Patent ID: 8406881

Claim:
An apparatus for delivering electrical neural stimulation therapy to a patient, the apparatus comprising: a power supply; circuitry connected to the power supply and adapted to detect tissue/electrode interface impedances; at least one stimulating electrode, wherein the circuitry includes a charged capacitor adapted to be electrically connected to the at least one stimulating electrode; and a current output pulse generator connected to the at least one stimulating electrode, the generator comprising a programmed amplitude of stimulation current, wherein the generator is configured to deliver electrical neural stimulation therapy at the programmed amplitude, the generator further comprising: an adjustable compliance voltage source connected to the power supply, the voltage source configured to provide an adjustable voltage level and different potentials for the different tissue/electrode interface impedances, the voltage source comprising: a supply capacitor; two variable current sources connected in parallel with the supply capacitor; and switches configured to control the delivery of electrical neural stimulation therapy, wherein the switches are connected to the current sources and supply capacitor, wherein the pulse generator is configured to receive the detected impedances, maintain the programmed amplitude of stimulation current for the different tissue/electrode interface impedances and adjust the compliance voltage source by adjusting the voltage level based on the programmed amplitude of the stimulation current and the detected impedances; and wherein the charged capacitor is adapted to be electrically connected to the at least one stimulating electrode for a pre-determined amount of time, and wherein the tissue/electrode interface impedances are determined by measuring a voltage difference across the charged capacitor before and after connecting it to the at least one electrode.