to the top edge  110 . A sound inlet tube  128  that includes a mounting plate  130  and a sound passage  132  can be positioned adjacent to the sound inlet port  126  to direct the received acoustic waves into the base  106 . The mounting plate  130  secures the sound inlet tube  128  to the base  106 . The mounting plate  130  can be fixedly attached using, for example, a glue or epoxy, or removably attached using any known fastener. The sound passage  132  provides an acoustic path to the sound inlet port  126 . The sound passage  132  can be formed through the sound inlet tube  128  in any suitable manner such as drilling, punching or molding. A damping element or filter  134  (see  FIG. 4 ) positioned within the sound passage  132  provides an acoustical resistance to the microphone assembly  100 . In operation, sonic energy or acoustic waves enter the microphone assembly  100  via the sound passage  132 . Thereafter, the sonic energy or acoustic waves communicates to the sound inlet port  126 . The sound inlet tube  108 , as discussed above in connection with the housing  102 , can be manufactured from a variety of materials such as, for example, stainless steel, alternating layers of conductive materials, alternating layers of non-conductive materials (e.g., metal particle-coated plastics).  
         [0015]     The microphone assembly  100  further includes a diaphragm assembly  124 , and a backplate assembly  134 . The shape of the diaphragm assembly  124  generally corresponds to the base  106  and mounting frame  108 , but may take the form of the various shapes and sizes in different embodiments. The diaphragm assembly  124  includes a support plate  136  and a diaphragm  138  fixedly attached to the support plate  136 . The diaphragm assembly  124  positioned within the base  106  and supported by the support members  106   a ,  106   b.    
         [0016]     The support plate  136  can consist of any electrically conductive material such as stainless steel; however, any material that includes a conductive coating may be utilized. The diaphragm  138  comprises an electrically conductive material or a thin polymer film peripherally attached to the bottom surface of the support plate  136 .  
         [0017]     The backplate assembly  134  may include a connecting wire  142  fixedly attached to a backplate  140 . In particular, the connecting wire  142  attaches to a top surface the backplate  140  by, for example, bonding with adhesive. The connecting wire  142 , in turn, extends through an opening  144  of the mounting frame  108  to electrically couple an input point  146  of the preamplifier assembly  122 . In other words, the backplate assembly  134  and diaphragm assembly  124  are communicatively coupled to the preamplifier assembly  122  via the opening  144  to transmit and provide acoustic signals thereto.  
         [0018]     The bottom surface of the backplate  140  can be plated with any polarized dielectric film or electret material such as, for example, TEFLON®. The plated backplate  140  forms a fixed electrode and is mounted by adhesive fillets (not shown) to the support plate  136  of the diaphragm assembly  124  and, in turn, to peripheral portions of the diaphragm  138 . The dielectric film or electret material on the bottom surface of the backplate  140  cooperates with the diaphragm  138  to develop an acoustic signal. The resulting combination of the backplate assembly  134  and the diaphragm assembly  124  define an electret microphone portion. It will be understood that the operation of the microphone assembly  100  is generally based on the fixed electrode of the backplate assembly  140  and the movement of the diaphragm  138  in response to exposure to acoustic waves or sonic energy to generate a representative electrical signal.  
         [0019]     The preamplifier assembly  122  may include a preamplifier such as, for example, a source-follower field effect transistor (FET)  150  integrated circuit. The preamplifier assembly  122  further includes the plurality of electrical connection terminals  120 , the input point  146 , the ground point  148 , and the PCB  112 . The PCB  112  electrically connects the plurality of electrical connection terminals  120  positioned external to the cover  104  with the FET  150  positioned internal to the cover  104 . The preamplifier assembly  122 , in turn, electrically connects to the mounting frame  108  by means of a conductive adhesive  152 ,  154 . The conductive adhesives  152 ,  154  cooperate with a wire bonding  156  affixed within the housing  102  to effectively short-circuit RFI generated by nearby communication devices.  
         [0020]      FIG. 3  illustrates an enlarged exploded view of the microphone assembly of  FIG. 1 . The backplate assembly  134  and the diaphragm assembly  124  are affixed adjacent to the support members  106   a ,  106   b  within the base  106 . In particular, the backplate assembly  134  attaches to the diaphragm assembly  124 , the resulting combination is, in turn, positioned opposite the opening  144  of the mounting frame  108 . The mounting frame  108 , the preamplifier assembly  122  and the cover  104  collectively constitute a back volume portion arranged to convert the electrical capacitance generated by the electret microphone portion to the acoustic signal indicative of the acoustic wave transmitted to the diaphragm assembly  124 .  
         [0021]     As discussed above, the preamplifier assembly  122  electrically connects via the input  146  and the connecting wire  142  to the backplate assembly  134 . Moreover, the preamplifier assembly  122  is grounded to the diaphragm  138  via the ground point  148 , the mounting frame  122 , and the base  106 . The plurality of electrical connection terminals  120  can comprise an input connection  158 , an output connection  160 , and a ground connection  162 . The input connection  158  supplies electric power to the preamplifier assembly  122 . The input connection  158  and the output connection  160  are communicatively connected to an input (not shown) the preamplifier assembly  122 . The ground connection  162  connects the ground point  148  to reduce the sensitivity to low and high radio frequency interference signals generated by communications devices such as, for example, cellular phones.  
         [0022]     To further reduce the sensitivity to low and high radio frequency interference signals, the preamplifier assembly  122  connects to the base  106  via the mounting frame  108  by means of the conductive adhesive  152 ,  154  to ground the RFI signals caused by communications device. The cover  104  is, in turn, grounded to the preamplifier assembly  122  by the wire bonding  150 . Thus, the RFI present with the amplifier output signal supplied by the output connection  160  is suppressed.  
         [0023]     The preamplifier assembly  122  can be a capacitively coupled circuit including the FET  134  adapted to reduce the RFI generated by communications devices. The circuit can further include an electrical ground path between the ground connection  162  and the cover  104  via the wire bond  156 . The electrical ground path formed between the cover  104  and the ground connection  162  effectively short-circuits undesirable RFI generated by any nearby communication devices. The wire bond  156  fixedly connects to the opening  114  of the cover  104  using a conductive adhesive such as an epoxy with suspended metallic flakes. In particular, the conductive adhesive can be a two-part silver epoxy adhesive that provides high electrical conductivity and strong conductive bonding. Conductive adhesive can replace traditional tin lead (Sn—Pb) solder and can further act as an effective heat sink.  
         [0024]     The preamplifier assembly  122  can further include a first resistance-capacitance network and a second resistance-capacitance network (not shown) communicatively connected to the FET  150 . The first resistance-capacitance network connects to the ground point  148  by means of conductive adhesive  152  to suppress the undesirable RFI generated by nearby communication devices. The second resistance-capacitance network connects to the base  106  via the mounting frame  108  by means of conductive adhesive  154  to suppress the undesirable RFI generated by nearby communication devices.  
         [0025]      FIG. 4  illustrates a cross-sectional view the exemplary microphone assembly  100 . The diaphragm assembly  124  attaches within the base  106  adjacent to the sound inlet  126 . The sound inlet port  126  is fluidly connected to a first side  164  of the diaphragm  138  to provide acoustic waves received through the sound inlet tube  128 . The backplate assembly  134  mounts to the top surface the diaphragm assembly  124 . As previously discussed, the backplate assembly  134  and the diaphragm assembly  124  constitute the electret microphone portion.  
         [0026]     The mounting frame  108  mounts to the top edge  110  of the base  106  and supports the preamplifier assembly  122 . The preamplifier assembly  122  attached to the mounting frame  108  by means of conductive adhesive  152 ,  154  to provide an electrical path to ground and thereby effectively short-circuit RFI generated by nearby communication devices.  
         [0027]     The input point  146  of the preamplifier assembly  122  couples to the wire connection  142  of the backplate assembly  134  to provide an acoustic signal thereto. The preamplifier assembly  122  partially protrudes through the opening  114  of the cover  102  (as shown in  FIG. 1 ) to provide electrical access to the plurality of electrical terminals  120  including the ground connection  162 . The preamplifier assembly  122  is further grounded to the cover  104  by means of wire bonding  150 .  
         [0028]     The mounting frame  108 , the preamplifier assembly  122  and the cover  104  collectively constitute a back volume portion  166  to convert the electrical capacitance generated by the electret microphone portion to the acoustic signal indicative of the acoustic wave transmitted to the diaphragm assembly  124 . In other words, the diaphragm assembly  124  and the backplate assembly  134  electrically connect to the preamplifier assembly  122  through the connecting wire  142  to communicate the acoustic signal generated by the diaphragm  138 .  
         [0029]     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extend as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.  
         [0030]     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.  
         [0031]     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.