Abstract:
A speech processor unit ( 12 ) for a cochlear implant system. The speech processor unit ( 12 ) comprises a signal processor for processing incoming auditory signals and for forwarding processed signals to an implanted component ( 18 ) of the system, a monitoring means for monitoring a predetermined parameter, and a controller, controlled by the signal processor, for placing the unit in an idle state in the absence of the parameter. The predetermined parameter can comprise the presence or absence of the implanted receiver antenna coil ( 22 ) relative to the external antenna coil ( 16 ). The invention allows the speech processor unit ( 12 ) to be supplied without a physical on and off switch.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority from Provisional Patent Application No 2003905570 filed on Oct. 13, 2003, the contents of which is incorporated herein by reference. 
   BACKGROUND 
   1. Field of the Invention 
   This invention relates to a speech processor unit for an auditory prosthesis. More particularly, the invention relates to an external speech processor unit for a cochlear implant system. 
   2. Related Art 
   Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person may have hearing loss of both types. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss is often helped by use of conventional hearing aids which amplify sound so that acoustic information reaches the cochlea and the hair cells. 
   In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. This type of hearing loss is due to the absence of, or destruction of, the hair cells in the cochlea which transduce acoustic signals into nerve impulses. These people are thus unable to derive suitable benefit from conventional hearing aid systems, no matter how loud the acoustic stimulus is made, because there is damage to, or absence of, the mechanism for nerve impulses to be generated from sound in the normal manner. 
   It is for this purpose that cochlear implant systems have been developed. Such systems bypass the hair cells in the cochlea and directly deliver electrical stimulation to the auditory nerve fibres, thereby allowing the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered to the auditory nerve. 
   Typically, cochlear implant systems consist essentially of two components, an external component commonly referred to as a processor unit and an internal, implanted component commonly referred to as a stimulator/receiver unit, the latter receiving signals from the processor unit to provide the sound sensation to a user. 
   The external component includes a microphone for detecting sounds, such as speech and environmental sounds, a speech processor that converts speech into a coded signal, a power source such as a battery, and an external transmitter coil. 
   The coded signal output by the sound processor is transmitted transcutaneously to the implanted stimulator/receiver unit situated within a recess of the temporal bone of the user. This transcutaneous transmission occurs via the external transmitter antenna coil which is positioned to communicate with an implanted receiver antenna coil of the stimulator/receiver unit. Therefore, the communication serves two essential purposes; firstly to transmit, transcutaneously, the coded signal and, secondly, to provide power to the implanted stimulator/receiver unit. The transcutaneous link is, normally, in the form of a radio frequency (RF) link, but other such links have been proposed and implemented with varying degrees of success. 
   The implanted stimulator/receiver unit includes, in addition to the receiver antenna coil that receives the coded signal and power from the external processor component, a stimulator that processes the coded signal and outputs a stimulation signal to an intracochlea electrode assembly which applies the electrical stimulation directly to the auditory nerve producing a hearing sensation corresponding to the originally detected sound. 
   The external component is carried on the body of the user, such as in a pocket of the user&#39;s clothing, a belt pouch or in a harness, while the microphone is mounted on a clip mounted behind the ear or on the lapel of the user. 
   More recently, the physical dimensions of the sound processor have been able to be reduced allowing for the external component to be housed in a relatively small unit capable of being worn discreetly behind the ear of the user. The external transmitter antenna coil is still positioned on the side of the user&#39;s head to allow for the transmission of the coded sound signal and power from the sound processor to the implanted stimulator unit. 
   Such behind the ear units (BTEs) have provided a degree of freedom and subtlety for the recipient which has not traditionally been possible with body worn devices. There is no longer a need for extensive cables connecting the body worn processor to the transmitter antenna coil, nor is there a need for a separate microphone unit or battery pack, as the BTE unit contains all the components in one housing. 
   One common feature of all BTE units is the provision of a dedicated mechanical switch for turning the unit on or off. Such a switch is typically small in size and difficult to manipulate, especially in the case of elderly recipients or those who are not very dexterous. Continuous use of the switch causes mechanical fatigue resulting in the switch failing to operate and requiring repair or replacement. 
   A further problem with BTE devices of current designs is that the area around the switch permits the ingress of moisture that can damage or destroy the device. 
   Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. 
   SUMMARY 
   Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 
   According to the invention, there is provided a speech processor unit for a cochlear implant system, the speech processor unit comprising:
         a signal processor for processing incoming auditory signals and for forwarding processed signals to an implanted component of the system;   a monitoring means for monitoring a predetermined parameter; and   a controller, controlled by the signal processor, for placing the unit in an idle state in the absence of the parameter.       

   The unit may include a microphone for receiving external auditory signals and for feeding these signals to the signal processor. 
   The microphone may be connected to a pre-amplifier and an analogue-to-digital converter (ADC). The pre-amplifier and ADC may be implemented as a single module which may normally draw power supplied by a bias circuit. The bias circuit may have a power down control operable under the control of the signal processor. 
   As is the case with a conventional external speech processor unit, the unit may include a data encoder/formatter which is used to send stimulation commands to an implanted component of the cochlear implant. The implanted component, or implant, may include an implanted receiver and a stimulator unit. The stimulator unit may feed received signals to an electrode array arranged in a cochlea of a recipient. 
   The formatter may communicate with the implanted component via a transcutaneous inductive link. Thus, the formatter may feed signals in the form of stimulation commands, being coded sound signals, and power signals via a transmitter antenna coil arranged externally of the recipient&#39;s body. 
   This link may also be used to receive messages from the implanted component which may be fed back via the formatter to the signal processor. 
   The unit may further include a memory and a battery supply for supplying power to the unit. To reduce power consumption of the unit, the signal processor (which may be a digital signal processor), the data encoder/formatter and the memory may be implemented by way of CMOS circuitry. 
   In one embodiment of the invention, the parameter monitored by the unit may be the presence of the implanted component. The monitoring means may therefore be implemented as a part of the digital signal processor. Thus, the digital signal processor may, periodically, send an interrogation signal to determine if the implanted component is present. It will be appreciated that, should the external unit have been removed from the recipient&#39;s body, normally behind the recipient&#39;s ear, the implanted component will not be detected by the digital signal processor. This may be taken as an indication that the external component is not being used, for example, due to the recipient being asleep or in a situation where the cochlear implant is not being used, for example, while bathing, etc. 
   In such circumstances, the digital signal processor may disable the bias circuit causing the preamplifier and ADC module to enter a low power state. The digital signal processor may also stop sending commands to the implanted component and may stop accessing memory, the latter step causing the memory to stop drawing power. 
   Finally, the signal processor may send a “pause” signal to the controller which interrupts a clock signal from an oscillator to the signal processor. In this state, all CMOS circuits are idle and only the oscillator and the controller may draw power. 
   The unit may remain in this state for a predetermined delay period, the delay period being generated by the controller. A typical value may be about 1 second. When the delay is complete, the clock signal to the signal processor may be resumed. The signal processor may then send a further command to the implanted component. Assuming the implanted component is still not detected and the signal processor receives no response, the signal processor may immediately re-enable the controller. 
   The controller may be a pause-and-gate circuit. The pause-and-gate circuit may be implemented either as hardware or as software in the signal processor. In the latter case, the function of the pause-and-gate circuit may be performed by the signal processor. 
   Further, the signal processor may include a set of event counters for timing real-time-events. These event counters may be suitable for implementing the pause-and-gate function whereby the counters may generate an interrupt signal when they have run for their pre-allocated time. This interrupt may start the signal processor running again. 
   In another embodiment of the invention, the parameter monitored by the unit may be motion of the recipient. Thus, the unit may include a motion-detecting means. The motion-detecting means may operate the pause-and-gate circuit of the unit. The motion-detecting means may be in the form of a mercury switch. In the absence of motion, the switch may cause the unit to enter an idle state. 
   In yet a further embodiment of the invention, the parameter being monitored may be a value of reflected impedance as “seen” by the signal processor. When the receiver antenna coil has been removed, the reflected impedance as detected by the signal processor may be much higher than when the receiver antenna coil is present. Thus, by appropriate calculation to take into account current drawn during stimulation and the current drawn by the components of the unit itself, the signal processor can determine whether or not the implanted component is present. If not, the signal processor may follow substantially the same procedure as described above with reference to the first embodiment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is now described by way of example with reference to the accompanying drawings in which: 
       FIG. 1  shows a schematic representation of a cochlear implant system, in accordance with an embodiment of the invention; 
       FIG. 2  shows a block diagram of an external speech processor unit, in accordance with the invention, for the implant of  FIG. 1 ; 
       FIG. 3  shows a block diagram of another embodiment of part of the unit; 
       FIG. 4  shows a block diagram of the pause-and-gate circuit of  FIG. 2 ; 
       FIG. 5  shows a flow chart of the operation of the unit of  FIG. 2 ; and 
       FIG. 6  shows a flow chart of the unit being placed in an idle mode. 
   

   DETAILED DESCRIPTION 
   Referring initially to  FIG. 1  of the drawings, reference numeral  10  generally designates a cochlear implant system including an external speech processor  12 , in accordance with the invention. The system  10  includes an external component  14  made up of the speech processor  12  and a transmitting device, in the form of a transmitter antenna coil  16 , and an internal component, or implant,  18 . The internal component  18  includes an implanted receiver and stimulator unit  20  implanted in a recess in a temporal bone of a recipient. The stimulator unit  20  receives signals from an implanted receiver antenna coil  22 . The stimulator unit  20  is connected via a conductor or lead  24  to an intracochlea electrode array  26  mounted in the cochlea  28  of the recipient. The received signals are therefore applied by the electrode array  26  to the basilar membrane  30  of the recipient and nerve cells within the cochlea  28  to effect stimulation of the auditory nerve  32  to provide a hearing sensation for the recipient. 
   In one implementation of the system  10 , the external speech processor unit  12  is of sufficiently small dimensions to be mounted behind an outer ear  34  of the recipient. The external speech processor unit  12  includes a microphone  36  for detecting sounds such as speech and surrounding environmental sounds. 
   Referring now to  FIG. 2  of the drawings, a block diagram of the external speech processor unit  12  is shown in greater detail. The processor unit  12  comprises a digital signal processor  38 . Auditory inputs from the microphone  36  are fed to a pre-amplifier and ADC module  40 . The module  40  is controlled by a bias circuit  42 . The bias circuit  42  has a power-down control. When the power-down control is activated, the module  40  ceases operation. When the module  40  ceases operation it is put in a mode which draws only a relatively minute amount of power. 
   The unit  12  is powered by a set of internal batteries  44 . It is a desire of the industry to reduce power consumption so that the batteries  44  require replacement as infrequently as possible. 
   Further, the unit  12  includes a memory  46 . The memory  46  contains psychophysical data, such as threshold and comfort levels of the recipient as mapped from each of the electrodes of the electrode array  26 . 
   Data from the signal processor  38  are fed to a data encoder/formatter  48 . The formatter  48  is used to send stimulation commands and power across a transcutaneous link  50  to the implant  18  of the system  10 . The transcutaneous link  50  is made up of the transmitter antenna coil  16  of the external component  14  and the receiver antenna coil  22  of the implant  18 . 
   The signal processor  38  is also formatted to interrogate the implant  18  and to receive messages back from the implant  18  via the formatter  48 . When stimulation commands are to be sent by the signal processor  38  to the implant  18 , the information is encoded by the formatter  48  into a coded signal, being stimulation commands representative of the sound signal received from the microphone  36 . 
   The signal processor  38  analyses received sound signals from the microphone  36 . The received sound signals are split up into frequency bands in accordance with the tonotopic arrangement of the electrodes of the array  26 . The signal processor  38  analyses the amplitude of the signals in each discrete frequency band in accordance with a specific sound processing strategy. For example, the signal processor  38  can detect the “n” largest outputs for each filter channel, measure the amplitude of each filter channel and rank them accordingly. 
   Following frequency analysis and processing of the sound signals, the signal processor  38  can access data allocating each frequency band to an electrode pair of the electrode array  26  from the memory  46 . Using this information, the sound signal is mapped to a recipient&#39;s electrode array  26  by selecting the electrodes assigned to the particular frequency and choosing a level between comfort and threshold to represent the loudness of that frequency component. 
   The unit  12  includes an oscillator  52 . The oscillator  52  generates a master clock signal  78  for the entire unit  12 . 
   The speech processor unit  12  is, where applicable, made using CMOS circuitry for all digital circuits and, more particularly, the signal processor  38 , the formatter  48  and the memory  46 . In addition, the oscillator  52  is a CMOS design which draws approximately 100 μA or less. 
   The oscillator feeds its output to a pause-and-gate circuit  54 . The circuit  54  consists of a low-power counter that gates the clock from the oscillator  52  to the signal processor  38 . In a normal operating mode the circuit  54  passes the clock signal  78  from the oscillator  52  to the signal processor  38  and, from there, to the rest of the speech processor unit  12 . In a pause mode, the circuit  54  interrupts the clock signal  78  to the signal processor  38  and waits for a delay signal from the signal processor  38 . The signal processor  38  controls when the pause-and-gate circuit  54  enters its pause mode. 
   The external speech processor unit  12  operates as follows. The operation is described with reference to  FIGS. 5 and 6  of the drawings. It is assumed that the system  10  is operating normally and processing sound. All circuits of the external speech processor unit  12  are active. Periodically, for example, once every 10 seconds, the signal processor  38  polls the implant  18  with a message that includes a telemetry command at step  100  in  FIG. 5  and awaits a reply  102 . If the signal processor  38  receives a response from the implant  18 , it “knows” that the implant  18  is present and continues processing sound  104 . If, however, the signal processor  38  does not receive a telemetry response, it can send one or more telemetry commands to the implant  18  to detect if its receiving antenna coil  22  is present. After confirming that the receiving antenna coil  22  is not present, the speech processor unit  12  assumes that this is because the receiving antenna coil  22  is not in communication with the transmitting antenna coil  16  of the external component  14 . This is taken as a message to “switch off”, i.e. to enter an idle state as shown at step  106  ( FIGS. 5 and 6 ). 
   The signal processor  38  (or “DSP”) then starts its shut-down routine as described with reference to  FIG. 6  of the drawings. This routine initially involves disabling the bias circuit  42  at step  108 . Disabling the bias circuit  42  causes the pre-amplifier and ADC module  40  to enter a low-power state as shown  110 . The signal processor  38  also stops sending commands to the implant  18  and stops accessing the memory  46  at step  112 . 
   When the signal processor  38  stops accessing the memory  46 , this causes the memory  46  to stop drawing power from the batteries  44  as shown at  114 . 
   Finally, the signal processor  38  sends a “pause” signal, via a pause input  64  (see  FIG. 4 ) to the pause-and-gate circuit  54  at step  116 . This causes the circuit  54  to enter its pause mode whereby the clock signal  78  from the oscillator  52  to the signal processor  38  is interrupted as shown at  118 . 
   In this state, all CMOS circuits are in an idle state  120 . The oscillator  52  and the pause-and-gate circuit  54  continue to draw power from the batteries  44  but no other components do or, more accurately, the power drawn is so small as to be relatively negligible. In this state, the power drawn by the unit  12  is that drawn by the oscillator  52  and is typically less than 100 μA. 
   The unit  12  remains in this state for the delay generated by the pause-and-gate circuit  54 . A typical value for this delay is of the order of about 1 second. When this delay is completed, the clock signal  78  from the oscillator  52  to the signal processor  38  is re-applied by the pause-and-gate circuit  54  to the signal processor  38 . The signal processor  38  then sends a telemetry command to the implant  18  as shown at  122  in  FIG. 5  of the drawings. Assuming the implant  18  is still not present, the signal processor  38  will receive no response. This causes the signal processor  38  to instruct the pause-and-gate circuit  54  to enter its pause mode once again. 
   The unit  12  can remain in this mode for any time period ranging from minutes to many hours as long as the transmitter antenna coil  16  is not placed on the recipient&#39;s head which would re-establish the transcutaneous link  50  to the implant  18 . Thus, if the recipient has placed the transmitter antenna coil  16  in register with the receiver antenna coil  22 , the link  50  is re-established. Thus when the signal processor  38  again sends a detection command to the implant  18 , it will receive a response. It then knows that it has to start processing sound again. In this configuration, the signal processor  38  re-enables the pre-amplifier and ADC module  40 , waits a short time for any analogue circuitry to stabilise and recommences sound processing. 
   A typical speech processor unit  12  draws between 2-25 mA when operating. For the sake of the example, it is assumed that the current drawn is 15 mA on average. It is also assumed that it takes 1 ms for the speech processor to re-activate, send a telemetry command, receive a reply and shut down again. Thus, with a signal processor  38  with a 10 MHz clock, this allows 1000 instructions for operation which is well within the capabilities of a standard signal processor  38 . In its idle state, the unit  12  draws approximately 100 μA. Thus, the average current drawn by the speech processor unit  12  is approximately 105 μA. This is sufficiently low that a battery could provide this power for a long period of time. A typical battery has a capacity of 300 mAH. Thus, the processor unit  12  can operate for nearly 3000 hours in this mode. 
   An implementation of the pause-and-gate circuit  54  is shown in  FIG. 4  of the drawings. The circuit  54  has a pause input  64  that, as described above, is asserted by the signal processor  38  when it has failed to detect the implant  18  and so initiates the low-power routine. A delay module  66  allows the DSP clock signal  78  to continue while the signal processor  38  clears the pause input  64  to prevent the unit  12  from locking up. 
   Further, as indicated above, the oscillator  52  provides the clock signal  78  for the signal processor  38  and a clock signal  80  for a counter  68  of the pause-and-gate circuit  54 . 
   The counter  68  sets the time for the “idle” state for the unit  12 . The counter  68  has two outputs, an “Overflow” output  70  and an “Overflow*” output  72 . The “Overflow” output  70  is asserted when the count has reached its maximum value. The “Overflow*” output  72  is the logical inverse of “Overflow” output  70 . An AND gate  74  gates the “Overflow*” output  72  and the oscillator  52  to provide the clock signal  80  for the counter  68 . A second AND gate  76  gates the “Overflow” output  70  and the oscillator  52  to provide the clock signal  78  for the signal processor  38 . 
   The circuit  54  operates in the following manner. Under normal operating conditions, when the implant  18  is detected, the oscillator  52  is running and the Overflow output  70  is high. This allows the clock signal  78  to toggle and drive the signal processor  38 . The “Overflow*” output  72  is low so the AND gate  74  prevents the oscillator  52  clocking the counter  68 . 
   To enter the low-power state, the signal processor  38  sets the pause signal  64 . This initiates a pulse in the delay module  66 . The signal processor  38  then resets the pause signal  64 . The delay module  66  has as many stages as the number of clock cycles required by the signal processor  38  to clear the pause signal  64  to allow the pause signal  64  to be reset. 
   A pulse from the delay module  66  resets the counter  68 . Resetting of the counter  68  causes the “Overflow” output  70  going low which, in turn, results in the clock signal  78  to the signal processor  38  being inhibited by AND gate  76 . The “Overflow*” output  72  goes high so the oscillator  52  clocks the counter  68  via the AND gate  74 . The counter  68  has sufficient stages that it can count for the time for which the unit  12  must be in its low-power state. At the end of this time, when the counter  68  has reached its maximum count value, the “Overflow” output  70  goes high, allowing the clock signal  78  to the signal processor  38  to resume. The “Overflow*” output  72  goes low blocking the clock signal  80  to the counter  68 . The clock signal  78  is then available to the signal processor  38 , allowing it to check for the presence of the implant  18 . 
   In a variation of the invention, the pause-and-gate circuit  54  can be implemented as software in the signal processor  38  if the signal processor  38  is configured to run a software timer at sufficiently low power. 
   Further, if the signal processor  38  has a set of event counters for timing real-time events, these might be suitable for implementing the pause-and-gate function. These counters generate an interrupt when they have run for the pre-allocated time. The interrupt starts the signal processor  38  running again. 
   In another embodiment of the invention, illustrated in  FIG. 3  of the drawings, the speech processor unit  12  includes a motion detecting mechanism in the form of a motion detecting switch  56 . The motion detecting switch  56  is connected to the pause-and-gate circuit  54 . In the absence of motion for a predetermined period of time, the switch  56  causes the pause-and-gate circuit  54  to enter its pause mode interrupting the clock signal  78  from the oscillator  52  to the signal processor  38 . This causes the unit  12 , in the absence of the implant  18  to enter its idle state, as described above. 
   Conveniently the motion switch  56  is a mercury switch having a pair of contacts  58  which, when the switch  56  is closed, is bridged by a blob of mercury  60 . The contacts  58  and mercury  60  are housed in an envelope  62  of a non-conductive material, such as glass. The switch  56  is arranged so that, in the absence of motion, the mercury  60  does not bridge the contacts  58 , thereby disabling the switch  56 . Movement of the recipient is required to move the mercury  60  so that it bridges the contacts  58 . When this occurs, the pause-and-gate circuit  54  enters it normal mode. 
   Thus, as long as the external component  14  of the implant  12  is left idle, for example, on a bedside table during the night while the recipient is a sleep the speech processor unit  12  will remain in its idle mode. If the unit  12  is, for example, bumped then the signal processor  38  will be activated, but detect that the implant  18  is absent and the unit  12  will again be placed in its idle state. 
   Yet a further embodiment of the invention relies on reflected impedance. In this embodiment of the invention, the reflected impedance of the implant receiver antenna coil  22  affects the input impedance of the transmitter antenna coil  16  as detected by the signal processor  38 . This embodiment operates in a similar manner to the implementation described above with reference to  FIG. 2  of the drawings except that the signal processor  38  measures current used to drive the implant  18 . 
   For this embodiment of the invention, the battery  44  has a small resistor in series forming an ammeter so that the signal processor  38  can measure the supply current. 
   Since the supply current of the speech processor unit  12  varies with the stimulation rate, the signal processor  38  must compensate for the rate at which it is sending radio frequency (RF) signals across the link  50  the implant  18 . For this purpose the signal processor performs the following steps:
         records the rate at which it sends RF frames to the implant  18 ;   measures the current drawn from the battery  44  using the ammeter;   subtracts from the values measured, the current drawn by the signal processor  38  itself, the analogue circuitry etc.;   from the previous step, calculates the power drawn from the battery  44  for each stimulation;   from the calculation in the preceding step, determines whether or not the implant  18  is present.       

   Typically, when the signal processor  38  is driving the implant  18  it draws a current of about 12 mA maximum. When the receiver coil  22  is absent, the drawn current can reach levels of up to 80 mA. As a result, this large difference in values means that errors from the ammeter or from the calculation are not critical. 
   Accordingly, it is an advantage of the invention that a cochlear implant system  10  is provided which omits a mechanical on/off switch in the external processor. Such a mechanical switch is prone to failure as it is used many times by the recipient. In addition, because of the small size of behind the ear external speech processor units  12 , the switch itself is also of small dimensions. This makes it difficult for older people or less dexterous people to manipulate such switches. Because the invention obviates the need for a switch, this problem is also overcome. 
   In addition, one of the causes of failures of external speech processor units  12  is the ingress of moisture. Often the ingress of moisture is through the aperture in a casing of the external speech processor unit for a lever of an on/off switch. Once again, because the on/off switch is able to be eliminated in the present invention, this problem is also, to at least a large extent, overcome. Thus, this renders the system  10  more versatile as it is now possible for recipients to use the system  10  even in wet environments such as when showering or out in the open and being caught in the rain. 
   It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.