Abstract:
A system, method and implantable medical for concurrently providing a therapeutic output to a patient while communicating transcutaneously with an external device. The therapeutic output is provided to the patient with an implantable medical device wherein an electromagnetic signal is associated with at least one of recharging of a rechargeable power source and providing the therapeutic output. Bi-directional transcutaneous communication is conducted via via telemetry between the implantable medical device and an external device using a telemetry signal while the telemetry signal and the electromagnetic signal occur simultaneously.

Description:
RELATED APPLICATION 
     This application claims priority to provisional U.S. application Ser. No. 60/589,393, filed Jul. 20, 2004, and provisional U.S. application Ser. No. 60/589,950, filed Jul. 21, 2004. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to implantable medical devices and, more particularly, to implantable medical devices providing a therapeutic electrical output and transcutaneous telemetry. 
     BACKGROUND OF THE INVENTION 
     Implantable medical devices for producing a therapeutic result in a patient are well known. Examples of such implantable medical devices include implantable drug infusion pumps, implantable neurostimulators, implantable cardioverters, implantable cardiac pacemakers, implantable defibrillators and cochlear implants. Some of these devices, if not all, and other devices either provide an electrical output or otherwise contain electrical circuitry to perform their intended function. 
     It is common for implantable medical devices, including implantable medical devices providing an electrical therapeutic output, to utilize transcutaneous telemetry to transfer information to and from the implanted medical device. Information typically transferred to an implanted medical device includes transferring instructions or programs to the implanted medical device from an external device such as an external programmer. Information typically transferred from an implanted medical includes information regarding the status and/or performance of the implanted medical device. 
     Existing implantable medical devices and/or external programmers, such as typical neurological stimulators, can not receive telemetry when the implanted medical device is providing therapy. The noise generated by creating electrical stimulation therapy pulses and the pulses themselves can be coupled onto the telemetry receiving antenna and the resulting noise can prevent the telemetry signal from being received. In implantable stimulators such as the Itrel 3™ stimulator, Synergy™ stimulator, and Kinetra™ stimulator manufactured by Medtronic, Inc., Minneapolis, Minn., the telemetry receiver is turned on briefly between electrical stimulation pulses. If the telemetry receiver detects any signal on its antenna between stimulation pulses, the telemetry receiver turns off the stimulation pulses momentarily in order to quiet the system to receive the downlink. After the telemetry signal is received, processed, and the resulting uplink response is sent via telemetry, the electrical stimulation pulses can then be turned on again. The window that looks for telemetry occurs every 2 milliseconds with a window width of about 220 microseconds. A wake-up burst that is at least 2 milliseconds long is then sent so that the 175 kiloHertz signal would be received by at least one of the reception windows. 
     A disadvantage of this technique is that electrical stimulation therapy might need to be stopped to allow for telemetry communication. If the telemetry communication duration is long (such as receiving large blocks of data from the device or downloading a new application into the implanted medical device), electrical stimulation therapy might be disabled for long periods and the side effects of not having electrical stimulation therapy enabled could impact the patient, e.g., a tremor could return for a tremor patient, pain could return for a pain patient, etc. 
     A technique used in implantable medical devices used in cardiac pacing is to interleave the telemetry data between electrical stimulation therapy pulses. Alternatively, pacing systems also attempt telemetry during therapy and, if the communication is unsuccessful, the system can retry the communication at a later time. Both of these methods can work well for cardiac pacing therapy, where the pulse rate of the electrical stimulation therapy is less than 2 Hertz. However, in typical neurostimulators, a pulse rate of 260 Hertz or higher for electrical stimulation therapy, so interleaving telemetry data or retrying when the electrical stimulation therapy corrupts data communication becomes impractical, as the data rate is greatly diminished. 
     BRIEF SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides a system for telemetry communication with an implantable medical device concurrent with the delivery of therapeutic output to a patient. 
     The receiver used in an embodiment of the present invention provides a true differential input receiver and has extremely good common mode noise rejection. Common mode filtering was accomplished by splitting a single parallel tank tuning capacitor into two series capacitors with the midpoint referenced to ground. This provides common mode filtering because the energy coupled into the antenna from the delivery of the therapy is seen equally on both sides of the antenna, so the noise does not cause a different voltage at each end of the antenna. 
     Diodes are placed in parallel to the split capacitors for full wave rectification while providing a reference to ground and input circuit protection. The split capacitor design minimizes diode conduction and preserves tuning, therefore maximizing the signal on the antenna. 
     In some embodiments, the above design alone can be susceptible to differential noise (fields generated outside the device). To reduce susceptibility to differential noise filtering is incorporated in some embodiments of the invention. Filtering may use a fixed minimum threshold detector which prevents detection until a signal has reached a fixed voltage level or a dynamic threshold detector which prevents detection of signals at a certain percentage of the peak signal. These filters are processed in parallel with the incoming signal and combined at the end of the receiver channel resulting in a filtered signal output. 
     To increase the signal to noise ratio (which allows a higher success to communicate rate in a noisy environment by moving the programming head closer to the device), the receiver can operate on the voltage being provided on the receiving antenna if the voltage on the antenna is higher than the voltage supply provided by the battery in the device. In a preferred embodiment, a 4 volt regulated voltage is used to supply the energy to operate the receiver. When the voltage on the antenna rises above 4 volts, the regulator supply is switched to a voltage supply created off of the antenna. A Zener diode can be used to clip the voltage at 7 volts to keep an excessively high signal from damaging internal components in the receiver. 
     In an embodiment, the receiver also has a logarithmic front end, which allows the receiver to have a wide dynamic range of signal strengths. 
     This allows telemetry communication with an implanted medical device without interrupting electrical stimulation therapy. This prevents potential side effects that can occur when stopping and starting electrical stimulation therapy and allows successful emergency downlinks even if the programmer can not detect the uplink because of high noise levels. 
     In an embodiment, the present invention provides an implantable medical device having a therapy module providing a therapeutic output to a patient and a telemetry module, operatively coupled to the therapy module, providing bi-directional transcutaneous telemetry communication using a telemetry signal with an external device. An electromagnetic signal is associated with at least one of recharging of a rechargeable power source and providing the therapeutic output. the bi-directional transcutaneous communication occurs while the telemetry signal and the electromagnetic signal occur simultaneously. 
     In a preferred embodiment, the implantable medical device further comprises a rechargeable power source operatively coupled to the therapy module and wherein the electromagnetic signal is associated with recharging the rechargeable power source. 
     In a preferred embodiment, the rechargeable power is recharged using inductive coupling and wherein the electromagnetic signal arises from the inductive coupling. 
     In a preferred embodiment, the electromagnetic signal is associated with delivery of the therapeutic output. 
     In a preferred embodiment, the therapeutic output is an electrical stimulus signal and wherein the electromagnetic signal is derived, at least in part, from the electrical stimulus signal. 
     In a preferred embodiment, the bi-directional telemetry occurs while the telemetry signal and the electrical stimulus signal occur simultaneously. 
     In a preferred embodiment, the electromagnetic signal occurs during delivery of the therapeutic output. 
     In a preferred embodiment, the therapy module comprises a drug delivery module having a drug pump and wherein the electromagnetic is generated by the drug pump. 
     In a preferred embodiment, the electromagnetic signal is associated with an activity of the implantable medical device prefatory to delivery of the therapeutic output. 
     In a preferred embodiment, the implantable medical device comprises a defibrillator, wherein the therapeutic output comprises an electrical stimulus signal and wherein the electromagnetic signal is generated during charging of the implantable medical device in preparation for delivery of the electrical stimulus signal. 
     In an alternative embodiment, the present invention provides an implantable medical device for providing a therapeutic output to a patient having a therapy module providing a therapeutic output to a patient. An electromagnetic signal is associated with at least one of recharging of a rechargeable power source and providing the therapeutic output. An intermediate grounded receiving coil is adapted to receive a transcutaneous telemetry signal. A telemetry module, operatively coupled to the intermediate grounded receiving coil and to the therapy module, provides transcutaneous telemetry communication using the telemetry signal with an external device. The transcutaneous telemetry communication occurs while the telemetry signal and the electromagnetic signal occur simultaneously. 
     In a preferred embodiment, the secondary coil is a center grounded receiving coil. 
     In a preferred embodiment, the telemetry module is a dual channel threshold detector. 
     In a preferred embodiment, the telemetry module of the implantable medical device further is a differential amplifier operatively coupled to the receiving coil for receiving the transcutaneous telemetry communication and a common mode amplifier operatively coupled to the receiving coil. 
     In a preferred embodiment, the telemetry module further is a common mode amplifier operatively coupled to the receiving coil for a first one of the dual channel threshold detector and one of a differential trigger and a fixed threshold for a second one of the dual channel threshold detector. 
     In a preferred embodiment, the common mode amplifier is configured to utilize one of a low voltage trigger and a high voltage trigger. 
     In a preferred embodiment, the implantable medical device further comprises a rechargeable power source operatively coupled to the therapy module and wherein the electromagnetic signal is associated with recharging the rechargeable power source. 
     In a preferred embodiment, the rechargeable power is recharged using inductive coupling and wherein the electromagnetic signal arises from the inductive coupling. 
     In a preferred embodiment, the electromagnetic signal is associated with delivery of the therapeutic output. 
     In a preferred embodiment, the therapeutic output comprises an electrical stimulus signal and wherein the electromagnetic signal is derived, at least in part, from the electrical stimulus signal. 
     In a preferred embodiment, the electromagnetic signal occurs during delivery of the therapeutic output. 
     In another alternative embodiment, the present invention provides a system for providing a therapeutic output to a patient using the implantable medical device described herein and an external device configured for transcutaneous telemetry communication with the implantable medical device. 
     In another alternative embodiment, the present invention provides a method for providing a therapeutic output to a patient. The therapeutic output is provided to the patient with an implantable medical device wherein an electromagnetic signal is associated with at least one of recharging of a rechargeable power source and providing the therapeutic output. Bi-directional transcutaneous communication is conducted via via telemetry between the implantable medical device and an external device using a telemetry signal while the telemetry signal and the electromagnetic signal occur simultaneously. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an implantable medical device used in conjunction with an external device; 
         FIG. 2  is a more detailed block diagram of a portion of the external device; 
         FIG. 3  is a more detailed block diagram of a portion of the implantable medical device; 
         FIG. 4  is a schematic diagram of the receive module in implantable medical device; 
         FIG. 5  shows an ideal telemetry burst; 
         FIG. 6  shows an non-ideal telemetry burst; 
         FIG. 7  illustrates in between burst peak tracker operation; 
         FIG. 8  illustrates a peak tracking signal on a telemetry burst; 
         FIG. 9  is a fixed threshold control block circuit diagram; 
         FIG. 10  illustrates a trigger signal flow diagram; 
         FIG. 11  illustrates differential trigger operation; and 
         FIG. 12  illustrates a pulse width timer signal flow diagram; 
         FIG. 13  is a schematic block diagram of a receive module in an external device. 
         FIG. 14  is a schematic diagram is a power supply switched voltage circuit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention have usefulness in many different implantable medical devices. A preferred embodiment of the present invention is especially useful in an implantable medical device providing electrical stimulation therapy. An example of such a device, system and method is described in U.S. Pat. No. 6,505,077, Kast et al, Implantable Medical Device With External Recharging Coil Electrical Connection, the content of which are hereby incorporated by reference. 
     A close-up diagrammatic view of implantable medical device  10  implanted into patient  12  is illustrated in  FIG. 1 . Implantable medical device  10  is generally composed of therapy module  14  which provides a therapeutic output  16  to patient  12 , telemetry module  18  and power supply  20  providing electrical power to both therapy module  14  and telemetry module  18 . In general, implantable medical device may by any of a variety of commonly available implantable medical devices providing a therapeutic output  16  to a patient  12 . Examples, of such devices include, but are not limited to, implantable neurostimulators, drug pumps, cardiac pacemakers and defibrillators and other devices. Therapy modules  14  associated with such implantable medical devices  10  are well known in the industry. 
     Telemetry module  18  may be any of a variety of commonly known and available modules for supporting transcutaneous communication between implantable medical device  10  and external device  22  which is generally used for controlling or programming implantable medical device  10  or for providing information regarding the condition, state, status or history of implantable medical device  10  or information relating to patient  12 . Telemetry techniques are commonly known in the industry and typically involve the transmission and reception of an electromagnetic wave between implantable medical device  10  and external device  22 . Any of a number of commonly available telemetry schemes may be utilized. 
     Power source  20  may be any of a variety of commonly known and available power supply such as chemical batteries and, in particular, rechargeable batteries. Power source  20  may provide electrical power to both therapy module  14  and telemetry module  18  although it is to be recognized and understood that therapy module  14  and telemetry module  18  may have their own separate power sources. 
     Telemetry antenna  24 , coupled to telemetry module  18 , is adapted to receive electromagnetic signals sent transcutaneously from external device  22  and to transmit electromagnetic signals toward external device  22 . 
     Power antenna  26 , coupled to power source  20 , is adapted to receive electromagnetic energy from external device  22  for the purpose of supplying energy to implantable medical device  10 , including, but not limited to, recharging of power source  20 . 
     While shown separately, telemetry antenna  24  may be nested with power antenna  26  or, in an alternative embodiment, telemetry antenna  24  may be combined with power antenna  26 . 
     External device  22  contains control module  28  which is coupled to telemetry antenna  30  and is adapted to either control or program implantable medical device  10  or provide information about implantable medical device  10  or patient  12  through telemetry communication with implantable medical device  10  using transcutaneous electromagnetic signals between telemetry antenna  30  of external device  22  and telemetry antenna  24  of implantable medical device. 
     External device  22  also contains charging module  32  which is coupled to charging antenna  34  and is adapted to transmit electromagnetic energy to power source  20  of implantable medical device  10  through power antenna  26 . Such transcutaneous electromagnetic energy transfer is conventional and well known in the art. 
     It is to be noted that while external device  22  is shown as containing both control module  28  and charging module  32 , it is to be recognized and understood that the control and/or programming functions and energy transfer function of external device  22  could be implemented in separate and independent devices. 
       FIG. 2  illustrates a partial block diagram view of external device  22  showing control module  28  and telemetry antenna  30 . Control module  28  operates to communicate bi-directionally with implantable medical device  10  through transmit module  36  and receive module  38 . Transmit module  36  is responsible for providing data and communication formatting for communication from external device  22  to implantable medical device  10 . Receive module  38  is responsible for decoding transmitted information received from implantable medical device  10 . Transmit module  36  and receive module  38  are illustrated coupled to a single telemetry antenna  30 . It is to be recognized and understood that transmit module  36  and receive module  38  may utilize a common telemetry antenna  30  or may utilize separate and independent antennas. 
       FIG. 3  illustrates a partial block diagram view of implantable medical device  10  showing telemetry module  18  and telemetry antenna  24 . Telemetry module  18  operates to communicate bi-directionally with external device  22  through transmit module  40  and receive module  42 . Transmit module  40  is responsible for providing data and communication formatting for communication from implantable medical device  10  to external device  22 . Receive module  42  is responsible for decoding transmitted information received from external device  22 . Transmit module  40  and receive module  42  are illustrated coupled to a single telemetry antenna  24 . It is to be recognized and understood that transmit module  40  and receive module  42  may utilize a common telemetry antenna  24  or may utilize separate and independent antennas. 
     Implantable medical device  10  may generate significant electromagnetic energy in its normal operation. Such electromagnetic energy may be generated, for example, in the provision of an electrical stimulus pulse or signal train in a neurostimulator. Even drug pumps may produce significant electromagnetic energy in the provision of a medicant to patient  12  since such devices may employ an electrically operated motor or pump which may produce electromagnetic signal or noise spikes during their operation. Alternatively or in addition, substantial electromagnetic is associated with the provision of transcutaneous energy transfer to either supply power to implantable medical device  10  or to recharge power source  20 . 
     In such situations, electromagnetic noise may drown out telemetry signals passing either from external device  22  to implantable medical device  10  or vice versa. Implantable medical device  10  employs receive module  42  adapted to enable to receipt of intelligible telemetry information from external device  22  even while implantable medical device  10  is generating significant electromagnetic signals through the provision of therapeutic output  16 , e.g., an electrical stimulus or noise associated with a drug pump, or while implantable medical device  10  is receiving electromagnetic energy from charging module of external device  22 . 
     Capacitors  44  and  46  (see  FIG. 4 ) are center grounded and coupled to receiving coil  48 . Zener diode  50 , capacitor  52  and resistor  54  along with center grounded capacitors  44  and  46  provide a floating reference level around which telemetry signals appearing at receiving coil  48  may be detected. Receive module  42  operates to produce a digital “one” provided that the amplitude of the oscillating telemetry signal appearing on center-grounded receiving coil  48  are above a predetermined level of the floating reference level. 
     Input stage  56  provides a common mode amplifier feeding both high trigger circuit  58  and low trigger circuit  60 . High trigger circuit  58  is fed to a high pulse width timer  62  to provide a known minimum pulse width output from high trigger circuit  58 . Low pulse width timer circuit  64  similarly provides a known minimum pulse output from low trigger circuit  60 . 
     Dual high and low trigger circuits  58  and  60  provide a dual channel threshold detector. 
     Receive module  42  also contains differential amplifier  66  providing a differential output from receiving coil  48  adjustable from adjustable resistor  54 . Differential pulse width timer  68  provides a known pulse minimum width output from differential amplifier  66 . 
     Common mode amplifier  70  is referenced to a constant voltage, in this case 800 millivolts. 
     The output of common mode amplifier  70  is “ORed” with the output from differential pulse width timer  68  in OR gate  72 . In other words, OR gate  72  passes a high signal whenever either the output from common mode amplifier  70  or differential pulse width timer  68  is high. 
     The output of each of high pulse width timer  62  and low pulse width timer  64  is “ANDed” with the output from OR gate  72  in AND gates  74  and  76 , respectively. In other words, the output from AND gate  74  is high whenever the outputs from both high pulse width timer  62  and OR gate  72  is high. Similarly, the output from AND gate  76  is high whenever the outputs from both low pulse width timer  64  and OR gate  72  is high. 
     The outputs of OR gates  74  and  76  are “ORed” in OR gate  78 . The result is that receive module  42  passes a high signal whenever the output of either high trigger circuit  58  or low trigger circuit  60  is if either the output of differential trigger  66  or common mode amplifier is high. 
     In a preferred embodiment, the telemetry signal broadcast by the external device  22  has a base band of 4.4 kilobits per second and a carrier frequency of 175 kiloHertz. The telemetry signal is amplitude modulated. One&#39;s and zero&#39;s are communicated using a psuedo-AM (amplitude modulation) communication scheme where the length of each pulse and the time in between pulses determines if the pulse represents a 1 or a 0.  FIG. 5  shows an ideal Telemetry N burst with the 1&#39;s and the 0&#39;s labeled to show timing differences between the two. 
     The external device  22 , however, may not produce an ideal telemetry burst. A non-ideal telemetry burst may have a rise time where the beginning cycles do not reach full amplitude for a certain amount of time.  FIG. 6  shows an example of a non-ideal telemetry burst. 
     Receive module  42  provides peak tracking and dynamic threshold control. The first function is tracking the peak of the received telemetry signal. A RC time constant is set to hold this peak value for a certain amount of time in between bursts and after the end-of-message signal. The second function is to set the dynamic threshold. This is accomplished by taking a certain percentage of the peak voltage (determined by the peak tracking function) and sending it on, in the form of an offset, to the trigger circuits  58  and  60 . 
     The peak of the received telemetry signal is tracked using the peak tracker. The peak voltage is set-up on the hybrid capacitors  44  and  46 . A time constant is involved in setting up the peak voltage because of the RC time constant. 
     The peak tracker is designed to hold the dynamic threshold to a certain percentage of the peak voltage in between bursts. It is the intent of the peak tracker to only let the peak voltage set on the capacitor drop 10% in between bursts. The worst-case ˜2 millisecond time constant allows the peak tracker to only lose 10% of the peak value during the longest low-time of the message.  FIG. 7  illustrates in between burst peak tracker operation. 
     The longest low-time in a message is 48 cycles, or 275 microseconds, just before the 16 cycle end-of-message burst. If we again look to the equation 
               0.9   ⁢           ⁢     V   0       =       V   0     ⁢     ⅇ         -   275     ⁢   uS     τ               
and set V to 90% of V O  and set the time to be 275 microseconds we can solve for the time constant needed to keep the peak tracker at 90% of the peak signal in between bursts.
 
     After the message is finished the voltage on capacitors  44  and  46  will clear according to the time constant as well. The capacitors  44  and  46  will be defined as cleared once it has decayed down to 10% of its original value. 
       FIG. 8  shows a reasonable telemetry burst with an exponentially rising peak tracking signal. 
     The dynamic threshold control uses the voltage created by the peak voltage detector and takes some percentage of that voltage. The percentage of the peak voltage is used as the new receiver threshold during a message. The dynamic threshold allows communication in a noisy environment by increasing the detection threshold when there is sufficient signal on the coil. 
     The design has the option of changing the percentage of the peak received voltage that the dynamic threshold will rise to is adjustable resistor  54 . 
     The fixed threshold control block controls the fixed threshold level. This block uses the peak of the signal measured using the peak signal from the peak detector and dynamic threshold control block and compares it to a fixed threshold level set for a specific device. If the peak of the signal is larger than the fixed threshold level the receiver&#39;s comparator block is activated using a signal. If the peak signal is smaller than the fixed threshold level of the receiver the comparator block is de-activated. 
       FIG. 9  shows that the fixed threshold level is realized by sending a current through a resistor and measuring the voltage across that resistor. This voltage is then compared to the peak voltage measured in the peak tracker and dynamic threshold control. 
     As noted in the purpose statement, receive module  42  senses and conditions the telemetry antenna voltage received at the physical layer and creates a digital signal that represents the telemetry signal at the data-link layer. Receive module  42  also provides the signal-to-noise ratio necessary to maintain operation during stimulation. 
     A peak tracker tracks the peak of the antenna voltage across Zener diode  50 . A time constant sets the growth and decay properties of the peak voltage as compared to the telemetry (or noise) burst. The voltage created using the RC is considered the peak of the telemetry burst. This peak voltage is then used in the fixed threshold to determine if the telemetry burst is above the fixed threshold. The peak voltage is also used to set the dynamic threshold. 
     The peak tracker block also provides a bias for input stage  56 . 
     Input stage  56  acts as a pre-amplifier with non-linear compression and gain for the high and low signal paths of the receive module  42 . Input stage  56  amplifies the differential and filters the common mode signal between both sides of the antenna. These amplified signals are both sent directly to the high and low trigger circuits ( 58  and  60 ) for further processing. When the signal level is greater, the signal is sent to the low channel trigger circuit  60 . When the signal level is less, the signal is sent to the high channel trigger circuit  58 . 
     Input stage  56  also provides a band pass function. 
     Common mode amplifier  70  provides a fixed threshold control ensuring that a signal below the fixed threshold does not cause the receive module  42  to trip. The fixed threshold control uses a comparator  70  to compare the peak voltage of the received signal from the peak tracker to the fixed threshold voltage (800 millivolts). If the peak voltage of the received signal is larger than the fixed threshold level comparator  70  will be activated. If the peak of the received signal is smaller than the fixed threshold level the comparator  70  will be de-activated. 
     High and low trigger circuits  58  and  60  are identical and are basically Schmitt triggers that trigger when one input goes negative or positive relative to the other input. The high and low trigger circuits are then able to create a digital signal that should represent the carrier frequency of 175 kiloHertz. 
     The basic signal flow is shown in  FIG. 10 . 
     The differential noise trigger  66  provides a dynamic threshold to filter out low-level noise when the signal level is large enough. 
       FIG. 11  shows how the differential noise trigger  66  ignores the low-level noise when the signal level seen on receive coil  48  is large enough. 
     The high and low pulse-width timers ( 62  and  64 ) are identical and perform the same function for their respective signal paths. They are re-triggerable time-out timers that use the output of the triggers (high and low respectively.) 
     The pulse-width timers ( 62  and  64 ) effectively filter out the carrier frequency of 175 kiloHertz and create a 4.4 kilobits per second signal. The timers accomplish this by looking for the input signal to go high (2 volts) and setting a timer. As soon as the input signal goes high the timer is set and the output signal goes high. If the input signal is high when the timer has expired the timer will reset and the output signal will remain high. If the input signal is low when the timer expires the output signal will go low. 
       FIG. 12  shows the signal flow of the pulse width timers  62  and  64 . The signal from the triggers is taken and the pulse-width timer creates the 4.4 kilobit per second signal. 
     Differential pulse width timer  68  performs the same function for differential trigger  66  as the high and low pulse width timers ( 62  and  64 ) do for high and low triggers ( 58  and  60 ) and is also re-triggerable. 
     Differential trigger  66  acts as a switch to turn on the differential noise filtering. Differential trigger  66  compares a percentage of the voltage of the received signal across receive coil  48  to a predetermined voltage level. When the received voltage is larger than a predetermined voltage value, differential filtering is enabled. Differential filtering filters out low-level noise when there is a large amplitude on the received telemetry signal. 
     After a transmission has occurred, the capacitor on the peak tracker should be cleared. If the capacitor is not cleared, the receive module  42  could ignore a telemetry downlink because the dynamic threshold would be set high because of a voltage on the peak tracker capacitor. The capacitor is shorted when the transmitter is inactive and the receiver is active. 
     Uplink telemetry communication is achieved by utilizing transmit module  40  in implantable medical device  10  and receive module  38  in external device  22 . Transmit module  40  is conventional in nature and well known in the art using conventional techniques. 
     Receive module  38  in external device  22  is much more straight forward than receive module  42  in implantable medical device. Telemetry antenna  30  is coupled directly to transformer  80 . The signal from transformer  80  is amplified in amplifier  82  and full wave rectified in full wave rectifier  84 . Peak detector  86  uses a series diode and a parallel capacitor to detect a peak value. A threshold is established is threshold block  88  consisting of a voltage divider. Comparator  90  compares the signal from full wave rectifier  84  and the signal from the threshold block  88  to produce a positive output when the full wave rectified signal is above the threshold signal. 
     Operation of any circuitry in implantable medical device consumes power. Since size and longevity are usually primary concerns for implantable medical devices, any power savings can yield either size or longevity improvements or both. The telemetry module  18  as well as transmit module  40  and receive module  42  consume power in implantable medical device  10 . This is particularly true since many components contained in the transmit and receive modules  40  and  42  are analog components and, as such, may require voltages and currents in excess of that typically required by digital components. 
     Switched supply block  92  provides power to one or more of telemetry module  18 , transmit module  40  and/or receive module  42  from the telemetry signal when implantable medical device  10  is receiving a telemetry signal. Switched supply block  92  provides power to circuits that need a high-voltage power supply when high voltage levels are seen on telemetry antenna  24  while receiving a telemetry transmission. Switched supply block  92  illustrated in  FIG. 14  is a two-FET well-switcher that places the voltage from either the internal power source or switched supply from the telemetry antenna depending on which one is larger. Peripheral circuitry has been added to the well-switcher to ensure proper operation under all system conditions. 
     Switched supply block  92  is a well switcher that chooses the higher of the two voltages to supply a number of circuits in receive module  42 . Switched supply block  92  allows the receive module  42  to use the energy on the receive coil  48  to power the receive module  42  during telemetry reception when the received signal amplitude creates a voltage that is larger than the internal power source voltage. 
     Switched supply block  92  has hysteresis around 4.0 volts. When the voltage on receive coil  48  is increasing the switched supply block  92  will begin using this voltage as a supply voltage as soon as it is greater than the voltage of the internal power source. 
     Voltage  94  from the internal power source is available to switched supply block  92 . Also available is voltage  96  from receive coil  48 . Voltage  94  from the internal power source of implantable medical device  10  is fed to field effect transistor (FET)  98  while voltage  96  from receive coil  48  is fed to field effect transistor (FET)  100 . Switch control logic  102  is coupled to both voltages  94  and  96  and controls FETs  98  and  100  to effectively switch between voltage sources depending upon which voltage source is higher. The switched supply block  92  output voltage  104  is taken from the outputs of both FETs  98  and  100  and stabilized with capacitor  106 . 
     The contents of provisional U.S. application Ser. No. 60/589,393, filed Jul. 20, 2004, and provisional U.S. application Ser. No. 60/589,950, filed Jul. 21, 2004, are hereby incorporated by reference. 
     Thus, embodiments of the concurrent delivery of treatment therapy with telemetry in an implantable medical device are disclosed. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.