Circuitry for Using High-Speed Low-Power Voltage Comparator for Compliance Voltage Monitoring in Current-Mode Neurostimulator
Publication Date: 2002-Apr-04
The IP.com Prior Art Database
In the implantable medical device field, a medical device, configured to perform a desired medical function, is implanted in the living tissue of a patient so that a desired function may be carried out as needed for the benefit of the patient. Numerous examples of implantable medical devices are known in the art, ranging from implantable pacemakers, cochlear stimulators, spinal cord stimulators, peripheral nerve stimulators, glucose sensors, and the like. The present invention relates mainly to Spinal Cord Stimulation (SCS) systems and more particularly to monitoring the compliance voltage in current-mode using high-speed, low-power voltage comparator circuitry. In a constant current output circuit, a compliance voltage greater than the voltage across the electrode is required to achieve the desired current level. This compliance voltage accommodates for losses in the circuit drive components and also for modest changes in the complex impedance that might occur with changes in the stimulated tissue, electrode position, chemical balance in the fluids nearby the electrodes, and other factors resulting in complex impedance changes. As long as the compliance voltage is sufficiently high, these changes in impedance will not result in changes in the desired delivery of current because the output circuitry maintains the current desired. But, additional voltage over and above the driver losses must be consumed as a resistive drop and represents wasted power in the output circuitry. Additionally, generation of high voltages is difficult and may be less efficient compared to voltage generation at lower output levels. Therefore, theres a need to minimize the compliance voltage to what is needed to deliver the desired current.