Browse Prior Art Database

Circuitry for Using High-Speed Low-Power Voltage Comparator for Compliance Voltage Monitoring in Current-Mode Neurostimulator

IP.com Disclosure Number: IPCOM000007552D
Publication Date: 2002-Apr-04
Document File: 4 page(s) / 19K

Publishing Venue

The IP.com Prior Art Database

Abstract

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.

This text was extracted from an HTML document.
This is the abbreviated version, containing approximately 37% of the total text.

Circuitry for Using High-Speed Low-Power Voltage Comparator for Compliance Voltage Monitoring in Current-Mode Neurostimulator

Summary

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, there's a need to minimize the compliance voltage to what is needed to deliver the desired current.

In order to generate the voltage that is required and not any more, the impedance of the tissue at the electrode interface must be monitored and that information used for control of the compliance voltage. The circuit described herein indirectly accomplishes that function by looking at the voltage across one of the driver elements which, if there is sufficient compliance voltage available, will always be above a certain voltage (e.g., about 1.2 volts), and if an insufficient compliance voltage is available, then that component voltage will be below that level. The compliance voltage can be continuously adjusted in very small steps with automatic measurements such that the compliance voltage control will track the voltage that is necessary to maintain the circuit element voltage required. Thus, as impedance changes, which should be a slowly occurring event, close tracking of the compliance voltage is maintained, allowing minimized power losses.

As medical devices have become more useful and numerous in recent years, there is a continual need to provide very low power sensors and stimulators that may...