Circuits and Methods for Using a High Impedance Battery in an Implantable Stimulator

Abstract

An implantable stimulator includes a housing configured to be implanted beneath a skin surface of a patient and having a first surface adapted to face inwardly into tissue of the patient at or near a target tissue location; pulse generation circuitry located within the housing and electrically coupled to at least two electrodes, the pulse generation circuitry being adapted to deliver stimulation sessions by way of the at least two electrodes to the target tissue location, wherein each stimulation session included in the stimulation sessions has a duration of T3 minutes and a rate of occurrence of once every T4 minutes, wherein a ratio of T3 to T4 is no greater than 0.05; and a primary battery contained within the housing and electrically coupled to the pulse generation circuitry, the primary battery having an internal impedance greater than 5 ohms.

What is claimed is: 
     
         1 . An implantable stimulator, comprising:
 a housing configured to be implanted beneath a skin surface of a patient and having a first surface adapted to face inwardly into tissue of the patient at or near a target tissue location;   pulse generation circuitry located within the housing and electrically coupled to at least two electrodes, the pulse generation circuitry being adapted to deliver stimulation sessions by way of the at least two electrodes to the target tissue location, wherein each stimulation session included in the stimulation sessions has a duration of T 3  minutes and a rate of occurrence of once every T 4  minutes, wherein a ratio of T 3  to T 4  is no greater than 0.05; and   a primary battery contained within the housing and electrically coupled to the pulse generation circuitry, the primary battery having an internal impedance greater than 5 ohms.   
     
     
         2 . The implantable stimulator of  claim 1 , wherein the at least two electrodes are located on the first surface. 
     
     
         3 . The implantable stimulator of  claim 2 , wherein the at least two electrodes comprise:
 a central electrode located substantially in a center of the first surface of the housing; and   a circumferential electrode located substantially around and at least 5 mm distant from a center of the central electrode.   
     
     
         4 . The implantable stimulator of  claim 3 , wherein the circumferential electrode is an anode electrode and the central electrode is a cathode electrode. 
     
     
         5 . The implantable stimulator of  claim 3 , wherein the circumferential electrode is a cathode electrode and the central electrode is an anode electrode. 
     
     
         6 . The implantable stimulator of  claim 3 , wherein the circumferential electrode comprises a ring electrode attached around a perimeter edge of the housing. 
     
     
         7 . The implantable stimulator of  claim 1 , wherein the at least two electrodes are located on a lead that is attached to the implantable stimulator. 
     
     
         8 . The implantable stimulator of  claim 1 , wherein the housing is coin-shaped having a diameter no greater than about 25 mm and a thickness of no greater than about 2.5 mm. 
     
     
         9 . The implantable stimulator of  claim 1 , wherein the primary battery has sufficient capacity to power the pulse generation circuitry for a minimum of two years. 
     
     
         10 . The implantable stimulator of  claim 1 , wherein the primary battery has a nominal output voltage of 3 volts. 
     
     
         11 . The implantable stimulator of  claim 10 , wherein the pulse generation circuitry includes:
 a boost converter circuit that boosts the nominal voltage of the primary battery to an output voltage VOUT that is at least three times a nominal battery voltage;   means for selectively turning the boost converter circuit OFF and ON to limit the amount of current that may be drawn from the primary battery; and   an output circuit powered by VOUT that generates the stimulation sessions.   
     
     
         12 . The implantable stimulator of  claim 11 , wherein the means for selectively turning the boost converter circuit OFF and ON comprises a control circuit configured to generate a digital signal that modulates the boost converter circuit between an OFF state and an ON state, with the ON state comprising no more than about 2% of the time that the implantable stimulator is operating. 
     
     
         13 . The implantable stimulator of  claim 11 , wherein the means for selectively turning the boost converter circuit OFF and ON comprises a boost converter circuit having a shut down feature which automatically places the boost converter circuit in an OFF state whenever a battery voltage of the primary battery falls below a set minimum value, wherein the set minimum value of the primary battery below which the boost converter is placed in an OFF state comprises a voltage that is sufficiently high to continue to power other digital processing circuits within the pulse generation circuitry even when the boost converter is turned OFF. 
     
     
         14 . The implantable stimulator of  claim 11 , wherein the pulse generation circuitry further includes means for reducing leading edge transient signals that may be present in the stimulation sessions. 
     
     
         15 . The implantable stimulator of  claim 14 , wherein the output circuit of the pulse generation circuitry includes a programmable current source, and wherein the means for reducing leading edge transient signals comprises a cascode circuit at the input of the programmable current source. 
     
     
         16 . The implantable stimulator of  claim 15 , wherein the pulse generation circuitry further includes means for kick starting the programmable current source when low amplitude stimulation pulses are generated, wherein such kick starting eliminates or reduces undesired delays in the leading edge of the stimulation sessions. 
     
     
         17 . The implantable stimulator of  claim 1 , wherein the electronic circuitry includes power management circuitry that limits an amount of instantaneous current that can be drawn from the primary battery. 
     
     
         18 . The implantable stimulator of  claim 1 , further comprising a sensor contained within the housing responsive to operating commands wirelessly communicated to the implantable stimulator from a non-implanted location, the operating commands allowing limited external control of the implantable stimulator. 
     
     
         19 . The implantable stimulator of  claim 1 , wherein a second surface of the housing, on an opposite side of the housing from the first surface, when implanted, is adapted to be closest to the patient's skin. 
     
     
         20 . The implantable stimulator of  claim 1 , wherein, during each stimulation session, stimulation pulses having a specified width and a specified amplitude are generated at a specified rate.