Patent Publication Number: US-6710744-B2

Title: Integrated circuit fractal antenna in a hearing aid device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application No. 60/346,404 entitled “INTEGRATED CIRCUIT FRACTAL ANTENNA IN A HEARING AID DEVICE” and filed on Dec. 28, 2001. The disclosure of the above-described filed application is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to fractal antennas, and more particularly a fractal antenna in an integrated circuit. 
     2. Description of the Related Art 
     Programmable hearing aids allow precise adjustment of the specific parameters of hearing aid operation so as to achieve reasonably good operation personalized for the user. 
     Hearing aids have traditionally been programmed with a multi-wire interface, including a physical connection to a device worn on the body that incorporates a wired link to the hearing aid programmer, e.g. a multi-wire interface directly between the programmer and the hearing aid. The use of a wire interface requires the hearing aid to incorporate a connector, or multiple connectors, into its structure for the programming cable, which can be cumbersome and complicated for the user. 
     Typical programming interfaces use serial data transmission employing two to four electrical connections located on the hearing aid device. Alternately, newer connection schemes use the battery terminals on the hearing aid device to supply power and transmit data to the hearing aid. This approach, however, sometimes requires additional battery contacts depending on the nature of the serial data interface. These data transmission methods require special programming cables and small sized connectors that are fragile and costly to manufacture. In addition, due to the physically small size of hearing aids, reliable wire connections to the hearing aid device from the programming device can be difficult to achieve. 
     Wireless programming methods, such as infrared and ultrasonic links, have been used in the past in place of a multi-wire programming interface, but generally require relatively complex circuitry and introduce additional limitations to the device and programming capabilities. Infrared and ultrasonic links generally experience high rates of power consumption and are susceptible to interference and undesirable directional characteristics. 
     Therefore, an improved wireless programming interface would greatly increase the ease and reliability of programming a hearing aid. 
     SUMMARY OF THE INVENTION 
     A programmable hearing aid, configured to transmit and/or receive a signal to and/or from a programming device, comprises a semiconductor substrate, a conductive pattern, disposed on the semiconductor substrate so as to transmit and/or receive a signal to and/or from the programming device, wherein the conductive pattern comprises a plurality of fractal elements of different scales and orientations. The programmable hearing aid further comprises transmit and/or receive circuitry, disposed on the semiconductor substrate, coupled to the conductive pattern and configured to receive and process a signal from the conductive pattern, and/or process a signal to be transmitted to the conductive pattern. The plurality of fractal elements can be of a generally + shaped geometry. 
     A method of programming a plurality of parameters in a wireless hearing aid comprises receiving a programming signal at a fractal antenna in the hearing aid, wherein the fractal antenna comprises a conductive pattern disposed on a substrate, and wherein the conductive pattern comprises a plurality of fractal elements, repeated in multiple scales and orientations. The method further comprises processing the programming signal in a receiver circuit in the hearing aid, thereby producing a processed programming signal, the receiver circuit coupled to said fractal antenna, and modifying at least one parameter in the hearing aid with at least one of the parameters from the processed programming signal. 
     A fractal antenna comprises a plurality of fractal elements, wherein each fractal element comprises a generally +-shaped geometry, and the plurality of fractal elements are repeated in a plurality of scales and orientations. The fractal antenna can be disposed on a semiconductor substrate as a conductive pattern, and can be incorporated in a hearing aid device. 
     An integrated circuit comprises a semiconductor substrate, a conductive pattern, defining a plurality of fractal elements of a generally + shaped geometry of different dimensions, disposed on said semiconductor substrate. The integrated circuit may further comprise a receiver circuit, coupled to the conductive pattern and configured to receive a signal from the conductive pattern. The integrated circuit may also further comprise a transmit circuit, coupled to the conductive pattern and configured to transmit a signal to the conductive pattern. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exemplary illustration of a hearing aid device. 
     FIG. 2 is an illustration of a fractal antenna structure, referred to herein as a Pollard antenna structure. 
     FIG. 3 is a magnified illustration of the Pollard antenna of FIG.  1 . 
     FIG. 4 is an illustration of an alternative Pollard antenna structure. 
     FIG. 5 is an exemplary schematic diagram of a signal transmission circuit. 
     FIG. 6 is an exemplary illustration of a signal transmission circuit disposed on a substrate for a fractal antenna. 
     FIG. 7 is a substrate layer diagram, corresponding to the signal transmission circuit illustrated in FIG.  6 . 
     FIG. 8 is more detailed illustration of one embodiment of a capacitor for incorporation in the signal transmission circuit of FIG.  6 . 
     FIG. 9 is a more detailed illustration of one embodiment of a signal transmission line for incorporation in the signal transmission circuit of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiments of the invention will now be described with reference to the accompanying Figures, wherein like numerals refer to like elements throughout. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive manner, simply because it is being utilized in conjunction with a detailed description of certain specific embodiments of the invention. Furthermore, embodiments of the invention may include several novel features, no single one of which is solely responsible for its desirable attributes or which is essential to practicing the inventions herein described. 
     Wireless data transmissions typically include the use of signal transmission antennas, which can vary in size and shape depending on the application. An arbitrary reduction in the size of a conventional antenna can result in a large reactance and degradation in the performance of the antenna. A small sized loop antenna, or short dipole, requires significant space due to its performance dependence upon the physical area of the antenna. Therefore, due to the small size of hearing aids, the use of conventional signal transmission antennas does not readily apply. 
     Recently, research in fractal antennas has proved their behavior to be concurrent with their physically larger counterparts, while maintaining a size five to ten times smaller than an equivalent conventional antenna. Nathan Cohen developed a number of fractal antennas and reported his findings on their capabilities in 1994, and continues to focus on antennas optimized for a frequency of 900 MHz for an antenna size as small as an eighth of a wavelength. A research group in Spain has persisted in development and documentation of fractal antennas, and several academic research groups continue to study the operation and applications of fractal antennas. 
     For incorporation into small electronic devices, such as hearing aids, a conductive pattern can be deposited on a substrate to form a plurality of fractal elements, resulting in a resonator, or fractal antenna. The plurality of fractal elements can be of different dimensional sizes and in a number of spatial orientations. 
     As shown in FIG. 1, a fractal antenna  20  can be incorporated in a hearing aid  10  to facilitate communications with a programming box  30 . It will be appreciated that the antenna  20  can be used to transmit and/or receive signals from devices other than the programming box  30 , such as a wireless telephone. The programming box  30  can communicate hearing aid parameters to the hearing aid device  10 , and can receive information from the hearing aid device  10 . The fractal antenna  20  can be implemented as a conductive pattern, disposed on a substrate, comprising a number of fractal elements repeated in multiple orientations and scales. The fractal antenna  20  can be configured to receive and/or transmit signals to and/or from the programming box  30 . The hearing aid  10  can appropriately have receive and/or transmit circuitry (not shown), so as to process a received signal, or process a signal for transmission. 
     Fractals have been used to model many environmental phenomenon, such as trees and lightning, and common references in the art are authored by Hans Lauwerier, and Benoit Mandlebrot. Fractals consist of similar or identical elements repeated in different orientations, positions, and degrees of magnification, typically in an interconnected order. Most fractals have an infinite complexity and detail, thus the complexity and detail of the fractals remain no matter how far an observer magnifies the fractal object. The combination of infinite complexity and detail, in addition to the self-similarity inherent to fractal geometry, makes it possible to construct very small sized antennas with fractal structures, which can operate at high efficiency at multiple frequencies. Although a fractal is infinite by definition, a practical fractal is referred to herein where the multitude and level of scales at which the fractal is repeated can change as implementation technology permits. 
     As used herein, a fractal antenna is a pattern of conductive or semi-conductive material in two or three dimensions having at least one geometric feature that is repeated on different scales, different positions, and/or in different orientations. In one embodiment, described in additional detail below, the repeated feature is a “+”, “x”, or cross. 
     A fractal antenna structure can produce a directive radiation pattern at a given frequency, and can therefore be useful in a wireless hearing aid communication system due to the structure&#39;s size reduction capabilities. The fractal antenna  20  is appropriate for a low energy, low power system such as the hearing aid  10  due to both size constraints of the device and the prospect of matching the load impedance by selecting a frequency in a range such as about 1 MHz to 1 GHz. 
     Very few fractal patterns, such as Hilbert curves and the Sierpenski gasket, have been implemented as fractal antenna structures. The use of fractals in an antenna geometry, in addition to being simple and self-similar, can allow a plane to be filled with different size iterations of similar geometry, and such properties can be exploited to form a reduced size resonant antenna. 
     FIG. 2 illustrates a fractal antenna structure, referred to herein as a Pollard structure. The Pollard antenna structure consists of a fractal geometry similar to an X-shape, or cross, repeated in multiple orientations and scales to form, in one embodiment, a structure such as that illustrated in FIG.  2 . As can be seen, looking at a specific area of the antenna in FIG. 2, such as area  60 , as the level of magnification is increased, the X-shape, + shape, or cross geometry is maintained, but on a smaller scale, as shown in FIG.  3 . 
     Fractal antennas can be extensively reduced in size while maintaining resonant characteristics which correspond to much larger antennas, including deposition on something as small as an integrated circuit substrate. The fractal Antenna of FIG. 2 can be formed by depositing connected substantially linear segments of conductive material on a substrate in the pattern illustrated in FIG.  2 . An alternate fractal antenna can be formed by depositing linear segments of conductive material on a substrate in a pattern defined by the opposed edges of the linear segments shown in FIG.  2 . This embodiment is illustrated in FIG.  4 . The antenna pattern of FIG. 4 can be formed by depositing thick linear segments in the solid pattern of FIG. 2, and then etching away the central portion of the thick linear segments, thereby leaving behind an outline of conductive material defined by the perimeter of the linear pattern shown in FIG.  2 . The Pollard antenna design can be reduced from about 1.4 mm on a side, down to about 0.4 mm on a side for incorporation in small electronic devices, such as the hearing aid illustrated in FIG.  1 . 
     The incorporation of a fractal antenna in the hearing aid device  10  can allow the device to communicate, or be programmed by a remote device without incorporating additional connectors onto the device. Such receive and transmit capabilities can allow the device to be programmed without wired connections, or to receive specialized signals in environments modified for hearing aid device users. 
     Many performance and concert venues have recently been constructed or updated to assist hearing aid users in such environments, and cellular phones can be adapted to function in combination with a hearing aid device. It would be beneficial for hearing aid users to have the capability to utilize such enhancements and adaptations without having to adjust settings on their individual devices, or without having to use an additional external device and connection in such an environment. Such capabilities can be realized by the incorporation of the fractal antenna  20  in the hearing aid  10  of FIG.  1 . The hearing aid  10  can receive signals from the modified environment or communication device at the fractal antenna  20 , without having to use an additional aiding device or wire connection. 
     Since antennas typically operate with reciprocity, a transmitter can also be used as a receiver to assist in determining antenna characteristics. The majority of the following description of a fractal antenna and corresponding circuitry will pertain to transmission capabilities of the device, however, it will be appreciated that such design approaches are applicable to receive capabilities and the device may be optimized for either or both functions. 
     Although antenna drive circuitry for a fractal antenna can be developed by those skilled in the art, an exemplary drive circuit is described herein. FIG. 5 is a schematic diagram of an exemplary signal transmission circuit  200  for use with a fractal antenna, such as the Pollard antennas illustrated in FIGS. 2-4. The circuit can be implemented in the hearing aid  10  of FIG. 1, including the fractal antenna  20 . The circuit  200  comprises a first voltage controlled oscillator (VCO 1 )  204  and second voltage controlled oscillator (VCO 2 )  206 , wherein the oscillation frequencies of such signal sources  204 ,  206  can be set by applying a DC voltage. The voltage controlled oscillators  204 ,  206  can operate at a 50% duty cycle at frequencies of about 1 KHz to about 1 GHz. A logic gate  210 , in this case an AND gate, receives output signals from the pulse train source  204 , the envelope source  206 , and a control input  208 . Thereby, the AND gate  210  transmits one or a series of pulse trains from the first voltage controlled oscillator  204  when the control input  208  is triggered. 
     A signal from the output of the logic gate  210  is received at a buffer  214 , or network of buffers, etc. More particularly, the buffer  214  can be implemented as a ladder structure, wherein each parallel rung is a buffer in series with a resistive element. The output of the buffer  210  is connected to a switch, which is implemented in this embodiment as a PMOS transistor  218 , wherein the output of the buffer  210  is connected to a gate terminal  219  of the PMOS transistor  218 . The source terminal of the PMOS transistor  218  is coupled to a capacitor  220 , which receives a charging voltage from a source V cc    224  through a resistor  226 . A first end of a transmission line  225  can be connected to the drain terminal of the transistor  218 , and a second end of the transmission line  225  can be connected directly to the fractal antenna  20 . As the PMOS transistor  218  is turned off by a signal from the logic gate  210 , via the buffer  214 , the capacitor  220  is allowed to charge from the voltage source V cc    224 . When the control input  208  is triggered, the enveloped pulse train is transmitted via the logic gate  210  and buffer  214  to the PMOS transistor  218 , and the capacitor discharges through the transistor  218  to the transmission line  225 . 
     A transmission line termination  226  can be connected between the transmission line  225  and the antenna  20 , such that the signal transmission circuit  200  can be de-coupled from the antenna  20 , and the termination impedance of the transmission line can be controlled. In this embodiment, the termination  226  comprises a resistor  228  in series with an NMOS transistor  230 , wherein the gate terminal of the NMOS transistor  230  receives a voltage signal V adj    232  so as to adjust the termination impedance of the transmission line  225 . A receiver circuit  240  can also be connected to the antenna  20 , and the termination  226  can decouple the receive circuitry from the antenna  20 . 
     FIG. 6 illustrates a top view of one embodiment of the transmission circuit  200  implemented on a substrate, and a corresponding substrate stack diagram. The first and second voltage controlled oscillators  204 ,  206 , control input  208 , and buffer  214  are shown simply as blocks in FIG. 6, while the voltage sources  224 ,  230  are not illustrated. 
     In FIG. 6, the capacitor  220  is implemented as a slotted capacitor, which can be formed on a substrate by a plurality of metal layers to optimize the capacitance. This layered structure can be seen more clearly in FIG.  7 . However, it will be appreciated that a capacitative charge portion can be formed or implemented in alternative embodiments known to those of skill in the art. Only one layer of the capacitor  220  is illustrated in FIG.  6 . In the present embodiment, the transmission line  225  is formed of multiple, tapered or curved portions of a conductor plane, wherein the width of the transmission line  225  can be designed to decrease exponentially so as to increase the impedance as a signal travels along the transmission line  225 . 
     Referring to FIG. 6, the capacitor  220  is charged with current from the voltage source  224  (not shown), and when the logic gate  210  is enabled, the gate of the PMOS transistor  218 , located between the capacitor  220  and the transmission line  225 , is active and the transistor  218  transmits across the gap between the capacitor  220  and the transmission line  225 . When the PMOS switch  218  is closed, the pulse, or pulses from the first voltage controlled oscillator travel from the capacitor  220  down the transmission line  225 . As the pulse travels down the transmission line  225  toward the antenna  20 , the transmission line  225  acts as an impedance transformer due to its size and shape, such that the pulse is fed to the antenna  20  from a matched impedance point on the transmission line  225 . 
     The switch  218  can be implemented with a PMOS transistor as shown, or light activated switches may be used to increase switching speed, such as those described in U.S. Pat. No. 5,394,415 to Zucker et al. The use of the pulsed signal source can provide higher peak transmission than a continuous wave source, and can produce, for example, a peak transmission power of over a Watt. 
     FIG. 7 is a substrate layer diagram corresponding to the signal transmission circuit illustrated in FIG.  6 . The capacitor  220  can be seen as comprising three deposited metal layers  220 A-C, and the source terminal of the PMOS transistor  218  is connected to the capacitor  220 . The gap between the capacitor  220  and the transmission line  225  is illustrated, wherein the gate terminal  219  of the PMOS transistor is located in the gap between the capacitor  220  and the transmission line  225 . A level is illustrated where a conductive pattern, forming the fractal antenna  20 , can be located, and the transmission line can be fed directly to an approximate center of the antenna  20 . At the connection point between the transmission line  225  and the antenna  20 , the termination  226  can be seen comprising the termination resistor  228  and NMOS transistor  230 . 
     FIG. 8 is a more detailed illustration of one embodiment of the capacitor layer  220 A-C having slots void of conducting material. The slot shaped voids can optimize fabrication of the capacitor  220  wherein a solid plane of conducting material may not function as well. 
     FIG. 9 is a more detailed illustration of one embodiment of the transmission line  225 . In one advantageous embodiment, the width of the transmission line  225  decreases exponentially, however, ellipses of particular dimension can be used to fit the exponentially curved portions of the transmission line  225 . An ellipse curve may be more readily available and easier to use than an exponential curve for a printed circuit board layout and production process. Additionally, holes, or voids of conducting material can be punched or etched in the transmission line  225  conduction plane so as to optimize fabrication of the transmission line  225 , these holes are illustrated in FIG.  9 . 
     The transmission line can feed the pulse signal to the antenna structure using proximity feed or direct connect feed. In one embodiment, a direct connect feed is used to connect the transmission line  225  directly to the antenna  20 . Proximity feed can be used in combination with an aperture to terminate the transmission line, and for proximity feed it is possible to stack multiple antenna elements so as to increase the bandwidth of the antenna capabilities. 
     The transmission line termination  226  can also be controlled so as to de-couple the rest of the signal transmission circuitry from the antenna  20  to optimize reception capabilities of the antenna  20 . The inclusion of the fractal antenna  20 , using the Pollard antenna designs illustrated in FIGS. 2-3, for example, can improve a hearing aid device&#39;s capabilities for customized programming and enhance performance due to more effective compatibility with newly modified, hearing aid friendly environments. 
     The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention can be practiced in many ways. As is also stated above, it should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to including any specific characteristics of the features or aspects of the invention with which that terminology is associated. The scope of the invention should therefore be construed in accordance with the appended claims and any equivalents thereof.