Abstract:
This invention relates to a system ( 100 ) for communicating wirelessly. The system ( 100 ) comprises an inductive antenna circuit ( 110 ) for transmitting and receiving inductively coupled signals, a driving means ( 102, 104 ) connected to inductive antenna circuit ( 110 ) and driving the inductive antenna circuit ( 102, 104 ) during a transmit mode, and comprises an amplifier means ( 112 ) connected to the inductive antenna circuit ( 110 ) and detecting and amplifying received signals differentially a receiving mode.

Description:
FIELD OF INVENTION  
       [0001]     This invention relates to a system for wireless communication between for example a remote controller and a hearing aid such as a behind-the-ear (BTE), an in-the-ear (ITE), an in-the-canal (ITC) or a completely-in-canal (CIC), or an implanted hearing aid.  
       BACKGROUND OF INVENTION  
       [0002]     Transmit/receive switching means in hearing aids, such as disclosed in American patent application no.: US 2005/111682, are used for providing switching between transmit and receive modes in hearing aids for wireless communication. This American patent application describes a system wherein an inductive coil operating as an antenna is switched between an equivalent series resonant circuit reducing inductive load in transmit mode and an equivalent parallel resonant circuit increasing inductive load in the receive mode. The system further utilises a transmit/receive-switch to establish a voltage protection during the transmit mode of a low noise amplifier (LNA) used for amplifying received data during the receive mode.  
         [0003]     Despite the advances achieved within the hearing aid technology by the above described transmit-receive switching means there still is a need for providing improvements of the noise rejection during receive mode, improvements of the voltage protective elements, and provide means for switching between transmit and receive mode without changing the antenna matching.  
       SUMMARY OF THE INVENTION  
       [0004]     An object of the present invention is to provide a system for providing wireless communication with an improved noise rejection.  
         [0005]     It is a further object of the present invention to provide a hearing aid comprising a system for wireless communication between a hearing aid and a remote controller as well as binaurally between a set of hearing aids.  
         [0006]     A particular advantage of the present invention is the provision of a simple protection of a low noise amplifier amplifying the received communication.  
         [0007]     Another advantage is the provision of transmit/receive switching without loss of performance.  
         [0008]     The above objects and advantages together with numerous other objects, advantages and features, which will become evident from below detailed description, are obtained according to a first aspect of the present invention by a system for communicating wirelessly and comprising an inductive antenna circuit adapted to transmit and receive inductively coupled signals and having a first and second set of terminals, a driving means connected to said first set of terminals and adapted to drive said inductive antenna circuit during a transmit mode, an amplifier means connected to said second set of terminals and adapted to detect and amplify an incoming differential signal during a receiving mode.  
         [0009]     The system according to the first aspect achieves a common mode rejection of signals electrically coupled to the two antenna terminals. Hence the amplifier means coupled as a differential amplifier ensures a significantly improved noise reduction scheme.  
         [0010]     The system according to the first aspect of the present invention further may comprise a current sensing means interconnecting said second set of terminals with a non-inverting input and an inverting input of said amplifier means. The current sensing means may comprise a low input impedance buffer having current to voltage conversion capabilities. The low input impedance buffer may convert a sensed current to a voltage for the inverting and non-inverting input of the amplifier means. Hence the problems inheritably associated with prior art switching between a transmitting and receiving mode are avoided, namely problems relating to the amplifier means being exposed to damaging high voltages induced by the inductive antenna circuit during the transmit mode and disturbance of the resonance frequency of the inductive antenna circuit by stray and blocking capacitances or any other protective elements.  
         [0011]     The low impedance buffer according to the first aspect of the present invention may comprise a common base coupled transistor. Thus the impedance buffer effectively may convert the current generated in the inductive antenna circuit to a voltage to be amplified by the amplifier means.  
         [0012]     The driving means according to the first aspect of the present invention may comprise a first power output presenting a square wave to a first terminal of said first set of terminals and a second power output presenting an inverted square wave to a second terminal of said first set of terminals. Hence the inductive antenna circuit advantageously is presented with a square wave alternating between a positive and negative maximum, which enables a differential voltage signal to be transmitted as well as received and differentially amplified by the amplifier means.  
         [0013]     The inductive antenna circuit according to the first aspect of the present invention may comprise a series connection of tuning capacitors on either side of a transmit/receive inductor between said first and second set of terminals. Hence the first and second set of terminals are connected together and therefore no switching between components is required when changing from transmit to receive mode.  
         [0014]     Additionally, or alternatively, the inductive antenna circuit may comprise a series connection of transmit/receive inductors on either side of a tuning capacitor between said first and second set of terminals. This series connection provides a well defined zero point between the first and second set of terminals, and provides, as the above mentioned series connection, an inductive antenna solution which does not require switching between components when changing from transmit to receive mode.  
         [0015]     The inductive antenna circuit according to the first aspect of the present invention may alternatively comprise a first series connection of tuning capacitors on either side of a transmit inductor between said first set of terminals, or a first series connection of transmit inductors on either side of a tuning capacitor between said first set of terminals. The inductive antenna circuit may further comprise a second series connection of tuning capacitors on either side of a receive inductor between said second set of terminals, or a second series connection of receive inductors on either side of a tuning capacitor between said second set of terminals.  
         [0016]     The inductive antenna circuit according to the first aspect of the present invention may further comprise a magnetic coupling core. The magnetic coupling core advantageously increases the magnetic flux permeability and therefore the transmit inductor and the receive inductor are capable of being reduced in size. This obviously is particularly advantageous for implementation of the system according to the first aspect in a hearing aid. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawing, wherein:  
         [0018]      FIG. 1 , shows a system for communicating wirelessly according to a first embodiment of the present invention;  
         [0019]      FIG. 2 , shows an inductive antenna circuit according to the first embodiment of the present invention;  
         [0020]      FIG. 3 , shows an inductive antenna circuit according to a second embodiment of the present invention;  
         [0021]      FIG. 4 , shows an inductive antenna circuit according to a third embodiment of the present invention; and  
         [0022]      FIG. 5 , shows an inductive antenna circuit according to a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]     In the following description of the various embodiments, reference is made to the accompanying figures, which show by way of illustration how the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention.  
         [0024]      FIG. 1 , shows a system for communicating wirelessly, which is designated in entirety by reference numeral  100 . The system  100  comprises a set of drivers  102 ,  104  operating 180° out of phase in transmit mode, shown in graphical representations  106 ,  108 , respectively, so as to establish a square wave transmit signal across a transmit/receive antenna  110 , which alternates between a positive maximum and negative minimum, shown in graphical representation  109 .  
         [0025]     In transmit mode the transmit/receive antenna is driven as a full bridge class D transmitter. That is, enveloping the transmit data in pulse width of the square wave transmit signal. In an alternative embodiment the transmit/receive antenna is driven as a half bridge class D. The square wave transmit signal may be coded in accordance with any protocol known to a person skilled in the art including any proprietary protocols.  
         [0026]     The system  100  further comprises a low noise amplifier  112  receiving the received signal across a first  114  and second  116  input port. The low noise amplifier  112  comprises a differentially coupled operational amplifier  118  amplifying the voltage difference between the first  114  and second  116  input ports and providing an amplified difference signal on output port  120 . In this context the term “amplified” should be construed as an amplification range from unity to 1000, such as 10 or 100, which amplification obviously is controlled by the value of resistances R 1  and R 2 . It should be understood that this difference amplifier circuit may be implemented in any configurations known to a person skilled in the art.  
         [0027]     The system  100  further comprises current sensing amplifiers  122 ,  124  interconnecting the end terminals of the transmit/receive antenna  110  and the input ports  114 ,  116  of the low noise amplifier  120 . The current sensing amplifiers  122 ,  124  in the first embodiment of the present invention comprises a low input impedance buffer, such as a common base transistor configuration, for transforming current input signals from the transmit/receive antenna  110  to output voltage signals, which are forwarded to the input ports  114 ,  116 .  
         [0028]     The low input impedance implementation of the current sensing amplifiers  122 ,  124  further ensures that the resonance frequency of the transmit/receive antenna  110  is not significantly disturbed by the complex imaginary part of the input impedance.  
         [0029]      FIG. 2 , shows an inductive antenna circuit  110  according to first embodiment of the present invention, which comprises a series connection of tuning capacitors  202 ,  204  on either side of a transmit/receive inductor  206  between end terminals  208 ,  210 . The end terminal  208  is connected to driver  102  and current sensing amplifier  122 , and end terminal  210  is connected to driver  104  and current sensing amplifier  124 . The inductor may be an air coil or a wounded on a ferrite material core.  
         [0030]      FIG. 3 , shows an inductive antenna circuit  110  according to second embodiment of the present invention, which comprises a series connection of transmit/receive inductors  302 ,  304  on either side of a tuning capacitor  306  between end terminals  308 ,  310 . The end terminal  308  is connected to driver  102  and current sensing amplifier  122 , and end terminal  310  is connected to driver  104  and current sensing amplifier  124 . The two inductors may be air coils or both inductors wound on a single or two separate ferrite material cores.  
         [0031]      FIG. 4 , shows an inductive antenna circuit  110  according to a third embodiment of the present invention, which comprises a first series connection  402  of tuning capacitors  404 ,  406  on either side of a transmit inductor  408  between end terminals  410 ,  412 . The end terminals  410 ,  412  are connected to drivers  102  and  104 .  
         [0032]     The inductive antenna circuit  110  according to the third embodiment of the present invention further comprises a second series connection  414  of tuning capacitors  416 ,  418  on either side of a receive inductor  420  between end terminals  422 ,  424 . The end terminals  422 ,  424  are connected to current sensing amplifiers  122  and  124 .  
         [0033]     The inductive antenna circuit  110  according to the third embodiment of the present invention further comprises a magnetic core  426  for supporting the windings of the transmit inductor  408  and the receive inductor  420 .  
         [0034]      FIG. 5 , shows an inductive antenna circuit  110  according to a fourth embodiment of the present invention, which comprises a first series connection  502  of transmit inductors  504 ,  506  on either side of a tuning capacitor  508  between end terminals  510 ,  512 . The end terminals  510 ,  512  are connected to drivers  102  and  104 .  
         [0035]     The inductive antenna circuit  110  according to the fourth embodiment of the present invention further comprises a second series connection  514  of receive inductors  516 ,  518  on either side of a tuning capacitor  520  between end terminals  522 ,  524 . The end terminals  522 ,  524  are connected to current sensing amplifiers  122  and  124 .  
         [0036]     The inductive antenna circuit  110  according to the fourth embodiment of the present invention further comprises a magnetic core  526  for supporting the windings of the transmit inductors  504 ,  506  and the receive inductors  516 ,  518 .