Current Management System for a Stimulation Output Stage of an Implantable Neurostimulation System

A stimulation output stage of a neurostimulation system that is at least partially implantable in the body of a human patient comprising:

• a plurality of stimulation electrodes implantable in the patient so that each is adjacent or in the patient's tissue wherein each stimulation electrode can be selectively engaged to perform any of the following functions at a given time during a stimulation episode:
• source current into the patient;
• sink current out of the patient;
• present a high impedance;
• and provide a short circuit to ground;
• a reference electrode the electrically conductive surface area of which is at least an order of magnitude greater than the electrically conductive surface area of any of the plurality of stimulation electrodes;
• digital control and timing signals sufficient to determine whether a stimulation electrode is used in a stimulation episode, what function the stimulation electrode performs at what time(s) during the stimulation episode and, if the function is to source or sink current, the amplitude of the current to be sourced or sunk;
• for each stimulation electrode, a voltage reservoir associated with a stimulation electrode drive circuit adapted to respond to the digital control and timing signals and configurable to establish a reference current for the stimulation electrode when the stimulation is programmed to source or sink current;
• and
• for the reference electrode, a constant reference voltage associated with a reference electrode drive circuit adapted to maintain the reference electrode at a constant voltage during the stimulation episode so that the reference electrode sinks or sources current to balance the current being sourced or sunk by the stimulation electrodes.

A method for steering the amount of current to be sourced or sunk to a patient through each of a plurality of stimulation electrodes under the control of a neurostimulator in a neurostimulation system comprising:

• providing a stimulation electrode drive circuit for each stimulation electrode configurable to cause the associated stimulation electrode to perform one of four functions at any given time period in a stimulation episode, namely, sourcing current into the patient, sinking current out of the patient, presenting a high impedance, or providing a short circuit to ground;
• providing programmed instructions in the form of digital control and timing signals to each electrode drive circuit to cause the associated stimulation to perform one or more of the four functions at selected time periods during the stimulation episode;
• providing a voltage reservoir for the stimulation electrode drive circuits when the stimulation electrode drive circuits are programmed to source or sink currents;
• providing a reference electrode drive circuit that maintains a housing of the neurostimulator at a constant reference voltage during the stimulation episode, causing the reference electrode to source or sink an amount of current equal to the total amount of current being sunk or sourced by the stimulation electrodes at each selected time period, thus allowing the current sourced or sunk through any one stimulation electrode to be independent of the amount of current being sourced or sunk through any other stimulation electrode at any given time period in the stimulation episode.