Abstract:
Disclosed herein, among other things, are methods and apparatuses that provide a manufacturable RF transmission line to go through the bend area of a flexible circuit to be used in a compact design, such as in a compact hearing aid design. One aspect of the present subject matter relates to using multiple inner layers of the flexible circuit to route RF transmission. By not using outer layers, the RF transmission line will be less susceptible to delamination from the polyimide dielectric layer. One aspect of the present subject matter relates to choosing copper transmission line to have dimensions that allow for narrower transmission lines with good RF return loss. The copper transmission line dimensions also allow for manufacturing in a standard process without adding extra cost.

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to hearing assistance devices, and in particular to waveguides for hearing assistance devices. 
     BACKGROUND 
     Modern hearing assistance devices, such as hearing aids, are electronic instruments worn in or around the ear that compensate for hearing losses by specially amplifying sound. Hearing aids typically include electronic components mounted on or attached to printed circuit boards to enhance the wearer&#39;s listening experience. 
     To accommodate the relatively small hearing aid form factor, hearing aid radio frequency (RF) transmission lines may be implemented on flexible circuit boards. However, the performance of RF transmission lines is limited when using flexible circuit boards, especially in areas of the flexible circuit boards that are bent to accommodate the hearing aid form factor. 
     In order to provide a manufacturable RF transmission line for a flexible circuit bend area that provides improved RF performance, existing solutions use microstrip or stripline configurations. These microstrip or stripline configurations may use external layers. However, these microstrip or stripline exhibit excessively narrow transmission lines. Such excessively narrow transmission lines are difficult to manufacture, as the manufacturing tolerance variations tend to exceed the requirements of the narrow transmission lines. Additionally, microstrip or stripline antennas using the external layers of the flexible circuit would have problems with delamination of the copper from the flexible circuit polyimide layer. 
     Some existing coplanar waveguides include methods of constructing coplanar waveguides on semi-rigid boards. These are a combination regular circuit board and flexible circuit board. Other existing coplanar waveguides include an air gap within the coplanar waveguide. 
     What is needed in the art is an improved system that provides a manufacturable RF transmission line for a flexible circuit bend area that provides improved RF performance. 
     SUMMARY 
     Disclosed herein, among other things, are methods and apparatuses that provide a manufacturable RF transmission line to go through the bend area of a flexible circuit to be used in a compact design, such as in a compact hearing aid design. 
     One aspect of the present subject matter relates to using multiple inner layers of the flexible circuit to route RF transmission. By not using outer layers, the RF transmission line will be less susceptible to delamination from the polyimide dielectric layer. One aspect of the present subject matter relates to selecting copper transmission line dimensions that can withstand manufacturing tolerance variations. The copper transmission line dimensions also allow for manufacturing in a standard process without adding extra cost. Other aspects are provided without departing from the scope of the present subject matter. 
     This Summary is an overview of some of the teachings of the present application and not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details about the present subject matter are found in the detailed description and appended claims. The scope of the present invention is defined by the appended claims and their legal equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a circuit diagram of a hybrid circuit configured for use in a hearing aid, according to one embodiment of the present subject matter. 
         FIG. 2  shows a circuit diagram of a hybrid circuit with integrated match filter configured for use in a hearing aid, according to one embodiment of the present subject matter. 
         FIG. 3  shows a perspective diagram of a coplanar waveguide according to one embodiment of the present subject matter. 
         FIG. 4  shows a diagram of a multiple layer coplanar waveguide according to one embodiment of the present subject matter. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein, among other things, are methods and apparatuses for transmitting radio waves from an RF source to an antenna, such as in a compact hearing aid design. 
       FIG. 1  shows a circuit diagram of an embodiment of a hybrid circuit  100  configured for use in a hearing aid. Hybrid circuit  100  includes a microphone  105 , a signal-processing unit  110 , an RF drive circuit  115 , a coplanar waveguide  120 , a standing acoustic wave (SAW) filter  125 , a match filter  130 , and an antenna  135 . Physically, hybrid circuit  100  can be realized as a single compact unit having an integrated coplanar waveguide  120 . 
     Signal processing unit  110  provides the electronic circuitry for processing received signals from the microphone  105  for wireless communication between a hearing aid in which hybrid circuit  100  is configured and a source external to the hearing aid. The source external to the hearing aid can be used to provide information transferal for testing and programming of the hearing aid. 
     Signal processing unit  110  may provide processed signals to the RF drive circuit  115 , which may have leads to couple to coplanar waveguide  120 . Because the coplanar waveguide  120  provides a low-profile transmission line that may be mounted directly on a circuit board, the coplanar waveguide  120  may be used in compact designs. Additionally, the coplanar waveguide  120  may provide high frequency response, as the design of the coplanar waveguide  120  avoids parasitic discontinuities in the ground plane. 
     Coplanar waveguide  120  may be coupled to a SAW filter  125  to use an analog filter to match the complex impedance of the coplanar waveguide to the impedance of the antenna  135 . Complex impedance may be matched further by coupling the coplanar waveguide  120  and SAW filter  125  to a match filter  130 . Impedance matching may also be performed within the coplanar waveguide  120  by distributing impedance matching elements within the coplanar waveguide  120 . For example, the coplanar waveguide  120  may include a matching network (e.g., inductors, capacitors, etc.) to perform impedance matching. In some embodiments, the coplanar waveguide  120  may include a series of waveguides connected through various RLC networks. 
     Signal processing unit  110  may also provide the processing of signals representing sounds, whether received as acoustic signals or electromagnetic signals. Hybrid circuit  100  may also include an amplifier  140  and a speaker  145 . Signal processing unit  110  provides an output that is increased by amplifier  140  to a level that allows sounds to be audible to the hearing aid user. Amplifier  140  may be realized as an integral part of signal processing unit  110 . As can be appreciated by those skilled in the art upon reading and studying this disclosure, the elements of a hearing aid housed in a hybrid circuit that includes an integrated coplanar waveguide can be configured in various formats relative to each other for operation of the hearing aid. 
     The elements of hybrid circuit  100  are implemented in the layers of hybrid circuit  100  providing a compact circuit for a hearing aid. In an embodiment, a hearing aid using a hybrid circuit shown as hybrid circuit  100  is a CIC hearing aid operating at a frequency suitable for wireless communication exterior to the hearing aid. In an embodiment, the coplanar waveguide for the CIC hearing aid is configured in a hybrid circuit as a substrate based coplanar waveguide. In another embodiment, the coplanar waveguide for the CIC hearing aid is configured in a hybrid circuit as a flex coplanar waveguide. The resulting circuit may be designed for a number of different frequencies, or may be designed to be relatively frequency independent. For example, in one embodiment, the circuit is adapted to operate at about 916 MHz. As another example embodiment, the circuit is adapted to operate at about 900 MHz. Other frequencies of operation are possible, and the ones stated herein are intended to demonstrate the flexibility of the circuit design. In various embodiments, the circuit is designed to be relatively frequency independent, to operate over a range of frequencies. Therefore, various embodiments of hybrid circuit  100  may operate at different frequencies covering a wide range of operating frequencies without departing from the present subject matter. 
       FIG. 2  shows a circuit diagram of an embodiment of a hybrid circuit  200  with integrated match filter configured for use in a hearing aid. Hybrid circuit  200  includes a microphone  205 , a signal-processing unit  210 , an RF drive circuit  215 , a match filter  230 , a coplanar waveguide  220 , and an antenna  235 . The RF drive circuit  215  may be manufactured to include the match filter  230  to enable a compact design. Hybrid circuit  200  may also include an amplifier  240  and a speaker  245  to provide for processing of signals representing sounds. 
       FIG. 3  shows a perspective diagram of a coplanar waveguide  300 . One layer of the coplanar waveguide  300  may include a first ground conductor  305  (e.g., ground trace), a conductor  310 , and a second ground conductor  315 . The first ground conductor  305  and the conductor  310  may be separated by a first gap  320 , and the conductor  310  and the second ground conductor  315  may be separated by a second gap  325 . The conductor  310  and the first and second ground conductors  305  and  315  may be affixed to a dielectric  330 . The coplanar waveguide  300  may include an optional third ground conductor  335 , where the optional third ground conductor  335  may be affixed to the side of the dielectric  330  opposite from the conductor  310  and the first and second ground conductors  305  and  315 . In some embodiments, a second dielectric may be arranged on the first and second ground conductors  305  and  315  and on the conductor  310 . The second dielectric may fill the first and second gaps  320  and  325 . 
     If the coplanar waveguide is limited to a single layer, manufacturing tolerances may vary excessively, degrading return loss below the desired performance level. With the coplanar waveguide implemented on the two layers, however, the return loss performance may increase from approximately 10 dB to greater than 30 dB, such as is shown in  FIG. 4 . 
       FIG. 4  shows a diagram of a multiple layer coplanar waveguide  400 . One layer of the multiple layer coplanar waveguide  400  may include a first ground conductor  405 , a first conductor  410 , and a second ground conductor  415 . The first ground conductor  405  and the first conductor  410  may be separated by a first gap  420 , and the first conductor  410  and the second ground conductor  415  may be separated by a second gap  425 . The first conductor  410  and the first and second ground conductors  405  and  415  may be affixed to a second dielectric  430 , and the second dielectric  430  may fill the first and second gaps  420  and  425 . The first conductor  410 , first and second ground conductors  405  and  415 , and second dielectric  430  may be affixed to a first dielectric  435 . The first dielectric  435  may be affixed to a third ground conductor  445 , a second conductor  450 , and a fourth ground conductor  455 . The third ground conductor  445  and the second conductor  450  may be separated by a third gap  460 , and the second conductor  450  and the fourth ground conductor  455  may be separated by a fourth gap  465 . The second conductor  450  and the third and fourth ground conductors  445  and  455  may be affixed to a third dielectric  440 , and the third dielectric  440  may fill the third and fourth gaps  460  and  465 . The arrangement of second dielectric  430 , first and second ground conductors  405  and  415 , first conductor  410 , and first and second gaps  420  and  425  may form a first coplanar waveguide layer  470 . Similarly, the arrangement of third dielectric  440 , third and fourth ground conductors  445  and  455 , second conductor  450 , and third and fourth gaps  460  and  465  may form a second coplanar waveguide layer  475 . In various embodiments, additional layers of coplanar waveguide layers may be formed on the first or second coplanar waveguide layers  470  and  475 . 
     The ground conductors  405 ,  415 ,  445 , and  455  may be mutually electrically coupled. For example, first and second ground conductors  405  and  415  may be physically connected, such as forming a U-shape. The first and second ground conductors  405  and  415  may be electrically coupled to the third and fourth ground conductors  445  and  455  using an electrically conductive via (e.g., a buried via) through the first dielectric  435 . The ground conductors  405 ,  415 ,  445 , and  455  may be electrically coupled using wires or other means. 
     The first conductor  410  and second conductor  450  may be mutually electrically coupled. For example, first and second conductors  410  and  450  may be physically connected at the beginning and end of the line. The first and second conductors  410  and  450  may be electrically coupled using an electrically conductive via (e.g., a buried via) through the first dielectric  435 . 
     The geometry of the various elements within the multiple layer coplanar waveguide  400  (e.g., conductor line width, conductor height, gap width, dielectric height) and dielectric material selection may determine the characteristic impedance of the first and second conductors  410  and  450 . The geometry of gaps  420 ,  425 ,  460 , and  465  may be arranged according to the wavelength of the intended transmission frequency, where the ratio of the line width to the gaps is adjusted to provide optimum return loss. In some embodiments, the gaps  420 ,  425 ,  460 , and  465  may be arranged to provide proper spacing in the first and second conductors  410  and  450 . For example, the first and second conductors  410  and  450  may be approximately twice as wide as the gaps  420 ,  425 ,  460 , and  465 . In some embodiments, the gaps  420 ,  425 ,  460 , and  465  may be arranged to avoid signal degradation due to higher harmonics. For example, the gaps  420 ,  425 ,  460 , and  465  may be arranged at a spacing of 40 millimeters, which may reduce adverse effects from fourth or fifth harmonics. The gaps  420 ,  425 ,  460 , and  465  may be generated by etching. The gaps  420 ,  425 ,  460 , and  465  may include a polyimide layer, where the polyimide may function as an adhesive. Because of the reduced sensitivity of the line width and gap width to manufacturing tolerances, the multiple layer coplanar waveguide  400  is able to yield better return loss over manufacturing tolerances. 
     The layers used in  FIG. 4  may be implemented in a compact, flexible circuit design. However, flexible circuit designs are subject to delamination of outer layers. Existing RF transmission lines may use micro-strip or stripline within these internal layers. Within the inner layers of the flexible circuit, the dielectric thickness may be reduced to 0.001 inch or less. The thin dielectric layers within microstrip, stripline, and single-layer CPW, yield narrow line widths. These narrow line widths would be susceptible to standard manufacturing tolerances for polyimide flexible circuit technology, resulting in inconsistent (unit-to-unit) or significantly degraded performance of the transmission line. 
     The layers used in  FIG. 4  may be implemented within a flexible circuit board. By implementing the coplanar waveguide on inner layers within a flexible circuit board, the multi-layer design may improve performance of the RF transmission line, while meeting the design constraints of the flexible circuit design. The flexible circuit design may be used to allow folding of the circuit board to fit compactly in a hearing aid design. In various embodiments, the coplanar waveguide may be used within ceramic substrate designs and on rigid printed circuit board designs. Additional layers can be used in various embodiments. 
     In some embodiments, the dielectric layers  430 ,  435 , and  440  may be selected to include materials that are lightweight, flexible, and resistant to heat and chemicals. For example, the dielectric layers dielectric layers  430 ,  435 , and  440  may be selected to include one or more polyimides. In some embodiments, the first and third dielectric layers  430  and  440  include a first dielectric material, and the first dielectric layer  435  includes a different dielectric material than the second and third dielectric layers  430  and  440 . 
     It is understood that variations in communications circuits, protocols, antenna configurations, and combinations of components may be employed without departing from the scope of the present subject matter. Hearing assistance devices typically include an enclosure (e.g., housing), a microphone, a speaker, a receiver, and hearing assistance device electronics including processing electronics. It is understood that in various embodiments the receiver is optional. Antenna configurations may vary and may be included within an enclosure for the electronics or be external to an enclosure for the electronics. Thus, the examples set forth herein are intended to be demonstrative and not a limiting or exhaustive depiction of variations. 
     It is further understood that a variety of hearing assistance devices may be used without departing from the scope and the devices described herein are intended to demonstrate the subject matter, but not in a limited, exhaustive, or exclusive sense. It is also understood that the present subject matter can be used with devices designed for use in the right ear or the left ear or both ears of the wearer. 
     It is understood that hearing aids typically include a processor. The processor may be a digital signal processor (DSP), microprocessor, microcontroller, other digital logic, or combinations thereof. The processing of signals referenced in this application can be performed using the processor. Processing may be done in the digital domain, the analog domain, or combinations thereof. Processing may be done using subband processing techniques. Processing may be done with frequency domain or time domain approaches. Some processing may involve both frequency and time domain aspects. For brevity, in some examples may omit certain modules that perform frequency synthesis, frequency analysis, analog-to-digital conversion, digital-to-analog conversion, amplification, and certain types of filtering and processing. In various embodiments, the processor is adapted to perform instructions stored in memory that may or may not be explicitly shown. Various types of memory may be used, including volatile and nonvolatile forms of memory. In various embodiments, instructions are performed by the processor to perform a number of signal processing tasks. In such embodiments, analog components may be in communication with the processor to perform signal tasks, such as microphone reception, or receiver sound embodiments (i.e., in applications where such transducers are used). In various embodiments, different realizations of the block diagrams, circuits, and processes set forth herein may occur without departing from the scope of the present subject matter. 
     The present subject matter is demonstrated for hearing assistance devices, including hearing aids, including but not limited to, behind-the-ear (BTE), receiver-in-canal (RIC), and completely-in-the-canal (CIC) type hearing aids. It is understood that behind-the-ear type hearing aids may include devices that reside substantially behind the ear or over the ear. Such devices may include hearing aids with receivers associated with the electronics portion of the behind-the-ear device, or hearing aids of the type having receivers in the ear canal of the user, including but not limited to receiver-in-canal (RIC) or receiver-in-the-ear (RITE) designs. The present subject matter can also be used with in-the-ear (ITE) and in-the-canal (ITC) devices. The present subject matter can also be used with wired or wireless ear bud devices. The present subject matter can also be used in hearing assistance devices generally, such as cochlear implant type hearing devices and such as deep insertion devices having a transducer, such as a receiver or microphone, whether custom fitted, standard, open fitted, or occlusive fitted. It is understood that other hearing assistance devices not expressly stated herein may be used in conjunction with the present subject matter. 
     This application is intended to cover adaptations or variations of the present subject matter. It is to be understood that the above description is intended to be illustrative, and not restrictive. The scope of the present subject matter should be determined with reference to the appended claims, along with the full scope of legal equivalents to which such claims are entitled. 
     The preceding detailed description of the present subject matter refers to subject matter in the accompanying drawings that show, by way of illustration, specific aspects and embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present subject matter. References to “an,” “one,” or “various” embodiments in this disclosure are not necessarily to the same embodiment, and such references contemplate more than one embodiment. The following detailed description is demonstrative and not to be taken in a limiting sense. The scope of the present subject matter is defined by the appended claims, along with the full scope of legal equivalents to which such claims are entitled.